Plant for producing biogas, pretreatment device and method for operating a plant for producing biogas

Abstract

The invention refers to a plant for producing biogas, having at least one pretreatment tank (2) in which a substrate (14) is accommodated, the substrate (14) containing at least one organic substance (10) or being formed by at least one organic substance (10) which has at least one fermentation-inhibiting and oxidizable component. Furthermore, at least one oxidation device (8) is provided, which is arranged at least partially in the at least one pretreatment tank (2). Furthermore, at least one control device (11) is provided, by means of which the at least one oxidation device (8) can be controlled in such a way that a predetermined amount of a gaseous or liquid oxidizing agent (9) can be supplied to the substrate (14) at predetermined times in such a way that at least a part of the at least one oxidizable component is oxidized by means of the oxidizing agent (9) and a pretreated substrate is present in the pretreatment tank (2). Finally, at least one fermenter tank (3) is provided in which at least a part of the pretreated substrate can be fermented. The invention further refers to a pretreatment device and method for operating a plant for producing biogas.

Description

[0001] Description

[0002] Plant for producing biogas, pretreatment device and method for operating a plant for producing biogas

[0003] The invention refers to a plant for producing biogas, further to a pretreatment device for use in a plant for producing biogas and to a method for operating a plant for producing biogas.

[0004] Biogas plants are vital components of the renewable energy landscape, utilizing organic materials to produce biogas through the process of anaerobic fermentation. The term anaerobic fermentation in this context is synonymous with anaerobic digestion. These facilities begin by receiving a diverse array of organic substrates, ranging from byproducts, agricultural residues to food waste and energy crops. These substrates serve as the feedstock for biogas production and are introduced into the fermenter, the core of the biogas plant. Within the fermenter, organic substrates undergo anaerobic fermentation, facilitated by a complex consortium of microorganisms including bacteria and archaea. In the absence of oxygen, these microorganisms break down complex organic compounds into simpler molecules through a series of enzymatic reactions. This fermentation process leads to the production of biogas, primarily composed of methane (CH4) and carbon dioxide (CO2), along with trace gases such as hydrogen sulfide (H2S).

[0005] Biogas produced in the fermenter is collected and stored in gas storage facilities. The collected biogas is then utilized for various purposes, with electricity generation being one of the primary applications. Biogas can be combusted in gas engines or turbines to produce electricity, which can be used on-site to power equipment or fed into the grid to meet energy demands. Additionally, biogas can undergo purification processes to upgrade it to biomethane, a renewable fuel suitable for transportation or injection into natural gas lines.

[0006] After the fermentation process, the remaining material, known as digestate, is separated from the biogas. Digestate is rich in nutrients and organic matter, making it a valuable fertilizer for agricultural purposes. By returning nutrients to the soil, digestate management completes the cycle of resource utilization within the biogas plant, contributing to sustainable agriculture practices. Polyphenol-rich substrates pose a significant challenge in biogas production due to their inherent properties. These substances, abundant in various organic materials such as agricultural residues, food waste, and byproducts like for example olive pomace, exert inhibitory effects on anaerobic fermentation processes crucial for biogas generation. Polyphenols, natural defense molecules produced by plants, function as potent antioxidants against external aggressors. However, their presence hampers the efficiency of anaerobic fermentation by impeding microbial activity and substrate degradation.

[0007] It is therefore an object of the present invention to provide a plant for producing biogas, a pretreatment device for use in a plant for producing biogas and a method for operating a plant for producing biogas which improves the quality of the performance of an anaerobic fermentation for polyphenol-containing organic starting products for biogas production.

[0008] This object is solved by the independent claims. Preferred embodiments are claimed in the sub-claims.

[0009] The invention relates to a plant for producing biogas, having at least one pretreatment tank in which a substrate is accommodated, the substrate containing at least one organic substance or being formed by at least one organic substance. Said organic substance has at least one fermentation-inhibiting and oxidizable component.

[0010] Furthermore, at least one oxidation device is provided, which is arranged at least partially in the at least one pretreatment tank.

[0011] Furthermore, at least one control device is provided, by means of which the at least one oxidation device can be controlled in such a way that a predetermined quantity of a gaseous or liquid oxidizing agent can be supplied to the substrate at predetermined times in such a way that at least a part of the at least one oxidizable component is oxidized by means of the oxidizing agent and a pretreated substrate is present in the pretreatment tank.

[0012] Furthermore, at least one fermenter tank is provided in which at least a portion of the pretreated substrate can be fermented.

[0013] The solution according to the invention thus proposes that the substrate to be fed to a fermenter, in particular biomass, be treated with an oxidizing agent before being fed to the fermenter in order to oxidize the at least one fermentation-inhibiting component contained in the organic substance of the substrate. This can significantly reduce the inhibitory effect of this fermentation-disrupting component, such as polyphenol, on the fermentation process of a fermenter in a biogas plant. As the inventor's experiments have shown, this significantly increases not only the quantity but also the quality of the biogas produced, additionally avoiding the slowdown of the process or its interruption. This applies in particular to the pH stability of the digestate produced within an optimum alkaline range, and also to the absence of volatile fatty acids with a higher molecular weight, such as propionic acid, butyric acid and valeric acid, and also to the prevention of the accumulation of acetic acid. These results are generally obtained for all fermentation-inhibiting and oxidizable components, but particularly excellent results can be obtained if the substrate is containing polyphenols, especially preferably if the substrate is olive pomace and contains polyphenols as fermentation-inhibiting and oxidizable components. Olive pomace is usually a two-phase olive press cake, which is a by-product of olive oil production and contains both solids and liquids. It is worth mentioning that not only chemical oxidizing agents but also oxidative biological processes may perhaps contribute to this oxidation process. That means that the microbial activities within the pre-treatment tank could play a role in oxidizing the organic matter, potentially enhancing the efficiency of the pre-treatment process.

