US2138851A - Tunnel kiln - Google Patents

Description

M. E. GATES TUNNEL KILN Filed April 6,1936 2 heet 1 +4; Ira/mica I II M M W E M. E. GATES TUNNEL KILN Illlllllllll Ill! llllllllllllllll'llllllll' InUe/ZZO' lllllllllllIllllllllllllllll l-l lllllllllllllllllllllllllllllIlllllllllllllll Illllll lllllllllllillllllfllllllllllllllllllllllllllll fllllllllfllllll lllllllllllll llllllllllllllllllll llllllllllll) Ncgjorfl GaZ'a Filed April 6, 1956 Dan. 6, 1938.

Patented Dec. 6, 1938 UNITED STATES PATENT OFFICE 5 Claims.

This invention relates to improvements in tunnel kilns, and among other objects aims to provide an improved tunnel kiln adapted for burning brick, block and the like.

The nature of the invention may be readily understood by reference to one illustrative construction embodying the invention and shown in the accompanying drawings.

'In said drawings:

Fig. 1 is a plan View, partly in section, of the illustrative tunnel kiln;

Fig. 2 is a fragmentary broken plan view on a larger scale, illustrating the arrangement of ware on the traveling floor of the kiln;

Fig. 3 is a vertical section taken on the broken plane 33 of Fig. 4, which cuts the top position of the kiln at A-A of Fig. 1 and the lower position of the kiln at BB of Fig. l in the region of the burners approximately on plane 3-3 of Fig. 1;

Fig. 4 is a fragmentary sectional elevation taken approximately at the plane 44 of Figs. 2 and 3, further illustrating the arrangement of ware in the kiln; and

Fig. 5 is a sectional elevation, on the plane 5-5 of Fig. 1, adjacent the entrance end of the kiln.

A tunnel kiln is characterized by a slowly moving floor or cars on which the ware to be burned is arranged, which travels through an elongated tunnel wherein heat is applied to burn the ware. The ware is stacked on the floor or cars at the entrance to the tunnel and removed after it issues from the other end of the tunnel. If the kiln be a circular tunnel kiln as here shown by way of illustration, the travelling floor is annular in form and is surrounded, except for a short segment of its circumference (where burned ware is removed and green ware is stacked on the floor), by an annular kiln structure. The heating burners are placed on opposite sides of the structure intermediate its ends, and the travel of gases is from the discharge end of the kiln to the entrance end. The entering air thus cools the hot burned ware and is in turn heated to a relatively high temperature before it reaches the hot zone or region of the burners. Beyond the latter, the hot gases gradually deliver their heat to the incoming green ware which is gradually heated thereby to a relatively high temperature before it reaches the hot zone.

Despite their obvious advantages, it is difficult to secure uniform distribution of heat or uniform temperatures at any given cross-section in a tunnel kiln. The hot gases naturally tend to rise and to flow along the top of the kiln and along the outer faces of the stack of ware through the spaces which must be provided between the stack of ware and the walls of the kiln. The relative movement between the ware and the tunnel walls require that these spaces be much larger than would be the case if there were no relative movement. The problem of heat distribution is considerably aggravated when an effort is made to burn brick, block or other thicksectioned articles (as contrasted with thin-sectioned ware which requires relatively less heat energy for burning and which, by reason of its character is stacked much more openly than brick or block, thereby providing larger spaces for the travel of gases), which, by reason of their shape, can be and are customarily stacked with relatively close spacing compared to the thickness of the ware. Among other explanations, the increased difficulties may be ascribed to the high heat absorption or content of brick or block, as compared with thin sectioned ware, necessitating the delivery of a vastly greater amount of heat energy to effect proper burning. Moreover, the close spacing of the ware makes it impossible, by usual methods, to secure uniform temperatures throughout the stack of ware at any given section. This lack of free and rapid travel of heat to the interior of the stack results in relatively low temperatures in the interior of the stack and excessively high temperatures on the exterior and particularly at the top of the stack.

It is impossible under these conditions to effeet the temperature control required for a particular kind of ware or for efficient operation. Some ware containing a substantial amount of oxidizable material should be raised quickly to oxidizing temperatures of between 1000 F. and 1500 F. and should be held within this range for as long a period as possible before being raised to vitrifying temperatures, in order to insure completion of oxidation before vitrification. Other ware having a low oxidizable content preferably has a different temperature gradient. Moreover, unless it be possible to exert such control as to secure reasonable uniformity in temperatures at any given cross-section in the stack of ware, it is obviously futile to attempt to secure any given temperature gradient for the ware, the gradient on the exterior being totally different from that on the interior. But with temperature control, it would be possible both to give the ware the temperature gradient its character required and to pass the ware through the kiln at maximum speed and elficiency.

