US2531068A - Defluorinating phosphatic material - Google Patents

Description

Nov, 21, 1950 E. J. MAUST DEFLUORINATING PHOSPHATIC MATERIAL 3 Sheets-Sheet 1 Filed June 25, 1946 INVENTOR W; MIC

QMM 5 ATTORNEYS Nov. 21, 1950 E. J. MAUST 2,531,053

DEFLUORINATING PHOSPHATIC MATERIAL Filed June .25, 1946 q 3 Sheets-Sheet 2 men ix; 22

2 '7 :ccse wwww '23 Z5 ATTORNEYS J. MAUST 2,531,068

3 Sheets-Sheet 3 Nov. 21, 1950 DEFLUORINATING PHOSPHATIC MATERIAL Filed June 25, 1946 INVENTOR W J M m E N R O T T A Patented Nov. 21, 1950 UNITED STATES PATENT OFF-ICE DEFLUORINATING PHOSPHATIC DIATERIAL Ernest J. Maust, Lakeland, Fla., assignor to Coronet Phosphate Company, New York, N. Y., a corporation of New York Application June 25, 1946, Serial No. 879,178

'1 Claims. (CI. 71-44) This invention relates to the treatment of phosphatic materials with gases, and has for its object the provision of an improved method of treating a material at an elevated temperature with a gas. The invention is more especially concerned with the defluorlnatlon of phosphate rock or other fluorine-containing phosphatic material by calclnatlon in the presence of water vapor, and in this connection aims to provide certain improvements in defluorinating phosphatic materials by treatment with gas, and more particularly water vapor, at elevated temperature. V

In its broad aspect, the method of the invention involves supporting a plurality of layers of the material to be treated by a gas in vertically spaced positions within a vertical heating chamber, progressively moving the material downwardly through the chamber from one material-supporting position to the next lower position, and passing a finely disseminated gas upwardly through the entire mass of each layer of the material while so supported. Fresh material is introduced to the uppermost material-supporting position and a substantially equivalent amount of treated material is discharged from the lower end 2 tional views of the combination of the multihearth vertical furnace with a rotary kiln.

The furnace illustrated in the drawings comprises a vertically elongated brick-work structure of inner heat-resistant brick surrounded by ordinary brick. The structure encloses a vertical heating chamber l of generally rectangular or square section. and for convenience the opposite vertical walls II and I! of the heat-resistant brick will be called the end walls and the other opposite vertical walls It and M will be called the side walls. A gas outlet l having a damper l8 communicates with the upper end of the heating chamber, and a material-discharge chute ll communicates with the lower end of the chamber. A laterally disposedcombustion or firing chamber it, of the commonly called Dutch 'Oven type, communicates with'the lower end of the heating chamber, and is provided with fuel burners l9 adapted to burn oil, gas, powdered coal or other suitable fuel. The heating chamber may be heated in anyother appropriate manner, as for example, electrically or by the of the heating chamber in correlation with the passage of material from one position to the next lower position, so that the operation as a whole is conducted in a substantially continuous manher. The temperature of the material being treated is preferably controlled within a predetermined temperature range by regulating the amount and temperature of the gas passing through the supported layers of material. The application of the invention to various methods of defiuorinating phosphate rock is hereinafter more particularly described. 4

The foregoing and other novel features of the invention-will be best understood from the following descripiton taken in conjunction with the accompanying drawings, in which,

Fig. 1 is a sectional elevation of a multiple porous hearth furnace particularly adapted for practicing the invention,

Fig. 2 is a transverse section immediately above one of the porous hearths,

Hg. 3 is a detail sectional elevation on the sectionlineHofFiga 1 Fig. 4 is an enlargedsectional detail of the cooling arrangement for the pushing device,

Fig. 5 is a sectional detail of a modified construction of porous hearth,

Figs. 6 and 'l are vertical and transverse sectional views, respectively, of another modified construction of porous hearth, and

Figs. 8 and 9 are vertical and transverse sechot combustion gases from a rotary kiln as hereinafter more particularly described.