[0014] In the context of the present invention, a "substrate" is preferably understood to be a substance or a mixture of substances which is flowable or pumpable to at least a certain extent, i.e. in addition to pure liquid phases, it also comprises liquid phases with a solid content, as long as the latter are flowable or pumpable to a minimum extent. This ensures that the oxidizing agent can distribute itself well within the substrate. Accordingly, according to a particularly preferred embodiment, the substrate is a liquid phase with a predetermined viscosity, for example a viscosity (at 20°C) up to 10000 cP (Centipoise).

[0015] As already mentioned, in principle any oxidizing agent is suitable for converting the solution according to the invention. However, these are often to be kept in separate tanks and may be less environmentally friendly, such as hydrogen peroxide (H2O2) as an example of such a liquid oxidizing agent or chlorine (CI2) as an example of such a gaseous oxidizing agent. Accordingly, the use of a gaseous oxidizing agent is preferred which is formed by oxygen (02) or at least contains oxygen, as is the case in particular with air, which neither requires separate storage facilities nor is toxic and is also present in the environment to an unlimited extent. This makes the solution according to the invention particularly advantageous, simple and inexpensive to implement. Another preferred example of an oxidizing agent that contains oxygen is or ozone (03).

[0016] In principle, the pretreatment tank can have any shape and / or geometry, e.g. cylindrical, angular or oval, to name just a few examples. However, a cylindrical tank with a circular-cylindrical circumferential geometry is particularly preferred, especially for manufacturing reasons.

[0017] Furthermore, according to a first embodiment, the pretreatment tank can be designed as a pretreatment tank that is at least partially open at the top, in particular in conjunction with air as oxidizing agent. In such an open tank, for example, the air as oxidizing agent, after it has flowed through the substrate from bottom to top with respect to the vertical axis direction, can simply escape into the environment at the top. However, there is always a risk of contamination or tampering with open tanks, which can be better avoided by using a closed pretreatment tank. Accordingly, according to an alternative second embodiment, the pretreatment tank is designed as a closed tank which has a top wall, preferably accessible respectively walkable, which closes the top of the pretreatment tank. In the case of such a closed pretreatment tank and a gaseous oxidizing agent, at least one gas outlet is provided, by means of which a gaseous oxidizing agent accumulating in the region above the substrate can be discharged from the pretreatment tank. Such a gas outlet can, for example, be designed in the form of a chimney, via which air can be released unhindered into the environment as a gaseous oxidizing agent without storage, filtering or other treatment. Moreover, closing the pretreatment tank guarantees the treatment of a constant quantity of substrate, avoiding any dilution caused by rain and / or the evaporation of moisture in particularly rainy or dry sites, respectively.

[0018] According to a particularly preferred specific embodiment, the oxidation device has at least one oxidizing agent source and / or the oxidation device is coupled to at least one oxidizing agent source. Starting from this at least one oxidizing agent source, the liquid or gaseous oxidizing agent is guided into the area of the substrate by means of at least one oxidizing agent line, preferably from the at least one oxidizing agent source arranged outside the pretreatment tank into the interior of the pretreatment tank and from there into the area of the substrate. This type of oxidizing agent line enables the oxidizing agent to be fed into the substrate area in a functionally safe and reliable manner. In addition, such an oxidizing agent line can be provided with at least one shut-off element, for example at least one valve element, and / or with at least one sensor element, for example at least one flow meter, which can then preferably be controlled via the control device in order to control the timing, location and quantity of a targeted addition of an oxidizing agent.

[0019] According to a further particularly preferred specific embodiment, the at least one oxidizing agent line has a substrate line region running in the substrate. With such a substrate line region, it is possible to introduce the oxidizing agent into the substrate in a simple and functionally reliable manner. A particularly preferred embodiment in this context is one in which this substrate line region in the substrate extends over at least a partial region of the horizontal plane, preferably essentially over the entire horizontal plane, of the pretreatment tank and / or that this substrate line region, with respect to the vertical axis direction, extends in a bottom-side or near-bottom region of the pretreatment tank. With each of these preferred measures, it is possible to distribute the oxidizing agent evenly in the substrate, so that a functionally reliable oxidation of the fermentation-inhibiting component, such as the polyphenols, is achieved. In particular, the arrangement of the line region in a bottom-side or near-bottom area also makes it possible for the oxidizing agent to flow through the substrate from bottom to top in relation to the vertical axis direction, thus providing sufficient time and opportunity to oxidize the oxidizable components. This is particularly easy with a gaseous oxidizing agent. When using a liquid oxidizing agent, it must be ensured that the oxidizing agent can mix within the substrate, preferably by using at least one mixing and / or stirring device as described below.

[0020] In principle, there are various ways of routing the oxidizing agent line from outside the pretreatment tank into the interior of the pretreatment tank. One embodiment is particularly easy to implement and easily accessible, for example in connection with maintenance work, in which the oxidizing agent line is routed from the gas source located outside the pretreatment tank above the substrate into the interior of the pretreatment tank and from there downwards along the inner wall of the tank into the bottom or near-bottom area, preferably as far as the bottom wall, where the substrate line region is then connected.

