A typical biomass gasification plant comprises a large number of process units, of which the biomass-handling unit is the most important. Unlike coal-fired boiler plants, an ash-handling system is not a major component of a biomass gasification plant because biomass contains a relatively small amount of ash. Normally it does not produce a large volume of spent catalysts or sorbents. Transportation, feed preparation, and feeding are more important for biomass than they are for coal — or oil-gas-fired units.

The biomass-handling system can be broadly classified into the following components:

• Receiving

• Storage and screening

• Feed preparation

• Conveying

• Feeding

The design of the handling system is very similar to that of a biomass-fired steam plant. Figure 8.2 illustrates the layout of a typical plant showing receiv­ing, screening, storage, and conveying.

Major considerations for the design of feeding and handling systems are transportation, sealing, and injection. The feed should be transported smoothly

from the temporary storage to the feed system, which must be sealed against the gasifier’s pressure and temperature. The fuel is then injected into the gas­ifier. Metering or measurement of the fuel feed rate is an important aspect of the feed system, as it controls the entire process.

The following subsections discuss the individual components of a solids — handling system for biomass. They assume the biomass to be solid, although some biomass, such as sewage sludge, is in slurry or semisolid form.