US2657033A - Kiln - Google Patents

Description

Oct. 27, 1953 H. sTRucKMANN KILN 5 Sheets-Sheet 1 Filed Feb. 17, 1950 /n yen for Ho/ger Sfruc/rmann Attorneys Oct. 27, 1953 H. STRUCKMANN KILN 5 Sheets-Sheet 3 Filed Feb. 17, 1950 /n1/en far Ho/gerSfruc/rmann QM Altar/1e ys Oct. 27, 1953 H STRUCKMANN 2,657,033

. KILN Filed Feb. 17, 1950 5 Sheets-Sheet 4 IIIIIIIIIIIIIIIIIIII I III/ lnvemor Ho/gerSfruc/rmann A from eys Oct. 27, 1953 H. STRUCKMANN 2,657,033

KILN

Filed Feb. 17, 1950 5 Sheets-Sheet 5 HHHHI HUN"! Ill lhven/or Ho/ger Sfruckmann Attorneys Patented Get. 27, 1953 UNITED STATES PATENT OFFICE KILN Holger Struckmann, Bethlehem, Pa.

Application February 17, 1950, Serial No. 144,744

13 Claims. 1

This invention relates to kilns, more particularly rotary kilns mounted to rotate about an axis having a high angle to the horizontal.

Kilns constructed according to the teachings of the invention may be used for a variety of purposes to carry out the processes now carried out in kilns of other types such as stationary vertical shaft kilns and rotary kilns mounted with but a slight pitch. This novel kiln is particularly suited for heat treating those materials which, due to their agglomerating properties, must now be handled in the uneconomical low angle rotary kiln. It can do this either as a single unit or as a final unit preceded by a pressurized heat recuperator. Furthermore, due to the intimate contact between the materia1 and the gases and the close control over operating conditions which. the kilns design makes possible, the kiln lends itself to the eflicient treatment of those materials requiring oxidizing or reducing atmospheres at the same time providing a means, when needed, for the quick quenching of the final product. The kiln hereinafter particularly described as illustrative of the invention is designed for the making of cement clinker which is presently being made in kilns of the aforesaid known types, the disadvantages of which are well known. The shaft kiln, though more efficient in fuel consumption than low angle rotary kilns, has a low capacity and produces a non-uniform product. The low angle rotary kiln is quite inefficient in fuel consumption, occupies a great amount of space and is subject to occasional flooding which is likely to spoil a large quantity of mate rial.

The general objects of the present invention are to provide a kiln which is more economical with respect to initial cost and operating expense, which occupies less space yet has a high capacity and which permits of precise quality control of the product. The novel kiln, moreover, is capable of handling raw materials of a wide variety of sizes ranging from large lumps to fine powders but is particularly effective in handling powdered materials such as cement meal with fluidization thereof without mass bed turbulence, the heating and fluidizing gases moving counter to the flow of the materials in the kiln without producing channeling and with eflicient heat transfer and low heat loss. Another object is to provide a kiln in which the motion of the treated materials is accelerated as they reach the temperature of incipient fusion to produce forces tending to prevent agglomeration in large masses and in which the materials are subjected to a tumbling action at the point of fusion so as to produce medium sized agglomerates or nodules. A further object is to provide a kiln in which combustion air may be introduced under substantial pressure and effectively preheated by intimate contact with the hottest materials, at

the same time serving to 0001 them with conservation of the extracted heat. A principal feature of the invention is the means by which the product is removed from the kiln through elongated cooling chambers substantially filled with continuously advancing materials which serve to impede the flow of gaseous products through the discharge openings and force them to flow counter to the flow of materials being treated. Further objects are to provide means for introducing powdered solid fuels into the kiln, to provide novel sealing means between relatively movable parts of the kiln, and means for removing cooling air fed into the kiln when it is in excess of that needed for combustion.

Other objects and advantages will in part appear and in part will be apparent from the following detailed description of the present preferred embodiment of the invention, taken in conjunction with the drawings in which:

Fig. l is a central sectional elevation through a kiln and its supports;

Fig. 2 is a View taken on the line 2-2 of Fig. 1, some parts being shown in section and others partially broken away;

Fig. 3 is a section taken on the line 3-3 of Figs. 1 and 2;

Figs. 4, 5, 6 and 7 are detailed central sectional elevations of various forms of discharge controls which may be used in the conduits through which the material is removed from the kiln;

Figs. 8 through 13 are diagrammatic representations of the flow of material in the tumbling chamber and discharge tubes illustrating the conditions existing in different positions of the kiln;

Fig. 14 is a central sectional view of apparatus suitable for use in supplying pulverized solid fuel and oxygen to the kiln;

Fig. 15 is a sectional detailed view showing in enlarged form the air connection between two sections of porous fuel pipe;

Fig. 15 is a cross-section of the fuel pipe taken on the line l6-l 6 of Fig. 15; and

Fig. 1'7 is an enlarged central sectional elevation of means for making a substantially airtight seal between relatively rotatable sections of the fuel pipe shown in Fig. 14.

