CFD MODELING OF MICROCHANNEL REACTOR FOR DIRECT DIMETHYL ETHER SYNTHESIS FROM SYNGAS

Abstract

The present work entitled CFD Modeling of Microchannel Reactor for direct Dimethyl Ether synthesis from syngas is based on the modeling of the microchannel porous bed reactor. The experimental set up of 1-ladipour and Sohrabi is modeled using FLUENT 14.5 and simulated for certain operating conditions. The geometry used in the modeling is designed in GAMBIT. The geometry is tested to give grid independent results and flow in the microchannel is validated with data from literature. The kinetics used in the modeling are taken from literature. The transient simulations for the present model are run at operating conditions of 250 °C temperature and 8 bar pressure. The composition of the reactant in the feed streams are 0.32 CO, 0.64 H2 and 0.04 CO2. All reactions are occurred in the gaseous phase. A UDF is also written to incorporate the reaction rate expression of direct DME synthesis. The partial pressure at the outlet of the reactor are validated with experimental data. The conversion of CO at reactor outlet is coming out with a maximum error of 20% upto a time of 100 mm, but as the flow develops the error reduced to 3%. The results shows that initially the methanol formation reaction is dominant and as methanol reaches its maximum value methanol dehydration reaction takes over resulting in an increase in DME concentration at the outlet of the reactor. After time 300 mm, DME formation and CO conversion become constant and steady state is reached. The concentration profile of DME, CO and H2 in the reactor are analyzed. Gibbs Free Energy reactor is used to optimize the operating condition, it is observed that the pressure affects DME synthesis. For Gibbs Free Energy reactor analysis ASPEN is used and the conversion of CO on the basis of minimum free energy is observed for different pressures at a constant temperature in the reactor. the results from the ASPEN shows that pressure has positive effect on the conversion of CO in direct DME synthesis. At 250 °C temperature, conversion increase from 88.8% to 95.3% when pressure is varied from 2 MPa to 5 MPa respectively. The optimal pressure value(5 MPa) from ASPEN is used in present CFD to simulate the process at at 5 MPa pressure and 250 °C temperature, and the conversion of CO was found to be 80%.