Reduction of efficiency penalty for a natural gas combined cycle power plant with post-combustion CO2 capture: Integration of liquid natural gas cold energy

Abstract

The high energy consumption requirements of the post-combustion CO2 capture (PCC) process of a natural gas combined cycle (NGCC) power plant will result in a significant reduction in power generation efficiency, and the energy integration of the system can effectively reduce power plant efficiency penalties. However, the existence of a large amount of low-temperature waste heat in NGCC power plant is difficult to utilize due to its low temperature. In this paper, the integration of LNG cold energy with NGCC power plant with PCC process is proposed. For the 391 MW NGCC plant with MEA-based PCC system, the impact of the exhaust gas recirculation (EGR) process is firstly considered and a basic case of 35% EGR is obtained. Then the internal energy integration of the NGCC + PCC + EGR system (case 1) reveals that there are a large number of different temperature waste heat sources in the system, and then the dual-pressure ORC is integrated into the system for energy integration (case 2). Finally, in order to integrate the low temperature waste heat that has not yet been utilized and recover the cold energy of LNG, the LNG and the two-stage condensation Rankine cycle are integrated with case 2. The results show that the net power output of case 3 is 17.55 MW higher than that of NGCC + PCC + EGR system, the total efficiency is increased by 2.51%, and the efficiency penalty is reduced to 7.9%. It can be seen that the combination of LNG cold energy and NGCC power plant can effectively improve the power generation efficiency and reduce the energy penalty.