Abstract:
An apparatus for cooling bulk material with a grate flowed through by cooling gas. The apparatus comprises a plurality of planks configured to move forward and back in the direction of conveyance and, between the planks, a sealing device having spatially separate outer and inner sealing elements. The sealing device has between the sealing elements a conveying duct, which runs along the length of the planks and on which a gas supply is configured to produce a gas stream along the length of the conveying duct. Bulk material which has infiltrated through the outer sealing element can be transported away before it can reach and migrate through the inner sealing element. The accompanying sealing effect can considerably reduce the undesirable material through-fall, while enabling the use of low-wearing seals, which provide excellent wear resistance.

Description:
REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a national stage application under 35 USC 371 of International Application No. PCT/EP2007/007102, filed Aug. 10, 2007, which claims priority of European Patent Application No. 06 016 751.7, filed Aug. 10, 2006, the contents of which are incorporated herein by reference in their entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to an apparatus for cooling bulk material with a gas, which apparatus has a grate which conveys a layer of the bulk material from a feed end in a direction of conveyance to a delivery end and is flowed through by cooling gas, wherein the grate comprises a plurality of planks moved alternately forward and back in the direction of conveyance and, between adjoining planks, a sealing device is provided, comprising two mutually separate sealing elements. 
       BACKGROUND OF THE INVENTION 
       [0003]    Cooling apparatuses of this type serve to cool bulk material through the use of gas, in that the bulk material is deposited as a bed onto a grate and is transported along this, while gas is supplied from beneath the grate for cooling purposes. The gas rises through the bulk material bed and cools this in the process. In cooling apparatuses of this type, the cooling grate has two functions. One function is to support the bulk material in order to form a material bed, and the other is a transport function for conveying the bulk material from a feed end to a delivery end. For the fulfillment of the two functions, various basic constructions have become known. In this context, the construction featuring a plurality of planks extending in the direction of conveyance, which planks are moved alternately forward and back, is of interest. In this conveying principle, which is also referred to as a “walking floor”, one difficulty consists in the fact that at the boundaries between adjoining planks bulk material falls through into a grate pit. In coolers, unlike in comparable grates of furnaces, this poses a considerable problem. For the fallen-through bulk material steadily collects in the grate pit of a cooler, while in the grate pit of a furnace it generally combusts and thus disappears by itself. The accumulation of bulk material which has fallen through the grate is undesirable and leads to wear and ultimately damage to components of the cooling apparatus. In this context, the construction featuring the longitudinally moved planks is particularly problematical, since both a same movement between the adjoining planks and a contrary movement can take place, which must both be reliably sealed. This has proved difficult. In order to solve this difficulty, various approaches have been proposed in practice. 
         [0004]    EP-B-0 730 722 discloses a seal which acts as a side seal between the outer moved planks and a surrounding wall of the cooling grate. It has a sealing air duct, via which sealing air is blown into a gap seal encompassing the outer edge of the planks. This arrangement calls for a really high gas stream and thus a correspondingly large-sized duct for the supply, so that it is only suitable for use on the margin of the outer planks and not between the planks. 
         [0005]    WO-A-98/48231 discloses a seal construction in which the mutually adjacent movable planks have on their mutually facing longitudinal edges a vertically upright, raised flange. This is covered by a joint, U-shaped profile, which is open downward toward the grate. A drawback of this arrangement is that the seal is disposed in a region which is totally surrounded by bulk material. Though the seal has a long sealing gap, it is arranged such that gravitational force encourages the material to fall through. 
         [0006]    EP-A-1 475 594 in turn discloses a sealing arrangement, which in principle is built similarly to the one described above. The sealing arrangement has, in addition to the seal on the top side, a second seal, which is arranged inversely on the bottom side and is formed with an upwardly open, U-shaped profile. Though a really good sealing effect is thereby achieved, one problem consists in the fact that material, once entered into the sealing arrangement, can only be retrieved with difficulty. It can accumulate and thus impair the effect of the sealing arrangement. 
       SUMMARY OF THE INVENTION 
       [0007]    Starting from the last-named, known sealing arrangement, the object of the invention is to provide an improved sealing arrangement which further reduces the through-fall through the grate. 
