International Journal of Oil, Gas and Coal Engineering
Volume 3, Issue 2, March 2015, Pages: 24-32

Fluid Flow Analysis of a Transmission Line of Jalalabad Gas Transmission and Distribution System Limited

Jahan Labiba Nusrat1, *, Dey Debotosh1, Hashan Mahamudul2

1Department of Petroleum and Mining Engineering, Shahjalal University of Science and Technology, Sylhet, Bangladesh

2Ecole Nationale Superieure de Geologie, University of Lorraine, Nancy, France

Email address:

(J. L. Nusrat)

To cite this article:

Jahan Labiba Nusrat, Dey Debotosh, Hashan Mahamudul. Fluid Flow Analysis of a Transmission Line of Jalalabad Gas Transmission and Distribution System Limited. International Journal of Oil, Gas and Coal Engineering. Vol. 3, No. 2, 2015, pp. 24-32. doi: 10.11648/j.ogce.20150302.12


Abstract: In present world the prime concern of a country is energy. Bangladesh, a developing country, is also facing the challenge to meet its energy demand. For the energy, Bangladesh mainly depends on its natural gas. Bangladesh has a gas reach province in the eastern part. Gas produced in Bangladesh is mainly dry gas, but some fields are also producing condensates. Natural gas is transported by pipeline, which is the most cost efficient way. With the edge of economy, gas transmission through pipeline brings some difficulties. Before transmitting the natural gas, condensates are separated in the gas field. In spite of the separation, some condensates are formed in the pipeline while transmitting gas. This leads to pipeline blocking, corrosion, reduction of heating value. In this study the fluid flow through Khadim-Debpur-Kumargaon (KDK) pipeline is analyzed, which is a part of the pipeline network operated by Jalalabad Gas Transmission and Distribution System Limited. To analyze the fluid flow through pipeline, pressure was calculated by single phase flow equations like Weymouth, Panhandle A and panhandle B. The pressure was also calculated using software Feket (Piper) and a statistical analysis of error calculation was done. The research focuses on the following points: i) the fluid flow pressure was under designed ii) a record of liquid formation in the pipeline should be kept iii) a chromatographic test on Kumargaon station should be done for improvement of the study iv) liquid formation gives hints of two phase flow in the pipeline, which demands more investigation.

Keywords: Natural Gas, Transportation, Pipeline, Pressure Loss, Fluid Phase


1. Introduction

Bangladesh has been known as a prospective gas province since the discoveries of major gas fields in the east during 1960s. All the gas fields are located in the eastern part of the country [1].

Transporting natural gas through pipeline is the easiest means to transfer it from one location to further distant locations. Pipelines carrying natural gas usually buried underground and operate under higher pressure. Other means of transporting natural gas are liquefied form that is known as LNG (Liquefied Natural Gas) and hydrate form where gas is allowed to mix with water to form hydrate. Hydrate form is still under experimental stage. LNG and Hydrate requires huge capital investment and moderate operating cost. In contrary, gas pipeline needs huge initial cost but operating cost is very low [2].Bangladesh already has an established pipeline network and Khadim-Debpur-Kumargaon (KDK) pipeline is located in Sylhet District and operated by Jalalbad Gas Transmossion and Distribution System Limited (JGTDSL) (Figure.1). It mainly transports gas to northeastern part of Bangladesh. Total length of the KDK pipeline is almost 17 km and diameter varies from 10.02 to 11.376 inches. Most of the industries, power plant and fertilizer factory depend on this line. Any operation problems in this pipeline will severely affect the power sector and the industries. KDK line was divided into 02 (two) segments for calculation purposes.

Table 1 gives them below.

Table 1. Description of KDK line.

No. of the segment Name of the segment Length, Km Diameter, inch
1 Khadim DRS- Debpur DRS 5 11.376
2 Debpur DRS –Kumargaon DRS 12 10.02

Figure 1. Gas Transmission Flow Diagram of Bangladesh (www.petrobangla.org.bd/data/flow_large.jpg).

When operating parameters i.e. flow rate, pressure and temperature changes or any operating condition change in the processing plants, liquid separate out from the gas stream because of multi- component nature of natural gas and its associated phase behavior. The separated out liquid might accumulate in the pipeline or carry over by the gas stream. Though gas is transmitted as dry gas, Jalalbad Gas Transmossion and Distribution Company Limited (JGTDCL) sometime having complains about excessive condensate in pipeline gas from her bulk customers. Sometimes they also face liquid accumulation in the pipeline; to remove it they do gas purging.

