The invention is related to a reactor for producing biogas from biomass using anaerobic digestion, which includes

- a frame comprising two ends, namely an upper end and a lower end, delimiting within itself a reaction space for biomass, the frame being channel-like for plug flow of biomass and including at least three successive blocks with related microbial strains,

- feed equipment arranged at the upper end of the frame for feeding biomass into the frame,

- agitation equipment for agitating biomass and feeding microbes into biomass, arranged at least partly within the frame,

- recovery equipment for recovering the biogas produced while microbes consume organic material of biomass, and

- removal equipment for solid material arranged at the lower end of the frame for removing solid material.

The invention is related to reactors for producing biogas from biomass . Biogas production is a method for processing organic waste and a method for producing renewable energy. Biogas production is based on a biological process known as anaerobic digestion. In anaerobic digestion, microbes digest organic material or biomass in oxygen-free conditions to produce methane-containing biogas as the end product. Anaerobic digestion is a multi-step process involving several different microbes in the different steps of the digestion chain as shown in Figure 1. Digestion chains for decomposing biomass can be described in a simplified way as follows :

1) Polysaccharides ( carbohydrates ) -> Sugars -> Short-chain fatty acids, H2, CO2 -> CH4, CO2

2) Proteins -> Peptides, amino acids -> Short-chain fatty acids H ₂ , C0 ₂ -> CH ₄ , C0 ₂ 3) Lipids -> Long-chain fatty acids -> Short-chain fatty acids, H ₂ , C0 ₂ -> CH ₄ , C0 ₂ .

For example, the digestion chain of cellulose contained in lignocellulose is as follows, described in steps:

1) Decomposition of cellulose into sugars via hydrolysis:

( ObHioq ₅ ) h + nfLO -> hObHinOb

2) Decomposition of glucose units into acetate via acid fermentation :

C ₆ HI ₂ 06 + 4H ₂ 0 -> 2CH3COO- + 2HCO3- + 4H ⁺ + 4H ₂

3) Decomposition of acetate into methane via methanogenesis : 2CH3COO- + H ₂ 0 -> CH ₄ + HCO3-

4H ₂ + HCO3- + H ⁺ -> CH ₄ + 3H ₂ 0

Microbes active in the different steps of the digestion chain also have different optimal conditions. Biogas generating as the end product of anaerobic digestion can be utilised as renewable energy in power and/or heat production or as traffic fuel.

The traditional biogas technology is mainly designed for the processing of wet waste fractions, such as wastewater sludge and animal manure. In this case, the processing most often takes place in completely stirred vertical cylindrical tank reactors at a low dry content (most often <10%), i . e . , at a high water content (>90%) . The most significant problem related to this method is that more than 90% of the raw material contained in the reactor is water. Energy (biogas) cannot be produced from water; instead, heating large quantities of water consumes remarkable amounts of energy. In addition, when it is desired to process dryer waste fractions in this type of completely stirred reactor, it is necessary to dilute the input with a liquid. It is also possible to recirculate liquid back to the reactor ; however , this involves several problems , for example, an inhibiting effect of decomposition products and nitrogen compounds that accumulate in the recirculated liquid. Furthermore, a problem related to the use of a completely stirred tank is that all microbial strains live in the same space in homogeneous conditions; therefore, the reaction conditions must be optimised according to the slowest step of the digestion chain, i.e., methane generation. In this case, the action of microbes that are active in the other steps of the digestion chain is not optimal .

Biogas production technologies based on so-called dry fermentation processes have been developed for the processing of dryer waste fractions. These processes can be operated at a notably higher dry content compared to the traditional biogas technology. Thus, a notably higher energy yield per reactor volume can be achieved.

One method of implementing a biogas plant based on a dry process is a biogas reactor operated on the so-called plug-flow principle. A biogas reactor operated on the plug-flow principle is most often a horizontal tank reactor into which biomass is fed from one end of the reactor and the material processed is removed from the other end of the reactor. During the processing, the material thus passes through the horizontal reactor based on a plug-type flow. A biogas reactor operated on the plug-flow principle can be operated at a remarkably higher dry content compared to traditional biogas processes (for example, at a dry content of 10% to 30%) . The process thus allows a large raw material base due to the possibility of processing also drier materials, as well as a high energy yield per reactor volume and more compact reactor constructions . Compared to traditional high water content processes, the process contains less water to take up the reactor volume; therefore, the process also contains a larger amount of decomposable organic matter per reactor volume. A horizontal plug-flow reactor for producing biogas proposed in publication WO 2015/075298 A1 represents prior art. However, a problem with this type of biogas reactor is that digestate and other solid material remaining in the reactor are removed from the end of the reactor. In this case, heavier material carried along by raw material, such as glass, metal and stone material, starts to collect and accumulate on the reactor bottom over the entire range of the reactor. Heavy material complicates the operation of agitators eguipped with horizontal agitation shafts of the reactor, when the agitators must also transfer, in addition to material that is to be decomposed, undecomposable and heavy solid material. Furthermore, the removal of solid material is problematic, since solid material can plug the discharge connection when removing digestate from the reactor using a vacuum . In addition, a problem with this type of plug-flow reactors is their high space requirement .

Another object of the invention is to provide a reactor for producing biogases from biomass that is more reliable compared to prior art reactors, wherein the heavier and undecomposable material carried along by raw material does not cause problems. The characteristic features of this invention are set forth in the appended claim 1.

