METHOD AND DEVICE FOR RECYCLING ORGANIC MATERIALS

Description

[0001] The present invention relates to a process and an integrated system for producing hydrogen and methane from organic waste and biomass.

[0002] The separate production of hydrogen and methane from organic waste is a way to generate energy without burning fossil carbon and releasing it into the atmosphere as CO2. Microorganisms are capable of producing hydrogen and methane either through photosynthesis or, more specifically, through fermentation. In biogas production, organic matter is converted to methane anaerobically in two stages: hydrolysis and methanogenesis. Hydrolysis produces hydrogen, which in turn is used as an electron donor by many methane-producing microorganisms (methanogens) in the second stage of the process. Separating the two stages is possible to collect hydrogen from the first stage. The second stage then serves to further treat the remaining acidification products. Hydrogen and methane can be utilized separately.

[0003] DE 10 2009 011 868 A1 describes a biogas plant for the methanation of biomass with a high solids content. It comprises a digestion tank system (also called fermentation tank or fermenter) with a plurality of gas- and liquid-tight sealable digesters. The system includes a percolate storage tank, a first and a second percolate tank. More than two separate percolate circuits can also be provided. The plant has a heterogeneous design, meaning the digesters are designed for different percolates.

[0004] The publication DE 10 2010 048 549 A1 sets out to create a cost-effective, lightweight, low-energy biogas plant. One advantage of the plant is that malfunctions do not result in a complete shutdown. Furthermore, the plant can be flexibly adapted to the amount of biosubstrate required and features extremely small transport units.

[0005] The biogas plant operates according to the principle of dry fermentation. The hydrolysis stage and the methane production stage are not separated. Furthermore, the plant requires high gas pressures to operate, necessitating particularly stable containers.

[0006] The publication DE 10 2014 011 479 A1 concerns a process for the anaerobic fermentation of biomass and its implementation in a plant with the goal of parameter-controlled production of a liquid phase. The process is strictly anaerobic and operates batchwise. Technically, the process is implemented in a modular container-based plant. The feedstocks are delivered using special transport containers and loaded into modular garages along with the containers. Only hydrolysis and acidogenesis processes take place. Therefore, no methane is produced, but biogas is nevertheless produced. This is converted in a container reactor for hydrogenotrophic methanogenesis, e.g., in external bioreactors. However, these are explicitly not part of the proposed technical solution.

[0007] DE 10 2014 113 413 B3 proposes a method for controlling a biogas plant, wherein the biogas plant comprises a feed device for supplying a substrate to a fermenter and a gas utilization device. Operation of the biogas plant using the control system is intended to be particularly low-maintenance. A modular biogas plant is not disclosed here.

[0008] German patent application DE 10 2008 015 609 A1 discloses a biogas plant and a method for producing biogas, in particular methane gas, in a multi-stage process with a spatially separated hydrolysis process and a methane formation process. The biogas plant has at least two hydrolysis tanks and a fermenter for a methane formation process. This biogas plant is not modular, mobile, or particularly compact. Furthermore, this biogas plant does not provide for remote maintenance or remote control. Relocation to another location or reconfiguration on site is not planned.

[0009] The German utility model DE 20 2005 012 340 U1 shows a biogas plant with at least one fermenter and modules that accommodate the plant's technical components, in particular the control and regulation technology, the pumping technology, and at least one combined heat and power plant. The biogas plant can be constructed flexibly in a modular manner, as the individual modules are housed in prefabricated garages. The modules are highly airtight, offer improved sound insulation, reduce vibration problems, and are more cost-effective.

[0010] US Pat. No. 5,656,491 shows a mobile modular facility mounted on a tractor trailer or railcar for the development and production of biotechnological products on a pilot scale. The facility consists of at least two interconnectable mobile modules. The modules can be converted into actual production modules and auxiliary modules. The facility offers a high degree of flexibility, allowing the user to equip themselves with the type and number of modules required to meet their needs.

[0011] US Pat. No. 10,633,622 B2 discloses a method and an integrated system for preventing contamination of microbial hydrogen-producing cultures with methane-producing cultures during hydrogen and methane production in a fully mixed bioreactor. A gravity settler is installed downstream of a hydrogen reactor.

