US2675223A - Draft sintering apparatus - Google Patents

Description

April 13, 1954 o. ROLFSEN 2,675,223

DRAFT SINTERING APPARATUS Filed May 3, 1950 5 Shets-Sheet l JIJ :FILIZI Ole A e/{San /N VENTOE 7 EMA-w...) lndm 134 Arrys,

April 13, 1954 O..ROLFSEN 2,575,223

DRAFT SINTERING APPARATUS Filed May 3, 1950 3 Sheets-Sheet 2 Apnl 13, 1954 o. ROLFSEN 2,675,223

DRAFT SINTERING APPARATUS Filed May 3, 1950 3 Sheets-Sheet 3 016 fo/fSen HVVEN J 0 Arwyg,

- pan at a time.

Patented Apr. 13, 1954 UNITED STATES PATENT OFFICE DRAFT SINTERING APPARATUS Ole Rolfsen, Oslo, Norway Application May 3, 1950, Serial No. 159,710

Claims priority, application Sweden May l, 1949 Claims. I

In the usual sintering processes the charge, after fuel has been added thereto, is placed on a grate and ignited, while a fan draws air preferably downwards through the grate. The charge is burnt in layers, and the gas escapes with a gradually rising temperature, whereby considerable heat is lost. In the last phase of the burning the further drawback is encountered that loose particles are entrained by the gas and occasion wear in the conduit system. Because of the expensive repeated ignition of new charges it is necessary to work with rather thick charge layers and hence with a relatively high suction which increases the cost of the sintering equipment.

It is known, however, to avoid the drawback of repeated ignition of new charges by using two grate pans placed upon each other and at intervals to exchange these with freshly charged pans in a cyclic sequence. With downward draft this is effected in the manner that at first, when the upper pan is burnt down, this pan is removed and the lower pan is moved aside, whereafter a new pan is placed at the bottom and the previously lowermost pan is placed on top of it. When the burning of this latter pan is then finished, the charge in the lower pan is heated by the exhaust gases and radiant heat from the upper pan and thereby ignited. However, with this method the exchanging step becomes rather troublesome and no ideal heat utilization is obtained, since when using only two pans the exhaust gases will still have to escape at a rather high temperature, neither will the drawback of suspended particles be avoided.

If on thecontrary more pans are used, i. e. a complete stack of for example 3 to 6 pans, the heat economy can be considerably improved, since the heat of the downwardly moving exhaust gases can still be used for heating the charge of freshly inserted pans at the bottom of the stack, which charge also withholds suspended particles from the burning layers, while at the same time the incoming combustion air can be preheated by passing through pans which have burnt down.

It may be mentioned that it is also known in connection with treatments of solids with gases, including roasting processes, to use a stack of grate pans with downward draft and resting on a bottom box and at intervals to exchange one With this construction the gas :enters the uppermost pan through a fixed dome and leaves through the bottom box. Exchanging is effected in the manner that the bottom box is lowered somewhat more than the height of one pan, the stack following a short distance so that the uppermost pan gets clear of the dome and can be removed laterally, whereaiter the stack remains stationary at a suitable level above the bottom box fOr permitting a freshly charged pan to be introduced in-between. By the lowering of the bottom box the connection of the same with the gas outlet is interrupted, and in the case of a combustion process such as roasting, the combustion will have to be initiated by using heated oxygen-containing gas. This again requires a low ignition temperature, and in the case of powdered material a preceding agglomeration or briquetting will be required.

A drawback which is common to all the known processes referred to is that the gas current through the charge must be interrupted during each exchanging step, which apart from retarding the process may in many cases cause undesirable secondary reactions, particularly since a considerable time is required for the exchanging step in View of the large furnace areas and consequent pan dimensions required when operating on a commercial scale. Another drawback of known structures is the heat loss which occurs partly in connection with the exchanging intervals and partly by heat conduction through the pan walls, as well as the consequent uneven combustion. Further the discharge of the pans may involve difiiculties because the burnt charge is likely to stick to the hot grates.

