Abstract:
A transport device for biomass in a fermenter for the generation of biogas and a large-scale fermenter equipped therewith are provided, in which transport device or fermenter a sufficient capacity for transporting the biomass through the transport passage is ensured. This is achieved by the provision of transport cushions on the base, on the side walls and/or at the top or the cover of the transport passage. By the transport cushions being periodically filled and emptied again, the biomass is moved through the transport passage by means of a peristaltic motion.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a transport device for biomass in a fermenter for the generation of biogas, to a large-scale fermenter for the generation of biogas from biomass, and to a method of operating such a large-scale fermenter. 
       BACKGROUND OF THE INVENTION 
       [0002]    Biogas technology has hitherto been mainly concentrated on the “wet fermentation” of liquid manure and biowaste from the municipal sector. Installations and apparatuses for generating biogas from biomass according to the wet fermentation process are known, for example, from publications AT 408230 B, WO 96/12789, DE 3228391 A1, AT 361885 B and DE 19746636 A1. 
         [0003]    From DE 3228391 A1 a digester in the form of an elastic tube is known in which digester the biomass is conveyed through the tube by artificially generated peristalsis. The peristaltic motion is generated by means of loops which are drawn over the tube and are pulled tight, by means of sleeves which are drawn over the tube and to which compressed air is applied, or by means of plungers which are distributed over the length of the tube and press successively into the tube. 
         [0004]    A digester in the form of a round silo is known from DE 19746636 A1, the actual digester being arranged in the center of the round silo and being surrounded by an annular intermediate region. 
         [0005]    A digester in the form of a round silo is likewise known from AT 361885 B, said digester comprising a cylindrical outer wall and a cylindrical inner wall, as a result of which an annular transport passage is formed. The liquid biomass is fed, flows through the transport passage and is removed again. It is also known from AT 361885 B to provide a cylindrical central wall between the inner and the outer wall, as a result of which an inner and an outer transport passage ring are formed. 
         [0006]    Vegetable renewable raw materials having a high content of dry substances (e.g. corn, grass, whole-plant silage) or solid manure can only be admixed to a limited extent in the case of these “liquid” methods. 
         [0007]    “Dry fermentation” allows pourable biomasses from agriculture, from biowaste and cultivated municipal areas to be methanized without converting the materials into a pumpable, liquid substrate. Biomasses having a proportion of up to 50% of dry substances can be fermented. This dry fermentation method is described, for example, in EP 0 934 998. 
         [0008]    During the “dry” fermentation, the material to be fermented is not stirred up into a liquid phase, as is the case, for example, with the liquid fermentation of biowastes. Instead, the fermentation substrate introduced into the fermenter is constantly kept moist by the percolate at the fermenter base being drawn off and sprayed again over the biomass. Optimum living conditions for the bacteria are thus achieved. During the recirculation of the percolate, the temperature can be additionally regulated, and it is possible to provide additives for optimizing the process. 
         [0009]    A bioreactor or a fermenter in the form of a prefabricated garage is known from WO 02/06439, said bioreactor or fermenter being operated according to the principle of dry fermentation by the “batch process”. In this case, after inoculation with material already fermented, the fermenter is filled with the fermentation substrate using wheeled loaders. The fermentation container constructed in a garage shape is closed with a gastight door. The biomass is fermented with the exclusion of air; in the process, no further intermixing takes place and no additional material is fed. The percolate seeping from the fermentation material is drawn off via a drainage channel, is stored intermediately in a tank and is sprayed again over the fermentation substrate for the moistening. The fermentation process takes place within the mesophilic temperature range at 34-37° C.; the temperature regulation is effected by means of floor and wall heating. 
         [0010]    A method and an apparatus for the anaerobic treatment of organic substances having a high proportion of solids, in which biogas is also produced, is known from DE 3341691 A1. In this case, the biomass in a channel is subjected to a rolling, peristaltic motion and is thus conveyed through the digester. The peristaltic motion is achieved by the edges of the channel performing an up and down movement parallel to one another. At the same time, during the up and down movement, pockets are pressed from below into the channel for producing the rolling motion. 
