WO2012152266A2

WO2012152266A2 - Process for producing biogas from predominantly animal excrements

Info

Publication number: WO2012152266A2
Application number: PCT/DE2012/100124
Authority: WO
Inventors: Lothar Günther
Original assignee: Dge Dr.-Ing. Günther Engineering Gmbh
Priority date: 2011-05-10
Filing date: 2012-05-04
Publication date: 2012-11-15
Also published as: WO2012152266A3; DE102011108462A1; EP2707491A2

Abstract

The invention relates to a process for producing biogas from predominantly animal excrements, in particular liquid manure or chicken manure, individually or as a mixture. Proceeding from the disadvantages of the prior art, a process is to be provided which is distinguished by a higher yield of crude gas or biogas and also a higher content of methane in the crude gas and enables an economically improved mode of operation. In addition, the biogas produced is intended to have a very low fraction of nitrogen. The proposed process relates, inter alia, to the following measures: - fermentation substrate is mixed with reduced-ammonia fermentation liquid supplied at least in an amount via which a loading of 2.5 g of NH47I or below is set in the fermentation substrate, - the resultant fermentation substrate is subjected to a first fermentation during a time period from one to four days at a pH of below 6.5, wherein a hydrolysis and acidogenesis take place and a weak gas is produced as first biogas stream, - the fermented fermentation substrate is then pumped into a following fermenter and in this is subjected to a further fermentation, wherein further acidogenesis, acetogenesis and methanogenesis take place and in this process a second biogas stream having a lower hydrogen sulphide content than the weak gas is generated.

Description

Process for the production of Bioqas from predominantly animal excreta

The invention relates to a process for the production of biogas from predominantly animal excreta, in particular manure or chicken manure, individually or as a mixture, by a multi-stage anaerobic reaction in one or more fermenters.

The production of biogas is carried out in a conventional manner in one or more reactors or fermenters that can be operated mesophilic (temperatures below 45 'Ό) or thermophilic (temperatures 45 to 80' Ό).

As biomass organic materials are used, for example, as farmyard manure, renewable resources and biological waste materials incurred. Sewage sludge is only suitable for anaerobic conversion if it is obtained from organically polluted wastewater or process water with a COD content of more than 5,000 mg / l, and thus is anaerobically convertible biomass. COD is the abbreviation for "Chemical Oxygen Demand, which uses a COD measurement to determine how much oxygen the chemical digestion / purification processes in wastewater consume. For the production or production of biogas, various biodegradation processes take place during the reaction, such as hydrolysis, acidification, acetic acid formation and methane formation. The decomposition processes caused by bacteria can take place under aerobic or anaerobic conditions. The most commonly used method is wet fermentation where the dry matter content TS is <15% and the water content is> 85%.

Depending on the raw materials used and the process conditions, biogas with a methane content of up to 65% can be achieved in practice.

Biogas is used inter alia for heating purposes, e.g. used in combined heat and power plants, or as an energy source for feeding into natural gas networks.

In addition to the removal of other impurities, in particular hydrogen sulfide, nitrogen and ammonia, the CO ₂ contained in the biogas still has to be separated in order to obtain a high quality methane gas suitable for further processing.

The purification or processing of biogas is a technologically complicated process, which is associated with a high expenditure on apparatus.

As the proportion of methane in the biogas produced increases, so does the cost of subsequent purification or workup to methane gas. From practice it is known that for the production of biomass animal excrements, such as manure, are used only as an additive to other starting materials, especially on a vegetable basis. The proportion of slurry as an additive is about 20 to 30%, based on the total amount used per hour.

For the production of biogas from predominantly animal excrements, only a small number of solutions are known in comparison to other fermentation substrates.

Due to the differences in their compositions, animal excreta can not be anaerobically fermented according to the same procedure as other biomass substrates. One problem is the relatively high level of ammonia in such substrates. Since, as is known, ammonia / ammonia compounds are additionally formed during fermentation, their rate of formation of methane is considerably impaired.

The result is a very long fermentation period and the formation of biogas with comparatively lower concentrations of methane.

From DD 217 786 A1 a method for the production of biogas from manure is known, manure is fermented in two stages successively under aerobic and anaerobic conditions.

In DD 217 787 A1 procedure is described, according to which pig manure and cattle manure are fermented in two stages successively sour and alkaline anaerobic.

Also known (DD 264 910 A1) is a process for obtaining biogas from pig manure, chicken manure, bovine manure or the like, with increased biogas production rate and biogas yield by a special material guide in the reactor.

A temporal change of the reaction between a process step with series connection and parallel connection of the reactors is proposed in DD 291 743 A4.

A method is known from DE 3 843 789 A1, according to which fresh manure is first introduced into a hydrolysis reactor and stored in order to remove CO ₂ and H ₂ S and then the manure is fed to a solids separation and subsequent fixed-bed flow reactor in order to remove methane gas.

According to the procedure specified in DE 10 340 307 A1, manure is first to be separated into a solid and liquid phase in order to produce biogas from the solid phase.

For these reasons, no economic method is known in practice in which exclusively or predominantly animal excreta, such as e.g. Manure, used for the production of biogas.

