Burners for Fired Heaters in
General Refinery Services
API RECOMMENDED PRACTICE 535
SECOND EDITION, JANUARY 2006
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Copyright American Petroleum Institute
Provided by IHS under license with API
No reproduction or networking permitted without license from IHS
Licensee=Chevron Texaco API 22 loc/6 usr Part 1/1000001100, User=Heron, Jonathan
Not for Resale, 07/30/2006 11:33:30 MDT
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Copyright American Petroleum Institute
Provided by IHS under license with API
No reproduction or networking permitted without license from IHS
Licensee=Chevron Texaco API 22 loc/6 usr Part 1/1000001100, User=Heron, Jonathan
Not for Resale, 07/30/2006 11:33:30 MDT
Downstream Segment
API RECOMMENDED PRACTICE 535
SECOND EDITION, JANUARY 2006
Copyright American Petroleum Institute
Provided by IHS under license with API
No reproduction or networking permitted without license from IHS
Licensee=Chevron Texaco API 22 loc/6 usr Part 1/1000001100, User=Heron, Jonathan
Not for Resale, 07/30/2006 11:33:30 MDT
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Burners for Fired Heaters in
General Refinery Services
SPECIAL NOTES
API publications necessarily address problems of a general nature. With respect to particular
circumstances, local, state, and federal laws and regulations should be reviewed.
Neither API nor any of API's employees, subcontractors, consultants, committees, or other
assignees make any warranty or representation, either express or implied, with respect to the
accuracy, completeness, or usefulness of the information contained herein, or assume any
liability or responsibility for any use, or the results of such use, of any information or process
disclosed in this publication. Neither API nor any of API's employees, subcontractors, consultants, or other assignees represent that use of this publication would not infringe upon privately owned rights.
API publications may be used by anyone desiring to do so. Every effort has been made by
the Institute to assure the accuracy and reliability of the data contained in them; however, the
Institute makes no representation, warranty, or guarantee in connection with this publication
and hereby expressly disclaims any liability or responsibility for loss or damage resulting
from its use or for the violation of any authorities having jurisdiction with which this publication may conflict.
API publications are published to facilitate the broad availability of proven, sound engineering and operating practices. These publications are not intended to obviate the need for
applying sound engineering judgment regarding when and where these publications should
be utilized. The formulation and publication of API publications is not intended in any way
to inhibit anyone from using any other practices.
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Any manufacturer marking equipment or materials in conformance with the marking
requirements of an API standard is solely responsible for complying with all the applicable
requirements of that standard. API does not represent, warrant, or guarantee that such products do in fact conform to the applicable API standard.
All rights reserved. No part of this work may be reproduced, stored in a retrieval system, or
transmitted by any means, electronic, mechanical, photocopying, recording, or otherwise,
without prior written permission from the publisher. Contact the Publisher,
API Publishing Services, 1220 L Street, N.W., Washington, D.C. 20005.
Copyright © 2006 American Petroleum Institute
Copyright American Petroleum Institute
Provided by IHS under license with API
No reproduction or networking permitted without license from IHS
Licensee=Chevron Texaco API 22 loc/6 usr Part 1/1000001100, User=Heron, Jonathan
Not for Resale, 07/30/2006 11:33:30 MDT
FOREWORD
Nothing contained in any API publication is to be construed as granting any right, by implication or otherwise, for the manufacture, sale, or use of any method, apparatus, or product
covered by letters patent. Neither should anything contained in the publication be construed
as insuring anyone against liability for infringement of letters patent.
This document was produced under API standardization procedures that ensure appropriate
notification and participation in the developmental process and is designated as an API standard. Questions concerning the interpretation of the content of this publication or comments
and questions concerning the procedures under which this publication was developed should
be directed in writing to the Director of Standards, American Petroleum Institute, 1220 L
Street, N.W., Washington, D.C. 20005. Requests for permission to reproduce or translate all
or any part of the material published herein should also be addressed to the director.
Generally, API standards are reviewed and revised, reaffirmed, or withdrawn at least every
five years. A one-time extension of up to two years may be added to this review cycle. Status
of the publication can be ascertained from the API Standards Department, telephone (202)
682-8000. A catalog of API publications and materials is published annually and updated
quarterly by API, 1220 L Street, N.W., Washington, D.C. 20005.
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Suggested revisions are invited and should be submitted to the Standards and Publications
Department, API, 1220 L Street, NW, Washington, DC 20005, standards@api.org.
iii
Copyright American Petroleum Institute
Provided by IHS under license with API
No reproduction or networking permitted without license from IHS
Licensee=Chevron Texaco API 22 loc/6 usr Part 1/1000001100, User=Heron, Jonathan
Not for Resale, 07/30/2006 11:33:30 MDT
--`,,``,,`,`,,,`,,`,``,,`,,`,,,-`-`,,`,,`,`,,`---
Copyright American Petroleum Institute
Provided by IHS under license with API
No reproduction or networking permitted without license from IHS
Licensee=Chevron Texaco API 22 loc/6 usr Part 1/1000001100, User=Heron, Jonathan
Not for Resale, 07/30/2006 11:33:30 MDT
CONTENTS
Page
1
GENERAL. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.2 Referenced Publications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.3 Definition of Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2
ENVIRONMENTAL CONSIDERATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.2 Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.3 Flue Gas Emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.4 Fuel Composition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.5 Excess Air . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.6 Burner Selection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
3
COMBUSTION AIR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.1 Draft . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.2 Design Excess Air . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3 Combustion Air Preheat. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.4 Turbine Exhaust Gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.5 Combustion Air Adjustment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.6 Flame Stability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4
GAS FIRING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
4.1 Raw Gas firing (Nozzle Mix) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
4.2 Premix Firing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
5
LIQUID FUEL FIRING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.1 Types of Fuel Oil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.2 Atomization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.3 Fuel Physical Properties. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.4 Turndown . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.5 Excess Air . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.6 Flame Characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.7 Burner Liberation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.8 Combination Firing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
23
23
24
25
27
27
27
28
28
6
LOW NOX BURNERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.2 Low NOx Burner Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.3 Staged Air Burners. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.4 Staged Fuel Burners. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.5 Flue Gas Recirculation (FGR). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.6 Alternate Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.7 Troubleshooting Gas Fired Low NOx Burners . . . . . . . . . . . . . . . . . . . . . . . . . .
6.8 Other Design Considerations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.9 Fuels Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.10 Retrofit Considerations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
29
29
29
30
31
31
34
35
36
38
39
7
PILOTS AND IGNITORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
7.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
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Copyright American Petroleum Institute
Provided by IHS under license with API
No reproduction or networking permitted without license from IHS
1
1
1
1
18
18
19
19
19
19
20
v
Licensee=Chevron Texaco API 22 loc/6 usr Part 1/1000001100, User=Heron, Jonathan
Not for Resale, 07/30/2006 11:33:30 MDT
CONTENTS
Page
7.2
7.3
Pilot Burners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Ignitors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
8
MECHANICAL. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.1 Plenum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.2 Air Registers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.3 Burner Tile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.4 Fuel Tips. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.5 Ports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.6 Materials of Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.7 Burner Piping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
43
43
43
43
44
44
44
45
9
OPERATION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.1 Light-off Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.2 Excess Air Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.3 Draft Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
47
47
49
49
10 MAINTENANCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.1 Shipping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.2 Burner Parts Inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.3 Installation and Initial Set-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.4 Post-Installation Checkout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.5 Maintenance Program. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
50
50
53
53
53
53
11 TESTING. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11.2 Test Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11.3 Test Fuels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11.4 Air Supply. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11.5 Pilot and Ignitors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11.6 Main Burner Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11.7 Test Instrumentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11.8 Measurements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
54
54
55
55
56
57
57
59
59
12 TROUBLESHOOTING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12.1 Burner Plugging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12.2 Scale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12.3 Liquid/Aerosol Carryover . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12.4 Unsaturates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12.5 Amines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12.6 Chlorides and Ammonia. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12.7 Burner Operation Trouble Shooting Table. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
60
60
60
60
63
63
63
63
APPENDIX A Burner data sheet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
Figures
1
Raw Gas Burner . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2
Premix Gas Burner . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3
Radiant Wall Burner . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
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Copyright American Petroleum Institute
Provided by IHS under license with API
No reproduction or networking permitted without license from IHS
Licensee=Chevron Texaco API 22 loc/6 usr Part 1/1000001100, User=Heron, Jonathan
Not for Resale, 07/30/2006 11:33:30 MDT
CONTENTS
Page
4
5
6
7
8
9
10
11
12
13
14
15
16
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Tables
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
Copyright American Petroleum Institute
Provided by IHS under license with API
No reproduction or networking permitted without license from IHS
Combination Oil and Gas Burner . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Low NOx Stage Air Combination Oil and Gas Burner . . . . . . . . . . . . . . . . . . . . . 10
Low NOx Staged Fuel Gas Burner . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
High Intensity—Combination Oil and Gas Burner . . . . . . . . . . . . . . . . . . . . . . . . 12
Effect of Excess Oxygen on NOx in Raw Gas Burners . . . . . . . . . . . . . . . . . . . . . 13
Effect of Combustion Air Temperature on NOx Production in Low NOx Burners 13
Effect of Firebox Temperature on NOx Production . . . . . . . . . . . . . . . . . . . . . . . . 14
Effect of Hydrogen Content of the Fuel Gas Hydrogen on NOx Production . . . . 14
Effect of Fuel Oil Nitrogen Conten on NOx Production . . . . . . . . . . . . . . . . . . . . 15
Inside Mix Atomizer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Port Mix or Steam Assist Atomizer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Graph of Development in Low NOx Burner Technology for
Typical Gas Fired Burners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Approximate Conversion Factor from #/MM Btu NOx (HHV)
to ppmv (3% O2 Dry Basis) Based on Typical Refinery Fuel . . . . . . . . . . . . . . . . 31
Staged Air Burner . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Staged Fuel Burner . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Example of One Type of Enhanced Flue Gas Recirculation Burner . . . . . . . . . . . 35
Burner-to-furnace Interaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Typical Draft Profile in a Natural Draft Heater . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
Natural Draft Heater Adjustment Flow Chart. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
Burner Performance Test Points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
Typical Burner Test Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
Clarification Table Comparing Definitions in API Standard 560 and RP 535. . . . . 5
Effects of Reduced Excess Air on Burner Emissions. . . . . . . . . . . . . . . . . . . . . . . 17
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Typical NOx Emissions for Oil Firing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Air Register Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Fuel Gas Burner Components. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
Fuel Oil Burner Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
Burner Housing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
Burner Tile. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
Optimum Excess Air Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
Guideline to Adjust Stack Damper and Burner Registers . . . . . . . . . . . . . . . . . . . 50
Conventional Gas Burners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
Oil Burners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
Low NOx Burners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
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Burners for Fired Heaters in General Refinery Services
1 General
1.1 SCOPE
This recommended practice provides guidelines for the selection and/or evaluation of burners installed in fired heaters in general
refinery services. Details of fired heater and related equipment designs are considered only where they interact with the burner
selection. This recommended practice does not provide rules for design but indicates areas that need attention. It offers information and descriptions of burner types available to the designer/user for purposes of selecting the appropriate burner for a given
application.
The burner types discussed are those currently in industry use. It is not intended to imply that other burner types are not available
or recommended. Many of the individual features described in these guidelines will be applicable to most burner types.
1.2 REFERENCED PUBLICATIONS
The editions of the following standards, codes and specifications that are in effect at the time of publication of this recommended
practice shall, to the extent specified herein, form a part of this recommended practice. Changes in referenced standards, codes
and specifications shall be mutually agreed to by the owner and the vendor.
API
RP 556
Std 560/
ISO 13705
Instrumentation and Control Systems for Fired Heaters and Steam Generators
Fired Heaters for General Refinery Services
AMCA1
Std 500
Test Methods for Louvers, Dampers and Shutters
ASTM2
D396
Specification for Fuel Oils
NFPA3
85
Boiler and Combustion System Hazards Code
1.3 DEFINITION OF TERMS
1.3.1 adiabatic flame temperature: The adiabatic flame temperature is the theoretical flame temperature calculated at adiabatic conditions.
1.3.2 aerosols: A suspension of fine solid or liquid particles in gas (smoke, fog, and mist are aerosols).
1.3.3
ratio.
air/fuel ratio: The ratio of the combustion air flow rate to the fuel flow rate. Air/fuel ratio is the reciprocal of fuel/air
1.3.4 air register: That part of a burner that can admit combustion air through openings around the burner assembly.
1.3.5 atomization: The breaking of a liquid into tiny droplets to improve fuel-air mixing and improve combustion. Steam, air
and fuel gas can be used as atomizing media. Steam is the most common in the refining industry. Atomization may also be
accomplished by mechanical means.
1.3.6 auto-ignition temperature: The lowest temperature required to initiate self-sustained combustion in the absence of a
spark or flame.
1.3.7 blowoff: The lifting of a flame due to the velocity of the fuel-air mixture exceeding the flame velocity. This usually
results in the flame being extinguished.
1Air Movement and Control Association International, Inc. 30 W. University Drive, Arlington Heights, Illinois, 60004. www.amca.org.
2ASTM International, 100 Barr Harbor Drive, Wes Conshohocen, Pennsylvania 19428-2959. www.astm.org.
3National Fire Protection Association, 1 Batterymarch Park, Quincy, Massachusetts 02169, www.nfpa.org.
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API RECOMMENDED PRACTICE 535
1.3.8 burner: A device for the introduction of fuel and air into a heater at the desired velocities, turbulence and air/fuel ratio to
establish and maintain proper ignition and stable combustion.
The type of burner is normally described by the fuel(s) being fired, the method of air supply and emission requirements. Some
fuel examples are gas, oil and waste gas. Examples of air supply are natural draft and forced draft. Emission requirements are primarily directed towards NOx limitations.
1.3.9 burner throat: A restriction in the air flow path formed by the burner block and other burner components. The restriction initiates turbulence for the mixing of the fuel and air.
1.3.10 coalesce: To grow together.
1.3.11 coalescer: A process where aerosols in a fluid stream come in contact with the filter media, combining and growing to
a droplet size on the downstream surface of the media, which is of a size capable of being drained away by gravity.
1.3.12 CO break through: The point at which the CO level begins to increase rapidly upon reduction of excess air. This
break through will vary depending upon the fuel and the type of burner.
1.3.13 combination burner: A burner capable of burning gas or oil individually or simultaneously (Figure 4).
1.3.15 combustion products: Flue gases consisting of products of combustion including carbon dioxide, water vapor, and
additional components such as sulfur dioxide and ash.
1.3.16 draft: The difference in pressure that causes the flow of combustion air into the heater and flue gases through the heater.
The pressure differential is caused by the difference in the densities of the combustion products in the heater and stack and the air
external to the heater in natural draft heaters.
1.3.17 draft loss: Generally referred to as the air side pressure drop across a burner or the flue gas pressure drop across a portion of the heater system depending which heater component is being referred to.
1.3.18 excess air: The amount of air above the stoichioetric requirement for complete combustion, expressed as a percentage
1.3.19 filter: A porous article or mass (paper, sand, etc) through which a gas or liquid is passed to separate out matter in suspension.
1.3.20 firing rate: The rate at which fuel is supplied to a burner or heater. Usually expressed in heat units such as Btu/hr
(MW).
1.3.21 firing ports: The orifices in the fuel tip through which the fuel passes.
1.3.22 flame stabilization point: The location of the area within a burner that acts as a continuous ignition zone for the
flame. In natural draft burners, this is usually associated with a bluff body in the air stream or ledge in the burner tile in which a
flow eddy is located. In the case of some forced draft burners with an air-stabilized flame, a swirler in the air flow creates high
rotational flow patterns including reversing flow axial to the flow path which serves to anchor the flame just on or just above the
swirler.
1.3.23 flame stabilizer: A solid or perforated restriction in the combustion air stream which creates a flame stabilizing vortex downstream of the restriction. Bluff body stabilizer—see flame stabilizer.
1.3.24 flame temperature: The temperature reached during sustained combustion within the burner flame based upon the
degree of fuel mixing, excess air and heat radiating from it.
1.3.25 flame velocity: The rate at which a flame propagates through a combustible mixture.
1.3.26 flashback: The phenomenon that occurs when a flame front instantaneously propagates back into the direction of the
fuel-air mixture flow. Flashback occurs when the flame velocity exceeds the velocity of the fuel-air mixture through a burner nozzle.
1.3.27 forced draft: The difference in pressure produced by mechanical means that delivers air into a burner at a pressure
greater than atmospheric.
1.3.28 fuel: Any matter which releases heat when combusted.
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1.3.14 combustion: The rapid combination of fuel and oxygen which liberates heat.
BURNERS FOR FIRED HEATERS IN GENERAL REFINERY SERVICES
3
1.3.29 heat release: The heat liberated from the fuel, utilizing the lower heating value of the fuel, expressed as Btu/hr.
1.3.30 heating value, higher: The total heat obtained from the combustion of a specified fuel at 60°F, expressed as Btu per
pound or per cubic foot which includes the latent heat of vaporization of water; also called gross heating value.
1.3.31 heating value, lower: The higher heating value minus the latent heat of vaporization of the water formed by combustion of hydrogen in the fuel, expressed as Btu per pound or per cubic foot; also called net heating value.
1.3.32 high intensity burner: A burner in which combustion is completed within a fixed volume resulting in a combustion intensity greater than 1,000,000 Btu/hr/cu.ft (Figure 7).
1.3.33 hydrogen/carbon ratio: The weight of hydrogen in a hydrocarbon fuel divided by the weight of carbon.
1.3.34 ignition ports: Orifices in the burner tip that fire a portion of the fuel (typically 10%) onto a tile ledge or flame holder
to form a continuous ignition zone that is used to stabilize the main burner flame.
1.3.35 ignitor: A device used to light a pilot or main burner.
1.3.36 induced draft: The difference in pressure (between inside and outside of the heater) produced by mechanical means
resulting in a negative pressure in the heater that causes the flow of combustion air into the heater.
1.3.37 inspirator: A venturi device used in premix burners that utilizes the kinetic energy of a jet of gas issuing from an orifice to entrain all or part of the combustion air.
1.3.38 knock out drum: A device to remove and store condensables and entrained liquids present in the gas stream.
1.3.39 light off: Initial ignition of a fuel.
1.3.40 low NOx burner: A burner which is designed to reduce the formation of NOx below levels generated during normal
combustion in conventional burners.
1.3.41 mist eliminator: A device which creates a surface on which particles are able to coalesce and drop out of the gas
stream. A metal or plastic mesh mist eliminator is effective down to ~ 5 microns. A vane mist eliminator is effective down to ~ 20
microns.
1.3.42 muffler: A device used to reduce combustion noise propagated back through the burner.
1.3.43 natural draft: A difference in pressure resulting from the tendency of hot furnace gases to rise thus creating a partial
vacuum in the heater. This serves to draw combustion air into the burner.
1.3.44 pilot burner: A small burner that provides ignition of the main burner.
1.3.45 plenum: A chamber surrounding the burner(s) used to distribute air to the burner(s) or to reduce combustion noise;
windbox.
1.3.46 preheated air: Air heated prior to its use for combustion. The heating is most often done by heat exchange with hot
flue gases.
1.3.47 premix burner: A gas burner in which all or a portion of the combustion air is inspirated into a venturi-shaped mixer
by the fuel gas flow. The fuel and air are mixed prior to entering the initial combustion zone (Figure 2).
1.3.48 primary air: That portion of the total combustion air that first mixes with the fuel.
1.3.49 radiant wall burner: A premix burner where the flame does not project into the firebox but fans out alongside the
wall on which it is installed (Figure 3).
1.3.50 raw gas burner: A gas burner in which combustion takes place as the fuel is mixed with the combustion air downstream of the fuel tips; nozzle mix burner (Figure 1).
1.3.51 secondary air: That portion of the total combustion air that is supplied to the products of combustion downstream of
the primary combustion zone.
1.3.52 secondary fuel: The remaining portion of fuel that is injected downstream of the burner block in a staged fuel burner.
1.3.53 specific gravity: The ratio of the density of a gas to the density of dry air at standard temperature and pressure.
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API RECOMMENDED PRACTICE 535
1.3.54 spider: Gas tip configuration resembling the hub of a wheel and spokes where the spokes contain the gas exit orifices
1.3.55 spud: A device with a small gas orifice designed to limit gas flow to a desired rate. Pilot burners contain a spud controlling the amount of gas that flows into the fuel/air mixing venturi.
1.3.56 stability: That quality of a burner enabling it to remain lit over a wide range of fuel-air mixture ratios and input rates.
1.3.57 staged air burner: A low NOx burner in which a portion of the combustion air is injected downstream of the burner
block to mix with the combustion products from the primary combustion zone (Figure 5).
1.3.59 stoichiometric air: The chemically correct amount of air required for complete combustion with no unused fuel or
air.
1.3.60 stoichiometric ratio: The ratio of fuel and air required for complete combustion such that the combustion products
contain no oxygen.
1.3.61 strainer: A device to retain solid pieces while a gas/liquid passes through the device. Typical strainer basket size is
1/64 in. perforation (40 mesh, approx. 380 microns).
1.3.62 swirl number: The ratio of angular to axial discharge momentum. It defines the amount of mixing and internal flame
recirculation.
1.3.63 tertiary air: A third portion of the total combustion air that is supplied to the products of combustion in addition to primary and secondary air.
1.3.64 tile: Refractory block surrounding the burner components. The block forms the burner's air flow opening and helps stabilize the flame; burner tile; muffle block; quarl.
1.3.65 turndown: The ratio of the maximum to minimum fuel input rates of a burner while maintaining stable combustion.
1.3.66 Wobbe Index: An index to show gaseous fuel interchangeability. Wobbe number or index is equal to the gross heating value in Btu/cubic foot (MJ/cubic meter) divided by the square root of the gas specific gravity.
Table 1 is a comparison, for clarification purposes, of the definitions in API Standard 560 and this document.
2 Environmental Considerations
2.1 GENERAL
Combustion reactions can produce noise and chemical species that may be of concern to humans, animals and the environment.
Different localities may have standards that regulate these pollutants. The user must be aware of them. This publication is not
undertaking the duties of employers, manufacturers, or suppliers to warn, properly train and equip their employees, and others
exposed, concerning health and safety risks, nor is it undertaking their obligations under local, state or federal laws.