In the illustrative kiln are embodied the in- Ventive principles by which a tunnel kiln is adapted for the efficient burning of brick, block and the like. The annular floor II], on which the ware is stacked, travels in a clockwise direction (Fig. 1), the burned ware being progressively removed as it issues from the discharge end H and the green ware being stacked on the cleared floor before it reaches the entrance I 2. The flow of gases is in a counterclockwise direction, as indicated by arrow I3. The burners I4 are located at an intermediate point in such number and arrangement as the nature of the ware requires.

As here shown, the brick (block or the like) I5 are arranged in a generally herring-bone pattern, inclining toward the direction of travel of gases, i. e., in a counterclockwise direction, with gas passages I6, inclined in the direction of travel of the gases. The passages It between the brick need be no greater than customary, but their inclination serves to direct the gases in the proper direction of travel and minimizes excessive turbulence of the gases at the exterior of the stack which would result both in an over-heating at the exterior and such reduction of gas velocity as substantially to interfere with the travel of gases toward the interior of the stack. Preferably, several tier of brick are omitted at the center of the bottom of the stack to provide a tunnel I! through the stack to facilitate the travel of gases through its interior. The tunnel should be of such section as readily to carry the gases and to minimize the turbulence which would ensue if the gases, on reaching the interior of the stack, had no adequate passages through which to travel toward the entrance end of the kiln. The burners I4 may be correspondingly inclined relative to the direction of travel of the ware so that the direction of gases issuing from the burners will conform to the inclined arrangement of the ware and thus minimize the loss in velocity of gases as they pass to the interior of the stack. Such inclined arrangement of burners is not, however, essential, since the inclined faces of the ware will themselves direct the gases properly, even though they issue from the burners in a direction perpendicular to the direction of travel of the ware. On the other hand, if the ware be of such character that it cannot be arranged to present inclined faces to direct the flow of hot gases, the burners themselves may be inclined so that the initial direction of the'gases is toward the entrance end of the tunnel.

It will be understood that occasional stretcher courses I8 of brick or block are employed to bond the stack of brick together. Preferably, such stretcher courses should not be set opposite the nozzles. In the arrangement shown, which of course illustrates only one method of setting the ware, a stretcher course It is placed between every two courses of inclined ware; thus positioning the inclined courses opposite the burners (see Fig. 3).

At a point beyond the hot zone, in the dire c tion towards the entrance end of the kiln, means are provided for checking the current of extremely hot gases, which otherwise naturally occurs in the spaces I9 at the top of the kiln and in the upper portions of the adjoining side spaces, between the stack of ware and the roof and walls of the kiln. The free travel of this extremely hot current of gases from the hot zone in the upper portion of the kiln would result in an .under.

heating of the brick in the interior of the stack and possibly an over-heating of the brick of. the

exterior. In any event, the temperature of the brick on the interior of the stackat any given cross-section would be quite dissimilar to that of the exterior of the stack near the top, and the operation of the kiln would be correspondingly ineificient.

The checking means are here shown in the form of one or more small streams of relatively cool gases introduced into the upper portion of the kiln beyond the hot zone, at a relatively high Velocity. Such streams are here shown introduced through the passages 22, which are formed at one or more points at the top of the kiln. For a kiln of the character illustrated from one to three openings forming an orifice of about onehalf square inch operating under air pressure of about one pound per square inch will be effective. The temperature of the gases introduced will depend somewhat on whether the ware at the top and upper portion of the sides of the kiln is over heated at this point. If so, the air introduced may be relatively cool. If any cooling of the top of the stack would be undesirable then the air introduced should preferably be heated.

The temperature of the gases introduced does not, however, influence their action in retarding gas flow along the top and sides of the kiln, nor is the mere volume of gases introduced instrumental to this end, since the volume is relatively very small. Apparently, it is the velocity of the gases which makes them effective.

If=the gases thus introduced need be above atmospheric temperatures, they may be heated by a separate burner or withdrawn from some point in the kiln where they occur at the proper temperatures, and injected at a substantial velocity into the upper portion of the kiln. Special equipment capable of withstanding high temperatures will not be required for this purpose, both because of the small volume of gases handled and because their temperatures will ordinarily be relatively low.