[0012] WO 2008 / 034153 A1 relates to a biogas plant with a fermenter having a first and at least one second fermentation chamber for fermenting the fermentation medium, as well as a riser pipe between the two chambers. Furthermore, the invention relates to a method for mixing fermentation medium in a fermenter. The document describes a single-stage process and a plant without modularity.

[0013] The state of the art, therefore, is to produce hydrogen and methane in separate stages of a biogas plant. The generic prior art is disclosed in DE 10 2018 121 050 A1 and describes a modular plant with a number of tanks that can be used for hydrolysis or fermentation and are interconnected by pipelines, allowing, for example, the inventory to be pumped from a hydrolysis tank to a fermentation tank. The produced biogas is stored in the form of methane in a gas storage facility until consumption.

[0014] WO 2020 / 044150 discloses a modular biogas plant comprising a plurality of tanks for storing biomass. The plurality of tanks are fluidly interconnected.

[0015] A disadvantage of the current technology is that the biomass must be processed in batches, and the hydrolysate from hydrogen production is transferred directly to a fermentation process for methane production on-site. Any unused methane must then be stored in a gas storage facility until it is needed. Such storage facilities are large and inflexible. Transporting the methane to other consumption points is complex and expensive.

[0016] The object of the present invention is therefore to create a modular, scalable biogas plant and a method for biogas production in which hydrogen production and methane production can be decoupled in time and space. In particular, storage and transport in the form of an energy-containing medium are to be enabled, which can be carried out more simply and flexibly than methane storage. This object is achieved by a modular biogas plant having the features of claim 1 and by a method having the features of claim 10.

[0017] Features of preferred embodiments are set out individually or in combination in the dependent claims.

[0018] Because in a modular biogas plant with a number of tanks for receiving biomass, which is transported through the biogas plant in a mass flow, wherein the tanks comprise at least two hydrolysis tanks in which the biomass is converted into a hydrolysate with a pH value of less than 7, and the hydrolysis tanks each have an inlet and an outlet, and the mass flow is transported from the inlet to the outlet and remains in the hydrolysis tanks for a treatment period, it is provided that the outlet of each hydrolysis tank is hydraulically connected to at least one liquid reservoir, into which the produced hydrolysate can be introduced after conversion and stored, the hydrolysate can remain there until it is needed for methane production. In this way, large amounts of energy contained in the hydrolysate in the form of chemical energy can be stored easily and safely.

[0019] If, in addition, a sanitization device is provided upstream of the inlet, in which the biomass is thermally pretreated at a temperature between 70°C and 120°C prior to the inlet, a defined biological environment for hydrolysis can be created. Preferably, a dispenser for hydrolyzing bacteria is assigned to the inlet and / or each hydrolysis tank, from which appropriate suspended bacteria can be released into the biomass. It is particularly advantageous if the dispenser contains a suspension for metered release containing hydrolyzing bacteria of the strains Clostridium acetobutyricum, Bacillus thuringiensis, and / or Clostridium butyricum.

[0020] It can also be provided that a dispenser for pH regulators is assigned to the inlet and / or each hydrolysis tank. This allows the biological process to be optimally adjusted and / or specifically influenced. It is advantageous if the pH regulators are one or more reagents from the group consisting of soda, sodium bicarbonate, sodium hydroxide, calcium hydroxide, magnesium hydroxide, nitric acid, and hydrochloric acid. These reagents are effective and inexpensive to use at this stage of biogas production.

[0021] The modular biogas plant preferably comprises one or more

[0022] Fermentation tanks are located downstream of the at least one liquid storage tank and are hydraulically connected to it. In these fermentation tanks, the temporarily stored hydrolysate can then be used specifically for methane production when needed, for example, for heating or power generation in a combined heat and power plant or the like. Particular advantages arise when the hydrolysis tanks and the fermentation tanks are essentially identical in construction. "Essentially" means that they differ only in other peripheral components, e.g., in terms of measurement and control technology, but are otherwise identical in construction. A hydrolysis tank and a fermentation tank can also be arranged in each standard transport container. A connection to an externally arranged liquid storage tank then enables the aforementioned decoupling of hydrolysis and methane production.