It is known that in the production of biogas from animal excrements, in particular manure, due to adjusting ammonium loads in the fermentation substrate, the biological see implementation to biogas quickly inhibited. This means that in direct manure fermentation or even its concentrate only extremely poor degradation rates can be achieved. There is a very rapid formation of biogas, but then requires an almost infinite amount of time for a high-grade degradation, which is additionally inhibited. Furthermore, all fermentations of animal excrement have the disadvantage that due to accompanying biological Anamox implementation atomic nitrogen is produced. This inevitably leads to high levels of nitrogen in the biogas of 1 to 10 vol .-%. Since the content of nitrogen with the customary in biogas formation gas measurement via sensors or IR measurement can not be determined, this proportion is generally not specified. As long as the produced biogas is emitted in a CHP this is acceptable. If, on the other hand, the produced biogas is to be treated as biomethane, an inferior biomethane is produced here, which must be refined by additional calorific value adjustment.

The invention has for its object to provide a method for the production of biogas from predominantly animal excrement, which is characterized by a higher yield of raw or biogas and a higher content of methane in the raw gas and enables an economically improved operation. Furthermore, the produced biogas should have a very low content of nitrogen.

According to the invention the object is achieved by the features specified in claim 1. Advantageous developments of the procedure are the subject matter of claims 2 to 14.

The starting substrate used can consist exclusively of animal excrements. However, the animal excrements can also be converted into biogas together with biomass of non-animal origin, such as, for example, renewable raw materials or biological waste materials, the quantitative proportion being less than 50%. Fermentation substrate (starting substrate) with a TS content of less than 15% is mixed at least with supplied ammonia-reduced fermentation liquid, in an amount over which a loading in the range of 2 to 2.5 g NH ₄ I or below in the fermentation substrate. If the supplied fermentation substrate (starting substrate) does not have the required DM content, it is adjusted by appropriate dilution or concentration.

In the lower part of the TS content should be 1 to 6%.

If sanitation is required, the suspension is heated to a temperature of 65 to 90 ° C, which is maintained for a predetermined period of a few hours.

Experiments showed that higher TS contents, above 6%, require longer residence times and significantly lower methane yield during fermentation. The methods for measuring or determining the content of ammonium / ammonia in the fermentation substrate are known per se.

In the context of the invention, ammonia-reduced fermentation liquor is to be understood which only has an ammonium content of less than 2000 mg / l.

The ammonia-reduced fermentation liquid may originate from the ongoing process, with a liquid fermentation substrate being removed from one of the fermenters or secondary fermenters and removed at temperatures of from 90 to 180 ° C., preferably to 150 ° C., and a pressure of at least 0.5 bar, preferably up to 2 bar, above the pressure of the corresponding boiling point of water is treated. The thermal treatment duration of the fermentation substrate should be less than two hours.

The fermentation substrate used to produce the ammonia-reduced fermentation liquid can also come from another biogas production process, or possibly also the fermentation liquid.

The circled fermentation liquid is pumped in a loop through a first heat exchanger and heated to temperatures of up to 1 10 'Ό and then fed to another, second heat exchanger and further heated in this up to a maximum of 180' Ό. As a result of the pumping process, the stripped fermentation liquor is compressed to a pressure of 1.5 to 12 bar, preferably at least 0.5 bar, above the pressure of the corresponding boiling point of water. After the second heat exchanger, the compressed hot fermentation substrate or fermentation liquid enters a closed container. In this, traces of H ₂ S and water vapor are released by a relaxation or while maintaining the container internal pressure from the fermentation substrate C0 ₂ , ammonia and discharged as a gas mixture via a pressure-controlled exhaust pipe integrated into the container. The ammonia-reduced fermentation liquid is removed via a line from the container and added after cooling to substrate temperature to the fermentation substrate to adjust the desired loading of NH ₄ ⁺ .

Optionally, a subset of ammonia-reduced fermentation substrate can be returned to the fermenter.

Preferably, the elimination of a partial amount of fermentation liquid from the fermenter takes place only after reaching a limit value for the release of a methane formation inhibiting amount of ammonia.

With the removal of ammonia from the fermentation substrate is prevented due to the anamox biology of the bacterium Candidadus Brocatia or others according to the subsequent reaction

NH ₄ + NO ₂ - - »N ₂ + 2 H ₂ O

NH ₃ + HNO ₂ - »N ₂ + 2 H ₂ O formed in the fermenter, Nachgärer or fermentation residue fermentation molecular nitrogen, educated or existing urea quickly decomposed to ammonia and carbon dioxide and these shares are deposited and forming amino acids biologically react with ammonia on to organic substances that are then no longer available for biogas.

