US3589691A

US3589691A - Treatment of material on a moving support

Info

Publication number: US3589691A
Application number: US765455A
Authority: US
Inventors: Melvin J Greaves
Original assignee: Arthur G McKee and Co
Current assignee: Arthur G McKee and Co
Priority date: 1968-10-07
Filing date: 1968-10-07
Publication date: 1971-06-29
Anticipated expiration: 1988-06-29
Also published as: OA03144A; FR2020059A1; ZM14969A1; GB1271290A; BR6913079D0; DE1950527A1; BE739934A

Abstract

Apparatus and method for treating particulate material, such as ore agglomerates, on a traveling support by treating gases that pass through the bed of particulate material on the support and through the support an even number of times that provides important benefits. Particular advantages are provided in the application of the invention to a circular grate in which a permeable grate travels in a circular path through various treating zones in which treating gases are passed through the grate and bed of particulate material on the grate, since higher pressure gases can bed used on only one side of the grate. This makes possible the use of a high-pressure resistant grate seal, such as a liquid seal, on only such side of the grate and lower pressure resistant seal on the other side of the grate. This method is inherently more thermally efficient than conventional methods used for pelletizing iron ore and solves the problem of inadequate cooling that is troubling many plants now in operation.

Description

United States Patent [72] Inventor Melvin J. Greaves Cleveland, Ohio [21] Appl. No. 765,455 [22] Filed Oct. 7, 1968 [45] Patented June 29, 1971 {73] Assignee Arthur G. McKee & Company Cleveland, Ohio [54] TREATMENT OF MATERIAL ON A MOVING SUPPORT 28 Claims, 18 Drawing Figs.

[52] US. Cl 263/28, 266/21 [51] Int. Cl F27b 9/00, F 27b 21/02 [50] Field of Search 263/28; 266/21; 75/5 [56] References Cited UNITED STATES PATENTS 3,005,699 10/1961 Erck et al. 266/21 3,214,264 10/1965 Bogdandy 266/21 3,302,936 2/1967 Ban 3,393,904 7/1968 Taylor t.

Primary Examiner-John J. Camby AtmrneyBosworth, Sessions, Herrstrom and Cain ABSTRACT: Apparatus and method for treating particulate material, such as ore agglomerates, on a traveling support by treating gases that pass through the bed of particulate material on the support and through the support an even number of times that provides important benefits. Particular advantages are provided in the application of the invention to a circular grate in which a permeable grate travels in a circular path through various treating zones in which treating gases are passed through the grate and bed of particulate material on the grate, since higher pressure gases can bed used on only one side of the grate. This makes possible the use of a highpressure resistant grate seal, such as a liquid seal, on only such side of the grate and lower pressure resistant seal on the other side of the grate. This method is inherently more thermally efficient than conventional methods used for pelletizing iron ore and solves the problem of inadequate cooling that is troubling many plants now in operation.

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Jmhomfieam ATTORNEYS PATENTED JUN29 1971 sum 10 or 1o m m m m TM 60 mEg aT m m u m V L WB m TREATMENT OF MATERIAL ON A MOVING SUPPORT BACKGROUND OF THE INVENTION This invention relates to apparatus and method for treating particulate material on a moving support, and more particularly to the treatment of particulate material on a moving support by passing treating gases through a bed of material on the support and through the support in several passes.

While the invention may be employed in various types of treating apparatus, and in connection with the treatment of various types of particulate materials, it will be discussed primarily'in connection with the treatment on a horizontal moving grate of particulate agglomerated iron oxide material to form heat hardened pellets having sufficient strength and hardness to permit them to be handled, shipped, stored and charged into a blast furnace or other smelting apparatus.

In the production of such heat hardened iron oxide pellets, finely divided iron oxide or beneficiated ore concentrate, flue dust, or other iron-bearing material, either alone or with particles of solid fuel, flux materials or other substances, are mixed together with water to form a moist mudlike mass that is then formed into green balls by suitable known means. When the balls are generally spherical as is common practice, to as great an extent as possible they are of uniform desired size, generally about one-fourth inch to about 1 inch in diameter and preferably between about three-eighths inch and about one-half inch in diameter. Pelletizing involves heating these balls under temperature and other conditions to dry and harden them, so that they may thereafter be handled, shipped, stored and charged into smelting furnaces by conventional apparatus. Horizontal traveling grate-pelletizing apparatuses have been widely used for pelletizing the green balls to form heat hardened pellets. Other apparatus for pressure forming pellets with or without water are also well known and widely utilized.

Horizontal grate apparatuses that have been commercially used in general have been of the straight grate type. Recently it has been proposed to use pelletizing apparatus in which the grate travels in a generally circular horizontal path.

In both straight and circular pelletizing apparatuses, there is a moving gas-permeable grate which carries the particulate material from a charging location, through several treating zones, to a discharging location. There is gas enclosing means above and below the grate by which gases are caused to pass through a bed of particulate material on the grate and through the grate to impart to the material desired treatments such as drying, heat hardening and cooling. ln horizontal grate apparatuses it is necessary to provide adequate seals between the moving grate and the gas enclosures above and below the grate to prevent undesired leakage of gas out of or into enclosures. It is difficult to provide satisfactory seals at these locations, particularly if there are substantial pressure differentials. Furthermore, in order to move the desired large volumes of gas through the various treating zones along the grate for high volume production, it has been necessary to use large fans which usually must be made of heat resistant materials to withstand the hot gas temperatures. These fans are expensive, require considerable power for operation, and also are susceptible to deterioration and high maintenance costs.

