US3241824A

US3241824A - Apparatus for treating small particle size materials

Info

Publication number: US3241824A
Application number: US113854A
Authority: US
Inventors: Richard E King
Original assignee: Northern Natural Gas Co; W S MOORE CO
Current assignee: Northern Natural Gas Co; W S MOORE CO
Priority date: 1961-05-31
Filing date: 1961-05-31
Publication date: 1966-03-22
Anticipated expiration: 1983-03-22
Also published as: GB981231A; SE303144B; BE618400A

Description

R. E. KING March 22, 1966 APPARATUS FOR TREATING SMALL PARTICLE SIZE MATERIALS 1 9 e 5 N s h E 9 S V m ,v e t n 9 d M r m m a S I h f 2 .M m R Y B Gas Filed May 51. 1961 R. E. KING March 22, 1966 APPARATUS FOR TREATING SMALL PARTICLE SIZE MATERIALS 2 Sheets-Sheet 2 Filed May 31, 1961 Pipe Jmmwev, in.

9 mm K vmr m M a m w R HfforneyS United States Patent Ofifice 3,Z4l,82i Patented Mar. 22, 1956 3,241,824 APPARATUS FOR TREATHNG SMALL PARTHCLE lZE MATERIALS Richard E. King, Birmingham, Ala, assignor, by direct and mesne assignments, of one-half to W. S. Moore (10., a corporation of Minnesota, and one-half to Northern Natural Gas (Jompany, a corporation of Delaware Filed May 31, 1961, Ser. No. 113,854 8 Claims. (Cl. 266-20) This invention relates to apparatus for treating small particle size materials and more particularly to apparatus for roasting fine particle size materials, such as ore, and the like, and which is adapted for carrying out the process described and claimed in the co-pending application Serial No. 89,984, now abandoned, filed in my name and in the name of Robert E. Lacey on February 17, 1961 and entitled Process for Treating Fine Particle Size Materials.

An object of my invention is to provide apparatus for roasting fine particle size materials, such as ferruginous ores, by complete suspension of the fine particles of material in a stream of hot reducing gases with the. particles of material flowing concurrently with the stream of reducing gases.

Another object of my invention is to provide apparatus for the chemical reduction of small particle size ores in which the reduction takes place in a minimum of time and the apparatus required to handle the ore is reduced to a minimum.

Another object of my invention is to provide apparatus of the character designated which shall be particularly adapted for the roasting of non-magnetic ores, such as hematite, oethite, and the like, whereby they are converted into the oxide magnetite.

Another object of my invention is to provide apparatus of the character designated which shall embody a multiple stage system in which the flow of solids and gas is concurrent within each stage, but the overall flow within the system is countercurrent, whereby the unreduced ore contacts the depleted gas and becomes partially reduced before it contacts the rich gas, thus bringing about faster and more complete reaction.

Another object of my invention is to provide apparatus of the character designated which shall embody a multiple stage system in which at least one stage is employed as a reactor with at least one other stage employed as a preheate-r to effect heat economy.

A more specific object of my invention is to provide apparatus of the character designated which shall include means for bringing about proper flow of gases and solids through the apparatus without the use of mechanical devices, therebymaking my apparatus adapted for troublefree operation at elevated temperatures.

A further object of my invention is to provide apparatus of the character designated which shall be simple of construction, economical of manufacture and which shall be adapted for hand-ling a large volume of materials in a continuous manner.

As is well known in the art to which my invention relates, many ores, such as Mesabi slaty ore, cannot be smelted by the conventional type blast furnace for the reason that the silica, alumina and other compounds in the ore require the generation of a large volume of slag which increases the heat requirement in the furnace and lowers the yield of metallic iron. Also, such ores are soft whereby upon handling or shipment, the ore disintegrates into small particles which are unsatisfactory for use in the blast furnace. Furthermore, the low content of iron in such ores requires the shipment and handling of almost three parts by weight of ore to yield one part by weight of metallic iron.

There are large quantities of iron-bearing, low-grade ferruginous ores now available which could constitute a great potential source of iron. The iron contained in many of these low-grade ores occurs largely in the oxide hematite or as hydrated oxides such as goethite or limonite, which are not adapted for magnetic separation in the usual manner. By roasting these iron oxides in a reducing atmosphere, the oxides are converted into magnetite which is magnetic and is recovered by magnetic separation in a manner well understood in the art. The reducing gases usually employed are carbon monoxide, hydrogen or mixtures of these two gases. The gases are generally used in a mixture of other gases which result from the partial combustion of fuel, such as natural gas, oil, coal or the like.

