DE102007056916A1 - Plant for the production of biogas through fermentation, comprises a fermentation reactor in which fermentable substances are fermented through bacteria under formation of biogas, thickening devices and/or floatation unit - Google Patents

Abstract

The plant for the production of biogas through fermentation, comprises a fermentation reactor (18) in which fermentable substances are fermented through bacteria under formation of biogas, first and second thickening devices (20, 22) and/or floatation unit (26), a mixing container (14) for mixing the fermentable raw materials with water and/or a hydrolysis vessel. The first thickening device is a rotatable plate filter or a centrifuge and the second thickening plate is a screw press, a centrifuge or a screen belt press. The plant for the production of biogas through fermentation, comprises a fermentation reactor (18) in which fermentable substances are fermented through bacteria under formation of biogas, first and second thickening devices (20, 22) and/or floatation unit (26), a mixing container (14) for mixing the fermentable raw materials with water and/or a hydrolysis vessel. The first thickening device is a rotatable plate filter or a centrifuge and the second thickening plate is a screw press, a centrifuge or a screen belt press. The floatation unit is a pressure release floatation unit with a pressure release floatation reactor. The pressure release floatation unit has a supply line for a pH-adjusting unit, a supply line for precipitating agent and/or a flocculation agent, a supply line for compressed gas, and a gas separation equipment, which is connected with the pressure release floatation unit over a pipeline and in which the compressed gas supply line ends. The fermentation reactor comprises a supply line for supplying a suspension or solution containing fermentable substances, a gas removal line for biogas, and a removal line for the fermented suspension or mixture. The removal line for the fermented suspension is connected with the first thickening device, which has a first removal line for a first filtrate and a second removal line for thickened suspension. The second removal line for the thickened suspension of the first thickening device is connected with the second thickening device, which has a first removal line for a second filtrate and a second removal line for the thickened suspension. The first removal line for the first filtrate of the first thickening device is connected with the floatation unit. The mixing container is arranged upstream to the fermentation reactor. The floatation unit has a first removal line for solid material and a second removal line for third filtrate. The removal line for the third filtrate is connected directly or indirectly with the mixing container. The removal line for the fermented mixture is connected with the floatation unit. The first removal line for the suspension is connected with the first thickening device, which has a first removal line for a second filtrate and a second removal line for thickened suspension. The second removal line for the thickened suspension of the first thickening device is connected with the second thickening device, which has a first removal direction for a third filtrate and a second removal line for the thickened suspension. The first removal line for the second filtrate guides from the first thickening device to the removal line for the fermented mixture of the fermentation reactor. The first removal line for the third filtrate of the second thickening device guides in the removal line for the fermented mixture of the fermentation reactor. The hydrolysis vessel is arranged downstream to the mixing container and upstream to the fermentation reactor. An independent claim is included for a method for the production of biogas through fermentation.

Description

The The present invention relates to a plant and a method for Production of biogas by fermentation.

by virtue of The shortage and increase in the price of fossil fuels is gaining Regenerative energy production is becoming increasingly important. A well-known A process for regenerative energy production is the production of biogas from fermentable, biomass-containing starting materials, such as residues, such as sewage sludge, biowaste or leftovers, from manure, such as manure and manure, or from plants such as corn and the like. In these Process is carried out by anaerobic fermentation of the organic starting materials Biogas produces, so a mixture of the main components of methane and carbon dioxide. Besides methane and carbon dioxide, biogas can also contain other gases, such as hydrogen, ammonia and nitrogen, wherein the energetically used portion of the methane is.

at The known process for the production of biogas is the fermentable Starting material first mixed with water to form a suspension before this suspension in a fermentation reactor under anaerobic conditions is fermented under the formation of biogas. To this procedure as possible Economically, this becomes common carried out continuously, with part of the used Water is circulated as process water. at Such a process is after the removal of the fermented Mixture of the fermentation reactor part of the discharged in the Mixture of water contained separated from the suspension, purified and again used to suspend the starting materials. Indeed is common in the known plants for the production of biogas the achieved degree of purification for the process water is insufficient, so that only a comparatively small proportion of process water in the Circulation can be performed and therefore significant amounts of fresh water are necessary. Other methods which provide adequate Purification of the process water reach, so that a comparatively large part of the process water is recycled can be used, cleaning devices, which are both high Investment costs as well as high operating costs require, and / or can only be operated with a relatively low throughput.

