Parametric Analysis of a New CCHP System Utilizing Liquefied Natural Gas (LNG)

Abstract

Liquefied natural gas (LNG) contains considerable cold energy because a significant amount of energy is consumed to produce low-temperature LNG. So, finding a good way to utilize the LNG effectively, particularly its cold energy, is an important issue to solve the problem of energy crisis. In the present study, a new CCHP system utilizing liquid natural gas is proposed to provide cooling, heat and electricity output simultaneously to meet user’s different energy requirements. This CCHP system consists of a gas/steam combined cycle and an ejector refrigeration cycle. For cold energy utilization, LNG is firstly considered as a heat sink to condense the steam turbine exhaust in Rankine cycle, then cools down the suction air of compressor in Brayton cycle, and finally enters the combustion chamber after preheated by HRSG exhaust. The steam turbine has two streams of extraction steam. One is used to drive an ejector refrigeration cycle to produce the cooling effect, and the other is used to provide the heat. To evaluate the system performance, the exergy efficiency is selected as an evaluation criterion to eliminate the difference of energy quality. A thermodynamic simulation of the new CCHP system utilizing LNG is achieved using a simulation program. A parametric analysis is conducted to examine the effects of several key thermodynamic parameters on the performance of the proposed CCHP system. The results indicate that as gas turbine inlet temperature, pressure ratio of compressor and steam turbine inlet pressure increase, the exergy efficiency increases. In addition, as steam turbine back pressure, extraction mass rate ratio for heat, extraction mass rate ratio and extraction pressure for refrigeration increase, the exergy efficiency decreases.