The heating chamber I0 is provided with a plurality oi vertically spaced superposed porous hearths. As illustrated in the drawings, there are two sets of these hearths 20 and 2| alterhating with one another. The porous hearths it of one set extend from approximate the end wall it to a short distance from the opposite end wall it. The porous hearths 2! of the other set alternate with the hearths 20' and extend from approsdxnate the end wall H to a short distance from the opposite end wall 92. While Fig. 1 of the drawings shows a furnace with four porous hearths 2| and three alternately positinned porous hearths 20, any desired number of hearths may be provided within the heating chamber.

, As shown in Figs. 1, 2 and 3, the porous hearths are made up of an impervious tray or sagger plate 22 covered by a pervious tile or plate 23, thus providing a hollow interior 2. The hearths are supportedjin their spaced relation by heattile 25 set closely against the side walls [I and I! (Figs. 2 and 3). The trays 22 may advantageously be made 01' a gas impermeable or impervious ceramic such for example as dense Silicon carbide or fire brick, while the plates 23 may be made of coarsely bonded alunite or alunoperating tray by a suitable high temperature cement.

Gas is admitted to the hollow interior of each hearth by a ceramic tube 26 extending through the side wall l3 of the furnace structure. The tubes 26 may be made of dense silicon carbide, quartz or the like, and are connected to a common header 21 through a metal bellows 28 for taking up contraction and expansion. A valve 29 is associated with each gas inlet tube to regulate and control the amount of gas supplied to each porous hearth. Where it is advantageous or desirable to preheat or superheat the gas, as is frequently the case with water vapor, the header 21 may be connected to the delivery end of a heating coil 30 suitably mounted in the upper part of the heating chamber H]. The coil 30 may be made of nickel or other suitable heat-resistant material. Gas is supplied to the other or feed end of the coil 30 by a supply pipe 3 l. The header 2! and exposed portions of the tube 26 may be appropriately insulated to conserve the heat of the hot gas flowing therethrough. The amount and temperature of the gas supplied to each porous hearth can be adjusted and controlled through the valves 29, the amount of preheating in the coil 30, and the heat conservation or dissipation characteristics of the header 2'! and pipes 26.

Each porous hearth is provided with a pusher 32 for pushing the material supported or resting on the hearth towards the end of the hearth spaced a substantial distance from the adjacent end wall. The hearths 20 are separated from the end wall l2 (and the hearths 2| are similarly separated from the end wall H) by just suflicient distance to permit material to drop off this end of the hearth, and hence not build up behind the pusher, as the pusher returns to its initial or in position. The other ends of the hearths are separated from their respective adjacent end walls by a considerably greater distance, sufficient to permit material to drop from hearth to hearth and to provide an unrestricted zig-zag path for the flow of hot heating gases and spent treating gas upwardly through the heating chamber. The pushers of the hearths 20 and the pushers of the hearths 2| are actuated alternately by separate and independent mechanism positioned respectively on opposite ends of the furnace, and since the two mechanisms are identical they are indicated on the drawings by the same reference numerals.

Each pusher isattached to the inner end of a pipe 33, as for example between a washer 34 and cap 35 screw-threaded or otherwise secured to the pipe. Near their other outer ends the pipes 33 are secured to a vertical operating bar 36. The bar is operatively secured to the piston rods 3'! of two vertically spaced fluid pressure actuated cylinders 38. The piston rods pass through stationary guide plates 39. A Suitable fluid under pressure, such as compressed air, can be admitted to either end of each cylinder 38 through supply pipes 40 and 4|, respectively. A rotary valve 42 controls the admission of fluid from a supply pipe 43 to either the pipes 40 or the pipes 4|, and the exhaust of fluid through a pipe 44. When the valve 42 is in position to admit fluid to the pipes 40, the piston 45 of the cylinders 38 are actuated and, through the piston rods 31, operating bar 36 and pipes 33, move the pushers 32 of one set of hearths to push material off those hearths onto the other set of hearths. Thereupon, the valve 42 is moved to admit fluid to the pipes 4|, and the pistons 45 are actuated in the reverse direction and return the pushers to their initial or "in" positions adjacent the end wall II (01' I2 as the case may be).

