Design and Control of a Methanol Reactor/Column Process

Methanol is one of the prime candidates for providing an alternative to petroleum-based liquid transportation fuels. It can be made from any renewable biomass hydrocarbon source by partial oxidation in an oxygen-blown gasifier to produce synthesis gas, which is then converted into methanol. The purpose of this paper is to develop the economically optimum design of a methanol reactor/distillation column system with three gas recycle streams to produce high-purity methanol from synthesis gas. The economics consider capital costs, energy costs, the value of the methanol product, and the heating value of a vent stream that is necessary for purging off inert components entering in the feed. A plantwide control structure is developed that is capable of effectively handling large disturbances in the production rate and synthesis gas composition. The unique features of this control scheme are a lack of control of pressure in the reactor/recycle gas loop and a high-pressure override controller to handle stoichiometric imbalances in the composition of the synthesis gas feed.