US2246313A - Rotary kiln - Google Patents

Description

June 17, 1941. P. 'r. LINDHARD 2,246,313

ROTARY KILN Filed July 6, 1940 4 Shets-Sheet 1,

713M471; M' wv ATTORNEY5 June 17, 1941. -|NDHARD 2,246,313

ROTARY KILN Filed July 6. 1940 4 Sheets-Sheet 2 ff hhhy v ATTORNEYS Patented June 17, 1941 ROTARY KILN Povl T. Lindhard, Rumson, N. 1., assignor to F. L. Smidth & 00., New York, N. Y., a corporation of New Jersey Application July 6, 1940, Serial No. 344,225

25 Claims.

- which the materials are later burned, and is concerned more particularly with a novel apparatus in which such preheating operations can be advantageously carried on. An example of the use of the new apparatus is the preheating of raw materials to be burned into cement clinker in a rotary kiln and since the apparatus is of the rotary type, it may either be formed as part of such a kiln or be a separate piece of equipment. For purposes of explanation, a form of the apparatus which is directly associated with a rotary kiln willbe illustrated and described and its construction as a separate unit will be readily understood therefrom.

The new apparatus includes a cylindrical grate supporting a layer of the material through which the hot gases pass and such a grate is disclosed in Vogel-Jorgensen Patent No. 2,024,453, issued December 17, 1935. In addition, the new apparatus includes various features by which the action of the grate is rendered more efficient and its operation less expensive.

The kiln of the Vogel-Jorgensen patent comprises the usual tubular structure supported and rotated in the ordinary manner and at its inlet end, the kiln has a cylindrical extension within which is a cylindrical grate. The material to be burned is deposited on the surface of the grate by a suitable distributing device to form a pervious layer, and the hot gases issuing from the kiln pass through and preheat the layer as the kiln rotates. After the materials have travelled with the grate through the major part of a revolution, they are discharged therefrom by air which is continuously discharged through a hood and passes through the grate'from the side opposite to that with which the layer is in contact. From the point of discharge of the material, the bare grate advances to the distributor where additional materials are deposited thereon.

The apparatus of the patent is generally satisfactory in operation, but the discharge of the material from the grate by the use of a continuous air blast represents a substantial item of operating expense. Also, air used in the manner disclosed in the patent for discharging the material from the gate is not always completely effective for the purpose and occasionally material which has been preheated adheres to the grate and in the course of time may clog the passages therethrough.

The present invention is directed to the provision of an improved preheating apparatus generally similar to that of Vogel-Jorgensen but including novel means for effecting complete removal of the preheated material from the grate, While the discharge means makes use of compressed air,'the quantity of air required is less than that employed in the patented kiln and the air is used more effectively. In addition, the discharge means includes a device by which the surface of the grate on which the material was supported is mechanically freed of adhering particles.

In a rotary kiln equipped with the new preheater, the grate is mounted within and spaced from a hollow extension from the inlet end of the kiln and the space between the grate and extension is subdivided by partitions into lengthwise passages which lead to an annular outlet disposed within a mantle and having ports in registry with the passages. The passages are of decreasing cross-sectional area from end to end and compressed air employed for discharging the material is admitted into the passages at the large ends, the decrease in the size of the passages insuring that the air will act on the material on the grate with substantially uniform pressure throughout the length of the grate. Preferably, the air is admitted through the ports in the gas outlet and is supplied under the control of a mechanism which operates in timed relation to the rotation of the kiln to admit a. large volume of air into each port when it comes into registry with an air supply hood. The air thus suddenly admitted is quickly cut off so that the air operates with an impulse effect and the sudden blast ordinarily discharges the material completely. Since the air is being delivered through the grate only for a short period at any one time and is not flowing continuously, the cost of the operation is substantially less than that employed with the patented kiln. In addition, the air is used more eifectively both because of its uniform pressure against the grate from end to end thereof and because of its impulse action.

Beyond the point at which the material is discharged by an air blast, means are provided for mechanically removing any particles of the material still adhering to the grate and this means may advantageously take the form of a rotary brush fast on a shaft which extends through the end plate of the extension and is carried by a movable mounting. The mounting is motor driven, so that the brush may travel back and forth lengthwise of the grate in contact with the surface thereof, and means are provided for regulating the pressure with which the brush acts against the grate.

