US2958587A - Cleaning apparatus for exhaust pipe assemblies in sublimed oxide furnaces - Google Patents

Description

5 Sheets-Sheet 1 G. R. GRIMES fr /1 fffffff lr INVENTOR my@ Z. rz'zvres.

Nov. l, 1960 CLEANING APPARATUS FOR EXHAUST PIPE ASSEMBLIES IN SUBLIMED OXIDE FURNACES Filed June 20, 1958 NOV' 1, 1960 G. R. GRlMr-:s 2,958,587

CLEANING APPARATUS FOR EXHAUST PIPE ASSEMBLIES IN SUBLIMED OXIDE FURNACES Filed June 20. 1958 5 Sheets-Sheet 2 Nov. 1,1960 Y G R GMES 2,958,587

CLEANING APPARATUS FR EXHAUST PIPE ASSEMBLIES IN SUBLIMED OXIDE FURNACES Filed June 20, 1958 5 Sheets-Sheet 3 5607?@ @feb-wes.

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NOV. 1, 1960 G, R GRlMEs 2,958,587

CLEANING APPARATUS FOR EXHAUST PIPE ASSEMBLIES IN SUBLIMED OXIDE FURNACES Filed June 20, 1958 5 Sheets-Sheet 4 azul/st Nov. l, 1969 MES 2,958,587

G. R. GRI CLEANING APPARATUS FOR EXHAUST PIPE ASSEMBLIES IN SUBLIMED OXIDE FURNACES Filed June 20, 195B 5 Sheets-Sheet 5 INVENTOR opy@ )Y @rz '777e s.

United States Patent Oce 2,958,587 Patented Nov. 1, 1960 CLEANNG APPARATUS FOR EXHAUST PIPE lAISEhgBLIES lN SUBLIMED OXIDE FUR- C George R. Grimes, Burgettstown, Pa., assigner to American Metal Climax, Inc., a corporation of New York Filed .lune 20, 1958, Ser. No. 743,281

3 Claims. (Cl. 23-264) This invention relates generally to furnaces and more particularly to a furnace for producing molybdenum trioxide (M003), sometimes called molybdic anhydride or molybdic acid, and commonly referred to in the molybdenum processing eld as oxide, by subliming a high purity molybdenum trioxide from a lower purity feed material.

Prior furnaces for obtaining high purity oxide (better than 99% M003) from technical grade oxide (approximately 90% MOOS and containing some M002 and insoluble impurities such as aluminum oxide, silica and iron oxide) have utilized a rotating hearth located below the furnace heating units. Technical grade oxide, continuously fed to the hearth which is heated by radiant heaters to approximately 2100 degrees Fahrenheit, starts volatilizing at about 110() degrees Fahrenheit which is approximately 300 degrees below its melting point. Air streams passed over different sections of the hearth sweep the sublimed oxide out of the furnace to be cooled, collected, densied and placed in containers at the baghouse. One of the principal problems in furnaces of this type has been that since uniform conditions do not exist at all sections of the hearth, it has been diicult to obtain oxide of uniform purity from all of the hearth sections. If the air stream at a hearth section is too large, it picks up impurities from the oxide on the hearth so that the resulting oxide is below the required purity, and cools the oxide on the hearth to an extent such that the production rate is lowered. If the air stream is too small, the oxide bed on the hearth becomes molten, rather than remaining in the desired sticky non-llowable mass, and the rate at which oxide is removed from the hearth section is reduced so that the output of the furnace is lowered.

In the furnace disclosed in application Serial No. 743,282, filed June 20, 1958, owned by the assignee of this invention, these problems are solved by providing an individual exhaust pipe assembly for each hearth section. However, in order to maintain a substantially constant rate of air flow at each hearth section, it is necessary to maintain lthe exhaust pipe assemblies free of solid oxide resulting from cooling of the volatilized oxide which is being continuously drawn through the tubes. 'I'he manual cleaning of these exhaust pipe assemblies required to maintain a constant rate of air flow is both expensive and unreliable.

-The principal object of this invention, therefore, is to` provide an improved furnace of the above type which includes automatically operable cleaning mechanisms for the exhaust pipe assemblies.

