US3836131A

US3836131A - Apparatus for cooling a moving bed of solid, gas permeable particles

Info

Publication number: US3836131A
Application number: US00428146A
Authority: US
Inventors: D Beggs
Original assignee: MILDREX CORP
Current assignee: ZURICH BRANCH OF MIDREX INTERNATIONAL BV A NETHERLANDS Corp; Midrex Corp; MILDREX CORP
Priority date: 1973-12-26
Filing date: 1973-12-26
Publication date: 1974-09-17
Anticipated expiration: 1991-09-17
Also published as: BR7410604D0; GB1485429A; KE3098A; NO744603L; BE823546A; SE7416088L; IN139654B; DE2461094B2; NL7416616A; FR2256388B1; ATA1013574A; FR2256388A1; CA1019569A; SE424914B; JPS5320706B2; DE2461094A1; NO139795B; ZA748088B; NO139795C; AT328481B

Abstract

Apparatus is provided for efficiently cooling a moving bed of gas permeable particles descending downwardly through a converging bin. The apparatus includes a support mechanism and an especially configured gas distributor depending downwardly therefrom within the bin. The distributor includes a plurality of tiered gas units in nested relationship with one another and arranged in progressively smaller sizes from the top of the distributor. Each gas unit contains a predetermined number of peripherally spaced gas outlet ports to provide streams of cooling gas under sufficient pressure at each unit to effectively cool the bed of particles.

Description

I451 Sept. 17, 1974 United States Patent [1 1 Beggs APPARATUS FOR COOLING A MOVING BED OF SOLID, GAS PERMEABLE PARTICLES Primary ExaminerGerald A. Dost Attorney, Agent, or Firm-Morgan, Finnegan, Durham & Pine [75] Inventor: Donald Beggs, Toledo, Ohio [57] ABSTRACT Apparatus is provided for efficiently cooling a moving [73] Assignee: Mildrex Corporation, Toledo, Ohio [22] Filed: Dec. 26, 1973 bed of gas permeable particles descending downwardly through a converging bin. The apparatus in- [21] Appl. No.: 428,146

cludes a support mechanism and an especially configured gas distributor depending downwardly therefrom within the bin. The distributor includes a plurality of tiered gas units in nested relationship with one another and arranged in progressively smaller sizes from the top of the distributor. Each gas unit contains a predetermined number of peripherally spaced gas outlet ports to provide streams of cooling gas under sufficient pressure at each unit to effectively cool the bed of particles.

[56] References Cited UNITED STATES PATENTS DeVaney 266/20 Beggs et 266/29 5 Claims, 3 Drawing Figures PAIENIEnsm mm mm 1 0r 2 Ill SCRUB AND COOL APPARATUS FOR COOLING A MOVING BED OF SOLID, GAS PERMEABLE PARTICLES This invention relates generally to an apparatus for cooling gas pervious particles and more particularly to apparatus for cooling abed of such particles flowing downwardly through a converging bin.

The invention is particularly applicable to vertical shaft-type furnaces which directly reduce iron oxideto metallic iron and employ a cooling leg at the lower portion thereof to cool the metallic particles and will thus be described with particular reference thereto. However, it will be appreciated by those skilled in the art that the invention has broader applications and may be applied as a means for cooling any moving bed of gas permeable solid particles.

Vertical shaft furnaces employing counterflow gas principles have been found to be especially suited for heat treatment of pelletized, sized or lump iron ore whether the ore is to be indurated into oxide pellets in an oxide furnace or directly reduced from oxide pellets into metallic iron in a reduction furnace. With both types of furnace it is desirable to cool the pellets before discharging same into the atmosphere. Cooling is especially critical in a direct reduction furnace because the metallic iron (Fe) is in a very active state at its relatively high reduction temperature, typically l,300l ,500F. If the metallic iron pellets are not thoroughly cooled to nominally 125F., the pellets tend to become critically pyrophoric in nature when exposed to air at ambient temperature.

