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Biomass Fuels: Their Characteristics and Preparations

This version was saved 13 years, 6 months ago View current version Page history

Saved by jim mason
on November 14, 2009 at 11:45:59 pm

Key Properties of Biomass Relavent to Gasification:

Moisture Content

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

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.

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

from:

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 http://www.cedarcreek.umn.edu/biblio/fulltext/t2065.pdf.