Patent Publication Number: US-2012040328-A1

Title: Fermenter feed system for fermentable biomass of a biogas system and method for operating the feed system

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a fermenter feed system for fermentable biomass of a biogas system, as well as a method for operating the feed system. 
     In commonly known biogas systems, a fermented wet anaerobic breakdown process is used to extract biogas biomass. Automated fermenter feed systems are customarily used to feed the fermenter with fermentable biomass, whereby pumps are provided for liquid substrate components. Delivery and treatment devices are provided for solid substrate components, and delivery and treatment devices are provided for solid substrate components, between a solid biomass depot and a fermenter feed port. As a rule, such a delivery and treatment device comprises a dosing feeder as well as conveying means, in particular conveyor belts and/or screw conveyors, leading to the fermenter. A known dosing feeder consists of a container, for example, that can be filled with biomass, which sits on weighing cells, from which a predetermined biomass amount is fed to the fermenter by means of a floor conveyor belt connected to extruding screws on the face side for further transport to the fermenter. 
     The biogas produced is either injected directly into the gas pipelines after cleaning, or used for power generation in a thermal power station. The economic effectiveness of a biogas system depends essentially on the type of the biomass that can be injected, its availability, as well as the effectiveness of the fermentation process with the shortest possible substrate dwell time in the fermenter with a high degree of breakdown for a high biogas yield. 
     Furthermore, a method for the production of plant substrates for the growing of cultivated plants in the garden and landscaping is known (DE 44 44 745 C1) with which the wood waste premixed with sewage sludge, liquid manure and biocompost are broken down, fiberized and vigorously mixed together in a screw extruder, wherein temperatures rise to over 100° C. As a result, pathogens, bacteria, etc. are killed off, so that the largely sterile plant substrate on the extrusion head is discharged for further use. Furthermore, a similar method for the disposal of biological waste from cities and towns is known (DE 195 14 975 A1). 
     From EP 1 978 086 A1 a process for the hybrid breakdown of water- and lignocellulose-containing biomass by means of defibration and hydrolysis is known, in which in a first stage lignocellulose-containing biomass is treated by a defibration device, and then, in a subsequent stage, the treated, lignocellulose-containing biomass is heated in a thermal hydrolysis process in a high-pressure microwave and hydrolyzed before finally, in a last stage, the hydrolyzed lignocellulose-containing biomass is subjected to an aerobic fermentation process. Within the thermal hydrolysis of the biomass in a high-pressure microwave, the water-containing biomass is briefly heated to far over 100° C., so that through high temperatures and the evaporated water from the biomass, thermal hydrolysis takes place. The temperature rise thereby takes place from 160 to 220° C., for example, with a great increase in pressure from 5 to 25 bar. The defibration of the biomass is preferably carried out by means of an extruder, which may be designed as a single screw extruder or a twin-screw extruder or a twin-worm extruder. With this type of process, a shortening of the customary dwell time and fermentation time in the fermenter of a biogas reactor should be achieved in addition to the increase in biogas yield. This type of design is relatively energy-intensive and also expensive to manufacture, in particular due to the use of a high-pressure microwave. 
     SUMMARY OF THE INVENTION 
     An object of the invention is thus to propose a fermenter feed system and a method for operating this type of fermenter feed system, wherein the fermenter feed system is simply constructed and can be operated with a low energy cost. The fermenter feed system can be used with a wide range of types of biomass for biomass production and thus can be simply processed in such a way that the subsequent fermentation process can run efficiently and reliably, even with high dry substance content with short substance dwell times and a high degree of breakdown and thus a higher biogas yield. 
     This objective is achieved according to one embodiment of the invention by providing a fermenter feed system for fermentable biomass of a biogas system which has a delivery and treatment device between a biomass depot, preferably designed as a traveling silo, and which has at least one fermenter, in particular at least one fermenter feed port, whereby the delivery and treatment device has at least one conveying means for the biomass to be fed to the fermenter. Furthermore, a preferably mechanical cell breakdown apparatus for biomass is integrated into the feed and treatment device, via which at least a part of the biomass to be delivered to the fermenter is conducted and is fed to the fermenter after the cell breakdown. 
