Co-Optimization of Design and Energy Economics of a Multi-Functional Catalytic Reactor for Combined Water–Gas Shift and COS Hydrolysis

A model-based methodological framework is presented for optimization of catalytic water–gas shift (WGS) and COS hydrolysis reactions that occur during the conditioning of syngas derived from carbonaceous fuels, for 100 metric tonnes/day methanol production. A 1D + 1D model is used to simulate a conventional system of two parallel fixed-bed reactors, and the system is optimized using the multiobjective NSGA-II algorithm to achieve the desired CO conversion (40%) while maximizing the COS conversion. Pareto-optimal fronts involving decision variables such as feed split in each reactor, operating temperature, catalyst particle diameter, and quantity are obtained. Design conditions required to attain low deviation from the desired CO conversion result in a lower COS conversion. Further, the total COS conversion is predominantly dependent on the design of the WGS reactor. A multifunctional reactor is then optimized, and the required CO and COS conversions could be achieved in the optimized single reactor. Reactor designs with low feed temperatures (220–280 °C) and high molar ratio of steam and CO (>0.95) result in high COS conversions, and the former is attributed to equilibrium limitations. Techno-economic optimization of the multifunctional reactor is further performed wherein the reactor and the associated heat exchanger network are optimized simultaneously, in contrast to the conventional sequential optimization. It is shown that higher feed temperatures (283–305 °C) are preferable from the perspective of heat integration and could eliminate the need for hot utility. While a high steam-to-CO ratio (∼1) results in high COS conversion, it also results in high operating costs. The multifunctional reactor is found to yield performance comparable to that of the conventional system, albeit with a lower total annualized cost.