Document Gm1n3jxXRzQQJR8ZJ9M7KxdOV

352 CHAPTER 17 1949 Guide - Automatic Fuel Burning Equipment 353- Fro. 6. Underfeed Screw Stoker, Bin Type, Class 2, 3 or 4 COAL COAL HOPPER AGITATOR COAL PLUNGER Fig. 7. Underfeed Side .Cleaning Stoker Fig: 51 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 pOrdsity of'the coke formed will vary'according to the size and character^. istics of the 6oal.- While some of the ash fuses into1 ^Articles 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' td the higher "temperatures surrounding the retort fuses into a ' clinker.^-The *r Fig. 8. Overfeed Traveling-Grate Stoker ;' 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.: