US2073059A - Mechanical stoker - Google Patents

Description

March 9, 1937. B. M. GUTHRIE MECHANICAL STOKER Filed June 6, 1935 X QN QL E T @T 10 reverse direction 15 common practice Patented e 9, "19311 UNI-TED STAT-Es was MECHANICAL s'ro'xnn Bernard Morse Guthrie,I Chicago, Ill.. alig'nor to poratlonof cago.; Illa a corv vruminanti. Juneys, 1935, sei-inne. 25,236

' This invention relates to improvement( in mechanical stokers, "and more particularly 'to y stokers of the type employinga-screw-conveyoi'. In oneform of mechanical stoker, coal orv other 5 fuel is fed by apower-driven screw conveyor, from a hopper, through a conveyor 'casing or duct, into a retort wherit is-co ed.. ill/common difL nculty) with this type or Stoker is to be found in theV occasional tendency of smoke to ilow in a from the retort, vthrough the conveyor duct,and out thr'ough the hopper. Such a. condition would; of course, render vthe use of the stoker objectionable.V j i Asa means for overcoming this difficulty, it is in some ofthe' older prevailing types of stokr's, to provide a-by-pass air connection between, say, thacombustion chamber air lsupply line and the conveyor duct,this connection to tnecici: being made ai; a suitable poinigusuauy '20 near the` retort end thereof. `Such lan arrangement is intended to effect a region of'fhigh ah' pressure in'tlieconveyor duct, for preventing a `backilow. of smoke through the duct. 'lhis\-a1j rangement, however, has not' proven, altogether g5 satisfactory in preventing such backow; since if the coal is -not packed tightlyenough -in the worm and duct, the resis ce air through the coal inV conveyor tube may .be so slight'as to prevent theformatiomofa 301 region Aif-high If, foiany reason the coal being conveyed 'along v. the duct 'should become loo's enough, the consequent backilow of air may resultin coal dust and smoke being discharged from the hopper, If'in a..`further attempt to overcome the lnoted' objections, the bottomof the hopper andthe worin aresdesigned to pack the coal solidly throughout the length of the worm. an excessive a amount @spawns will be w force the 40' coal through the connectingduct and into Ithe retort. .In some cescoal will become so tightly wedged between the conveyor duct and the worm, that the worm cannot revolve,with the a result thatthe usual pin will be broken, or f5 eral objective of the present 1, on is attained in the elimination of the no and objectionable features folmd in the heretofore prevailing stokenassemblies of the type de# 50 scribed.

A further object of the present invention is to provide an improved conveyor structure for mechanical stokers Vof the type described. specifically, a feature of the invention is to be found in the-provision of a. minimum operating' to a backllow'of,

pressure. in the. conveyor tube.-

thel driving motor stalled. the lem- More clearance between the screw conveyor and .the conveyor duct, ywhereby toprevent packing of fuelbetween these two members. A furtherfeature residesintheprovisionofmeansonthescrewconveyor d spaced from the retort end' thereof, adapted 5 cause the fuel to become packed overa portion of the conveyor adjacent said means. -The region of packed fuel thus formed, allows a. sufficient air pressure to be maintained inthe conveyor duct for preventing a backfiow of smoke through the 10 hopper, and the length of the packed fuel zone isf not su has would require an abnormal amount of powe to drive the screw. `In vorder to against any-jamming of the screw conveyor asa result of the extension of the region of packed fuel l5 `'beyond the packing means and toward the retort 'end of ,the conveyor duct, the pitch or lead of the' screw, ,and -hence the rate of movement of the .fueL is'increased between the packing means ands the retortend of the screw. ,Th screw conveyor 20 `is thus characterized by "a, lesser pitch between the hopper end thereof and the packing means, or a point somewhat beyond the packing means, 'and a greater pitch from this pointto the retort end- A further object is to provide an' improved screw. conveyor structure for mechanical stakersl jof; the type described, which will effectively-prevent the escape `of Ismoke from the hopper, an'd which will not I/addappreciably eitherto the cost odiflicultyof manufacture.

Further objects,- and advantages will appear from the following ydetailed description of parts', an'd from the accompanying drawing, in which:

V1 isa vertical longitudinal sectional view.v of a stoker embodying the/features of this invention, andlFig. 2 is van enlarged fragmentary sectionalview of a portion of the conveyor screw, astakenalong line 2- 2 oflEigQ 1.

- Referring-to thedawingvthe numeral Ill -denotes, generally, a stoker hopperpf standard construction. A motor or` other 'driving means I i,

-which may besecured to the frame of the hopper lIl, is provided for operating a .worm or conveyor screw l2,r\ th e driving' connection thereto being 45 by preference, made tbroughashear pin. It@ The structural details of the shearpin connection be'-v tween the motor II andthe shaft Il of'the conveyor'need not ,be shown or described, as'it forms f no part ofthe present invention.- The use of 'a'. shearpin, such as the pin I3, is conventional, and is uti1ized to ,sever the drivingconnection in the event -of an excessive load upon the screw conveyor.