The object of a reactor according to the invention can be achieved with a reactor that includes a frame comprising two ends, namely the upper end and the other end, delimiting within it a reactor space for biomass, the frame being channel-like in the vertical direction for vertical plug flow of biomass and including at least three successive blocks with related microbe strains, an external skeleton arranged on the outside of the frame for supporting the frame externally against hydrostatic pressure generating inside the frame, and a bottom cone comprising a wider upper end and a narrower lower end, connected to the lower end of the frame for collecting solid material . In addition, the reactor includes feed equipment arranged at the upper end of the frame for feeding biomass into the frame, agitation equipment for agitating biomass and feeding microbes into biomass, arranged at least partly within the frame, recovery equipment for recovering the biogas produced while microbes consume organic material of biomass, and removal equipment for solid material arranged at the lower end of the bottom cone for removing solid material, located at the lower end of the frame, for removing solid material.

In such a reactor, biomass moves by gravity as plug flow downward in the reactor towards the removal equipment and, at the same time, undecomposable solid material carried along by biomass automatically moves in the reactor towards the removal equipment. In this way, solid material automatically arrives by gravity at the removal equipment via the bottom cone at the lower end of the frame and is led further out from the reactor frame. Thus, adverse effects of solid material accumulating within the reactor, such as plugging and reduction of reaction space, can be avoided. On the other hand, when arranged in the vertical direction, the reactor according to the invention only takes up a notably small footprint area in the production plant, and it is easy to increase the production capacity by placing reactors according to the invention in parallel. When an external skeleton is used, the reactor frame can have a fairly light construction, since the outwards force caused by the hydrostatic pressure acting within the frame can be received with the external skeleton that supports the frame without increasing the thickness of the reactor frame.

Advantageously, the agitation equipment includes a reject collection and feed system for collecting reject from the blocks and feeding it to at least three blocks as high consistency stock. With such a reactor, the operating conditions of microbes used in each anaerobic digestion reaction can be optimised by adjusting the condition of the block concerned. Optimised conditions improve the action of microbes and thereby accelerate the decomposition of biomass into the desired end product , i.e., methane. The reject collection and feed system enables supply of the concentrated microbial strain contained in the reject in front of the block as high consistency stock, which ensures a sufficient microbial strain immediately in the initial part of this block. By feeding reject to each block, it is also possible to reduce the motor power required by the agitation equipment.

Advantageously, the agitation equipment is implementedusing shafts disposed transversely relative to the vertical direction of the reactor frame for agitating biomass block-specifically . A transverse shaft enables independent agitation of each block regardless of the number of successive blocks.

Advantageously, the reject collection and feed system is arranged to feed reject as high consistency stock via the agitation equipment for reducing friction. At the same time, the microbial strain can be moved from the end of the block to its initial part or , if necessary , from one block to another. If necessary, the same feed equipment can be used to supply the reactor with a specific input, which is not useful when supplied to the initial part of the reactor where the conditions are not optimal for the specific input supplied .

The reject collection and feed system may include a high consistency stock pump for feeding reject at a dry content of3%to35%, preferably 15% to 25 %. Thus, the reject contains a sufficient amount of solid material, on the surface of which, for example, methanogens, i.e., a microbial strain responsible for the generation of methane, mainly live . According to an embodiment, the supporting and operating elements of the agitation equipment of each block are located outside the frame. Thus, maintenance of the agitation equipment can be performed outside the reactor, which remarkably facilitates maintenance.

Advantageously, the reaction space is divided into blocks specifically to the reaction steps of anaerobic digestion including at least a hydrolysis block, an acid fermentation block and a methanogenesis block. Thus, the conditions of each block can be optimised specifically for each reaction to optimise biogas production. Advantageously, the length of the hydrolysis block is 25-35% of the total length of the reaction space, the length of the acid fermentation block is also 25-35% and the length of the methanogenesis block is 30-50% of the total length of the reaction space .

When referring to a block-specific microbial strain, it is obvious to those skilled in the art that each block has mixed populations of microbes of different blocks . In the hydrolysis block, the strain of microbes that are essential for hydrolysis is 50-95% of the number of all microbes, and the same applies to the acid fermentation block. The microbial strain of the methanogenesis block is more sensitive and therefore, the microbial strain corresponds to 30-90% of the total microbial strain of this block.

Advantageously, the reactor also includes independent temperature control equipment for controlling the temperature of biomass separately in each block. In this way, the temperature of biomass can be more accurately controlled, thus facilitating optimisation of conditions.

Advantageously, an external skeleton is arranged to support the blocks against each other . The external skeleton ensures the overall rigidity of the reactor structure and the support required by the fastening points of the shafts of the agitation equipment.

Advantageously, the reactor includes equipment for independent monitoring and control of inoculation, agitation and heating of each block. Thus, each block can be controlled independently of the other blocks.

According to an embodiment, the reactor includes second feed equipment for feeding biomass and/or biogas from the walls of the reaction space into biomass for facilitating the flow. By feeding high consistency stock or biogas, it is possible to reduce the friction between the reactor frame and biomass while simultaneously inoculating biomass.

Advantageously, the reactor includes recirculation equipment for biogas connected to recovery equipment for recirculating recovered biogas in a pressurised state to the other end, i.e., the lower end of the reactor frame for agitating digestate and separating biogas from digestate . With the recirculation equipment, digestate can be agitated so that biogas remaining among digestate can become released and rise up to a gas space at the upper end of the reactor, wherefrom it can be further recovered.

The recirculation equipment for biogas may include a flow channel for connecting the recovery equipment to the lower end of the reactor frame for recirculating biogas, and a pump arranged in the flow channel for aspirating biogas from the recovery equipment and pressurising recovered biogas before feeding biogas into the reactor frame, to the lower end of the frame.

Advantageously, the reactor frame includes subframes that are identical with each other except for their lengths and heights. Such a construction makes the reactor affordable to manufacture. Advantageously, a subframe includes planar modules, which are identical with each other in each subframe. A modular reactor can be easily packed in marine containers for transportation and its installation ready for operation is quickly done at the installation site .

