Document 71kzenanGQvLXEjO7RVmwXMZe

358 CHAPTER 15 1953 Guide Automatic Fuel Burning Equipment 359 Fig. 3. Undebfeed Anthracite Stoker with Automatic Ash Removal, Bin Type Fig. 6. Underfeed Screw Stoker, Bin Type, Class 2, 3 or 4 COAL COAL HOPPER AGITATOR Feed screw- Fig. 4. Stoker-Fired Winter Air Conditioning Unit COAL PLUNGER Fig. 7. Underfeed Side Cleaning Stoker Fig. 5. Underfeed Screw Stoker, Hopper Type, Class 2, 3 or 4 A rapid evolution of the combustible volatile matter occurs during and directly after the plastic stage. The distillation of volatile matter con tinues above the plastic zone where the coal is coked. The strength and porosity of the coke formed will vary according to the size and character istics of the coal. While some of the ash fuses into particles on the surface of the coke as it is released, most of it remains on the hearth or grates and, as this ash layer becomes thicker with time, that portion exposed to the higher temperatures surrounding the retort fuses into a clinker. The temperature in the fuel bed, the chemical composition and homogeneity of the ash, and the time of heating govern the degree of fusion. Most bituminous coal stokers of Classes 1, 2, 3 and 4 require manual removal of the ash in clinker form.