The pushers 32 are rectangular slabs made of silicon carbide, fire brick or other suitable heatresistant ceramic or refractory. The pipes 33 are made of heat-resistant metal such for example as nickel or inconel metal (an alloy of about 83% nickel, 13% chromium and 6% iron), and are additionally protected by artificial cooling as shown in Fig. 4. Thus, with the pipe 33 closed at each end, a cooling medium, such as water, is introduced at the inner end of each pipe 33 through an inclosed pipe 46 of smaller diameter, and the heated or spent cooling medium is discharged through an outlet 41 at the opposite end of the pipe 33. The pipes 46 and outlets 41 are connected by flexible hose or the like 48 and 49 to vertical supply and exhaust headers 50 and 5|, respectively. The pipes 33 have a fairly tight sliding contact with the heat-refractory end wall H (or l2 as the case may be) through which they pass, while their sliding contact with the outer brick end wall structure may be loose with the space between the pipe and end wall filled 0r packed with a silicone or other suitable heat-resistant lubricant 33. This lubricant seeps into the contact between the pipe and heat-refractory wall to provide effective lubrication, and also provides a suitably gastight connection between the moving pipes and the stationary furnace structure.

When the porous hearth is constructed of an impervious tray 22 and a pervious cover 23 eemented thereto, materials for these parts should have as nearly as possible the same coeificients of expansion to avoid rupturing the cemented joint. In the modified hearth construction of Fig. 5, this difficulty is overcome by a monolithic box-like structure 52 made of pervious ceramic or refractory material, with a hollow interior. An impervious shell or coating 53 is applied to the bottom and sides of the structure 52, whereby gas supplied to the hollow interior can pass only through the uncoated and pervious top. In the modified construction of Figs. 6 and 7, the hearth is made up of tubes 54 of pervious ceramic or refractory material, of rectangular section and closed at their inner ends. The tubes 54 are supported on an inverted sagger plate or tray 55 of impervious refractory or the like. The tubes 54 extend through the side wall of the furnace structure and are connected at their outer open ends to a common gas manifold 56 supplied with gas from the header 21 as hereinbefore described. The tubes 54 are cemented together (51) where they pass through the side wall of the furnace structure and the assembly of tubes is tied into the furnace wall in a substantially gas-tight manner.

In practicing the method of the invention in the furnace shown in the drawings, material to be treated is fed to the uppermost porous hearth 2| throughthe feed chute 58. Since the chute 1 extends into the heating chamber I0, it is prefactuating fluid to the pipes 40 of the cylinders 11 (left end mechanism of Fig. 1), and the operatively-related pushers 32 push the load of material on the hearths 2| onto the hearths 20 immediately below. The same valve 42 then moves to admit actuating fluid to the pipes 41 or the same cylinders 38, and the pushers 32 are returned across the hearths 2| to their initial or in positions. Thereupon, the valve 42 and cylinders 38,

of a slide valve 60 controlled and actuated by a fluid pressure cylinder 6|. The slide valve prevents entrance of cold air into the lower end of the heating chamber. Preferably, the slide valve 60 is actuated simultaneously with the star wheel feed 59 to permit the withdrawal from the chute ll of an amount of treated material equivalent to that fed to the uppermost hearth 2i. The cycle of operation is thus for the mechanism on one end to reciprocate in unison all of the pushers of one set of hearths whereby the loads on those hearths are pushed off and drop onto the then-empty hearths below and the pushers are returned to their initial or in positions, and then the mechanism on the other end similarly reciprocates the pushers of the other set of hearths. The cycle can be made as slow or as rapid as desired, depending upon the time required to complete the reaction between the gas and the material being treated.