         [0011]    The biogas generated can be used in a combined heat and power plant or cogeneration system for generating electricity and heat. So that sufficient biogas is always available for the combined heat and power unit, a plurality of fermentation containers are operated at staggered intervals in the dry fermentation plant. At the end of the dwell time, the fermenter space is completely emptied and then filled again. The fermented substrate is fed for subsequent composting, such that conventional composting of comparable organic manures results. Such a plant has run very successfully in Munich for several years. 
         [0012]    As a rule, known large-scale fermenters work in batch operation, i.e. the biogas production of the fermenter must be interrupted for loading and unloading and the fermenter filled with biogas must be flooded with air. A large-scale fermenter working according to the principle of dry fermentation would therefore be desirable, in which large-scale fermenter fresh biomass is continuously fed and spent biomass is continuously discharged without the generation of biogas being interrupted. To this end, it is necessary to provide a transport device in the large-scale fermenter, by means of which transport device the biomass is transported from a loading region to an unloading region. 
         [0013]    WO 93/17091 discloses a closed composting apparatus in which compressed air bubbles are arranged in the container base in order to intermix the biomass in the container and in order to transport it through the container from a loading region to a removal region. On account of the associated leakage problems (risk of explosion), this transport method is unsuitable for the generation of biogas with the exclusion of air. 
         [0014]    A transport device for biomass in fermenters is known from WO 2005/085411 A2, in which transport device transport cushions are arranged on the base and on the side walls of the fermenter, which transport cushions can be successively acted upon by a fluid and thus generate a wave motion in order to move the biomass through the fermenter. The transport capacity of such transport cushions is restricted under certain operating conditions of the fermenter. 
       SUMMARY OF THE INVENTION 
       [0015]    Based on the transport device known from WO 2005/085411 A2, an object of the present invention is therefore to provide a transport device having an improved transport capacity for biomass in a fermenter for generating biogas. 
         [0016]    This object is achieved by the features of claims  1  and  7 . 
         [0017]    In the case of the large-scale fermenter known from WO 2005/085411 A2, it has been found that so much percolate results at certain operating states that the biomass floats. Therefore the transport cushions fastened to the base no longer act on the biomass and stir mainly in the percolate. In addition, the biogas experiences a volumetric expansion due to the formation of biogas, such that the biomass also butts against the top or cover of the transport passage and consequently is prevented from being transported further or floated further. An improved transport capacity is achieved by the provision of transport cushions at the top or the cover of the transport passage and/or at the side walls of the transport passage. A sufficient transport capacity is thus also ensured if the biomass floats on an accumulation of percolate on the base or by the biomass striking the cover. The transport device according to the invention comprises a plurality of transport cushions which are arranged one behind the other in the transport direction and are successively filled with fluid and emptied again. 
         [0018]    According to a preferred embodiment, the transport cushions are also additionally arranged and fastened on the base plate of a digester. A wave motion transporting the biomass is generated over the entire width of the transport passage by the up and down motion of the transport cushions. 
         [0019]    The transport cushions on the base are preferably operated with liquid, in particular with hot water, whereas the transport cushions at the cover are preferably operated with a gas which does not form an explosive mixture with the biogas. 
         [0020]    The provision of a transport cushion cover prevents biomass from being deposited between the transport cushions and remaining there. 
         [0021]    Transport cushions can additionally be assigned to one another in pairs and be arranged opposite one another at the side walls. In this way, too, a peristaltic motion of the biomass through the transport passage is achieved or assisted. 
