US3119605A - Process and device for preheating pulverulent material - Google Patents

Description

Jan. 28, 1964 w. BERZ 3,119,605

PROCESS AND DEVICE FOR PREHEATING PULVERULENT MATERIAL Filed June 30, 1961 2 Sheets-Sheet 1 w. BERZ 3,119,605

PROCESS AND DEVICE FOR PREHEATING PULVERULENT MATERIAL Jan. 28, 1964 2 Sheets-Sheet 2 Filed June 30, 1961 FIG.2

United States Pate My present invention relates to a process and a device for-preheating pulverulent material adapted to be introduced into a furnace or the like. This application is a 'continuation-in-part of my co-pending-application Ser. No.- 549,122, filed November 25, 1 955, and now abandoned.

An object of 'the' invention resides in the provision of an improved preheatingdevice for-pulverulent materials adaptedto afford highly eflicient transfer of heat from a hot gas to the particularized material;

Another object of my invention is to provide-an-effi cient process for maintaining a mass of free-flowing solid particles in prolongedcontact' with a stream of heating gas therefor. H.

-Afurther object of this inventionis to provide a device forpreheating comminuted material, morespecifically dry; rawcement free from any binder and adapted to.be fed continuously into conventional kiln, with efiicient utilization of the heat content of furnace orwkiln exhaust gases.---.

According to a featureof my invention, a preheating device for 'pulverulent materialscomprises a preheating chamber formed with at least.one apertured collecting plate or partition disposed transversely to a descending stream of particles and an ascending flow of furnace or kiln exhaust gas, the collecting plate being formed withpassages adaptedto admit the exhaust gas to the upper compartment of the chamber substantially tangentially,

thereby sweeping the comminuted material falling onto the plate into a vortex and maintaining it in contact with.

the gas stream for prolonged periods. Gradually and continuously, however, these particles traverse the passages in the plate and enter the lower compartment of thechamber whence they may be conveyed to the main heating or firing furnace. The preheating chamber may, advantageously, be provided with two or more stages formed bya succession of spaced-apart collecting plates, thereby increasing the efiiciency of the device still further. According to a more specific feature of the invention, the cyclonic effect of thetangential passages in each collecting plate is enhanced by the provision of means on the upper surface of the plate-for subdividing the vortex in the'upper compartment into a pluralityof concentric cyclonic'whirls. Such means may includea ridge lo cated between two concentric annular arrays of the aforementioned passages and forming a pair of downwardly converging annular troughs which open into the upper compartment and are adapted to funnel the descending stream of particles toward the passages While directing the vortex upwardly so as to spread the stream of circulating particles over substantially the entire region above the plate. a Moreover, as mentioned in the above-identified copending application, I have found that it is advisable to control the quantity of particles permitted to pass through the passages in accordance with the quantity of pulverulent material present above a collecting plate; in this manner, given a predetermined supply rate for this material, the average length of exposure of the particles to the hot gas can be-adjusted to an optimum value. I have further found that it is possible to stabilize the treatment time by measuring the pressure differential between the compartments respectively formed above and below the partitioning plate. Although a portion of this differential arises as a consequence of a pressure drop as the rising stream'of exhaust gas traverses the passages in the plate, the major portion of the pressure differential 'ap-,

pears to result from a pressure drop as the gas passes through the swirling cloud of comminuted material floating above the plate. Ltherefore, prefer to providemeans responsive to a pressure differential on opposite sides of a collecting plate for controlling the openings'of the passages in this plate. Suitable meansof this type may comprise an apertured valve member juxtaposed with; the collecting plate, the-valve member and the collecting plate being relatively angularly shiftable for selectively Ili1ll of FIG. 2, still further enlarged; and

obstructing the passages therein to a varying extent with-- out, however, closing them completely in the normal operation of the device, I In'a general manner, the width of the passages is made to vary instep with the pressure differential so that any change in the thickness of the float-- ing layer is compensated by an altered rate of descent of theparticles through these passages.

