US2335611A

US2335611A - Apparatus for heat treating oil shale and other finely divided materials

Info

Publication number: US2335611A
Application number: US409422A
Authority: US
Inventors: William O Pray
Original assignee: PRAY RES CORP
Current assignee: PRAY RES CORP; PRAY RESEARCH Corp
Priority date: 1941-09-03
Filing date: 1941-09-03
Publication date: 1943-11-30
Anticipated expiration: 1960-11-30

Description

W. O. PRAY APPARATUS FOR HEAT TREATING OIL. SHALE AND OTHER FINELY DIVIDED MATERIALS Filed Sept 5, 1941 NQ K 3 Sheets-Sheet 1 Nov. 30, 1943.

Nov. 30, 1943. w. o. PRAY APPARATUS FOR HEAT TREATING OIL SHALE AND.

OTHER FINELY DIVIDED MATERIALS 'Filed Sept. 5, 1941 5 Sheets-Sheet 2 Nov. 30, 1943. w. o. PRAY 2,335,611

APPARATUS FOR HEAT TREATING OIL SHALE AND OTHER FINELY DIVIDED MATERIALS I Filed Sept. 3, 1941 3 Sheets-Sheet 3 Patented Nov. 30, 1943 SHALE AND OTHER FINELY MATERIALS DIVIDED William 0. Pray, De Beque, 0010., assignor to Pray Research Corporation,

ration of Colorado De Bcque, 0010., a corpo- Application September 3, 1941, Serial No. 409,422

13 Claims. (01. 202-111) This invention relates, generally, to improvements in apparatus for the extraction of oils from shales, coal, and other carbonaceous materials; and also embraces an apparatus adaptable to the treatment of other finely divided materials where heat must be uniformly applied while the material is stirred and conveyed over heating surfaces in the form of a continuous layer or layers. 1

A major object of the invention pertains to improvements in design and operation of a stirring and conveying device commonly known as a chain-drag or pusher conveyor, which, in the ordinary type, comprises an endless impellerchain, to which is attached a series of solid flights in the form of various shaped plates, bars, or circular discs. As commonly employed, the principal function of the flights is to convey the material by a dragging or pushing motion, the materialbeing distributed along a trough or hearth in the form of an uneven layer, part of which is banked high in front of the moving flights, while an unfilled gap or scanty layer is left in the space directly behind. When attempts are made to move a relatively thin layer of material with a conveyor of this type, there is no uniformity in the distribution of the material, and the stirring is both inadequate and irregular.

The disadvantages inherent in such a device have militated against its practical use in the heat treatment of materials such as finely divided oil shale, which tends to cake under heat unless it is uniformly and. frequently stirred. Such a material when banked against a solid flight, will start to cake when bitumenization begins, and if pushed ahead in this condition, only a small part of the shale will contact the heating surfaces, and this part will be overheated while the remainder may be relatively cool or insufllciently heated. Such conditions retard heat transfer and result in the accumulation of carbon deposits on the heating surfaces unless special provision is made to keep these surfaces scraped clean.

A further disadvantage when -employing the solid-flight conveyor in shale retorts is th limitation of treatment time to one revolution of the endless chain. Obviously, where the material is pushed continuously ahead, each revolution of the chain will discharge all of the material fed into its path during the time taken to make the circuit. Thus, if the time of treatment under the most favorable conditions should require six minutes, and if the chain must be slowed down toone revolution in this time, it is obvious that the material will not be properly stirred; particularly so, where banking occurs against a solid flight and the flight pushes it ahead without properly turning it over and over.

In the present invention, these disadvantages have been considered, and while utilizing the general principle of the ordinary chain-drag conveyor, the major objective is to provide improved stirring and conveying elements, to attain more frequent and uniform stirring and to move the material over the heating surfaces in a substantially uniform layer, the advance taking place in stepwise progression, without pushing. any part of the material continuously forward.