[0021] As already explained above, it is particularly advantageous if the substrate line region extends over at least part of the horizontal plane, preferably essentially over the entire horizontal plane, of the pretreatment tank. According to a first particularly preferred specific embodiment, this is achieved, for example, with a substrate line region that extends in a meandering manner in the area of the pretreatment tank close to or on the bottom. Alternatively, however, the substrate line region can also have a tree-like structure with a central first line section which extends in the area of the pretreatment tank close to the bottom or on the bottom side from one side of the inner wall of the tank in a trunk-like or lance-like manner towards the center of the tank, preferably towards the center of the tank and beyond, as well as towards the opposite side of the inner wall of the tank in the direction of extension. On both sides of the first line section, a plurality of spaced-apart second line sections project in a branch-like manner. Preferably, the second line sections lie in the horizontal plane and project at right angles from the first line section. Alternatively, however, these second line sections can also project upwards at least partially at an angle in relation to the vertical axis direction. With such a tree-like structure of the substrate line region, a particularly advantageous distribution of the oxidizing agent in the substrate is achieved. This applies to an even greater extent to another particularly preferred embodiment according to which it is provided that a plurality of spaced-apart third line sections project in a branch-like manner from the second line sections, preferably on both sides of the second line section. Preferably, the third line sections lie in the horizontal plane and project at right angles from the second line sections. Alternatively, however, these third line sections may also project upwards at least partially at an angle in relation to the vertical axis direction.

[0022] According to a further particularly preferred embodiment, it is provided that at least part of the substrate line region, preferably the second and / or third line sections in the case of a substrate line region having a tree-like structure, has an oxidizing agent outlet region via which the oxidizing agent flows into the substrate. With such a defined oxidizing agent outlet region, the substrate can be exposed to the oxidizing agent in a particularly targeted manner. This applies in particular to a particularly preferred embodiment, according to which the oxidizing agent outlet region is formed by a plurality of outlet openings spaced apart from one another. Alternatively or additionally, it can also be provided that the oxidizing agent outlet region has a semi-permeable membrane which is permeable to the oxidizing agent but not to the liquid phase of the substrate. This ensures particularly reliable operation because it prevents the liquid phase of the substrate from escaping from the interior of the tank via the oxidizing agent outlet area.

[0023] As the above explanations show, the solution according to the invention can be implemented particularly simply and reliably, especially in conjunction with an oxidizing agent line which is designed as a gas line and is coupled to a gas source as an oxidizing agent source. In this context, it is then also further particularly preferred if the oxidizing agent outlet region is a bubble diffuser which is preferably suitable and designed to generate gas bubbles with a defined size and / or diameter, for example large gas bubbles with a diameter of for example 4 mm. A predetermined and defined size of the gas bubbles has proven to be well suited for distributing a gaseous oxidizing agent, in particular air as oxidizing agent, in the substrate. However, gas bubbles that are too large tend to rise upwards too quickly, which in turn also reduces the contact time and, above all, requires the use of large quantities of oxidizing agent.

[0024] According to a particularly preferred embodiment, it is provided that the oxidation device has an air intake device, preferably a blower or a compressor, arranged outside the pretreatment tank, via which air can be drawn in as oxidizing agent from the environment as oxidizing agent source, preferably can be drawn in and compressed. As has been explained many times before, air is ideally suited as an oxidizing agent and is available in almost unlimited quantities. In addition, the air can also be advantageously compressed in the desired manner, in particular in conjunction with a compressor as an air intake device, in order to generate a suitable oxidizing agent flow in the direction of the substrate.

[0025] Particularly preferably, the oxidation device, preferably an air intake device of the oxidation device, can be controlled by means of the control device in such a way that at least one of the following features is fulfilled:

[0026] - 20 to 400 cubic meters of oxidizing agent, preferably air as oxidizing agent, are added to the substrate per cubic meter of substrate;

[0027] - 0.1 to 2.0 cubic meters of oxidizing agent, preferably air, are added to the pretreatment tank per cubic meter of pretreatment tank volume;

[0028] - the substrate is exposed to oxidizing agent for a period of 1 to 30 min / h, preferably aerated with air as oxidizing agent.

[0029] With such measures, which are carried out both individually, but particularly preferably together, a particularly advantageous oxidation of the fermentation-inhibiting components, especially polyphenols, in organic substances is achieved, especially with regard to the quantity and quality of the biogas produced, the pH value stability in the alkaline range, the absence of volatile acids with a higher molecular weight and the lack of accumulation of acetic acid.

[0030] A particularly advantageous and reliable distribution of the oxidizing agent in the substrate is achieved with a particularly preferred embodiment, according to which it is provided that at least one mixing and / or stirring device is provided, by means of which the substrate accommodated in the at least one pretreatment tank can be mixed and / or stirred in a controlled manner by the at least one control device for a predetermined mixing and / or stirring time, preferably for mixing the substrate with the oxidizing agent. It is particularly preferred here that the at least one mixing and / or stirring device can be controlled by means of the control device in such a way that the substrate is stirred at the same time as or with a time delay (for example with a time delay of one minute) to the start of the supply of the oxidizing agent for a predetermined period of time, preferably at least until the end of the respective oxidizing agent supply phase. In this context, it has proven to be advantageous for particularly energy-efficient operation if stirring takes place with a power of 0.02 to 0.4 kW per cubic meter of useful tank volume of the pretreatment tank.

