US2081954A

US2081954A - Tunnel kiln and method of operating same

Info

Publication number: US2081954A
Application number: US739223A
Authority: US
Inventors: Phillips Gordon Dudley
Original assignee: Individual
Current assignee: Individual
Priority date: 1934-08-10
Filing date: 1934-08-10
Publication date: 1937-06-01
Anticipated expiration: 1954-06-01

Description

June 1, 1937. Q PHlLLlPs Q 2,081,954

TUNNEL KILN AND METHOD OF OPERATING SAME Original Filed Aug. 10, 1934 2 Sheets-Sheet l FEET * INVENTOR Ga/wa/v Duazzyfimuas Q Ma.

TTORNEY June 1937- cs. D. PHILLIPS 2,081,954

TUNNEL KILN AND METHOD OF OPERATING SAME Original Filed Aug. 10, 1954 2 sheets-sheet 2 Patented June 1, 1937 TUNNEL KILN AND gIETHOD OF OPERATING Gordon Dudley Phillips, Portville, N. Y.

Application August 10,

1934, Serial No. 739,223

Renewed August 10, 1936 20 Claims.

My present invention relates to kilns of the type commonly called continuous tunnel kilns, in which goods are subjected to a heat treatment by progressively advancing them through an elongated kiln chamber in which they are subjected to such temperature modifying effects that as each piece or portion of the goods treated is moved through the kiln chamber, its temperature is varied in more or less close accordance with a predetermined program. For many purposes, including those for which the present invention is especially useful, such akiln includes a heating up or preheating section extending away from the entrance end of the kiln in which a substantial portion, and usually the major portion, of the increase in goods temperature is efiected, and an adjacent high temperature section in which a further increase in goods temperature is effected. Usually also such a kiln includes a cooling section between the high temperature section and the exit end of the kiln in which the goods temperature is suitably reduced prior to the discharge of the goods from the kiln.

The general object of the present invention is to provide improved heating conditions in the preheating sections of kilns of the above mentioned type. More specifically considered, the object of the invention is to provide means for so regulating the supply of heat to, and the flow of heating gases through the preheating section of such a kiln, as to insure a proper graduation in the temperatures attained by the goods at different points along the length of the preheating section of the kiln, and to maintain a suitable uniformity in goods temperatures at all points in a plane transverse to the length of the kiln and intersecting the goods space of the latter at any point along the length of its preheating section. Aj fur'ther object of the invention is to provide for the attainment of the objects previously mentioned under conditions of kiln operation varying as a result of variations in the rate of kiln operation and/or in the character of the goods treated and in the nature of the heat treatmerit to which they are subjected.

Ari understanding of the invention and its especial characteristics may be facilitated by the immediately following explanations concerning general operating conditions in kilns of the above mentioned type and particularly in the preheating sections of such kilns, and concerning certain special problems encountered in effecting the general improvements in operation attained by the use of the present invention.

(In many uses made of continuous tunnel kilns,

the character of the goods treatment and/or the nature of the heat treatment to which the goods are subjected require that the goods temperatures increase efiected in the preheating section should be relatively slow and gradual. For example, in the production of vitrified tiles, the heating up operation involves in addition to the mere increase in tile temperature, an initial tile drying action and a subsequent tile oxidizing action, the latter eliminating sulphur compounds and/or other objectionable constituents of the ceramic material from which the tiles are made. The drying and oxidizing actions each require an appreciable amount of time to permit the gradual expulsion from the tiles of the vapors or gases which must be expelled slowly to avoid warping and disruptive effects within the tile bodies or at their surfaces. It the tile surfaces are heated to the vitrification temperature prior to the expulsion of all of the gases which should be expelled in the drying and oxidizing stages, the ultimate product is necessarily imperfect as a result'of the retention of gases in the tiles or the surface marring efiect of gases expelled after surface vitrification begins, or from both causes.

Regardless of the character of the goods treated or of the nature of heat treatment, uniformity of goods temperatures at all points along any transverse plane through the heating up section of the kiln is generally desirable for various reasons and particularly because it is conducive to the maximum permissible rate of heating up, for unless such uniformity of heating up is suitably approximated some portion of the goods will be heated more slowly than other portions and in practice, the time required for suitably heating up the portion of the goods which heats up more slowly must be the time required for the entire heating up process. Any necessity for slowing the heating up process to avoid or minimize the injurious effects of nonuniformity in goods heating is generally objectionable, since it results in a reduction in the full load capacity of the kiln, or, stated differently, requires a longer and more expensive kiln for a given full kiln load output thanwould be required if the heating up operation were conducted more rapidly.

In continuous tunnel kilns as heretofore constructed and operated, non-uniformity in heating up different portions of the goods treated results primarily from kiln heating conditions tending to higher goods temperatures at the tops of "the goods stacks mounted on the kiln car platforms or movable kiln hearth than at the bottoms of the stacks and tending to higher temperatures at the surfaces of the stacks and particularly the stack surfaces adjacent the sides of the kiln chambers, than in the interior of the stacks. Any approm'mation to uniform heating of a stack of goods requires a circulation of the kiln atmosphere through the goods or over the surfaces of the saggars in which the goods are contained. Heat transmitted to a stack of goods by radiation from the kiln walls to the stack tends inevitably to a more rapid heating of the goods adjacent the exterior surfaces of the stacks than of the goods in the interior of the stacks.

In practice as already indicated, a satisfactory solution of the problem of uniformity in the rate of heating up, must take into account the fact that in ordinary kiln operation the rate of goods movement through the kiln chamber must vary from time to time in accordance with variations in the demand for the goods treated, or in the rate at which they can be prepared for treatment. In other words, in ordinary practice, a tunnel kiln may be operated at full capacity at some times and at part capacity at other times. Thus for the same heattreatment of the same goods it may be necessary, for example, to move each piece of goods treated through the kiln in 30 hours While at other times it may be practically desirable to so reduce the kiln capacity that 50 or 60 hours will be required for the passage of a piece of goods through the kiln.

