Ethanol from Wood Chips (Gasification and Mixed Alcohols Synthesis)

The process under analysis comprises four major sections: (1) Feedstock Gasification; (2) Syngas Treatment; (3) Alcohol Synthesis and Purification; and (4) Power Generation.

Feedstock Gasification. Woodchips particles are grounded in a hammer mill for size reduction, then dried by contact with hot flue gas in rotary dryers. The dry feedstock is fed to a Gasifier along with oxygen, steam, and olivine, yielding synthesis gas (syngas), char, and ash. Virtually all olivine and char are removed from the gasifier outlet in two-stage cyclone separators, while the syngas is routed to the Tar reformer.

Syngas Treatment. In the Tar reformer, hydrocarbons are converted to additional CO and H2. Recycled CO2 is also fed to this reactor to be converted to CO. The hot syngas is routed to Quenching, where it is cooled and scrubbed with water, removing impurities. The quenched syngas is sent to the Acid Gases Scrubber, which employs a monoethanolamine solution to remove H2S and CO2. The syngas is routed to a multi-stage compressor, while the acid gases are discarted. CO2 is partially recycled upstream, with its remainder being vented to the atmosphere.

Alcohol Synthesis and Purification. The purified syngas is compressed, mixed with recycled methanol, and fed to the Alcohol Synthesis Reactor, where it is converted to linear alcohols. The reactor outlet is degassed and dried: unreacted syngas is recovered, while water is removed from the product stream by adsorption in molecular sieves. The dried alcohols are then separated in two columns, yielding ethanol and mixed alcohols product streams that are condensed and sent to storage, and a methanol stream that is used to wash water off of the molecular sieves in the degassing and drying area, which is recycled to the Reactor.