[0031] Depending on the size of the pretreatment tank, which can have heights of 1 m to 20 m and / or diameters of 10 m and more, one or more mixing and / or stirring devices can be used to support sufficient mixing of the substrate with oxidizing agent. Especially in connection with large-volume pretreatment tanks, it has proven to be particularly advantageous to pivot at least one mixing and / or stirring device on a top wall of the pretreatment tank, preferably in the area above the substrate line region and / or to pivot it in different spatial directions.

[0032] Alternatively or additionally, at least one mixing and / or stirring device can also be height-adjustable in the vertical axis direction and / or guided above the substrate line region on a vertical guide mast arranged in the pretreatment tank, preferably pivotable about its longitudinal axis. This guide mast can, for example, be mounted with an upper end section in a service dome, which detachably covers a top wall opening of the top wall of the pretreatment tank. In the case of a gaseous oxidizing agent, the service dome has at least one gas outlet via which a gaseous oxidizing agent accumulating in the area above the substrate can be discharged from the pretreatment tank, preferably into the environment in the case of air as the gaseous oxidizing agent.

[0033] According to a further particularly preferred embodiment, it is provided that the input quantity of substrate is predetermined as a function of the volume of the pretreatment tank and the hydraulic retention time in the pretreatment tank according to the following equation:

[0034] Q = V / HRT with

[0035] Q = Input quantity in cubic meters per day

[0036] V = tank volume in cubic meters

[0037] HRT = hydraulic retention time in days As the inventor's tests have shown, very good results are achieved with hydraulic retention times in the pretreatment tank of 1 day to 20 days.

[0038] The pretreatment process can be carried out either continuously or as a batch process. In a batch process the tank is filled with substrate, oxidized and then completely emptied. Both methods allow better control of the process, making it easier to monitor and adjust tank conditions, and offers more flexibility in processing different substrates.

[0039] Furthermore, it can be beneficial to arrange a heating device in the pretreatment tank, preferably a heating device in the form of heating pipes running around at least sections of the inner wall in the area close to the floor. This is particularly advantageous in cold locations where the substrate may have a tendency to freeze, and consequently cool the digestate in the anaerobic tank making unstable and slowing the whole process of anaerobic fermentation.

[0040] In principle, the substrate or the organic substance can be fed to the pretreatment tank in any desired manner or the pretreated substrate can be discharged from the at least one pretreatment tank in any desired manner. However, a substantially automated solution is particularly preferred, in which a feeding device is provided, by means of which the substrate and / or the organic substance, preferably olive pomace, and / or liquid can be fed to the at least one pretreatment tank in a controlled manner by means of the control device and / or a discharge device is provided, by means of which the pretreated substrate can be discharged from the at least one pretreatment tank in a controlled manner by means of the control device and can be fed directly or indirectly to the at least one fermenter tank.

[0041] As already mentioned, the pretreatment tank can have any desired shape. In this context, it is particularly preferable for the pretreatment tank to be made of concrete, with the top wall also being made of concrete in conjunction with a top wall provided. Such a tank made of concrete is particularly robust and weatherproof. In addition, such a top wall made of concrete can also be easily walked on by personnel. There is no risk of the top wall lifting off due to gas pressure (keyword: hydraulic press), as unlike fermenter tanks, for example, no critical gas pressure is built up inside the tank and the oxidizing agent escapes from the tank in a gaseous state.

[0042] The aforementioned object is also solved with a pretreatment device for using a plant for producing biogas or with a method for operating a plant for producing biogas. The resulting advantages are identical to the advantages mentioned above in connection with the plant, so that reference is made to the explanations given above in order to avoid repetition.

[0043] The invention is described below by way of example with reference to figures and a specific embodiment.

[0044] The figures show:

[0045] Fig. 1 is a schematic representation of an exemplary embodiment of the plant for producing biogas according to the invention,

[0046] Fig. 2 is a schematic top view of the pretreatment tank of Fig. 1 ,

[0047] Fig. 3 is a schematic sectional view along line A-A of Fig. 2,

[0048] Fig. 4 is a schematic sectional view along line B-B of Fig. 2,

[0049] Fig. 5 is a diagram showing the results of the biogas production according to the invention.

[0050] Fig. 1 shows a schematic and exemplary perspective principle sketch of a plant 1 for producing biogas according to the invention, which has a pretreatment tank 2 downstream of which is a fermenter tank 3. A storage tank 4 is connected upstream of the pretreatment tank 2, in which, in the example shown here, polyphenol-rich olive pomace is stored as organic substance, which is to be fed to the substrate in the pretreatment tank 2.

[0051] As can also be seen from Fig. 1 , a final storage tank 5 is located downstream of the fermenter tank 3, in which the digestate 12 formed in the fermenter tank 3 after the anaerobic fermentation process is temporarily or finally stored, while the biogas 6 also formed is fed to a further utilization process.

[0052] Fig. 1 also shows that a compressor 7 is assigned to the pretreatment tank 2, which is part of an oxidation device 8 assigned to the pretreatment tank 2 and described in detail below, with which air 9 is sucked in as an oxidizing agent and fed to the pretreatment tank 2.

[0053] The olive pomace 10 held in the storage tank 4 is fed to the pretreatment tank 2 by means of a feeding device, which is controlled by a control device 11 and is not shown here. Specifically, the olive pomace 10 is fed to a substrate held in the pretreatment tank 2 and subjected there to a pretreatment with oxidizing agent, which is described in detail below.