The stirring elements of the present invention are designed particularly for operation in a tubular conduit, the conduit comprising two elongated tubes, set horizontally, one above the other, in a combustion furnace; heat from the furnace being transmitted through the tube walls to the material being conveyed therethrough. The tubes are connected at opposite ends, through packed glands, to a common header or end chamber. The end chambers are anchored rigidly to set foundations, the linear expansion of the tubes taking place through the packed glands. This construction also permits of turning the tubes occasionally to equalize the wear of the inner surfaces, and provides a structure particularly .tions, the danger of distorted heat transfer surfaces is practically eliminated if control of furnace temperatures is properly exercised.

In operation, the finely divided shale is continuously fed into one end of the upper tube in a preheated condition, and is then further heated while it is being moved through the upper and lower tubes by the endless chain-conveyor; .lnally being dropped into a receiving hopper at the discharge end of the lower tube, and from there, it is discharged in a spent condition by a sealed screw-conveyor.

While, for the purpose of simplicity, the illustrations and descriptions bear largely but not solely, on a unit comprising only one set of tubes and a single conveyor assembly, it is obvious that two or more sets of tubes, with necessary conveyor assemblies, may advantageously be com- Ordinarily, when treating a material such as oil shale, the shale is crushed to pass a oneeighth inch opening, but this may require variation with variations in the character of the shale and the size of the apparatus employed. The diameter and length of the tubes, and the size of the stirring elements, can, of course, be varied over a wide range withoutdeparting from the general principles of operation and mode of construction. With any large increase in the diameter of the tubing and relative size of the stirring elements, the depth of the shale layer can be increased proportionately, and to a certain extent, the material may be treated in a coarser condition according to the time allowable for treatment of the maximum sized particles. Thorough and frequent stirring reduces the time factor, and where, as in the present invention, the stirring elements are designed to keep the heating surfaces scraped clean, a further reduction in treatment time is possible. A thin layer of carbon or spent shale on these surfaces is suflicient to greatly retard heat transfer and extend the period of time necessary for the eduction of thevolatile elements. At a temperature of around 650 F. most shales soften and become bitumenized, and on further heating, the bitumen is converted into volatile oils. During this stage the shale will cake if not stirred frequently, and a layer of carbon or coke will form on the heating surfaces unless special provision is made to keep these surfaces scraped clean. Furthermore, if th shale particles in direct contact with the heating surfaces are not moved away frequently, a layer of carbonized spent shale will accumulate and prevent heat from reaching the balance thereof. v The shale particles must be kept in rotation or a state of turbulence, so that each particle in the layer will be brought into contact with the heating surfaces at frequent intervals and then moved back into the layer as soon as it has acquired its proper quantity of heat.

The present invention is a result of the study of the above-mentioned requirements, and I have provided scraping elements which not only keep the tube walls free of carbon accumulations,

but also make a clean pick-up of the shale in contact with the heating surface and turn it back into the adjacent .mass, at the same time, advancing the material a short step in the tubes without pushing any part of it continuously forward.

Having stated the general objects and principles of the invention, the apparatus will be more particularly explained hereinafter in connection with the accompanying drawings illus trating the preferred construction, which is particularly suitable for treating oil shale.

In the drawings:

Figure 1 is a vertical sectional view of the retort unit, the section being taken longitudinally of the retort construction, with the furnace structure and part of the tubing omitted to more clearly bring out the details of the end portions.

Figure 2 is a side elevation of the retort unit shown in Figure 1, also partly in vertical section.

Figure 3 is a fragmentary transverse sectional view on a reduced scale and taken on the line 3-3 of Fig. 2. In this view certain parts are omitted;

Figure 4 is a side elevation of a portion of the endless conveyor chain, showing one form of constrution of the stirring link with an oval ring attached thereto, the special link being hooked to a standard detachable chain link.

Figure 5 is a plan view, partly in section, of the stirring link shown in Figure 4.

' Figure 6 in an end view of the stirring link shown in Figures 4 and 5, and illustrating the same in relationship to one of the tubes.

Figure '7 is a view similar to Figure 4 but showing a modification.

