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Handle ash and cinders easily

Excellent

Good

Fair

Source: Power from Coal: Special Report, Power, February 1974. With permission.

Source: Power from Coal: Special Report, Power, February 1974. With permission.

Unfortunately, because there are many examples of commercial equipment with more than one pattern of combustion air and fuel feed, disagreement is sometimes found in the literature over which type predominates in a given stoker application, which also leads to differences in system classification. For our discussion here, underfeed stokers include single- and multiple-retort stokers; overfeed stokers include chain grate, traveling grate, and water-cooled vibrating grate stokers; and spreader stokers are classified into several groups, depending on the type of grate selected: stationary, dumping, reciprocating, vibrating, traveling, or water-cooled vibrating grate. Some characteristics of the stokers and their fuel requirements and capacities are given in Tables 5-3 through 5-5. Figure 5-10 illustrates the working principles of the three groups of stokers [19].

Underfeed Stokers Underfeed stokers are used primarily for burning coal in small boilers serving relatively constant steam loads of less than 30,000 lb/hr [7]. Coal is introduced beneath the active fuel bed and is moved from a storage hopper by means of a screw or ram into a retort. As coal is fed into the retort, the force of the incoming fuel causes the coal to rise in the retort and spill over onto the fuel bed or grate surface on either side of the retort. No air is supplied in the retort proper; it comes through openings, called tuyeres, in the grate section adjoining the trough. Underfeed stokers

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