Advantageously, the subframes form a straight flow channel, which serves as the reaction space. A vertical channel-like construction enables the advancement of biomass as plug flow.

According to an embodiment, the high consistency stock pump is a hydraulic piston pump. Such a pump is particularly suitable for pumping high consistency stock.

The number of blocks may be at least three, advantageously between three and six. Thus, there is at least one block for each main digestion reaction, and the conditions of each block can be optimised for each microbial strain.

In this context, when referring to blocks it is obvious to those skilled in the art that the blocks proposed in this application are reactor components each with its own main microbial strain and preferably with independent control. An individual block can include one or more modular subframes and agitation devices. The boundaries of the blocks can vary according to the reaction areas generated by the biomass supplied . Advantageously, a block boundary means the area where the main population of the microbial strain changes from one population to another. Advantageously, there are no mechanical limitations between the blocks, such as intermediate walls or equivalent, but the biomass supplied can pass through the reactor unobstructed passing through different blocks. The conditions in each block are advantageously different . In addition, when referring to biomass, it is obvious to those skilled in the art that it means the raw material supplied to the reaction space and anaerobically digested therein, whereas digestate and reject mean the high consistency stock discharging from the reaction space, produced as the end product of anaerobic digestion.

Advantageously, the recovery equipment for biogas is arranged at the upper end of the reactor frame. In the reactor, biogas rises up in a liquid bed formed by biomass and it can be most easily removed from the upper end of the reactor, i.e., the upper end.

According to an advantageous embodiment, the external skeleton is a separate lattice beam construction made of steel . Such a skeleton is easy to transport to the application site in a disassembled state and assemble on site. On the other hand, a lattice beam construction made of steel is fairly light-weight in relation to its rigidity. In other words, the external skeleton does not form part of the frame but is a separate entity relative to it.

According to another embodiment, the external skeleton is made of fibre concrete. Fibre concrete can be 3D printed, which removes the need of manual welding work during the manufacture of the skeleton .

According to an embodiment, the reactor frame is made of a steel sheet with a thickness of 4-20 mm. In this case, the reactor frame is fairly light-weight and implementable at affordable material costs, as the necessary strength is provided with a separate skeleton external to the frame.

Alternatively, the reactor frame can be a construction with a thickness of 100-400 mm, 3D cast from fibre-reinforced concrete. When implemented with fibre concrete, strikingly little manual welding work is required in the manufacture of the reactor frame. Advantageously, the height of the reactor frame is 2- to 4-fold relative to the width or length of the reactor. Thus, the reaction volume can be high relative to the floor area occupied, as the reactor volume is oriented mainly in the vertical direction.

Advantageously, the cross-section of the reaction space is a square or a rectangle in the material flow direction . Thus, the construct ion is easy to manufacture and it has a sufficiently resistant structure when supported with an external frame structure.

Advantageously, the lattice beam construction includes two vertical parts on both sides of the reactor frame and a horizontal part connecting the vertical parts. Thus, the vertical parts of the lattice beam construction receive lateral support from both the floor and the horizontal part that connects the vertical parts.

According to an embodiment, the external skeleton is fastened to a floor slab formed under the reactor for preventing the horizontal movement of the vertical parts of the external skeleton. This is particularly important, since the greatest horizontal forces are exerted on the connection point of the vertical parts on the floor via the reactor frame due to the hydrostatic pressure acting within in .

The lattice beam construction is advantageously formed of hollow tubes that are welded together. In this way, the lattice beam construction becomes light-weight and rigid.

According to an embodiment, the agitation equipment includes blade agitators supported with shafts horizontally to the reactor frame, a drive motor for rotating the blade agitators , a gear system arranged between the drive motor and the blade agitators for transmitting force, while the shaft bearings are located on the outside of the reactor frame. Thus, maintenance of the agitation equipment is easy, as the items requiring maintenance are located on the outside of the frame.

A reactor according to the invention can be used for producing biogas from biomass using anaerobic digestion in a method where biomass is fed as an input to a reaction space using mechanical feed equipment while simultaneously pushing biomass further in the reaction space as plug flow downwards in the vertical direction . Biomass is agitated separately in each block in the reaction space divided into successive blocks for feeding biomass to block-specific microbial strains and transferring biomass further in the reaction space, which has at least three blocks each including a main microbial strain of its own. Biogas generating as the result of anaerobic digestion of biomass is recovered . The microbial strain of each block is fed in front of the corresponding block and, at least in two of these blocks, the supply consists of reject obtained from the block as high consistency stock. Using block-specific adjustment of conditions, each anaerobic digestion reaction can be performed in more optimal conditions than in prior art methods. In this context, "in front of" means the beginning of a block, i.e., the opposite direction relative to the travel direction of biomass . The location to which a microbial strain is fed determines the starting point of the block, since the microbial strain gains strength in this location in a remarkable way. The object of the invention is achieved, because the supply of the microbial strain in front of each block increases the concentration of the microbial strain and notably accelerates the growth of the microbial strain to its optimum in this block, which in turn improves the reactions provided by the microbes and thereby the production of biogas.

Advantageously, a microbial strain is recirculated inside the block as reject from the end to the beginning of the block. This recirculation transfers the concentrated microbial strain at the end of the block to the beginning of the block, where the microbial strain is inherently weak.

Reject can be fed backward in front of the block, to the suction valves, at regular intervals via a reject collection and feed system for keeping the reject collection and feed system clean. This backward feed can efficiently prevent plugging of the collection system. In other words, reject can sometimes be fed backward via the discharge connection to the block from which the reject was taken .

