API 73rd Fall Refining and Equipment
Standards Meeting
Los Angeles November 10, 2008
Combustion Analysis Options for Process
Heaters
David Fahle – VP of Marketing
Hydrocarbon Processing
precision and expertise
ENABLE YOU TO GO FURTHER
Experts in Gas Analysis
Markets
Products
Technology
Support
• Industrial Gas
• Process Oxygen
• Paramagnetic
• Product Support
• Hydrocarbon Processing
• Photometric
• Zirconia
• Committed to your Success
• OEM Transducers
• Combustion
• Photometric
• Quality Focus
• Laser
• Thick Film
• OEM transducers
• Tuneable Diode Laser
• Analytical Systems
Gas Analysis is what we do - And we do it best
Servomex Proud 50 Year History
• Servomex Controls Limited formed
• First paramagnetic cells made based on licence from
Distillers
• Bought by Sybron Corporation and integrated into Taylor
Instruments Group
• MBO from Sybron Corporation
• Stock market flotation (London Stock Exchange)
• Acquired by The Fairey Group
• The Fairey Group renamed as Spectris plc
1952
1961
1971
1987
1989
1999
2001
Global
GlobalPresence
Presence
Combustion
Applications
Index of Applications

Thermal power generation

Incineration

Hydrocarbon Processing

Industrial Gases

Specialty Chemicals and Pharmaceuticals

Cement

Iron and steel
 Hydrocarbon
Processing
 Hydrocarbon Processing
Application Types
Process Heaters
Direct-fired heat exchanger that uses
the hot gases of combustion to raise the temperature of a
feed flowing through coils of tubes aligned throughout the
heater. Typical temperatures 400°C-550°C (800-1000°F)
Thermal Crackers
Heat exchanger where reactions take place while the feed
travels through the tubes, i.e. Ethylene cracking furnace.
Typical temperatures 980°C-1200°C (1800-2200°F)
On-site Incinerators
Designed to combust both solid and liquid chemical waste.
The type depends upon the type of waste being disposed
and include fluidized bed, multiple hearth and rotating kiln incinerators.
Typical temperatures 1100°C (2000°F) or greater.
 Hydrocarbon Processing
Application Types
Process Heaters and Thermal Crackers pipes run inside heating chamber to transfer heat
• Why measure gases during combustion?
• Detecting oxygen rich conditions: O2 measurement
• Detecting fuel rich conditions: CO measurement
• Combustion Analyzer Types
Combustion:
Why measure gases?
Complete Combustion
CxHy + (x+(y/4))O2  xCO2 + (y/2)H2O + HEAT
FUEL + OXYGEN  CARBON DIOXIDE + WATER + HEAT
Combustion Efficiency
FUEL RICH
incomplete combustion
%
CO
Ideal
Too little oxygen =
some fuel not burnt:
2000ppm excess
CO above ideal
means 1% extra
fuel cost
-20
O2
-10
0
% Excess Air
10
20
Combustion Efficiency
FUEL RICH
incomplete combustion
AIR RICH
complete combustion
%
CO
Too much air
Ideal
= cooling effect:
1.5% excess oxygen above
ideal means 1% extra fuel cost
Too little oxygen =
some fuel not burnt:
2000ppm excess
CO above ideal
means 1% extra
fuel cost
-20
O2
-10
0
% Excess Air
10
20
Combustion Efficiency
FUEL RICH
20
CO
AIR RICH
16
NOx
12
EFFICIENCY
8
4
IDEAL
O2
-20
-10
0
% Excess Air
1
0
20
Review - Breakthrough Concept
Typical COe 'Breakthrough' Event - 10 hour data period
1500
10.0
1400
9.0
1300
1200
8.0
1100
7.0
900
6.0
800
5.0
700
600
4.0
500
3.0
400
300
2.0
200
1.0
100
0
0.0
0
1
2
3
4
5
Time (hours)
COe Reading (ppm)
Example 1: Coal data, 10h sample
6
See Detail
Zoom
7
8
O2 Reading (%)
9
10
O2 Reading (%)
COe reading (ppm)
1000
Review - Breakthrough Concept