         [0008]    The solution lies in a sealing arrangement having features as broadly described herein. Advantageous refinements are the subject of the embodiments described below. 
         [0009]    In an apparatus for cooling bulk material with a gas, which apparatus has a grate which conveys a bulk material layer from a feed end in a direction of conveyance to a delivery end and is flowed through by cooling gas, wherein the grate comprises a plurality of planks moved alternately forward and back in the direction of conveyance and, between adjoining planks, a sealing device is provided, comprising two spatially separate sealing elements, it is provided according to the invention that the sealing device also has between the sealing elements a conveying duct, which runs along the length of the planks and on which at least one gas supply for a gas stream flowing along the length of the conveying duct is configured in such a way as to convey bulk material, introduced through one of the packing seals, to a delivery point. 
         [0010]    Some of the terms that are used are explained below. 
         [0011]    By bulk material is understood powdery or granular material, especially clinker material. 
         [0012]    A direction of conveyance is that direction in the plane of the grate along which bulk material present on the grate is transported from the feed end to the delivery end. 
         [0013]    By planks moved alternately forward and back are understood board-like elongated structures, which are moved forward and also back again along their longitudinal direction. The movement is here generally controlled such that a plurality of planks move simultaneously forward, but non-simultaneously back. A conveying effect can thus be obtained, whereby it is possible to dispense with separate conveying devices on the grate. 
         [0014]    By a conveying duct is understood a conduit which is suitable for both transporting gas and fallen-through bulk material. 
         [0015]    By outer sealing element is meant that sealing element which separates the conveying duct from the bulk material layer. The inner sealing element separates the conveying duct from the grate pit. 
         [0016]    The invention is based on the combination of two effects. On the one hand, the quantity of through-falling material is reduced by the dual sealing elements. On the other hand, the material which has overcome the first sealing element is intended to be carried away in a controlled manner before it can reach the second sealing element. A large part of the infiltrated bulk material (hereinafter referred to as stray material) can thus be carried away before it comes into any kind of contact with the second sealing element. The likelihood of material also crossing the second sealing element and making its way into the grate pit is thereby considerably reduced. The wear upon the second element is also thereby reduced to a minimum, so that the sealing effect is long maintained. Finally, by virtue of the conveying duct according to the invention, accumulations of stray material are also prevented. The sealing elements remain clear and are protected from damage and wear. 
         [0017]    It is fundamentally possible to carry away stray material evacuated via the conveying duct to any chosen location. It is expedient, however, to arrange the delivery point of the conveying duct at the delivery end. The evacuated stray material then falls off at the place at which the cooled material is also ejected from the grate. However, it is not absolutely necessary to provide a separate delivery point. This can also be integrated in the outer sealing element. That region of the cooling grate which is situated at the rear in the direction of conveyance lends itself particularly well to this purpose. There, provided there is sufficient gas pressure in the conveying duct, the fed stray material can be blown out back into the bulk material bed. 
         [0018]    The grate pit is often divided into a plurality of chambers, which, viewed in the direction of conveyance, can be differently pressurized. The invention can advantageously exploit this by providing as the gas source for the conveying duct at least one connection to one of the chambers, which chamber has a higher pressure than other chambers. By higher pressure shall here be understood that it is sufficient to generate a pressure gradient for transport of the stray material in the conveying duct. The conveying duct itself is expediently not divided into chambers, but is chamber-free. This ensures an unhindered evacuation of the stray material. 
         [0019]    The outer and inner sealing element can preferably be formed as a gap-labyrinth seal. This seal construction is known per se for coolers of this type and has proved successful. In contrast to contact-based seals, it is low-wearing; it does, however, have a higher leakage rate. By virtue of the inventive arrangement having the conveying duct, the grate through-fall specifically does not however increase. The invention understands to decouple the leakage rate and the grate through-fall quantity. Expediently, at least one of the sealing elements is made self-adjusting. It is preferably constituted such that the nominal size of the sealing gap is reduced in manufacture to 0 mm and that in operation (due to production tolerances, different bending lines of the components bearing the sealing element) a desired gap size is quickly obtained, which persists until the sealing element is replaced. A deliberate wear is thus produced, to be precise up to a desired target gap size. With such a bedding-in process, the target gap size can ultimately be set more accurately than would be possible in the case of a direct manufacture. 