The agitation equipment may consist of rotating blade elements, and the agitation equipment of the block located last in the travel direction of biomass is operated in the direction opposite to that of the agitation equipment of the other blocks. An opposite agitation direction facilitates the release of biogas bubbles generating during methanogenesis from the solid biomass.

Advantageously, biomass is inoculated by rotating the agitation equipment backward. In this context, "backward" means that the agitation equipment is rotated in such a way that its force for moving biomass is applied towards the upper end of the reactor, from where at least the main part of biomass is fed to the reactor. By moving decomposable biomass backward in the reactor, it can be ensured that the microbial strain is spread to the raw material that is to be decomposed and that the decomposition products are moved away from the area around microbes.

According to an embodiment, a liquid input is fed to the reactor via the agitation equipment. In this way, the input can be fed to a selected point in the reactor in accordance with the processing time required by the input. In other words, for example, the first block of the reactor can be excluded for an easily decomposing raw material, reducing in this way the dwell time of biomass in the reactor.

Advantageously, the temperature of biomass is block-specifically adjusted in each block. Block-specific temperature adjustment enables more accurate optimisation of conditions, which improves biogas production. In this context, temperature adjustment may mean either heating or cooling of biomass depending on the conditions. Advantageously, biomass supplied to the reactor requires heating, and heat can be recovered from the biomass discharged at the end of the reactor; i.e., biomass can be cooled for preheating the raw material supplied, for example.

Inoculation and heating of each block can be independently monitored and controlled. In this way, it can be ensured that each anaerobic digestion reaction can take place in conditions that are favourable for the reaction. With independent control, the blocks and thus also the reaction conditions are at least almost independent of each other .

According to another embodiment, biogas can be fed from the walls for facilitating the biomass flow. Biogas efficiently separates biomass from the walls of the reaction space by separating biogas bubbles within biomass. This is significant particularly in the last block of the reactor, since the method prevents the removal of biogas together with the digestate.

In a reactor according to the invention, agitation is carried out by agitating biomass in the reaction space of the reactor block-specifically . An advantage of this agitation method is that the reactor can be agitated block-specifically by moving the stock locally forward or backward. The operation of each agitator can be separately adjusted; that is, the efficiency and direction of agitation as well as the temperature (between 20°C and 55°C) of the reactor are adjustable for each block. The conditions of the reactor (such as pH, temperature, gas production) can be monitored in real time locally and block-specifically (sensors in the area of each block ) , and information obtained can be compared to agitation and the reactor load. By moving the microbial strain of at least two blocks as high consistency reject backward in the travel direction of biomass in front of the block, a sufficient population of the microbial strain is ensured in the entire block. The difference compared to biogas reactors based on a longitudinal agitation shaft is that the microbial strain can be moved backward in the reactor locally and block-specifically thereby locally increasing the active microbial strain in the anaerobic digestion step that takes place in the area of this block. At the same time, the conditions of the reactor can be optimised block-specifically and the conditions can be locally optimised according to the optimum conditions of microbes involved in the different steps of the digestion chain. Thus, a better digestion result can be achieved and biogas production is maximised.

The feed equipment of the reactor can be arranged in the frame in such a way that the feed equipment feeds biomass below the liquid level within the frame of the reactor. Thus, it can be ensured that air cannot enter together with the input, which would harm the microbial strain for anaerobic digestion.

The construction of the reactor according to the invention is advantageously based on prefabricated modules. Modules refer to the concrete plate-like frame components, which are combined to form channel-like subframes and which form the reactor frame when placed successively. Advantages of a biogas plant based on prefabricated modules include, inter alia, that the size of the plant is easily scalable (by increasing the number and length of subframes; i.e., by adjusting reactor dimensions), the plant can be quickly installed and taken into use on site (compared to traditional biogas plant solutions, which are often cast in a mould from concrete on site, for example) , and the manufacture of modules with standard dimensions enables utilising serial work, which reduces the manufacturing costs. Furthermore, modules enable easy transportation of the reactor using normal marine containers. In this context, subframes mean the physical construction that forms the frame wherein the modules form a reaction space within the subframe, whereas blocks mean a construction that is independent in terms of adjustment and control and can be composed of one or more subframes.

A reactor according to the invention is capable of decomposing biomass in a quantity corresponding approximately up to 9-12 kg of organic matter per a volume corresponding to one reactor cubic meter in a day (9-12 kgVS/m ³ /d) . This quantity may vary remarkably depending on the characteristics of the input. The benefit of the reactor according to the invention can be seized, for example, by manufacturing a reactor that is notably smaller than would be required by prior art reactors .

The invention is described below in detail by making reference to the appended drawings that illustrate some of the embodiments of the invention, in which:

Figure 1 is a basic view illustrating anaerobic digest ion of biomass from raw material into an end product

Figure 2 is a lateral cross-sectional basic view of the reactor according to the invention

Figure 3 is a basic cross-sectional end view of the reactor according to the invention

Figure 4 is a lateral basic view of the reactor according to the invention

Figure 5 is a process chart of an embodiment of the reactor according to the invention Figure 6 is a basic view of the entire reactor according to the invention .

