US2572484A - Apparatus for expanding perlite and the like - Google Patents

Description

Oct 23, l951 E. o. HowLE ETAL APPARATUS FOR EXPANDING PERLITE AND THE LIKE Filed Sept. 17. 1947 3 Sheets-Sheet, l

22 er JEC/429022 34.9702721477 ./sir c3 Oct. 23, 1.951 E, Q HOWLE ErAL 2,572,484

APPARATUS FOR EXPANDING PERLITE AND THE LIKE Filed Sept. 17. 1947 3 Sheets-Sheet 2 Oct. 23, 1951 E. o. HowLE ErAL APPARATUS FOR EXPANDING PERLITE AND THE LIKE` 3 Sheets-Sheet 5 Filed Sept. 17, 1947 Patented Oct. 23, 1951 APPARATUS FOR EXPANDIN G PERLITE AND THE LIKE Ernest O. Howle and Roger W. Jackson, Chicago, Ill., and Norman M. Foster, New Castle, Ind.; said Jackson and said Foster assignors to said Howle Application september 17, 1947, serial No. 774,614

7 claims. (ci. 263-21) This invention relates to the expansion of perlite, and among other objects, aims to provide a method of and means for more efliciently expanding perlite.

Another object of the invention is to increase the yield of expanded perlite.

Another object is to provide an improved method of and means for controlling the expansion of the perlite.

The nature of the invention and other objects and advantages thereof will readily Pppear by reference to one illustrative method and appartus embodying the invention, described inthe following specification and illustrated in the accompanying drawings.

In said drawings:

Fig. 1 is an elevation, partly in section of the apparatus;

Fig. 2 is an elevation of adjustable driving means for feeding perlite to the expanding apparatus; and

Fig. 3 is a plan view of controlling means for the feeding apparatus;

Fig. 4 is an elevation of other details of such controlling means;

Fig. 5 is an elevation taken partly from the plane 5 5 of Figure 2, of the actuating means by which adhering perlite is dislodged from the walls of the furnace;

Fig. 6 is a diagram of the thermostatic regulator for the feeding apparatus;

Fig. 7 (Sheet 2) is a sectional elevation taken from the plane 1 1 of Fig. 2, showing the delivery end of the feeding mechanism; and

Fig. 8 is a section taken on the plane 8-8 of Fig. 1, of a nozzle of the flame retention type.

'I'his application is a continuation in part of our copending application Serial No. 684,452, later abandoned.

Perlite is a siliceous material of volcanic origin, and rhyolitic in composition. It contains about 2 to 5% of combined water. When quickly heated to its softening temperature range the steam formed puffs the material to many times its original size to produce a. material of very low bulk density, e. g. 2 to 14 pounds per cubic foot, depending on the degree and ei'ciency of expansion. Perlite differs considerably, depending on the locality where found, in the time required for expansion, and in its softening range. The softening range is generally somewhere between 1600 degrees F. to 2600 degrees F. A relatively wide softening range is desirable to permit more eilicient and better control of. expansion. It is difficult to prevent the material in its softened condition from cohering or agglomerating and from adhering to the walls of the expanding furnace, with the result that much material is wasted and frequent removal of the layer of glass from the Walls of the furnace is necessary. In this respect, among others, perlite presents serious problems not encountered in the treatment `of other materials. Even with the most careful grading (which greatly increases the cost) it is not possible to obtain material of sufficiently uniform grain size to respond alike to expanding temperatures. If the larger grains be expanded properly, the smaller grains will be excessively softened, losing their porosity and adheringto other granules and to the walls of the furnace.

According to our invention, granules of various sizes may be simultaneously expanded without pregrading; and a given granule is exposed to expanding temperatures only long enough to expand it. When expanded, and as a consequence of such expansion, it is automatically removed from the expanding zone. The heavier or larger particles remain in the expanding zone a longer time. We utilize the large particle bulk (i. e. lower bulk density) resulting when the granule expands, to carry the particle out of the expanding zone, by subjecting the granules to an upward current of gases of such velocity as to be capable of carrying the particles away in the gas stream when adequately expanded. Until a granule expands, it remains in the highly heated expanding zone, its bulk being insufficient to be levitated by force of the gas stream. Rock impurities which do not expand, eventually fall below the heated zone into a collection space and are thereby automatically separated from the perlite.

