(410a) Plant-Wide Modeling of An Indirect Coal-Biomass to Liquids (CBTL) Plant With CO2 Capture and Utilization Integrated With a Combined Cycle Plant

Addition of moderate amounts of biomass to coal for the production of liquids can substantially reduce life cycle analysis (LCA) CO₂ emissions relative to a petroleum diesel baseline¹. As an example, 20% less CO₂ is produced with 8% biomass addition, with carbon capture and storage (CCS) with CO₂ utilization. With this motivation, a high-fidelity model of a coal-biomass to liquids (CBTL) plant with CCS and CO₂ utilization has been developed. The plant is integrated with a combined cycle plant for producing electric power.

 An entrained-flow gasifier is used for gasifying a bituminous coal mixed with a biomass. A water gas shift (WGS) reactor produces the desired concentration of CO:H₂ in the syngas by taking into account the desired amount of Fischer-Tropsch (FT) liquid and extent of CO₂ capture. A significant portion of CO₂ present in the syngas is captured in an acid gas removal (AGR) process and then compressed to supercritical phase for sequestration. A portion of the captured CO₂ is utilized by producing methanol. A portion of the CO₂-lean syngas from the AGR unit is used for H₂ production while the remaining portion goes to the FT reactors. The liquid products from the FT reactors are sent to the product recovery and upgrading section where a novel integrated hydrotreater is used for decreasing the capital cost and increasing the thermodynamic efficiency. The light gases from the product recovery and upgrading section are sent to a tri-reforming process that helps to tailor the syngas composition and utilizes a portion of CO₂ to yield more fuel. The tri-reforming process is a combination of dry methane reforming, steam reforming, and partial oxidation of methane and consumes about 25% less energy than the conventional steam reforming and 50% less energy than CO₂ reforming of methane². A combination of the isomerization unit, catalytic reforming unit (CRU), and non-H₂ isomerization unit is considered for satisfying the current specifications of aromatics content and octane number in the gasoline pool. The off-gas from the entire process is used in a combined cycle plant that uses a gas turbine integrated with a heat recovery steam generator coupled with a steam turbine to produce more electric power.

The plant-wide model has been developed in Aspen Plus. Models of individual sections have been developed based on the experimental or operational data, whenever available, in the open literature. Aspen User2 Blocks are used to connect models developed in Excel with Aspen Plus models of other unit operations. In this talk, we will present the plant-wide model and the results of a number of important performance measures in response to the key input and operational variables.

References

1. Affordable, Low Carbon Diesel Fuel from Domestic Coal and Biomass, DOE/NETL 2009/1349, January 2009

2. Song, C and Pan W, “Tri-Reforming of Methane: A Novel Concept for Catalytic Production of Industrially Useful Synthesis Gas with Desired H₂/CO Ratio”, Catalysis Today, 2004, 98, 463-484