2.2 NOISE
The design of the burner can affect noise production. Fuels requiring hgh velocities, such as used in high intensity burner designs
or containing high hydrogen, may raise noise levels. Fans, burners, ducts and stacks may have to be equipped with noise attenuating materials. Different localities may have regulations that regulate noise.
2.3 FLUE GAS EMISSIONS
2.3.1 Nitrogen Oxides, NOx (usually reported as NO2)
Nitrogen oxides is the generic term for a group of gases, all of which contain varying amounts of nitrogen and oxygen. Many of
the nitrogen oxides are colorless and odorless. Nitrogen oxides (NO) form when fuel is burned at high temperatures, as in the
combustion process of a fired heater. The majority of the nitrogen oxides formed in fired heaters is in the form of nitric oxide
(NO). NO is eventually transformed to nitrogen dioxide (NO2) after discharging into the atmosphere. Nitrogen dioxide (NO2) is a
reddish brown, highly reactive gas.
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1.3.58 staged fuel burner: A low NOx burner in which a portion of the fuel is mixed with all of the combustion air within
the burner block while the remainder of the fuel is injected downstream of the burner block to provide delayed combustion (Figure 6).
BURNERS FOR FIRED HEATERS IN GENERAL REFINERY SERVICES
5
Table 1—Clarification Table Comparing Definitions in API Standard 560 and RP 535
API Std 560/ISO 1370
Burner Heat Release
API RP 535
Definition
Burner Heat Release
Definition
Maximum Stable Heat Release
The maximum heat release for the
burner at the point of CO breakthrough with the air register at the
same setting as “design” heat
release or 100% open
Maximum
The heat release for the burner
with design excess air and design
draft loss with air register 100%
open
Design
The heat release per burner includ- Design
ing a defined capacity margin as a
percent of the calculated “normal”
heat release
The specified “design” heat
release for the burner with the air
register set for the design excess
air with design draft loss
Normal
Normal
The heat release per burner
required for the design total
absorbed duty for the heater
divided by the calculated fuel efficiency
The specified “normal” heat
release for the burner with the air
register set for the design excess
air with design draft loss
Minimum
The heat release per burner for the Minimum
specified turndown of the heater
or burner
The specified “minimum” heat
release for the burner with the air
register set at the same setting as
the “normal” heat release or with
the air register set for the design
excess air
Minimum Stable Heat Release
The minimum heat release for the
burner at the point of CO breakthrough with the air register at the
same setting as “normal” heat
release
NOx Production Trends
Effect of Excess Oxygen
NOx concentrations will increase as the excess oxygen increases in raw gas burners and will decrease in premix burners. This is
true for typical refinery heater excess oxygen levels (1 – 5% O2 wet basis). As excess air is increased further to a raw gas burner,
the NOx concentration will reach a maximum. Beyond this point, the NOx concentration begins to decline with a further increase
in excess oxygen. This maximum may occur at excess air levels in the vicinity of 60 – 70% (7 – 8% O2, wet basis).
Figure 8 shows the effect excess oxygen has on NOx production in raw gas burners. This figure is representative only and not
intended for design or correction.
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API RECOMMENDED PRACTICE 535
Air
Air
Gas
Pilot
Figure 1—Raw Gas Burner
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BURNERS FOR FIRED HEATERS IN GENERAL REFINERY SERVICES
7
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Secondary air
Primary air
Spud
Pilot
Gas
Figure 2—Premix Gas Burner
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API RECOMMENDED PRACTICE 535
Gas
Air
Figure 3—Radiant Wall Burner
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BURNERS FOR FIRED HEATERS IN GENERAL REFINERY SERVICES
Gas tips (typical 4)
Secondary tile
Primary tile
Secondary air
Primary air
Pilot
Oil gun
Figure 4—Combination Oil and Gas Burner
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9
10
API RECOMMENDED PRACTICE 535
yy
@@
;;
@@
;;
yy
yy
@@
;;
@@
;;
yy
Tertiary air
Tertiary air
Secondary air
Gas
Primary air
Pilot
Oil
Steam
Figure 5—Low NOx Stage Air Combination Oil and Gas Burner
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BURNERS FOR FIRED HEATERS IN GENERAL REFINERY SERVICES
11
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yy
@@
;;
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;;
yy
@@ yy
;;
yy
@@
;;
Secondary fuel
Primary fuel
Air
Air damper
Pilot
Secondary fuel
connection
Primary fuel
connection
Figure 6—Low NOx Staged Fuel Gas Burner
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12
;@yy;@ yy
@@
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;;;;
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@@@@
;;;;
yyyy
API RECOMMENDED PRACTICE 535
Combustion
chamber
Air inlet
Oil connection
Steam connection
Figure 7—High Intensity—Combination Oil and Gas Burner
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Gas connection
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Ratio of NOx at new condition to
baselin econdition
Ratio of NOx at new condition to
baseline condition
1.00
1.20
1.40
1.60
1.80
2.00
1.00
2.00
3.00
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50
100
150
200
5.00
6.00
7.00
250
350
400
450
500
Combustion air temperature (degrees F)
300
600
650
8.00
700
Figure 9 Effect of Combustion Air Temperature on NOx Production in Low NOx Burners
550
Figure 8 Effect of Excess Oxygen on NOx in Raw Gas Burners
Note: This figure is a generic curve and not applicable to idnividual low NOx burner designs
0
4.00
Percent oxygen in combustion products
Note: This figure is representative only and not intended for design or correction.
0.00
1.00
1.20
1.40
1.60
1.80
2.00
750
800
9.00
BURNERS FOR FIRED HEATERS IN GENERAL REFINERY SERVICES
13
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Ratio of NOx at new condition to
baseline condition
Ratio of NOx at new condition to
baseline condition
1350
1400
1450
1500
1550
1650
1.600
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0
10
20
1750
1800
30
50
60
Volume percent hydrogen in fuel gas
40
1900
Figure 11—Effect of Hydrogen Content of the Fuel Gas Hydrogen on NOx Production
70
80
1850
Figure 10—Effect of Firebox Temperature on NOx Production
Note: This figure is a generic curve and not applicable to idnividual low NOx burner designs
1.000
1.050
1.100
1.150
1.200
1.250
1.300
1.350
1.400
1.450
1.500
1.550
1700
Furnace firebox temperature (degrees F)
1600
Note: This figure is a generic curve and not applicable to idnividual low NOx burner designs
1300
1.00
1.20
1.40
1.60
1.80
2.00
2.20
2.40
90
1950
100
2000
14
API RECOMMENDED PRACTICE 535
Figure 12—Effect of Fuel Oil Nitrogen Content on NOx Production
Weight percent fuel nitrogen in liquid fuel
Note: This figure represents a general trend and is not intended to be a general correction applied to burner data.
1.00
1.50
2.00
2.50
3.00
0
0.10
0.20
0.30
0.40
0.50
0.60
BURNERS FOR FIRED HEATERS IN GENERAL REFINERY SERVICES
Ratio of NOx at new condition to
baseline condition
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API RECOMMENDED PRACTICE 535
Effect of Combustion Air Temperature
NOx production is favored by high temperatures. Local flame temperatures and NOx concentrations will increase as the temperature of the combustion air increases.
Figure 9 shows the effect the combustion air temperature has on NOx production in low NOx burners.
NOx concentrations will increase as the firebox temperature increases. The choice of burners can have an effect on the firebox
temperature therefore affecting the NOx. Burners creating different heat flux variations within a furnace will produce differing
firebox temperature patterns. The style of burner and the degree of swirl can affect box temperatures and the conversion to nitrogen oxides.
Figure 10 shows the effect the firebox temperature has on NOx production.
Effect of Hydrogen in the Fuel Gas
Increasing the hydrogen content will typically raise the flame temperature. The increase in flame temperature will produce more
NOx.
Figure 11 shows the effect the hydrogen content of the fuel gas has on NOx production. Note: This graph shows a typical trend
and does not apply to all burners as some of the new generation burners mitigate these effects.
Effect of Nitrogen in the Fuel Oil
Nitrogen in fuel oil is converted to what is called “fuel” NOx. The greater the quantity of bound nitrogen in the fuel oil, the greater
the total NOx produced.
Figure 12 shows the effect the fuel oil nitrogen content has on NOx production.
2.3.2 Sulfur Oxides, SOx (usually reported as SO2)
The production of sulfur oxides is a function of sulfur, hydrogen sulfide (H2S) and other sulfur compounds in the fuel. Sulfur
dioxide (SO2) may make up 94 – 98% of the total sulfur oxides produced. The remainder is sulfur trioxide (SO3). Operation at
low excess air levels will reduce the conversion of SO2 to SO3.
According to the U.S. EPA, together, SO2 and NOx, are the major precursors to acid deposition (acid rain).
2.3.3 Carbon Monoxide (CO) and Combustibles
Carbon monoxide (CO) is a colorless, odorless, poisonous gas formed when carbon in fuels is not burned completely. The carbon
monoxide content exiting from a burner will increase slowly as the excess air level decreases. The increase will accelerate as
excess air levels continue to decline. At a certain point, a further drop in excess air will produce an asymptotic increase in these
levels. The concentration curves of CO and combustibles will be similar in response to reducing excess air levels.
The point at which the CO level begins to increase rapidly upon reduction of excess air is referred to as the CO break through.
This break through will vary depending upon the fuel and the type of burner.
2.3.4 Particulates
All fuels will contain or produce particulates. Particulates will be formed in greater quantities in fuel oils (especially in heavy fuel
oils) than fuel gases. Ash in the fuel will be carried out the stack as particulates. Pyrolysis and polymerization reactions may produce highly viscous or solid particles that remain unburned when firing heavy fuel oils. These contribute to the quantity of the particulates which increase with heavier fuel oils. The asphaltene content and Conradson carbon number of a fuel oil can be an
indication of the particulate forming tendencies.
All particulates do not come from the fuel. Some may come from tube or fuel line scale as well as eroded refractory. Particulate
matter may be entrained within the combustion air in some locations.
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Effect of Firebox Temperature
BURNERS FOR FIRED HEATERS IN GENERAL REFINERY SERVICES
17
2.3.5 Volatile Organic Compounds (VOC)
According to the U.S. EPA (40 CFR, part 51.100), volatile organic compounds (VOC) are defined as any compound of carbon
which can participate in atmospheric photochemical reactions. Among the gases excluded are methane, carbon monoxide, carbon
dioxide, carbonic acid, metallic carbides, and ammonium carbonate.
2.4 FUEL COMPOSITION
The fuel composition will have a direct impact in the quantity of emissions leaving the heater. Care must be taken when firing gas
and oil in combination within the same burner as it may lead to increased emissions.
2.4.1 Nitrogen Oxides, NOx (usually reported as NO2)
Fuel gases will generally produce lower NOx levels than fuel oils.
Fuels with higher adiabatic flame temperatures will generally produce more NOx. High hydrogen fuels (producing high flame
temperatures) will frequently produce higher NOx levels than others.
Similarly, the addition of high end (C4+) unsaturates will frequently raise flame temperatures and NOx concentrations.
2.4.2 Sulfur Oxides, SOx (usually reported as SO2)
The quantity of sulfur or H2S in the fuel will govern the quantity of SOx produced. Reduction of SOx emissions involves switching to a sweeter fuel or providing removal facilities downstream.
2.4.3 Carbon Monoxide (CO) and Combustibles
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The combustion of hydrogen and paraffin rich fuel gases will produce a minimum of combustibles including CO. The presence of
unsaturated hydrocarbons, chlorides, amines, etc. can lead to plugging or damage burner tips disrupting the desired fuel/air mixing. This can raise the CO combustibles levels.
Heavy oils are more likely to produce greater levels of combustibles (including carbon monoxide) than lighter oils. The heavier
components are not as easily atomized and therefore not completely combusted. Polymerization and pyrolysis reactions are more
likely to occur which can lead to plugging and increased emissions.
2.4.4 Particulates
Heavy fuel oils are more likely to produce greater levels of particulates than light oils. The Conradson carbon number and ash
content can give the user a good comparative basis of the particulate forming ability of two fuels.
2.5 EXCESS AIR
Reducing excess air below design level will typically have the effects on the emissions from any one style of burner as shown in
Table 2:
Table 2—Effects of Reduced Excess Air on Burner Emissions
Pollutant
NOx
SOx
Carbon Monoxide
Combustibles
Particulates
Effect of Reducing Excess Air
Decrease
No change to the total SOx
Less SO2 will be converted to SO3
Increase
Increase
Increase
2.6 BURNER SELECTION
The owner should be aware that a burner chosen to limit one pollutant may produce higher emissions of another. For example, an
oil burner designed to produce a minimum of NOx may produce high particulates levels.
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API RECOMMENDED PRACTICE 535
2.6.1 Nitrogen Oxides (NOx) (usually reported as NO2)
The fuel composition will normally determine the NOx level leaving a conventional burner with no NOx reduction techniques.
The NOx levels may be reduced 30% if staged air burners rather than conventional burners are employed.
The NOx levels may be reduced 60% or more if staged fuel burners (currently applicable to fuel gas firing only) rather than conventional burners are employed.
NOx levels may be reduced further than 60% using the latest generation of low NOx burners with the addition of flue gas recirculation as well as fuel gas staging.
For additional information, see Section 6, Low NOx Burners.
2.6.2 Carbon Monoxide (CO) and Combustibles
Burners that provide a superior degree of mixing allow improved combustion at lower excess air levels. This results in reduced
combustibles and CO emissions at equivalent excess air levels.
2.6.3 Particulates
Burners with greater swirl and/or higher combustion air pressures (such as forced draft burners) are likely to produce lower particulates since they provide a superior degree of mixing which reduces the formation of particulates.
3 Combustion Air
Burners are broadly categorized into two types—natural draft and forced draft. Burners are sized based on consideration of the
total air side pressure drop or “draft loss” across the burner. The primary draft loss for a burner is across the burner throat with
other components such as air registers and entrance effects accounting for the balance. The burner sizing and the draft loss shall
consider corrections for both temperature and atmospheric pressure.
Ideally at burner design conditions for conventional NOx emission gas burners only, a minimum of 90% of the available draft with
the air register fully opened should be utilized across the burner. In addition, a minimum of 75% of the draft loss with the air registers fully open should be utilized across the burner throat.
3.1.1 NATURAL DRAFT BURNERS
The combustion air for natural draft burners is induced through the burner either by the negative pressure inside the firebox or by
fuel gas pressure educting the air through a venturi.
Natural draft burners are the simplest and least expensive burners available. They are the most common found in refinery service.
3.1.2 FORCED DRAFT BURNERS
Forced draft burners operate with combustion air supplied at a positive pressure. The term “forced draft” is so designated because
the combustion air or other oxygen source is normally supplied by mechanical means (i.e., a combustion air fan).
Forced draft burners normally operate at an air side delivery pressure in excess of 2 in. H2O (g). They utilize the air pressure to
provide a superior degree of mixing between fuel and air.
Forced draft burners are often used with air preheat systems. They are also used when turbine exhaust gas is supplied as a source
of oxygen.
The operating disadvantage of a forced draft system is the reliability of the fan and driver. Failure of either may shutdown the
heater and unit. The user must determine whether spare fans and drivers are required, incorporate measures to ensure reliability or
accept reduced load under natural draft conditions in the event of combustion air fan failure.
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3.1 DRAFT
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19
3.1.3 NATURAL DRAFT BURNERS IN FORCED DRAFT SYSTEMS
Natural draft burners are sometimes specified in air preheat systems where natural draft is required for continued operation when
the air preheater, fans or drivers fail. In such cases, air doors in air supply ductwork should open automatically to provide a source
of ambient air upon any of the above failures.
Burners have to be sized for the natural draft application. This may necessitate oversized burners for the forced draft air preheat
cases or reducing firing rates at natural draft conditions. Burner overdesign factors should be carefully reviewed or the system
may be unsatisfactory for forced draft operation.
The user should not specify additional margins to the forced draft maximum heat release if the burners are required to provide
maximum heat release under natural draft conditions.
Careful layout of the ducting and fresh air doors is recommended when natural draft burners are used for both natural and forced
draft applications. Equal air distribution to the burners under natural draft conditions must be considered when locating the fresh
air doors .
The ducting design should supply the air uniformly into the burner plenum. To obtain good air distribution the air supply ducting
should be properly designed with respect to air velocity and distribution. The velocity should be reduced at the air distribution
header at the heater. The velocity head in the air distribution header should not exceed 10% of the burner pressure drop to ensure
uniform air distribution to each burner. Avoid abrupt transitions that could cause air maldistribution into the burner plenum. The
use of turning vanes in elbows and transitions reduces pressure drop and provides more uniform flow patterns. CFD and cold flow
modeling are good tools to ensure proper air distribution.
3.2 DESIGN EXCESS AIR
3.2.1 For multiple burner applications, the user should consider limiting the reduction in excess oxygen to prevent some burners from running sub-stoichiometrically due to maldistribution of combustion air and/or the heater condition. Running below 2%
excess oxygen warrants additional safeguards, such as separate air control measurement and CO monitoring. In a poorly maintained heater where significant air leakage affects excess oxygen readings it may not be possible to run as low as 2% excess oxygen.
3.2.2 Excess oxygen required for good combustion depends on the burner design, the source of oxygen, the fuel fired and the
fuel conditions. Typical excess air conditions for fired heater design are given in Sections 4 and 5 for the respective fuels fired.
3.2.3 The design excess air of the burners may be lower than the specified excess air for the fired heater. This takes into consideration the number of burners, air distribution and air leakage into the fired heater.
3.3 COMBUSTION AIR PREHEAT
3.3.1 The addition of heat to the combustion air increases the efficiency of the combustion process. Combustion air preheat systems are described in Appendix E of API Standard 560.
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3.3.2 Higher air preheat temperatures will increase flame temperatures. This will increase the percentage of NOx in the flue gas.
This has to be considered when specifying equipment for low NOx emissions.
3.4 TURBINE EXHAUST GAS
3.4.1 The oxygen for the combustion of fuels in fired heaters can be supplied by oxygen containing gas streams such as the
exhaust from a gas turbine.
3.4.2 Gas turbine exhaust streams contain between 13 to 17 volume percent of oxygen at temperatures between 850°F and
1050°F and up to 10 in. H2O (g) pressure.
3.4.3 Burners can operate with oxygen contents down to approximately 15 volume percent in turbine exhaust streams. Combustion can become unstable below this level depending upon the temperature and burner type.
3.5 COMBUSTION AIR ADJUSTMENT
3.5.1 Burners are normally provided with airside control devices to adjust the air rate into the burner. Air registers or dampers
are provided for this purpose. Damper controls with positive click positions may be preferred to prevent involuntary movement of
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API RECOMMENDED PRACTICE 535
the air damper and allow for uniformity of excess air to each burner in a multi-burner system.
3.5.2 Some burners are provided with a single air flow adjustment. Others have two or three separate devices to allow the operator to distribute the air in different proportions within the burner.
3.5.3 Dampers or registers are provided on forced draft burners. Dampers or registers trim the air or provide a directional spin
to aid mixing of the fuel and air. Some forced draft burner vendors use the burner damper to evenly distribute the air throughout
the burner. Designing the damper for tight shutoff allows the burner to be removed from service without affecting the firebox
excess air level.
3.5.4 Total air flow to the fired heater is normally controlled at the inlet of the forced draft fan. When a forced draft fan serves
multiple branches of ductwork, control louvers in the combustion air duct should also be provided.
3.6 FLAME STABILITY
3.6.1 Good fuel and air mixing is one of the most important requirements for stable combustion. It affects the fuel/air proportioning, ignition temperature and speed of burning.
3.6.2 The mixing energy is measured at the point of discharge of the burner. It is provided by the potential and kinetic energies
of the fuel, the atomizing medium and the combustion air.
3.6.3 The mixing of the combustion air with the fuel is critical to flame stability. Too high a velocity will not allow mixing to
take place. The use of bluff body stabilizers to create local low pressure eddies can improve the mixing between the fuel and air.
3.6.4 Forced draft burners typically use high air-side pressure differential across the burner throat. This creates turbulence
within the burner improving the mixing process and enhances flame stability.
3.6.5 Mixing energy can be provided by the fuel discharge velocity and its direction of flow. Natural draft burners have to rely
more on fuel energy for mixing than do forced draft burners. They are more likely to have poorer mixing with burner turndown.
Natural draft burners normally require larger excess air rates than forced draft burners, particularly when operating at turndown.
3.6.6 The flame will extinguish if the temperature of the fuel/air mixture drops below the auto-ignition temperature. This can be
a problem on low NOx burners in cold fireboxes (below 1200°F). To insure flame stability of oil fired burners in turndown conditions, combustion air should be reduced proportionately. To maintain flame temperature, sufficient air for combustion must be
maintained for all firing conditions.
3.6.7 Stabilization of the flame can be achieved by the design of the refractory burner block. The burner block reradiates the
heat back into the mixture to keep the temperature above the auto-ignition conditions.
4 Gas Firing
4.1 RAW GAS FIRING (NOZZLE MIX)
4.1.1 Fuel Gas Pressure
Raw gas burners can be designed to operate over a wide range of fuel gas pressures. The gas pressure is normally selected as 15 –
20 psig for design liberation. This is to ensure reasonable tip drillings to reduce fouling problems during operation. It provides
reasonable pressures for fuel/air mixing at turndown.
Some process off-gas streams are only available at low pressures [around 8 in. H20 (g)]. They may be fired in raw gas burners with
proper tip design or in combination with other fuels in separate burner guns.
Burner capacity curves should be used as a guide for the acceptable gas pressure range. For pressures above the capacity curve,
consult with the burner manufacturer as lift-off and lack of combustion air may become problems.
Fuel gas pressure is typically read at a point in a supply header, but users should note that burner performance is determined by
pressure at the burner tip which can be substantially lower.
4.1.2 Fuel Composition and Effects
Raw gas burners are most suitable for handling fuel gases with a wide range of gas composition, gravity and calorific values.
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Fuel gas compositions can vary from high hydrogen contents to large percentages of hydrocarbons with high molecular weights.