"I0 obviate ;the formation of channels within the pulverulent material, I prefer to provide agitator means adapted to sweep the collecting plates. Such agitator meansmay comprisea radially extending arm disposed a limited distance above the upper surfaces of each 'col-.

lecting' plateandrot'ated continuously. When the device is a-multi-stage preheater, theagitating arms of several collectingplates are, preferably, ganged for rotationin unison by a single drive. I I v 7 While the exhaust gas may be introduced into the preheating chamber under a pressure sufficient to drive it through the passages of the collecting plates, I prefer to provide a reduced-pressure'chamber above the preheatingchamber for drawing'the exhaust gas'upwardly. The reduced-pressure chamber may advantageously, cornprise a precipitator adapted to collect dust andv the like carried along with the gas and connected in series with a suction-device. Suitable feed m eans may be provided for returning the comminuted material accumulated by. the precipitation device to the main heating furnace, either directly or via one or more-of the associated preheating stages. I

' The above and other. objects, features and advantages of my present invention will become more readily appar-. ent from the following description, reference being made to'the accompanying drawing in which: f

' FIG. 1 is a cross-sectionalview of a preheating device, illustrated somewhat schematically, according to the invention; I f 7 FIG. 2-is a cross-sectional view taken along line II.-II of FIG. 1, drawn to an enlarged scale; 7

.- FIG. 3 is a cross-sectional View taken along line FIG. 4 is a cross-sectional view taken along line IV-IV of FIG. 1 and drawnto the same scale as FIG. 2.

' In the drawing, a conventional rotary kiln 10 for firing cement or the like, iournaled on rollers 11, is connected via a duct 12' to a cylindrical casing 13 which encloses a preheating chamber 14. The latter is subdivided into an upper compartment 15, an intermediate compartment 16 and a lower compartment 17 by a pair of axially spaced. collecting plates 18 and 19 forming horizontal partitions therein. A feed hopper 2i) and a feed roller 21, adapted to admita continuous stream of 'comminuted material 2am a housing23 communicating with the upper compartment .15 of the chamber 14, are mounted nponithe top of this housing. The latter also enclosesa precipitating cone 2.4 which is connected to a suction pumpQSby .a conduit26 and has a series of'periphera'l inlet ports 27 The dust and fine particles entrained by the. gases emerging from the preheater are separated therefrom by deflection of the fiowwithin cone 24 and are returned to v the kiln 10 via a screw feed 28' and a duct 29 represented diagrammatically by dot-dash lines.'

Patented Jan. 28, 1964 The collecting plate 19, shown in greater detail in FIGS. 2 and 3, is formed with two concentric annular arrays of arcuate throughgoing slots 30 and 31 provided with respective deflecting vanes 32, 33 forming helicoidally ascending ramps therein. As shown in FIGS. 2 and 3, the vanes 32 and 33 are inclined upwardly in the counter-clockwise direction and adapted to impart a tangential direction to the ascending gas stream symbolized by arrows 34 in FIG. 1. The plate 19 is also provided with an upstanding central conical portion 35, an outer conical wall 36 and a ridge 37 with conical wall portions intermediate the slots 30 and 31. The cone 35, the wall 36 and the ridge 37 form a pair of concentric troughs 38, 39, respectively communicating with the slots 30, 31, of downwardly converging configuration and adapted to funnel the descending particles 22a to the slots, at the same time sustaining independent vortices arising from the tangential flow of ascending gas which issues from the passages constituted by the vanes 32, 33 and the slots 30, 31. A valve disk 40 abuts the lower surface of plate 19 and is rotatable upon a ring 41 secured to the casing 13. A solenoid 42 has its armature 43 pivoted to the disk 40 along its periphery and is adapted to displace it relatively to the plate 19 whereby the bores 44 in the disk will be angularly displaced out of alignment with the passages 30 and 31 and the quantity of pulverulent material traversing the latter will be propressively reduced.

The upper collecting plate 18 (FIGS. 1 and 4) consists of a central member 45 and an outer member 46 each formed with a respective array of angularly spaced slots 48, 47. The slots are provided with deflecting vanes 50, 51 of the type described above for imparting a tangential component to the ascending flow of gas. Each of the members 45, 46 is articulated to a connecting rod 52, 53, respectively joining them to the armatures 54, 55 of a pair of solenoids 56, 57, and is rotatable relatively to a stationary valve disk 58 whose bores 59 are alignable with the slots 47 and 48 as described with respect to the movable valve plate 40.

A pair of agitator blades 60, 61, adapted to sweep the upper surfaces of plates 18 and 19, respectively, and to prevent the formation of ducts for the gas stream through the overlying mass of comminuted material which would then tend to settle upon the plates, are each secured to a shaft 62 journaled axially in the chamber 14. Shaft 62 is driven via a bevel-gear linkage 63 by a motor 64. The speed of shaft 62 is, of course, such that the blades 60, 61 rotate at a rate different from the angular velocity of the swirling gas stream.