. 1-3, the kiln of the invenl' -drical metal shell 2% having ating in a cylindrical neck l at the bottom to a flange ata hollow flanged trunnion or bearing member 25 which rests on thrust rollers 25 mounted in a bearing plate 28 secured to a concrete pier The flanged trunnion 25 is rotatably supported in a bearing sleeve a?! mounted in plate At its upper end the shell 22 is rotatably supported by means of a circumferential carrying tire iii which rests on suitable rollers, not shown, carried by the pier 32. the kiln is produced through the medium of a drive shaft i l driven by a speed reducer 35 and carrying a drive pinion 36 which en ages the ring gear The neck 22 has a rotatable connection with a stationary flue 39, the joint between these parts being sealed by means hereinafter described and generally indicated at it. Materials to be treated are introduced into the kiln through a feed pipe ii. Flue 39 will be provided with a control damper (not shown) by which the gas flow out of drum it can be com trolled.

The space within the cylindrical supporting shell 2i? is occupied in part by the kiln proper which comprises the cylindrical drum t2 having a flat bottom as in which is a central discharge opening 5 leading to a constricted extension 36 of the drum 42. This extension is shown as having an enlargement G8 which, in the embodiment shown, serves as a combustion chamher which opens into an elongated tumbling chamber the ends of which extend at 5i? and bi through suitable openings in the shell It will be understood that the bottom 64, extension it, enlargement 38 and chamber it are all con structed of metal plates securely interconnected to form a rigid gas-tight structure, supported by the gas-tight shell 28 and rotating therewith, these parts being lined with fire brick or other suitable refractory material as indicated in the drawings. The ends of chamber 2-9 have removable refractory lined doors it giving access to the interior.

Liquid or gaseous fuel is supplied to the combustion chamber it through porou blocks 53 or orifices mounted its wall and fed by pipes 530. extending inwardly from a ring-shaped manifold The manifold is supplied through a fuel supply line It which extends through the trunnion 25 and branches 55 which extend upwardly around the chamber &9. Since pipe 5 rotates with the kiln, the fuel is fed to it through a rotatable union 56. Pipe E i is supported in the cover plate bl which caps the end of the trunnion. Combustion air is supplied by a blower 58 connected by pipe tit which may be flexible, with a stationary air box 653 which surrounds the lower end of trunnion 25 which is rotatable therein, the trunnion being provided with openings 65 through which the air flows, as indicated by the arrows, into the space within the shell 2%] below the floor a l of the kiln drum. The flow of air from this chamber into the kiln will be described later.

As may best be seen in Fig. 2, the tumbling chamber 9 is both longer and narrower than the cross-section of shell 28 and at its ends, where it extends beyond the shell, it is connected on its opposite sides with a pair of spirally arranged discharge tubes A and B shown as rectangular in cross-section and arranged concentrically about the outside of shell 26), from which they Rotation of may be supported by any suitable means (not shown). These tubes are likewise made of sheet metal so as to be gas-tight and lined with refractory. In the embodiment shown, each tube makes about one complete turn around the kiln. However, these discharge tubes may be made either longer or shorter as may be required by specific processes to be carried out. The entrance into tube A from the end of chamber 69 is indicated at .r in 1. The terminal ends of the tubes A and B lie approximately over the ends 59 and 5% of the tumbling chamber 49 and are there connected to downwardly extending discharge chutes E i. lhe ends of these chutes extend into a circular collecting trench formed in the pier 29. Attached to the ends of the chutes '54 is a closure ring 36 which underlies and is spaced slightly from a pair of cooperating rings 58 and as which extend inwardly from the edges of the trench the trench being connected to an exhaust stack 79 leading to a chimney or exhaust fan for the removal of fumes from the trench. The draft will create a flow of air inwardly around the edges of ring 66 as shown by arrows which will have a cooling eifect. The orifice i! in ring 55 through which the chutes (it discharge are of smaller diameter than the chutes so that the flow of material therein will be restricted. Material discharged from these rotating chutes into the trench 65 falls to the bottom thereof, whence it is removed by a drag conveyor 12.

Various other means for restricting the discharge from the tubes A and B, which may be used in place of restriction of th openings 1!, are shown in Figs. 4 through 7. Fig. 6 is a simple form or" fixed restricted orifice in the form of a plate l4 clamped between the end of the tube A or B and an elbow 15. These parts would replace the upper portions of the chutes E4, in which case the apertures ll would be enlarged to the full diameter of the chutes 64. Fig. 7 shows an adjustable discharge orifice in which the elbow 78 carries a pivoted gate it, the position of which may be adjusted by hand screw 8!? acting through lever 82.

Figs. s and 5 show two forms of discharge control means having motor driven devices for feeding the material. The use of motors on rotating kilns is common practice and it will be understood that power for them can be delivered through appropriately placed slip rings such as 83 (Fig. 14.) mounted on insulators 83a and connected with insulated lead in plugs 83bpassing through cover plate 5?. The slip rings are carried on a cylindrical flange 83c held by bolts 81 which secure cover plate 5?. In Fig. 4 the discharge end 82 of the tube A or B is shown as equipped with a short screw-conveyor 84 carried on a shaft 85 rotated through drive means 86 by the slow speed, gear reduced motor 83 mounted on the housing 89. Slidably mounted on the outer end of shaft 85 is a compactor plate 90 urged toward the end of pipe 82 by springs 9| mounted on guide rods 92 which are secured in the collar 93 of housing 89 and pass through apertures in the compactor 93. When no material is moving out of the tube end, plate 99, urged by springs 9| can be used to close the tube completely but will yield to let material out. In Fig. 5 the discharge pipe end is equipped with a revolving drum feeder 85 driven by a motor 96. Identical means will of course be used on each of the discharge tubes A and B.

The simple pipe system of fuel delivery shown in Figs. 1-3 is suitable for liquid or gaseous fuels together with oxygen, if required. However, it is desired to provide means by which the kiln may be operated on pulverized solid fuel such as powdered coal and also means by which a supply of commercial oxygen may be fed into the kiln as an aid to combustion. To these ends there is shown in Fig. 14 a fuel delivery system by which powdered coal and oxygen may be introduced. The powdered fuel is fed through a pipe lined with porous material through the inner surface of which a steady air flow is maintained to keep the fuel in a suspended or fluidized state. The drawing shows the lower end of the trunnion 25 and its cover plate 51 with the adjacent stationary air box 60. Since this air box may be of substantial size and therefore quite heavy, it is supported by a thrust bearing 98 which is supported on the flange of the cover 51. An airtight connection is formed between the box 60 and trunnion 25 by providing the latter with circumferential sealing rings 99 which extend into cooperating grooves formed in the air box 60. The latter will of course be made in separable parts so that the box can be assembled over the rings. Similarly constructed joints are employed to provide substantially gas-tight connections between a stationary oxygen supply box I and a rotating oxygen chamber IDI and between a stationary air supply box I 02 and a rotating fuel supply pipe I04. Oxygen under pressure is delivered to the box I Ilil through the conduit I and compressed air is delivered to the box I02 through the conduit IIJB. Oxygen pipes I 68 lead from the chamber IUI through cover plate 51 to any parts of the kiln where it is desired to inject oxygen to promote combustion.

The fuel supply pipe I04 is a metal pipe having a lining Id!) of substantial thickness of very porous material through which air can flow with very little resistance. There are various types of materials available which may satisfactorily be used for this porous lining, for example, clean graded sand bonded by the fusion of a bonding agent, various dry concrete mixes, micro-porous porcelains or vitrified clays or graded powdered metals bonded together through fusion. At certain points, as for example where the fuel pipe passes through the cover plate 57, it may be necessary to make a joint between separate sections of pipe in which case it will be necessary to conduct the compressed air from one section of porous lining to another. This is done by providing alined cylindrical recesses in the opposed ends of the porous linings as shown at H0 in Fig. 15. A connector consisting of a rigid pipe I I I surrounded by a soft rubber sleeve H2 is forced into the opposing cylindrical recesses and the opposed ends Il3 of the pipe lining sections are sealed to prevent the escape of air therefrom. Other exposed pipe ends such as H4 will of course likewise be sealed.

The purpose of this highly permeable lining is to distribute air to the entire inner surface of the fuel supply pipe through which surface it is desired to have a continuous discharge of air. The air is introduced into the lining from box It! through holes II5. A highly permeable material suitable for distribution of the air, is, however, too porous to accomplish such distribution unless its exposed surface is treated to reduce its porosity. This treatment, which may consist of painting, enameling, metalizing or electroplating, reduces the sizes of the pores on the surface so as to effectively throttle the air flow, it being understood that the treated surface is such as to contain evenly distributed minute pores. The thus treated surface layer is indicated in the drawings at H6. The appreciable throttling action of this lining is so great that it assures that there will be an even discharge of air therethrough throughout the length of the fuel supply pipe which makes it impossible for pulverized material to lodge on the porous surface and lose its fluidity. This throttling action is such that considerable pressure fluctuation can exist on the downstream or inner passage side of lining II6 without fluctuations occurring in the flow rate per unit area for a given upstream pressure, that is the pressure within the lining I09. It is to be understood that the fuel pumped into the supply pipe is in a fluidized condition by reason of having been previously aerated. Any fuel which momentarily deposits on the supply pipe lining will immediately be reaerated by the air passing through the lining so that it will return to the flowing stream. The fuel supply pipe IIB which is joined to the pipe I04 and extends inside of the kiln trunnion 25 is, of course, carried to the point in the kiln where the fuel is to be utilized, for example the combustion chamber 48. The use of a supply pipe having an aerated inner surface enables the use of bends in the pipe having rather short radii of curvature without danger of stoppages occurring at such bends.