While supported on each ofthe porous hearths, gas in a finely disseminated state passes upwardly through the layer of material onthe hearth. Moreover, as the material drops from hearth to hearth it passes through an upward stream of the gas issuing from the pervious tops oi. the empty or unloaded hearths. Thus, intimate, positive and continuous contact of the gas with all parts of the material undergoing treatment is assured. The valves 42, star wheel 59 and slide valve 60 may be automatically synchronized to operate in the sequence hereinbefcre described,

i. e. (1) valve 42 of; left end mechanism and (2) valve 42 of right end mechanism simultaneously with star wheel 59 and slide valve 60. The furnace is preferably operated under a slight pressure so that hot gas tends to push out at any openings in the wall of the heating chamber. Such slight pressure is obtained by throttling the gas discharged through the outlet i by suitable adjustment of the damper IS.

The method of the invention is admirably adapted for the deiluorination of phosphate rock by calcination in the presence of water vapor by the method described in my aforementioned patent applications, or by the methods described in the copending patent applications of Clinton A. Hollingsworth and myself Ser. Nos. 665,344 filed April 26, 1946, issued as Patent No. 2,479,389 August 16,.1949, 665,345 filed April 26, 1946, now abandoned, and 665,346, filed April 26, 1946, issued as Patent 2,478,200 August 9, 1949. The method of the invention may also be applied with advantage in defiuorinating phosphate rock by replacing the fluorine of the fluorapatite by chlorine as described in the patent application of Clinton A. Hollingsworth Ser. No. 665,347, f led April 26, 1948. In the detluorinating methods with water vapor, temperatures 01' from about 2600 F. up to 3000" F. are required, while in the defiuorinating method with a chlorine-containing gas,temperatures of from about 2000" F. up to 2400" F. are required. One of the advantages oi the invention is that these required operating temperatures can be accurately maintained and controlled, even with flame temperatures in the combustion chamber I8 of 3200 to 3400 F. Thus, by regulating the amount and temperature of the gas supplied to the porous hearths and passing through the layers of material on those hearths, the treating or reaction temperature can be held at 2600" F., or even lower, although the heating gases entering the heating chamber from the combustion chamber may be considerably hotter. In this way the length of the eifective hot zone can be greatly extended, and can be much longer than obtainable in a rotary kiln.

In the defluorinating of phosphatic material by any of the methods hereinbefore mentioned, superior results are generally attained by forming the finely divided material into nodules, pellets, briquets or the like. For example, suitable nodules, generally round in shape and varying in diameter from to 1 inch, may be made by moistening the finely divided material with water and tumbling at room temperature in a rotating cylinder, barrel or the like. Such nodules or other agglomerated shapes of the finely divided phosphatic or other material may be fed to the furnace and treated on the porous hearths as hereinbefore described.

The invention is admirably adapted for the decarbonizing by water vapor oi nodules of finely divided material mixed with carbonaceous material for the production of porous nodules by the method described in the copending patent application of Clinton A. Hollingsworth and myself Serial No. 665,348, filed April 26, 1946. In accordance with that method, nodules made up of .a mixture of the finely divided material and from 5 to by weight of carbonaceous material are subjected to the action of water vapor at a temperature between about 2000 F. and about 2400 F. to eliminate substantially all of the carbon of the carbonaceous material with evolution of the resulting gaseous products, and thereby imparting a highly effective porosity to the nodules. Where the invention is applied to the practice of that method, or to the treatment of an material with a gas at a relatively low elevated temperature (e. g. 1800 to 2500 F.), the vertical heating chamber may advantageously be heated by the exhaust gases of a rotary kiln, as illustrated in Figs. 8 and 9 of the :i'ccompanymg drawings.