In this paper we tried to figure out a) the effect of pressure loss calculation by single phase correlations b) Build knowledge about fluid flow parameters. C) Build knowledge about problems associated with transmission of gas through pipeline.

2. Methodology

Daily Transmission data and average input to the different DRS were collected from the JGTCL. This daily report contains the operation variables like pressure, temperature and gas flow rates. Using FEKET-PIPER software pressure drop was calculated. The pressure drop was also calculated by single-phase equations like Weymouth, Panhandle A and Panhandle B. Later on a statistical analysis was carried out to find the best correlation for pressure drop.

2.1. Schematic Diagram

Figure 2, shows the schematic view of the KDK Pipeline, where major input and output were shown only. Pipeline was assumed straight line and undulation of pipeline was ignored.

Figure 2. The Schematic Diagram of Khadim-Debpur-Kumargaon Pipeline.

2.2. Pressure Calculations

Engineering of long-distance transportation of natural gas by pipeline requires a knowledge of flow formulas for calculating capacity and pressure requirements. The basis for fluid flow calculations in pipes is conservation of mass, momentum and energy. Application of these principles allows the calculation of changes in pressure and temperature with distance.

There are several equations in the petroleum industry for calculating pressure in pipelines. In the early development of the natural gas transmission industry, pressures were low and the equations used for design purposes were simple and adequate. However, as pressure increased to meet higher capacity demands, equations were developed to meet the new requirements. Several equations are available that relate the gas flow rate with gas properties, pipe diameter and length, and upstream and downstream pressures. Probably the most common pipeline flow equation is the Weymouth equation, which is generally preferred for smaller-diameter lines (D 15 in. ±). The Panhandle equation and the Modified Panhandle equation are usually better for larger-sized transmission lines [3]. In commercial software like Fekete, Panhandle – B is used for pressure calculations. Assumptions for various pipeline flow equations are given in Table 2.

Table 2. Assumptions of Various Pipeline Flow Equations.

No. of Pressure Equations Name of Pressure Equations Assumptions
1 Weymouth No mechanical work.
Isothermal Steady –State flow.
Constant Gas Compressibility
Factor.
No undulation.
Negligible kinetic energy change.
Fully turbulent flow in pipe with diameters around NPS 36.
2 Panhandle A Pipe diameter from NPS 6 to NPS 24.
Reynolds number greater than 300,000 with partially turbulent flow.
3 Panhandle B Long pipelines with diameter greater than NPS 24.
4 Fekete Software (Piper) Single-phase flow using Panhandle B as governing equation.

2.2.1. Weymouth Equation

The following form of Weymouth equation commonly used in industry [3]

 

qh = gas flow rate, cfh at pb and Tb

Tb = base temperature, R

Pb = base pressure, psia

P1 = inlet pressure, psia

p2 = outlet pressure, psia

D = inside diameter of pipe, in.

ϒg = gas specific gravity (air = 1)

 = average flowing temperature, R

L = length of pipe, miles

= gas deviation factor at average flowing temperature and average pressure.

2.2.2. Panhandle A Equation—Horizontal Flow

The Panhandle A pipeline flow equation assumes that f varies as follows

 

The pipeline flow equation is thus

 

Where

q is the gas flow rate, cfd measured at Tb and pb

Tb = base temperature, °R

Pb = base pressure, psia

P1 = inlet pressure, psia

p2 = outlet pressure, psia

D = inside diameter of pipe, in.

ϒg = gas specific gravity (air = 1)

 = average flowing temperature, R

L = length of pipe, miles

 = gas deviation factor at average flowing temperature and average pressure

2.2.3. Modified Panhandle (Panhandle B) Equation—Horizontal Flow

This is probably the most widely used equation for long lines (transmission and delivery) [3]. The modified Panhandle equation assumes that f varies as

 

and results in

 

2.3. Statistical Analyses

Any correlation that is presented in this study should be checked statistically in order to obtain a quantitative measurement about the accuracy of the prediction. Some basic statistical parameters used for correlation performance evaluation are average percentage relative error (APRE), average absolute percentage relative error (AAPRE) and standard error of estimate (SEE).

