The distance piece (9) is so designed that it may be moved along its axis, thus moving the impeller plate (15) in and out with reference to the balded cone (3), and decreasing or enlarging at will the clear area for the passage of air around the outside of the impeller plate.

By means of a set screw (16) the impeller plate (15), together with distance piece (9) and atomizer (12) may be fastened in any desired position. To adjust the distance between the tip of the atomizer (12) and the center opening in the impeller plate (15), a headless set screw (17) is unscrewed, then by holding the

FIG. 113. The Babcock and Wilcox mechanical oil burners showing double front construction for forced draft.

distance piece (9) with the set screw (16), the coupling (10) may be rotated on the distance piece (9) to bring it to any position desired.

The distance between the tip of the atomizer (12) and the central opening in the impeller plate (15) should be maintained at approximately 1/4 inch, and when the coupling (10) is moved up on the distance piece (9) sufficiently to give this distance, the headless set screw is driven home.

In Fig. 113 a spacing collar (20) is shown which is used when the number of burners is such that the outer front plate must be moved out to give the proper flow area for the air supplied to the burners by means of the forced draft.

The curve in Fig. 111 for the efficiency secured at different ratings with steam atomizing burners is based on tests that were made on a 14-high B. & W. boiler in 1907 at the Redondo plant of the Pacific Light & Power Company. In these tests California oil of about 14° Baume was burned which has a heat of combustion of approximately 18,000 B.t.u. per pound.

The curve for mechanical atomizing oil burners shown in Fig. 111 is based on tests made on a 14-high B. & W. boiler at the Bayonne works of the Babcock & Wilcox Company with Mexican oil 14 to 16° Baume, having a heat of combustion of approximately 18,300 B.t.u. per pound. The conditions existing in the tests of the mechanical atomizing burners were as follows:

The oil pressure at the burner varied from 100 to 200 lbs. per sq. in., depending on the capacity at which the boiler was operated and upon the size of the sprayer or orifice plates which are used inside the tip of the mechanical atomizers. The best atomization was obtained when the oil was heated to give a viscosity of from 3° to 5° Engler, which required a temperature of from 220° to 250°F. Live steam was used for heating the oil from about 110° to the temperature specified, the amount approximating one half of one per cent. of the total steam generated.

In the tests the amount of steam required for driving a rotary pump which was used for pumping the oil amounted to from 1 to 11⁄2 per cent. of the total steam generated. The pump was considerably larger than required and therefore wasteful. In a large plant the amount of steam required for pumping the oil would be in the neighborhood of 11⁄2 of 1 per cent. of the total steam generated and the exhaust steam from the pump could be used for the preliminary heating of the oil.

The number of burners for use in a given boiler may be determined on the basis of one burner per 120 to 130 rated boiler h.p. This capacity may be exceeded in certain instances.

The variation in load is taken care of by adjusting the oil pressure at the pump between the limits of 100 to 200 lb. per sq. in. and by cutting burners in and out. Throttling the oil at any individual burner should not be done and a valve to a given burner should remain always wide open or tight shut.

It is not advisable to attempt to regulate the air to any great extent with the air doors on individual burners. The best way to adjust the air is through the use of the boiler dampers for natural draft installations. Where a forced draft is employed

the air is regulated through the use of the boiler dampers and the adjustment of the air blast.

A boiler fitted with mechanical atomizing burners requires more draft to operate it at a given rating than one fitted with steam atomizing burners, as the air for combustion must be drawn through the burner registers at a velocity that will cause it to mingle intimately with the atomized oil. With no forced draft the amount of draft suction required at the damper of a 14-high B. & W. boiler for drawing the air through the burner registers and for drawing the gases through the boiler when operating at rating, 150 per cent. of rating, 200 per cent. of rating and 250 per cent. of rating is 0.25, 0.6, 1.0, and 1.65 in. water column, respectively. Where a forced draft is used at the burners, the draft suction required at the boiler damper to overcome the resistance of the gases flowing through the boiler is 0.15, 0.20, 0.35, and 0.50 in. water column, respectively, and when operated at 250 per cent. of rating the forced draft required at the burners is 1.15 in. water column.

CHAPTER XXIII

RULES FOR EFFICIENT OPERATION OF OIL FIRED

BOILERS

Since the advent of steam turbines the relative importance of the fireroom crew as a factor in economical operation has increased considerably compared with the engine-room crew. This is because the steam turbine, after it has once been properly set up, operates continuously at a fixed steam consumption for a given load and nothing can be done to improve its economy other than to keep the turbine, condenser and auxiliaries clean and in good operative condition. In the boiler room, on the other hand, continual watchfulness is necessary to keep the boilers operating at good efficiency, and the slightest laxity in attention to the various details results in a large waste of fuel. To assist the operators of oil-fired boilers in obtaining the best economy possible, the writers have prepared the following set of rules, which if carefully followed will bring the daily operating efficiency of the plant very close to test results:

1. Regulate Air to Suit Load. The regulation of the air supply is one of the most important things in the operation of oil-fired boilers. If there is not enough air, a great waste of fuel may occur as part of the atomized oil will simply pass up the chimney unburned. On the other hand, it is possible to waste just as much fuel by allowing too much air to enter the furnace as all of the extra air is heated up and passes out at the temperature of the chimney gases, carrying away with it an enormous amount of heat. To determine accurately the amount of air required for the best conditions it is necessary to analyze the flue gases.

Many plants, however, are not provided with the apparatus necessary for this, and in such cases the air may be regulated with a fair degree of accuracy by an observation of the smoke discharged from the stack. For perfect combustion there should be no smoke, and if any smoke appears it means incomplete combustion and not enough air. If there is no smoke, however, it does not follow that the conditions are right, as no smoke may mean either just the right amount of air or a large excess of air.

FIG. 115.

FIG. 116.

FIGS. 114-116.-Stacks of station A, Pacific Gas and Electric Company, San Francisco. This plant is one of the largest fuel oil operated power plants in the world. The first view shows improper combustion, the second proper combustion, and the third instances of proper and improper combustion in varying degrees.

FIG. 114.