For the same heat treatment, it is in general desirable that all pieces of goods moving through the kiln shall attain substantially the same temperature at any particular distance from the entrance end of the kiln, regardless of the rate of goods travel through the kiln, and notwithstanding the fact that a reduction in the rate of goods travel reduces the amount of heat necessarily supplied to the kiln for the treatment of the goods and tends to a corresponding reduction in the volume of heating gas flow through the preheating section of the kiln.

With well designed and constructed kilns, it is practically desirable to regulate the heat supply to the high temperature section of the kiln as required to maintain suitable temperature conditions therein with a wide variation in the rate of goods travel through, or operative capacity of the kiln, but whether the kiln be of the muffle heated or open fire type, differences in the rate of heat supplied to the high temperature section of the kiln tend to modify the kiln atmosphere circulation and temperature conditions in the preheating section of the kiln. This is especially apparent in the case of open fire kilns, wherein all or a large portion of the heat absorbed by the goods in the preheating section is absorbed from the heating gases entering that section from the high temperature or furnace section of the kiln and necessarily increasing and decreasing in volume as the rate at which the goods moved through the kiln increases and decreases. From the practical standpoint therefore, a satisfactory control of heating conditions in the heating up section of the kiln requires a capacity for adjustment to compensate for the effect of variations in the rate at which goods are moved through the kiln.

Regardless of special eifects due to special conditions of use and operation, there are certain general factors of kiln operation which in all ordinary uses of continuous tunnel kilns tend to produce temperatures in the upper portion of the preheating zone of a continuous tunnel kiln in excess of the temperatures in the lower portion of said zone at corresponding points along the length of the kiln. For one thing more heat is ordinarily needed in the lower than in the upper portion of the preheating zone because of the need to heat up the kiln cars or movable hearth employed to carry the goods through the kiln. When that hearth is composed, as it usually is, of kiln cars which have relatively massive upper body port-ions of refractory material, and which are initially introduced into the kiln at atmospheric temperatures or at least at temperatures materially lower than the maximum goods temperature obtained in the preheating section of the kiln, a large portion of the heat used in the preheating section of the kiln is used in heating up the kiln car bodies, and unless the latter heat up as rapidly as the goods, they rob heat from the goods and particularly from the goods in the lower portion of the kiln.

There is a natural tendency for the gases in the upper portion of the kiln to be hotter than the gases in the lower portion, because of the differences in density of gases at different temperatures. goods temperatures in the upper portion than the lower portion of the kiln is especially pronounced in the preheating zone of the kiln b cause the relatively rapid rate of goods temperature increase occurring in that zone tends to relatively wide temperature differentials therein.

The excess of top temperatures over bottom temperatures in the preheating section of the kiln tends to produce a movement of the kiln atmosphere which is commonly referred to as drift, or longitudinal drift, and which is characterized by a movement towards the entrance end of the kiln chamber of the gases in the upper portion of the chamber relative to the gases in the low-er portion of the chamber. In the case of an ordinary muffle heated kiln, there is an actual flow of kiln atmosphere toward the entrance end of the kiln in the upper portion, and away from said entrance end in the lower portion of the preheating section of the kiln chamber. In an open fired kiln in which the heating gases are withdrawn from the bottom of the kiln chamber at or near its entrance end, the heating gases ordinarily flow towards the point or points of withdrawal at all levels in the preheating section of the kiln, but the velocity of flow longitudinally of the kiln is substantially higher in the upper portion of the kiln chamber than in the lower portion thereof.

Heretofore various expedients have been employed and prcposedfor controlling or modifying circulation and temperature conditions in the preheating section zone of -a continuous tunnel kiln for the purpose of improving heating conditions thereon, but so far as I am aware no expedients heretofore employed or suggested, for the purpose have been adequate, at least to the extent of satisfactorily taking care of some conditions of operation which may be taken care of suitably by the use of the present invention, wherein some of those expedients are used in new combinations including one or more expedient not heretofore used or proposed for said purpose.

One prior expedient employed in an effort to minimize difficulties due to longitudinal drift, consists in the injection of an air or gas jet or stream into the top of the kiln chamber at or adjacent and directed away from the entrance end of the kiln, as set forth in the Dressler Patent The resultant tendency to higher .l"

1,369,330 granted February 22, 1921. Advantageous use of that expedient may sometimes be made in the practice of the present invention where so used in connection with other features of the present invention advantageous results are obtained which are not obtainable with said expedient when used alone, for while such a longitudinal air or gas jet or stream may modify the longitudinal drift, it can not of itself eliminate such drift, nor can it of itself insure similar temperature conditions at the top and bottom of the kiln, except perhaps in an unduly short localized portion of the heating up zone of the kiln. Other prior expedients which are used in the practice of the present invention and contribute to the attainment of advantages and results not obtainable from the use of such expedients as heretofore employed or proposed for use, include provisions for the withdrawal of gases from the bottom of the kiln chamber at points adjacent but at different distances from the entrance end of the kiln, and recirculating provisions for returning to the top of the kiln chamber some of the gases withdrawn from the bottom of the kiln chamber, as collectively shown, for example, by the Dressler Patent 1,509,195, granted September 23, 1924, and the Weber and Schleiffarth Patent 1,575,470, granted March 2, 1926.

The method of and provisions for withdrawing gases from, and returning more or less of the gases withdrawn to the kiln in accordance with the present invention, depart from the prior art materially in respect to the location, and relative location, of the points at Which gases are withdrawn from and returned to the kiln. In the preferred form of the invention, a portion of the gases withdrawn from the kiln, is withdrawn from the kiln chamber partly at or immediately adjacent the low temperature end of the preheating zone of the kiln, and preferably is so withdrawn from the lower portion of the kiln, and another portion of the gases withdrawn is withdrawn from the lower portion of an intermediate section of that zone appreciably removed from its low temperature end but between the latter and the high temperature end of the zone. More or less of the gases so withdrawn are returned to the top of the kiln at points in a longitudinal section thereof displaced from the low temperature end of the preheating zone relative to the kiln section including the points from which the gases so returned are withdrawn from the kiln. In consequence, the gases so returned to the top of the kiln are low enough in temperature to maintain temperature conditions in the upper portion of the kiln chamber adjacent the points of return which are lower than would normally there exist if the gases were not so returned. The gases returned at the top of the kiln thus tend to a reduction of the top temperatures in the preheating zone directly by virtue of the temperatures of those gases, as well as by their drift opposing action.

