DE102009050867A1 - Producing biogas by dry fermentation, useful for aerating the fermenter, comprises aerating the fermenter with the biogas or the combustion product of the biogas - Google Patents

Abstract

Producing biogas by dry fermentation, comprises aerating the fermenter with the biogas or the combustion product of the biogas. An independent claim is also included for a biogas plant for producing the biogas by dry fermentation, comprising a device for recirculating the biogas from the fermenter or a biogas storage tank, into the fermenter, and/or a device for recirculating the biogas combustion product from a combustion motor into the fermenter.

Description

FIELD OF THE INVENTION

The present invention relates to the field of biogas production and, more particularly, to dry fermentation for producing biogas.

The term "biogas" refers to flammable gas mixtures that are produced by the anaerobic decomposition of biomass naturally or in biogas plants. Anaerobic degradation of biomass, also referred to as fermentation or digestion, results in a water-saturated gas mixture containing 55-75% methane and 24-44% carbon dioxide as main constituents. In traces of nitrogen, oxygen, hydrogen sulfide, hydrogen and ammonia may be included in the gas mixture.

TECHNICAL BACKGROUND OF THE INVENTION

Biogas is mainly used to generate energy. The most widespread in Germany is the combustion of biogas produced in biogas plants after appropriate treatment in combined heat and power plants. Here, a biogas-powered engine or a biogas-powered turbine drives the generator of the combined heat and power plant, which produces electricity. At the same time the waste heat of the combined heat and power plant is used.

For the utilization of biogas, the proportion of methane is the most important, because the methane as an oxidizable compound releases energy during its combustion. The carbon dioxide and the water vapor are not usable. Hydrogen sulfide and ammonia are removed during the treatment of the raw biogas before combustion, as they would lead to corrosion in engines.

In the production of biogas, a distinction is made between wet fermentation and dry fermentation.

The content of dry matter in the substrate to be fermented in wet fermentation is less than 15% and the water content is over 85%. The method of wet fermentation is applicable to liquid substrates and only to solid substrates which have been diluted to the corresponding dry matter content. For wet fermentation, the pumpability of the substrate is an essential prerequisite.

Due to the high liquid content, a good mixing of the substrate with the fermenting microorganisms and a good nutrient and energy exchange between the microorganisms and the substrate succeeds. Gas formed in the fermentation can leave the liquid almost unhindered and be discharged for further use.

Due to the comparatively low dry matter content of the substrates for the wet fermentation, comparatively large reactor volumes are necessary in order to ensure sufficient residence times and degrees of degradation. Thus, the average residence time of the substrate in a wet fermenter is about 50 days.

Another disadvantage of the wet fermentation process is that 20% or more of the electricity that can be generated with the aid of the biogas obtained is needed to operate the pumps and agitators of the biogas plant.

In contrast to wet fermentation, the dry fermentation process is suitable for substrates with a high solids content, so that they are stackable. The content of dry matter in the substrate to be fermented in the dry fermentation is usually over 90%. In dry fermentation, the moist medium required for fermentation is produced by percolation of the substrate with process water, preferably with conditioned process water (process liquid), in a controlled cycle.

For dry fermentation, stackable substrate, for example so-called "biowaste", organic raw materials, corn silage, fats and the like are stored in a dry-sealable, dry-fermenter. The feed of the dry fermenter is preferably carried out with a wheel loader or spreader.

After filling, the dry fermenter is hermetically sealed and aerated on the bottom side in order to loosen the stored dry substrate, so that the process liquid, which is sprayed from the fermenter cover, can penetrate deep into the embedded drying substrate. This aeration takes place abruptly or suddenly, preferably via fluidizing lances which can be driven over into the fermenter bottom, which are also referred to as air lances or sword nozzles. In this shock ventilation, air is suddenly blown into the stored dry substrate at up to 15 bar air pressure. As a result, the drying substrate is loosened in such a way that capillaries or channels form in the substrate. This process step is also referred to as pre-aeration.

