CHAPTER VI HEATING, STRAINING, PUMPING AND For the most effective atomization all fuel oil should be heated in order to increase its fluidity and all fuel oil below 20 degrees Baume gravity must be heated in order to insure the proper flow of oil through the burners. Certain crude oils at the ordinary temperature of the atmosphere are of great viscosity, which viscosity increases as the temperature gets lower. At 30° to 40° F., which is not an unusual outdoor temperature, the fluidity of the oil is so slight that it is almost impossible to pump the oil or to force it to the burner. It is therefore necessary where fuel oil is to be used in regions which are subjected to severe winter temperatures that there should be means for heating the oil so that the oil may more readily flow to the pumps. The usual manner of accomplishing this is not to attempt to heat the whole tank or bunker of oil, but simply to heat the oil immediately surrounding the suction pipe to the pumps. This can be easily accomplished by placing a coil of a few turns of steam pipe about the suction pipe. In all pipes intended for the transmission of crude oil it is desirable that connections should be made to them so that steam can be turned into the pipes after shutting off the oil. These pipes can be thus cleaned by the heat and the force of the blowing steam, and any deposited asphalts, paraffins, or condensed hydrocarbons can be cleared out before the pipes become choked so as to impair their efficiency. The heating of the oil should be always recommended as an aid to secure better operation of pumps and burners, but, this heating should never be carried to such a degree of temperature as will cause decomposition of the hydrocarbons of the oil. Heating fuel oil above its flash point increases the fire hazard and should be avoided. One of the best methods of providing for uniform fluidity. throughout the system is to parallel the oil pipe lines with steam lines. When this is done and when a suitable pre-heater is also installed a uniform flow of oil is provided. Exhaust steam has nearly as great a heat content as live steam and is usually used for heating oil. The fluidity necessary to be obtained for perfect atomization depends upon the capacity of the burner. Fig. 30 shows a temperature capacity curve for a mechanical oil burner. In the case of oil as heavy as 10 to 12 degrees Baume' or lower, a separate heater should be used with live steam and exhaust steam. Various types of heaters are on the market. The heater shown in fig. 31 can be used with exhaust or live steam or with both. The oil enters at the bottom and passes up through the heater in a thin film as the oil passage is formed by the space between two thin cylinders placed concentrically. Steam is admitted at the top, surrounds the outer cylinder, and also flows into the inside of the inner cylinder thus keeping the oil surrounded on all sides by a steam jacket. The oil travels up and out the top while the steam enters at the top and exhaust from the bottom so that the hot oil leaving the heater is always drawn from that part of film nearest the hottest steam. The outer steam space is made by a large-sized pipe of suitable length which surrounds the outer cylinder mentioned above. This large pipe is insulated by means of asbestos and magnesia pipe covering which reduces the radiation loss from the sides of the heater. Fig. 32 shows a spiral oil heater. The oil entering this heater unit between the two shells takes a spiral course upward to the space between the two shell heads from whence it flows down through the seamless steel coil and out to the discharge header. In the event of an operator closing the inlet and outlet oil valves without cutting out the steam to heater, thereby causing the dead oil in the unit to heat and expand to a pressure which might create a rupture, a safety valve "A" is provided for each unit and set to operate before an excessive pressure can be attained. Steam is admitted and condensate carried off as shown. Fig. 33 shows the installation of pumps and heaters at the City and County Hospital power plant, San Francisco. When using air either at high or low pressure as a spraying medium it is exceedingly desirable that the air be superheated before passing to the spraying tip, as thereby a considerable gain in efficiency can be anticipated. Inasmuch as crude oils have been obtained from the earth they necessarily carry more or less sand or grit. The more viscous the oil the easier the sand and grit are held in suspension. In any installation of an oil burning plant special provision should be made for straining out all sand and foreign matter. Sand in oil not only clogs the burner openings but also wears out the small annular nozzles. Nearly all of the strainers inserted in oil burning systems are simple in construction and are often formed of a wire-gauze gasket set in the joints of the oil pipe. In order to take out the strainer for cleaning, however, it is necessary with such an installation to unbolt the joints of pipe and the FIG. 30. Temperature-Capacity Curve for Mechanical Oil Burner. Texas crude oil (gravity, 18° B., flash point, 240° F.) used in a Peabody burner producing a round flame at 200-pound pressure. more satisfactory arrangement is to use some strainer of the type shown in Fig. 34. Strainers of this type can be easily removed without tools or wrenches. The wire-gauze used in strainers should be made of wires of a width of mesh work equal to about one-half the width of the oil orifice in the burner. In the best practice a strainer is placed on each side of the oil pump, serving the two purposes of preventing sand from entering the pump and keeping any particles of old packing or other material from the pump itself from going through the system into the burner. Fig. 35 shows another type of strainer. By simply removing one cap screw the strainer can be withdrawn from the casing and thoroughly cleaned. Any water entering an oil storage tank will settle to the bottom of the tank. When the oil is drawn from a fixed outlet at the tank bottom, this water will enter the system. There is no practicable device that will directly separate the water from the oil. This separation can only be satisfactorily effected by allowing the water to settle to the bottom of the tanks by gravity. It therefore follows that if the suction to the oil pumps are placed in the bottom of the tanks, water will be often drawn when only oil is desired. A thread of water blown into |