US2505249A - Process and furnace for expanding perlite - Google Patents

Description

April 25, 1950 v w. E. JOHNSON ETAL 2,505,249

PROCESS AND FURNACEFOR EXPANDING PERLITE Filed Feb. 15, 1946, 2 Sheets-Sheet 1 FIG.|

WILBUR E.JOHNSON ARMAN D R. BOLLAERT mvcu'roas Ap 25, 1950 w. E. JOHNSON ETAL PROCESS, AND FURNACE FOR EXPANDING PERLITE 2 Sheets-Sheet 2 Filed Feb. 15, 1946 FIG.4

FIG.7

WILBUR E. JOHNSON ARMAND R. BOLLAERT .qih

INVENTORS FlG.lO

ORNEY Patented Apr. 25, 1950 PROCESS AND FURNACE FOR EXPANDING PERLITE Wilbur E. Johnson, Hawthorne, and Armand R. Bollaert, Palos Verdes, Calii., assignors to Great Lakes Carbon Corporation, a corporation of Delaware Application February 15, 1946, Serial No. 647,822

9 Claims.

The invention relates broadly to internally fired heat-treating kilns through which the hot gases and the material being treated flow in the same direction.

The invention relates more specifically to a horizontal, internally fired kiln having a rotating heat-treating section interposed between a stationary combustion chamber and a stationary collecting and discharge section.

The primary objective of the invention is to provide a kiln adapted to the inflation and vesiculation of pulverized rocks of volcanic origin which contain water and which soften and intumesce when heated.

An objective of the invention is to provide a kiln for the above purpose which is free from tendency to ball or aggregate the material being treated or to accumulate deposits of the expanded material.

An object of the invention is to provide a kiln of the type described which has a large throughput capacity per unit of volume.

The invention will best be understood with reference to the attached drawings, showing an illustrative embodiment of the apparatus, together with the following description thereof, in which Fig. 1 is a side elevation of the complete apparatus;

Fig. 2 is a vertical, longitudinal section through the apparatus, the supporting elements not being shown;

Fig. 3 is a ground plan of the apparatus;

Fig. 4 is an elevation of the left or firing end of the kiln, as on the line 44 of Fig. 1;

Fig. 5 is a cross section through the combustion chamber, as on the line 5-5 of Fig. 1;

Fig. 6 is a cross section through the rotating element of the kiln, as on the line 6-6 of Fig. 1;

Fig. 7 is a cross section through the right hand or discharge element of the kiln, as on the line 'I! of Fig. 1;

Fig. 8 is a section on an enlarged scale of the joint between the stationary feed element B and the rotating treating element C;

Fig. 9 is a similar section of the joint at the right end of the rotating section, and

Fig. 10 is a diagram illustrating a manner in which the kiln may be connected with accessory elements.

Referring first to Fig. 1, the apparatus comprises four main elements: a firing section generally indicated at A, a feeding section B, a heattreating section C and a collecting section D. Section C rotates on its own axis: the remaining 2 sections do not rotate and are stationary while in use but are so arranged that they may be moved from and toward the rotating section and each other for convenience in effecting repairs and for adjusting the gaps between the elements.

The firing section A consists of a flanged ring [0 of steel plate containing a layer of hightemperature insulating material H and a refractory lining I2. At spaced points along the length and on opposite sides, projections from the shell, lined with refractory material, provide openings l3 and I4 for the insertion of tangentially arranged oil or gas burners.

The outer end of combustion chamber I5 is closed by a head block l6 having ports I! and I8 for the insertion of longitudinally disposed fuel burners, and provided also with two inspection ports I9 and 20. While the head block may conveniently be separable from the ring to it is bolted to and supported by this ring.

The supporting means for the firing section is shown in side elevation in Fig. 1, in end elevation in Fig. 4 and in cross section in Fig. 5. It consists of two saddle plates 2| and 22, welded to the shell close to its ends, side plates 23 and 24 and a bottom plate 25. These plates are welded at their edges to form a rigid box frame. The lower corners of the frame carry beating boxes 26-26 enclosing axles 2'l21. Flanged wheels 28-28, at the ends of these axles, ride on a track composed of a pair of I-beams 2929 which extend the length of the kiln and for a convenient distance beyond it at each end. These beams are permanently and rigidly supported, as

on a concrete pad.

