a new method to measure flare combustion … · a new method to measure flare combustion efficiency...
TRANSCRIPT
Presented by
Yousheng Zeng, PhD, PE and Jon Morris
Providence
at
A&WMA Louisiana Section 2012 Fall Conference
October 30-31, 2012
A NEW METHOD TO MEASURE FLARE COMBUSTION
EFFICIENCY IN REAL-TIME
1
INTRODUCTION
2
2010 TULSA FLARE STUDY
Captured flare plume gases, analyzed composition, and determined Combustion Efficiency (CE) and Destruction and Removal Efficiency (DRE)
Yielded important findings regarding steam and air assist and their impact on CE and DRE
Demonstrated high variability in CE and DRE – potential benefits if CE could be monitored and fed back to operator in real time
Extremely large effort; not suitable for routine monitoring
FTIR-BASED HYPER-SPECTRAL IMAGER
Advantages – Imaging the flare plume (2-D compared to a path
measurement; 3-D data cube)
– High spectral resolution
Disadvantages – Low frame rate (~1 scan/sec) – flare plume may
have changed significantly during the same measurement cycle
– Specialist required for data reduction and analysis
– Not suitable for unmanned operations or long-term monitoring
4
PASSIVE FTIR
Advantages
– High spectral resolution
Disadvantages
– Path measurement – representativeness and
aiming issues
– Low scan rate with respect to the rate of
change in flare plume
– Specialist required for data reduction and
analysis
5
THE CONCEPT OF FLARE CE MONITOR
Patented and patent-pending technologies using a 4-band MWIR imager that can – Image the flare plume, and
– Measure flare CE at pixel level
– Determine overall flare CE
Major difference from FTIR based measurement – high frame rate: ~30Hz. As a result, temporal and spatial changes of flare plume within each CE measurement cycle become negligible
Design objective: real time CE output suitable for integration into plant data systems for – Flare operators, or/and
– Process control
6
SETUP OF THE NEW FLARE CE MONITOR
7
Sky
Flare
Flare CE
monitor
Not a path measurement
No scanning; high frame rate
No operator required
THEORETICAL BASIS FOR THE NEW FLARE
CE MONITOR
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𝐶𝐸(%) =𝐶 𝐶𝑂2
𝑛𝑖 𝐶 𝐻𝐶𝑖𝑖 + 𝐶 𝐶𝑂2+ 𝐶 𝐶𝑂 Eq. (1)
Typical Flare Combustion:
Fuel = hydrocarbon (HC); generically expressed as CnHy
CnHy + n𝑦
2O2 → nCO2 +
𝑦
2H2O
plus some CO if combustion is incomplete
Flare Combustion Efficiency (CE):
GENERAL IDEA
Use a 4-band, high frame rate (~30 fps) Infrared (IR) imager to measure CO2, CO, and HC and calculate CE – Band 1 (Ch1) for HC
– Band 2 (Ch2) for CO2
– Band 3 (Ch3) for CO
– Band 4 (Ch4) for reference
Each pixel in the image represents a region in the flare plume; CE measured at pixel level