The combustion air which is to be admixed with the fuel in the combustion chamber is first caused to flow through the hot material which is on its way out of the kiln from the combustion chamber in order to cool the material, preheat the air and thus conserve heat. As above explained, the air is injected by the blower 58 into the space 62 in the bottom part of the kiln shell 20 which it cools so as to protect the steel plates and the refractory linings of the adjacent parts of the bottom 44, chambers 4s and 48 and tumbling chamber 49, and then it flows out of this space into the discharge tubes A and B at points spaced from the discharge ends of said tubes by a distance such that the resistance to air flow inwardly and upwardly through the materials in the kiln is less than the resistance to air flow through the materials in the discharge tubes between the point of air inlet and the restricted orifices through which the materials finally discharge. As shown in Fig. 2, the air flows from the space 62 into the tubes A and B through the pipes I I 9 and I20 respectively which slope downwardly from their connecting openings in kiln shell 20 to the connecting openings in the sealing tubes in such a manner that gravity, together with screens I23 if desired, prevent material from the sealing tubes entering space 62. These pipes are shown as spaced approximately one-quarter the length of the tubes from their inner ends where they are connected to the tumbling chamber 49. (Tube A starts at end 50 of chamber 49 and tube B starts at end 5!.) The air thus passes in a direction counter to the flow of materials in the tubes and flows through the tubes into the tumbling chamber 49, and up Wardly through the combustion chamber 48, where it combines with the fuel after having been raised to a high temperature by reason of its contact with the hot materials through which it has passed, the tubes and the tumbling chamber being substantially full. This arrangement causes the incoming air to pass through the hottest material, some of which is in the discharge tubes, rapidly cooling it; .iiByusinga sufficient volume of air a quenching action on the hot material, such as cementclinker, may be produced, if desired. The air of course may be injected at other points further removed from the discharge ends of tubes A and B as into the tumbling or combustion chambers directly. Intense and rapid combustion takes place as the combustible mixture of fuel and air comes in contact with the material in the combustion chamber which is at a temperature higher than the ignition temperature of the said mixture. The kiln is, of course, fired in the usual way and then operated continuously thereafter. The products of combustion then pass up through the material in the kiln drum 42 leaving at the top of the kiln by way of the neck 22 and passing into the flue 38.

In some processes there may not be more cooling air than that required for combustion while in others there will be excess which must be removed before reaching the combustion-zone. The means of removing this air may be'seen in Figs. 1 and 2 where there are shown air pipes 550 having nearly vertical risers I55, in which are screens I52 for separating material from the air to be removed. The air pipes lead from the ends of tumbling chamber all down to the trench 65 from which the air passes out through the exhaust stack It. Throttling valves N53 for regulating air flow are located between the discharge end of the air pipes and the screens I52. In general it will be better to have a slight amount of excess air to be bled off so that in the event conditions arise requiring the use of more fuel, additional combustion air can be supplied by throttling down on the amount of cooling air drawn off rather than increasing the output of the blower 58.

The air pressure throughout thekiln may be above atmospheric and to maintain this pressure it is necessary to provide a seal between the neck of the rotating kiln and the stationary flue. This seal is constructed in a manner similarto another seal utilized between the stationary and rotating sections of the fuel supply pipe shown at the bottom of Fig. 14, this seal being shown on an enlarged scale in Fig. 1'7. These seals are of such a nature that the sealing medium which is interposed between the relatively moving parts is a layer of dust compacted and held in position by means of a surrounding cylindrical porous member so mounted in a chamber or jacket that a vacuum may be maintained on the outside of said member tending to draw the dust against its inner surface. Referring to Fig. 1'7, the rotatable pipe is it? and the stationary pipe is i2I, the latter being provided with a flange 22 to which is attached a cylindrical flanged vacuum jacket i724 having an air evacuating pipe we and a cylindrical porous member I25 which surrounds and is spaced slightly from the surface of pipe IM. Jacket IE4 is provided at its upper end with a neck portion 528 and a flange I29, the neck being spaced somewhat further from pipe IM to provide room for an annular packing member I36. A flanged packing gland I3! is used to hold the latter in place. Into the space between pipe I04 and the member I26 dust is introduced, being drawn in by the air flow through member I25, until this space is completely filled. With the maintenance of a partial vacuum in jacket I24 this dust will be caused to adhere to the surface of porous member I26 and will build up thereon a layer which forms a bearing surface against pipe I04 and which effectively seals off .and prevents any blow-through of gases from the regions of high pressure to regions of lower pressure. The dust forming the seal is supplied through a conduit I32 from a dust pump I3l having a manually actuated piston ISE, the conduit I32 containing a shut-off valve I36. Obviously, other means may be used for injecting the sealing dust which may be automatic in operation, if desired, to keep the space filled. Packing I30 serves to prevent the loss of sealing dust and the filling of the space between pipe 1M and member I26 with this dust prevents powdered coal from getting into the space. It is desirable to keep coal dust out of this space because it may contain abrasive particles and friction might generate sufficient heat to ignite the coal. 7

