Abstract:
The invention relates to a multi-level furnace for thermal treatment of the material flow which has at least two process chambers arranged one above another, each providing at least two level floors, and is equipped with one or more transfer devices for transferring the treated material flow from an upper process chamber to a lower process chamber. In order to separate the two process chambers in terms of gas flow, the transfer device has means for forming a material column in the transition region between the upper and the lower process spaces, wherein said means for forming a material column comprise at least one conveying unit or at least one chute, and the at least one conveying unit or at least one chute also forms a material removal device for the upper process chamber and/or a material input device for the lower process chamber.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is the United States national phase of International Application No. PCT/EP2013/073349 filed Nov. 8, 2013, and claims priority to German Patent Application No. 10 2012 111 050.6 filed Nov. 16, 2012, the disclosures of which are hereby incorporated in their entirety by reference. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to a multi-level furnace and to a method for the thermal treatment of a material flow, preferably a material flow containing carbon. 
     Description of Related Art 
     The thermal treatment of a material flow is understood as also meaning in particular a torrefaction, in which biomass is thermally treated by pyrolytic decomposition at relatively low temperatures of 250° to 450° C. with the exclusion of air. 
     WO 2012/007574 A1 discloses a device and a method for the drying and torrefaction of at least one carbon-containing material flow in a multi-level furnace. The drying and the torrefaction take place there in two different process chambers that are spatially separate from one another. This spatial separation makes it possible for the atmosphere to be specifically set to suit the respective process (drying or torrefaction). In this way, the efficiency, and consequently also the throughput, of the device can be increased significantly. The transfer device provided between the two process chambers is not specified any more precisely in this document. It is however conceivable to realize the gas separation of the process chambers by cellular wheel sluices or double swing valves. However, the installation of these sluices is only possible outside the process chambers, and so a separate furnace is required for each process chamber. 
     SUMMARY OF THE INVENTION 
     The invention is therefore based on the object of reducing the structural complexity of the gastight separation of the two process chambers. 
     The multi-level furnace according to the invention for the thermal treatment of a material flow, preferably a material flow containing carbon, has at least two process chambers arranged one above the other, which respectively provide at least two floors for the levels, and is equipped with one or more transfer devices for transferring the treated material flow from an upper process chamber to a lower process chamber, the transfer device having for the gastight separation of the two process chambers means for forming a column of material in the transitional region between the upper process chamber and the lower process chamber, the means for forming a column of material comprising at least one delivery unit or at least one chute or a slider and the at least one delivery unit or at least one chute at the same time forming a material output device for the upper process chamber and/or a material input device for the lower process chamber. 
     In the case of the method according to the invention for the thermal treatment of a material flow, preferably a material flow containing carbon, this material flow is treated in a multi-level furnace in at least two process chambers arranged one above the other and separated gastightly from one another and respectively equipped with at least two floors for the levels. The material flow is transferred by a transfer device from an upper process chamber to a lower process chamber, a column of material being formed in the transfer device for the gastight separation of the two process chambers, the forming of the column of material being performed by at least one delivery unit or at least one chute or a slider and the at least one transfer device being used not only for transferring the material flow from the upper process chamber to the lower process chamber but also for discharging at least part of the material flow from the multi-level furnace and/or for introducing material into the multi-level furnace from outside. 
     Using the material to be treated to ensure the gastight separation of the two process chambers can be realized in a structurally comparatively simple manner. The further advantage is especially also that the transfer device can be realized within the multi-level furnace. 
     The fact that the at least one delivery unit at the same time forms a material output device for the upper process chamber and/or a material input device for the lower process chamber gives rise to the possibility of being able to discharge partly treated material or feed in additional material while bypassing an upper process chamber. 
     Further refinements of the invention are the subject of the subclaims. 
     In this case, at least three process chambers arranged one above the other and at least two delivery units may be provided, the two delivery units being connected to one another in such a way that at least one process chamber arranged between the two delivery units is bypassed. It is also conceivable that one or both delivery units is/are in connection with at least one material store and/or intermediate store. 