Relative strength of signals are measured per Eq. (1); calibrations are achieved through the Ref. Channel (Ch4)
Overall CE is determined by averaging pixel level CE on pixels that form the flare plume “envelope” (pattern recognition algorithms are used to determine the envelope)
10
98 98 98 98 98
98 95
95
92 92
92
95 95 95
98
98
70
SELECTION OF FOUR SPECTRAL BANDS
11
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0
α
λ(µ)
CO2
CO
Propane
Methane
H2O
Ch1
Ch4
Ch2
Ch3
SIMPLIFIED RADIATIVE TRANSFER EQUATION (RTE)
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𝐼 = 𝜀 λ 𝐵 𝑇𝑏, λ 𝑒𝑥𝑝 −𝛼 λ 𝐶𝐿 + 𝐵 𝑇𝑔, λ − 𝐵 𝑇𝑔, λ 𝑒𝑥𝑝 −𝛼 λ 𝐶𝐿
When Tg >> Tb,
𝐼 ≈ 𝐵 𝑇𝑔, λ − 𝐵 𝑇𝑔, λ 𝑒𝑥𝑝 −𝛼 λ 𝐶𝐿
𝑒𝑥 = 1 +𝑥
1!+𝑥2
2!+𝑥3
3!+ ⋯ , −∞ < 𝑥 < ∞ Taylor Expansion:
When x << 1, 𝑒𝑥 = 1 + 𝑥
𝐼 ≈ 𝐵 𝑇𝑔, λ − 𝐵 𝑇𝑔, λ 1 − 𝛼 λ 𝐶𝐿 = 𝐵 𝑇𝑔, λ 𝛼 λ 𝐶𝐿
𝐶 =𝐼
𝐵 𝑇𝑔,λ 𝛼 λ 𝐿 Eq. (2)
𝐵 𝑇 , λ =2ℎ𝑐2
λ51
𝑒ℎ𝑐
λ𝑘𝐵𝑇 − 1
EQUATION FOR FLARE CE MEASUREMENT
13
𝐶𝐸(%) =
𝐼2𝐵 𝑇𝑔,λ2 𝛼 λ2
𝑛 𝐼1
𝐵 𝑇𝑔,λ1 𝛼 λ2+
𝐼2𝐵 𝑇𝑔,λ2 𝛼 λ2
+𝐼3
𝐵 𝑇𝑔,λ3 𝛼 λ3
Eq. (3)
Substitute C in Eq. (1) with Eq. (2);
Use subscripts 1, 2, 3 for HC (Channel 1), CO2 (Channel 2), and CO (Channel 3), respectively;
Cancel out L; and
Use weighted avg. n and α for HC.
Eq. (2) becomes:
VARIOUS MEASUREMENT APPROACHES CONSIDERED
B(Tg,λi): – Method 1 – Assume the 4 λ’s are
close enough and B(Tg,λ) for the three channels are equal (and cancelled out)
– Method 2 – Use the Ref. Band (Ch4) and Planks law to determine Tg and calculate B(Tg,λi) for other 3 channels – Not desirable and not used at this time
– Method 3 – Calculate ratios of B(Tg,λi)/B(Tg,λRef) in the expected temp. range (e.g., 800-1200 OF)
14
𝐶𝐸(%) =
𝐼2𝐵 𝑇𝑔,λ2 𝛼 λ2
𝑛 𝐼1
𝐵 𝑇𝑔,λ1 𝛼 λ2+
𝐼2𝐵 𝑇𝑔,λ2 𝛼 λ2
+𝐼3
𝐵 𝑇𝑔,λ3 𝛼 λ3
Eq. (3)
0.00E+00
5.00E+08
1.00E+09
1.50E+09
2.00E+09
2.50E+09
3.00E+09
3.00 3.50 4.00 4.50 5.00
B(T
g,λ
)
λ (µ)
VARIOUS MEASUREMENT APPROACHES CONSIDERED
α(λi):
– For CO2 and CO, values of α(λ) are calculated
based on their IR spectra
– For HC, use weighted avg. (need some
knowledge of flare gas composition)
– Correction for H2O – see next slide
15
𝐶𝐸(%) =
𝐼2𝐵 𝑇𝑔,λ2 𝛼 λ2
𝑛 𝐼1
𝐵 𝑇𝑔,λ1 𝛼 λ2+
𝐼2𝐵 𝑇𝑔,λ2 𝛼 λ2
+𝐼3
𝐵 𝑇𝑔,λ3 𝛼 λ3
Eq. (3)
EFFECT OF GAS PHASE H2O
Correction factor=α λ1
α λ4
Where α(λ)=absorption coefficient of H2O at wavelength of Ch1 and Ch4
16
0.00E+00
2.00E+06
4.00E+06
6.00E+06
8.00E+06
1.00E+07
1.20E+07
1.40E+07
1.60E+07
2.652.752.852.953.053.153.253.353.453.553.653.753.853.954.054.154.254.354.454.554.654.754.854.95
IR In
ten
sit
y
Mid-point λ(µ) in each 0.1 µ spectral band
CO2
CO
H2O
Aerosol?
Methane
Ethane
Propane
Butane
Pentane
Benzene
Propene
Total
𝐼1𝐼4=
𝐵 𝑇𝑔, λ1 𝛼 λ1 𝐶𝐻2𝑂𝐿
𝐵 𝑇𝑔, λ4 𝛼 λ4 𝐶𝐻2𝑂𝐿
𝐼1𝐼4=
𝐵 𝑇𝑔, λ1
𝐵 𝑇𝑔, λ4
𝛼 λ1𝛼 λ4
Independent
of H2O conc.!