The seal generally designated at at the neck 22 of the kiln as shown in Fig. it operates on the same principles, the cylindrical vacuum jacket being shown at its, the porous me .un at I39 and the vacuum pipe at Mb. The air leaving the kiln will be sufiiciently dust-laden to provide an adequate supply of dust to build up a seal on the member or a supply of special non-abrasive dust may he provided if desired. Any dust-laden air escaping between. neck 23 flue 39 will have to p"s over porous member its and the vacuum 1;" intained behind this member will cause a layer of dust to be built up until the space is filled and a seal is formed. These seals, it will be observed, it t. ernselves to the space and are continuously self-restoring so that they cannot be worn out.

Operation The kiln above described is adapted to the handling of a variety of materials including large lumps, coarse granular material, uniformly sized nodulized compositions or fine powders. In each case the action of the high angle rotary kiln tends to minimize the channeling of combustion gases, makes possible the maintaining-of uniform temperature controls throughout, reduces the size of masses formed by incipient fusion, insures a high degree of preheating of the air used for combustion, and permits the ready withdrawal of the final product. The kiln is designed especially for handling powdered raw materials which are capable of being fluidized by the injection of air and particularly such materials as pulverized limestone or cement meal. The raw materials are charged into the kiln through the pipe 4! until the drum section 42 is filled to the level indicated by the load lines designated in Fig. l as max. and min. The level of material may be controlled automatically by means of a load controller hi2 of known type having sensing elements Hi l. The kiln is caused to rotate at a speed preferably as high as possible without bringing centrifugal forces into play.

Taking the production of cement clinker from powdered raw materials as an example, the products of combustion rising from the discharge opening 55 and fanning out through the bed of materials in the drum 42 are caused to how through substantially all portions of the bed by the rotation of the kiln, preferably maintaining the bed in a state ranging between quiescent fiuidizati-on (dense bed) and particulate fluidization (partially expanded bed) without causing turbulence throughout. The heat of the products of combustion is lost to the bed of raw materials being calcined. The greatest movement of material occurs in the constricted part 46 and inthe combustion chamber 48 just as incipient fusion starts. The more rapid movement of the material in this clinkering zone aids in obtaining uniform material temperature which in turn promotes better temperature control. Uniform temperature is promoted by good gas distribution which is aided by the movement within th material. The heat resulting from exothermic reactions in the clinkering zone will be more uniformly distributed where a relatively high rate of movement occurs within the material than where this movement is slow. The more precise the temperature control of the material, at or near its highest temperature, the less is the danger of excessive balling or agglomeration. The kiln also provides for a drastic tumbling action of the material as it leaves the combustion chamber and enters the tumbling chamber 49 so that it will agglomerate in medium sized nodules.

In the drum section 42 the area available for gas travel is several times greater than in the constricted extension 46. This enlargement produces a slower rate of gas travel, reducing turbulence and permitting a true counter flow of gas through the material. The slower gas flow also reduces the dust carried away by the escaping gases. Furthermore, in the larger diameter section the bulk of the material will receive less wall support and will therefore be less subject to channeling. Any channels which tend to be formed by the rising of the gas through the material will be destroyed by the shifting of the material as the kiln rotates and the gases will therefore constantly be seeking new paths, producing a better heat exchange between the gas and the materials, as well as sweeping away the carbon dioxide formed in calcining so as to hasten this reaction.