The gases can contain quantities of other compounds, such as inerts (i.e, CO2, N2, water vapor and unsaturated hydrocarbons), all
of which have to be considered in the burner design and selection.
Raw gas burners are used when the fuel gas hydrogen content is over 70 mole percent, when the fuel composition is constantly
fluctuating, or the fuel gas contains a significant fraction of inerts (> 15 mole percent).
Raw gas burners may not be suitable for gases containing droplets of liquid or a high level of unsaturated hydrocarbons. Coke or
polymers can form in the burner tip blocking the tip drillings.
A raw gas burner with two separate gas nozzles can be supplied if burners are required to operate with a wide range of fuel gas
compositions and pressures.
Waste gas or gases containing a high percentage of inerts may require supplementary firing with another gaseous or liquid fuel to
stabilize the flame.
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Low heating value fuel gases without hydrogen will require special review by the burner designer. A waste gas stream with a heating value of 300 Btu/scf normally can operate without supplementary firing. Operation at lower heating values are possible if the
fuel gas contains hydrogen.
When the waste gas represents a large portion of the heater liberation, it should be spread over a large number of burners so that it
does not exceed 10 percent of the individual burner liberation. This is particularly important when the flow of the waste gas is
uncontrolled. Unsaturated hydrocarbons can quickly plug the smaller burner tip holes on all low NOx burners.
Higher hydrogen content in the fuel gas may result in higher NOx production. It also increases the stability of the flame.
4.1.3 Turndown
Raw gas burners can operate with a turndown ratio of 5 to 1 based upon a single fuel composition.
The range of fuel composition, gravity, calorific value, and available fuel pressure will affect the acceptable operating range of the
burner.
The low fuel gas pressure alarm and shutdown settings have to be selected within the stable operating range of the burner.
4.1.4 Excess Air
The following excess air values (excluding air leakage) are normally acceptable for good combustion on raw gas burners:
Table 3
Natural Draft
Forced Draft
Single Burner Systems
10 – 15 percent
5 – 10 percent
Multi-Burner Systems
15 – 20 percent
10 – 15 percent
4.1.5 Draft
Raw gas burners require draft in the range of 0.15 to 0.20 in. water gauge at the burner level for stability.
The amount of air supplied to a raw gas burner is largely dependent on the draft available at the burner because, unlike a premix
burner, very little air is inspirated by the fuel gas.
4.1.6 Flame Characteristics
The flame shape is determined by the burner tile, the drilling of the gas tip and the aerodynamics of the burner.
Round burner tiles are used to produce a conical or cylindrical flame shape. Flame lengths of 1 to 2 ft/MM Btu/hr for natural draft
burners are typical for fuel gases.
The gas tip drilling angle of a centered gas nozzle in a round burner tile affects the length of the flame; a 70° firing port total
included angle produces a relatively long narrow flame while a 100° total included angle gives a relatively short, wide flame pattern.
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API RECOMMENDED PRACTICE 535
Flat flame burners are designed with rectangular burner tiles and produce a fish tail shaped flame. These burners are used when firing close to refractory walls or where the tube clearance is limited.
4.1.7 Burner Liberation
Natural draft, raw gas burner liberation is normally within the range of 1.0 MM to 15 MM Btu/hr.
Forced draft burner liberation range is normally 4 MM to 20 MM Btu/hr for fired heater applications.
High intensity burners have heat liberations from 15 to 70 MM Btu/hr.
4.2 PREMIX FIRING
4.2.1 Fuel Gas Pressure
The fuel pressure in a premix burner is used to inspirate combustion air through a venturi prior to ignition at the tip of the burner.
The fuel gas pressure range is 15 – 35 psig at design liberation.
The minimum fuel pressure is restricted by the composition and range of the fuel specified. Typically, 3.0 psig is the minimum.
The burner capacity curve should be used as a guide for the acceptable gas pressure range. For pressures above the capacity curve,
consult with the burner manufacturer, as lift-off may become a problem.
Fuel gas pressure is typically read at a point in a supply header, but users should note that burner performance is determined by
pressure at the burner tip which can be substantially lower.
4.2.2 Fuel Composition and Effects
The premix burner produces a very stable and compact flame when operating under the appropriate conditions.
The velocity of the fuel/air mixture leaving the burner tip must exceed the flame speed, otherwise, the flames will burn back inside
the venturi (flashback). This is applicable to all operating conditions.
The turndown is severely limited when using gases with high flame speeds such as hydrogen. Fuels containing a hydrogen content of more than 70 mole percent are not generally recommended for premixed burner designs.
A variation in fuel gas composition may change the operating pressure of the fuel for a given heat liberation. This directly affects
the amount of combustion air inspirated.
Premix burners may not be suitable for fuels where the gas composition is constantly changing.
Waste gas can be burned via a premix burner, but may be severely limited by its pressure and composition. An eductor can be used
to introduce the fuel to the firebox with low pressure waste gas. Natural gas or steam can be used as the educting medium.
4.2.3 Turndown
The premix burner is normally limited in turndown to 3 to 1 for a single fuel gas composition.
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The burner turndown ratio may be limited when operating with a range of gas compositions.
Turndown is normally limited by flashback inside the venturi when considering high hydrogen content fuels.
The maximum liberation may not be achieved when operating with fuel gases much heavier than the design fuel. This is because
of the lack of air inspiration due to the low fuel gas pressure. Additional secondary air must be supplied to make up the deficiency.
4.2.4 Excess Air
Premix burners can operate at lower excess air values than raw gas burners because of the improved air/fuel mixing, 5 to 10%
excess air may be achieved in a single burner.
While premix burners can be utilized in forced draft applications, they are typically used for natural draft heaters only. This is due
to the burner’s unique air inspirating capabilities. Caution should be used when preheated air is considered with premix burners,
since high air temperature may cause ignition inside the burner tip and venturi.
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The primary air rate inspirated into the burner varies from 30 to 70% of the total combustion air requirement for typical refinery
premix burners. Unique furnace designs may require premix burners with as much as 100% primary air.
Table 4
Percent Excess Air
Operation
Natural Draft
Forced Draft
Burner Type
Raw Gas
Premix
Raw Gas
Single Burner
Systems
10 – 15
5 – 10
5 – 10
Multi-burner
Systems
15 – 20
10 – 20
10 – 15
4.2.5 Draft
Premix burners can be stable with very low draft (0.05 to 0.10 in. H20 minimum at the burner level when 100% premix air is used).
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The amount of primary air inspirated into the burner is dependent upon the fuel pressure and the design of the eductor.
Large heat release (greater than 4 MM Btu/hr) burners may not be capable of operating without a higher percentage of secondary air.
4.2.6 Flame Characteristics
The flame volume of a premix burner is smaller and more defined when compared to a raw gas design.
The flame shape is determined by the design of the gas tip and, to a certain extent, the shape of the refractory tile.
Designs with round tips produce a thin pencil-like flame.
Spider tips produce a short compact flame.
Fish tail tips produce a fan shaped flame for flat flame applications.
With radiant wall burners, the flame is designed to spread across the burner tile and the furnace wall refractory without any forward projection into the firebox.
4.2.7 Burner Liberation
The heat release for various burner designs normally varies from 0.5 to 15 MM Btu/hr.
5 Liquid Fuel Firing
5.1 TYPES OF FUEL OIL
5.1.1 Liquid fuels vary in composition, specific gravity and viscosity from light fuel oils, such as naphtha and light distillate
fuel, to heavy residual fuel oils. Other liquid fuels which are waste products of the process plant, such as tar, asphalt and pyrolysis
fuel oil, are also burned in fired heaters. It is necessary to atomize the liquid fuel into a fine mist to allow rapid vaporization and
proper mixing of the combustion air and fuel. Successful combustion of liquid fuels is dependent upon the atomizer design and
the fuel/atomizing medium conditions. Specification for grades of liquid fuels can be found in ASTM D396.
5.1.2 Lighter oils are easier to burn than heavier oils. Very heavy oils are difficult to atomize, especially in small heat release oil
guns due to small passages in the tips. Conversion from light to heavy oil and vice versa may require a different oil gun to obtain
good flame patterns.
5.1.3 Naphtha and Light Distillate Fuels
Naphtha is a mixture of liquid hydrocarbons having a true boiling point (TBP) range as broad as 60 to 400°F and a flash point
below ambient temperatures. The ability to vaporize at ambient temperatures, coupled with the low flash point requires specially
designed atomizers and safety features.
Naphtha is a highly flammable liquid and vaporizes at relatively low temperatures. It requires more stringent safety precautions to
protect against fire risk and furnace explosions.
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If liquid naphtha enters the combustion chamber and is not combusted, the unburned liquid will quickly evaporate and produce
dense vapors. It becomes a greater potential explosion hazard than fuel oil which, depending on the surrounding temperature, may
not vaporize.
Purging before light-off, burner gun removal and after shutdown is most important for naphtha and light distillate fuels. A purge
connection should be provided from the purge line to the fuel line at each burner. Use of this connection allows both the gun and
the last section of piping to be purged of fuel oil to prevent accidents.
The length of the fuel oil piping should be minimized to reduce the quantity of fuel to be purged. The rate of purging should be
controlled to avoid explosions.
It is mandatory that a safety interlock be provided at each burner when firing naphtha and light distillate fuels. This interlock
ensures that the fuel flow is shut off before the burner gun may be removed. It requires a purge of the gun before removal. The
interlock should ensure that the fuel flow cannot be turned on while the gun is removed, and that the oil cannot be opened prior to
opening the steam valve.
5.2 ATOMIZATION
5.2.1 Atomizer types commonly used in industry are as follows:
Atomizing medium. Atomizing media such as steam or air may be employed. Almost any gas or vapor can be used to atomize liquid fuel if it is available in sufficient quantity and pressure.
Mechanical atomization. The term mechanical atomization is normally associated with pressure jet atomization.
5.2.2 Steam Atomization
Steam is the most common medium for liquid fuel atomization in refinery practice.
Steam must be supplied dry or slightly superheated. Typically atomizers require a pressure of 100 – 150 psig. Higher steam pressures (300 – 400 psig) may be required when atomizing heavy liquid fuels such as residuals and pitch.
Wet steam must be avoided to prevent water droplets forming in the piping or burner gun. The heat to vaporize the water will
absorb much of the heat necessary for ignition and complete combustion.
A high degree of steam superheat can partially vaporize the liquid fuel within the burner gun and atomizer. This can cause oil gun
vapor lock.
Steam atomization and steam assist atomization are most common. The difference between the two types of atomization is the
degree of pressure atomization utilized. A steam assist system normally requires higher fuel oil pressures and uses less steam.
5.2.2.1 Steam (Inside Mix) Atomizers
A steam or internal mix atomizer is shown in Figure 13. Item 1 is a limiting orifice for fuel oil flow. Steam is injected through the
steam ports (Item 2) and mixed with partially atomized fuel oil. The steam and oil mixture is discharged through the tip ports
(Item 3) where additional atomization and flame shaping occurs.
Fuel pressure is typically in the range of 80 – 120 psig. Lower fuel oil pressures normally limit the turndown while higher fuel oil
pressures will reduce steam consumption. The atomizing steam pressure is normally maintained at a constant differential pressure
of approximately 20 to 30 psi above the fuel pressure.
The nominal steam consumption is approximately 0.15 – 0.30 pounds per pound of fuel oil. Higher rates may be required when
firing heavy and viscous fuels. The steam rate is dependent upon the differential utilized and the design fuel oil pressure. High
pressure atomizer designs require less steam while low pressure atomizer designs may require substantially more.
Advantages of the steam atomizer include a large fuel orifice that is less susceptible to plugging and a low fuel oil pressure
requirement. The main disadvantage is high steam consumption.
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5.2.2.2 Steam Assist (Port Mix or Y Jet) Atomizers
A steam assist or port mix atomizer is shown in Figure 14. The fuel oil is supplied through a series of limiting orifices in the tip
(Item 1). A set of steam orifices (Item 2) is also found in the tip. The fuel oil and steam mix in the discharge port where final atomization takes place.
Steam pressure is normally held constant at approximately 100 – 150 psig throughout the operating range.
The steam consumption is approximately 0.10 to 0.20 pounds per pound of fuel oil at maximum liberation. The steam rate per
pound of fuel will increase at turndown since the steam is at constant pressure.
The steam assist atomizer is mainly selected for larger heat release burners. The main advantage of this atomizer is low steam consumption while the disadvantages include small fuel oil ports and high fuel oil and steam pressure requirements.
Steam atomizers designed for light fuel oils, such as naphtha and light distillates, are provided with separate tubes for the oil and
steam. This is to prevent the steam temperature from vaporizing the oil in the gun.
5.2.3 Air Atomization
Air atomization is often recommended when light fuel oils are to be fired to prevent vapor lock.
Compressed air can be used to atomize fuel oil when steam is not available.
Compressed air systems use the same atomizer type as described in the steam atomizer designs. Generally 100 – 120 psig plant air
pressure is suitable.
Low pressure (1 – 2 psig) air atomization can be provided in some burner designs.
5.2.4 Mechanical Atomization
The term mechanical atomization is normally associated with pressure jet atomization. Other mechanical designs are available but
are not regularly used in refinery fired heaters.
The pressure jet atomizer breaks the liquid down into small droplets by using a high pressure drop across the burner tip.
The fuel supply pressure has to be sufficiently high to obtain a suitable turndown unless a high pressure recirculation type of
atomizer is used.
The fuel oil pressure at minimum turndown is approximately 80 – 100 psig. To obtain a turndown of 3 to 1, the fuel pressure for
the design liberation would be 700 – 900 psig.
This type of atomization is usually only found with forced draft burners of high heat release. The orifice size is small and is susceptible to fouling with small burners.
The high fuel oil pressures used for this type of atomizer requires special safety considerations.
Mechanical atomization is normally used when no other atomizing media is available and is not recommended for natural draft
service because the fuel/air mixing is poor.
5.3 FUEL PHYSICAL PROPERTIES
5.3.1 Temperature and Viscosity
Fuel oil temperatures must be sufficient to get the correct viscosity for proper combustion.
Table 5
Design Viscosity
120 SSU
20 cS
Maximum Viscosity
200 SSU
45 cS
Viscous liquid fuels (such as #6 oil, vacuum bottoms, pitch, tar, etc.) generally do not atomize well unless heated to reduce viscosity. Experience with the fuel and atomizer type will dictate the amount of heating required and the type of control system necessary. The fuel temperature for fuel oils with a wide boiling range must not be too high or vaporization in the oil gun will occur.
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API RECOMMENDED PRACTICE 535
5.3.2 Fuel Composition and Effects
5.3.2.1 Water
High water levels in the fuel can result in an oil that will not burn properly. The presence of water can affect burner operation and
disrupt atomization. The latent heat of the water will absorb much of the heat necessary for ignition and complete combustion.
Water can also contribute to erosion of the burner tips.
Water can be of benefit if it forms an emulsion with the oil. Special chemicals or mechanical devices are available to produce
emulsions. These emulsions, in some cases, can improve combustion and aid efficiency. They may increase erosion of the burner
tip and require frequent tip replacement.
The content of water and sediment in the fuel should be not more than 1% by weight unless emulsifiers are employed.
5.3.2.2 Solids
Sediment often leads to atomizer plugging and flameout. Special hardened steels are required to reduce erosion (see 8.6.2). The
fuel oil should be filtered through a duplex strainer to prevent burner plugging. The strainer should contain screens whose openings are no larger than one-half the diameter of the smallest downstream orifice. Severe erosion can result when fine particulates
such as catalyst fines are present.
5.3.2.3 Ash
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High vanadium and/or sodium levels will cause degradation of the burner refractory. Special high alumina refractory can be used
in the burner tiles to reduce degradation. The need of higher grade refractory is dependent upon the choice of burner and the
degree of sodium and vanadium in the fuel. The burner vendor should be consulted as to the choice of burner tile material and
expected frequency of replacement.
5.3.2.4 Carbon Content
Excessive soot and particulate emissions often occur with oils that have high asphaltenes, C/H ratio, or Conradson carbon (above
10 wt. %). High asphaltene oils are more prone to burner tip coking problems. These problems can be overcome by proper fuel
blending and tip design.
5.3.2.5 Unstable Oil Blends
Certain cracked oils may not blend into a stable mixture with certain light cutter stocks. Burner tip and strainer plugging result
from unstable oil blends that cause asphaltene precipitation and polymer formation. Fuel oils containing unsaturated hydrocarbons may crack in the oil gun. This can cause fouling of the burner tip.
5.3.2.6 Wide Boiling Range Blends
Burner pulsation can result with steam atomizing when low boiling fractions prematurely vaporize. Ignition and stability problems can occur with wide boiling range oil blends.
5.3.2.7 High Wax Content
Fuel oils with high wax contents are prone to plugging if proper storage and delivery temperatures are not employed.
5.3.2.8 Nitrogen Content
Fuel bound nitrogen results in higher NOx emissions.
5.3.3 Flame Stability
Flame stability is dependent upon good fuel/air mixing. There must be good atomization to achieve good mixing.
The oil tip is positioned in the primary tile or oil stabilization device to maximize flame stability for oil firing. The stabilizing
device creates a low pressure zone in the vicinity of the oil tip. This forces the recirculation of an oil mist into the hot combustion
zone created by the primary tile. This stabilizes the flame and aids in vaporization of the fuel oil.
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27
The position of the oil tip is critical. If the oil tip is raised too high in the stabilizing device, the recirculation effect is lost and
flame stability suffers. If the oil tip is too low in the stabilizing device, impingement of raw oil on the stabilizing device occurs and
coking and oil spillage may result.
Unstable conditions will occur when fouled oil guns or atomizers prevent proper mixing. Operation at too great of a turndown will
cause flame instability.
5.4 TURNDOWN
5.4.1 The turndown of liquid fuel burners is dependent upon the fuel pressure available and the atomizer design.
5.4.2 Typical turndown ratios and fuel pressures are as follows:
Table 6
Turndown Design Pressure,
Minimum
Ratio
psig
Pressure, psig
Internal Mix Atomizer 3 to 1
120
30
Port Mix Atomizer
4 to 1
150
30
Mechanical Atomizer
2 to 1
600
100
5.4.3 The size of the burner is a factor in determining the turndown. Small burners have a lower turndown ratio.
5.5 EXCESS AIR
5.5.1 Typical excess air values for burners firing a single liquid fuel are as follows:
Table 7
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Operation
Fuel
Natural Draft Naphtha
Heavy Fuel Oil
Residual Fuel Oil
Forced Draft Naphtha
Heavy Fuel Oil
Residual Fuel Oil
Single Burner
Multi-Burner
Systems, percent Systems, percent
10 to 15
15 to 20
20 to 25
25 to 30
25 to 30
30 to 35
10 to 12
10 to 15
10 to 15
15 to 25
15 to 20
20 to 25
5.5.2 The minimum excess air is determined by stability and complete combustion. A rapid increase in unburned particles of
fuel is detected in the combustion products when combustion is not complete.
5.5.3 Burners should be able to operate with a maximum carbon monoxide content of 50 (v) ppm for naphtha and 150 (v) ppm
for residual fuels at design firing rate.
5.5.4 Specific emission limitations may determine the excess air required to prevent pollution in the atmosphere.
5.6 FLAME CHARACTERISTICS
5.6.1 Oil flames are generally larger in volume than gas flames of the same heat release and produce higher flame luminosity
and radiant heat flux.
5.6.2 The majority of liquid fuel burners are designed with round burner tiles and produce conical flame shapes. Special flat
flame burners are available with rectangular tiles and special tip drillings to produce a flat, fishtail flame shape. These are used in
close proximity to refractory walls and where clearances to the heating surfaces are limited.
5.6.3 The drilling of the oil tip determines the shape and length of the flame. The normal included angle of a burner tip is 40 to 70°.
With a 50° included angle, the flame length will be approximately 2 feet per MM Btu/hr for natural draft burners. Reducing the angle
to 40° produces a longer, narrower flame. Increasing the angle to 70° produces a shorter, bushier flame.
5.6.4 Forced draft burners produce a shorter flame because of the better mixing between the air and fuel.
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API RECOMMENDED PRACTICE 535
5.7 BURNER LIBERATION
5.7.1 Natural draft burner liberation is normally in the range of 3 to 15 MM Btu/hr.
5.7.2 Forced draft burner liberation can be in the range of 5 to 70 MM Btu/hr.
5.7.3 High intensity burner liberation is normally in the range of 10 to 70 MM Btu/hr.
5.8 COMBINATION FIRING
5.8.1 Some refinery fired heater burners are designed to operate with both liquid and gas fuels.
5.8.2 The oil gun is located on the centerline of the burner and the gas tips are arranged around the outside perimeter of the oil stabilization device (primary tile, swirler, bluff body, etc).
5.8.3 Combination burners are designed to operate on either oil or gas. A combination burner can normally operate on either
fuel at the full heat release of the burner.
5.8.4 Combination burners are commonly designed to operate on both fuels simultaneously. It is important that the design heat
release of the burners is not exceeded, otherwise there will be insufficient air for proper combustion.
5.8.5 The burner tips may be designed for partial heat release of the burner to improve the turndown performance of each fuel.
5.8.6 Firing in combination with both liquid and gas fuels will increase the length and volume of the flame and may cause coking of the oil and gas tips.
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Sleeve
2
Atomizer
Oil tip
Oil spud
3
Steam
Oil
1
Figure 13—Inside Mix Atomizer
Oil tip
Male inner channel seal
1
Oil
Steam
2
Figure 14—Port Mix or Steam Assist Atomizer
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29
Typical Gas Firing Only
140
0.18
0.16
0.14
100
0.12
80
0.1
60
0.08
184
0.06
40
0.04
1986
20
NOx , lb/MMBTU, HHV
NOx ppmvd @ 3% O2
120
1992
0.02
2001
0
Enhanced Internal
Flue Gas
Recirculation
Internal Flue Gas
Recirculation
Staged Fuel
Staged Air
Conventional
0
Figure 15—Graph of Development in Low NOx Burner Technology for Typical Gas Fired Burners
6 Low NOx Burners
6.1 GENERAL
The production of nitrogen oxides occurs in three ways during the combustion process: (1) Prompt or immediate conversion
(prompt NOx)— the production of NOx from N2 within the early stages of the combustion process through a hydrocarbon radical
mechanism. (2) Thermal conversion (thermal NOx)—the temperature dependent oxidation of molecular nitrogen (N2) to NOx.