A further object of this invention is to provide a furnace of the above type with an independently operable cleaner mechanism at each exhaust pipe assembly.

Further objects, features and advantages of this invention will become apparent from a consideration of the following description, the appended claims and the accom- `panying drawing in which:

f `Figure 1 is a fragmentary vertical sectional View of a furnace provided with the cleaning apparatus of this invention;

Fig. 2 is an enlarged fragmentary sectional View looking along the line 2-2 in Fig. l;

Fig. 3 is a plan view of the furnace shown in Fig. l, with some parts broken away and other parts shown in section for the purpose of clarity;

Fig. 4 is an enlarged transverse sectional View looking along the line 4 4 in Fig. 3;

Fig. 5 is a sectional view looking along the line S-S in Fig. 3;

Fig. 6 is a horizontal sectional View of the distributor box in the furnace shown in Fig. l;

Fig. 7 is a sectional view looking along the line 7--7 in Fig. 4; and

Fig. 8 is a fragmentary sectional view looking along the line 8-8 in Fig. 3.

With reference to the drawing, a sublimed oxide furnace 10 provided with the cleaning apparatus of this invention, is illustrated in Fig. l as including a main frame 12 which supports an annular hood or furnace shell 14 at a position above a supporting floor surface 16. The hood 14 has tubular inner and outer walls 18 and 20 arranged in a concentric relation and connected by a top wall 22 of substantially annular shape.

An annular hearth 24, of substantially trough-shape in transverse section, is located within the lower portion of the hood 14. As shown in Fig. 2, the width of the hearth 24 is less than the width of the hood 14 so that spaces 26 and 28 are provided between the hearth and the inner and outer hood walls 18 and 20, respectively. The hearth 24 is mounted on a supporting I-beam 30 which is in turn carried on a ring gear 32 rotatably driven by any suitable means and supported on rollers 34.

A pair of spaced partitions 23 and 25, which extend 4substantially radially of the hood 14, project upwardly from positions adjacent the top side of the hearth 24 soI as to divide the furnace into a small feeding zone 27 and an elongated heating zone 29 which extends from the partition 25 in a counterclockwise direction, as viewed in Fig. 3, to the partition 23.

Below its top wall 22, the hood 14 is provided with a refractory arch 36 which extends the complete length of the heating zone 29 and forms the top wall of a heating chamber 40 disposed between the hearth member 24 and the arch 36. A plurality of heating elements 42 extend substantially radially of the hood 14 through the chamber 40 and are positioned adjacent their ends in refractory blocks 44 supported on plates: 46 carried by the inner and outer side walls 18 and 20 of the hood 14. Each heating element 42 is of the silicon carbide electrical resistance type such as the Globar elements manufactured by the Carborundurn Company and is supported at its ends by metal clips (not shown) which are supported on the furnace main frame and function as the electrical contacts for the heating elements.

At substantially equally spaced locations in the heating zone 29, hollow exhaust port members 48 are supported on the outer plate 46. Each member 48 is positioned between two groups of heating elements 42 and extends from a point above the hearth to the outer side wall 20 of the hood 14. At the wall 20, each port member 48 communicates with the horizontal portion 5l) of an exhaust tube 52 which extends upwardly from the hood 14. At its upper end, each tube 52 -is connected to a downwardly extending pipe 54 on a distributor box 58 located above the hood 14 so that its axis coincides with the vertical axis 56 of rotation of the hearth 24.

Since the hearth 24 is rotated in a counterclockwise difrection as viewed in Fig. 3, the exhaust tubes 52 are provided with consecutive letter suix designations from a-n, inclusive,.also ina counterclockwise direction about the hearth, to facilitate reference hereinafter to individual tubes. All of the exhaust tubes 52c-n, inclusive, are of substantially the same length and are connected by the :pipes 154 to :the distributor box 58 which forms a part of an upwardly extending draft tube connected to any suitable fan orother air suction means for exerting substantial upward drafts in the tubes 52c-n. The 'box 58 has a Vcone shape bottom 59 lto facilitate a smooth kupward flow pf volatilized oxide fromV the tubes v52.

