WHAT IS GASIFICATION?
Gasification is a unique process that transforms a carbon-based material, such as MSW or biomass, into other forms of energy without actually burning it. Instead, gasification converts the solid and liquid waste materials into a gas through a chemical reaction. This reaction combines those carbon-based materials (known as feedstocks) with small amounts of air or oxygen (but not enough to burn the materials), breaking them down into simple molecules, primarily a mixture of carbon monoxide and hydrogen.
What’s produced is a synthesis gas (syngas) that can be converted into electricity and valuable products. With gasification, MSW and wastes are no longer useless, but they become feedstocks for a gasifier. Instead of paying to dispose of and manage the waste for years in a landfill, using it as a feedstock for gasification reduces disposal costs and landfill space, and converts those wastes into valuable electricity, fuels, chemicals or fertilizers.
FEEDSTOCK
Gasifiers capture the remaining “value” from a variety of MSW streams Feedstocks can include wood waste (sawdust and bark), crops, agricultural waste (corn stalks), wastewater treatment plant biosolids, MSW, animal wastes (stall wastes) and blends of the various feedstocks. Generally, the feedstock requires some pre-processing to remove the inorganic materials (such as metals and glass) that cannot be gasified. In addition, the MSW is typically shredded or ground into very small particles as well as dried before being fed into the gasifier.
GASIFIER
The feedstock is fed into the gasifier along with a controlled amount of air or oxygen (and steam for some gasifiers). The temperatures in a gasifier for MSW typically range from 1,100 to 1,800ºF (600-1,000ºC). Plasma gasifiers operate at higher temperatures and are discussed later in this brochure.
SYNGAS CLEANUP
Many downstream processes require that the syngas be cleaned of trace levels of impurities. Trace minerals, particulates, sulfur compounds, mercury and unconverted carbon can be removed to very low levels using processes common to the chemical and refining industries. More than 95% of the mercury can be removed from syngas using commercially-available activated carbon beds.
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WHAT IS GASIFICATION USED FOR?
Gasification has been used worldwide on a commercial scale for making “town gas” from coal for heating, lighting and cooking for over 200 years. It has been used for more than 80 years by the chemical, refining and fertilizer industries and for more than 35 years by the electric power industry. It is currently playing an important role in meeting energy needs around the world, using a wide range of feedstocks that include coal, petroleum coke, and biomass. Gasification is now being adapted for smaller-scale applications to solve the problem of waste disposal and to extract valuable energy from waste.