Where intimate contact of the reducing gas and the solid iron oxide is maintained at elevated temperatures, the reduction of the iron content of the ore from hematite to magnetite proceeds rapidly. Accordingly, the surf-aces of large particles of ore are readily contacted by the reducing gases and the gaseous reaction products are easily removed whereby reduction of the oxides on the surface takes place rapidly. On the other hand, the iron oxides on the interior of a large particle of ore are not reduced as quickly due to the fact that the reducing gas must diffuse through the solid material before it contacts the iron oxide. The product gas must then diffuse outwardly through the solid material to escape from the reaction area and be replaced by reducing gas so that the reaction may continue. The rate of gas diffusion through the solid particles of ore thus becomes a major factor which limits the speed of the reaction.

Apparatus heretofore employed for the roasting of iron ore has included the vertical shaft furnace, the

' rotary kiln, the multiple hearth furnace, the horizontal traveling grate and the fluidized solid reactor. The size of the ore generally employed in all of the processes, other than the fluidized solid reactor, is substantially coarser than one-quarter inch and the reaction requires long periods of time ranging from thirty minutes to several hours to effect the desired reduction. The fluidized solid reactor may process ore at a size finer than one-quarter inch but the gas velocity must be sufliciently low to retain the solids in the reactor. The productive capacity of the reactor is thus limited by the rate at which the reducing gas can be supplied to the ore material and removed therefrom.

Apparatus embodying features of my invention is illustrated in the accompanying drawings, forming a part of this application, in which:

FIG. 1 is a flow sheet showing a two-stage system;

FIG. 2 is a chart showing a graphic representation that the gas pressure developed at the bottom of an upwardly extending pipe by the flow of solids is directly proportional to the length of the pipe and the pressure developed increases with the increasing rate of solids flow and decreasing pipe diameter; and,

FIG. 3 is a flow sheet showing the complete treatment of the materials in a multi-state system.

Referring now to the drawings for a better understanding of my invention, I show a two-stage system in FIG. 1 which comprises a first upwardly extending riser 10 and a second upwardly extending riser 11. A gas inlet 12 is provided at the lower end of the riser 10 while the upper end of the riser 1t} communicates with a cyclone separator 13 which separates the gas from the solid particles. The solid particles are discharged from the cyclone separator 13 through a discharge conduit '14. Communicating with the gas discharge of the separator 13 is a downwardly extending conduit 17 which in turn communicates with the lower end of the second riser 11 \.9 whereby the stream of gases indicated by the dotted arrow 18 are conveyed upwardly through the second riser 11. The upper end of the riser 11 communicates with a cyclone separator 19 having a gas outlet 21 and an outlet 22 for discharging solid particles.

The low ends of the risers and 11 are provided with 'venturi throats 23 and 24, respectively. Communicating with the venturi 24- is an inlet conduit 26 for supplying the small particle size materials to be roasted. The materials thus introduced through the conduit 26 are conveyed upwardly by the upwardly moving stream of gases, the flow of the solid particles being indicated by the solid arrows 27. As the concurrently flowing stream of gas and solid particles pass through the separator 19, the gases are discharged through the outlet 21 while the solid particles are discharged downwardly through the outlet 22.

Communicating with the solid discharge outlet 22 is the upper end of a conduit 28. The lower end of the conduit 28 communicates with the venturi 23 whereby the solid particles are introduced into the lower end of the first riser 10.

From the foregoing description, the operation of the apparatus shown in FIG. 1 will be readily understood. The hot gases are continuously introduced through the inlet 12 whereby they flow upwardly through the riser 10 and the separator 13 and then fiow downwardly through the conduit 17 to the venturi 24 at the lower end of the second riser 11. After passing through the venturi throat 24, the gaseous stream passes upwardly through the riser 11 and is finally discharged through the outlet 21 of the separator 19. The solid materials are fed into the venturi 24 through the conduit 26 whereby they are conveyed upwardly and flow concurrently with the stream of gas to the separator 19. The solid particles are discharged from the separator 19 through outlet 22 into the conduit 28 whereupon the solids are introduced into the venturi 23 of the riser 10. The solid particles then flow upwardly and concurrently with the hot gases introduced through the inlet 12 to the separator 13. The solid particles are discharged from the separator 13 through the outlet 14. The volume of gases introduced into the riser 10 and the size of the riser 10 is such that the velocity of the gas stream will suspend the fine particle size materials and convey them to the separator 13. This velocity is dependent largely upon the particle size and density of the fine ore. In actual practice, I have found that a velocity greater than 10 feet per second is usually required to prevent particles of ferruginous ore from settling out of the gas stream due to the forces of gravity.