[0023] Because a process for producing biogas from biomass, which is transported in a mass flow through the biogas plant, involves the following process steps: a) collecting biomass in the form of plant residues, food waste or other organic waste or raw materials, b) hydrolyzing the biomass during a residence time in a number of hydrolysis tanks connected in parallel in the mass flow, whereby the biomass is converted into a hydrolysate with a pH value of less than 7, c) collecting the gas formed in step b) and separating the resulting hydrogen from other gases, in particular from CO2, d) transferring liquid hydrolysate formed in step c) from each of the hydrolysis tanks into a common liquid storage tank located downstream of the hydrolysis tanks, e) delivering the hydrolysate to one or more fermenters for the extraction of methane from the hydrolysate, in particular with the addition of methane-producing bacterial cultures, the advantages described above in connection with the proposed modular biogas plant can also be achieved.

[0024] Here, too, it is advantageous if, prior to step a), the biomass is thermally pretreated in a sanitizing device at a temperature between 70°C and 120°C. Furthermore, for operation under controlled biological conditions, it is advantageous if hydrolyzing bacteria, in particular Clostridium acetobutyricum, Bacillus thuringiensis, and / or Clostridium butyricum, are added to the biomass at the beginning of step b).

[0025] Biological activity is stopped when the biomass is sanitized at the end of hydrolysis and before being released into the liquid storage tank. This can occur through temperature exposure, but also when the bacteria in question have consumed all their nutrients and then die or become inactive.

[0026] Advantageously, the hydrolysate in step e) can also be transported by tank transport to a methane-producing facility located remotely from the hydrolyzer. The hydrolysate, which contains, for example, carboxylic acids and alcohols in liquid form, can thus be sold as an energy source.

[0027] The hydrogen obtained from the hydrolysis in step c) can advantageously be used at the site where the process is carried out, for example by means of a fuel cell, to generate electricity, and the electricity generated can thus be used to operate the plant.

[0028] An advantage can also arise if the biomass is transported by motor vehicle for hydrolysis, and the sanitization provided for in step a) is carried out at least partially during transport using the waste heat from the vehicle's combustion engine. This minimizes the energy required for sanitization. Sanitization is important, for example, in the collection of food waste from restaurants or food production, but also in the collection of animal excrement.

[0029] Two preferred embodiments of the invention are described below with reference to the drawings. They show: FIG. 1 is a block diagram showing a process flow using an apparatus according to the present invention; and FIG. 2 shows a different procedure that differs from the one in Fig. 1shown in that different biomass and different methane utilization are planned.

[0030] In general, the embodiments described here are directed to an integrated system for hydrogen and methane production from organic waste and biomass. When referring to a mass flow, this does not refer to a continuous flow, but rather to a batch-based, discontinuous operation in which the biomass is conveyed, pumped, or otherwise transported from one station to the next.

[0031] The term "fully mixed bioreactor" refers to a mechanically or hydraulically mixed vessel containing microorganisms in suspension and a growth medium typically consisting of nutrients such as organic carbon, nitrogenous compounds, phosphorus-containing compounds, and mineral trace solutions.

[0032] The term "fermentation tank" refers to all common designs used for the anaerobic conversion of organic waste into methane and carbon dioxide. Fermentation tanks include, among others, single-stage continuously stirred tank reactors.

[0033] The term "hydrogen-producing microorganisms" refers to microorganisms capable of fermenting organic matter under anaerobic conditions to produce hydrogen, carbon dioxide, and a variety of organic acids and alcohols.

[0034] The term "organic waste" refers to wastes containing carbon and hydrogen, such as, but not limited to, alcohols, ketones, aldehydes, volatile fatty acids, esters, carboxylic acids, ethers, carbohydrates, proteins, lipids, polysaccharides, monosaccharides, cellulose, and nucleic acids.

