DE102007056916B4 - Plant and process for the production of biogas - Google Patents

Abstract

Plant for producing biogas by fermentation, comprising: - at least one fermentation reactor (18), in which fermentable substances are fermented by bacteria to form biogas, - a first thickening device (20), the first thickening device (20) being a disc filter or a rotating one Gravity thickener, - a second thickening device (22), the second thickening device being a screw press or a belt press, and - a flotation device (26), the flotation device (26) having a pressure release flotation reactor (52) having a pressure release flotation device which has at least one feed line ( 66) for compressed air, wherein i) the fermentation reactor (18) comprises a supply line (36) for supplying a suspension containing fermentable substances, a gas discharge line (38) for biogas and a discharge line (40) for fermented suspension, the discharge line ( 40) for fermented suspension is connected to the first thickening device (20), which has a first discharge line (44) for a first filtrate and a second discharge line (42) for thickened suspension, the second discharge line (42) for thickened suspension of the first Thickening device (20) is connected to the second thickening device (22), which has a first discharge line (48) for a second filtrate and a second discharge line (46) for thickened suspension, and wherein the first discharge line (44) for the first filtrate first thickening device (20) is connected to the flotation device (26), or ii) the fermentation reactor (18) has a supply line (36) for supplying a solution containing fermentable substances, a gas discharge line for biogas (38) and a discharge line (40) for fermented Mixture comprises, the discharge line (40) for the fermented mixture being connected to the flotation device (26) which has a first discharge line (74) for suspension and a second discharge line (30) for a first filtrate, the ...

Description

The present invention relates to a plant and a process for the production of biogas by fermentation.

Due to the shortage and increase in the price of fossil fuels, regenerative energy production is becoming increasingly important. A known method for regenerative energy production is the production of biogas from fermentable, biomass-containing starting materials, such as residues, such as sewage sludge, biowaste or food waste, from manure, such as manure and manure, or from plants, such as corn and the like. In these processes, biogas is produced by anaerobic fermentation of the organic starting materials, ie a mixture of the main components methane and carbon dioxide. In addition to methane and carbon dioxide, biogas may also contain other gases, such as hydrogen, ammonia and nitrogen, with the energetic part being methane.

In the known processes for the production of biogas, the fermentable starting material is first mixed with water to form a suspension, before this suspension is fermented under anaerobic conditions in a fermentation reactor to form biogas. To carry out this process as economically as possible, this is often carried out continuously, with a portion of the water used is recycled as process water. In such a method, after the removal of the fermented mixture from the fermentation reactor, part of the water contained in the discharged mixture is separated from the suspension, purified and reused to suspend the starting materials. However, in the known plants for the production of biogas, the degree of purification achieved for the process water is often insufficient, so that only a comparatively small proportion of the process water can be circulated and consequently considerable amounts of fresh water are necessary. Other methods which achieve sufficient purification of the process water so that a comparatively large portion of the process water can be recirculated use cleaning devices which require both high investment costs and high operating costs, and / or can only be operated at a comparatively low throughput ,

A corresponding system and a corresponding method for the production of biogas is for example from DE 10 2005 050 927 A1 In this process, fermentable starting material, namely bakery waste monosubstrate, is mixed with water in a suspending unit to form a suspension, the suspension thus produced is subsequently hydrolyzed in a hydrolysis vessel and finally fermented in a main reactor and in a downstream post-fermentation reactor. While the biogas produced in the fermentation reactors is withdrawn via gas discharge lines and then cleaned, a portion of the water contained in the suspension is separated from the suspension of the fermented suspension by ultrafiltration, reverse osmosis and vacuum distillation, purified and returned as process water in the suspension unit. However, reverse osmosis and vacuum distillation, based on the throughput, time-consuming and particularly costly process steps, which lead to a low cost of the process. Moreover, this method can only be carried out with a comparatively low throughput.

From the DE 601 04 401 T2 For example, there is known a solid waste treatment method in which waste is diluted with water into a slurry, this slurry is screened, iron particles from the sieved slurry are separated with a magnet, and the slurry is finally dewatered, with the water after the dewatering step is recycled.

In the DD 130 339 A1 A process for the anaerobic biological treatment of manure is described in which a part of rotting medium is taken from a digester, after which a solid-liquid separation is carried out and the liquid phase is subjected to a treatment for the removal of dissolved volatile nitrogen and sulfur compounds and then returning the purified liquid phase and a portion of the solid phase back to the digester.

The object of the present invention is therefore to provide a cost-effective plant for the continuous production of biogas by means of fermentation, in which the process water, especially if the plant is operated at a high throughput, is cleaned efficiently, so that a large proportion of the process water in the Circulation can be performed without impurities accumulate in the process water, and only small amounts of fresh water must be supplied so that the system can be operated efficiently and economically. Another object of the present invention is to provide a continuous process for the production of biogas by means of fermentation, which can be carried out efficiently and economically with a high throughput and with low operating costs.