Average Percentage Relative Error (APRE) is a measure of the relative deviation of the predicted values from the experimental values in the percentage. The equation is given as follows,

APRE = () x ∑ []

The smaller the error is the more evenly distributed the positive and negative differences between predicted and experimental values.

3. Results and Discussion

In calculations pipeline network was simplified with considering all intakes and off takes into few major points. Effects of valves, strainer and geometry like elbow, undulation etc were ignored. As the gas flowing through the pipeline is produced from Horipur gas field, we consider the gas properties of Horipur gas field for the calculation of several physical properties of gas.

3.1. Segment 1(Khadim DRS- Debpur DRS)

3.1.1. Pressure Calculation

In pressure calculations, Reynolds’s Number and all physical properties are determined in average temperature and pressure. Also, pressure was calculated by Weymouth, Panhandle A, Panhandle B and Fekete Software (Piper, using Panhandle B) for single-phase flow. All results are given in the tables below.

Table 3. Comparison of measured and calculated pressure data for Segment 1.

Date Measured Weymouth Panhandle A Panhandle B Piper
01-02.07.14 954.7 1003.02 1010.809 1008.187 989.98
02-03.07.14 944.7 1002.135 1010.538 1007.705 989.76
03-04.07.14 984.7 1003.736 1011.03 1008.578 992.34
04-05.07.14 994.7 1005.675 1011.634 1009.639 995.67
05-06.07.14 994.7 1007.151 1012.1 1010.451 998.24
06-07.07.14 969.7 1002.801 1010.742 1008.068 997.89
07-08.07.14 954.7 1000.95 1010.177 1007.062 998.87
08-09.07.14 914.7 1000.145 1009.933 1006.625 991.76
09-10.07.14 914.7 1000.124 1009.927 1006.613 991.54
10-11.07.14 934.7 1001.063 1010.211 1007.123 990.75
11-12.07.14 960.7 1002.008 1010.499 1007.636 992.76
12-13.07.14 969.7 1001.322 1010.29 1007.263 991.23
13-14.07.14 944.7 1001.634 1010.385 1007.433 987.12
14-15.07.14 981.7 1001.656 1010.392 1007.445 989.23
15-16.07.14 954.7 1002.587 1010.676 1007.952 987.35
16-17.07.14 994.7 1002.967 1010.793 1008.159 988.34
17-18.07.14 964.7 1000.552 1010.056 1006.845 986.18
18-19.07.14 949.7 1002.549 1010.665 1007.931 990.87
19-20.07.14 954.7 1001.104 1010.224 1007.145 991.53
20-21.07.14 991.7 1002.059 1010.515 1007.664 987.79
21-22.07.14 929.7 1000.664 1010.09 1006.906 987.25
22-23.07.14 934.7 1000.451 1010.026 1006.791 986.52
23-24.07.14 939.7 1000.398 1010.009 1006.762 982.4
24-25.07.14 929.7 999.9933 1009.887 1006.542 989.27
25-26.07.14 934.7 1000.709 1010.103 1006.93 986.26
26-27.07.14 954.7 1001.247 1010.267 1007.223 993.26
27-28.07.14 989.7 1005.663 1011.63 1009.633 992.49
28-29.07.14 999.7 1010.56 1013.209 1012.341 997.76
29-30.07.14 1002.7 1012.687 1013.935 1013.536 996.27
30-31.07.14 1004.7 1013.234 1014.13 1013.847 994.25
31-01.08.14 984.7 1012.797 1013.974 1013.598 992.26

Figure 3. Pressure vs. Date for Segment 1.

3.1.2. APRE Values for Segment 1

APRE values for different pressure equations are given in the table below.

Table 4. Comparison of measured and calculated APRE values for Segment 1.