.In me conveyogiinusmd, the scw i: tuerelopening I5 in an end wall IB thereof.

of is, by preference and for purposes of Subsequent description, to be considered as including vtween the lines :ic-:z: and y-y, Fig. 1.

The hopper I Il is provided with a discharge The conveyor extends along' the bottom of, and projects beyond the hopper I0, through the discharge opening to a furnace retort generally designated by the numeral I8. The portion of the conveyor between the hopper and the retort is enclosed by a conduit I9, the conduit being secured at its ends, to the vertical walls of the hopper and retort respectively, in any suitable manner, as by flange joints Il.

As a means for preventing a backiiow of smoke from the retort, through the conveyor conduit I9 and the hopper I G, air under a predetermined pressure is, by preference, introduced to the portion of the retort containing the free end 20 of the conveyor, the air being conducted from a suitable source of supply (not shown) through a duct 22. The duct 22 may be supplied directly from the principal source of supply for combustion purposes; or may be connected as a by-pass tube to be supplied from the main air duct directed to the wind box. The air thus supplied through duct 22 forms a pressure region about the fuel delivery end 20 of the conveyor, for preventing a backow of smoke as above described. However, this result cannot be obtained unless the coal being conducted to the retort by the conveyor, is packed sufliciently to prevent a reverse iiow of air from the pressure region through the conduit and out of the hopper. If, however, the fuel is so packed over any considerable part of the length of the conveyor, there results an excess requirement of driving energy, and an unwarranted torque demand on, say, the motor II. In order to effect a relatively tight packing of the coal in the conveyor suiiicient to constitute an effective seal, and yet to restrict in length the zone of such seal, a projection 24 is provided on a portion of the working surface of one ofthe conveyor flights. In practice, it has been found expedient to locate the projection on one of the intermediate flights, but somewhat nearer the discharge end of the conveyor. The projection may be formed as an integral part of the flight, or it may consist of a separate element, conveniently a bolt, as illustrated in the drawing, and located substantially midway between the shaft and periphery of the flight.

An excessive amount of power would be required to operate the conveyor, if the coal were packed tightly along its entire length, say as a result of the packin'geffect of the projection 24. This diiiculty is overcome in the example disclosed, by forming the conveyor worm with certain ights of differing pitch. For example thoseflights between the projection 24 and the end flightin the hopper I 0, are: characterized by a pitchA, a substantially greater pitch B being given the flights between the projection 24 and the fuel discharge end 20 of the conveyor worm. Accordingly, in the operation of the' conveyor worm or screw, the projection 24 will effect a relatively tight packing of the fuel in the flights preceding the projection. As a result of the increased pitch of the ights extending beyond the projection to the discharge end of the worm, the packed fuel conveyed beyond the projection will be considerably loosened, whereby to relieve the conveyor driving motor of an excessive load which, otherwise, might result in damage to or complete stoppage of the motor. The tightly packed coal in the conveyor flights preceding the projection, servesI effectively to confine the pressure region of air to that portion of the conveyor extending between the projection and the retort, and soserves to prevent the escape of smoke from the Stoker into the furnace room or building. The presently improved construction also operates to minimize -jamming of the wormI conveyor in the conduit I9, by minimizing the length of the zone of packed fuel.

It will, of course, be understood that the present detailed description of parts and the accompanying drawing relate only to a preferred executional embodiment of the invention, and that substantial changes may be made in the described construction and arrangement of parts, without departingl from the spirit and full intended scope of the invention.

I claim as my invention:

l. In a mechanical stoker, in combination, a hopper, a conveyor duct, a retort, a conveyor wormy arranged to transfer fuel through the duct from the hopper to the retort, means projecting from a blade portion of the worm tending to the packed fuel in said intermediate zone of the duct coacting with said air supply means to direct said air stream toward and beneath the fuel bed in the retort.

2. In a mechanical stoke, in combination, a hopper, a conveyor duct, a retort, a conveyor worm arranged to transfer fuel through the duct from the hopper to the retort, a projection on one of the flights of said worm serving to pack the fuel in an intermediate zone of said duct, said conveyor worm having two different pitches, the portion of its lengthhaving the lesser pitch being located nearest the hopper, the remaining portion of greater pitch being located nearer said retort, and means for supplying air under being located nearest the hopper, a projection on oneI of the flights located on the portion of the worm having the lesser pitch, said projection serving to pack the fuel conveyed by said worm in the zone of said projection, and an air inlet located in a portion of the conveyor duct in the region of that portion of the worm having the greater pitch, for admitting air into the conveyor duct, the air entering the duct through said inlet and said packed fuel in the zone of the projection coacting to prevent the flow of gases from the retort, through the conveyor duct and into the hopper. BERNARD MORSE GUTHRIE.

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