THE COLLIERY GUARDIAN ■ AND JOURNAL OF THE COAL AND IRON TRADES. Vol. CXIII. FRIDAY, MAY 25, 1917. No. 2943. Burning Coke Oven Breeze. Coke breeze is ‘ to the coke industry what the culm pile is to the coal mine. Each represents, a fuel that at one time had no value, although containing suffi- cient heat units to warrant burning, if means could be found to burn it. The solution of the culm pile has been found in the washery; that of coke breeze in a mechanical stoker. Attempts which have resulted in varying degrees of success have frequently been made to burn beehive oven coke breeze under hand-fired conditions. One of the difficulties has been to keep firemen because of the arduous conditions due to the extreme heat to which the men are exposed, and the additional weight of fuel to be handled in order to develop the required rating of the boilers.. Owing to the many difficulties encoun- tered, hand-fired coke breeze with the ordinary grate and design of furnace is not successful;' and experi- ments in burning this fuel under return tubular boilers carried on by the Frick Coke Company have shown that the fuel requires a forced draught to fur- nish the necessary air supply. The steam jet type was used, and a special pattern of shaking and dumping grate was also designed. Before the proper ratio of grate to boiler heating surface to give the best results was determined, a number of changes were necessary, and the proportion of air space in the grates was changed several times; the air pressure in the ashpit was also, altered. Whenever a change or combination of changes was made, tests were conducted until a standard of grate surface, air space, and blower capa- city for different types and sizes of boilers was decided upon. It is impossible to handle coke breeze fuel in other than a quiescent or an unagitated state, the use of Fig. 1.-—Dumping, Shaking and Running Position of Frick Grate. Fig. 2.—Section Showing Depth of Fuel Bed. stokers that agitate the fuel resulting in the formation . of a mass of clinkers sufficient to compel the shutting down of the plant after a few hours’ run, while the fires are being cleaned. Operating under such condi- tions would make the cost of maintenance practically prohibitive, and the labour cost would be about one- ,third greater than when hand-firing. . The average coke breeze produced Contains from 25 to 35 per cent, of sand, sulphur, and fireclay, all of which go to make up a considerable clinker formation. The necessity of handling these materials is what led to the development of an overfeed stoking system that distributes the fuel evenly oyer the grate surface from above the top of the fire bed. The principle of the stoker system is that the fuel flows through the hopper by gravity on to a pusher plate, from where it is pre- cipitated into an impelling chamber by the pusher that is operated by a rocking arm in contact with a cam, or from an eccentric attached to the rocking arm. The impellers distribute the fuel over the fuel bed in any required amount up to that necessary to operate the boiler greatly in excess of its normal rating. To handle the clinkers produced in burning coke breeze fuel, a specially designed rocking, cutting, and dumping grate is used. (Fig. 1.) The fuel bed is carried about 8 in. thick at the front of the furnace, and as the grates are pitched, a depth of 18 in, is carried at the bridge wall. At intervals the grates are operated for shaking; that is, the points of the grates are dropped about 3 in., and as the clearance space between the bars remains the same, nothing but fine ashes is sifted to the ashpit. The shaking move- ment is so slight that the fire bed is not disturbed to any great extent. This movement also prevents the amalgamation of clinker-forming impurities. The fuel bed as carried by this system is divided into three zones. (Fig. 2.) The first is about 5 in. thick at the front, to 15 in. at the back. This residue formation diffuses the air over the grate area, and pre- vents blow-holes in the fire that would be caused by an unequal air pressure. The second fuel zone' is carried about 3 in. thick all over the grate surface, and is composed of the incandescent particles of carbon in the fuel. The third zone is the green fuel that is continu- ally sprinkled over the second zone. The moisture in the fuel is evaporated by the heat from below, and also by the heat reflected from the arch above. During the process of combustion the impurities are separated from the combustible, and work their way through the layer of residue forming the first zone, where they come in contact with the cold air, and are chilled before they become fused in large quantities with one another. , With this kind of fuel it is necessary to bperate the cut-off movement of the grates about every two hours, which removes about 1 in. from the bottom of the residue at each stroke. In thig way the fires are cleaned without disturbing the fuel bed and without the use of fire tools. The grates have a 40 per cent, air space, and sufficient steam is used under them to ensure the chemical decomposition of the clinkering matters. By-product coke oven breeze does not contain the same nature or quantity of clinker-forming properties as beehive oven breeze, and a two-stage turbo-blower is used because it has a greater efficiency than the steam blower. Also it is not necessary to saturate the loor Door Ash Pit Air Duct Fig. 3.