     Due to such cell breakdown, biomass solids can advantageously be used during the biogas production in the fermentation process, particularly straw and grass, which otherwise are not fermentable or are only ineffectively fermentable. Furthermore, a reduction in size of the biomass solids occurs with the cell breakdown, so that these are more accessible for the bacteria in the fermenter and thus in the fermentation process, and form a structure which is more easily attacked, so that a high dry substance content in the substrate with lower dwell times and higher biogas yield is possible. In addition, savings can thus be achieved in the dimensioning and operation of the fermenter mixing process, whereby a tendency to form floating layers or sinking layers is reduced. Due to this pretreatment, the biogas yield is considerably increased, which in turn results in low use of biomass and which is reflected in smaller sizes for the fermenter, so that the biogas system is cheaper to purchase and to operate than the customary biogas systems. 
     According to the invention, the diameter of an outlet opening of the cell breakdown apparatus, preferably the diameter of an outlet opening or nozzle of a cell breakdown extruder, may be varied by way of an adjustable actuating member, in particular an actuating member that can be controlled by an electric, hydraulic or pneumatic drive. Furthermore, at least one temperature sensor and/or pressure sensor is associated with the cell breakdown apparatus by means of which the temperature and/or the pressure in a predetermined region of the cell breakdown apparatus and/or biomass is/are detected. Furthermore, a diameter regulator is provided, to which the output signal of the temperature sensor is fed as an actual temperature value and/or of the pressure sensor as an actual pressure value. The actual value is compared to a predetermined target value, and the regulator is activated when the actual value falls below the target value for a defined, predetermined reduction of the outlet opening diameter. 
     With the fermenter feed system according to the invention, a desired cell breakdown process can be ensured in a simple and operationally reliable way, and the required temperature and/or pressure required in the cell breakdown apparatus can be ensured. Specifically, the measuring values of the temperature sensor and/or pressure sensor can be arranged, for example, in the proximity of the outlet nozzle of a cell breakdown apparatus, and supplied to the diameter regulator as actual values, which can be set at a target value and/or target pressure for a reliable cell breakdown, particularly a target temperature value default of at least 40° C., most preferably at least 60° C. If there is a trend towards a fall in the actual temperature value and/or of the actual pressure value below the particular predetermined target value, then the actuating member for the reduction of the outlet opening diameter is triggered by the regulator. As a result, for comparable power consumption of the cell breakdown apparatus, more energy is introduced in the current delivered and treated biomass, so that an optimal biomass adapted to this particular case can be made available for a fermentation in a fermenter of a biogas system. 
     The temperature sensor and/or pressure sensor in the cell breakdown apparatus is/are preferably arranged directly upstream from or in the outlet opening, in particular directly upstream from or in an outlet nozzle of a cell breakdown extruder. For example, it can be provided that the temperature sensor and/or the pressure sensor is arranged in a wall region or in an inner lining region of the cell breakdown apparatus in the proximity of the outlet opening. These possible attachments of the sensors, previously stated as examples, demonstrate that there are various possibilities in the region of the cell breakdown apparatus to detect an actual temperature and/or an actual pressure in order to directly or indirectly deduce whether, in the region of the biomass treated in the cell breakdown apparatus, a desired cell temperature and/or pressure for an optimal cell breakdown exists. An indirect detection the temperature means that it is possible, for example, to measure the temperature in a wall region in the proximity of an outlet opening of the cell breakdown apparatus, on the basis of which the temperature in the treated biomass may be deduced. 
     The cell breakdown apparatus can be advantageously integrated into the conveying path for the biomass between a dosing feeder and the fermenter. As a result, the cell breakdown apparatus is arranged in the outer region and exposed to the weather conditions. Thus, it is proposed to design a thermally insulated cell breakdown apparatus, either by means of direct thermal insulation in the manner of an insulated casing or indirect thermal insulation in the form of an insulated housing. Such thermal insulation is advantageous and essential in particular, for example, when a cell breakdown extruder with worm shafts, preferably a double worm shaft extruder having a dosing feeder and an outlet nozzle, is used. However, optionally the thermal insulation is sufficient even only if provided in the region of the worm shafts. Cell breakdown takes place with this type of extruder by the introduction of mechanical energy into the biomass conveyed in the extruder by means of friction of the biomass, rotating with the worm screws, against the stationary housing cylinder wall. High pressures and high temperatures can thus be produced in the biomass. Discharge of the biomass at the outlet nozzle then causes a pressure relaxation and/or temperature cooling, which leads to the cell breakdown. 
