A comparison of co-current and counter-current modes of operation for a dual-type industrial methanol reactor

In this paper, the dynamic behavior of a dual-type methanol reactor is investigated. For simulation purposed, a heterogeneous one-dimensional model has been developed. In the dual-type reactor system, a system with two-catalyst bed instead of one single catalyst bed is developed for methanol synthesis. In the first catalytic reactor, the synthesis gas is partly converted to methanol in a conventional water-cooled type reactor. In the second reactor, the reaction heat is used to preheat the feed gas to the first reactor. The continuously reduced temperature in this reactor provides increasing thermodynamic equilibrium potential. The proposed model was validated against measured daily process data of a methanol plant recorded for a period of 4 years and a good agreement was achieved. The validity of this model is also shown to be satisfactory for the investigation of the effect of co-current and counter-current flow pattern on performance of reactor. In the co-current mode, feed gas is entered into the tubes of the second reactor in the same direction with the reacting gas stream in shell side while in the counter-current mode the gas streams are in the opposite direction. Simulation results for both co-current mode and counter-current mode have been compared in terms of temperature, activity and methanol production rate. The results of this work show that the reactor in co-current mode operates with lower conversion but with longer catalyst lifetime in comparison with counter-current mode.