CHAPTER XXII

MECHANICAL ATOMIZING OIL BURNERS

While steam atomizing oil burners are used almost exclusively in stationary power plant work at the present time, the mechanical atomizing oil burner has found great favor in marine work, and is the standard method of firing oil burning marine boilers.

There is a good deal of interest shown at present in the use of the mechanical atomizing burner in stationary plants, and it is possible that it may eventually entirely displace the steam atomizing burner. The mechanical atomizing burner, sometimes called

FIG. 108.-General arrangement Koerting mechanical oil burning system on a stationary boiler.

the pressure jet burner, is made in a number of different forms all of which operate on the same principle. It consists essentially of a nozzle containing a small conical shaped orifice through which the oil is forced at high pressure, the oil being first heated to a temperature approaching its flash point. Inside the nozzle means are provided to give the oil a whirling motion of sufficient intensity to make it fly into a spray on account of the centrifugal force as soon as it leaves the nozzle. The burners are placed in the boiler front and each burner is provided with an air regulating device which admits the air around the burner, at the same time

regulating the quantity of air to suit the combustion requirements. In some makes of mechanical burners the air is given a twisting motion as well as the oil, which adds to the effectiveness of the mixing of air and oil for combustion.

There are so many different makes of mechanical atomizing burners that no attempt will be made to describe them all. A brief description of a few of the most prominent will, however, be of interest.

Koerting Burner.-In this burner, which is illustrated on page 174 the oil is given a rotary motion by being forced through the passages of a helical screw into a small conical chamber containing the outlet orifice. The air enters through a cylindrical chamber having openings parallel to the axis of the burner, and is controlled by an adjustable cover which is rotated over these openings.

Dahl Burner. In this burner, the oil is given its rotary motion by passing through small channels formed between two parts of the burner. These channels deliver the oil tangentially at the periphery of the conical chamber in the tip, through which it passes in the form of a vortex to the orifice outlet. The air is controlled by the furnace doors, and the mixture adjusted by a conical deflector surrounding the burner.

Peabody Mechanical Burner. In this burner the rotary motion is secured by means of a flat disc having a 1/4 inch hole, and four slots which lead the oil tangentially toward this central hole. This slotted disc fits into the burner tip which contains the conical chamber and orifice outlet, the diameter of the conical chamber at its base being the same as that of the central hole in the disc.

With this burner the air is given a rotary motion as well as the oil. This is done by means of a cast iron truncated cone provided with blades, in the center of which is placed a so-called impeller plate, also bladed. The impeller plate gives a rotary motion to the air entering close to the burner, and the cone gives a rotary motion to the air entering around the edge of the impeller plate. In operation, the impeller plate and the burner may be moved in and out together, being fixed in relation to each other but adjustable in relation to the truncated

cone.

Moore Shipbuilding Company Burner.-In this burner the oil is forced through slots cut longitudinally on the outer surface of

a plug, the slots being curved at the end to give the necessary rotary motion to the oil as it enters the conical chamber in the burner tip. The position of the slotted plug in relation to the burner tip may be adjusted while the burner is in operation by means of a rod passing through the burner.

Coen Burner. In this burner, which is illustrated in Fig. 109 the oil is delivered to the central chamber by means of small tangential channels, whose area can be altered by means of a rod inside the burner running its full length, operated by the hand-wheel of a special angle valve. It is thus possible to regulate the fire from individual burners without altering the oil pressure.

FIG. 109.-The

The main air supply is controlled by a sliding plate in front of the cylindrical burner chamber, and a sliding cylinder surrounding this chamber controls a secondary air supply.

Draft.-Mechanical atomizing burners operate satisfactorily with natural draft at limited capacities, but if the boilers are to be forced much above their rated capacity it is necessary to equip them with forced draft fans, delivering the air under a slight pressure to the burner air chambers.

Pressure and Temperature of Oil.-The operation of mechanical atomizing burners varies with both the pressure and temperature of the oil. The pressure must be at least 25 lb. in order to produce good atomization and it may be increased up to 200 lb. Pressures higher than 200 Coen mechan- lb. are not required and only cause unnecessary ical atomizing stress of the oil piping. The quantity of oil burned is regulated by varying the pressure from 25 lb. up to 200 lb. If more oil is required than can be obtained at the higher pressure it is necessary in most makes of burner to change the nozzles, using tips with larger orifices. If less oil is needed than passes through the burners at 25 lb. pressure it is necessary to shut off some of the burners.

burner.

A temperature of at least 150°F. is required to properly atomize the oil. The atomization is improved by increasing the temperature up to about 200°. Above this temperature no change is made in the atomization but the flame becomes shorter and the

combustion occurs closer to the burner as the oil is heated to a higher temperature. As the oil is heated the first effect is to reduce its viscosity resulting in a greater quantity of oil passing through the burner. At the higher temperatures, however, the increased temperature has little effect on the viscosity, but owing to the increased volume of the oil the capacity of the burner is reduced.

The following table gives the quantity of oil that will flow through a burner having a 16 in. diameter orifice at a pressure of 200 lb., the oil having a gravity of 20° Baumé and a flash point of 220°F.:

Advantages of Mechanical Atomizing. The principal advantage of the mechanical atomizing system is that a large quantity of oil can be burned in a furnace of a given volume."

The steam atomizing burner as applied to stationary boilers produces a flat flame and the combustion occurs on the upper and lower surfaces of this flame, with the result that a considerable proportion of the volume of the furnace is not made use of. With the mechanical atomizing burner, on the other hand, there is what may be called volume combustion, the mixture of air and gases occurring throughout the entire furnace. It is therefore, possible to completely burn more oil in a given size of furnace by this method than by the steam atomizing method, or if the same quantity of oil is burned in both cases the combustion with the mechanical atomizing system will be more complete in the furnace proper, so that the flame will not travel so far among the boiler tubes and the entire efficiency of the boiler will be greater. The cooling of the gases by their coming in contact with the boiler tubes before the combustion is completed is one of the principal causes of low efficiency in boilers that are forced

FIG. 110. The mechanical fuel oil atomizers installed under two 250 h.p. Heine boilers. The view is the standard equipment at eleven pumping stations of the Shell Company of California oil pipe line, installed by Sanderson and Porter. The operation is entirely automatic, oil being supplied to the burners under the control of the pump governors so as to maintain constant pressure.