Hydrogen from biomass for power

Published: 14 September 2005  01:19 PM
Source: Process Engineering

According to Eckhard Dinjus of the Institute for Technical Chemistry in Karlsruhe, Germany, biomass could also be a source of hydrogen for the next generation of fuel cell-based power plants.

Dinjus and his colleagues have worked out two methods of generating hydrogen from waste wood — one for dry material, and one for wet, where the moisture content is above 70%.

For dry wood, Dinjus uses a two-step process. First, the wood undergoes a fast pyrolysis at around 500°C, in small, compact plants to produce a stable slurry of oil and char which can be stored or transported.

The researchers have developed a twin-screw reactor, a type of mechanised fluidised reactor that does not require a fluidising gas, which allows very fast and effective pyrolysis. Dinjus believes that several of these plants — maybe several dozen — located at sources of biomass, would produce the feed for a central gasifier.

The slurry is fed into a central entrained-flow gasifier, where it is treated with heat and oxygen to produce synthesis gas (syngas), a mixture of carbon monoxide and hydrogen.

For wet biomass, conversion can be done in a single step, using a supercritical water gasification process. Slurried biomass is treated with supercritical steam at 300bar and 600°C, which converts it directly into hydrogen and carbon dioxide; a carbon dioxide scrubber can be incorporated into this system, so that it produces fairly pure, high-pressure hydrogen, Dinjus says.

The team has built a 150kg/hr pilot plant to demonstrate the feasibility of the system, he says, and results are so far extremely promising.

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