Similar reference characters are used to designate the same parts wherever they appear 1n the several views.

Referring to the drawings in detail, and particularly, to Figures 1 to 4 inclusive, the retort structure is generally indicated by the reference character 8, comprising one or more pairs of tubular conduits 20, 20a; the conduits of each pair being set horizontally, one above the other, in a suitable furnace 2i and connected at opposite ends, through packed glands 22, to end chambers 9 and Ill. The end chambers are preferably rectangular in form, and are closed at the outer ends by

detachable plates

23 and 24.

Plates

25 and 26 at the confronting ends of the chambers have openings in line with the openings in the packed glands 22. The glands (Fig. 1) are preferably, detachably mounted on the end plates, in order to facilitate the installation or removal of the tubes. The outer end plates have openings ll, covered by removable plates I2 to provide access tov the interior of the chambers for inspection and minor adjustments.

End chambers 9 and ill are anchored rigidly to set foundations (not shown), and may be either heavily insulated against the loss of heat, as indicated at the left in Fig. 2, or may be jacketed by an extension l3 of the furnace walls and be heated by a portion of the combustion gases from the furnace, which may be by-passed through dampered openings M in the walls below the base of the chambers, and thence around the chamber walls to passages connected with the main fiues of the furnace, as shown at the right in Fig. 2. This precaution against loss of heat in the chambersis necessary, in order to avoid condensation and redistillation of heavy fractions and resultant accumulation of tarry products or coke. This particularly applies to chamber I0, through which the volatile products pass on their way to vapor outlet 21.

The combustion furnace (Figs. 2 and 3) is, preferably, divided into several combustion zones 15 by spaced transverse partitions iii, the partitions extending to the bottom of the lower tubular member and serving as bases for the support of the latter. Each combustion zone may be fired by one or more burners ll, the number of zones and burners being determined by the size and length of the tubular members and the number of tube-sets combined in the retort unit.

' Inasmuch as these factors may vary over a wide range, no attempt is made to describe or illustrate the furnace construction in exact detail. The arrangement of the furnace fiues it also is influenced by these factors, and for this reason, are not shown in detail. Furnace cover plates I9 should be easily removable to permit access to the packing glands and removal of the tubes when necessary.

Shafts

28 and 29 are mounted in the end chambers of the retort and carry gap-sprockets 30 and 3| over which the endless chain conveyor 3Ia passes. The chain is impelled by sprocket 30 secured to shaft 28 journaled in suitable bearings mounted on the side walls of chamber 9. One end of the shaft projects through a packed gland (not shown) in the wall, and is preferably aaaacn 3 driven by a variable speed mechanism (not shown) so'that the travel of the chain through the tubes may be adjusted to any desired rate of speed. At the opposite end of the retort, the

chain passes around idler-sprocket 3i secured to shaft 29 which projects through slots 3lb in the side walls of chamber l and is journaled in bearings of adjustable bearing plates 32 which are secured to the walls by suitable clamping boits'32a which pass through slots 32b in the bearing plates, so that the latter, with the shaft ,bearings may be moved to adjust the tension of the conveyor chain when taking up or relieving it during periods of heating and cooling.

The endless chain conveyor, as shown in the illustrations-is made up of a series ofstandard detachable chain links. of the open-hook type, linked, alternately, with specially designed attachment links 34, to which are secured flights 34a of the form shown in Figures 4, 5 and 6; the flights serving to support the chain links out of length equal to about one-third of the inner circumeference of the tube wall with which 'it is in contact, as shown in Fig. 6. The perimeter. or outer surface of the ring, is beveled to form a sharp cutting edge 34d where it contacts the tube wall, and also to prevent the ring from riding on the particles of shale in direct contact operating the chain at greater speed, several revolutions of the chain being possible during a given period of treatment, in contrast with the single revolution required when the material is pushed continuously ahead. Given two chains of similar length, equipped with an equal number of stirring elements, the chain with my open rings, making three complete'revolutions during a given treatment time, will effect three times the,number of stirrings as would the solid-flight chain which is limited to one revolution. Furthermore, with the'open-ring stirrer, the material is moved through the heating tubes in the form of a uniform layer, while with the solid flights, it is banked against the flights, instead of being distributed evenly over the heating surfaces. The effect on treatment time through accelerated stirring and uniformity in distribution is obvious.