A corresponding system and a corresponding method for the production of biogas is for example from DE 10 2005 050 927 A1 known. In this process, fermentable starting material, namely monosubstrate from bakery waste, mixed in a suspending with water to form a suspension, the suspension thus produced is then hydrolyzed in a hydrolysis and finally fermented in a main reactor and in a subsequent Nachgärreaktor. 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.

task Therefore, the present invention is a low-cost To provide plant for the continuous production of biogas by means of fermentation, when the process water, especially if the system with is operated at a high throughput, is cleaned efficiently, so that a large portion of the process water in the circulation can be performed without causing contamination in enrich the process water, and only small amounts of fresh water need to be supplied, so that the plant efficient and can be operated economically. Another task of the present The invention is to provide a continuous process for the production of biogas by fermentation, which with a high throughput and low cost of ownership efficient and economical can be carried out.

• – wenigstens einen Fermentationsreaktor, in dem fermentierbare Substanzen durch Bakterien unter Bildung von Biogas fermentiert werden,
• – eine erste Eindickvorrichtung zur Rückgewinnung bzw. Reinigung von Prozesswasser,
• – eine zweite Eindickvorrichtung zur Rückgewinnung bzw. Reinigung von Prozesswasser sowie
• – eine Flotationseinrichtung zur Rückgewinnung bzw. Reinigung von Prozesswasser.

According to the invention this object is achieved by a plant according to 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 for the recovery or purification of process water,
• - A second thickening device for the recovery or purification of process water and
• - A flotation device for the recovery or purification of process water.

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 being irritated by the circulation accumulate in the process water. 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 system, based on the throughput, low, because it is at the individual components used for the purification of process water, namely the two thickeners and the Flotationseinrchtung, relatively inexpensive system parts. 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.

Under a thickening device is within the meaning of the present invention a device understood, which consists of mixtures, such as suspensions, water separated so that water or filtrate and a thickened suspension, d. H. a suspension with one compared to the solids content the suspension before the thickening increased solids content, results. Insofar referred to thickening in the sense of the present Invention, a drainage of a mixture, in particular a suspension.

Around a particularly effective thickening with low space requirements and at low investment costs for the device, which nevertheless has a high thickening capacity, too ensure is in development of the inventive concept proposed in the inventive system as the first thickening device a rotating thickening device provided.

Especially, if the first thickening device is a rotating disc thickener, is a centrifuge or a rotating gravity thickener get good results. A preferred example of a disk thickener is a disk filter, whereas a precooked table a preferred example of a gravity thickener. An advantage of using a disc filter is that this by adjusting the internal fluid volume and by adjusting the revolutions of the rotating discs per Time unit to possibly different feed rates the suspension can be adjusted.

Out For the above reasons, it is preferable that the second thickening device is a rotary thickening device.

Quality In particular, results are obtained when the second thickening device a screw press, a centrifuge or a screen belt press is.

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

Around a particularly good and effective removal of impurities in the process water, especially at a high throughput, too achieve, is proposed in development of the inventive idea, the flotation device as having a Druckentspannungsflotationsreaktorende Provide pressure relief flotation device.

Preferably the pressure release flotation device has at least one Feed line for a pH adjusting agent, such as a base, For example, caustic soda, on to in the process water for a an efficient and complete removal of impurities from the process water in the flotation optimal pH adjust. In this way, in particular, the hardness of the process water are efficiently reduced.

Out for the same reason, it is preferable in the pressure release flotation device at least one supply line for a precipitant and / or for a flocculant aid.

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, the mixture thus produced compressed gas, preferably compressed air, is added and this mixture is pressurized before the pressurized mixture in a Druckentspannungsflotationsreaktor relaxed or egg nem reduced pressure is exposed, whereby the previously added pressurized gas at least largely bubbles out in the form of gas bubbles from the process water 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 feed line for a compressed gas and a gas-solution device, which is connected to the pressure-release flotation reactor via a line and into which the compressed gas feed line opens.