A portion of the gases withdrawn from the intermediate section of the preheating zone as above described, is returned to the lower portion of a section of the kiln between said intermediate section and the low temperature end of the preheating zone. The gases so withdrawn from and returned to the lower portion of the kiln are hot enough to maintain temperatures in the lower portion of the kiln section to which they are returned suitably higher than would normally there exist if gases were not so returned.

The withdrawal of gases from the lower portion of the kiln at or immediately adjacent the low temperature end of the preheating zone coupled with the return of relatively hot gases into the lower portion of an adjacent section of the kiln, permit of the maintenance in the last mentioned kiln section of suitably related bottom and top temperatures, and the maintenance in that kiln section of gas pressure and flow conditions which preclude the longitudinal drift flow in that section of the kiln, characteristic of prior kilns, and especially serious and objectionable in a kiln of the open fired type because of the inevitable inflow of air into the kiln past the door normally closing the kiln entrance doorway, as it is not practically feasible to employ an entrance door which will tightly seal the entrance doorway.

The invention in its preferred form is further characterized by the return of gases to the upper portion of the kiln wholly or largely in jets which because of their jet velocity and disposition provide gaseous curtains or baffles extending transversely across the upper portion of the kiln and tending directly to prevent the longitudinal drift iiow toward the entrance end of the kiln in the upper portion of the kiln chamber.

The drift preventing jet action just referred to may be secured with jets extending vertically downward from the top of the kiln chamber, or with jets which enter the upper portion of the kiln chamber proper with a generally horizontal direction of flow away from the entrance end of the kiln chamber. In either case, the jet flow should extend transversely across the width of the upper portion of the kiln chamber. In some cases horizontal jets, rather than vertical jets, are necessarily or desirably employed because of kiln structure features or, and more importantly, because of the character and disposition of the wares treated. For example, in firing vitrified plates which are assembled in stacks with a dust of fine clay or other suitable material between the plates to prevent them from sagging, high velocity vertical jets would have a tendency to dislodge some of the dust. Moreover, plates stacked up as just described are ordinarily mounted on cars having multiple loading decks, and the car decks would interfere with a vertical jet. action effective to prevent longitudinal drift. In general with vertical jets a higher jet velocity and a smaller jet gas volume are required than when the jets are introduced horizontally. A high velocity vertical jet apparently prevents the drift tendency primarily as a result of the kinetic energy of the jet which forms a drift resisting veil or curtain across the upper portion of the kiln chamber and induces an adjacent downflow of the main volume of gases moving through the preheating section of the kiln toward its entrance end. With the larger volume and velocity of the horizontally introduced jets, the iatter bodily oppose and tend to push back the main kiln atmosphere in the upper portion of the kiln, and to an appreciable degree, atleast, the general downflow of the main volume of gases thereby produced is apparently due to the relatively high density of the jet gases which are introduced at temperatures lower than those of the main volume of heating gases the points of jet introduction. With horizontallyintroduced jets there is tendency to thermal shock to the wares than with the vertical jets, a horizontally introduced jet creates a desirable chest in a longer section of the kiln than does a vertical jet.

In its preferred form the invention is further characterized by the introduction of heating gases into the lower portion of a more or less extended section of the preheating zone adjacent the high temperature end of that zone, to supplement the bottom heating effect of the main body of heating gases coming to the preheating zone from the high temperature zone of the kiln. This supply of additional heat to the lower portion of the kiln tends directly to the maintenance of bottom temperatures which are suitably related to the top kiln temperatures, but the amount of additional heat so supplied is necessarily restricted by the necessity for a suitableprogressive variation in the kiln temperatures longitudinally of the'preheating zone.

In effect, the use of the invention makes it possible to obtain the normal preheating zone temperature increase in a preheating section of the kiln which is shorter than has been required heretofore to avoid excessively high top kiln temperatures at the extreme entrance end. In other words, without the use of the other driftpreventing expedients herein provided, the use of the auxiliary burners at the high temperature end of the preheating zone would result in topkiln chamber temperatures altogether too high in the portion of the kiln between those burners and. the entrance end of the kiln.

As those skilled in the art will now understand, the invention is characterized generally by the use of different expedients in different longitudinal sections of the preheating zone of the kiln. In the section of the zone adjacent the high. temperature end of the latter, conditions are directly improved wholly or mainly by the add;- tional heat supplied to the bottom of the section. In an intermediate section of the zone, the recirculating provisions directly improve conditions. by increasing the volume of longitudinal flow in the lower portion of the kiln relative to that in. the upper portion, and by the downfiow through the kiln due to the above mentioned thin transverse jets or streams. In the section of the preheating zone adjacent the low temperature end of the latter, conditions are directly improved. mainly by supplying gases to and withdrawing gases from the lower section of the kiln. It will be apparent, however, that the improvement in conditions in each such longitudinal section of the preheating zone directly due to the special expedients employed in connection with that section of the zone, is facilitated and to a certain extent made possible by the improvements in conditions directly effected by other expedients in the other sections of the zone.

The use of the invention tends generally to an increase in the volume, and hence in the velocity, of the gas flow through the preheating zone of the kiln, and thus increases the amount of heat which can be transferred from the gases to the goods and correspondingly reduces the temperature of, and consequently the amount of heatcarried away from the kiln by the gases which are withdrawn from and not returned to the preheating zone of the kiln.

In its preferred form of embodiment, the invention is further characterized by the flexibility of regulation provided, whereby the temperature modifying and flow controlling effects of the auxiliary heat supplying means and recirculating provisions may be modified as changes in the rate of kiln operation, or in the character of the goods heated or the character of their heat treatment may make desirable. A practically important advantage of the invention arises from its availability for use in kilns already constructed as well as in kilns to be constructed wherein the general kiln construction and arrangement is in accordance with standards heretofore developed and found desirable. In other words the use of the invention requires little or no change in kiln construction except by way of the addition of easily added parts.

The various features of novelty which char- :acterize my invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, however, and its advantages and specific objects obtained with it, reference should be had to the accompanying drawings and descriptive matter in which I have illustrated and described a preferred embodiment of the invention.

