EP2370562A2

EP2370562A2 - Method for reducing methane slack when starting and stopping biogas fermenters and biogas system for carrying out the method

Info

Publication number: EP2370562A2
Application number: EP09795366A
Authority: EP
Inventors: Peter Lutz
Original assignee: Bekon Energy Technologies GmbH and Co KG
Current assignee: Bekon Energy Technologies GmbH and Co KG
Priority date: 2008-12-01
Filing date: 2009-12-01
Publication date: 2011-10-05
Also published as: EA018254B1; US20110236947A1; JP2012510264A; CN102232108B; JP5442753B2; DE102008059803A1; US8272436B2; EA201170733A1; CN102232108A; WO2010063709A2; US8408293B2; WO2010063709A3; US20120329120A1

Abstract

The invention relates to a method for reducing methane slack when operating biogas systems comprising at least one biogas fermenter and to a biogas system for carrying out the method. When starting up a freshly charged fermenter, the methane portion in the biogas produced is initially so low and the fractions of carbon dioxide and nitrogen are so high that direct use of the biogas in a combined heat and power (CHP) plant is not possible. During this startup phase of a freshly charged fermenter, the biogas generated with the low methane fraction is therefore discharged directly to the atmosphere or is flared off if the methane fraction is higher. This results in the non-use of a portion of the methane produced, methane slack. In order to prevent this, the biogas with the low methane fraction produced in the startup phase is fed to a gas treatment unit in which non-methane components of the gas mixture are partially separated and the remaining gas mixture with a higher methane fraction is returned to the biogas fermenter until the methane fraction is high enough.

Description

description

Method for reducing methane slippage when starting up and shutting down biogas digesters and bioreactor for carrying out this method

The invention relates to a method for reducing methane slip in the operation of biogas plants with at least one biogas fermenter.

The so-called "dry fermentation" makes it possible to methanize pourable biomass from agriculture, from biofouling and communal care areas, without transferring the materials into a pumpable, liquid substrate. It can be fermented biomasses with up to 50% dry matter content. This dry fermentation process is described for example in EP 0 934 998.

In the case of "dry" fermentation, the material to be fermented is not stirred into a liquid phase, as is the case, for example, with the liquid fermentation of biowaste. Instead, the fermentation substrate introduced into the fermenter is kept constantly moist by withdrawing the percolate from the fermenter bottom and re-spraying it over the biomass. This ensures optimal living conditions for the bacteria. In addition, temperature can be regulated during recirculation of the percolate, and it is possible to add additives for process optimization.

From WO 02/06439 a bioreactor or a fermenter in the form of a prefabricated garage is known, which is operated according to the principle of dry fermentation in the so-called batch process. Here, after an inoculation with already fermented material, the fermentation substrate is filled with wheel loaders in the fermenter. The garage-shaped fermentation tank is closed with a gas-tight door. The biomass is fermented under exclusion of air, there is no further mixing and it is fed to any additional material. The percolate seeping out of the fermentation material is drawn off via a drainage channel, stored temporarily in a tank and sprayed to moisten again over the fermentation substrate, the fermentation process takes place in the mesophilic temperature range 34-37 ⁰ C instead, the tempering is carried out by means of a floor and wall heating.

The resulting biogas can be used in a combined heat and power plant to generate electricity and heat. To ensure that enough biogas is always available for the combined heat and power plant, several fermentation tanks are operated at different times in the dry fermentation plant. At the end of the residence time, the fermenter room is completely emptied and then refilled. The fermented substrate is supplied to a post-composting, so that a conventional compost comparable organic fertilizer is produced.