In the apparatus of Figs. 8 and 9, the main features of the furnace structure are the same as hereinbefore described and are indicated by the same reference numerals. The furnace, however, has no directly-communicating combustion or firing chamber, but is heated by the hot gaseous products discharging from the upper or materialfeed end of a slightly-inclined rotary kiln 62. The rotary kiln has a heat-refractory lining and may be of the conventional constructioncommonly used in the cement industry and has the usual circumferential trunnion rails 63, driving ear 64 and fire box 65 with fuel burners 66 at its lower or firing end. Water vapor (steam) or other suitable treating gas, is introduced into the firing end of the kiln through appropriately positioned pipes 61. The lower end of the heating .7 chamber l 0! the furnace is structurally tied and communicates directly with the upper end of the rotary kiln, and a gasket or the like 68 provides a substantially gas-tight connection between the rotary kiln and the adjacent stationary furnace structure. Material pushed oil the lowermost porous hearth 2| of the furnace slides a down a chute 69, of heat-refractory material, and constitutes the feed of the rotary kiln. Treated material is discharged from the lower end of the kiln through a discharge device 10.

In defluorinating phosphate rock in accordance with the method described in the aforementioned application Ser. No. 665,348, in the combined apparatus illustrated in Figs. 8 and 9, nodules of mixed phosphatic and carbonaceous materials are fed to the uppermost porous hearth, and from there are progressively moved from hearth to hearth and subjected to the action of water vapor at a temperature of about 2000- 2400 F. The water vapor is introduced through the porous hearths, and-may be appropriately preheated or superheated, as hereinbefore described, and its temperature thereby suitably regulated to maintain the nodulized material at the required treatment temperature. The water vapor reacts with the hot carbon of the carbonaceous material with the evolution of hydrogen and carbon monoxide (C+H2O- H2+CO) in much the same way that water gas is formed. The furnace is so operated that by the time the nodules reach the lowermost porous hearth substantially all of the carbon has been eliminated, and the nodules have consequently acquired a high degree of porosity, which will depend upon the amount of carbonaceous material initially mixed with the finely divided material. Air in controlled amount is preferably admitted to the heating chamber l0, through the porous hearths or in other appropriate manner, for combustion with the evolved hydrogen and carbon monoxide, thereby extending the zone at which effective reaction takes place between the hot carbon and water vapor, andeconomically utilizing the heat value of the carbon.

The decarbonized and hence porous nodules discharged from the lowermost hearth 2i and fed to the rotary kiln are therein subjected at a temperature of from about 2600 F. to 3000 F. to the action of water vapor (supplied through the pipes 61) for the elimination of fluorine according to any oi the methods hereinbefore referred to. The hot gases discharged from the upper end of z. mineral supplement in animal feeds or as a forizer.

The two-stage defluorinating method of the aforementioned Hollingsworth application Ser. No. 665,347, may be advantageously carried out in accordance with the present invention in the combined apparatus of Figs. 8 and 9. Thus, porous nodules of finely divided phosphatic material are fed, to the uppermost hearth of the vertical furnace and in progressively moving through the heating chamber III are subjected at a temperature of from about 2000 to about 2400 F. to a chloridizing gas (such as hydrochloric acid gas, chlorine gas and water vapor etc.) introduced through the porous hearths. The fluorine content of the phosphatic material is therethe kiln (which include the fluorine compounds resulting from the deiluorination of the phosphate rock) pass upwardly through the heating chamber lit and impart the requisite elevated temperature to the nodules undergoing decarbonization therein. The fluorine compounds may. if desired be recovered from the gases exhausting from the top of the heating chamber. The rotary kiln is preferably operated under a pressure slightly in excess of atmospheric pressure in order to assure positive penetration of water vapor throughout the mass of the nodulized charge while passing through the kiln, and henc substantially complete defiuorination, as more particularly described in my application Ser. No.