In the subsequent start-up phase of the dry fermentation, the aeration of the dry substrate is stopped and the percolation of the Dry substrate with process fluid begins to initiate fermentation and biogas production.

In the subsequent fermentation phase, after the required biogas quality has been achieved in the dry fermenter, the resulting biogas is discharged into a biogas storage facility. During the methanogenic fermentation phase, biogas production in the dry fermenter goes through a maximum and then decays slowly.

In the fermentation phase, the substrate is stored immobile in the dry fermenter and is fermented by the addition of water or process liquid. This forms a layer on the substrate, which is poorly permeable to liquid. Therefore, the substrate must be periodically loosened again in the approximately 20-day fermentation phase by a corresponding surge ventilation, so that the forming on the surface of the substrate and liquid is poorly transmitting layer broken. Due to the channels formed by the impact ventilation in the substrate, process liquid can again penetrate into the substrate and continue the fermentation process.

The fermentation phase is followed by a decay phase during which the anaerobic fermentation process is terminated by terminating the percolation of the drying substrate, allowing the substrate to drain for dewatering and venting the fermentor to degas the substrate. For reasons of safety, the ventilation in the decay phase preferably takes place in two stages. The two-stage ventilation consists of a continuous ventilation, which is combined with a surge ventilation.

Usually, a fermentation cycle of the batch fermentation dry fermentation in biogas plants for decentralized power supply with a power of about 0.5 MW to 1 MW takes 20 to 21 days.

The advantages of dry fermentation compared to wet fermentation are that stackable substrate can be used to produce biogas, the average residence time of the substrate in the fermenter is much shorter, the electrical energy required to operate the plant less than 2% of producible with biogas production electric Energy is high, the yield of biogas is high and the substrate residues can be spent on fields regardless of the season and the weather as a high quality fertilizer almost odorless.

A disadvantage of dry fermentation, however, is seen in the loosening of the drying substrate required for biogas production. The gas evolution in the dry fermenter shows a wave-like course. The initially good evolution of gas decreases after some time, increases after shock ventilation and further percolation again. The loosening of the dry substrate is effected by shock ventilation, in which air flows through the drying substrate at a pressure of up to 15 bar. However, the impact ventilation with air dilutes the methane produced in the fermentation phase. In addition, air contains a high level of oxygen which impairs the anaerobic fermentation required for biogas production, thus delaying the progress of biogas production and reducing the efficiency of biogas production.

After the biogas production has ended, the fermented substrate must be removed again from the fermenter. To ensure that the fermenter can be opened safely, a residence time of 2 to 3 days must be observed. If during this time the gradually decreasing gas production is vented with air, the already smaller amount of biogas in the fermenter is further diluted and then no longer suffices for combustion. The non-usable residual biogas is the sludge that is harmful to the environment and must be disposed of at a cost.

PRESENTATION OF THE INVENTION

The present invention therefore an object of the invention to provide a more efficient method for the production of biogas, in which the quality of the biogas produced and the efficiency of biogas production by the loosening of the dry substrate during the methanogenic fermentation phase is not affected and that also a use of still in The decay phase resulting, ever lower biogas volume allows.

The object is achieved in that the loosening of the dry substrate is not done with air, but is fumigated with biogas or the combustion product of the biogas, and / or the fermenter in the decay phase with the combustion product of biogas and / or biogas. According to the invention, even at a dry matter content of 50%, still usable economic methane yields can be achieved.

In a preferred method biogas is used for the fumigation in the pre-aeration phase and in the fermentation phase. By using biogas, the anaerobic fermentation process is started faster and the resulting biogas is not diluted.

In a preferred method, the biogas is used for fumigation, preferably previously in a fermentation process Biogas plant was generated. Since in the biogas plants for which the method according to the invention is particularly suitable, several dry fermenters are operated with a time delay, at any time sufficient biogas for the shock fumigation available.

