Document 8RXRrbezoBjOdv287yJwNgrae

Heating Ventilating Air Conditioning Guide 1938 Stokers also may be. classified according to their size based upon coal feed rates. The following classification has been made by' the United Siates Department of Commerce in cooperation with the Stoker Manu facturers' Association. Class 1. Up to and including 60 lb of coal per hour. Class 2. 60 to 100 lb of coal per hour. Class 3. 100 to 300 lb of coal per hour. Class 4. 300 to 1200 lb of coal per hour. (A fifth class is included covering stokers having a feeding capacity above 1200 lb of coal per hour). Class 1 and Class 2 Stokers, Household Since these stokers are used primarily for home heating, it is desirable that their design be simple and attractive in appearance, and that they be quiet and automatic in operation. A common type of stoker in this class consists, essentially of a coal reservoir or hopper, a screw for conveying the fuel from the hopper to the burner head or retort, a fan which supplies the air for combustion, a Chapter 11. - Automatic Fuel Burning Equipment ment of Commerce has issued commercial standards for household anthra cite burners, which may be obtained by application. . Standards of performance for bituminous coal stokers are also being developed by Bituminous Coal Research, Inc. The standards for anthracite stokers are described in the next paragraphs. Operating Requirements for Anthracite Stokers Efficiency. The over-all efficiency of the unit at alt points above 50 per cent of maxi mum coal feed shall be above 50 per cent when, installed in a round sectional cast-iron boiler having three intermediate sections and \\4 in. of asbestos insulation or its equiva- Fig. 5. Underfeed Screw Stoker, Hopper Type 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 as indicated in Fig. 5. The shape of the retort in this class of stokers is usually round although rectangular retorts ^are favored by some manu facturers. In all cases, however, the retort incorporates tuyeres through which the air for combustion is admitted. Some household stokers are provided with an automatic grate-shaking mechanism together with screw conveyors for removing the ash from the ashpit (Fig. 6) and depositing it in an ash receptacle outside the boiler. Certain types can also be provided with a coal conveyor which takes coal from the storage bin and maintains a full hopper at the stoker. In some cases the coal bin functions as the stoker hopper as shown in Fig. 7, and an extended worm is used to convey the fuel to the combustion furnace. Domestic stokers may feed coal to the furnace either intermittently or with a continuous flow regulated automatically to suit conditions. Household stokers are made for all classes of fuel; anthracite, bitu minous and semi-bituminous coals, and coke. The United. States Depdrt- 204 Fig. 6. Underfeed Screw Stoker with Automatic Ash Removal lqnt in good condition of repair, operating at 50 per cent or more of the boiler capacity: The efficiency shall be maintained for any continuous period of .4 hours during any test or observation run. Ash Loss. Combustible in ash shall not exceed 7.5 per cent of the Btu content of the coal as fired at any rate of coal feed above 50 per cent of maximum. 'Methods of test" according to Code No. 3 of the A.S.H.V.E.1 are to be followed in all details applicable" to stoker testing. Clinker. Ash removing systems should at all times be capable of disposing of any clinker which may be formed under any conditions of operation with the coals prescribed. T*S5Sio^: for Steam HeaUn* 5011(1 Fuel Boi,ere (Code 3). (A.S.H.V.E.. 205