Techno-Economic Analysis of Indirect, Direct, and Hybrid Coal-Biomass to Liquids (CBTL) Plants with CO2 Capture and Storage (CCS)

Indirect coal liquefaction (ICL) and direct coal liquefaction (DCL) technologies are commercially available for producing alternative transportation fuels. However, both processes are plagued with high CO₂ emission. Because the syncrude produced in the ICL and DCL reactors cannot satisfy the current specification of transportation fuels, additional upgrading technologies are required. For example, syncrude from the ICL process has low octane number for naphtha cut but high cetane number for diesel cut, while syncrude from the DCL process has high octane number for naphtha cut but low cetane number for diesel. Therefore the hybrid coal liquefaction (HCL), a combination of ICL and DCL technologies, can reduce the penalty of downstream syncrude upgrading unit by optimal blending. Addition of biomass and application of carbon capture and storage (CCS) technologies are two possible solutions to reduce the carbon footprint, but would lead to higher operating cost and capital investment. Several studies have been conducted for indirect coal-biomass to liquids (CBTL) plants with CCS, while few studies have been conducted for direct and hybrid CBTL processes at the systems level. With this motivation, we will present a techno-economic study conducted in Aspen Process Economic Analyzer^® (APEA^®) environment for indirect, direct, and hybrid CBTL plants with CCS using high fidelity process models developed in Aspen Plus^® and Excel.

In the indirect CBTL plant, coal and biomass are first gasified to syngas. Then the syngas is converted to syncrude via Fischer-Tropsch (FT) synthesis. CO₂ is captured from both raw syngas and FT vapor product. In the direct CBTL plant, coal and biomass are directly converted into syncrude in the catalytic two-stage liquefaction (CTSL) unit by adding hydrogen produced from gasification of coal/biomass/liquefaction residue or reforming of shale gas. Significant amount of CO₂ that is generated in the hydrogen production unit(s) is captured to satisfy the target extent of CO₂ capture. In the hybrid CBTL plant, pre-processed coal and biomass are sent to either syngas production unit or the CTSL unit. Produced syngas is sent either to FT unit or hydrogen production unit. Naphtha and diesel products from the FT unit and the CTSL unit are blended to reduce the syncrude upgrading penalty. Different CCS technologies are considered and optimized for the indirect, direct and hybrid CBTL plant depending on the sources of CO₂ containing stream and corresponding CO₂ partial pressure.

The focus of this presentation will be on optimal synthesis of the hybrid plant. In particular, following aspects will be presented: (1) development of plant-wide process model and rigorous economic model in Aspen Plus^®, Aspen Exchanger Design and Rating^®, Excel, and APEA^®, (2) sensitivity studies to analyze the impact of key design parameters (i.e. biomass/coal ratio, extent of CCS, CCS technologies, blending ratio of indirect and direct syncrude in the hybrid route) and investment parameters (i.e. price of coal and biomass, project life, plant contingency and plant capacity) on key economic measures, such as net present value (NPV), internal rate of return (IRR) and break-even oil price (BEOP), (3) analysis of the potential environmental credits due to use of biomass and CCS for all liquefaction approaches, (4) comparisons and analysis of trade-offs of indirect, direct, and hybrid CBTL plants.