Analysis and optimization of a natural gas multi-stage expansion plant integrated with a gas engine-driven heat pump

Abstract Excessive preheating energy consumption is a persistent issue in natural gas expansion power plants. In this paper, a novel system is proposed to solve this problem by using multi-stage expansion and gas engine-driven heat pumps (GHP). A dynamic model based on phase equilibrium theory is established to predict hydrate formation. A control strategy with continuously variable transmission (CVT) for optimizing engine efficiency is investigated through simulation and experiment. Finally, the efficiency and economic performance are compared among GHP, electric heat pump (EHP), and cogeneration (CHP) in a case study. The results show that the engine efficiency of CVT is 4.89% higher than that for multi-level transmission. Compared to single-stage expansion, multi-stage design can reduce preheating temperature by 46%, preheating load by 4.41%, and improve the performance coefficient (COP) of GHP 1.4-fold. The COP of GHP is 33.38% higher than that of EHP, and the primary energy ratio (PER) is 1.81 times that of CHP accordingly. The annual average profit margin for GHP is 1.89 times that of CHP and 7.15 times that of EHP. Thus, the proposed system has significant energy savings and economic advantages.