The thermal NOx reactions are favored by high temperatures. (3) Fuel bound nitrogen conversion (fuel NOx)—the conversion of
nitrogen compounds within the fuel to NOx. Thermal NOx formation can be significantly reduced by burner technology. Fuel
NOx is a function of fuel composition. The higher the chemically bound nitrogen in the fuel, the higher the NOx emissions. The
fuel NOx can be reduced 30 – 50% in staged air burners.
The thermal NOx production is limited by reducing the flame temperature. This will reduce the NOx formed, since the reaction to
NOx is favored by high temperatures. The thermal NOx production is time-temperature dependent.
Prompt NOx typically accounts for only a small quantity of NOx formation. It becomes a significant portion of the total NOx
when low NOx burners significantly reduce the total NOx.
6.2 LOW NOx BURNER DEVELOPMENT
Initial designs for low NOx burners utilized a staged air NOx reduction mechanism.
This technique was used for both gas and oil firing. Representative NOx values for the various technologies are shown Figure 15.
All charts are for a standard refinery type heater that utilizes floor firing and ambient air. While this technique is still used for oil
firing and some gas designs, additional methods have been developed to achieve lower NOx when gas firing only. Staged air continues to find application with oil firing while most gas firing NOx reduction techniques involve either staged fuel or flue gas recirculation or a combination of both. Low NOx gas firing designs utilize a multiplicity of gas injection tips in differing zones within
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API RECOMMENDED PRACTICE 535
a single burner. Attempting similar designs with multiple oil guns in one burner is impractical when one considers the high maintenance attention and small ports of a single oil gun.
NOx reduction technology for oil fired burners has produced 20 – 30% reductions from conventional levels. Tightening of environmental regulations have reduced the opportunity for application of oil fired burners while development of low NOx gas firing
technology has seen dramatic changes in recent times.
The table below compares typical conventional and staged air low NOx burner NOx emissions.
Table 8—Typical NOx Emissions for Oil Firing
Conventional
Burners (ppmv)
Heavy Oil (#6 Fuel Oil) With 0.3 wt. %
fuel bound nitrogen
Light Fuel Oil (#2 Fuel Oil) with 0.0 wt.
% fuel bound nitrogen
300
Staged Air, Low
NOx Burners (ppmv)
200* – 250
120 – 150
95 – 110
*Forced draft operation
NOx emission regulations are normally based on a lbNOx/MMBtu fired (HHV) basis. However, NOx meters read in ppmvd units.
This raw ppmvd NOx value is typically corrected to a 3% O2 dry basis. This correction is done using Equation 1:
( 21 – 3 )
NOx correct to 3% O2 dry basis = NOx measured raw (ppmvd) x ------------------------------------------------------------( 21 – measured O 2 %dry )
(1)
With ppmv corrected to 3% O2 dry basis convert to lbNOx/MMBtu (HHV) using the conversion factor in Figure 16 and equation
2.
NO X ( corrected to 3% O 2 dry basis)
lbNOx/MMBTU (HHV) = ------------------------------------------------------------------------------------conversion factor
(2)
Conventional burners such as raw gas, premix and oil fired burners are discussed in the previous sections.
6.3 STAGED AIR BURNERS
6.3.1 General
Staged air burners are classified as low NOx burners and used primarily for oil fired applications. They limit the production of
thermal NOx by limiting the temperature in the combustion reaction zone. They reduce the production of fuel NOx by providing a
fuel rich zone in which the fuel bound nitrogen can be converted to molecular nitrogen. The staged air burner is illustrated in Figure 17.
A staged air burner is designed with primary, secondary and tertiary air registers or entry ports. Typical air split range is as follows: primary 15 – 25%, secondary 25 – 35% and tertiary 40 – 55%.
Primary Combustion Zone (Stage 1)
All fuel is injected in to the primary combusion zone with only a portion of the total air. Much of the fuel does not ignite since
there is insufficient air available. This incomplete combusion results in a lower flame temperature than in a conventional burner.
The flame envelope loses heat as heat radiates to the surroundings. The lower flame temperatures and limited oxygen concentrations contribute to lower thermal NOx production.
Fuel NOx is limited because the fuel molecules dissociate under fuel rich (reducing) conditions.
Secondary Combusion Zone (Stage 2)
Combusion is partially completed in the secondary combustion zone (located in most cases outside the buner block).
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Approximate Method to Convert NOx Measurement in ppmvd to lb/MMbtu HHV
BURNERS FOR FIRED HEATERS IN GENERAL REFINERY SERVICES
31
1300
1250
1200
Conversion Factor
1150
1100
1050
1000
950
900
850
800
750
700
0
10
20
30
40
50
60
70
80
90
100
Percent Hydrogen in Fuel
Figure 16—Approximate Conversion Factor from #/MM Btu NOx (HHV) to ppmv (3% O2 Dry Basis)
Based on Typical Refinery Fuel
Tertiary Combusion Zone (Stage 3)
Tertiary air is injected external to the secondary burner tile. Combustion is completed as the remaining air is injected into the combustion gas stream via the tertiary air zone. Flame temperatures will not approach those in a conventional burner. Radiant heat has
already been lost to the surroundings during the initial combustion stage.
Staged Fuel Burner is illustrated in Figure 18.
6.4.1 General
There are two separate firing zones or stages in the staged fuel burner. A majority of the fuel is released in the secondary stage.
The remainder is released in the primary stage. A center riser or multiple risers release the primary fuel within the burner block.
Primary Combustion Zone (Stage 1)
All the combustion air enters the primary combustion zone. Only a portion of the fuel enters the primary zone. Combustion of the
primary fuel is completed with an overabundant quantity of air. The primary fuel mixes with 100% of the air entering through the
air registers. Typically, 30% (with a range of 20 – 40%) of the total fuel is mixed with 100% of the total air. By increasing the percentage of primary fuel (i.e. 40%) flame length will be short and NOx emissions will increase. The additional air quenches the
flame producing flame temperatures lower than in conventional or staged air burners leading to lower NOx.
Secondary Combustion Zone (Stage 2)
Secondary or staged fuel risers inject the remaining fuel into the combustion gas/air stream downstream of the burner block. By
increasing the percentage of staged fuel (80%) flame length will increase, NOx emissions will be reduced. The excess oxygen
from the primary zone provides the oxygen necessary to complete the combustion of the remaining fuel. The peak flame temperatures will not reach the temperatures of conventional burners.
Typical flame lengths for staged fuel burners will be 50% longer than conventional burners.
6.5 FLUE GAS RECIRCULATION (FGR)
Flue gas may be recirculated into the combustion gases. The inert flue gas cools the flame, reduces the partial pressure of oxygen
and lowers NOx emissions. Flue gas recirculation can reduce these emissions further when used with staged combustion burners.
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6.4 STAGED FUEL BURNERS
32
API RECOMMENDED PRACTICE 535
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Figure 17—Staged Air Burner
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Figure 18—Staged Fuel Burner
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API RECOMMENDED PRACTICE 535
Flame lengths from low NOx burners are longer because staging mechanisms, both staged air and staged fuel, introduce a delay in
fuel/air mixing as compared to conventional burners. This mixing delay produces a lower average flame temperature and reduced
levels of NOx. A longer flame will usually produce a larger flame diameter as well. Staged air, staged fuel and internal flue gas
recirculation burners all produce longer flames and larger diameter flames than conventional burners. Establishing flame length
and diameter during testing tends to be subjective. Firebox temperature can play a major role in the assessment of the flame envelope. Extremely hot(bright) furnaces can mask the true "flame" envelope. It is a common practice to utilize a water-cooled probe
to take CO samples within the test furnace. Taking these measurements at varying heights and insertion depths can objectively
establish the flame envelope. It is normally accepted that a CO threshold of 2000 ppmv will define the flame envelope.
6.5.1 External Flue Gas Recirculation
Flue gases may be withdrawn from a furnace (usually downstream of the convection section) and ducted to the burners. This may
require an induced draft fan to pull flue gases out an exit duct and back into the burner.
6.5.2 Internal Flue Gas Recirculation
The burner itself may inspirate flue gases from the firebox into the burner. This can be accomplished by utilizing the combustion
air or fuel gas streams to produce a low pressure area. This can drive firebox gases into the burner through openings in the burner
block.
Internal fuel gas recirculation burners may or may not employ fuel staging. They inspirate firebox gases into the burner. This can
reduce NOx from that of staged fuel alone burners more than one-third. These burners are classified as internal flue gas recirculation burners. They are commonly known as ultra-low NOx burners.
Flue gas recirculation rates into combustion air can affect flame stability. The burner vendor should be consulted as to the recommended flue gas recirculation rates.
Burners with internal flue gas recirculation must be careful to avoid similar problems found with premix burners such as flashback.
6.5.4 Enhanced Flue Gas Recirculation
Lower NOx emissions can be achieved by using higher internal flue gas recirculation. The split between primary and secondary
fuel is modified to achieve lower NOx emissions. More secondary fuel is used in enhanced flue gas recirculation burners.
In one type of enhanced flue gas recirculation, part of the fuel is injected into the ports on the burner tile. The injected fuel induces
recirculated flue gas into the flame zone as shown in Figure 19.
6.6 ALTERNATE METHODS
Fuel Dilution. In certain applications fuel is diluted using cooler recirculated flue gas. The diluted fuel produces lower adiabatic
flame temperatures which results in lower NOx production.
Steam Injection. Steam injection dilutes the combustion air and reduces peak flame temperatures similar to the use of flue gas
recirculation. Steam can be injected upstream of the flame zone or directly into the flame zone depending on the specific application. Unlike FGR the thermal efficiency penalty (operating cost) is large since the steam is discharged out of the stack and all of
the steam’s energy is lost. The installed cost can be lower than external FGR systems since no fans or large ducting is used. In certain applications, steam is injected into the fuel gas rather than into the combustion air.
Water Injection. Water injection works the same as steam injection or FGR by diluting combustion air and reducing peak flame
temperatures. Water has somewhat lower thermal efficiency penalties as compared to steam injection and similar installed costs.
The primary difference between water and steam injection is that water injection requires evaporation of droplets to absorb heat.
Therefore, to reduce peak flame temperatures and NOx emissions efficiently with the use of water injection requires injection of
very small droplets (atomization) or droplet evaporation prior to its introduction into the flame zone.
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6.5.3 Considerations
BURNERS FOR FIRED HEATERS IN GENERAL REFINERY SERVICES
35
ENHANCED
FLUE GAS
RECIRCULATION
BURNER
SECONDARY
FIREBOX
PRIMARY
GASES
FIREBOX
GASES
Figure 19—Example of One Type of Enhanced Flue Gas Recirculation Burner
6.7 TROUBLESHOOTING GAS FIRED LOW NOx BURNERS
Burners designed to emit low NOx levels, will have operational considerations that differ from standard gas or oil burners due to
the differences in burner design.
Low NOx burners often require more fuel gas tips than other burners. Fuel gas tip orifices in low NOx burners are often much
smaller than those in standard burners. The smaller orifice sizes are more conducive to plugging.
Many low NOx burners have burner tips containing both firing and ignition ports. The ignition ports help keep the flame stable.
The firing ports can be the same size or much larger than the ignition ports. The ignition ports can be relatively small and are
prone to plug more readily than firing ports.
The flame produced from the primary fuel ports ignite the secondary fuel gas. Failure of the primary fuel to ignite may prevent
ignition of the secondary fuel.
Routine visual inspection of the burner flames is required to monitor for fuel gas tip plugging.
Due to the complicated nature of low NOx burners, care must be taken to ensure that all components are kept in good mechanical
condition. Any troubleshooting efforts should first confirm that the tip orientation and positions are correct; the flame holder is
undamaged and positioned correctly; the tile is undamaged; the tips are not plugged; and the tip orifices have not been eroded.
Table 17 delineates some of the potential operating problems and solutions related specifically to low NOx burners.
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API RECOMMENDED PRACTICE 535
6.8 OTHER DESIGN CONSIDERATIONS
This section addresses other design considerations as they apply to design of low NOx burner systems in new heaters.
6.8.1 Limitations of Burner Technology
6.8.1.1 Heater geometry imposes constraints on the selection and design of burner technology. All burner systems are integral
to the design of a heater. Low NOx burners require more volume for equivalent heat release.
6.8.1.2 Low NOx burners utilize NOx reduction techniques that tend to limit the range of stable operation when compared to
conventional burners. This type of burner may not be suitable for application requiring cold firebox temperature.
6.8.2 Interaction
6.8.2.1 Flame envelope and different types of interactions are discussed in Sections 6.10.1 and 6.10.6. NOx emissions produced
by burners in a single burner test furnace may be different than the actual operating conditions.
6.8.2.2 Burner to burner flame interaction could result in higher NOx, lower quality flame, flame impingement (enlarged flame
dimensions) and instability. Burner suppliers should specify minimum distance required between adjacent burner tiles.
6.8.2.3 Burner-to-burner Interaction
Burner technology that uses internal flue gas recirculation for achieving lower NOx emissions may become less effective when
burners are too close together and sufficient area is not provided for the recirculation of flue gas.
In vertical cylindrical heaters, if the burners are too close together on a single burner circle, all burner tips in the inner portion of
the burner circle may not get sufficient amounts of recirculated flue gas. Alternative designs, such as installing burners on two different burner circles, reducing the number of burners, or clustering groups of burners, may be explored.
In vertical cylindrical heaters, if burners are too close to each other, the flames may produce a low pressure zone in the center of
the heater causing the flames to merge together and form a spike.
Merged flames are significantly longer than single burner flames and could impinge on the tubes.
6.8.2.4 Burner to Furnace Interaction Problems
Burner flame direction may change with the presence of a target wall causing higher NOx as shown in Figure 20. In cabin type
heaters horizontal flames shooting towards the target wall may turn back towards the floor raising the temperature of the recirculated flue gas close to the floor and resulting in higher NOx.
6.8.3 Safety Considerations
6.8.3.1 Low NOx burners may become unstable at specific operating conditions (i.e., high turndown). Unstable burner systems
may lead to unsafe conditions and cause a flame-out. Additional instrumentation can be installed on the heater to reduce the associated risk. Further discussion of instrumentation is included in 6.10.
6.8.3.2 Some of the reasons for unstable operation that apply to low NOx burners specifically are as follows:
1. Cool, internally recirculated flue gas may lead to unstable operation, especially at low excess air levels. Floor / verticallyfired heaters having low NOx burners may become unstable when the floor temperature approaches 1000°F at any operating
condition and excess O2 level below 6 – 8%.
2. Multiple fuels and fuels with low flame velocities may create additional reasons for unstable operation. Each anticipated
fuel composition should be provided to the burner vendor prior to the burner design. A very wide fuel range may require
greater burner sophistication, higher NOx levels and greater burner cost. Failure to include certain operating fuels may result in
burner instability when these fuels are fired.
3. Extreme draft conditions such as high or low draft or a sudden increase or decrease in draft may lead to burner instability.
4. High altitude applications pose unique problems due to the reduced partial pressure of oxygen.
6.8.3.3 Before finalizing the burner design, a review of operating conditions of the heater should be conducted. The operable
range of the burner should be confirmed during the burner test. Set-points for safety alarms and shut-down logic should be derived
based on the burner test results.
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BURNERS FOR FIRED HEATERS IN GENERAL REFINERY SERVICES
37
Horizontal
Firing Wall
Mounted
Burner
Effect of Target Wall on Flame
Figure 20—Burner-to-furnace Interaction
6.8.4 Operating Considerations
6.8.4.1 Low NOx burners rely on having sufficiently high fuel pressure to induce (inspirate) the flue gas into the flame. If the
burners operate at a turned down condition most of the operating time, then the burners need to be designed to have adequate fuel
pressure at the turned down condition.
6.8.4.2 When a furnace is used at turned down condition by shutting down a few of the burners, then the operators need to close
the air registers on the burners that are shut down. If shutting off some of the burners is required to meet certain operating scenarios,
then the air registers should be designed to achieve the specified closure (typically 2 – 4% open area).
6.8.4.3 If natural gas is used as a fuel for startup or for future conditions only, then it should be clearly specified to the burner supplier before the burner design. Design of the burner for natural gas as an optional fuel can result in a burner design that yields higher
NOx than if natural gas was not considered.
6.8.4.4 The fuel composition most commonly used in the operating cycle of the heater should be used to guarantee NOx performance unless local pollution requirements demand otherwise. Extreme fuel compositions should be treated as special cases where
NOx emissions are greater.
6.8.5 Basic Application Requirements
6.8.5.1 Fuel Cleaning—Low NOx burners typically have much smaller openings at the burner tips than in conventional burners. A fuel filter / coalescer is recommended to remove particulates, scale and condensed liquids in the fuels, if present in sufficient quantities. A detailed discussion of fuel system requirements is provided in 6.9.
6.8.5.2 Combustion Air Control—Controlling and minimizing the excess air level may be required to achieve the guaranteed
NOx. Automated combustion air control may be useful to reduce oxygen and NOx.
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API RECOMMENDED PRACTICE 535
6.8.6 Computer Modeling
6.8.6.1 Computer based techniques such as computation fluid dynamics (CFD) have been used to model the heater geometry
and gain useful insight into the operation of an existing heater or predict how a new or retrofitted heater will perform with new
burners before a final design is completed.
6.8.6.2 A typical CFD model of the heater firebox is created using the following information:
•
•
•
•
•
Physical dimensions of the heater
Design operating mode of the heater
Burner design and details such as burner tip size
Design fuel composition and heat releases in the operating range
Location of tubes, tube geometry.
6.8.6.3 A CFD model is typically used for the following purposes:
•
•
•
•
•
Interactions: burner to burner, burner to furnace, burner to tubes,
Indicate that there is no flame impingement on the tubes,
Predict flue gas temperature and velocity profiles in the radiant section,
Ensure that there will not be tube metal temperature increase beyond the limits in the furnace sections,
Heat flux distribution in the furnace.
6.8.6.4 Success of the CFD model depends on specifying accurate boundary conditions, and the experience of the modeler. It is
also important to make a special effort to validate the model from actual experience. In many cases a model of an existing furnace
of similar design is developed and actual field data is compared with the CFD model.
6.8.7 Cold Flow Modeling
Cold flow modeling has been used to design heater air plenums.
6.8.7.1 Cold flow modeling is used to simulate fluid flow and obtain useful design guidance. For low NOx multi-burner applications, it is important to ensure that combustion air is distributed equally among all the burners.
6.8.7.2 This modeling technique involves creating a hydraulically similar model of the plenum and simulating flow of fluid
using smoke or colored fluid. Results obtained from the model are applied to actual conditions based on experience. Quantitative
data is provided by measurements made using a hot wire anemometer.
6.8.8 Issues related with instrumentation to be used for the furnace are discussed in API RP 556.
6.9 FUELS TREATMENT
6.9.1 While many conventional burners have orifices 1/8 in. (3 mm) and larger, all low NOx burners have tip drillings as small as
in. (1.5 mm). These small orifices are extremely prone to plugging and require special protection. Most fuel systems are
designed with carbon steel piping. Pipe scale forms from corrosion products and plugs the burner tips. Tip plugging is unacceptable for any burner, but it is even more important not to have plugged tips on low NOx burners. Plugged tips can result in stability
problems and higher emissions. Many companies have installed austenitic stainless steel piping downstream of the fuel coalescer/
filter to prevent scale plugging problems.
1/16
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6.9.2 Coalescers and/or fuel filters are recommended on all low NOx burner installations to prevent tip plugging problems. The
coalescers are often designed to remove liquid aerosol particles down to 0.3 to 0.6 microns. Some companies install pipe strainers
upstream of the coalescer to prevent particulate fouling of the coalescing elements.
6.9.3 Piping insulation and tracing should be used on fuel piping downstream of the coalescer/fuel filter to prevent condensation (fuel gas from reaching dew point). Some companies have used a fuel gas heater to superheat the fuel gas in place of pipe
tracing.
6.9.4 Natural gas is more difficult to fire than typical refinery fuel gas for certain burner designs. A burner test is recommended
should natural gas or a similar fuel gas be one of the fuels to be fired.
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39
6.10 RETROFIT CONSIDERATIONS
6.10.1 Flame Envelope
6.10.1.1 Conventional raw gas and premix burners have luminous flames. The combustion reaction occurs within the visible
flame boundaries. The flame envelope is defined as the visible combustion length and diameter. Many low NOx burners have less
luminous flames. Much of the combustion reaction is not visible. The flame length and diameter are often determined by inserting
a CO probe into the firebox and defining the flame envelope with CO concentrations as discussed earlier in 6.5.
6.10.1.2 All low NOx burners have longer flame lengths than conventional burners. Longer flame lengths change the heat transfer profile in the firebox. Longer flame lengths can result in flame impingement on the tubes and mechanical supports.
6.10.1.3 The flame diameter is often defined in terms of ratios of the burner tile outside dimension. Many burners have flame
diameters that are 1 to 11/2 times the diameter of the burner tile. Since the tile diameters are often larger for low NOx burners, the
flame diameters at the base of the flame many be slightly larger. The flame diameter often necks outs, giving a wider flame at the
top.
6.10.2 Physical Dimensions of Firebox
6.10.2.1 Optimized designs have burner spacing that is designed to have gaps between the flame envelopes. Since the tile diameters are often larger for low NOx burners, retrofits can result in closer burner-burner spacing and flame interaction. Flame interaction can produce longer flames and higher NOx values. Flame interaction and congealing can interrupt the flue gas convection
currents in the firebox, reducing the amount of entrained flue gas in the flame envelope. This condition increases the NOx levels.
All low NOx burners should be spaced far enough apart to allow even flue gas recirculation currents to the burners.
6.10.2.2 The burner centerline to burner centerline dimension is one of the most important dimensions in the firebox. Many
tube failures are caused by flame and hot gas impingement. When low NOx burners are being retrofitted, the larger size of the
flame envelope must be evaluated. Firebox convection currents can push the slow burning flames into the tubes.
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6.10.2.3 Flame impingement on refractory often causes damage. When low NOx burners are being retrofitted, the larger burner
diameter may result in the burners being spaced closer to the refractory. Unshielded refractory may require hot face protection.