To alleviate this tendency, several cooling arrangements have been employed in the cooling leg portion of such furnaces. Such cooling leg portions may be viewed as discharge bins which converge into a throat section to assure an accurate pellet descent rate through the furnace. One known arrangement simply comprised an upright, hollow cone and cooling gas was directed into the interior thereof. Such arrangement proved generally unsatisfactory because the cooling gas simply could not permeate a sufficent amount of pellets within the bed to adequately cool the bed. Another possible attempt directed at providing sufficient quantities of cooling gas to the bed consisted of applying a number of cooling gas pipes in axially spaced arrangement through the wall of the converging bin. Such arrangements are unsatisfactory because the fastest moving particles at the center of the bin did not receive sufficient amounts of cooling gas which was primarily directed at the slowest moving particles adjacent the converging walls of the bin. In an attempt to overcome such difficulties, it has been known to employ a gas distributor extending downwardly in a converging configuration into the bin and having at axially spaced locations theralong discharge ports through which cooling gas is introduced into the bed. While such apparatus did improve cooling because the cooling gas was introduced adjacent the fastest moving portion of the bed at several locations, the design of the mechanism was such that most of the cooling gas exited at the upper ports of the distributor which correspondingly diminished the effectiveness of the cooling gas at the lower portions of the distributor.

It is thus an object of the subject invention to provide apparatus for cooling a downwardly flowing bed of gas permeable particles in a converging bin by introducing streams of cooling gas adjacent the fastest flowing areas of particles within the bed to provide improved utilization of the cooling gas.

This object along with other features of the subject invention is achieved by providing an especially configured gas distributor within a converging bin through which a bed of solid, gas permeable particles descends. The gas distributor extends downwardly in a converging configuration within the bed and includes a predetermined plurality of gas discharge ports peripherally spaced about the distributor in arrays which are axially spaced along the length thereof. The number of ports and correspondingly the net discharge area associated with each array is sized as a function of 'the array position within the bed to assure, at the least, approximately equal discharge rates of the cooling gas from each discharge port array. This configuration assures that the fastest moving particles at the center of the descending bed are subjected to several streams of cooling gas as they descend past the distributor to assureef- ,fective cooling of the entire bed.

In accordance with another feature of the subject invention, the converging configuration of the gas distributor comprises a plurality of successively smaller sized tiered gas units, one nested within the other. Each unit comprises a continiuous side wall having a top end at which is formed an outwardly extending support flange. The support flange of any given unit is positioned at a given distance within the side wall of the next larger unit immediately thereabove. Thus the bottom end of the side wall of each gas unit comprises a leading edge to define an overhanging lip which surrounds the upper side wall portion of the smaller unit positioned directly below. This leading edge prevents particles from flowing into the gas discharge ports which are spaced closely adjacent the top end of each side wall. In the event that particles do enter the gas distributor, blockage is prevented by an exit provided as an opening in the end wall of the smallest gas unitat the bottom of the distributor. This opening adds to the net discharge area of that gas unit, as such discharge area, without the opening in the end wall, may not be sufficient to establish an adequate stream of cooling gas flow therethrough because of the small size of that unit.

It is thus another object of the subject invention to provide an apparatus for cooling a downwardly flowing bed of gas permeable particles by a plurality of axially spaced discharge gas ports which are shielded in a manner to prevent blockage thereof.

The invention may take physical form in certain parts and arrangement of parts, a preferred embodiment of which will be described in detail herein and illustrated in the accompanying drawings which form a part hereof and wherein:

FIG. 1 is an elevated view, in section, of a vertical shaft furnace employing the cooling apparatus of the subject invention;

FIG. 2 is a larger elevation view, in section, of the cooling apparatus shown in FIG. 1; and

FIG. 3 is a cross-sectional view of the cooling apparatus taken along line 33 of FIG. 2.

Referring now to the drawings wherein the showings are for the purpose of illustrating a preferred embodiment of the invention only and not for the purpose of limiting same, there is shown in FIG. 1 a refractory lined, vertical shaft furnace 10 having a cooling leg section 12 at the bottom thereof and cooling apparatus 13 disposed within cooling leg 12 for cooling a descending bed of gas permeable solid particles 14, herein defined as iron oxide pellets, lumps or sized ore.

