Optimal design and thermo-economic analysis of an integrated power generation system in natural gas pressure reduction stations

A massive amount of byproduct energy of natural gas including pressure and cold energy is released during the natural gas depressurization process in pressure reduction stations. In this paper, a novel integrated power generation system is proposed to make joint use of the byproduct energy in pressure reduction stations and low-grade heat. The integrated system consists of two subsystems: a natural gas expansion subsystem recovers the pressure energy of natural gas, an organic Rankine cycle subsystem retrieves the cold energy of natural gas and low-grade heat. A multi-objective optimization model which comprehensively considers the thermodynamic and economic performance of the proposed system is established. Optimal determination of key design parameters including intermediate temperature and minimum approach temperatures is investigated under different heat source conditions. Based on the optimization results, the thermo-economic analysis of the proposed system is conducted to give guidance for further optimization. The simulation result shows that there exhibit positive linear correlations between optimal intermediate temperature and minimum approach temperatures with heat source conditions. With the optimized parameters, the performance of the proposed system is enhanced compared to the separated natural gas expansion and organic Rankine cycle systems. Net power output and exergy efficiency are improved by 17.15% and 22.37%. The cost of electricity is reduced by 42.23%. This paper provides an efficient solution to retrieve the byproduct energy in pressure reduction stations as well as low-grade heat.