For a better understanding of the invention, reference may be had to the accompanying drawings in which:

Fig. 1 is a view of the new kiln, partly in section on the line ll of Fig. 2, and partly in elevation;

Fig. 2 is a view of the apparatus shown in Fig.

1 with parts illustrated in section on the line 22 of Fig. 1;

Fig. 3 is a sectional view on the line 3-3 of Fig.

Fig. 4 is a sectional view of a modified construction on the line 4--4 of Fig. 8;

Fig, 5 is a view in front elevation of the brush and its mounting;

Figs. 6 and '7 are sectional views on the lines 6-45 and 'I-| of Fig. 5;

Fig. 8 is a fragmentary sectional view on the line 88' of Fig. 4;

Fig. 9 is a view, partly in section and partly in elevation, of the control mechanism for the air blast;

Fig. 10 is a sectional view showing a modified form of the control mechanism; and

Fig. 11 is a sectional view on the line ll-ll of Fig. 10.

Referring to the drawings, the kiln illustrated includes the usual shell provided with tires 2| supported on rollers 22 having trunnions 23 mounted in bearings 24 supported on foundations 25. The shell is provided with the usual lining 26 and at its intake end has a conical extension 21 at the end of which is an annular gas outlet 28, which may be a casting and is subdivided into ports by partitions 29. The outer ends 30 of the ports lie within a mantle 3| from which a duct 32 leads to the intake side of a fan 23 having an outlet duct 34 leading to a stack. Beyond the outlet 28 is mounted a hollow extension 35 rotating with the kiln and enclosing a cylindrical grate 36 having its forward edge in alignment withgthe inner edge of the outlet 28. The space between the grate and extension is subdivided by partitions 31 into longitudinal passages 38, each of which leads to one of the ports of the outlet and within each passage is a longitudinal bafile 39 disposed in such position that the passage is of decreasing cross-section from one end to the other, with its large end in communication with a port. The end of the extension 35 is closed by an end plate 40. The end plate is stationary and has a peripheral flange surrounding the extension 35 which rotates within the flange and also moves longitudinally with respect thereto as the kiln contracts and expands.

The material to be burned is supplied through a hopper 4| to a distributing device 42 mounted on parallel links 43 on a foundation 44, the device being reciprocated by an arm 45 connected to an eccentric pin on a rotary disc 46. The distributor extends through an opening in the end plate 40 and deposits the material in a layer on the inner surface of the grate from one end to the other thereof. As the grate rotates, the material in the layer is held in place thereon by the hot gases drawn from the kiln and through the grate by the fan 33. These gases, which are at high temperature, preheat the material and may partially calcine it, and the material remains on the grate throughout the major portion of the revolution of the latter,

Within the mantle in alignment with the outlet ends of the ports is a hood 41 supplied with compressed air through a pipe 48. The discharge end of the hood is of the same cross-sectional size as one of the ports, and a closure plate 49 extends over the outlet ends of the orts from one side oi. the hood, and a similar plate 50 closes the ends of a number of the ports at the other side of the hood. Air is supplied to the hood by mechanism to be described, whenever one of the ports is in registry with the end of the hood, and the air blast blows the material from the inner surface 01 the grate and into a trough 50 supported within the grate in any suitable manner and containing a screw conveyor 5| which operates to force the material along the trough to a chute 52 through which the material is discharged into the conical section 21 of the kiln. Within this section are lifters 53 in such arrangement that the material is advanced by their action into the main body of the kiln. The screw conveyor 5| is driven in any suitable manner, as by means of a. pulley 54 on a portion of the shaft thereof which projects through the end plate 40.

Beyond the trough 50,'any particles of material adhering to the inner surface of the grate are removed therefrom by mechanical means and for the purpose a rotary brush 55 may be used, the brush being driven by mechanism to be described. The trough, the brush, and the distributor lie relatively close together and the hot gases flowing through the interior of the grate are kept from contact therewith by means of a bafile 56 supported in any suitable manner and provided with a refractory lining. The baflle 58 may be supported in any suitable way as by a plate 55a secured at one end to the hood 4!]. At its inner end, plate 56a is connected to the ballie by a plate 562) and plate 564: extends to the trough 50 and has a portion forming an enclosure for the brush 55.