Shaft furnace is equipped with a feed hopper 16 at the top thereof which is fed pellets from a source 18. A pellet feed pipe 20 supplies the pellets to the reduction furnace 10 wherein a first stockline 11 is established by the angle of repose of the pellets within the furnace. The bottom of furnace 10 is defined by a throat section 22 which enters into the cooling leg section 12. Spaced above throat section 22 is a bustle and tuyere arrangement 25 which receives hot reducing gas, shown as arrows 26, from a gas inlet pipe 28 which in turn is connnected to a source of reducing gas 29. Reducing gas is introduced radially inwardly into the shaft furnace by a series of wall ports 30 in the bustle and tuyere arrangement 25 and the reducing gas flows vertically upward in counterflow relationship to the descending bed 14. The reacted reducing gas exits from bed 14 at stockline 21 and thence through an off-take pipe 32.

Hot pellets, now reduced into metallic iron by the reducing gas, flow downwardly into cooling leg section 12 through throat 22 to establish a second stockline 33 within cooling leg 12. Cooling leg 12 may be properly viewed as a discharge bin formed in part by an external wall closed about a predetermined periphery to define a coverging configuration. This converging configuration is shown herein as a frusto-conical wall portion 35 which is disposed between a circular throat portion 36 at the bottom of the cooling leg and a larger circular wall portion 37 which defines a pellet retaining area at the top of the cooling leg. The gravitational rate of descent of the bed 14 of pellets within cooling leg 12, furnace 10 and feed hopper 16 is controlled by a suitable belt feeder assembly 38 positioned below cooling leg throat 36 and driven by a motor 39.

Cooling apparatus 13 within cooling leg 12 generally comprises a support mechanism 40 extending through and supported by frusto-conical wall 35 and in turn supporting a gas distributor 42 depending downwardly therefrom and centered on vertical centerline 43 of frusto-conical wall 35 which coincides with the centerline of cooling leg 12 anf furnace 10. A pressurized cooling gas indicated by arrows 45 is directed from distributor 42 into bed 14 in a manner to be explained hereafter and leaves the bed at stockline 33 whereupon it exits from the cooling leg as a relatively hot gas through off-take pipe 46 adjacent stockline 33. The heated or spent cooling gas is then cleansed and cooled in a suitable cooler-scrubber 47 and pressurized in a compressor 49 before being introduced into the cooling apparatus 13 to define a closed loop cooling circuit.

Referring now to FIGS. 2 and 3, support mechanism 40 is shown to comprise a bustle 50 circumferentially extending about frusto-conical wall portion 35 and a central discharge unit 52 positioned at the geometric center of bustle 50. Central discharge unit 52 is supported by four diamond shaped feed pipes 53 which are spaced 90 apart from one another and extend radially inwardly towards the center of bustle 50 and through frusto-conical wall portion 35 which in turn supports the entire support mechanism 40. As best seen in FIG. 2, central discharge unit is defined by a frusto-conical side wall 55 which is open at its bottom end 56 and closed at its top end by a top wall 57. Cooling gas enters bustle 50 through suitable connections (not shown) and exits from the bustle through feed pipes 53 into central discharge unit 52 and exits from the bottom thereof into gas distributor 42.

Generally described, gas distributor 42 extends downwardly into cooling leg 12 in a coverging configuration characterized by a predetermined number of peripherally spaced gas discharge ports 60 arranged in axially spaced arrays 61 along the. distributor length. More particularly, each port array 61 is contained within a gas discharge unit 63. Each discharge port 60 is shown herein to be equally sized and the number of ports which constitutes a given arry 61 defines a net discharge area for that array. It is desirable for optimum cooling results that the net discharge area progressively increase for arrays progressively spaced from the top of gas distributor 42. As a matter of practice, the size of gas distributor 42 may limit the net discharge area of the lowest arrays in which case it is desirable to maintain the area of such arrays as nearly equal to that of the higher arrays as possible.