The feed section B is similar in cross section to the firing section A except for the omission of burner openings l3 and I4 and for the provision of two inclined openings 30 and 3| along the upper center line, through which the pulverized or fragmental material to be heat-treated is fed. This section is provided with a frame and wheeled support identical with that above described in connection with section A.

It is convenient and desirable that sections A and B should be separable and separately supported, but in use they are abutted end to end and may be bolted together and suitable gaskets inserted to prevent leakage of fire gases.

The rotatable heat-treating section C has a cylindrical shell 32 of steel plate, carrying two rigid trunnion rings 33 and 34. These rings rest on pairs of adjustable trunnion rolls 35-3li which in turn rest on cross beams 36-38. The ring is. rotated in the conventional manner by a shaft 31 connecting two of the trunnion rolls and driven through a sprocket 38 from any convenient source of power not shown.

Endwise movement of the rotating section is prevented by a pair of idler rolls 39 horizontally mounted below the ring and engaging the sides of trunnion ring 33 or 34.

The lining of the heat-treating section consists of an outer layer 40 of high temperature insulating material and an inner layer 4| of .firebrick or other refractory. Through a substantial part of the length of this section, rows 42 of firebrick project inwardly to form lifters for the charge under treatment and to prevent it from sliding down the rising side of the cylinder.

The collecting and air-preheating section D consists of a short ring 43 delivering into a downwardly converging section 44 which terminates in a delivery spout 45. These elements, which in use are continuously subjected to high temperature, are preferably formed of a heat-resistant alloy such as 25-12 stainless steel. Around element 44 is formed a jacket 48 of boiler or tank plate having an intake collar 41, a vent connection 48 and a plurality of bafiies 49 by means of which a stream of cold air introduced at 41 is caused to take a circuitous course through the jacket and to emerge at 48 in a highly preheated condition.

The collecting section, which of course is nonrotatable, is mounted on a carriage similar to that described in connection with firing section A.

As there is of necessity a leakage channel for fire gases at each end of the rotating section, where the adjacent fixed sections abut it, it is desirable to use a heat-resistant steel such as 25-12 at these points, as illustrated in Figs. 8 and 9.

In Fig. 8, illustrating the joint between sections B and C. the cylindr cal ring In, of boiler or tank plate, has welded to its end a fiat ring 49 of 25-12 plate, to which is attached a flange C of the same material. Similarly, the cylindrical shell 32 of the rotating section, of boiler or tank plate, carries an end ring of stainless steel which in turn has two flanges 52 and 53 projected in opposite directions. The Z-shaped channel thus formed reduces leakage to a minimum and the materials of which its walls are formed resists buckling and distortion at high temperature and permits the channel tobe reduced to narrow dimensions without bringing the plates into rubbing contact.

At the opposite end of the rotating section the tendencv toward leakage of fire gases is reduced by the lower pressure existing at the outlet end of the kiln. It suffices to use at this point the joint illustrated in Fig. 9, in which the end ring 55, of stainless steel, is brought into close proximity to a stainless steel flange 56 formed at the end of ring section 43' of the collecting section D.

A convenient manner of connecting up the assembly above described is shown on a much reduced scale in the diagram of Fig. 10.

The solids discharged by the kiln, together with the spent fire gases, pass from outlet 45 into a conduit 58 through which they are aspirated into a pebble trap 59 in which any heavy granular matter is separated. It may be desirable to admit a stream of cold air into this conduit, as by leaving an opening between its end and the discharge spout 45, to reduce the temperature in succeeding elements.

The gases laden with fine treated material pass from trap 59 through one or more cyclone separators 60, in which the coarser suspended solids are collected, and thence through conduit 6| to a conventional baghouse 62 where the finest solids are recovered and the gases cleaned.

5 A suction fan or blower 63 creates a negative pressure in the baghouse and cyclone, thus producing the above described flow of gases through these elements. By regulating vent valve 64 the pressure at the outlet end of the kiln (i. e., in collecting section D) may be controlled. The pressure at this point will ordinarily be close to atmospheric but may be very slightly negative to reduce or eliminate gas leakage.