When, as is desired to conserve heat, hot gases are taken from one zone on a grate, removed from the pelletizing machine and then reintroduced to another zone after passing through a fan, as is common practice, it has heretofore been necessary to provide long lengths of expensive duct work that must resist heat and be adequately heat insulated to reduce heat losses to a feasible minimum. Provision for expansion in these large ducts is both expensive and is limited by the practical size of the machine that can be built.

SUMMARY OF THE INVENTION Apparatus and method are provided according to the present invention that may, if desired, be designed to overcome all of the above disadvantages, as well as others. In the apparatus and method of the invention treating gas such as air flows through the grate of a horizontal grate apparatus four or a greater even number of times. Thus, in a four pass flow, which is preferable, the gas passes downwardly through the bed of particulate materials and grate in a first downdraft cooling zone, upwardly through the grate and bed thereon in a second updraft cooling zone, downwardly through the grate in a downdraft indurating zone, and then upwardly through the grate in an updraft drying zone, after which it may pass to the waste stacks. Therefore, it is possible to have on one side of the grate, preferably the upper side, all higher gas pressures that move the gas through the grate and bed of material on the grate. Consequently, it is possible to have seals suitable for resisting escape of higher pressure gases on only one side such as the upper side of the grate.

Thus, for example, if the apparatus is a circular grate apparatus arranged so that the higher gas pressure is on the upper side of the grate, liquid seals which are more capable of withstanding high gas pressures with minimum leakage need only be supplied to seal the upper side of the grate to the gas enclosing means above the grate. Mechanical seals then may be used to seal the lower side of the grate to the gas enclosing means below the grate. Moreover, it is possible to eliminate most, and if desired all, of the lengthy ducts, insulated or otherwise, heretofore required to transport hot gases from one treating zone to another, since essentially all gases can pass to and through the heating zones along the grate by being passed through the enclosures above and below the grate.

The invention thus reduces the problems of sealing referred to above, makes possible the reduction in the amount of extraneous ducts and the number of fans necessary to move gas, and makes possible lower cost and more efficient apparatus.

The above and other features of the invention provide the above and other advantages particularly effectively in circular grate pelletizing apparatuses, and therefore, the invention will hereafter be disclosed in connection with such type of apparatus but the features of this invention can also be utilized to advantage in straight grate apparatuses.

DESCRIPTION OF DRAWINGS The above and other advantages and features of the invention are apparent from the following description of several preferred embodiments of the invention in connection with the accompanying drawings in which:

FIG. 1 is a perspective of one illustration of the circular grate-pelletizing apparatus embodying the invention;

FIG. 2 is a somewhat diagrammatic plan of the apparatus of FIG. 1;

FIG. 3 is a diagrammatic view of the apparatus grate as extended, illustrating the grate, the enclosures above and below the grate, and path of gas flow in the apparatus of FIGS. 1 and FIG. 41 is another diagrammatic view of the grate as extended, illustrating typical temperatures and volume rates of gas flow at various zones along the grate in the apparatus of FIGS. l-3, with the numbers referring to flow rates in terms of standard conditions of temperature and pressure;

FIG. Sis a section along line 5-5 of FIG. 2;

FIG. 6 is a section along line 6-6 of FIG. 2;

FIG. 7 is an enlargement at the lower portion of FIG. 6, showing the grate sealed to the enclosures above and below the grate to prevent passage of gas;

FIG. 8' is a detail to a larger scale of one form of sealing means that may be used between the lower portion of the grate and the gas-enclosing means below the grate;

FIG. 9 is a plan of portions of the grate and adjacent apparatus, particularly showing the ball-feeding and pelletdischarging locations on the grate;

FIG. is a somewhat diagrammatic side elevation of the dumping portion of the grate of the apparatus in FIG. 1, illustrating how the center sections of the grate are caused to dump, this figure generally corresponding to line 10-I0 of FIG. 9;

FIG. 11 is a detail of one of the sealing means below the grate;

FIG, 12 is a view ofFIG. 11 from line I2-12 of FIG. 11;

FIG. 13 is a cross-sectional detail of one of the transverse sealing means above the grate between two zones of the hood enclosure above the grate;

FIG. 14 is a view of the apparatus in FIG. 13 from line l4l4 of FIG. 13;

FIG. is a cross section transverse to the grate of the sealing means at the location where the grate passes into the drying hood;

FIG. 16 is a view of the sealing means of FIG. 15 from line 16-16 ofFIG. 15;

FIG. 17 is a sectional view along the direction of travel of the grate ofthe seal between the bed of hot pellets on the grate and the end of the cooling hood where the pellets leave the cooling hood; and

FIG. 18 is a cross-sectional elevation of another embodiment of the invention in which the sealing means above and below the grate both are liquid-sealing means, the figure being otherwise generally similar to FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The apparatus of FIGS. 1--l8 comprises (FIGS. 1, 2 and 9) a grate 1 that is circular in plan and designed to travel about a vertical axis A in a circular path in the direction indicated by the arrows. This grate 1 comprises a gas permeable hearth 2 and upstanding gas

impermeable sidewalls

3 and 4. The

sidewalls

3 and 4 extend entirely around the outer and inner circumferences of the grate, and with the hearth, define a grate of generally channel-shaped cross section.

The grate is supported by a rigid frame 5 rotatable about axis A and comprising a member 6 that extends around the outer circumference of the apparatus adjacent the outer sidewalls 3 of the grate and a member 7 that extends around the inner circumference of the apparatus adjacent the inner sidewall 4 ofthe grate. The lower portion of member 6 carries a circular rail 8 that rides on and is supported by rotatable rollers 9 mounted in supports 11 spaced around the outer periphery of the apparatus. Lower portion of member 7 carries a circular rail 12 that rides on rollers 13 mounted on supports 14 spaced around the inner periphery of the apparatus. At least some of the outer rollers 9 are driven by shafts 15 through speed reducers 16 from motors 17 (FIGS. I and 6).

