Logging residues; Trees, shrubs, and wood residues; Sawdust, bark etc.
Biomass is biological organic matter but is more often used to refer to (i) energy crops grown specifically to be used as fuel, such as fast-growing trees or switch grass, (ii) agricultural residues and by-products, such as straw, sugarcane fiber, and rice hulls, and (iii) residues from forestry, construction, and other wood-processing industries.
Many different types of biomass can be grown for the express purpose of energy production (Table B-15).
Table B-15 Sources, processing options, and uses of biomass-derived products*.
| Resources | Collection | Conversion | End products |
|---|---|---|---|
| Stage 1 | Stage 2 | Stage 3 | Stage 4 |
| Agricultural crops | |||
| Energy crops | |||
| Forestry | |||
| Herbaceous plants | |||
| Oil-bearing plants | |||
| Wastes | |||
| Harvesting | |||
| Handling | |||
| Pretreatment | |||
| Biochemical processes | |||
| Chemical processes | |||
| Physical processes | |||
| Thermochemical | |||
| Biodiesel | |||
| Electrical power | |||
| Heat | |||
| Solid fuels | |||
| Transportation fuels | |||
| *The sub-categories are listed alphabetically and are not listed in an order of preference for processing. The choice of processing preference is dependent upon the type of biomass and the desired product. | |||
Crops that have been used for energy include sugar cane, corn, sugar beets, grains, elephant grass, kelp (seaweed), and many others. There are two main factors which determine whether a crop is suitable for energy use. Good energy crops have a high yield of dry material per unit of land (dry tonnes/hectare). A high yield reduces land requirements and lowers the cost of producing energy from biomass. Similarly, the amount of energy which can be produced from a biomass crop must be less than the amount of energy required to grow the crop. In some circumstances like the heavily mechanized corn farms in the U.S. Midwest, the amount of ethanol which can be recovered from the corn is barely larger than the fuel required for tractors, fertilizers, and processing.
The components of biomass include triglycerides, sterols, alkaloids, resins, terpenes, terpenoids, and waxes. This includes everything from primary sources of crops and residues harvested/collected directly from the land to secondary sources such as sawmill residuals, to tertiary sources of post-consumer residuals that often end up in landfills. A fourth source, although not usually categorized as such, includes the gases that result from anaerobic digestion of animal manures or organic materials in landfills.
Primary biomass is produced directly by photosynthesis and includes all terrestrial plants now used for food, feed, fiber, and fuel wood. All plants in natural and conservation areas (as well as algae and other aquatic plants growing in ponds, lakes, oceans, or artificial ponds and bioreactors) are also considered primary biomass. However, only a small portion of the primary biomass produced will ever be harvested as feedstock material for the production of bioenergy and by-products.
Biomass feedstocks and fuels exhibit a wide range of physical and chemical properties (Table B-16).
Table B-16 Selected properties of representative biomass materials.
| Mass %, dry | Wood | Grain* | Municipal Solid Waste** | Animal Wastes (Manure) |
|---|