     An advantageous formation of the conveying path with the incorporated cell breakdown apparatus, in particular with a cell breakdown extruder, is provided. In the process, a first conveyor, preferably a first belt conveyor, goes from the dosing feeder into a region above the cell breakdown apparatus. A second conveyor, preferably a second conveyor belt, goes out from a region under the outlet opening or outlet nozzle of the cell breakdown apparatus to the fermenter. With the first conveyor belt, biomass can be fed directly to the cell breakdown apparatus, for example, via a feed hopper with a motor-drivable stuffing screw. In the event of a malfunction of the cell breakdown apparatus, due to hard impurities, in particular metal pieces, in order to ensure continued feeding of the fermenter, an activatable damper is preferably provided, by means of which either the cell breakdown apparatus is fed according to the adjusted position, or a bypass directly to the second conveyor belt for direct transport to the fermenter. 
     Alternatively, a third conveyor belt connected to the first conveyor belt is provided, whose running direction is reversible, so that the cell breakdown apparatus can be fed in the one direction, while the biomass can be transported directly in the other direction, for example, via a pipe socket, in a direct and bypass path to the second conveyor. In this embodiment with a third conveyor, in particular a conveyor belt, the above-explained damper connected with the bypass at that location is unnecessary. 
     To protect the cell breakdown apparatus, in particular a cell breakdown extruder, and for improved reliability, at least one malfunction detection device for impurities in the biomass, for example, for metal pieces, stones, etc. is provided in the dosing feeder. With substance impurity detection, the above-mentioned damper to the bypass and/or transport direction can be reversed for the third conveyor, whereby this process is preferably automated. 
     In order to equalize the power consumption, in particular of an electric drive for the cell breakdown apparatus, to a suitable level, a regulation of the extruder feed quantity via a feed regulator is proposed whereby this regulation acts on a rotationally driven stuffing screw. For this purpose, the power consumption is measured as the actual value and, for example, for power consumption which is predetermined or which tends to decrease, the screw conveyor speed is increased via the feed regulator for a greater biomass feed. This regulator is appropriately designed via suitable control parameters for a quicker control response in comparison to the nozzle diameter control of the outlet opening. 
     The object regarding the method is achieved by the features of claim  11 . The resulting advantages have already been increased in connection with the advantages for the fermenter feed system. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The present invention shall now be explained in more detail by reference to several preferred embodiments thereof, schematically represented in the drawings. 
         FIG. 1  is a perspective view of a fermenter feed system according to the invention; 
         FIG. 2  is a top view of the fermenter feed system according to  FIG. 1 ; and 
         FIG. 3  is a cell breakdown extruder illustrated as a twin-screw extruder. 
     
    
    
     DESCRIPTION OF A PREFERRED EMBODIMENT 
       FIGS. 1 and 2  show a fermenter feed system  1  in a perspective top view, whereby a dosing feeder  2  (indicated only schematically) is arranged downstream from a biomass depot (not shown) as a traveling silo. 
     Weight-controlled biomass is fed from dosing feeder  2  to a first conveyor belt  3  (Arrow  4 ), by means of which the biomass is conveyed upwards (Arrow  5 ), specifically, into a cell breakdown extruder  6  which forms a cell breakdown apparatus. Under the upper end of the first conveyor belt  3  and above a cell breakdown feeder  7 , particularly above a breakdown extruder  6 . A third conveyor belt  9  is attached which cooperates, directly or indirectly via the breakdown feeder  7 , with a second conveyor belt  8 . Preferably the breakdown feeder is a type known as a hopper feeder. 