The mechanism by which air is supplied to the hood 4'] in timed relation to the operation of the kiln, so that air issues from the hood only when one of the ports in the gas outlet is in alignment therewith, includes a valve 51 operated by a pilot valve 58. The pilot valve is operated by a solenoid supplied with current through ,a circuit 59 which includes a switch 60 having a movable member 6| which is operated by a cam disc 62 rotated in synchronism with the kiln and at such a rate that switch 60 is closed whenever one of the ports in the gas outlet is in registry with the hood 41.

The valve 51 comprises a housing 63 connected at its top to an air vessel 64 and at its bottom to the pipe 48. Within the valve housing'is a multiple partition 85 providing a plurality of ports 66 and through the partition is a cylindrical bore within which lie a plurality of pistons 51, one for each of the ports 66. The pistons are mounted on a piston rod 68 and the piston 61a at one end of the group is thicker than the others which are all alike. The piston rod also carries another piston 69 which is of larger diameter than the pistons 61 and lies within an extension 10 of the housing. At one end of the partition 55 within the housing is a passage II leading from a hollow boss 12 to which the air supply pipe 13 is connected. When the pistons within the bore are in such positions as to close the ports 66, air entering the housing through the boss flows through the passage 1| into the space 14 between of the housing which is in communication with the air vessel. The air supply line is thus directly connected to the air vessel when the valve 51 is closed.

From the end of the hollow extension from the housing, a pipe 16 leads to the atmosphere, flow through the pipe being controlled by the solenoid operated valve 58. A by-pass 11 from the supply line 13 leads to an opening in the end plate of the extension 10 and this by-pass contains a manually operated regulating valve 18.

In the operation of the device, whenever one of the ports 38 in-the annular gas outlet 28 moves into registry with the, hood 41, the circuit through the solenoid of valve 58' is closed by the action of the cam disc 62 and the solenoid acts to open the valve and permit the escape of air from the left side of piston 69. The air under supply line pressure in the chamber 18 at the right of piston 69 thereupon moves the piston to the left and thus causes piston 61a to close oif passages 1|, and the other pistons 61 to open the ports 66. Air immediately flows from the vessel through the passages and the pipe 48 to the hood 41. When the solenoid circuit is again opened, the valve 58 is closed and air flows through the bypass 11 until a pressure has built up at the left side of the piston 69 suflicient to return that piston and pistons 61, 61a to their original positions. In such movement, pistons 61 shut off the flow of air from the vessel to the pipe 48 and piston 61a opens the connection between the supply line 13 and the air vessel. The air supply valve remains in this condition until it is again opened by the action of of the solenoid operated valve 58.

The ends of the piston rod 68 fit closely in each choke valve including a ball 94 resting on a seat 85 and having its upward motion limited by a'stop 96. An adjusting screw' 91 extends into the body of the valve and contacts with the ball so that the latter may be held slightly ofi its seat so that flow through the pipe 90a, 90b away from the housing 8| is restricted to an extent determined by the relation of the balls to their seats, while flow into the housing through pipes 90a, 90b is unrestricted.

The pipes 92a, 92b are connected to a threeway valve 88 comprising a casing within which are pistons 99a, 99b connected to a rod I00 which is attached to a spindle |0| connected to the plunger of a solenoid I02. The valve 98 is attached to a bracket I03 secured to the housing of valve 8| and the solenoid is mounted on a similar bracket I04. An air supply line I05, connected to the main supply line 13, leads into the casing of valve 98 between the openings to which pipes 92a, 82b lead.

The operation of the device is as follows: Assuming that the valve 8| is closed with its piston assembly to the left and both ports 83 closed, the piston assembly in valve 51 is in closed position to the right, as shown in Fig. 9. When the plunger of the solenoid I02 moves to its lowermost position, the'pistons 99a and 99b will take such-positions that air supplied through line I05 will flow through valve 98, pipe 92a, choke valve 93, and pipe 90a into the housing of valve 8| at the left of piston 88a. The piston assembly in valve 8| will then begin to move to the right,

extensions 19a, 191; from the end plates of the 1 housing 63 and act as buffers to cushion the movements of the pistons. The extension 19b may, if desired, be provided with an inlet containing a check valve 80 to release the piston rod quickly when it is moving back toward closed position.

In some cases, where unusually rapid action of the valve 51 is required, the solenoid operated valve 58 may not be suitable because the solenoid may become too highly heated when energized at short intervals. Also, the hammering of the valve 58 on its seat may cause diificulties. When this situation arises, a mechanism including a secondary pilot valve may be employed and a form of apparatus suitable for the purpose is illustrated in Figs. 10 and 11.