     According to a preferred refinement of the delivery unit, it has a first feed opening, in connection with the upper process chamber, and a first outlet opening, provided at an end region of the delivery unit and in connection with the lower process chamber. Furthermore, a second feeding device may be provided, connected to a material charge, for directly charging filter dust, reject materials, odor-intensive materials or materials for increasing the reactivity or the delivery capacity into the lower process chamber. Furthermore, the delivery unit may also have a second outlet opening, in connection with the area outside the multi-level furnace, for discharging material from the multi-level furnace. The delivery unit or units is/are therefore appropriately equipped with a reversible drive, in order to connect the feed opening to the first or second outlet opening in terms of delivery. 
     Instead of a delivery unit, according to another exemplary embodiment of the invention the means for forming a column of material may also comprise a chute in which a column of material forms. 
     For monitoring the gastight separation of the two process chambers, according to a further aspect of the invention it is provided that the differential pressure between the upper process chamber and the lower process chamber is determined. Then there is also the possibility that the delivery rate of the at least one delivery unit is controlled in dependence on the measured differential pressure in such a way that a gastight separation of the two process chambers is ensured. 
     This gastight separation of the process chambers makes it possible that the temperature and/or the humidity and/or the pressure in the two process chambers can be set individually. The thermal treatment of the material flow in the individual process chambers in this case preferably takes place with the aid of a stream of treatment gas, which is fed to each process chamber and, after acting on the material flow, is removed again. The gastight separation of process chambers lying one above the other provides the possibility of individually setting the direction of flow of the treatment gas with respect to the direction of the material flow, the direction of flow of the treatment gas preferably being set in co-flow in at least one upper process chamber and in counter-flow in at least one lower process chamber. The co-flow treatment is of advantage in particular for the drying of the material flow, while the torrefaction appropriately takes place in counter-flow. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further refinements of the invention are explained more precisely below on the basis of the description of a number of exemplary embodiments and the drawing, in which: 
         FIG. 1  shows a schematic representation of a multi-level furnace according to a first exemplary embodiment, 
         FIG. 2  shows a schematic view of a detail of the transfer device formed as a delivery unit, 
         FIG. 3  shows a schematic representation of a multi-level furnace according to a second exemplary embodiment and 
         FIG. 4  shows a schematic representation of a multi-level furnace according to a third exemplary embodiment. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     The multi-level furnace represented in  FIG. 1  for the thermal treatment of a material flow serves for example for the drying and torrefaction of a material flow containing carbon. It has two process chambers  1 ,  2 , which are arranged one above the other and respectively have multiple floors for the levels  5  to  11 . The material flow  25  to be treated is fed to the process chamber  1  from above by way of a feeding device  12 . The transporting of the material on the floors for the levels takes place by way of customary transporting devices, such as for example a rabble arm system  27  rotating with a central column  13 , which transport the material to inner- or outer-lying openings, where the material falls onto the floor for the next-lower level. It is of course also conceivable in principle that the floors for the levels rotate with the central column  13  and interact with fixed strippers. In  FIG. 1 , only one rabble arm system  27  is represented in the region of the floor for the level  5 . It goes without saying that such rabble arm systems may also be provided in the region of the floors for the other levels. 
     The heat treatment of the material flow  25  in the upper process chamber  1  takes place with the aid of a first stream of treatment gas  14 , which is fed in by way of an input  15 , provided in the upper region of the process chamber  1 , and is removed by way of an output  16 , provided in the lower region of the process chamber  1 . In the case of this arrangement, the heat treatment takes place in cross-flow or co-flow with the direction of material flow. Depending on the application, however, it may also be appropriate to carry out the heat treatment in counter-flow. It is also conceivable that there are multiple streams of treatment gas, for example a stream of treatment gas is respectively fed in and removed from the floor for each level. In a similar way, a second stream of treatment gas  19  is fed in and removed in the lower process chamber  2  by way of an input  17  and an output  18 . Here, the treatment of the material flow takes place in counter-flow with respect to the treatment gas. Here, too, further streams of treatment gas may of course also be fed in and removed. Finally, at the lower end of the lower process chamber  2  there is an output device  20  for the treated material flow  25 ′. 