An important aspect of the invention is the removal of the materials, such as clinker, formed in the kiln, this removal being effected by means of the spiral discharge tubes A and B. This material discharge, together with the tumbling action, is diagrammatically illustrated in Figs. 8-13 which will now be explained. Tubes A and B are not only discharge tubes for the products of the kiln but they also provide an impedance to gas flow by reason of which the combustion air and other gases forced into the kiln are caused to flow upwardly through the kiln instead of out with the product, this function of the tubes being due to their length and to the fact that they are at all times substantially full of product. In Fig. 2 the tubes A and B are shown as making about one complete turn of 360 around the kiln, threequarters of which serves as an impedance to the outward flow of gases when they are introduced, as shown, through pipes H9; and I29. It may be desirable to introduce the air at other points or to make the tubes even longer so that they are .1 /2 or 2 turns in length, the principle being to interpose sufficient resistance to gas flow to force it up through the kiln. Figs.813 being merely diagrammatic representations, each tube is shown as constituting but a half turn which facilitates an understanding of the operation. The tubes are designated a and b and the tumbling chamber as c. The junction between tube a and chamber c is designated :r. In all of these figures it is assumed that one is looking downwardly from the top of the kiln along its axis.

In Fig. 8 tube a is inactive, being filled with material which cannot slide back into the chamber due to the fact that the chamber is filled with material adjacent the outlet x. Tube b is discharging by gravity through its restricted orifice, the material sliding downwardly through the tube. emptying it near the top. I

In Fig. 9 the kiln has rotated about to tube b has moved out of its discharge position and the empty upper end of this tube has: filled with material pouring from the upper end of chamber 0. Tube a has not yet begun to discharge. Note that the direction of rotation is such as to pour material from chamber 0 into the end of tube b as the kiln rotates.

In Fig. 10 tube a is beginning to discharge and to create an empty space near the discharge end of the tube. The material is beginning to shift in the chamber 0 toward the left-hand end.

In Fig. 11, tube it continues to discharge at a rate determined by the size of its discharge orifice, creating more space in the tube and the material is shifting in the tube, moving this empty space toward point r. The empty space in the chamber 0 adjacent the port leading to tube 12 is filled by a surge of material from the high to the low end of the chamber due to the increasing inclination of the chamber. As this shifting of all of the material in the chamber from one end to the other takes place, there is a loss of support for the material in combustion chamber 48 (Fig. 1) and some material moves therefrom into the tumbling chamber. There is thus a delivery of material into the tumbling chamber twice in each revolution corresponding to a discharge from one of the tubes A or B.

Figs. 12 and 13 correspond toFigs. 8 and 9 except that the tube 0, instead of tube It) is shown discharging in Fig. 12 and being filled up again by flow through at in Fig. 13.

The term high angle as used herein to describe the kiln inclination refers to a range of angles having 45 as the approximate median. It is intended to distinguish from vertical kilns on the one hand and substantially horizontal kilns on the other. Roughly, the range intended to be included is from 30 to 60 above the horizontal. The particular angle selected requires a balancing of various factors taking into consideration the nature of the materials dealt with and the process to be carried out. The

lower angles favor more effective reduction of channeling of the gas flow in the drum section and more violent movement in the tumbling chamber which, together with reduction of load pressure on the hottest materials, tends to prevent fusion into larger masses. Low angle also improves the discharge from the spiral tubes. The higher angles tend to reduce the total void volume within the material in the drum and make for better gas distribution therein by re ducing the tendency for the gases to escape along the uppermost side of the kiln. It will thus be seen that the angle is not critical but a matter of selection and that variation over. a considerable range is possible while.retainin the benefits of the invention. The above mentioned angles of 30 and 60 are not to be regarded as rigid limits. I

While the details of construction of one particular kiln have been herein described as an illustration of the invention it is to be understood that these details are subject to modification in many particulars within the scope of the invention. For example, the combustion cham her, that is the point at which the fuel is introduced, may be otherwise than as shown. The

fuel might be injected inthe constricted portion 46 or into the drum section 42 adjacent the opening 45 or into the tumbling chamber 158 around its junction with the part 43.

The portions 46 and 48 might have the same diameter or be somewhat greater in diameter relative to the diameter of the drum section. Two spiral discharge tubes A and B have been shown but a different number might be used. One spiral could be used with the chamber 49 as shown so that discharge would take place once in each revolution or, with modification of the shape of chamber as three or more spirals might extend from it. The spirals may also wind downwardly of the kiln instead of upwardly as shown. Instead of blowing air into the kiln from a fixed blower, one or more blowers might be attached to the kiln to revolve with it. The air might be introduced elsewhere than into the spiral tubes, as for example directly into chamber 4s. The drum section 52 may advantageously have a conical bottom instead of a fiat bottom as shown. In view of such possible modifications the invention is not to be limited by the disclosure of'one specific embodiment but is to be construed broadly within the purview of the claims.