It will thus be seen that the solid particles and gas flow concurrently as they pass upwardly through the risers 10 and 11 whereby the solid particles are suspended in the moving gases. However, the overall flow of the solids is countercurrent to the flow of gases. That is to say, the sol-id particles are introduced into the lower end of the second riser 11 and are then passed through the first riser 10 before being discharged. Accordingly, the second riser 11 senves as a preheater while the first riser 10 serves as a reactor. Since down flow of solid materials in conduit 28 is essential to the maintenance of pressure balance and proper direction of gas flow, the introduction of solids at 26 must be started at a relatively low rate .and gradually increased to the proper operating level. Also, if desired, a suitable valve may be provided in conduit 28 whereby the flow of gas through conduit 28 is restrained until the system is placed in operation. That is, the valve 25 would be gradually moved to open position after a solids feed rate has been established. Also, the solid-s discharge outlet 14 is connected to a solids discharge system which restricts the flow of gas into and out of the system. As the solids flow upwardly concurrently with the gas stream, gravity restrains upward movement of the larger particle size materials more than it restrains upward movement of the smaller particle size materials whereby the larger particle size materials are subjected to longer exposure to the hot gases thereby bringing about the required roasting of the larger particle size materials.

Unless counteracted, the gas introduced at inlet 12 will tend to pass upwardly through the solids downcomer 28 to the separator 19, thereby short-circuiting the reaction zone and greatly lowering the separating efiicie-ncy of the separator 19. That is, because of frictional losses in the system, the gas at the inlet will be at a higher pressure than the gas within the separator 19, unless counteracted. The desired flow of gas is through the venturi 23 and upwardly through the first riser 10 to the separator 13 and then downwardly through the conduit 17 to the lower end of the second riser '11 where the gas flows upwardly therethrough and is finally discharged through the outlet 21. This problem cannot be solved by providing a mechanical air-lock device, such as a rotary feeder or a gravity trickle valve due to the fact that such devices would not be satisfactory for use at temperatures employed for the reduction of iron.

In accordance with my invention, I provide a venturi and select a venturi throat configuration such that where gas alone is flowing through the system, the pressure drop of the gas flowing through the desired path in my apparatus is almost completely equalled by the venturi pressure change so that essentially no pressure exists to cause fiow of gas upwardly through the conduit or solids downcomer 28. In actual practice, I find that when solids are being conveyed by gas in my apparatus, the pressure drop through the desired path is increased while the differential of pressure brought about by the venturi is not materially affected by the presence of solids. I have also found that by proper choice of the diameter and length of the solids downcomer 28, the solids falling down the solids downcomer 28 will increase the gas pressure near the bottom of the downcomer and shortcircuiting of gas, when the system is conveying solids, can be prevented.

The pressure developed by solids falling in a standpipe is important in the function of my multi-stage system due to the fact that the solid particles flow down the downcomer 28. I have found that the gas pressure developed at the bottom of a standpipe by the flow of solids is directly proportional to the length of the standpipe. FIG. 2 of the drawings shows that the pressure developed also increases with the increasing rate of solids flow and decreasing pipe diameter. The iron ore employed in obtaining the results shown in FIG. 2 was minus 20 mesh iron. The curves show that the pressure developed is much reduced in larger diameter pipe, such as would be used in commercial operation. However, a compensating factor is that the resistance offered to gas flow in the riser and other parts of the system will also be reduced in larger diameter pipes, as shown by the dashed line in FIG. 2. Accordingly, the pressure developed by falling solids would be equally useful in a large commercial system to prevent upward flow of gas through the solids downcomer 28. The pressure developed is indicated in FIG. 2 by inches of water, on the water gauge, over the length of the conduit, measured in feet. Thus, by properly selecting the length and width of the downcomer, a pressure increase can be developed, from the top to the bottom of the downcomer, equal to the pressure decrease caused by conveying solids through portions of the desired path in the apparatus.