6.10.2.4 Many heaters are designed for flame lengths that are 1/3 to 1/2 the firebox height. All natural draft low NOx burners
typically have flame heights of 1.5 – 2.5 ft/million Btu (2 – 2.5 m/MW). Longer flame heights from low NOx burners may change
the heat transfer profile in the firebox. The longer flames may result in flame or hot gas impingement on the roof and shock tubes.
These tubes may require protection to prevent failures. Protection may include metallurgical upgrades, increased tube thickness or
tube shielding. Some older heaters have very short firebox heights and may not be suitable for retrofits to low NOx burners.
6.10.2.5 When retrofitting burners, many companies test prototype burners in a test furnace with similar orientation, combustion
conditions, and fuels as the heater to be retrofitted.
6.10.2.6 Where a solid refractory Reed wall (firebrick walls 12 – 18 in. tall between tubes and burners) exists, it needs to be
removed due to effect on recirculation of flue gas and NOx.
6.10.3 Fuel Treatment
Fuel treatment is extremely important in retrofit for low NOx burners. Additional information is provided in 6.9.
6.10.4 Air Control
6.10.4.1 Low NOx burners must be operated at design excess air levels to control NOx emissions. See Figure 8. Operation
below recommended excess air limits could result in higher unburned combustibles, flame instability and uncontrolled flame patterns.
6.10.4.2 Most refinery general service heaters are natural draft heaters. It is important to control the draft at the design value,
usually 0.1 in. (3 mm) H2O at the top of the radiant section. High drafts increase tramp air ingress and often result in higher excess
air levels at the burners. This condition results in higher NOx levels in the heater. Automated draft control has been installed on retrofits to obtain better excess air control.
6.10.4.3 Low NOx burners are usually supplied with individual plenum boxes and individual damper controls. Because excess
air control is so important on these burners, some companies have installed individual actuators on each burner damper for better
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API RECOMMENDED PRACTICE 535
control. Others have connected all the burner dampers on a jack shaft to control the excess air levels.
6.10.4.4 New heaters are designed with seal welded construction to prevent tramp air ingress. Many older heaters have bolted
panel design. High temperature silicon and foil tape have been used on these heaters to reduce tramp air. Observation openings
should be designed to minimize excess air ingress. Observation openings should be closed when not in use. Use of high temperature glass should be considered on observation ports to minimize air leakage.
6.10.4.5 Low NOx burners are supplied with mufflers to control noise emissions. The mufflers are often an effective device to
eliminate excess air fluctuations due to wind. Windscreens are often installed to eliminate wind effects when burner mufflers are
not used. A 15 mph wind can cause a ± 0.11 in. H2O draft variation at the burner, resulting in a ± 15% change in excess air level
for a burner designed at 0.4 in. H2O draft.
6.10.4.6 Forced draft systems may be considered for low NOx burner retrofits. The forced draft system provides better excess air
control, eliminates wind effects, and the increased burner pressure drop often results in a smaller flame envelope.
6.10.4.7 Low NOx burners may be installed in a common air plenum. A common plenum should be analyzed to ensure uniform
air distribution to and around each burner. Internal baffles may be required to obtain even air distribution.
6.10.4.8 An oxygen analyzer should be installed at the exit of the radiant section. For long convection sections (over 30 ft) multiple oxygen analyzers should be considered. Periodic calibration is recommended. Periodic checking with a portable oxygen analyzer may be one way of verifying accuracy.
6.10.5 Structural Considerations
6.10.5.1 Hole for hole replacement is the most economical option for retrofits. However, since many low NOx burners can have
larger burner tiles and larger burner cutouts, hole for hole replacement cannot occur. It is often more economical to replace the
floor or existing common plenum when hole for hole replacement is not an option.
6.10.5.2 Low NOx burners often weigh more than conventional burners. Retrofits may require additional structural bracing.
6.10.5.3 Heater floor steel should be level to ensure proper installation and alignment of new burners. Bowed sections should
be repaired or replaced to level them.
6.10.5.4 The floor refractory thickness should be checked to ensure the heater floor steel is designed for actual temperature.
The floor refractory thickness should be checked against the general arrangement drawings to supply accurate information to
burner vendor.
6.10.5.5 Physical constraints below the firebox floor should be checked. There should be sufficient space underneath the burner
plenum for tip removal.
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6.10.6 Process Related Parameters
6.10.6.1 Low NOx burners often have longer flames that change the heat flux profile. This is especially important on cracking
heaters such as cokers and visbreakers. The longer flames may increase the bridgewall temperature and change the duty split between
the radiant section and convection section.
6.10.6.2 When the heat flux profile changes, the location of the maximum tube metal temperature changes. Retrofitting low
NOx burners in short fireboxes can result in high roof and shock tube metal temperatures.
6.10.6.3 Low NOx burners may have less turndown capability than conventional burners. High CO levels can occur when firebox temperatures are below 1300ºF. Flame instability and flameout can occur when firebox temperatures are below 1200ºF and at
low oxygen levels or floor temperature is less than 1000°F.
6.10.6.4 Conventional raw gas burners can handle a wide variation in fuel gas composition. Since low NOx burners are often
designed at the limit of stability, a fuel composition change may cause a stability problem. Since methane fuel is the hardest fuel
to burn, many companies specify a test using methane as the test fuel.
6.10.6.5 The proper design basis for the burner retrofit is extremely important. Sometimes the process requirements have
changed significantly since the furnace was designed. Important design basis items include:
• Emission requirements
• Process duty requirements
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BURNERS FOR FIRED HEATERS IN GENERAL REFINERY SERVICES
•
•
•
•
•
•
•
41
Heater general arrangement drawings
Turndown requirements
Fuel composition and ranges
Fuel pressure
Startup considerations
API heater datasheet
Existing burner datasheet
6.10.6.6 It is important to review existing plant data in conjunction with the original design data. Heater tube fouling may result
in higher bridgewall temperatures. Fouled convection sections may result in higher firing rates. Tramp air may result in high
excess air levels. Stack dampers are often frozen in place therefore draft and oxygen levels cannot be maintained properly.
6.10.7 Instrumentation
6.10.7.1 When retrofitting low NOx and latest generation burners, consideration should be given to review the heater instrumentation. Consideration must be given to oxygen and draft measurements linked to the control room. When retrofitting low NOx
burners, additional heater instrumentation is often required. This includes oxygen and CO or combustibles analyzers.
6.10.7.2 When retrofitting burners, many companies install the firebox draft indication and damper control on the DCS system
to obtain better excess air control. A floor temperature measurement may be considered to detect operating conditions that could
lead to an unstable flame condition (see 6.8.3.2 and 6.10.6.3).
6.10.7.3 When retrofitting burners, minimum fuel gas pressure instrumentation may be required to protect against flameouts
during turndown and startup situations.
6.10.7.4 The heater should have a bridgewall temperature indicator on the DCS system.
6.10.8 Operations
6.10.8.1 Low NOx burners with enhanced flue gas recirculation often burn with a flame that may, at best, be barely visible and
most visible at night (light pollution minimized). Operators must be trained to recognize proper flame characteristics and visible
symptoms of poor operation.
6.10.8.3 Special startup and considerations for safe operating procedures may be required for low NOx burners with enhanced
flue gas recirculation.
6.10.8.4 Operating procedures must consider that low NOx burners and low NOx burners with enhanced flue gas recirculation
have less turndown capability than conventional burners.
6.10.8.5 Low NOx burners are designed to operate within specified oxygen levels to obtain the lowest levels of NOx and satisfactory performance. This requires more operator attention than with conventional burners.
6.10.9 Installation Checkout
6.10.9.1 Correct burner installation is extremely important.
6.10.9.2 Tip size, orientation, and height should be checked against the vendor's drawings.
6.10.9.3 The burner tile must be installed in accordance with the vendor's specifications and tolerances. Check the diameter in different locations to ensure concentricity of burner tips, tiles and internals. Improper burner operation can be caused by burner tiles
missing or improperly applied mortar.
6.10.9.4 The air control damper or air registers should be checked to ensure freedom of movement through the full operating
range. Register or damper opening shall match the position indicator. This is best checked before and after the air ducting is
installed.
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6.10.8.2 Bright burner tile or flame holder color is often an indication that the gas tips are operating properly in low NOx burners with enhanced flue gas recirculation.
42
API RECOMMENDED PRACTICE 535
6.10.9.5 An inspection record should be maintained showing all dimensional alignment of the unit for initial and subsequent
burner inspections.
6.10.10 Computational Fluid Dynamic (CFD) Modeling
6.10.10.1 For retrofit design, CFD modeling is a useful tool in modeling firebox, common plenum and combustion air ductwork conditions. It has been used in multi-burner systems to analyze problems such as air maldistribution, flame interactions, firebox currents, and localized high heat fluxes. For additional information refer to 6.8.6.
6.10.10.2 CFD modeling capability is improving as companies gain experience. However, field results may vary from the
model results. Success of the CFD model depends on specifying accurate boundary condition, the experience of the modeler and
validation of the model from actual experience.
7 Pilots and Ignitors
7.1 GENERAL
Pilot burners, commonly known as pilots, are used to ignite and reignite the main burner flame over its full opertating range. The
combustion airflow rate may need to be reduced for satisfactory re-ignition, particularly for forced draft and some low NOx burners. Pilot burners shall be provided on each burner unless stated otherwise by the owner.
Ignitors provide a safe method of lighting pilots.
7.2 PILOT BURNERS
7.2.1 Pilot burners shall be gas fueled. The fuel gas for the pilot should be from a reliable, independent fuel source. Natural gas
is a preferred fuel gas for the pilot.
7.2.2 Pilot burners shall be positioned to assure ignition of the main burner for all operating conditions.
7.2.3 The pilot flame shall be clearly visible at all times.
7.2.4 Pilot burners shall be removable for cleaning and maintenance when the heater is in operation.
7.2.5 Positive identification of the pilot flame shall be made upon ignition.
7.2.6 Continuous Pilot Burners
Pilots shall have a minimum heat release of 65,000 Btu/hr. The minimum heat release must be approved by the owner when
accompanying a high intensity burner or a burner whose heat release is 15 MMBtu/hr or greater.
The pilot shall be provided with a continuous supply of combustion air under all operating conditions. This includes operation
with the main burner in or out of service.
The pilot shall remain stable over the full design range of the main burner. It shall remain stable upon loss of main burner fuel
while operating in the design range of the main burner . Stability of the pilot burner may be affected by conditions such as excessive heater draft or high firebox pressure.
7.3 IGNITORS
Manual ignition of pilot burners shall be accomplished with gas or electric portable ignitors unless otherwise specified by the
owner.
Table 9—Air Register Characteristics
Air Controlability
Leakage
Cost
Complexity
Ease of Maintenance
Applicability for common plenum
Concentric Cylinders
Poor
Poor
Good
Fair
Fair
Good
Slotted Cylinder with Blades
Fair
Fair
Fair
Poor
Poor
Fair
Single or Multi-blade Damper
Good
Good
Good
Good
Good
Fair
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8 MECHANICAL
8.1 PLENUM
Plenums are used to distribute combustion air (or other oxygen source) to the burner(s). Plenums are also used to reduce noise
produced by the burner. Multiple burners can be installed in a common plenum or each burner can have a separate individual plenum. Some burners have no plenum.
All burners, whether mounted in a plenum or not, should have an air register to control the flow of combustion air to the burner.
The air register is normally manually adjusted. It can also be adjusted by an automatic control device.
Combination oil and gas burners typically have separate air registers to control combustion air to the oil and gas flames independently.
Three types of registers are commonly found. Early designs consisted of two concentric metal cylinders, each with slots. One cylinder is stationary while the other can be rotated such that all or a portion of the slot on one cylinder can be aligned with those on
the other. This allows air to flow through the slots into the burner.
A second air register design is made with slots cut in a single, stationary cylinder. Each slot is fitted with an individual damper
blade on a shaft. Each shaft is connected to a common air register control.
A third type of air register consists of a single or multiblade damper at the inlet of an individual plenum. This type is most commonly used for new equipment.
Table 9 summarizes the characteristics of the three air register types.
The combustion air register should be designed so that it is fully open during operation at maximum heat release with the design
fuel at the maximum specified air flow rate.
When requested by the purchaser, pressure taps should be positioned so that the pressure drop across the air register and burner
throat can be accurately measured in a repeatable manner for the purpose of balancing air to individual burners.
Air leakage through a closed air register on an out-of-service burner can reduce combustion efficiency. Fully closed rotating concentric cylinder air registers have leakage rates up to 50 % of the fully-open flow rate. Fully closed damper type air registers have
leakage rates up to 25% of the fully-open flow rate. Sealing strips can be specified for use with damper type air registers to
achieve leakage rates as low as 5% of fully-open flow rate.
Air register controls must be easily accessible. Means of indicating the position of the dampers or registers shall be provided.
Control handles should be supplied with a locking mechanism such as a multiple notch positioner. For registers in plenums and
other cases where the register is not easily visible, a positive means of securing the position indicator to the register or register
shaft shall be provided to maintain accurate position indication.
The shafts of damper type air registers can be specified with either bushings or ball bearing supports. Consideration should be
given to the use of corrosion-resistant materials to avoid seizures. Linkage of multi-blade damper type registers can be designed
for parallel or opposed blade operation. Opposed blade operation, in which adjacent blades rotate in opposite directions, provides
more accurate air control at low flow rates than does parallel blade operation. Parallel blade dampers can detrimentally influence
air flow if placed close to the burner throat. Multi-blade dampers give better control than single blade dampers, however, multiblade dampers are difficult to fit to smaller burners (less than 2 MM Btu/hr).
8.3 BURNER TILE
Burner tile refractory is designed to control the mixing of air, fuel, and flue gas. Burner tiles play an important role in flame shape,
flame stability, and emissions.
The high temperature attained by oil burner tiles, called regen tiles, plays an important role in stabilizing oil flames.
Burner tiles are exposed to high temperatures. Installation must allow them to expand and contract independent of the furnace
refractory. Each tile may be made up of several pieces to aid in installation. The number of pieces should be minimized. Hydraulic
setting (water based) burner tiles should be supplied in a dried ready to fire condition. Burner tiles made of acid based refractory
do not require drying before firing.
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8.2 AIR REGISTERS
44
API RECOMMENDED PRACTICE 535
The combustion air will experience a pressure drop through the burner that is composed of a pressure drop at the air register and a
pressure drop at the burner tile. The burner tile should be sized so that the air register will be fully open during operation at maximum heat release with the design fuel and at maximum air flow rate.
8.4 FUEL TIPS
Oil guns and gas risers shall be easily removable for cleaning while the heater is in operation. Oil tips can be designed to be
removed without disconnecting piping. Fuel tips should be threaded for easy replacement unless welded construction is requested
by the purchaser. High temperature anti-sieze should be used on threaded tips. Fuel tips should be designed with the largest fuel
orifices possible to minimize tip plugging. The diameter of fuel tips and risers should be minimized to decrease tip temperature
and tip plugging associated with coking of liquid condensate in fuel gas. When possible, risers should be designed without bends
to facilitate inspection and cleaning. Tip match-marking or other means of positive alignment shall be provided if needed. Consider burner numbering or marking to prevent mixing of parts.
8.5 PORTS
Sight ports shall be provided to observe the pilot and main flames. A manual lighting port shall also be provided for lighting the
pilot or main flame. Provision for electronic ignition and flame scanners should also be provided when requested by the purchaser.
8.6 MATERIALS OF CONSTRUCTION
The materials used for construction of a burner shall be chosen for the strength, temperature resistance and corrosion resistance
suitable for the anticipated service. Carbon steel is generally used for metal parts unless temperature or corrosion considerations
require a more suitable alloy.
8.6.1 Fuel Gas Burner Components (Burner & Pilot)
Table 10—Fuel Gas Burner Components
COMPONENT
Fuel gas manifold and piping
Fuel gas riser pipe
Fuel gas tip
Premix venturi
Flex hose internal lining
Flex hose external braiding
OPERATION
Normal
When each of the following is present:
> 100 ppmv H2S
> 300°F fuel
Normal
> 700°F combustion air
When each of the following is present:
> 100 ppmv H2S
> 300°F fuel
> 400°F combustion air
Normal
Normal
Normal
Normal
MATERIAL
Cast iron or carbon steel
316L stainless steel
Carbon steel
304 stainless steel
316L stainless steel
310 stainless steel
Cast iron or carbon steel
316L stainless steel
304 stainless steel
A metallurgist should be consulted to select appropriate materials to use with corrosive or chloride containing fuels.
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BURNERS FOR FIRED HEATERS IN GENERAL REFINERY SERVICES
45
8.6.2 Fuel Oil Burner Components
Table 11—Fuel Oil Burner Components
COMPONENT
Oil gun receiver and body
Oil gun tip
OPERATION
Normal
Normal
Erosive oils*
Normal
Erosive oils*
Normal
Atomizer
Other
MATERIAL
Ductile iron
416 stainless steel
T-1 or M-2 tool steel
Brass or 304 stainless steel
Nitride hardened Nitraloy
Carbon Steel
Note: Erosive oils are defined as fuel oils that contain 3% or more by weight S or catalyst fines or particulates or other heavy metals.
8.6.3 Burner Housing
Table 12—Burner Housing
COMPONENT
OPERATION
Exterior casing
Flame stabilizer or cone
Insulation and noise reduction linings
Other interior metal parts
Normal
Preheated combustion air
Normal
≤ 750°F combustion air
> 750°F combustion air
Normal
> 750°F combustion air
MATERIAL
Carbon steel
Insulated carbon steel
300 series stainless steel
mineral wool *
mineral wool covered with erosion protection
liner *
Carbon steel
A242 or 304 stainless steel
*Castable for oil firing on surfaces that can be soaked with oil.
8.6.4 Burner Tile
Table 13—Burner Tile
TILE
Normal
High intensity combustor
Oil firing tile: ≤ 50 ppm (wt.) V + Na
Oil firing tile: > 50 ppm (wt.) V + Na
MATERIAL
> 40% alumina refractory
> 85% alumina castable refractory/firebrick
≥ 60% alumina refractory
> 90% alumina refractory
8.7 BURNER PIPING
The operation and control of a fired heater is facilitated by a properly designed fuel delivery system. The basic requirements of
such a system are:
•
•
•
•
•
Properly sized headers to effect uniform flow distribution to individual burners while maintaining reasonable velocities.
Provisions for adequate and properly situated drains to permit drainage and cleaning of the manifold system.
Properly sized control valves.
Individual burner isolation valves.
Pressure tap and valve.
8.7.1 Fuel Gas Piping
The following are guidelines for the design of manifold systems for gas, oil and combination firing. Specific conditions may dictate some variations.
Fuel gas is usually supplied from a constant pressure mixing drum. The fuel gas system should include a knockout pot or drum
with demisting pad for condensate removal. Consider a fuel gas filter/coalescer to minimize burner plugging. The placement and
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A metallurgist should be consulted to select appropriate materials to use with corrosive or chloride containing fuels.
46
API RECOMMENDED PRACTICE 535
location of the fuel gas filter/coalescer is key to the performance of the liquid removal. The coalescer should be located as close to
the heater as possible to minimize the chance of additional condensation after the filter. Consistent temperature and pressure in the
system will help to minimize the condensation.
The main gas supply header branches to each furnace. Each branch acts as a gas distribution header to its heater. The gas distribution header should slope in the direction of gas flow without low spots in the line. A drip leg should be fitted at the lowest point in
the line and should be drained on a routine basis.. The distribution header should be heat traced and insulated in climates where
ambient temperatures could result in heavy condensate formation. All fuel gas drains should be piped to a collection system feeding a flare or other safe disposal system.
Flex hoses require special attention to avoid failure due to kinking. The fuel supply piping and burner piping should be positioned
so that the flex hose is within its design radius of curvature. A union should be provided to avoid kinking of the flex hose due to
rotation during installation. A backing wrench should be used to stabilize the flex hose when tightening nearby joints.
Take-off leads to each burner should be from the top side of the distribution header to minimize the potential for dirt and scale
being carried to the burners. Where condensation of liquids is common, a bottom drain should be installed at the end of the fuel
header and should be drained on a routine basis. The piping system of headers, branches and lead connections should be designed
as symmetrically as possible to yield an equal flow of gas to all burners.
The gas distribution header size is based on the number of burners and the maximum heat release to be supplied from the header.
The header velocity normally should not exceed 50 ft/sec. The velocity in a takeoff lead to an individual burner should not exceed
75 ft/sec.
The fuel flow control valve should be installed near the furnace in the distribution header between the main gas supply header and
the first branch. Piping to each burner should include a block valve to allow individual burners to be taken out of service.
The fuel gas filter/coalescer should be installed downstream of the flow control valve. The rapid expansion of the gas through the
flow control valve can cause the gas to cool (Joule-Thompson effect) to its dewpoint temperature. All piping downstream of the
fuel gas filter/coalescer should be kept the same size or smaller to eliminate expansion of the gas and the possibility of additional
condensation.
A pressure gauge should be positioned in the piping system to accurately reflect the pressure at the burner.
8.7.2 Fuel Oil Piping
Heavy fuel oil is normally supplied from a central storage and preparation area. It is delivered through an insulated loop system
circulating oil to each oil-fired furnace and back to the storage tank. A non-circulating fuel oil system is unacceptable when firing
heavy oils requiring heating. Dead ended systems result in oil chilling with consequent combustion problems.
The loop system should circulate a minimum of 1.5 times the fuel to be consumed. This rate may be increased for cold ambient
conditions. The excess oil flow assists in maintaining a uniform temperature and a constant viscosity. It stabilizes the oil supply
pressure since load changes will cause individual control valves to affect a smaller fraction of the total flow. Oil velocity in the
loop system should not normally exceed 6 ft/sec.
Take-off leads to individual burners should come off the top of the loop header. This will minimize the flow of particulates to the
burners. The lead to each burner should be as short as possible to minimize oil cooling. Oil headers and leads should be heated as
well as insulated in climates where ambient temperatures can result in significant oil cooling.
Light oils normally do not require heating. They may be piped in a manner similar to fuel gas systems. The oil velocity should not
exceed 3 ft/sec.
