The invention relates to a method for producing and processing feed material for a biogas reactor, in which method at least one first feed fraction is received, which has a first dry matter content, and feed material for the biogas reactor is pro- ducedfrom received feed fractions. The invention further relates to an apparatus used in the method.

Biogas is produced in biogas production facilities by digesting organic sludge, so- called feed material, either with a wet or dry digesting method. In wet digesting the dry matter content of the feed material used in the facility is under 10 weight-% and in dry digesting the dry matter content of the feed material is at least 15 weight-%. The feed material is led to a bioreactor included in the facility, in the digesting occurring in which biogas is generated. Biogas can be utilized in connection with the production facility e.g. by using it as fuel in electricity and/or heat pro- duction. Biogas can also be recovered and if necessary purified and stored. The feed material which has passed through the digesting process, the so-called reject, can be utilized for example as fertilizer.

Known biogas production facilities are large-scale facilities, which are usually designed and built in connection with or immediately close to a facility producing feed material to be digested, such as a domestic animal farm. The digesting method of the production facility is selected to be either the wet or dry digest method according to what kind of feed material the facility in connection with the production facility mainly produces. The properties and processability of the feed material change according to the dry matter content of the feed material, wherefore the devices processing feed material in production facilities designed for wet digesting and dry digesting differ from each other technically and structurally. In practice this means that only feed material according to the planned dry matter content can be processed in the production facility. This limits the biogas facility's possibilities to receive biomaterial with different consistencies. Changes happening in the feed ma- terial's dry matter content and/or texture immediately affect gas production and may increase delays in the bioreactor. On the other hand, facilities which produce small amounts of organic by-products, such as crop farms and food producers, do not always find a suitable production facility for utilizing by-products, whereby the by-products must be disposed of for example by taking them to a landfill. Trans- portation and disposal of by-products causes surplus costs and at the same time raw material suitable for biogas production remains unutilized. An object of the invention is to present a method and apparatus for producing and processing feed material for a biogas reactor so that deficiencies related to prior art can be reduced. The objects of the invention are obtained with a method and an apparatus, which are characterized in what is presented in the independent claims. Some advantageous embodiments of the invention are presented in the dependent claims.

The invention relates to a method for producing and processing feed material for a biogas reactor. In the method at least one first feed fraction is received, which has a first dry matter content, and feed material for the bioreactor is produced from received feed fractions. In the method at least one second feed fraction is additionally received, which has a second dry matter content, which second dry matter content is substantially larger than the first dry matter content. The first feed fraction and the second feed fraction are mixed into a mixture and the mixture is homogenized into a substantially uniform feed material. In an advantageous embodiment of the method according to the invention the dry matter content of the first feed fraction is under 8 weight-%, advantageously under 5 weigh-%, most advantageously under 3 weight-%. The first feed fraction can be sludge manure generated in barns and piggeries, which includes animal urine, excrements, litter, fodder and water. In a second advantageous embodiment of the method according to the invention the dry matter content of the second feed fraction is over 10 weight-%, advantageously over 15 weight-%, most advantageously over 20 weight-%. The second feed fraction can comprise animal litter, grain harvesting residue, such as straws, crop parts, such as potato stalks or by-products of the food industry. In a third advantageous embodiment of the method according to the invention the second feed fraction is crushed before the first feed fraction and second feed fraction are mixed. In the crushing the second feed fraction is minced, whereby its particle size becomes smaller. The crushing is useful especially when the second feed fraction contains plant straws and stalks. In still another advantageous embodiment of the method according to the invention, liquid is removed from the first feed fraction and/or the second feed fraction before the first feed fraction and second feed fraction are mixed. The liquid removal can be done with a screw separator. In still another advantageous embodiment of the method according to the invention the mixture is homogenized by mixing the mixture with a mechanical mixer. The mechanical mixer can be a screw mixer or a blade mixer. Alternatively or additionally, the mixture can be homogenized by leading the mixture through a crush- ing pump. The mixture can be circulated through the crushing pump several times for so long that a pursued uniformity of the feed material is reached.

In still another advantageous embodiment of the method according to the invention, pieces that are unsuitable for biogas production are removed from the mixture in connection with the homogenization. Especially the second feed fraction con- taining crop stalks can also contain rocks which have come from the field. Such foreign objects can be removed from the feed material in connection with the homogenization.

In still another advantageous embodiment of the method according to the invention, a feed material is produced, the dry matter content of which is over 10 weight- %, advantageously over 15 weight-%. The aim is to raise the dry matter content of the feed material to be produced in the method as high as possible, so that water is not unnecessarily led into the bioreactor, which water does not have any use in the biogas production. For the sake of the processing of the feed material it is however important that the feed material can be transferred into the biogas reactor by pumping along a pipe. Due to effective homogenization, the feed material has adequate pumping properties, even if its dry matter content is high.