By increasing the temperature in the ammonia removal to 180 'Ό, the urea formed can be hydrolyzed again. Furthermore, it is also possible to add to the fermentation substrate in the fermenter enzymes, such as urease, in very small amounts in order to achieve biologically the decomposition of urea or uric acids to ammonia and carbon dioxide. If insufficient enzymes are present, the decomposed ammonia reacts again to urea or urea derivatives. Therefore, ammonia contained in the culled fermentation substrate must be separated. If this is not the case, the urea derivatives with dissolved organic compounds in the fermentation substrate react to protein complexes and other previously unknown compounds, which can then not be biologically converted to methane in the fermenter, which reduces the methane yield. If the proportion of ammonium in the fermentation substrate is too high, a biogas with a high nitrogen content is formed via the forming organic and inorganic nitrogen complex. The nitrogen content may be more than 2 vol .-% depending on the residence time of the fermentation substrate in the fermenter at ammonium loadings of more than 3 g / l in the fermentation substrate. As the ammonium content increases and the residence time increases, the proportion of nitrogen in the biogas formed also increases. In particular, then in the post-fermenter or in the subsequent fermentation fermentation with extremely high nitrogen contents of 5 to 20 vol .-% is expected.

It is also possible to use ammonia-reduced fermentation liquor originating from another biogas production process, e.g. in a parallel biogas plant for the fermentation of biomass on a vegetable basis.

In the ammonia-reduced fermentation liquid, a residual content of ammonium should still be present, since this is for the further biological conversion (bacteria formation) of importance.

Apart from ammonia-reduced fermentation liquor, fermentation liquor and / or solids separated from fermentation substrate may be added to the fermentation substrate in the further fermentation process.

The present after the addition of ammonia-reduced fermentation liquid fermenting substrate with a loading of about <2.5 g of NH ₄ 7I is subjected to a first fermentation for a period of one to four days at a pH of less than 6.5, preferably 5 to 6, whereby hydrolysis and acidogenesis take place, whereby a utilizable weak gas is used as first biogas stream with up to 50% of the total proportion of C0 ₂ and the superfluous amount of H ₂ S and a part of NH ₃ arise. It is a so-called Hydrofermstufe (process step a)).

According to the invention, the per se conventional single-stage fermentation process is separated into two stages, which are referred to as Hydroferm- and Methanofermstufe. The separation into these two stages and the reduction of the Ammomiumgehaltes a higher methane formation rate is achieved over known biogas processes and created a biomilieu, which allows reduced ammonia inhibition higher methane conversion.

Subsequently, the fermented fermentation substrate is pumped into the first fermenter and in this during a residence time of 10 to 30 days for further fermentation at temperatures of 35 to 60 'Ό and a pH of 7 to 8 subjected to another Acidogenese, acetogenesis and Methanogenesis take place while a second biogas with methane contents of 65 to 75 vol .-% and lower hydrogen sulfide content than the produced lean gas is formed. This process step c) is referred to as Methanofermstufe.

The methane content in the biogas obtained after process step c) is at least a factor of 2 higher than the methane content in the weak gas produced according to process step b). After completion of this process step incurred fermented fermentation substrate is subjected to at least one further fermentation step with a residence time of 20 to 80 days. The further fermentation can be carried out in one or more fermenters connected in series, wherein a retention time of 20 to 80 days is to be maintained in each fermenter or secondary fermenter. Each fermenter also produces a separate biogas stream.

After at least one or each fermentation step, the resulting fermentation substrate is separated into a liquid and a more viscous to solid phase. The liquid phase should have a TS content of less than 5% and the thicker to solid phase a TS content of 20 to 30%. The thicker to solid phase is pumped into the subsequent fermenter. The liquid phase is fed in whole or in part to the starting substrate and / or fermentation substrate during one or both treatments according to process steps a) and b). The liquid phase can be partially or completely fed to one of the upstream fermenters.

In the last fermenter or Nachgärer accumulating solid digestate is removed or stored after dilution.

It is advantageous that the biogas produced in the methanoferm stage has low contents of H ₂ S and NH ₃ and is free of oxygen. This results in much lower Expenses for the subsequent purification of biogas, in particular for desulfurization.

Comparably higher methane contents of more than 60% by volume, on average 70% by volume, can be achieved in the biogas.

The entire biogas process is now considerably more economical, due to the separation of the fermentation in two stages (Hydroferm and Methanoferm) and the lower ammonium content in the fermentation substrate. This is also reflected in the fact that the fermenters, in particular the secondary fermenter are smaller than previously dimensioned and pumps, and agitators can be installed with lower power.

It is also advantageous that the resulting fermentation residue has a considerably lower ammonia load, which is advantageous for the environment, in particular with regard to the occurrence of lower odor nuisance.

Extensive research has found an association between ammonium content and organic dissolved carbon (TOC). The TOC results from the solution and biological conversion of organic dry matter (oTS) of the components to be fermented. It was found that from a loading of 1 to 2 g NH ₄ 7I in the fermentation substrate, the TOC content increases significantly. An increase from 10 to 25 g / l TOC means that the difference of 15 g / l already of organically dissolved carbon due to the higher ammonium content is no longer available as a result of biologically inhibited conversion to biogas.

The amount of solid arising after the fermentation stages can be divided, e.g. a subset is admixed to the starting substrate for adjusting the TS content and the other subset is fed to one of the fermenter or secondary fermenter. The generated biogas streams are, either individually or merged into a total stream, subjected to further purification and treatment.

The first fermenter and the second fermenter or secondary fermenter are designed in their useful volumes so that a volume ratio of greater than 1: 1 to 4: 1 is present. The secondary fermenter should therefore have a lower useful volume, preferably half of the first fermenter. The volume of digestate used should be reduced continuously, starting from the first fermenter to the last fermenter or post-fermenter, by half to one tenth, preferably to one fifth.

