CLOSED APPARATUS FOR PREPARING BIOGAS FROM MANURE

Abstract: A closed apparatus (1) for both the production of biogas from manure and the storage of the biogas pro­ duced, under a substantially constant pressure, in a dry gas buffer vessel. The apparatus comprises a means (37, 38, 41), In the form of a tubular sub-assembly through which a fluid can flow, for both heating and stirring the manure. The gas buffer vessel (10) comprises a roof (12) of adjustable weight, connected in gas-tight manner to the silo wall along the circumference thereof, and movable up­ wardly and downwardly, preferably in a self-stabilizing manner.

Description: Closed apparatus for preparing biogas from manure. This invention relates to a closed apparatus for preparing biogas from manure, comprising a wall member and including a manure fermenting section, means for supplying manure to be fermented to, and means for discharging fermented manure from, said manure fermenting section, and means for discharging the biogas prepared from the apparatus, and the apparatus further comprising means for heating the manure and means for stirring the manure. Such an apparatus is described in the periodical Landbouwmechanisatie 30 (1979) 645-649. The basic unit in constructing the as prior apparatus may be a silo, such/an enamelled steel silo, as used on the farm, for example, as a fodder silo, with a diameter of 10.3 m and a height of 3 m, as a manure fermenting container. The biogas generated in this manure fermenting container by controlled anaerobic fermentation, which is a mixture of, mainly,methane and carbon dioxide, may be used for various purposes, for example, for firing the central heating installation, cooking, driving a gas generator. It is recommendable to carry out the anaerobic fermentation at elevated temperature, e.g. at a temperature of approximately 300C. For this purpose in the prior apparatus, tubes are arranged in the manure fermenting container, or a heat exchanger is used, through which water 0 is pumped of a temperature of, for example, 45 C. An optimally proceeding manure fermenting reaction is promoted if the composition of the manure is as homogeneous as possible. For this purpose, in the prior apparatus, the manure is agitated in the manure channels. This may be effected periodically by a mixer driven by a tractor, or by circulating the manure, the mixed manure being daily pumped over into the manure fermenting container in a given quantity. The direction of delivery of the pump can be adjusted by using a three-way valve, so that delivery may be directed to the bottom and the top of the manure fermenting container, which prevents the formation of settled and supernatant layers. In order to provide for distribution of the heat supplied to the manure by means of the tubes or heat exchanger provided in the manure fermenting container, produced biogas is insufflatedback into the manure being fermented in the manure fermenting container at regular intervals. It has been found that, in spite of the mixing effect of the insufflated biogas the heating tubes or the heat exchanger yet becomes incrusted with manure, as a result of which heat transfer deteriorates. In the prior device, the biogas produced in the fermenting container can be collected in an overhead gas buffer vessel, constructed as a floating steel gas-holder, the weight of which provides for a gas pressure of 60-70 mm of water. A gas buffer vessel in the form of a floating gas-holder construction has disadvantages, including the fact that it is never completely sealed as far as stench is concerned. Moreover, in practice, the gas holder may hang askew owing to atmospheric conditions, e.g., wind and/or snow loads, and this may also lead to pressure variations in the gas. The part of the wall of the floating steel gas-holder contained in the water seal involves technical difficulties of thermal insulation, which is a disadvantage in connection with maintaining the above optimum temperature for anaerobic manure fermentation of approximately 300C. Finally, in the construction of silos problems of unroundness are normally encountered, which with a construction as that of the floating steel gas-holder are apt to lead to its becoming jammed during rising and descending. It is an object of the present invention to eliminate the disadvantages outlined above and, in conjunction therewith, one object of the invention is to provide a solution for mixing the manure in the manure fermenting container in an optimum manner, and at the same time maintaining as constant a heat transfer to the manure as possible, and uniform distribution of heat in the manure. Another object of the invention is to provide apparatus for producing biogas in which the above disadvantages inherent in the gas buffer vessel do not occur. According to the present invention, there is provided apparatus of the above kind which is characterized in that the means for heating the manure and the means for stirring the manure are combined into a tubular assembly through which a fluid can flow and