The apparatus according to the invention for producing and processing feed material for a biogas reactor comprises a homogenization unit, which has a mixing tank for receiving the first feed fraction and the second feed fraction. The mixing tank has a bottom. The first feed fraction has a first dry matter content and the second feed fraction has a second dry matter content, which is substantially larger than the first dry matter content. The homogenization unit additionally has mixing means for mixing the first and second feed fractions into a mixture and for homogenizing the mixture into a substantially uniform feed material. In an advantageous embodiment of the apparatus according to the invention said mixing means comprise a mechanical mixer inside the mixing tank, such as a screw mixer or blade mixer. Alternatively or additionally, said mixing means can comprise a crushing pump and a circulation pipe for leading the mixture from the mixing tank to the crushing pump and from the crushing pump back into the mixing tank. In a second advantageous embodiment of the apparatus according to the invention the homogenization unit further comprises separation means for separating pieces that are unsuitable for biogas production from the mixture, such as rocks. Advantageously, said separation means comprise a rock screw inside the mixing tank, between the mechanical mixer and the bottom. The rock screw is a screw conveyor rotated with a motor, with which the rocks landing on the bottom of the mixing tank are transferred outside the mixing tank.

A third advantageous embodiment of the apparatus according to the invention further comprises a feeding pump for pumping produced feed material into the biogas reactor. The feeding pump is advantageously a so-called pressure increase pump, which has an adequate pumping effect to transfer feed material with a high dry matter content along a pipe. The apparatus can further comprise a return valve and a return pipe for leading feed material pumped by the feeding pump back into the mixing tank. Still another advantageous embodiment of the apparatus according to the invention further comprises first feeding means for leading the first feed fraction to the homogenization unit. Said first feeding means advantageously comprise a separator for separating liquid from the first feed fraction and/or an inlet pipe. The separator can be a screw separator. Still another advantageous embodiment of the apparatus according to the invention further comprises second feeding means for leading the second feed fraction to the homogenization unit. Said second feeding means can comprise a crusher for reducing the particle size of the second feed fraction and for transporting it.

An advantage of the invention is that it improves the quality of feed material fed into the biogas reactor, which makes production of biogas quicker and shortens the feed material's delay time in the reactor.

An advantage of the invention is further that it makes possible the production of a uniform feed material from feed fractions with different dry matter contents and textures, which diversifies and increases the raw material supply for a biogas pro- duction facility and improves the utilization rate of the facility.

Still another advantage of the invention is that it minimizes the amount of water in the feed material, due to which a maximal amount of biomaterial participating in the production of biogas can fit into the biogas reactor. A smaller amount of water in the feed material reduces the amount of water to be heated, which improves the heat economy of the biogas reactor.

In the following, the invention will be described in detail. In the description, reference is made to the enclosed drawings, in which figure 1 shows as an example an apparatus according to the invention seen from the side and figures 2a, 2b and 2c show the homogenization unit in the apparatus according to the invention seen from different directions.

Figure 1 shows as an example an apparatus according to the invention for produc- ing and processing feed material C used in a biogas reactor. The apparatus has a receiving silo 30 and a homogenization unit 10, which are connected together with a feeding pipe 32. The homogenization unit has a mixing tank 12, which has a bottom 13. The receiving silo has an end wall, to which a separator 26 is attached. The separator shown in figure 1 is a screw separator. The separator has a sludge feeding pipe 34, through which sludge containing biomaterial in liquid form, such as sludge manure, is fed into the apparatus. The dry matter content of the sludge is typically 3-12 weight-%. This presentation uses the term the first feed fraction A for such a sludge. In the separator the dry matter and liquid of the sludge are separated from each other and the dry matter is led into the receiving silo 30. The liq- uid separated from the sludge or part of it can be led along an inlet pipe 36 out of the separator or the liquid can be led completely or partly to the mixing tank 12 of the homogenization unit 10 along the inlet pipe 36. The target for the liquid exiting the separator is adjusted with a valve 38. The first feed fraction A in liquid form can also be led into the inlet pipe past the separator. The receiving silo 30 is meant for receiving biomass used in the production of feed material, the dry matter content of which is substantially larger than the dry matter content of the pumped sludge. This presentation uses the term the second feed fraction B for such a biomass. The second feed fraction can comprise food industry by-products, fodder plants, crop straws and stalks, farm animal litters or ma- nure. The second feed fraction is dosed into the receiving silo through the open upper part of the silo. Inside the receiving silo there is a screw-shaped crusher 28, which minces possible long pieces in the second feed fraction, such as plant straws and stalks, into smaller and shorter pieces. The crusher also functions as a conveyor, which transfers the minced second feed fraction along a feeding pipe 32 to the mixing tank 12 of the homogenization unit.

In the homogenization unit the first and second feed fraction are mixed together into a mixture, which is homogenized into a substantially uniform feed material C. The produced feed material is led along a transfer pipe 18 to a feeding pump 24, with which the feed material is pumped into a biogas reactor not shown in the figure.

The apparatus can further be equipped with heat exchangers, with which heat is recovered from reject returning from the biogas reactor and feed to be led into the reactor is heated. The apparatus can further comprise a motor operating with biogas, with which a generator producing electricity is rotated. All the parts belonging to the apparatus can be installed as a ready-to-use set in a transferable container.