Figure 'I shows a modification of the stirringelement, in which a link 50 with a'half ring 5| is substituted for the full ring shown in Figures with the wall. The inner part of the ring has a rounded or convert surface 3%, the radius of the .curve being such as to provide sufficient resistance to the-movement of the shale through the ring to' cause a stirring and mixing of the particles as they passtherethrough. It will be noted that the ring-opening contracts toward the back edge 34 the sectional area at the rear being smaller than the area at, the cutting edge. The relative areas are so proportioned that the resistance to the movement of the shale particles is just sufllcient to cause the proper stirrin'g action.

In operation, as the cutting edge of the ring 34a slides over an inner surface of the tube (20, 20a), it cuts away that part, of the shale in direct contact with the heating surface; then forces this portion, together with the balance of the segment of shale, through. the ring. In passing therethrough, the gradual contraction of the area of the opening tends to turn the shale over,

mixing the hotter particles with cooler particles, and then spilling, the whole over the back edge ofthe ring and depositing it on the inner surface of the tube in a. uniform layer, as will be apparent from Figure 1. This action is repeated by each successive-ring, each ring,v in turn, elevatinc. turning over, and laying ,back the material, while' simultaneously advancing it a short 1 step forward-as it rides, momentarily, over the inner surface of the moving ring. The action of the-rings results in an intermittent or stepwise'movement of 'the material through the tubes, in contrast with the continous dragging or pushfing action of solid-flight conveyors, and permits here, it is moved to the opposite end of the tube by the endless conveyor No, where it drops on-" 4, 5 and 6. Except for the division of the rin and carrying it on two links instead of one, there is no change involved which would alter the effect attained with the full ring mounted on a single link, as the two half-rings, mounted on two links directly connected, are equivalent in action to one full-ring link joined alternately to standard chain links. In either case, the pitch of the chain is the same, andit operates over similar sprockets. Preference, however, is given the full-ring link, particularly in the larger sizes.

It is to be understood that the use of the particular .type of chain shown in the drawings, and the method of incorporating the ring attachment into the chain, does not limit the invention to. this particular structure. Obviously. other types of chain and other methods of mounting the rings on the chain might advantageously be used in structures of large dimensions. The chain illustrated in the drawings is employed in tubes five inches in diameter, this size of tubingbeing about the smallest practical for commercial use. In tubes of relatively large diameter, the rings. may be attached to double strands of chain, the'cormections being made at opposite ends of the oval ring. This construction would require twin sprockets to carry the chains instead of the single sprockets shown on each shaft in the drawings.

In the operation of the apparatus, the finely crushed shale is continuously fed into the retort through the inlet port 35 by a screw-conveyor 36, the screw being driven independently by any suitable variable speed mechanism (not shown) capable of varying the speed as desired. The shale is fed onto extension nipple 31, which is.

rigidly attached tothe inner surface of end plate 25 of chamber 9, in line with, but indea pendent, of the mouth of the upper tube 20.

The end of the nipple is flared, in order to guide the stirring-elements as they leave the driving sprocket 30 to enter the upper tube. From to plate 38 and slides into a U-shaped trough 40 at the bottom of chamber l0. Here, it is again propelled by the chain and conveyed.

through the lower tube 2la to the spent-shale hopper]! in the bottom of chamber 9, from whence it is finally discharged in a spent condition by a sealed screw-conveyor 42 to a waste conveyor system, not shown.