This method of expansion may advantageously be used for expanding other materials such as vermiculite and mixtures of various expandable materials. When expanded the bulk density of the material is low enough to insure its being carried out of the expanding zone by the moving gases. Until adequately expanded it remains in the high temperature zone. As regards mixtures, it is considerably cheaper to mix the expandable materials in the proper proportion before expanding, than afterwards; and the illustrative method and apparatus advantageously permits this because, regardless of size or character of the expanded material, it remains in the high temperature zone until expanded suiiiciently to be carried away with the upwardly traveling gases.

The broad subject matter involving expansion of the perlite by introducing it into an upwardly rising stream of gases of such velocity as to carry the particles upward and out of the expanding heat immediately on expansion of the particles Ibut not otherwise, is claimed in copending application Serial No. 39,048,

The serious problem of adhesion of the softened perlite to the furnace walls is solved by employing a thin metal liner suspended inside the walls of the furnace and separated therefrom so that it can be vibrated or otherwise slightly jarred or disturbed to dislodge any particles thereon. Cooling air may be circulated outside the liner, and as presently explained, excessive temperatures inside the liner are prevented by temperature responsive mechanism which adjusts the feed of materials into the furnace to absorb excessive heat and to maintain temperatures uniform inside the furnace.

In the illustrative furnace the liner comprises a cylindrical metal tube or shell advantageously made of an alloy, such as stainless steel, capable of withstanding the temperatures to which it is exposed. In this instance its length is about twelve times its diameter. In the illustrative furnace its diameter is about l8 inches. It is indirect-lv supported adjacent its upper end upon the refractory furnace wall from which it is separated by a space I2 for the circulation of cooling fluid, in this case air.

The source of heat is a pre-mixed gas-red burner located at the lower end of tube I0, comprising a gas nozzle I4 advantageously of the flame retention type (Fig. 8) and a tuyre Il whose mouth is located inside but separated from the tube walls to provide a space I6 through which rock impuritiemay escape from the furnace into a collecting box I1. The box is sufficiently open to permit the passage of coolingr air therethrough to the coolingr space I2. 'I'he tuyre is advantangeously cooled by a water iacket I8 to which water circulatinc pines I9 and 20 are connected. The flame retention nozzle I4 is characterized by a chamber 2| surrounding the nozzle orifice 22 and supplied by gas from small orifices 23. Gas velocitv in chamber 2| if relatively low (substantially below that of the velocity of Fame propagation) and therefore serves to maintain ignition of the high velocit` vas stream issuing from oriflce 22, whch generally exceeds the speed of flame propagaton. The velocity of the gases issuing from the nozzle is, of course, high enough to insure a velocity up the larger diameter expansion chamber sufficient to levitate the material as and when it expands to a low bulk density.

A motor driven gas-air mixing, proportionlng and regulating unit 24 supplies fuel and air to the burner. Its details are conventional and are not relevant to the present invention. In an expanding furnace like that here illustrated having an internal diameter of 18 inches, we have found that 2,000 cubic feet of natural gas per hour mixed 4with 18,800 cubic feet of air will create a temperature during expanding operations, of about 1700 degrees F., on the outside of tube I about three feet above the point where combustion starts. The temperature of the gases is of course substantially above this temperature (e. g. about 3000 degrees FJ, but the effective temperature, that is the temperature to which the granules are heated is about 1700 to 1900 degrees F. The supply of granules normally present in the high temperature zone during operation, has a substantial cooling efl'ect on the hot gases. If the supply of granules be cut off or their rate of supply be subing zone would rise substantially higher. Con' versely, in the presence of an increased supply of granules, the effective temperature would be lowered.

At their combustion temperature, the gases expand to such volume that the velocity of the gases up the tube is about 1100 feet per minute. This is sufficient to provide the force necessary to levitate perlite granules having a maximum bulk density of about 8 pounds per cubic foot and thereby carrying them out of the furnace when expanded. For heavier or larger granules the gas velocity is correspondingly increased (by increasing the supply of gas and air) suiliciently to carry the granules away when they have been adequately expanded. Gas velocity may also be increased by increasing the temperature, which correspondingly increases the volume of the gases, but this must be limited to proper expanding temperatures.