Due to the batch mode, the individual fermenters have to be switched off from time to time. h the biogas production must be stopped, the fermented biomass must be removed from the respective fermenter and fresh biomass must be filled into the fermenter and the biogas production must be resumed When starting a fresh loaded fermenter is initially the methane content in the biogas produced so low and the shares Carbon dioxide and nitrogen are so high that immediate use of the biogas in a CHP is not possible. The addition to already running in batch mode parallel fermenters is not possible because the quality of the biogas produced in the fresh fermenter fermentator is too bad and would lead to the fact that the quality of the total gas flow would not be sufficient to in a CHP to be used. Depending on the size of the container and the type and quality of the biomass, it takes between 5 and 12 hours until the biogas produced in the freshly loaded fermenter has reached a quality which makes it possible to use it in a CHP or to add it to biogas from fermenters that have been operating for some time During this start-up phase of a freshly loaded fermenter, the produced biogas with a low methane content is therefore released directly to the atmosphere or flared at higher methane content. This means that part of the methane produced is not used - methane slippage. From patent applications DE 10 2007 024 911.1 and EP 08 156 915 4 filed by the applicant, which represent state of the art according to § 3 (2) PatG, it is known that in the case of a plurality of fermenters operated in parallel, the common biogas line is initially treated with a gas treatment. In the gas treatment plant, the methane ante! increased by filtering away nitrogen and carbon dioxide. Since the gas treatment plant is connected to the common biogas line, only the quality of the mixed biogas in the common biogas pipeline can be improved, but not the quality of the biogas produced in the individual fermenters. Consequently, it is not possible to reduce the methane slip which occurs, in particular, during the startup of freshly loaded fermenters.

From DE10047264A1 a method for the use of methanhal- tiger biogas is known, in which the biogas is split by a gas treatment facility in a partial flow with high methane content and in a partial flow with low methane content. The substream with a high methane content is fed into a gas engine as fuel and the substream with a low methane content is returned to the biogas producing process.

It is therefore an object of the present invention to provide a method for reducing methane uptake and a biogas plant using this method.

The solution of this object is achieved by the features of claims 1, 5, 6, 8, 10, 13 and 14, respectively.

When starting biogas fermenters loaded with fresh biomass, the methane content in the gas mixture escaping from the biogas fermenter increases over a period of a few hours until it is high enough for the biogas produced to be supplied to its intended use. Instead of flaring off the gas mixture with too little methane anion or emitting it directly to the environment, it is fed to a gas treatment facility. Be in the gas treatment facility Non-methane components of the gas mixture partially separated and the remaining gas mixture with a higher proportion of methane is returned as long as back to the Bϊogasfeimenter until the Methaneantei! is high enough

The dependent claims relate to advantageous embodiments of

Invention.

Further details, features and advantages of the invention are shown in the following description of exemplary embodiments with reference to the drawings:

It shows:

1 schematically shows a first embodiment of the present invention a biogas fermenter;

2 shows schematically a second embodiment of the invention with a biogas fermenter;

FIGS. 3 to 5 show different phases of starting up a biogas fermenter loaded with fresh biomass;

Fig. 6 to 14 are schematic representations of a third embodiment of the invention with a plurality of parallel operated biogas fermenters in different operating conditions.

Figure 1 shows a basic first embodiment of a biogas plant according to the present invention with a single fermenter 2, the fermenter 2 is cuboid and has approximately the construction of a final garage. Via a loading and unloading opening 4, which extends over one of the end faces of the cuboid fermenter 2, biomass 8 can be filled into the fermenter 2 by means of a wheel loader and removed again. With regard to the exact structure of the fermenter 2, reference is made to WO 02/06439. The fermenter 2 further comprises a biogas outlet 8, which is connected to the input of a gas treatment device 20. The output of the gas treatment device 20 is connected to a biogas line 12, which ends in a three-way valve 13. The three-way valve 13 is via a biogas return line 14 with a gas inlet 16 in the biogas fermenter 2 and with a Biogasverwertungs- or Biogasverarbeitungungs- device 18, z. B. a CHP, connectable. The gas inlet 16 opens into the bottom region of the biogas fermenter 2. A measuring and control device 22 is connected to a measuring sensor 32 for detecting the methane concentration at the outlet of the gas conditioning device 20 and to the three-way valve 13. Between the three-way valve 13 and the output of the gas treatment device 20 is a gas conveyor 24, for. B. arranged in the form of a blower,

By means of the gas treatment device 20, the quality of the biogas produced is increased by means of pressurized water washing, filters or membranes, in which non-methane constituents, in particular carbon dioxide, are partly separated. This increases the methane concentration in the gas mixture at the outlet of the gas treatment device 20. The separated non-methane components are discharged via an exhaust 25 to the environment.