         [0020]    Expediently, the outer sealing element is arranged lower than the inner sealing element. Gravitational force thus additionally deters stray material from passing from the outer sealing element through the conveying duct to the inner sealing element. 
         [0021]    Preferably, the sealing device has a protruding bar on a longitudinal edge of one of the planks and a branched profile, reaching over the bar, on one of the adjoining planks. A gap seal can thus be realized in a simple manner, which acts as the outer sealing element. In the case of a downwardly open arrangement of the branched profile, said gap seal is also broadly protected from the introduction of bulk material. Expediently, it is provided that a free end of the branched profile interacts with the bar. The bar can have a rectangular cross section. It preferably, however, has a step, the flanks of which form a labyrinth seal with the free end of the branched profile. An even better sealing effect is thereby achieved. In addition, it is preferably provided that the branched profile has an additional branch to form a so-called U-shaped profile. That branch is fastened to an upwardly projecting flange disposed on the adjoining plank in order thus to achieve a seal also with respect to the adjoining plank. 
         [0022]    Preferably, on the adjoining plank an auxiliary bar is arranged, which forms with the bar a gap seal as the inner sealing element. This means that the bar can be used not only to form the outer sealing element, but also to form the inner sealing element. The number of required parts is thereby minimized. Expediently, the auxiliary bar is here configured as an L-shaped profile. Particularly preferably, the auxiliary bar is arranged in an upright element of the adjoining plank such that the inner sealing element which it forms is arranged higher than the outer sealing element. Gravitational force thus deters the stray material from being transported from the outer to the inner sealing element. The aforementioned upright element can preferably be formed by the upwardly projecting flange. 
         [0023]    Expediently, on the mutually opposing longitudinal sides of adjoining planks, downwardly protruding end plates are provided and form a gas duct, which emerges via the inner sealing element into the conveying duct. The conveying duct is here expediently shaped such that it has a cross section which is roughly 10 to 80 times, preferably 15 to 50 times as large as that of the sealing elements. 
         [0024]    Preferably, the inner sealing element is designed such that its flow resistance is less than that of the outer sealing element. The effect is that the gas flowing in the conveying duct does not flow backward through the outer sealing element back into the bulk material bed. The risk of blockages of the outer sealing element by recycled stray material is thereby eliminated. A ratio of, for example, 1:2 to 1:50 has proved successful. 
         [0025]    It can be expedient to configure the inner sealing element between an inner face of the branched profile and an auxiliary plate disposed on the bar. The inner sealing element is thereby located high up in the conveying duct. Infiltrated stray material can barely reach it. It is thus well protected from wear. Moreover, this arrangement is robust against unfavorable tolerances or against a sealing gap enlarged by bending loads. In such cases, too, material through-fall would not occur, or only to a very small extent. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]    The invention is explained in greater detail below with reference to the appended drawing, in which an advantageous illustrative embodiment of the invention is represented and in which: 
           [0027]      FIG. 1  shows a schematic side view of a cooling apparatus according to an illustrative embodiment of the invention; 
           [0028]      FIG. 2  shows schematic views of different work stages of a grate of the cooling apparatus; 
           [0029]      FIG. 3  shows a cross-sectional view through a part of the cooling apparatus; 
           [0030]      FIG. 4  shows a cross-sectional view of a first embodiment of a sealing arrangement according to the invention; 
           [0031]      FIG. 5  shows a cross-sectional view of a second embodiment of a sealing arrangement according to the invention; 
           [0032]      FIG. 6  shows a cross-sectional view of a third embodiment of a sealing arrangement according to the invention; and 
           [0033]      FIG. 7  shows an enlarged part cross-sectional view of a fourth embodiment of a sealing arrangement according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0034]    In  FIG. 1 , a schematized view of a cooling apparatus and its integration in a cooling plant is represented. Located at the beginning in a cooler housing  1  is a feed shaft  2 , into which a discharge pipe  3  of an upstream rotary furnace (not represented) emerges. Material emanating from the rotary furnace falls into the feed shaft  2  onto a cooling grate, more precisely onto its feed end  4 . It has a slightly downward-sloping, ramp-shaped design, so that the deposited material slides in the direction of a horizontally disposed main portion of the grate. If the grate is referred to below without further detail, then this main portion  5  of the cooling grate is meant. It has a plurality of longitudinally movable planks  51 - 53 , which exert a conveying effect upon the material such that it is led away from the feed end  4  and along the grate  5 . At the opposing ends, the grate has a delivery end  6 , that in the illustrative embodiment is configured as an inclined skidpan. It serves to discharge the cooling material in a purposeful manner at the delivery end, for example onto an underlying crusher  66 . 