If multiple digesters are connected in series, the temperatures in the fermenters should either be kept at the same level or rise from fermenter to fermenter.

The ammonia-reduced fermentation liquor can be stored for a predetermined period of time before being fed to the fermentation substrate to improve the biology. In the first stage, to adjust the TS content of manure, either a portion of liquid may be separated or a fermentation substrate derived from a subsequent stage may be added as a solid. In individual cases, this depends on the composition of the manure.

In animal feces present in relatively firm consistency, e.g. Hühnertrockenkot, it is necessary to reduce the TS content in the first stage, optionally by adding manure and / or fermentation liquid.

The procedure according to the invention enables a particularly economical utilization of animal excrements to biogas.

If, as starting substrates, animal excrements and biomass of non-animal origin are to be processed into biogas, the claimed process stages a), b) and c) are separated for each starting substrate and carried out in parallel. After completion of process step c), the respectively angegorenen substrates are pumped for further common treatment in the first fermenter. All other process steps then continue, as previously described, from.

The advantage of this variant is a better economical utilization of the biogas plant under the aspect of a higher biogas yield with higher methane content and lower nitrogen contents.

The invention will be explained below with some examples.

In the accompanying drawing a system for performing the method is shown simplified. In connection with the examples, the system shown in the drawing will be explained with.

example 1

For the production of biogas, the starting substrate used is 7000 m ^{3 of} bovine manure per year. The manure has the following composition:

TS content 10.5%

OTS content 76.5%

NH ₄ ⁺ 4.6 g / l total

2.1 g / l of it dissolved.

As a starting substrate only cattle manure is used.

The biogas plant consists of a two-stage fermentation substrate preparation unit B for manure or HTK, a fermenter F1, which is connected to a loop K for the elimination of liquid, already fermented fermentation substrate, which is returned after removal of ammonia in the second stage B2 of the fermentation substrate preparation unit B. Into the circulation loop K, a separator R for the removal of ammonia is inserted. prevented. Furthermore, the biogas plant also includes a second fermenter or secondary fermenter F2 and a digestate storage GRL1.

In addition, a single-stage fermentation substrate preparation unit HF can be integrated into the biogas plant in order to additionally produce biomass on a non-animal basis, such as e.g. Corn silage, with to process, as explained in Example 3.

The first stage B1 of the fermentation substrate preparation unit B for liquid manure is fed via line 1 continuously 1 m ³ / h of cattle manure. In line 1, a tube bundle heat exchanger W is included, in which the manure is preheated. The fermentation substrate processing unit B is designed as a heatable container, which is subdivided into two chambers, as first stage B1 and second stage B2. The slurry pumped into the first chamber B1 is heated to a temperature of 80 ° C. with gentle stirring. The heating takes place via an indirect heat transfer medium. The temperature is maintained for a period of about 2 hours. Hygienisation is carried out at this stage to ensure the required hygienic safety. Thereafter, the manure passes into the second stage B2, in which the circulation loop K is incorporated for the recirculate.

In continuous operation of the first fermenter F1 4 m ³ / h liquid

Digested fermentation substrate as recirculated and fed via the line 7 to the separator R for ammonia removal. In it, the ammonium content in the culled liquid fermentation substrate is reduced from 2100 mg / l to 850 mg / l. Further details of a device for removing or reducing ammonium in the fermentation substrate are shown in the patent application 10 201 1016 604.1.

Via line 2, 3 m ³ / h of ammonia-reduced fermentation liquid are pumped into the second container B2 and 1 m ³ / h via line 3 into the first fermenter F1.

The ammonium content of fermented manure varies extremely strongly and is dependent on the urea, urine and uric acid contained in the manure, which are also subject to considerable fluctuations. The removal of ammonia and recycling of the recirculate in the ongoing biogas process, the ammonium content in the fermenter can be selectively influenced in order to avoid exceeding critical conditions to inhibit methane formation.

In the second stage B2 of the fermentation substrate preparation unit B, the supplied manure, ammonia-reduced liquid, already fermented fermentation liquid (fermentation substrate) having a temperature of about 50 'Ό via the line 2 and after the fermenter or post-fermenter F2 separated liquid fermentation substrate in an amount of 1 m ³ / h via the lines 1 1, 4 supplied and intimately mixed with each other in the container B2.

The residence time of the mixture (pH 6) in the second container B2 is 4 days. Within this time, biology is building up and the first fermentation processes (hydroforming stage), which lead to methane gas production. Decisive for this is the reduction of the ammonia content in the supplied manure by mixing with liquid, ammonia-reduced fermentation substrate in the ratio 1: 3 and separated fermentation liquid, as explained above. This results in a total mixing ratio of 1: 4. The loading of NH ₄ I in the fermentation substrate is less than 2 g, for example 1 g.

If necessary, liquid fermentation substrate, which is obtained after the post-fermenter F2, via the lines 1 1 and 5 in the first stage or the first chamber B1 are introduced if the manure has too high a content of TS.

