A typical biomass energy system comprises farming, collection, transportation, preparation, storage, feeding, and conversion. This is followed by transmission of the energy produced to the point of use. The concern here is with the handling of biomass upstream of the conversion system—that is, a gasifier in the present context. Biomass farming is a subject by itself and is beyond the scope of this chapter.

Biomass fuel can be procured from the following sources:

• Energy crop or forestry

• Ligno-cellulose wastes that are from forestry, agriculture, wood, or other industries

• Carbohydrates such as fat, oil, and other wastes

Chemicals

Pulp mill/chemical plant

FIGURE 8.1 Biomass is used for the production of energy or for commercial products such as paper or chemicals.

Biomass has two major (Figure 8.1) applications: (1) energy production through gasification or combustion, and (2) production of chemicals and fiber-based items (e. g., paper).

The collection methods for biomass vary depending on its type and source. Forest residues are a typical ligno-cellulose biomass used in gasification plants. They are collected by various pieces of equipment and transported to the gas­ification plant by special trucks (or rail cars in some cases). There, the biomass is received, temporarily stored, and pretreated as needed. Sometimes the plant owner purchases prepared biomass to avoid the cost of onsite pretreatment. The treated biomass is placed in storage bins located in line with the feeder, which feeds it into the gasifier at the required rate.

Biomass typically contains only a small amount of ash, but it is often mixed with undesirable foreign materials. These materials require an elaborate system for separation. If the plant uses oxygen for gasification, it needs an air — separation unit for oxygen production. If it uses steam, a steam generator is necessary. Thus, a biomass plant could involve several auxiliary units. The capacity of each of these units and the selection of equipment depend on a large number of factors. These are beyond the scope of this chapter.

Forestry and agriculture are two major sources of biomass. In forestry, large trees are cut, logged, and transported to the market. The logging process involves delimbing, and taking out the large-diameter tree trunks as logs. The processes involved in biomass harvesting, such as delimbing, deburking, and chipping, produce a large amount of woody residue, all of which constitutes a major part of the forest residue. The entire operation involves chopping the tree into chips and then using those chips to make fuels or feedstock for pulp industries.