Of the drawings:

Fig. 1 is a diagrammatic elevation of the entrance end portion of a kiln and circulation and temperature control provisions associated therewith;

Fig. 1A is a diagrammatic elevation of a portion of a kiln illustrating circulation conditions therein when horizontal drift preventing jets are introduced into the top of the kiln chamber;

Fig. 2 is a temperature diagram illustrating goods temperature conditions obtainable in the kiln of Fig. 1;

Fig. 3 is an elevation, and Fig. 4 is a plan view, each partly in section, of the entrance end portion of a commercial type kiln adapted for use with the temperature control provisions illustrated diagrammatically in Fig. 1; and

Fig. 5 is a transverse section on the line 5-5 of Fig. 4 with a kiln car shown in the kiln.

In Fig. 1, I have illustrated somewhat diagrammatically the entrance end portion of a continuous tunnel kiln A provided with one form of embodiment of my invention for controlling temperature conditions in the preheating zone or section of the kiln. In normal operation, kiln cars are successively introduced in the kiln A at its entrance end through a lateral opening nor mally closed by the doors, and are moved progressively through the portion of the kiln chamber shown in Fig. l and thereafter through the unillustrated portion of the kiln at the right of the portion shown in Fig. l.

The temperature control provisions associated with the portion of the kiln shown in Fig. 1, include devices B-B and 1), b b etc. for supplying a gaseous heating medium to the lower portion of the along the length of the kiln. In a direct fired kiln of the type specifically illustrated in Fig. 1, and as shown, the devices BB and b, b b etc. may and ordinarily would be gas or oil burners, and each individually regulatable, as by means of a throttling damper or valve C. In addition to the above mentioned heating devices, the temperature condition controlling means shown in Fig. 1 include low and high temperature exhaust and recirculating fans D and F, respectively, and conduit connections thereto for withdrawing gases from and returning a portion thereof to the kiln chamber at suitable points, and for discharging the portion of the gases Withdrawn from the kiln chamber and not returned to the latter. In addition to the heating medium supplied to the kiln chamber by the above mentioned burner devices B-B and b, b b etc., in an open fired kiln of the type shown diagrammatically in Fig. 1 a large volume of heating kiln at points suitably distributed "gases normally flows into the right hand portion of the kiln shown from the. unshown portion of the kiln containing the main furnace or high temperature kiln burners.

As will be apparent, the portion of the air and gases withdrawn by the fansD, and F from the kiln and not returned tothelatter must be equal in amount to the total amount of air and gases entering the preheating section of the kiln from the high temperaturesection of the kiln and through the burners discharging directly into the preheating section, and expelled from the goods heated in the heating up operation.

The lowtemperature exhaust and recirculating fan ,D has its intake connection D. leading from the lower portion of the kiln chamber at the extreme. entrance end of, the, latter. A portion of the gases exhausted from the kiln chamber by the fan D may be discharged to the atmosphere through the fan outlet D which may be connected to .or constitute the discharge stack of the kiln, and more or less of the gases exhausted by the fan D maybe returned to the kiln through inlet nozzles E and E at the top ofthe kiln chamber to which gases are passed by branch pipes D and Di respectively. .The relative amounts of gases passingthrough the pipes D D and D are controlled by dampers C and the pipes D and D and by a damper C, in the main outlet pipe D at the outlet side of the connectionof the latter to the branch pipes D and D The throttling effect of the damper C is adjusted to insure a suitable static pressure at the fan intake and in the branch pipes D and D The return or inlet nozzle E is located adjacentbut at some distance from the entrance end of the kiln, and the nozzle E at a somewhat greater distance from said kiln end.

The high temperature exhaust and recirculating fan F is shown as provided with an intake comprising branches F, F F opening from the lower-portion of the kiln chamber at suitably distributed pcints along the length of the latter, and each regulable by adjustments of a'corresponding throttling damper C The fanF discharges gases into a distribution piping shown as including branches F F F F and F The branches F and F returngases to the lower portion of the kiln. at points adjacent but progressively spaced. away from the kiln entrance end, and between the latter and the points at which the branches F F and F lead fromv the kiln. As shown the branches F and F are connected to the kiln at points between the kiln entrance door and the nozzle E. The discharge through each of the branches F and F is directly controlled by a corresponding damper C The discharge branches F and F are connected to recirculation or inlet nozzles e and e discharging downward into the kiln chamber at its top at suitably distributed points along the length of the kiln chamber, the discharge through each nozzle being directly controlled by a corresponding damper C The discharge branch F delivers into the previously-mentioned discharge stack or stack connections D at the outlet side of the damper C in the latter, fiow through the branch F being controlledby a damper C The throttling effect of the damper C is adjusted to assure a suitable static pressure at the fan intake and in the branch pipes F F F ,-and F".

The goods may be moved through the kiln chamber on cars each like the usual type of the kiln car I-I showninfFig. 5, which comprises a goods supporting platform I-I above a space H stacked up in saggers on the kiln cars.

formed in the car body beneath its platform, and through which the kiln atmosphere may circulate transversely of and in the direction of the length of the kiln car. The space H of each kiln car is open at the sides and ends of the car and communicates with the goods space proper above the car platform through ports or openings in the latter. In a, kiln in which such cars are employed, the various burners BB 1), b etc. and the recirculating inlets F and F are advantageously duplicated at the two sides of the kiln spaces H The low temperature fan D may well have its intake D opening centrally into the lower portion of the kiln chamber through the entrance end Wall of the latter. Advantageously each of the recirculation top inlets E, E, e and 6 extends across the top of the kiln chamber for substantially the full width of the latter, and is preferably arranged so that it discharges gas downward into the kiln in the form of a vertical sheet or veil extending transversely across the kiln chainber.

. The distribution longitudinally of the kiln chamber of the various heating devices B'B b, 19 etc. and the recirculation connection F F and the inlets E, E, e and e and indeed the number of said burners and recirculating connections, and the proper adjustment of the various control dampers, may obviously vary widely as variations in the character of the goods treated, in the goods temperature conditions desired and in other operating conditions may make desirable.

