US2598931A - Clinker cooler - Google Patents

Description

J. NARSTED CLINKER COOLER June 3, 1952 10 Shets-Sheet 1 Filed March 14, 1950 s A W Y @w R 9 W HQVV 9 Q 3 3 a VQ x \v MW, M. w NW 9% I h J o 4 a o o o o o o m c o yr, f x n a MN MM; QN MM WN m 0 1 Hm w E P 1 NM 1 2 i I In fl-F um \N V v -w v w\ \\.M\ Q Q $5 N\ m AV M June 3, 1952 J. NARSTED 2,593,931

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CLINKER COOLER Filed March 14, 1950 1o Sheets-Sheet s INVENTOR.

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J. NARSTED CLINKER COOLER June 3, 1952 10 Sheets-Sheet 10 Filed March 14, 1950 lllllLLlLLlfvl Patented June 3, 1952 OFFICE CLINKER COOLER John Narsted, Hampstead, Montreal, Quebec, Canada, assignor to Fuller Company Application March 14, 1950, Serial No. 149,496

8 Claims. (01. 34233) The invention relates to the cooling of refractory materials occurring in a substantial range of particle size, and more particularly to the rapid cooling of materials continuously formed into a moving bed, through which air, or other gas, is forced or drawn to extract heat therefrom. It has especially to do with the cooling of materials such as ores, lime, Portland cement clinker, or the like, when continuously discharged from furnaces, such as rotary kilns, for the rapid reductionof the temperature of the material, the recuperation of sensible heat, or both, or to complete the cooling of such materials discharged from a recuperator.

Heretofore, various methods of cooling material of this nature have been employed, such as the rotary shell type of cooler. There are a number of variations of this type of cooler, but the basic principle of the operation is the same, that is, passing cooling air through the interior of the cooling shell while the shell 1'0- tates, causing a cascading of material down the sides of the shell to contact the cooling air in one manner or another. There are a number of disadvantages to this type of cooler from an operational and a maintenance standpoint. The amount of air necessary to cool the material is great because of the poor contact of the cooling air with the material. Regardless of the type of rotary cooler used the area of material presented to the cooling air is small as compared to the total mass of the material;

There is a relatively small amount of breaking up of the mass of material to present a greater area to the cooling air in the rotation of the shell, compared to the large amount of agitationand sliding of the material within, and on the liner of, the shell. Because of their relatively slow initial cooling rate, in the temperature range above 2200 degrees F., and their lower heat recuperation capacity, as compared with modern air-quenching coolers, the rotary coolers have now become practically obsolete, at least for the cooling of Portland cement clinker.

In the event that cement clinker, or other materials of similar abrasive characteristics, is the material being cooled a serious maintenance problem is presented. The abrasive qualities of the cement clinker are high and a great amount of wear will take place when the clinker moves over metal parts to any great extent. Such movement of clinker over the metal linerof a shell is present in a rotary cooler and therefore the wear, and replacement, of the parts of the cooler in contact with the clinker is a serious maintenance problem.

Another method of cooling is by passing air, or other gas, through the material formed as a continuously moving bed through a coolerhousing. This continuously moving bed is supported by some form of grate through which the cooling air can. pass up through the material.

One type of such cooling operates on the principle of a shaker conveyor. The shaker platform forms a support for the material bed, and provides the means for conveying the material through the cooler. Means are provided to impart a rapid shaking motion to the platform supporting the bed of material, with this shaking motion producing the movement of the bed of material toward the discharge end of the cooler. It is obvious that when material of an abrasive characteristic is cooled in this manner an excessive amount of wear of the supporting platform will be produced by the shaking motion.