• – wenigstens einen Fermentationsreaktor, in dem fermentierbare Substanzen durch Bakterien unter Bildung von Biogas fermentiert werden,
• – eine erste Eindickvorrichtung, wobei die erste Eindickvorrichtung ein Scheibenfilter oder ein rotierender Schwerkrafteindicker ist,
• – eine zweite Eindickvorrichtung, wobei die zweite Eindickvorrichtung eine Schneckenpresse oder eine Siebbandpresse ist, sowie
• – eine Flotationseinrichtung, wobei die Flotationseinrichtung eine einen Druckentspannungsflotationsreaktor aufweisende Druckentspannungsflotationseinrichtung, welche wenigstens eine Zufuhrleitung für Druckluft aufweist, ist,

wobei

• i) der Fermentationsreaktor eine Zufuhrleitung zur Zuführung einer fermentierbare Substanzen enthaltenden Suspension, eine Gasabfuhrleitung für Biogas und eine Abfuhrleitung für fermentierte Suspension umfasst, wobei die Abfuhrleitung für fermentierte Suspension mit der ersten Eindickvorrichtung verbunden ist, welche eine erste Abfuhrleitung für ein erstes Filtrat und eine zweite Abfuhrleitung für eingedickte Suspension aufweist, wobei die zweite Abfuhrleitung für eingedickte Suspension der ersten Eindickvorrichtung mit der zweiten Eindickvorrichtung verbunden ist, welche eine erste Abfuhrleitung für ein zweites Filtrat und eine zweite Abfuhrleitung für eingedickte Suspension aufweist, und wobei die erste Abfuhrleitung für das erste Filtrat der ersten Eindickvorrichtung mit der Flotationseinrichtung verbunden ist,

oder

• ii) der Fermentationsreaktor eine Zufuhrleitung zur Zuführung einer fermentierbare Substanzen enthaltenden Lösung, eine Gasabfuhrleitung für Biogas und eine Abfuhrleitung für fermentierte Mischung umfasst, wobei die Abfuhrleitung für die fermentierte Mischung mit der Flotationseinrichtung verbunden ist, welche eine erste Abfuhrleitung für Suspension und eine zweite Abfuhrleitung für ein erstes Filtrat aufweist, wobei die erste Abfuhrleitung für Suspension mit der ersten Eindickvorrichtung verbunden ist, welche eine erste Abfuhrleitung für ein zweites Filtrat und eine zweite Abfuhrleitung für eingedickte Suspension aufweist, wobei die zweite Abfuhrleitung für eingedickte Suspension der ersten Eindickvorrichtung mit der zweiten Eindickvorrichtung verbunden ist, welche eine erste Abfuhrleitung für ein drittes Filtrat und eine zweite Abfuhrleitung für eingedickte Suspension aufweist, wobei die erste Abfuhrleitung für das zweite Filtrat von der ersten Eindickvorrichtung in die Abfuhrleitung für die fermentierte Mischung des Fermentationsreaktors führt und die erste Abfuhrleitung für das dritte Filtrat der zweiten Eindickvorrichtung in die Abfuhrleitung für die fermentierte Mischung des Fermentationsreaktors führt.

According to the invention this object is achieved by a system according to the patent claim 1 and in particular by a plant for the production of biogas by fermentation comprising:

• At least one fermentation reactor in which fermentable substances are fermented by bacteria to form biogas,
• A first thickening device, wherein the first thickening device is a disc filter or a rotating gravity thickener,
• - A second thickening device, wherein the second thickening device is a screw press or a belt press, and
• A flotation device, wherein the flotation device is a pressure-release flotation device having a pressure-release flotation reactor and having at least one compressed air supply line,

in which

• i) the fermentation reactor comprises a feed line for feeding a fermentable substance-containing suspension, a gas discharge line for biogas and a discharge line for fermented suspension, wherein the discharge line for fermented suspension is connected to the first thickening device, which comprises a first discharge line for a first filtrate and a second Having discharge line for thickened suspension, wherein the second discharge line for thickened suspension of the first thickening device with the second thickening device is connected, which has a first discharge line for a second filtrate and a second discharge line for thickened suspension, and wherein the first discharge line for the first filtrate first thickening device is connected to the flotation device,

or

• ii) the fermentation reactor comprises a feed line for supplying a fermentable substance-containing solution, a gas discharge line for biogas and a discharge line for fermented mixture, wherein the discharge line for the fermented mixture is connected to the flotation device, which comprises a first discharge line for suspension and a second discharge line for a first filtrate, wherein the first discharge line for suspension is connected to the first thickening device having a first discharge line for a second filtrate and a second discharge line for thickened suspension, wherein the second thickened suspension discharge line of the first thickening device is connected to the second thickening device which has a first discharge line for a third filtrate and a second discharge line for thickened suspension, wherein the first discharge line for the second filtrate from the first thickening device into the The discharge line for the fermented mixture of the fermentation reactor leads and leads the first discharge line for the third filtrate of the second thickening device in the discharge line for the fermented mixture of the fermentation reactor.

