New Approach to Optimizing Fired
Heaters
• Ashutosh Garg, Furnace Improvements
Sugar Land Texas, USA
Energy Consumption
• Petroleum Refining
▫ 7.5% of the total energy
consumption in USA
• 0.40 MMBtu/ BBL of oil
• Total Energy consumed in
refining- 7.1 Quadrillion BTU/yr
• Energy cost -$6/MMBtu
• Total Energy Cost- 42 Billion /yr
• Fired heaters -40-70% of the
energy
Energy Consumption
•
•
•
•
A Typical refinery process 100,000 BPD
Consumption of 0.40 MMBTU/BBL
$6 per MMBTU
Energy bill of $ 87.6 million per year.
Potential Saving
• 1% Efficiency improve
• $876,000/Year
Fired Heaters
• Essential component in
Petrochemical and Chemical
Plants
• Each refinery has ≈ 20-50 fired
heaters
• Design efficiency - 70-90%
▫ Operating efficiency is even less
than design.
Maintaining Design Operation
• Maintain the design conditions
(very difficult)
• In the field, heater loads
change constantly due to
variations in:
▫
▫
▫
▫
Feed flow rate
Feed temperature
Fuel composition
Ambient temperature
• The heater will be operating a
non-optimal conditions
• Requires optimization 24/7
How to Maintain the Design Efficiency?
• When the heater conditions
change, adjustments in the heater
are required.
• Manual adjustments are
provided- not adequate
• Optimizing the fired heater will:
▫ Reduce Energy Consumption
▫ Increase run length
▫ Minimize maintenance
• FIS has proposed two prong
approach
• Software based- Heater
Performance Index
• Hardware based- Draft & Excess
O2 Control
Fired Heater
• Heat liberated by the
combustion of fuels is
transferred to fluids
contained in coils
• Fired Heater:
▫ Radiant Section
▫ Convection Section
▫ Stack
www.heatflux.com
Typical heater efficiency
• Natural Draft- 70-84%
• Balance Draft-90-92%
• Natural Draft heaters in
Industry- 86%
• Balanced Draft heaters in
Industy-12%
• Typical stack temperature –
500-800 F
• Typical stack Oxygen- 2-10%
• Target Oxygen-2-3%
• Plenty of room for
optimization
Combustion
• Combustion Requires
▫ Air ( 0.21O2 + 0.79 N2)
▫ Fuel
▫ Ignition source
• Complete Combustion
▫ Excess air
• Incomplete Combustion
▫ Energy Loss
▫ CO and H2 are released
Draft
• Pressure inside the heater
▫ Combustion air is drawn inside the
heater through the burner’s air
register
▫ Hot Flue gas flows out of the heater
through the stack
• Types of Draft
▫
▫
▫
▫
Natural Draft (ND)
Forced Draft (FD)
Induced Draft (ID)
Balanced Draft
> 80%
< 1%
≈ 10%
≈ 10%
Draft
• Stack Dampers
helps control the
draft
STACK
EXIT LOSS
STACK
(SE)a STACK
EFFECT
IN STACK
________
Pc
• Excess or
shortage of draft
is not acceptable
(SE)c
CONVECTION
SECTION
RADIANT SECTION
• Arch is the
highest pressure
point in the
heater
0.05"- 0.1"
W.G. DRAFT
DRAFT AT RADIANT
SECTION OUTLET,
R0
NEGATIVE PRESSURE
0.05"- 0.1" W.G. AT
TOP OF RADIANT
SECTION
Pb
(SE)r
Pa
BURNERS
NEGATIVE
POSITIVE
PRESSURE PRESSURE
0
Burner Operation
• Correct combustion in
firebox include:
▫ The firebox is clear
▫ No smoky appearance
▫ Burners flames are
steady and well-formed
• Check burners regularly
• Adjusting burner
registers to control air
intake
Air Leakages
• Air entering in to furnace
from a number of places:
▫
▫
▫
▫
Peepholes
Header box doors
Tube guide opening
Feed tubes entering and
exits
▫ Not pressure tight
structure
Heater Optimization
• Target set 2-3% O2 in
the flue gas.
• Operating conditions
fluctuates :
▫ Manual control
/adjustments
▫ Operators
 Number going down
 Experience going down
 Need training
Optimisation Case Study -1
• FIS performed a tuning job for a
refinery.