As shown in Fig. 4, each exhaust tube 52 has a damper l,assembly 60 disposed ina vertical portion 62 thereof adjacent the horizontal portion 50. Each damper assembly 60 ,includes a plate 64 mounted for movement about a horizontal shaft 66 to different adjusted positions. Each damper `assembly 60 is operable to control the amount of air and volatilized oxide which flows upwardly in the tube 52 'in'which the assembly 60 is installed.

To maintain the porthole members 48 clear of solidified oxide, a porthole cleaning mechanism 70 of this invention is mounted adjacent each porthole member 48. Each mechanism 70 is mountedon a supporting bracket 72 secured to the outer wall 20 of the hood 14, and includes a pneumatic piston and cylinder assembly 74 consisting of a horizontal cylinder 76 secured to the bracket 72 and a piston rod 78 which extends from the cylinder 76 toward the porthole member 48. On its terminal end, the piston rod 78 carries a circular plate 80 located within the horizontal portion 50 of the adjacent tube 52 and provided with pointed blades 82, The piston rod 78 extends through an opening in Aa vertical back door 84, for the exhaust tube portion 50, which can be opened for manual cleaning of the portion 50 and maintenance of the mechanism 70.

n operation of the cylinder assembly 74 to extend the piston rod 78, which is shown in its retracted position in Fig. 4, the plate 80 is moved to a position adjacent to but slightly inwardly of the inner end 85 of the exhaust port member 48. In this position of the plate 80 the blades 82 project out of the member 48 so that substantially all of the solidified oxide in the member 48 has been dislodged to maintain the passage 86 through the member 48 clear for the travel of gaseous products therethrough.

In the use of the furnace 10, the hearth 24 is lled with sand 88, and technical grade oxide, which is in powder form, is fed from storage bins to the upper end of a feed hopper 90 located above the hearth in the feeding zone 27. As shown in Figs. and 8, the zone 27 has atop wall 91 supported on horizontal beams 93 which are a part of the main frame 12. The oxide in the hopper 90 is discharged from the lower end 94 thereof by a feed roll 98 which is driven by a motor 116 and extends radially across the hearth 24. The roll 98 is generally cylindrical in shape and has grooves 99 in its outer surface. On rotation of the roll 98, each groove 99 fills with oxide in the hopper 90 and then deposits this oxide onto the upper end of an inclined feed plate 100 positioned below the hopper 90. The feed plate 100 is suspended from the frame 12 by rods 101 and is formed with small downwardly extending grooves 102. which maintain the form of the oxide issuing from the feed roll 98 as a wide stream and deposit the oxide on the hearth 24. This bed of oxide then travels with the rotating hearth 24 in a counterclockwise direction as viewed in Fig. 3 so that yafter it travels under the partition 25 it -is exposed to the heat from the heating elements 42. The heat in the chamber 40 quickly brings the temperature of the oxide to a volatilizing temperature.

The oxide bed on the hearth 24 which is in a position opposite the rst exhaust tube, indicated at 52a in Fig. l, is in a heated condition such that some volatilized oxide is present. This volatilized oxide is drawn upwardly through the exhaust tube 52a which communicates with a draft tube 104 which is also connected to the draft tube 52b opposite the next porthole member 48. The draft tube 104 also communicates with an exhaust duct 106 which terminates at its lower end in the feeding zone 27 SQ 'that any dust in the zone 27 is drawn upwardly through the duct 106 to the draft tube 104 where it is mixed with the oxide fumes drawn upwardly through the exhaust tubes 52a and 52b. In the draft tube 104 the temperature of the oxide and air is lowered to about l-200 F. and the resulting solid or crystallineloxide is conveyed by the air to a secondary baghouse where it is fed into a conveyor mechanism which terminates in a upright feeder tube '105 (Figs. 3 and 5) located in the feeding zone 27. The tube 105 deposits this oxide, which is of a lower purity than desired, onto the hearth 24fo1' travel into theheating zone 29. Removal of the dust from the feeding zone 27 through the duct 106 prevents any of the dust from being drawn into the heating zone 29 and adversely affecting the purity of the volatilized oxide therein.

