Introduction to Biomass Combustion

Combustion of biomass used to heat greenhouses.

Fire, or combustion of biomass, is arguably the oldest known and most widely used controllable energy source on earth. In recent years, rising costs of fossil fuels and the development of advanced equipment have made biomass combustion an economical, efficient, and practical energy source.

Principles of Combustion

Combustion is familiar to all of us, but many do not realize that it is essentially a chemical reaction. In the process of combustion, two ingredients (biomass and oxygen) are combined in a high temperature environment to form carbon dioxide, water vapor, and heat.
 

CH_1.44O_0.66 + 1.03 O₂ = 0.72 H₂O + CO₂ (+Heat)

 

Note: CH_1.44O_0.66 is the approximate chemical equation for the combustible portion of biomass.

 

The amount of heat that is produced varies depending on species, climate, and other factors, but it is generally about 20 Megajoules of energy per dry kilogram of biomass.
In order for combustion to be efficient and clean, the ingredients must be well mixed at the right temperatures for the right amount of time. Practically speaking, this means that you need the right amount of fuel, the right amount of air, and the right conditions.

Water content in biomass is an important factor when it comes to combustion. The best burning fuels are dry. However, biomass almost always includes some amount of moisture. For example, green wood chips are usually about 50% water and 50% dry matter. Fresh leaves from a plant can be as high as 95% moisture and 5% dry matter. Ideally, biomass should be no more than 20% moisture.

Feedstocks for Biomass Combustion

A feedstock is merely the fuel that will be burned for energy. While wood is the most common feedstock for biomass combustion, almost any plant material can be used as a combustion feedstock.

Processing Biomass for Combustion

Biomass can often benefit from a certain amount of processing to make it more suitable as a combustion fuel. This includes sizing, drying, and/or densification.

Utilizing Biomass as an Energy Source

The smoky fireplace of past generations is a far cry from the combustion equipment that is available today. While those old fireplaces are still used in some homes, high-efficiency biomass combustion requires carefully designed and operated equipment that works well with the available fuel. Depending on your needs, biomass combustion systems can produce hot air, hot water, steam, electricity, or a combination. To find out more about equipment, efficiency, and air quality from biomass combustion, see Using Combustion Heat for Energy.

For Additional Information about Biomass Combustion

• Heating with Wood series. Oklahoma State University Extension.
• Woody Biomass Properties
• Direct Firing. Technologies, Applications, Economics, and Environmental Impacts. Sun Grant BioWeb.

• An Introduction to Biomass Heat. Penn State Cooperative Extension.

Other articles in this Combustion Series:

• Biomass Feedstocks for Combustion
• How Much Heat Does BioFuel Have?
• Introduction to Biomass Combustion
• Processing Biomass for Combustion
• Shell Corn as a Fuel for Greenhouse Heat
• Using Combustion Heat for Energy
• Wood Heat for Greenhouses

• Primary Processing of Woody Biomass

Contributors to This Article

Author

• Daniel Ciolkosz, Extension Associate, Penn State

Peer Reviewer

• Sarah Ashton, Program Coordinator, Southern Regional Extension Forestry, University of Georgia
• Raymond Huhnke, Oklahoma State University, Associate Director of Sun Grant Initiative – South Central Region