Due to accelerated formation of biogas, biogas is already produced in the second stage or chamber B2 as a lean gas in an amount of 8.5 m ³ / h of the following dry composition:

CH ₄ 18 to 21% by volume

C0 ₂ 76 to 78% by volume

H2 1 to 2 vol.%

H ₂ S 2000 to 4000 ppm

NH ₃ 800 to 2000 ppm.

The gas composition fluctuates because it is a dynamic process and the slurry composition is not constant. The resulting first biogas stream is discharged via line 16 and is a non-combustible gas which is fed to a downstream first purification stage, are removed in the biologically hydrogen sulfide and remaining amounts of ammonia in a conventional manner. After leaving the first purification stage, the lean gas still has a content of H ₂ S of 30 to 100 ppm and NH ₃ of 20 to 60 ppm. In a second purification stage C0 _{2 is separated} from the lean gas according to known per se procedure. Thus, 3.3 m ³ / h of combustible biogas created with the following dry composition:

CH ₄ 52% by volume

C0 ₂ 43 vol.%

N ₂ 0.5 to 2.5% by volume

H ₂ 2 vol.%

H ₂ S 20 to 80 ppm

NH ₃ <10 ppm.

After drying, this biogas can either be supplied to a CHP for generating electric power or mixed with the second biogas stream, which is produced in the main fermenter F1 and is withdrawn via line 17. 7 kWh of electricity and 10.5 kWh of heat energy can be generated from the biogas produced in a quantity of 3.3 m ³ / h.

After completion of the residence time of the fermentation substrate mixture in the second stage B2 of the fermentation substrate preparation unit B this is pumped in an amount of 5 m ³ / h via the line 6 in the first fermenter F1. The residence time of the fermentation substrate mixture (pH 7.5) for further fermentation is about 12 days while maintaining a fermenter temperature of about 55 'Ό. The fermenter has a volume of 1500 m ³ .

After about 10 to 1 1 days residence time of Gärsubstratgemisches in the first fermenter F1 are continuously removed via the line 7 of the loop K 4 m ³ / h of liquid fermentation substrate and at a pressure of 3 bar and a temperature of 1 15 ° C in the separator R subjected to a combined separation of ammonia with simultaneous thermal digestion of bio-unreactable organic components of the liquid fermentation substrate. Due to the increase in temperature escape from the fermentation substrate C0 ₂ , NH ₃ and small amounts of water vapor. In a closed system, a system pressure of 7.5 bar would occur at 1 15 ° C. Since this is limited to 3 bar, escape under these conditions, the separating from the fermentation substrate components C0 ₂ and ammonia as gas. Water would evaporate under these conditions at about 1, 8 bar.

Depending on the amount of urea or uric acid which accumulates during the fermentation process or may be formed from the ammonia during the fermentation process, it may be necessary to increase the working temperature in the circulation loop for the separation of ammonia to up to 180 °. Under these conditions, urea decomposes to ammonia and carbon dioxide, which are discharged with the gas stream. The residence time for the thermal decomposition of urea is sufficient for 30 minutes for the present conditions. This is particularly necessary if the liquid fermentation substrate is circulated over a very long period of many months.

The separated in the separator R ammonium / ammonia is removed via line 8 and converted to ammonium sulfate, which is used as fertilizer.

The ammonia-reduced fermentation liquor (4 m ³ / h) obtained after the above-mentioned treatment with a residual ammonia content of about 850 mg / l is, as already explained above, fed to the second stage B2 of the fermentation substrate preparation unit and the fermenter F1. The remaining amount (about 1 m ³ / h) of fermented fermented substrate is discharged from the fermenter F1 and passed via line 9 in the second fermenter or post-fermenter F2, which has a volume of 1000 m ³ . In this case takes place at a residence time of about 40 days, a biological conversion of not yet fermented organic substance Biogas, whereby a third biogas stream is generated, which is fed via the line 18 into the conduit 17 for the second biogas stream.

Under the abovementioned conditions, 38 m ³ / h of biogas having a mean dry composition of (together from fermenter F1 and secondary fermenter or fermenter F2) are mixed together

CH ₄ 59 to 69% by volume

C0 ₂ 30 to 40 vol.%

N ₂ 0.2 to 1.5% by volume

H ₂ 300 ppm

H ₂ S 2000 to 3500 ppm

NH ₃ 800 to 1500 ppm

receive. In the fermenter or post-fermenter F2, the fermentation substrate is reduced to a TS content of 2.5 to 5%, an OTS of 68.5%, a TOC of 6540 mg / l and an ammonium content of 1, 52 g / l.

In the fermenter or post-fermenter F2 resulting fermentation residue is passed via line 10 to a separator D and separated into a liquid and a solid phase.

The liquid phase is divided as follows: a first subset is via the lines 1 1, 12 in the fermenter or post-fermenter F2, a second subset via the lines 1 1, 4 or 5 in the slurry processing B and the rest via the line first 1, 13 pumped into the digestate storage GRL1.

The proportion of water introduced with the starting substrate slurry can be compensated for by adding solid digestate from the fermentation residue storage to adjust the TS content of the liquid manure. In this example, the required amount of solid (1 600 kg / d, TS content 28%) passes via the indicated transport path 15 in the second stage B2 of the fermentation substrate preparation unit B or can via the transport path 14 in the Grestrestlager GRL1.