The shale, as it enters the retort is in a preheated condition, the heat being preferably deof preheat is dependent on the temperature and volume of the waste gases available, and may vary from 200 to 400 degrees Fahrenheit. During its transit through the upper tube, the shale is further heated, but preferably, not to the point of bitumenization, which for practical purposes, may be assumed as around 650 degrees F., though this may vary considerably with shales of different character and richness. While traveling through the upper tube, the shale has been stirred to such an extent that it is substantially uniformly heated when it is dropped into the trough 40 of the lower tube. The shale should reach this point just short of the reaction temperature. Heat should then be added rapidly, to convert the organic matter into primary bitumen and a part thereof into volatile products. Enough light hydrocarbons must be formed to lower the vapor pressure to a point where the heavy products can vaporize under partial pressure conditions.

The vaporized products are drawn from the retort through vapor outlet 21 under a moderate suction, the normal pressure being reduced sufficiently to insure rapid withdrawal of the products once they are formed. As aforementioned, the walls, of chamber I0, through which chamber the vapors pass, should be kept hot enough o avoid condensation of the heavier fractions. It will be noted that all volatile products are pulled under suction toward the vapor outlet, the travel of the vapors through the tubes being in this direction only. This avoids the accumulation .of vapors in chamber 9, so that the heating of the walls of this chamber is not so essential. The walls should be protected, however, against heat radiation.

In an apparatus constructed for small scale commercial use, the tubes are five inches inside diameter and twenty feet long. The chain-conveyor is fifty feet long, comprising, seventy-five standard chain links and. an equal number of the ringed links. The pitch of the chain is, four inches, the ringed links being spaced eight inches apart. The pitch diameter of the sprockets is about fifteen and one-half inches, each sprocket having six teeth alternating with six gaps which accommodate the stirring-rings. The rings are shaped from steel tubing and welded to special cast steel link-frames. three-quarter inch wide and about three-sixteenths inch thick, and the minor axis, three and one-half inches. The scraping edges are surfaced with a hard alloy and ground to a knifeedge finish. When in operation, one half of the ring in the upper stretch of the chain is in cooperation with the trough of the upper tube, while on reversal, the other half-section cooperates with the lower tube. Each half of the ring is exactly similar in shape, the active scraping edge of each half being in the form of a true circular are about five and three-quarter inches long, conforming to, and cooperating with a little over one-third of the inner circumferences of the tubing (Fig. 6).

A ring of these dimensions operates satisfactorily in a five-inch tube, with the shale layer in the form of a segment about one and onehalf inches high. If the diameter of the tube is doubled, the dimensions of the ring are increased proportionately, but the segment of shale in thelarger tube, with a height of three inches,

segment in the smaller tube. Thus, for a given length of tubing, the larger tube will contain four times the volume of shale compared with the smaller tube. If the height of the segments is in proportion, the effective heat transfer surface of the ten-inch tube will be only twice that of the five-inch tube, but by doubling the length of the ten-inch tube, the effective surface can beincreased to four times that of the smaller tube twenty feet long, making possible the treatment of the larger volume without unduly increasing the time of treatment. Because of the flexibility of the chain, and its well balanced construction, it will operate as effectively in fortyfoot tubes as twenty-foot tubes, and considering the relatively small extra cost involved, the longer tubes are preferable.

Referring again to the five-inch tubes, twenty feet long, one set of two tubes will have an effective heating surface of about nineteen square feet, the height of the shale segment being assumed as one and one-half inches. With a shale segment of this height, the weight of the shale in the tubes will vary with shales of different, character and richness. Thericher shales may weigh forty-eight pounds to the cubic foot, while leaner shales may weigh up to sixty-five pounds. Assuming fifty pounds to the cubic foot, the two tubes, with a total length of forty feet, will contain about sixty-eight pounds. Allowing six minutes treatment time, the shale will be fed to the apparatus at the rate of six hundred and eighty pounds an hour. In assuming a treatment time of six minutes, it is to be understood that the shale enters the retort in a highly preheated condition, and further, that the retort is operated on a basis of economic recoveries of the oil products rather than complete eduction. The figures presented in the foregoing, are given with the understanding that they are not to be taken as limitations. They are presented with the object of illustrating, generally, the

The finished ring is will have:an area four times the area of the u principles and utility of the invention.