[0035] In Fig. 1A process sequence is shown schematically in which, in a harvesting process 1, biomass is first obtained which is biologically in a state that allows direct hydrolysis. The biomass is therefore not contaminated with a bacterial environment that would impair the biological processes in hydrolysis. Examples of this are green waste, such as that which accrues at municipal green waste collection points, lawn clippings, or agricultural products that are not suitable for human or animal consumption. These materials are therefore collected in the harvesting process 1 and, if necessary, mechanically processed, shredded, cleaned, and their water content adjusted. These materials are then fed as biomass into a number i of hydrolysis tanks 1,1 to 1,i. The biomass has preferably been adjusted beforehand so that it is pumpable.It can then be pumped from a storage tank or a collection tank into the hydrolysis tanks.

[0036] These hydrolysis tanks themselves are designed as identical modules. They comprise an inlet and an outlet for the biomass and the inventory remaining after hydrolysis, as well as a gas connection through which the gas produced during hydrolysis can be removed and collected. This gas essentially contains hydrogen and carbon dioxide. The hydrolysis tanks are preferably designed as plastic containers and have a volume in the range of approximately 1 m³ to 3 m³. Larger hydrolysis tanks are also conceivable. The geometric shape of the hydrolysis tanks should be chosen so that they fit into one half of a commercial 20-foot transport container.

[0037] Each hydrolysis tank is assigned sensors and / or actuators for the process measurement and control technology. These sensors can include temperature sensors, pH sensors, level sensors, and pressure sensors. The actuators are preferably a device for mixing the inventory, in particular an agitator, and optionally a heating device for setting a desired temperature of the inventory, especially at the beginning of the biological process.

[0038] In addition, each hydrolysis tank is equipped with dosing devices that allow for the targeted addition of suspensions of specific bacterial strains that are particularly suitable for hydrolysis. It is also advantageous to have a separate dosing device containing substances for regulating the pH in the hydrolysis tank, which can be added to the inventory if necessary. Suitable bacterial strains and pH regulators are listed in the introduction to the description.

[0039] Under these conditions, the inventory transferred to hydrolysis tanks 1.1 to 1.i can be biologically converted. Long-chain hydrocarbons (fats) in particular are broken down, forming carboxylic acids such as acetic acid and propionic acid, as well as alcohols. This breakdown produces carbon dioxide and hydrogen. These two gases can be separated relatively easily due to their different densities, allowing the hydrogen to be captured and used, for example, as an energy source to operate the biogas plant.

[0040] Once the biological process is complete, i.e., the conversion into carboxylic acids and alcohols is almost complete and / or gas production has ceased, the processed biomass is transferred to a storage facility 1. There, the biomass exists as an acidic liquid containing a significant proportion of hydrocarbons and thus a relatively high chemical energy content. The liquid can be easily stored long-term and does not need to be processed immediately. It can also be traded, sold, and transported based on its energy content if on-site utilization is not necessary or not possible.

[0041] In the procedure according to Figure 1However, further processing is planned on-site. For this purpose, whenever there is a need for methane, the contents of storage tank 1 can be transferred to fermentation tanks labeled "Methane 1.1 to 1.i." In these fermentation tanks, the biomass coming from the storage tank will undergo biological fermentation, converting the hydrocarbons contained therein largely into water, dissolved minerals, methane, and carbon dioxide. This process is familiar from biogas production and need not be explained in detail here. The bacterial strains to be added, if necessary, and any advantageous temperature control are also known.

[0042] However, in the known processes, methane production continues until methane formation has essentially come to a standstill. The resulting liquid biomass residues are almost inorganic and have a high nitrate content. These residues are often used in agriculture to fertilize fields. This practice is problematic in several respects. Firstly, fertilization is often not based on the needs of the cultivated plants, but rather the residue is applied in excess, meaning that unused residues cannot be bound in the soil but instead enter the groundwater or surface waters. This significantly impairs water quality. Secondly, these nitrate-containing, inorganic residues have a high oxygen content, which negatively affects the pH value of the soil when applied.

