Document V3zemvrG1odg6LgwvkJxkgOXZ

400 CHAPTER 15 1958 Guide their viscosities range from 900 to 10,000 seconds Saybolt Universal (50 seconds to 300 seconds Saybolt Furol). A number of factors affect the selection of a fuel oil preheating method. The three basic factors are: 1. Type of installation (commercial heating, industrial process, power generating, etc2.)..Type of operation (automatic, semi-automatic, manual, intermittent, con tinuous). 3. Type of fuel (No. 5, No. 6, Bunker C). Table 1. Preheating Temperatures to Obtain Suitable Viscosities fob Atomizing Viscosity op Oil* Oil Tempebattjbe (Fabbenheit) Reqtjibed Desired SSU Viscosity 122 F AT 100 F 100 150 200 300 450 2i 26 100 150 200 300 400 100 80 70 . - 61 120 100 90 77 135 110 100 87 150 128 115 100 160 138 128 108 50 66 75 88 96 30 39 50 60 75 500 750 1000 1200 1500 170 185 190 200 205 145 160 168 175 180 133 147 155 160 168 115 126 133 138 145 102 114 120 125 132 100 115 135 145 160 2000 2500 3000 3500 4000 215 220 225 229 235 190 195 200 205 208 175 182 187 190 194 150 156 160 162 165 137 143 146 150 152 170 190 200 220 260 4500 5000 5500 6000 7000 237 240 245 248 250 212 215 218 220 225 197 200 204 208 210 167 168 172 175 177 155 157 160 162 165 285 320 342 8000 9000 10,000 254 227 214 258 230 216 260 235 218 180 167 183 169 186 171 * 8SF = seconds Saybolt Furol viscosimeter. SSU = seconds Saybolt Universal viscosimeter. From Fuel Oil Manual, by Paul F. Schmidt (Tie Industrial Press) 1951, p. 105. Columns for 300 and 450 viscosity from Davis Engineering Corp. The pour point of an oil is another characteristic that could influence the preheating requirements, especially in areas subject to severe winter temperatures. An oil with a sufficiently high pour point may require pre heating and continuous circulation at temperatures above its pour point at all stages between storage tank and burner to insure its easy pumpability. Oil specifications should be checked for this characteristic and limitations imposed, if feasible. Otherwise the oil piping system must be designed with this high pour specification in mind. Four mediums for preheating fuel oil are in common use: steam, hot water, gas, and electricity. With steam as the heating medium the heater may be of shell-and-tube (either straight or U-tube) type or the heaters may be of a bayonet type Automatic Fuel Burning Equipment 401 inserted in the oil tank. In a bayonet-type heater an open-end tube is enclosed in a larger tube which has a closed outer end. Steam enters through the inner tube while condensate is drained from the outer tube. A heater of bell-shaped type may also be connected into the oil suction line at the tank for the purpose of raising the temperature of the oil drawn from the tank. The steam preheating method has several limitations. Mainly, it is dependent upon continuity of burner operation to keep steam available to prevent viscosities beyond pumpability. Therefore, its practicability and economy is limited to installations having continuous operation. Another limitation is that the relatively high temperature of steam may cause changes in the chemical structure of lighter grades of residual fuel oils. To prevent excessively high viscosities in the fuel oil piping, constant oil circulation is maintained or the oil piping is enclosed with steam fines in the same thermal insulation^ The economy of the steam preheating method is also dependent on the availability of steam at the pressure and quantity required, and on the distance from boiler to storage tank. The hot water preheating method utilizes equipment similar to that used for steam. Because of the possibility that oil may penetrate into the boiler through faulty heat exchangers, some devices have been developed to prevent this condition. Double-transfer heaters and fuel-oil detectors are those most frequently used. Similarly, as with steam, continuity of burner operation, or cycling burner operation, is needed to maintain the temperature of the heating medium. Since oil heating is limited by the water temperature in the boiler less transmission and transfer losses, such losses must be taken into account, particularly on installations having a considerable length of oil piping. The indirect gas-fired preheating method is a package arrangement that uses gas as the primary energy source. It generates its own supply of low pressure steam in a closed vapor-condensate cycle. The oil is pumped through the steam oil heater as required to compensate for radiation losses in the oil-circuit lines, whenever pumping action stops. During the lay over period, the main boilers and oil burners are entirely inactive. If sep arate oil transfer pumps are not available, a small circulating oil pump is added to the package to provide circulation in the oil lines during the gas firing periods. The electrical preheating method involves use of immersion heaters plus one of two special arrangements for heating the fuel oil piping. One special arrangement is a heating cable (soil cable or plastic covered wire) wrapped around the supply fine or all oil piping together with a vertical-element im mersion heater in the suction pipe in the oil tank. The closeness and even ness of the spiral winding of the cable determine the heat input. The on-off periods are thermostatically controlled. For protection of the heating cable, the temperature of the oil piping has to be limited, and usually must n MXc.ee.^ 1^0 F. Where pipe and oil temperatures permit wrapping of ml oil piping, constant oil circulation is not required. The efficiency of this preheating method is lower than for element immersion or electric impedence heating because of transfer losses between the heating element and the pipe. "^e otjler sPecial arrangement for electrical preheating is a packaged yste.m ` electric impedence heating for all oil piping together with im- a 131011 element heating sufficient to heat the oil used. Low-voltage highthe^e-r.a^? alternating current of the 60-cycle frequency is passed through il piping itself, generating an even amount of heat in the pipe walls.