Document k6Ede9K8VO3J6ppG06e2J5prn

American. Society of Heating and Ventilating Engineers Guide, 1937 while larger sizes are power operated. The number of retorts and dimen sions of furnaces are practically unlimited. r The V-type stoker is practically obsolete although many are still in operation. In this stoker, the grates are inclined downward from both sides of the furnace to a low point at the middle where there is either a dump plate for periodic disposal of the ash or a rotary ash grate for con tinuous discharge of ash. In this stoker, the fuel is fed into a hopper at the top of the grate on each side of the furnace and advanced down the grates to the center where the refuse is accumulated. This stoker is always provided with a combustion arch over the entire furnace for the purpose of assuring thorough combustion of the solid fuel and providing a furnace temperature sufficiently high to burn the volatile gases. Because of this high furnace temperature and because so little of the boiler surface is exposed to the fire to assist in carrying off the heat by radiation, this stoker is characterized by severe clinkering in the ash area. With all types of overfeed stokers, the most desirable installations are in boilers which are operated with comparatively uniform loads and moderate rates of combustion, since, even with good combustion arches, fluctuating loads or high combustion rates result in smoke. Table 1 gives recommended setting heights for heating boilers equipped with mechanical stokers. 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. Heat production is thus only one of many functions to be performed by a heating system. Efficient heat production with any kind of fuel requires that all com bustible matter in the fuel shall be completely consumed and that it shall be done with no more excess air than necessary. The combustion of oil is a rather rapid chemical reaction. Excess air provides an over supply of oxygen so that all of the oil, composed of carbon and hydrogen, will be completely oxidized and thus produce all the heat possible. The use of unnecessary excess air means no increase or decrease in the heat produced but it does mean that some air is needlessly heated and thrown away. This loss cannot be counteracted by any other part of the heating system and is therefore chargeable to the fuel-burning device. Oil is a highly concentrated fuel composed exclusively of hydrogen and carbon. In its liquid form oil cannot burn. It must be converted into a gas or vapor by some means. If the excess air is to be kept within efficient limits it means that air must be supplied in carefully regulated quantities. The air and oil vapor must be vigorously mixed to get a rapid and complete chemical reaction. The better the mixing, the less excess air that will be needed. The combustion must take place in a space that maintains the temperatures high so the reaction will not be stopped before completion. When equipped with a means of igniting the oil and safety devices to guard against mishaps, the oil burner possesses all of the elements to be efficient and automatic. 506 1 Chapter 28--Automatic Fuel Burning Equipment The number of combinations of the characteristic elements of domestic 1 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 (b)--primary air supply by fan or blower and secondary air supply by natural chimney draft. 2. METHOD OF OIL PREPARATION a. Vaporizing--oil distills on hot surface or in hot cracking chamber. b. Atomizing--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. b. Non-luminous--Bunsen-type flame (.., blue flame). 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. Gas. (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. 5. MANNER OF OPERATION a. On and off--burner operates only a portion of the time (intermittent). b. High and loro--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. A trade classification of oil burners consists of the following general types: (a) gun, (f>) rotary and (c) pot. The gun type is characterized by an air tube, usually horizontal, with oil supply pipe centrally located in the tube and soarranged that a spray of atomized oil is introduced and mixed in the firepot 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 507