US3774786A

US3774786A - Furnace feeding and delivery apparatus

Info

Publication number: US3774786A
Application number: US00175574A
Authority: US
Inventors: C Cruse
Original assignee: Armco Inc
Current assignee: Armco Inc
Priority date: 1971-08-27
Filing date: 1971-08-27
Publication date: 1973-11-27
Anticipated expiration: 1990-11-27

Abstract

A pressure maintenance feeding and/or delivery system for a gravity feed shaft furnace comprising one or more groups of spaced apart funnels disposed in axial relationship within said furnace whereby the material charged into said furnace passes through said groups of funnels prior to or subsequent treatment therein.

Description

United States Patent 1 Cruse 1 Nov. 27, 1973 FURNACE FEEDING AND DELIVERY [56] References Cited APPARATUS UNITED STATES PATENTS [75] Inventor: Clyde L. Cruse, Middletown, Ohio 2,365,240 12/1944 Arnold 214/17 C 2,619,344 11/1952 Mursch 214/35 R [73] Asslgneei Arm) Steel cmpwaton 2,926,802 3/1960 Stuewer 214 17 B Middletown, Ohio [22] Filed: Aug. 27, 1971 Primary ExaminerR0bert G. Sheridan 1 pp No: 175,574 Attorney Melvll e, Strasser, Foster & Hoffman Related US. Application Data 57 ABSTRACT [63] Continuation-impart of Ser. No. 858,778, Sept. 17, A pressure maintenance feeding and/or delivery 1969 abandoned tem for a gravity feed shaft furnace comprising one or 2 l 2 more groups of spaced apart funnels disposed in axial g1 14/35 152 relationship within said furnace whereby the material l l charged into said furnace passes through said groups 1 0 17 3 of funnels prior to or subsequent treatment therein.

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ATTORNEYS PATENIEDNBVZY 191a SHEET 2 BF 3 CLYDE L. CRUSE mym,,%a

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ATTORNEYS 1 FURNACE FEEDING AND DELIVERY APPARATUS RELATED INVENTION This application is a continuation-in-part application of Ser. No. 858,778, filed Sept. 17, 1969, now abandoned, and entitled, FURNCE FEEDING APPARA- TUS AND METHOD.

BACKGROUND OF THE INVENTION This invention relates primarily to a unique feeding arrangement for a gravity feed shaft furnace wherein the charged material enters through said arrangement for treatment within the furnace. More specifically, this invention is directed to a gravity feed furnace such as a blast furnace where periodic charges containing coke, limestone and iron ore are made through the top thereof for conversion within the furnace into pig iron. However, it is also applicable to a direct reduction furnace of the type reducing iron oxide pellets or lumps.

One of the operating problems associated with the furnaces of the former type is the inability to properly control and maintain the pressure needed within the furnace in order to carry out the intended operation in an efficient manner. That is, in a gravity feed furnace such as a blast furnace, it is necessary to operate the furnace, whose internal pressure differs from that of the surrounding atmosphere, in a continuous manner without materially affecting this pressure differential. It will be appreciated that the unique feeding and/or delivery system of this invention is applicable whether the pressure differential within is greater or less than the outside. Nevertheless, and without limiting this invention, the further description will be directed primarily tothe blast furnace which is normally operated at a higher internal pressure, more specifically to the feeding aspects thereof.

The blast furnace represents, and has constituted for the past sixty years, the primary method for producing iron. However, with advances in technology and the requirement for new and greater quantities of iron and steel products, further demands have been placed on the furnacesQl-leretofore, the primary demands on the charging mechanism were that it provides the charge material when needed while maintaining an internal pressure at the top on the order of about 2 pounds per square inch higher than the outside pressure.

It was discovered that greater efficieny could be achieved with furnaces operated at higher top pressures, i.e., a pressure differential as high as 25 pounds per square inch. However, conventional apparatus for charging a blast furnace are not suitable for continuous operation under high pressure conditions.

This conventional arrangement typically includes a series of two or more bells, with associated hoppers, to supply the charge to the furnace to produce iron. The difficulty of this prior system lay in its inability to maintain an adequate pressure seal between the bell seat and the hopper. Without an effective seal, particularly at high operating pressures, there is the likelihood that hot gases and highly abrasive dust particles will bypass the seal to erode and otherwise damage the charging mechanism to the point of requiring replacement and- /or shut down of the furnace for maintenance.