The perlite may advantageously be fed into the furnace at a point just above the point of maximum temperature of the flame, and as here shown the perlite fed therein through an alloy spout 25 passing through an opening 26 in tube I0 large enough to permit the latter tube to expand and contract without disturbing the feeding spout 25. The latter is widened at its outlet (see Fig. 7) to fan out the ore, and thereby to distribute it over the area of the furnace. Spout 25 is also equipped with a baille 21 separate from the liner walls, but covering the opening 26 in the liner.

As the perlite falls into the flame it is heated to expanding temperatures and softened, and as soon as the material expands adequately. its large bulk and low density causes the particle to be carried away with the rapidly upwardly traveling hot gases. Material not expanded sufficiently remains in the expanding zone until it has expanded sufficiently. Unexpandable rock impurities eventually fall below the frame and escape through the space I6 between the lower end of the tube and the tuyre into the collection box The stack effect of the heated tube I0 induces a current of air to flow upwardly through space I2 to aid in cooling the tube. The tube is supported adjacent its upper end from a ring 3| surrounding the tube and welded or otherwise attached thereto. The ring in turn is carried on a plurality of flexible or hinged suspension mem- Y bers 32 depending from a transverse open frame 33 supported on the upper end of the refractory wall II by posts 34. The tube thus hangs freely inside the furnace, and being unconnected at its lower end is free to expand and contract with changing temperatures.

Appropriate vibrating or jarring means are provided for periodically vibrating or jarring the tube so as to dislodge any particles of perlite which because of an excessively softened condition become attached to the walls of the tube. Any appropriate mechanism of this character may be employed. In the present case the vibrating mechanism is in the form of an anvil 38 connected with the tube support and a hammer 39 which periodically strikes the anvil to send a shock or vibration down the tube (see Figs. 2 and 5). The frequency of the hammer is in this case determined by the rate of rotation of the ore feeding screw. which is from 14 to 34 R. P. M.; but it is unnecessary that the frequency be that high or that it correspond to the rate of rotation of vthe feeding screw. The hammer in this case is impelled by springs 4I connected thereto and which are periodically compressed by the flexible connection 42 extending to the ore feeding mechanism presently described (Figs. l and 2) by which it is periodically pulled to compress the spring and then periodically released. In the present case a cam 43 (slowly rotated by the feeding screw) rocks lever 44 (pivoted at 45) to which the flexible line 42 is connected. Hammer 39 is thereby retracted, and springs 4I compressed. The latter and lever 44 are suddenly released when the lever passes the high point 46 on the cam.

The material when expanded as above described is carried by the heated gases out the top of tube I to a storage bin 41 to which it is connected by the alloy elbow 48. The latter of course is highly heated by contact with the hot granules and gases. Preferably it simply rests on the upper end of the tube supporting structure so that it may be readily removed for inspection of the furnace and for replacement. The elbow is covered by a jacket 49 spaced therefrom and hinged at its lower edge for access to the elbow. A shield or baille 50 in the shape of an inverted trough directs the hot granules down into the bin and protects the upper portion of the bin from direct heat from the granules. The lower portion of the bin being covered by granules is thereby insulated from the heat of the freshly expanded granules entering the bin.

In the illustrative bin a grading of the expanded perlite into three sizes is effected. The proportion of coarse, intermediate and line expanded material corresponds generally to the proportion of coarse, intermediate and fine material in the ore as fed into the furnace. In the present bin the aforesaid separation is effected by a baille whose upper edge is so located in relation to the stream of material entering the bin, that the heavier and coarser material fails to clear the baille whereas the finer material passes over it. As here shown, the baille comprises the wall 53 which divides the bin into a compartment 54 for the coarse material and a compartment 55 for the intermediate material. The upper edge E of the baille is ad'usted in relation to the stream of material entering the bin to effect the above separation. Both intermediateand very fine material pass into compartment 55 where the ne material which settles with difliculty is drawn Y into a cyclone separator 51 through a tangential inlet 58. To prevent entrance into the cyclone separator of any intermediate grade material while suspended in the stream, a baille 59 is placed across the path of the stream entering compartment 55 to remove the kinetic energy from the heavier particles, thereby causing these particles to fall to the bottom of compartment 55. Only the finer material which remains in suspension after striking the baille enters the cyclone separator. The suction for the separator is provided by fan El driven by motor 62. The ilne material is thrown out and falls to the bottom 63 of the separator from which it may be periodically discharged into a collecting bin 64.

