1. Evaluating a tunable filter spectrometer online gas analyzer
Juan Escobar, measurement specialist, Saudi Arabian Oil Company (Aramco)
May 2015
© Copyright 2015, Saudi Aramco. All rights reserved.

2. Contents Introduction Relevance of composition in Measurement
Alternative Technologies
Tunable Filter Spectroscopy
Analyzer Testing Results

3. Saudi Aramco Gas Pipelines Network

4. Over 120 customers Kingdom-wide
FEEDSTOCK AND FUEL
Refineries
Power Plants
Petrochemicals
Mining
Large and Small scale industry

5. Volumetric Flow Rate gas equation
AGA 3
Orifice calculation factor
Reynolds number
Fluid velocity
Density is heavily depending on composition (AGA 8)

6. Compressibility is heavily depending on composition (AGA 8)
Slope factor
Real gas relative density factor
Real gas relative density
Molecular weight
Supercompressibility factor
Compressibility is heavily depending on composition (AGA 8)

7. GC is the incumbent methodology
PROS
Very well-known technology. Gas Chromatography has been the reference technique since late 1970s
Heating value (BTU) & Wobbe Index for energy content
Hydrocarbons C1 through C9+, COx, NOx, H2S, Diatomics
CONS
Long response time. Requires the physical separation of molecules in the samples which takes long.
Carrier gas requirement (He, Ar, H2, N2) and safety considerations
Relative method with calibration gases
Complicated and costly operations and maintenance
Bulky and requires a lot of space

8. GC Alternatives over the years
Mass Spectroscopy
GC-MS
FTIR (optical vibrational, absorption)
Raman (optical vibrational, emission)
NIR/FT-NIR (optical vibrational, emission)
TDL (tunable diode laser)
QCL (quantum cascade laser)
Now enters TFS (tunable filter spectroscopy)

9. Tunable Filter Spectroscopy
PROS
Near real-time gas composition response time with fast updated results.
Easy installation with less space requirements.
Field mounted, robust and rugged; suitable for harsh industrial environments and hazardous area installation.
Minimal maintenance with no consumables.
No requirement of carrier gases or calibration gases.
CONS
New technology.
No direct measurement of the diatomic homonuclear components such as H2 (hydrogen), O2 (oxygen) and N2 (nitrogen).

10. Operational Principle
Chemometrics
Example Configuration
Ch. #
Compound
Range
Accuracy 1
Methane %
+/- 0.2% 2
Ethane
0 – 25% 3
Propane 4
iso-Butane
0 – 10%
+/- 0.1% 5
n-Butane 6
Propylene 7
Ethylene
Speciated and Quantified Compounds

12. Lab trial - Natural Gas Mixtures
TFS
Ref
Error
CH4
81.23
81.301
0.071
C2H6
2.80
2.833
0.033
C3H8
0.34
0.391
0.051
iC4H10
0.00
0.064
nC4H10
0.14
0.073
-0.067 C5
0.02
0.043
0.023 N2
14.50
14.19
-0.31
CO2
1.02 1
-0.02 C6
N/A
CV (Superior, Gross)
34.901
35.09
0.1881
Wobbe Index
43.486
43.7
0.2131
TFS
Ref
Error
CH4
81.78
81.864
0.084
C2H6
3.07
3.08
0.01
C3H8
0.44
0.482
0.042
iC4H10
0.03
0.077
0.047
nC4H10
0.16
0.095
-0.065 C5
0.00
0.055 N2
12.30
12.015
-0.285
CO2
2.23
2.209
-0.021 C6
N/A
CV (Superior, Gross)
35.393
35.68
0.2869
Wobbe Index
43.922
44.23
0.3077
TFS
Ref
Error
CH4
87.68
87.505
-0.175
C2H6
7.54
7.539
-0.001
C3H8
1.65
1.721
0.071
iC4H10
0.25
0.17
-0.08
nC4H10
0.19
-0.06 C5
0.02
0.049
0.029 N2
0.80
0.939
0.139
CO2
1.86
1.848
-0.012 C6
N/A
0.03
CV (Superior, Gross)
42.506
42.45
Wobbe Index
53.262
53.17

13. Lab trial - Synthetic Mixtures
TFS
Ref
Error
CH4
86.29
86.183
-0.107
C2H6
8.47
8.542
0.072
C3H8
1.84
1.963
0.123
iC4H10
0.31
0.227
-0.083
nC4H10
0.48
0.422
-0.058 C5
0.02
-0.02 N2
1.10
1.12
CO2
1.55
1.543
-0.007 C6
CV (Superior, Gross)
43.163
43.107
Wobbe Index
53.712
53.676
TFS
Ref
Error
CH4
83.37
83.284
-0.086
C2H6
3.07
3.056
-0.014
C3H8
0.40
0.46
0.06
iC4H10
0.10
0.073
-0.027
nC4H10
0.11
0.093
-0.017 C5
0.00 N2
11.23
11.344
0.114
CO2
1.72
1.69
-0.03 C6
CV (Superior, Gross)
35.975
Wobbe Index
44.972
44.971
TFS
Ref
Error
CH4
82.10
82.091
-0.009
C2H6
3.88
3.893
0.013
C3H8
0.88
0.949
0.069
iC4H10
0.18
0.146
-0.034
nC4H10
0.17
0.148
-0.022 C5
0.00 N2
9.80
9.793
-0.007
CO2
3.01
2.979
-0.031 C6
CV (Superior, Gross)
36.731
36.742
0.0106
Wobbe Index
45.310
45.336
0.0257

14. Field trial – Natural Gas Mixtures
TFS
Ref
Error
CH4
88.878
88.492
0.386
C2H6
8.348
8.2506
0.097
C3H8
0.410
0.5854
-0.175 N2
2.268
1.7188
0.549
TFS
Ref
Error
CH4
89.338
88.587
0.751
C2H6
8.037
8.1416
-0.105
C3H8
0.273
0.4544
-0.181 N2
2.258
1.7114
0.547
TFS
Ref
Error
CH4
89.963
89.037
0.926
C2H6
7.402
7.6049
-0.203
C3H8
0.167
0.3566
-0.190 N2
2.382
1.7509
0.631
Errors obtained when the equipment is tested in a field environment are bigger than the ones obtained at a lab environment.
It is planned to perform another trial with an extended composition, C1-C6+ which is normally used for custody applications, and throughout the year to assess the impact of different seasons on instrument performance.

15. Thank You