Still another method of cooling employs a cooler consisting of a horizontal metal support-' ing grate over which the material is drawn by an endless continuously operating drag chain, and cooling air is passed up through the ma.- terial bed from below the metal grates. The drag chain is in direct contact with the grate. and therefore the material being pulled by the drag chain is in direct sliding contact with the grate. Here again, if the material being cooled is of an abrasive characteristic, an excessive amount of wear will take place in the grate structure and the drag chain. A further disadvantage of the use of a continuously operating drag chain sliding across the supporting surface is that it tends to produce, due to its grinding action, an undesirable amount of fines. A still further disadvantage of the use of a continuously operating drag chain is the difficulty of maintaining an evenly distributed material bed. A kiln discharge is irregular, thus providing varying amounts for the drag chain to pick up. The drag chain operated at a con-, stant rate of speed, so that as the drag chain pulls the material away from the opening into the cooler, there will be variations in thickness of the bed depending upon the rate .of discharge of the kiln at any given element of time. This uneven thickness in the material bed creates an unsatisfactory cooling condition, since the cooling air will follow the path of least resistance, which will be through the thinner areas of the material bed, and leave the thicker areas without the proper amount of cooling.

In the'above mentioned material bed type of coolers, the particles of material are subjected to continuous agitation in their conveying movement. It has been found that this constant agitation causes the bed of material to become graded with the smaller particles at the bottom and the larger particles at the top. The process of grading "of the various sized material begins immediately upon the movement of the material bed through the cooler.

during its travel through the cooler, and due to the gradation of the bed, the smaller parti cles are the first to be contacted by the cooler air, and as the surface area of these, small particles is large in comparison to the quantity of heat which they contain, they soon become cooled to the desired temperature. However, the particles of larger size have less su fa e area per unit volume and quantity of heat contained, and are located on top of the material bed at the "point. furthest from the ooler air. Th result of this con i on is that he dischar e from the cooler will ontain a lar e amount of material, the large par le r n e. that ha n t. beenpr perly cooled.

=Thenormal operation of the drag chain will in itself produce a disadvantage in this type of cooler. Most of the dra chains are of the 'link hain and sprocket wheel type and therefore the pitch of the links must remain constant in order to pass. over. th sp o k t wheel teeth. The dra hain usu l y consis f. tw r re l nk-chains connected together by a drag bar. Sincethe ch ins mu t run in un son with relation to each other, any variation in the chain links will produce a locking or bindin :of the drag chain. The variations in length may be produced by the links of chain expanding as they pass through the hottest zone of the cooler, thereby changing the pitch of .the link chain, or, one of the chains riding overa large particle of material will produce a relatively uneven length between .the two chains and cause a binding on the sprocket wheel.

Anotherfeature of the type of cooler that forces air through the bed of material as it is being conveyed through the cooler, that is a disadvantage is that, as the material passes over the open.- i s in the bed structure provided for the admission of air, particles of material fall through these openings and some means must be provided to remove these particles from the windjbox, which usually entails taking the cooler out of service.

Air-quenching, inclined grate coolers, overcome many of the disadvantages described above; but

this type *requires substantial headroom in a space or basement below the kilnroom or burner floor. "This'requirement makes their installation difiicult in some existing plants where headroom is notavailable, and for new plants where'ground wateror rock make deep basements expensive.

Excepting for the rotary types, inmost of the coolers of the prior art, fine clinker particles sift into the air or plenum-chamber below the clinker bed. Sinceall cement clinkers contain a -proportion of fines, and in some; the -proportion represents :a substantial part of the total clinker pro- The cooling air" is passed upwardly through the bed of material duced, the removal of fines from the plenum 4 discharged from rotary kilns, since it is especially appropriate for satisfying the peculiar cooling requirements of this material. This clinker is preferably discharged from the kiln at a temperature of at least 2500 degrees F.; and the objective is to cool it abruptly, within the temperature range 2350 degrees to 2200 degrees F., and within two to three minutes, to convert a maximum of the liquid phase compounds to undercooled liquid, or glass, rather than to permit crystallization to take place, for reasons now understood in the art of cement manufacture. Rapid cooling should continue until the temperature is reduced to about degrees F., at the cooler discharge, to facilitate grinding. The low commercial price of cement, and the large quantity of sensible heat available in the clinker, as discharged from the kiln, make recuperation of a maximum of the heat essential; and this is preferably accomplished by utilizing the kiln combustion air, or at least the quantity reguired'as secondary combustion air, as part of the clinker cooler r nd p s i through the hottest zone of the cooler, whereby a maximum heat transfer can beeffected, and

