Biopower Technologies May Vary by Region
Technologies for biobased heat and power, and the resulting economic and environmental benefits, may vary because of the regional availability of resources and needs. In Maine, for instance, the Manomet Center for Conservation Sciences has published a report that finds burning of whole trees for electricity production may not be as carbon neutral as once thought and that it will take 40 years for the carbon balance to catch up.
This study does, however, conclude that trees used for combined heat and power (CHP) have a much more positive effect on efficiency and carbon balance. The Manomet study makes assumptions about the use of forest assets that can tend to make the projections less favorable for trees used for heat and power. This study is also an example of the regional differences in application of biomass for heat and power and the assumptions that must be made to project the efficacy of individual biomass technologies.
In contrast to Maine, the type of biomass applications you would find in the Central Plains states of the United States are quite different. In the Plains states, agriculture residues and energy crops would be the primary source of biomass for use in heat and power generation.
Biomass feed systems, burner retrofits and emissions control will be different for agricultural residues or energy crops compared to the use of trees.
Recent studies at the Energy & Environmental Research Center have shown that cocombusting woody biomass with coal has the potential to remediate some of the fouling issues in the furnace, thereby enhancing the overall plant efficiency, but this will depend on the type of woody biomass and the combustion conditions.
Cofiring sawdust can reduce the amount of inorganic material or ash that will be available in the furnace to impact heat-transfer surfaces and reduce the cause of fouling and slagging issues, while cofiring bark or hog fuel with inherent higher inorganic ash content may not reduce fouling and slagging issues.
For agricultural residues such as wheat straw, cofiring can also be problematic because of very small silica phytoliths that are contained in the plant material to give rigidity. These phytoliths are an amouphous form of silica, can have low melting temperatures, and will mix with other inorganic elements in the ash to produce sticky ash material that will adhere to heat-transfer surfaces reducing thermal efficiency of the furnace. This can be overcome by adjusting the design of the furnace and the way the straw is combusted.
EERC pilot testing shows that it is imperative to match technology applications with resources to properly utilize the vast biomass resources available in the United States to offset our fossil fuel use and reduce overall carbon emissions.
In the end, smart planning, matching biomass technologies with biomass resources, and learning from the experience of others will ensure the continued growth of biomass and U.S. energy security while reducing carbon emissions.
Author: Bruce Folkedahl
Senior Research Manager, Energy & Environmental Research Center