Here's a detailed description by NREL of a June 2000 project of a low-pressure, indirect gasification system in Vermont, USA. This system does not use oxygen but steam, which erduces the cost of operation.
The process mixes wood chips with very hot sand at a temperature of about 830°C, or 1500°F, in a steel tank called a gasifier. The hot sand breaks down the wood and, helped by added steam, causes the resulting carbon, hydrogen, and oxygen to form into combustible gases. The gases and sand leave the gasifier and the gas is cleaned for use as fuel. This fuel burns cleanly with a heat content of about 500 Btu per cubic foot. This gas can be used directly in unmodified gas turbines.
The Battelle gasifier differs from others producing medium-heat content gas because it does not use pure oxygen; therefore, it costs much less to build and operate. Steam replaces oxygen in this modern process. The Vermont gasifier processes biomass much more quickly than other gasifiers, which means that smaller, less costly
equipment is needed for a given amount of biomass. This, in combination with low-pressure operation, further reduces its construction cost.
Full details here
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