         [0022]    The transport device according to the present invention can be installed in conventional bioreactors or fermenters as are known, for example, from WO 02/06439 A or WO 2005/085411 A2. Large-scale fermenters as claimed in claim  7  are thereby provided. In the large-scale fermenters as claimed in claim  7 , fresh biomass in a loading region is introduced via a transfer lock into the large-scale fermenter constantly producing biogas. In the large-scale fermenter, the biomass is transported from the loading region to an unloading region by the transport device. During the transport of the biomass, biogas is generated and the biomass is “spent”. In the unloading region, the “spent” biomass is removed via a transfer lock. Thus continuous operation is also possible during the generation of biogas according to the principle of the methanization of solids. 
         [0023]    In particular in large-scale fermenters for generating biogas from biomass, leakage problems often occur, in particular at the corners and edges of the containers and at the openings for loading and unloading. Round containers, which have fewer corners and edges with leakage problems, are therefore known from the sector of wet fermentation, in which the liquefied biomass can be pumped into and out of the digester. In the case of the methanization of solids in large-scale fermenters, these round containers are not used on account of the problems during loading and unloading in batch operation. Due to the transport device according to the present invention and the continuous operation possible with said transport device, round containers can also be advantageously used in the case of “dry fermentation”—claim  9 . 
         [0024]    Due to the round type of construction of the large-scale fermenter, sealing problems are considerably reduced, since the outer wall and the inner wall are merely loaded in compression and tension, respectively. However, the normal leakage problems at corners and edges are avoided. The design having an inner wall in the form of a circular ring and an outer wall in the form of a circular ring and surrounding the inner wall results in an annular fermenter container with an annular transport passage. This circular-ring cylinder is subdivided by a dividing wall. The biomass is continuously fed in a loading region on one side of the dividing wall and is continuously discharged in an unloading region on the other side of the dividing wall at the end of the transport passage. The feeding of the fresh biomass in the loading region and the removal of the spent biomass in the unloading region are effected via transfer locks, for example through a liquid bath like a siphon. 
         [0025]    According to an advantageous configuration of the invention, a thrust cushion is provided in the region of the loading device in addition to the bottom, top and/or lateral transport cushions, and this thrust cushion can expand in the transport direction and thus additionally presses the biomass in the transport direction—claims  8  and  11 . 
         [0026]    It is also an object of the present invention to specify a method of operating a large-scale fermenter according to the present invention. 
         [0027]    This object is achieved by the features of claim  13 . 
         [0028]    In particular when using vegetable renewable raw materials as biomass, a high liquid content of the biomass may lead to excessive liquefaction of the biomass in the digester. This would lead to considerable impairment of the transport effect of the transport device having transport cushions. The excessive liquefaction is avoided owing to the fact that the only half-fermented biomass, after one pass, is removed from the digester, dewatered and fed into the digester for a renewed pass. 
         [0029]    According to a preferred embodiment, the percolate extracted from the half-fermented biomass is filtered and the filtrate produced is fed again to the digester together with the microorganisms concentrated therein. This improves the biogas production. 
