Optimization of compact multitubular fixed-bed reactors for the methanol synthesis loaded with highly conductive structured catalysts

摘要

By computer simulation, we analyze the performances of a compact (2 meter-long) externally-cooled multitubular reactor for the methanol synthesis loaded with highly conductive structured catalysts, namely washcoated copper honeycomb monoliths and copper open-cell foams. Such a reactor is simulated as inserted in a synthesis loop including an ideal condenser, a recycle and a purge stream. Parametric analysis of the catalyst volumetric fraction points out that compact methanol structured reactors can be operated even with loadings as low as 0.30 m~3 catalyst/m~3 tube, but they would grant lower CO_x conversions per pass, resulting in higher recycle ratios. The excellent radial heat transfer performances of the structured reactors enable however the catalyst intrinsic activity and/or the coolant temperature to be properly optimized to compensate for the lower catalyst loads, eventually granting lower recycle ratios (i.e. keeping CO_x conversion per pass close to the equilibrium value) as well as limited hot-spot temperatures. Furthermore, reactor tubes with larger diameters can be adopted in compact conductive structured reactors loaded with limited catalyst volumetric fractions, thus allowing for reduction of investment costs. In particular, we show that, thanks also to the efficient radial heat transfer, the greater thermal loads generated in the configurations with larger tubes can be effectively managed to enhance the reactor performances.