By the plant next to the at least one fermentation reactor comprises a cleaning device for process water, which has two thickening devices and a flotation, the run in the plant process water can be efficiently cleaned, so that the process water can be completely or at least almost completely recycled , without contaminants accumulating in the process water due to the circulation. In particular, a required degree of purity of the process water with a controlled particle size of solids possibly containing can be ensured so reliably. This allows a minimization of the fresh water requirement of the system. In particular, owing to the flotation device which softens the process water, accumulation of lime in the process water can be reliably prevented. Furthermore, the plant according to the invention can be operated at a high throughput due to the high cleaning efficiency. In addition, the investment costs for the plant, based on the throughput, low, because it is in the individual components used to clean the process water, namely the two thickeners and the flotation, are relatively inexpensive parts of the system. A further advantage of the present invention is that the devices required for the purification of the process water, in particular the two thickening devices, require only little space.

For the purposes of the present invention, a thickening device is understood to be a device which separates from mixtures, such as suspensions, of water so that water or filtrate and a thickened suspension, ie. H. a suspension with a compared to the solids content of the suspension before thickening increased solids content results. In this respect, thickening in the sense of the present invention refers to a dehydration of a mixture, in particular a suspension.

In the system according to the invention a particularly effective thickening with low space requirement and low investment costs for the device, which nevertheless has a high thickening capacity, achieved by a rotating disc thickener or a rotating gravity thickener is used as a first thickening device. A preferred example of a disc thickener is a disc filter, whereas a prefessure is a preferred example of a gravity thickener. An advantage of using a disk filter is that this can be adjusted by adjusting the internal volume of liquid and by adjusting the revolutions of the rotating disks per unit time to any different feed rates of the suspension.

For the aforementioned reasons, it is provided according to the invention that the second thickening device is a screw press or a wire belt press.

According to a particularly preferred embodiment of the present invention, the first thickening device is a disc filter and the second thickening device is a screw press. The combination of a disc filter and a screw press saves space and allows efficient and high thickening of a suspension, for example up to a solids content of at least 35%.

In addition, with the system according to the invention a particularly good and effective removal of impurities in the process water, in particular at a high throughput, achieved because the flotation is provided as a Druckentspannungsflotationsreaktor having Druckentspannungsflotationseinrichtung.

The pressure-release flotation device preferably has at least one feed line for a pH-adjusting agent, such as a base, for example sodium hydroxide solution, in order to set an optimum pH in the process water for efficient and complete removal of impurities from the process water in the flotation device. In this way, in particular, the hardness of the process water can be reduced efficiently.

For the same reason, it is preferable to provide at least one feed line for a precipitant and / or for a flocculation aid in the pressure-release flotation device.

In Druckentspannungsflotation the process water to be treated is preferably first by adding a pH adjusting agent, for example sodium hydroxide, to a suitable for the precipitation of solids, such as lime, neutral or alkaline pH, which is preferably between 7 and 10, more preferably between 7 and 9, and most preferably between 7.5 and 8.5. Optionally, precipitants and / or flocculants may be added to the water to facilitate calcification and to form precipitates from other contaminants. While polyaluminum chloride has proven to be a precipitant, a preferred example of a suitable flocculant is polyacrylamide. Subsequently, compressed air is added to the mixture thus produced, and this mixture is pressurized before the pressurized mixture is expanded in a pressure-release flotation reactor or subjected to reduced pressure, whereby the previously added compressed air at least largely bubbles out of the process water in the form of gas bubbles and flows upwards. The gas bubbles tear the impurities contained in the water from impurities, so that they are separated from the water. For this reason, the pressure-release flotation device preferably has at least one supply line for a compressed air and a gas-solution device which is connected to the pressure-release flotation reactor via a line and into which the compressed gas supply line opens.

In order to achieve an efficient separation of impurities, such as lime, it is proposed in a further development of the invention to design the pressure-release flotation device such that the pressure difference between the pressurization and the expansion is at least 2 bar, preferably at least 3 bar, more preferably at least 4 bar and all more preferably at least 5 bar. The larger the aforementioned pressure difference, the smaller are the gas beads formed during the expansion, so that an increased separation of impurities is achieved on account of the larger surface area to volume ratio of the gas bubbles.

Thus, the pressure release flotation device preferably comprises a precipitation device in which impurities are precipitated from the process water by addition of a substance selected from the group consisting of pH adjusters, precipitants, flocculants, and any combinations thereof, as well as a solids separation device in which the precipitated solids from the process water be separated. For example, as stated above, the precipitator may comprise a pH adjuster and a precipitant and / or flocculation aid feed line, whereas the solids separator preferably comprises a pressurized gas admixing unit, a gas solution reactor for physically dissolving the pressurized gas in the process water, and a pressure flotation flotation reactor.

