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for coal. With the g-in. standard stoker from 350 to 1,200 lbs. of coal per hour may be burned. Fig. 122 is a view of the American stoker before being placed in position in the furnace.

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K. Automatic steam motor for driving conveyor.
R. Air pipe to wind-box.

S. Gas ducts for returning volatile products
from entering coal to furnace.

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The air jets, passing out from the tuyeres in a horizontal direction, and from opposite sides, cut through the rounded bed of coal and the gases are thus ignited and consumed immediately after being distilled

from the coal, while the pressure of the coal rising from underneath forces the already coked fuel over the edges of the trough or box onto the grates which occupy the space between the side walls and the coal trough. The air is first delivered from the fan into the air box that surrounds the coal trough on three sides and from thence it passes to the tuyeres. If this stoker is properly handled very good results may be obtained by its use, but, like all other devices for burning coal under boilers, it is bad policy to endeavor to force it beyond its capacity.

In the Jones under-feed stoker the coal is pushed forward and up into the furnace through a cast iron retort or trough. The impelling force is a steam ram connected to the outer end of the retort, and the speed of the ram is regulated automatically by the steam pressure, or by hand as desired. The coal is supplied to the ram through a cast iron hopper having a capacity of 125 to 140 lbs.

Forced draft is also employed in this stoker, the air being conducted from the fan or blower through galvanized iron pipes into the closed ash pit, which really forms an air box, as the space on either side of the retort that is usually occupied by grate bars is in this case covered by solid cast iron dead plates upon which the coked fuel lies until it is consumed. These plates, being hot, serve to heat the air coming in contact with them in its passage to the cast iron tuyeres through which it passes to the bed of burning fuel in the retort. Air entirely surrounds the retort on the sides and back end, and is at. a constant pressure in the ash pit, but can only pass into the furnace through the tuyeres, the jets of air. cutting through the rounded heap of incandescent fuel from opposite sides and in a direction inclined upwards.

Coal is supplied to the hopper either by hand, or by mechanical means where the plant is fitted with coal handling machinery. The opening through which it passes from the hopper to a position in front of the ram is 8 x 10 in. in size. Each charge of the steam

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ram carries forward 15 to 20 lbs. of coal. to the ram and moving in conjunction with it is a long rod extending through the retort near the bottom. Upon this rod are carried shoes that act as auxiliary plungers and facilitate the movement of the coal.

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Fig. 123 is a sectional view of the Jones stoker, showing the machine full of coal, with the ram ready to make a charge. Fig. 124 shows the stoker complete before being placed in the furnace.

It is claimed by the builders of under-feed stokers, and the claim appears to have good foundation, that by pushing the green coal up so as to meet the upper crust of glowing fuel the gases on being distilled immediately come in contact with and are consumed by the burning mass, and the formation of smoke is thus prevented. Both the Jones under-feed and the American stokers have proved to be very successful in the burning of the cheaper bituminous coals of the West. One feature tending to commend them is the fact that practically all of the coal is utilized, there being no waste caused by the slack coal or fine screenings dropping through the grate bars into the ash pit unconsumed.

A good substitute for the mechanical stoker is an outside furnace, by which is meant a boiler installation having the furnace in front of instead of underneath the boiler. One of the principal hindrances to good combustion in the ordinary type of boiler furnace is the fact that the temperature of the boiler shell or water tubes with which the gaseous products of combustion come in contact can never be higher than the temperature of the water contained within the boiler. This temperature ranges from 297° for steam at 50 lbs. gauge pressure, up to 407° for 255 lbs. pressure, while the temperature of the furnace, according to Dr. Thurston and other high authorities, ranges from 2,010° to 2,550°.

It is evident that perfect combustion does not take place until these high temperatures are reached. Each time the furnace is charged with fresh coal, especially if the boiler be hand-fired, a large volume of volatile gases is liberated but not consumed. If these gases are allowed to immediately come in contact with a

comparatively cool surface, as for instance the heating surface of the boiler, the result is a cooling of the gases, incomplete combustion and the formation of smoke and soot. If on the other hand the furnace is so constructed that these gaseous products first impinge against hot surfaces, such as fire brick arches or bafflers that have a temperature corresponding to that of the furnace, good combustion is assured. This condition is in a large degree attained by the use of outside furnaces that permit the construction of a fire brick arch to cover the entire grate surface.

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ft. outwards from the boiler front and of a width to correspond to the diameter of the boiler. The arch rests securely upon brick work inclosed in a well ventilated iron casing. There is practically no heat radiated from this furnace, all the heat generated

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