     Provided between the two process chambers  1  and  2  is a transfer device  21 , which has a delivery unit  21 . 1  formed as a delivery screw, in order to transfer the material flow from the upper process chamber  1  to the lower process chamber  2  while forming a column of material  24 . The floor for the lowermost level  8  of the upper process chamber  1  at the same time forms the ceiling of the lower level chamber  2 . The opening  8 . 1  in the floor for the level  8  in this case represents the connection between the two process chambers, the delivery unit  21 . 1  being arranged directly under the opening  8 . 1 . 
     Further details are explained more precisely below on the basis of  FIG. 2 . 
     The delivery unit  21 . 1  is in connection with the opening  8 . 1  in the floor for the level  8  by way of a first feed opening  21 . 2  in such a way that the material flow  25  located on the floor for the level  8  enters the delivery unit  21 . 1  by way of the opening  8 . 1 , while forming a column of material  26 . The delivery unit  21 . 1  has a drive  21 . 3 , in order to transport the material flow  25  to a first outlet opening  21 . 4 , arranged at one end of the delivery unit. There, the material flow falls onto the floor for the level  9  of the second process chamber  2 . The gastight separation of the two process chambers  1  and  2  is formed by the column of material  26  forming, which in the case of this exemplary embodiment continues in the delivery member  21 . 1 , formed as a delivery screw, up to the first outlet opening  21 . 4 . The delivery rate is controlled by way of the drive  21 . 3  in such a way that there is always a sufficient column of material  26  to ensure the gastight separation of the two process chambers  1 ,  2 . For this purpose, the differential pressure between the upper process chamber  1  and the lower process chamber  2  could be determined, in order to monitor the gastight separation, the delivery rate of the delivery unit  21 . 1  being controlled in dependence on the measured differential pressure in such a way that the gastight separation of the two process chambers is ensured. 
     In the case of the exemplary embodiment represented here, the delivery unit  21 . 1  is provided at its end opposite from the first outlet opening with a second outlet opening  21 . 5 , which is in connection with the area outside the multi-level furnace. In this way, the reversible drive  21 . 3  provides the possibility of not transferring at least part of the material flow  25  into the second process chamber  2 , but instead discharging it by way of the second outlet opening  21 . 5 . This may be used for example for bypassing at least one process chamber or for discharging at least part of the material flow into a material and/or intermediate store. The second outlet opening  21 . 5  could also be used for the purpose of taking samples. Furthermore, the delivery unit  21 . 1  has a second feed opening  21 . 6 , which is provided outside the multi-level furnace and by way of which additional material, such as filter dust, reject materials, odor-intensive materials or materials for increasing the reactivity and the delivery capacity, can be fed to the second process chamber  2 . The transfer device  21  consequently serves not only for establishing the gastight separation of the two process chambers but also in the embodiment shown here for discharging and/or feeding in material. The reversible drive  21 . 3  of the delivery member  21 . 1  also offers the possibility of responding to a blockage or a jam in the transfer region. There is also the possibility of accelerated discharge of the material flow from the process chamber arranged thereabove, for example in the event of an accident. 
     The delivery unit  21 . 1  is in this case preferably formed and arranged in such a way that it is only mounted outside the multi-level furnace, i.e. in a cold region, but the first feed opening  21 . 2 , in connection with the opening  8 . 1  in the floor for the level  8 , and the first outlet opening  21 . 4  are arranged inside the multi-level furnace. The two process chambers  1  and  2  consequently do not have to be realized in two separate furnaces, but rather can be accommodated in one and the same multi-level furnace. 
     In the exemplary embodiment represented, the delivery member  21 . 1  is formed as a delivery screw. However, it is also conceivable within the scope of the invention for it to be formed as a slider. 