Again referring to the proposed modification of the apparatus, wherein several tube-sets may be combined in a single unit, it is obvious (Fig. 3) that two or more sets of tubes may be connected to common end chambers, and may be enclosed in a single combustion furnace. A separate chain-conveyor assembly is provided for each set of tubes, but the carrying sprockets may be mounted, in spaced relation, on single shafts operating in each end chamber, the drivingsprockets being revolved by a mechanism common to all. A separate feed-screw should be provided for each set of tubes, but the several screws may be connected to a supply hopper in common, and be driven at a uniform speed by one shaft geared with the necessary connections, so that the quantity of shale fed to each tube-set is substantially the same. A single spent-shale hopper and discharge screw may be employed to dispose of the spent material from the several sets of tubes. Inasmuch as these modifications involve no fundamental changes, and are within the skill of competent mechanics, it is not considered necessary to illustrate them or describe them in detail.

From the foregoing, it is evident that the apand the effective manner in which they operate in tubular conduits. Another important feature consists in mounting the tubes so they may expand freely without disturbing other parts of the apparatus that require rigid settings. Further advantages are: the stability of tubular conduits under heat; the comparative freedom of expansion strains in the tubes of the present invention, because of the provisions made for free linear expansion through the packed glands; the ease with which the tubes may be removed and replaced; and provisions made in the setting of the tubes so they may be turned at intervals to equalize the wear of the inner walls. The relative cheapness of tubular heating surfaces is evident when compared with structures requiring thick hearths and complicated construction.

All heat requirements are put into the present apparatus through the simple tubular members, and because of their extended length, and the possibility of dividing the furnace into multiple combustion zones, the heat can be applied under close control in the zones where it is most needed. Further, because of the ease with which heat may be conducted through the relatively thin tube walls, and the rapid absorption of this heat through efiicient stirring of the material and positive scraping of the heating surfaces, a high rate of heat transfer can be steadily maintained without dangerously heating the tubing or the material being treated within it. Inasmuch as the stirring-rings follow each other at intervals less than two seconds, it is obvious that the individual particles of shale in contact with the heating surface, remain there only momentarily, and then are cut away and turned back into the adjacent mass of material.

Under the conditions above described, the finely ground shale takes up heat very rapidly, and this accounts for the relatively short time of treatment, compared with the longer time necessary under less favorable heat-transfer conditions.

The apparatus is simple in construction, as well as in operation, and its m intenance is relatively small, the tubing being the only part subject to furnace temperatures, and this can readily be replaced at very moderate cost. The chain-conveyor assembly is simple and rugged, in construction, and is subject only to the comparatively moderate temperatures prevailing inside the tubing. The impeller chain is supported out of contact with the tubing by the stirring-rings or semirings, the chain, itself, being supported high enough above the shale layer to keep it from being dragged therein. Only the sharp cutting edges of the rings are in contact with the tubing, and as these may be shod with a hard alloy, the rings can be operated over a long period without replacement. The frictional wear of the tubing can be kept equalized, because the tubes are mounted in a manner permitting periodical turning to new positions. The wear is minimized, to a great extent, by the relatively small frictional surface presented by the knife edges of the rings. The wear is further reduced by the presence of a film of very finely divided shale between the ring and tubing, the material being somewhat of a lubricant, and preventing actual metal to metal contact. That the chain-rings operate with comparatively little frictional drag is evidenced by the fact that the total power requirements for the small scale commercial unit, heretofore mentioned, having forty feet of five-inch tubing and a chain fifty feet long, is less than one horsepower,

comprising a substantially horizontal tube, a con- I veyor having a portion movable through the tube from one end thereof to the other, flights secured to said portion of the conveyor in spaced relation to one another, each flight including a front edge portion to scrape substantially the entire material supporting surface of the tube as the flight is dragged thereover, each flight also having a surface receding from said edge portion and shaped to lift and turn over material scraped from said surface of the tube, and means for applying heat to the tube.