If necessary, digestate can also be added to the first fermenter F1 and / or second fermenter or post-fermenter F2 in order to change the TS content of the fermentation substrate.

The pumped into the fermentation residue GRL1 digestate (1 m ³ / h) has a dry matter content of 3% and is used for example as an agricultural fertilizer. The advantage is the relatively low content of ammonium / ammonia, whereby the odor is significantly reduced.

The biogas produced according to this example has an average methane content of 65% by volume, which is about 3 to 5% higher in comparison with known processes. Also obtained is a larger amount of biogas (38 m ³ / h with a mean CH ₄ content of 65% by volume) compared to the previous value of 26.8 m ³ / h (CH ₄ content 61, 3 +/- 1, 9% by volume = 16.43 m ³ / h CH ₄ ). This corresponds to an increase in the energy yield by 60.8%. Furthermore, compared with known processes, the TOC content is lower by a factor of 2 to 4 and demonstrates the better biological conversion of the organic mass of the slurry to biogas.

Example 2

For the production of biogas, the starting substrate used is a quantity of 500 kg of poultry dry manure (HTK) per day. The HTK has the following composition:

TS content 62.0%

OTS content 63.8%

NH ₄ ⁺ 5.4 g / l total.

The structure of the biogas plant is analogous to the plant described in Example 1. Only the size is adapted to the smaller amount of substrate. 500 kg of HTK are fed once a day to the first stage B1 of the fermentation substrate preparation unit B, which mixture is mixed with 1000 l of liquid fermentation substrate via the line 5 to form a suspension and adjusted to a TS content of 14%.

In the container B1 of the first stage of the fermentation substrate preparation unit B, the HTK suspension is heated with gentle stirring to a temperature of 80 'Ό. The temperature is maintained for a period of about 2 hours. At this stage, the HTK suspension is sanitized.

Subsequently, the HTK suspension is pumped into a second container B2 (second stage), in which the line 2 of the circulation loop K is integrated for the supply of ammonia-reduced fermentation substrate. In continuous operation, 1 m ³ / h liquid fermentation substrate are removed from the first fermenter F1, the main fermenter, subjected to ammonia removal and pumped into the second container B2. The supplied ammonia-reduced fermentation substrate has a temperature of 50 'Ό. For putting in the second stage B2 on the indicated line 15 solid digestate (20 kg / d) and via the line 4 0.2 m ³ / h liquid fermentation substrate from the solids deposition in the separator D is introduced and intimately mixed. The loading of NH ₄ 7I lies in the fermentation substrate well below 2 g.

The residence time of the mixture in the second container B2 is 4 days, with a TS content of less than 5%.

The reaction volume of the second container B2 is about 80 m ³ . Within this time, biology builds up and already the first fermentation processes, which lead to a gas formation. Decisive for this is the lowering of the ammonia content in the liquid manure supplied by mixing with liquid, ammonia-reduced fermentation substrate in the ratio 1: 20. As a result, biogas formation is accelerated and biogas is already produced in the second tank as a lean gas in an amount of 0.5 m ³ / h of the following dry composition:

CH ₄ 12 to 20% by volume

C0 ₂ 76 to 86 vol.%

N ₂ 0.5 to 2 vol.%

H ₂ 1 to 2 vol.%

H ₂ S 1700 to 2800 ppm

NH ₃ 400 to 700 ppm.

The gas composition varies because the HTK composition is not constant. After completion of the residence time of the fermentation substrate mixture in the second stage B2 of the fermentation substrate preparation unit B, this is pumped into the fermenter F1 in an amount of 1250 l / h. The residence time of the fermentation substrate mixture for fermentation is about 14 days while maintaining a fermenter temperature of about 55 ° C. The fermenter has a volume of 500 m ³ .

During further fermentation, 4.6 m ³ / h of biogas with the following composition are withdrawn at the top of the fermenter:

CH ₄ 62 to 69% by volume

C0 ₂ 76 to 86 vol.%

N ₂ 0.5 to 2 vol.%

H ₂ 0.1-0.2 vol.%

H ₂ S 1200 to 2200 ppm

NH ₃ 200 to 600 ppm.

The withdrawn biogas is purified and dried according to the desired quality in a conventional manner. Shortly before the end of the residence time of the fermentation substrate mixture in the fermenter, after about 12 to 13 days, 1, 5 m ³ / h of liquid fermentation substrate on the recirculation loop K are removed and subjected to ammonia removal under analogous conditions as in Example 1, with a residual content to ammonium of about 940 mg / l.

1 m ³ / h of ammonia-reduced fermentation liquor are fed to the second stage B2 of the fermentation substrate processing unit and the remaining 0.5 m ³ / h are returned to the first fermenter F1.

After the residence time of the fermentation substrate in the second stage B2 has ended, about 250 l / h of fermentation substrate are passed via line 9 into the secondary fermenter or fermenter F2, where a further fermentation process takes place. The post fermenter or fermenter F2 has a volume of 300 m ³ . The residence time of the fermentation substrate in the post-fermenter F2 is 62 days. Under these conditions, a reduction of 60% of the organic dry matter contained in the fermentation substrate (oTS).