In the aforementioned embodiment, in order to achieve homogeneous mixing of the process water with the substance selected from the group consisting of pH adjusting agents, precipitating agents, flocculants and any combinations thereof, U.S. 4,163,963 Plant according to the invention preferably has a mixing unit for homogeneous mixing of the abovementioned at least one substance.

In addition to the at least one fermentation reactor in which fermentable substances are fermented by bacteria to form biogas, and to the cleaning device comprising the first thickening device, the second thickening device and the flotation, the plant according to the invention preferably further comprises a mixing container for mixing the fermentable Starting material with water, which consists primarily of recirculated process water and possibly a small amount of fresh water, on.

Furthermore, it is preferred that the system according to the invention comprises a hydrolysis container in which the mixture consisting of fermentable starting material and water is incubated in order to hydrolyze the starting material. This can be done by enzymatic hydrolysis or by acidogenesis. While in enzymatic hydrolysis polymers, such as polysaccharides, polypeptides and fats, are degraded by microorganism-derived exoenzymes to their monomers, such as sugars, amino acids and fatty acids, these monomers, in acidogenesis by acidogenic microorganisms, become organic acids, alcohols, aldehydes , Converted to hydrogen and carbon dioxide. In addition, in the hydrolysis vessel or the hydrolysis reactor, by adding suitable nutrients and trace elements, the growth conditions suitable for the anaerobic microorganisms used in the at least one subsequent fermentation reactor can be set. Likewise, in the hydrolysis tank, the pH values of the process water suitable for the growth of the microorganisms in the subsequent anaerobic reactor can be adjusted by adding appropriate pH adjusting agents.

According to a first preferred embodiment of the present invention, the at least one fermentation reactor of the system according to the invention comprises a feed line for feeding a fermentable substances containing suspension, a gas discharge line for biogas and a discharge line for fermented suspension, wherein the discharge line for fermented suspension is connected to the first thickening device comprising a first discharge line for a first filtrate and a second discharge line for thickened suspension, wherein the second thickened suspension discharge line of the first thickening device is connected to the second thickening device comprising a first discharge line for a second filtrate and a second thickened suspension discharge line and wherein the first discharge line for the first filtrate of the first thickening device is connected to the flotation device.

Preferably, according to this embodiment, the plant according to the invention comprises a mixing vessel arranged upstream of the fermentation reactor for mixing the fermentable feed with process water, and the flotation means is a pressure-release flotation device comprising a pressure-release flotation reactor having a first solids discharge line and a second third filtrate discharge line the discharge line for the third filtrate directly or indirectly, d. H. via further device parts, is connected to the mixing container.

In this embodiment, the first discharge line for the second filtrate of the second thickening device may lead into the mixing container or lead into the flotation device. Furthermore, a partial flow line for the second filtrate can also lead from the second thickening device into the mixing tank, whereas another partial flow line for the second filtrate leads into the flotation device.

In addition, the second discharge line for thickened suspension of the second thickening device can be returned to the mixing container or, what is preferred, lead to a disposal container. Furthermore, it is also possible to lead from the second thickening device a partial flow line for thickened suspension in the mixing container, while another partial flow line leads to a disposal container.

According to a second preferred embodiment of the present invention, the fermentation reactor of the plant according to the invention comprises a feed line for supplying a fermentable substances containing solution, a gas discharge line for biogas and a discharge line for fermented mixture, wherein the discharge line for the fermented mixture with the flotation device is connected a first discharge line for suspension and a second discharge line for a first filtrate, wherein the first discharge line for suspension with the first thickening device is connected, which has a first discharge line for a second filtrate and a second discharge line for thickened suspension, wherein the second discharge line for thickened suspension of the first thickening device is connected to the second thickening device, which comprises a first discharge line for a third filtrate and a second discharge line for thickened Suspensi on, wherein the first discharge line for the second filtrate from the first thickening device leads into the discharge line for the fermented mixture of the fermentation reactor and the first discharge line for the third filtrate of the second thickening device leads into the fermentation mixture discharge line for the fermentation reactor.

Preferably, the plant according to the invention also has a mixing vessel arranged upstream of the fermentation reactor for mixing the fermentable starting material with water, and the flotation device is a pressure-release flotation device having a pressure-release flotation reactor, the second flotation device's first filtrate leading directly or indirectly to the flotation device Mixing container is connected.

In all the above embodiments, it is preferred that downstream of the mixing vessel and upstream of the fermentation reactor, i. H. between the mixing vessel and the fermentation reactor, a hydrolysis vessel is provided to hydrolyze the starting material either by enzymatic hydrolysis and / or by acidogenesis. Alternatively, it is also possible to combine the mixing vessel and the hydrolysis vessel, i. H. to carry out the mixing of the process water and the starting material and the hydrolysis of the suspension thus prepared in a container or reactor.

