Gas Detection 15
Figure 3 shows the relationship between the calculated results from equation (5) and the actual calorifi c value of each gas.
Every gas data point is on or near the straight line which has a slope of 1.
Figure 4 is data from a fi eld test performed at a Japanese city gas company. The test was performed by intentionally varying the calorifi c value of gasifi ed LNG by changing the amount of N2-blended BOG or gasifi ed LPG being injected to the gasifi ed LNG. The plot shows that the measurement results of the Opt- Sonic Method obtained from equation (5) perfectly matches the results of the GC measurements. Furthermore, the calorimeter implementing the Opt-Sonic Method can measure short-term calorifi c value changes that the GC, which measures in intervals, cannot pick up.
Figure 2 shows the relationship between the speed of sound in medium and its calorifi c value. The function Qsonic, the straight line in Figure 2, describes the relationship between the speeds of sound in hydrogen and paraffi nic hydrocarbon gas mixtures and their calorifi c values.
If the fuel gas comprises only paraffi nic hydrocarbons and hydrogen, the calorifi c value can be obtained from the functions Qopt or Qsonic. However, errors are introduced to the functions if the fuel gas (i.e., natural gas) includes miscellaneous gases such as N2
, CO2 , O2
Note that the Opt-Sonic Method data has been shifted to make it easier to compare the results with the GC analyzer results. This was necessary because the T90 for the Opt-Sonic Method is fast at less than 5 seconds and was outputting results 30 minutes faster than the GC.
4. Calorimetry of Hydrogen-Blended Natural Gas
A test with simulated hydrogen-blended natural gas was performed with standard gas cylinders. Table 1 shows the
, and CO. These gases are indicated with solid
triangles ( ▲ ) in Figures 1 and 2, and do not align with the linear functions Qopt and Qsonic.
The calorifi c value Q for gas mixtures containing the miscellaneous gases may be expressed by the following equations:
Q = Qopt – (kN2 XN2 + kO2 Q = Qsonic – (k’N2 XN2 XO2 + k’O2 + kCO2 XO2 XCO2 + k’CO2 ) XCO2 ) and k’ i (1) (2)
Where Xi represents the volume fraction of gas component i, and k i
represent the error coeffi cients of gas component i.
The latter error coeffi cients are shown as vertical dashed lines in Figures 1 and 2.
Although k i and k’ i have different values, the ratio between the
two remains approximately constant as expressed in equation (3) regardless composition:
k N2 = α k’ N2 , k O2 ≈ α k’ O2 , k CO2 ≈ α k’ CO2 (3)
Using equation (3), equation (2) can be transformed into equation (4): Q = Qsonic
– α (k N2 X N2 + k O2 X O2 + k CO2 X CO2 ) (4)
Since the second term of equation (4) is α times the second term of equation (1), we get simultaneous equations (1) and (4) that can be solved to obtain equation (5), which can solve the calorifi c value from the speeds of sound and light:
Q ≈ Qopt – (Qopt – Qsonic ) / (1- α) (5) Components #1
Methane Ethane
Propane
iso-Butane n-Butane
iso-Pentane n-Pentane n-Hexane Nitrogen
Carbon dioxide
Carbon monoxide Oxgen
Hydrogen Helium
Theoretical Calorifi c Value Experimental results
Accuracy (%) (Net,MJ/m3)
90.87 5.019 0.944 0.151 0.202
0.0501 0.0501 0.0497 1.002 0.498
0.0508. 0.0102 0.998 0.05
37.51 37.49
-0.07%
Reference conditions : 0 °C, 0 °C 101.325kPa Net calorifi c value are calculated according to ISO 6976:2016
Author Contact Details Tomoo Ishiguro, Senior Chief Researcher, RIKEN KEIKI CO., LTD. • 2-7-6 Azusawa Itabashi-Ku, Tokyo 174-8744 Japan • Tel: +81-3-3966-1113 • Email:
intdept@rikenkeiki.co.jp • Web:
www.rikenkeiki.co.jp
#2
79.15 10.01 1.268 1.274
0.0095 0.1895 0.402 0.15
2.619 1.009 ---
0.0853 3.763 ---
39.06 39.05
-0.02%
% mol / mol #3
49.76 29.94 0.1
2.464 --- --- --- ---
7.535 3.028 2.01
0.0607 5
0.103 40.87 40.69
-0.45%
evaluation results performed at a European gas company. Five standard cylinders with simulated hydrogen-blended natural gas were measured. The theoretical calorifi c values (calculated based on the composition) were compared with the measurement results from the Opt-Sonic method.
As shown in the table, the measurement accuracy is within ±0.5%, which is compliant to R140, CVDD Class A of the OIML (International Organization of Legal Metrology).
Internal testing at Riken Keiki has shown that accuracy within ±0.5% can be achieved for hydrogen concentrations of up to 10 vol%.
5. Summary
Adoption of environmentally sustainable energy sources including solar power and wind generation will continue to increase.
As a result, P2G technology will become increasingly indispensable as a solution for moderating the weather-induced fl uctuations in energy production.
The calorimetry technology demonstrated by the Opt-Sonic Method is capable of measuring hydrogen-blended natural gas with high accuracy, continuously, and with fast response times, and is ideally positioned to provide a solution that will facilitate effi cient use of new resources synthesized from renewable energy.
#4
70.85 14.9
4.856 ---
2.491 0.1
0.01059 0.01008 3.818 1.505 ---
0.1253 1.324 ---
42.75 42.92
0.38%
#5
85.53 7.686 1.906
0.3083 0.491
0.0504 0.0516 0.0502 2.737 1.191 --- --- --- ---
38.58 38.60
0.07%
www.envirotech-online.com IET September / October 2019
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