Around to achieve efficient separation of impurities, such as lime, is proposed in development of the inventive concept, the Druckentspannungsflotationsvorrichtung be interpreted that the pressure difference between the pressurization and the relaxation at least 2 bar, preferably at least 3 bar, more preferably at least 4 bar, and most preferably at least 5 bar. The larger the aforementioned pressure difference is, the smaller are the gas beads formed during the relaxation, so because of the larger surface area to volume ratio of the gas bubbles increased Separation of impurities is achieved.

therefore includes the Druckentspannungsflotationsvorrichtung preferably a precipitation device in which by adding a from pH adjusting agents, precipitants, flocculants and any combinations thereof existing group selected Substance impurities precipitated out of the process water and a Feststoffabtrenneinrichtung in which the precipitated Solids are separated from the process water. For example the precipitating device, as stated above, a pH adjusting device and a supply line for Contain precipitants and / or flocculants, whereas the Feststoffabtrenneinrichtung preferably a Zumischeinheit for compressed gas, a gas-solution reactor for physical Solution of the compressed gas in the process water and a Pressure Relief Flotation has.

Around in the aforementioned embodiment, a homogeneous mixing the process water with the from the pH-adjusting agents, precipitants, Flocculants and any combinations thereof Group to achieve selected substance, the plant of the invention preferably a mixing unit for homogeneous mixing of the aforementioned at least one substance.

additionally to the at least one fermentation reactor in which fermentable Substances fermented by bacteria to produce biogas and to the cleaning device, which is the first thickening device, the second thickening device and the flotation device comprises, the plant according to the invention preferably Furthermore, a mixing container for mixing the fermentable Starting material with water, which mainly from the circulation Run process water and possibly a small part of fresh water, on.

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

in principle the order of the three cleaning devices of the system according to the invention, d. H. the order of the first thickener, the second Thickening device and the flotation device, each other be chosen as long as the required degree of cleaning for the process water is reached.

According to a first preferred embodiment of the present invention, the at least one fermentation reactor of the plant 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 discharge line for thickened suspension of the first thickening device is connected to the second thickening device, which 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 of the first thickening device is connected to the flotation device.

Preferably has the system according to the invention according to this Embodiment one upstream of the fermentation reactor arranged mixing vessel for mixing the fermentable starting material with process water on and is the flotation one, one Pressure Relief Flotation Reactor Pressure Relief Flotation Device, which a first discharge line for solid and a has a second discharge line for a third filtrate, wherein the discharge line for the third filtrate directly or indirectly, d. H. over other device parts, with the Mixing container is connected.

at This embodiment, the first discharge line for the second filtrate of the second thickening device in the mixing container lead or lead into the flotation facility. Furthermore, from the second thickening device and a partial flow line for the second filtrate into the mixing container, whereas another partial flow line for the second Filtrate leads into the flotation device.

moreover may be the second discharge line for thickened suspension the second thickening device back into the mixing container or, which is preferred, lead to a disposal container. Furthermore, it is also possible from the second thickening device a partial flow line for thickened suspension in the To lead mixing container while a other partial flow line leads to a disposal container.

According to one second preferred embodiment of the present invention the fermentation reactor of the invention Plant a supply line for supplying a fermentable Substances containing solution, a gas discharge line for Biogas and a discharge pipe for fermented mixture on, with the discharge line for the fermented mixture is connected to the flotation device, which 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, which is 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 is 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 thickener in the discharge line for the fermented mixture of Fermentation reactor leads and 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 leads.

Preferably also indicates the system according to the invention according to this Embodiment one upstream of the fermentation reactor arranged mixing vessel for mixing the fermentable Starting material with water and is the flotation device a, a Druckentspannungsflotationsreaktor having Druckentspannungsflotationseinrichtung is, wherein the second discharge line for the first filtrate the flotation device directly or indirectly with the mixing container connected is.