• – Fermentieren einer fermentierbare Substanzen enthaltenden Mischung durch Bakterien unter Bildung von Biogas,
• – Eindicken wenigstens eines Teilstroms der Mischung oder eines Filtrats der Mischung in einer ersten Eindickvorrichtung,
• – Eindicken wenigstens eines Teilstroms der Mischung oder eines Filtrats der Mischung in einer zweite Eindickvorrichtung sowie
• – Reinigen wenigstens eines Teilstroms der Mischung oder eines Filtrats der Mischung in einer Flotationseinrichtung,

wobei das Verfahren in der zuvor beschriebenen erfindungsgemäßen Anlage durchgeführt wird, und zwar besonders bevorzugt kontinuierlich durchgeführt wird.Another object of the present invention is a process for the production of biogas by fermentation. According to the invention, the method comprises the following steps:

• Fermenting a mixture containing fermentable substances by bacteria to form biogas,
• Condensing at least one partial stream of the mixture or of a filtrate of the mixture in a first thickening device,
• - Thickening at least a partial flow of the mixture or a filtrate of the mixture in a second thickening device and
• Purifying at least one partial stream of the mixture or of a filtrate of the mixture in a flotation device,

wherein the method is carried out in the plant according to the invention described above, and is particularly preferably carried out continuously.

Hereinafter, the present invention will be described purely by way of example with reference to advantageous embodiments and with reference to the accompanying drawings.

Showing:

1 a schematic view of a plant for the production of biogas according to a first embodiment of the present invention,

2 a schematic view of a plant for the production of biogas according to a second embodiment of the present invention and

3 a schematic view of a plant for the production of biogas according to a third embodiment of the present invention.

The in the 1 shown inventive system 10 according to a first embodiment comprises a reservoir 12 for a hydrolysable, vegetable raw material, for example maize, a mixing container arranged downstream thereof 14 for the mixing of the vegetable raw material with process water to produce a suspension containing vegetable raw material, a hydrolysis container 16 for the hydrolysis and / or acidogenesis of the vegetable raw material, a fermentation reactor 18 containing anaerobic microorganisms which produce biogas from the hydrolyzate of the vegetable raw material, a first thickening device 20 , which is configured in this embodiment as a disc filter, a second thickening device 22 , which is designed in this embodiment as a screw press, a storage container for filtrate 24 from the first thickening device 20 and a flotation device designed as a pressure-release flotation device 26 ,

The storage tank 12 is with the mixing container 14 via a solids supply line 28 connected. It also leads into the mixing container 14 a supply line 30 for process water to the vegetable raw material in the mixing container 14 to mix with process water to form a suspension. The in the mixing container 14 prepared suspension is passed over the line 32 in the downstream of the mixing vessel 14 arranged hydrolysis tank 16 promoted. Furthermore, the hydrolysis container 16 a supply line 34 for pH adjusters, nutrients, trace elements and the like as well as a hydrolyzate removal line 36 for feeding the hydrolyzed suspension into the fermentation reactor 18 on.

At the fermentation reactor 18 are a biogas discharge line 38 for removal of the in the fermentation reactor 18 by anaerobic fermentation of the organic components of the fermentation in the reactor 18 introduced hydrolyzate from the vegetable raw material produced biogas and a discharge line 40 for removing the fermented suspension from the fermentation reactor 18 provided, the discharge line 40 for the fermented suspension in the first thickening device 20 leads, where from the fermented suspension of water or filtrate is separated. From the first thickening device 20 leads a suspension discharge line 42 in the second thickening device 22 and a discharge line 44 for that in the first thickener 20 accumulating filtrate in the storage vessel 24 , In the second thickening device 22 where from the first thickening device 20 fed, thickened suspension of water is separated and compared with that in the first thickening device 20 Thickened suspension obtained in the suspension obtained is a discharge line 46 for the thickened suspension (or sludge) and a discharge line 48 for that in the second thickener 22 provided filtrate provided, wherein the discharge line 48 for that in the second thickener 22 resulting filtrate with the mixing container 14 connected is.

In the storage vessel 24 this will be from the first thickening device 20 discharged filtrate to a continuous filtrate feed to the flotation 26 to ensure. From the storage vessel 24 leads a partial flow line 50 to the first thickening device 20 back, whereas a further partial flow line 50 ' to the flotation device 26 leads.

The flotation device 26 comprises a pressure-release flotation reactor 52 , In the to the pressure release flotation reactor 52 leading partial flow line 50 ' opens a supply line 54 , which with a mixing unit 56 is connected, in which supply lines 58 . 58 ' open, via which into the mixing unit 56 pH adjuster, precipitant and / or flocculants. In addition, the pressure-release flotation reactor has 52 a circulation line 60 on, with an admixing unit 62 and with a gas-solution reactor 64 that with a pressurized gas supply line 66 equipped, is connected. Also in the admixing unit 62 lead supply lines 68 . 68 ' over which into the mixing unit 62 pH adjusters, precipitants and / or flocculants can be added. From the pressure-release flotation reactor 52 leads the supply line 30 for process water in the mixing tank 14 ,

Finally, the attachment points 10 another fresh water supply line 70 on which to the first thickening device 20 leading partial flow line 50 empties.