Supports 11 and 14 are carried by horizontal members 18 of a stationary supporting frame 19 having

vertical columns

21 and 22. Suitable green balls B, such as those previously mentioned, are deposited on the grate by charging means 23 (FIGS. I and 9) at a charging location C, and travel on the grate around the circumference of the apparatus in the direction indicated by the arrows in FIG. 1 and other figures while being treated to heat harden them to pellets P, to a discharging location D closely adjacent to and upstream of charging location C, where the resulting pellets are discharged from the grate by means to be described later.

Supported by stationary frame 19 over grate I are stationa

ry hoods

24, 25 and 26 (FIGS. 1 and 2) interconnected by intermediate portion 27 between

hoods

24 and 25 and intermediate portion 28 between

hoods

24 and 25. At these intermediate hood portions are located sealing means 29 and 30 (FIG. 3) to be described later, that separate the interiors of adjacent hoods so that little, if any, gas can pass above the layer of pellets from one hood into an adjacent hood. Conventional sealing means 20 is located at the entrance end of hood 24 to prevent passage of gas above the layer of green balls entering that hood, and sealing means 33, described later, is

located at the discharge end of hood 26 to prevent passage of gas above the bed of hot pellets leaving that hood.

A stationary wind box main 32 extends directly under the grate throughout the portion of the circumference of the apparatus covered by the hoods, being closed at its ends 34 and 35 and subdivided by

partitions

36, 37 and 33 and their respective sealing means 39, 40 and 41, to be described later, into

wind box sections

42, 43, 44 and 45. These partitions and sealing means prevent any substantial amount of gas from passing immediately below the grate from one section of main 32 to an adjacent section.

Partitions

36 and 33 and their sealing means 39 and 41 are located generally beneath sealing means 29 and 30. The sealing means and partitions below the grate with the sealing means 29 and 30 above the grate and the

intermediate portions

27 and 28 above the grate, subdivide the hood and wind box portions of the apparatus between which the grate passes into various treating zones.

Hood 24 and its associated wind box section 42 define a drying zone 46 in which the green balls are subjected to drying and preheating by hot gases passing updraft through the layer of balls on the grate while they are carried through this zone by the moving circular grate. Section 2511 of hood 25 extending between sealing means 29 and intermediate portion 27 to wind box partition 37 and its sealing means 40, and its associated wind box section 43, define an indurating zone 47 in which the preheated and predried green balls are subjected to high temperatures to indurate or heat harden them by means of oxide conversions, recrystallizations and grain growth in known manner by hot gases passing downdraft through the layer of balls on the grate as it travels through the zone 47. Hood section 25b constituting the remainder of hood 25 and its associated wind box section 44 define a zone 48 in which the hot heat hardened pellets are preliminarily cooled by a passage of air updraft through the layer of hot pellets on the grate traveling through the zone. Hood section 26 and its wind box section 45 define a final cooling zone 49 through which the pellets are carried by the traveling grate and from which they are discharged under sealing means 33.

As is apparent from FIG. 7, the wind box main sections are each formed of a metal shell 51 and an inner heat resistant, heat insulating refractory lining 52. At spaced locations the wind box main has similarly constructed downwardly depending portions 53 for accumulating dust from the gases and discharging it through a trap 54 into a flume 55 from which it may be removed by a water stream.

The

hood portions

24 and 26 have the cross-sectional shape shown in FIG. 5, Each includes an outer metal shell lined with heat-resistant, heat insulating refractory material in the usual manner and suspended from supporting frame 19. The lower edges of the hood sidewalls closely approach the upper edges of the sidewalls of the grate 1.

The cross-sectional shape of hood portion 25 is shown in FIG. 6. This hood portion has sidewalls 56 the lower edges of which closely approach the upper edges of the grate sidewalls. The hood itself has an outer metal shell 60 and is lined with a layer of heat insulating, heat-resistant refractory material 57. The hood itselfis supported from frame 19.

Each side of hood portion 25 has several fuel burners 58, such as burners capable of burning gas or oil supplied with fuel by conventional means (not shown). Each of these burners is also supplied with primary combustion air by a branch conduit 59 communicating with one of the

conduits

61 and 62 that communicate with the cooling zone 49 through conduit 31. These conduits are preferably insulated to conserve the heat of the hot air emanating from that zone. If desired, tempering or cooling air at ambient temperatures can also be introduced into each

conduit

61 and 62 by a cross duct 50 controlled by valve 70 shown in FIGS. 2 and 3.

FIGS. 1, 2, 3, and 4 depict the means for handling gases and the pattern of gas flow into the apparatus of FIGS. 1-18. Ambient air is initially introduced into the system and apparatus into the hood 26 of cooling zone 49 through conduit 63 by conventional fan apparatus 64 and maintains substantial superatmospheric pressure of air in hood 26, for example about 20 inches of water at standard conditions. The air passes downwardly through the layer of hot pellets on the grate and the grate into the wind box section 45 which is maintained at a lower but substantial superatmospheric pressure, as about to inches of water at standard conditions. From section 45 the heated air, for example, at a temperature between about 100 C. and about 500 C. passes laterally under or through partition 38 into wind box section 44 and then upwardly through the grate and bed of hot pellets on the grate in the zone 48 into the hood portion 25b, in which it is preferably at slightly superatmospheric pressure. This heated air passes laterally from hood portion 25b to hood portion 25a in which it is preferably at about atmospheric pressure, and then downwardly through the bed of green balls on the grate that are being heat hardened into pellets by added heat supplied by the burners S8 in the induration zone 47.