Structurally, gas discharge units 63, and specifically identified as 63a to 63f with corresponding parts identified by like subscripts where applicable, are nested one within another and extend in a tiered arrangement which becomes progressively smaller in size from the top unit 63a to the bottom gas unit 63f. Each gas unit 63 is shown to comprise a peripherally extending open ended sidewall 67. At the top of each side wall an outwardly extending support flange 68 is formed. Each support flange 68 of each gas unit 63 is positioned within and secured to the side wall 67 of that gas unit immediately thereabove. The side wall 67 of each gas unit thus extends below the support flange 68 of the next lower unit to define an overhanging lip 69 which circumscribes and shrouds the top portion of the side wall 67 of each gas unit. Each overhanging lip 69 thus forms a stockline 70 at eachlgas unit 63 to prevent pellets from clogging distributor 42 by entering outlet ports 60 which importantly are spaced adjacent the top end of each gas outlet side wall 67 and thus shrouded by overhanging lip 69. In the event that some pellets do enter distributor 42, an exit path through the distributor is provided by an opening 72 in an end wall 73 at the bottom of the side wall of the smallest gas unit 63f. Opening 72 is included in the net discharge area for gas unit 63f. Distributor 42 is similarly connected to central discharge unit 52 of support mechanism 40 by the support flange 68a of the largest gas unit, being nested within frusto-conical side wall 55 in a manner similar to which the other gas units 63 are connected to one another.

As thus described, streams of cooling gas will exit from each gas outlet unit 63 to effectively cool the bed 14 of pellets as it passes downwardly by distributor 42. Cooling of the bed occurs because distributor 42 is optimized in design in accordance with geometric considerations involved in passing a moving bed of pellets through a converging area. That is known flow considerations of the pellets establish that the pellets within the bed at the centerline 43 of the cooling leg or bin 12 will be traveling the fastest of all the pellets within the bed, the pellets adjacent exterior frusto-conical wall 35 will have the slowest velocity of the pellets within the bed, and a velocity gradient will occur across the bed by which the speed of the other pellets can be determined accordingly. Because distributor 42 introduces the cooling gas adjacent the fastest moving pellets within the bed, sucy pellets are initially impinged by the gas while high in cooling quality. As the cooling gas permeates radially-outwardly through the bed, it loses its high cooling quality but the slower moving pellets are exposed to the cooling gas for a longer period of 5 time to accordingly compensate for this loss.

It has been found, especially in cooling leg sections of shaft furnaces which directly reduce iron ore into metallic iron, that the introduction of only one stream of cooling gas into the cooling leg section 12 will not sufficiently cool the pellets passing through the cooling leg. Furthermore, it was found that providing a plurality of discharge ports at axially spaced locations along the length of the distributor did not result in optimum cooling of the bed because of static head pressure conditions within the bed. That is, the pressure gradient between stockline 33 and point of discharge into the cooling stream is a minimum at the uppermost gas unit 63a and a disproportionate amount of cooling gas thus tends to exit from the uppermost gas unit which also establishes the shortest flow path through the bed. In accordance with the subject invention, the pressure gradient in effect is neutralized throughout the bed by the number of gas discharge ports 60 provided within each array 61 in distributor 42. More particularly, it has been found that if the net area of all discharge ports for each gas unit were at least made equal and preferably progressively larger for the smaller gas units, sufficient quantities of cooling gas would be supplied at each gas unit to effectively cool the bed of pellets as same passes by distributor 42. The distributor 42 is thus characterized as being positioned along its entire length closely adjacent to the fastest moving particles within the descending bed and having pluralities of peripherally spaced discharge ports 60 arranged in axially spaced arrays 62 with each array having a net discharge area defined by its ports which is sized with respect to the other array areas to produce sufficient quantities of gas leaving each array for effective cooling of the particle bed.

The invention has been described with reference to a preferred embodiment. Obviously, modifications and alterations will occur to others, upon reading and understanding the specification. It is my intention to include all such modifications and alterations insofar as they come within the scope of the present invention.