About the line 10 0.25 m ³ / h or every 4 hours 1 m ³ of fermented fermentation substrate discharged from the fermenter F2 and passed through a separator D for separation into a liquid and a solid phase. The liquid phase is returned to the fermenter F2. The separated solid phase has a TS content of 20 to 30%. Based on the quantities used, 260 kg / d of solids with a solids content of about 28% are produced. This amount is supplied via the transport path 14 to the digestate storage GRL1.

The resulting digestate can be used as agricultural fertilizer.

The separated liquid fermentation substrate is returned to the fermentation stages, tank B2, main fermenter F1 and post-fermenter F2, to adjust the required DM content. In order to maintain the water balance in the fermentation substrate preparation in about 135 liters of water are needed. The operation of the biogas plant can thus be carried out without wastewater.

According to this example, HTK biogas in a particularly economical mode of operation produces 5.1 m ³ / h of biogas with an average CH ₄ content of 62% by volume.

An amount of 122.4 m ³ of biogas is produced per day, which is used for further energy recovery.

Example 3

For the production of biogas, 7,000 m ^{3 of} cattle manure and 5,000 t of corn silage per year are used as the starting substrate. These have the following composition:

Manure corn

TS content 10.5% 48.2%

OTS content 76.5% 88.0%

TOC 26020 mg / l

NH ₄ ⁺ 4.6 g / l total

2.8 g / l of it dissolved.

The different starting substrates are treated separately, manure analogously as in Example 1. The process steps a), b) and c) according to the invention, including the so-called hydroferm stage, are carried out separately for manure and corn silage. Only for the subsequent fermentation in the first fermenter F1 (main fermenter), the different fermentation substrates are brought together into a mixture. Plant technology, the biogas plant is compared to the above-described embodiment still extended to a single-stage fermentation substrate processing unit consisting of a fermenter HF with a metering screw 20 for feeding corn silage, a line 21 for the discharge of biogas and a line 22 for forwarding angegorenem substrate in the first fermenter F1 consists. The fermenter (volume 300 m ³ ) is also in the existing piping system for supplying ammonia-reduced fermentation liquid via line 23 and separated fermentation liquid (in the separator D) via the lines 1 1, 24 integrated.

According to this example, the starting substrate cattle slurry is treated analogously as in Example 1.

The fermentation tank HF is fed via a metering screw 20 corn silage (580 kg / h). 24 liquid fermentation substrate (5 m ³ / h) at a temperature of 40 to 55 'Ό, at the same time via lines 1 1, supplied which is obtained after the solid-liquid separation in the separator D. Due to the elimination of fermentation liquid from the first fermenter F1 and the removal of ammonia, the proportion of ammonium / ammonia in the entire cycle of the biogas plant is reduced. In addition, ammonia-reduced liquid fermentation substrate can also be fed via line 23.

With stirring and a mean residence time of 48 hours, the hydrolysis and acidogenesis (hydroferm stage) take place at an initial pH of less than 6.5, with formation of 82 m ³ / h of biogas with the following dry composition:

CH ₄ 18 to 22 vol.%

C0 ₂ 72 to 78 Vol .-%

N ₂ 0.5 to 2 vol.%

H ₂ 0.5 to 2 vol.%

H ₂ S 1 100 to 3100 ppm

NH ₃ 400 to 600 ppm.

In the fermentation tank of maize silage, a non-flammable gas with a mean methane content of 16.4 m ³ / h is produced. This biogas stream is combined with the first biogas stream from the second stage of the fermentation substrate preparation B2 and purified.

From fermented corn silage (31, 5 m ³ / h) and manure (3.3 m ³ / h), a combustible biogas (34.8 m ³ / h) is produced with a share of 18.1 m ³ / h of methane. This biogas has the following dry composition:

CH ₄ 52% by volume

C0 ₂ 43 vol.%

N ₂ 0.5 to 2.5% by volume

H ₂ 2 vol.% H ₂ S 20 to 80 ppm

NH ₃ <10 ppm.

After the respective residence time has ended, 5.5 m ³ / h of fermented corn silage and 5 m ³ / h of fermented liquid manure are pumped out of the tank B2 into the first fermenter F1 from the fermentation tank.

The residence time of the fermentation substrate mixture in the first fermenter F1 for further fermentation is about 12 days while maintaining a fermenter temperature of about 55 'Ό. The fermenter F1 has a volume of 3000 m ³ .

After about 10 to 1 1 days of residence time of the fermentation substrate in the first fermenter F1 are continuously circulated over the loop K 9 m ³ / h of liquid fermentation substrate and at a pressure of 3 bar and a temperature of 1 15 ° C in the separator R a Combined separation of ammonia under simultaneous thermal digestion of bio-unreactable organic components of the liquid fermentation substrate subjected. Due to the increase in temperature escape from the fermentation substrate C0 ₂ , NH ₃ and small amounts of water vapor.

The ammonia purification is carried out analogously to Example 1.

