(417b) Mathematical Modeling and Optimization of Commercial-Scale Catalytic Two-Stage, Ebullated Bed, Direct Coal Liquefaction Reactors

Due to the insecurity in crude oil supply and uncertainty in its prices, finding alternative fuel source is critical. Direct coal liquefaction (DCL) is one of the technically feasible solutions to convert coal to transportation fuels. However, this technology has not been widely commercialized due to the high capital investment, uncertainty in economic feasibility and several operating challenges. In the DCL technology, catalytic two-stage liquefaction (CTSL) unit with a configuration similar to the hydroprocessing reactor systems uses two ebullated bed reactors (EBR), in which coal reacts with the recycled solvent and hydrogen to produce syncrude. Since the conversion, and yield obtained in the CTSL reactors are probably the most important factor in the profitability of the DCL plants, the CTSL process must be optimized. A rigorous mathematical model of the CSTL unit is required for optimization. However, most of the models of the DCL reactors have been developed by assuming ideal reactor performance, with very simple reaction kinetics or by using simplified yield correlations developed using experimental observations.

In this work, a first-principles model of the CTSL reactors have been developed and validated by comparing with the commercial operating data. The ebullated-bed DCL reactors are simulated as axially dispersed reactor (ADR) with recycle stream based on rigorous reaction kinetics, hydrodynamics and mass and heat balances. Other standard unit operations, including heaters, pumps and flash drums, are modeled using mass and energy conservations. The capital cost of the reactors is estimated based on the pilot plant data, while that of other equipment items is estimated using Aspen Process Economic Analyzer (APEA). The CTSL unit is optimally designed to minimize an annuitized operating cost that includes operating and capital costs along with the revenue earned by selling the products. To summarize, the presentation will include the following: (1) two configurations of the CTSL unit- with and without heat integration, (2) rigorous modeling of the EBRs, (3) systems level models of the CTSL unit, (4) capital and operating cost estimates, (5) sensitivity studies of the key operating and design parameters, and (6) process optimization.