         [0035]    The structure of the grate  5  in schematized representation, and its working method, are represented in  FIG. 2 . As already stated, it consists of a plurality of mutually adjacent elongated planks  51 - 53 . The working principle for the transport of the bulk material in a direction of conveyance  50  is represented with its basic phases in the individual diagrams of the figure. The basic principle of this illustrative embodiment is a motional sequence in which all planks  51 - 53  move in the direction of conveyance  50 . In  FIG. 2   a , a phase of the cycle is depicted in which the planks  51 - 53  are moved into their front end setting. The next phase is represented in  FIG. 2   b . The plank  51  is retracted until it reaches its rear end setting. For the phase represented in  FIG. 2   c , the plank  53  moves back until reaching its rear end setting. Finally, the plank  52  also moves into its rear end setting, so that the position represented in  FIG. 2   d  is reached. The cycle then begins anew. In this way, a pattern of motion is obtained, in which all planks are jointly moved forward, while they are individually retracted one after the other. It should be pointed out that it is not absolutely necessary for all forward moving planks to have the same speed. In accordance with the normally occurring speed profile of the bulk material, it can also be provided that the marginal planks  51 ,  53  move more slowly than the centrally arranged plank  52 . 
         [0036]      FIG. 3  shows a cross-sectional representation over a part of the grate width according to the illustrative embodiment of the invention. At the right-hand edge of the picture, a side wall  15  for the grate is represented. The side wall  15  can be realized as a stand-alone wall structure which delimits the grate to the side. It can also, however, be realized in combination with a side wall of the housing  1 , in which case the side wall  15  forms a bracket-like protrusion on the side wall of the grate space. The first plank  51  and the second plank  52  are respectively disposed one after the other from right to left; other following planks are not represented for simplification reasons. However, the equivalent applies in terms of their structure. The planks  51 ,  52  have on their surface a plurality of evenly spaced ribs  59 , which are orientated transversely to the direction of conveyance  50 . They serve to improve the frictional engagement between the planks  51 ,  52  beneath the overlying bulk material. They also form pockets between them, which are filled with bulk material. The surface of the planks  51 ,  52  is thus not directly subjected to hot bulk material and is thus protected from harmful effects due to heat and abrasion from the hot bulk material. On their front side, the planks  51 ,  52  have partition walls  58 . Extending respectively on the longitudinal edges of the planks  51 ,  52  are downwardly protruding end plates  56 ,  57 . Between the main surfaces of mutually opposing end plates  56 ,  57  of adjoining planks  51 ,  52 , a gas supply duct can be formed. This will be explained in greater detail later. The partition walls  58  are preferably arranged in multiple at regular intervals along the length of the planks  51 ,  52 . Together with the end plates  56 ,  57 , chambers  90  are thereby formed on the grate  5 , which chambers can be pressurized with compressed gas. It is here possible to subject the individual chambers  90  to different pressures in order thus to achieve a desired distribution of the compressed gas along the extent of the grate  5 . 
         [0037]    Between adjoining planks  51 ,  52 , there is respectively provided a sealing device  7  extending along the longitudinal edges. For the sealing of the most marginal plank  51 , together with the wall structure  15 , a modified sealing device  7 ′ is provided. The structure and the working method of the sealing device  7  are explained in greater detail below with reference to  FIG. 4 . The sealing device  7  essentially comprises a bar  71  and a branched profile  77  which reaches over said bar. The bar  71  is arranged, via a mounting adapter, on the top edge of one of the planks  51 . The bar has a substantially rectangular profile and extends over the entire length of the plank  51 . It terminates, in the direction of the outer side, flush with the outer face of the end plate  56  of the plate  51 . On its opposite side orientated toward the rib  59 , the bar  71  preferably has a step  72 . The step  72  can be formed particularly easily by a two-part version of the bar  71 , in which two bar elements of rectangular cross section are arranged mutually offset. The step  72  serves to interact with the branched profile  77 . 