When starting up the biogas fermenter 2 loaded with fresh biomass, the fresh biomass 6 is sprayed with percolate and there is very little biogas in the biogas fermenter 2. The gas mixture escaping from the biogas fermenter 2 via the biogas outlet 8 is treated with methane in the gas treatment device 20 concentrated. As long as the measured by the sensor 32 at the output of the gas treatment device 20 methane concentration is below the predetermined limit (C _M0 ), the three-way valve 13 is switched by the measuring and control device 22 so that the output of the gas treatment device 20 connected to the biogas return line 14 is. Thus, the biogas with insufficient methane content on the biogas return line 14 and the gas inlet 16 back into the biogas fermenter 2. Only when the methane concentration in the biogas at the output of the biogas upgrading device 20 via is the limit C _M0 , the biogas is fed via the three-way valve 13 to the CHP 18. In this way the so-called methane slip is reduced,

Hereinafter, a second embodiment of the invention will be described with reference to FIGS 2 to 4. Corresponding components are provided with identical reference numerals. With the exception of the three-way valve 13, all components of the first embodiment are also present in the second embodiment

The three-way valve is replaced in the second embodiment of the invention by an arrangement of three valves 10-1, 10-2 and 10-3. From the biogas line 12, a biogas / exhaust gas line 11 branches off after the gas delivery device 24. The valve 10-1 is arranged in the biogas line 12 in front of the CHP 18. The valve 10-2 is arranged in the biogas return line 14. The valve 10-3 is arranged in the biogas / exhaust gas line 11. The biogas / exhaust pipe 11 opens into an exhaust stack 19th

Furthermore, the fermenter 2 comprises a purge gas inlet 16 'which, in contrast to the gas inlet 16, opens in the ceiling region of the biogas fermenter 2. The purge gas inlet 16 'is connected via valves 10 with an exhaust pipe 26 or a fresh air line 28. In the exhaust pipe 26, an exhaust fan 27 is arranged, by means of which exhaust gas can be pumped into the fermenter 2. In the fresh air line 28, a fresh air blower 29 is arranged for sucking in fresh air from the environment. About the exhaust pipe 26 is carbon dioxide-containing exhaust gas as purge gas and the fresh air line 28 fresh air is fed into the fermenter 2.

The valves 10 in the exhaust pipe 26 and the fresh air line 28 are connected to the measuring and control device 22 and are opened or closed by them. The measuring and control device 22 is connected in addition to the measuring sensor 32 for methane concentration with a sensor 34 for detecting the carbon dioxide concentration and with a Meßfühier 36 for detecting the gas flow rate. Both the sensor 34 as well as the measuring sensor 36 are also arranged at the outlet of the gas treatment device 20

In FIGS. 3 to 5, different phases of the startup of the biogas fermenter 2 loaded with fresh biomass 6 are shown, with active

Lines and positions of components are shown marked wide

3 shows the first phase of the startup of the biogas fermenter 2 charged with fresh biomass 2. Be and discharge opening 4 is closed, the connection between biogas outlet 8 and exhaust gas chimney 19 via the biogas / exhaust gas line 11 is switched through. The biogas upgrading device 20 is not active in this phase and merely passes the gas mixture through. The measuring and control device 22 opens the valve 10 in the exhaust gas line 26 so that the exhaust gas containing carbon dioxide is pumped into the biogas fermenter 2 until the carbon dioxide concentration detected by the second measuring sensor 34 reaches or exceeds an upper limit value C _KDO at the outlet of the inactive gas-conditioning device 20. In addition, the methane concentration at the outlet of the inactive gas-conditioning device 20 is detected by the measuring sensor 32 reaches or exceeds the detected methane concentration a lower one

Limit value C _Mu , the gas treatment device 20 is activated, the valve 10-3 is closed and the valve 10-2 is opened, so that in the gas treatment device with respect to methane on concentrated gas mixture via the biogas return line 14 and the gas inlet 16 back into the biogas fermenter 2 becomes

This biogas recirculation is continued until the methane concentration detected by the measuring sensor 32 at the outlet of the gas treatment device 20 reaches and exceeds an upper limit value CM ₀ . The valve 10-1 is opened and the valve 10-2 is closed so that the biogas concentrated in the gas processing device is supplied to the CHP 18 - FIG. 5. The "normal" biogas production phase is reached The switching off of the biogas fermenter 2 takes place in the same way as described in the patent application EP 08 156 915.4. In this regard, EP 08 156 915.4 is incorporated by reference in its entirety