The secondary pilot device comprises a valve 8| having a housing provided with a central partition 82 forming a pair of ports 83 therethrough. The ends of the housing are closed by cover plates and the housing is provided with an extension 85 connected by a line 86 to the housing 63 of the main air valve 51, the pipe 86 corresponding in location and use to the pipe 16 in the construction shown in Fig. 9. The housing 8| is also provided with an outlet 81 to the atmosphere and within the housing are three pistons 88a, 88b, 880 connected to a common piston rod 89. The pistons 88a and 880 are of the same thickness and the piston 88b is thinner.

Leading from the housing, of valve 8| at opposite ends thereof are pairs of pipes 90a, 9Ia and 90b, 9|b, each pair of pipes at one end of the cylinder being connected to a common pipe 92a, 92b. The passages 9| a, 9Ib enter the housing at such points as to be closed by pistons 88a,

' 880, respectively, when the group of pistons is in central position. The pipes 90a and 90b are provided with chokevalves 93a, 931), respectively,

and during such movement, the ports 83 will be opened and the piston 880 will close the outlet to pipe 9Ib. The air trapped at the end of piston 880 will then escape through pipe 90b, choke valve 93b, line 92b, and the casing of valve 98 to the atmosphere. Since the air so entrapped escapes slowly, the closure of the outlet to pipe 9|b by piston 880 will slow down the movement of the piston assembly to the right. During the I continued movement of the piston assembly,

valve 63 will remain open until the air vessel 64 empty, the ports 83 in valve 8| will have been closed, so that air flowing through the by-pass 11 will not escape to the atmosphere but will act on piston 68 and restore the piston assembly in valve 51 to closed position. In such movement, passages 1| and 15 will be uncovered and the vessel will again be filled from the line 13.

When a solenoid I02 is again energized and the pistons 98a and 98b in valve 98 are raised, air from pipe I05 will flow through pipe 92b, choke valve 93b, and pipe 901) into the righthand end of the housing of valve 8|, and this will move the piston assembly in the valve to the left. During such movement, the ports 83 will be opened and closed, with resultant actuation of valve 51 to empty the air vessel 64 and again fill it.

By the use of the secondary pilot valve, therefore, the valve 51 will be operated through a complete cycle for each movement of the spindle IOI corresponding to energization or deenergization of a solenoid I02. Accordingly, the solenoid will be energized only half as often as the valve 51 is operated. This, of course, requires that the cam 62 be so formed as to keep the switch 60 closed for one-half a revolution of the cam and that the speed of the cam be reduced to one-half of that required when the direct acting solenoid operated valve 58 is employed. With a very large kiln, there may be one hundredof the passages 38 between the extension and the grate and if the kiln rotates at one revolution per minute, this arrangement requires one hundred strokes per minute of the valve 64, if valve 58 is used and fifty strokes per minute, if the secondary pilot cross-section from end to end. Instead of this arrangement, the construction shown in Fig. 4 may be employed in which an extension 350. is used, this extension being conical and of such a taper as to cause the cross-sectional areas of the passages to decrease from end to end, as desired. As shown in Fig. 4, the inner end of the annular gas outlet 28, to which the large ends of the passages are connected, is protected in part by'the liner I06 in the conical section 21 of the kiln and in part by a high temperature metal liner plate I91.

In Fig. 8, that portion of the grate not covered by the material is illustrated as being protected by an inclined plate I08 provided with a refractory lining I09, This plate is supported on the stationary hood or end plate 49 by means of a structure consisting of the plate H9 which is secured at one end to the hood 40 and acts as a girder of the cantilever tyne. At its inner end, the plate III! is protected by a plate III provided with a refractory lining H2. The plate III) has a portion forming the trough 50' and another portion I I3 forming an enclosure for the mechanical means for removing from the grate such material as has not been removed pneumatically.

The mechanical means for removing the material comprises a rotary brush II4 partly enclosed within a casing II5 disposed-within the passage H3. The brush is mounted on a shaft IIB supported in bearings II'I within a tube IIB, which extends through. an opening H9 in the hood 40, the opening being large enough for the passage of the casing I 05 and brush II4, When the brush is inside the grate, the opening is closed by a door I20 which has a smaller opening through which the tube II8 extends.

