Primary Gasification

A solid char product may also be produced, and may represent the bulk of the weight of the original coal. This type of coal being processed determines (to a large extent) the amount of char produced and the analysis of the gas product. 

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The primary gasification agent, which is typically a mixture of oxygen and steam, is injected toward the center of the circulation zone through a number of opposing injectors at only one level (compare Figure 9.8). Because of radial injection... 

Figure 9.3 Temperature distribution and velocity vectors at primary gasification agent nozzle level (two-dimensional (2D), 30 bar, 500 MW, South African (SAf) coal).

Secondary gasification involves gasification of the char from the primary gasifier, usually by reaction of the hot char and water vapor to produce carbon monoxide and hydrogen. 

Goal Processing to Synthetic Fuels and Other Products. The primary approaches to coal processing or coal conversion are thermal decomposition, including pyrolysis or carbonization (5,6), gasification (6), and Hquefaction by hydrogenation (6). The hydrogenation of coal is not currently practiced commercially. 

The primary applications for large-scale jetting fluidized beds are in the area of coal gasification as described by Yang et al. (1995), Kojima et al., (1995), and Tsuji and Uemaki (1994). Smaller scale applications are for fluidized bed coating and granulation to be discussed in Chapter 6. 

SASOL [Suid-Afrikaans Sintetiese Olie] Not a process but a large coal gasification complex in South Africa, operated by the South African Oil and Gas Corporation. It first operated in 1955 but took several years to be fully commissioned. A Lurgi fixed-bed gasification unit is used for the primary process. Downstream processes include the following ones, described under their respective names Aige, Fischer-Tropsch, Rectisol, Sulfohn, Synthol. 

Solid by-products of gasification and combustion processes are significantly different. The primary solid by-product of a low-temperature gasification process is char. Char consists of unreacted carbon and the mineral matter present in the gasifier feed. The most important and significant use of char is as a source of activated carbon. 

Coal gasification technologies can be classified according to the flow configuration of the gasifier unit. The primary configurations are ... 

Electrostatic filters have been used in many coal-fired power stations, and they have been used in some biomass combustion facilities. Their use in medium- or large-scale gasification systems is limited. Electrostatic filters are best suited for large-scale operation due to their physical size and cost, and the primary impediment to their use in current gasification systems is an economic one. 

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