Typical COe 'Breakthrough' Event - 1 hour data period
1500
10.0
3. Oxygen level
returns to 'excess
air'. COe reading
drops quickly to base
level
1400
1300
9.0
1200
8.0
1. Process stable.
Oxygen level controlled
at approx 5%. COe at
low background levels.
COe Reading (ppm)
1000
7.0
900
6.0
800
5.0
700
600
4.0
500
2. COe 'breakthrough'
event. Oxygen level
400
drops 2%
3.0
 COe
level
increases
300
O2 Reading (%)
1100
2.0
200
1.0
100
0
0.0
6.0
6.1
6.2
6.3
6.4
6.5
6.6
6.7
6.8
6.9
7.0
Time (hours)
COe Reading (ppm)
Example 1: Coal data, 1h
O2 Reading (%)
Review - Breakthrough Concept
1500
10.0
1400
9.0
1300
1200
8.0
1100
7.0
900
6.0
800
5.0
700
600
4.0
500
3.0
400
300
2.0
200
1.0
100
0
384
385
386
387
388
389
390
391
392
Time (mins)
COe Reading (ppm)
Example 1: Coal data, 5mins
O2 Reading (%)
393
0.0
394
O2 Reading (%)
COe Reading (ppm)
1000
Review - Breakthrough Concept
25
500
400
20
300
200
10
100
5
0
0
0
50
100
150
200
250
300
350
TIME (hours)
Oxygen (%) AI05005.PV
Example 2: Gas data, 3 week sample
COeq (ppm) AI05041.PV
400
450
-100
500
COe (ppm)
Oxygen (%)
15
Review - Breakthrough Concept
25
500
400
20
300
200
10
100
5
0
0
420
421
422
423
424
425
426
427
428
TIME (Hours)
Oxygen (%) AI05005.PV
Example 2: Gas data, 10h sample
COeq (ppm) AI05041.PV
429
-100
430
COe (ppm)
OXYGEN (%)
15
Combustion Efficiency
FUEL RICH
20
CO
AIR RICH
16
NOx
12
EFFICIENCY
8
4
IDEAL
O2
-20
-10
0
% Excess Air
1
0
20
Combustion Control: O2 Measurement
Detecting air rich conditions
How can oxygen be measured?
Paramagnetic
• High accuracy
• Need extractive sample system with moisture removed
“Zirconia” (zirconium oxide, ZrO2) based analysers
• Suitable accuracy, measure hot and wet
• Fast analysis, low maintenance and low cost
Tuneable Diode Laser
• In-situ analysis
• Hot, corrosive, particulate latent samples
Combustion Control: O2 Measurement
Detecting air rich conditions
Paramagnetic
Technology
Oxygen is unique.
O2
O2O O2
2
O 2 O2
O2O2
O2
O2 O2 O
2
NO
NO O2
O2
O2 O2
O2
O2
NO2
NO2
NO2
O2 SO2
HClSO CO O2 CO SO O2 SO2
CO2 SO2 CO
2
2
2 CO HCl
2
2
CO
CO
CO
CO
2
2
HCl CON2 N
HCl
CO
2
N2 CO N2
It is strongly attracted
into a magnetic field.
It is described as being
“ paramagnetic ”
Paramagnetic Cell
Magnet pole pieces
Nitrogen filled spheres
Feed back coil
Suspension & mirror
LED source
Photocell sensor
Combustion Control: O2 Measurement
Detecting air rich conditions
Paramagnetic Technology Provides:
Performance
•
Fast response
•
Exceptional linearity and repeatability
•
High stability & accuracy
Economics
•
Long operational life
•
Extractive sample system required
•
Simple validation / calibration
Combustion Control: O2 Measurement
Detecting air rich conditions
Zirconia Oxide
Technology
Combustion Control: O2 Measurement
Detecting air rich conditions
Zirconium oxide (zirconia) based techniques
Heated Chamber
Zirconia disk
At high temperatures, zirconia
conducts electricity through the
movement of oxygen ions.
Electrodes
Combustion Control: O2 Measurement
Detecting air rich conditions
Zirconium oxide (zirconia) based techniques
Sample
Reference
When the oxygen concentration
on each side is different,
an emf related to oxygen
concentration is generated.
Nernst Equation
7000C
Cell output, E = K x Ln ( Pr/ Ps) mV
assuming a constant cell temperature
0
100
Combustion Control: O2 Measurement
Detecting air rich conditions
Zirconia Oxide Technology Provides:
Performance
•
Fast response
•
Unaffected by background gases
