Study of cryogenic CO2 capture with solar-assisted VAR system

Abstract

One of the major contributors to the rise in global warming potential (GWP) is the continuous accumulation of carbon dioxide (CO2) in the atmosphere. Carbon capture and storage (CCS) is a modern approach to capture CO2 from various industrial processes and store it efficiently for further use. In the cryogenic carbon capture method, CO2 is liquefied by condensation and separated from the CO2 contained gas. The CO2 capture by the cryogenic method can yield high purity CO2 and negligible secondary emissions. However, huge energy is required for the condensation process. In the present study, a low energy penalty method for a post-combustion carbon capture process by the application of the cryogenic technique is performed using process simulation. To reduce energy consumption, a solar integrated vapor absorption refrigeration (VAR) system is designed. The designed solar VAR system provides the required refrigeration cooling load for condensing CO2 in a flue gas stream. For this purpose, the flue gas mixture composed of CO2, N2, and water vapor with respective molar fractions of 15%, 75%, and 10% is considered. The mass flow rate of the flue gas considered is 673.4 kg/s at 1.1 bar and 40 °C. CO2 is separated by condensing the gas at a pressure of 40 bar and temperature of −28 °C. The heat energy required to operate the VAR is 83.3 MW at 75 °C which is supplied by the solar collector. The simulation result indicates that for a post-combustion process, a high-grade electrical energy penalty is found to be about 1.26 MJ/kg CO2 captured, which is better than the most common approaches like absorption, adsorption, and membrane methods. It is also observed that with the increase in the CO2 concentration from 15 to 25 mol% in the flue gas, the energy penalty is reduced by about 37.5%. The performance analysis is also carried out by varying the CO2 recovery rate and purity. It is observed that the energy penalty is decreased by about 10.3% with the increase of CO2 recovery from 90% to 100%. Also, the energy penalty is increased by 4.2% with the increase of CO2 purity from 95% to 100%. The specific CO2 capture process cost is found to be about 1.008 million USD/(kg.s−1).