US1572327A - Continuous kiln - Google Patents

Description

mwa? WM 5 Sheets-Sheet 1 ZWQUQ,

H. R. STRAIGHT CONTINUOUS KILN Filed March 17,

Feb. 1926.

3 Sheets-Sheet 2 Filed March 1'7 1924 Feb. 9 1926. l 1,572,327

H. R. STRAIGHT CONTINUOUS KILN Filed MaICh 17 1924 3 Sheets-Sheet 3 Patented Feb. 9, 1926.

UNITED ,STATES HALVEB R. STRAIGHT, 0F ADEL, IOWA.

CONTINUQUS KILN.

Application filed March 17, 1924. Serial No. 699,754.

To aU whom it 'may concern.'

le it known that I H ALvEl: R. S'ruAmnfr, a citizen ot' the United States, and a resident of Adel, in the county of Dallas and State oi' Iowa, have invented a certain new and useful Cont'nuous Kiln, of which the following is a speciiication.

This invention relates to what is commonly known as a continuous kiln, and is particularly designed for the purpose of burning brick, tile and hollow building blocks.

It is the object ot' my invention to provide a continuous kiln so arranged and proportioned that a very large amount of material may be burned at a comparatively small cost lor the construction of the kiln and the apparatus to make it operative, and at the same time to reduce the actual operating cost, such as for fuel and the like.

A further object is to provide a continuous kiln so constructed and arranged that the ware that is burned therein will have a better color.

More specifically it is the object of my in venten to provide a continuous kiln with improved lmeans for circulating the air through the kiln in such a manner that the ware may be quickly brought to the burning temperature without warping or cracking it; and also .so arranged that the ware maybe quickly cooled after it has passed through the burning zone.

A turther object is to provide in a continuous kiln employing' a. seres of movable ware bearing cars and arranged to be divided into a series of zones, improved means ot maintaining and regulating the amount and pressure ot air which travels through the various zones.

My invention consists in the construction` arrangement and combination of the various parts of the device, whereby the objects contemplated are attained, as hereinafter more fully set forth. pointed out in my claims. and illustrated in the accompanying drawings, in which:

Figure 1 is a plan view of my improved kiln.

Figure 2 is a vertical longitudinal sectional view of the same.

Figure 3 is an enlarged detail horizontal sectional View taken on the line S51-3 of Figure 2, with the cars removed.

Figure 4 is a. detail sectional view taken on the .1211@ H 0f Figure 3- Figure 5 is a taken on the line Figure 6 'is a view taken on the line (3e-6 of Figure 3.

Figure 7 is transverse sectional view taken on the line 7-7 ot' Figure 3.

Figure 8 is a detail sectional view taken on the line 8-8 of Figure 3.

Figure 9 is an enlarged detail sectional view showing a portion of the mechanism for advancing the cars in the kiln.

Figure 10 is a. front end elevation; and

Figure 11 is a rear end elevation.

My improved kiln comprises substantially two parallel upright walls 10 spaced apart ya 'considerable distance, between which is provided a pair of serpentine wall members 11, the wall members having their' innersurfaces arranged with the convex portion of one opposite the concave portion of the other one, as clearly illustrated in Figure 3. The space between the wall members 10 and 11 is filled with aninsulat'ng material 12. The convex portion o'f one wall member is connected with the concave portion ot' the opposite wall member at their top edges by means ot what I shall term drop arches 13. The radial center of said drop 'arches falling in a common vertical central longitudinal plane of the kiln. So that, all of the drop arches will lie in a common cylindrfcal plane.

Between each alternate set of drop arches 13 I have provided what I shall term an intermediate arch 14. The said intermediate arches have their radial centers in a vertical longitudinal plane at one .side of the centra] longitudinal plane. The other alternate spaces between the drop arches are provided with intermediate arches havingtheir centers on the opposite side` of the vertical longitudinal center. v

Extending longitudinally and centrally over the bottom ot' the kiln I have provided tracks 15 designed to receive a series oi ware bearing cars 16 mounted on wheels 1T and designed to travel over the tracks 15. Adjacent to each side ot the tracks 15 I have provided walls 1T, the faces of which are parallel wlth each other and parallel with said tracks. The top edge ot the walls 17 is provided with longitudinal grooves 18 1n which sand or similar material 19 is placed for the purposeof forming a seal between the lower portion of the kiln and the upper portion, as hereinafter describec,

transverse sectional view 5-5 of Figure 3.