the combustion air may be delivered to the kiln at the highest possible temperature. The extreme temperature of the incoming clinker, and

its highly abrasive nature makes maintenance of metal. surfaces, which it may contact, both diffi'r cult and expensive.

it is. accordin ly, am ng the purposes of th invention to satisfy these requirements by providing a substantially permanent layer of clinker; to form the principal wearing surface, over which the clinker to be cooled is conveyed, in the process of cooling. It is also a purpose to limit the surface oi the convey r'metalli par e posed t heat and abrasive cont t with the linker to the minimum required to convey it; and to provide for easy replacement of these parts, after they pass the ischargeend of the cooler, where their low temperature permits handling. It is a fur.- r p rpose to so form and s pport this subantially permanent layer of clinker particles that voids between thein form a multiplicity of a sag wa hrou h which cooling air is diffused, uniformly and continuously, in intimate contact with the individual particles of the moving bed of hot material, and throughout the bed. to provide for thorough and rapid cooling and maximum recovery of sensible heat. The supporting structure for the permanent layer is desi n d so that the fine particles of clinker cannot sift through the voids and support to accumulate in the plenum chamber. It is also an objective to provide a cooler requiring relatively little head room, whereby it may be installed as a .replacee merit for rotary coolers, without requiring sub-.- tantial changes in existing buildings and their foundations.

lngeneral, the apparatus comprises a generally horizontal y disposed elongated chamber, having an inlet opening into the upper part, at one end, to receivehot clinker, and a discharge end open ing at the other, fromwhich the cooled material andischarge, preferably by .gravity. The chainher is divided in .a generally horizontal plane by a fixed supporting structure, to form an upper cooling chamber and a lower plenum chamber.

The supp rting structure preferably comprises spaced :bars, extending transverselyof the chamber, for example .2 bars, which may be inclined from the vertical, to avoid formation of free passageways through which fine particles may sift and gravitate to the plenum chamber,

without, however, obstructing the free upward passage .of cooling air. Two longitudinal rails, disposed inwardly from the walls of the cooling chamber, and spaced above the supporting bars, to provide space for the permanent layer of clinker particles above the supporting. structure, support an endless .conveyonwhich distributes the incoming clinker to form a rela ively uniformly flatbed and conveys it along the upper surface of the permanent layer of clinker to the cooler discharge.

'This conveyor comprises parallel chains connecting spaced drag bars riding upon the rails, the conveyor being caried over idler drums, preferably beyond each end of the cooling chamber, with the return strand carried below the plenum chamber on suitable idler rolls. The conveyor may be driven continuously, or by intermittent motion, which may conveniently be imparted by a reciprocating fluid motor, having an element engaging-the lower strand of the chain and drag bar assembly.- I

Air is supplied to the plenum chamber, preferably under positive pressure, the pressure re quired being suflicient to overcome the resistance of both the permanent layer of clinker and the moving bed. The draft of the kiln draws that quantity of the cooling air required 'to satisfy the combustion requirements, from the hottest zone of the cooling chamber, and this air preheated to the highest possible temperature, promotes rapid flame development within the kiln, permitting clinker burning near the discharge end, whereby the clinker will enter the cooler well above the temperature range of crystallization,

and the effective volume of the kiln is increased.