SIMULATION RESULTS
17
SIMULATED FLARE PLUME
Flare gases: typical
refinery fuel gas (ref. John
Zink Combustion
Handbook)
Assumptions for Base
Case (Case 1):
– Plume temp=800 F
– Plume depth=1 m (3.28 ft.)
– Distance from flare to the
CE monitor=300 ft.
Compound Conc. CO2 12.000% CO 0.200% H2O 15.960%
Methane 0.720% Ethane 0.360%
Propane 0.400% Butane 0.040% Pentane 0.000%
Benzene 0.000% Propene 0.160%
Assumed Composition
in flare plume
SIMULATED RESULT – BASE CASE (CASE 1)
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77.52% 77.01% 81.59% 79.30%
0.00%
10.00%
20.00%
30.00%
40.00%
50.00%
60.00%
70.00%
80.00%
90.00%
True CE "Measured"CE-Method 1
"Measured"CE-Method 3
"Measured"CE-Avg. 1&3
CE
SIMULATED RESULTS – CASES 2-7
EFFECT OF FLARE GAS COMPOSITION AND H2O
Case 2: Unburned fuel=1/2 of Case 1
Case 3: Unburned fuel=1/10 of Case 1
Case 4: Double the conc. of ethane and add pentane and benzene
Case 5: Add 10% more H2O in the plume
Case 6: Add 30% more H2O in the plume
Case 7: Add 30% more CO2 in the plume
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0.0%
20.0%
40.0%
60.0%
80.0%
100.0%
120.0%
Case 2 Case 3 Case 4 Case 5 Case 6 Case 7
CE
True CE M1 M3 Avg. M1&M3
A SIMPLE EXPERIMENT
USING A BUTANE BURNER AND LAB MULTI-SPECTRAL IR IMAGER
21
A SIMPLE FIELD EXPERIMENT
USING 2 SPECTRAL BANDS
Dual cooled Mid-Wave IR cameras with different spectral filtering (i.e., 2 of the 4 bands required for CE monitor)
Emission plume with steam and propane thoroughly mixed
Steam emission rate: 1200 lb/hr
Propane emission rate: 3 lb/hr
Plume diameter at release: 3 inches
Distance from cameras: 175 feet
Demonstrated the ability to identify and isolate propane from steam at the pixel level using spectral radiance
22
EFFECT OF PLUME TEMPERATURE
23
50.0%
55.0%
60.0%
65.0%
70.0%
75.0%
80.0%
85.0%
90.0%
0 500 1000 1500 2000
CE
Flare Plume Temerature (F)
M1 M2 M3 True CE Avg. M1&M3
Note:
pixels are
expected
to cover
flare’s
high and
low T
regions
EFFECT OF ERROR IN
HC ABSORPTION COEFFICIENT ESTIMATION
24
50.0%
55.0%
60.0%
65.0%
70.0%
75.0%
80.0%
85.0%
90.0%
-60% -40% -20% 0% 20% 40% 60%
CE
Error in α(λ) Estimation
M1 M3 Avg. M1&M3 True CE
EFFECT OF BACKGROUND EMISSIVITY
AND FLARE PLUME DEPTH
25
50.0%
55.0%
60.0%
65.0%
70.0%
75.0%
80.0%
85.0%
0 0.1 0.2 0.3 0.4 0.5 0.6
CE
Background Emissivity
M1 M3 Avg. M1& M3 True CE
50.0%
55.0%
60.0%
65.0%
70.0%
75.0%
80.0%
85.0%
0 2 4 6 8 10 12C
E
Flare Plume Depth (ft.)
M1 True CE
CONCLUSION
26
CONCLUSION
Theoretical analysis and model simulation results demonstrate the feasibility of the real-time flare CE monitoring device – Influential factors: plume temperature, estimate of HC
absorption coefficients based on knowledge of flare gas composition
– Less significant factors: plume depth, background, flare gas composition, actual CE
– Calibration is accomplished inherently through the Reference Channel in the CE calculation which relies on relative measurements at the pixel level; no external calibration is required
Field experiment with propane and steam demonstrates the feasibility of cancelling out interferences by using two spectral bands
NEXT STEPS
Perform field experiment using a 42-band
laboratory spectral imager to further prove
the concept and narrow the design
parameters
Design and develop the first prototype
Extensive field testing
Launch commercial product