         [0030]    The other subclaims relate to advantageous configurations of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]    The description below of exemplary embodiments shows further details, features and advantages of the invention with reference to the drawings, in which: 
           [0032]      FIG. 1  shows a schematic illustration of an elongated large-scale fermenter, the base of which is covered with transport cushions; 
           [0033]      FIG. 2  shows a plan view of the transport passage of the embodiment according to  FIG. 1  with a thrust cushion; 
           [0034]      FIGS. 3   a - 3   c  show sectional illustrations for illustrating the wave motion, generated by the transport cushions, by means of exemplary activation; 
           [0035]      FIGS. 4   a - 4   c  show sectional illustrations for illustrating the wave motion, generated by the transport cushions, by means of alternative activation; 
           [0036]      FIG. 5  shows an alternative configuration of the transport cushions; 
           [0037]      FIG. 6  shows an alternative configuration in which the transport cushions are provided with a cover which transmits the wave motion to the biomass lying above it; 
           [0038]      FIG. 7  shows a schematic illustration of a large-scale fermenter in a round type of construction according to the present invention; 
           [0039]      FIG. 8  shows a plan view of the base of the round large-scale fermenter according to  FIG. 7  with correspondingly shaped transport cushions; 
           [0040]      FIG. 9  shows a sectional illustration through the transport passage of the embodiment according to  FIG. 1  or  FIG. 7 ; and 
           [0041]      FIG. 10  shows an alternative configuration of a round large-scale fermenter. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0042]      FIG. 1  schematically shows an elongated, parallelepiped-shaped large-scale fermenter  2  having a rectangular base plate  4 , a top wall  5 , a right-hand side wall  6 , a left-hand side wall  7 , an end wall  8  and a rear wall  9 . The large-scale fermenter  2  comprises, at one end, a loading region  10  having a loading device  12  (indicated by an arrow) passing through the end wall  8  and, at the other end, an unloading region  14  having an unloading device  16  (likewise designated by an arrow) passing through the rear wall  9 . A transport passage  18  defined by the two side walls  6  and  7  is formed between loading region  10  and unloading region  14 . The transport passage  18  is provided with a transport device  20 . Fresh biomass  22  is continuously fed in the loading region  10  by means of the loading device  12 . The biomass  22  is delivered to the other end of the large-scale fermenter  2  to the unloading region  14  by the transport device  20 . Biomass  22  is removed from the unloading region  14  by means of the unloading device  16 . The feeding of fresh biomass and the discharge of the fermented biomass may also be effected through the top  5  or the side walls  7  and  8 . The transport device  20  consists of a plurality of transport cushions  24 - i  arranged directly adjacent to one another in the transport passage  18  on the base plate  4 . As can be seen from  FIG. 1 , the individual transport cushions  24 - i  extend over the entire width of the large-scale fermenter  2  and are in the form of cylinders bisected heightwise and having an oval base area. That is to say, the top side of the transport cushions is arched and does not appear so straight as in the illustrations in  FIGS. 1 to 6 . The expansion of the individual transport cushions  24 - i  upward can be periodically increased and reduced by periodic feeding and removal of fluid by means of a fluid control device  26 . A wave motion can be generated by the feeding of fluid to and removal of fluid from directly adjacent transport cushions  24 - i , the biomass  22  being conveyed from the loading region  12  to the unloading region  14  by said wave motion. 
         [0043]      FIG. 2  shows a plan view of the front part of the transport passage  18  of the large-scale fermenter according to  FIG. 1 . In the loading region  10 , a thrust cushion  25 , which presses biomass in the transport direction by fluid being applied to it repeatedly, is arranged on the end wall  8 . Depending on the height of the end wall  8  or of the transport passage  18 , a plurality of thrush cushions  25  arranged one above the other may also be provided. 
         [0044]    The continuous transport of biomass  22  by the transport cushions  24 - i  is shown schematically in  FIGS. 3   a ,  3   b  and  3   c  for a large-scale fermenter  2  filled with biomass  22 . In order to illustrate the transporting wave motion,  FIGS. 3   a ,  3   b  and  3   c  each show ten transport cushions  24 - 1  to  24 - 10  distributed over the transport passage  18 . No transport cushion is provided in the unloading region  14 . 
         [0045]    First of all, according to  FIG. 3   a , fluid is pumped into the last transport cushion  24 - 10  upstream of the unloading region  14  against the weight of the biomass  22  carried on the last transport cushion  24 - 10 , and the biomass  22  carried on the last transport cushion  24 - 10  is lifted and falls partly into the free unloading region  14 . After that, the fluid is removed from or pumped out of the last transport cushion  24 - 10 . According to  FIG. 3   b , fluid is pumped simultaneously into the penultimate transport cushion  24 - 9 . The transport cushion  24 - 8  is thereupon inflated while the transport cushion  24 - 9  is emptied— FIG. 3   c —until finally the first transport cushion  24 - 1  is inflated and emptied again (not shown). The process then begins again at the last transport cushion  24 - 10 . This generates a wave motion, which continuously conveys the biomass  22  from the loading region  10  to the unloading region  14 . With this activation of the individual transport cushions  24 - i , the wave motion runs against the transport direction. This activation ought to be especially suitable in the case of a very large proportion of dry substances in the biomass  22 . 