At its outer end, the tube is mounted on a slide I 2I secured to and movable along the lower flange of a beam I22 attached to the lower ends of arms I23 pivotally secured to their upper ends to fixed supports I 24. A motor I25 for driving the shaft I I6 is mounted on the slide and the slide is movable back and forth along the beam by means of a nut I25 on the slide which is engageable with a screw threaded spindle I21 mounted on the beam and operable by a double worm geared motor I28 attached to the end of the beam. The driving means for the slide I2I are of such construction that the slide may be caused to move back and forth along the beam continuously or stopped, as desired.

At the outer end of the grate 3B is a liner ring I29 provided with flights I30 so arranged as to prevent material from spilling over the upper end of the kiln, in the event that too thick a layer of material is deposited on the grate by distributing means. When the brush is withdrawn from the grate, it must be moved to clear the flights and for this purpose, the beam I22 carries an arm I3I nto which is threaded one end of a rod I32 having right and left-hand threads at its opposite ends and carrying a hand wheel I33 between the threads. The other end of the rod I32 is threaded into an arm I34 attached to a lever I35 carrying a weight I36 and pivotally mounted on a fixed pivot I31. By operating the hand wheel I33, the brush may be readily moved toward and away from the grate, as desired.

To facilitate the adjustment of the brush relative to the grate, an arm I38 is attached to the beam and carries a counterweight I39. At its end, the arm I33 is connected to a rod I40 connected to a piston in a dashpot I4I The counterweight I39 may be adjusted along the arm I38 so as to counterbalance the weight of the assembly and proper adjustment of the weight makes it possible to move the brush toward and away from the grate without difliculty. The dashpot acts to prevent the brush assembly from vibrating or oscillating.

In order to cool the bearings I I1, air is supplied to the interior of the tubular member IIB through the air hose I42 connected to the member at its outer end, The air escapes past the bearings into the housing H5 and also serves to cool the brush during operation.

The preheater of the invention operates more efficiently than prior similar apparatus, in that the air used for discharging the preheated material from the grate is used in less amounts and with greater effect. The air flows only in blasts, once for each port in the gas outlet, instead of continuously, and the sudden discharge of the air gives itan impulse action. The mechanical means for removing particles not removed by the air supplements the pneumatic discharge and keeps the grate clean and prevents clogging. This facilitates passage of the hot gases through the pervious layer of materials on the grate without imposing an additional load upon the fan resulting from restriction of the gas passages through the grate.

In the foregoing, the preheating apparatus of the invention has been described as including a hollow extension from the main shell of a rotary kiln at the inlet end thereof, but it will be readily understood that the new apparatus may be a piece of equipment separate from such a kiln. In that event, the construction employed will be in all respects simi ar to that illustrated and described, except that the cylindrical grate and the housing rotating therewith will be provided with a suitable mounting and drive for effecting rotation thereof. The material discharged from the grate will then be collected and delivered to the inlet end of the kiln by conventional means.

I claim:

1. In a rotary kiln, the combination of a main kiln shell having a hollow extension from the inlet end thereof, a cylindrical grate mounted within and coaxially of the extension and spaced therefrom, the grate being connected to the shell to rotate therewith, means for distributing material on the surface of the grate to form a layer through which flow hot gases issuing from the shell, and means for removing the material in the layer from the grate including means for blowing air through the grate from the side opposite to that with which the layer is in contact and means for mechanically dislodging from the grate material not removed by the air.

2. In a rotary kiln, the combination of a main kiln shell having a hollow extension from the inlet end thereof, a cylindrical grate mounted within and coaxially of the extension and spaced therefrom, the grate being connected to the shell to rotate therewith, means for distributing material on the surface of the grate to form a layer through which flow hot gases issuing from the shell, and means for removing the material in the layer from the grate including means for blowing air in a series of blasts through the grate from the side opposite to that with which th layer is in contact and means for mechanically dislodging from the grate material not removed by the air.

3. In a rotary kiln, the combination of a main kiln shell having a hollow extension from the inlet end thereof, a cylindrical grate mounted within and coaxially of the extension and spaced therefrom, the grate being connected to the shell to rotate therewith, partitions movable with the grate and forming a series of passages extending lengthwise of the grate and closed thereby along one side, the passages being of decreasing crosssectional area from one end to the other, means for distributing material on the surface of the grate opposite to that closing the passages to form a layer through which flow hot gases issuing from the shell, and means for removing the material in the layer from the grate including means for blowing air into the passages through their large ends and means for mechanically dislodging from the grate material not removed by the air.