The patent to W.E. Slagley, U.S. Pat. No. 3,152,703, discloses the conventional bell system but utilizes an expandable sealing means between the bell and the hopper. The solution was merely temporary however as it still used the conventional bells and hoppers. There was still the cost of maintaining the bells.

In an effort to eliminate the shortcomings inherent with the bell and hopper arrangement, the patentee noted above assisted in developing a new system to replace the conventional one. The disclosed system in U.S. Pat. No. 3,394,826, includes a material-receiving, open-mouthed, hollow receptacle movably mounted within the upper portion of the furnace. With the assistance of suitable sealing means, the vessel is operated by pivoting from a receiving to a discharging position without affecting the pressure differential built up in the furnace. Despite the elimination of the bells and associated hoppers, maintenance problems were not eliminated. The effectiveness of movingparts, particularly when subjected to. the concurrent action of heat and abrasion, is reduced quickly where continuous operation involving said parts is attempted.

The present invention represents a further improvement over the conventional and modified systems by providing an effective charging and pressure maintenance system without the need for moving parts. In addition, by adopting the principles of the charging sys tem to the delivery portion of the furnace, an effective delivery system results.

SUMMARY OF THE INVENTION The foregoing, to the extent of the feeding, is accomplished by the use of one or more groups of funnels axially disposed adjacent the charging chute at the top of the furnace. The funnels each comprise an inverted cone whose base may be contiguous with the inside of the shaft furnace, or connected to the sides thereof. Each group of funnels is arranged in series such that the charge first contacts the uppermost funnel which directs the charge to the next lower or adjacent funnel for feeding into the treatment bed of the furnace. This sytem assures a constant supply of charge for the furnaces; and in so doing, assures that the proper level of pressure will be maintained at the top thereof.

To assit in directing the charge during its gravitational feed into the furnace, at least the lower funnel is provided with a tube member disposed axially from the apex of the cone. The funnels are arranged in such a way that the lowermost portion of the upper funnel, is positioned near the uppermost portion of the next lower funnel.

BRIEF DESCRIPTION OF THE: DRAWINGS FIG. 1 is a simplified sectional view of the top portion of a gravity feed shaft furnace illustrating the unique feeding system of this invention.

FIG. 2 is a simplified sectional view similar to FIG. 1 but illustrating the details of a modification to the invention.

FIG. 3 is a simplified sectional view of the top portion of a gravity feed shaft furnace illustrating a plurality of parallel feed delivery funnels in accordance with the invention herein.

FIGS. 4-6 are simplified sectional views of three delivery systems for use in a gravity feed shaft furnace, particularly of the type used in the direct reduction of iron oxide pellets or lumps.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS In the preferred practice of this invention, with particular reference to FIG. 1, there is illustrated the upper portion of a gravity feed shaft furnace, such as a blast furnace, which includes a first embodiment of the unique feeding mechanism 12 of this invention. The upper portion 10 is typically characterized by

concentric portions

14 and 16, the former containing the charge retaining and pressure maintenance elements for the furnace. Each of the concentric portions are provided with gas offtake outlets l8 and 20, respectively.

At the uppermost end of portion 14, there is provided an opening 22 for receiving the charge or burden into the furnace. While the capacity of a blast furnace will dictate the precise size thereof, it may be generally stated that the blast furnace is amulti-story structure. This being the case, the charge, which consists of coke, limestone and iron ore, is delivered by means of a conveyor or skip cars riding on an inclined rail. By the use of two such cars for example in tandem, it is possible to periodically charge the furnace at frequency intervals.

In operation, the charge enters through opening 22 where it is deposited in the feeding mechanism 12, to be described presently. This mechanism preferably comprises at least two funnels, specifically upper funnel 24 and lower funnel 26, respectively, which are spaced apart in axial alignment in the portion 14. Each said funnel may be characterized as in inverted

cone

28, 28a, having an opening 30, 30a, at its apex for discharging material deposited therein. From the opening 30, 30a, there is provided a

tubular member

32, 32a, to assit in transferring said discharged material.