[0054] As can be further seen from Fig. 1 , after pretreatment in the pretreatment tank 2, the pretreated substrate 13 is then fed, again controlled by the control device 11 , by means of a discharge device not shown, to the fermenter tank 3, in which the pretreated substrate 13 is then subjected to an anaerobic fermentation process in order to produce the biogas 6.

[0055] As can now be seen in particular from Fig. 2 to 4, a pumpable and flowable substrate 14 is accommodated in the pretreatment tank 2, which is either formed by the olive pomace 10 itself or by a mixture of olive pomace 10 and a liquid, such as water, as a liquid phase.

[0056] In the example shown here, the pretreatment tank 2 is designed as a closed tank, which has a cylindrical side wall 15, a base wall 16 and a top wall 17, which is designed here as a walk-on top wall 17 and runs horizontally. Preferably, the side wall 15, the base wall 16 and the top wall 17 are made of concrete.

[0057] The oxidation device 8 referred to in connection with Fig. 1 uses the ambient air 9 as an oxidizing agent source and has the compressor 7 as an air intake device, from which a gas line 18 as an example for an oxidizing agent line is led into the area of the substrate 14.

[0058] Specifically, this gas line 18 is routed here, for example, from the compressor 7 above the substrate into the interior 19 of the pretreatment tank 2 and from there along the inner wall of the side wall 15 down into the bottom or near-bottom area, where a substrate line region 20, which forms a part of the gas line 18, is connected.

[0059] As can be seen in particular from Fig. 2, the substrate line region 20 has a tree-like structure with a central first line section 21 , which extends in the near-bottom or bottom-side area of the pretreatment tank 2 from one side of the tank inner wall of the side wall 15 in a trunk-like or lance-like manner towards the center of the tank and beyond that towards the opposite side of the tank inner wall of the side wall 15 in the direction of extension.

[0060] On both sides of the first line section 21 , a plurality of spaced-apart second line sections 22 project in a branch-like manner. In the example shown here, the second line sections 22 lie in the horizontal plane of the pretreatment tank 2 and project at right angles from the first line section 21. In the example shown here, a plurality of spaced-apart third line sections 23 project in two directions from these second line sections 22 on both sides of the line sections 22. In the example shown here, the third line sections 23 lie in the horizontal plane of the pretreatment tank 2 and project at right angles from the second line sections 22.

[0061] As can be seen in particular from the combined view of Fig. 2 and Fig. 4 and the gas bubbles or air bubbles 24 indicated there, the third line sections 23 in the example case shown here are designed as oxidizing agent outlet regions 25 which have, for example, a plurality of outlet openings spaced apart from one another, via which the air drawn in and compressed by the compressor 7 and conveyed via the gas line 18 into the substrate line region 20 can enter the substrate 14. Preferably, the oxidizing agent outlet region 25 is equipped with a semi-permeable membrane, for example, which ensures that only the oxidizing agent can escape into the substrate 14, but not liquid from the substrate 14 into the oxidizing agent outlet region 25.

[0062] The oxidizing agent outlet region 25 is preferably designed as a bubble diffuser, with which large gas bubbles with a diameter of, for example, 4 mm generated.

[0063] As can be seen in particular from Fig. 4, a mixing and / or stirring device 26 is pivotably articulated to the top wall 17, namely, as can be seen in particular from Fig. 2, in the region above a first end 27 of the first line section 21. This mixing and / or stirring device 26 can thus be pivoted in a central region above the substrate line region 20, preferably in different spatial directions, which is shown schematically in Fig. 4 by the arrow 29 and the two pivot positions of the mixing and / or stirring device 26.

[0064] Furthermore, in the example shown here, in the region above the second end 28 of the first line section 21 , which is essentially opposite the first end 27, a further mixing and / or stirring device 30 is guided in a vertically adjustable manner in the vertical axis direction on a vertical guide mast 31 arranged in the pretreatment tank 2, which guide mast 31 is preferably pivotable about its longitudinal axis. The guide mast 31 is mounted here merely by way of example with an upper end region in a service dome 32, which detachably covers a top wall opening 33 of the top wall 17. As can also be seen from Fig. 4, the service dome 32 also has a chimney-like gas outlet 34 through which a gaseous oxidizing agent (air in the example shown here) accumulating in the gas chamber 35 in the area above the substrate 14 can escape from the pretreatment tank 2 (as indicated by arrow 36). As shown further in connection with Fig. 3 merely by way of example and schematically as an optional variant, a heating device can also be arranged in the pretreatment tank 2, which is formed here merely by way of example by heating pipes 37 running around the inner wall of the side wall 15 of the tank.

[0065] The oxidation device 8 or preferably the compressor 7 of the oxidation device 8 is preferably controllable by means of the control device 11 in such a way that the following features are fulfilled individually or preferably cumulatively:

[0066] - 20 to 400 cubic meter of air per cubic meter of liquid phase are added to substrate 14;

[0067] - 0.1 to 2.0 m2per cubic meter tank volume of the pretreatment tank 2 is fed into the pretreatment tank 2;

[0068] - the substrate 14 is aerated with air as an oxidizing agent for a period of 1 to 30 min / h.

[0069] During the aeration phase, the air or gas bubbles 24, as shown schematically and exemplarily in Fig. 4, can then migrate from the bottom wall 16 in vertical axis direction upwards through the substrate 14, oxidizing at least the polyphenols of the olive pomace and then collecting as air in the gas space 35 above the substrate 14, which can escape via the gas outlet 34 (as also indicated by arrow 36).