detail transverse sectional Figure 4 ot' the dran-"ugs vmi The bottoms of each of the cars 16 are provided with heat insulat'ng material20, which may be formed of tire clay or similar substance, having alayer of insulator material 21 on its upper face. On top of the 1nsulatng material 21 I have provided a series of supporting blocks 22, each ot' which has its back and front edges provided with longitudinal grooves 23 sulostantially senncircular in cross section, so arranged that when two blocks are placed-side by side, a continuous passage will extend transversely over the bottom of the car, the upper side edges of eac-h of the blocks being cut away slightly to form slots 2l in conununicat-ion witht-he grooves 23, as clearly shown in The hollow blocks are set on top of the supports 22 in t-he manner shown in Figure 5, the said blocks being placed vertically so that vcrtical passages 26 are formed, the lower ends of which communicate with the grooves 23 and 2st. The outer edges of each of the insulating portions 2O and 21 are provided with plates 27, the lower edges of which extend into the sand 19 and into the grooves 1S.

Above the upper edge of the walls 17 I have provided a batile wall 28 built in the time the cars enter.

lower ends of the concave portions ot the` walls 11. The said wall 28 is of such height that its top edge will be substantially lin alincmcnt with the top of the supports 22, as clearly shown in Figures t, 5, and 6. Each of the walls 28 is provided with a series of notches or depressions 2S). the b ottoms of which are` substantially level with the bottoms of the grooves 23 of the supports 22. Thee depressions 29 are so aranged that one depression is immediately below each alternate intermediate arch 14, as clearly shown in Figure 4.

The top face oli' a stack of tile or ware which rests on the cars is provided with a series of circular segmental walls 30, the top edge of which is formed on the same radius as the inner face of the drop arches. These jwalls 30A are arrange-d transversely rnd spaced apart. a distance slightly less than the width of the drop arches, so that as the cars are advanced beneath the drop arches, the walls 30 will form a seal between the drop arches and said segmental walls, so that. the space between two adjacent drop arches will be praeti ally sealed between the space between the two other adjacent drop arches; This wil-l prevent a current ot' air from being drawn longitudinally through the kiln above the top surfaceot the stackof ware, but will permit currents of air to travel transversely over the top of the ware and between two adjacent drop arches. T he stack of ware on the car is of such width that it will Seal vthe space between the inner faces of the inwardly extending convex por? end. The boxing 42 tion of the walls 11. 'lhat is, thestack of ware so fits the inner lace of the walls l1 that a current of air could not be drawn longitudinally through the kiln above the supports 22.

In Figures l, 2, 3, and 4 it is assumed that the right hand end ot the kiln, as illustrated in said figures, is the inlet end, while the left hand end o'l said ligures is the delivery end of the kiln. '.l`hat is, the cars will travel from the right to the left as they pass through the kiln.

A suction 'fanl'l is located at the l'ront end of the kiln and has a delivery pipe 3; which extends into the drier kiln 23?. 'l`lu` -l'ront cud ol the kiln is provided with a pair oi' doors '-l arranged lo lle closed cach 'l'he cars are advanced through the kiln hy means ot a contimiousLy moving chain 235 mounted on suitable sprockets 36 and 57. rl`he. said sprockets may lne driven by any of the convenient wellknown methods. The said chain is provided with a series of lugs 38 which are spaced apart a distame equal to the length ot' the cars, and arranged in such a n'ianncr that they will engage the axle, as clearly shown in Figure 9, and will push the rear one ol the cars forwardly, which in turn will push the next car ahead of it.v and so on.

The chain 35 is mounted in a longitudinally extending hex 3f) of a height equal to thel distance between the lower i'ace of the axles and the floor, and of a width. equal to the distance between the supporting niembers for the axles, and of a length slightly gre-.iter than the length o'f a car. Each ol the cars is-provided with a transverse plate 40 which extends downwardly from the bottomo' the car and is provided with a notch 4lin its lower edge to fit the box 39. This provides means whereby the compartment below the bottom of the cars may be sealed l rom the compartment above the bottom of thevcars or above the .fand seals 18.

A similar boxing 42 is located in the opposite end of the kiln. These two boxings 'provide means together with the plates 40, whereby the compartment below the bottom of the cars is substantially scaled at each is provided with a door 43 for the purpose of permitting air to enter the delivery end of the kiln if so desired, the door being' hinged and designed to be propped open as desired. The said door forms a valve so that the tlow ot air beneath the oar may be regulated as here inatter described.

