US1388714A - Mechanically-stoked furnace - Google Patents

Description

AfHOFMANN. MECHANICALLY STOKED FURNACE. APPLICATION FILED OCT. 31. 1918. 1,388,714. I Patented Aug. 23, 1921.

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MECHANICALLY STOKED FURNACE. APPLICATION FILED OCT. a1, 1918.

1,388,714. Patented'Aug- 23, 1921.

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ALFRED HOFMANN, OF ZURICH, SWITZERLAND.

MECHANICALLY-STOKED FURNACE.

Application filed October 31, 1918.

T 0 all whom it may concern Be it known that I, ALFRED HOFMANN, a citizen of the Republic of Switzerland re siding at 7 Asylstrasse, Zurich, in the anton of Zurich, Republic of Switzerland, have=invented certain new and useful Improvements in Mechanically-stoked Furnaces; and I do hereby declare the following to be a full, clear, and exact description of tl'ie invention, such as will enable others skilled in the art to which it appertains to make and use thesame, reference being had to the accompanying drawings, and to letters of reference marked thereon, which form a art of this specification.

his invention has for its 0b3ect to provide an improved mechanically-stoked furnace.

According to this invention the improved furnace includes two or more travellng grates arranged one above the other in such a manner that each lower traveling g'ate receives the fuel dropping from an upper traveling grate and is adapted to convey away the slag and ashes.

F igure 1 is a side view of a furnace provided with my improvements. In this view certain parts are shown in section, certain parts are showndiagrammatically and other parts are shown partly broken away for the sake of clearness.

In the accompanying drawings Fig. 2 is an end view of the furnace.

Fig. 3 is a front elevation with parts in section taken on the linel-II-III-IV- V-VI of Fig.1.

Fig. 4: is a diagrammatic detail sectional view of oneof the traveling grates.

Fig. 5 is a transverse vertical sectional detail view of the mechanism shown in Fig. and illustrating means for air cooling one of the plates which is arranged on the side of the fire-box to prevent the slag from adhering to the sides of the brickwork casing of the furnace.

Fig. 5 is a view similar to Fig. 5 but showing a modification in which the plate is' water-cooled.

Figs. 6 and 7 show a side view and sectional View respectively of the pawl and ratchet mechanism used in driving one of the grates.

Fig. 8 is a side view of the pawl and ratchet mechanism used in driving the other grate.

Specification of Letters Patent.

Patented Aug. 23, 1921.

Serial No. 260,560.

Fig. 8 is a detail end View of the pawl mechanism for driving the last mentioned grate.

Fig. 9 is a diagrammatic sectional view of a modified form of the invention.

Fig. 10 is a top planview of a couple of the flap plates used for preventing the entrance of an excessive amount of air at the exit end of one of the grates.

Referring first to Figs. 1 to 8 and 10, the fuel is charged into a hopper 1 from which it is delivered by a power-driven feeder 2 of known type and an inclined plate 3 on to the upper traveling grate 5. In order to prevent pieces of coal from rolling down and the advancing coal from becoming too highly heated a damper 4 is pro vided which is adapted to be operated from the outside and serves also to prevent entrance of the hot gasesinto the fuel-feed passage. This damper is raised when fuel is being fed on to the grate 5. The fuel is carried along by the grate 5 and then drops on to the lower t aveling grate 6. During this advance the fuel is pre-heated, gasified and ignited by the forwardly deflected fire gases (indicated by the arrow I), the resulting smoldering or partial combustion causing at first an increase in its volume and afterward a decrease in its volume when the fuel has become completely, degasified.

In passing from the upper grate on to the lower grate the layer of caked fuel is broken up and turned by the outwardly opening grate bars in somewhat the same manner as is done in hand-etching with a poker for the purpose of loosening the layer of fuel.

The removal of the slag takes place at the exit end of the lower grate where the slag is removed continuously as the grate travels. The larger pieces of coal pass on to the lower grateG while still only in the first stage of combustion, whereas the smaller pieces, the dust and the small coal have had suflicient time to be completely burned. The result of this is a diminution in the volume of the burning fuel so that, as is generally the case with traveling grates, vacant spaces or holes occur in the layer of burning fuel tl'irough which an injurious excess of air passes up through the fuel. For the purpose of diminishing these holes and the losses occasioned thereby, and so as to keep the lower grate always completely covered,

the speed of the lower grate is reduced as hereinafter described relatively to the speed of the upper grate in proportion to the diminution in volume of the fuel layer in such a manner that the large pieces shall also be completely burned, and that only slag, that is only incombustible matter, shall drop off at the rear.