[0070] For good mixing and for bringing the air bubbles 24 into good contact with the polyphenols of the olive pomace, the substrate 14 can be stirred and mixed with the mixing and / or stirring devices 26, 30. For example, the mixing time can be selected here at least according to the aeration time, for example in the range from 1 to 30 min / h, whereby the mixing and / or stirring devices 26, 30 can be moved and swiveled in different directions, as explained above, in order to ensure good mixing of the substrate 14 with the air or gas bubbles 24.

[0071] The mixing and / or stirring devices 26, 30 are preferably stirred with a total power of 0.02 to 0.4 kW per cubic meter of tank volume of the pretreatment tank 2 in order to ensure energy-efficient operation of the mixing and / or stirring devices 26, 30. The input quantity Q (preferably in cubic meters per day) of olive pomace is specified as a function of the tank volume V (in cubic meters) of the pretreatment tank 2 and the hydraulic retention time HRT in the pretreatment tank 2 according to the following equation:

[0072] Q = V / HRT whereby the hydraulic retention time HRT in the pretreatment tank 2 is preferably 1 day to 20 days. The pretreatment process can be carried out either continuously or as a batch process. In the case of a batch process, the tank is filled with substrate, subjected to oxidation, and then completely emptied.

[0073] With such a setup and such a mode of operation of plant 1 , very good results can be achieved in terms of the quantity and quality of the biogas produced, as the following example shows:

[0074] Olive pomace was filled into a pretreatment tank with a diameter of 10 m and a height of 6 m up to a filling level of the pretreatment tank of approx. 4.8 m, which corresponded to a substrate volume of approx. 377 cubic meters with a usable tank volume of approx. 400 cubic meters. A total of approx. 45 tons of olive pomace were filled into the pretreatment tank per day, which corresponded to a hydraulic retention time of approx. 9 days, based on the usable tank volume of approx. 400 cubic meters.

[0075] The olive pomace was present as an olive oil milling residue, for example the two-phase olive press cake and / or the olive mill waste water, as a by-product of olive oil production and had an average solids content of 13.5 % by weight and a corresponding water content of 86.5 % by weight.

[0076] The substrate was aerated in the pretreatment tank for 3 minutes per hour with air as oxidizing agent, which was sucked in and compressed via a compressor, whereby 114 cubic meters of air per cubic meter of substrate and 0.65 cubic meters of air per cubic meter of tank volume.

[0077] The mixing and / or stirring time of two mixing and / or stirring devices was 5 min / h each with an electrical total power of 0.14 kWh per cubic meter tank volume. The mixing and / or stirring took place during and after aeration.

[0078] With such a setup, the results shown in Fig. 5 were achieved over several months with regard to the biogas quality, namely a high and stable CH4 content in the biogas of over 57 % and a permanently stable pH value in the range of over 7.5. In addition, the analysis results have shown that higher molecular weight volatile fatty acids are more or less absent and acetic acid is at optimal values. Without pre-treatment, on the other hand, the results for the CH4 content of biogas are well below 57 % and the pH value is out from the optimal range for the anaerobic fermentation.

[0079] List of reference signs

[0080] 1 Plant 29 Arrow

[0081] 2 Pretreatment tank 30 Mixing and / or stirring device

[0082] 3 Fermenter tank 31 Guide mast

[0083] 4 Storage tank 32 Service dome

[0084] 5 Final storage tank 33 Top wall opening

[0085] 6 Biogas 34 Gas outlet

[0086] 7 Compressor 35 Gas room

[0087] 8 Oxidation device 36 Arrow

[0088] 9 Air 37 Heating pipes

[0089] 10 Olive pomace

[0090] 12 Digestate

[0091] 13 Pretreated substrate

[0092] 14 Substrate

[0093] 15 Side wall

[0094] 16 Base wall

[0095] 17 Top wall

[0096] 18 Oxidizing agent line / Gas line

[0097] 19 Tank interior

[0098] 20 Substrate line region

[0099] 21 First line section

[0100] 22 Second line section

[0101] 23 Third line section

[0102] 24 Gas bubbles I air bubbles

[0103] 25 Oxidizing agent outlet region

[0104] 26 Mixing and / or stirring device

[0105] 27 First end

[0106] 28 Second end

Claims

Claims1 Plant for producing biogas, with at least one pretreatment tank (2) in which a substrate (14) is accommodated, wherein the substrate (14) contains at least one organic substance (10) or is formed by at least one organic substance (10) which has at least one fermentation-inhibiting and oxidizable component, with at least one oxidation device (8), which is arranged at least partially in the at least one pretreatment tank (2), having at least one control device (11), by means of which the at least one oxidation device (8) is controllable in such a way that a predetermined quantity of a gaseous or liquid oxidizing agent (9) is supplyable to the substrate (14) at predetermined times in such a way that at least some of the at least one oxidizable component is oxidized by means of the oxidizing agent (9) and a pretreated substrate is present in the pretreatment tank (2), with at least one fermenter tank (3) in which at least a portion of the pretreated substrate is fermentable.

2. Plant according to claim 1 , characterized in that the organic substance (10) is a polyphenol-containing organic substance, whereby it is preferably provided that the organic substance is or contains olive pomace comprising polyphenols as a fermentation-inhibiting and oxidizable component.