The

circumferential dimension

34, 34a, of each said

cone

28, 28a, may be the same as the furnace portion 14, or connected by a solid plate thereto, so as to minimize or eliminate the passage of particles or ascending gases between the funnel and the adjacent furnace wall portion. The funnels may be welded to the walls of the furnace to assit in preventing this passage.

Further, while the respective funnels are axially spaced within the furnace, it will be observed in FIG. 1 that the lowermost end 36 of tube member 24 terminates near the free surface of the material in cone 28a. This is desirable, assuming a sufficient quantity of charge material available, to maintain a continuous or uninterrupted charge between the respective funnels.

It should be evident from the above that the conventional bell and hopper arrangement are unnecessary. It will be recalled that one of the primary functions of the two or more bells is to maintain the top pressure in the furnace at a level higher than in the surrounding atmosphere. This pressure maintenance may be demonstrated in the present invention by reference to FIG. 1, which FIGURE shows the typical operating bed levels of the charge.

The solid charge, in granulated and/or lump form, is charged into the system through the opening 22 to descend through the tube member 32, the rate of descent being determined by the process being fed. No gas or air, or at most a minimal amount, flows through tube 32 because the surrounding chamber or plenum 33 is maintained at atmospheric pressure by removing gas therefrom through the offtake outlet 18, by a pump or other means, not shown. The gas or air that is removed from the said chamber surrounding tube 32 enters it from the free surface of the solid charge contained within cone 28a. The pressure in the chamber surrounding tube 32 and in the region above the free surface of the material in cone 28 are substantially the same, which practically precludes any gas flow through tube 32.

In any event, the quantity of gas entering the chamber 33 to be removed or added to by outlet 18 is determined by the length and cross-section of tube member 32a, the pressure in the chamber surrounding the latter tube member, and the physical size and shape of the solids. Thus, in part, the size and length of the tube 32a, through its effect on the resistance of flow of gases, can be used to control the quantity of gas surrounding tube 32 over a rather broad numerical range. All of this pressure control, whether the desired pressure differential is positive or negative compared to the external atmosphere, is made possible without the use of any positive closures such as the bell arrangement.

The interrelationship of the several factors above, in designing the system for proper control on the quantity of gas flow ascending the furnace, may be shown by the following equation, as applied to FIG. 1:

Where:

P =Top pressure in plenum, 39 (psia) P- Controlled pressure in plenum, 33 (psia) L Length of tube, 32a, 32b (ft).

K Constant (function of solids size, size distribution, shape, and voidage) T= Temperature (R) M Molecular weight W= Mass velocity of gas (lbs./in. /sec.)

From this equation the quantity of a given gas that will flow through a given diameter tube, of a given length, for a given pressure drop at a given temperature and a given solids material, can be determined. This is the quantity of gas that must be pumped to avoid or substantially eliminate any ascending gases from exiting into the atmosphere.

The effective length of the

tube

32a, 32b, must be such that the pressure drop per unit length will not result in a gas mass velocity great enough to hold up the downward flow of solids. As will be observed later, in a detailed discussion of FIGS. 4-6, this is not a factor in the discharging of the bottom as the gas is flowing in the same direction as the solids.

The free surface area 35 must be great enough to keep the velocity of the gas being drawn off, below the terminal velocity of the smallest particles. The radius or one-half the shortest dimension of the opening of tube 32 must be small enough that the temperature drop, horizontally from the center of the opening to the plenum or chamber 33, will be sufficiently small to prevent gas flowing up the center of tube 32, while the pressure in chamber 33 can be maintained at a level that will not cause air to flow down the inside wall, or walls, of tube member 32.

These design criteria are applicable, not only to the embodiment of FIG. 1, but to the further embodiments and modifications taught herein. Such additional embodiments and modifications will now be described.

During start up of the furnace, for example, or as the result of a charging delay, the stock line of charged material may not be sufficient to maintain the desired top pressure. Therefore, a closure latch 37 or other suitable means may be provided adjacent the top to meet this requirement. The latch may also be closed if there is danger of a slip" in the charge which might cause the level of charge to fall below the lowermost end 36 of tube 24.

