Plantwide Control of a Hybrid Integrated Gasification Combined Cycle/Methanol Plant

The coupling of an integrated gasification combined cycle (IGCC) electric power plant with a hydrogen-consuming chemical (methanol) plant can handle swings in electric power demand. Hydrogen gas from the combustion turbine and synthesis gas from the gasifier can be diverted to a methanol plant for the production of an easily stored, hydrogen-consuming liquid product. This paper extends previous work on dynamic studies of a gasifier and downstream units of an IGCC to explore the steady-state economic design, control, and successful turndown of the methanol plant. The plantwide control structure and interaction among units are also shown. The methanol plant is sized to reduce the power generation from an IGCC by 50%, producing a high-purity methanol stream of 99.5 mol %. Regulatory control structures are designed and play a significant role for the successful turndown of the methanol plant to 20% capacity. The exit temperature of the cooled tubular methanol reactor is controlled instead of a peak temperature within the reactor. During times of low capacity and minimum vapor rate within the distillation column, tray temperature is controlled by recycling a portion of the distillate and bottoms back upstream so that temperature can be effectively controlled by manipulating feed flow rate. The gasifier feed is held constant. The product hydrogen from the IGCC is fed to the combustion turbine as required by electric power demand. Synthesis gas fed into the methanol plant maintains pressure of the hydrogen stream. Make-up hydrogen is also fed to the methanol plant to maintain reaction stoichiometry by controlling the carbon monoxide composition of the recycle gas in the methanol plant.