Process modeling of direct coal-biomass to liquids (CBTL) plants with shale gas utilization and CO2 capture and storage (CCS)

Abstract

Direct coal liquefaction (DCL) technologies have been commercially demonstrated for producing transportation fuels from non-petroleum sources. However, significant amount of hydrogen is required in the DCL process due to the low H/C ratio in coal. As a result, DCL processes are usually associated with a high level CO2 emission from hydrogen production units. Hence, direct coal biomass to liquids (CBTL) processes with CO2 capture and storage (CCS) and shale gas utilization are proposed in this work as an option for reducing CO2 emission. In this study, the focus is on process simulation and calculation of material and energy balances of novel direct CBTL plants, which can be used as a basis for further studies, such as optimization, techno-economic analysis and life-cycle analysis. In this process, coal with moderate amount of biomass is converted into syncrude through reaction with H-donor solvent and gaseous hydrogen in a catalytic two-stage liquefaction unit. Hydrogen required for the liquefaction and product upgrading unit is produced from the liquefaction residue partial oxidation unit and the shale gas steam reforming unit or from the coal/biomass/residue co-gasification unit. Different CCS technologies are evaluated to achieve 90% overall carbon capture if high extent of CO2 capture is considered. Results of individual plant sections are validated with the existing data, if available. Sensitivity studies have been conducted to analyze the effects of key operating parameters and design parameters, such as the sources of hydrogen, CCS technologies, extent of CCS, and biomass/coal ratio. Key measures studied in this work include the fuel yield, thermal efficiency, CCS penalty and CO2 emission.