Control of operation It will be noted that the output of this kiln is determined by the rate of material withdrawal which is in sharp contrast to conventional rotary kilns where the feed rate controls the output. Thermocouples located at strategic spots in the kilns walls and sealing tubes can be used to bring, through the use of slip rings, temperature recordings to some control point. Continuous flue gas analysis can also be recorded at this same point. Controls for the kiln speed, blower output, excess cooling air throttlin valve, fuel delivery rate, and sealing tube discharge ilow rate can all be located at this same point so that the kiln operator has everything conveniently at hand for his intelligent operation of the kiln. Then, knowing constantly what are the conditions in the kiln by means of the instruments, he can make control changes, when required. These control changes will be quickly effective due to the intimate mixing of gas and material in the kiln, the kilns relatively high speed and the sensitiveness of product discharge iiow rate to control. This is in sharp contrast to the conventional rotary kiln'or the shaft kiln where control changes may take hours to be elfective while permitting an inferior product to be made in the meantime. 7

What is claimed is:

1. In a kiln mounted for rotation about an axis inclined at a high angle to the horizontal, in combin'ation, a cylindrical heating drum adapted to be substantially filled with material to be treated and having a central discharge opening in its bottom, a combustion chamber of substantially less diameter than the drum located beneath and communicating with said discharge opening, a tumbling chamber beneath and communicating with said combustion chamber and elongated in a direction normal to said high angle axis and adapted to receive material falling from said combustion chamber, whereby as said drum rotates the material in said chamber is subjected to tumbling action as the chamber is successively upended, means for withdrawing material from said tumbling chamber as the kiln rotates at a rate such as to maintain the same substantially full of material, and means for injecting fuel into the combustion chamber.

2. A kiln for the continuous treatment of powdered raw materials under, fiuidizing conditions comprising a cylindrical rotatable drum disposed at a high angle to the horizontal, means for supporting and rotating the drum, feeding means for maintaining a substantial bed of said materials in the drum, said drum having a restricted opening at its lower end through which said materials fiow out of the drum, means for injecting fuel into the materials in the vicinity of said opening whereby combustion takes place in the voids in said materials beneath said bed and the combustion products rise upwardly through said bed,

an elongated material discharge tube spirally arranged relative to the axis of rotation of the drum and communicating with said opening, means as sociated with said tube restricting the flow of materials therefrom whereby it is maintained substantially full of materials as the kiln rotates, means for delivering combustion air under pressure into said materials at a point so positioned intermediate the discharge opening of the drum and the outlet end of the discharge tube thatthe path of least resistance to flow of the air is up wardly through the bed of materials in said drum, whereby the upward flow of air and products of combustion maintains said bed in a fluidized state. 7

3. A kiln for the continuous treatment of powdered raw materials under fluidizing conditions comprising a cylindrical rotatable drum disposed at a high angle to the horizontal, means for supporting and rotating the drum, feeding means for maintaining a substantial bed of said materials in the drum, said drum having a restricted opening at its lower end through which saidmaterials fiow out of the drum, means for injecting fuel into the materials in the vicinity of said opening whereby combustion takes place in the voids in said materials beneath said bed and the combustion products rise upwardly through said bed, a tumbling chamber communicating with said opening and adapted to receive the materials passing therethrough, an elongated material discharge tube spirally arranged relative to the axis of rotation of the drum and adapted to receive material from said tumbling chamber, means associated with said tube restricting the flow of materials therefrom whereby it is maintained substantially full of materials as thekiln rotates, means for delivering combustion air (inder pressure into said materials at a point so positioned intermediate the discharge opening of the drum and the outlet end of the discharge tube that the path of least resistance to flow of the air is upwardly through the bed of materials in said drum, whereby the upward flow of air and products of combustion maintains said bed in a fluid-- ized state.

4. A high-angle rotary kiln adapted for operation at internal pressures greater than atmospheric pressure comprising a rotating refractory lined drum having inlet and outlet openings, a stationary fiue adjacent said outlet opening,

sealing means adapted to prevent the escape of is greater out through said tube than the re- '13 sistance to flow through the kiln toward said outlet opening.

5. In combination with a kiln comprising a rotating drum having a cylindrical neck portion surrounding an outlet opening, a stationary flue adjacent said neck, and sealing means for preventing iree flow of gas between the flue and the neck, said means comprising an annular member of porous rigid material closely surrounding but spaced from said neck, an annular jacket surrounding and supporting said member and having sealing engagement with said flue, and means for evacuating said jacket to produce a flow of air through said member, whereby suspended solid particles in air drawn through said member will be accumulated thereon to fill the space between said member and said neck.

6. In combination with a rotary kiln having a combustion space in which fuel and air are admixed and burned to heat the kiln product to a high temperature, means for removing the hot product from the kiln comprising an elongated spiral passage in communication with said combustion space and rotating with the kiln and closely confining the product, means for main taining said spiral passage substantially filled with said product, and air supply means for forcing air under pressure into said combustion space comprising a conduit directing the air into the interior of said spiral passage at a distance from said combustion space whereby the air flows through said hot product in contact therewith in a direction counter to the flow thereof extracting heat therefrom and becoming heated to a high temperature before reaching the combustion space.

