Document N2xvQq8zwe727xQ5pM0LyNmjb

410 CHAPTER IS 1958 ring burners, proportional mixers, or compressors, are purchased for as sembly in existing equipment, usually by the installer. Furnaces to pro-' vide particular atmospheres or for annealing, soaking pits, metal melting, etc. are usually engineered by industrial gas equipment manufacturers. Burners utilized in industrial equipment often operate at gas pressures higher than encountered in domestic usage.. High pressure.gas provides flexibility of control required in the production of constant temperatures. In addition, air-gas ratios can be closely maintained under throttling condi: tions, and heat liberation per cubic foot of combustion space is considerably greater than can be achieved with lower pressures. A few of the many basic types of burners used are as follows: single-pipe high pressure, proportional mixing, pre-mix, two-pipe high pressure, and atmospheric: ' The single-pipe high pressure burner system utilizes gas delivered to the orifice of a venturi at pressures from 10 to 50 psig. A constant pressure compressor, sometimes remotely placed, is occasionally .used to increase the Table 4. Multipliers fob Various Specific Gravities For Use With Table S Specifio Gravity Multiplier Specific Gravity Multiplier 0.35 0.40 0.45 0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.85 0.90 1.31 1.23 1.16 1.10 1.04 1.00 0.962 0.926 0.895 0.867 0.841 0.817 1.00 1.10 1.20 1.30 1.40 1.50 1.60 1.70 1.80 1.90 2.00 2.10 0.775 0.740 0.707 0.680 0.655 0.633 0.612 0.594 0.577 0.565 0.547 0.535 gas pressure. The velocity of the gas issuing from the orifice entrains primary air which is controlled by an air shutter on the venturi tube. An advantage of this system is that when the gas pressure is reduced (lowering the input) the air-gas ratio will remain constant over a fairly wide range. In the proportional mixing burner, an enclosed type venturi is used and high pressure air is delivered through an orifice. The resulting partial vacuum entrains the gas which is supplied through a zero pressure governor. When the air pressure is reduced, the amount of gas entrained is similarly reduced, thus maintaining a constant air-gas ratio over a wide fuel capacity range. The pre-mix burner system embodies a compressor which mixes air and gas intimately and discharges the mixture through pipes to the burners where it is discharged through orifices and burned. The pre-mix compres sor can be remotely installed and the mixture can be closely controlled. The two-pipe high pressure burner system utilizes both air and gas under pressure, both being delivered through orifices and mixed prior to delivery to the burner. The atmospheric burner system is not commonly used. It consists of a burner supplied with gas at a pressure of 2 to 12 in. water. A portion of the air or primary air required for combustion is entrained from the atmosphere by the stream of gas issuing from an orifice, and the air-gas mixture is Automatic Fuel Burning Equipment 411 delivered through a venturi mixing tube to the burner head and parts. About 40 to 60 percent of the air. required for combustion is in the form of primary air and the remainder, known as secondary air, is supplied from the air surrounding the flame. Each system embodies characteristics essential for certain applications. It is strongly recommended that proper and qualified engineering authori ties be consulted prior to the purchase, installation, or operation of indus trial gas equipment. FUEL BURNING RATES The- burning rate for automatic fuel burning devices is determined by the gross heat output required of the boiler, or furnace, to carry the net heating load, plus allowances for system losses and pick-up. General o 2468IO 12 14 16 GROSS OUTPUT - HUNDRED FEET STEAM RADIATION o S 10 e 20 25 GROSS OUTPUT - HUNDRED FEET WATER RADIATION Fig. 21. Coal Fuel Burning Rate Chart 20 values for these allowances have been given in preceding text. Detailed information for piping and pick-up allowances for steam and hot water systems, is given in Chapter 16, and for warm air systems, in Chapter 19. When the gross output, operating efficiency, and heat value of the fuel are known, the required rate of burning can be determined by means of *>gs. 21, 22 and 23 for the several fuels. rate of fuel burning is directly proportional to the load for a do"61? Tciency> these charts can be extended by moving the decimal P mts the same number of digits in both vertical and horizontal scales. l correct fuel burning rate can be determined directly from the onert C^arts for. d or gas burning installations, as these customarily usuall .n a strict,y intermittent basis. These fuel burning devices this m^0<fuce the fuel at a single fixed rate during the on periods, and stoke* v sufficient to carry the gross load. In the case of coal to or)18' * 1C^ 316 usually capable of variable rates of firing, it is desirable perate at as low a rate as weather conditions will permit, but the maxi-