At the present time the precise action of the jet or jets of introduced gases is not known with certainty but their effect is to check the stream of hot gases at the top of the kiln and cause the same to travel downwardly into the stack, thus elevating the temperature on the interior of the stack and bringing about much greater uniformity of temperatures at any given cross-section. They do not function by substantially cooling the stream of hot gases, Probably a localized pressure zone is created at the top of the kiln where the velocity head of the injected gases is converted to a static pressure head which is suificiently high, though localized because of the rather closely set ware, to cause the stream of hot gases to be deflected down inwardly into the stack of ware. Whatever the explanation, the result is the elevation of the temperature of the interior of the stack at a rate which approximates that for the exterior of the stack, thereby securing the uniformity, essential for effective con trol of the operation of the kiln.

The number and arrangement of inlet passages 22 and the volume on velocity of the cool gases injected into the upper portion of the kiln obviously will vary with the size of the kiln, character of the ware burned, and the size of the spaces I9 and 20 at the top of the kiln.

The aforesaid uniform temperatures can be more easily established and more readily maintained and controlled, if temperatures just inside the entrance to the kiln be substantially uniform throughout the kiln section adjacent the entrance. Means are therefore provided for checking the natural tendency of the heavycold outside air to enter the kiln along the floor atthe entrance counter to the flow of hot gases toward the entrance, crowding the latter toward the top portion of the kiln. The checking means is here shown in the form of suction fans 28 which withdraw a portion of the hot gasesfrom the top of the kiln adjacent the entrance and force them through conduits 2| into the bottom of the kiln adjacent the entrance. The warm gases, thus forced transversely into the kiln, on striking the inclined block or brick (see Fig. 2) are directed and caused to flow toward the entrance of the kiln, thus checking and preventing the entrance of heavy cold air at the bottom and creating an initial uniform temperature condition at the entrance. The fans 20 are here shown connected to the conventional stack which is usually connected with the top of the kiln at the entrance, and withdraw a portion of the hot gases from the stack. Additional openings in the top of the kiln at this point are thus made unnecessary. The gases at the top of the kiln are generally about 400 F., though this temperature may ob viously vary for different kilns and for different types of were. The speed of the fans should be adjusted to such speed as will be sufficient to check the inflow of cold air. For the ordinary kiln it is only necessary to introduce about one thousand cubic feet per minute at velocities of about twenty-five feet per second. Volume and velocity will, of course, also vary for different kilns and types of ware.

Because of the natural tendency of the gases to travel along the sides and top of the stack instead of through the stack, it is desirable to set the ware so that it fills the tunnel as completely as possible, thereby reducing the free space through which gases may pass. However, the small clearances thus resulting between the sides of the stack and the sides of the kiln walls, greatly increase the danger of wrecks within the kiln. Of course, elsewhere in the stack there must be adequate spaces for travel of gases either by spacing ware or making a tunnel through it or both. The danger of wrecks is aggravated by the circumstance that the natural expansion of the annular traveling floor in a circular kiln is in one direction, 1. e., outward. In prior constructions of "circular kilns, this has resulted in an outward and downward tilting of the floor, causing a wreck when the outer sides of the stack engage the kiln walls, with the ensuing serious consequences which are well known and need not be detailed here.

In such prior construction, the outward expansion of the kiln floor is aggravated by the circumstance that the sand, which is used to prevent adhesion between the stacked ware, gradually collects in increasing quantity between the brick or block 23 of the floor of the kiln during the repeated contraction of such brick or block on each revolution of the floor. It will be understood that such' contraction occurs when the highly heated brick of the floor reach the discharge end of the kiln and cool. This increases the space between the brick into which sand may sift, resulting in expansion and a progressive increase in the outer circumference of the annular floor. It will be obvious that expansion cannot occur inwardly since this would require the contraction in circumference of the floor. Therefore, all expansion is outward, serving to increase the outward circumference and a progressive outward travel of the floor.

To combat the serious consequences which ensue from a wreck inside the kiln, means are provided for exerting a continuous pressure on the floor block 23, so that as the latter contract, additional sand will not creep between them. In the present instance the weight of the load of ware in the kiln is employed to exert the aforesaid continuous pressure. As here shown (Fig. 3) the longitudinally extending structural members 24 which support the floor are provided with a web 25 which inclines toward the axis of the kiln, i. e., towards the inside edge of the annular floor. The slight defle'ction of the supporting members 24 under the weight of the load sets up an inward or centripetal component of force which tends .to move the floorradially inwardly and thereby produces a pressure between the block comprising the floor.