which, counted from one end, can be arranged for part of its length in the manure to be fermented, its other end being open and, through the wall member, giving access to the interior of the tubular assembly; the portion of the tubular assembly to be arranged in the manure being double-walled over at least part of its length, through which double-walled portion a heating fluid can be circulated through supply and discharge conduits connected thereto, and a stirring member, mounted for rotation on a shaft, being into inserted through the other end/ the tubular assembly over a distance beyond a manure supply opening formed in the wall of the tubular assembly. The stirring member may be a propeller stirrer, which, secured to the shaft, is inserted into the tubular assembly from outside the silo, and via the shaft can be rotated by means, for example, of an electric motor. As a result, a circulation current will be formed in the manure, whereby manure is "sucked" through the manure supply opening into the tubular assembly, and during the passage thereof is heated, and subsequently returned to the bulk of the manure. Preferably, the tubular assembly is arranged so that it extends diagonally downwardly through the wall member of the apparatus, and the manure supply opening is formed in a single-walled portion of the tubular assembly between the double-walled portion thereof and the wall member of the apparatus, at the top of the tubular assembly. By virtue of this arrangement, a circulation current is generated between the bottom and top layer of the manure. By heating the manure as it flows along the heated surface, an optimum transfer of heat is obtained and the occurrence of depositions is prevented. Where deposits occur all the same, these can be easily removed by removing the stirrer with the shaft and the electric motor axially from the tubular assembly, and loosening the deposits from the inner wall of the tubular assembly. The invention also relates to an apparatus in which the manure fermenting section is in communication with a gas buffer section with an open bottom member, a wall member and a vertically movable member forming a closed roof, which determines the gas pressure by its weight, said gas buffer section having a volume that is variable with the buffered volume of biogas through the displacement of the roof member, the apparatus being constructed in the form of a silo, in particular a silo having a circular cross-sectional configuration, the lower part of which is the manure fermenting section, above which, and within the silo circumference, the gas buffer section is provided, and the wall member of which is made of a flexible, gas-impermeable material and is sealingly connected to both the inner side of the silo wall along the circumference thereof and the roof-forming member along the circumference thereof, the apparatus being characterized by a member provided within the silo for carrying the roof member with a minimum gas buffer volume, and by the wall member of the gas buffer vessel being provided-with guide wheels, distributed over the outer surface thereof, which guide wheels can travel vertically upwardly and downwardly within corresponding channel sections connected to the inner wall of the silo. It is noted in this connection that German Offenlegungsschrift 2,024,119 discloses a dry gas buffer holder with a movable wall member consisting of a flexible material and mounted in gas-tight manner between the fixed holder wall and a vertically movable roof member, and in which the vertical movability of the roof member is ensured by providing the roof member with, preferably telescoping, guide means. The prior dry gas buffer holder, however, is a separate holder, used by itself, and is not designed within a silo in direct combination with a manure fermenting installation, and hence subject to the humid atmosphere prevailing in such an installation, and to the results of deposits caused, for example, by drops of manure being flung about, which makes heavy demands in particular on the guide means, such as the telescoping guide means, for the smooth guiding of the roof member during its vertical displacement. Some embodiments of the apparatus according to the present invention will now be described, by way of example, with reference to the accompanying drawings, in which Fig. 1 shows in elevational view, partly broken away, the gas buffer section of the apparatus according to the invention, executed within a type of fodder silo much used on the farm, and in which the flexible wall portion of the gas buffer section thereof is provided on the outside with guide means; Fig. 2 shows a cross-sectional view, taken on the line II-II of Fig. 1; Fig. 3 shows, on an enlarged scale, in plan view the constructicn encircled by III in Figs. 1 and 2; Fig. 4 is a side-view,partly broken away, showing the construction of Fig. 3; and Fig. 5 is an enlarged longitudinal sectional view of the construction encircled by V in Fig. 1, while Fig. 6 shows an apparatus similar to Fig. 1, in which however