According to one third preferred embodiment of the present invention the plant according to the invention has a mixing tank for mixing the fermentable starting material with water, of which one line, if necessary, via one or more further Devices leads to the first thickening device, which a first discharge line for a first filtrate and a has a second discharge line for thickened suspension, wherein the second discharge line for thickened suspension is connected to the second thickening device, which is a first Discharge line for a second filtrate and a second discharge line for thickened suspension, wherein the first discharge line for the first filtrate of the first thickening device with the flotation device is connected, which is a first discharge line for solid and a second discharge line for having a third filtrate, wherein the discharge line for the third filtrate directly or indirectly with the fermentation reactor connected is.

Also In this embodiment it is preferred that the flotation device a, a Druckentspannungsflotationsreaktor having Druckentspannungsflotationseinrichtung is.

Further In this embodiment it is preferred that the fermentation reactor a gas discharge line for biogas and a discharge line for fermented liquid, wherein the Discharge pipe for fermented liquid directly or indirectly connected to the mixing vessel.

at This embodiment, the first discharge line for the second filtrate of the second thickening device in the mixing container lead or lead into the flotation facility. Furthermore, from the second thickening device and a partial flow line for the second filtrate into the mixing container, whereas another partial flow line for the second Filtrate leads into the flotation device.

moreover may be the second discharge line for thickened suspension the second thickening device back into the mixing container or, which is preferred, lead to a disposal container. Furthermore, it is also possible from the second thickening device a partial flow line for thickened suspension in the To lead mixing container while a other partial flow line leads to a disposal container.

at all the aforementioned embodiments, it is preferable that downstream of the mixing vessel and upstream of the fermentation reactor, d. H. between the mixing container and the fermentation reactor, a hydrolysis tank provided is to the starting material either by enzymatic hydrolysis and / or hydrolyzed by acidogenesis. Alternatively, it is it is also possible the mixing tank and the hydrolysis tank to combine, d. H. 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.

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
• - Cleaning at least a partial stream of the mixture or a filtrate of the mixture in a flotation device.

Preferably the method is in the invention described above Plant performed, and more preferably continuously.

following The present invention is purely exemplary by way of advantageous Embodiments and with reference to the accompanying drawings described.

there demonstrate:

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,

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

4 a schematic view of a plant for the production of biogas according to a fourth 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 tion 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 performs a suspension discharge tung 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 supplied to the hydrolysis and / or acidogenesis of the maize in the Hydrolysebehäl ter 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 thickening device 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 filter rats 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 pressurized 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 of the fermentati onsreaktor 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.

Unlike the ones in the 1 and 2 shown plants 10 is the one from the first thickening device 20 , the second thickening device 22 and the flotation device 26 existing cleaning device in the in 3 illustrated plant 10 according to a third Ausfüh tion of the present invention upstream of the fermentation reactor 18 arranged.

Consequently leads in the in the 3 illustrated plant 10 the hydrolyzate discharge line 36 from the hydrolysis tank 16 in the first thickening device 20 , While in the first thickening device 20 resulting suspension via the line 42 in the second thickening device 22 is performed, where the suspension is further thickened, which is in the first thickening device 20 resulting filtrate on the filtrate 44 in the reservoir 24 directed. The in the second thickening device 22 resulting thickened suspension is via the discharge line 46 from the plant 10 whereas in the second thickener 22 resulting filtrate over the line 48 in the mixing container 14 is returned.

In the storage vessel 24 this will be from the first thickening device 20 drained filtrate to provide a continuous filtrate feed to the flotation device 26 which in the 3 is shown only schematically, but in the 1 detailed pressure release flotation device shown in detail 26 corresponds 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. In the plant 10 is a fresh water supply line 70 provided, which in the first thickening device 20 leading partial flow line 50 empties.

While in the flotation facility 26 resulting suspension via the line 72 from the plant 10 is deducted, which is in the flotation 26 resulting filtrate over the line 76 in the fermentation reactor 18 passed, in which the filtrate, which contains hydrolysis products of the vegetable raw material in dissolved form, is fermented. The resulting biogas is from the fermentation reactor 18 over the line 38 whereas the fermented solution from the fermentation reactor 18 over the line 30 as process water in the mixing tank 14 is returned.