530,156 filed April 8, 1944, issued as Patent 2,446,978 August 10, 1948. The vertical furnace is likewise operated under a slight pressure for reasons hereinbefore mentioned. The defluorinated product discharged from the rotar kiln is in the form of individual clinkered nodules, and after grinding is ready for marketing and use as by substantially replaced by chlorine, and is evolved principally, if not solely, as hydrofluoric acid gas. The resulting chlorinated, but defluorinated, nodules are discharged from the lowermost porous hearth into the rotary kiln and therein subjected at a temperature of from about 2600 F. to 3000 F. to the action of water vapor (supplied through the pipes 61) for the elimination of chlorine. The evolved chlorine-containing gases pass with the hot gases discharged from the upper end of the kiln upwardly through the heating chamber l0, and thus supplement, and correspondingly decrease the required amount of, the chloridizing gas supplied through the porous hearths. Fluorine as well as chlorine compounds 'in the gases discharged from the top of the heating chamber may be appropriately recovered.

While the aforementioned two-stage treatment methods for defluorinating phosphatic material are preferably carried out in the combined apparatus of Figs. 8 and 9, they may be satisfactorily practiced in the furnace of Fig. 1 by maintaining the required temperature gradient in the heating chamber I0. Thus, in the aforementioned two-stage decarbonizing and defluorinating treatment, decarbonization may be carried out in the upper half or so of the heating chamber l0 and defluorination carried out in the lower half or so of the chamber, with water vapor supplied to all of the porous hearths. To this end, the decarbonizing zone is maintained at a temperature gradient of from about 1900 to 2500 F., and the defluorinating zone is maintained at a temperature gradient of from about 2500 F. up to the required maximum temperature which may be as high as 3000 F. Similarly, in the aforementioned two-stage defluorinating and dechlorinating treatment, the defluoflnatlng zone in the upper part of the heating chamber I0 is maintained at a temperature gradient of from about 1800 to 2500 F. with a chloridizing gas supplied to the porous hearths of that zone,

-and the dechlorinating zone in the lower part of the chamber is maintained at a temperature maximum temperature, with water vapor supplied to the porous hearths of that zone. By suitably regulating and controlling the amount and temperature of the gas supplied to the porous hearths, the contemplated temperature gradients are readily established and maintained, and the treatment of the material with gas is carried out as a substantially continuous process or operation.

I claim:

1. In the method of defluorinating phosphatic material in which the finely divided material is subjected to the action of water vapor at elevated temperature, the improvement which comprises supporting a plurality of layers 01' the iinely divided material on porous hearths in vertically spaced positions within a vertical heating chamber, maintaining a temperature or between 1800 F. and 2500 F. in the heating chamber, progressively moving the material downwardly through said chamber from one hearth to the next lower hearth, passing finely disseminated water vapor upwardly through the porous hearths and the entire mass of each layer of the material while supported as aforesaid, introducing fresh material onto the uppermost hearth, discharging treated material from the lowermost hearth into the higher end of an inclined rotary kiln, heating said kiln by the combustion of incl at its lower end, passing the hot combustion gases from the kiln upwardly through said vertical heating chamber, and maintaining an atmosphere 01 water vapor and a temperature exceeding 2500 F. within said rotary kiln.

2. In; the method of defluorinating phosphatic material in which the material is subjected to the action of a gas at elevated temperature, the improvement which comprises supporting a plurality of layers of the phosphatic material on porous hearths in vertically spaced positions within a vertical heating chamber, progressively moving material downwardly through said chamher by transferring the material on each of said hearths to the next lower porous hearth respectively of a plurality of such hearths in vertically spaced positions between and alternating with said first mentioned porous hearths and then transferring the material on each of said next lower of the alternating porous hearths to the next lower porous hearth respectively of said .first mentioned porous hearths, introducing fresh material onto the uppermost porous hearth, discharging treated'material from the lowermost porous hearth, continuously passing finely disseminated gas upwardly through each of said porous hearths and through the entire mass of material while supported thereon as aforesaid, the material transferred from each porous hearth to the next porous hearth as aforesaid passin through an upwardly moving stream of gas issuing from said next lower porous hearth at a time that it supports no material, and maintaining a temperature above 2500" F. in the heating chamber.