But it is also possible to use the combustion product of biogas for the loosening of the dry substrate. Also, by using the combustion product of biogas, the anaerobic fermentation conditions for producing biogas in the start-up phase can be achieved faster than in the known surge ventilation. During the fermentation phase, although the methane content of the biogas decreases when the substrate with its combustion product is loosened, but the anaerobic fermentation conditions are not affected, since no oxygen is injected into the fermenter.

The combustion product of the biogas is preferably the exhaust gas of a combustion engine operated with biogas, particularly preferably the exhaust gas of the engine or the turbine of a combined heat and power plant, which is operated with the biogas from the dry fermentation.

The gassing of the fermenter takes place during the "pre-venting phase" and during the fermentation phase intermittently by the biogas or the combustion product of the biogas at high pressure (approximately between 8 and 15 bar) is blown from below into the drying substrate.

The inventive method for producing biogas by dry fermentation also includes embodiments in which the substrate is fumigated during the decay phase with the combustion product of biogas. As a result, the phase in which the biogas produced can be used can be extended considerably. Despite the decreasing biogas production in the fermenter, the biogas can be used, which would have to be disposed of if aerated with air.

By fumigating the fermenter in the decay phase with the combustion product of biogas, the proportion of usable biogas can be increased. This reduces the costs of disposing of non-usable biogas. In addition, the period for the spewing of unusable methane is reduced.

The present invention thus also encompasses the use of biogas and / or the combustion product of biogas for the fumigation of a fermenter for the production of biogas by the dry fermentation process.

The present invention also extends to biogas plants with which the method according to the invention can be carried out. The biogas plants according to the invention have a device for returning the biogas from the fermenter or a biogas storage in the fermenter and / or a device for recycling the combustion product of the biogas, for example, the exhaust gas of an engine or a turbine for operating a downstream combined heat and power plant.

The biogas plant comprises at least one gas-tight sealable fermenter with nozzles arranged in the bottom for introducing gas into the fermenter, a reservoir for biogas and optionally a percolate storage for the process liquid.

Preferred biogas plants, which are particularly well suited for carrying out the method according to the invention, have 4 to 16 dry fermenters with a capacity of about 400 m ³ each. Dry fermenters of this kind can be constructed, for example, in the form of garage-type concrete fermenters with dimensions of 20 × 4 × 5 m (L × W × H), which have gas-tightly closable doors or gates. Such biogas plants are generally used for decentralized power supply and can operate combined heat and power plants with an electrical power of about 0.5 MW to 1 MW.

The individual fermenters have air lances or sword nozzles which can be driven over at the bottom, via which biogas or the combustion product of biogas can be blown under pressure into the fermenter in accordance with the method according to the invention. The dry fermenters are connected via a device for returning gas to the biogas storage of the biogas plant and / or the outlet for exhaust gas of an internal combustion engine operated with the biogas. In addition to or instead of the connection to the biogas storage, the recirculation of the biogas can also take place from the ceiling of the fermenter.

The blowers and compressors suitable for the return of the biogas or its combustion product and subsequent fumigation of the fermenter are commercially available.

The above-mentioned and the claimed and described in the embodiments described components to be used in their size, shape design, choice of materials and technical design no special conditions of exception, so that the well-known in the field of application selection criteria can apply fully apply further details, features and advantages of the subject matter of The invention will become apparent from the dependent claims, as well as from the following description and the accompanying drawings, in which - by way of example - an embodiment of a biogas plant is shown. Also, individual features of the claims or of the embodiments may be combined with other features of other claims and embodiments.

BRIEF DESCRIPTION OF THE FIGURES

In the drawing show:

1 a block diagram illustrating the control lines and line connections of individual components of a biogas plant comprising eight dry fermenters;

2A a survey of the soils of the eight dry fermenters (TF I to TF VIII) and the arrangement of sword nozzles at the bottom of the dry fermenter;

2 B a gas supply unit for the jet nozzles of several dry fermenters located above the fermenter covers according to view "A" - "A" of 2A ;

3A from the biogas plant to 1 and 2A a sword nozzle in an enlarged view from above (fragmentary);

3B from the sword nozzle 3A a cross section along the line

3C from the sword nozzle 3A and 4A an end view "E";

3D from the sword nozzle 3A a cross section along the line "F" - "F".