In zone 47 the heated gas above the grate, which also contains products of combustion and is at temperatures of between about l,l00 C. and l,400 C. passes downwardly through the balls on the grate that are being heat hardened, into the wind box section 43 from which it passes laterally under or through partition 36 into wind box section 42 and thence upwardly through the grate and the green balls on the grate in the drying zone 46 into the hood 24. The hood exhaust fan 65 aids in exhausting the cooled gases and disposing of it as by passing it to a stack. A subatmospheric pressure of about minus 10 inches of water at standard conditions and a gas temperature of about 80 C. to 400 C. and preferably about 150 C. may be maintained in hood 24.

Fuel mixed with primary combustion air at a suitable temperature and supplied as indicated above, is burned by burners 58 in a conventional manner .in secondary combustion air, that is, the air supplied through the grate and its bed of pellets in zone 48, to provide the desired indurating temperatures between 1,100 C. and l,400 C. in zone 47. As the gas at these temperatures passes downwardly through the layer of balls on the grate in zone 47, they cause oxide conversions, recrystallization and grain growth that produces the heat hardened pellets that results in formation of pellets of the desired hardness and other characteristics.

From the illustrated gas flow system, it is thus apparent that only two

fans

64 and 65 are necessary to cause the abovedescribed flow of gases through the apparatus and four times through the grate and the bed of balls or pellets on the grate. The greatest superatmospheric pressure is in cooling hood 26 into which ambient air is forced by fan 64. The superatmospheric pressure in the direction of gas flow becomes progressively less and may even be at subatmospheric pressure in drying hood 24.

Moreover, the gas flows counterflow to the direction of travel of the green balls and resultant pellets on the grate.

The ambient air in the illustrated apparatus, being introduced into it initially contacts the hot pellets and becomes heated, the heated gas then carries its heat upstream of the paths of travel of the green balls and pellets where part of it is used for cooling, part for providing heated secondary combustion air, and part for indurating the green balls.

Since in the apparatus, FIGS. 1l-1l8 the maximum pressure is above the grate, it is possible, therefore, to have the seals providing greater gas pressure resistance only above the grate. Therefore, such apparatus embodies water-sealing means 68 and 69 (FIGS. 6, 7 and 8) at the sides of the grate for preventing leakage of gases into and out of the junctures of the grate and the hoods above the grate; and mechanical sealing means 711 and 72 at the sides of the grate for preventing leakage of gases into and out of the junctures of the grate and the wind box sections below the grate.

The water-sealing means for preventing passage of gases between the grate and hood means comprise annular channel shaped rotatable troughs 73 and 74 (FIG. 7) fixed in gas leakproof relation immediately adjacent the outer and

inner walls

3 and 4 of the grate 1 and carried by the

frame members

6 and 7 of the rotatable frame 5 that carries the grate. These troughs both carry water circulated by suitable means to prevent boiling. Shield walls 75 and 76 extend downwardly in gastight relation from the lower edge portions of the sidewalls of the hoods into the water in the troughs. Preferably these walls extend continuously throughout the length of all hoods from the beginning of the drying section to the end of the cooling section, preferably being connected at the ends of the hoods to transverse baffle members that prevent the escape of gases past the ends of the hoods over the water surface. The walls preferably have transverse members 77 to inhibit deposit of sediment, terminating in removable trays 78 to permit ready removal of deposited sediment. Therefore, when grate 1 rotates about its axis A the

troughs

73 and 74 travel with it while walls 75 and 76 remain stationary and by their projection into the water effectively seal the junctures of the grates and hoods against the escape of hot gases despite substantial superatmospheric gas pressures in the hood.

The mechanical sealing means 71 and 72 located to seal the grate to the wind box sections below the grate are adequate for the lower gas pressures that exist below the grate. The sealing means illustrated to advantage in FIGS. 7 and 8 is of the type disclosed and claimed in Grabau et al. U.S. Pat. No. 2,789,809. In the illustrated mechanical sealing means, a slide member 81, arcuate in plan is fixed to the upper portion of each side of the wind box main 32 by a fixed support member 80, and extends throughout the length of the main 32 at each side of the grate. Seal bar members 82, each forming a segment of an arc of suitable diameter, are supported by pins 83 spaced circumferentially and mounted in members 84 fixed to the lower depending portions of the associated

sidewall

3 or 4 of the grate. These pins 83 project into vertically elongated slots 85 in the seal bars 82. Thus each seal bar member 82 will move in a circular path along with the grate and may have limited vertical movement relative thereto to compensate for slight irregularities in the slide member 81. The bottom outwardly upwardly inclined sealing surface 86 of each seal bar 82 is adapted to engage and slide upon the correspondingly inclined upper surface 87 of the associated slide member 81 to form a substantially gastight seal between the grate and the wind box main as the grate moves in its circular path. The inclinations of the sealing surfaces 86 and 87 tend to cause the inner side face 88 of the seal bars 82 to remain in close engagement with the adjacent outer face 89 of the member 84 to maintain a substantially gastight relationship. The mechanical sealing means 71 and 72 may have the abutting

surfaces

86 and 87 constructed to operate dry or they may be lubricated with conventional lubricants, such as water, oil, grease, molybdenum disulfide, silicones or graphite.

The charging means for depositing green balls B on the moving grate 11 may be any one of various types, such as that diagrammatically shown in FIGS. 11 and 9 corresponding to FIG. 1 of US. Pat. No, 3,160,402 and comprising a conveyor 91 having a continuously traveling upper run that carries green balls toward the grate from a suitable source such as a conventional balling drum or disc, and discharges the balls onto a conveyor 92 comprising positively rotating ball-carrying rollers 93. The lengths of the rollers uniformly vary across the width of the grate, being related in proportion to the circumference of the grate beneath each dumping edge of each roller so a bed of green balls of essentially uniform thickness is deposited across the width of the grate between its

sidewalls

3 and 4 despite the increasing length of circumferences from the inner to the outer edges ofthe grate.