The oxide bed on the hearth 24 opposite the third exhaust tube 52e is in the desired sticky state. Consequently, the volatilized oxide withdrawn from the hearth through the exhaust tube 52C is of a higher quality than that withdrawn through the tubes 52a and 52b. This quality is maintained yby adjusting the damper assembly 60 for the tube 52C so that optimum conditions are maintained on the oxide bed on the section of the hearth 24 adjacent the exhaust tube 52e. The adjustment of the damper assembly 60 controls the amount of air which flows upwardly through the space 26 opposite the tube 52e so that the inner rim of the hearth is cooled and the volume of air traveling across the hearth 24 is suicient to maintain the oxide bed inthe desired state. Air also travels upwardly through the space 28 adjacent the exhaust tube 52e primarily for cooling the outer rim of the hearth. The amount of air which travels upwardly through the space 28 corresponding to each tube 52 is controlled by a pair of dampers 112 and 113 of manually adjustable type carried by the hood 14. kEach damper 112 is located in the outer Wall 20 adjacent the lower end of the space 28, and each damper 113 is located in a wall which closes the lower end of the space 28.

Adjustment of the dampers 112 and/or 113 is effective to control the ratio of air admitted to the inner side of the corresponding hearth section to the air admitted to the outer side of the hearth section. The restriction of the amount of air permitted to enter the space 28 insures an upward travel of air through the space 26, so that air sweeps across the hearth in sucient quantity to convey the sublimed oxide into the porthole members 48. By adjusting a corresponding pair of dampers 64 and 112 or 113, the air at the sides of the corresponding hearth section is regulated so that the inner and outer sides of the M003 bed on the hearth are cooled and solidify so that they form barriers to prevent any liquid portions of the bed from running off the hearth, and the desired volume of air is provided for sweeping the sublimed M003 from the hearth. Any spillage of oxide o the bed is noticeable at the dampers 113 and either or both dampers 112 and 113 are adjusted at each hearth section to provide the required air. Observation openings are also provided in the furnace wall 20 at positions horizontally aligned with the oxide bed and some air also enters the furnace at these openings. All of the exhaust tubes 52C to 5211, inclusive, communicate with the `distributor box 58`which is part of a draft tube connected to a suitable supply of suction air. The oxide in the tubes 52e to n, inclusive, is of high quality and after cooling to a solidifying temperature is further cooled and then conducted to the primary baghouse for collection and subsequent densifying and packaging.

The residue remaining on the hearth after a complete revolution of the hearth is removed by a tailing screw 114 (Fig. 5) which extends transversely of the hearth 24 in the feeding zone 27 at a position between the partition 23 and -the feed roll 98. As a' result of the continuous operation of the screw 114, al1 of the residue on each portion of the hearth is removed before additional oxide is deposited thereon by the feed roll 98. The dust resulting from operation of the screw 114 is removed from the zone 27 by the duct 106. A chain 115 extends about sprockets 117 and 119 on the tailing `screw 114 and -the feed roll 98, respectively, to provide for driving of the screw 11'4 by the motor 116. The residue removed from the hearth by the tailing screw 1-14 falls from the screw into a hopper 120 located below one end of the screw. This residue is equal to about 30-40% of the original oxide charge.

Each exhaust tube 52 and its corresponding exhaust port member 48 constitutes an exhaust pipe assembly through which volatilized oxide from the adjacent section on the moving hearth Z4 is withdrawn. Since the temperature of the volatilized oxide in each exhaust pipe assembly is lowered during the travel ofthe oxide through the pipe assembly, some solidifying of oxide in each assembly is continually taking place. The oxide in the vertical portion of each tube 52 which falls into the horizontal lower end portion 50 thereof is removable through a cleanout opening in the bottom side of the portion 50. The oxide which solidifies on each porthole member 48 is dislodged by the corresponding cleaning mechanism 70 for pick-up by the air stream in the member 48 or for travel back onto the heart-h. The amount of air `drawn across the corresponding hearth section is affected if the buildup of solid oxide in the porthole member 48 reduces the size of the passage 86 therein to -a size less than the opening in the corresponding exhaust tube 52 at the damper assembly 60. The setting of the assembly y60 is such that an optimum air travel condition prevails at the corresponding hearth section and when this condition is changed the efficiency of the furnace is impaired.

