In China, natural gas consumption is over 670?108 m3/year with expected growth rate of 10% per year. Most of the gas is transported from well heads to markets over cross-country gas networks, which requires construction of the West to East Gas Network – one of the largest gas network in the world. Presently, the network comprises four large-diameter pipelines and will include most major gas pipelines in China, in the future. It distributes about 300?108 m3 gas per year of which 3% to 5% is burned to power the gas transportation. At the current gas prices, gas transportation costs roughly 350 million dollars per year ? a considerable cost that could be reduced by improvements in network design and operation.
The paper reports on a study aimed at optimizing the network to minimize its energy consumption and cost. Large size and complex geometry of the network required breaking it down into simple components, optimizing operation of the components locally, re-combining the optimized components into the network and optimizing the network globally. This three-step approach employed four different optimization methods: penalty function method, pattern search, enumeration and non-sequential dynamic programming to solve the problem. The results show that cost savings due global optimization can be up to 23% and are inversely related to the network throughput. The increase of throughput from 67 million to 90 million m3/d would reduce the savings to a mere 1.2%. The result is explained by analyzing the state and the control variables, individual compressors' rate and compression ratio. It is explained why for compressors running in their designed workload, the optimized operation would approach the standard operation scheme.
Natural gas is considered a clean energy resource alternative to coal and oil. It is expected that global consumption of gas will double by 2030 [1]. With fast developing economy of China, domestic consumption of natural gas is presently over 60 billion m3/year, while worldwide consumption is approximately thirty times larger. Much of the gas is transported from well heads to market over cross-country gas networks, which prompts China to construct one of the largest gas transportation network in the world. Figure 1 shows the location of the network and table 1 gives the basic parameters.
From 3% to 5% of this gas is burned to power the transportation of the remaining amount [1]. At current prices, this is the equivalent of roughly 800 million dollars per year of wasted gas in China. Also, experts estimate that fuel consumption in gas pipeline can reduce by 20% by carefully optimizing the daily operation [2]. Many gas transportation companies have already managed to reduce costs dramatically by optimizing their gas pipelines [3,4,5, 6,7], their results also showed large reduction of CO2 and NOx emissions. Also, there has been considerable research work on the subject [7, 8, 9, 10, 11, 12, 13, 14].
With development of the gas industry, gas pipeline networks have evolved over decades into very large and complex systems.