•
Sample at hot / wet conditions
Economics
•
Very acceptable operational life
•
Low maintenance requirements
•
Simple validation / calibration
Combustion Control: O2 Measurement
Detecting air rich conditions
TDL
Technology
Optical Absorption Spectroscopy
• Based on Beer-Lambert law
• Used both in UV and IR
• Typical wideband techniques have low spectral resolution and
sensitivity is limited by cross-interference
• The alternative is single line spectroscopy using tuneable
diode lasers (TDL)
• TDL are available for a range of gases of interest
Optical Absorption Spectroscopy
• Beer Lambert law: T = exp(-Sg(f)NL)
– T is transmission
– S is the absorption strength
– g(f) is the line shape function
– N is the concentration of absorbing molecules
– L is the optical path length
• Measuring T and knowing S, g(f) and L, N can be found
• Use single absorption lines in the NIR
Single Line Spectroscopy
Gas under test, typical absorption linewidth 0.05 nm
Absorption lines from other (background) gases
Laser scan range, typically 0.2 - 0.3 nm, note
Laser spectral line width is ca. 0.0001 nm
UV / IR absorption spectroscopy linewidth > 2 nm
Single Line Spectroscopy
• Choose a single absorption line from available databases
• Ensure no cross interference from other gases
1.0000
Transmission
0.9998
0.9996
0.9994
0.9992
0.9990
0.9988
0.9986
5700
H2O
CH4
HCl
5720
5740
5760
Wavenumber (cm^-1)
5780
5800
Typical Gas Mix for
Waste Incinerator
– 10 mg/m3 HCl
– 15% H2O
– 6% O2
– 500 mg/m3 SO2
– 350 mg/m3 NOx
– 100 mg/m3 CH4
– 150 mg/m3 CO
– 10% CO2
Single Line Spectroscopy
1.0000
0.9998
Transmission
0.9996
0.9994
0.9992
A single
HCl line
H2O
CH4
0.9990
Laser scan
range
HCl
0.9988
0.9986
5737
5738
5739
5740
5741
5742
Wavenumber (cm^-1)
Absorption spectrum for offgas from waste incinerator
Measurement influences
•
Measurement influenced by:
–
–
–
Pressure
Temperature
Background gas composition
•
Just like conventional IR measurements!
•
Due to inter-molecular collisions, which
strongly affect the absorption line:
–
–
–
•
its amplitude
Its width
Its shape (asymmetry)
Note: 2f WMS signal is just filtered version
of line shape, so all information above is
still available (non-linear relations however)
4
amplitude
3
width
2
asymmetry
1
0
-2
-1
0
1
2
• Pressure influence
–
–
–
–
–
Frequency of collisions increases with gas density i.e. total pressure
Causes line broadening, hence the term “pressure broadening”
Line amplitude (per molecule) is unchanged
Small line centre shift occurs also
Maximum measurement pressure limited by pressure broadening smearing the
line so as to overlap an adjacent line
Pressure broadening measured for 2f WMS spectroscopy of O2 in N2
background
1.25 bar
1.0 bar
1.5 bar
2.0 bar
2.5 bar
3.0 bar
4.0 bar
5.0 bar
6
4
0.014
line width (nm)
lock-in amplifier output (V)
8
2
0.012
0.010
0.008
0.006
0
1.0
-2
-0.015
-0.010
-0.005
0.000
0.005
wavelength scan (nm)
0.010
0.015
1.5
2.0
2.5
abs. pressure (bar)
3.0
• Temperature influence
– Changes gas density and molecular velocity distribution, hence collision
frequency and line width
– Temperature also changes thermal excitation of molecular vibrations, hence the
line amplitude (per molecule)
– Can be exploited to distinguish hot gas from cold gas e.g. 2900 (NEO) oxygen
analyser
Oxygen lines at high temperature
-24
8x10
line intensity/(cm/mol)
From HITRAN database
6
800K
300K
1300K
4
2
0
760
765
770
wavelength/nm