Date Weymouth Panhandle A Panhandle B Piper
01-02.07.14 5.061253 5.877137 5.602539 3.6954
02-03.07.14 6.079681 6.969155 6.669349 4.76977
03-04.07.14 1.933169 2.673897 2.424922 0.77587
04-05.07.14 1.103332 1.702407 1.501903 0.09752
05-06.07.14 1.251716 1.749316 1.583477 0.35589
06-07.07.14 3.413512 4.232415 3.956697 2.90708
07-08.07.14 4.844493 5.810915 5.484604 4.62658
08-09.07.14 9.341312 10.41138 10.04969 8.42462
09-10.07.14 9.339018 10.41069 10.04845 8.40057
10-11.07.14 7.099937 8.078638 7.748233 5.99658
11-12.07.14 4.29976 5.183596 4.885631 3.33715
12-13.07.14 3.260988 4.185797 3.873699 2.22027
13-14.07.14 6.026674 6.952973 6.640515 4.49031
14-15.07.14 2.032827 2.922637 2.622497 0.76704
15-16.07.14 5.015924 5.863215 5.577836 3.41992
16-17.07.14 0.831149 1.617868 1.353062 -0.63939
17-18.07.14 3.716428 4.701579 4.368766 2.2266
18-19.07.14 5.564827 6.419343 6.131512 4.33505
19-20.07.14 4.860632 5.815815 5.493368 3.85776
20-21.07.14 1.044594 1.8972 1.609786 -0.39427
21-22.07.14 7.632984 8.646865 8.304397 6.19017
22-23.07.14 7.03447 8.058789 7.712698 5.54402
23-24.07.14 6.459311 7.482117 7.136513 4.544
24-25.07.14 7.560858 8.625051 8.265278 6.40744
25-26.07.14 7.062017 8.067132 7.727645 5.51621
26-27.07.14 4.87561 5.820368 5.501504 4.03897
27-28.07.14 1.612902 2.215832 2.014031 0.2819
28-29.07.14 1.086373 1.351314 1.26445 -0.19406
29-30.07.14 0.99603 1.120513 1.080679 -0.64127
30-31.07.14 0.849438 0.938597 0.91042 -1.04011
31-01.08.14 2.853329 2.972886 2.934709 0.76775

Figure 4. APRE comparison for various pressure equations for Segment 1.

3.2. Segment 2 (Debpur DRS- Kumargaon DRS)

3.2.1. Pressure Calculation

Pressure was calculated using different single phase equations and Feket (Piper) for Segment 2 (Debpur DRS- Kumargaon DRS). The comparison of different pressure values are given in the table below.

Table 5. Comparison of measured and calculated pressure data for Segment 2.

Date Weymouth Panhandle A Panhandle B Measured Piper
01-02.07.14 922.782 951.531 954.357 764.7 940.72
02-03.07.14 916.737 948.4 951.288 804.7 945.26
03-04.07.14 927.787 954.146 956.909 844.7 942.36
04-05.07.14 938.379 959.755 962.347 884.7 952.73
05-06.07.14 946.724 964.254 966.669 914.7 951.35
06-07.07.14 929.048 954.809 957.554 784.7 951.65
07-08.07.14 914.36 947.176 950.085 774.7 949.47
08-09.07.14 909.91 944.897 947.84 884.7 949.67
09-10.07.14 908.937 944.401 947.35 791.7 949.36
10-11.07.14 911.788 945.857 948.787 774.7 947.3
11-12.07.14 916.873 948.469 951.357 802.7 949.37
12-13.07.14 911.357 945.636 948.569 764.7 942.36
13-14.07.14 914.921 947.464 950.369 874.7 947.36
14-15.07.14 916.724 948.393 951.281 884.7 947.47
15-16.07.14 927.656 954.078 956.842 791.7 948.37
16-17.07.14 937.205 959.129 961.742 864.7 951.33
17-18.07.14 917.253 948.665 951.549 854.7 950.36
18-19.07.14 922.421 951.343 954.173 800.7 947.36
19-20.07.14 917.776 948.936 951.814 869.7 946.98
20-21.07.14 930.654 955.654 958.376 769.7 947.35
21-22.07.14 921.62 950.926 953.766 880.7 949.36
22-23.07.14 920.002 950.087 952.944 802.7 948.13
23-24.07.14 922.745 951.512 954.338 864.7 949.25
24-25.07.14 918.915 949.524 952.392 764.7 947.36
25-26.07.14 924.461 952.406 955.212 784.7 947.49
26-27.07.14 929.737 955.171 957.907 764.7 943.46
27-28.07.14 951.917 967.094 969.375 874.7 947.37
28-29.07.14 981.372 984.106 985.054 914.7 951.36
29-30.07.14 985.746 986.894 987.459 884.7 947.32
30-31.07.14 985.476 986.716 987.31 914.7 948.27
31-01.08.14 982.191 984.617 985.501 864.7 957.26

Figure 5. Pressure vs. Date for Segment.