The present invention relates to a process and an apparatus for draft sintering and for an object to avoid the above mentioned drawbacks encountered with known structures and to permit a continuous sintering to be effected in a particularly economical and favorable manner. A stack of grate pans is used which is open at the top so that the uppermost pan is accessible for the initial ignition. At the bottom the stack is connected to a suction device, and the pans are exchanged successively so that constantly a lower pan in the stack is preheated and ignited. by utilizing the heat developed in the superposed pans. The process is primarily characterized in that in each exchanging step a pan at the top of the stack, which pan has burnt down and been cooled by the incoming air while preheating the same, is moved aside in order to be discharged and charged anew while a freshly charged pan is introduced laterally under the stack in a lifted position of the latter.

The apparatus according to the invention, which is designed for carrying out this process 3 and which apart from the shaft furnace composed of roast pans with appurtenant suction box, comprises feeding, discharging and conveying means for the pans, is characterized by a device for lifting the pan stacks at intervals to a level so as to permit a freshly charged grate pan to be introduced between the stack and the suction box and for lowering the stack onto the new pan and the latter onto the suction box, in combination with a device adapted, before the arrival of the stack in its lowermost position, to catch the uppermost pan of the stack on a conveying structure for lateral removal from the stack.

When using the invention the several. advantages are obtained which have been referred to above and are due to the use of a stack of grate pans in which the heat content of pans which have burnt down is used for preheating the combustion air, and the heat content of the exhaust gases is used for heating freshly charged pans, the latter pans producing a filtering action by retaining suspended particles derived from the burning layers, and the initial ignition does not involve difficulties. Further, when using the invention, the pans may be exchanged during relatively short time interval, the connection bet Jeen the suction means and the pan stack being interrupted only in the intervals required for lifting the stack and introducing the new pan, since the tightening between the latter and both the superposed pan and the suction box is effected during the initial lowering movement and without any interruption of the connection between the outlet and the suction box, which latter may remain stationary. Further it is possible when using the invention to maintain the current through the pan stack uninterrupted during the exchanging step by effecting the insertion of the new pan in the bottom of the stack in a space which is shut off from the surrounding air.

Heat losses to the outside and burning of the charge onto the grate bars may be minimized according to the invention by maintaining through the walls and grate bars of the pans within the stack a circulating current of cooling medium, the heat of which may then be utilized.

To prevent uneven sintering du to heat conduction from the charge to the pan walls the latter are preferably provided with heat insulation at the inside.

Further features and advantages will appear from the following specification, reference being had to the drawings which illustrate a preferred embodiment of the apparatus.

Fig. l is a diagrammatic side view of the apparatus on a small scale and partly in section.

Fig. 2 is a corresponding top view in which structures at the top of the pan stack have been omitted for the sake of clearness.

Fig. 3 is an end view of a pan emptying device on a somewhat larger scale.

Fig. 4 is a top plan view of a grate pan on a still larger scale.

Fig. 5 is a fragmentary view on the same scale as Fig. 4 of the pan stack with the surrounding casing in section substantially along the line V-V in Fig. 2.

Fig. 6 is a cross sectional view on a still larger scale of an end wall of a grate pan taken along the line VI-VI in Fig. 4 and of a corresponding connecting means for a cooling water circuit.

Fig. 7 is a cross sectional view on the same scale of the lowermost portion of a side wall of a grate pan and the top of the corresponding side wall 4 of a pan located below the same (indicated by the line VII-VII in Fig. 4)

Fig. 8 illustrates two possible grate bar cross sections.

The drawings illustratively show a stack of five grate pans I resting on a circumferential flange 2 of a funnel-shaped bottom suction box 3 equipped with a suction pipe- 4 and an outlet 5 which may be closed for example with a sluice structure. For conveying the pans away from the top of the stack emptying the pans, and conveying freshly charged pans toward the stack conveyor means comprising plurality of rollers, 6, i, 8, Hiand II are provided which co-operate with longitudinal flanges [2 on both sides of the pans. The rollers 6 at the top of the stack are mounted on two pendulum members 13', which can be moved laterally outwardly by means of a pressure cylinder 14 (Fig. 5) in order to avoid interference with the laterally extending flanges l2 of the uppermost pan when the stack is lifted.

