US2068574A - Rotary kiln control arrangement - Google Patents

Description

Jan. 19, 1937. SMITH ROTARY KILN CONTROL ARRANGEMENT Filed Dec. 12, 1954 Inventor Aubrey Smith,

Attorneg.

Patented Jan. 19,931

ROTARY KILN CONTROL ARRANGEMENT Aubrey Smith, Schenectady, N. Y., assignor to General Electric Company, a. corporation of New York Application December 12, 1934, Serial No. 757,167

12 Claims.

The present invention relates to rotary kiln control arrangements, more specifically to the kind of control arrangements used for controlling rotary kilns in cement manufacturing plants, although it is not limited thereto necessarily.

In present day cement manufacturing plants inclined rotary kilns of considerable length are provided to effect incipient vitrification or iusicn of two materials, one material rich in lime such as limestone or marl known as calcareous ma= teriai, and another material rich in silica, alumica and iron oxide such as clay or shale known as argillaceous material. A homogeneous mixture of these materials is into the high end of a rotary kiln and during rotation of the kiln passes through the different zones thereof known as dehydration zone, calcining acne, and clinker ing zone. At the end of the latter zone the cement clinker is discharged and cooled. The union of the materials within the kiln is eiiected by the application of heat which in the usual arrangement is produced by a burner projecting into the lower end of the kiln and discharging combustible material therein. The final temperature at which incipient fusion takes place is of the order of 1506 centigrade. It is desirable to maintain substantially constant temperature within the kiln because a considerable variation of the temperature lowers the quality of the produced cement clinker and also the efficiency of the kiln.

The object of my invention is to provide an improved construction and arrangement of rotary kiln appurtenances, especially an improved control mechanism for such equipments whereby the quality of the clinker is improved and the output and thermal emciency of the kiln in= creased.

For a consideration of what i believe to be novel in my invention, attention is directed to the fol lowing description and the claims appended thereto in connection with the accompanying drawing.

. The figure oi the drawing shows diagrammatically a kiln control arrangement in accordance with my invention.

The arrangement comprises an inclined rotary kiln Ill which has a sheet steel cylinder H lined inside with refractory brick or like heat resistant material l2. The kiln is driven by a motor l3 through a. gearing l5 at aspeed of about 1 to 2 R. P. M. The motor i3 is connected through wires l6, l1, and 54 and a rheostat ill to a D. C. line I9, 20, the latter receiving electric energy from a source 2| connected to the line I9, through a. switch 22. The speed of the motor ll and accordingly the kiln l0 may be varied by adjustment of the rheostat Hi. In the present instance l have shown the lower end portion only of the kiln in which the clinkering takes place. A burner 23 for supplying combustible material to the lower end of the kiln is directed into the brick-lined cylinder ll. The burner 23 receives combustible material, in the present instance pulverized coal, from a bin 26 through a feed screw 25. The feed screw it is driven by a motor 26 through the intermediary of a gearing Z'l. The

motor is connected to lines it, Ell by means including wires "ill, 29, a manually controllable rheostat Elli, and an automatically controllable rheostat ll, permitting regulation of the speed of the motor 28, as will be iully described hereafter. I

During operation of the motor 28, fuel, in the present instance pulverized coal, is conducted to the burner and discharged therefrom together with vehicle air. This vehicle air is supplied to the burner by a motor driven blower or motor compressor 32. The latter has an inlet or suction conduit 33 and a discharge conduit 34 con nected to the burner. The motor 82 is connected to lines it, till by wires 35 and 36 including a manually adjustable rheostat 3!. The rheostat 3i permits adjustment of the speed of the motor compressor 32 to vary the amount of vehicle air in accordance with the speed oi the motor 26, that is, in accordance with the amount of combustible material conducted to the bm'ner 23.