Figures 2a, 2b and 2c show as an example the homogenization unit 10 belonging to the apparatus according to the invention. Figure 2a shows the homogenization unit seen from the first side, figure 2b seen from the end and figure 2c seen from the second side. Figures 2a and 2c show the homogenization unit substantially in the tilted position, which it has in a common use situation of the apparatus. In the following all the figures are described simultaneously.

The homogenization unit has a mixing tank 12, which has a trough-shaped bottom 13, a first side wall 15, a second side wall 17, a first end wall 19 and a second end wall 21 . The open upper part of the mixing tank is covered with a lid that can be opened, which is not shown in the figure. The first side wall has a hole, which is continued in the feeding connection 23 of the second feed fraction. The feeding connection is a short pipe, in the free end of which there is an attaching flange for connecting to the feeding pipe 32 (figure 1 ). In the second side wall of the mixing tank has a pipe-like feeding connection 27 for liquid sludge, in the free end of which there is an attaching flange for connecting to the inlet pipe 36.

On the side toward the second side wall 17 of the mixing tank there is a circulation pipe 40, the first end of which is connected to a hole penetrating the end wall in the first end wall 19 of the mixing tank, and the second end of which is connected to a hole penetrating the side wall in the second side wall 17. Between the first and second end of the circulation pipe there is a crushing pump 16 and an automatic three-way valve 29. The three-way valve is connected with a transfer pipe 18 to a feeding pump 24. In the part of the transfer pipe continuing after the feeding pump there can be a return valve 39, which is connected with a return pipe 47 to a circulation pipe leading to the mixing tank. The return valve is a three-way valve.

Inside the mixing tank there is a mixing screw 14, which is mounted on bearings by its first end to the first end wall 19 and by its second end to the second end wall 21 . The axis of the mixing screw passes through a hole in the second end wall and in the end of the axis there is a mixing motor 41 , with which the screw mixer is rotated. The screw mixer is a mechanical mixer, with the aid of which the feed fractions in the mixing tank can be mixed.

In the second end wall of the mixing tank there is a round hole delimited by the trough-like bottom, which continues in a separating pipe 42. The second end of the separating pipe is covered with a plate-like end piece 43. Inside the separating pipe and mixing tank there is a rock screw 22, which is mounted on bearings by its first end to the first end wall 19 of the mixing tank and by its second end to the end piece 43 of the separating pipe. The axis of the rock screw passes through a hole in the end piece and in the end of the axis there is a separating motor 44, with which the rock screw is rotated. In the wall of the second end of the separating pipe, close to the end piece 43, there is an outlet opening 45 penetrating the wall.

In the method according to the invention the homogenization unit functions in the following manner: The first feed fraction A in liquid form is led into the mixing tank. The first feed fraction can be unprocessed sludge manure, liquid separated from separated sludge manure or separated sludge. The second feed fraction B used in the production of feed material is led via the feeding connection 23 into the mixing tank 12. The dry mater content of the second feed fraction is substantially larger than the dry matter content of the first feed fraction. In the mixing tank the first and second feed fraction are mixed together mechanically by rotating the screw mixer with the mixing motor 41 . The shape of the threads of the screw mixer are selected so that as good as possible a mixing effect is achieved with the screw mixer. The axis of the screw mixer has a comparatively large cross-section, which prevents long biomaterial pieces, such as grass, straws and stalks from twisting and sticking around the screw mixer.

At the same time as the mixing with the screw mixer, mixture of the first feed fraction and second feed fraction is sucked with the crushing pump 16 through the hole in the first end wall 19 out of the mixing tank 12 and returned to the mixing tank through the hole in the second side wall 17. When passing through the crush- ing pump the pump crushes and minces biomaterial pieces in the mixture to a smaller particle size, whereby the mixture is homogenized. The mixture can be circulated through the crushing pump several times for so long that a substantially uniform homogenous feed material C is produced from the feed fractions. When the feed material is adequately uniform, the automatic three-way valve 29 leads the ready feed material along the transfer pipe 18 to the feeding pump 24. The feeding pump is a screw pump functioning as a so-called pressure increase pump, which pumps the feed material to the bioreactor. Due to the homogenized feed material and the pressure increase pump, the dry matter content of the feed material pumped into the bioreactor can be over 15 weight-%. Feed material led through the feeding pump 24 can if so desired be led back into the mixing tank by opening the return valve 39. The return valve thus makes possible the circulation of the feed material through the feeding pump at the homogenization stage. Stress of the feeding pump correlates well with the dry matter content of the pumped feed material, which makes possible the utilization of the feeding pump in monitoring the dry matter content of the feed material.

There can be rocks, nails etc. non-organic material especially in the second feed fraction, which is unsuitable for biogas production and which causes damage in the further processing of the feed material. Being heavier than water, rocks and nails fall to the tilted bottom of the mixing tank, from where they rise as forced by the rotating rock screw 22 along the bottom 13 to the separating pipe 42 and via the outlet opening 45 of the separating pipe out of the homogenization unit 10.

Some advantageous embodiments of the method and apparatus according to the invention have been described above. The invention is not limited to the solutions described above, but the inventive idea can be applied in different ways within the scope of the claims.