8.7.3 Atomizing Steam Piping
The atomizing steam system provides dry steam to the burner for fuel oil atomization. The burner design may require either a constant steam pressure or a constant differential pressure above the oil pressure. A differential pressure regulator is used to maintain
the steam pressure above the oil pressure when a constant differential is required.
The steam header and branches should be sloped in the direction of flow. They should be trapped at each low point to remove condensate. Steam take-off leads to individual burners should come off the top of the header branches. This will minimize condensate
and particulate carryover to the burners. Velocity in the steam piping normally should not exceed 100 ft/sec.
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47
8.7.4 Pilot Gas Piping
Fuel gas for pilot burners should be independent of the main fuel gas system.
Pilot burners have small orifices which make them susceptible to plugging. Pilot gas headers should be fitted with filters to keep
dirt and scale from the pilot burners. Recommended filter sizes are # 80 mesh or 25% of the smallest fuel orifice. Basket type filters are superior to Y-strainers. The filters should be cleanable during operation. Further protection can be achieved by providing
stainless steel piping from the filters to the pilot burners.
9 Operation
9.1 LIGHT-OFF PROCEDURES
9.1.1 The following is provided as a minimum only. User’s light-off procedures will take precedence.
9.1.2 Preparation for Light-off
Maintain flow through the tubes to protect the tubes from overheating. This may not be required during some refractory dryout
procedures. Heater vendor may not require flow through the tubes during dryout if dryout temperatures are not high and alloy
tubes are provided. Flow through the tubes will be required if normal heater operation directly proceeds after the dryout.
Determine all fuel and burner instrumentation is in operating condition. Set all instrumentation in a manual mode with safety trip
valves closed.
Verify all gas tips and oil burner guns are clean and unobstructed. Verify burner guns and tips are positioned in accordance with
the burner manufacturer’s drawings. Oil guns shall not be installed until the burner is about to be fired on oil.
Verify the push-button, electric ignitor system or portable ignitor is in readiness.
Block in and blind all fuel headers. All burner valves should be closed.
Drain condensate from all fuel gas (including pilot) and atomizing steam lines. Remove any water and solid particles. Drain liquid
from fuel knockout drums.
Verify fuels are at their correct operating temperatures and pressures. Confirm adequate fuel is available.
Determine atomizing media is at the appropriate conditions. Confirm the desired differential between fuel and atomizing media is
available. Atomizing steam shall be dry, saturated or slightly superheated.
Open vent valve on double block and bleed arrangements in fuel gas lines (if provided).
Determine the stack damper is operating properly. Assure stack damper position indicators match position of stack dampers. Open
stack damper wide.
Confirm burner dampers and/or registers can be adjusted easily from fully closed to fully open positions. Assure damper/register
position indicators match position of damper/register.
Check that entire heater is well-sealed to prevent leakage of air into the heater.
Burner manufacturer’s light-off procedures should be followed.
Steam or air purge the firebox for a minimum of 15 minutes. The volume of purge medium should be at least equal to three times
the firebox volume. Check the combustibles content of the firebox exit gases with a combustibles analyzer immediately upon
completion of the purge and immediately before lighting the first pilot.
Remove blinds in pilot gas lines immediately prior to lighting pilots. Remove blinds for main fuel gas lines after all pilots are lit
and prior to lighting main gas burners. Remove blind or blinds in fuel oil system. Start fuel oil circulation and establish fuel oil
pressure at burner block valve after all pilots are lit.
If pilots are provided, begin lighting the pilot burners. Each pilot shall be ignited with a portable gas or electric ignitor.
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9.1.3 Light-off Guidelines
48
API RECOMMENDED PRACTICE 535
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Ignite initial pilot burner. Re-purge the heater if the first pilot fails to ignite or extinguishes. Adjust pilot inspirating air as necessary. Adjust the pilot header fuel gas pressure to provide a glowing pilot burner, flame retention head. The pilot gas tube (immediately upstream of the pilot burner tip) shall not display any color. Continue lighting additional pilot burners after the first has been
ignited and proved.
Adjust main burner air registers and dampers to a fully closed then fully open position to test each pilot. Re-purge the heater if,
while testing the first pilot, it fails to remain lit. If other pilots are lit, block in the fuel to the extinguished pilot and open the air full
to that burner. Ignite another pilot distant from the one extinguished. Do not attempt to re-light an extinguished pilot for five minutes once it is blocked in.
Do not ignite any more pilots than necessary to bring the firebox to the initial temperatures required by dryout. Continue igniting
pilots as the need arises to maintain the dryout schedule.
If pilots are provided, all pilots should be lit before igniting any main burner.
Light main gas burner from the pilot. Light main gas burner from a portable gas or electric ignitor if pilot is not provided. Provide
good heat distribution when lighting subsequent burners.
• Attempt to blow out the flame by adjusting the burner dampers or registers to a fully open position. Shut off the fuel to the
burner if the burner fails to ignite or extinguishes. Do not attempt to reignite or ignite another burner for at least 5 minutes to
allow the pilots to purge the burner area.
Light oil burner from the pilot. Light oil burner from a portable gas or electric ignitor if pilot is not provided. Lighting of subsequent burners shall provide good heat distribution.
• Attempt to blow out the flame by adjusting the burner dampers or registers to a fully open position. Shut off the fuel to the
burner if the burner fails to ignite or extinguishes. Do not attempt to reignite or ignite another burner for at least 5 minutes to
allow the pilots to purge the burner area.
Firing oil on combination burner
• Heat up burner block with the main burner firing on gas at not more than 50% of the burner load. Air dampers or registers
should be fully open.
• Insert the oil gun to its proper position and immediately steam purge the gun and oil and steam lines to the burner prior to
cutting in the oil.
• The burner block should be heated (operating the main burner on fuel gas) for approximately 5 minutes prior to cutting in
the oil. Reduce the steam rate to the oil gun to appropriate levels. Slowly cut in the oil to the burner. Establish a compact,
stable flame.
• Cut out the gas from the main burner as soon as the oil flame is stabilized.
• Attempt to blow out the flame by adjusting the burner dampers or registers to a fully open position. Shut off the fuel to the
burner if the burner fails to ignite or extinguishes. Do not attempt to reignite or ignite another burner for at least 5 minutes to
allow the pilots to purge the burner area.
• Adjust the air rate to burner. Assure steam rates are satisfactory. Confirm the flame is not smoky, “sparklers” are not emanating from the burner and flames are not contacting the burner block.
Achieve good heat distribution to the heater with all fuels and atomizing steam.
9.1.4 Special Safety Reminders
Do not use adjacent burner or hot brickwork as an ignition source for pilot or main burners. Always use the appropriate ignitor or
a properly operating pilot to light burners.
Safety interlocks should be in service.
Re-initiate the start-up from the appropriate step if immediate ignition does not occur. Always shut off fuel valves and open steam
purge to oil guns after failure of burners. Fuel line blinds should be reinstalled if there will be an extended delay prior to relighting.
Do not remove an ignitor unless certain that the burner or pilot will remain lit.
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Do not close stack damper completely. During the initial light-off, it may be necessary to close the burner register completely on
that specific burner to maintain the ignitor in service.
Always use a face and eye shield (or safety glasses) when observing furnace flame pattern.
9.2 EXCESS AIR CONTROLS
9.2.1 Optimum Excess Air Levels
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There is an optimum level of excess oxygen in the flue gas for each type of heater, burner and fuel used. Typical excess air and
oxygen levels are as follows. The sophistication of the burners or the presence of only one burner may allow reduced levels:
A completely sealed heater containing a few burners and automatic oxygen and draft controls may allow a reduction in the above
O2 levels. An existing heater with significant casing leakage may not achieve the above oxygen levels. The optimum excess air
level is established or confirmed by testing. An additional “cushion” is provided to allow for small operational variations, fuel
changes, meteorological changes and potential burner plugging problems.
9.2.2 Disadvantages of Increased Excess Air
High excess air will reduce heater efficiency for the following reasons:
• More fuel is required to the heat the additional air entering the burners.
• Additional air lowers the flame temperature resulting in a lower radiant thermal efficiency.
• Increased excess air will increase the flue gas flow rate and raise the flue gas pressure differential. This may result in a positive pressure in the heater forcing a reduction in capacity.
9.2.3 Advantages of Increased Excess Air
Reduction in Radiant Section Tube Wall Temperatures
• Increased excess air will increase the convection section duty while reducing that in the radiant. This will slightly decrease
radiant section tube metal temperatures and slightly increase convection section tube metal temperatures.
Increased Convection Section Duty
• Increased excess air will raise the convection section duty. This may be of value if a greater duty is desired from a waste heat
coil (steam, reboiler, hot oil, etc.). Increased excess air will increase the convection section, tube metal temperatures and
slightly decrease it in the radiant section.
Table 14—Optimum Excess Air Levels
Burner Type
Natural Draft
Natural Draft
Natural Draft
Natural Draft
Forced Draft
Forced Draft
Combustion Air Supplied
with Forced Draft Fan
Yes/No
Yes/No
Yes
Yes
Yes
Yes
Fuel
Gas
Oil
Gas
Oil
Gas
Oil
Excess Air, %
15
20
10
15
10
15
O2 Content, % (dry basis)
3
4
2
3
2
3
9.3 DRAFT CONTROL
Refinery process heaters operate with a negative pressure (draft) in the firebox. Natural draft, forced draft and balanced draft systems will maintain a negative pressure throughout the furnace. Rarely are refinery process heaters designed to operate under a
positive pressure. Draft is the first item that should be closely watched when adjusting the heater in order to achieve safe and economical operation. Insufficient draft can result in insufficient combustion air being delivered to the burners. This can cause flame
impingement, afterburning or a flameout.
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50
API RECOMMENDED PRACTICE 535
9.3.1 Typical Draft Profile
A negative pressure must be maintained throughout a heater. A positive pressure inside the heater will cause flue gas leakage and
damage to the furnace casing and structure. It can also be a safety hazard to operating personnel.
Figure 21 shows a typical draft profile.
A draft reading of 0.05 to 0.10 in. H2O at the radiant arch is desired. Too much draft will increase air leakage. Efficiency will be
reduced and operation could be limited.
9.3.2 Excess Air Adjustment
Excess air and draft are inter-related. Adjust excess air by means of the air dampers or registers. This will affect the draft as the
flue gas rate changes. Correct the draft by means of the stack damper or induced draft fan suction damper. This will affect the flow
of air through the burners as the pressure at the burners changes. It may be necessary to readjust the air registers and damper until
the draft and excess air are properly set.
Always assure there is sufficient excess air available to combust all the fuel. Combustion air should be increased prior to an
increase in heater severity (requiring an increase in fuel).
An objective is to achieve an optimum excess air level for combustion without producing a positive pressure at the heater arch.
Achieve the desired excess air rate while maintaining a slightly negative pressure at the heater arch.
Do not use the stack damper or burner air register alone for draft and excess air control. A combination of the two adjustments is
necessary to obtain the proper draft and excess air. Table 15 is a guideline to adjust stack damper and burner registers.
Table 15—Guideline to Adjust Stack Damper and Burner Registers
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Heater Conditions
High O2 and high draft
Low O2 and low draft
High O2 and low draft
Low O2 and high draft
Adjustments
Close stack damper
Open stack damper if combustibles or carbon monoxide contents are within acceptable levels.
Close burner registers
Open burner registers if combustibles or carbon
monoxide contents are within acceptable levels.
Figure 22 is a draft adjustment chart.
For a given heater, with constant duty and fuel composition, closing the stack damper will, in general, have the following effects:
1. Reduced oxygen to the burners and in the flue gases.
2. Decreased draft at the radiant arch.
3. Increased flue gas temperature leaving radiant section. (For an all radiant heater, the radiant flux density is constant. When
the excess air level is reduced, the bridgewall temperature will be reduced.)
4. Decreased stack temperature.
5. Increased radiant heat flux density (an all-radiant process coil will have an unchanged radiant heat flux density).
6. Decreased convection heat flux density.
7. Increased heater efficiency.
Closing burner registers has the same effect on performance as closing the stack damper except the draft at the radiant arch will
increase.
See Section 12, Troubleshooting.
10 Maintenance
10.1 SHIPPING
All burner and pilot tips should be wrapped to keep them clean during shipment. Any exposed flanges or threaded connections
should be adequately protected. Burner tiles are generally shipped separately and should be adequately protected to avoid damage.
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51
Stack
Stack exit loss
(SE)a
Stack effect
in stack
∆Pc
Stack effect in
convection
section
section
Convection
Damper
(SE)c
Negative pressure
0.05" - 0.1" W.G.
at top of
radiant section
∆Pb
Radiant section
0.05" - 0.1"
W.G. draft
Draft at
radiant section
outlet, Ro
Stack effect in
radiant section
(SE)r
∆Pa
Burners
Negative pressure Positive pressure
0
(SE)r + Ro = Pa
(SE)a + (SE)c = Pb + Pc + Stack exit loss + Ro
∆Pa = Pressure drop across burners (draft available at burner level).
∆Pb = Flue gas pressure drop across convection section.
∆Pc = Losses due to damper, stack friction, stack entrance.
Figure 21—Typical Draft Profile in a Natural Draft Heater
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52
API RECOMMENDED PRACTICE 535
Check draft
Low
High
Target
Check 02
Check 02
High
Target
Low
High
Target
Low
Close
damper
Open air
registers
Open air
registers
Close air
registers
Open
damper
Open
damper
Close
damper
Close air
registers
Return
to start
Return
to start
Check 02
High
Target
Low
Close
damper
Open air
registers
Return
to start
Return
to start
Good
operation
High draft
= Draft at radiant section exit is higher (greater negative pressure) than the target level.
Low draft
= Draft at radiant section exit is lower (smaller negative pressure) than the target level.
Low or high O2 = Flue gas oxygen content at the radiant section exit is lower or higher than the target.
The action to be taken under low oxygen, as indicated in the figure above, assumes the combustibles
or carbon monoxide remains within acceptable levels.
Figure 22—Natural Draft Heater Adjustment Flow Chart
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Start
BURNERS FOR FIRED HEATERS IN GENERAL REFINERY SERVICES
53
10.2 BURNER PARTS INSPECTION
1. Burner parts shall be inspected to confirm they conform with the vendor drawings and data sheets.
2. The orifice sizes of the burner tips should be checked to ensure the proper gas tip is being used. The back side of a drill bit
may be used for this purpose.
3. Burner tip orientation should be in accordance with the burner drawing. Burner gas tips are often supplied with notch cuts
or arrow indicators to aid in proper tip alignment.
4. Gas risers should be inspected to confirm that they conform to the burner drawing.
5. All orifices should be free of deposits.
6. Primary air openings shall be inspected to confirm that they conform to the burner drawing.
7. Any noise dampening materials shall be verified to be intact and not broken or damaged during shipment.
8. All bolted or threaded connections should be checked for tightness.
10.3 INSTALLATION AND INITIAL SET-UP
Burners should be installed in accordance with burner manufacturer’s procedures. The burner should be installed properly to
obtain good flame quality at low excess air levels. Improper setup results in poor fuel-air mixing and flame stability problems. The
burner tile acts as an air orifice controlling the flow of air to each burner. Poor installation results in lopsided flames due to zones
of high excess air and zones of low excess air. The following tolerances are permissible in the absence of manufacturer’s tolerances:
1.
2.
3.
4.
5.
Burner tile diameter: ± 1/4 in.
Burner tile concentricity (out of roundness): ± 1/4 in.
Tip port angles: ± 4°
Bolting dimensions: ± 1/8 in.
Gas tip locations: Horizontal ±1/4 in.; Vertical ± 3/8 in.
10.4 POST-INSTALLATION CHECKOUT
Air registers and dampers should be checked for freedom of movement.
Primary air control devices should be tested for full movement.
Check the burner installation for plumb and check tile for level.
Insure expansion joint materials around the burner have been installed properly.
10.5 MAINTENANCE PROGRAM
A routine burner maintenance program for proper burner operation should be scheduled. The following items should be included
in a routine maintenance program.
10.5.1 Visual Inspection
Operating burners should be checked visually at least once per shift. Any unusual situation, such as flame impingement on tubes
and supports, improper flame dimensions, oil drippage, uneven heat distribution, smoky combustion, etc. should be noted and corrected as soon as possible.
10.5.2 Check Burners with Original Design
The following items should be checked with the original design to ensure compatibility with the present operating conditions:
1.
2.
3.
4.
Fuel pressure.
Fuel characteristics (heating value, composition, viscosity, sulfur content, etc.).
Gas tip and oil guns (orifice size, drilling angle and tip and gun position).
Turndown.
Replacement of burner tip or gun, or complete burner should be considered if the original burner cannot be operated satisfactorily.
10.5.3 Burner Cleaning
Each user should establish their own cleaning schedule based upon their experience.
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1.
2.
3.
4.
54
API RECOMMENDED PRACTICE 535
Oil guns normally require more frequent cleaning than gas tips. Oil guns should be cleaned at least once a week when burning No.
6 oil.
Gas tips and risers are typically cleaned when the gas pressure drop across the burner has increased approximately 30% above the
design pressure for a given fuel and heat release. They are cleaned when irregular flame patterns develop from a burner tip.
10.5.4 Burner Tile
The burner tile should be inspected. Cracks and spalled sections shall be repaired to a smooth surface commensurate to the original design. Repairs should be accomplished with a plastic refractory comparable to the existing material and with at least the same
temperature rating. Burner tiles requiring extensive repair should be replaced.
Air dampers and registers should be operable at all times.
10.5.6 Remove Unused Burners
As many burners as practicable should be in operation to achieve good heat distribution. Unnecessary burners should be removed
and the burner openings sealed to prevent air leakage. Remaining burners should be arranged to provide good heat distribution.
Oil guns not in operation should be removed. Burner oil tiles may be left in place.
Burners may be removed from the outside when the heater operations allow (i.e. negative pressure operations). Burner openings
should be covered with carbon steel plate insulated from the heat of the furnace.
Burners may be blanked from the inside of heater after shut-down.
10.5.7 Burner Replacement or Modification
Burners should be replaced or modified if the burners have deteriorated where substantial maintenance is required. They should
be replaced if satisfactory combustion with optimum excess air operation cannot be maintained.
Burners should be replaced or modified if the existing burners are unsuitable for the new operating requirements. These requirements may be environmental, fuel change, heat release, process, etc.
A burner manufacturer, or a qualified professional, should be consulted when burner replacement or modification is required.
10.5.8 Spare Parts
The number of spare parts depends on burner design, fuel, plant location and operation and maintenance experiences. It is recommended that 10% of all tips, oil guns and burner tiles should be purchased as a minimum as spares. When spare parts are used,
ensure that these parts are the correct components and are properly installed on the correct burners.
11 Testing
11.1 GENERAL
This procedure covers the requirements for testing a single burner in a test furnace. Note: Single burner tests do not necessarily
reflect operation in a multiple burner operation. Testing in multiple burner arrangements is often possible and may be considered
in critical applications.
Burner testing is intended to verify thermal, safe operating and environmental performance of a production burner. The testing is
used to determine the burner satisfactory operating range, emissions, noise and flame characteristics.
One production burner of each type and size should be tested to verify burner performance. Tests are recommended for each specified operating-mode, e.g., natural or forced draft, preheated air, fuel type, etc.
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10.5.5 Air Regulating Devices
BURNERS FOR FIRED HEATERS IN GENERAL REFINERY SERVICES
55
11.2 TEST REQUIREMENTS
11.2.1 General
1.
2.
3.
4.
5.
6.
7.
Heat release and intended operating range.
Fuel specifications.
Firebox configuration and burner clearances.
Bridgewall temperature for the defined operating cases.
Combustion air conditions and available draft.
Environmental performance requirements.
Maximum and minimum flame dimensions, as applicable.
The test furnace and burner orientation should be as similar as possible to the actual installation. The test facilities should be capable of reproducing similar firebox temperature and draft at the burner consistent with heater design.
A description of test facilities, measurement devices, proposed test procedures and fuels to be used shall be provided for purchaser review and approval prior to testing.
Calibration of all flue gas analytical instruments shall be conducted at the beginning of each test day or more if specified. Calibration information on other instrumentation such as fuel measurement devices shall be available for purchaser review. Flue gas analyzers shall be calibrated with span gas cylinders which have a composition characteristic of the burner guarantee values.
Complete burner retesting may be required if physical modifications are made to the burner or burner test system. The extent of
the retesting will be determined by mutual agreement between the purchaser and vendor.
11.2.2 Recommended Test Sequence
Following is the recommended sequence for testing. The extent of the testing shall be specified by the purchaser.
1.
2.
3.
4.
Damper/register leakage tests (if specified)
Pilot ignition and stability tests.
Single fuel burner tests.
Combination fuel burner tests (if specified).
11.2.3 Burner Design
The number, size and orientation of fuel orifices and number and location of fuel tips should be recorded for each test. Dimensions used in the successful tests should be included in the burner performance test report. In consideration of the proprietary
nature of a particular design, some orientation information may only be made available for inspection purposes at the time of the
test. As a minimum however, the number and size of the fuel orifices and the number and location of the fuel tips shall be
reported.
11.3 TEST FUELS
11.3.1 General
The fuels used for burner and pilot testing shall be mutually agreed to between burner vendor and purchaser prior to testing.
A. Blended Gas Fuels
In order to simulate the combustion characteristics of the fuel expected in the actual service, blending of various gas fuel streams
is most often required. Blending of a gas fuel requires accurate measurement of each gas stream as part of the overall calculation
of the simulated fuel. Rotoflow type flow elements or orifice runs are acceptable means of measurement. Fuel should be blended
considering the heating value, specific gravity, Wobbe number, flame speed, NOx and stoichiometric air requirement for the actual
service fuel gas as specified or as mutually agreed to with the purchaser. Hydrogen and inert content of the gas should be in the
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The purchaser shall provide information concerning proposed burner installation, site conditions and intended operation. This
information is provided through a data sheet such as those contained in API Standard 560. The following information should be
considered the minimum requirements:
56
API RECOMMENDED PRACTICE 535
same volumetric proportion as in the specified actual service fuel gas, if those proportions significantly impact burner performance.
B. Liquid Fuel Conditions
Liquid fuel viscosity shall be maintained by temperature control. When an atomizing media is required, both test atomizing media
temperature and pressure shall be measured at each point. The mass ratio of atomizing media shall be recorded at the maximum
condition.