the roof member of the gas buffer section can be vertically displaced without guide means in a self-stabilizing manner, and in which the manure fermenting section comprises the tubular assembly according to the present invention for circulating and heating manure. Referring to the drawings, shown at 1 is the wall of a cylindrical silo, made of curved sheets, and placed on a concrete floor 6, as used, with appropriate appurtenances, as a fodder silo on, for example, a dairy farm. Used within the framework of the apparatus according to the present invention, the bottom part of the silo is arranged as a manure fermenting container 2 which can be filled with manure up to level 3. From a manure store not shown, the manure is supplied to container 2 by means of a pump not shown through conduit 4, and the fermented manure can be discharged through pipe 5. Designated by 7 and 8 are the supply and discharge conduit, respectively, oF a heat exchanger mounted in the manure fermenting container, which heat exchanger will be described hereinafter (with reference to Fig. 6) and by means of which the manure is 0 kept at a temperature of approximately 30 C, which is the optimum temperature for anaerobic fermentation. The gas produced during the fermentation of the manure rises and is collected in a gas buffer vessel 10. Vessel 10 is suitably made of a polyvinyl chloride material reinforced with canvas, and comprises a wall 11 and the double-walled roof 12 with walls 13 and 14, the space enclosed by these walls 13, 14 being sub-divided into chambers 15. Chambers 15 contain water as a weighting means. Weighting the roof with water will naturally not be done until on the site where the silo is erected, by virtue of which a considerable saving on the cost of transportation of the gas buffer vessel is obtained. Horizontally mounted at some distance above the bottom section of the gas buffer vessel 10 is a grid 16, which via the flexible wall 11 of the gas buffer vessel 10 is fixedly secured to the silo wall. Grid 16 also serves as a carrier for the superjacent part of gas buffer vessel 10 and, as such, forms a limit below which roof 12 cannot descend when the amount of gas stored in buffer vessel 10 is decreased. In the drawing, the maximum difference in height of the variable part of the buffer vessel volume available for storage of biogas produced is indicated by h. In practice, however, the buffer vessel will be caused to rise and descend over a smaller difference in height h' by adjusting production of, and demand for, biogas to each other. In order that the buffer vessel may smoothly rise and descend, wall 11 is preferably pre-shaped as a bellows, as indicated at 17, over a height approximately corresponding to h. Designated by 18 is a gas discharge pipe which is connected to the gas storage compartment within buffer vessel 2, and by means of which biogas can be withdrawn from the stock. In order to further promote smooth rising and descending of the gas buffer vessel along the inner wall of silo 1, whereby the position of wall 11 of the buffer vessel relative to the silo wall is changed, pairs of wheels 19 are fixedly connected to wall 11 (Figs. 3 and 4) by means of a carrying frame 20, said pairs of wheels 19 being uniformly spaced over wall 11 one below anothervertical channel sections 21 are mounted circumferentially on the inside of the silo wall, within which pairs of wheels 19 are confined and can travel vertically up and down. A leak-proof connection of gas buffer vessel 2 to the open bottom member thereof is produced by securing flexible wall 11 along the circumference thereof to the silo wall by means of uniformly spaced bolt connections 24 (Fig. 5), preferably using a thrust ring 22. When care is taken that, in use, the connection zone of flexible wall 11 with the silo wall is below the manure level, it is ensured, in combination with a cement seal 23 provided between the adjoining sheets of which the silo wall is composed, that the apparatus is safely and securely sealed. It is recommendable for grid 16 to be supported towards its centre to prevent sagging thereof. For this purpose, for example, a support of annular cross-sectional configuration may be mounted on floor 6 within manure fermenting container 3. The canvas-reinforced polyvinyl chloride material is a material of great strength, by means of which a double-walled roof 12 can be made which by introducing water in the interspace can be considerably weighted. Thus it is possible for the roof to be weighted up to a weight of approximately 5.5 t, which with the current diameter of a silo leads to a pressure of the biogas stored in buffer vessel 10 of approximately 70 mm of water. With such a pressure the gas can be used as a fuel for domestic cooking appliances. Double-walled roof 12 with walls 13 and 14 may alternatively be constructed as a circumferentially tight steel container, the interior space of which is also sub-divided into chambers 15 by steel walls. Wall 11 should naturally be connected in gas-tight fashion along the bottom