Consequently, the porthole cleaning mechanisms 70 are operated automatically, by any suitable control mechanism, at time intervals necessary to maintain the porthole passages 86 substantially free of solid oxide. In each operation, the piston rod 78 is extended so that the disk 80 and blades 82 clear the porthole passage 86 of solid oxide and push it onto the hearth 24. It is to be understood that in the preferred construction of a mechanism 70, the disk 80 is provided with the blades 82; however, the majority of the cleaning action is accomplished by the disk itself and consequently a mechrism 70 can be operated satisfactorily without the blades It will be understood that the specific construction of the improved cleaning apparatus for exhaust pipe assemblies in sublimed oxide furnaces herein disclosed and described is presented for purposes of explanation and illustration, and is not intended to indicate limits of the invention, the scope of which is defined by the following claims.

What is claimed is:

1. In a furnace for producing high purity M003 from lower purity M003, said furnace including a horizontal annular hearth mounted for rotation in one direction about a substantially vertical axis, means for feeding said lower purity M003 to one portion of said hearth, an annular hood having horizontally spaced inner and outer side walls which extend downwardly to positions horizontally spaced from the inner and outer sides, respectively, of the hearth so as to provide spaces for the upward travel of air on the inner and outer sides of said hearth, heating means in the hood above the hearth, hollow exhaust port members mounted on peripherally spaced portions of said hood at positions above said hearth, each of said port members extending horizontally from a point above the hearth to the outer side wall of said hood, a plurality of exhaust tubes corresponding to said exhaust port members, each of said exhaust tubes communicating with its corresponding exhaust port mem- 6 ber and extending upwardly therefrom to a position above said hood, draft means connected to the upper ends of the exhaust tubes for providing upwardly traveling drafts therein, and damper means in each of said exhaust tubes for adjusting the draft therein to obtain optimum draft conditions at the hearth section corresponding thereto; a plurality of upright substantially circular disks of a size to be movable axially through said exhaust port members positioned outside said hood and axially aligned with said exhaust pont members for movement therethrough in a direction radially inwardly of said hearth for dislodging solid Mo03 from said exhaust port members, pneumatically operable piston and cylinder assemblies mounted on said frame and corresponding to said disks, each of said assemblies having a piston -rod axially aligned with and secured to a corresponding disk at a position within the exhaust tube for the exhaust port member with which said disk is aligned.

2. In a furnace for producing high purity M003 from lower purity M003, said furnace including a horizontal annular heart-h mounted for rotation in one direction about a substantially vertical axis, means for feeding said lower purity M003 to one portion of said hearth, an annular hood having horizontally spaced inner and outer side walls which extend downwardly to positions horizontally spaced 'from the inner and outer sides, respectively, of the hearth so as to provide spaces for the upward travel of air on the inner yand outer sides of said hearth, heating means in the hood above the hearth for volatilizing M003 thereon, hollow exhaust port members mounted on peripherally spaced portions of said hood at positions above said hearth, each of said port members extending horizontally from a point above the hearth to the outer side wall of said hood, a plurality of exhaust tubes corresponding to said exhaust port members, each of said exhaust tubes communicating with its corresponding exhaust port member and extending therefrom to a position spaced from said hood, draft means connected to the exhaust tubes for providing drafts therein for withdrawing volatilized M003 from said hood, yand damper means in each of said exhaust tubes for adjusting the draft therein to obtain optimum draft conditions at the hearth section corresponding thereto; a plurality of upright disks of a size to be movable axially through said exhaust port members positioned outside said hood and substantially axially aligned with said exhaust port members for movement therethrough in a direction radially inwardly of said hearth for dislodging solid M003 from said exhaust port members, and power means connected to each of said disks for moving each of said disks axially of the exhaust port member therefor.