Atomizing media shall be representative of anticipated operation, i.e. steam, high-pressure gas, etc. When steam is required, the
steam shall be within the burner manufacturer’s recommended temperature and pressure range.
11.3.2 Fuel Orifice Capacity Curves
The burner manufacturer shall provide capacity curves (fuel pressure vs. heat release) for each specified fuel covering the defined
operating range for the burner. Capacity curves for the primary fuel stage shall be provided for staged fuel burners as well as for
the entire burner if the burner is intended for use with the primary stage only.
11.4 AIR SUPPLY
11.4.1 General
Air supply for fired heaters is typically supplied by means of natural draft, forced draft, balanced draft or induced draft. In addition, the oxygen for combustion may be supplied as air, turbine exhaust gas or a mixture of air and recirculated flue gas.
During burner testing, the measured draft loss for the burner needs to be corrected for temperature and atmospheric pressure if the
test facility conditions are different than the operating site. The design combustion air temperature can readily be provided during
a burner test, however differences in atmospheric pressure cannot. The method of correction should be resolved in advance of the
burner test.
Preheated Air
Preheated air can be provided by either direct or indirect heating. Indirect air heating is necessary to determine burner emissions.
When direct heating is used, correction of oxygen content must be considered.
Oxygen-Reduced Air
A practical example of oxygen-reduced air is turbine exhaust gas. Turbine exhaust gas may be simulated by cooling post-combustion gases from a test furnace, duct burner or a direct fired air heater.
Flue Gas Recirculation
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Flue gas can be recirculated from the test furnace or it can be simulated. A direct fired burner with a heat exchanger placed downstream for temperature control can be used for simulating the flue gas.
11.4.2 Air Capacity Curves
When specified, the burner manufacturer shall provide air capacity curves for forced draft burners. The air capacity curves (draft
loss vs. heat release at design excess air) should include air at standard temperature as well as design temperature for applications
with air preheat. The curves shall include operating points consistent with the fuel capacity curves.
The air capacity curves shall be adjusted accordingly for changes in atmospheric pressure relative to the test facility.
Whenever staged air burners are used, information relative to the split between primary and staged air shall be provided.
11.4.3 Damper and Register Leakage Test
When specified, damper and register leakage tests may be performed in accordance with the Air Movement Control Association
(AMCA), AMCA Standard 500 or other method mutually agreed to by the purchaser and vendor. Purchaser shall specify the
acceptable damper/register leakage rate.
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11.5 PILOT AND IGNITORS
11.5.1 General
The pilot and/or ignitor system shall be the same as that proposed for the actual burner installation. The pilot shall be continuously
operated during the main burner testing unless interruptible pilot operation is specified.
Pilot fuel, when possible, shall be the same as specified for actual operation. Main burner fuel may be substituted for the pilot fuel
only on approval by the purchaser.
11.5.2 Pilots
Prior to main burner testing, the pilot shall be proven stable at the design draft and operating conditions under each of the following conditions:
1. Damper/register position adjusted from closed to 100% open in a “cold” firebox.
2. Damper/register quickly opened and closed.
3. Fuel pressure adjusted over the defined operating range.
The main burner test may also include additional pilot stability tests including a partial or full fuel trip.
The pilot must have sufficient liberation to reliably ignite the main burner fuel for all anticipated light-off conditions.
11.5.3 Ignitors
The ignitor shall be proven to reliably ignite the pilot, or main flame if so intended, under the burner recommended light-off conditions. The pilot ignitor shall also be proven with the damper/register in the recommended light-off condition.
11.6 MAIN BURNER TEST
11.6.1 General
The main burner shall be tested for each fuel and operating condition specified. The purchaser shall specify the number of test
points and required measurements for each point.
Recommended burner test points are illustrated in Figure 23, which are intended, to encompass the full defined and safe limits of
operation.
CAUTION: Since the test furnace operating conditions cannot completely reproduce those in the operating facility, it is recommended that those
points intended to establish the safe operating envelop for the heater be verified during commissioning and early stages of operation of the fired
process heater.
11.6.2 Test Points
Following is a description of the recommended test points (see Figure 23), which are to be mutually agreed between the burner
manufacturer and purchaser prior to testing. All test points are performed with design draft at the floor of the test furnace.
1. Point A—Normal heat release at design excess air.
2. Point B—Minimum specified heat release with the air register set in the same position as Point A.
3. Point C—Minimum stable heat release at CO limit (250 ppmvd) or flame instability with air register set in the same position as Point A.
4. Point D—Minimum heat release with air register adjusted for design excess air. (Note 1)
5. Point E—Design heat release. Air register set for design excess air.
6. Point F—Maximum stable heat release at CO limit (250 ppmvd) or flame instability. (Note 2)
7. Point G—Maximum heat release with air register 100% open.
Note 1: Test Point D is intended to establish the turndown capability of the burner while operating with design excess air. This point may require
a heat release greater than the minimum specified value. The information obtained from this test point can be useful in further defining the safe
operating envelope for the burner in particular when low NOx burner technology is applied.
Note 2: The maximum stable heat release Test Point F, is normally taken with the air register at the same setting as that for the design heat
release of the burner at design excess air (Test Point E). Alternately, if specified by the purchaser, the test point may be at the air register setting
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API RECOMMENDED PRACTICE 535
of points A or G. This test point may be considered as the upper safe heat release for the burner and is intended to demonstrate stable combustion
of the burner up to and including the point of CO breakthrough.
11.6.3 Combustion Stability
Burner operation is considered unacceptable if combustion instability is exhibited at any specified operating condition. Combustion instability exists if any of the following conditions are detected:
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1.
2.
3.
4.
5.
Pulsation or vibration of burner flame, burner or furnace.
Uncontrollable fluctuations in the flame shape.
Significant combustibles in the flue gas , i.e., over 250 ppmvd CO.
Flashback into the venturi on premix burners.
Loss of flame from one or more tips or from the flame stabilization point.
11.6.4 Recommended Test Procedure
The time required for a furnace/burner system to reach stable operating conditions will depend on the sequence of the test.
The following test procedure sequence is recommended to minimize the time to collect test data:
1. Follow the established work practices for the test facility to prepare equipment and personnel for the safe handling of fuels and
introduction of flame in the test furnace.
2. Establish pilot and perform pilot test if applicable.
3. Demonstrate satisfactory light-off and cold-firing stability of the burner. Record burner gas pressure at light-off.
4. Increase the heat release, open the burner register and stack damper as required to establish conditions for “design” heat
release, test point “E”. Record required data.
5. Increase the heat release with the air register set for test point “E” until CO limit (250 ppmvd) to establish the “maximum
stable heat release”. Record required data.
6. Adjust the air register to the full-open position. If the excess air exceeds design with design draft, increase the heat release to
meet design excess air and establish the “maximum” heat release, test point “G”. Record required data.
7. Establish conditions for the “normal” operating point (test point “A”, Figure 23). The oxygen content of the test furnace
flue gas shall be no greater than that quoted for normal operation. Record required data including noise data if specified.
8. Confirm burner and pilot stability in a high draft condition by quickly ramping back the heat release without adjusting
excess air to the “minimum” specified heat release as established for test point “B”.
9. Vary the fuel rate without changing other burner settings to establish the “minimum” specified heat release and the “minimum
stable heat release”, test points, “B”, and “C” respectively. Record required data for each test point.
10. Adjust the air register setting and adjust fuel rate as necessary to establish the “minimum heat release with design excess
air”, test point “D”. Record required data.
11. Fully isolate fuel to the burner and confirm stable operation of the pilot.
12. Repeat test points as required for each fuel composition
Special test procedures should be developed and agreed to by the purchaser and burner and heater manufacturers for more complicated burner systems or specialized operating conditions.
11.6.5 Combination Firing
When gas and oil combination burner test firing is specified, test the burner using the procedures in 11.6.4 for each gas and oil fuel
separately. The burner shall then be tested with combined fuel firing in the following gas/oil heat release ratios, 25/75, and 50/50
or as specified by purchaser at the design, normal and minimum heat release rate (test points “E”, “A”, and “B” respectively—
Figure 23).
11.6.6 Visible Flame Characteristics
A. Quality
Acceptable flames are free of smoke, haze, sparklers or fireflies. Carbon or oil deposited on the burner, burner throat or on furnace
walls are unacceptable.
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59
Flame characteristics of ultra-low NOx and internal flue gas recirculating burners are often difficult to visually define. Refer to 6.5
for determination of flame dimension parameters in particular for this style of burners.
B. Shape
Flame shape should be uniform, centered on the burner axis and with length and width within specified requirements.
C. Test Recording
The flame size (diameter or cross section and length), shape and intensity (color, luminosity and transparency) shall be recorded
for each test point. The test furnace dimensions (length, width and height) shall be recorded.
11.6.7 Noise
Noise level guarantees provided by the burner manufacturer are typically at a location 3 ft (1 m) directly in front of the burner air
intake at the same elevation as the centerline of the burner intake for natural draft burners. Noise level measurements for a single
burner shall be recorded at the design heat release for the burner. When several burners are installed in the operating facility, the
noise level at 3 ft (1 m) from the burner may be higher than for a single burner due to the noise contribution from surrounding
burners. The heater/burner manufacturer’s guarantee shall account for the contribution of multiple burners in multiple burner
applications.
11.7 TEST INSTRUMENTATION
11.7.1 General
Flow, temperature and pressure elements, gas analyzers and other instrumentation are required to conduct a burner test. A typical
burner test setup with required instrumentation is shown in Figure 24.
11.7.2 Flue Gas Analyzers
Continuous emission analyzers should be used. Continuous recording of data is recommended. Analyzers shall be zeroed and calibrated over the intended range of operation before, after and as required during testing. Certified analyzer calibration gases spanning the intended range of operation should be available for calibration.
Heated sample lines may be required to ensure accurate measurement of the flue gas components.
11.8 MEASUREMENTS
11.8.1 Fuel Gas
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1. Temperature.
2. Flow.
3. Pressure.
11.8.2 Liquid Fuel
1. Temperature.
2. Flow.
3. Pressure.
11.8.3 Atomizing Media
1. Temperature.
2. Flow.
3. Pressure.
11.8.4 Combustion Air (Air, Turbine Exhaust Gas or Air/Flue Gas Mixture)
1.
2.
3.
4.
Temperature.
Atmospheric pressure and humidity.
Oxygen concentration.
Pressure (forced draft systems).
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API RECOMMENDED PRACTICE 535
5. Draft loss across the burner / burner tile.
6. Air register position.
7. Air register leakage if specified.
11.8.5 Furnace
1. Floor draft.
2. Temperature exiting radiant section.
3. Floor temperature.
11.8.6 Flue Gas
1. O2 (%).
2. NOx (ppmvd).
3. CO (ppmvd).
11.8.7 Other
Noise (if required)
12 Troubleshooting
12.1 BURNER PLUGGING
Burner plugging can lead to flame and burner instability. Flame impingement can occur. Flames can blow out when higher burner
pressures and/or plugged burner ports disrupt the normal patterns within a burner. Increased fuel velocities may cause blowout of
the flames. Obstructions within the burner block can develop disrupting burner flow patterns.
A burner-plugging problem, in many instances, can be solved. The source of the plugging has to be determined. The following
can cause plugging:
1.
2.
3.
4.
5.
6.
Scale in the fuel gas lines.
Liquid/aerosol carryover into the burners.
Unsaturates, primarily propylene, in the fuel gas.
Amine carryover into the fuel gas system.
Chlorides.
High tip/riser temperatures.
The first two items may be the most likely of the six possibilities listed above. An analysis of the obstructions may give an indication of the cause of the plugging. The cause of the problem can sometimes be readily determined. Deposits present in a burner
riser may be analyzed. Plugging can be reduced if the burners are designed to operate at low fuel gas pressure.
12.2 SCALE
All fuel gas lines, gas manifolds, burner risers and tips downstream from the coaleser to the burner should be blown free of scale,
cleaned and flushed. Scale in the fuel gas lines can also be removed with steam and plant air. Cleaning the lines at the heater alone
may not be sufficient. Fuel gas lines should be inspected and cleaned, if necessary, at every turnaround.
It is recommended that strainers or filters be used in all fuel lines.
12.3 LIQUID/AEROSOL CARRYOVER
Burner plugging is often caused by liquid/aerosol carryover in the fuel gas lines. The flashing of this liquid causes coke formation
in the tips/risers. The presence of “stalagmites” or “stalactites” can denote the presence of significant liquid within the fuel gas.
These dark, solid shapes may form as plates, cones or other shapes within the burner block.
The following frequently cause liquid carryover:
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Minimum stable
heat release
61
Minimum
specified heat
Design excess air
C
B
Minimum stable
heat release
D
Minimum heat
release with
design excess air
Flue gas oxygen content
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Figure 23—Burner Performance Test Points
A
Normal heat
release
E
Design heat
release
F
G
Minimum
heat release
BURNERS FOR FIRED HEATERS IN GENERAL REFINERY SERVICES
62
API RECOMMENDED PRACTICE 535
O2, NOx, CO
flow
AI
Fuel gas
flow
TI
FI
PI
TI
Liquid fuel
flow
Firebox
TI
FI
PI
PI
Burner
TI
PI
Atomization media
flow
TI
FI
PI
Combustion air
flow
02
TI
FI
Pilot fuel
flow
PI
AI
(optimal)
PI
Figure 24—Typical Burner Test Setup
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1. Heavy hydrocarbons in fuel systems (C4 and higher).
2. An undersized fuel gas drum/high velocities in the drum.
3. Insufficient steam or heat tracing in fuel delivery lines–fuel gas condenses upon delivery to the burners.
Coalesers are used downstream of the fuel gas drum to aid in the removal of any further liquid/aerosol entrainment.
12.4 UNSATURATES
The presence of greater than 10% unsaturates, most notably propylene and butadiene, can plug burner tips/risers. When burner
design has not considered these components, it may be possible to reduce the plugging by reducing the number and increasing the
size of the burner firing orifices. This may not be applicable in all burners or in all heaters.
12.5 AMINES
The presence of amines in the fuel system can cause plugging of burner tips and risers. Carryover from the amine treating system
should be eliminated. Coalesers can be used downstream of fuel gas knock out drums as a way of removing amines.
Carbon steel manifolds and risers can corrode as a result of amine carryover. This can be corrected by using stainless steel components.
12.6 CHLORIDES AND AMMONIA
Chlorides and ammonia can form and possibly lead to burner tip/riser plugging. Chlorides may be present when guard beds
become saturated and cease removal.
Ammonia in the gas will produce ammonia salts and sulfur in the gas will produce iron sulfides, which could both be taken out at
the coalescer, if located properly. Un-reacted ammonia and sulfur will pass through the filter/coalescer and can react downstream
to cause the same problems. Filter/coalescers should be placed as close to the heaters/burners as possible.
12.7 BURNER OPERATION TROUBLE SHOOTING TABLE
Some of the troubles normally experienced in burner operation and possible causes and solutions are given:
(These Tables are solely suggestions and are not meant to replace the burner operating and maintenance manuals. The vendor
should be consulted whenever components are replaced or modified.)
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API RECOMMENDED PRACTICE 535
12.7.1 Conventional Gas Burners
Table 16—Conventional Gas Burners
TROUBLE
CAUSES
Burners go out
Gas/air mixture too lean (i.e.) too much air
Flame flashback (premix only)
Too much draft
Low gas pressure
High hydrogen concentration and fuel gas
Insufficient heat release
Low gas flow. Check for low gas pressure.
Burner tip orifices too small.
Tip/riser plugging.
Gas composition not per spec.
Pulsating fire or “breathing” (flame alternately Lack of oxygen/draft
ignites and goes out, sometimes with almost
explosive force).
Erratic flames (not a stiff flame).
Lack of combustion air
Incorrect position of burner tip.
Gas flame too long.
Gas flame too short.
Furnace currents
Excessive firing.
Too little primary air (premix only).
Worn/damaged burner tip.
Tip drilling angle incorrect.
Too much primary air (premix only).
Tip drilling angle incorrect.
SOLUTIONS
Reduce total air. Reduce primary air (premix
only)
Close stack damper or air register
Shut off burners to raise the fuel gas pressure
to the operating burners. It may be necessary
to reduce burner orifices’ size.
Adjust primary air. A new burner or tip drilling
may be required.
Increase gas flow.
Check with burner manufacturer. Determine
sufficient air will be available through the air
registers for the increased fuel rate.
Perform maintenance/cleaning. Determine
source of pluggage.
Correct the composition, or consult with
burner manufacturer.
Reduce firing rate immediately. Establish complete combustion at lower rate. Check damper
position. Check draft conditions. Reduce fuel
before increasing air.
Reduce firing then adjust air register and/or
stack damper.
Locate tips per burner manufacturer’s drawings.
Perform CFD modeling.
Reduce firing rates.
Increase primary air; decrease secondary air.
Replace tip.
Consult burner manufacturer.
Increase secondary air, decrease primary air.
Consult burner manufacturer.
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65
12.7.2 Oil Burners
Table 17—Oil Burners
TROUBLE
CAUSES
SOLUTIONS
Burners dripping.
Insufficient combusion air.
Coke deposits on burner blocks.
Improper atomization due to water in steam.
Coking of burner tip when firing fuel oil only. High oil viscosity.
Dark color/smoking.
Adjust air register and/or stack damper.
Correct steam conditions.
Check fuel oil type.
Increase fuel temperature to lower viscosity to
proper level.
Improper blending of oil constituents.
Check composition of fuel for heavier fractions.
Clogging of burner tip.
Clean or replace burner tip. Confirm burner tip
is in proper location.
Insufficient atomizing steam.
Increase atomizing steam.
Improper location of burner tip.
Adjust tip location.
Worn burner parts.
Replace worn parts.
Failure to maintain ignition.
Too much atomizing steam.
Reduce atomizing steam until ignition is stabilized. During start up, have atomizing steam
on low side until ignition is well established.
Too much primary air at firing rates.
Reduce primary air to minimum or eliminate it
entirely.
Too much moisture in atomizing steam.
Assure appropriate insulation is on steam
lines. Confirm steam traps are functioning.
Adjust quality of atomizing steam to appropriate levels.
Too low an oil pressure.
Raise oil pressure.
Coking of oil tip when firing oil in combina- High rate of gas with a low rate of oil resulting Increase atomization steam to produce suffition with gas.
in high heat radiation to the fuel oil tip.
cient cooling effect to avoid coking. Reduce
gas fire rate. Dedicate individual burners to
either fuel.
Incorrect oil gun position.
Adjust tip location.
Lack of steam purge on gun.
Purge oil gun prior to shut off.
Erratic flames (not a stiff flame).
Lack of combustion air.
Reduce firing then adjust air register and/or
stack damper.
Plugged burner gun.
Clean burner gun.
Worn burner gun.
Replace burner gun.
High rate of gas firing while firing a low rate of Reduce gas rate. Dedicate burners to either
oil.
fuel.
Excess smoke at stack (evidence of incomplete Insufficient atomizing steam.
Increase atomizing steam.
combustion).
High oil viscosity.
Increase oil temperature, check oil properties.
Low excess air.
Increase excess air.
Moisture in atomizing steam.
Requires knockout drum or increase in super
heat. Alter steam at steam source.
Fire flies or sparks.
Water in atomizing steam.
Requires knockout drum or increase in super
heat. Alter steam at steam source.
High oil viscosity.
Increase oil temperature. Check oil properties.
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66
API RECOMMENDED PRACTICE 535
12.7.3 Low NOx Burners
Table 18—Low NOx Burners
TROUBLE
Flame shape/appearance
Excessively long or large diameter.
Lazy/smoky flame.
Heat flux shift.
Flame Instability.
Flame lift off
Incomplete Combustion.
High combustibles (>500 ppm) in flue gas.
Afterburn.
High convection flue gas/tube temp.
High stack temperature.
High NOx emissions.
--`,,``,,`,`,,,`,,`,``,,`,,`,,,-`-`,,`,,`,`,,`---
Flame Pulsation.
Excessive heater vibration and excessive
noise.
Flame Impingement.
High tube skin temperature.
Coke formation on tubes.
Localized coking.
Heat flux shift.
Burner Tip Plugging.
Coke Formation.
Deposits on tubes, refractory, burner tile and
tips.
Copyright American Petroleum Institute
Provided by IHS under license with API
No reproduction or networking permitted without license from IHS
CAUSES
SOLUTIONS
Lack of air/too much fuel..
Incorrect fuel composition.
Adjust air registers.
Check for presence of heavy hydrocarbons in
the fuel composition.
Excessive fuel pressure.
Adjust firing to within defined operating envelope.
Burner spacing.
Consult manufacturer.
Excessive air flow.
Adjust air register/draft.
High fuel pressure.
Check/adjust fuel pressure.
Over-firing (above design).
Operate within design envelope.
Incorrect fuel composition.
Check/correct fuel composition.
Plugged orifices.
Clean burner orifices.
Excessive fuel pressure.
Clean tips.
Inadequate air.
Reduce firing. Adjust air registers. Check O2 /
combustibles meter calibration. Seal heater
leakage to remove source of oxygen and misleading oxygen reading.
Individual burner flameout.
Determine cause of flameout and reestablish
flame, if safe.
Over firing.
Reduce firing. Consult with burner manufacturer.
Incomplete combustion in radiant section (see Refer to incomplete combustion (see above).
in the Trouble column above) .
Adjust air register, if needed.
Air leakage in convection section
Seal air leakage
High fuel bound nitrogen in fuel (i.e. ammo- Verify fuel composition.
nia).
High excess air.
Reduce excess air.
Incorrect fuel composition.
Check fuel.
Excessive air preheat temperature.
Reduce air preheat if possible.
High furnace temperature.
Investigate reasons for high furnace temperature such as heat transfer surface fouling.
Tramp air.
Seal box against tramp air.
Inaccurate NOx measurement.
Calibrate and validate instruments.
Inadequate air.
Reduce firing before adjusting air registers and
draft.
Operation outside of design envelope.
Adjust firing.
Incorrect fuel composition.
Check/adjust fuel composition.
Flame operation in natural frequency.
Consult burner manufacturer.
Low floor level flu gas temperature.
Consult burner manufacturer.
Tip plugging.