The grate of the apparatus of FIGS. 1-18 also includes a hearth 2 in which only central portions or segments 94 (FIGS. 7, 9 and 10) tilt at the discharge location D to discharge heathardened pellets. Narrow shelf portions 95 on each wide of central portions 94 do not dump but carry the pellets in side layers 96 adjacent the sidewalls past the discharge location to a spreading means such as a plow 97 (FIG. 9) that spreads the pellets P from the side layers into a hearth layer 98 on which the green balls B are deposited by the charging means. Even if the pellets at the side layers may not have been as completely treated as the pellets in the central portion of the grate due to side layer effects, they are twice treated as they pass twice through the zones of the pelletizing machine, once as side layers and once as hearth layers; consequently the pellets discharged from the grate have highly uniform characteristics and hence are of exceptionally high quality.

The grate structure of FIGS. 1-18 is shown in more detail in FIGS. 6, 7, and 18. Each of the

sidewalls

3 and 4 is preferably formed of heat resistant lining material having heat insulating properties such as ceramic or refractory material fixed to supporting metal sheeting which as shown can form a wall of one of the

troughs

73 or 74 mounted on the

frame members

6 and 7. The side shelf portions 95 and dumping portions 94 of the hearth 2 are supported by water cooled tubular rotatable shafts 99 and water-cooled tubular shafts 101 stationary relative to rotatable frame 5. Both of these shafts are supported by the

frame members

6 and 7 of frame 5, the former by bearings 102.

The side shelf portions 95 comprise (FIGS. 7 and 18) spaced bar members 103 that, in known manner, are spaced sufficiently apart to permit adequate passage of gases but are sufficiently close together to prevent green balls or pellets from dropping therethrough. Similarly the dumping portions 94 each comprises (FIG. 7) spaced bar members 104 that sup port the green balls and pellets and are in known manner spaced sufficiently far apart to permit adequate passage of gases therebetween but sufficiently close together to prevent dropping of the balls or pellets. Each dumping portion 94 is rigidly fixed to rotatable shaft 99 and as shown in FIG. 10 it can be tilted by partial rotation of the shaft. Each dumping portion also is adapted to rest on one of the shafts 101 that is stationary relative to the rotatable frame 5.

Each shaft 99 is caused partially to rotate as required to tilt to dump pellets thereon by an arm 105 (FIGS. 6, 7, 10 and 18) rigidly clamped at one end to the shaft 99 and at its other end carrying a roller 106 that engages and travels in a track 107 fixed to the stationary frame 19 adjacent the discharge location D of the grate. The track 107 is shaped so that the traveling frame 94 rotates and carries the arms 105 with it. The arms 105 successively engage the track 107 and cause their as sociated shafts 99 partially to rotate on their axes and successively tilt the movable hearth portions 94 to cause the pellets on the portions 94 to dump into the discharge chute 108 that extends under the entire length and width through which the hearth portions 94 tilt and that carries the pellets to conveyor 109 (FIG. 1). Preferably as shown in FIG. 10, the portions 94 of the hearth tilt away from their direction of movement so that the pellet-carrying top surfaces face opposite to the direction of movement. Such reverse tilting of portions 94 as well as the location and extent of chute 108 insure that all pellets discharged at discharge location D will pass into the chute The water-cooling system for each of

shafts

99 and 101 may be understood by reference to FIGS. 6 and 18 showing shaft 99 only. There is a trough 111 separate from trough 73 supported from frame member 6 at the outer side of rotatable frame 5. This trough 111 extends entirely around the apparatus and is supplied and kept filled with water by suitable conventional means (not shown). A flexible tube 112 connects the lower portion of this trough with the interior of the rotatable shaft 99, outside of the associated bearing 102. Another flexible tube 113 is connected to the outer end of shaft 99 and discharges into the lower trough 152. The water thus flows by gravity from trough 111 through tube 112 to and through shaft 99 and through tube 113 to lower trough 152. The water-cooling system for each nonrotatable shaft 101 is similar.

Referring now to FIGS. 11 and 12 wherein one of the gas collector wind box seals 40 is shown, a plate 114 is positioned on partition 37 which separates wind box section 43 from wind box section 44. The plate 114, made up of an upper portion of refractory material 114a supported by a lower portion l14b of heat resistant metal, is positioned under the traveling grate 1 and extends completely across the wind box main 32, and is fixed in gastight relation to the sides of the wind box main 32, as shown in FIG. 125 The front edge 115 and rear edge 116 of the seal 40 slope downwardly. Each of the rotatable shafts 99 has a protective casting 117, and each nonrotatable shaft 101 has a protective casting 118, which completely surrounds

shafts

99 and 101. A sealing vane 119 is secured to each casting 117 and 118 and extends downwardly therefrom. Vane 119 is flexible and carries a flange 121 at its end remote from

castings

117 and 118. The flange is urged into gastight, sealing engagement by the flexibility of the same, and slides across the upper surface of plate 114. Sealing vanes 119 extend essentially completely across plate 114. Only seal 40 has been described; it should be understood that

seals

39 and 41 and the seals under the entrance and exit of the grate from the hoods may be similarly constructed.