The plates 40 are of a length to .tit between the wall members 17. The notches il provide means whereby after the plates et@ ha vr passed over vthe boxings 39 and 42, the air may be moved longitudinally through the compartment beneath the bottom ot' the cars.

Located adjacent to each side of the walls '52 located above the 10 I have the. furnaces being provided with a grate or Stoker 45.l Each of the furnaces 44 is provided with a series of tuyres 46 extended inwardly and upwardly into a compartn'icnt 47, the said compartment being provided with a flash wall 48 between it and the ware. The said flash wall is provided with a series of vertically arranged llues 49, the lower ends ofwhich communilale with an aix` duct 50 mounted adjacent to the floor line and in one of the wall members 17, as clearly shown in Figure 7.. Each of the ducts 50 is provided with an upwardly extending flue 5l, the upper end otl which communicates with a compartment arches 13 and 14 extending longitudinally with the kiln. This upper compartment provides means whereby any heated air which passes through the said arches 13 and 14 will be drawn through the tlues 51 and the ducts 50 to the flucs 49 and delivered to the gaseous fuels from the furnace to complete the combustion thereof.

It will be seen that the air at this point is of considerable temperature. The fur-- naccs are supplied with air through pipes 53 extending into the coi'npartment beneath the bottom of the cars. Each of the pipes 53 has included a. blower 54 operated by means of a suitable motor 55.

By'this arrangement it will be seen that warm air will be fed to the gratos of the furnaces and the amount of air fed to the furnaces can be controlled by means of the door 43, while the air which is fed to the lines 49 may be controlledby-means of dampers 56 having hand rods 57 extending through the outer wall of the kiln.

An opening 5S is provided in one of the arch members 14 and communicates with the compartment 52, this opening being located ahead of the furnace, as illustrated'I in dotted lines in Figure 1. `Two other openings 59 and 60 are also located in the arches 14 and connnunicate with the compartment 52 on the opposite, side of the furnaces. The opening 59 is located above the oxidizing zone, while the opening 60 is located in or above the water smoking zone. All of these last said openings may be controlled by valves 61 having a handle 62 extending upwardly through the upper arch of the compartment 52.

The practical operation of my device is substantially as follows:

The doors 34. are first moved to an open position and then the loaded cars are advanced forwardly through the said doors by means ofthe chain mechanism 3F, with each succeedingr car butting against its preceding car until the kiln is'full of cars. after which the doors 34 are closed andthe tire is kindled in the furnaces.

The blower 31 is then started which will provided a furnace 44, each of v produce a partial vacuum in the front end of the kiln.

Assuming-that a complete cycle of burn ing and cooling has taken place, or that the kiln has actually been brought to the working temperatures, air will then be pulled through the opening 63 in the rear end. of the, kiln, which will locate at one side of the ware and will enter one'of the notches 29 then through the grooves 23v wardly through the slots 24 into the passages 26 of the ware. The air is stopped from going through the grooves 23 by means of the wall 28 on the opposite end of the opening 63, shown in Figure 3. The air will then move across the top of the ware between the ,segmental members 30 and bctween the first pair of drop arches 13, and thence down under the second drop arch from the rear end and into the notch 29a* on the opposite side of the kiln. The air will then move again through that portion of the grooves 23 which is opposite the notch 29l and then again upwardly through the passages 26, and thence down under the third drop arch 13 .into the notch 29". This operation is continued until it reaches the division indicated by the character A in Figure 3, which is adjacent to the first one of the furnaces 44. The incoming air from the first furnace will move over the top of the Ware in the compartment D and clown through the passages 26, then longitudinally through the grooves 23 and upwardly to the compartment B at which point the preheated' air from the point A and the products of combustion from the first ful'- nace will intermix.

The heated gases will at this point reverse their movement through the ware and pass downwardly instead of upwardly, and be delivered to the notch 29, and thence upwardlv over the top of the ware and again moved downwardly at the point C and delivered to the notch 29d. This is repeated until the. air is finally exhausted by the fan 5 and thence up- It will be seen that as the ware is going through the succession of operations just described, it will continuously get hotter as it is moved toward the furnaces, the ware being consequently cooled as it is advanced, and should be cool enough as it is delivered from the furnace so it can be easily handled.

