Simulation study on the carbon capture system applying LNG cold energy to the O2/H2O oxy-fuel combustion

Abstract

At present, the oxy-fuel combustion (O2/CO2 circulating combustion) is dominant in natural gas generating systems, but it consumes much energy for air separation oxygen generation and carbon capture, leading to a severe reduction of generating efficiency. The O2/H2O combustion system, as the new generation of an oxy-combustion system, is superior to the oxy-fuel combustion, and its pollutant emission is lower, but during its combustion, air separation oxygen generation is still needed, so CO2 compression energy consumption is still higher. In this paper, a set of carbon capture system applying LNG cold energy to the O2/H2O combustion was developed, and its mathematical model was established to calculate thermal efficiency and exergy efficiency. And then, it was compared with the COOLCEP system which also makes use of LNG cold energy for carbon capture. The combustion process of this system is operated under high pressure with H2O as the circulation medium, and LNG is utilized in a cascading pattern, so the energy consumption of air separation oxygen generation and carbon capture system is reduced, the generating efficiency of the system is increased and carbon capture is conducted at low cost. The thermal efficiency and energy efficiency of this system increase continuously as the inlet temperature of gas turbine rises. When the flow rate of circulating water is 13.5 kmol/s, the combustion pressure is 1.6 MPa, and the inlet temperature of gas turbine reaches 1328.1 °C, the thermal efficiency and exergy efficiency is 57.9% (maximum) and 42.7%, respectively. Compared with COOLCEP system, the O2/H2O combustion system is much lower in energy consumption and its thermal efficiency and exergy efficiency are 6.3% and 5.4% higher, respectively. Keywords: LNG cold energy, Oxy-fuel combustion, Carbon capture, O2/H2O, COOLCEP system, Cascading utilization, Aspen plus, Thermal efficiency, Exergy efficiency