Modeling and optimization of a natural gas pressure reduction station to produce electricity using genetic algorithm

For longer distances, natural gas is transported through transit pipeline at high pressures. In a place of consumption or at passing into a lower pressure pipeline, the pressure of the gas must be reduced. In Iran, the common procedure of reducing pressure in natural gas station is using expansion valves, which causes the waste of large amount of energy. Combined heat and power (CHP) systems have many economic and environmental benefits. In this paper a CHP system which its prime components are boiler, expander, pump, heat exchanger and gas engine, is used in a pressure reduction station to produce electricity. A new and relatively quick method for selecting the number of each type of prime component, and determining their nominal power and their efficiency is also presented. In this method an objective function named Actual Annual Benefit in terms of dollar has been defined as the sum of the outcomes from selling electricity and natural gas minus capital cost, operating cost and maintenance cost of prime components of the system. Subsequently different parts of the objective function have been expressed in terms of 7 decision variables. Finally the optimum values of decision variables have been obtained by maximizing the objective function using genetic algorithm. Results of this research show that ambient condition, pressure and mass flow rate of inlet natural gas, efficiency of prime components and prices of electricity and natural gas have the key role in selecting the appropriate strategy for the system.