4. In a rotary kiln, the combination of a main kiln shell having a hollow extension from the inlet end thereof, a cylindrical grate mounted within and coaxially of the extension and spaced therefrom, the grate being connected to the shell to rotate therewith, partitions movable with the grate and forming a series of passages extending lengthwise of the grate and closed thereby along one side, the passages being of decreasing cross sectional area from one end to the other, means for distributing material on the surface of the grate opposite to that closing the passages to form a layer through which flow hot gases issuing from he shell, and means for removing the material in the layer from the grate including means.

for blowing blasts of air successively into the passages through their large ends and means for mechanically dislodging from the grate material not removed by the air.

5. In a rotary kiln, the combination of a main kiln shell having a hollow extension from the in-' let end thereof, a cylindrical grate mounted within and coaxially of the extension and spaced therefrom, the grate being connected to the shell to rotate therewith, partitions movable with the grate and forming a series of passages extending lengthwise of the grate and closed thereby along one side, the passages being of decreasing crosssectional area from one end to the other, means for distributing material on the surface of the grate opposite to that closing the passages to form a layer through which fiow hot gases issuing from the shell, and means for removing the mathrough the layer and into the passages, and means for removing the material in the layer from the grate including means for blowing air into the passages through their large ends and means for mechanically dislodging from the grate material not removed by the air.

7. In a rotary kiln, the combination of a main kiln shell having a hollow extension from the inlet end thereof, a cylindrical grate mounted within and coaxially ,of the extension and spaced therefrom, the grate being connected to the shell to rotate therewith, partitions subdividing the terial in the layer from the grate including means for blowing air successively into the passages through their large ends to escape therefrom through the grate.

6. In a rotary kiln, the combination of a main kiln shell having a hollow extension from the inlet end thereof, a cylindrical grate mounted within and coaxially of the extension and spaced therefrom, the grate being connected to the shell to rotate therewith, partitions 'subdividing'the space between the extension and grate into a plurality of passages extending lengthwise of the grate and closed thereby along one side, the passages being of decreasing cross-section from one end to the other, means for distributing material to form a layer on the inner surface of the grate, the hot gases from the shell passing space .between the extension and grate into a plurality of passages extending lengthwise of the grate and closed thereby along one side, the passages being of decreasing cross-section from one end to the other, means for distributing material to form a layer on the inner surface of the grate, the hot gases from the shell passing through the layer and into the passages, and means for removing the material in the layer from the grate including means for blowing blasts of air successively into the passages through their large ends.

8. In a rotary kiln, the combination of a main kiln shell having a hollow extension from the inlet end thereof, a cylindrical grate mounted within and coaxially of the extension and spaced therefrom, the grate being connected to the shell to rotate therewith, partitions subdividing the space between the extension and grate into a plurality of passages extending lengthwise of the grate and closed thereby along one side, the passages being of decreasing cross section from one end to the other, an annular outlet having ports with which the large ends of the passages are in communication, means for distributing material.

to form a layer on the inner surface of the grate, the hot gases from the shell passing through the layer and into the passages, and means for removing the material in the layer from the grate including means for blowing air through the ports in succession, the air flowing through the passages and grate to discharge the material from the latter, and means including a rotary brush for mechanically dislodging from the grate materialnot removed by the air.

9. In a rotary kiln, the combination of a main kiln shell having a hollow extension from the inlet end thereof, a cylindrical gratemounted within and coaxially of the extension and spaced therefrom, the grate being connected to the shell to rotate therewith, partitions subdividing the space between the extension and grate into a plurality of passages extending lengthwise of the grate and closed thereby along one side, the passages being of decreasing cross-section from one end to the other, an annular outlet having ports with which the large ends of the passages are in communication, means for distributing material to form a layer on the inner surface of the grate, the hot gases from the shell passing through the layerand into the passages, and means for removing the material in the layer from the grate including means for blowing blasts of air through the parts in succession, the air flowing through the passages and grate to discharge material from the latter.