775
Combustion Control: O2 Measurement
Detecting air rich conditions
TDL (Tuneable Diode Laser) Provides:
Performance
•
Fast response
•
In-situ measurement at process conditions
•
Temperature and moisture measurement possible
Economics
•
Long operational life
•
Low maintenance requirements
•
Inferred validation
Combustion Control: CO Measurement
Detecting breakthrough and flooding
How can CO be measured?
Thick film
• High accuracy at process conditions
• Cost effective measurement in combination with O2
Tuneable Diode Laser
• In-situ analysis
• Hot, corrosive, particulate latent samples
Combustion Control:
CO via Thick Film Sensor
Very thin platinum tracks are
printed onto a ceramic disk.
Combustion Control:
CO via Thick Film Sensor
Very thin platinum tracks are
printed onto a ceramic disk.
These form resistors in a
“Wheatstone bridge”, an
arrangement that allows small
changes in resistance to be
accurately detected.
Combustion Control:
CO via Thick Film Sensor
Very thin platinum tracks are
printed onto a ceramic disk.
These form resistors in a
“Wheatstone bridge”, an
arrangement that allows small
changes in resistance to be
accurately detected.
Each quadrant is thermally
isolated from next by slots.
Combustion Control:
CO via Thick Film Sensor
A special catalyst that is
selective to CO is then
printed over two quadrants
Combustion Control:
CO via Thick Film Sensor
CO
CO
CO
Any CO in the sample will
burn on the surface of the
catalytic material, creating a
change in temperature.
CO
CO
CO
CO
CO
CO
CO
CO
CO
CO
Combustion Control:
CO via Thick Film Sensor
CO
CO
CO
CO
CO
CO
CO
CO
CO
CO
CO
The change in temperature
is detected by the platinum tracks
CO
CO
underneath, changing their resistance,
which can be detected.
ServoTOUGH Fluegas
Servomex Combustion Analyzer
History
2700
700 B / N
700 Ex
Model 700 Combustion Analyzer
•
•
•
•
•
Model 700 was introduced circa 1987
Two Models 700B & 700EX
Key Features:
– Separate sensor head and remote control unit
– Oxygen only or with combustibles option
– Rugged design (IP55)/wide range of applications
– Comprehensive range of probes and filters
– Fast dynamic response
– Low flow (300 ml) extractive design
700B was discontinued in 1998
700EX was discontinued in 2003
700 B / N
700 Ex
Model 2700 Combustion
Analyzer
•
•
•
•
The 2700 was Introduced 1998
Three Models 2700, 2700B & 2700C
The 2700C was introduced in 2006
Key Features:
–
Same basic principal of operation
–
Standard flame traps
–
Simple Intuitive User Interface
–
Auto Calibration and assignable alarm relays
–
Integral auxiliary air supply
–
Introduced the TFx combustible sensor for COe
–
Easy access to servable parts
Sensor Head and Remote
Controller
Principal of Operation 2700B
Solenoid
Valve
Aspirator Air
O2 Cell
Auxiliary Air
COe
Sensor
Breather
Heated
Enclosure
Flame
Trap
Aspirator
Low Flow Extractive
Flame
Trap
Internal
Filter
Aspirator
& Sample
Outlet
AutoCal &
BlowBack
Sample
Inlet
Principal of Operation 2700C
Solenoid Valve
Aspirator Air
Heated
Enclosure
Aspirator
Aspirator
& Sample
Outlet
COe Cell
Aux
Air
Rest.
Internal
Filter
Probe
Sample
Inlet
200ml/min
Flame
Trap
100 ml/min
Flame
Trap
AutoCal &
BlowBack
O2 Cell
Breather
Servomex Zirconia Cell
Servomex 2700 ZrO2 Zirconia Sensor
Diaphragm Springs
Heater
Reference Air In
Sample in
Platinum
Electrodes
Zirconia Crucible
mV
Servomex Thick Film Sensor
 Sample enters and is
heated by sensor body
Heater