By way of illustration and example, and not by way of limitation, attention is directed to the temperature curves in Fig. 2, which represent desirable temperature conditions obtained in practical "operation of a continuous tunnel mm of commercial type which was originally constructed for'operation without, but was subsequently modified for operation with the recirculating provisions, and with the burners B'-B shown in Fig. 1. In Fig. 2 the abscissas are distances in feet measured longitudinally of the kiln from the entrance end of the latter, and the ordinates are temperatures measured in degrees Fahrenheit. Said commercial type kiln as originally installed was a typical example of the well known Dressler multi-burner open fired type, and included well approved features of construction and arrangement illustrated in Figs. 3, 4 and 5 and hereinafter described. Said kiln as originally constructed was practically effective for the purpose for which it was installed and was initially employed, but when it subsequently became desirable to use the kiln in the manufacture of certain forms of large vitrified tiles presenting greater drying and oxidizing dificulties than the goods initially treated, it was found difficult to suitably prolong the period required for heating the goods through a temperature range, critical in such case, and varying from about 1200 F. to about 1800, and practically impossible to maintain a suitably close approximation to uniform temperatures from the top to the bottom of the tiles The goods temperatures then obtained were very different from those obtained after the kiln was modified in construction and operation in accordance with the present invention.

In Fig. 2, T and T represent goods temperatures at the top and bottom, respectively, of the goods stacks on the cars, obtained as each particular stack moves away from the entrance end and through the preheating section of the latter illustrated in Fig. 1. As will be apparent to those skilled in the art, the diiferences between the temperatures shown by the curve T at any particular distance from the entrance end of the kiln are quite small, and by refinements in the regulation provided for in Fig. 1, it is possible to practically eliminate all differences between the temperature shown by the two curves.

The kiln shown in Figs. 3-5 as originally installed, included a preheating section joining with a furnace or high temperature kiln section at a point along the length of the kiln intermediate the burners B and b. As originally installed, the burners b, b and 13 formed part of the regulable high temperature kiln section heating means, and burners B and B were also included in the original installation, and were intended to extend bottom heating as far as possible toward the entrance end of the kiln.

In the kiln shown in part in Figs. 3-5, the said preheating section is approximately one hundred feet long, the intermediate high temperature section of the kiln is about eighty-one feet long, and the cooling zone section of the kiln extending between the high temperature section and the exit end of the kiln, is about eighty feet long. The maximum goods temperature obtained in the normal operation of the kiln, both as originally installed and as subsequently modified, has been in the neighborhood of 2200 F.

In said kiln as originally installed, under a normal operating condition in which suitable and suitably uniform goods temperatures were obtained in the furnace or high temperature section of the kiln, the goods temperature at the top of the kiln substantially exceeded the goods temperature at the bottom of the kiln during the goods travel through more than the initial forty per cent of its travel through the preheating section of the kiln, the temperature difference being about 250 F. at its minimum, and being in excess of 400 F. at its maximum. Furthermore, the critical increase of goods temperature between 1200 and 1800 was obtained while traveling through a portion of the length of the kiln which was appreciably shorter than, and in fact not more than about sixty per cent of the length of the kiln portion through which the goods travel while their temperatures change through said range, as shown in Fig. 2.

In the kiln shown in Figs. 3, 4 and 5, a vertical chamber A is formed in each side wall of the kiln and extends longitudinally of the latter for the major portion of the length of the preheating zone of the kiln. In the outer side wall of each chamber A are openings A distributed along the length of the chamber, and in the inner wall of each chamber A ports leading from the latter to the kiln chamber proper are formed one in line with each of the openings A The ports last mentioned were provided in the kiln, as originally installed, for use as gas exhausting or Withdrawal ports, each of which might be throttled or closed by the adjustment of the corresponding slide damper C mounted on a transverse damper guideway A As originally installed and used, each of the outer wall openings A was normally closed by a corresponding removable plug or closure part A as shown, the parts A being removed when necessary for the adjustment of the corresponding dampers.

In the kiln as originally installed and after its modification for use as illustrated in Fig. l, gases passing from the kiln chamber proper into each chamber A passed from the latter through a central bottom outlet port A controlled by a corresponding damper C and opening into a cross tunnel A beneath the kiln and to one end of which was connected the exhaust fan F. In the operation of the kiln shown in Figs. 3, 4 and 5, as originally installed, the fan F withdrew from the preheating section of the kiln all of the heating gases and excess air coming to the latter from the high temperature or furnace section of the din supplied by the auxiliary burners B and B and all of the vapors and gases expelled from the goods in the kiln.

The changes made in the kiln shown in Figs.

3, 4 and 5 as originally installed, to adapt the kiln for operation in the manner illustrated in Fig. 1, consisted in the addition to the kiln structure of the following parts; namely the burners 13 -43 the fan D, and the circulating provisions including the intake connection D from the fan D, to the entrance end of the kiln chamber, the top nozzles E, E, e and c and the discharge connections F and F from the fan F to the kiln. These additions required but little structural modification of the original kiln construction proper. As shown, the burners B -B comprise pipes which enter the chambers A through the opening A and extend through the chambers into the ports in line with the corresponding openings A The addition of these burners thus involved no structural change in the kiln other than the addition of suitable cement or other refractory material A to pack the joints between the burner pipes and the surrounding walls of the openings A and of the aligned inner wall ports. The addition of the discharge connections F and F and the intake connection D required no structural modification of the kiln other than the drilling of openings in the kiln side and end walls. The kiln ends of the intake connections F F and F are formed by the ports in line with the corresponding openings A and designated F, F and F in Fig. 4, and which have their dampers C adjusted to suitably open posi-- tions, all of the remaining dampers C shown being fully closed. The dampers C originally employed in connection with the ports receiving the burners B -l3 were removed when these burners were installed.

Each of the inlets E, E, e and e is shown as made of sheet metal and of box like form and extends downwardly into and fills the upper portion of a corresponding vertical slot A. in the crown or roof of the kiln.

