Biomass includes a wide range of materials, including energy crops such as switch grass and miscanthus, agricultural sources such as corn husks, wood pellets, lumbering and timbering wastes, yard wastes, construction and demolition waste, and biosolids (treated sewage sludge). Gasification can be used to convert biomass into syngas.
Biomass gasification plants differ in several aspects from the large-scale gasification processes typically used in major industrial facilities such as power plants, refineries, and chemical plants.
Biomass usually contains a high percentage of moisture (along with carbohydrates and sugars). The presence of high levels of moisture in the biomass reduces the temperature inside the gasifier, which then reduces the efficiency of the gasifier. Therefore, many biomass gasification technologies require that the biomass be dried to reduce the moisture content prior to feeding into the gasifier.
Biomass can come in a range of sizes. In many biomass gasification systems, the biomass must be processed to a uniform size or shape to feed into the gasifier at a consistent rate and to ensure that as much of the biomass is gasified as possible.
Most biomass gasification systems use air instead of oxygen for the gasification reactions (which is typically used in large-scale industrial and power gasification plants). Gasifiers that use oxygen require an air separation unit to provide the gaseous/liquid oxygen; this is usually not cost-effective at the smaller scales used in biomass gasification plants. Air-blown gasifiers use the oxygen in the air for the gasification reactions.
Benefits of Biomass Gasification:
- Converting what would otherwise be a waste product into high value products
- Reduced need for landfill space for disposal of solid wastes
- Decreased methane emissions from landfills
- Reduced risk of groundwater contamination from landfills
- Production of ethanol from non-food sources