There is a further variation which relates to the lowermost portion of the funnel 26. Since it must be recognized that the stock line of material may vary for one reason or another, the lower tube member 32a has been provided with a telescopic section 32b, only one having been shown for the purpose of illustration. However, any number may be provided. By this simple procedure, the effective length of tube member 32a may be varied over a considerable distance. The flexibility in the length of tube 32a will provide some control of the top pressure with any given flow through outlet 18.

FIG. 2 illustrates an additional variation which may be applied to the basic concept herein, or to any delivery system of the type utilizing granular and/or lump material. The use of flared skirt 38 or angled flange at the lowermost portion of the tube leading from the funnel 26 helps to prevent segregation of lump material due to theshape or size as the materials flow from the in-line source. Typically such material in the deposited condition takes on the appearance of a cone or umbrella. This flated skirt 38 prevents the larger or rounded pieces from rolling down the sloping sides of the pileas additional feed is made of the material. The skirt restrains such movement whereby assuring a proper mix of the charge pieces. Finally, to facilitate the flow of gases being generated in the treatment zone below, the flared skirt 38 may be provided with perforations. To render the'material restraint effective, the included angle of the skirt should be only slightly less than the natural angle a pile of the material being handled would assume. Such an angle can be readily determined, particularly by the workers skilled in the art. The said natural angle of a given material can vary depending upon the number of pairs of feeding funnels. This may be more apparent in the description to follow where like numerals are applied to similar or functionally equivalent elements.

FIG. 3 is a modified feeding system for a gravity feed shaft furnace comprising

concentric portions

14 and 16, between which are a plurality of funnels 26, only two being illustrated here. As with the earlier embodiment, each of said funnels is axially aligned with the funnel The use of a plurality of groups of feeding funnels helps to prevent size segregation of the feed material due'to the larger pieces rolling to the outside of the furnace wall at the stock line. For example, where a single feed tube group is used all of the fines remain in the center of the furnace being fed and the larger pieces roll down the slope of the stockline resulting in size segregation. With multiple tube groups the fines can be better distributed and the slope of the stockline becomes several slopes which are shorter making the segregation less severe and the stockline flatter so that all of the gas paths from bottom to top are more nearly the same length. The latter results in a better gas flow distribution.

Multiple tube groups give the added advantage of greater reliability in case one tube group becomes plugged or otherwise inoperative. The remaining operative tube groups would continue to operate whereas any troube with a single tube group installation would result in a shut down.

One significant difference over the embodiment of FIG. 1 is the spacing of

portions

14 and 16. This has been done to permit the placement of

valves

40 and 42, (more fully defined later), for easy access by maintenance personnel. Since, as explained above, the pressure in chamber or plenum 33 is maintained very nearly at atmospheric, there is little or no flow of gas in either direction through the charge or burden in portion 14. In order to operate the gas sytem with no solids, the gas tight shut-off valves 42 must be closed. If it is desired to close said valves, for emergency reasons when solids are flowing, solids shut-off valves 40 are provided to stop the flow of solids. This enables the maintenance personnel to close valves 42 without-interference from the descending solids.

It should be clear that if fully automated valves are used, or access thereto is not critical, the furnace portions 14 and l6 may be joined with only a single separating wall defining a common wall for

chambers

33 and 39.

While the foregoing, which utilizes one or more groups of aligned funnels for feeding a furnace, was directed to the charging of a gravity feed shaft type furnace, the principle thereof may be applied to the delivery end of the furnace.

Before turning to a discussion of FIGS. 4-6, all of which teach furnace delivery systems utilizing the principles taught herein, it will be recalled that the furnaces normally operate at pressure levels different from atmospheric.

Considering the situation of descending solids, such as reduced iron pellets, it will be observed that the solids are moving downwardly through the furnace portion 44. As it flows, due to gravity, through the

funnels

46 and 48, the material will assume its natural angle of repose below funnel 46; its free face will extend from the lower edge of the funnel 46 to the wall of the furnace portion 44. As the material flows from funnel 48 it is conveyed away by any suitable conveying or feeding device 50. So that no gas will flow through the funnel 48 in either direction, the pressure in the chamber 52, above the free face of the solids, must be maintained at exactly the same pressure that exists on the outside of funnel 48. This is accomplished by pumping gas either to or from chamber 52, such as by conduit 54, at a rate such that the pressure differential between chamber 52 and the zone above funnel 46 will be exactly equal to the pressure difference between said zone and the outside of funnel 48. This may be accomplished by controlling the gas flow rate or by controlling the length of funnel 46 by means of a telescoping arrangement, such as taught above, or by a combination of both of these methods.