Figures 6 to 14 show a third embodiment of the present invention in which three fermenters 2-1, 2-2 and 2-3 are used in parallel to biogas production. Corresponding components are provided with the same reference numerals. In the biogas plant according to FIGS. 6 to 14, each of the three fermenters 2-1, 2-2, 2-3 is provided with a purge gas inlet 16'-1, 16'-2 and 16'-3 and with a gas inlet 16-1, Provided 16-2 and 16-3, each of which can be shut off with a valve 10. The three purge gas inlets 16 ^! -i are combined to form a common purge gas inlet 42. In the common purge gas inlet 42 opens an exhaust gas line 26 and a fresh air line 28, each of which can be shut off by a valve 10. The purge gas inlets 16-i and 16'-i can also be combined to a Spülgaseiniass - not shown.

Each of the three fermenters 2-1, 2-2, 2-3 is provided with a Biogasauslass 8-1, 8-2 and 8-3, which are each shut off with a valve 10. The individual biogas outlets 3-i are combined after the valves 10 into a common biogas line 12, which flows into a CHP 18 as a biogas consumer. Between the valves 10 and the biogas fermenter 2-i branches from the Biogasauslässen 8-i each have a partial biogas / exhaust gas line 40-1, 40-2 and 40-3 from which can be shut off by a valve 10 and after the Valves 10 are combined to form a common biogas / exhaust gas line 40. The biogas / exhaust line 40 is connected to the inlet of a gas treatment device 20, the outlet of which is connected to a gas delivery device 24. The gas delivery device 24 opens into a four-way valve 30 which is switched by means of a control device 22. The other valves 10 are actuated by the control device 22, even if this is not explicitly shown in Figures 6 to 14. After the four-way valve 30, the biogas / exhaust gas line 40 leads to an exhaust gas chimney 19. From the four-way valve 30, a biogas return line 14 branches off into the gas intakes 16-i of the individual biogas fermenters 2-i From the From the Vierwegevenfil 30 branches a Biogaszuführ- sion 38, which opens into the common biogas line 12.

An exhaust line 44 from the CHP 18 opens a second exhaust gas chimney 46, the exhaust pipe 26 is connected via a 3-way ventii 48 with the

Exhaust pipe 44 connected, d. H. the carbon dioxide-containing exhaust gas obtained in the CHP 18 is used for flushing a fermenter 2-i to be switched off. By the 3-way valve, the volume flow of the exhaust gas, which is sent to flush a fermenter 2-i via the exhaust pipe 26 and the amount of exhaust gas, which is discharged via the second exhaust stack 48 to the environment, can be controlled.

A first measuring sensor 32 is arranged to detect the methane concentration in the common biogas line 12. A second measuring sensor 34 for detecting the carbon dioxide concentration, a third Iviessfühler 36 for detecting the flow rate and fourth sensor 50 for detecting the methane concentration is arranged in the common biogas / exhaust gas line 40 in the flow direction after the gas treatment device 20 and after the blower 24. The four probes 32, 34, 36 and 50 are connected to a control device 22. For clarity, these control lines are not shown in Figures 6 to 14.

The valve 10 in the Abgasieitung 26 can be omitted, since its function can also be taken over by the 3-way valve 48.

FIGS. 6 to 14 show different phases for switching off and restarting the second fermenter 2-2. The biogas production of the first and third fermenters 2-1 and 2-3 continues to run during shutdown and restart of the second fermenter 2-2.

First phase start - Fig. 6:

6 shows the first phase of switching off the fermenter 2-2 in the exhaust gas containing carbon dioxide from the CHP 18 via the 3-way valve 48 and the exhaust pipe 26, the exhaust fan 27 and the second flushing The second Bϊogasausiass 8-2 is still connected to the common biogas line 12, so that the biogas / exhaust gas mixture is further supplied to the CHP 18,

Second phase shutdown - Fig, 7;

Only when the detected by the first sensor 32 in the common biogas line 12 methane concentration has dropped below an upper limit C-MO, the valve 10 is closed in the second Biogasausiass 8-2 by the controller 22 and the valve 10 in the second partial biogas / Exhaust line 40-2 is opened as shown in Fig. 7. The biogas / exhaust gas mixture is concentrated in the gas treatment device 20 with respect to methane and fed via the four-way valve 30 and the biogas supply 38 of the common biogas line 12, as long as the fifth sensor 50 at the output of the gas treatment device methane concentration is above the upper limit C _M0 , In this second phase of switching off the fermenter 2-2, the carbon dioxide-containing exhaust gas is partly removed from the biogas / exhaust gas mixture in the partial biogas / exhaust gas line 40-2 and the remaining biogas / exhaust gas mixture in the gas treatment device 20 sufficient methane concentration is supplied to the BHKVV 18 together with the biogas from the biogas fermenters 2- 1 and 2-3.

