Production of high-purity methanol from hydrocarbon feedstocks such as natural gas, process offgases and LPG up to heavy naphtha. The process uses conventional steam-reforming synthesis gas generation and a low-pressure methanol synthesis loop technology. It is optimized with respect to low energy consumption and maximum reliability. The largest single-train plant built by Uhde has a nameplate capacity of 1,250 mtpd.
The methanol plant consists of the process steps: feed purification, steam reforming, syngas compression, methanol synthesis and crude methanol distillation. The feed is desulfurized and mixed with process steam before entering the steam reformer. This steam reformer is a top-fired box type furnace with a cold outlet header system developed
by Uhde. The reforming reaction occurs over a nickel catalyst. Outlet-reformed gas is a mixture of H2, CO, CO2 and residual methane. It is cooled from approximately 880°C to ambient temperature. Most of the heat from the synthesis gas is recovered by steam generation, BFW preheating, heating of crude methanol distillation and demineralized water preheating.
Also, heat from the flue gas is recovered by feed/feed-steam preheating, steam generation and superheating as well as combustion air preheating. After final cooling, the synthesis gas is compressed to the synthesis pressure, which ranges from 30 –100 bara (depending on plant capacity) before entering the synthesis loop.
The synthesis loop consists of a recycle compressor, feed/effluent exchanger, methanol reactor, final cooler and crude methanol separator. Uhde’s methanol reactor is an isothermal tubular reactor with a copper catalyst contained in vertical tubes and boiling water on the shell side. The heat of methanol reaction is removed by partial evaporation of the boiler feedwater, thus generating 1–1.4 metric tons of MP steam per metric ton of methanol. Advantages of this reactor type are low byproduct formation due to almost isothermal reaction conditions, high level heat of reaction recovery, and easy temperature control by regulating steam pressure. To avoid inert buildup in the loop, a purge is withdrawn from the recycle gas and is used as fuel for the reformer. Crude methanol that is condensed downstream of the methanol reactor is separated from unreacted gas in the separator and routed via an expansion drum to the crude methanol distillation. Water and small amount of byproducts formed in the synthesis and contained in the crude methanol are removed by an energy-saving three-column distillation system.
Licensor: Uhde GmbH is a licensee of Johnson Matthey Catalysts’ Low-Pressure Methanol (LPM) Process