3. Plant according to claim 1 or 2, characterized in that the substrate (14) is flowable and / or pumpable, preferably with a predetermined viscosity (at 20°C) up to 10000 cP.

4. Plant according to any one of preceding claims, characterized in that the gaseous oxidizing agent is oxygen or contains oxygen, preferably is formed by air (9).

5. Plant according to any one of preceding claims, characterized in that the pretreatment tank is designed as a pretreatment tank (2) which is at least partially open at the top or is formed by a closed pretreatment tank (2), preferably by a closed pretreatment tank (2) having a top wall (17) which can be walked on, whereby it is preferablyprovided, that, in the case of a closed pretreatment tank (2) and a gaseous oxidizing agent (9), at least one gas outlet (34) is provided, by means of which a gaseous oxidizing agent (9) accumulating in the region above the substrate (14) is dischargable from the pretreatment tank (2), preferably with air as the gaseous oxidizing agent into the environment.

6. Plant according to any one of preceding claims, characterized in that the oxidation device (8) has at least one oxidizing agent source and / or is coupled to at least one oxidizing agent source from which the liquid or gaseous oxidizing agent (9) is fed into the region of the substrate (14) by means of at least one oxidizing agent line (18), preferably from the at least one oxidizing agent source arranged outside the pretreatment tank (2) into the tank interior (19) of the pretreatment tank (2) and from there into the region of the substrate (14).

7. Plant according to claim 6, characterized in that the at least one oxidizing agent line (18) has a substrate line region (20) running in the substrate (14), whereby it is preferably provided that this substrate line region (20) extends in the substrate (14) over at least a partial region of the horizontal plane, preferably substantially over the entire horizontal plane, of the pretreatment tank (2) and / or that this substrate line region (20) extends, with respect to the vertical axis direction, line in a bottom-side or near-bottom region of the pretreatment tank (2).

8. Plant according to claim 7, characterized in that the substrate line region (20) extends meander-like in the near-bottom or bottom-side region of the pretreatment tank (2), or in that the substrate line region (20) has a tree-like structure with a central first line section (21) which extends in the near-bottom or bottom-side region of the pretreatment tank (2) from one side of the tank inner wall in a trunk-like or lance-like manner in the direction of the tank centre, preferably in the direction of the tank centre and beyond, and, as regards the direction of its extension, in the direction of the opposite side of the tank inner wall, with a plurality of spaced-apart second line sections (22) projecting in a branch-like manner on both sides of the first line section (21), whereby it is preferably provided that a plurality of spaced-apart third line sections (23) project in a branch-like manner from the second line sections (22), preferably on both sides of the second line section (22).

9. Plant according to claim 7 or 8, characterized in that at least part of the substrate line region (20), preferably the second and / or third line sections (22, 23) in the case of a substrate line region (20) having a tree-like structure, has an oxidizing agent outlet region (25) via which the oxidizing agent (9) flows into the substrate (14), whereby it is preferably provided that the oxidizing agent outlet region (25) is formed by a plurality of outlet openings spaced apart from one another and / or that the oxidizing agent outlet region (25) has a semi-permeable membrane which is permeable to the oxidizing agent but not to the substrate.

10. Plant according to any one of preceding claims 6 to 9, characterized in that the at least one oxidizing agent line is a gas line (18) which is coupled to a gas source as oxidizing agent source.

11. Plant according to claim 9 and 10, characterized in that the oxidizing agent outlet region (25) is a bubble diffuser which is preferably suitable and designed to generate gas bubbles with a defined size and / or diameter.

12. Plant according to claim 10 or 11 , characterized in that the oxidation device has an air intake device, preferably a blower or a compressor (7), arranged outside the pretreatment tank (2), via which air (9) is drawable in as oxidizing agent from the environment as oxidizing agent source, preferably is drawable in and compressed.

13. Plant according to any one of preceding claims, characterized in that the oxidation device (8), preferably an air intake device of the oxidation device, is controllable by means of the control device (11) in such a way that at least one of the following features is fulfilled:- 20 to 400 cubic meters of oxidizing agent, preferably air as oxidizing agent, are added to the substrate per cubic meter of substrate;- 0.1 to 2.0 cubic meters of oxidizing agent, preferably air, are added to the pretreatment tank per cubic meter of pretreatment tank volume;- the substrate is exposed to oxidizing agent for a period of 1 to 30 minutes per hour, preferably aerated with air as oxidizing agent.

14. Plant according to any one of preceding claims, characterized in that at least one mixing and / or stirring device (26, 30) is provided, by means of which the substrate (14) contained in the at least one pretreatment tank (2) is mixable and / or stirrable in a controlled manner by the at least one control device (11) for a predetermined mixing and / or stirring time, preferably for mixing the substrate (14) with the oxidizing agent (9).

15. Plant according to claim 14, characterized in that the at least one mixing and / or stirring device (26, 30) is controllable by means of the control device (11) in such a way that the substrate (14) is stirred for a predetermined period of time at the same time as or with a time delay to the start of the supply of the oxidizing agent (9), preferably at least until the end of the respective oxidizing agent feed phase, preferably with a power of 0.02 to 0.4 kilowatts per cubic meter of tank volume of the pretreatment tank (2).