An important feature of my invention is the arrangement for supplying air into the clinkering zone to maintain combustion of the fuel therein. The air supplied to the clinkering zone is preheated, more specifically a portion of the air is preheated along the outside of the kiln whereby heat from the hotter portions of the kiln shell is recovered and another portion of the air is Y preheated by the discharged clinker, thus reburner 23, and forming a projection 4| with a trap door 42 hinged thereto for permitting the removal of large chunks of clinker diverted by the screen 49. Air is supplied to the higher end of the wind box 38 by a motor compressor 43 having an inlet 44 communicating with the atmosphere, or any suitable source om: supply,and a discharge conmoved from time to time.

duit II with branched conduits 88, 88, and 41, of

which the first branch 88 is connected to the wind box 88. Good heat transfer between the rotary kiln and the air supply in the wind box is effected by the provision of a rotating spiral fin 88 secured to the kiln and defining. lether with the stationary cylinder 88 of the wind box, a spiral channel for the air. The air flows along the spiral channel and thereby cools eilectively the steel cylinder ll of the kiln. thus avoiding excessive temperatures of this kiln shell with consequent rapid deterioration. Atthe right hand end of the kiln the preheated air is discharged from the spiral channel into the interior of the kiln where it provides air for the combustion process. With this arrangement the heat otherwise lost from the shell of the kiln is largely recovered, serving to v preheat the combustion air. Furthermore, the average temperature of the outer structural shell of the kiln is prevented from reaching a destructive point by the forced ventilation described herein. The clinker working toward the lower end of the rotary kiln and discharged therefrom drops through an opening .or openings 88 in the lower portion of the wind box cylinder 88 onto the right hand end of a perforated conveyor 88 disposed in a casing 8|. vented from dropping onto the conveyor and collect near the trap door 42 whence they are re- The perforated conveyor 88 is driven by a motor 52 connected to the lines i8, 28 by wires 58 and 54 including arheostat 88. The motor 52 is connected to the conveyor 88 by a gearing 88. During operation the clinker dropping onto the right hand end of the conveyor 58 is transported and discharged from the left handend of the conveyor. The rheostat 58 in the present example is manually adjustable and in accordance with my invention this rheostat is combined with the rheostat ll of the kiln driving motor l8 whereby both motors for driving the kiln and the conveyor respectively, are regulated simultaneously. In case it is desirable .to increase the output of the kiln, the rheostat i8 is adjusted to effect an increase in speed of the motor II. This adjustment effects simultaneously a similar adjustment of the rheostat 55, causing a corresponding increase in speed of the conveyor 88. The left-hand end of the casing Si is connected to the top of a cooling tower 51, which latter is provided with baille plates 58 defining a long zigzag path for the clinker discharged from the left-hand end of the perforated conveyor 50. The lower end of the cooling tower is closed by a dumping wheel or air-locked rotary clinker dumper 89. The wall of the cooling tower 51 is surrounded by an air jacket 68 for receiving air from the aforementioned branch 41 and discharging the air into the lower end of the cooling tower through openings 6i. With this arrangement air flowing spirally downward through the air jacket into the lower end of the cooling tower is preheated. It is then forced upward through the clinker in the cooling tower and through the perforated conveyor into the lower end of the kiln where, joining with the air supplied through the wind box 88, it provides air for the combustion process. Thus the heat content of the discharged clinker is regained through preheating of the combustion air, thereby increasing the eillciency of the arrangement. The dumping wheel 58 is operated intermittently by means including a motor 82 having one terminal connected by a wire 88 to the line I8 and another terminal connected Large chunks of clinker are preby a wire 84, a rheostat 8!, a hand-operated switch 88, and a wire 81 to the line 20. Closing of the switch 88 connects the motor to the line, effecting operation of the motor 82 and through a worm gearing 88 rotation of the dumping wheel 88, permitting discharge of clinker from the cooling tower. A single rotation of 90 degrees permits normally the discharge of a substantially definite amount of clinker. The motor 82 may also be operated automatically. To this end the wire 84 is connected through normally closed contacts 88 and relay contacts 10, to the wire 81. The contacts 10 may be closed by a contact-making member ll forming a part of a relay I2 which also includes another contact-making member 18 for closing holding contacts 18. The relay I2 has an operating coil 18 having one end connected to the line II by a wire 18 and another end connected to the line 28 by either of two circuits, a first circuit through a wire I1, contacts 18, through the aforementioned contacts 14 and the wire 81; the other circuit for closing the relay I2 is formed by either of two pairs of contacts 18 and 80, one of two switches 8| and 82 and the wire 88. The contacts 18 and 88 are closed by contactmaking members 88 and 84. The contact-making member 88 forms a part of a temperature responsive device comprising a bellows 85 having one end connected to the contact-making member 83 and another end communicating with a closed tube 86 projecting into the cooling tower. During operation, decrease in temperature in the cooling tower causes contraction of a medium enclosed in the tube 86, permitting the bellows I! to collapse or contract, thereby causing closing of the contacts 19 by the contact-making member 88.