When operating in the 1 shown attachment 10 become the mixing container 14 continuously vegetable raw material, corn in this embodiment, from the reservoir 12 and process water via the supply line 30 fed, the process water and the corn with each other in the mixing vessel 14 are mixed to form a suspension having a solids content of 5 to 15 wt .-%. In the mixing container 14 agitators (not shown) and / or grinders (not shown) may be provided to facilitate mixing of the process water and corn and to achieve homogenization of the suspension. From the mixing container 14 The suspension is continuously in the hydrolysis 16 guided and with the hydrolysis tank 16 via the supply line 34 mixed pH adjusting agent. Optionally, the hydrolysis tank 16 also enzyme (s) or microorganisms are added to the hydrolysis and / or acidogenesis of the corn in the hydrolysis container 16 to accelerate. Further, in the hydrolysis tank 16 which is preferred, a temperature control (not shown) may be provided to set an optimum temperature for the microorganisms contained therein. In this case, the supply of the suspension to the hydrolysis is 16 and the removal of suspension from the hydrolysis tank 16 via the hydrolyzate discharge line 36 so controlled that the mean residence time of the suspension in the hydrolysis tank 16 so long is that in the hydrolysis tank 16 sufficient hydrolysis and / or acidogenesis of the maize takes place. The fermentation reactor 18 over the line 36 supplied hydrolyzate is in the fermentation reactor 18 which contains anaerobically-working microorganisms, fermented to form biogas containing mainly methane and carbon dioxide, the biogas continuously passing through the line 38 and the fermented mixture continuously over the line 40 from the reactor 18 subtracted from. Further, in the fermentation reactor 18 which is preferred, a temperature control (not shown) may be provided to set an optimum temperature for the microorganisms contained therein. The fermentation reactor 18 a further fermentation reactor designed as a post-fermentation reactor (not shown) can be connected downstream in order to optimize the fermentation of the maize hydrolyzate.

The from the fermentation reactor 18 withdrawn fermented mixture is over the line 40 the first thickening device 20 , which is designed as a disc filter, fed and thickened there. The thickened suspension is passed over the line 42 from the first thickening device 20 deducted and the second thickening device 22 fed, where the suspension is further thickened to a solids content of 20 to 60 wt .-%. While the thickened suspension from the second thickening device 22 over the line 46 from the plant 10 withdrawn and disposed of, for example, that is in the second thickening device 22 resulting filtrate over the line 48 in the mixing container 14 recycled. Alternatively, the Filtrate from the second thickener 22 also with the filtrate from the first thickening device 20 mixed and the storage vessel 24 be supplied. Furthermore, it is also possible to use a partial flow of the filtrate from the second thickening device 22 in the storage vessel 24 to lead and another partial flow of the filtrate from the second thickening device 22 in the mixing container 14 respectively.

From the storage vessel 24 is continuously filtrate from the first thickener 20 over the line 50 ' in the pressure-release flotation reactor 52 passed, the previously on the supply line 54 a mixture of pH adjuster, precipitating agent and flocculation aid is added to that for flotation in the pressure-release flotation reactor 52 optimal conditions, such as preferably a pH between 7.5 and 8.5 set.

From the pressure-release flotation reactor 52 is about the circulation line 60 continuously part of the in the pressure release flotation reactor 52 removed liquid located and this partial flow through the admixing unit 62 and the gas solution reactor 64 passed before the partial flow back into the pressure-release flotation reactor 52 is returned. In the mixing unit 62 be the partial flow through the supply lines 68 . 68 ' Precipitants and flocculants are added, which support the precipitation of solid, especially lime, and the formation of suitable sized for separation from the process water solid flocs. For example, polyaluminum chloride can be used as the precipitating agent, whereas polyacrylamide is an example of a suitable flocculant. In the downstream of the admixing unit 62 provided gas solution reactor 64 is the partial flow for the purpose of preparation for the subsequent Druckgasentspannungsflotation on the compressed gas supply line 66 a pressurized gas, for example air or another oxygen-containing gas or also an oxygen-free gas, is added and the partial flow mixed with the compressed gas is pressurized before the thus treated partial flow into the pressure-release flotation reactor 52 is returned. In the pressure release flotation reactor 52 The pressurized and gasified mixture expands abruptly so that the gas dissolved in the water bubbles out and in the form of gas bubbles in the pressure-release flotation reactor 52 ascends to the top. At the same time, due to the present precipitation and flocculation aids, the solids present in the water form flocs of suitable size and structure, so that they are agglomerated by the gas bubbles rising upwards to the water surface in the pressure-release flotation reactor 52 to be driven. During the formation of (solid) mud over the mud discharge line 72 from the pressure-release flotation reactor 52 is removed or to the first thickening device 20 is guided (not shown), the purified and freed of solid process water through the return line 30 directly into the mixing container 14 recycled. Depending on the type of starting material used can from the return line 30 a portion of the process water is withdrawn from the plant via a discharge line (not shown); This may be necessary in particular if the starting material contains comparatively much water. Alternatively, the purified and de-solidified process water may be prior to delivery to the mixing vessel 14 a further cleaning device (not shown), such as a distillation device supplied.