[0043] In the process described here, the fermentation in the individual fermentation tanks is therefore preferably monitored for methane production and terminated when the maximum methane production per unit of time is reached or shortly thereafter. The residue then found in the fermentation tanks still contains a significant organic content, particularly fibers and solids. This residue can be converted from the anaerobic state to an aerobic state by aeration and then subjected to aerobic decomposition. In this aerobic decomposition, the anaerobic and potentially pathogenic bacteria from the fermentation are inactivated. Aerobic bacteria and fungi further decompose the organic residues, forming a sanitized, dry substrate with a high fiber content.This substrate can then be used very advantageously for soil improvement, for example, in areas where the soils are characterized by a high sand content and low water absorption capacity. When incorporated into these soils, the substrate can improve water absorption capacity and thus make these soils more suitable for agricultural use, resulting in higher yields. An economic advantage is that the substrate produced in this way can also be marketed locally in smaller quantities, as it can be used in gardens, for example, instead of peat derived from drained moorland, which is extremely harmful from an environmental perspective.

[0044] The methane produced in the "Methan 1.1" and "Methan 1.i" fermentation tanks is captured and used, for example, in a combined heat and power plant to generate electricity and heat. It can also be compressed and used to fuel vehicles with combustion engines configured for natural gas operation.

[0045] The fermentation tanks are preferably essentially identical in design to the hydrolysis tanks mentioned above. In particular, the biogas plant can be designed so that one hydrolysis tank and one fermentation tank can each be accommodated in a standard transport container or a frame with the approximate dimensions of such a container. This transport container then also contains the control and regulation devices directly required for the operation of the two tanks, so that each transport container in itself represents a standalone biogas plant. The modularity results from the fact that several transport containers 1-i can be provided in parallel and can process the incoming biomass stream in batches in parallel.This design has the advantage that excessive effort is not required to ensure the reliability of individual modules, since the occasional failure of one module does not lead to the failure of the entire biogas plant. Accordingly, simpler components can also be chosen for the control and regulation of the modules, since their reliability does not have to meet the requirements required for a large, commercial, non-modular biogas plant.

[0046] If a hydrolysis tank and a fermentation tank are located in the same container, a siphon can be provided between these two elements to transfer the inventory after hydrolysis and before fermentation to storage 1. The inventory can then remain there until needed for methane production. In this case, the inventory can then be transferred from external storage 1 to fermentation tanks 1 to 1. This process can be carried out simply by pumping.

[0047] The Figure 2shows a different process sequence in which the harvesting / collection process k is first carried out with other biological materials. Here, for example, waste from food production, animal husbandry and / or the catering industry is collected. This waste may not be in a biological state that would allow immediate hydrolysis, as the substances have a bacterial environment that can interfere with hydrolysis. Therefore, in the process sequence downstream of the harvesting and collection process k, a sanitation k is provided, in which the microorganisms contained in the collected biomass are largely inactivated or killed. This sanitation can, for example, already take place during transport from the collection point to the biogas plant. This is described in more detail above in the introduction to the description. The sanitation is preferably carried out thermally at temperatures between 70 °C and 120 °C.

[0048] The hygienized raw materials are then processed in the same way as described above. Figure 1 The biomass is thus mechanically prepared and adjusted with regard to water content and then transferred to the various hydrolysis tanks. There, the hydrolysis is carried out and the resulting gas is collected and utilized. The liquid resulting from the hydrolysis, which also contains, among other ingredients, mainly carboxylic acids and alcohols, is stored until it can be utilized through fermentation. In this embodiment, it is provided that methane production is an alternative to the Figure 1The utilization described in individual fermentation tanks can also be carried out in another modular or non-modular biogas plant. For this purpose, the hydrolysate can be traded and transported in liquid form as an energy source, as described above, or utilized on-site through fermentation.

[0049] The device preferably also comprises temperature controllers for controlling the temperature, wherein a typical temperature range in which the temperature of the contents of both the hydrolysis and the fermentation is maintained is between about 20°C and about 60°C.

[0050] In summary, the method and apparatus disclosed here for hydrogen and methane production from organic waste and biomass is very advantageous for several reasons.

[0051] The effluent from the hydrolysis tanks is loaded with short-chain carboxylic acids, which are formed by the microbiological degradation of the incoming waste components by hydrogen-producing bacteria. This substrate can be stored and transported if necessary, and it also enables particularly high efficiency in subsequent fermentation and methane recovery by increasing the volumetric methane production rate, methane yield, and solids destruction efficiency, thus enabling higher volumetric and organic loading rates.

