Flow Optimization Sensitivity in Natural Gas Pipeline Network System

Abstract

Three control variables of interest namely upstream pressure, downstream pressure and gas specific gravity were considered to determine the sensitivities of the optimal flow capacity to changes in the aforementioned control variables. The sensitivity scheme covered five case study Pipelines namely: Elf Total Nig. Ltd, Shell Petroleum Development Company (SPDC), Agip Nig. Ltd and Nigeria Gas Company (NGC) Eastern Division. The Panhandle A and Modified Panhandle B models equations were both applied to each of the pipelines in the sensitivity evaluation scheme. The sensitivities were calculated with respect to small changes in upstream pressure P 1 , downstream pressure P 2 and the gas specific gravity G, within the limit of ± 20 %. It was seen that changes in optimal flow capacities were insignificant and therefore insensitive to changes in flow variables in the range upto ± 20 %. This gives credence, authenticates and establish the stability of the results of optimization of flow capacities carried out in the researcher’s previous works. The Panhandle-A flow model yielded lower values of changes in optimal flow capacities upto the limit of 1.0 %. In comparison, the Panhandle-B flow model gave sensitivities upto a maximum of 9.0 %, for all the Pipelines covered in the study and the flow control variables. In more explicit manner, the response of optimal flows capacities to changes in control variables for the transformed Panhandle-A and Modified Panhandle-B models for ElfTotal Nig. Ltd with respect to upstream pressure, downstream and gas specific gravity are respectively 0.4 %, 0.9 % and 0.16 % (Tables 1 a to 1b). Applying the same concept to Shell petroleum Development Company (SPDC), the response are respectively 3.2 %, 1.7 % and 0.16 % (Tables 2a to 2b). In the same vein, with respect to Agip Nig. Ltd, the respective data are 7.11 %, 0.03 % and 3.7 % (Tables 3a to 3b) and for the Nigeria Gas Company (NGC) Eastern Division the respective data are 7.11 %, 0.03 % and 3.7 % (Tables 4a and 4b). The graphical illustrations are in accordance with Figures (Fig.1a & b to 4a & b). The operating threshold based on off design analysis (Tables 6 to 10) confirmed that the line flow throughput could be varied within 1 m 3 /s to 6.5 m 3 /s. The nominal line diameter could be fixed within 30” and 65”. These condition are possible within the limit of pressure variation in the range of 30 bar to 170 bar at stream temperature of 40 0 C.