Referring now to FIG. 3 of the drawings, I show the complete treatment of the materials in a rnulti-stage system. The crushed ore is stored in a suitable bin 29 and is transferred to a dry-grinding system indicated generally at 31 whereby the ore is pulverized and dried simultaneously. The particle size to which the ore must be crushed to effect rapid reaction is determined by the physical characteristics of the natural ore. That is, some natural ores have a porous structure which permits some penetration of gas into the interior of the particles. These ores will reduce rapidly at a muchcoarser size than will an ore having a dense structure. In actual practice, I have found that many ores can be reduced in my improved apparatus by crushing the ores to a particle size whereby the largest particles will pass a standard mesh testing sieve.

The finely pulverized ore passes from the grinding system 31 to an air classifier 32 and then to a cyclone separator 33 where exhaust gases are removed as at 34. The pulverized ore is stored in a bin 36 and is then conveyed through a supply line 37 to an upwardly extending riser 38 which communicates at its upper end with a cyclone separator 39. The exhaust gases from the separator 39 are removed through a conduit 41 where they are conveyed through the grinding system 31, the air classifier 32 and the separator 33 whereby the gases dry the ore introduced into the grinding system. The fine particle size materials introduced into the riser 38 thus move concurrently and in suspension with the gaseous stream to the separator 39'.

The gaseous stream supplied to the line 38 comes from the exhaust of a cyclone separator 42. The fine particle size ore materials discharged from the lower end of the cyclone separator 39 enter a line 43 and are then discharged into a riser 44 which communicates the gas exhaust of a cyclone separator 45 with the cyclone separator 42. The upwardly moving stream of gas in the riser 44 picks up the fine particle size ore materials whereby they are suspended in the gas and conveyed concurrently therewith to the separator 42.

Communicating with the cyclone separator 45 is the upper end of riser 46. The lower end of the riser 46 communicates with a line 47 which supplies the gaseous stream from a gas generator 43. Solid materials discharged from the separator 42 are introduced into the lower end of the riser 46 by a line 49 whereby they move upwardly and concurrently in suspension with the gaseous stream to the separator 45. The reducing gases formed in the gas generator 48 may be provided by introducing air through a conduit 51 and natural gas through a conduit 52 whereby they are mixed and partially burned in the gas generator 48 prior to being introduced into the riser 46. The composition and temperature of the gases leaving the generator 48 may be controlled by recycling a portion of the gaseous stream exhausted from the cyclone separator 42 through a line 53 to the air supply line 51.

The movement of the fine particle size ore materials through the

risers

38 and 44 serves as a temperature preparation whereby the ore is preheated prior to being introduced into the riser 46 carrying the hot reducing gases. The fine particle size materials to be roasted are fed through the apparatus at a suitable rate whereby the particles are suspended completely in the reducing gases while passing through the riser 46. The riser 46 thus serves as a reaction zone whereby the fine particle size materials are not only suspended in this zone but flow concurrently with the reducing gases to the separator 45. The volume of the reducing gases introduced in the riser 46 and the size of the riser 46 is such that the velocity of the gas stream will suspend the fine particle size materials and convey them to the separator 45. As the ore particles pass through the separator 45, they are separated and are discharged into a cooler 54.

From the cooler 54, the reduced ore passes to suitable magnetic separators indicated generally at 56 whereby the magnetic materials are separated from the non-mag netic materials. The magnetic ore may then pass to suitable briquetting or pelletizing apparatus 57 in a manner well understood in the art.

In view of the fact that the fine particle size ore to be reduced and the hot reducing gases are flowing concurrently, it is desirable to have the ratio of reducing gases and the iron oxides at least equal to that required to produce the desired chemical reaction. That is, since the reaction occurs in the zone of the

risers

10 and 46, it is necessary that the quantity of reducing gas introduced into these risers be sufficient to reduce all of the iron contained in the ore to the desired oxide.

In order to convert one pound of hematite to magnetite, approximately 0.8 cubic feet of either carbon monoxide or hydrogen (dry basis, 60 F., 29.92 inches of mercury) is required. Where the reducing gas contains 15% carbon monoxide or hydrogen at a temperature of approximately 1400 F. and atmospheric pressure, the gas volume required for one pound of hematite is approximately 19 cubic feet. Approximately this volume of gas is required to suspend one pound of hematite and the other materials associated therewith in the natural ore.