16. Plant according to claim 14 or 15, characterized in that at least one mixing and / or stirring device (26) is pivotably articulated to a top wall (17) of the pretreatment tank (2), preferably in the region above the substrate line region (20) and / or is pivotably arranged in different spatial directions, and / or at least one mixing and / or stirring device (30) is height-adjustable in the vertical axis direction and / or is guided above the substrate line region (20) on a vertical guide mast (31) arranged in the pretreatment tank (2) and preferably pivotable about its longitudinal axis, whereby it is preferably provided that the guide mast (31) is mounted with an upper end region in the region of the top wall (17), preferably in a service dome (32), and / or that a service dome (32) detachably covers a top wall opening (33) of the top wall (17) of the pretreatment tank (2), whereby it is preferably provided that the service dome (32) has at least one gas outlet (34) in the case of a gaseous oxidizing agent (9), via which a gaseous oxidizing agent (9) accumulating in the region above the substrate (14) is dischargable from the pretreatment tank (2), preferably with air as the gaseous oxidizing agent (9) being dischargable into the environment.

17. Plant according to any one of preceding claims, characterized in that the input quantity (Q) of substrate is predetermined as a function of the tank volume (V) of the pretreatment tank (2) and the hydraulic retention time (HRT) in the pretreatment tank (2) according to the following equation:Q = V / HRT18. Plant according to claim 17, characterized in that the hydraulic retention time (HRT) in the pretreatment tank is 1 to 20 days and / or that the pretreatment-process is carried out either continuously or as a batch process.

19. Plant according to any one of preceding claims, characterized in that a heating device is arranged in the pretreatment tank, preferably a heating device in the form of heating pipes (37) running at least in sections around the inner wall in the bottom-near area.

20. Plant according to any one of preceding claims, characterized in that a feeding device is provided, by means of which the substrate and / or the organic substance and / or liquid is feedable to the at least one pretreatment tank in a controlled manner by means of the control device (11) and / or in that a discharge device is provided, by means of which the pretreated substrate is dischargable from the at least one pretreatment tank in a controlled manner by means of the control device (11) and is feedable directly or indirectly to the at least one fermenter tank (3).

21. Pretreatment device for use in a plant for producing biogas, in particular in a plant for producing biogas according to any one of the preceding claims, having at least one pretreatment tank (2) in which a substrate (14) is accommodated, the substrate (14) containing at least one organic substance (10) or being formed by at least one organic substance (10) which has at least one fermentation-inhibiting and oxidizable component, with at least one oxidation device (8), which is arranged at least partially in the at least one pretreatment tank (2), with at least one control device (11), by means of which the at least one oxidation device (8) is controllable in such a way that a predetermined quantity of a gaseous or liquid oxidizing agent (9) is supplyable to the substrate (14) at predetermined times in such a way that at least some of the at least one oxidizable component is oxidized by means of the oxidizing agent (9) and a pretreated substrate is present in the pretreatment tank (2).

22. Method for operating a plant for producing biogas, especially a plant for producing biogas according to any one of preceding claims 1 to 20,having at least one pretreatment tank (2) in which a substrate (14) is accommodated, the substrate (14) containing at least one organic substance (10) or being formed by at least one organic substance (10) which has at least one fermentation-inhibiting and oxidizable component, with at least one oxidation device (8), which is arranged at least partially in the at least one pretreatment tank (2), having at least one control device (11), by means of which the at least one oxidation device (8) is controlled in such a way that a predetermined quantity of a gaseous or liquid oxidizing agent (9) is supplied to the substrate (14) at predetermined times in such a way that at least some of the at least one oxidizable component is oxidized by means of the oxidizing agent (9) and a pretreated substrate is present in the pretreatment tank (2), with at least one fermenter tank (3) in which at least a portion of the pretreated substrate is fermented.

23. Method according to claim 22, characterized in that the oxidation device (8), preferably an air intake device of the oxidation device, is controlled by means of the control device (11) in such a way that at least one of the following features is fulfilled:- 20 to 400 cubic meters of oxidizing agent, preferably air as oxidizing agent, are added to the substrate per cubic meter of substrate;- 0.1 to 2.0 cubic meters of oxidizing agent, preferably air, are added to the pretreatment tank per cubic meter of pretreatment tank volume;- the substrate is exposed to oxidizing agent for a period of 1 to 30 minutes per hour, preferably aerated with air as oxidizing agent.

24. Method according to claim 22 or 23, characterized in that at least one mixing and / or stirring device (26, 30) is provided, by means of which the liquid phase (14) contained in the at least one pretreatment tank (2) is mixed and / or stirred in a controlled manner by the at least one control device (11) for a predetermined mixing and / or stirring time, preferably for mixing the substrate (14) with the oxidizing agent (9).

25. Method according to claim 24, characterized in that the at least one mixing and / or stirring device (26, 30) is controlled by means of the control device (11) in such a waythat the substrate (14) is stirred for a predetermined period of time at the same time as or with a time delay to the start of the supply of the oxidizing agent (9), preferably at least until the end of the respective oxidizing agent feed phase, preferably with a power of 0.02 to 0.4 kilowatts per cubic meter of useful tank volume of the pretreatment tank (2).

26. Method according to any one of claims 22 to 25, characterized in that the input quantity (Q) of substrate is predetermined as a function of the tank volume (V) of the pretreatment tank (2) and the hydraulic retention time (HRT) in the pretreatment tank (2) according to the following equation:Q = V / HRT27. Plant according to claim 26, characterized in that characterized in that the hydraulic retention time (HRT) in the pretreatment tank is 1 to 20 days and / or that the pretreatment-process is carried out either continuously or as a batch process.

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