3.2.2. APRE Values for Segment 1

APRE values for different pressure equations are given in the table below.

Table 6. Comparison of measured and calculated APRE values for Segment 2.

Date Weymouth Panhandle A Panhandle B Piper
01-02.07.14 20.67244 24.4319 24.801 23.01818
02-03.07.14 13.92289 17.8575 18.216 17.46738
03-04.07.14 9.836274 12.9568 13.284 11.5615
04-05.07.14 6.067435 8.48369 8.7767 7.689612
05-06.07.14 3.501037 5.41754 5.6815 4.006778
06-07.07.14 18.39532 21.6782 22.028 21.27565
07-08.07.14 18.02767 22.2636 22.639 22.5597
08-09.07.14 2.849557 6.80424 7.1369 7.343732
09-10.07.14 14.80822 19.2877 19.66 19.91411
10-11.07.14 17.69565 22.0933 22.472 22.27959
11-12.07.14 14.22357 18.1599 18.52 18.27208
12-13.07.14 19.17835 23.6611 24.045 23.23264
13-14.07.14 4.598237 8.31876 8.6508 8.306848
14-15.07.14 3.61975 7.19935 7.5259 7.09506
15-16.07.14 17.17269 20.51 20.859 19.78906
16-17.07.14 8.385004 10.9204 11.223 10.0185
17-18.07.14 7.318686 10.994 11.331 11.19223
18-19.07.14 15.20177 18.8139 19.167 18.31647
19-20.07.14 5.527933 9.1107 9.4417 8.885823
20-21.07.14 20.91127 24.1593 24.513 23.08042
21-22.07.14 4.646299 7.97394 8.2963 7.796071
22-23.07.14 14.61348 18.3614 18.717 18.1176
23-24.07.14 6.71274 10.0395 10.366 9.777958
24-25.07.14 20.16674 24.1695 24.545 23.88649
25-26.07.14 17.81081 21.372 21.73 20.74551
26-27.07.14 21.58191 24.9079 25.266 23.37649
27-28.07.14 8.827771 10.5629 10.824 8.307991
28-29.07.14 7.288962 7.58783 7.6915 4.007871
29-30.07.14 11.42149 11.5512 11.615 7.078106
30-31.07.14 7.737606 7.87323 7.9381 3.670056
31-01.08.14 13.58744 13.868 13.97 10.70429

Figure 6. APRE comparison for various pressure equations for Segment 1.

Pressure calculated by Panhandle B method gave good results. As, Piper used panhandle B as a governing equation, it gave satisfactory result also. Weymouth equation is valid for pipeline diameter <15 inch±, so it follows the measured value line. Panhandle A gave unsatisfactory results.

3.3. Problems Faced By JGTDSL

While transmitting gas through KDK pipeline JGTDSL faces following problems: a) Liquid forms in the pipeline, which sometimes block the pipeline. b) Temperature and heating value decreases. c) There is always a volume gain at Kumargaon Station. JGTDSL takes following steps to overcome the above problems: a) They do the gas purging to clear the block. b) Before delivering the gas to their customers, gas is heated by a water bath heater at kumargaon station. c) Currently they are not taking any steps relating to this problem as their attention is on heating value.

4. Conclusion

4.1. Conclusion

The present study has led to following conclusions that are important from the authors’ viewpoint. a) When pressure is calculated for single-phase flow, it is under designed. b) Statistical analysis supports this engineering problem. So, a computer generated pressure calculation may solve this problem. c) As liquids form in the pipeline during transmission, it indicates two phase flow in the pipeline, which demands further study.

4.2. Future Recommendation

As there are various assumptions in this work, it can be stated that improved results will come if proper information is used.  In future, one can improve this work by making the following corrections. a) If physical parameters like gas and liquid flow rates, pressures, diameters are known at Kuchai point, this study will be improved by completing the network analysis properly. b) As JGTDSL does not have  gas Chromatograph at Kumargaon Station, a gas sample can be collected and a  gas chromatographic analysis report will improve the result. c) At Kuchai point, no pressure data is found from Daily Production Report provided by JGTDSL. So, calculated pressure cannot be compared with measured data at this point. A real pressure data can change the result.

Acknowledgement

We would like to thank Engr. Md. Shaheenur Islam, GM Operation, Jalalabad Gas Transportation & Distribution System Limited, for his kind support and cooperation.


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