Third Phase Shutdown - FIG. 8: When the methane concentration detected by the fourth probe 50 in the common biogas / exhaust gas line 40 after the gas treatment device 20 has dropped below the upper limit C _M0 , the four-way valve 30 connects the common biogas / exhaust gas line 40 with the Biogasrückführleitung 14 and the biogas / exhaust gas mixture is in the other two Biogasfermenter 2-1 and 2-3 via the gas inlets 16-1 and

This third phase of switching off is carried out until the methane concentration detected by the first measuring sensor 32 drops below the upper limit value C _Mo or that by the fourth measuring sensor 50 in the common biogas / waste gas line 40 recognized Methane concentration falls below the lower limit C- _MU , whichever comes first

Turn off the fourth phase - Fig. 9; When the methane concentration detected by the first sensor 32 has dropped below the upper limit C _M0 or when the methane concentration detected by the fourth sensor 50 at the output of the gas processor 20 in the common biogas / exhaust gas line 40 has dropped below the lower limit C _MU , whichever occurs earlier, the valve 10 is closed in the exhaust pipe 26 and the valve 10 in the fresh air line 29 is opened by the control device 22. The controller 22 connects by means of Vierwegeventi! 30, the common biogas / exhaust gas line 40 with the first exhaust stack 19 and the gas treatment device 20 is deactivated. The biogas / exhaust gas / air mixture with a very low methane content is discharged via the first exhaust stack 19 directly to the environment. This fourth phase of the shutdown is carried out until the detected by the second sensor 34 in the common biogas line 40 carbon dioxide concentration has dropped below a lower limit C _KDU .

Fifth Phase Shutdown or Discharge - Fig. 10: When the detected by the second sensor 34 in the common biogas / exhaust gas line 40 carbon dioxide concentration has dropped below the lower C _KDU limit, the valve 10 in the fresh air line 28 by the controller 22nd closed and the Frischluftgeb! Äse 29 off, as shown in Fig. 10. The loading and unloading opening, not shown in FIGS. 6 to 14, is opened. At the same time fresh air is sucked in via the open loading and unloading opening via the fan 24 into the common biogas / exhaust gas line 40 and discharged via the exhaust gas chimney 19 to the environment. In this way, it is prevented that residual bogens still contained in the fermented biomass pose a danger to the operating personnel during unloading. Also exhaust gases of a wheel loader used for loading and unloading are thus sucked First phase start - Fig. 11:

If the fermenter 2-2 again loaded with fresh biomass, the loading and unloading is closed, the connection between the second biogas outlet 8-2 and exhaust stack 19 via the second Teü-biogas / flue line 40-2 and the common biogas Exhaust line 40 to the first exhaust stack 19 is maintained and the control device 22 opens the valve 10 in the Abgasieitung 26 and switches the 3-way valve 48 in the exhaust pipe 44 of the CHP 18, so the carbon dioxide-containing exhaust gas in the fermenter. 2 -2 is pumped. The Gasaufbereitungseϊnrichtung 20 is not active. This first phase of restarting the biogas fermenter 2 is continued until the detected by the fourth probe 50 methane concentration in the common biogas / exhaust gas line 40 reaches the lower limit C _Mu .

Second phase start - Fig. 12:

If this lower limit value C _{Mu is} reached, the supply of exhaust gas via the exhaust gas line 26 is stopped, the gas conditioning device 20 is activated and the common biogas / exhaust line 40 is connected via the four-way valve 30 and the control device 22 to the biogas recirculation line 14. The biogas / waste gas mixture concentrated in the gas treatment device 20 is returned via the biogas recycling line 14 to the biogas fermenter 2 to be approached. This second phase of the startup is maintained until the methane concentration detected by the fourth sensor 50 at the outlet of the gas treatment device 20 reaches the upper limit value C _Mo.