By this arrangement it will be seen that a very large amount of resistance is offered to the incoming air between the inlet open-` ing 63 and the fan 31. so thata considerable vacuum may be maintained at the forward end of the kiln, which is the preheating end. I have found that the ware will dry more rapidly under a partial vacuum. The air that is discharged from the fan 31 may be delivered to the drier kiln 33 which is still warm, and-partially saturated with moisture from the air of the kiln. I find that it is advantageous to use a somewhat saturated air in the drier kiln, as this helps to prevent the checking of the ware during its drying.

Referring to Figure Q, it will further be seen that it' a vacuum is produced in the l'oi'ward end of the kiln, a large amount of the preheated air from the cooling end of the. kiln may be by-passed through the passage 52 around the furnaces, a portion of which will be delivered through the opening 5f) to the oxidizing zone, and a portion of it to the water smoking zone.

B v this arrangementl it will be seen that the color of the ware may be materially improved after it has passed the point in the high temperature zone where the reduction takes place, by the proper manipulation of the valves 43, 56 and 6l, causing a portieri of the oxygen to be cut off as the ware passes through this position. Any oxygen that might be added after this period will not cause any further oxidation.

It will further be seen that arranging the furnaces in the manner illustrated and just described, each side of the stack of ware will be heated, one side being heated by the f rst furnace and the opposite side by the second furnace. In fact, the alternating movement throughout the entire length of the kiln has a tendency to heat or cool the ware uniformly. This enables me to build cars of considerable width, which increases the capacity of the kiln and reduces the expense of operation, especially in the amount of fuel consumed, due to the fact that there is but a small loss due to the upper radiation of the arches on account of the passage 52. In fact, the only perceptible loss through radiation would be through the side walls 10, in which case it is no greater in a wide kiln than in a narrow one. The heat, as it is radiated downwardly, is taken care of through the compartment beneath the cars and is regained through the primary air supply for the furnace.

By providing the boxes 42 and the plates l0 I have provided means where a partial vacuum is also being maintained in the compartment below the cars. This has a tendency to decrease the leakage through the sand seal 18, the leakage being somewhat in proportion to the difference in the amount of vacuum between the upper and lower compartments.

Thus it will be seen that I have provided a vkiln which may be continuously operated, and which will be economical in its operation. and which will produce a liner grade of material at a less cost than has been possible to do previously.

I claim as my invention:

1. In a continuous kiln comprising a tunnel designed to receive a series of movable ware bearing cars, means for sealing the space between the cars and the walls of said tunnel so as to divide the tunnel into an upper and lower compartment at the floor line of the car, means for sealing the intake end of said kiln of both upper and lower compartments, means for sealing the outlet end of said lower compartment, a furnace between its ends, means for comnmnicating the furnace with said upper compartment to receive the products of combustion therefrom, and means for communicating the furnace with the lower compartment of said kiln so as to supply the air for the initial combustion, and means for mechanically circulating air through the last conducting means.

2. In a continuous kiln comprising a tunnel designed to receive a series of movable ware bearing cars, means for sealing the space between the cars and the walls' of said tunnel so as to divide the tunnel into an upper and lower compartment, means for sealing the intake end of said kiln in both upper and lower compartments, means for sealing the out-let end of said outlet compartment, a furnace between the ends of said lkiln and adjacent to one of its walls, a second furnace adjacent to the opposite wall of said furnace, said furnaces lying on opposite sides of a transverse plane extending through said kiln, means for communicating the furnaces with said upper compartment to receive the products of combustion therefrom, means for communicating said furnaces with the lower compartment of said kiln to deliver air from said lower compartment to said furnaces to sus-- tain the initial combustion.

3. In a continuous kiln comprising a tunnel designed to receive a series of movable ware bearing cars, means for sealing the space between the cars and the walls of said tunnel so as to divide the tunnel into an upper and lower compartment at the floor line of the car, means for sealing the intake end of said kiln of both upper and lower compartments, and means for sealing the outlet end of Said lower compartment, a furnace between its ends, means for communicating the furnace wit-h said upper compartment to `receive the products of combustion therefrom, and means for communicating the furnace with Ythe lower compartment 0`f said kiln so as to supply the air for the initial combustion.