The contact-making member 84 forms a part of a pressure-responsive device comprising a bellows 81 having its lower end secured to the contactmakingmember 84 and its upper end cornmunieating through a pipe 88 with the air jacket 88 surrounding the cooling tower. Increase in pressure in the air jacket causes increase in pressure in the bellows 81 whereby the latter expands and causes the contact-making member 84 to bridge the contacts 80. The temperature and pressureresponsive devices permit automatic operation of the motor 82 either in response to temperature or pressure conditions in the cooling tower. When it is desired to operate the motor 62 in response to temperature conditions, the switch 82 is closed, and when it is desired to operate the motor 62 in response to pressure conditions in the air jacket, the other switch 8i is closed. Let us assume the switch 82 is closed, causing the motor 62 to be operated in response to temperature conditions in the cooling tower. When this is the case, decreasing temperature in the cooling tower causes collapsing of the bellows 85 until the contact-making member 83 bridges the contacts 19. This causes energization of the operating coil 15.01 the relay 12 which then is connected to the line "through the contacts 19, the switch 82, and the wire 88. Energization of the coil eflects upward movement of the relay, thereby closing the two pairs of contacts 18 and II. The contacts 14, as stated before, are holding contacts for the relay whose coil 15 is now connected to line 28 through a. second circuit comprising the wire 11, the contacts 18, the contacts H and the wire 81. The provision of the holding circuit isadvantageous in that it preventsdeenergization of the relay coil before the necessary operation of the motor 82 is completed.

. from the cooling tower.

the latter.

" the contacts 69. The holding member 9t for contacts 69 is secured to a pivotally supported insulating block lid which also carries one of the contacts it. The two pairs oi contacts til and '58 are normally heldclosed by a biasing spring During a rotation of 90 angular degrees of the dumping wheel hit, one oi the projections cl engages the left-hand end of the flat spring to and causes the latter to move downward whereby the member $32 engages the member and causes opening of the contacts or as well as the contacts it against the biasing force of the spring to. The two pairs of contacts are opened for a short period of time only, normally sufiiclent to deenergize the relay coil It, thus causing dropping oi the relay l2 and stopping of the motor M. Ii, however, the operating coil lb of the relay i2 is still connected to the line ill through contacts iii and the switch 232, the relay remains closed and causes further dumping operation of the motor This operation will continue until the temperature in the cooling tower has increased sufficiently or in case the automatic operation is effected by the pressure-responsive device bl until the pressure has sufficiently decreased.