Third phase start - Fig. 13:

If the methane concentration detected by the fourth measuring sensor 50 reaches the upper limit value CM ₀ , the common biogas / waste gas line 40 is connected to the biogas feed line 38 by means of the control device 22 and the four-way valve 30. In addition, the partial biogas / waste gas lines 40-1 and 40-3 are also connected to the common biogas / waste gas line 40, so that the biogas from all biogas fermenters 2-i is now concentrated in the gas treatment device 20. Normal operation - Fig. 14:

If the difference of the methane concentration after the fourth measuring sensor 50 and the first measuring sensor 52 of the gas treatment device 20 drops below the predetermined limit value C _M3 , the normal operation of the biogas plant is reached, ie the biogas produced in all the biogas fermenters 2-i is transferred via the Biogas outlets 8-i supplied directly to the common biogas line 12 and the gas processing device 20 is deactivated.

Instead of the normal operation of Fig. 14, the circuit of FIG. 13 can be maintained as normal operation. As a further alternative, in the normal operation according to FIG. 13, a further gas conditioning device (not shown) may be provided, which would be arranged directly in front of the CHP 18. Through the gas treatment facilities, the quality of the biogas produced is raised to the quality level of natural gas by means of pressurized water washing, filters or membranes, i. H. In particular, the proportion of methane is increased and the carbon dioxide content is reduced.

The following are examples of numerical values for the various limits:

Methane concentration- upper limit C _M0 30% to 50% lower limit C _Mu 0% to 3% Limit C _M3 0% to 1%

Carbon dioxide concentration: lower limit C _KDU 0.5% to 2% upper limit C _KDO 5% to 15%

Depending on the size of the fermenters and the amount of available exhaust gas, the exhaust gas volume flow in the exhaust pipe 26 is between 150 and 1000 m ³ / h. The fresh air volume flow in the fresh air line 28 is between 1000 and 5000 m ³ / h, LIST OF REFERENCE NUMBERS

2 fermenters

4 loading and unloading

6 biomass

8 biogas outlet

10 valve

11 biogas / flue gas line

12 biogas line

13 three-way valve

14 Biogas return line

16 gas inlet

16 'Spülgaseiniass

18 biogas utilization or biogas processing facility

19 exhaust stack

20 gas conditioning device

22 measuring and control device

24 gas conveyor

25 exhaust

26 exhaust pipe

27 exhaust fan

28 Fresh air line

29 fresh air freshener

30 four-way valve

32 sensors for methane concentration

34 sensors for carbon dioxide concentration

36 sensors for volume flow

38 biogas supply line

40 joint biogas / flue gas line

40-1 first part biogas / exhaust pipe

40-2 second Teii biogas / flue gas line

40-3 third part Bϊogas / exhaust pipe

42 common Spülgaseiniass

44 exhaust pipe second exhaust stack 3 ~ way valve fourth measuring sensor (methane concentration) fifth measuring sensor (methane concentration)

Claims

claims

1. A method for reducing methane slip when starting Bϊogasfermentern (2) by the following process steps: a) feeding the biogas produced in a freshly loaded biogas fermenter (2) to a gas treatment device (20), b) increasing the Methananteiis in the biogas by partial separation of non-methane constituents in the biogas in the gas treatment facility (20), c) measuring the methane concentration in the treated biogas, and d) returning the treated biogas to the biogas digester (2) if the measured methane concentration is below a predetermined limit (CM ₀ ) is located.

2. The method according to claim 1, characterized in that the biogas from the biogas upgrading device (20) is supplied to a Biogasverwer- processing device (18), if the measured in step c) methane concentration has reached the predetermined limit value (CM ₀ ).

3. The method according to claim 2, wherein the predetermined limit value (CM ₀ ) for the methane concentration measured in step c) is in the range between 15% and 50%, preferably between 30% and 50% and in particular in the range between 40% and 50 % lies.

4. The method according to any one of the preceding claims, characterized in that a plurality of Bϊogasfermentern (2-1, 2-2, 2- 3) are operated in parallel.

