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HEATING VENTILATING AIR CONDITIONING GUIDE 1944 smaller classes, although the principle of operation is similar. A stoker of this type is illustrated in Fig. 7. The rear cleaning underfeed stoker is usually of the multiple retort design and is used in some of the largest industrial plants and central power stations. Zoned air control has been applied on these stokers,^both longitudinally and transversely of the grate surface. CHAPTER 10. AUTOMATIC FUEL BURNINC EQUIPMENT Feed screw--/ Fig. 4. Stoker-Fired Winter Air Conditioning Unit Fig. 5. Underfeed Screw Stoker, Hopper Type, Class'2, 3 or 4 The overfeed flat grate stoker is represented by the various chain--or traveling-grate stokers. A typical trayeling-grate stoker is illustrated in Fig. 8. Another distinct type of overfeed flat-grate stoker is the spreader (Figs. 9 and 10) type in which coal is distributed either by rotating paddles or by air over the entire grate surface. This type of stoker is adapted to.a wide range of fuels and has a wide application on small sized fuels and on fuels such as lignites, high-ash coals, and coke breeze. The overfeed inclined-grate stoker operates on the same general com bustion principle as the flat-grate stoker, the main difference being that rocking grates, set on an incline, are provided in the former to advance the fuel during combustion. Combustion Process In anthracite stokers of the Class 1 underfeed type, burning takes place entirely within the stoker retort. The refuse of combustion spills 204 COAL COAL HOPPER AGITATOR COAL'. distribution , adjustment^ - CONNECTING ROD COAL FEED . ADJUSTMENT Fig. 7. Underfeed Side Cleaning Stoker 205