MECHANICAL BURNERS Among the thousands of oil burners which have been de signed there are many which affect vaporization by entirely mechanical means. Since the early clays of oil burning, various plans have been proposed to effect vaporization by entirely me chanical means. Early inventions contemplated the use of oil running over surfaces exposed to the action of flames and the burning taking place directly on the exposed surface of the oil.
All such plans proved decidedly inefficient owing to the fact that the air supply could never be brought to the burning surfaces of oil in quantities sufficient to effect complete combustion. Conse quently all mechanical burners operating on that plan have been long since abandoned. The next field of invention that gave indication of success was to design burners in which the oil would be sprayed positively by mechanical action. Mechanical action can be resorted to, for the purpose of spraying oil by two general methods : First, to force oil outward under considerable pressure from a properly formed orifice, by the action of a special pump ; second, by whirling or flinging the oil outward from a rapidly revolving mass or burner head. Figure 52 shows a mechanical burner which can be regulated very closely by means of the ad justing rod. With all mechanical burners the tips are required to be very small in the diameter of orifice, usually not over of an inch. The objection to burners of this type, as compared with the stcam-atomization type, is the equipment required. Also, the general conical shape of the flame and the tendency toward blast action frequently requires change in the furnace to insure successful use. Professor Jiles W. Haney of the Department of Mechanical Engineering, University of Nebraska, writing in Oil News,a has the following to say concerning mechanical burn ers : "A mechanical burner atomizes the oil by giving it a cen trifugal throw through small slots tangentially placed in the burner. The air is fed in around the burner so that it assists in
breaking up the oil. The oil, heated almost to its flash point, is pumped to the burner under pressure and as it passes a central spindle, spirally grooved, a rotary motion is given to the oil caus ing it to fly into a spray by centrifugal force on issuing from the nozzle. The particles of oil are burned when they come in con tact with the necessary air to effect combustion. This type of burner has the prime advantage of returning the steam used by the pumps and heaters as feed water to the boilers. The steam used for operating it is much less than that for other burners, ranging from percent to.1 percent of the total steam generated. These considerations have made its use in marine work quite general, and in stationary plants where feed water is an important item. The ease of control is another important advantage of the mechanical burner. For a given boiler capacity a greater number of these burners are installed than in the case of steam atomizing burners; the number of burners in operation varying as the load on the boiler. This scheme can be worked very satisfactorily since each burner has its individual air supply, which also can be shut off with the burner. This cannot be done when the main air supply conies through a checkerwork at the bottom of the furnace. Another control method is that of changing the pressure of the oil supplies to the burner. A good burner will atomize moderately heavy oil with an oil pressure varying from 30 to 200 pounds per square inch ; then since the rate of flow of the oil dis charged through a given orifice is proportional to the pressure the oil at the orifice, a low rate of flow will occur with a low pressure and a high rate of flow will result with a high pressure. The pumping equipment can be connected up so that it will auto matically control the rate of flow of the oil to the burners as the load varies."