In operation, the comminuted material 22 is percolated downwardly from the hopper 20 and the feed roller 21 through the preheating chamber 14 in countercurrent to an ascending stream of hot exhaust gas (indicated by the arrows 34) aspirated from the rotary kiln by the suction pump 25. As the gas rises through each plate 18, 19, the passages therein impart to the velocity of the gas a tangential component which entrains the descending particles in rising vortices above each plate so that the particles are floated for prolonged periods (e.g. of about to 40 minutes) and abstract a maximum amount of heat from the gas. The depleted gas then flows through the precipitator '24 for the recovery of accompanying solids and is discharged via pump 25.

To control the rate at which particles are fed to the kiln and to successively lower plates in the preheating chamber and to maintain the layers of particles above these plates 18 and 19 at a substantially constant thickness, a respective pressure cell 65, 66 and 67 is disposed in each compartment 15, 16 and 17. The cells 65, 66 are connected across a pressure-difierential-responsive switch 68 lying in series with a battery 69, representative of any convenient source of electric current, and the parallelconnected solenoids 56 and 57. A cutout switch 70 in series with the solenoid 57 serves to disconnect this solenoid from the differential switch 68 if the operation of solenoid 56 is sufiicient to control the flow of particles through the plate 18. Similarly, solenoid 42 is con nected in circuit with a battery 72 and a differential switch 71. The latter bridges the pressure- sensitive cells 66 and 67. This construction permits the rate of particle flow through each plate to be adjusted in keeping with the depth of the particle layers suspended thereabove.

The invention as described and illustrated is believed to admit of many modificaions and variations embraced within the spirit and scope of the invention as claimed and readily apparent to persons skilled in the art. Thus, for example, the eflective cross-sectional area of passages 30, 31 and/or 47, 48 might be controlled in response to parameters other than the pressure differential across the particle layer overlying the respective collecting plates, for the purpose of establishing a desired layer thickness along with an optimum floating time; also, the several preheating stages may all be provided with collector assemblies of the type shown either at 18 or at 19, with or without agitators, having their vortex zones arranged in a variety of geometric patterns.

I claim:

1. A device for heating pulverulent material, comprising a housing forming a heating chamber, duct means for introducing a flow of hot gas into a lower portion of said chamber, feed means for introducing a stream of pulverulent material into an upper portion of said chamber in counterfiow to said hot gas, a perforated collecting plate positioned intermediate said upper and lower portions for intercepting said stream of pulverulent material and said flow of hot gas, and valve means responsive to a pressure differential in said chamber on opposite sides of said plate for maintaining the thickness of a layer of said material deposited thereon near a predetermined value.

2. A device for heating pulverulent material, comprising a housing forming a heating chamber, duct means for introducing a flow of hot gas into a lower portion of said chamber, feed means for introducing a stream of pulverulent material into an upper portion of said chamber in counterflow to said hot gas, a perforated collecting plate positioned intermediate said upper and lower portions for intercetping said stream of pulverulent material and said flow of hot gas, said collecting plate being formed with a plurality of passages for imparting a substantially tangential displacement to the gas passing through said plate into said upper portion whereby particles of said material are entrained in a vortex of said gas rising from said plate, and valve means responsive to a pressure difierential in said chamber on opposite sides of said plate for maintaining the thickness of a layer of said material deposited thereon near a predetermined value.

3. In combination with a furnace, a device for preheating pulverulent material, said device comprising a housing forming a heating chamber, duct means connected to said furnace for introducing a flow of hot exhaust gas into a lower portion of said chamber, feed means for introducing a stream of pulverulent material into an upper portion of said chamber in counterflow to said hot exhaust gas, a pair of longitudinally spaced perforated collecting plates extending substantially horizontally intermediate said upper and lower portions for intercepting said stream of pulverulent material and said flow of hot gas, said collecting plates being formed with a plurality of passages for imparting a substantially tangential displacement to the gas passing through said plate into said upper portion whereby particles of said material are entrained in a vortex of said gas rising from said plate, valve means responsive to a pressure differential in said chamber on opposite sides of said plate for maintaining the thickness of a layer of said material deposited thereon near a predetermined value, and means for separating particles of said material from the gas flow passed by said late and returning them to said furnace.