5. biogas plant for carrying out the method according to any one of the preceding claims, with at least one operating on the principle of dry fermentation fermenter (2) for the production of biogas in batch operation with a Biogasausiass (8) and a Gaseiniass (16); a gas processing device (20), the input side with the Biogasauslass (8) of the biogas fermenter (2) is connected, and having a Biogasauslass, a gas return line (14) via a valve means (13) with the biogas outlet of the gas treatment device (8) is connected 5 bar and with the Gasemlass (18 ) of the biogas fermenter (2), a measuring and control device (14) for detecting the methane concentration sm biogas outlet of the gas treatment device (20) and connection of the gas return line (14) with the biogas outlet j 0 of the gas treatment device (20), as long as the Methane concentration in the biogas outlet of the gas treatment device (20) is below a predetermined limit (CM ₀ )

6. A method for reducing methane slip when starting 15 Biogasfermentern by the following process steps: a) closing the biogas fermenter loaded with fresh biomass

(2), b) winding the closed biogas fermenter (2) with carbon dioxide-containing exhaust gas until the carbon dioxide concentration in the biogas fermenter

20 ter (2) has reached a predetermined upper limit value (C _K D _O), c) terminating the supply of exhaust gas in the biogas fermenter (2) and supplying the gas mixture from the biogas fermenter (2) to a gas preparation device (20) when the upper limit for carbon dioxide concentration (C « _DO ) is exceeded,

25 d) increasing the vapor content in the gas mixture by partial

Separation of non-methane constituents in the gas treatment device (20), e) measurement of the methane concentration in the treated gas mixture, 0 f) recycling of the treated gas mixture into the biogas fermenter (2), if the methane concentration measured in step e) falls below a predetermined upper limit ( C _Mo ), and g) supplying the gas mixture to a biogas processing unit (18) if the methane concentration measured in step e) is above the upper limit (C _M0 ).

7 ^' . A method according to claim 6, characterized in that a

Majority of biogas fermenters (2-1, 2-2, 2-3) are operated in parallel,

C

8. biogas plant for carrying out the method according to claim 6 or 7, with at least one operating on the principle of dry fermentation fermenter (2) for the production of biogas in batch mode with0 a biogas outlet (8) and a gas inlet (16, 16 ^! ); a gas treatment device (20) which is connected on the input side to the biogas outlet (8) of the biogas fermenter (2) and which has a biogas outlet, an analyzer (32) for detecting the methane concentration 5 in the outlet of the gas treatment device (20), a gas return line (14 ), which is connectable to the biogas outlet of the gas treatment device (20) and connected to the gas inlet (16, 16 ') of the biogas fermenter (2), a purge gas supply (26, 27) for exhaust gas containing carbon dioxide, an exhaust stack (19) via a biogas / exhaust gas line (1 1) can be connected to the outlet of the gas treatment device (20), a control device (22) which is connected to the measuring device (32), for connecting the gas inlet (16, 16 ') of the biogas fermenter ( 2) with the purge gas supply (26, 27) or the biogas outlet of the gas treatment device (20), for connecting the biogas outlet (8) of the biogas fermenter (2) with the exhaust gas chimney (19), as long as the methane concentration in the biogas outlet of the gas treatment device (20) or in the biogas outlet (8) of the biogas fermenter below a predetermined lower limit (C _Mu ), and the connection of the gas return line (14) with the biogas outlet of the gas treatment device (20), as long as Methane concentration in the biogas outlet of the gas treatment facility (20) above the lower limit (CM _U ) and below an upper limit (CM ₀ ).

9. biogas plant according to claim 8, characterized by a fresh air supply (26, 27) by means of the control device (22) with the

Gas inlet (16, 16 ') of the biogas fermenter (2) is connectable.

10. biogas plant for the production of biogas with a plurality of biogas fermenters (2) operating on the principle of dry fermentation for the production of biogas in the batch

Operation, each comprising a biogas outlet (8-i) and a purge gas inlet (16'-i); a biogas line (12) into which the biogas outlets (8-i) of the individual biogas fermenters (2-i) open; an exhaust pipe (26) by means of the carbon dioxide-containing exhaust gas

SpuSgaseinlässen (16'-i) of the individual biogas fermenter (2-i) can be fed; a gas treatment device (20) which is connectable to the biogas outlets (8-i) of the individual biogas fermenters; a valve device (30) which is connected to the outlet of the gas treatment device (20) of a biogas supply line (38) which is connected to the common biogas line (12) and the Ventϊleinrichtung (30); a biogas return line (14) connected to the valve means (30) and to the purge gas inlets (16-i) of the individual ones

Biogas fermenter (2-i) is connectable; an exhaust stack (19) connected to the valve means via a biogas / exhaust conduit (40); a Frischluftieitung (28) which is connectable to the Spülgaseinlässen (16'-i) of the individual biogas fermenter (2-i); a control device (22) for connecting the individual biogas outlets (8-i) to the common biogas line (12) or to the inlet of the gas treatment device (20) and for connecting the individual purge gas ϊouts (16'-i) to the exhaust gas Line (28) or fresh-air line (28); and a measuring device (32, 34, 36, 50, 52), which is connected to the control device (22) and sensor (32, 50, 52) for detecting the methane concentration and sensor (34) for detecting the carbon dioxide in the from the at least one fermenter (2) exiting gas mixture.