     In terms of the form of the multi-level furnace, the exemplary embodiment according to  FIG. 3  corresponds to the exemplary embodiment according to  FIG. 1 . However, a transfer device  24  formed as a chute  24 . 1  is provided between the two process chambers  1  and  2 . The shaft-like chute  24 . 1  is connected directly to the opening  8 . 1  in the floor for the level  8  and ends above the floor for the level  9 , and so a conical heap forms between the end of the chute  24 . 1  and the floor for the level  9 . Also in the case of this exemplary embodiment, gastight separation of the two process chambers  1  and  2  is ensured by the column of material  26 , which here forms in the chute  24 . 1 . It is therefore required that the delivery rate at which the material flow moves on the floor for the level  9  and is fed to the floor for the next-lowest level  10  is set and possibly regulated in such a way that a sufficient column of material  26  to ensure the gastight separation has always formed in the transfer device  24 . The delivery rate of the material flow on the floors for the levels is ensured here by the rabble arm system  27  rotating with the central column  13 . It is therefore entirely appropriate if the rabble arm systems of the upper process chamber  1  and the lower process chamber  2  can be regulated in their speed independently of one another. For checking the gastight separation of the two process chambers, and possibly also for regulating the speeds of the rabble arm systems, the differential pressure between the two process chambers may also be determined in the case of this exemplary embodiment. 
     The exemplary embodiment represented in  FIG. 3  is distinguished by a transfer device of a simple construction. However, here it is not possible for material to be discharged or fed in from outside in the region of the transfer device. 
     A multi-level furnace with four process chambers  1 ,  2 ,  3  and  4  arranged one above the other is represented in  FIG. 4 . Provided between the individual process chambers are transfer devices  21 ,  22  and  23 , which are configured according to  FIG. 2 . Each of the process chambers  1  to  4  may be subjected by way of inputs  15 ,  17 ,  27 ,  28  to individual streams of treatment gas  14 ,  19 ,  31 ,  32 , which are discharged again by way of outputs  16 ,  18 ,  29  and  30 . In this way, a specific charge can be assigned to each process chamber. Thus, for example, drying may take place in the process chamber  1 , heating, calcination or torrefaction may take place in the process chambers  2  and  3  and cooling of the material flow may take place in the process chamber  4 . 
     The specific form of the transfer devices  21  to  23  makes it possible for part of the material flow to be discharged, in order that, while bypassing individual process chambers, it is fed again to a process chamber lying further below or discharged prematurely and charged to a material store  33 . 
     In the exemplary embodiment represented, for example, a partial flow of the material flow treated in the first process chamber  1  is discharged by way of the transfer device  21  and fed to the fourth process chamber by way of the transfer device  23 . As a result, a dried and cooled material flow that has not undergone torrefaction can be obtained for example. 
     It is also provided that a partial flow is discharged by way of the second transfer device  22  or the third transfer device  23  and charged directly to the material store  33 . 
     The material flows thereby discharged have been partially or completely thermally treated, but not cooled. Depending on the application, other bypassing or discharging operations may also be provided within the scope of the invention. 
     The gastight separation of process chambers arranged one above the other allows the temperature and/or the humidity and/or the pressure and/or the atmosphere in each of the process chambers to be set individually by way of the stream of treatment gas fed in. In addition, there is the possibility of individually setting the direction of flow of the treatment gas with respect to the direction of the material flow for each process chamber, in that the treatment gas is fed to the respective process chamber either at the top or at the bottom. This allows the direction of flow of the treatment gas to be set according to choice in co-flow, in cross-flow or in counter-flow with respect to the material flow. Depending on whether the process chamber is used for drying, thermal treatment (torrefaction, calcination, heating) or cooling, the direction of flow of the treatment gas with respect to the material flow that is preferred for the respective application can be selected in each case. It would also be conceivable within the scope of the invention that separate treatment gases are fed in and removed, at least for individual levels. In this case, one would say that the stream of treatment gas is fed in and removed in cross-flow with respect to the material flow.