Burner maintenance.
Refer to causes for long flame above.
Refer to actions for long flames above.
Refer to Section 12.1
Poor mixing of fuel and air.
Check alignment against design.
Heavy ends/liquid/aerosols/amines in fuel gas. Check fuel temperatures/composition/knock
out drum level.
Low fuel operating pressure.
Raise fuel gas pressure by cutting out burners.
Low fuel temperature.
Install system to heat fuel.
Licensee=Chevron Texaco API 22 loc/6 usr Part 1/1000001100, User=Heron, Jonathan
Not for Resale, 07/30/2006 11:33:30 MDT
67
Copyright American Petroleum Institute
Provided by IHS under license with API
No reproduction or networking permitted without license from IHS
Licensee=Chevron Texaco API 22 loc/6 usr Part 1/1000001100, User=Heron, Jonathan
Not for Resale, 07/30/2006 11:33:30 MDT
--`,,``,,`,`,,,`,,`,``,,`,,`,,,-`-`,,`,,`,`,,`---
APPENDIX A—BURNER DATA SHEET
68
API RECOMMENDED PRACTICE 535
PURCHASER / OWNER :
ITEM NO. :
SERVICE :
LOCATION:
GENERAL DATA
1
REV
2
TYPE OF HEATER
3 * ALTITUDE ABOVE SEA LEVEL, ft.
4 * AIR SUPPLY:
5
AMBIENT / PREHEATED AIR / GAS TURBINE EXHAUST
TEMPERATURE, o F. (MIN. / MAX. / DESIGN)
RELATIVE HUMIDITY, %.
DRAFT TYPE: FORCED / NATURAL / INDUCED
ACROSS BURNER, in. H2O.
DRAFT AVAILABLE:
ACROSS PLENUM, in. H2O.
--`,,``,,`,`,,,`,,`,``,,`,,`,,,-`-`,,`,,`,`,,`---
6
7
8
9
10
1 1 * REQUIRED TURNDOWN
1 2 BURNER WALL SETTING THICKNESS, in.
13
14
15
HEATER CASING THICKNESS, in.
FIREBOX HEIGHT, ft.
TUBE CIRCLE DIAMETER, ft.
BURNER DATA
16
17
18
MANUFACTURER
TYPE OF BURNER
19
20
MODEL / SIZE
DIRECTION OF FIRING
21
22
23
LOCATION ( ROOF / FLOOR / SIDEWALL )
NUMBER REQUIRED
MINIMUM DISTANCE BURNER CENTERLINE, ft.:
24
25
TO TUBE CENTERLINE ( HORIZONTAL / VERTICAL )
TO ADJACENT BURNER CENTERLINE ( HORIZONTAL / VERTICAL )
26
TO UNSHIELDED REFRACTORY ( HORIZONTAL / VERTICAL )
2 7 BURNER CIRCLE DIAMETER, ft.
2 8 * PILOTS:
29
30
NUMBER REQUIRED
TYPE
31
32
33
34
IGNITION METHOD
FUEL
FUEL PRESSURE, Psig.
CAPACITY, MM Btu/hr.
OPERATING DATA
35
3 6 * FUEL
37
38
HEAT RELEASE PER BURNER, MM Btu/hr. ( LHV )
DESIGN
39
NORMAL
40
MINIMUM
4 1 * EXCESS AIR @ DESIGN HEAT RELEASE, %.
42
43
44
45
AIR TEMPERATURE, oF.
DRAFT (AIR PRESSURE) LOSS, in. H2O.
DESIGN
NORMAL
46
47
48
MINIMUM
FUEL PRESSURE REQUIRED @ BURNER, Psig.
FLAME LENGTH @ DESIGN HEAT RELEASE, ft.
49
50
FLAME SHAPE (ROUND, FLAT, ETC.)
ATOMIZING MEDIUM / OIL RATIO, Lb/Lb.
51
52
53
NOTES:
54
55
56
57
BURNER DATA SHEET
API RECOMMENDED
PRACTICE
535
API STANDARD
560
Copyright American Petroleum Institute
Provided by IHS under license with API
No reproduction or networking permitted without license from IHS
CUSTOMARY UNITS
PROJECT NUMBER
DOCUMENT NUMBER
SHEET
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REV
BURNERS FOR FIRED HEATERS IN GENERAL REFINERY SERVICES
69
GAS FUEL CHARACTERISTICS
1 * FUEL TYPE
2 * HEATING VALUE ( LHV ) , ( ( Btu/scf )
REV
( Btu/Lb )
3 * SPECIFIC GRAVIRTY ( AIR = 1.0 )
4 * MOLECULAR WEIGHT
5 * FUEL TEMPERATURE @ BURNER, oF.
6 * FUEL PRESSURE; AVAILABLE @ BURNER, Psig.
7 * FUEL GAS COMPOSITION, MOLE % .
8
9
CH4
C2H6
--`,,``,,`,`,,,`,,`,``,,`,,`,,,-`-`,,`,,`,`,,`---
10
11
C3H8
C4H10
12
13
C5H12
H2
14
15
16
N2
TOTAL
LIQUID FUEL CHARACTERISTICS
17
1 8 * FUEL TYPE
1 9 * HEATING VALUE ( LHV ) , Btu/Lb.
2 0 * SPECIFIC GRAVITY / DEGREE API
2 1 * H / C RATIO ( BY WEIGHT )
2 2 * VISCOSITY, @
23
@
o
o
F. (SSU)
F. (SSU)
2 4 * VANADIUM, ppm.
2 5 * SODIUM, ppm.
2 6 * POTASSIUM, ppm.
2 7 * NICKEL, ppm.
2 8 * FIXED NITROGEN, ppm.
2 9 * SULFUR, % wt.
3 0 * ASH, % wt.
3 1 * LIQUIDS:
32
ASTM INITIAL BOILING POINT, oF.
ASTM END POINT, o F.
3 3 * FUEL TEMPERATURE @ BURNER, oF.
3 4 * FUEL PRESSURE AVAILABLE / REQUIRED @ BURNER, Psig.
3 5 * ATOMIZING MEDIUM:
36
37
38
39
40
BURNER PLENUM:
41
42
43
44
A
R
AIR / STEAM / MECHANICAL
TEMPERATURE, o F.
PRESSURE, Psig.
D
COMMON / INTEGRAL
MATERIAL
T
F
MISCELLANEOUS
PLATE THICKNESS, in.
INTERNAL INSULATION
INLET AIR CONTROL:
45
46
BURNER TILE:
47
48
NOISE SPECIFICATION
49
50
ATTENUATION METHOD
PAINTING REQUIREMENTS
51
52
IGNITION PORT:
SIGHT PORT:
DAMPER OR REGISTERS
MODE OF OPERATION
LEAKAGE, %.
COMPOSITION
MINIMUM SERVICE TEMPERATURE, o F.
5 3 * FLAME DETECTION:
54
55
SIZE / NO.
SIZE / NO.
TYPE
NUMBER / LOCATION
CONNECTION SIZE
5 6 SAFETY INTERLOCK SYSTEM FOR ATOMIZING MEDIUM & OIL
5 7 * PERFORMANCE TEST REQUIRED (YES or NO)
5 8 FUEL CONNECTIONS: TYPE/SIZE
MATERIAL/THICKNESS
59
6 0 NOTES:
BURNER DATA SHEET
API RECOMMENDED PRACTICE 535
Copyright American Petroleum Institute
Provided by IHS under license with API
No reproduction or networking permitted without license from IHS
CUSTOMARY UNITS
PROJECT NUMBER
DOCUMENT NUMBER
SHEET
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REV
70
API RECOMMENDED PRACTICE 535
EMISSION REQUIREMENTS
1
2
3
4
5
6
7
FIREBOX TEMPERATURE, oF.
NOx
CO
UHC
PARTICULATES
SOx
REV
*
*
*
*
*
ppmv(d) or
ppmv(d) or
ppmv(d) or
ppmv(d) or
ppmv(d) or
Lb / MM
Lb / MM
Lb / MM
Lb / MM
Lb / MM
Btu
Btu
Btu
Btu
Btu
(LVH)
(LVH)
(LVH)
(LVH)
(LVH)
8
* CORRECTED TO 3% O2 (DRY BASIS @ DESIGN HEAT RELEASE)
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
NOTES:
1. AT DESIGN CONDITIONS, MINIMUM OF 90% OF THE AVAILABLE DRAFT WITH AIR REGISTER FULLY OPEN SHOULD BE
UTILIZED ACROSS THE BURNER. IN ADDITION, A MINIMUM OF 75% OF THE AIR SIDE PRESSURE DROP WITH AIR
REGISTERS FULL OPEN SHALL BE UTILIZED ACROSS BURNER THROAT.
2. VENDOR TO GUARANTEE BURNER FLAME LENGTH.
3. VENDOR TO GUARANTEE EXCESS AIR, HEAT RELEASE AND DRAFT LOSS ACROSS BURNER.
BURNER DATA SHEET
API RECOMMENDED PRACTICE 535
CUSTOMARY UNITS
PROJECT NUMBER
DOCUMENT NUMBER
--`,,``,,`,`,,,`,,`,``,,`,,`,,,-`-`,,`,,`,`,,`---
Copyright American Petroleum Institute
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No reproduction or networking permitted without license from IHS
SHEET
3 OF 3
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REV
BURNERS FOR FIRED HEATERS IN GENERAL REFINERY SERVICES
PURCHASER / OWNER :
71
ITEM NO. :
SERVICE :
LOCATION:
GENERAL DATA
1
REV
2
TYPE OF HEATER
3 * ALTITUDE ABOVE SEA LEVEL, m.
4 * AIR SUPPLY:
5
AMBIENT / PREHEATED AIR / GAS TURBINE EXHAUST
TEMPERATURE, oC. (MIN. / MAX. / DESIGN)
6
7
RELATIVE HUMIDITY, %.
8
DRAFT TYPE: FORCED / NATURAL / INDUCED
9
DRAFT AVAILABLE:
ACROSS BURNER, Pa.
10
ACROSS PLENUM, Pa.
11 * REQUIRED TURNDOWN
12 BURNER WALL SETTING THICKNESS, mm.
13 HEATER CASING THICKNESS, mm.
14 FIREBOX HEIGHT, m.
15 TUBE CIRCLE DIAMETER, m.
BURNER DATA
16
--`,,``,,`,`,,,`,,`,``,,`,,`,,,-`-`,,`,,`,`,,`---
17 MANUFACTURER
18 TYPE OF BURNER
19 MODEL / SIZE
20 DIRECTION OF FIRING
21 LOCATION ( ROOF / FLOOR / SIDEWALL )
22 NUMBER REQUIRED
23 MINIMUM DISTANCE BURNER CENTERLINE, m.:
24
TO TUBE CENTERLINE ( HORIZONTAL / VERTICAL )
25
TO ADJACENT BURNER CENTERLINE ( HORIZONTAL / VERTICAL )
26
TO UNSHIELDED REFRACTORY ( HORIZONTAL / VERTICAL )
27 BURNER CIRCLE DIAMETER, m.
28 * PILOTS:
29
NUMBER REQUIRED
30
TYPE
31
IGNITION METHOD
32
FUEL
33
FUEL PRESSURE, kPa.g.
34
CAPACITY, MW.
OPERATING DATA
35
36 * FUEL
37 HEAT RELEASE PER BURNER, MW. ( LHV )
38
DESIGN
39
NORMAL
40
MINIMUM
41 * EXCESS AIR @ DESIGN HEAT RELEASE, %.
o
42 AIR TEMPERATURE, C.
43 DRAFT (AIR PRESSURE) LOSS, Pa.
44
DESIGN
45
NORMAL
46
MINIMUM
47 FUEL PRESSURE REQUIRED @ BURNER, kPa.g.
48 FLAME LENGTH @ DESIGN HEAT RELEASE, m.
49 FLAME SHAPE (ROUND, FLAT, ETC.)
50 ATOMIZING MEDIUM / OIL RATIO, kg/kg.
51
52
53
54
55
56
57
NOTES:
BURNER DATA SHEET
API RECOMMENDED PRACTICE 535
SI UNITS
PROJECT NUMBER
DOCUMENT NUMBER
SHEET
1 OF 3
Copyright American Petroleum Institute
Provided by IHS under license with API
No reproduction or networking permitted without license from IHS
Licensee=Chevron Texaco API 22 loc/6 usr Part 1/1000001100, User=Heron, Jonathan
Not for Resale, 07/30/2006 11:33:30 MDT
REV
72
API RECOMMENDED PRACTICE 535
GAS FUEL CHARACTERISTICS
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
* FUEL PRESSURE; AVAILABLE @ BURNER, kPa.g.
* FUEL GAS COMPOSITION, MOLE % .
CH4
C2H6
C3H8
C4H10
C5H12
H2
N2
TOTAL
LIQUID FUEL CHARACTERISTICS
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
REV
* FUEL TYPE
* HEATING VALUE ( LHV ) , ( ( kJ/Nm 3 ) ( kJ/kg )
* SPECIFIC GRAVIRTY ( AIR = 1.0 )
* MOLECULAR WEIGHT
o
* FUEL TEMPERATURE @ BURNER, C.
* FUEL TYPE
* HEATING VALUE ( LHV ) , kJ/kg.
* SPECIFIC GRAVITY / DEGREE API
* H / C RATIO ( BY WEIGHT )
o
C. (SSU)
* VISCOSITY, @
o
C. (SSU)
@
* VANADIUM, ppm.
* SODIUM, ppm.
* POTASSIUM, ppm.
* NICKEL, ppm.
* FIXED NITROGEN, ppm.
* SULFUR, % wt.
* ASH, % wt.
* LIQUIDS:
ASTM INITIAL BOILING POINT,
ASTM END POINT, oC.
o
* FUEL TEMPERATURE @ BURNER, C.
o
C.
* FUEL PRESSURE AVAILABLE / REQUIRED @ BURNER, kPa.g.
* ATOMIZING MEDIUM:
AIR / STEAM / MECHANICAL
TEMPERATURE, oC.
PRESSURE, kPa.g.
MISCELLANEOUS
38
39 BURNER PLENUM:
COMMON / INTEGRAL
40
MATERIAL
41
PLATE THICKNESS, mm.
42
INTERNAL INSULATION
43 INLET AIR CONTROL:
DAMPER OR REGISTERS
44
MODE OF OPERATION
45
LEAKAGE, %.
46 BURNER TILE:
COMPOSITION
MINIMUM SERVICE TEMPERATURE, oC.
47
48 NOISE SPECIFICATION
49 ATTENUATION METHOD
50 PAINTING REQUIREMENTS
51 IGNITION PORT:
SIZE / NO.
52 SIGHT PORT:
SIZE / NO.
53 * FLAME DETECTION:
TYPE
54
NUMBER / LOCATION
55
CONNECTION SIZE
56 SAFETY INTERLOCK SYSTEM FOR ATOMIZING MEDIUM & OIL
57 * PERFORMANCE TEST REQUIRED (YES or NO)
58
59
60
FUEL CONNECTION: TYPE/SIZE
MATERIAL/THICKNESS
NOTES:
SI UNITS
BURNER DATA SHEET
API RECOMMENDED PRACTICE 535
--`,,``,,`,`,,,`,,`,``,,`,,`,,,-`-`,,`,,`,`,,`---
Copyright American Petroleum Institute
Provided by IHS under license with API
No reproduction or networking permitted without license from IHS
PROJECT NUMBER
DOCUMENT NUMBER
SHEET
REV
2 OF 3
PP
Licensee=Chevron Texaco API 22 loc/6 usr Part 1/1000001100, User=Heron, Jonathan
Not for Resale, 07/30/2006 11:33:30 MDT
BURNERS FOR FIRED HEATERS IN GENERAL REFINERY SERVICES
73
EMISSION REQUIREMENTS
1
2
3
4
5
6
7
FIREBOX TEMPERATURE, oC.
NOx
CO
UHC
PARTICULATES
SOx
REV
*
*
*
*
*
ppmv(d) or
ppmv(d) or
ppmv(d) or
ppmv(d) or
ppmv(d) or
mg / Nm 3
mg / Nm 3
kg / kJ ( LHV )
kg / kJ ( LHV )
mg / Nm 3
8
* CORRECTED TO 3% O2 (DRY BASIS @ DESIGN HEAT RELEASE)
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
NOTES:
1. AT DESIGN CONDITIONS, MINIMUM OF 90% OF THE AVAILABLE DRAFT WITH AIR REGISTER FULLY OPEN SHOULD BE
UTILIZED ACROSS THE BURNER. IN ADDITION, A MINIMUM OF 75% OF THE AIR SIDE PRESSURE DROP WITH AIR
REGISTERS FULL OPEN SHALL BE UTILIZED ACROSS BURNER THROAT.
2. VENDOR TO GUARANTEE BURNER FLAME LENGTH.
3. VENDOR TO GUARANTEE EXCESS AIR, HEAT RELEASE AND DRAFT LOSS ACROSS BURNER.
BURNER DATA SHEET
API RECOMMENDED PRACTICE 535
SI UNITS
PROJECT NUMBER
DOCUMENT NUMBER
SHEET
3 OF 3
--`,,``,,`,`,,,`,,`,``,,`,,`,,,-`-`,,`,,`,`,,`---
Copyright American Petroleum Institute
Provided by IHS under license with API
No reproduction or networking permitted without license from IHS
Licensee=Chevron Texaco API 22 loc/6 usr Part 1/1000001100, User=Heron, Jonathan
Not for Resale, 07/30/2006 11:33:30 MDT
REV
74
API RECOMMENDED PRACTICE 535
Data Sheet B-1—Burner Test Data Sheet
(at burner level)
(Raw/Corrected)
Note: Use seperate burner test data sheets for each fuel.
--`,,``,,`,`,,,`,,`,``,,`,,`,,,-`-`,,`,,`,`,,`---
Copyright American Petroleum Institute
Provided by IHS under license with API
No reproduction or networking permitted without license from IHS
Licensee=Chevron Texaco API 22 loc/6 usr Part 1/1000001100, User=Heron, Jonathan
Not for Resale, 07/30/2006 11:33:30 MDT
BURNERS FOR FIRED HEATERS IN GENERAL REFINERY SERVICES
Data Sheet B-2—Burner Test Fuel Gas Specifications
--`,,``,,`,`,,,`,,`,``,,`,,`,,,-`-`,,`,,`,`,,`---
Copyright American Petroleum Institute
Provided by IHS under license with API
No reproduction or networking permitted without license from IHS
Licensee=Chevron Texaco API 22 loc/6 usr Part 1/1000001100, User=Heron, Jonathan
Not for Resale, 07/30/2006 11:33:30 MDT
75
76
API RECOMMENDED PRACTICE 535
--`,,``,,`,`,,,`,,`,``,,`,,`,,,-`-`,,`,,`,`,,`---
Data Sheet B-2—Burner Test Liquid Fuel Specifications
Copyright American Petroleum Institute
Provided by IHS under license with API
No reproduction or networking permitted without license from IHS
Licensee=Chevron Texaco API 22 loc/6 usr Part 1/1000001100, User=Heron, Jonathan
Not for Resale, 07/30/2006 11:33:30 MDT
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*Minimum Order – There is a $50 minimum for all orders containing hardcopy documents. The $50 minimum applies to the order subtotal including the $10 processing fee, excluding any
applicable taxes and freight charges. If the total cost of the documents on the order plus the $10 processing fee is less than $50, the processing fee will be increased to bring the order amount
up to the $50 minimum. This processing fee will be applied before any applicable deposit account, quantity or member discounts have been applied. There is no minimum for orders containing only
electronically delivered documents.
Copyright American Petroleum Institute
Provided by IHS under license with API
No reproduction or networking permitted without license from IHS
Licensee=Chevron Texaco API 22 loc/6 usr Part 1/1000001100, User=Heron, Jonathan
Not for Resale, 07/30/2006 11:33:30 MDT
There’s more where
this came from.
The American Petroleum Institute provides additional resources and programs
to the oil and natural gas industry which are based on API® Standards. For more
information, contact:
Phone:
Fax:
202-962-4791
202-682-8070
• American Petroleum Institute Quality Registrar
(APIQR®)
Phone:
Fax:
202-962-4791
202-682-8070
• API Spec Q1® Registration
Phone:
Fax:
202-962-4791
202-682-8070
• API Perforator Design Registration
Phone:
Fax:
202-962-4791
202-682-8070
• API ISO/TS 29001 Registration
Phone:
Fax:
202-962-4791
202-682-8070
• API Training Provider Certification Program
Phone:
Fax:
202-682-8490
202-682-8070
• Individual Certification Programs
Phone:
Fax:
202-682-8064
202-682-8348
• Engine Oil Licensing and Certification System (EOLCS) Phone:
Fax:
202-682-8516
202-962-4739
• API PetroTEAM™ (Training, Education and Meetings)
202-682-8195
202-682-8222
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• API Monogram® Licensing Program
Phone:
Fax:
Check out the API Publications, Programs,
and Services Catalog online at www.api.org.
Helping You Get
The Job Done Right.®
Copyright American Petroleum Institute
Provided by IHS under license with API
No reproduction or networking permitted without license from IHS
Licensee=Chevron Texaco API 22 loc/6 usr Part 1/1000001100, User=Heron, Jonathan
Not for Resale, 07/30/2006 11:33:30 MDT
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01/06
Copyright American Petroleum Institute
Provided by IHS under license with API
No reproduction or networking permitted without license from IHS
Licensee=Chevron Texaco API 22 loc/6 usr Part 1/1000001100, User=Heron, Jonathan
Not for Resale, 07/30/2006 11:33:30 MDT
Additional copies are available through Global Engineering
Documents at (800) 854-7179 or (303) 397-7956
Information about API Publications, Programs and Services is
available on the World Wide Web at: http://www.api.org
.5VTGGV0QTVJYGUV
9CUJKPIVQP&%
Copyright American Petroleum Institute
Provided by IHS under license with API
No reproduction or networking permitted without license from IHS
--`,,``,,`,`,,,`,,`,``,,`,,`,,,-`-`,,`,,`,`,,`---
Product No. C53502
Licensee=Chevron Texaco API 22 loc/6 usr Part 1/1000001100, User=Heron, Jonathan
Not for Resale, 07/30/2006 11:33:30 MDT