The several sets of rollers, which may be driven in groups, may be operated by electric motors or other conventional driving means (not shown). The rollers 1 are placed at thesame level as the rollers 6 and serve to convey finished pans to a tilting emptying device [5 comprising a discharge funnel it, which by means of annular rims I1 is rotatable on rollers I B of a. lowering structure I9. The structure or transfer t9 comprises a frame adapted to be raised and lowered by means of pressure cylinder 20 and. preferably propped by rollers 2| engaging vertical rails 22. Apart from the driven grooved rollers 8, onto which the pans are passed with their lateral'fianges, the tilting structure l-5 also comprises a set of grooved rollers 23-, which engage the top side of these flanges and serve to keep the pan in position when the latter is turned by means of the tilting device so as to be emptied through the. funnel Hi, the latter engaging with a circumferential flange the top of the pan walls. By means of the lowering structure l9, while being turned upside down and back again by the rollers 18 the pans are lowered from the level of the rollers I to the level of the rollers 9 and H), which are adapted to support the pans at a slightly higher level than after they haveregained their normal position is effected by the rollers 8 and the rollers 9, which move the pan into position under the feeding or charging device 24. This device consists of for example two oppositely threaded screw conveyors indicated at 25, which feed the charge inwards over the pan from both sides through passages 25 which in the central area over the pan are each rovided with a pair of pivoted bottom flaps operated by means of a link mechanism from a pair of pressure cylinders 29 for-each screw conveyor. By means of the feeding device the pans are conveniently filled substantially tov the brim, scraping devices or the like being used if desired for evening the charge so that it attains a substantially equal level, above the pan grate 30.

When using tilting and feeding devices of the construction described, it. is possible to effect discharging'and charging so rapidly that the time required from the moment when a pan is removed from the stack and tillthe moment when it is again ready for insertion at the bottom of the stack will not be longer than that which the process will usually require between twoconsecutive exchanging intervals.

A casing or enclosure 3 l. surrounds the suction box 3 and the lower part of the pan stack and defines a low pressure zone which communicates with an air lock chamber 32 in which the conveyor rollers it are mounted and which is provided with a couple of vertically movable air loclr gates 33 and Ed operated by pressure cylinders 35 and 35 respectively. Upon the arrival of a freshly charged pan from the feeding device 24, the gate 33 is open and the gate 3 closed, and thereafter, to permit insertion of the pan beneath the bottom of the stack the gate 33 is kept closed when the gate at is opened. This malres it possible to introduce the pans into the casing 31 without the admission of outer air. To facilitate operation of the gates the air loci; chamber 32 may be equipped with pressure-equalizing by-pass conduits provided with cocks 3i and 38.

The rollers H which feed freshly charged pans beneath the bottom of the stack from the air lock chamber 32 are rotatably mounted on a pair of parallel beams 39 extending along both sides of the suction box 3 within the casing 3i and adapted to be raised and lowered by pressure cylinders lli. Each of the beams to also carries two upwardly extending supporting members 4| (Fig. 5) for pivotally mounted lifting arms 42, adapted to engage the bottom side of the lateral flange of the lowermost pan of the stack in order to raise the stack of pans when the beams 39 are raised. Each lifting arm H2 is formed as a lever with a guiding roller ts at one end thereof which engages a vertical rail M during the lifting movement. When the beam is lowered relative to the newly inserted pan, the lifting arms 4 may turn pivotally to move freely past the flange thereon.

At the top the casing 3! is formed with a rectangular pressure sealing shaft it surrounding the stack over a somewhat greater height than the vertical dimensions of one pan. For airtight engagement with the shaft the pans l are formed with flanges extending around their entire peripheries, the side flanges l2 merging through rounded corners with end flanges 45. At their outer edges the flanges I2, 46 may be equipped with resilient packing strips ll for example of asbestos steel and as shown in Figs. 6 and '7 with an internal hollow space. In the preferred embodiment in which the walls and grate bars of the pans are made hollow for passing cooling water or other cooling medium therethrough, the hollow space of the packing strips may communicate with that of the pan walls for example through a conduit 48 provided with cook 49 so as to provide a resilient tightening pressure.