The amount of air necessary to reduce thetem-' perature of the material to a desired extent for subsequentgrinding is greater than that needed for secondary combustion air, and the excess can be vented to atmosphere through a stackcontrolled bya conventional damper. For a better understanding of the invention, reference is made to the accompanying drawings,

in which 5 a Fig. 1 is an elevation, partly in section, ofthe apparatus and furnace,

Figs. 2, 2A and'2B are an enlarged sectional elevation of the apparatus,

Fig. 3 is a cross sectional elevation on line 33 of Fig. 2A, and showing a permanent layer or bed of clinker on the grate bars, as well as the cement clinker which is being subjected to cooling, I g

Figs. 4, 4A and 4B arean enlarged cross sectional plan view on line 44 of Fig. l, I

- Figs. 5 and 5A are an enlarged plan view of the lower drag chain support and actuating carriage.

In the preferred construction, the material cooler 13 is positioned below a rotary kiln H, and attached by a material passage, or throat l2, in such a manner as to allow the material being cooled to flow from the kiln into the interior of the cooler. The interior of the cooler, the cooling chamber I3, is defined by a top wall [4, two side walls l5 and [6, two end walls I! and I8, and a bottom wall 23. Positioned below the throat l2, and extending into the cooling chamber I3, is a shelf 2| used as a means have formed a natural angle of repose, the de- After the clinker particles have accumulated upon the shelf 2|, and

scendingclinker particles are distributed by the pile thus formed and pass on into. the coolingv chamber I 3 without having come in contact with any of the cooler surfaces.

Located below the shelf 2|, and extending the length of the cooling chamber, is -a grate. structure 22 used as a means of supportingthecement clinker bed formed in the cooler during the cooling operation. The grate structure is formed by lateral supporting members 23 positioned along the length of the cooler and extendingfrom .one cooler side wall to the other. Extending longitudinally through the center of the cooler is another supporting member 24 positioned above and supported by the lateral members 23. Two supporting flanges 25 are also provided on each side of the cooler wall at the same height as the top of the longitudinal member 24. Extending across the cooler from wall to wall, resting on the two flanges 25 and the longitudinal member 24, are a series of spaced grate bars, 26 of generally Z-shape, positioned at regular intervals for the complete length of the cooling chamber. These bars are held in a spacedrelation by an end plate 21, to which each bar is welded, thereby forming a rigid grate structure. This grate structure is of such design that it affords a path for the air to pass up through the openings formed by these bars while at the same time preventing the cement clinker above the grates from falling down through the openings.

Located in a position inwardly from each cooler wall are two series of connection flanges 28 and 29. These flanges are welded along a longitudinal line to adjacent bars 26 at regularly spaced intervals along the length of the cooler. Attached to these flanges, and therefore running along the same longitudinal lines, are two rails 30 and 3!, used as a riding support for a drag chain 32, to be described later.

An air chamber, located below the grate structure 22, is defined by two end walls 33 and 34 and the bottom wall 20 of the cooling chamber. Air under pressure, for the purpose of cooling the clinker, is brought into the air chamber at any convenient location from the discharge of a blower, not shown, and is discharged from the air chamber up through the openings, formed by adjacent grate bars 26, into the bed of hot clinker in the cooling chamber I3. The cooling chamber is divided into at least two compartments by a dividing wall 35. The clinker C as it first falls to the grate structure 22 is formed in piles, and is then spread out to a level. bed B by the motion of the drag chain 32. Until this clinker is leveled off, the pile is thicker than'the normal bed thickness in the balance of the cooler. This differencein the bed thickness will cause a greater resistance to the flow of air through the thicker bed, resulting in an uneven distribution of air, with the forward end of the cooling chamber receiving an insufficient amount of cooling air. To overcome this, the air chamber is divided into at least two compartments, one along each section of the clinker bed of different levels of clinker. The air pressure is so regulated in each of the compartments that an even flow of air is provided throughout the entire bed of clinker in the cooling chamber.

The conveying structure comprises an endless drag chain 32 supported at each end of the cooler by two freely rotating drums 36 and 31. The drag chain is made up of a series of drag bars 38, connected one to the other by links 39.- The chain issupported by the two longitudinal rails portion of the cooler riding .on the rollers 40.