2. An apparatus for heat treating materials, comprising a substantially horizontal tube of circular cross-section, a conveyor having a portion movable through the tube from one end thereof to the other, flights secured to said portion of the conveyor in spaced relation to one another, each flight including a curved part conforming in shape to a segment of the inner surface of the 7 ble means in the chambers for guiding the conveyor, a driving element operatively connected with said means for moving the conveyor, flights connected to the conveyor and secured to the latter in spaced relation to one another, each flight having a front edge portion for scraping material from the inner 4 surface of the bottom portion of the first tube, each flight also having a surface receding from its edge portion and shaped to lift material in the first tube and to cause it to roll backwardly through the flight, means for heating said tubes, means for introducing material to be treated into ohe end portion of the first tube, means for.discharglng spent m'aterial from the corresponding end of thesecond tube, and means at the opposite ends of the tubes for transferring material undergoing treatment from the first tube to the second tube.

- 4. In an apparatus of the characterrlescribed, upper and lower tubes, end chambers connected to the ends of the tubes, an endless conveyor having portions extending through said tubes, movable means in the chambers for guiding'the conveyor, a driving element operatively connected with said means for moving the conveyor, flights connected to the conveyor and secured to the latter in spaced relation to one another, each flight having an edge portion for scraping material from the inner surface of the bottom portion of the upper tube, each flight also having a surface receding from its edge portion to lift material in the upper tube and to cause it to roll backwardly through the flight, means for heating said tubes from the exterior thereof, means for introducing material to be treated into one end portion of the upper tube, means for discharging spent material from the corresponding end of the lower tube, and means at the opposite ends of the tubes for transferring material undergoing treatment from the upper tube to the lower tube.

5. In an apparatus of the character described, first and second tubes, end chambers connected to the ends of the tubes, expansion joints connecting the ends of the tubes to said end chambers, an endless conveyor having portions extending through said tubes, movable means in the chambers for guiding the conveyor, a driving element operatively connected with said means for moving the conveyor, flights connected to the conveyor and secured to the latter in spaced relation to one another, each flight having a front edge portion for scraping material from the inner surface of the bottom portion of the first tube, each flight also having a surface receding from its edge portion and shaped to lift material in the first tube and to cause it to roll backwardly through the flight, means for heating said tubes, means for introducing material to be treated into one end portion of the first tube, means for dischargingspent material from the corresponding end of the second tube, and means at the opposite ends of the tubes for transferring material undergoing treatment from the first tube to the second tube.

6. In an apparatus of the character described, first and second tubes, end chambers connected to the ends of the tubes, means removably securing the ends of the tubes to theend chambers, an

endless conveyor having portions extending through said tubes, movable means in the chambers for guiding the conveyor, a driving element operatively connected with said means for moving the conveyor, flights connected to the conveyor and secured to the latter in spaced relation to" one another, each flight having a front edge portion for scraping material from the inner surface of the bottom portion of the,first tube, each flight also having a surface receding from its edge portion and shaped to lift material in the first tube and to cause it to roll backwardly through the flight, means for heating said tubes, means for introducing material to be treated into one end portion of the first tube, means for discharging spent material from the corresponding end of the second tube. and means at the opposite ends of the tubes for. transferring material undergoing treatment from the first tube to the second tube... I V

'7. In an apparatus of the character described, upper and lower tubes, end chambers connected to the ends of the tubes, an endless, conveyor having portions extending through said tubes, movable means in the chambers for guiding the conveyor, a driving element operatively connected with said means for moving the conveyor, flights connected to the conveyor and secured to the latter in spaced relation to one another, each flight having an edge portion for scraping material from the inner surface of the bottom portion of the upper tube, each flight also having a surface receding from its edge portion to lift material in the upper tube and to cause it to roll backwardly through the flight, means for heating said tubes from the exterior thereof, means for introducing material to be treated into one end p n 01' the upper tube, means for discharging spent material from the corresponding end of the lower tube, means at the opposite ends of the tubes for transferring material undergoing treatment from the upper tube to the lower tube, and means for preventing heat loss from one of said end chambers.

