Document MJwEpwM4Njx6yzB5yjOwKnyrz

HEATINC VENTILATING AIR CONDITIONING GUIDE 1940 and rate of burning of stoker-fired solid fuels it is not sufficient to analyze a grab sample. A continuous gas sample drawn at a constant rate through out an operating period of reasonably long duration should be used. A C02 reading of 12.5 to 14 per cent indicates that the excess air supplied is in the range of 30 to 50 per cent. The presence of CO indicates a loss due to improper mixing of the air and the gases of combustion. As an increase in excess air maintained during on periods will decrease the tendency toward smoke in the off periods of intermittently operated bituminous coal stokers, care should be taken that the delivery of air by the fan is great enough to avoid smoke. Controls The industry developed by stokers in Classes 1, 2, 3 and 4 has been due as much to the application of proper controls as to the stoker itself. This is especially true of Class 1 stokers because of their application to resi dential heating, a field wherein the mjaority of owners and users are not familiar with control problems or stoker operation. The usual controls applied are: (a) thermostats, (6) limit controls, (c) stack temperature or time controls, (d) relays, (e) safety or overload cutouts, and (J) low water cutouts. DOMESTIC OIL BURNERS An oil burner is a mechanical device for producing heat automatically and safely from liquid fuels. This heat is produced in the furnace or firepot of hot water or steam boilers or warm air furnaces and is absorbed by the boiler, and thus made available for distribution to the house through the heating system. The number of combinations of the characteristic elements of domestic oil burners is rather large and accounts for the variety of burners found in actual practice. Domestic oil burners may be classified as follows: 1. AIR SUPPLY FOR COMBUSTION a. Atmospheric--by natural chimney draft. b. Mechanical--electric-motor-driven fan or blower. c. Combination of (a) and (f>)--primary air supply by fan or blower and secondary air supply by natural chimney draft. 2. METHOD OF OIL PREPARATION a. Vaporising--oil distills on hot surface or in hot cracking chamber. b. Atomising--oil broken up into minute globules. (1) Centrifugal--by means of rotating cup or disc. (2) Pressure--by means of forcing oil under pressure through a small nozzle or orifice. (3) Air or steam--by high velocity air or steam jet in a special type of nozzle. (4) Combination air and pressure--by air entrained with oil under pressure and forced through a nozzle. c. Combination of (a) and (b). 3. TYPE OF FLAME a. Luminous--a relatively bright flame. An orange-colored flame is usually best if no smoke is present. i b. Non-luminous--Bunsen-type flame (i.e., blue flame). CHAPTER H. AUTOMATIC FUEL BURN,NG EQUIPMENT 4. methods of ignition . a. Electric.(1) Spark--by transformer producing high-voltage sparks. Usually shielded to avoid radio interference. May take place continuously while the burner is operating or just at the beginning of operation. (2) Resistance--by means of hot wires or plates. b. Cos. (1) Continuous--pilot light of constant size. (2) Expanding--size of pilot light expanded temporarily at the beginning of burner operation. c. Combination--electric sparks light the gas and the gas flame ignites the oil. d. Manual--by manually-operated gas torch for continuously operating burners. 6. MANNER OF OPERATION a. On and off--burner operates only a portion of the time (intermittent). b. Higk and low--burner operates continuously but varies from a high to a low flame. c. Graduated--burner operates continuously but flame is graduated according to needs by regulating both air and oil supply. Fig. 10. Gun Type Pressure Atomizing Oil Burner A trade classification of oil burners consists- of the following general types: (a) gun or pressure atomizing, (b) rotary and (c) pot or vaporizing. The gun type, illustrated in Fig. 10 is characterized by an air tube, usually horizontal, with oil supply pipe centrally located in the tube and arranged so that a spray of atomized oil is introduced and mixed in the combustion chamber with the air stream emerging from the air tube. A variety of patented shapes are employed at the end of the air tube to influence the direction and speed of the air and thus the effectiveness of the mixing process. The most distinguishing feature of vertical rotary burners is the principle of flame application. These burners are of two general types; the center flame and wall flame. In the former type, (Fig. 11) the oil.is atomized by being thrown from the rim of a revolving disc or cup and the flame burns in suspension with a characteristic yellow color. Combustion is supported by means of a bowl-shaped chamber or hearth. The walL 211