About the partial flow line 50 gets out of the reservoir 24 continuously a partial flow of the first thickening device 20 coming filtrate to the trained as a disc filter first thickening device 20 returned to the filter discs of the disc filter to rinse and clean them. In addition, the partial flow line 50 over the line 70 added a small amount of fresh water.

The in the 2 illustrated attachment 10 according to a second embodiment of the present invention differs from that in the 1 shown by the fact that the individual devices downstream of the fermentation reactor 18 arranged, from the first thickening device 20 , the second thickening device 22 and the flotation device 26 existing cleaning device are arranged with each other in a different order. While at the in the 1 illustrated embodiment, the flotation device 26 the first thickening device 20 is downstream, is the flotation device 26 at the in the 2 illustrated embodiment upstream of the thickening devices 20 . 22 arranged. This is due to the fact that in the in the 2 illustrated embodiment of the vegetable raw material in the mixing container 14 is not mixed with the process water to form a suspension, but in the mixing container 14 from the over the line 28 supplied vegetable raw material and the over the line 30 supplied process water an aqueous solution having a solids content of less than 200 ppm is prepared, which then the hydrolysis 16 and then the fermentation reactor 18 is supplied. Consequently falls in the fermentation reactor 18 no fermented suspension, but only a trace of solid having fermented solution from which in the fermentation reactor 18 downstream flotation device 26 first a suspension which has, for example, 2 to 4 wt .-% solids, is generated, which then in the flotation 26 downstream thickening devices 20 . 22 is thickened.

For this reason, the discharge line leads 40 for the fermented mixture from the fermentation reactor 18 directly into the flotation device 26 which in the 2 is shown only schematically, but in the 1 detailed pressure release flotation device shown in detail 26 equivalent. That in the flotation facility 26 resulting filtrate or purified process water is over the line 30 in the mixing container 14 recycled, with the process water before feeding into the mixing vessel 14 optionally a further purification step, for example, a distillation step, can be subjected. On the other hand, in the flotation facility 26 resulting suspension via the line 74 in the first thickening device 20 in which it is thickened to form a filtrate. While that in the first thickener 20 resulting filtrate over the line 74 ' in the from the fermentation reactor 18 into the flotation device 26 leading line 40 is passed in the first thickening device 20 resulting suspension via the line 42 in the second thickening device 22 led, where the suspension is thickened further. That in the second thickening device 22 resulting filtrate is passed over the line 74 '' in the from the fermentation reactor 18 into the flotation device 26 leading line 40 whereas in the second thickener 22 resulting suspension having a solids content of, for example, 20 to 60 wt .-% via the line 46 from the plant 10 is dissipated.

The in the 3 illustrated attachment 10 according to a third embodiment of the present invention differs from that in the 1 shown by the fact that between the reservoir 12 and the mixing container 14 a pre-thickening device 78 is provided. This embodiment is particularly suitable for relatively liquid starting materials, such as manure, such as cattle manure. In this embodiment, the starting material becomes in the pre-thickening device 78 initially thickened, namely, for example, to a solids content of 8 to 12%, before the pre-thickened starting material in the mixing vessel 14 guided and from there into the hydrolysis tank 16 to be led. In this embodiment, the mixing container 14 also omitted. The filtrate from the pre-thickening device 78 is over the line 80 in the reservoir 24 guided. Part of the process water pipe 30 returned, purified process water is from the plant 10 over the line 82 deducted.

LIST OF REFERENCE NUMBERS

10

Plant for the production of biogas

12

Storage container for vegetable raw material

14

mixing tank

16

hydrolysis tank

18

fermentation reactor

20

first thickening device

22

second thickening device

24

Storage tank for filtrate

26

flotation

28

Solid feed line for vegetable raw material

30

Supply line for process water

32

suspension line

34

Inlet line for pH adjustment agent

36

Hydrolysatabfuhrleitung

38

Biogas discharge line

40

Discharge line for the fermented suspension

42

Suspension removal line

44

Discharge line for filtrate

46

Sludge removal line

48

Discharge line for filtrate

50, 50 '

Partial flow line

52

flotation

54

supply line

56

mixing unit

58, 58 '

Inlet line for pH adjusters, precipitants and / or flocculants

60

Circuit line

62

mixing in

64

Gas solution reactor

66

Pressure gas supply line

68, 68 '

Feed line for pH adjusters, fillers and / or flocculants

70

Fresh water supply line

72

Sludge removal line

74, 74 ', 74' '

management

76

management

78

Voreindickvorrichtung

80

filtrate

82

withdrawal line

Claims (11)