The grate Zitl of each pan is preferably placed at a considerable distance above the bottom edge of the pan, as shown in Fig. 5, in order that even when the underlying pan has been filled to the brim an ignition chamber will be provided above the same, whereby a uniform heating of the charge of an underlying pan may be obtained by heat radiation from the overlying pan supplementing the hot downward gas current, since both radiation shadows and lee areas may be equalized in the ignition chamber. Further, in order to obtain the best possible efi'ect in this respect grate tubes of circular cross section may be used as shown at in Fig. 3, or, if desired, an extension may be welded thereto so as to afford a streamline shape as shown at 3%. These tubular grate bars which in the construction shown extend longitudinally of the rectangular pan may be slidably supported in the end walls of the pan in order to accommodate dimensional changes caused by thermal expansion and contraction. As shown in Fig. 6, the end of the hollow grate bar 30 is provided with a gland memher 5! which engages resilient packing El to form a fluid tight seal, thereby preventing leakage of cooling fluid circulating through the grate bars and the passages formed in the walls of the pan.

The pan walls are thermally insulated from the charge by means of an internal lining 52 for example of asbestos, which may be protected by a plate 53 of stainless steel or an iron plate coated with stainless steel.

For sealing against air leakage through the joints between the pans of the stack, the pan walls, which generally are of hollow rectangular cross section, are provided at the top with a longitudinal rib 54 (Figs. 4 and 7) fitting between a pair of ledges 55 on the bottom side of the overlying pan a-nd engaging packings 55 withheld by the ledges. A rib identical to the rib 54 may also be provided on the flange 2 of the suction box 3.

In order to transfer heat from the pans and prevent burning of the sintered material onto the grate bars, a continuously circulating current of cooling medium such as water is maintained flowing through the hollow walls and grate bars of the pans within the stack. By means of a pump 5'! in an external portion of the cooling circuit this medium is forced through a conduit 55 with cock Tl into the lowermost pan through a connection device in the suction box flange 2 and flows through all the pans in series and out from the uppermost pan through a connection device 59 into the outer circuit where it returns through a flexible conduit 60 and a heat exchanger ill to the suction side of the pump. The connecting device 59 can be moved up and down by a pressure cylinder 62. In the heat exchanger iii the heated cooling water delivers its heat in directly to a circuit 53 in Which it may be utilized in any desired manner.

The cooling water enters each pan through a sleeve 6 5 (Fig. 6) threaded into the bottom of one of the hollow end walls thereof and provided with a spring-actuated check valve and leading into an inlet chamber 65 which is closed at the top and both sides by dividing walls 6! (Fig. 6) and 68 (Fig. 4) respectively. From the inlet chamber 66 the water then flows through the grate tubes 38 into the opposite end wall of the pan and then back through the side walls into the space 69 above the dividing Wall 67. From this space the water leaves the pan at the top through a spring-actuated valve ill which is normally closed, but which, when positioned within the stack, is kept open by engagement of upward projections l! of the valve member ill with the sleeve i l of the overlying pan or, for the uppermost pan, by engagement with a corresponding sleeve "52 of a check valve 73 in the connecting device 59. In a similar manner the sleeve 64 of the lowermost pan opens a valve in the connecting device of the suction box flange 2. This valve has not been shown, since it may be similar to the valve it. A sealing against leakage of cooling water when passing from one pan to another is obtained by an annular upwardly extending projection M at the outlet from each pan (and also on the suction box flange), which fits into a corresponding recess surrounding the lower end of the sleeve 6 of the overlying pan, and likewise surrounding the sleeve ll of the outlet connection member 59 above the top of the stack, and engages an annular gasket 15 or 16 respectively.