The drum 36 on .the intake end :of the cooler "is provided with flanges-through; which the chain is held in the .proper traveling position as it enters the cooling chamber 13 .of the .cooler.

The 'dra'gbars 38 normally tend ".to' float "in thexclinker C :andas'sthey'are free to lift, 'no crushing or grinding" action takes place between the 'metal iparts in' the 1 event. a clinker :particle passes between :a drag bar 38 'and the rails 30 and 31. .As the 'grate :isxdesigned with "a "very liberal ar'eaythe drag bars are only 'required to move the clinker forward over the grate at a very slowrate .offlspeed, therebyreducing-the wear and resulting in agreat increase .inzrthelifecof the unoving parts of the cooler.

, The .advantage of using the free rotating drums 36 and :31 at .each' end .of the :cooler' for the chainto pass over is that 'the-diflicult'ies encountered with aapower sprocket chain wheel, such-as-fouling and jumping of sprocket teeth, are eliminated. A' further advantage of the drums over 'the sprocket chainr wheels .is that the pitch-oftthe sprocketchain would 'vary while under the-influence of the heat of the hot clinker and fail to properly engage the teeth of the sprocket chain :wheel. Since the drag bardoes not ride'in any rigid position, any expansion due'to heat does notaffect the operation of the chain: V

The drag chain '32 is .moved over the stationaryagrate by the action of a reciprocating carriage 42,,operating on'the'lower run of thechain.

The carriage is located beneath the drag chain, and is provided with-.wheels'543 rolling on flanges 44:" :The'carriage isikeptin proper alignment by two centerguide wheels i'aylocated at each end-20f the": carriage, fitted; between rtwoguide flanges 4.6. .Thetwo'center guide wheels 45 are free ;-to"rotate between the-:g-uide:- flanges -46 and maintain proper alignment ,of- -the--carriage wheels l3'ronrthe flanges 4.6." Awdrag chain'engaging" member-is provided on-top-of -the carriage'v and comprises two pawis- H; provided with inrbearings'fifl. 'Thef-counterweights 48 arepro vided efoi'z'thet purpose Ef-"-rotating the -:shat 1.49, in-i'such a directionz-a'swtoalways keepthe pawls 4T :engag'ed with: the" links of the'drag=chain.-

' .The carriage is" actuated by a "variable speed redipiocating'*rfiuid motorwl, .attachedto the carriage--by:-.means'rofea shaft 7 52; and provided with'da' :bellows protection--53 to ;:prevent foreign matter from =Tentferi-ng the .IHOtOI'.

the-motor 5 l. imparts areciprocating moti'onitoithe carriage .42;- the-pawls j! :willengage corresponding links .13 9 'o'f i the drag 'chainand move the chain-= forward;-- When-Hthef motor reaches-.the enda-o'f sitszstroke; it wi1l -beg-in-its return! stroke bringingtherbjarriage Wit-hit. Due to the design :zcurvature :iof' th'e; pawls, they -:will not -e1igage therlink-pins: in the;return=--stroke, but wilhslipotzer the-pins and fall :behind them in arpositi'on-qioratheinextrpower stroke.- The length: of the stroke sofrthemotords greater than the pitch of the chain links :so as tzto as'sure that the*pawls :will always retract :fa "suiiicienti distance to engage themext: link:pin-for the powerjstroke. This isiimportant when itsis-consideredfihat. the chain -l ink* wi-ll'-vary inv pitch due rt-owthe expansionfrom the heat 'Of-thSiCllIIkGl, .orzth'e position of the chain may vary if the :chain should-the riding over a :piece of large clinker in the-cool ing chamber:

' ;Two discharging-hoppers 1'54 and 255 are-p rovidedyat thedischarge'endzof the cooling chamber; Beneath-thetwohoppers. are two conveyors 56'and 51 used asa-means of transportingthe cooled cement clinkeraway from the icoolerufor further processing.