         [0046]      FIGS. 4   a  to  4   c  show alternative activation of the individual transport cushions  24 - i  in order to transport the biomass  22  in the transport passage  18  from the loading region  10  to the unloading region  14 . In particular in the case of biomass  22  having a smaller proportion of dry substances and a liquid level above the transport cushions, in which liquid level the dry substance of the biomass floats, a wave motion in the transport direction is suitable. This is shown schematically in  FIGS. 4   a  to  4   c.    
         [0047]    First of all, according to  FIG. 4   a , liquid is pumped into the first transport cushion  24 - 1  in the loading region  10  against the weight on the biomass  22  carried on the first transport cushion  24 - 1  and the liquid above the first transport cushion  24 - 1  is displaced. Next, the second transport cushion  24 - 2  is inflated with liquid—see  FIG. 4   a . Then, see  FIG. 4   b , the liquid is drained from the first transport cushion  24 - 1  and at the same time the third transport cushion  24 - 3  is inflated, while the second transport cushion  24 - 2  remains inflated. Next, see  FIG. 4   c , the liquid is drained from the second transport cushion and the fourth transport cushion  24 - 4  is inflated, while the third transport cushion remains inflated. In this way, a “transport wave” is generated in the transport direction, and this “transport wave” conveys the biomass  22  from the loading region  10  to the unloading region  14 . In this case, the unloading region  14  is not free of biomass  22 . 
         [0048]    Depending on the length of the transport passage, a plurality of “wave crests” moving through the transport passage and in the form of transport cushions  24 - i  filled with liquid may also be formed. In a similar manner to the activating method according to  FIGS. 3   a  to  3   c , the direction of the wave motion can reversed here too. 
         [0049]      FIG. 5  schematically shows an alternative configuration of the transport cushions in such a way that the surface of the transport cushions  24 - i  is inclined in the transport direction in the inflated state. The conveying effect is increased by this configuration. 
         [0050]      FIG. 6  shows a further configuration of the transport device according to the invention, which differs from the embodiments described above in that the biomass  22  does not rest directly on the transport cushions  24 - i  but rather on a transport cushion cover  28  in the form of film which rests on the transport cushions  24 - i . This prevents biomass from being permanently deposited between adjacent transport cushions  24 - i  and  24 - i+ 1. 
         [0051]      FIG. 7  shows a large-scale fermenter  40  in a round type of construction with a circular-cylindrical digester  42 . The large-scale fermenter  40  comprises a planar base plate  44 . A circular-cylindrical outer wall  46  extends vertically from the base plate  44 . The circular-cylindrical outer wall  46  encloses a circular-cylindrical inner wall  48  of smaller diameter. The space between the outer and the inner wall  46 ,  48  is closed by a cover (not shown). The base plate  44 , the outer wall  46 , the inner wall  48  and the cover, which are connected to one another in a gastight manner, form the digester  42 . 
         [0052]    The digester  42  is subdivided in the interior by a dividing wall  52 . A loading region  54  having a loading device  56  passing through the outer wall  46  is provided on one side of the dividing wall  52 . An unloading region  58  having an unloading device  60  passing through the outer wall  46  is provided on the other side of the dividing wall  52 . 