The operation of the apparatus is as follows:

During the intervals between the exchanging pans in the stack all the pans except the one which is in transit and being emptied and filled again are at rest within the stack which assumes the position shown in Figures 1 and 5, a constant downward draft through all the grates of the stacked pans in series is maintained by means of the suction box 3 connected to the suction conduit 4, and the cock ii in the water circuit reopen, the outlet connection member 55 being at the same time kept pressed against the uppermost pan by the pressure cylinder 62, so that all the cooling water Valves of the pans of the stack are likewise kept open and hence the cooling water flows through the pans in series. In the uppermost pan of the stack where fresh combustion air enters from the top, the air is preheated in the course of its passage through the uppermost pan which has burnt down, thereby cooling the latter and then causes combustion and consequent sintering of the charge in the hottest intermediate zone of the stack, and in the lowermost zone of the stack the combustion cooled while passing through the charge of the pan or pans last inserted, and these lowermost pans are at the same time preheated and ignited partly by heat transfer from the combus tion gases and partly by heat radiation from above. a

At the moment when an exchange of pans is to be initiated, a freshly charged pan is ready in the air lock chamber 32, and the gates 33 and 34 are closed. Now the cook 11 of the water circuit is closed (or if desired the pump 51 may be stopped), the pressure at the top of the piston within the outlet connection control cylinder 62 is removed and the stack lifting cylinders 46 are connected for lifting the beams 38, while the air lock cylinders 36 after opening the pressure equalizing cook 38 are connected for lowering the air lock gate 34. In this manner, the entire stack of sintering pans is lifted off from the suction box 3 by means of the pivotally mounted lifting arms 42 during the upward movement of the latter. However, suction through conduit 4 is maintained, and in spite of the fact that the stack is no longer connected directly to the suction box 3, the downward draft in the stack will still be maintained because of the reduced air pressure within the casing 31!, with which the suction box 3 still communicates, is shut off from the outer air by means of the outer air lock gate 33 and the pressure sealing engagement between the shaft walls d and the circumferential flange on the pan or pans contacting shaft walls. By shutting off the water circuit by means of the cock Tl, the check valves 65 close and thereby prevent the cooling water from escaping, and likewise the connecting device on the suction box flange is closed by the lifting of the stack therefrom. During the upward movement of the stack water outlet connection device 59 is lifted off from the uppermost pan by means of the pressure cylinder 62, whereby the outlet valve ll of this pan closes so that the water space of the uppermost pan is completely shut off from the outside. Further, during the lifting movement the pendulum members iii are moved laterally outwards by means of the pressure cylinders i l so that the lateral flange 52 of the uppermost pan can pass the. rollers ii, whereafter these rollers are again turned back into normal position under the flange, as seen in Fig. 5 in which the upper- Q I. most position of the pan has been indicated "in dash-and-dot lines;

When the beams 39 have arrived in the uppermost position the rollers H are level with the air lock rollers l0 which are then operated for inserting the newly charged pan into the space between the bottom of the stack and the top of the suction box 3. When then this freshly charged pan has arrived in the required position, the lowering of the beams by means of the cylinders All is initiated, whereby the new pan will engage the suction box 3, the uppermost pan is caught by the rollers 6 and the previously lowermost pan of the stack shortly afterwards will engage the new pan. The pan which has'been lifted off is at once moved aside by means of the rollers 6, and the water outlet connecting member 59 is again pressed down onto the new uppermost pan, whereby the water circuit is again completed so that the cock i1 may be opened anew. At the same time the air lock cylinders 36 are operated for upward movement and as soon as the gate 34 has been closed thereby and likewise the low pressure equalizing cook 33 has been closed, the atmospheric pressure equalizing cook 37 may be opened and the outer gate 33 lowered so that the air lock chamber is ready to receive the removed pan as soon as the latter has been emptied and filled anew by means of the emptying and charging devices l5 and 24 respectively.

The pressure cylinders'shown may be driven in any usual known manner with either pneumatic or hydraulic pressure and controlled by suitable valves. The operation of these valves as well as the starting and stopping devices for the motors of the rotating rollers etc. and of the cock H may conveniently be automatic. Means for this purpose have not been shown since they may be of usual known construction. The operation thereof may be time-controlled or the exchanging step may be initiated by means of sensing means responsive to the temperature 0 any desired zone of the stack. 7 a

The start of the process will not involve difilculties, the uppermost pan of the stack being accessible for the ignition which may be effected in the usual manner with admixture of inflammable fuel. Admixture of fuel to the charge or placing of arbottom layer of inflammable ma terial on the grates may of course also be effected during the continuous operation, but may be dispensed with for many uses of the present process.