3E from the sword nozzle 3A a cross section along the line "G" - "G";

4A the bottom of a dry fermenter 2A in supervision;

4B from one of the sword nozzles 4A a vertical sectional view along the line "H" - "H".

4C from one of the sword nozzles 2A and 4A a connection area in supervision (detail "Z");

4D from the connection area 4C a frontal sectional view

5 from the dry fermenter 4A a vertical sectional view taken along the line "J" - "J" and

6 from the dry fermenter 4A a vertical sectional view along the line "K" - "K".

DETAILED DESCRIPTION OF EMBODIMENTS

As can be seen from the figures, in the dry fermenters TF I to VIII of the biogas plants according to the invention are sword nozzles 14 arranged in a gutter in the screed, so that the upper edge of the screed is slightly higher than the sword nozzles 14 and these are sunk in the longitudinal direction completely in the bottom of the fermenter ( 2A . 4A / B / D and). As a result, the sword nozzles are mounted overrun.

The sword nozzles 14 are preferably arranged in pairs in each fermenter such that their distal ends face the opposite ends of the fermenter. The longitudinal direction of the Schwertdüsen runs in the longitudinal direction of the fermenter, preferably, the center line of the Schwertdüsen runs along the center line of the fermenter, so that the Schwertdüsen divide the fermenter in longitudinal extension in two halves.

In a preferred fermenter length of about 20 meters, the two arranged therein Schwertdüsen preferably have a length of 9 meters each.

The sword nozzles preferably have a triangular cross-section, particularly preferably in the form of an isosceles triangle and very particularly preferably in the form of an isosceles triangle with a roof inclination angle of 45 °. However, sword nozzles with a different cross section, for example a semicircular cross section, can also be used. Usually, the sword nozzles are made of sheet steel, particularly preferably sheet of stainless steel, wherein the sheet metal roof of the sword nozzle is welded to a bottom plate ( 3B to 3E ).

In the preferred embodiment, the sword nozzles have a cross-section tapering from their proximal end to the distal end.

The sword nozzles 14 are attached via their bottom plate to the bottom of the dry fermenter, preferably in a gutter in the ground. The sword nozzles for dry fermenters according to the invention have, in contrast to sword nozzles, as for example from the patent DE 37 17 216 C2 are known, no lateral openings between their roof and their bottom. The vents for the ventilation or fumigation of the dry fermenter are rather with openings in their roof provided so that the Stoßbegasung can take place in the overlying substrate. In this case, the openings, for example in the form of slots or holes, are arranged on both sides along the center line of the sword nozzle.

In the particularly preferred embodiment, the outlet openings are mutually arranged, which means that the outlet openings are arranged on one side of the sword nozzle in the region of the spaces between the outlet openings on the opposite side of the sword nozzle.

Through different outlet cross-sections of the openings sword nozzles can be provided for different intensities of a Stoßbegasung. By varying the outlet cross-sections of the openings of a sword nozzle, it can be achieved that the gas exits are relatively uniform along the sword nozzle. The sum of the Ausbasquerschnitte preferably corresponds to the area of the inlet cross-section.

How out 1 can be seen, sword nozzles 14 via a large-volume pressure vessel 1 charged with biogas or its combustion exhaust gas. The pressure switch 2 and 3 Check the tank internal pressure via a pressure gauge 32 also separately readable. Directly at the pressure vessel 1 fluidly connected are so-called boosters 4 , which makes a sudden gas delivery to the Schwertdüsen 14 allow which pairs of each booster with the interposition of a tee 8th and a switchable butterfly valve 7 for each a dry fermenter fluidly downstream. By means of a magnetic valve cabinet 21 and terminal box 22 can the boosters 4 and butterfly valves 7 the sword nozzles 14 optionally controlled.