According to Figure 1, the process of anaerobic digestion includes several steps 100, during which microbes decompose organic matter . Since each reaction is best carried out in conditions that are optimal for each reaction, efficient utilisation of anaerobic digestion in biogas production is greatly dependent on the optimisation of the various subprocesses. In conditions that are favourable for the hydrolysis of polysaccharides 102 and fermentation, the pH range is approximately between 6.5 and 7. In conditions that are favourable for the fermentation of sugars, i.e., acid fermentation 104, the pH range is approximately between 5 and 6. In conditions that are favourable for the generation of acetic acid 106, the pH range is approximately between 6.5 and 7.5. In conditions that are favourable for the generation of methane 108, i.e., methanogenesis , the pH range is approximately between 6.5 and 8.0. The microbial strain essential for methanogenesis is killed if the pH is below 6. In addition, for the hydrolysis step, it is useful if the oxygen content of stock is low, whereas oxygen is extremely toxic for the microbes of the methanogenesis step. In addition, microbes involved in the methanogenesis and acetogenesis steps are very sensitive to accumulation of inhibition agents (e.g., short-chain fatty acids, ammonia) . For example, the temperature range used in the process may be between 35°C and 37°C or approximately 55°C. However, the temperature may vary according to the input and the microbial strain used. Since the composition of biomass used as raw material in the method may vary remarkably, the reactions included in anaerobic digestion can also vary.

Below is a more detailed description of the construction of the reactor according to the invention. According to Figures 2 and 4, the reactor 10 according to the invention is composed of a modular frame 12. More precisely, the modular frame 12 advantageously includes between 3 and 10 subframes 46, which form the channel-like frame 12 of the reactor 10 in the vertical direction delimiting a reaction space 14, where biomass 16 is decomposed into biogas and digestate via anaerobic digest ion . If necessary, the subframes can be well above ten in number. The subframes 46 are channel-like constructions with equal diameters and shapes, and only the lengths of the subframes 46 may vary in the travel direction of biomass, i.e., in the vertical direction of the reactor. For example, the width and length of the subframes may be 2.2 metres, in which case only the height of subframes and the number of subframes vary according to the volume required for the reactor. For example, the height of a subframe may be 3 m. In this context, the vertical direction of the reactor 10 means the same direction as the travel direction of biomass 16 advancing as plug flow in the reaction space 14. The modules forming the subframes can be prefabricated, surface-finished and insulated. Advantageously, the subframes 46 are locked in place with an external skeleton 50 included in the reactor 10, illustrated in Figures 2 and 4, and sealed together using seals or by welding. A separate external skeleton 50 locks the subframes 46 to form a continuous frame 12 of the reactor 10. The shape of the subframes 46 can be a square, for example, and the cross-section of the reaction space 14 delimited by these can also be a quadrangle or a square . On the other hand, the cross-section of the reaction space can also have some other shape, such as a round shape; however, in this case, it will be necessary to use a vertical shaft for the agitation equipment, to which the agitation equipment of different blocks is connected with a clutch, for example .

The external skeleton 50 is preferably a lattice beam construction 94 made of steel and separate from the frame, as shown in Figure 4, where beams are welded in a lattice form to provide a rigid construction. Advantageously, the lattice beam construction 94 includes two vertical parts 94.1 on both sides of the frame 12 of the reactor 10 and a horizontal part 94.2 connecting the vertical parts 94.1. Both vertical parts 94.1 are supported to the frame 12 of the reactor 10, to its outer surface , from the side . Hydrostatic pressure within the reactor frame tends to push the walls of the reactor outwards, but the counterforce provided by the external skeleton acts as a counterforce for this. For example, the external skeleton 50 may be fastened to a floor slab 11 formed under the reactor 10, as shown in Figure 4, or bolted to the floor of the production hall so that the vertical parts 94.1 of the external skeleton 50 cannot move in the horizontal direction. The beams of the lattice beam construction can be, for example, hollow tubes that are welded together. Thus, the construction is affordable in terms of its material costs, yet a very rigid structure. The use of an external skeleton enables implementation of the reactor frame as a fairly thin construction, which would be impossible without the external support provided by the external skeleton. Alternatively, a skeleton external to the lattice beam construction can also be formed as a cable construction.

In addition to the frame 12 and the external skeleton 50, the reactor 10 includes a bottom cone 17, which collects together solid material i.e. digestate that has passed downward in the reactor and the undecomposable material, such as glass, metals and stone material, carried along by biomass. The bottom cone 17 includes an upper end 90 with equal dimensions with the lower end 13.2 of the frame 12 of the reactor 10 and a lower end 92 that is narrower than the afore-mentioned one, to which the removal equipment 27 of the reactor is connected. The conical shape of the bottom cone collects the solid material present within the frame in such a way that it arrives near the removal equipment by gravity without separate transfer equipment or scrapers. The removal equipment 27 for solid material is used to discharge digestate and other solid material accumulating on the bottom of the reactor 10 via the bottom cone 17. For example, the removal equipment 27 for solid material may consist of a screw conveyor that is capable of transferring solid material out from the reactor frame.

In addition to the removal equipment 27 for solid material, the reactor 10 includes feed equipment 25 that is used to feed biomass below the liquid level in the reaction space 14 within the frame 12 of the reactor 10. The feed equipment 25 can be mechanical, such as a screw conveyor or equivalent, which feeds biomaterial into the first subframe 46. Arranged near the screw conveyor 25.1, there may be a feed funnel 25.2, via which raw material is fed to the screw conveyor 25.1. The feed equipment and the removal equipment for solid material can be located on the same side of the frame, in which case the footprint area required by the entire reactor is still smaller than when placing the feed equipment and the removal equipment for solid material on the opposite sides.

According to Figure 2, the reactor 10 also includes agitation equipment 20 arranged at least partly inside the frame 12, the agitation equipment 20 being used for agitating biomass 16 serving as raw material inside the frame 12. According to the invention, each block 24 advantageously includes agitation equipment 20 of its own, which may consist of blade agitators 36, as shown in Figure 3, supported by a shaft 48 disposed transversely relative to the vertical direction of the reactor 10 through the subframe 46. A block 24 refers to a controlled and adjusted unit of one or more subframes 46 wherein the conditions can be adjusted to suit the microbial action of the main microbe strain dominant in the area of the block. According to an advantageous embodiment of the invention, each block 24 includes at least one blade agitator 36 of its own, enabling agitation of biomass 16 separately for each block. Alternatively, instead of blade agitators, a screw agitator or an equivalent mechanical device or a combination of a blade agitator and a screw can be employed, which can move biomass in the reaction space in different directions, also in the shaft direction. According to Figure 2, blade agitators 36 may be equal in number with the subframes 46. Thus, the number of blocks 24 can also be equal.