3. The improvement in the method of defluorinatingphosphatic material as set forth in claim 2 in which a temperature between 1900 F. and 2500 F. is maintained in an upper portion of the heating chamber and a temperature above 2500" F; is maintained in a lower portion of the heating chamber. g

4. In the method of deiiuorinating phosphatic material in which the material is subjected to the action of water vapor at elevated temperature. the improvement which comprises supporting a plurality oi layers of the phosphatic material on porous hearths in vertically spaced positions within a heating chamber, progressivel moving material downwardly through said chamber by transferring the material from each porous hearth to the next lower porous hearth, introducing fresh material onto the uppermost porous I hearth, discharging treated material from. the lowermost porous hearth, continuously passing finely, disseminated water vapor upwardly through each of said porous hearths and through the entire mass of material v 10 supported thereon, the material transferred from each porous hearth to the next lower porous hearth passing through an upwardly moving stream of water vapor issuing from the porous hearths therebelow, and maintaining a temperature above 2500 F. in the heating chamber.

5. The improvement in the method of deiiuorinating phosphatic material as set forth in claim 4 in which a temperature between 1900 F. and 2500" F. is maintained in an upper portion of the heating chamber and a temperature above 2500 F. is maintained in a lower portion of the heating chamber.

6. In the method of defluorlnating phosphatic material in which the material is subjected to the action of water vapor at elevated temperature, the improvement which comprises supporting a plurality of layers of nodules of mixed phosphatic and carbonaceous material on porous hearths in vertically-spaced positions within a vertical heating chamber, maintaining a temperature of from 1800 F. to 2500 F. in the heating chamber, progressively moving the nodules downwardly through the chamber from one hearth to the next lower hearth, passing finely disseminated water vapor upwardly through the porous hearths and the entire mass of each layer of nodules while supported as aforesaid, introducing fresh nodules onto the uppermost hearth, discharging treated nodules from the lowermost hearth into one end of a calcining kiln, heating the kiln to a temperature above 2500 F. b the -heating chamber and into contact with the nodules passing downwardly therethrough, whereby the water vapor will react with the carbonaceois material of the hot nodules with the evolution of gas to leave the nodules with a, porous structure better adapted for their subsequent treatment in the kiln.

7. In the method of defluorinating phosphatic material in which the material is subjected to the action of water vapor at elevated temperature, the improvement which comprises supporting a plurality of layers of nodules of mixed phosphatic and carbonaceous material on porous hearths in vertically-spaced positions within a vertical heating chamber, maintaining a temperature of from 1800 F. to 2500 F. in the heating chamber, progressively moving the nodules downwardly through the chamber from one porous hearth to the next lower porous hearth, introducing fresh nodules to the uppermost porous hearth, discharging treated nodules irom the lowermost porous hearth into one end of a calcining kiln, heating the kiln to a temperature above 2500 F. by the combustion of fuel at its other end, maintaining an atmosphere of water vapor within the kiln and passing the hot products of combustion and water vapor from the kiln upwardly through the heating chamber and into contact with the nodules passing downwardly therethrough, introducing additional water vapor into the heating chamber through the porous hearths, the water vapor in the heating chamber reacting with the carbonaceous material of the hot nodules with the evolution of hydrogen and cargen and carbon monoxide evolved from the nodules.

- ERNEST J. MAUsT.

summons crrnn.

UNITED STATES PATENTS Number Name Date Perino Sept. 22, 1914 Newberry Mar. 7, 1918 Number 12 Name Date Boner Nov. 8, 1921 Caldwell Mar. 28, 1933 Mitchell Oct. 16, 1934 'lromel Sept. 14, 1937 Luscher Feb. 6, 1940 Hartley Mar. 20, 1945 McNeil Feb. 19, 1946

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