         [0053]    An annular transport passage  62  defined by the inner wall  48  and the outer wall  46  is formed between loading region  54  and unloading region  58 . A transport device  64  of the type described with reference to  FIGS. 2 to 5  is provided in the transport passage  62 , said transport device  64  comprising a plurality of transport cushions  66 - i  which are arranged directly adjacent to one another on the base plate  54 . As can be seen from  FIG. 8 , the transport cushions  66 - i  have roughly the shape of pieces of cake with a cut-off tip, i.e. they are wider in the region of the outer wall  46  than in the region of the inner wall  48 . 
         [0054]    The double arrow  50  in  FIG. 7  designates an unloading and loading device which is arranged between the loading region  54  and the unloading region  58  in such a way as to pass through the outer wall  46 . Via the unloading and loading device  50 , the half-fermented biomass  22  is removed from the digester  42 , dewatered and returned again into the digester  42 . The dewatering may be effected, for example, by means of a separator. The percolate accumulating in the separator is filtered and the filtrate produced is returned again into the digester. The conversion rate of the biomass  22  is increased and the biogas production is thus improved by the microorganisms contained in the filtrate. 
         [0055]    The transport device  64  with the transport cushions  66 - i  is shown in  FIG. 8  in a view from above. The transporting wave motion is generated in an analogous manner to the embodiment according to  FIG. 1 . 
         [0056]      FIG. 9  shows a sectional illustration through the transport passage  18  or  62  according to  FIG. 1  or  7 , respectively. As can be seen from  FIG. 9 , top transport cushions  67 - i  are also arranged at the cover  5 . The top transport cushions  67 - i  are arranged at the cover  5  in mirror image to the bottom transport cushions  24 - i ,  66 - i . In addition, lateral transport cushions  68 - i  may also be provided at the side walls  6 ,  7  or at the outer wall  46  and the inner wall  48 . Here, the transport cushions  68 - i  opposite one another are in each case assigned to one another in pairs and are activated synchronously. The top and bottom transport cushions  24 - i ,  66 - i  and  67 - i  can also be activated synchronously in pairs. The activation of the transport cushions  67 - i  and  68 - i  is otherwise effected in an analogous manner to the activation of the transport cushions  24 - i  or  66 - i . The top, the bottom and the lateral transport cushions in one plane can be activated synchronously, such that a peristaltic motion like an intestine is obtained. 
         [0057]      FIG. 10  shows an alternative embodiment of a transport device  70  in an illustration corresponding to  FIG. 8 . The transport device  70  likewise comprises a plurality of bottom transport cushions  72 - i  which are distributed in an inner transport passage ring  74  and an outer transport passage ring  76 . The inner and the outer transport passage ring  74 ,  76  are separated from one another by a central wall  78  arranged concentrically to the inner and the outer wall  48 ,  46 . In this case, the number of transport cushions  72 - i  in the outer transport passage ring  76  is greater than in the inner transport passage ring  74 . In the exemplary embodiment shown in  FIG. 10 , the number of transport cushions  72 - i  in the outer transport passage ring  76  is twice that in the inner transport passage ring  74 . This takes into account the fact that the transport path in the outer transport passage ring  76  is longer than in the inner transport passage ring  74 . The transporting wave motion is generated in an analogous manner to the embodiments according to  FIGS. 1 and 7 . As in the embodiments described above, lateral and top transport cushions may also be provided. 
         [0058]    A transport cover according to  FIG. 6  may also be provided in the case of the transport devices  64  and  70 . The configuration of the top side of the transport cushions according to  FIG. 5  may also be provided. Likewise, in the embodiments according to  FIGS. 7 and 10  or in the case of the transport devices  64  and  70 , one or more thrust cushions  25  may be arranged according to the illustration in  FIG. 2  in the loading region  54  at the dividing wall  52  in order to assist the transport of the biomass away from the dividing wall  52 . 
         [0059]    The large-scale fermenters according to the invention for continuous operation are especially suitable for biomass from renewable raw materials, since said biomass, on account of its homogeneity, can easily be conveyed by the transport device according to the invention. 
         [0060]    The illustrations described above are not true to scale but rather are diagrammatic illustrations.