Figure 3 is a cross-sectional vertical end view of areactor according to the invention. Advantageously, supporting of the agitation equipment 20 can also be arranged in the reactor 10 in association with the external skeleton 50 of Figure 4. In this case, the drive motor and gear system 66 of each blade agitator 36 and the bearings 64 of the shafts 48 are located outside the frame 12 of the reactor 10. This remarkably facilitates the maintenance of the agitation equipment 20.

The reactor 10 may also include temperature adjustment equipment 18 (shown in Figure 5) for adjusting the temperature of biomass 16 to a temperature that is optimal for the microbial action. Using agitation and temperature control equipment that is preferably independent relative to the blocks, the conditions and agitation can be made optimal for the microbial action in each block. For example, the temperature control equipment 18 may consist of resistances installed in the modules 52 of the subframe 46, shown in Figure 4, which are used to heat the constructions of the subframe 46 and thereby the biomass 16. Heating is important for the first two blocks, whereas in the block or blocks following these, where methanogenesis takes place, it is no longer absolutely necessary to heat biomass , or it can be even cooled without noticeably affecting the yield of biogas . Cooling can be carried out using heat exchangers included in the temperature control equipment, which may preheat the biomass supplied to the reactor, for example. Heating can also be carried out with gas boilers to heat the water in the heating circulation system, which can be advantageously controlled in three or more block-specific circuits. To recover biogas obtained as the product, the reactor 10 includes recovery equipment 22 for collecting biogas from the reaction space 14. The recovery equipment 22 may consist of a pipework 54 of Figure 2, formed in the upper part, i.e., the upper end 13.1 of the frame, for recovering the generating biogas in a storage tank 78 or equivalent .

In the reactor 10 according to the invention, the agitation equipment 20 advantageously includes a reject collection and feed system 56 of Figure 2. The reject collection and feed system 56 is arranged beside the subframes 46, and this collection and feed system 56 collects reject from the decomposing biomass 16 to feed it in front of the block 24. The collection and feed system is not shown in Figure 4; however, it is obvious to those skilled in the art that the subframes 46 include such equipment. In this context, reject means high consistency stock. The dry content of high consistency stock is in the range of 3-35%, preferably 15-25%. On the other hand, stock at a dry content of 3-5% can also be called low consistency stock in some contexts. According to Figure 2, the collection and feed system 56 advantageously includes a single high consistency stock pump 57 for transferring reject in the pipework. A valve system 88 arranged in the pipework opens valves 82 and 84 of the desired block 24 and closes valves 82 and 84 of the other blocks 24, in accordance with the control of the control system of the reactor 10. Advantageously, reject supply in front of a block means the supply of reject to the feed connection preceding the reject discharge connection; however, in some cases, reject can also be supplied even to a feed connection located earlier relative to the feed connection that precedes the discharge connection. Advantageously, reject is collected beside each subframe, because the liquid present in the reactor inherently creates a liquid pressure facilitating the reject transfer. Since the collection of reject is advantageously a part of inoculation, it must be ensured that the reject collection and feed system is kept clean and in good operating conditions. For this purpose, reject can sometimes be fed backward via the discharge connection to the block from which reject was taken. In this way, plugging of the pipework is prevented. For example, a cleaning supply can be carried out two times a day or when an obstruction is detected on the suction side of the pump or pumps while the automation system monitors the flow rate. In this case, the automation system automatically tries to remove the obstruction by means of a counterflow.

Reject removed from a block can be supplied at a high pressure along the pipework 40 shown in Figure 3 to the channel located within the hollow shafts 48 of the blade agitators 36 and therethrough to the blades 45 of the blade agitator 36. In this context, high pressure means a pressure ranging between 0.2 and 20 bar. The blades can include nozzles through which reject is supplied into biomaterial when using blade agitators. Alternatively, instead of or in addition to reject, liquid biomass can be fed through the agitation equipment as input.

According to an embodiment, the reactor additionally includes equipment 30 shown in Figure 2 for reducing friction between biomass and the biomass contained in the reaction space, the equipment 30 including equipment 58 of Figure 2 for feeding high consistency stock and/or biogas from the walls 44 of the subframe 46 of Figure 4 into the subframe 46 using a pump, for example. Reference number 42 denotes the floor 42 of the subframe 46. The high consistency stock and/or biogas supplied reduces the friction between the biomass 16 in the subframe 46 and the module 52, which in turn decreases the power requirement of the agitation equipment 20. High consistency stock and/or biogas can be supplied in a pointwise manner, in which case high consistency stock and/or biogas supplied into biomass displaces biomass and forms an opening therein, thus improving the advancement of decomposable biomass in the reaction space. Advantageously, the high consistency stock is biomass reject. While the high consistency stock and/or biogas reduces the friction between biomass and the reactor frame, it also simultaneously inoculates the reactor. In addition, agitation of liquid/gas "releases" gas bound to solid material and ensures that methane is not removed with the reject digestate.

In this context, it is obvious to those skilled in the art that in addition to agitation, the agitation equipment, such as blade agitators, also functions as main elements, besides gravity, to push biomass further as plug flow. According to an embodiment, the inner surface of the frame can be coated with a coating corresponding to a Teflon coating, for example, which reduces the friction between biomaterial and the frame and prevents biomaterial from attaching to the inner surface of the frame.