The sealing means 29 of the illustrated apparatus at the intermediate portion 27 between

hoods

24 and 25 is more clearly shown in FIG. 13. Access to the interior of the hood 25 is provided by a door 123 suspended from frame 19 by support members 124. Members 124 are secured at their upper ends to trolleys 125 attach ed to the frame 19 in order that the door 123 may be moved laterally as shown in FIG. 14, thereby providing access to the interior of the hood 25 for inspection or repairs. The seal 29 is carried by two I-beams 126 fixed to the intermediate portion 27 and extending above and completely across the hearth 2 of the traveling grate 1 of the apparatus. The supports 126 carry I-beams 127 extending in the direction of travel of the pellets P on the hearth of the grate of this apparatus. Secured to each I-beam 127 are suspended baffle members 128 and spacer members 129 of refractory material. The I-beams 127 and baffle members 128 are sufficient in number to cause the bafile and spacer members to extend substantially completely across the hearth of the grate 1 from sidewall 3 to sidewall 4, as shown in FIG. 14. The baffle members thus define spaced baffles 131 the lower ends of which are closely adjacent the top of the traveling bed of pellets P, so that little or no gas will escape across the top of the pellets from h0od 25 to hood 24. Several rows of baffles 128 are provided to aid in the sealing action by providing a tortuous path through which the gases would be required to pass.

The sealing means 30 between

hoods

25 and 26 may be identical to sealing means 29.

The sealing means 20 of the illustrated apparatus at the en trance of the grate into the drying hood 24 is shown in FIGS. 15 and 16. The sealing means 20 is supported by

crossmembers

132 and 133 secured by conventional means to the metal shell of hood 24. TI-

Iese crossmembers

132 and 133 extend substantially across the grate 1. A plurality of supporting rods 134 depend from

crossmembers

132 and 133 and support adjustably as to height the three overlapping

sections

135, 136 and 137 of the means 20. Each

section

135, 136 and 137 comprises a flat top plate 138 and a plurality of depending baffle vanes 139. The baffle vanes 139 extend downwardly from the top plate 138 to locations just above the bed of green balls B moving thereunder. The three sections of the seal are con structed and arranged so their baffle vanes extend substantially completely across the hearth 2 and are arranged to present a tortuous path through which the gas or air would be required to pass essentially to prevent passage of ambient air into the hood 24, or escape of hot gases from the hood 24.

Sealing means 33 that seals the exit end of the hood 26 is shown in FIG. 17. It comprises a rectangular cross-sectional body 140 of cast refractory material that extends essentially completely across the grate 1. It is pivotally supported from one of its corners from the outer shell 51 of hood 26 by support 141 so the outer surface 142 of the body 140 rests on the top of the bed of pellets P exiting from hood 26. The body 140 thus essentially seals the hood 26 against the escape of hot gas to the ambient air and entrance of ambient air into the hood 26. The body 140 is preferably made up of several blocks 144 of cast refractory material, each having one or more holes 145, which are clamped to a backing plate 146 by bolts 147. The backing plate 146 is provided at both its longitudinal edges 149 with a U-shaped bracket 148 that extends the full length of the body 140. The bracket 148 above one edge of plate 146 rests on support 141. Since the body 140 is pivotally mounted on the support 141, the body is movable vertically so its outer corner portion 142 always contacts the top of the bed of pellets P as they exit from the hood 26. The hard pellets P contacting the surface 142 may, after substantial periods of time, wear away the portion 142 until the body 140 assumes the position shown in dotted lines in FIG. 17. As the wear progresses to a point that the lower portion of the body 140 is no longer effective to maintain the desired gastight seal, the body 140 is removed from support 141 and turned over so the other bracket 148 will rest on the support 141 and the upper portion of the body 140 will then contact the top surface of the pellets P to form the desired seal.

An alternative means for sealing the sides of the wind box main 32 to the grate against escape or entry of gases is shown in FIG. 18. Two

stationary troughs

151 and 152 are located on the inside and outside borders of the wind box main 32 in gasleakproof relation; they extend entirely around the circumference of the apparatus. Water is maintained in each of the

troughs

151 and 152 to a suitable level. Downwardly extending

shield walls

153 and 154 are fixed in gastight relation to the bottoms of

upper troughs

73 and 74 and the

shield walls

153 and 154 have their lower ends immersed in the water in their associated

troughs

151 and 152; these

walls

153 and 154 therefore move with the grate 1.

Walls

153 and 154 have traverse members 155 which inhibit deposition of sediment in

troughs

151 and 152. All other portions of the apparatus may be as previously described. Apparatus like that of FIG. 18 has particular benefit when the gas pressures below the grate are substantial.

The processes and apparatus of this invention make possible important and unique advantages in providing increased thermal efficiency and more effective and uniform treatment of particulate material on a horizontal grate. The essentially gastight sealing means comprising water seals to seal the grate to the hoods above the grate and mechanical seals to seal the grate to the wind box main below the grate provide efficient utilization of the two types of sealing means and permits easier access to the machine for maintenance and other purposes. When, as illustrated above, the treating gas flows sequentially in an even number of passes, particularly four passes, through the grate in a series of treating zones, it is possible to have the pressure differential that moves the gases into and out of the bed all on one side of the grate, as on the upper side of the grate as in the first described embodiment. Consequently, itis possible to have the high pressure seals on only one side of the grate and only two fans need be used to move the gases through the apparatus of this invention. The illustrated flow of air relative to the pellets on the bed in the illustrated apparatus is such that essentially all of the air passes through all of the zones in countercurrent flow relationship, thereby providing great heat recovery efficiency.

While this apparatus has been described with reference to the use of traveling water troughs, it should be understood that water troughs affixed to the hoods and traveling sealing members affixed to the grate may also be used. In addition, mechanical seals other than the continuous sliding seal as shown in FIG. 8 may be utilized.

lt is thus apparent that the apparatus and processes provided above can produce all of the previously described advantages and overcome the previously described deficiencies of prior art apparatus and processes and can also provide other advantages. It is also apparent that modifications may be made in the apparatus and process described as embodying this invention without departing from the spirit of the invention.