Claims

1. Modular biogas plant having a number of tanks for receiving biomass which is conveyed in a mass flow through the biogas plant, wherein the tanks comprise at least two hydrolysis tanks, in which the biomass is converted to a hydrolysate having a pH value of less than 7, and the hydrolysis tanks each have an inlet and an outlet and the mass flow is conveyed from the inlet to the outlet and remains in the hydrolysis tanks for a treatment period, characterized in that the outlet of each hydrolysis tank is hydraulically connected to at least one liquid storage tank into which the hydrolysate produced can be introduced after the conversion and can be stored therein.

2. Modular biogas plant according to claim 1, characterized in that a hygienization device is provided upstream of the inlet, in which the biomass is thermally pretreated at a temperature between 70°C and 120°C upstream the inlet.

3. Modular biogas plant according to claim 1 or 2, characterized in that a dispenser for hydrolysing bacteria is assigned to the inlet and / or each hydrolysis tank.

4. Modular biogas plant according to claim 3, characterized in that a suspension for metered delivery is provided in the dispenser, the suspension containing hydrolysing bacteria of the strains Clostridium acetobutyricum, Bacillus thuringiensis and / or Clostridium butyricum.

5. Modular biogas plant according to one of the preceding claims, characterized in that a dispenser for pH regulators is assigned to the inlet and / or each hydrolysis tank.

6. Modular biogas plant according to claim 5, characterized in that the pH regulators are one or more reagents from the group soda, sodium bicarbonate, sodium hydroxide, calcium hydroxide, magnesium hydroxide, nitric acid and hydrochloric acid.

7. Modular biogas plant according to one of the preceding claims, characterized in that the tanks comprise one or more fermentation tanks which are arranged downstream of the at least one liquid storage tank and which are hydraulically connected thereto.

8. Modular biogas plant according to claim 7, characterized in that the hydrolysis tanks and the fermentation tanks are essentially identical in construction.

9. Modular biogas plant according to claim 8, characterized in that a hydrolysis tank and a fermentation tank are each arranged in a standard transport container.

10. Method for the production of biogas from biomass which is conveyed in a mass flow through the biogas plant, characterized by the following method steps: a) Collecting biomass in the form of plant residues, food waste or other organic waste or raw materials, b) Hydrolyzing the biomass during a residence time in a number of hydrolysis tanks connected in parallel in the mass flow, whereby the biomass is converted to a hydrolysate with a pH value of less than 7, c) Collecting the gas formed in step b) and separating the resulting hydrogen from other gases, in particular CO2, d) Transferring liquid hydrolysate formed in step c) from each of the hydrolysis tanks to a common liquid storage tank located downstream of the hydrolysis tanks, e) Delivery of the hydrolysate to one or more fermenters for the recovery of methane from the hydrolysate, in particular with the addition of methane-producing bacterial cultures.

11. Method according to claim 10, characterized in that, prior to step a), the biomass is thermally pretreated in a hygienizing device at a temperature of between 70°C and 120°C.

12. Method according to claim 10 or 11, characterized in that hydrolysing bacteria, in particular Clostridium acetobutyricum, Bacillus thuringiensis and / or Clostridium butyricum, are added to the biomass at the beginning of step b).

13. Method according to any of the preceding claims 10 to 12, characterized in that the biomass is hygienized at the end of the hydrolysis and before being delivered to the liquid storage.

14. Method according to any one of the preceding claims 10 to 13, characterized in that the hydrolysate is transported in step e) by means of tank transport to a methane-producing device arranged remotely from the hydrolyzer.

15. Method according to one of the preceding claims 10 to 14, characterized in that the hydrogen obtained in step c) is used to generate electricity at the site where the method is carried out, for example by means of a fuel cell, and in that the electricity generated is used to operate the plant.

16. Method according to one of the preceding claims 11 to 15, characterized in that the biomass is transported by a motor vehicle for hydrolysis and in that the hygienization provided before step a) is carried out using the waste heat of an internal combustion engine of the motor vehicle at least partially during the transport.