Advantageously, the reactor according to the invention includes a notable number of measuring sensors, which monitor the conditions of each block in real time. Parameters that are to be measured include at least the pH and temperature in each block as well as the overall gas production of the reactor. Based on these, separate control parameters are formed at least for the agitation equipment, temperature control equipment and reject supply, specifically for each block . Advantageously, a control parameter is also established for the equipment for reducing friction, based on the same criteria . The amount of organic matter contained in biomass may also be an object of measurement.

In the method according to the invention, a major part of the reaction space is filled with liquid and biomass such that new raw material supplied to the reaction space, i.e., biomass that is to be decomposed, is fed below the liquid level. This guarantees that air cannot enter the reaction space with biomass , which would destroy the microbial strain that carries out anaerobic digestion. Although, for the sake of clarity, the liquid level and biomass are not shown in Figure 2, it is obvious to those skilled in the art that the reaction space 14 is filled with biomass almost up to the ceiling and the liquid level extends to a distance of about 20-200 cm from the upper end 13.1 of the frame 12 of the reactor 10; that is , the end to which biomass is fed . The removal of digestate is controlled in the reactor in such a way that the necessary liquid level is always maintained. The microbial strain itself can be transferred to the reaction space from another reactor, for example, during the activation of the reactor. The biomass supplied can be biodegradable biomass generated in communities, agriculture or industry, such as animal manure , biowaste produced by households , restaurants, trade or the food industry, sludge from wastewater cleaning, plant biomass or equivalent; however, not material with a high lignin content, such as wood pulp, without lignin decomposition .

Advantageously, the dry content of stock in the reaction space can range between 10% and 35% by dry weight, but materials dryer than this are difficult to agitate . The dry content decreases towards the end of the reactor where decomposition has proceeded further. Biomass can be supplied to the reaction space with a screw feeder, for example. For example, feeding can take place at hour-long intervals 24 hours a day, depending on the organic matter content and biodegradability of biomass used as raw material.

In the method according to the invention, according to Figure 2, biomass 16 can be inoculated in four different ways: by rotating the agitation equipment 20, by feeding reject with the reject collection and feed equipment 56 through the agitation equipment 20, by feeding high consistency stock and/or biogas from the sides of the frame 12 of the reactor 10 using equipment 30 for reducing friction, or by adding reject into the input already before feeding it to the reactor . When anaerobic digestion reactions are in process in the reaction space, gas production, pH and temperature are continuously monitored, whereas inoculation and agitation are advantageously intermittent for energy saving purposes. As a consequence of these changes, reactor agitation, heating, biomass supply and reject supply are controlled by the reject collection and feed system. For example, if it is detected that the pH drops to an insufficient level or gas production decreases in the area of a block, it is possible to locally influence the conditions by improving agitation in this block and by increasing or decreasing reject supply to this block.

The purpose of the agitation equipment 20 is to advance biomass 16 in the reaction space 14 and to agitate biomass 16 so that the microbes receive fresh nutrition. If agitation is not performed frequently enough, a layer of decomposition products, which may inhibit the microbial action, is generated around microbes. For example, agitation can be performed for 15 minutes at hour-long intervals while simultaneously feeding reject to the block. Advantageously, in addition to the agitation direction providing the lateral force, agitation is carried out in the direction opposite to the plug flow direction, which provides a different type of agitation. For example, when using a blade agitator, parallel agitation always moves biomass in a certain place in a certain direction relative to the blade agitator. A change in the agitation direction adds different agitation directions, which improves biomass agitation, microbial inoculation and the yield of organic raw material for microbes. Generally, the pass through of biomass in a reactor may range between 11 and 50 days depending on the biomass used as raw material.

Agitation and its direction are determined according to the values measured; however, backward agitation is generally performed slightly before starting the agitation that advances biomass. The efficiency of agitation varies for each block in the reaction space . In the last block, agitation is advantageously the most efficient in order to separate even the rest of biogases, which may exist as bubbles within solid digestate in so-called gas pockets, from the digestate exiting the reaction space. This is important to achieve efficient biogas recovery and to prevent escape of methane with digestate to the atmosphere, where it is a strong greenhouse gas. Advantageously, in the last block, agitation equipment is rotated in the opposite direction compared to the other blocks, for improving agitation. Digestate removed from the reactor can be delivered to separation, where liquid is separated from it. This liquid can be used for cleaning the reject collection and feed system, for example.

In the oxygen-free conditions of the reaction space, the microbial action provides anaerobic digestion of biomass, which, according to prior art, includes the steps of hydrolysis, acid fermentation ( acidogenesis ) , acetic acid generation ( acetogenesis ) and methane generation (methanogenesis ) . Of these, individual steps and related reactions take place gradually and partly overlapping each other in the reaction space . Advantageously, hydrolysis and acidogenesis take place mainly in the initial part of the reaction space, whereas acetogenesis and methanogenesis occur mainly at the end of the reaction space. As the consequence of the reactions, biogas containing about 50-75% (v/v) of methane (CfU) can be produced from biomass as the end product, while the rest consists mainly of carbon dioxide (CO2) . In addition to these, the end product may contain small amounts of other gases and impurities, such as 100-3,000 ppm of hydrogen sulphide (H2S) . Depending on the end use of biogas, biogas obtained with the method can be purified to remove carbon dioxide, in case biogas is used, for example, as fuel in the road traffic. On the other hand, if biogas is used in combustion boilers for energy and district heat production, it can be used as such. As a consequence of decomposition reactions, 50% to 90% of the organic matter contained in the input is converted to biogas and liquid in the reaction space. If necessary, digestate generating as a by-product may be dried or processed further in other ways and utilised for fertilisation purposes or as a soil conditioner, for example.