Another important feature of my invention comprises the provision or means for automatically controlling the operation of the motor cornpressor t3 and'the fuel supply motor 26 in response to a condition within the clinker zone oi the rotary kiln, more specifically in reponse to temperature changes in. the clinker zone in order to maintain substantially constant the temperature at which incipient fusion or clinker-ling takes place. The means for automatically operating the motor compressor id and the fuel supply motor 26 includes a temperature responsive device, in the present instance, a photo-electric cell 96, secured to or supported near the end plate Ml of the stationary wind box casing and trained onto the clinkering zone or region in the kiln. The photo-electric cell 9% is connected by wires 91 and 98 to an amplifier lilo, which latter receives energy from lines Hit and I02 oi. a threephase alternating current line connected to a source I03 through a switch I04. Any suitable amplifier I00 may be used. In the present instance, the amplifier IIlll includes a rectifier and a wave smoothing filter a for supplying a substantially constant D. C. potential across a voltage divider b. The latter is connected in a well known manner to a discharge valve or tube 0 having a control grid e-and a cathodev f. The grid potential is normally negative with respect to the cathode f and varies in response to temperature changes in the kiln. The grid potential determines the magnitude oi the current flowing through the tube 0. As the details of such amplifier form no part oi! my invention, the amplifier indicated by way of example in thedrawing is not further described, it being sufficient to indicate that this amplifier, together with the photo-electric cell 96, serves for energizing a suitable relay, in the present instance an operating coil I 01 an electromagnetic relay I06 in response to temperature changes in the clinker zone. One end of the coil I05 is connected to the line dl and the other end of the coil is connected through a millia'cmeter (MA) to the valve cof the ampliher. The relay lilo has a contact-making member will disposed between two pairs of contacts Hi8 and tilt respectively. The contact malzing member not is normally disposed intermediate between the two pairs of contacts Hill and ltd, as indicated in dotted lines. The two pairs of contacts serve for closing the circuit of a reversible motor Mil having an armature connected by wires ill and M2 to the line ill and through a wire iii to the field windings li t and lilo". The field winding lid is connected by a wire M8 and the contacts Hi9, and a wire ill to the line 89. The other field winding i it": is connected by a wire M8 to the contacts tilt and the wire i ill to the line iii. With this arrangement, closing or" the contacts tilt by the relay lot, in response to decreasing fiow of current through the discharge valve 0, causes energization of the field winding lit and operation of the motor liil in one direction and closing of the contacts tilt by the relaylil l in response to increasing flow of current through the discharge valve 0, causes energizetion of the field winding ii i and operation of the motor in the opposite direction. The motor I] Hi serves for adjusting two pairs of contacts [12d and 52H respectively secured to a W2, provided with a screw Hill, which latter is driven from the motor till through a gearing Ilii l and a nut i260! Operation of the motor Elli in one direction causes movement of the contact bar 622 to the right and operation of the motor ill in the opposite direction causes movement of the contact bar 622 toward the left. The contacts 82d serve for closing the circuit of a reversible motor l25 which has one terminal connected to the line Illl and two other terminals connected by wires l26 and lil to the two contacts i241, and a contact-making member I28 and a wire E29 to the line I02. The contact-making member lilil forms a part of a load-responsive device which may be'a wattmeter I38 for connecting the motor of the motor compressor it to the three-phase alternating current line comprising theaforementioned lines HM and ill? and a third line Hi. The reversible motor i25 serves for adjusting a gate valve I132 connected to the motor by a gearing ISM.

An arrangement of this kind is more fully disclosed in the patent to H. V. Crawford, No. 1,783,036, issued November 25, 1930, and assigned to the same assigne'e as the present invention. The provision of the reversible motor I25 and the load-responsive device or wattmeter I30 in cooperation with the motor of the motor compressor 43 serves to normally maintain the load on the motor 43 constant whereby, with the particular kind of motor compressor, a constant weight of air is normally discharged by the compressor. In case the weight of the air discharged by the motoncompressor 43 changes due to change in atmospheric air temperature or pressure, the electric input to the motor compressor 43 changes accordingly, whereby the member I23 is turned, causing closing oi! the circuit 01' the reversible motor I23 through either of the wires I23 or I21. The motor I25 then being energized causes adjustment of the gate valve I32, which latter represents in substance a means for varying the resistance to flow in the discharge conduit of the compressor. In case the weight of the discharged air has dropped, the gate valve I32 is turned to reduce said resistance to flow so that the weight of the discharged air is brought back to its normal value. Thus, during normal operation, that is, while the temperature within the kiln remains constant, a constant amount, more specifically a constant weight, of air per minute is supplied to the kiln. A change in temperature in the kiln, as pointed out above, causes operation of the motor II3 which in turn effects the setting of the contact bar I22. In case the temperature of the kiln drops, the contact bar I22 is automatically adjusted to cause an increased supply of energy to the motor compressor 43, resulting in an increased supply of air. Simultaneously the supply of fuel is increased, as will be described later.