A second fan or blower 65 takes in atmospheric air which is discharged through conduit 66 into the intake connection 41 of the preheater. The heated air discharged at 48 is conducted through a system of conduits 61 to the burners at l3, 14, IT and I8. Spent fire gases from the baghouse may be introduced into the air supply through conduit 68 and valve 69 if it is desired to increase the gas velocity through the kiln or to control the temperature in the combustion chamber.

The requirement for a pebble trap in this assembly may be avoided by providing an arcuate slot 10, of considerable length, at the lower part of element 43, closely adjacent the rotating section. A shield H is so arranged as to move over the slot and adjust its effective width.

Any unexpanded particles of perlite or of impurities which may occur in the raw mineral tend to pass through this slot as they emerge from the rotating section of the kiln. By maintaining a slight negative pressure in the collecting chamber, a current of air of controllable velocity is induced through the slot, carrying any entrained light particles forward to discharge nozzle 45 and allowing only the heavy waste particles to pass through the slot and out of the system.

The inflation of glassy volcanic rocks of the type exemplified by the mineral perlite may be made to produce filling and bodying powders of the most extreme lightness, weighing in some instances as little as four pounds per cubic foot. This result is produced by the formation of innumerable extremely minute vesicles within each particle, this vesiculation being due apparently to the presence of combined water in the volcanic glass and to the evolution of steam at 5 temperatures at which the glass is plastic; 1. e.,

at the temperature of incipient fusion.

As the temperature of fusion lies not far above that of the plasticity requisite to vesiculation, a desirably light product will be obtained only by maintaining the most exact control over the temperature to which the mineral particles are subjected. If the temperature be too low, the expansion will be incomplete, while if it be too high, the mineral will be fused, partially or entirely, the vesicular structure will be lost and the particles will aggregate into balls and tend to stick to the wall of the kiln. Either variation from the optimum increases the weight of the product and correspondingly reduces its value. 65 The optimum temperature of treatment varies with the relative fusibility of the particular lot or sample of mineral and may be anywhere between 1500 and 2200 Fahr. But for any given specimen of the mineral there is an optimum 7o temperature, determinable only by experiment, which lies closely below the fusing point, which must not be exceeded materially and which should be as rapidly and as closely approached as possible. It is therefore essential that the 75 furnace in which the expansion is conducted should be free from superheated zones and should have a slightly declining temperature gradient from the point at which the mineral is introduced to the outlet end. a

The form of furnace shown is particularly adapted to the expansion of perlite and similar minerals for a number of reasons. First, the use of a combination of longitudinally and .tangentially arranged burners produces extreme turbulence in the combustion chamber and ensures the delivery into the feed section of a column of flue gas at an absolutely uniform temperature which is under complete control. This high turbulence ensures the completion of combustion and the attainment of the maximum temperature prior to in the fire gas stream. This costly and otherwise undesirable fine grinding is avoided by the provision of the rotating section C. In feeding a mineral crushed to a much larger size, as for example inch and finer, the fine particles are expanded while in suspension in the fire gas stream and are swept through the rotating section without coming into contact with its walls. The larger particles, which require more time for the high temperature to penetrate, subs de in the rotating section, in which they are continuously turned over and showered through the hot gases by the lifters 42. As these larger particles rise in temperature internally, they decrepitate, forming fine fragments and flakes which heat through and expand very rapidly. As these finer particles become sufiiciently lightened by expansion to remain in suspension in the gas stream, they are swept away into the collecting chamber and thus removed from the system. The funct on of the rotating section is thus to collect all particles of such size as to be incapable of substant ally instantaneous vesiculation and to retain them in the zone of effective heating until they are suffic ently lightened by repeated spontaneous subdivision to pass back into suspension.

Finally. the function of the preheating jacket surrounding the collecting chamber is not merely to economize fuel by preheating the air supply,

. but to a much more important degree is to maintain the end wall of the kiln, against which the stream of inflated solid particles impinges. at a temperature below that at which sticking and building up of deposits can occur. The sudden cooling of the spent gas stream, by even a few degrees. also tends toward the avoidance of any aggregation of the inflated particles in the outlet of the kiln.