• Heater:
▫ Depentanizer reboiler heater
▫ Horizontal tube box
▫ Absorbed heat duty - 87 MMBtu/hr
▫ 15 up fired burners
▫ The stacks is connected to a large
common stack
▫ Two off take ducts provided with
manual dampers
Optimisation Approach
• Check draft
▫ Adjust using off-take
dampers
• Check excess O2
▫ Adjust burner register
• Check burners
▫ Light up all burners
▫ Check Flames/Firebox
Draft
0.7
Draft , in H2O
0.6
0.5
0.4
0.3
0.2
0.1
10:48
12:00
13:12
Time (7/22/09)
14:24
Excess Oxygen
Excess Oxygen, %
6.0
5.5
5.0
4.5
4.0
3.5
3.0
2.5
2.0
10:48
12:00
13:12
Time (7/22/09)
14:24
Stack Temperature, °F
Stack Temperature
645
635
625
615
605
Stack Temp. A
Stack Temp. B
595
10:48
12:00
13:12
Time (7/22/09)
14:24
Thermal Efficiency
Thermal Efficiency, %
83.0
82.0
81.0
80.0
79.0
78.0
10:48
12:00
13:12
Time (7/22/09)
14:24
Crude Heater Tuning
Case Study -2
• Natural Draft Crude
Heater
• Horizontal tube
• Up-fired burners
• 11 burners
3440
20
3420
18
3400
16
14
3380
12
3360
10
3340
3320
8
Flue Gas Flow,
MSCFD
6
3300
3280
4
Fuel Gas
Pressure, psig
2
3260
0
11:15 AM 11:30 AM 11:45 AM 12:00
PM
12:45 PM 1:00 PM 1:15 PM 1:30 PM
Fuel gas pressure, psig
Fuel gas flow, MSCFD
Fuel gas Flow and Pressure
Before & After Tuning
Tube Skin Temp
Before & After Tuning
760
740
720
T Skin, °F
700
680
660
640
620
600
580
11:15 AM 11:30 AM 11:45 AM 12:00 PM
12:45 PM 1:00 PM
1:15 PM
1:30 PM
Observations in Refineries
•
•
•
•
Furnace working off design conditions
Poor quality of dampers
Lower number of operators
Operator without sufficient training
Recommendations
• Software
▫ Heater Performance Index
(HPI)
• Hardware
▫ Draft control system
▫ Excess O2 control system
Heater Performance Index
• Analyzes the
performance of Fired
Heater 24/7
• Built into DCS
• Generates guidelines
• Built in intelligence
• Customized modeling
▫ Thermal Efficiency
▫ Fuel gas rate,
▫ Draft,
▫ Excess O2,
▫ Tube skin
temperatures,
▫ Feed flow rate,
▫ Pressure drop,
▫ Coking rate,
▫ Air preheater
performance
Crude Flow Rates
TAG No.
SERVICE
UNITS
SET
POINT
8/15/2009
8/16/2009
8/17/2009
Data 1
Data 2
Data 3
PROCESS
57FC0009.PV
Total Crude Flow
BPH
4337.6
5249.1
4807.3
4637.7
57FC0001.PV
Crude Flow to Pass 1
BPH
542.2
709.5
711.6
668.0
57FC0002.PV
Crude Flow to Pass 2
BPH
542.2
676.5
725.0
725.0
57FC0003.PV
Crude Flow to Pass 3
BPH
542.2
670.8
671.1
635.6
57FC0004.PV
Crude Flow to Pass 4
BPH
542.2
729.1
731.1
686.3
57FC0005.PV
Crude Flow to Pass 5
BPH
542.2
729.1
731.2
686.3
57FC0006.PV
Crude Flow to Pass 6
BPH
542.2
695.1
710.1
680.2
57FC0007.PV
Crude Flow to Pass 7
BPH
542.2
737.4
743.8
711.8
BPH
542.2
706.7
717.7
684.7
Average
Coil Inlet Pressure
TAG No.
SERVICE
UNITS
SET
POINT
8/15/2009
8/16/2009
8/17/2009
Data 1
Data 2
Data 3
PROCESS
57PI0054.PV
Crude Inlet Pressure (Pass 1)
psig
147.9
278.9
287.4
286.0
57PI0055.PV
Crude Inlet Pressure (Pass 2)
psig
147.9
296.0
309.6
309.8
57PI0056.PV
Crude Inlet Pressure (Pass 3)
psig
147.9
275.9
282.8
284.8
57PI0057.PV
Crude Inlet Pressure (Pass 4)
psig
147.9
286.0
294.8
293.0
57PI0058.PV
Crude Inlet Pressure (Pass 5)
psig
147.9
281.7
290.4
288.7
57PI0059.PV
Crude Inlet Pressure (Pass 6)
psig
147.9
283.8
292.4
290.2
57PI0060.PV
Crude Inlet Pressure (Pass 7)
psig
147.9
298.2
310.0
306.8
psig
147.9
285.7
295.3
294.1
Average
Fluids Cross-over Temperatures.