4. In a continuous kiln comprising a tunnel designed to receive a series of movable ware bearing cars, means for sealing the space between the cars and the walls of said tunnel so as to divide the tunnel into an upper and lower compartment, means for sealing the intake end of said kiln in nient, a furnace both upper and lower compartments, means for scaling the outlet end of s aid outlet compartment, .the last said sealing means beingr provided with an opening, an adjustable door for said opening, a furnace between the ends of said kiln and adjacent to one of its Walls, a second furnace adjacent to the opposite wall of said furnace, said furnaces lying on opposite sides ofa transverse plane extending through said kiln, means for communicating the furnaces with said upper compartment to receive the products of combustion therefrom,- and means for communicating said furnaces with the lower compartment of said kiln to deliver air from said lower compartment to said furnaces to sustain the initial conibustion.

5. A continuous kiln comprising a tunnel designed to receive a series of movable ware bearing cars, said cars being sealed with the sides of said tunnel in such a manner as to divide the tunnel into an upper and lower compartment, means for closing the intake end of both of said compartments, means for closing the outlet end of the lower compartinent, and an adjustable door in the last said closed end.

6. A continuous kiln comprising a tunnel designed to receive a series of movable ware bearing cars, said cais being scaled with the sides of said tunnel in such a manner as to divide the tunnel into an upper and lower compartment, means for closing the intake end of both of said compartments, means for closing the outlet end of the lower compartment, an adjustable door in the last said closed end, a compartment above the sald tunnel, means for creating a partial vacuum at the intake end of said upper compartadjaceiit to one side of said kiln, means for communicating the furnace with the upper compartment to receive the partial products of combustion from said furnace, means for communicating` the said furnace with said lower compartment to snppllv air for producing a partial conibustion of the fuel, the furnace being so located as to divide the kiln int-o cooling, preheating and burning zones, means for 'communicating the compartment above the kiln with the cooling Zone, and means for communicating said compartn'ient with the prelieating zone.

'7. A continuous kiln comprising a tunnel designed to receive a series of movable ware bearing cars, said cars being sealed Awith the sides of said tunnel in such a manner as to divide the tunnel into an upper and lower compartment, means for closing the intake end of lboth of said compartments, means for closing the outlet end of the lower compartment, an adjustable door in the last said closed end, a compartment above the said tunnel, means for creating a partial vacuum'at the intake end of said upper compartment, a furnace adjacent to one side of said kiln, means for communicating the furnace with the upper compaitineiit to receive the partial products of combustion from said furnace, means for communicating the said furnace with said lower coinpartment to supply air for producing a 'partial combustion of the fuel, the furnace being so located as to divide the kiln into cooling, preheating and burning zones, means for Communicating the compartment above the kiln with the cooling zone, means for communicating said compartment with the preheating zone, and means for coniiuuiiicating with the compartment above said kiln for supplying auxiliary air to said burning zone, the air being made to pass the furnace in such a manner as to come preheated.

8. A continuous kiln comprising a tunnel to receive a series of movable ware bearing cars, means for sealing the bottoms of the cars to the sides of said tunnel in suoli a manner as to divide the tunnel into upper and lower compartments, means for closing one end of said compartments, means for closing the opposite end of the lower compartment, means for producing a partial vacuum in the closed end of said upper compartment, and a furnace for supplying heated gases to said tunnel, and means for drawing air from the lower compartment and delivering it to said furnace for producing combustion.

9. A continuous kiln comprising a tunnel having its inner vertical Walls formed serpentine with the concave portions of one wall opposite the convex portions of the opposite wall, and the concave portions of each of said walls being in alinement.

10. A continuous kiln con'iprising a timnel having its inner vertical walls formed serpentine with the concave portions of one wall opposite the convex portions of the opposite wall, the concave portions of each of said walls being in alineinent, a series of drop arches over said convex and concave portions of said Walls, an intermediate arch between each pair of said drop arches, the spaces between each alternate pairs having their arches in a common center of said intermediate arches taken to one side of the center of said drop arches, the intermedia-te arches between the alternate pairs having their centers taken at the opposite side of the centers of said drop arches, substantially as described.