4. In a device for heating pulverulent material, in combination, a housing, substantially horizontal partition means in said housing subdividing the interior thereof into a lower and an upper compartment, said partition means being formed with at least one passage interconnecting said compartments, a source of pressure differential between said compartments, means including said source for passing a flow of hot gas upwardly through said passage from said lower to said upper compartment, adjustable valve means in said passage, feed means for continuously introducing a supply of said pulverulent material into said upper compartment in counterflow to said gas, and gas-pressure-responsive control means sensitive to the pressure diiferential between said compartments and coupled with said valve means for maintaining the rate of gas how at a value adapted to hold said pulverulent material fioatingly suspended above said partition means for an extended period.

5. In a device for heating pulverulent material, in combination, a housing, substantially horizontal partition means in said housing subdividing the interior thereof into a lower and an upper compartment, said partition means being formed with an array of helicoidally ascending passages interconnecting said compartments, a source of pressure differential between said compartments, means including said source for passing a flow of hot gas upwardly through said passages from said lower to said upper compartment, adjustable valve means in said passages, feed means for continuously introducing a supply of said pulverulent material into said upper compartment in counteriiow to said gas, and gas-pressure-responsive control means sensitive to the pressure diiferential between said compartments and coupled with said valve means for maintaining the rate of gas flow at a value adapted to hold said pulverulent material floatingly suspended above said partition means for an extended period.

6. In a device for heating pulverulent material, in combination, a housing, substantially horizontal partition means in said housing subdividing the interior thereof into a lower and an upper compartment, said partition means being formed with at least one passage interconnecting said compartments, a source of pressure differential between said compartments, means including said source for passing a flow of hot gas upwardly through said passage from said lower to said upper compartment, adjustable valve means in said passages for changing the effective cross-sectional area thereof, feed means for continuously introducing a supply of said pulverulent material into said upper compartment in counterr'iow to said gas, gas-pressure-responsive control means sensitive to the pressure differential between said compartments and coupled with said valve means for maintaining the rate of gas fiow at a value adapted to hold said pulverulent material floatingly suspended above said partition means for an extended period, said control means being differentially connected with said compartment for varying said cross-sectional area substantially in step with the pressure drop across said partition means and a layer of said material floating thereabove, thereby maintaining the thickness of said layer substantially constant.

7. In a device for heating pulverulent material, in combination, a housing, substantially horizontal partition means in said housing subdividing the interior thereof into a lower and an upper compartment, said partition means being formed with an array of helicoidally ascending passages interconnecting said compartments, a source of pressure differential between said compartments, means including said source for passing a flow of hot gas upwardly through said passages from said lower to said upper compartment, adjustable valve means in said passages for changing the effective cross-sectional area thereof, feed means for continuously introducing a supply of said pulverulent material into said upper compartment in counterflow to said gas, gas-pressure-responsive control means, sensitive to the pressure differential between said compartments and coupled with said valve means for maintaining the rate of gas flow at a value adapted to hold said pulverulent material floatingly suspended above said partition means for an extended period, said control means being differentially connected with said compartment for varying said cross-sectional area substantially in step with the pressure drop across said partition means and a layer of said material swirling thereabove, thereby maintaining the thickness of said layer substantially constant.

References Cited in the file of this patent UNITED STATES PATENTS 2,078,955 Lipscomb May 4, 1937 2,634,116 \Vitt Apr. 7, 1953 2,668,041 Knibbs Feb. 2, 1954 2,785,886 Muller Mar. 19, 1957

Claims (1)

1. A DEVICE FOR HEATING PULVERULENT MATERIAL, COMPRISING A HOUSING FORMING A HEATING CHAMBER, DUCT MEANS FOR INTRODUCING A FLOW OF HOT GAS INTO A LOWER PORTION OF SAID CHAMBER, FEED MEANS FOR INTRODUCING A STREAM OF PULVERULENT MATERIAL INTO AN UPPER PORITON OF SAID CHAMBER IN COUNTERFLOW TO SAID HOT GAS, A PERFORATED COLLECTING PLATE POSITIONED INTERMEDIATE SAID UPPER AND LOWER PORTIONS FOR INTERCEPTING SAID STREAM OF PULVERULENT MATERIAL AND SAID FLOW OF HOT GAS, AND VALVE MEANS RESPONSIVE TO A PRESSURE DIFFERENTIAL IN SAID CHAMBER ON OPPOSITE SIDES OF SAID PLATE FOR MAINTAINING THE THICKNESS OF A LAYER OF SAID MATERIAL DEPOSITED THEREON NEAR A PREDETERMINED VALUE.

Images