7. A kiln comprising a generally cylindrical shell, means for supporting the shell at a high angle for rotation about its axis, a refractoryline drum section in the upper portion of said shell, a refractory-lined combustion chamber in the lower portion of said shell spaced from the walls thereof and communicating with said drum section, means for delivering air under pressure into the space in said lower portion surrounding said combustion chamber, and means for conducting air from within the lower portion of said shell to said combustion chamber.

8. A kiln comprising a generally cylindrical shell, means for supporting the shell at a high angle for rotation about its axis, a refractorylined drum section in the upper portion of said shell, a refractory lined combustion chamber in the lower portion of said shell spaced from the walls thereof and communicating with said drum section, a tumbling chamber communicating with said combustion chamber, means for delivering air under pressure into the space in said lower portion surrounding said combustion chamber, and conduit means for delivering air from within the lower portion of said shell to said tumbling chamber.

9. In a kiln, in combination, a cylindrical heating drum having a bottom, means rotatably supporting the drum with its cylindrical axis inclined at a high angle to the horizontal whereby said drum may be substantially filled with material to be treated, said bottom having a central discharge opening, a tumbling chamber adjacent the bottom of the drum and communicating with said opening, said chamber comprising a relatively long and narrow box disposed in a plane normal to said axis and having discharge openings adjacent its ends on opposite sides, and a spiral discharge tube connected to each of said 14 openings, said chamber and said tubes being mounted for rotation with said drum, whereby material leaving the drum tumbles back and forth in said chamber as it rotates and a portion thereof is discharged from the chamber at each half revolution thereof.

10. ,A kiln for the continuous treatment of materials comprising a rotatable drum having a bottom wall, said drum being disposed at a high angle to the horizontal, means for supporting and rotating the drum, feeding means for maintaining a substantial bed of materials in the drum above said bottom wall, said bottom wall having an opening through which said materials flow out of the drum, an elongated material discharge tube spirally arranged relative to the axis of rotation of the drum and communicating with said opening, and means associated with the outlet of said tube restricting the flow of materials there through whereby it is maintained substantially full of materials flowing from said drum as the kiln rotates.

11. A kiln mounted for rotation about an axis position at a high angle to the horizontal whereby it may be substantially filled with material flowing by gravity from its upper to its lower end, means for rotating the kiln, a discharge tube communicating with the lower end of the kiln and spirally arranged about said axis, means restricting the discharge of material from said tube whereby it may be maintained substantially full of material, and air injection means for introducing combustion air into the materials in the kiln, the point of air injection by said means being so positioned that the resistance to air flow upwardly through the materials in the kiln is less than the resistance to air flow downwardly through the materials in said tube when said kiln is filled for normal operation, whereby air may be forced upwardly through said materials during the maintenance of continuous gravity discharge.

12. A rotary kiln for operation at internal pressure greater than atmospheric pressure comprising, a rotating drum having its axis oi rotation at a high angle to the horizontal and having an outlet opening in its bottom, an elongated discharge tube arranged spirally relative to the axis of rotation of said drum and communicating with said outlet opening whereby the product leaving the kiln moves by gravity into said tube, and means restricting the flow of material through the outlet end of said tube whereby it is maintained substantially full of material so as to impede the flow of gas through the tube.

13. A rotary kiln for operation at internal pressure greater than atmospheric pressure comprising, a rotating drum having inlet and outlet openings and having its axis of rotation at a high angle to the horizontal, an elongated discharge tube arranged spirally relative to the axis of rotation or" said drum and communicating with said outlet opening whereby the product leaving the kiln moves by gravity into said tube, means restricting the flow of material through the outlet end Of said tube whereby it is maintained substantially full of material so as to impede the flow of gas through the tube, and means for introducing combustion gas under pressure into the kiln at a point where the resistance to its flow is greater out through said tube than the resistance to flow through said kiln toward its outlet opening.

HOLGER STRUCKMANN.

(References on following page) References Cited in the file of this patent UNITED STATES PATENTS Number Name Date Scott-Moncriefi" Mar. 25, 1924 5 Engel Oct. 13, 1944 Deventer Dec. 22, 1931 Arrowood Dec 29, 1931 Angell Sept. 15, 1934 Number Morrow May '7, 1935 10 2,484,911

16 Name 3 Date Avansoe May 28, 1935 Treshow Oct. 14, 1941 Lindhard Oct. 21, 1941 Roubal May 12, 1942 Kohler Jan. 2, 1945 Petersen Apr. 30, 1946 Parker July 12, 1949 Petersen Oct. 4,1949 Seil Oct. 18, 1949

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