As can be seen in Fig. 3, there isa: space defined by thebottom of the drag chain 3,8, the ;t0p orthe grate bars 2 6 and-the two cooler walls 1 5 and 1 G in which there can be placed aclinker layer B that will not be afi'ectedz-by the movement-of the.--d rag chain 32 This space :extendsthe length of the cooling chamber and is the same :depth "228113118 height of jthe-.two1-.rai1s-30 and-'31 that are the: support for the drag-chain as-rit moves through; the cooling chamber. In the (preferred-method;

. ingto the normal size of :the clinker discharged from the kiln and areplaced'in a layeroveifethe entire surface areaof the grate bars; .With-the' permanent clinker distributed over the topisur face of the'gratebars, the cooling-air that passes up-throug-h the openings inthe grate fromithe air'chamber is diffused as it'passes through the permanent clinker layer, thereby-preventing=any jet action or spots oflower resistance :tor the coolingair flowing into the coolingjchamberaof the cooler, This arrangement ,will insure an even air distribution into the coolingchamber.-

The advantage of thisr type of arrangement- 1s that as'the hot clinker is moved through the cooling chamber by the action of the drag chain, the hot clinker will movefover the permanent clinker layer instead of the grate bars, thereby eliminating the wear caused by theabrasive characteristics of cement clinker, found in the coolers of the prior art where the moving clinker is in direct contact with-its, supporting structure. In the present invention, the wear is clinker. on

' clinker insteadof clinker ion 'elements' of -.';the

cooler. It will also be noted-that the ends. ofiithe drag bar-38do not extend to the walls *IS-and l6, therefore there-is-.-a-deposit :of permanent clinker-formed in'this space-that will :absorb the wear instead of 'wear being on the walls of the cooler. A further advantage of this permanent clinker layer is that the ahot'c'linker to be cooled does not come into-direct-contactwith the metal grate bars, thereby eliminating thecost of expensiveheat resistant metal for these barssince; asthey are "protected-from the'heat of the :hot clinker and by radiant heatirom. the discharge end of the kiln by the permanent clinker layer, they can .-be: made fromgordi-nary steel 'without any special treatment;

Theoperation of the apparatus-willbe generany apparent from the foregoing. clinker falls iromthe kiln l-lto thevshelf 21, through the throat I 2 of'the cooler. "After- -the clinker particles have accumulated :on the shelf 2|, and have formed aznatural angle of repose, the descending clinker particles ;are distributed bythe pile j thus formed and fall to the -gi at structure 22. As these particles' of clinker ;f,orm into a pile, they are moved further into the cooling. chamber-J3 by the action of )the dra g chain fi. The. movement of the drag. chain-,will

The hot .9 form the particles of clinker into an evenly distributed bed as they are moved through the cooler. Cooling air from the air chamber'passes up through the grate openings, through the permanent clinker layer, into the moving bed of hot clinker. In passing through the particles of clinker in the permanent clinker layer, the air is duced at a .very rapid rate, or air quenched,

thereby. greatly increasing the quality of the cement. The cooling air then passes on into the combustion chamber of the kiln where it is utilized as secondary combustion air.

The moving clinker bed passes on through the cooling chamber where it is progressively cooled until it reaches the end of the grate structure. Here the drag chain pulls the clinker from the grate structure into the hopper 54. The conveyor 56 takes the cooled clinker discharge from the hopper and transports it to another point in the plant where it is further processed. Any clinker particles that remain on the drag chain are discharged into the hopper 55 as the drag chain passes over the drum 31, and are carried away by the conveyor 51.

As previously stated, the cooling air is used as secondary combustion air in the kiln, but under normal operation, the kiln does not require the total amount of air used for cooling. A vent stack 58 is provided to exhaust the excess air, and a damper 59 is provided to regulate the draft pressure within the cooler.