At the outlet of funnel 48 a cone 54 is shown, placed in usch a way as to permit the material to flow out over it and also so that in an emergency, such as a pump failure, this cone could be raised to close off the delivery outlet 56. A more convenient shut-off system, such as disclosed above, may be employed. For example, valves 58 and 60 (similar to valves 40 and 42) may be placed in the lower portion of funnel 46.

FIG. 5 shows how the principles herein would operate on a furnace delivery system either at pressure or under vacuum. Consider the former where heated process gas enters the system through conduit to ascend countercurrent to the solids flow.

A second system of solids cooling gas enters the system through conduit 72. If mechanical seals were used to discharge the solids, all of the gas entering through conduit 72 would rise to mix with the stream entering through conduit 70; then they would ascend to gas offtakes (not shown) higher in the furnace. But with this development, the stream of gas entering through conduit 72 would be increased sufficiently to supply the gas that would be removed, from chamber 74 by pump 76. Thus the stream from conduit 72 is split in the column in this case with the amount needed for the process being permitted to go up funnel 78 and the amount needed to cause the desired pressure drop is pumped downward through funnel 80.

By controlling the lengths of

funnels

78 and 80, the volumes of gas that will pass through each of these funnels for any given pressure. differences can be regulated. This can be done to the point of zero flow through funnel 78. Then by controlling the pressure and/or the flow rate in conduit 72, the direction of flow in funnel 78 may be changed or the flow may be stopped.

FIG. 6 shows an arrangement of great flexibility as regards modes of operation. In this particular embodiment gases are drawn off through conduits 82 and 84. This could be by a common pump with proper valving or they could go to separate systems. Gases enter the furnace portion 44 through conduits 86 and 88. Flow control in conduits 82, 84, 86 and 88, and the diameters and lengths of funnels 90, 92 and 94 together with the pressure the whole system imposes in chamber 96, will cause the gases entering the system at conduits 86 and 88 to go either up or down, or both.

In any of the above cases it may be desirable to have a flow of any proportion in either direction in the final solids discharge funnel 98. This of course is a simple matter of pressure control in chamber 100.

If the pressure in chamber 100 is less than the pressure where the material is being discharged, gas from a pressurized source must be admitted to chamber 100 instead of being drawn off. This pressurized source might well be a pump pumping from some other chamber thereabove.

All of these delivery systems have an advantage over existing systems as they eliminate any need for pressure seals. Where seals have been required, maintenance has been high. Finally, the conveyor mechanism 52, which is essentially the only moving part of the delivery operation, is positioned outside the furnace for easy maintenance. However, where pressure seals have been required in the past, it was necessary to maintain the conveyor in a pressurized area which is not readily accessible for maintenance or adjustment.

While the foregoing represent several embodiments and modifications which are specifically contemplated by this invention, it is believed that others may become apparent to those skilled workers upon reading these specifications. Therefore, no limtation is intended to be imposed on this invention except as set forth in the following claims.

The embodiment of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a gravity feed shaft furnace operated at a pressure level different from the surrounding atmosphere, in which said furnace has an opening at the top thereof for receiving a charge of material for treatment therein and is provided with a charging portion and a treatment portion axially aligned therewith, the improvement comprising in combination therewith, the provision of at least one group of axially spaced funnels, said funnels being positioned to provide through communication between said charging portion and said treatment portion, each said funnel comprising an inverted cone whose base is angled toward the inside of said furnace, whereby each said funnel is directly connected to the inside of the furnace such that the only communication between said portions is by way of said funnels, and that each said funnel is arranged within said furnace to define a large chamber between the furnance wall and said funnel, and means communicating with each of said chambers for controlling the pressure therebetween.

2. The apparatus according to claim 1 wherein there is a plurality of groups of funnels communicating between said charging portion and said treatment portion.

