Techno-economics of natural gas pipeline compression system.

The demand for the natural gas is on the increase as a result of industrialization and urbanization. There is need of transporting this natural gas from production fields to consumer market through long distances pipelines. Transporting natural gas through a long distance requires constructing of compressor station driven by a gas turbine at a suitable distance along the pipeline. Pipeline construction is capital expensive that requires important data such as the pipe diameter, pipe thickness, pipeline length, proper gas compressor and gas turbine sizes, flow rate and required operating pressure. The technical and economic success of a pipeline compressor station depends on the operation of gas compressor and gas turbine involved. Therefore, to techno-economic tool to assess the pipeline project becomes imperatives. The objective of this research is the application of TERA on gas turbine compressor station in natural gas pipeline taking into account the station location, equipment selection, power matching based on ambient temperature variation while optimizing for the project lifecycle lowest cost. The model and methodology developed to provide useful decision-making guide for Nigerian government on investment of Trans-Sharan gas pipeline. This research was divided into two aspects, the performance aspect, and the economic aspect. The performance presents a model for booster station definition along the gas pipeline. The model was developed using thermodynamic gas properties, HYSYS and Weymouth gas flow equation. The model also accounts for the variation in the elevation and ambient temperature at each of the compressor stations located along the pipeline network. For each of the stations gas compressor and gas turbine model was selected. The model has been verified using pressure ratio and a number of booster station spacing of a pilot project, Trans-Sahara gas pipeline (TSGP). The project was aimed at exporting natural gas from Niger Delta, Nigeria to the consumer market in Europe via Niger and Algeria. The project is expected to transport 30bcm/year of natural gas through 56-inch pipe diameter and a total distance of 4180km with 18 compression stations. For the power matching, the daily three hourly temperature measurements for winter, hot, and dry seasons were recorded for each of the compressor stations along the gas pipeline. The power requirement for the centrifugal compressors was calculated based on the three hourly intervals. The gas turbines were simulated in Turbomatch based on these ambient temperatures. The result shows that both the centrifugal compressor polytropic head and the gas turbine output power are strongly influenced by the ambient temperature with gas turbine power output dropping by average 0.95% for every 10oC rise in ambient temperature and the centrifugal compressor polytropic head increasing by average of.1% for every 10oC rise in ambient temperature vis-viz increase in the centrifugal shaft power. The major costs associated with the natural gas pipeline is the capital cost and operating cost. At baseline case, the project capital cost is USD 15.7 billion and the project lifecycle cost is USD 27.6 billion. The project life cycle cost is made of the following 33% fuel cost,10% maintenance cost, 26% pipeline cost, 6% gas turbine cost, 12% gas compressor cost, and 13% auxiliary cost. For this baseline, The NPV at 15% discount rate negative. For the optimised case, the studies considered two gas turbines of 43.3MW and 100MW capacities. For the first case, optimisation study was done for two 43.3MW gas turbine driving two gas compressors while for case 2, one 100MW gas turbine was used to drive one gas compressor. The result shows 10 number of compressor stations along the pipeline. The optimized result also shows a reduction in the lifecycle cost from USD 20.1 billion in 43.3MW to USD 18.8 billion in 100MW. The NPV at 15% discount rate for both engines is seen to be positive.