11. A continuous kiln comprising a tunnel having its inner vertical walls formed ser pentine with the concave portions of one wall opposite the convex portions of the opposite wall, tlie concave portions of 'each of said walls being in alinement, a series of drop arches over said convex and conplane and thel cave portions of said walls, an intermediate arch between each pair of said drop arches, the spaces between each alternate pairs having their arches in a common plane and the center of said intermediate arches taken to one side of the center of said drop arches, the intern'iediate arches between the alternate pairs having their centers taken at the opposite side of the centers of said drop arches, the bottom edges of said side walls being provided with shallow walls having parallel faces, the upper edges of said shallow walls being provided wit-h a series ot notches.

l2. In con'ibination, a continuous kiln coniprising a tunnel. having its vertical side walls formed serpentine with the convex portions of one wall opposite the concave portions of the opposite wall, said tunnel being designed to receive a series of ware bearing cars of a width equal to the distance between the convex portions of said vertical walls, each of the cars being provided with a platform having a series of transversely arranged grooves, the cars being designed to receive ware stacked in such a manner that perpendicular bases will be formed in con'imunication with said transverse grooves, a series of arches above said walls so arranged as to form the space above said cars into a series of compartments, means located at one end of said kiln for prodiufine a partial vacuum and for drawingl air nrst through the transversely arranged grooves and upwardly through the ware, then down the opposite side of said cars again through the transverse grooves inthe opposite direction, and thence upwardly and then down the rst side of said cars, the air being advanced forwardly in each operation.

13. In combination, a continuous kiln comprising a tunnel having its vertical side walls formed serpentine with the convex portions of one wall opposite the concave portions of the opposite wall, said tunnel being' designed to receive a series of ware bearing cars of a width equal to the distance between the convex portions of said vertical walls., each of the cars being pro-- vided with a platform having a series of transversely arranged grooves, the cars being designed to receive ware stacked in such a manner that perpendicular bases will be formed in communication with said transverse grooves, a series of arches above said walls so arranged as to form the space above said cars into a series of compartments, said cars being provided with means for sealing the top and outer edges of the platform of said cars with the side walls of said tunnel so as to form upper and lower compartments, the lower edges of said side walls being provided with a series of notches of a depth equal to the depth of said trans- .verse grooves of said platforms and of a height level with the top of said transverse grooves.

14. In combination, a tunnel kiln having cooling, burning and preheating zones, a series ot ware bearing cars, each of which is provided with a floor having transversely arranged conductors for supporting the ware thereon, the ware arranged in such a manner as to produce vertical passages having their lower ends in communication with said transverse conductors, means for closing one end of said kiln, means for producing a partial vacuum at the said closed end, the said tunnel being arranged with deflectin' means whereby air will be caused to enter the open and delivery end of said kiln as the vacuum producing' means is operated to enter the transverse passages of said cars and up- 'ardly through-the ware for a given section and downwardly to one side of theware and again through' horizontal passages in the opposite direction from the first said passages throughout the cooling zone, means 'for reversing the direction of the air causing it to move downwardly through the, ware outwardly through the transverse passages and up the sides as it goes through the preheating zone.

15. In combination, a tunnel kiln having cooling, burning and preheating zones, a series of ware bearing cars designed to move successively through said zones, said cars being designed to carry ware arranged in such a manner as to produce vertical passages, means for moving air through the ware first from the cooling zone so as to move upwardly through the ware, thence to be delivered to the burning zone where it 1s mixed vwith the products of combustion, then designed to move downwardly' through the ware as it passes through the preheating zone, and means for moving and exhausting the air from the preheating zone. .16. A continuous kiln having preheatlng, burning and cooling Zones and a furnace, a series of ware bearing cars, means for dividing the tunnel into upper and lower compartments at the floor line of said cars. and means for exhausting the air from the lower compartment and supplying it to the furnace to produce initial combustion.

17. A kiln construction comprising substantially. upright and parallel wall members, the wall members being provided with aseries of .vertical recesses, the top of said kiln comprising a series of drop arches and intermediate arches, the drop arches having the centers of their radius in a common central longitudinal plane, and each alternate intermediate arch having its center in a plane parallel with and to one side of the first said plane and the other alternate in termediate arches having their radial centers in a common plane at the opposite side n furnace adjacent to one of the said central longitudinal pla-ne, substantially as described and for the purposes stated.

18. In u tunnel kiln of the class described, side of the kiln, a` bag Wall interposed between the furnace und the interior of said kiln, said bag wall being provided with u series of vertical passages, and means for permitting air to move through said passages to complete the secondary conibustion, the top edge of said bag Wall being near the lop of the kiln. Des Moines.v Iowa, December Q0, 1923 HALVER R. STRAIGHT.

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