Integration of SNG plants with carbon capture and storage technologies modeling

Several power plant configurations have been recently studied as an alternative to conventional technologies in the field of energetic conversion of coal. The price of natural gas shows a volatile trend and when at its maximum promotes a renewed interest in technologies converting coal into synthetic natural gas (SNG). Moreover, in an low-carbon economy these processes include the capture of CO2 in the base plant configuration. This paper analyzes the possible integration of SNG plants with Carbon Capture and Storage Technologies (CCS). The studied SNG facilities are based on commercial coal gasification and methanation technologies currently available worldwide. The major problem in optimizing the methanation reaction, one of the most important stages of the whole process, is to achieve an efficient removal of the reaction heat to avoid catalyst sintering and prevent carbon particle formation. For this reason, in this study two different process configurations were compared. In the first configuration (case A), the removal of CO2 is operated before the methanation section and the reaction is carried out in a series of adiabatic fixed bed reactors with inter-cooling and product recycle. In the second configuration (case B) the dilution of the methanation feed with CO2 and steam controls the heat of reaction, being CO2 captured downstream the process. For both the plant configurations, performance is analyzed and the energy penalty caused by the introduction of CCS is evaluated. Particular attention is devoted to heat integration between different sections of the plant. Results show similar efficiency in both the cases and that more than 50% of the input energy can be converted to synthetic natural gas. The CCS integration leads to a slight efficiency reduction of about 1 percentage point. The selected plant configurations were tested and performance evaluated and compared in the Aspen Plus v. 8 simulation environment.