Weights of the various grades of expanded granules may be varied as presently explained. When fully expanded the ne grade having a maximum mesh size roughly of minus weighs 21/2 to 3 pounds per cubic foot. The intermediate size having a maximum mesh size of minus 8 weighs about 4 to 5 pounds per cubic foot; and the large size having a maximum mesh size roughthe hot particles in the bins from conduits 66v whose discharge ends 6l are submerged in the mass oi' particles. The air is advantageously supplied (by fans 68) by withdrawing it through pipes $9 from the regions adjacent the tops of the bags 10 under the filling spouts, to carry away the dust created on filling. The air discharged into the highly heated perlite also carries away some acid from the perlite (perlite is slightly acidic) thereby adapting it for uses where perlite not so treated would be unsuitable. The subject matter involving storing and bagging is claimed in our copending application Serial No. 793,926.

Encient operation of the furnace depends substantially on securing complete or efficient expansion of the granules without over-softening them to the point where they will collapse and cohere.

We have discovered that efficient and effective regulation of furnace temperatures may be effected by varying the rate at which the perlite is introduced into the furnace. Thus a much more prompt response of furnace temperature is obtained than would be possible by attempting to regulate the burner itself. It is thus possible to regulate the temperature independently of the Velocity of the gases of combustion, which have the added function of carrying the material out of the high temperature zone as and when it is properly expanded. Indeed, regulation by varying fuel supply is impracticable because it correspondingly affects gas velocity whose force is used to carry away the expanded granules. Reduction in the supply of fuel for example would have the effect of reducing the gas velocity and thus holding the ore in the furnace for a longer period, thereby neutralizing the control sought to be obtained by reduction in temperature through reduction in the supply of fuel.

On the other hand, we have discovered that the degree of expansion of the perlite, that is the Weight per cubic foot of expanded material, may be varied by simultaneously varying the rate of i ore feed and the flow of fuel and air to the furnace. For example, a stronger material than that resulting from maximum expansion, may be desired, such as an aggregate for concrete. This, of course, weighs more per cubic foot than the material having maximum expansion. Contrary to what one might expect, reduction in degree of expansion (with increase in weight and strength) may be effected by increasing the rate of fuel and ore feed. The increased rate of ore feed has a cooling eiect and prevents the undesired rise in temperature which would otherwise ensue. The increased volume of gas increases the velocity and levitating force of the gases, thereby carrying away the granules with a higher bulk density (i. e. expanded to a lesser degree) than would be the case if the gas velocity were lower. The result is heavier and stronger granules.

Increase in degree of expansion (i. e. reduction in weight per cubic foot of the material) may be accomplished in the reverse manner.

Variation in rate of fuel feed is of course 7 eected by regulation of the mixing and proportioning unit 24.

One illustrative ore feeding means is shown in Figs. 1 to 4. Any appropriate feeding mechanism responsive to the furnace temperatures may be employed. In the present case the perlite ore is supplied from a bin 1| to a conveyor in the form of a screw conveyor 12. A valve 13 is advantageously incorporated in the feed pipe 14 to interrupt feed if desired. The screw conveyor carries the ore to the feeding spout 25 down which it slides by gravity into the expanding zone of the furnace. The conveyor is rotated at a speed varying roughly from 14 to 34 revolutions per minute through a variable driving mechanism here shown in the form of an adjustable cone pulley drive. Such driving mechanism is characterized by driving and driven pairs of cone pulleys 15 and 16, the spacing of the former of which (15) may be varied to increase or decrease the effective diameter'of the pulley and thereby to vary the driving rate. The details of such driving mechanisms are well known and need not be described beyond pointing out that in the illustrative driving mechanism the cone sections of driving pulley 15 are drawn together by springs which tend to increase the effective diameter of the pulley. By means of increasing the tension of the driving belt 11, the cones are wedged apart by the belt, thereby decreasing the speed of rotation of the feed screw 12. Pulley 16 drives screw 12 through a speed reducer 18.