As will be apparent, the operation of a kiln constructed as shown in Figs. 3, 4 and 5 and modified for use in the manner illustrated in Fig. l, is characterized by a substantial and desirable flexibility, whereby the withdrawal of gases from, and the supply of gases to the preheating section of the kiln may be varied as widely as normal differences in operating conditions may make desirable. The regulation of the recirculation through a wide range, both in respect to the total amounts of gases withdrawn from and returned to the kiln chamber, the points of withdrawal, and the volumes withdrawn and returned through the different outlets and inlets, may be widely varied by adjustment A except such of those ports as receive the burners B -B In a kiln constructed generally as shown in Figs. 3, 4 and 5- and adapted for operation as:

shown in Fig. 1, suitable equalization of top and bottom kiln chamber temperatures in the portion of the kiln immediately adjacent its entrance end,

is effected primarily by the withdrawal of gases from the entrance end of the kiln through the intake connection D of the fan D coupled with the introductionv of gases into the lower portion of the kiln chamber through the outlets F and F from'the circulating fan F. The gases introduced into the lower portion of the kiln through the connections F and F serve two main purposes, namely those gases: are at temperatures high enough to suitably increase the temperatures in the lower portion of the kiln, and they also increase the gas pressure in the kiln adjacent the points of introduction by an amount which while quite small, is suflicient to insure that a suitable portion of the total gas flow longitudinally of the kiln to the intake D is through the lower portion of the kiln.

In general in any given operating condition, some particular volume of outflow through the outlet connection D will give the best operative results, and either an increase or decrease in that optimum volume of outflow will result in an increase in top temperatures over bottom temperatures adjacent the entrance end of the kiln. An increase in the outflow above the optimum volume increases top temperatures by creating or permitting longitudinal drift flow. A decrease in the outflow below the optimum volume results in high top temperatures because of the resultdampers C to increase or decrease the amount of gases supplied to the inlets F and F are effective to make the kiln bottom temperatures adjacent the entrance end or" the kiln lower than, equal to, or even higher than the corresponding kiln top temperatures.

The control action effected by regulation of the inflow of gases into the kiln through the connections F and F is facilitated and in,- creased in efficiency'b-y the substantial elimination of longitudinal drift of the kiln atmosphere and kiln top and bottom temperature equalization in the intermediate portion of the preheating section resulting from the auxiliary supply of heat furnished by the burners B -B and from the withdrawal of the gases from the lower portion of the kiln chamber through'the outlets F F and F intermediate the last mentioned burners and the return connections F and F and from the return of gases to the top of the kiln chamber through the nozzles E, E, e and c The withdrawal of gases from the kiln chamber through the outlets F F and F by increasing the longitudinal flow in the lower portion of the kiln away from thehigh temperature section of the latter, tends directly to an increased heat absorption inthelower portion of the kiln adjacent the outlets F1, F2 and F3 and between the latter and the high temperature section of the With the outflow kiln, and would do so if the burners B -'-B were not used. However, the use of the latter directly increases the amount of heat available for bottom heating, and as a result of the recirculating action of the fan F, the heat supp-lied by the burners 3 -13 as well as a substantial portion of the heat supplied by the adjacent burners b 1) etc; is utilized mainly in sup-plying the heat requirements of the lower portion of the preheating zone of the kiln.

The effectiveness of the special provisions mentioned in the preceding paragraph is augmented by the return of gases to the kiln chamber at its top through the inlets E, E, e and 6 The gases introduced into the kiln through these nozzles tend to top and bottom temperature equalization, not only because the gases so returned at the top of the kiln are drawn from bottom portions of the kiln, respectively closer to the entrance end of the kiln than the portions of the kiln into which the gases are returned are at lower temperatures than would exist at the points of return if there were no such gas return, but also because such return of the gases results in a general downfiow of gases and thus increases the bottom temperature. The gases returned through the nozzles E, E, e and e thus have a desirable tendency to a reduction in temperature in the upper portion of the kiln adjacent the points of return.

The discharge of the gases returned through the nozzles E, E, e and e in thin downwardly flowing streams or jets extending transversely across the upper portion of the kiln chamber provides gaseous barriers highly effective in reducing the longitudinal drift tendency toward the entrance end of the latter.

Instead of producing the drift preventing barriers by thin vertical jets, it has been found more advantageous, in general, to produce those bar 'riers by thicker jets directed horizontally away from the entrance end of the kiln. The use of such horizontally directed jets is illustrated in Fig. 1A, wherein E E and E represent jetnozzles extending through'the crown of the kiln chamber'in the preheating zone of the latter, and located at progressively greater distances from the entrance end of the kiln. As shown, each of the nozzles E E and E is in the form of a sheet mosphere circulation as modified by the jets de livered by the nozzles E E and E Each jet initially hcrizontalis itself curved and deflected downwardly by kiln gases moving toward the entrance end of the kiln and engaged and deflected downwardly by the jet. ered by the nozzle E most remote from the en trance end of the kiln has the most important direct effect upon the general kiln atmosphere circulation, as it opposes and deflects downwardly the relatively heavy flow of heating gases moving toward the entrance end of the kiln into the zone of action of the jet delivered by the nozzle. At the kiln entrance side of each of the down curving jets delivered by the difierent nozzles E E and E there will be an upfiow of gases due to the tendency of the hotter gases to rise, but

Each nozzle, or at least the delivery end of The jet delivthe gases rising back of each of the nozzles more remote from the entrance end of the kiln and turning toward the entrance end of the kiln will be again deflected downward by the jet delivered by the adjacent nozzle nearer the entrance end of the kiln.

As will now be apparent to those skilled in the art, all of the special provisions described for the control of temperatures and flow conditions in the preheating section of the kiln mutually contribute to the full attainment of the improvement in conditions made possible by the use of the present invention. As those skilled in the art will understand, however, some of the special control provisions described may be utilized with advantage in some cases without a corresponding use of other of those features, and those skilled in the art will also understand that many changes in the form of embodiment disclosed may be made without departing from the spirit of my invention as set forth in the appended claims. In some cases the heating gases injected into the kiln chamber adjacent its entrance end through the inlets F and F may advantageously be hot air from the cooling zone which because of its dryness facilitates the goods drying operation.