I claim:

1. A process for treating particulate material on a generally horizontal gas-permeable circular traveling grate on which the particulate material is supported, comprising passing treating gases through the material on the grate sequentially in at least four and an even number of zones extending in series along the grate.

2. A process according to claim 1 wherein the number of zones is four. 1

3. A process according to claim 1 wherein said treating gases are introduced under pressure in the last of said zones and exhausted from the first of said zones.

4. A process according to claim 1 including the steps of operating pump means in only one of the end zones of said series of zones to pass treating gases through the material on the grate, and operating exhaust means in only the other end zone of said series of zones to exhaust said treating gases.

5. A process for treating particulate material on a generally horizontal gas-permeable traveling grate on which the particulate material is supported, comprising passing treating gases through the material on the grate in each of at least four and an even number of zones along the grate, operating pump means in only one of said zones along said grate to pass said treating gas through the material on the grate, and operating exhaust means in only one of the other of said zones along said grate to exhaust said treating gases. 7

6. A process according to claim 5 including the steps of operating pump means in only the last of said zones to pass said treating gases through the material on the grate and operating exhaust means in only the first of said zones to exhaust said treating gases.

7. A process according to claim 1 wherein the zones through which the material passes in sequence are drying, heating, precooling and cooling zones.

8. A process according to claim 4 wherein the zones through which material passes are in sequence drying, heating, precooling and cooling zones, and in which said pump means is operated in said cooling zone and said exhaust means is operated in said drying zone.

9. A process for treating particulate material on a generally horizontal gas-permeable traveling grate on which the particulate material is supported, comprising passing treating gases through the material on the grate in each of at least four and an even number of zones along the grate, said zones along the grate through which the material passes in sequence being drying, heating, precooling and cooling zones, in which process cool gas is passed under pressure into said cooling zone and passed downdraft through said material and said grate in said cooling zone to cool said material in said gas, then passed updraft through said material and said grate in said precooling zone, then passed downdraft through said material on said grate in said heating zone, and then passed updraft through said material on said grate in said drying zone.

10. An apparatus for treating particulate material comprising a generally circular traveling grate having a gas-permeable bottom hearth portion, gas enclosing means mounted on one side of said traveling grate and gas-enclosing means mounted on the other side of said grate, a trough containing liquid carried by one of said grate and said gas-enclosing means, shield means extending from one of said gas-enclosing means and said grate into said liquid to form an essentially gas-impervious seal, mechanical sealing means coacting between the other of said gas-enclosing means and said grate to form an essentially gas-impervious seal, means associated with said gas-enclosing means toprovide a series of treating zones along said grate, and means for passing treating gas through the material on the grate sequentially through said zones.

11. An apparatus according to claim 10 wherein said trough is carried by said grate and said shield means extends from said gas-enclosing means.

12. An apparatus according to claim 10 wherein said trough is carried by said gas-enclosing means and said shield means extends from said grate.

13. An apparatus according to claim 10 wherein each of said gas-enclosing means is stationary and said shield means are disposed at each side of one of said gas enclosing means, and said mechanical sealing means are disposed at each side of the other of said gas enclosing means.

14. An apparatus for treating particulate material comprising a generally circular traveling grate having a gas permeable bottom hearth portion, gas-enclosing means mounted above said grate and gas-enclosing means mounted below said grate, a trough containing liquid carried by one of said grate and said gas-enclosing means, said trough being below said gas enclosing means that is disposed above said grate, shield means extending from one of said gas-enclosing means and said grate into said liquid to form an essentially gas-impervious seal said shield means being disposed at each side of said gas enclosing means, and mechanical sealing means coacting between the other of said gas-enclosing means and said grate to form an essentially gas-impervious seal.

15. An apparatus according to claim in which said gasenclosing means is disposed above said grate and said trough, said gas-enclosing means being stationary and extending over said grate, said shield means being disposed at each side of said gas-enclosing means, and said other gas-enclosing means being disposed below said grate.

16. An apparatus for treating particulate material comprising a traveling gas-permeable generally circular grate, means for depositing particulate material on said grate, means providing an even number of treating zones sequentially disposed on said grate in the direction of grate travel, means through which gas enters the last of said zones and means for supplying gas to said last zone under superatmospheric pressure sufficient to cause the gas to pass through said grate in each of said zones.

17. An apparatus according to claim 16 wherein said lastnamed means comprises pumping means operated at a pressure sufficient to cause the gas to pass through said zones without passing through additional pumping means.

18. An apparatus according to claim 16 wherein four zones are provided.

19. An apparatus according to claim 18 in which said treating zones are drying, heating, precooling and cooling zones.

20. An apparatus according to claim 16 wherein said treating zones include gas enclosing means above said grate, gas enclosing means below said grate, a trough containing liquid carried by said grate, shield means extending from said gas-enclosing means above said grate into said liquid to form an essentially gas-impervious seal, and mechanical sealing means coacting between the circular grate and the gas-enclosing means below the grate to form an essentially gas-impervious seal.

21. An apparatus according to claim 16 wherein sealing means are provided above and below said grate between said precooling and cooling zones to prevent passage of gas along said grate.

22. An apparatus according to claim 21 wherein additional sealing means are provided between said heating and drying zones above and below said grate.

23. An apparatus according to claim 16 wherein the superatmospheric gas flows countercurrent to the movement of the material on said grate.