One typical floor construction is shown in Fig. 3 wherein the lower layer of block or brick 26 rests upon sections of metal plate or metal supports 21 secured to the supporting structural members 24. Angles or other flanged members 28 are provided to hold the lower layer of block 26 in place. The top layer of brick or block 23 rests upon the layer 26 and is retained by flanges or other appropriate formation 29 on the lower layer. The top layer 23 of block can, of course, be readily renewed when they become excessively burned by the heat of the kiln. It will be understood that the refractory material of the fioor of the kiln is of suflicient depth to protect the metal supporting elements, wheels and tracks, from the heat of the kiln. The wheels on which the floor rests are not shown, but it will be understood that they lie below the supporting members 24. The floor is built up in segmentary sections (as partly illustrated in Fig. 1), which are not so rigidly or closely connected as to prevent some slight inward radial movement pursuant to the radial components of force set up by the load of the ware, as explained above.

It will be apparent from the foregoing that the inwardly directed radial pressure resulting from the load of ware is communicated by flanges 28 and 29 to the top or surface layer of block which are thus pressed inwardly continuously. Preferably, the top layer of block comprising the floor are laid with substantial spaces 36 between them. The spaces 39, which are filled with sand, are of such width that excess sand may be readily forced out of such space, merely by the lateral pressure of the block. The spaces at the ends of the block are closed to prevent escape of sand, in this case by flanges 3i formed integral with the blocks.

It will be apparent from the foregoing that the uniform distribution of heat which is made possible by the inventive construction above described and the control thus made possible effects substantially increased efiiciency. The speed of travel of the ware through the kiln need not be retarded as heretofore to allow time for burning the ware in the interior of the kiln, since this ware is burned at the same rate as that on the exterior of the stack. Consequent production of defective Were is of course very substantially reduced.

Obviously the invention is not limited to the details of illustrative constructions as these may be variously modified. Moreover, it is not indispensable that all features of the invention be used conjointly since various features may be used to advantage in different combinations and subcombinations.

Having described my invention, I claim:

1. ha tunnel kiln of the character described the combination comprising an annular traveling floor composed of a plurality of floor segments, refractory brick surfacing said floor, metallic supporting members for said floor having webs capable of material deflection inclined toward the axis of said floor, whereby the weight of the load on the floor sets up a component of force directed toward the axis of said floor.

2. In a tunnel kiln of the character described the combination comprising an annular traveling floor composed of a plurality of floor segments, refractory brick surfacing said floor, metallic supporting members for said floor having webs capable of material deflection inclined toward the axis of said floor, whereby the weight of the load on the floor sets up a component of force directed toward the axis of said floor, said floor brick having such substantial spaces between them filled with sand that the lateral pressures set up between the brick are sufiicient to cause a portion of the sand to flow out of the spaces between said brick.

3. The method of creating a counterflow of hot gases toward the entrance end of a tunnel kiln having a rotating annular floor and adapted to burn brick, block and the like which is characterized by arranging the brick or block on the rotating annular floor of the kiln in rows inclined in a direction opposite to that of the travel of the floor through the kiln and directing the flame from the heating burners against the inclined faces of the ware and thereby directing the gases toward the entrance end of the kiln,

4."I'he method of improving the efficiency of tunnel kilns having a rotating annular floor and adapted to burn brick or other thick sectioned ware which is characterized by arranging the ware on the rotating annular floor of the kiln at an angle to the direction of travel of the 11001 and spacing the ware to provide gas passages inclined in the direction opposite to that of the direction of travel of the ware to direct the hot gases issuing from the kiln burners in a direction opposite to the direction of travel of the ware and also arranging the ware to provide a longitudinal passage of substantial section on the interior and near the bottom of the stack for said gases, and at a point between the burners and the kiln entrance injecting relatively cool gases into the top of the kiln at such velocity as to deflect the upper current of hot gases into the interior of the stack.

5. The method of improving the efficiency of tunnel kilns having a rotating annular floor and adapted to burn brick or other thick sectioned ware which is characterized by arranging the ware on the rotating annular floor of the kiln at an angle to the direction of travel of the floor and spacing the ware to provide gas passages inclined in a direction opposite to the direction of travel of the ware to direct the hot gases issuing from the kiln burners in a direction opposite to the travel of the ware and also arranging the ware to provide a longitudinal passage of substantial section on the interior and near the bottom of the stack for said gases.

MAJOR E. GATES.

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