11 biogas plant according to claim 10, characterized in that the measuring device (32) for detecting the methane concentration in the common biogas line (12) is arranged.

12, biogas plant according to claim 10 or 11, characterized in that the measuring device (50) for detecting the methane concentration between the valve device (30) and gas treatment device (20) is arranged

13. A method for reducing methane slip when starting from one of a plurality of biogas fermenters in a biogas plant according to one of the preceding claims 10 to 12 with the method steps: a) closing the biogas fermenter loaded with fresh biomass (2-2), b) rinsing the closed biogas fermenter (2-2) with carbon dioxide-containing exhaust gas via the exhaust pipe (26) and the gas inlet (16'-2) of the biogas fermenter to be approached (2-2) until the carbon dioxide concentration in the biogas fermenter (xi) a upper limit value (C _KDO ) and / or until the methane concentration in the biogas fermenter (2-2) has reached a lower limit value (CM _U ), c) feeding the gas mixture from the biogas fermenter (2-2) to be approached to the gas processing device ( 20) when the upper limit (C _K D _O ) for the carbon dioxide concentration and / or the lower limit for the methane concentration (CM _U ) is exceeded. d) Increasing the methane content in the gas mixture by partial removal of non-methane constituents in the gas treatment unit (20) ₁ e) measurement of the methane concentration in the treated gas mixture by means of the measuring device (50), f) recycling of the treated gas mixture into the Bϊogasfermenter (2-2) to be approached if the methane concentration measured in step e) falls below a predetermined upper limit value (C _Mo ) and g) supplying the treated gas mixture via the biogas feed line (38) into the common biogas line (12) if the methane concentration measured in step e) is above the upper limit (C _M0 ).

14. A method for reducing methane slip when switching off one of a plurality of biogas fermenters in a biogas plant according to one of the preceding claims 10 to 12 with the method steps: a) connecting the biogas outlet (8-2) of the biogas fermenter to be switched off (2 -2) with the input of the gas treatment device; b) connecting the exhaust pipe (26) to the gas inlet (16'-2) of the Bϊogasfermenters (2-2) to be switched off; c) connecting the Biogaszuführleitung (38) with the output of the gas treatment device (20) via the valve means (30); d) supplying exhaust gas in the biogas fermenter (2- 2) to be shut off via the exhaust pipe (26) until the methane concentration detected by the measuring device (50) at the outlet of the gas treatment device (20) has dropped to a predetermined upper limit (C _M0 ); e) separating the biogas feed line (38) from the outlet of the gas treatment device (20); f) connecting the biogas return line (14) with the biogas / exhaust gas

Conduit (40) through the valve means (30); g) connecting the biogas recirculation line (14) to the purge gas inlets (16-1, 16-3) of the other still biogas-producing biogas fermenters (2-1, 2-3), h) recirculating exhaust gas into the biogas fermenter menter (2-2) until the methane concentration in the biogas / Äbgas- line (40) has dropped to a lower limit (C _M11 ) or until the methane concentration in the common biogas line (12) to the upper limit (C _M0 ) dropped is; i) separating the exhaust gas line (26) from the purge gas line (16'-2) of the biogas fermenter (2-2) to be switched off; j) separating the biogas return line (14) from the biogas / exhaust line (40) and connecting the Bϊogas / exhaust line (40) with the exhaust stack (19), k) connecting the fresh air line (28) to the gas inlet (16 '; -2) of the biogas fermenter (2-2) to be switched off and supply of fresh air into the biogas fermenter (2-2) to be switched off until the carbon dioxide concentration detected by the measuring device (34) in the biogas fermenter (2-2) to be switched off reaches a predetermined lower limit ( C _KDU ) has dropped, and

I) Opening the switched-off biogas fermenter (2-2)