circumference of the steel container, for which any suitable method can be applied. The double-walled roof 12 thus constructed at a steel container may suitably be filled with, for example, concrete, sand or rubble. With a diameter of approximately 8 m and a height of, for example, 20 cm, the steel container can easily be given a weight of approximately 15,000 kg. As a result a pressure of at least 30 cm is realized in the gas, which is sufficient to operate an internal combustion engine with it. Owing to the heavy weight of the double-walled roof of the gas buffer vessel 10 when it is constructed as a steel container, it must be well-supported if there is no gas in the gas buffer vessel and the steel container is in its lowermost position. Such a good support is provided by the ring mounted on floor 6 of the manure fermenting container of, for example, concrete, referred to hereinbefore. If necessary, a combination of two or three concentric ring is used,while grid 16 may be omitted. The use of a ring or combination of two or more concentric rings mounted on floor 6 offers the possibility of a controlled throughput of the manure to be fermented through the manure fermenting container. Thus the manure to be fermented may be supplied to the space between the outer wall and the first ring and, through overflow slots formed in the walls of the respective rings, successively supplied through the annular spaces within the several rings ultimately to the space enclosed by the inner or innermost ring to be ultimately discharged to the outside through conduit 5. This manner of passing the manure through the manure fermenting vessel 2 prevents manure still to be fermented from becoming mixed with manure already contained in the manure fermenting container for a longer period of time, as a result of which a better fermentation efficiency may be expected. Naturily, insufflation conduits may be provided in the successive spaces between the several rings for keeping the manure present therein in properly mixed condition. In the embodiment of the apparatus according to the present invention shown in Fig. 6, the roof 30 of the gas buffer section 10 is of frusto-conical form with a top surface 31 and wall 32. At the base end of the cone, a concrete disk 33 is connected to it as a weighting body. The weight of disk 33 is selected to suit the desired gas pressure of the biogas in the gas buffer container 10. Owing to the low location of the heavy disk 33 relative to roof 30, and in combination with the conical wall 32 of the roof it is achieved that the pressure of the gas against the inside of wall 32 and the weight of disk 33 cooperate in such a manner that roof 30 can rise and descend without being laterally supported, or in other words, the roof is displaceable in a self-stabilizing manner. In its lowest position, roof 30 is supported through disk 33 on a supporting table 34 at a pre-determined distance above the manure level to be maintained in the apparatus. A dip pipe 35, open at both ends, and connected co-axially to roof 30, functions as a safety element. When, for one reason or another, the gas pressure in gas buffer holder 10 becomes too high, the upper end of pipe 35 can rise into an opening 36 of the silo wall, while at the same time its bottom end rises above the manure level 3, owing to which biogas can be bled off from the gas buffer holder 10 through pipe 35 to the atmosphere. In Fig. 6, 37 designates a circulation pump, which can also be used as a heat exchanger. The circulation pump is of tubular form with an end 42 extending diagonally downwardly, and from this end it is of double-walled construction over a given length to form a section functioning as a heat exchanger 38 with supply and discharge pipes 7 and 8 for heating fluid, for example water. Axially mounted within the circulation pump is a propeller stirrer 41 which via a shaft not shown and via the open other end 39 is connected to an electric motor, not shown, mounted outside the silo. The sub-assembly of the electric motor and the shaft with the propeller stirrer 41 connected thereto is of such construction that it can be axially removed from the pump as a unit, should this be desired, for example, for cleaning purposes. Designated by 40 is a manure supply opening, through which when the propeller stirrer rotates manure is drawn in, whereafter, owing to the thrust action of stirrer 41, the manure flows back into the manure fermenting container 2 through the open bottom end 42. For optimizing the heat balance it is ensured, in a manner not shown, that the fermented manure discharged from the apparatus through conduit 5 is in heat-exchange contact with the manure to be fermented, supplied to the apparatus through conduit 17. The apparatus according to the invention is fully commensurate with installations already in use in farming, which makes for technical simplification and hence economy. Naturally, the apparatus described above and shown in the accompanying drawings may be modified without departing from the scope of the invention.