3. In a furnace for producing high purity M003 from lower purity M003, said furnace including a horizontal annular hearth mounted for rotation in one direction about a substantially vertical axis, means for feeding said llower purity M003 to one portion of said hearth, an annular hood having horizontally spaced inner and outer side walls which extend downwardly to positions horizontally spaced from the inner and outer sides, respectively, of the hearth so as to provide spaces for the upward travel of air on the inner and outer sides of said hearth, heating means in the hood above the hearth for volatilizing M003 thereon, hollow exhaust port members mounted on peripherally spaced portions of said hood at positions `above said hearth, each of said port members extending horizontally from a point above the hearth to the outer side wall of said hood, a plurality of exhaust tubes corresponding to said exhaust port members, each of said exhaust tubes communicating with its corresponding exhaust port member and extending therefrom to a position spaced from said hood, draft means connected to the exhaust tubes for providing drafts therein for withdrawing volatilized M003 from said hood, and damper means in each of said exhaust 7 tubes for adjusting the draft therein to obtain optimum 'draft conditions at the hearth section corresponding thereto; a plurality of upright disks of a size to be movfable axially through said exhaust port members positioned outside ,said hood and substantially axially aligned with said exhaust `port members for movement therethrough in a direction radially inwardly of said hearth -for dislodging solid M003 from said exhaust port members, fluid operable piston and cylinder assemblies mounted on said frame and corresponding to said disks, each -of said assemblies having a piston rod secured to a 8 corresponding disk for moving said disk Yaxially `of `the exhaust port member therefor.

References Cited in the tile of this patent UNITED STATES PATENTS 520,369 Melville May 22, 1894 2,574,842 Prescott Nov. 13, 1951 2,603,471 McDonald July l5, 1952 FOREIGN PATENTS 785,322 Great Britain Oct. 23, 1957

Claims (1)

1. IN A FURNACE FOR PRODUCING HIGH PURITY M0O3 FROM LOWER PURITY M0O3, SAID FURNACE INCLUDING A HORIZONTAL ANNULAR HEARTH MOUNTED FOR ROTATION IN ONE DIRECTION ABOUT A SUBSTANTIALLY VERTICAL AXISMEANS FOR FEEDING SAID LOWER PURITY M0O3 TO ONE PORTION OF SAID HEARTH, AN ANNULAR HOOD HAVING HORIZONTALLY SPACED INNER AND OUTER SIDE WALLS WHICH EXTEND DOWNWARDLY TO POSITIONS HORIZONTALLY SPACED FROM THE INNER AND OUTER SIDES, RESPECTIVELY, OF THE HEARTH SO AS TO PROVIDE SPACES FOR THE UPWARD TRAVEL OF AIR ON THE INNER AND OUTER SIDES OF SAID HEARTH, HEATING MEANS IN THE HOOD ABOVE THE HEARTH, HOLLOW EXHAUST PORT MEMBERS MOUNTED ON PERIPHERALLY SPACED PORTIONS OF SAID HOOD AT POSITIONS ABOVE SAID HEARTH, EACH OF SAID PORT MEMBERS EXTENDING HORIZONTALLY FROM A POINT ABOVE THE HEARTH TO THE OUTER SIDE WALL OF SAID HOOD, A PLURALITY OF EXHASUT TUBES CORRESPONDING TO SAID EXHAUST PORT MEMBERS, EACH OF SAID EXHAUST TUBES COMMUNICATING WITH ITS CORRESPONDING EXHAUST PORT MEMBER AND EXTENDING UPWARDLY THEREFROM TO A POSITION ABOVE SAID HOOD, DRAFT MEANS CONNECTED TO THE UPPER ENDS OF THE EXHASUT TUBES FOR PROVIDING UPWARDLY TRAVELING DRAFTS THEREIN, AND DAMPER MEANS IN EACH OF SAID EXHAUST TUBES FOR ADJUSTING THE DRAFT THEREIN TO OBTAIN OPTIMUM DRAFT CONDITIONS AT THE HEARTH SECTION CORRESPONDING THERETO, A PLURALITY OF UPRIGHT SUBSTANTIALLY CIRCULAR DISKS OF A SIZE TO BE MOVABLE AXIALLY THROUGH SAID EXHAUST PORT MEMBERS POSITIONED OUTSIDE SAID HOOD AND

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