An important practical advantage of the invention, not previously mentioned, is that with its use a kiln may be heated from atmospheric temperatures to working temperatures in preparing the kiln for operation initially, or after a period or" disuse, without moving heat absorbing material through the kiln during the heating up operation. This has never been possible with prior kilns for the reason that in such kilns, when empty, the longitudinal drift is so pronounced that the term peratures at the entrance end of the kiln are but little below the kiln temperatures in the high temperature section of the kiln. This advantage is of practical importance because the heating up operation ordinarily takes several days, and if the heat absorbing material then moved through the kiln on the kiln cars consists of wares to be fired, those wares are improperly fired, and if the heat absorbing material does not consist of wares to be fired, but is material used simply because of its heat absorbing and space filling capacity, its use involved car loading, unloading, and handling expense which may be avoided in a kiln constructed and operated in accordance with the present invention. In referring herein, and in the appended claims, to the introduction of gases into, and the withdrawal of gases from the kiln chamber, I mean the kiln chamber proper, wherein the gases may come in contact with the goods being heated or treated, and do not intend to include a chamber or space such as the space beneath the kiln car bodies, which is separated from the kiln chamber proper by the car bodies and sand seals or other sealing provisions.

While in accordance with the provisions of the statutes, I have illustrated and described the best form of embodiment of my invention now known to me, it will be apparent to those skilled in the art that changes may be made in the form of the apparatus disclosed without departing from the spirit of my invention as set forth in the appended claims and that in some cases certain features of my invention may be used to advantage without a corresponding use of other features.

Having now described my invention, what I claim as new and desire to secure by Letters Patent is:

1. In the operation of a continuous tunnel kiln, the method of regulating gas flow and temperatures in the preheating zone of the kiln which consists in withdrawing kiln gases at the low temperature end of said zone as required to maintain a suitably large volume of gas flow through a section of said zone adjacent said end, and in injecting hot gases into the lower portion of said section.

2. The method of equalizing kiln temperatures in planes extending transversely to the length of the kiln through the preheating zone of a continuous tunnel kiln while maintaining temperatures therein progressively increasing longitudinally of the kiln with the distance from the entrance end of the kiln which consists in withdrawing gases from lower portions of the kiln distributed along the length of said zone and returning a portion of the gases to the upper portions of sections of the kiln distributed along the length of the kiln and respectively more remote from the entrance end of the kiln than the said lower portions from which the gases so returned are withdrawn from the kiln, and in introducing into the kiln the gases so re turned thereto, in jets, each directed away from the entrance end of the kiln and of substantially the full width of the kiln.

3. In the operation of a continuous tunnel kiln, the method of minimizing longitudinal drift flow of the kiln atmosphere in the upper portion of a section of the kiln chamber adjacent the entrance end of the latter, which consists in withdrawing gases from the lower portion of said kiln section and injecting gases into the upper portion of the kiln section in thin downwardly directed streams extending transversely of the length of the kiln across the upper portion of the kiln chamber.

4. In the operation of a continuous tunnel kiln, the method of regulating gas how and temperatures in the preheating zone of the kiln which consists in Withdrawing kiln gases at the low temperature end of said zone as required to maintain a suitably large volume of gas flow through a section of said zone adjacent said end, and in injecting hot gases into the lower portion of said section, and which consists in increasing the volume of flow and giving the latter a vertical downward component in an intermediate section of the preheating zone between the first mentioned section and the high temperature end of said zone by withdrawing gases from a lower portion of said intermediate section and returning more or less of the last mentioned gases to an upper portion of said intermediate section displaced further from the entrance end of the kiln than the said lower portion of said intermediate section.

5. The method of equalizing kiln temperatures in planes extending transversely to the length of the kiln through the preheating zone of a continuous tunnel kiln while maintaining temperatures therein progressively increasing longitudinally of the kiln with the distance from the entrance end of the kiln which consists in withdrawing gases from lower portions of the kiln distributed along the length of said zone and returning a portion of the gases to the upper portions of sections of the kiln distributed along the length of the kiln and respectively more remote from the entrance end of the kiln than the said lower portions from which the gases so returned are withdrawn from the kiln, and returning another portion of the gases so withdrawn to a lower portion of the kiln less remote from the entrance end of the latter than the lower portion or portions of the kiln from which the last mentioned portion of the gases is withdrawn.

6. In the operation of a continuous tunnel kiln, the method of regulating gas flow and temperatures in the preheating zone of the kiln which consists in withdrawing kiln gases at the low temperature end of said zone as required to maintain a suitably large Volume of gas flow through a section of said zone adjacent said end, and in injecting hot gases into the lower portion of said section, and which consists in increasing the volume of flow and giving the latter a vertical downward component in an intermediate section between the first mentioned section and the high temperature end of said zone by withdrawing gases from a lower portion of said intermediate section and returning some of the last mentioned gases to an upper portion of said intermediate section displaced further from the entrance end of the kiln than the said lower portion of said intermediate section and which consists in injecting gases into a lower portion of a section of said zone between said intermediate section and the high temperature end of said zone.

'7. In the operation of a continuous tunnel kiln, the method of retarding longitudinal flow of the kiln atmosphere in the upper portion of a section of the kiln chamber adjacent the en trance end of the latter which consists in withdrawing gases from the lower portion of said kiln section, and in injecting gases into the upper portion of the kiln section in thin streams extending across the kiln chamber at different distances from and directed away from the entrance end of the kiln and reacting with the kiln atmosphere gases to create a general downflow of gases in an adjacent portion of said section.

8. The combination with the preheating zone portion of a continuous tunnel kiln, of means for withdrawing gases from the kiln chamber at the low temperature end of said zone and means for injecting heating gases into the lower portion of the kiln chamber adjacent said end.

9. The combination with the preheating zone portion of the kiln chamber of a continuous tunnel kiln, of means for withdrawing gases from the lower portion of the kiln chamber in one longitudinal section thereof and means for returning gases so withdrawn to the top oi" the kiln chamber in a longitudinal section thereof displaced further from the low temperature end of said zone than the first mentioned section, the last mentioned means including a nozzle opening to the kiln in a horizontal direction leading away from the low temperature end of said zone.

10. The combination with the preheating zone portion of the kiln chamberof a continuous; tunnel kiln, of a circulating fan, connections through which said fan withdraws gases from the lower portion of the kiln chamber at a plurality of points displaced longitudinally of the kiln in a longitudinal section of said zone, and connections through which said fart returns gases so withdrawn to the top of the kiln chamber at longitudinally displaced points of a longitudinal section of said zone displaced further from the low temperature end of said zone than the first mentioned section, said connections including a nozzle at each of said points, extending transversely to the kiln chamber for substantially the full width of the latter, and opening away from the low temperature end of said zone.

