HEATING, STRAINING, PUMPING AND REGULATING For the most effective atomization all fuel oil should be heated in order to increase its fluidity and all fuel oil below 20 de grees 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 de composition 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 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 ad mitted at the top, surrounds the outer cylinder, and also flows into the inside of the inner cylinder thus keeping the oil sur rounded 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.