Document 3NkLrEd9w5G493D0dwy6mEKVO

HEATINC VENTILATING AIR CONDITIONING CUIDE 1943 CLASSIFICATION OF STOKERS ACCORDING TO CAPACITY Stokers may be classified according to their capacity or coal feeding rates. The following classification has been made by the U. S. Department of Commerce, in cooperation with the Stoker Manufacturers Association, Class 1. Capacity under 61 lb of coal per hour. Class 2. Capacity 61 to 100 lb of coal per hour. Class 3. Capacity 101 to 300 lb of coal per hour. Class 4. Capacity 300 to 1200 lb of coal per hour. Class 5. Capacity 1200 lb of coal per hour and over. Class 1 Stokers These stokers are used primarily for home heating and are, therefore, designed for quiet, automatic operation. Simple, trouble-free construc- . Fig. 5. Underfeed Stoker, Hopper Type; Class 1 CHAPTER 10. AUTOMATIC FUEL BURNING EQUIPMENT Units are available in either the hopper type, as shown in Fig. 5, or. in the type as shown in Figs. 6 and 7, which feeds the coal directly to the furnace from the coal bin. Some stokers, particularly those designed for use with anthracite coal, have equipment for automatically removing the ash from the ash pit and depositing it in an ash receptacle outside of the furnace, as shown in Fig. 7: Most of the bituminous models, however, operate on the principle of removing the ash from the fuel bed after it is fused into a clinker at the outer periphery of the tuyere. Most of the stokers in this class feed coal to the furnace intermittently in accordance with temperature or pressure demands. A small amount of heat is also released from the fuel bed during the inoperative period of the stoker. Through the use of automatic controls (see Chapter 34), it is possible to maintain temperatures or pressures within very close limits when using stoker firing equipment. Fig. 6. Underfeed Stoker, Bin Feed Type, Class 1. tion and attractive appearance are very desirable characteristics of these small units. Equipment of this capacity is also used extensively for commercial and industrial applications requiring the burning of small quantities of fuel under automatic control. x . A common type of stoker in this class (Fig. 5) consists essentially of a coal reservoir or hopper, a screw for conveying the coal from the reservoir to the burner head or retort, a fan which supplies the air for combustion, a transmission for driving the coal feed worm, and an electric motor or motors for supplying the motive power for both coal feed and air supply. Air for combustion is admitted to the fuel through tuyeres at the top of the retort and in this class, the tuyeres and retort are usually round, although they may be either round or rectangular. Stokers in this class are made for burning anthracite, bituminous, semi-bituminous, and lignite coals and coke. The U. S. Department of Commerce has issued commercial standards for household anthracite stokers1. Household Anthracite Stoker Standards (U- S. Department of Commerce, National Bureau of Standards, Commercial Standard No. CS48-40). 208 > Fig. 7. Underfeed Anthracite Stoker with Automatic Ash Removal, Bin Type Stoker-Fired Boiler and Furnace Units Boilers, air conditioners, and space heaters especially ^designed for stokers are now available having certain design features closely coordi nating the heat absorber and the stoker. Although very efficient and satisfactory performance can be obtained from the application of auto matic stokers to existing boilers and furnaces, some of the combination stoker-fired units (Fig. 8) are more compact and attractive in appearance in addition to other design features. Class 2 and 3 Stokers Stokers in this class are usually of the screw feed type without auxiliary plungers or other means of distributing the coal. They are used exten sively for heating plants in apartments and hotels, also, for industrial plants, such as laundries, bakeries, and creameries. They are primarily of the underfeed type and are available in both the hopper type, as illustrated in Fig. 9, and also, the bin feed type, which delivers the coal directly to-the furnace from the coal bin, as illustrated 209