In the present regulating means, the belt driving motor 19 is slidably mounted on the base 80 to increase and decrease belt tension. It is moved in this instance by a ratchet wheel 8| traveling on a stationary screw 82, carried by base 80. The rim of ratchet wheel 8| slidably engages the motor base and, as the ratchet moves along the screw, it carries the motor with it, either tightening or loosening the belt tension. The ratchet wheel carries on its opposite faces oppositely directed ratchet teeth 84 and 85 adapted to be selectively engaged by a forked pawl 86. The .pawl is oscillated by an eccentric' 81 (driven by motor 19) through a connecting link 88 to which the pawl is pivoted (Figs. 2 and 4). The forks of the pawl comprise a pair of ratchet engaging members 89 and 90 adapted selectively to engage the ratchet teeth 84 and 85 onv the ratchet wheel. Y

Pawl 86 is made responsive to the temperature in the furnace, in the present instance, by athermostatic controlin the form of a thermocouple 93 engaging the outside of the metal furnace shell (through an opening in refractory wall I I) and located so as to be responsive to the 'level of temperature in the expansion zone of the furnace, that is the region of maximum furnace temperature (Fig. 6). It is held in resilient contact with the outside wall by springs 94, thereby maintaining contact during movement and vibration of tube I0. The thermo-couple is connected to pyrometer 95 (see Fig. 6) which in turn (through conventional relay circuits 96 and 91) controls solenoids 98 and 99. The latter rare alternately energized and serve to move predetermined value, thermo-couple 93 responds to increase the rate of feed of ore and thereby to reduce the temperature. Reduction in temperature in the furnace below the predetermined level causes a reduction in the rate of ore feed, thereby permitting a rise in temperature. During neutral periods when the pyrometer v95 is not energized, pawl 86 is held in neutral position and simply oscillates idly without operating ratchet wheel to vary the rate of feed. In such case the feed remains constant.

By means of the foregoing method and apparatus, it is possible to obtain a quality of material and an efficiency of operation not heretofore possible. Imperfections in the exterior shell of the individual granules are minimized, thereby greatly reducing water absorption and penetration and increasing the strength of the granules in relation to their bulk density. Acidity of the granules is reduced by the method of circulating air through the granules when highly heated.

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

Having described our invention, we claim:

1. Apparatus for expanding mineral comprising in combination a cylindrical sheet metal expanding chamber, a support for suspending said chamber from a point adjacent its top so that it hangs freely from its support, a fuel supply introducing burning gaseous fuel into said chamber to provide an expanding zone heated to temperatures suilicient to expand said minerals, a mineral feeder for introducing mineral to be expanded into said high temperature zone, and mechanism for periodically delivering a blow to said metal walls to dislodge mineral material adhering thereto.

2. Apparatus for expanding mineral comprising in combination an expanding chamber having metal'walls, a fuel supply introducing burning gaseous fuel into said chamber to provide an expanding zone heated to temperatures sufficient to expand said mineralsl a mineral feeder for introducing mineral to be expanded into said high temperature zone, and a thermostat in contact with said metal on the exterior of said chamber adjacent said high temperature zone, and mechanism responsive'to said thermostat for regulating the effective temperature of said zone.

3. Apparatus for expanding mineral comprising in combination an expanding chamber, a fuel supply introducing burning gaseous fuel into .said chamber to provide an expanding zone heated to temperatures sufficient to expand said minerals, a mineral feeder for introducing mineral to be expanded into said high temperature zone, a thermostat in contact with said metal wall on the exterior of said chamber adjacent said high temperature zone, mechanism for periodically agitating said metal walls to dislodge mineral adhering to said walls, mechanism responsive to said thermostat for regulating the effective temperature of said zone, and means for resiliently holding said thermostat against said walls.