As stated above, the air discharged by the compressor is diverted into the branched conduits or branches 43, 41, and 33 respectively. The amount of air flowing into the branch 46 is automatically controlled by means including a gate valve I35 connected to a motor I33 through a gearing I31. The motor I36 is reversible and is connected to the lines IN and I32 by a wire I38 and another wire I33 and one set of two pairs of contacts I43 and HI. Closing of the contacts is effected by a contact-making member I42 connected to a pressure-responsive device comprising a bellows I43 connected to the contact-making member I42 and communicating with the branched conduit 46 beyond valve I35. When the pressure in the conduit 43 increases, the pressure-responsive device effects closing of one pair of contacts I43 or I4I to cause operation of the motor I33 in such a direction that the gate valve I35 is moved in the closing direction. By this means the amount of air circulating through the kiln jacket may be maintained as desired. The relative amount of air flowing through the branch 41 into the air jacket 63 of the cooling tower may be adjusted by a manually or automatically operable gate valve I44 in the branch 41. The aforementioned conduit 33 for conducting vehicle air to the compressor 32 is also connected to the discharge conduit of the motor compressor 43. Thus, the conduit 33 receives compressed air which is further compressed by the compressor 32. The latter accordingly may be considered a booster, Hence the total amount of air necessary for operating the kiln passes through the motor compressor 43 which is controlled by the load-responsive device or wattmeter I33 and means for setting the contact bar I22.

The circuit for the fuel supply motor 23 includes, as pointed out before, a variable resistance or rheostat 3|. This rheostat is automatically controlled in accordance with my invention by means responsive to temperature changes in the kiln. These means including the aforementioned contacts I2I which, together with a loadresponsive device, which may be a wattmeter or an ampere meter I45, serve for controlling the circuit of a reversible motor I46. One terminal of the motor I43 is connected to the line I3 by a wire I41. The motor has two fields which are connected to the two contacts HI and through 9.

contact-making member I43 and the aforementioned wire II2 to the line 23. Engagement of the contact-making member I43 with one of the contacts I2I closes the motor circuit whereby the motor is rotated in a certain direction and causes a part of the resistance 3| to be cut out or in. This is accomplished by securing a handle or lever I49 for the resistance 3I to a member I33 screwed onto a projection ISI 01' the motor shaft. Rotation in one direction of the motor, as will be readily understood, causes the lever I43 to be moved to the right and vice verse. to the left when the direction of the motor is reversed. Adjustment of the resistance 3| causes change in speed of the fuel supply motor 23. The circuit for the motor 23 includes the wire 23, the loadresponsive device I43 and the wire II2 connected to the line 23. Under normal conditions, that is, with constant temperature in the kiln, the reversible motor, together with the load-responsive device I46 effect regulation of the rheostat 3I to maintain the speed of the fuel supply motor 26 constant. Constant speed of the motor 23 means substantially constant fuel supply to the burner 23. similar to the one disclosed in the aforementioned patent. The arrangement is such that with increasing supply of air by the motor compressor 43 the speed of the motor 26 is also increased to effect increased flow of fuel to the burner 23.

