Enhancing the Potential of Methane Combined Reforming for Methanol Production via Partial CO 2 Hydrogenation

Abstract

A process for methanol production from high CO2 content natural gas (50 - 60%) is presented and analyzed in technical and economic terms. A conceptual design is proposed on the basis of partial hydrogenation of the feed by the RWGS reaction, prior to a combined reforming operation. Both the RWGS reactor and a Lurgi-type methanol reactor were rigorously simulated via gPROMS by taking into account kinetic expressions of commercial catalysts. The mentioned reactors, the reformer and flash separator were all simulated as separate modules and interconnected as a whole plant. The effect of the CO2 content, the feed fraction to be hydrogenated, the influence of the H2/CO ratio and the methanol recycle ratio on the total CO2 conversion, the H2 consumption, the methanol reactor size and the CO2 emissions were investigated. It was found that the hydrogenation of 40% of a feed containing 60% CO2 by using a H2/CO2 ratio of 1.7 followed by a combined reforming furnace leads to a syngas that has an optimum composition for methanol production. An economic analysis demonstrated that the proposed process entails lower investment costs partially due to the smaller reformer size, as compared to a methanol plant of similar production based on CH4 steam reforming. On the other hand, the operating costs are higher mainly due to the cost of H2. Consequently, a negative NPV value is obtained under present market prices. However, for a feed containing 50% CO2 the proposed process would be economically viable for a H2 price of 2.4 U$S/kg or a methanol price of 500 U$S/ton. Slightly higher price variations are necessary to obtain a financially feasible project for a feed containing 60% CO2. Nevertheless, the reduced H2 demand has lower economic incidence, as compared to a methanol plant based on CO2 and H2 as raw materials.