While the actual dimensions of this structure may vary over a wide range. according to the throughput capacity desired, the relative dimenvent the deposition of the larger and heavier feed particles on the bottom of the stationary tube.

Finally, the rotatable section constituting the heat treating chamber should be of materially greater free cross section than the stationary tube, preferably at least in the ratio 1.5:1.0, to retard the gas velocity and permit untreated or partially treated mineral particles to separate from the gas stream before it reaches the discharge breeching. As above described, particles so separating in the heat treating chamber are reduced in dimensions and in relative weight by decrepitation and are brought back into suspension only when properly inflated, while if theypass out of the heat treating chamber prior to full inflation, they correspondingly increase the weight and reduce the value of the product.

We claim as our invention:

1. The method of producing light weight powders from minerals of the perlite type which comprises: comminuting said mineral; establishing a horizontally flowing stream of hot combustion gases; feeding a stream of said comminuted mineral into said hot gas stream and thereby vesiculating the finer particles of said mineral while in suspension in said gas stream; permitting larger and incompletely vesiculated mineral particles to separate from said stream; collecting said separated particles and returning said collected particles into repeated contact with said hot gases, downstream from said flame until said particles are brought into suspension by decrepitation and vesiculation, and removing from the heating zone a stream of combustion gases having only vesiculated mineral particles in suspension.

2. The method of producing light weight granular products from minerals of the perlite type which comprises: comminuting said mineral; burning fuel under conditions of turbulence and thereby produc ng a stream of combustion gases of equalized temperature; introducing a stream of said comminuted mineral into said gases at a. point downstream from the zone of combustion and thereby expanding and vesiculating only the finer particles of said mineral; moving the stream of combust on gases substantially horizontally at such velocity that the expanded particles are carried in suspension from said zone of heating while the unexpanded and heavier particles remain therein, and continuously returning the unexpanded and heavier particles into said stream of combustion gases to be further heated, said return being effected at points downstream from said zone of combustion and without return of said particles into said zone.

3. The method of producing light weight granular products from comminuted minerals of the perlite type which comprises: burning fuel under condit ons of turbulence to produce a short hot flame and a stream of hot combustion products moving horizontally awayfrom said flame; feeding a stream of said comminuted mineral into said stream of combustion products at points downstream from said flame; maintaining the temperature of said combustion products at such level that only the finer particles of said mineral are expanded and vesiculated on first entering said stream; removing the expanded particles in suspension in said horizontally moving stream of combustion products, and retaining the heavier unexpanded particles in motion, in contact with said combustion products and out of contact with said flame until they expand sumclently to pass into suspension and be carried away in said horizontally moving stream.

4. The method of producing light weight granular products from minerals of the perlite type which comprises: reducing said mineral to particles of unequal size; establishing a stream of hot combustion gases moving horizontally to a point of discharge; feeding a stream of said mineral particles into said gas stream at the end opposite said point of discharge; controlling the temperature and velocity of said gas stream to expand and vesiculate only the finer particles of said mineral, said expanded particles remaining in suspension in said gas stream and being carried therewith to said point of discharge; per-.- mitting the unexpanded and heavier particles of said mineral to subside from said gas stream; collecting said heavier particles as they subside, and showering said collected particles through said gas stream, downstream from said flame, in a direction normal to the direction of gas flow, thereby causing said heavier particles to expand and vesiculate and to pass into suspension in said gas stream and to be carried thereby to said point of discharge.

5. In a kiln for vesiculating comminuted minerals of the perlite type: a horizontally disposed, internally fired, refractory tube so arranged that the combustion gases and the mineral feed travel therethrough concurrently, and a breeching member arranged at the discharge end of said tube, said member including a plate of stainless steel against which said combustion gases and mineral particles suspended therein impinge, and means for passing an air stream over the rearward face of said plate.