Summarizing the operation of the kiln control arrangement, a constant weight oi! air and a definite amount of fuel is normally supplied to the kiln. This is accomplished by the motor compressor 43 and its control mechanism including the watt-responsive device and the reversible motor I25 and by the fuel supply motor 23 and its control mechanism including the load-responsive device I45 and the reversible motor I43. A portion of the air discharged by the motor compressor 43 flows through the conduit 33 into the motor compressor or booster 32 and is discharged therefrom through the conduit 34 into the burner 23. This portion of the air serves for discharging fuel supplied to the burner 23 by the feed screw 25. A portion of the air in the discharge conduit 45 of the motor compressor 43 flows through the conduit branch 43 into the wind box 33 and another portion of air flows through the branch 41 into the air jacket 63 of the cooling tower. These two portions of the air are preheated in the wind box and in the cooling tower respectively and are supplied to the kiln where they maintain combustion of the fuel discharged by the burner 23. The kiln and the perforated conveyor 53 are driven by the two motors I3 and 52 respectively whose circuits include rheostats I3 and 55 respectively. The two rheostats are adjusted simultaneously whereby an increase in speed of the kiln I3 effects simultaneously an increase in speed of the conveyor 53. It the temperature of the clinker in the clinkering zone changes, for instance decreases, the supply of fuel and air are increased. This is accomplished by means including the photo-electric cell 33, the amplifier I33, and the relay I33 for controlling the circuit of the reversible motor II3 to eii'ect resetting or adjustment of the contact bar I22. In case the temperature in the kiln drops, the contact bar I22 is moved in a direction to effect increased air discharge from the motor compressor 43 and to correspondingly increase the fuel supply by increase in the speed of motor 23.

Clinker discharged into the lower portion oi the cooling tower 31 may bedischarged. there The arrangement is in this respect from manually or automatically in response to either 1 temperature conditions in the cooling tower or pressure conditions in the air jacket 60.

In accordancewith the provisions of the patent statutes, 1 have described the principle of operation of my invention, together with the apparatus which I now consider to represent the best embodiment thereof, but I desire to have it understood that the apparatus shown is only illustrative and that the invention may be carried out by other means.

What I claim as new and desire to secure by Letters Patentof the United States, is

l. The combination of a rotary kiln for heating a material, a motor for driving the kiln at substantially constant speed, a stationary closed wind box surrounding the kiln, means including a motor for supplying fuel into the kiln, means in-= eluding a motor compressor for forcing air through the wind box into the kiln to maintain combustion, and means for automatically controlling the fuel and air supply means in. response to changes of a condition of the material heated in the kiln at constant motor speed.

2. The combination of a rotary kiln for heating a material, a motor for driving the kiln at substantially constant speed, means for supplying fuel and air into the kiln, and means including a photo=-electric cell trained onto the material in the interior Of the kiln, and an amplifier connected to the cell for automatically controlling the fuel and air supply means in response to temperature changes in the kiln at constant Inctor speed.

3. The combination of a rotary kiln for heating material, a motor for driving the kiln at substantially constant speed, means for supplying fuel to the kiln, a. cooling tower connected to the discharge end of the kiln for receiving and cooling material discharged by the kiln, means for forcing air through the cooling tower into the kiln, and means for automatically controlling the fuel and supply means in response to temperature changes or" the material heated in the kiln at constant motor speed.

4. The combination of a rotary kiln for heating a material, a motor for driving the kiln at substantially constant speed, means for supplying fuel to the kiln, a cooling tower connected to the discharge end of the kiln for receiving and cooling material discharged by the kiln, means for forcing air through the cooling tower into the kiln, means for automatically controlling the fuel and air supply means in response to temperature changes of the material heated in the kiln at constant motor speed, said cooling tower includ ing an air-locked rotary dumper for intermittently discharging material from the tower, and means for automatically actuating the dumper in response to temperature changes in the tower.