         [0038]    The branched profile  77  is of generally U-shaped design. It comprises a main branch  78  and an auxiliary branch  79 , connected by an intermediate piece. Preferably, the main branch  78 , the intermediate piece and the auxiliary branch  79  are realized in one piece. The branched profile  77  is disposed on the end plate  57  of the adjoining plank  51 . The dimensions are here chosen such that said branched profile reaches over the bar  71  with a main branch  78  in such a way that the main branch  78  engages with its free end in the step  72  of the bar  71 . At the same time, the outer side of the main branch  78  terminates flush with the outer side of the bar  71  that points toward the rib  59 . Between the bar  71  and the free end of the main branch  78 , a gap seal is formed, which acts as the outer sealing element  70 . Due to the engagement of the free end in the step  72 , the gap of the outer sealing element  70  has a 90° bend. It thus constitutes a labyrinth seal. 
         [0039]    In addition, an inner sealing element  74  is provided. For this purpose, an auxiliary bar  75  is disposed on the auxiliary branch  79 . This auxiliary bar  75  has an L-shaped cross section. It is fastened to the auxiliary branch  79  by its longer branch, and its shorter, free branch protrudes perpendicularly thereto in the direction of the bar  71 . It should be pointed out that the auxiliary bar  75  does not necessarily have to be disposed directly on the auxiliary branch  79 . In  FIG. 4 , a preferred variant is represented, in which the auxiliary branch  79  back-grips a portion of the end plate  57  which projects upward in the manner of a flange, and the auxiliary bar  75  is arranged correspondingly on this flange region of the end plate  57 . The auxiliary bar  75  interacts with its protruding branch preferably with the top side of the bar  71  such that, between them, a gap is formed. This acts as a sealing gap of the inner sealing element  74 . The sealing gap of the outer sealing element  70  has, for example, a 2 mm width. The sealing gap of the inner sealing element  74  can be roughly equal in size, but is expediently dimensioned such that the flow resistance of the inner sealing element  74  is less than that of the outer sealing element. For example, the sealing gap of the outer sealing element  70  has a cross section of 0.5 cm 2  in respect of a 2 mm gap, and the inner sealing element has a cross section of 0.2 cm 2  in respect of a likewise 2 mm gap. 
         [0040]    The outer sealing element  70  and the inner sealing element  74  delimit a conveying duct  8  framed by the branched profile  77 . For this purpose, the branched profile  77  forms with the bar  71  and a prominent part of the end plate  57  a gas space of roughly rectangular cross section. The conveying duct  8  is connected by a narrow interstice  82  and the outer sealing element  70  to the top side of the grate plank  51 , i.e. to the top side of the grate  5 . In addition, the conveying duct  8  is connected to an interstice formed between the mutually facing surfaces of the adjoining end plates  56 ,  57 . It forms a connection with grate pit  9 . The sealing elements  70 ,  74 , by virtue of their construction as gap seals, where appropriate as labyrinth seals, are hard wearing and provide guaranteed sealing tightness even in the event of a longitudinal movement of the adjoining planks  51 ,  52  relative to each other. Such a longitudinal movement has no bearing on the sealing tightness. 
         [0041]    The conveying duct  8  serves to carry away infiltrated stray material. For this purpose, a propellant gas source  80  can be provided on the feed-side end of the grate  5 . It supplies a gas via a corresponding propellant gas connection  81 , the propellant gas flowing along the conveying duct  8  to the delivery side end  6 , and emerges there. The result is that any introduced stray material which enters through the outer sealing element  70  into the conveying duct  8  is transported away along this to a delivery point  86  arranged at the delivery end  6  before it reaches the inner sealing element  74  or might even traverse this and thus reach the grate pit  9 . By virtue of the evacuation into the conveying duct  8 , the quantity of stray material which finally reaches the grate pit  9  can thus be considerably reduced. Given the above-stated dimensions of the sealing elements  70 ,  74 , for example, the conveying duct  8  has a cross section of 32.5 cm 2 . 