6. In a kiln for heat-treating minerals which decrepitate and vesiculate when heated: a, relatively narrow nonrotatable tubular combustion chamber provided with a tangentially arranged fuel burner to produce turbulence therein; an opening for feeding comminuted mineral through the wall of said combustion chamber near the discharge end thereof; a relatively wide, rotatable, horizontally disposed tubular heat-treating chamber in which the velocity of the combustion gases is retarded to permit separation and retreatment of partially treated mineral particles, and means for withdrawing from said heattreating chamber a stream of spent combustion gases and treated mineral particles suspended therein while retaining partially treated particles within said chamber.

7. In a kiln adapted to the expansion and vesiculation of minerals of the perlite type: a nonrotatable combustion chamber; a nonrotatable feed chamber arranged to receive a stream of opposite that at which said feed concurrent flow.

8. In a kiln adapted to the expan ion and vesiculation of minerals of the perlite ype: a tubular combustion chamber; a tubula extension of said chamber; means associated with said extension for introducing a feed of a comminuted mineral into the hot gas stream from said combustion chamber at a medial point in the length of said kiln; a heat-treating chamber arranged to be rotated on a horizontal axis and to receive the hot gases and mineral delivered by said tubular extension, and means for discharging the combustion gases and the expanded solid product from said heat-treating chamber in concurrent flow.

9. In a kiln for heat-treating minerals which decrepitate and vesiculate when heated: a. horizontally disposed, nonrotatable, refractory tube provided with fuel burners arranged to produce extreme turbulence and complete combustion in one end of said tube; means for feeding a stream of a comminuted mineral into the end of said nonrotatable tube opposite that in which combustion occurs; a rotatable refractory tube aligned with said nonrotatable tube and receiving hot gases and mineral therefrom, said rotatable tube being provided internally with projections for bringing mineral particles subsiding in said tube into repeated contact with said hot gases, and means associated with said rotatable tube for removing said hot gases and the heat-treated mineral product therefrom in concurrent flow.

rsandin WI'LBUR E. JOHNSON. ARMAND R. BOLLAERT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 920,334 Huges May 4, 1909 1,800,247 Buckbee Apr. 14, 1931 1,976,208 Agthe et a1 Oct. 9, 1934 1,977,767 Klencke Oct. 23, 1934 2,116,030 Lindman May 3, 1938 2,129,523 Butler Sept. 6, 1938 2,190,271 Powell Feb. 13, 1940 2,265,358 Denning Dec. 9, 1941 2,306,462 Moorman Dec. 29, 1942 2,309,810 West Feb. 2, 1943 2,387,014 Gibson Oct. 16, 1945 2,421,902 Neuschotz June 10, 1947 2,435,395 Hopkins Feb. 3, 1948 FOREIGN PATENTS Number Country Date 505,483 Germany Aug. 19, 1930 613,945 Germany May 28, 1935 OTHER REFERENCES Kozu: Thermal studies of obsidian, pitchstone and perlite from Japan," article in Science Reports, Tohoku Univ., Series 3, vol. 3, pp. 227- 230. Copy in Div. 3 in 252-378.

Claims (1)

1. THE METHOD OF PRODUCING LIGHT WEIGHT POWDERS FROM MINERALS OF THE PERLITE TYPE WHICH COMPRISES: COMMINUTING SAID MINERAL; ESTABLISHING A HORIZONTALLY FLOWING STREAM OF HOT COMBUSTION GASES; FEEDING A STREAM OF SAID COMMINUTED MINERAL INTO SAID HOT GAS STREAM AND THEREBY VESICULATING THE FINER PARTICLES OF SAID MINERAL WHILE IN SUSPENSION IN SAID GAS STREAM; PERMITTING LARGER AND INCOMPLETELY VESICULATED MINERAL PARTICLES TO SEPARATE FROM SAID STREAM; COLLECTING SAID SEPARATED PARTICLES AND RETURNING SAID COLLECTED PARTICLES INTO REPEATED CONTACCT WITH SAID HOT GASES, DOWNSTREAM FROM SAID FLAME UNTIL SAID PARTICLES ARE BROUGHT INTO SUSPENSION BY DECREPITATION AND VESICULATION, AND REMOVING FROM THE HEATING ZONE A STREAM OF COMBUSTION GASES HAVING ONLY VESICULATED MINERAL PARTICLES IN SUSPENSION.

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