The suspension of fine particle size materials in reducing gases is maintained at an elevated temperature which is below the fusion point of the various components of the material. That is, it is desirable to prevent the particles from passing into the liquid or melted state during the reaction. The relationship of the size of the fine particle size materials to the velocity of the reducing gases is maintained at or above a value which prevents any particles of the ore from settling out of the gaseous stream due solely to the action of gravity.

As an example of the operation of my apparatus, an iron ore containing 43.6% iron was crushed to pass a 14 mesh testing sieve. This ore was reduced in a two-stage apparatus similar to that shown in FIG. 1 in which the risers were of standard 1% inch pipe approxiately 7 feet long. The reducing gas contained 16.5% carbon monoxide and hydrogen. The measured temperature of the gas was maintained at approximately 1540 F. Essentially complete reduction of the iron oxide to magnetite was obtained at an ore rate of approximately 188 pounds per hour and a gas rate of 10 standard (60 F., 29.92 inches of mercury) cubic feet per minute.

From the foregoing, it will be seen that I have devised improved apparatus for treating ore-like materials, such as ferruginous ores. While I have described my apparatus as being particularly adapted for use in treating ferruginous ores, it will be apparent that it is adapted for roasting other materials, such a pyrite and the like. By roasting the fine particle size materials while they are in complete suspension in the hot gases, the roasting or reduction takes place in a minimum of time. Also, by constructing and arranging the apparatus whereby the pressure drop of gas flowing through the risers and the equipment associated therewith is substantially equal to the change of pressure at the venturi in the first riser and that created by solids flowing down the solids downcomer, there is substantially no pressure drop across the solids downcomer to cause flow of gas directly from the gas inlet to the separator associated with the second riser.

I wish it to be understood that my improved apparatus is adapted for operation under a wide range of conditions, as will be apparent to one skilled in the art, and is not liimted to any specific proportions of gases to solids.

While I have shown my invention in two forms, it will be obvious to those skilled in the art that it is not so limited but is susceptible of various other changes and modifications without departing from the spirit thereof, and I desire, therefore, that only such limitations shall be placed thereupon as are specifically set forth in the appended claims.

What I claim is:

1. Apparatus for reducing fine particles of solid material, said apparatus comprising:

a first upwardly extending riser;

first separator means, adjacent the upper end of said first riser, for separating particles of solid material from gas;

a second upwardly extending riser;

second separator means, adjacent the upper end of said second riser, for separating particles of solid material from gas;

means communicating the lower portion of said second riser with said first separator means and in position to receive gas discharged from said first separator means;

means for supplying a continuously moving stream of heated reducing gas to the lower end of said first riser; said first riser, said first separator means, said communicating means, said second riser and said second separator means defining a path for the passage of said gas from the first riser through the first separator to the second separator; means for introducing particles of solid material tobe-reduced into said second riser adjacent the lower portion thereof, whereby said particles are fully suspended in a dilute, finely divided state in said stream of gas moving upwardly through the second riser for movement concurrently with said gas to said second separator means; substantially unobstructed conduit means, extending downwardly from said second separator means to a junction with the lower portion of said first riser, for transferring particles of solid material separated in said second separator means to said first riser, whereby said particles are fully suspended in a dilute, finely divided state in said upwardly moving stream of gas in said first riser for movement concurrently with said gas to said first separator means;

said first riser extending upwardly from said junction;

and means, at the junction of said downwardly extending conduit means and said first riser, for providing a pressure drop at said junction equal to the pressure drop of gas moving along said path, whereby movement of gas through said downwardly extending conduit means is impeded;

said apparatus including means for maintaining the velocity of said stream of gas at a value to convey said particles continuously in an upward direction through said risers and to prevent said particles from settling out of said stream by the action of gravity alone; 7

and means for removing said particles from said first separator means.

2. Apparatus as recited in claim 1 wherein said pressure-drop means at said junction comprises a venturi throat in communication with said downwardly extending conduit means for receiving said particles of solid material.

3. Apparatus as recited in claim 1 wherein said downwardly extending conduit means has a cross-sectional area and length constituting means for providing a pressure increase in said conduit means from the second separator means to said junction, when said particles of solid material fall through said conduit means, equal to the pressure drop caused by said particles moving, with said gas, through the apparatus along portions of said path, whereby movement of gas through said downwardly extending conduit means is prevented.

