Chapter 9 – Biomass Gasification: Process Overview, History, and Development (pp. 167-180)
Authors: (Daniel T. Howe, Pacific Northwest National Labortatory, Richland, WA, USA) | |
Abstract: The current unsustainable use trends of petrochemical fuels has increased the demand for renewable energy alternatives, and thermochemical processes such as gasification will be required to meet these demands. Gasification is a process that involves the high-temperature partial oxidation of carbon-containing fuels such as lignocellulosic biomass to produce a product gas consisting of hydrogen, carbon monoxide, carbon dioxide, methane, and condensable aromatic liquids known as tars. The non-condensable product gas can be either purified into synthesis gas, a mixture of hydrogen and carbon monoxide used in Fischer-Tropsch synthesis of gasoline or diesel fuel, or sent to gas engines for the generation of heat and electricity. Gasification has been in use for over 180 years, with coal being the primary feedstock. Over the course of its development gasification technology has resulted in three general types of reactors: moving bed gasifiers, fluidized bed gasifiers, and entrained bed gasifiers. Moving bed gasifiers employ a fixed bed of fuel that moves downward under gravity while contacting an oxidant in either counter-current or co-current flow. Fluidized bed gasifiers use a bubbling fluidized bed of inert particles as a heat transfer medium while the oxidant serves as the source of fluidization. Entrained flow gasifiers use a dense suspension of fine solid particles in the oxidant to create a high-temperature, high-throughput system. The choice of a specific type of gasifier is determined by the end use of the gas as well as engineering constraints. While the use of biomass in gasifiers is a relatively new phenomenon, a number of success stories do exist. |