         [0042]    It is not absolutely necessary that the propellant gas required for the conveyance into the conveying duct  8  is supplied via a separate propellant gas connection  81  from a separate propellant gas source  80 . It can also be provided to supply the propellant gas via the interstice between the end plates  56  and  57 , to be precise preferably in the region of the feed end  4 . This produces a (desired) gas flow through the inner sealing element  74  such that the gas flows into the conveying duct  8 . Due already to this inflow, stray material is thus deterred from passing out of the conveying duct  8  through the inner sealing element  74 . 
         [0043]    It is often provided that the grate pit  9  is divided into various chambers. Accordingly, the conveying duct  8  can also be divided into chambers. This is not absolutely necessary, however. It can also be provided that the conveying duct  8  is continuous, while the grate pit  9  is divided into chambers. It is important that the propellant gas supply is chosen such that, along the entire length of the conveying duct  8 , a sufficient (positive) pressure gradient between the pressure in the duct  8  and above the grate  5  is given at the respective location. 
         [0044]    The sealing device  7 ′ is correspondingly configured. As is represented in  FIG. 5 , an outer sealing element  70  and an inner sealing element  74  is similarly formed by a step  72  on the bar  71  and between the bar  71  and the auxiliary bar  75 , respectively. The difference lies in the fact that the branched profile  77 ′ has no auxiliary branch  79 , but rather is fixedly connected to the side wall  15 . The advantage of this design is that all elements involved in the formation of the seal, inclusive of the main branch  78  of the branched profile  77 ′, can be constituted precisely the same as in the sealing device  7  between the adjoining planks  51 ,  52 . The sealing device  7 ′ thus achieves the same advantageous sealing effect. 
         [0045]    The third embodiment represented in  FIG. 6  differs from the first embodiment represented in  FIG. 4  essentially by a different arrangement of the inner sealing element  74 ′. This difference is explained in greater detail below; otherwise, the comments made with respect to  FIG. 1  apply analogously. In the first embodiment, the inner sealing element  74  is formed between the bar  71  and an auxiliary bar  75 , which are disposed in the lower region of the conveying duct  8 . In the third embodiment, the inner sealing element  74 ′ is formed between an inner face of the branched profile  77  and an auxiliary plate  75 ′ disposed on the bar  71 . The auxiliary plate  75 ′ is arranged, projecting upward at right angles, on that face of the bar  71  which points toward the end plate  57 . The upper end of the auxiliary plate  75 ′ meets the inner face of the intermediate piece of the branched profile  77  and thus forms the gap of the inner sealing element  74 ′. Owing to its higher specific density compared to the propellant gas, stray material which has made its way into the conveying duct  8  appears mainly in the lower region of the conveying duct  8 . 
         [0046]    The inner sealing element  74 ′, by virtue of its high-situated arrangement at the upper end of the auxiliary plate  75 ′, is subjected only weakly, or not at all, to the stray material. The wear to the inner sealing element  74 ′ is thus reduced to an almost negligible minimum. In addition, this arrangement of the inner sealing element  74 ′ has the advantage that, even in the case of a worn or defective sealing element, the quantity of stray material which finally reaches the grate pit  9  is very small. This embodiment of the sealing element  74 ′ is thus not only hard wearing, but is also robust against unfavorable tolerances or against a sealing gap enlarged by bending loads. 
         [0047]    In  FIG. 7 , a further variant of the first embodiment is represented. It differs from the latter essentially by the fact that the sealing elements  70 ″,  74 ″ are of self-adjusting construction. This means that they are made with a sealing gap of zero width (0 mm). In operation, a bedding-in takes place, in the course of which abrasion occurs due to unavoidable production tolerances or different deflections of the components, so that a desired gap size (target gap size) is established relatively quickly, for example in the order of magnitude of about 2 mm (cf.  FIG. 4 ). With such a construction, not only is a more rational production enabled, but a self-adjusting sealing gap is created, the gap size of which ultimately lies closer to the target gap size than would be economically feasible in the case of conventional direct production.