24. An apparatus for treating particulate material comprising a traveling gas-permeable circular grate, means for depositing particulate material on said grate in a bed, gas-enclosing means above said grate, gas-enclosing means below said grate, said enclosing means being constructed and arranged to provide a drying zone, a heating zone, a precooling zone and a cooling zone, a trough containing liquid carried by said grate, shield means extending from gas-enclosing means above said grate into said liquid, sealing means encircling and connected to said gas-enclosing means below said grate, sealing means encircling and connected to said grate and constructed and arranged to maintain sliding and gas sealing contact with said sealing means carried by said gas-enclosing means, means for supplying gas to said cooling zone at superatmospheric pressure sufficient to cause the gas to pass downdraft through said grate in said cooling zone and maintain the gas at superatmospheric pressure at the same side of said grate in said heating zone, sealing meansabove and below said grate between the precooling and cooling zones, means for withdrawing gas from said cooling zone and passing it updraft through said grate in said precooling zone, means for withdrawing gas from said heating zone after it has passed downdraft through said grate and passing it updraft through the grate in said drying zone, and means for withdrawing gas from said drying zone after it has passed through said grate, and means for discharging said particulate material after it has passed through said zones.

25. An apparatus according to claim 24 wherein said gasenclosing means extend from the means for depositing particulate material on said grate to the means for discharging the material from said grate.

26. An apparatus for treating particulate material comprising a traveling gas-permeable circular grate, means for depositing particulate material on said grate in a bed, gas-enclosing means above said grate, gas-enclosing means below said grate, said gas-enclosing means being constructed and arranged to provide at least four zones the last of which is a cooling zone, liquid-sealing means coacting between the circular grate and one of said gas-enclosing means, mechanical sealing means coacting between the circular grate and the other of said gas enclosing means whereby the zones defined by said gas-enclosing means above and below said grate are sealed at their marginal edges from the ambient atmosphere, means for supplying cooling gas to said cooling zone, means for maintaining essentially only in the gas-enclosing means sealed by liquid sealing means to the grate the pressure differential that forces treating gas including gas supplied in said cooling zone through said grate in said zones, and means for discharging said particulate material after it has passed through said zones.

27. A horizontally disposed circular traveling grate machine comprising a circular grate, stationary gas-confining hood means disposed above said grate covering at least a major portion of said grate, stationary gas confining wind box means disposed below said grate in chamber forming relationship with said hood means, liquid sealing means coacting between the circular grate and said stationary hood means, mechanical sealing means coacting between the circular grate and said stationary wind box means whereby the chamber defined by the hood means and the wind box means is sealed at its marginal edges from the ambient atmosphere, means separating the said chamber into at four and equal in number treating zones, and means for introducing gas into the last of said zones under superatmospheric pressure sufficient to cause the gas to pass through said grate in each of said zones.

28. A circular grate machine according to claim 27 wherein said last-named means comprises pumping means operated at a pressure sufficient to cause the gas to pass through said zones without passing through additional pumping means and including gas exhausting means only in the first of said treating zones.

Claims

2. A process according to claim 1 wherein the number of zones is four.

5. A process for treating particulate material on a generally horizontal gas-permeable traveling grate on which the particulate material is supported, comprising passing treating gases through the material on the grate in each of at least four and an even number of zones along the grate, operating pump means in only one of said zones along said grate to pass said treating gas through the material on the grate, and operating exhaust means in only one of the other of said zones along said grate to exhaust said treating gases.

10. An apparatus for treating particulate material comprising a generally circular traveling grate having a gas-permeable bottom hearth portion, gas enclosing means mounted on one side of said traveling grate and gas-enclosing means mounted on the other side of said grate, a trough containing liquid carried by one of said grate and said gas-enclosing means, shield means extending from one of said gas-enclosing means and said grate into said liquid to form an essentially gas-impervious seal, mechanical sealing means coacting between the other of said gas-enclosing means and said grate to form an essentially gas-impervious seal, means associated with said gas-enclosing means to provide a series of treating zones along said grate, and means for passing treating gas through the material on the grate sequentially through said zones.

15. An apparatus according to claim 10 in which said gas-enclosing means is disposed above said grate and said trough, said gas-enclosing means being stationary and extending over said grate, said shield means being disposed at each side of said gas-enclosing means, and said other gas-enclosing means being disposed below said grate.

17. An apparatus according to claim 16 wherein said last-named means comprises pumping means operated at a pressure sufficient to cause the gas to pass through said zones without passing through additional pumping means.

18. An apparatus according to claim 16 wherein four zones are provided.

24. An apparatus for treating particulate material comprising a traveling gas-permeable circular grate, means for depositing particulate material on said grate in a bed, gas-enclosing means above said grate, gas-enclosing means below said grate, said enclosing means being constructed and arranged to provide a drying zone, a heating zone, a precooling zone and a cooling zone, a trough containing liquid carried by said grate, shield means extending from gas-enclosing means above said grate into said liquid, sealing means encircling and connected to said gas-enclosing means below said grate, sealing means encircling and connected to said grate and constructed and arranged to maintain sliding and gas sealing contact with said sealing means carried by said gas-enclosing means, means for supplying gas to said cooling zone at superatmospheric pressure sufficient to cause the gas to pass downdraft through said grate in said cooling zone and maintain the gas at superatmospheric pressure at the same side of said grate in said heating zone, sealing means above and below said grate between the precooling and cooling zones, means for withdrawing gas from said cooling zone and passing it updraft through said grate in said precooling zone, means for withdrawing gas from said heating zone after it has passed downdraft through said grate and passing it updraft through the grate in said drying zone, and means for withdrawing gas from said drying zone after it has passed through said grate, and means for discharging said particulate material after it has passed through said zones.

25. An apparatus according to claim 24 wherein said gas-enclosing means extend from the means for depositing particulate material on said grate to the means for discharging the material from said grate.