—Section of Coxe Grate and Setting. Boiler Front Fuel J Hopper Coke- Fuel Feeder? ■Combustion Arch Relieving Arch '' *:&• Ignitionbust ion / \Burning< I n^Doprs - * o • A . air with steam to the same extent as with beehive breeze. In tests made on an 80 horse-power fire tube boiler, the furnace.of which was equipped with an overfeed stoker, the water evaporated per lb. of combustible from and at 212 degs. Fahr, averaged 5-96 lb. This evaporation may seem Jow, but it is from a fuel that has. had no market value, and, in fact, has had to be hauled away at an expense for which there has been no return. ' . The efficiency of the boiler and furnace averaged 53-48- per cent, for the tests, which is low as compared with what would be expected when burning a better grade of fuel. However, several items that are not apparent on the surface enter into the results obtained. The ash content of the fuel is high, there was no arch over the fires, and the direct contact,of the gases with the cold boiler shell, and the limited area for the expansion of the gases, all naturally affected the combined efficiency and increased the cost of a unit quantity of steam. , The boiler plant in question contains four 80 horse-power return tubular boilers, all equipped with the overfeed type of stoker and system for burning coke breeze. The plant supplies steam for the mine pumps of the Oliver and Snyder Steel Company, near Uniontown, Pennsylvania. The intensity of the fires is governed by the speed at which the stokers are run and the force of the steam jet at the blower. The fuel gives an intense heat, and no trouble is experienced in burning it. Another type of equipment (originally designed for the combustion of anthracite culm) has been found readily adaptable to the burning of coke breeze, viz., the Coxe travelling grate (fig. 3), which is now being successfully operated with coke breeze in several plants. The stoker shafts are of cold rolled steel, and are 4f in. in diameter; keyed on each shaft are two cast iron sprockets, located just inside of the side frames. Oast iron flanges project inward from the side frames. To these flanges are bolted sheet-steel plates, forming a floor between the side frames, about 10 in. from the bottom, with vertical air baffles at each end of the stoker. On top of the floor are built two air boxes, or tuyere boxes, extending across the stoker between the side frames, and communicating on one end through rectangular openings in one side frame, with the air connections from the forced draught air duct. The tuyere boxes are constructed of cast iron and sheet steel, and on the front and back sides of each box are register or grid dampers of cast iron, through which the draught may be admitted to the air com- , partments under the grate. The fuel supporting surface is made up of keys or grate tops, which are small castings approximately f in. wide, 9 in. long, and 2 in. deep. The top surface is curved, and the front end of each key matches the rear end of the next key. Pads on one side of each key space the keys about V^in. apart, thus forming the air openings. The keys are supported on carrier bars of cast iron, to which are bolted dovetail sections on the upper surface; on the bottom of the keys are cast dovetails which engage with those on the carrier bars'; and at each end of the carrier bars is riveted a steel forging which projects downward between the links of the carrying chain, to which it is fastened by a bolt. The chains, which are made of drop forgings, held by steel pins, all of ample section to carry the load, are carried over the sprockets at the front and rear end of the stoker, returning under the floor of the air com- partments. The rear shaft is the driver, and extends through the side wall of the boiler, where it is keyed to a cast iron worm wheel mounted in a heavy cast iron enclosed gear case. Suitable shearing pins are pro- vided between the rim and web of the worm wheel, to guard against wrecking the stoker in the event that any obstruction chances to get into the chain. ‘ The worm which drives the main gear is of steel, and is keyed to a cold rolled steel transmission shaft 2J in. in diameter. The transmission shaft may extend either forward to the front of the boiler or back.toward the rear to any convenient point. On the end of the transmission shaft is keyed a second cast iron worm wheel, suitably housed in a closed cast iron gear case. The worm shaft that actuates this gear may be driven either by belt from a line shaft, by electric motor, or by small steam engine. Both gears are run in oil. On the front end of the stoker is the coal hopper, which is constructed of sheet steel reinforced by angle iron, and is carried between the cast iron hopper sides bolted to the top of the stoker side frames. The coal gate is a heavy casting, protected with special fire- brick tile on the side toward the fire. The'gate is raised and lowered by a cross shaft carrying cast iron pinions engaging in cast iron racks attached to the coal gate. A hand whe'el is provided at one side of the hopper for manipulating the gate. At the bottom of the hopper, and supported between the side frames, is a coal apron made of cast iron sections, and lined with 'firebrick. The upper ends of these apron sec- tions may be lowered so that there is sufficient open- ing across the stoker to fire by hand when starting the fire. It is recommended that the air for combustion’ be supplied at a static pressure of 2 to 2| in. of water.