Claims: CLAIMS 1. A closed apparatus for preparing biogas from manure, comprising a wall member and including a manure fermenting section, means for supplying manure to be fermented to, and means for discharging fermented manure from, said manure fermenting section, and means for discharging the biogas prepared from the apparatus, and the apparatus further comprising means for heating the manure and means for stirring the manure, characterized in that the means for heating the manure and the means for stirring the manure are combined into a tubular assembly through which a fluid can flow and which, counted from one end, can be arranged for part of its length in the manure to be fermented, its other end being open and, through the wall member, giving access to the interior of the tubular assembly; the portion of the tubular assembly to be arranged in the manure being double-walled over at least part of its length, through which double-walled portion a heating fluid can be circulated through supply and discharge conduits connected thereo, and a stirring member, mounted for rotation on a shaft, being inserted through the other end into the tubular assembly over a distance beyond a manure supply opening formed in the wall of the tubular assembly. 2. Apparatus as claimed in claim 1, characterized in that the tubular assembly is arranged so that it extends diagonally downwardly through the wall member of the apparatus, and the manure supply opening is formed in a single-walled portion of the tubular assembly between the double-walled portion thereof and the wall member of the apparatus, at the top of the tubular assembly. 3. Apparatus as claimed in claim 1 or 2, in which the manure fermenting section is in communication with a gas buffer section with an open bottom member, a wall member and a vertically movable member forming a closed roof, which determines the gas pressure by its weight, said gas buffer section having a volume that is variable with the buffered volume of biogas through the displacement of the roof member, the apparatus being constructed in the form of a silo, in particular a silo having a circular cross-sectional configuration, the lower part of which is the manure fermenting section, above which, and within the silo circumference, the gas buffer section is provided, and the wall member of which is made of a flexible, gas-impermeable material and is sealingly connected to both the inner side of the silo wall along the circumference thereof and the roof-forming member along the circumference thereof, characterized by a member provided within the silo for carrying the roof member at a minimum gas buffer volume, and by the wall member of the gas buffer vessel being provided with guide wheels, distributed over the outer surface thereof, which guide wheels can travel vertically upwardly and downwardly within corresponding channel sections connected to the inner wall of the silo. 4. Apparatus as claimed in claim 3, characterized in that the roofforming member of the gas buffer section is of double-walled construction defining between the walls thereof a closed interspace into which a weighting means can be introduced. 5. Apparatus as claimed in claim 4, characterized in that the closed interspace is divided by means of partitions into chambers that can be provided with said weighting means. 6. Apparatus as claimed in either of claims 4 and 5, characterized in that the roof member of the gas buffer section is made of the flexible material used for the wall member thereof. 7. Apparatus as claimed in either of claims 4 and 5, characterized in that the roof member of the gas buffer section is constructed as a metallic container, the interior space of which is subdivided by metallic partitions into chambers to be provided with a weighting means. 8. Apparatus as claimed in claim 3, characterized by one or more concentric rings being mounted on the bottom of the manure fermenting section, by means of which rings the roof member of the gas buffer section can be carried. 9. Apparatus as claimed in claim 3, characterized in that the roofforming member of the gas buffer section is radiosymmetric, in particular of conical or frusto-conical shape and adjacent the base thereof is connected to a weighting body, said roof-forming member and said weighting body forming a sub-assembly that is vertically displaceable without guide means in a self-stabilizing manner, the centre of gravity of said sub-assembly being located in the cone axis or the prolongation thereof. 10. Apparatus as claimed in claim 9, characterized in that an opening is formed in the roof of the silo and a dip pipe connected to the apex of the cone or the top surface thereof is providec coaxially with said cone to function as a gas lock in cooperation with the level of the manure in the manure fermenting section. 11. Apparatus as claimed in claim 10, characterized in that the opening in the roof is concentric with said cone.

Inventors: VELLINGA, SJOERD
Applicants: PAQUES B.V.
Application year: 1980
Main classification: C02F3
IPC codes: C02F3, C12M1