Gasification Theory and Modeling of Gasifiers
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This chapter introduces the basics of the gasification process through a discussion of the reactions involved and the kinetics of the reactions with specific reference to biomass. It also explains how this knowledge can be used to develop a mathematical model of the gasification process. The design and operation of a gasifier requires an understanding of the gasification process and how its design, feedstock, and operating parameters influence the performance of the plant. A good comprehension of the basic reactions is fundamental to the planning, design, operation, troubleshooting, and process improvement of a gasification plant, as is learning the alphabet to read a book. Gasification is the conversion of solid or liquid feedstock into useful and convenient gaseous fuel or chemical feedstock that can be burned to release energy or used for production of value-added chemicals. Gasification and combustion are two closely related thermochemical processes, but there is an important difference between them. Gasification packs energy into chemical bonds in the product gas; combustion breaks those bonds to release the energy. The gasification process adds hydrogen to and strips carbon away from the feedstock to produce gases with a higher hydrogen to carbon (H/C) ratio, while combustion oxidizes the hydrogen and carbon into water and carbon dioxide, respectively. Gasifying agents react with solid carbon and heavier hydrocarbons to convert them into low-molecular-weight gases like CO and H 2 . The main gasifying agents used for gasification are oxygen, steam, and air.