Plant for the production of biogas by fermentation comprising: - at least one fermentation reactor ( 18 ), in which fermentable substances are fermented by bacteria to form biogas, A first thickening device ( 20 ), wherein the first thickening device ( 20 ) is a disc filter or a rotating gravity thickener, - a second thickening device ( 22 ), wherein the second thickening device is a screw press or a belt sieve press, and - a flotation device ( 26 ), the flotation device ( 26 ) a pressure-release flotation reactor ( 52 ) having at least one supply line ( 66 ) for compressed air, wherein i) the fermentation reactor ( 18 ) a supply line ( 36 ) for supplying a fermentable substances containing suspension, a gas discharge line ( 38 ) for biogas and a discharge line ( 40 ) for fermented suspension, the discharge line ( 40 ) for fermented suspension with the first thickening device ( 20 ), which has a first discharge line ( 44 ) for a first filtrate and a second discharge line ( 42 ) for thickened suspension, wherein the second discharge line ( 42 ) for thickened suspension of the first thickening device ( 20 ) with the second thickening device ( 22 ), which has a first discharge line ( 48 ) for a second filtrate and a second discharge line ( 46 ) for thickened suspension, and wherein the first discharge line ( 44 ) for the first filtrate of the first thickening device ( 20 ) with the flotation device ( 26 ) or ii) the fermentation reactor ( 18 ) a supply line ( 36 ) for supplying a fermentable substances containing solution, a gas discharge line for biogas ( 38 ) and a discharge line ( 40 ) for fermented mixture, the discharge line ( 40 ) for the fermented mixture with the flotation device ( 26 ), which has a first discharge line ( 74 ) for suspension and a second discharge line ( 30 ) for a first filtrate, wherein the first discharge line ( 74 ) for suspension with the first thickening device ( 20 ), which has a first discharge line ( 74 ' ) for a second filtrate and a second discharge line ( 42 ) for thickened suspension, wherein the second discharge line ( 42 ) for thickened suspension of the first thickening device ( 20 ) with the second thickening device ( 22 ), which has a first discharge line ( 74 '' ) for a third filtrate and a second discharge line ( 46 ) for thickened suspension, wherein the first discharge line ( 74 ' ) the second filtrate from the first thickening device ( 20 ) in the discharge line ( 40 ) for the fermented mixture of the fermentation reactor ( 18 ) and the first discharge line ( 74 '' ) for the third filtrate of the second thickening device ( 22 ) in the discharge line ( 40 ) for the fermented mixture of the fermentation reactor ( 18 ) leads. Plant according to claim 1, characterized in that the first thickening device ( 20 ) is a Vorseichtisch. Plant according to claim 1 or 2, characterized in that the pressure-release flotation device ( 26 ) at least one supply line ( 58 . 68 ) for a pH adjusting agent. Plant according to at least one of the preceding claims, characterized in that the pressure-release flotation device ( 26 ) at least one supply line ( 58 ' . 68 ' ) for a precipitant and / or a flocculant. Plant according to Claim 1, characterized in that the pressure-release flotation device ( 26 ) a gas solution device ( 64 ), which with the pressure-release flotation reactor ( 52 ) via a line ( 60 ) is connected and in which the compressed gas supply line ( 66 ) opens. Plant according to at least one of the preceding claims, characterized in that it further comprises a mixing vessel ( 14 ) for mixing the fermentable starting material with water and / or a hydrolysis container ( 16 ). Installation according to claim 1, characterized in that the feature i) of claim 1 is met and the plant upstream of the fermentation reactor ( 18 ) arranged mixing container ( 14 ) for mixing the fermentable starting material with water and the flotation device ( 26 ) a pressure-release flotation reactor ( 52 ) is a pressure relief flotation device having a first discharge line ( 72 ) for solids and a second discharge line ( 30 ) for a third filtrate, wherein the discharge line ( 30 ) for the third filtrate directly with the mixing container ( 14 ) connected is. Installation according to claim 1, characterized in that the feature ii) of claim 1 is met and the plant upstream of the fermentation reactor ( 18 ) arranged mixing container ( 14 ) for mixing the fermentable starting material with water and the flotation device ( 26 ) a pressure-release flotation reactor ( 52 ) having pressure-release flotation device, wherein the second discharge line ( 30 ) for the first filtrate of the flotation device directly to the mixing container ( 14 ) connected is. Plant according to at least one of claims 7 or 8, characterized in that downstream of the mixing container ( 14 ) and upstream of the fermentation reactor ( 18 ) a hydrolysis tank ( 16 ) is provided. Process for the production of biogas by fermentation comprising the steps of: - fermenting a mixture containing fermentable substances by bacteria to form biogas, - thickening at least one partial stream of the mixture or a filtrate of the mixture in a first thickening device ( 20 ), - condensing at least one partial stream of the mixture or of a filtrate of the mixture in a second thickening device ( 22 ) and - cleaning at least one partial stream of the mixture or of a filtrate of the mixture in a flotation device ( 26 ), characterized in that in an annex ( 10 ) is carried out according to one of claims 1 to 9. A method according to claim 10, characterized in that it is carried out continuously.

Images