5. The combination of a rotary kiln for producing clinker, a motor for rotating the kiln, means for supplying fuel into the kiln, an enclosed porous conveyor having one end disposed to receive clinker discharged from the kiln, a cooling tower for receiving clinker from the other end of the conveyor, a motor compressor for supplying air through the cooling tower into the kiln, means for-automatically regulating the discharge of clinker from the cooling tower in response to "temperature changes in said tower, and other means including said motor compressor for supplying additional air to the kiln in response 'to temperature changes in the kiln at constant motor speed.

6. The combination of a rotary kiln for producing clinker, a. motor for rotating the kiln at constant speed, means for supplying fuel into the kiln, an enclosed porous conveyor for clinker having one end for receiving clinker discharged from the kiln, a cooling tower for receiving clinker from the other end of the conveyor, a'motor compressor for supplying air through the cooling tower into the kiln, a motor for driving the conveyor, and means for simultaneously regulating the motors for driving the conveyor and the kiln.

7. The combination 01' a rotary kiln for producing clinker, a motor for normally rotating the kiln at constant speed, means for supplying fuel into the kiln, an enclosed porous conveyor for clinker having one end for receiving clinker discharged from the kiln, a cooling tower for receiving clinker from the other end of the conveyor, 9. motor compressor for supplying air through the cooling tower into the kiln, and means for automatically maintaining constant the weight of the supplied air at constant temperature of the clinker.

8. The combination of a rotary kiln ior producing clinker, a constant speed motor for rotating the kiln, means for supplying fuel into the kiln, an enclosed porous conveyor for clinker having one end for receiving clinker discharged from the kiln, a cooling tower for receiving clinker from the other end of the conveyor, a motor compressor for supplying air through the cooling tower into the kiln, means for controlling the motor compressor in response to temperature changes in the kiln comprising a temperature-responsive device connected to the kiln, and means including a wattresponsive device connected to the motor connpressor for varying the resisttmce to flow to be overcome by the compressor in response to temperature changes.

9. The combination of a rotary kiln ior pro ducing clinker, a wind hon surrounding the kiln and communicating at the discharge end with the kiln, a cooling tower for receiving and cooling clinker discharged by the kiln, a motor compressor having a branched discharge conduit with one branch connected to the wind box and another branch connected to the cooling tower for preheating air in the wind box and the cooling tower and forcing the air into the kiln, and means for supplying fuel into the kiln including a motor compressor having an inlet conduit connected to the discharge conduit of the first mentioned motor compressor. I

10. The combination of a rotary kiln for producing clinker, a wind box surrounding the kiln and communicating at the discharge end with the kiln, a cooling tower for receiving and cooling clinker discharged by the kiln, a motor com-' pressor having a branched discharge conduit with one branch connected to the wind box and another branch connected to the cooling tower for preheating alr in the wind box and the cooling tower and forcing the air into the kiln, means for supplying fuel into the kiln including a motor compressor having an inlet conduit connected to the discharge conduit of the first mentioned motor one branch connected to the wind box and another branch connected to the cooling tower for preheating air in the wind box and the cooling tower and forcing the air into the kiln, means for supplying fuel into the kiln including a motor compressor having an inlet conduit connected to the discharge conduit 01 the first mentioned motor compressor, and means for simultaneously automatically varying the air supply and the fuel supply in response to temperature changes in the kiln and a motor for driving the kiln at constant speed.

12. "I'hecomblnation oi a rotary kiln for heating a material, a constant speed motor for driving the kiln, means including an electric motor ior supplying fuel to the kiln, other means including another electric motor ior supplying air into the kiln to maintain'combustion therein, and means for simultaneously controlling said motors in response to temperature changes in the kiln, said means comprising a pilot motor and a load-responsive device for each oi said motors, and an electric circuit for the pilot motors including an element of the load-respmsive devices and a contact bar associated with the devices, a reversible motor for adJusting the contact bar, and means including a temperature-responsive device for causing operation of the reversible motor in response to temperature changes in the kiln.

AUBREY SMITH.

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