10. The combination with a rotary kiln having a cylindrical grate rotatable therewith and means for depositing a layer of material on the grate to be heated by hot gases from the kiln flowing which the material lies, a supply of air under pressure, a receiver, connections between the supply and the receiver and between the receiver and the hood, a valve controlling the connections and operating to open one as it closes the other, and means for operating the valve to cause it alternately to connect the receiver to the hood and to connect the receiver to the supply.

11. The combination with a rotary kiln havin a cylindrical grate rotatable therewith and means for depositing a layer of material on the grate to be heated by hot gases from the kiln flowing therethrough, of means for discharging material from the grate comprising a hood for delivering air to the surface of the grate opposite to that on which the material lies, a supply of air under pressure, a receiver, connections between the supply and the receiver nd between the receiver and the hood, a valve controlling the connections and operating to open one as it closes the other, and means operating in timed relation to the rotation of the kiln for operating the valve to cause it to connect the receiver alternately to the hood and to the supply.

12. The combination with a rotary kiln having a cylindrical grate rotatable therewith and means for depositing a layer of material on the grate to be heated by hot gases from the kiln flowing therethrough, of means for discharging material from the grate comprising a hood for delivering air to the surface of the grate opposite to that on which the material lies, a supply of air under pressure, a receiver, connections between the supply and the receiver and between the receiver and the hood, a valve controlling the connections and operating to open one as it closes the other, pneumatic means for operating the valve to cause it to connect the receiver alternately to the hood and to the supply, and means actuated in timed relation to the rotation of the kiln for operating the pneumatic means.

13. The combination with a rotary kiln having a cylindrical grate rotatable therewith and means for depositing a layer of material on the grate to be heated by hot gases from the. kiln flowing therethrough, of means for discharging material from the grate comprising a hood for delivering -air to the surface of the grate opposite to that on which the material lies, a supply of air under pressure, a receiver, connections between the supply and the receiver and between the receiver and the hood, a, valve controlling the connections and operating to open one as it closes the other, pneumatic means for operating the valve to cause it to connect the receiver alternately to the hood and to the supply, and means actuated in timed relation to the operation of the kiln for controlling the operation of the pneumatic means, said control means including a solenoid-operated valve.

14. The combination with a rotary kiln having a cylindrical grate rotatable therewith and means for depositing a layer of material on the grate to be heated by hot gases from the kiln flowing therethrough, of means for discharging material from the grate comprising a hood for delivering air to the surface of the grate opposite to that on which the material lies, a supply of air under pressure, a receiver, connections between the supply and the receiver'and between the receiver and the hood, a valve controlling the connections and operating to open one as it closes the other, pneumatic means for operating the valve, and means including a solenoid-operated valve for controlling said pneumatic means, said control means normally functioning to cause the pneumatic means to maintain the valve in a position closing the connection between the receiver and hood.

15. The combination with a rotary kiln having a cylindrical grate rotatable therewith and means for depositing a layer of material on the grate to be heated by hot gases from the kiln flowin therethrough, of means for discharging material from the grate comprising a hood for delivering air to the surface of the grate opposite to that on. which th; material lies, a supply of air under pressure, a receiver, connections between the supply and the receiver and between the receiver and the hood,'a valve controlling the connections and operating to open one as it closes the other, pneumatic means for operating the valve, and means for controlling the operation of the pneumatic means, including a pneumatically operated valve, a control device therefor, and a solenoid energized in timed relation to the rotation of the kiln for operating the control device.

16. The combination with a rotary kiln having a cylindrical grate rotatable therewith and means for depositing a layer of material on the grate to be heated by hot gases from the kiln flowing therethrough, of means for discharging material from the grate comprising a hood for delivering air to the surface of the grate opposite to that on which the material lies, a supply of air under pressure, a receiver, connections between the supply and the receiver and between the receiver and the hood, a valve controlling the connections and operating to open one as it closes the other, pneumatic means for operating the valve, and means for controlling the operation of the pneumatic means, including a pilot valve, a solenoid for operating the pilot valve, and means operated in timed relation to the rotation of the kiln for intermittently energizing the solenoid.

1'7. The combination with a rotary kiln having a cylindrical grate rotatable therewith and means for depositing a layer of material on the grate to be heated by hot gases from the kiln flowing therethrough, of means for discharging material from the grate comprising a hood for delivering air to the surface of the grate opposite to that on which the material lies, a supply of air under pressure, a receiver, connections between the supply and the receiver and between the receiver and the hood, a valve controlling the connections and operating to open one as it closes the other, pneumatic means for operating the valve, and means for controlling the operation of the pneumatic means, including a pneumatically operated pilot valve, a valve for controlling the operation of the pilot valve, a solenoid for actuating the control valve, and means operating in timed relation to the operation of the kiln for intermittently energizing the solenoid.

