GEK Wiki / Biomass Fuels: Their Characteristics and Preparations
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Biomass Fuels: Their Characteristics and Preparations

Page history last edited by jim mason 13 years ago


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Fuel Preparation Techniques and Machines

Chippers, chunkers, loppers, splitters, shredders, disintegrators, etc

Densification Machines: Pelleting, Briquetting, Baling, etc.




Key Properties of Biomass Relevant to Gasification:


Moisture Content

Fuel inside the reactor should generally be below 20% moisture (dry basis).


Particle Size

Different gasifier designs can handle different sizes of fuel. The standard downdraft Imbert type reactor that ships with the GEK will work best with fuels in the range of 1/2" - 1.5". Wood pellets perform poorly with the stock GEK dimensions. Fluidized beds are often used for fine materials. New reactor types will extend the range of acceptable fuel sizes.


Fixed Carbon to Volatile Ratio

Volatiles produce tars during pyrolysis, fixed carbon produces char. In a gasifier, the tars can either be combusted with oxygen or thermally cracked. Char is needed for reduction. Gasifiers will generally operate better with more fixed carbon in the fuel.  Wood averages 20% fixed carbon, 80% volatiles.  This produces much more tar than is needed for combustion, thus we have to crack the excess.  Lower volatile content woods reduce the problem.  Using charcoal as fuel mostly eliminates it.


Void Space

The amount of void space in a fuel will impact proper combustion. More void space is generally better.


Bulk Density

Indicates the volume required to store a given mass of fuel.


Ash Content

Ash (mineral content) can lead to slagging. Specific minerals can reduce slagging temperatures (and therefore the likelihood that slagging will occur at a given temperature). Grasses are often high in silica.


Hazardous Compounds

Materials including municipal solid waste (MSW), biosolids (sludge), coal, and plastics can contain high levels of compounds including chlorine, sulfur and heavy metals. These materials require special consideration, testing, and handling and should not be used without professional consultation.




Characterizing Biomass

Biomass Proximate and Ultimate Analysis Composition for Common Biomass Types

Energy Density of Biomass and Other Fuels



Run Issues and Experience with Specific Fuels

Wood pellets as downdraft gasifier fuel

BioPlugs: Large pellets with plastic binder 

Rice Hulls and Straw



Growing and Using Biomass: Argiculture, Silviculture, and Integrated Agro-energy Systems

Biomass Yields


Grasslands and Praries:

Energy yields from biodiverse plantings are higher than from monocropped biomass energy. Other benefits, such as wildlife value may also be higher.

Graph showing Net Energy Balance of Different Biomass Energy Production Systems



Tillman, D., Jason, H., & Lehman, C. (2006). Carbon-Negative Biofuels from Low-Input High-Diversity Grassland Biomass. Science, 314, 1598-1600. Retrieved June 30, 2008, from



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