3. The apparatus according to claim 1 wherein said portions are spaced apart to provide access to at least one of said funnels communicating therebetween.

4. The apparatus according to claim 3 including at least one valve means within said funnel to control the flow of products therethrough.

5. The apparatus according to claim 4 including two valves in each said funnel, one to control the flow of solids and the other to control the flow of gases therethrough.

6. The apparatus according to claim 1 including a tube leading from the apex of each of said lowermost cones for transferring said charge into said furnace for treatment.

7. The apparatus according to claim 1 including a discharging system below said treatment portion, comprising at least one group of axially spaced funnels, the arrangement of said funnels being such as to define a chamber between each said funnel and the furnace wall, and means communicating with each of said chambers for controlling the pressure therebetween.

8. The apparatus according to claim 7 including external means connecting said last named chambers for transferring furnace gases from one to another.

9. The apparatus according to claim 7 including a gas conduit just above the uppermost discharging system funnel.

10. The apparatus according to claim 9 including two axially aligned funnels in the discharging system.

11. The apparatus according to claim 7 including means for closing the discharge end of the furnace.

12. In apparatus for the continuous feeding of a gravity feed shaft furnace operating at a pressure level different from the surrounding atmosphere, in which said furnace has an opening at the top thereof for receiving a charge of material for treatment therein and is provided with a charging portion and a treatment portion axially aligned therewith, each of which communicate with one another through the center thereof, the improvement comprising in combination therewith, the provision of a group of axially spaced funnels, with one of said funnels being in each said furnace portion, each said funnel comprising an inverted cone whose base is angled toward and connected to the inside of its said furnace portion such that no openings exist therebetween, each said funnel defining a large annular chamber throughout its axial extend with its said furnance portion, and means communicating with each said annular chamber for controlling the pressure therebetween.

13. The apparatus according to claim 12 including a tube leading from the apex of each said cone for transferring said charge into said furnace for treatment.

14. The apparatus according to claim 13 including a continuous out-turned flange at the lowermost end of the tube leading from one of said cones.

15. The apparatus according to claim 13 wherein the lowermost tube is composed of at least two sections in telescopic relation so as to extend the length thereof.

16. The apparatus according to claim 14 wherein said tube is composed of at least two sections in telescopic relation so as to extend the length thereof.

17. The apparatus according to claim 14 wherein said flange is provided with a plurality of perforations so as to permit the passage of gas therethrough.

18. A method of charging material to a gravity feed shaft furnace operating at a pressure level different from the surrounding atmosphere, and having a material treatment zone at the lower end thereof, comprising the steps of establishing first and second distinct zones of material to be treated in said furnace, periodically charging said material to the top of the furnace to produce and maintain said first and second distinct zones of said material above said treatment zone, said second zone intermediate to and having uninterrupted communication with the treatment and first zones, said first and second zones each characterized by a cross section which decreases in a gravity flow direction over a portion thereof, maintaining the pressure above the second zone substantially equal to the surrounding atmosphere, and repeating the charging to said furnace so as to maintain said first and second zones of material.

19. In a gravity feed shaft furnace operated at a pressure level different from the surrounding atmosphere, in which said furnace has an opening at the top thereof for receiving a charge of material for treatment therein and is provided with a charging portion, a treatment portion, and a discharge portion axially aligned, the improvement comprising in combination therewith, the provision of at least one group of axially spaced funnels below said treatment portion, said funnels being positioned to provide through communication between said treatment portion and said discharge portion, each said funnel comprising an inverted cone whose base is angled toward the inside of said furnace, whereby each said funnel is directly connected to the inside of the furnace such that the only communication between said portion is by way of said funnels, and that each said funnel is arranged within said furnace to define a large chamber between the furnace wall and said funnel, and means communicating with each of said chambers for controlling the pressure therebetween.

20. The apparatus according to claim 19 including external means connecting said last named chambers for transferring furnace gases from one to another.

21. The apparatus according to claim 19 including a gas conduit just above the uppermost funnel and below the treatment portion.

22. The apparatus according to claim 21 including two axially aligned funnels below said treatment portion.

23. The apparatus according to claim 19 including means for closing the discharge end of the furnace.