     For this purpose, the conveying direction of the third conveyor belt  9  can be reversed (Double arrow  10 ), so that (in normal operation) biomass, which is transported from the first conveyor belt to the third conveyor belt, is supplied via the breakdown feeder  7  to the cell breakdown extruder  6 , and following the treatment there, is fed to the second conveyor belt  8  (Arrow  11 ). With a reversal of the running direction of the third conveyor belt  9 , for example after an automated recognition of impurities in the conveyor path to the cell breakdown extruder  6 , the biomass reaches the region of the beginning of the belt of the second conveyor belt  8  (Arrow  13 ) in a direct path via a conveying tube  12  as bypass through free fall. 
     With the second conveyor belt  8 , treated biomass from the cell breakdown extruder  6  (Arrow  11 ) or biomass is transported upwards (Arrow  14 ) via the direct path, specifically, via a transverse fourth conveyor belt  15 , which runs between two fermenter feed connectors  16 ,  17 , whereby only a partial section of a fermenter wall of the associated adjacent fermenter ( 18 ,  19 ) is shown (see  FIG. 2 ). The running direction of the fourth conveyor belt  15  can be reversed (Double arrow  34 ), so that, depending on the running direction, fermenter  18  or fermenter  19  is fed with biomass. 
     In  FIG. 3 , a schematic drawing of the front part of the cell breakdown extruder  6  depicts a twin-screw extruder in which the interacting twin-screw extruders  20  are driven and arranged in a narrow screw housing  21  in such a way that fed biomass (Arrow  22 ) is conveyed outward, with a high pressure build-up and a high temperature increase, against and through an outlet nozzle  23  (Arrow  11 ), where the defibrated and frayed biomass is again relaxed and cooled with cell breakdown. 
     The structure of the breakdown feeder (not yet installed in  FIG. 3 ) can be seen in  FIG. 1  and comprises here, for example, a hopper feeder  7  with an associated stuffing screw  24 . The stuffing screw  24  is thereby rotationally driven in a controlled manner, so that the biomass feed (Arrow  22 ) is metered quantitatively to the cell breakdown extruder  6  in such a way that the electric drive motors  35  for the twin screws  20  are operated essentially with equal power, advantageously in an upper effective power region. 
     The diameter of the outlet nozzle  23  is designed here with a diameter regulator  25  so that it is temperature-controlled, since for cell breakdown a cell temperature of the biomass should reach at least 65° C. in the screw housing  21  upstream from the outlet nozzle  23 . A temperature sensor  26  is thus provided in this region as the actual temperature value sensor whose actual value signal is fed to the diameter regulator  25  (Arrow  27 ). As the target value (Arrow  28 ) a temperature of 70° C., for example, is set at the diameter regulator  25 , which is compared with the actual temperature value. If there is a control deviation, the diameter regulator  25  emits a control signal (Arrow  29 ) to a servomotor  30 , which by means of a spindle drive  31  displaces a slider  32  in the outlet opening of the outlet nozzle  34  in such a way that when the actual temperature value falls below the set target temperature, the slider  32  is inserted further into the outlet opening of the outlet nozzle  23  to reduce the diameter. 
     Since the cell breakdown extruder  6 , as a component of the relatively large fermenter feed system  1 , is to be set up outdoors, and a high temperature upstream from the outlet nozzle  23  in the region of the twin-screw  20  is required for cell breakdown, this region in particular is designed so that it is thermally insulated. For this purpose, the insulation half-shells  33 , made of insulating material, depicted in  FIG. 1  and having the required cutouts for the breakdown feeder  7 , are placed on the screw housing  21 , or optionally on the entire extruder for thermal insulation thereof. As a result, if there is a change in temperature, the extruder operation is equalized and the regulation is stabilized, whereby the power requirement of the cell breakdown extruder  6  is also advantageously reduced in comparison to a lack of thermal insulation. As additional weather protection, the extruder region can be further covered (not shown). Furthermore, for installation and maintenance purposes a platform ( 34 ) accessible by ladders (not shown) can be attached at the height of the third conveyor belt  9 . 
     While a preferred embodiment of the invention has been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the following claims.