TAG No.
SERVICE
UNITS
SET
POINT
8/15/2009
8/16/2009
8/17/2009
Data 1
Data 2
Data 3
PROCESS
57TI0583
Crude Inlet Temperature
o
542
557.2
553.8
555.3
57TI0590
Cross-over Temp. (Pass-1)
o
610
585.1
581.9
583.6
57TI0591
Cross-over Temp. (Pass-2)
o
610
589.7
586.9
587.9
57TI0592
Cross-over Temp. (Pass-3)
o
610
592.0
589.4
590.3
57TI0593
Cross-over Temp. (Pass-4)
o
610
597.1
594.2
595.8
57TI0618
Cross-over Temp. (Pass-5)
o
610
594.5
591.9
593.2
57TI0619
Cross-over Temp. (Pass-6)
o
610
590.9
588.4
589.7
57TI0620
Cross-over Temp. (Pass-7)
o
610
594.4
591.1
593.0
610.0
590.9
588.0
589.4
AVERAGE Cross-over Temp.
F
F
F
F
F
F
F
F
o
F
Coil Outlet Temperatures
TAG No.
SERVICE
UNITS
SET
POINT
8/15/2009
8/16/2009
8/17/2009
Data 1
Data 2
Data 3
PROCESS
57TI0633
Coil Outlet Temp. (Pass 1)
o
730
686.8
687.0
687.4
57TI0634
Coil Outlet Temp. (Pass 2)
o
730
678.6
678.3
677.5
57TI0635
Coil Outlet Temp. (Pass 3)
o
730
680.2
680.6
679.0
57TI0636
Coil Outlet Temp. (Pass 4)
o
730
678.5
678.6
679.9
57TI0629
Coil Outlet Temp. (Pass 5)
o
730
683.4
683.5
683.7
57TI0630
Coil Outlet Temp. (Pass 6)
o
730
670.1
670.0
670.9
57TI0631
Coil Outlet Temp. (Pass 7)
o
730
683.0
682.2
683.3
730.0
679.9
679.9
680.1
AVERAGE Coil Outlet Temp.
F
F
F
F
F
F
F
o
F
Heater Performance Index. Remarks
Operating- Data 1
Operating- Data 2
Operating- Data 3
Operating- Data 4
Operating- Data 5
Operating- Data 6
Operating- Data 7
Design CLEAN
Design FOULED
Metallurgical Limit
RADIANT COIL TUBE METAL TEMP.
CRUDE HEATER 537-F-001
Temperature, Deg F
1200.00
1100.00
1000.00
900.00
800.00
700.00
PASS1
PASS2
PASS3
PASS4
PASS 5
PASS 6
PASS 7
PASS 8
Heater Performance Index. Remarks
THERMAL EFFICIENCY
CRUDE HEATER 537-F-001
90.60
Thermal Efficiency, (%)
90.40
90.32
90.25
90.20
90.00
89.73
89.80
89.57
89.56
89.60
89.69
89.35
89.40
89.26
89.20
89.00
88.80
88.60
Design
Data 1
Data 2
Data 3
Data 4
Data 5
Data 6
Data 7
Heater Performance Index
Oxygen & Draft Control System
(Natural Draft Heater)
Draft Control
System
Stack dampers
•
•
•
•
Reliable
Correctly sized
Pneumatically operated
Opposed blades
Reliable Dampers
Opposed blades
vs.
Parallel Blades
Excess O2 Control
• Control air supply to burners
• Pneumatically operated
dampers or registers
• Provide proper control scheme
• Damper opening is provided
based on
▫ Draft
▫ Excess O2
▫ Firing rate
▫ Other parameters
• Savings realized through out
the day
Summary
• Manual controls are not
adequate
• Energy prices are high
• Advanced Controls possible
• Use DCS based or PLC based
• Provide adequate safe guards
• Intelligent analysis of heater
parameters
• Substantial savings can be
realized
• Payout will be less than a year
in most cases
Thank you very much
• Questions and comments are welcome