Glossary of Terms


Field crop residues

Residues derived from field crops, such as small-grain cereals (wheat, barley, oat, rye, and rice), maize and oil crops (sunflower and rapeseed). These residues are incorporated into the soil, burned in the field, or collected and used for various purposes (such as animal feed, bedding, and mushroom cultivation).

Fly ash

Airborne ash carried through the combustion chamber by the hot exhaust gases, and typically deposited in the passages of the boiler heat exchanger.


The primary combustion chamber of a biomass burner. The term also refers to warm-air heating appliances. Gasification: The pyrolysis reaction in which heated biomass is converted to combustible gases in the primary combustion zone. Also refers to the conversion of char to combustible gases in the absence of oxygen and to the overall process of converting biomass, in an oxygen-starved environment, to combustible medium-Btu-content gases that are not immediately burned, but are cooled and cleaned to be used in a variety of ways.


Green biomass fuel

Biomass fuel that has not been significantly dried, with approximately the same moisture content as at harvest.


Heat exchanger

A device that transfers heat from one fluid stream to another. The most common heat exchanger in biomass combustion systems is the boiler, which transfers heat from the hot combustion gases to boiler water. Heat load: The demand for heat of a building at any one time. Peak heat load refers to the maximum annual demand for heat, and is used in sizing heating plants.

Heat transfer medium

A fluid (either water, steam, or air) that carries heat from the combustion system to the point of use.

Heating consumption

The annual total amount of heat a building requires. Can be expressed in energy units (kWh) or fuel units (tons of biomass).

Hogged fuel

Biomass fuel produced by grinding up various forms of wood and bark, possibly mixed with sawdust. Often refers to a variable low-quality fuel. If produced from clean, high-quality dry scrap, can be a very high-quality fuel. Logging residues: woody biomass byproducts (branches, treetops and leaves or needles) created during the harvesting of commercial timber. They are usually left at the logging site, both because of the high cost of collection and because they help to maintain the soil.