11. The combination with the preheating zone portion of the kiln chamber of a continuous tunnel kiln, of means for discharging gases into the top of the kiln chamber intermediate the ends of said zone in a thin downwardly directed stream extending transversely of the kiln chamber through substantially the full width of the upper portion of said chamber.

12. The combination. with the preheating zone portion of the kiln chamber of a continuous tunnel kiln, of means for injecting gases into the upper portion of the kiln chamber in a plurality of thin streams, each extending downwardly through substantially the entire width of the kiln adjacent the top of the latter, said streams being displaced relative to one another longitudinally of a portion of said zone intermediate the ends of the latter.

13. The combination with the preheating zone portion of the kiln chamber of a continuous tunnel kiln, or" means for discharging gases into the top of the kiln chamber intermediate the ends of said zone in a plurality of thin streams each extending transversely of the kiln chamber through substantially the full width of the latter, and entering the upper portion of the kiln chamber at difierent distances from, and moving away from the low temperature end of said zone.

14. The combination with the preheating zone of a continuous tunnel kiln, of gas exhausting and recirculating provisions comprising a fan withdrawing gases from the kiln chamber at the low temperature end of said zone, a fan withdrawing gases from the lower portion of a longitudinal section of the kiln chamber intermediate the low and high temperature ends of said zone, and

outlet connections from said fans through which some of the gases withdrawn from the kiln chamher by each fan are returned to the kiln chamber at the tops of longitudinal sections of the kiln respectively more remote from the low temperature end of said zone than the sections from which the gases so returned were withdrawn from the kiln, and by which some of the gases withdrawn by each fan are passed away from the kiln.

15. The combination with the preheating zone portion of a continuous tunnel kiln, of means for withdrawing gases from the kiln chamber at the low temperature end of said zone, means for withdrawing gases from the lower portion of the kiln chamber in an intermediate longitudinal section of said zone, and for returning one portion of the gases so withdrawn from said intermediate section to the lower portion of the kiln chamber in a longitudinal section thereof between said intermediate section and the low temperature end of said zone, and for returning another portion of the gases withdrawn from said intermediate section to the kiln chamber to the top of a longitudinal section thereof displaced further than said intermediate section from the low temperature end of said zone.

16. The combination with the preheating zone portion of an open fire continuous tunnel kiln, or" an exhaust fan withdrawing gases from said kiln chamber at the low temperature end of the latter and having an outlet comprising a waste gas discharge branch and a second branch opening to the top of the kiln chamber between the low and high temperature ends: of said zone, and a second exhaust fan withdrawing gases from the bottom of the kiln chamber at one or more points intermediate the low and high temperature ends of said zone and having an outlet comprising a waste gas discharge branch, a branch opening into the lower portion of the kiln chamber between the low temperature end at said point or points of withdrawal, and one or more branches discharging into the top of the kiln chamber at a point or points respectively more remote from the low temperature end of the zone than said withdrawal point or points, and means for variably restricting the outflow through said waste gas discharge branches.

17. The combination with the preheating zone portion of a continuous tunnel kiln, of means for supplying heating gases to the bottom of the kiln chamber in low and high temperature end sections of the latter, and for withdrawing gases from the kiln chamber at the low temperature end of the latter and from the lower portion of a section of the kiln intermediate said end sections, and means for injecting heated gases into the top of the kiln chamber at temperatures low enough to produce temperature reducing effects in the upper portion of the kiln chamber.

18. The combination with the preheating zone portion of the kiln chamber of a continuous tunnel kiln of the open fire type, of regulable auxiliary burners supplying heated gases to the lower portion of said kiln chamber at points distributed along the high temperature end of said zone, recirculating means for withdrawing gases from the lower portion of a longitudinal section of the kiln chamber between the low temperature end of said zone and said burners and returning a portion of the gases so withdrawn to the lower portion of a longitudinal section of the kiln chamber between the previously mentioned section and the low temperature end of said zone and for returning another portion of the gases so withdrawn to the top of a section of the kiln chamber more remote than the first mentioned section from the low temperature end of said zone, means for regulating the amount of gases so withdrawn and for regulating the said portions thereof returned to the kiln chamber, and means for withdrawing a regulated amount of gases from the kiln chamber at the low temperature end of said zone.

19. In the operation of a continuous tunnel kiln, the method of retarding longitudinal flow of the kiln atmosphere towards the entrance end of the kiln in the upper portion of a section of the kiln chamber adjacent the entrance end of the latter which consists in withdrawing gases from the lower portion of said kiln section, and in injecting gases into the upper portion of the kiln section in thin streams extending across substantially the full width of the kiln chamber and reacting with the kiln atmosphere gases to create a general downflow of gases in an adjacent portion of said section.

20. The method of equalizing kiln temperatures in planes extending transversely to the length of the kiln through the preheating zone of a continuous tunnel kiln while maintaining temperatures therein progressively increasing longitudinally of the lnln with the distance from the entrance end of the latter which consists in withdrawing gases from the lower portions of sections of the kiln distributed along the length of said zone and passing a portion of these gases away from the kiln and returning another portion of those gases to the upper portions of sections of the kiln distributed along the length of the kiln and at such distances from the entrance end of the kiln relative to the distances from the latter of the first mentioned sections, that the gases returned maintain temperatures in said upper portions lower than would exist if said gases were not so returned.

GORDON DUDLEY PHILLIPS.

CERTIFICATE OF CORRECTION.

Patent No. 2,081,954. June 1, 1957.

GORDON DUDLEY PHILLIPS.

It is hereby certified that the above numbered patent was erroneously issued to the patentee, whereas said patent should have been issued to Swindell Dressler Corporation, of Pittsburgh, Pennsylvania, a corpora.- tion of Pennsylvania, as assignee of the entire interest as shown by the records of assignments in this office; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 24th day of August, A. D. 1937.

!Leslie Frazer (Seal) Acting Commissioner of Patents.