In order to prevent the entry of an injurious excess of air at the point where the slag is removed, freely movable depending flaps 7 are provided at the exit of the lower grate. These fiaps are caused by their own weight to bear against the grate bars and thus act as a closure against the entry of air in all positions of the grate. When a third grate 6' is employed, as shown in ,Fig. 9, for carrying away the slag and travels therefore only at a very low speed, the flaps 7 are provided at the third grate and the layer of slag is kept sufficiently high to prevent any entry of air between the two grates.

ries a fixed constant-throworank 11.

In order to prevent the slag from adhering to the sides of the brickwork casing of the furnace, both the longitudinal sides of the grate are provided with metal plates 8 or 9 which are prevented from burning by being cooled by means of air as at 8, or water as at 9. The residues, such as slag and ashes, are removed from underneath the grate by a conveyer 6 and raised to a point whence they can be taken away by hand.

The furnace mechanisms are driven from a pulley 10 fixed on a shaft 10. This shaft carries a fixed gear 1O that drives a gear 10 fixed on a shaft 10, which also car- This crank imparts a constant throw through a connecting rod 12 and a lever 13 to a pawl 14. The lever 13 is loosely mounted on a shaft 15. Since the amount of coal to be burned must be varied to suit the steam consumption, it is necessary to vary accordingly the speed of the ratchet wheel 16, which is fixed on the shaft 15 and controls all the mechanisms. This variation is effected by arranging the pawl 14 to slip idly over more or less of the periphery of a shield 17 when a reduced steam production is desired. By this means the speed of the shaft 15 may be varied at will from nil to the maximum, and the feed and removal of the fuel may be regulated according to requirements. The alteration in the position of the shield 17 is effected by means of a piston 19 working in a cylinder 19' and being under the influence of boiler pressure through the medium of the pipe 19". This piston moves up when the boiler pressure rises and descends when the boiler pressure falls. The movement of the piston is transmitted, by rods 21 connectedto the piston rod 20, to a lever 23 fulcrumed on the shaft 22. One end of the lever is connected by a rod 120 to the shield 17 and the other shifting of the lower shield 17 is efiected from the upper shield 17 through the medium of the connecting rod 28 which may be lengthened or shortened by means of a threaded sleeve 28*, whereby the shield 17" can be given more or less lead over the upper shield 17, and thus the speed of the grate 6 can be reduced as desired relatively to the speed of the upper grate 5.

The grates are driven by means of worm gears 29 mounted on the shafts 15 and 15.

hese gears engage worm gears 29 fixed to the drive shafts of the grates.

The shaft 15 also supplies the motion for driving the mechanism actuating the fuel feeding apparatus 2 and the slag-removing conveyer underneath the grates 5 and 6. By thi means all the drives for adapting the combustion to the steam consumption are derived from a single shaft 15. As above stated the rates are constructed as traveling grates or the purpose of preventing the losses that occur with ordinary rates due to small coal dropping through. he transversely arranged grate bars 30 are held at both ends in chains 31 by means of noses 32, 33 projecting from the inner fishplates of the chains, and are kept from falling out when inverted by means of pins 34.

As the grate bars pass over the chain wheels the bars 0 en outwardly and thus form wide spaces etween the bars whereby the layer of caked fuel is broken up.

The improved furnace may be a plied to various types of boilers but in the drawings I have shown it applied to a flue boiler.

In the modification illustrated in Fig. 9, the fuel drops from the second slightly upwardly inclined traveling grate 6 on to a likewise inclined third traveling ate 6 whose speed is somewhat less than t e speed of the grate 6.

What I claim is 1. In a furnace, an inclined upper traveling grate, a lower traveling grate extending partially beneath the u per grate and re ceiving the fuel direct y dropping from the upper grate and conveying away the slag, means for driving the travelin rates at adjustable different s ds, and ioiler steam controlled means or regulating the air supply and the conveying away of the slag to suit the steam consumption.

2. In a furnace, an inclined upper traveling grate, a lower traveling grate extending partially beneath the upper grate and receiving the fuel directly dropping from the upper grate and conveying away the slag,

a rotatable shaft, a crank actuated by said shaft, a main shaft for driving the upper traveling grate, a ratchet mechanism placed on the main shaft and actuated by the crank to impart to the shaft a step by step movement, a shield loosely mounted on the mainshaft, automatic means actuating said shield to vary the extent of said step by step movement for causing the main shaft to be driven automatically at different speeds, a third shaft for driving the lower traveling grate, a ratchet mechanism placed on the said shaft and actuated by the said crank to impart to this shaft a step by step movement, a shield loosely mounted on the third shaft and connected to the first mentioned shield for automatically varying the extent of the last mentioned step by step movement for causing the third shaft to be driven automatically at different speeds.

In testimony whereof, I have signed my name to this specification.

ALFRED HOFMANN.

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