The in the 4 illustrated attachment 10 According to a fourth 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.

10

investment for the production of biogas

12

reservoir for vegetable raw material

14

mixing tank

16

hydrolysis tank

18

fermentation reactor

20

first thickening

22

second thickening

24

reservoir for filtrate

26

flotation

28

Solid supply line for vegetable raw material

30

supply line for process water

32

suspension line

34

supply line for pH adjuster

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, on 50 '

Partial flow line

52

flotation

54

supply line

56

mixing unit

58 58 '

supply line for pH adjusters, precipitants and / or flocculants

60

Circuit line

62

mixing in

64

Gas solution reactor

66

Pressure gas supply pipe

68 68 '

supply line for pH adjusters, precipitants 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

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• DE 102005050927 A1 [0004]

Claims (22)

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 ), - a second thickening device ( 22 ) and - a flotation device ( 26 ). Plant according to claim 1, characterized in that the first thickening device ( 20 ) is a rotating thickening device. Plant according to claim 2, characterized in that the first thickening device ( 20 ) is a rotating disc thickener, preferably a disc filter, a centrifuge, or a rotary gravity thickener, preferably a prefessure table. Plant according to at least one of the preceding claims, characterized in that the second thickening device ( 22 ) is a rotating thickening device. Plant according to claim 4, characterized in that the second thickening device ( 22 ) is a screw press, a centrifuge or a belt sieve press. Plant according to at least one of the preceding claims, characterized in that the flotation device ( 26 ), a pressure-release flotation reactor ( 52 ) having Druckentspannungsflotationseinrichtung is. Plant according to claim 6, characterized in that the pressure-release flotation device ( 26 ) at least one supply line ( 58 . 68 ) for a pH adjusting agent Plant according to claim 6 or 7, characterized in that the pressure-release flotation device ( 26 ) at least one supply line ( 58 ' . 68 ' ) for a precipitant and / or a flocculant. Installation according to one of claims 6 to 8, characterized in that the pressure-release flotation device ( 26 ) at least one supply line ( 66 ) for a compressed gas. Plant according to Claim 9, 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 ). Plant according to at least one of the preceding claims, characterized in that 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 ) connected is. Plant according to claim 12, characterized in that it has an 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 or indirectly with the mixing container ( 14 ) connected is. Plant according to at least one of claims 1 to 11, characterized in that 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 a having thickened suspension, wherein the first discharge line ( 74 ' ) for 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 14, characterized in that it has an 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 or indirectly with the mixing container ( 14 ) connected is. Installation according to at least one of claims 1 to 11, characterized in that this a mixing vessel ( 14 ) for mixing the fermentable starting material with water, from which a line ( 32 ) possibly via one or more further devices ( 16 ) to the first thickening device ( 20 ), which 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 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, wherein the first discharge line ( 44 ) for the first filtrate of the first thickening device ( 20 ) with the flotation device ( 26 ), which has a first discharge line ( 72 ) for solids and a second discharge line ( 76 ) for a third filtrate, wherein the discharge line ( 76 ) for the third filtrate directly or indirectly with the fermentation reactor ( 18 ) connected is. Plant according to claim 16, characterized in that the flotation device ( 26 ), a pressure-release flotation reactor ( 52 ) having Druckentspannungsflotationseinrichtung is. Plant according to claim 16 or 17, characterized in that the fermentation reactor ( 18 ) a gas discharge line ( 38 ) for biogas and a discharge line ( 30 ) for fermented liquid, the discharge line ( 30 ) for fermented liquid directly or indirectly with the mixing container ( 14 ) connected is. Plant according to at least one of claims 13, 15, 16, 17 or 18, characterized in that downstream of the mixing vessel ( 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 ). Process for the production of biogas by fermentation, preferably a process according to claim 20, characterized in that this in a plant ( 10 ) is carried out according to one of claims 1 to 19. Method according to claim 20 or 21, characterized that this is done continuously.