8. In an apparatus of the character described, upper andlower tubes, end chambers connected to the ends of the tubes, an endless conveyor having portions extending through said tubes, movable means in the chambers for guiding the conveyor, a driving element operatively connected with said means for moving the conveyor, flights connected to the conveyor and secured to the latter in spaced relation to one another, each flight having an edge portion for scraping material from the inner surface of the bottom portion of the upper tube, each flight also having a surface receding from its edge portion to lift material in the upper tube and to cause it to roll backwardly through the flight, means for heating said tubes from the exterior thereof, means for introducing material to be treated into one end portion of the upper tube, means for dischargingrspent material from the corresponding end of the lower tube, means at the opposite ends of the tubes for transferring material undergoing treatment from the upper tube to the lower tube, and a passageway extending about one of the end chambers for by-passing a portion of the heat from the heating means to the last-mentioned end chamber to prevent cooling of that chamber.

9. In an apparatus of the character described, upper and lower tubes, first and second end chambers connected to the ends of the tubes, an endless conveyor having portions extending through said tubes, movable means in the chambers for guiding the conveyor, a driving element operatively connected with said means for moving the conveyor, flights connected to the conveyor and secured to the latter in spaced relation to one another, each flight having a front edge portion for scraping material from the inner surface of the bottom portion of the upper tube, each flight also having a surface receding from its edge portion and shaped to lift material in the upper tube and to cause it to roll backwardly through the flight, means for heating said tubes by gases of combustion, means for introducing material to be treated into the first end chamber and for depositing the material into one end portion of the upper tube, means for discharging spent material from the first end chamber,

means for preventing the dissipation of heat from the first end chamber, means within the second end chamber for transferring material undergoi'"; treatment from the upper tube to the lower tube, and means for utilizing a portion of said combustion gases to prevent cooling of the second end chamber.

10. In an apparatus of the character described, a tube of circular cross-section, an endless chain having a portion extending through the tube, means at the ends of the tube for guiding and propelling the chain, flights connected to the chain and arranged in spaced relation to one another, each flight comprising a substantially oval shaped ring with a portion conforming to a segment of the inner surface of the tube, said portion of the flight having a forward scraping edge from which an inner surface of the flight recedes toward the axis of the tube.

11. In an apparatus for treating finely divided materials, a substantially horizontal tube of circular cross-section, an endless chain having a portion extending through the tube, means at the end of the tube for guiding and propelling said chain, flights connected to the chain and arranged in spaced relation to one another, each flight having a portion in the form of a semi-ring conforming in shape to a segment or the inner surface of the tube, said semi-ring portion having a forward cutting edge from which a surface recedes toward the axis of the tube.

12. An apparatus for heat treating substantially solid materials, comprising a substantially horizontal passageway having an internal bottom surface throughout the length thereof which is of substantially U-shaped cross section, a conveyor having a portion movable through the passageway from one end thereof to the other, flights rigidly secured to said portion of the conveyor in spaced relation to one another, each flight including a front edge portion corresponding to the U-shaped bottom surface of the passageway, extending across the passageway and engaging said bottom surface for scraping said surface as the flight moves through the passageway, each flight also having a surface receding from said edge portion at substantially an acute angle at all places lengthwise of the flight and shaped to lift and turn over material scraped from said surface, and means for applying heat to the passageway.

13. An apparatus for heat treating substantially solid materials, comprising a substantially horizontal passageway having an internal bottom surface throughout the length thereof, a conveyor movable through the passageway from one end thereof to the other, flights secured to the conveyor in spaced relation to one another, each flight including a front edge portion corresponding-in shape to the bottom surface of the passageway, extending across the passageway and engaging said bottom surface for scraping said surface as the flight moves through the passageway, each flight also having a surface receding, from said edge portion at substantially an acute angle at all places lengthwise of the flight and shaped to lift and turn over material scraped from said surface as the flight moves through the passageway, and means for applying heat to the passageway.

WILLIAM O. PRAY.