Water Gas Shift Reactor Modelling and New Dimensionless Number for Thermal Management/Design of Isothermal Reactors

Abstract A new simplified modelling approach for using power law kinetics has been presented together with a methodology for modelling internal heat transfer inside the catalyst bed to a heat exchanger steam generator. The model has been validated and shown to be in good agreement with the performance of industrial scale water gas shift reactors. Furthermore, a case study has shown that isothermal shifting is able to reduce the catalyst volume compared to adiabatic shifting, however, a strong dependency upon the cooling density is observed. The here introduced rate optimization number (Ro) which compares the impact of temperature on the thermal driving force to the chemical driving force can help reactor designs to make effective use of the catalyst. For the water-gas-shift reaction, a value of -1 represents the optimum reaction rate. By designing the heat exchanger in the isothermal shift reactor in accordance with the Ro number a reduction of the required catalyst volume from initially 112.1 m3 (adiabatic reference case) to 54.9 m3 was possible; a reduction of 57.5%. The optimization with the Ro number has shown that an adiabatic inlet section is favorable and most of the cooling is needed after the adiabatic inlet length. The ideal temperature profile follows an almost linear temperature increase at the adiabatic inlet followed by an exponential decay along the reactor axis. Moreover, the application of the Ro number has shown to be highly accurate even under severe transport limitations.