The resulting ammonia-reduced fermentation liquor (9 m ³ / h) with a residual ammonia content of about 820 mg / l is, as explained above, fed to the second stage B2 of the fermentation substrate preparation unit and / or the corn pretreatment (fermentor HF) and / or the fermenter F1 , The residual amount (about 1.5 m ³ / h) of fermented fermentation substrate is discharged from the fermenter F1 treated further, as described in Example 1 (separator D, second fermenter or post-fermenter F2, etc.).

Under the conditions mentioned above, 161 m ³ / h of biogas with the following average dry composition are obtained together (from fermenter or secondary fermenter F 2 and fermenter F1).

CH ₄ 62 to 74% by volume

C0 ₂ 25 to 35 vol.%

N ₂ 0.2 to 1.5 vol.

H ₂ 300 ppm

H ₂ S 450 to 280 ppm

NH ₃ 100 to 300 ppm.

There are produced 109.48 m ³ / h of methane.

Including the first stage, a total of 127.5 m ³ / h of methane is produced.

This corresponds to an increase in the energy yield of 46.6%. In the fermenter or post-fermenter F2, the fermentation substrate is reduced to a TS content of 2.5 to 5%, an OTS of 68.5%, a TOC of 5840 mg / l, and the ammonium content is 1.35 g / l.

The digestate (1, 3 m ³ / h) pumped into the GRL1 digestate store has a TS content of 2.5 to 5% and is used, for example, as agricultural fertilizer.

Compared with known processes, the TOC content is lower by a factor of 2 to 4.

Claims

claims

1 . Process for the production of biogas from predominantly animal excrements as starting substrate, in particular manure or chicken manure, individually or as a mixture, by a multi-stage anaerobic conversion, characterized by the following process steps:

a) fermentation substrate with a dry matter content of below 15% is mixed at least with supplied ammonia-reduced fermentation liquor, in an amount, over which a load of 2.5 g NH ₄ I or below sets in the fermentation substrate,

b) the fermentation substrate obtained according to process step a) is subjected to a first fermentation for a period of one to four days at a pH of less than 6.5, wherein a hydrolysis and acidogenesis take place and thereby a usable, but non-flammable, lean gas as the first biogas stream arise with up to about 50% of the total amount of C0 ₂ and the predominant amount of H ₂ S and NH ₃ ,

c) the fermented fermentation substrate after completion of process step b) is pumped into the first fermenter and in this during a residence time of 10 to 30 days of further fermentation at temperatures of 35 to 60 'Ό and a pH value of 7 to 8 is subjected, wherein a further Acidogenese, an ace- genesis and methanogenesis take place and thereby a second Biogasstrom with methane contents of 60 to 75 vol .-% is produced, which has a lower hydrogen sulfide content than the obtained according to process step b) lean gas.

2. The method according to claim 1, characterized in that after step c) incurred fermented fermentation substrate at least one further fermentation step is subjected to a residence time of 20 to 80 days.

3. The method according to any one of claims 1 or 2, characterized in that after at least one or each fermentation stage accrued fermentation substrate is separated into a liquid and a thicker to solid phase, wherein the thicker to solid phase is transported to the subsequent fermenter and the liquid Phase is supplied in whole or in part to the starting substrate and / or fermentation substrate during one or both treatments according to the process steps a) and b) or one of the upstream fermenter.

4. The method according to any one of claims 1 to 3, characterized in that ammonia-reduced fermentation liquid is provided by during the ongoing process of the first fermenter liquid fermented substrate and circled at temperatures of 90 to 150 'Ό and a pressure of 0.5 to 2 Bar is treated above the water vapor pressure.

5. The method according to claim 4, characterized in that the thermal treatment duration of the fermentation substrate is not more than 2 hours.

6. The method according to any one of claims 1 to 5, characterized in that the temperature for separating ammonia is increased to up to 180 ^, depending on the accumulating during the fermentation process or the forming from the ammonia during the fermentation process amount of urea or uric acids ,

7. The method according to any one of claims 1 to 6, characterized in that ammonia-reduced fermentation liquid is used, which originates from another Biogasherstel- lungsprozess.

8. The method according to any one of claims 1 to 7, characterized in that the generated biogas streams, individually or combined, are subjected to further purification and treatment.

9. The method according to any one of claims 1 to 8, characterized in that the volume of the fermentation residue used is continuously reduced, starting from the first fermenter to the last fermenter or Nachgärer by half to one-tenth, preferably to one-fifth.

10. The method according to any one of claims 1 to 9, characterized in that ammonia-reduced fermentation liquid is stored for improving the biology over a predetermined period.

1 1. Method according to one of claims 1 to 10, characterized in that the starting substrate is adjusted to the desired TS content, which should be at least 2%.

12. The method according to any one of claims 1 to 1 1, characterized in that in an arrangement of a plurality of fermenters connected in series, the temperatures in the fermenters are maintained at a level or increase from fermenter to fermenter.

13. The method according to any one of claims 1 to 12, characterized in that is driven at an arrangement of several series-connected fermenter of the last fermenter or Nachgärer with the highest temperatures.

14. The method according to any one of claims 1 to 13, characterized in that the decanted liquid fermentation substrate and / or the fermentation substrate in the fermenter, an enzyme, preferably urease, for the decomposition of urea to ammonia and carbon dioxide is added during the treatment of the liquid fermentation substrate is separated as a gaseous component within the cycle loop.