Heater

 Hot sample reaches
sensor and CO
combusts - calibrated as

CO equivalents (COe)
Thick Film Sensor Structure
Heater band
Outlet
PRT
Sensor housing
Inlet
Sensor disc
Header
assembly
Thick Film Sensor Location
Heater
Combustibles
Sensor
Flame
Trap
Aspirator
Internal
filter
Oxygen
Cell
Thick Film Sensor Location
Insulated
cover keeps wetted
components above
210°C
Keep it hot =
Increase performance.
Stop condensation.
Stop blockage.
Stop corrosion.
Increase life.
Thick Film
Sensor
Zirconia
Sensor
2700 Flame Traps and Filter
Internal
Sample
Filter
(5 micron)
Flame
Arrestor
(tested by
external agency)
Flame traps prevent risk of sensors igniting unburnt fuel at
start up and causing an explosion
2700 Probes
Modular Design
• Open, standard filter or large filter
• Variable lengths, with or without probe retention
• Wide range of temperatures: <700°C to 1750°C (<1300°F to
3182°F)
• Special materials eg ceramics or alloys
• 4” ANSI Standard, 3” ANSI, JIS, DIN, 700B or Thermox flanges
Filter Element
Sample
Tube
½” NPT Probe Fitting
Internal
Filter &
Flame Trap
Assembly
2700 Probes
3182
2732
1500
Haynes Alloy 556 Probe used for
temperatures < 1832F Max temp will
1832
be dependent upon probe length
1000
1292
S.S 316
Haynes Alloy 556
Ceramic
High Temperature Ceramic Probe
for temperatures < 3182F
1750
Stainless Steel 316 Probe
can be used up to 1292F 932
at any probe length
°
F
32
700
500
°
C
0
Questions on Analyzer Operation
•
How does the analyzer respond in a low oxygen and /or high combustible
conditions?
–
•
What are the analyzer/sensor response times?
–
•
When installed with a typical probe for heater applications and unfiltered software the T90
response time for oxygen is 10 seconds and 20 seconds for combustibles at 300 ml/min
sample rate.
Is output signal damping available?
–
•
The analyzer will continue to measure what it sees. The combustible measurement is
maintained by the auxiliary air. The oxygen reading is maintained but will be reduced from
the true reading by an amount which is dependent on the combustible gas species and
concentration. The sensors will not be adversely affected.
The software allows dampening of both the oxygen and combustible outputs and displays. It
can be applied by differing amounts and can be switch out if required.
How does the analyzer measure combustibles?
–
The combustibles analysis is wet and is optimized and calibrated for carbon monoxide to
enhance its use for combustion control. The combustibles sensor will respond to most
flammable gases apart from methane. Its response to hydrogen is twice that of carbon
monoxide.
Questions on Analyzer Operation
•
What is the recommended testing frequency?
–
•
The initial calibration intervals are 3 months for oxygen and 1 month for combustibles but
after operational experience this may typically be extended to 12 months and 2 months
What are the known failure modes for the analyzer?
–
Internal failures
•
•
•
•
•
–
External failures
•
•
•
–
Temperature control oxygen
Temperature control combustibles
Sensor heads
Wiring faults
Block heater
Aspirator air supply
Restricted probe
Sensor head temperature
External issues
•
•
•
Mounting flange temperature
Radiated heat from process
Ambient temperature hot and cold
Questions on Analyzer Operation
•
What are the common known failure modes for the analyzer?
–
–
–
–
–
Loss of sample flow due to probe blockage
Loss of air pressure for aspiration, purging, etc.
Controller power
Sensor head power
Sensor head block heater
Best Practice for Installation
•
•
•
•
•
•
•
•
•
•
•
•
Serviceable location
Ensure ambient temperature is within specifications
Protect from wind chill
Protect from radiant heat
Minimize flange distance from wall to insulation
Use correct cable
Minimize distance between sensor head and controller
Insure proper wiring termination
Use probe retention flange when temperature is above 700C
Locate utilities in a stable ambient environment
Consider blowback for high sulfur high particulate samples
Leave sensor head off process until ready to power up
ServoTOUGH Laser
ServoTOUGH Laser Gas II
Dual Modulation Technique
• Laser wavelength chosen to match absorption line, fine
tuning with temperature and current
• Tune diode laser by temperature to pin-point the centre
wavelength of a single absorption line (+/-5mK)
• Laser wavelength scanned by applying ramp current
• High frequency modulation added for 2nd harmonic detection
• 2nd harmonic signal extracted by use of mixer
• CPU computes gas concentration
Dual Modulation Technique
Diode
current
Diode
laser
power
Ramp
current
High freq.
modulation
()
Temp. contr.
Diode laser
(2)
Process
Detector
Mixer
Second harm.
Signal
processing
gas
Filter
Direct signal
Det. current
Differences from conventional IR spectroscopy
•
•
•
Laser radiation is monochromatic i.e. a specific wavelength, whereas conventional IR source
is “multi-chromatic”
Allows TLDS to measure a single absorption line by scanning across it
Signal is the line shape or a filtered version of it (2f WMS)
Free of cross interfering absorptions if suitable line is chosen i.e. no other lines nearby.
3
2
lock-in signal (V)
•
1
0
-1
-0.010
0.000
0.010
wavelength scan (nm)
Second harmonic WMS,
2nd derivative of line shape
Direct absorption scan
Transmitter
Diode
Laser
Collimating
lens
Receiver
Flanges
Purge gas
inlet
Purg e gas
inlet
Focusing lens Detector
Instrument
window
Process
gas
Loop cable
Set-up for a in-situ cross stack TDLAS system
HARNESS THE POWER OF
expertise
SERVOTOUGH Combustion Solutions