To ensure a uniform flowing of cooling medium through the grate tubes of the pan stack, the tubes may, if desired, be inclined slightly upwards in the direction of ,flow so as to contribute to the flow by thermosyphon effect. This can be done either by giving the tubes a slight inclination with respect to the top and bottom faces of the pan walls or by arranging the whole stack slightly inclined. Besides, if necessary, the cooling water circuit may pass through a reservoir ahead of the pump in which losses of cooling Water due to leaking are covered and at the same time air bubbles, if any, may escape. Further, if desired, a tapping valve may be placed behind the closing cook or the circuit for applying a transitory suction to oppose leaking from the outlet of the uppermost pan of the stack incidental to the lifting of the connecting device 59.

Also in other ways the embodiment shown may be supplemented or modified within the scope of the invention. Thus, instead of resilient packing means on the pan flanges for tightening against amazes the surrounding shaft on the way out of the casing 3| it is possible to use shaft walls subjected to a resilient pressure, or other means than a direct sliding fit may be used, such as a sluice structure which may comprise pivoted or rotating tightening flaps or vanes, whereby a sliding fit, if any, will only be required at the corners. Further, the conveying of the pans may take place in other manners than by means of driven rollers, thus for example if sluice structures as mentioned above are used for tightening during the movement of the pans out of the casing, the pans themselves may be provided with rollers which run on stationary rails, the movement being effected by means of chains or in other suitable manner.

The invention may be applied for many purposes, such as sintering of iron ore or cement or in other fields where calcination, agglomeration, burning of calcium silicates, de-sulphurization or similar processes are involved.

I claim:

1. Draft sintering apparatus of the class described, comprising: at least three sintering pans each having side walls and a bottom grate for retaining a charge and permitting the downward flow of combustion air therethrough, said pans being disposed in vertically stacked relationship; elevating means acting on the lowermost of said pans for raising said pans in said stacked relationship; conveyor means for inserting a freshly charged pan beneath said raised stack; further conveyor means for removing the uppermost pan from said stack; and suction means disposed beneath the bottom of said stack for drawing combustion air downwardly through said stacked pans.

2. Draft sintering apparatus according to claim 1, wherein said side walls and grates of said pans have passageways for a cooling medium formed therein, said apparatus further comprising: circulating means for delivering a fluid cooling medium to said passageways; and separable connecting members interconnecting the passageways of adjacent pans in said stack.

3. Draft sintering apparatus according to claim 1, further comprising: enclosing means defining a low pressure zone surrounding the lower portion of said stack, said pans being vertically movable in pressure sealing engagement with said enclosing means; and air lock means communicating between the exterior and interior of said enclosing means, said first named conveyor means extending through said air lock means, whereby said freshly charged pan may be inserted beneath said stack without interrupting said downward flow of combustion air.

4. Draft sintering apparatus according to claim 1, further comprising: pan charging means disposed in proximity to said first named conveyor means; pan emptying means disposed to receive pans from said further conveyor means; and transfer means for moving an emptied pan from said emptying means to said first named conveyor means, said first named conveyor means including means for moving said emptied pan to be filled by said charging means.

5. Draft sintering apparatus according to claim 1, in which said elevating means includes means for lowering said freshly charged pan onto said suction means for engagement therewith and for lowering said raised stack into engagement with said freshly charged pan, whereby said freshly charged pan becomes the lowermost pan of said stack, and means engageable with said freshly charged pan after completion of said lowering movement for acting on said freshly charged pan to raise said stack, and wherein said further conveyor means includes means engageable with the uppermost of said stacked pans in the raised position of said stack for removal of said uppermost pan after said stack has been lowered.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,045,853 Kauffman Dec. 13, 1912 1,050,079 Kauffman Jan. '7, 1913 1,278,166 Kilbourn Sept. 10, 1918 2,202,245 Cramp May 28, 1940

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