The cooling mechanism has been shown applied to the cooling leg section of a shaft furnace for illustrative purposes only. It should be clear from the above description that the cooling mechanism may be applied to any moving bed of gas permeable solid particles heated by means other than a shaft furnace.

It is thus the essence of the subject invention to provide in a converging discharge bin through which a moving bed of particles pass, a cooling apparatus which utilizes a plurality of discharge areas sized in relation to one another to assure a plurality of effective cooling gas streams exiting therefrom to efficiently cool the moving bed of particles in the discharge bin. Having thus defined my invention, 1 claim: 1. Apparatus for cooling a gas permeable bed of descending solid particles comprising:

an axially-extending wall portion, closed about a predetermined periphery to define a hollow body converging towards its bottom end; means for introducing said particles into said body and withdrawing same from the bottom thereof; cooling means within said body for introducing a cooling gas under pressure in counterflow relationship to said descending bed, said cooling means including: a. support means extending within said wall portion and carrying said cooling gas, and b. a gas distributor secured to said support means and receiving said cooling gas therefrom, said distributor extending in a converging configuration downwardly into said body and having a predetermined number of peripherally spaced gas discharge ports arranged in axially spaced arrays along its length whereby said distributor introduces said cooling gas to said particles at predetermined flows along its length. 2. The apparatus according to claim 1 wherein: the total area of said discharge ports in any given array is sized as a function of bed pressure adjacent said given array. 3. Apparatus according to claim 2 wherein: said downwardly extending converging configuration of said distributor is defined by a plurality of successively smaller sized tiered gas discharge units, each discharge unit nested within an adjacent gas unit spaced vertically thereabove and each unit containing an array of said predetermined number of peripherally spaced gas discharge ports. 4. The apparatus of claim 3 wherein: each gas unit includes a side wall having a top and bottom end, a support flange extending outwardly from said top end and said plurality of discharge ports positioned adjacent said top end; and said support flange of each unit positioned within said side wall of an adjacent unit, each side wall of each unit extending downwardly beyond each support flange of an adjacent unit thus positioned to define an overhanging lip shrouding said ports of a gas unit immediately therebelow. 5. The apparatus of claim 4 wherein: the smallest in size gas unit has an end wall extending from said bottom of said side wall thereof, said bottom wall having a gas discharge port extending therethrough.

Claims

1. Apparatus for cooling a gas permeable bed of descending solid particles comprising: an axially-extending wall portion, closed about a predetermined periphery to define a hollow body converging towards its bottom end; means for introducing said particles into said body and withdrawing same from the bottom thereof; cooling means within said body for introducing a cooling gas under pressure in counterflow relationship to said descending bed, said cooling means including: a. support means extending within said wall portion and carrying said cooling gas, and b. a gas distributor secured to said support means and receiving said cooling gas therefrom, said distributor extending in a converging configuration downwardly into said body and having a predetermined number of peripherally spaced gas discharge ports arranged in axially spaced arrays along its length whereby said distributor introduces said cooling gas to said particles at predetermined flows along its length.

2. The apparatus according to claim 1 wherein: the total area of said discharge ports in any given array is sized as a function of bed pressure adjacent said given array.

3. Apparatus according to claim 2 wherein: said downwardly extending converging configuration of said distributor is defined by a plurality of successively smaller sized tiered gas discharge units, each discharge unit nested within an adjacent gas unit spaced vertically thereabove and each unit containing an array of said predetermined number of peripherally spaced gas discharge ports.

4. The apparatus of claim 3 wherein: each gas unit includes a side waLl having a top and bottom end, a support flange extending outwardly from said top end and said plurality of discharge ports positioned adjacent said top end; and said support flange of each unit positioned within said side wall of an adjacent unit, each side wall of each unit extending downwardly beyond each support flange of an adjacent unit thus positioned to define an overhanging lip shrouding said ports of a gas unit immediately therebelow.

5. The apparatus of claim 4 wherein: the smallest in size gas unit has an end wall extending from said bottom of said side wall thereof, said bottom wall having a gas discharge port extending therethrough.