It will be understood that a relative flat clinker bed forms on the grate surface, and is moved toward the discharge end of the cooling chamber at a regular intermittent rate. The thickness of the bed and the rate of travel are controlled by the rate of reciprocation of the fluid motor. The individual clinker particles are subjected to a continuous agitating and rolling movement as they are conveyed through the cooling chamber. Since the discharge from the kiln is not a constant flow of material, but an intermittent flow with different quantities of clinker falling, the operation of the drag chain is regulated to a speed that will allow an average deposit of clinker pile to form before it is moved through the cooling chamber. As the deposited pile of clinker is moved, it is levelled off by the agitation produced by the drag chain. This agitation is created by the forward motion of the drag bar on the static pile of material, that is, as the bottom of the pile moves with the drag bar, the top of the pile is rotated in a reverse direction to be moved forward by the next drag bar. This agitation is produced throughout the cooling chamber, but is not of suflicient magnitude to cause the sifting or grading, of the smaller particles of clinker to the bottom of the moving bed, thereby causing an uneven distribution of the clinker particles throughout the moving clinker bed.

Iclaim:

1. Apparatus for cooling material comprising an elongated cooling chamber having means for introducing material into one end thereof and for discharging material at the other end thereof. gas-pervious supporting means extending lengthwise 'of the'cooling chamber and constructed and arranged to maintain a fixed layer of discrete particles of material thereon, guide rails extending lengthwise of .thecooling chamber and having their guide surfaces spaced vertically above the supporting means, conveying means including chains and transversely-extending spaced drag bars'forconveying material to be cooled'through the cooling-chamber, said conveying means-riding on 'the guide rails and being vertically spaced above the supporting means a distance sufiicient to permit a layer of discrete particles of material to be maintained on the supporting means and below the path of travel of the conveying means, whereby material being conveyed by the conveying means will be dragged along the upper surface of a fixed layerof material, and means for introducing air under'pres'sure below the supporting means to pass upwardly therethrough and through the fixed layer of material and the 'material being dragged along the upper surface thereof.

2. Apparatus for cooling material as defined in claim 1 in which the ends of the drag bars are spaced from each side of the cooling chamber to provide spaces between the sides of the cooling chamber and the ends of the drag bars, during the passage of the drag bars along the guide rails, for fixed bodies of discrete particles of material.

3. Apparatus for cooling material as defined in claim. 1 in which an intermittent motion is imparted to the conveying means.

4. Apparatus for cooling material as defined in claim 1 in which the conveying means is endless and the lower flight thereof passes beneath the cooling chamber, and means are provided for engaging the lower flight to impart an intermittent motion to the conveying means.

5. Apparatus for cooling material as defined in claim 1 in which the supporting means comprises spaced grate bars which are of generally Z-shape and are so positioned that they afford a path for the passage of air between them while substantially preventing overlying particles of material from falling through the spaces between them.

6. Apparatus for cooling material comprising an elongated cooling chamber having means for introducing material into one end thereof and for discharging material at the other end thereof, gas-pervious supporting means extending lengthwise of the cooling chamber, guide rails mounted on said supporting means and extending length- Wise of the cooling chamber, said guide rails having their guide surfaces spaced vertically above the supporting means, a fixed layer of discrete particles or material on the supporting means, conveying means including chains and transversely-extending spaced drag bars for conveying material to be cooled through the cooling chamber, said conveying means riding on the guide rails and above the upper surface of said fixed layer of material, whereby material being conveyed by the conveying means will be dragged along the upper surface of said fixed layer of material, and means for introducing air under pressure below the supporting means to pass upwardly therethrough and through the fixed layer of material and the material being dragged along the upper surface thereof.

7. Apparatus for rapidly cooling cement clinker comprising an elongated cooling chamber having means for introducing cement clinker into one end thereof and for discharging cement clinker at the other end thereof, spaced grate bars at the

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