4. Apparatus for expanding mineral comprising in combination a vertical cylindrical metal tube open at its ends, means for suspendingthe tube adjacent its upper end so that the same hangs freely, a burner at the lower end of said Q. tube for introducing burning fuel gas into the lower end of the tube to provide a high temperature expanding zone in the lower portion of the tube, means for introducing mineral into said high temperature zone, a thermostat in contact with the exterior of said tube adjacent the'` high temperature zone for regulating the rate of feed of said mineral.

5. Apparatus for expanding mineral comprising in combination a vertical cylindrical metal tube open at its ends, means for suspending the tube adjacent its upper end so that the same hangs freely, a burner at the lower end of said tube for introducing burning fuel gas into the lower end of the tube to provide a high temperature expanding zone in the lower portion'of the tube, means for introducing mineral into said high temperature zone, and mechanism for peri odically jarring said tube to dislodge mineral adhering thereto.

6. Apparatus for expanding perlite comprising in combination a walled supporting structure, an elongated tubular refractory metal shellin said structure and supported adjacent its upper end by said structure and hanging freely inside said structure and spaced from the walls thereof, the said space being constructed and arranged for passage of cooling air to cool Isaid shell, said shell forming an expansion chamber open at its upper end, a burner adjacent the lower end of. said shell, means for projecting from said burner an upwardly directed stream of'hot gases through said shell of a velocity sumcient to levitate granules of perlite when they have expanded substantially to reduce their bulk density, said velocity being insufficient to levitate unexpandable material, said chamber having an opening at its lower end to permit unexpandable material to fall downwardly out of said chamber, and` means for feeding granules of perlite into said stream oi'l hot gases.

7. Apparatus for expanding perlite comprising in combination an expansion chamber comprising a substantially vertical elongated tubular shell vsupporting structure surrounding and spaced from the exterior of said shell to provide acooling air space between the supporting structure and the shell, means for supporting said tube at its ore into the interior of said shell at a point above said burner.

. ERNEST O. HOWLE.

ROGER W. JACKSON. NORMAN M. FOSTER.

REFERENCES CITED The` following references are of record in the ille of this patent: l

UNITED STATES PATENTS Number Name Date 247,003 Beidler Sept. 13, 1881 761,684 Kibler June 7, 1904 1,963,275 Iabus June 19, 1934 2,112,643 Baensch et al. Mar. 29, 1938 2,129,523 Butler Sept. 6, 1938 2,203,821 Hinchman June 11, 1940 2,210,103 Stoner Aug, 6, 1940 2,306,462 Moerman Dec. 29, 1942 2,331,419 Patterson Oct. 12, 1943 2,334,578 Potters Nov. 16, 1943 2,421,902 Neuschotz June 10, 1947 2,424,330 Robertson July 22, 1947 2,431,884 Neuschotz Dec. 2, 1947 2,451,024 Ellerbeck Oct. 12, 1948 OTHERREFERENCEB Perlite-Source of Synthetic Pumice IC 7364, Bureau of Mines, August 1946.

Kom: Thermal Studies of Obsidian, Pltchstone, and Perlite from Japan. Science Report Tohoku made of relatively thin gauge stainless steel and 45 Imspelfial University Series 3 V01' 3' me 225" open at its upper and .lower ends, a refractory

Claims (1)

1. APPARATUS FOR EXPANDING MINERAL COMPRISING IN COMBINATION A CYLINDRICAL SHEET METAL EXPANDING CHAMBER, A SUPPORT FOR SUSPENDING SAID CHAMBER FROM A POINT ADJACENT ITS TOP SO THAT IT HANGS FREELY FROM ITS SUPPORT FOR SUSPENDING SAID DUCING BURNING GASEOUS FUEL INTO SAID CHAMBER TO PROVIDE AN EXPANDING ZONE HEATED TO TEMPERATURES SUFFICIENT TO EXPAND SAID MINERALS, A MINERAL FEEDER FOR INTRODUCING MINERAL TO BE EXPANDED INTO SAID HIGH TEMPERATURE ZONE, AND MECHANISM FOR PERIODICALLY DELIVERING A BLOW TO SAID METAL WALLS TO DISLODGE MINERAL MATERIAL ADHERING THERETO.

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