Techno-Economic Study of an Indirect Coal-Biomass to Liquids (CBTL) Plant with CO2 Capture and Storage (CCS)
Yuan Jiang, Debangsu Bhattacharyya
Department of Chemical Engineering, West Virginia University, Morgantown, WV 26506, USA
The synthetic fuels producing by indirect coal liquefaction can be directly used in the current gasoline and diesel engines. However, the uncertainty of the economic feasibility and the high CO2 emission in comparison to the petroleum-based fuels are the two major reasons preventing the commercialization of coal to liquids plants in United States. Applying CCS and adding moderate amount of biomass to the feed can make the process be more environmental friendly, but at the cost of higher capital and operating cost. For evaluating the impact of technology choices and design parameters, a techno-economic study is conducted in Aspen Process Economic Analyzer® (APEA®) environment for an indirect CBTL plant with CCS using the high fidelity process model developed in Aspen Plus® and Excel.
In the indirect CBTL process with, coal and biomass is first converted to syngas in the gasifier, and then converted to syncrude in the Fischer-Tropsch reactor. The syncrude is updated to on-spec gasoline and diesel in the upgrading units. CO2 produced in the system is captured by different CCS units, while light gases are sent to either autothermal reformer or combined cycle power plant to generate more syngas or process electricity. The steady-state process model is validated by using the data available in the open literature. The outside battery limit (OSBL) section is designed using Analyzer Utility Modules (AUM) and then integrated with the inside battery limit (ISBL) units for economic analysis. Impacts of a number of candidate technologies such as different CCS and hydrotreating technologies and design parameters such as coal/biomass ratio, biomass types, Fischer-Tropsch and autothermal reformer operating conditions, and extent of CCS on the various economic matrices such as net present value (NPV), payout date, and internal rate of return (IRR) are evaluated. The study shows that the techno-economic optimization of the indirect CBTL plant can substantially improve the plant economics without violating the operational constraints and environmental emission limits while satisfying the desired fuel specifications.
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