18. The combination with a rotary kiln having a cylindrical grate rotatable therewith and means for depositing a layer of material on the grate to be heated by hot gases from the kiln flowing therethrough, of means for removing material from the grate comprising a rotary member adapted to operate on the surface of the grate on which the layer was deposited, a drive shaft for the member, a support for the shaft and member extendin out of the end of the grate, and means for reciprocating the support.

19. The combination with a rotary kiln having a cylindrical grate rotatable therewith and means for depositing a layer of material on the grate to beheated by hot gases from the kiln flowing therethrough, of means for removing material from the grate comprising a rotary member adapted to operate on the surface of the grate on which the layer was deposited, a drive shaft for the member, a support for the shaft and member extending out of the end of the grate, means for reciprocating the support, and means for shifting the support laterally to vary the position of the member relative to the grate.

20. The combination with a rotary kiln having a cylindrical grate rotatable therewith and means for depositing a layer of material on the grate to be heated by hot gases from the kiln flowing therethrough, of means for removing material from the grate comprising a rotary member adapted to operate on the surface of the grate on which the layer was deposited, a drive shaft for the member, a support for the shaft and member, a slide to which the support is attached, a track along which the slide is movable, means for shifting the track laterally to vary the position' of the member relative to the rate, and means for reciprocating the slide.

21. A preheating apparatus which comprises a rotary casing of generally cylindrical shape, a cylindrical grate mounted within and coaxially of the casing and spaced therefrom, the grate being connected to the casing to rotate therewith, means for distributing material on the surface of the grate to form a layer thereon, means for passing hot gases through the layer and grate, the gases holding the layer in'place as the grate rotates, and means for removing the material in the layer from the grate including means for blowing air through the grate from the side opposite tothat with which the layer is in contact and means for mechanically dislodging from the grate material not removed by the air.

22. A preheating apparatus which comprises a rotary casing of generally cylindrical shape, a cylindrical grate mounted within and coaxially of the casing and spaced therefrom, the grate being connected to the casing to rotate therewith, means for distributing material on the surface of the grate to form a layer thereon, means for passing hot gases through the layer and grate, the gases holding the layer in place as the grate rotates, and means for removing the material in the layer from the grate including means for blowing air in a series of blasts through the grate from the side oppositeto that with which the layer is in contact and means for mechanically dislodging from the grate material'not removed by the air.

23. A preheating apparatus which comprises a rotary casing of generally cylindrical shape, a'

cylindrical grate mounted within and coaxially of the casing and'spaced therefrom, the grate being connected to the casing to rotate therewith, partitions movable with the grate and forming passages lengthwise of the grate and closed thereby along one side, the passages being of decreasing cross-sectional area from one end to the other, means for distributing material on the surface of the grate opposite to that closing the passages to form a layer, means for passing hot gases through the layer, and means for removing the material in the layer from the grate including means for blowing air into the passages through their large ends.

24. A preheating apparatus which comprises a rotary casing of generally cylindrical shape, a cylindrical grate mounted within and coaxially of the casing and spaced therefrom, the grate being connected to the casing to rotate therewith, partitions subdividing the space between the casing and grate and forming passages extending lengthwise of the grate enclosed thereby along one side, the passages being of decreasing crosssectional area from one end to the other, means for distributing material on the surface of the grate opposite to that closing the passages to form a layer, means for passing hot gases through the layer and grate, the gases holding the layer in place as the grate rotates and escaping through the passages, and means for removing the material in the layer from the grate including means for blowing air into the passages through their large ends in a series of blasts.

25. In a preheating apparatus including a rotary casing of generally cylindrical shape, a cylindrical grate mounted within and coaxially of the casing and spaced therefrom, the grate rotating with the casing, and means for depositing a layer of material on the grate to be heated by hot gases flowing through the layer and grate, means for removing residual material adhering to the grate comprising'a rotary member adapted to operate on the surface of the grate from which the layer has been removed, a drive shaft for the member, a support for the shaft and member extending out of the end of the grate, and means for reciprocating support.

Povn 'r. LINDHARD.

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