4. Apparatus for reducing fine particles of solid material, said apparatus comprising:

a first upwardly extending riser;

a second upwardly extending riser;

means for supplying a continuously moving stream of heated reducing gas to the lower end of said first riser;

said first riser, said first separator means, said communicating means, said second riser and said second separator means defining a path for the passage of said gas from the first riser through the first separator to the second separator;

means for introducing particles of solid material tobe-reduced into said second riser adjacent the lower portion thereof, whereby said particles are fully suspended in a dilute, finely divided state in said stream of gas moving upwardly through the second riser for movement concurrently with said gas to said second separator means;

substantially unobstructed conduit means, extending downwardly from said second separator means to a junction with the lower portion of said first riser, for transferring particles of solid material separated in said second separator means to said first riser, whereby said particles are fully suspended in a dilute, finely divided state in said upwardly moving stream of gas in said first riser for movement concurrently with said gas to said first separator means;

said first riser extending upwardly from said junction;

said downwardly extending conduit means having a cross-sectional area and length constituting means for providing a pressure increase in said conduit means from the second separator means to said junction, when said particles of solid material fall through said conduit means, equal to the pressure drop caused by said particles moving, with said gas, through the apparatus along portions of said path, whereby movement of gas through said downwardly extending conduit means is impeded;

said apparatus including means for maintaining the velocity of said stream of gas at a value to convey said particles continuously in an upward direction through said risers and to prevent said particles from settling out of said stream by the action of gravity alone;

and means for removing said particles from said first separator means.

5. In an apparatus for treating fine particles of solid material:

a first upwardly extending riser;

a second upwardly extending riser;

separator means, adjacent the upper end of said second riser, for separating solid particles from gas;

gas passage means communicating the lower portion of said second riser with the upper portion of said first riser;

means for supplying a continuously moving stream of gas to the lower end of said first riser;

said first riser, said gas passage means, said second riser and said separator means defining a path for the movement of said gas from the first riser through the second riser to the separator means;

means for introducing fine particles of solid material into said second riser adjacent the lower portion thereof, whereby said particles are fully suspended in a dilute, finely divided state in said stream of gas moving upwardly through the second riser, for movement of said particles concurrently with said gas to said separator means;

substantially unobstructed conduit means, extending downwardly from said second separator means to a junction with the lower portion of said first riser, for transferring particles of solid material separated in said separator means to said first riser, whereby said particles are fully suspended in a dilute, finely divided state in said upwardly moving stream of gas in said first riser for movement concurrently with said gas in said first riser;

said first riser extending upwardly from said junction;

said apparatus including means for maintaining the velocity of said stream of gas at a value to convey said particles continuously in an upward direction through said risers and to prevent said particles of material from settling out of said stream by the action of gravity alone,

said gas passage means including a gas-solids separator at the top of the first riser.

6. Apparatus as recited in claim wherein said pressure-drop means at said junction comprises a venturi throat in communication with said downwardly extending conduit means for receiving said particles of solid material.

7. Apparatus as recited in claim 5 wherein said downwardly extending conduit means has a cross-sectional area and length constituting means for providing a pressure increase in said conduit means from the separator means to said junction, when said particles of solid mate rial fall through said conduit means, equal to the pressure drop caused by said particles moving, with said gas, through the apparatus along portions of said path, whereby movement of gas through said downwardly extending conduit means is prevented.

8. In an apparatus for treating fine particles of solid material:

a first upwardly extending riser;

a second upwardly extending riser;

said first riser extending upwardly from said junction;

said downwardly extending conduit means having a cross-sectional area and length constituting means for providing a pressure increase in said conduit means from the separator means to said junction, when said particles of solid material fall through said conduit means, equal to the pressure drop caused by said particles moving, with said gas, through the apparatus along portions of said path, whereby movement of gas through said downwardly extending conduit means is impeded;

said apparatus including means for maintaining the velocity of said stream of gas at a value to convey said particles continuously in an upward direction through said risers and to prevent said particles of material from settling out of said stream by the action of gravity alone;

References Cited by the Examiner UNITED STATES PATENTS Re. 17,212 2/1929 Stockton 263--21 1,310,455 7/1919 Tainton -9 2,274,789 3/1942 Horesi 3410 X 2,343,780 5/1944 Lewis 75-26 2,559,551 7/1951 Weber 34-10 X 2,683,077 7/1954 Lewis 759 X 2,757,921 8/1956 Petersen.