The dimensions of a reactor according to the invention can remarkably vary depending on the application. For example, the size of the reactor may be 2 m x 2 m x 4 m (l,w,h), but it is also scalable to a size class of 12 m x 12 m x 50 m or larger. For large reactor sizes, several feed devices can be used to achieve uniform supply. Here, 12 m refers to the length and width of the reactor and 50 m refers to the height of the reactor in the plug flow direction.

The control of a reactor according to the invention can be implemented, for example, using a conventional PC as a user platform, on which the control software of the reactor runs. A field bus is provided for the data transfer between the PC and actuators, sensors and other devices, such as valves, required for the control . A method according to the invention can be fully automated, in which case the software controls the operation of the reactor according to preselected criteria based on preselected rules.

Figure 5 shows a reactor according to an embodiment of the invention as a process chart together with auxiliary equipment associated with the reactor. In an embodiment, the process is started at a feed table, to which solid biomass is supplied preferably as bales, which are broken into smaller chops with a bale breaker. The feed table and the bale breaker are not shown in the figures. From the bale breaker, the input drops into a feed funnel 25.2 passing therethrough to a screw conveyor 25.1, which supplies the input to the reactor 10 via the feed connection 71 at regular preset intervals, such as once an hour. A crusher pipe, which further breaks down the input, may be placed in the feed connection 71. In addition to solid biomass, the feed connection 71 can be supplied with liquid reject from the reactor through the line 75, for reducing friction. The reactor 10 can also be supplied with liquid input, such as lipids, which can be stored in the tank 76. Liquid input can be delivered to the reactor via the high consistency stock pump 57 of the reject collection and feed system 56.

According to Figure 5, the reactor 10 may include four mechanical agitators, which can be blade agitators 36 inthiscontext. Agitators can also be placed in parallel, in which case the diameter of an individual agitator is smaller. Each blade agitator 36 advantageously has a motor 65 and a frequency converter of its own, which can be used to adjust the speed of rotation. For example, the output of an individual motor can be 4 kW and the speed of rotation 6 revolutions per minute. The frame 12 of the reactor 10 is divided into at least three blocks 24, i.e., a hydrolysis block, an acid fermentation block and a methanogenesis block. In each block 24, reject is supplied in front of the block with the reject collection and feed system 56. According to Figure 5, reject is removed from the block via the discharge connection 60 and supplied to the collection and feed system 56 preferably as high consistency stock utilising a vacuum generated by the high consistency stock pump 57. For example, at the third blade agitator 36', reject is removed via the discharge connection 60' when the discharge valve 82' is open. Reject passes via the high consistency stock pump 57 and is supplied to the reject feed connection 62' through the open feed valve 84' . In this case, the reject feed connection 62' is preferably located on the blades of the blade agitator 36 ' . Generally, reference number 62 denotes a feed connect ion, reference number 82 a discharge valve and reference number 84 a feed valve.

In other words, the microbial strain of each block is advantageously recirculated within the block in such a way that the microbial strain is removed from the block as reject and is advantageously fed back to the block via the agitation equipment. In each block, the reject discharge connection is located at a distance from the agitation equipment or the reject feed connection, where reject is fed back to the block. This distance varies according to the scale of the reactor; preferably, however, the feed connection and the reject discharge connection are located at a distance corresponding to 0.2-0.6 times the block length, with the reject discharge connection as close as possible to the end of the block. The distance enables the microbial strain to develop naturally within the block.

Decomposed biomass i.e. digestate is removed from the end of the reactor 10, i.e., from the last block 24, using a pump 68. The pump is used, based on the measurement of the liquid level meter of the reactor 10, when the preselected liquid level is exceeded. Digestate removed is advantageously delivered to a dry digestate store where the dry matter and liquid are separated using a matrix pipe. Biogas generating in the reactor can be recovered in a gas store 78. Advantageously, a condensate well 81 is also provided associated with the gas store, to which water condensing from biogas at 100% moisture is collected. Part of biogas can be used for heating the liquid heating circuit 77 of the reactor with a gas boiler 74.

According to an embodiment, the reactor 10 includes recirculation equipment for biogas connected to the recovery equipment 22, for recirculating recovered biogas under pressure to the lower end of the reactor frame for agitating digestate and separating biogas from digestate. As shown in Figure 2, the recirculation equipment for biogas may include a flow channel for connecting the recovery equipment 22 to the lower end 13.2 of the reactor 10 frame 12 for recirculating biogas, and a pump 33 arranged in the flow channel for aspirating biogas from the recovery equipment and pressurising biogas that is to be recirculated before feeding biogas into the reactor 10 frame 12, to the lower end 13.2 of the frame 12.

The frame of the reactor according to the invention is advantageously made of a steel sheet by welding, but the frame can also be made of material that can be 3D printed. For example, such materials include concrete , fibre concrete or composite . In turn, the external skeleton is advantageously made of steel , but basically the external skeleton can also be 3D printed using concrete or fibre concrete. A reactor according to the invention provided with a vertical frame is advantageous also for 3D printing, since the transfer distances of the print head of the 3D printer are smaller than in a horizontal reactor .

Reactors according to the invention can be easily installed side by side without a gap, which enables easy increase of capacity of the complete whole. The small footprint area of the reactor according to the invention allows such side-by-side placement. In the reactor 10 according to the invention, the feed equipment 25 and the removal equipment 27 for solid material can be placed on the same side, in which case the building made for the feed equipment 25 of the reactor 10 and the building made for the removal equipment 27 for solid material can be one and the same building 99. Biomass can be transported to the building with a truck 98, for example.