In the illustrated and in so far preferred embodiment extend as shown 1 . 2A and 2 B apparent, two pressure vessels 1 the gas supply units for the jet nozzles 14 the dry fermenter above the fermenter cover approximately centrally across the width of several dry fermenters TF I to IV and TF V to VIII.

How best 4A . 5 and 6 can be seen, lead the supply pipes 12 to the sword nozzles 14 along the fermenter side walls from the top to the bottom of the fermenter and there to the sword nozzles 14 in the area of the gutters 34 subsequent pipe bends 12A ,

The side walls of the fermenters are provided with perforated plates arranged at a distance from the fixed walls, in order to permit lateral outflow of the percolate water.

The released from the fermenters TFI to TFVIII biofuels are withdrawn via individual tubes, not shown, and a manifold and the side channel compressor 24 fed.

To charge the pressure vessel 1 with biogas or its combustion exhaust gas is on the one hand at least one, preferably constructed as a radial compressor; Side channel blower 24 via a controllable butterfly valve 6 with the filling nozzle 18 of the pressure vessel 1 with the interposition of a vibration compensator 10 connected in a pressure-limited manner. The side channel blower 24 used to selectively fumigate the biomass in the dry fermenter with biogas or its combustion exhaust gas at high flow, from z. B. 1000 m ³ / h, and only a slight overpressure of z. B. 300 mbar during at least one of, preferably all, process phases. On the other hand, the pressure vessel 1 with biogas or its combustion exhaust gas optionally via a compressor 23 to an overpressure of z. B. 15 bar charged to perform during at least one of, preferably all, process phases Stoßbegasungen the biomass at certain intervals. The pressure switch 2 . 3 and valves 27 . 28 allow you to switch back and forth between these two operating phases.

LIST OF REFERENCE NUMBERS

1

pressure vessel

2

pressure switch

3

pressure switch

4

booster

5

Tee

6

butterfly valve

x

5/2-way solenoid valve

7

butterfly valve

x

3/2-way solenoid valve

8th

Tee

9

Rubber compensator

10

Rubber compensator

11

Pressure relief valve

12

pipe

12A

elbow

14

sword nozzles

15

flange

16

cover

17

Schlagdüse

18

pipe

19

retaining bracket

20

retaining bracket

21

Solenoid valve cabinet

22

terminal box

23

compressor

24

fan

25

air line

26

air line

27

2/2-way Angle slit valve

28

2/2-way Angle slit valve

29

polyamide hose

30

Protective armor tube

31

Cable from solenoid valve

32

Pressure gauge 0

33

silencer

34

floor channels

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 3717216 C2 [0057]

Claims (8)

Process for the production of biogas by dry fermentation, characterized by a fumigation of the fermenter with biogas or the combustion product of the biogas. A method according to claim 1, characterized in that the gassing of the fermenter takes place as shock gassing during the pre-gassing phase and / or the fermentation phase. A method according to claim 1 or 2, characterized in that the fumigation takes place during the decay phase with the combustion product of the biogas. A method according to claim 3, characterized in that the gassing is effected by a combination of continuous gassing and shock gassing. Method according to one of the preceding claims, characterized in that the biogas or the combustion product of biogas is blown in the collision fumigation at a pressure of 8 to 15 bar in the fermenter. Use of biogas or the combustion product of biogas for fumigation of the fermenter in the production of biogas by dry fermentation. Use according to claim 6, characterized in that the fumigation takes place in the form of a shock fumigation in which the biogas or its combustion product is injected at a pressure of 8 to 15 bar in the fermenter. Biogas plant for the production of biogas by dry fermentation, characterized by a device for returning the biogas from the fermenter or a biogas storage in the fermenter, and / or a device for returning the combustion product of biogas from an internal combustion engine in the fermenter.

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