2,821,471 7/1958 Sellers 7526 3,03 1,293 4/1962 Meissner 7526 FOREIGN PATENTS 775,356 5/1957 Great Britain.

OTHER REFERENCES Zenz et al.: Fluidization and Fluid Particle Systems, pp. 158160, 343-345, Reinhold Publ. Corp., New York, 1960.

WHITMORE A. WILTZ, Primary Examiner.

WINSTON A. DOUGLAS, DELBERT E. GANTZ,

MORRIS WOLK, Examiners.

Claims

1. APPARATUS FOR REDUCING FINE PARTICLES OF SOLID MATERIAL, SAID APPARATUS COMPRISING: A FIRST UPWARDLY EXTENDING RISER; FIRST SEPARATOR MEANS, ADJACENT THE UPPER END OF SAID FIRST RISER, FOR SEPARATING PARTICLES OF SOLID MATERIAL FROM GAS; A SECOND UPWARDLY EXENDING RISER; SECOND SEPARATOR MEANS, ADJACENT THE UPPER END OF SAID SECOND RISER, FOR SEPARATING PARTICLES OF SOLID MATERIAL FROM GAS; MEANS COMMUNICATING THE LOWER PORTION OF SAID SECOND RISER WITH SAID FIRST SEPARATOR MEANS AND IN POSITION TO RECEIVE GAS DISCHARGED FROM SAID FIRST SEPARATOR MEANS; MEANS FOR SUPPLYING A CONTINUOUSLY MOVING STREAM OF HEATED REDUCING GAS TO THE LOWER END OF SAID FIRST RISER; SAID FIRST RISER, SAID FIRST SEPARATOR MEANS, SAID COMMUNICATING MEANS, SAID SECOND RISER AND SAID SECOND SEPARATOR MEANS DEFINING A PATH FOR THE PASSAGE OF SAID GAS FROM THE FIRST RISER THROUGH THE FIRST SEPARATOR TO THE SECOND SEPARATOR; MEANS FOR INTRODUCING PARTICLES OF SOLID MATERIAL TOBE-REDUCED INTO SAID SECOND RISER ADJACENT THE LOWER PORTION THEREOF, WHEREBY SAID PARTICLES ARE FULLY SUSPENDED IN A DILUTE, FINELY DIVIDED STATE IN SAID STREAM OF GAS MOVING UPWARDLY THROUGH THE SECOND RISER FOR MOVEMENT CONCURRENTLY WITH SAID GAS TO SAID SECOND SEPARATOR MEANS; SUBSTANTIALLY UNOBSTRUCTED CONDUIT MEANS, EXTENDING DOWNWARDLY FROM SAID SECOND SEPARATOR MEANS TO A JUNCTION WITH THE LOWER PORTION OF SAID FIRST RISER, FOR TRANSFERRING PARTICLES OF SOLID MATERIAL SEPARATED IN SAID SECOND SEPARATOR MEANS TO SAID FIRST RISER, WHEREBY SAID PARTICLES ARE FULLY SUSPENDED IN A DILUTE, FINELY DIVIDED STATE IN SAID UPWARDLY MOVING STREAM OF GAS IN SAID FIRST RISER FOR MOVEMENT CONCURRENTLY WITH SAID GAS TO SAID FIRST SEPARATOR MEANS; SAID FIRST RISER EXTENDING UPWARDLY FROM SAID JUNCTION; AND MEANS, AT THE JUNCTION OF SAID DOWNWARDLY EXTENDING CONDUIT MEANS AND SAID FIRST RISER, FOR PROVIDING A PRESSURE DROP AT SAID JUNCTION EQUAL TO THE PRESSURE DROP OF GAS MOVING ALONG SAID PATH, WHEREBY MOVEMENT OF GAS THROUGH SAID DOWNWARDLY EXTENDING CONDUIT MEANS IS IMPEDED; SAID APPARATUS INCLUDING MEANS FOR MAINTAINING THE VELOCITY OF SAID STREAM OF GAS AT A VALUE TO CONVEY SAID PARTICLES CONTINUOUSLY IN AN UPWARD DIRECTION THROUGH SAID RISERS AND TO PREVENT SAID PARTICLES FROM SETTLING OUT OF SAID STREAM BY THE ACTION OF GRAVITY ALONE; AND MEANS FOR REMOVING SAID PARTICLES FROM SAID FIRST SEPARATOR MEANS.