DE20202722U1 - Device for desulfurizing biogas with microorganisms - Google Patents

Description

Device for desulfurization of biogas with microorganisms

The present invention relates to a device for desulfurizing biogas with microorganisms, in particular bacteria.

Through anaerobic fermentation in a biogas reactor, the organic compounds, such as those contained in liquid manure, biomass, etc., are converted into biogas and bacterial mass under certain conditions. Biogas is usually a mixed gas that consists mainly of combustible methane (CH ₄ ) and non-combustible carbon dioxide (CO ₂ ) as well as traces of other gases. Hydrogen sulphide (H ₂ S) is one of these trace gases. When the biogas is reused, the combustion of the hydrogen sulphide produces, among other things, sulphur dioxide, which can lead to corrosion damage, for example, to engines or pipe fittings.

Depending on the composition of the substrate to be decomposed in the biogas reactor, the hydrogen sulphide content in the biogas in agricultural biogas plants, for example, is around 5000 ppm. According to the requirements of most manufacturers of so-called

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In combined heat and power plants, the hydrogen sulphide content in the biogas should not exceed the limit of 150 ppm in order to avoid damage. For this reason, the biogas must usually be desulfurized.

The so-called dry desulfurization process based on iron hydroxide (FE(OH) ₃ ), which is fundamentally suitable for this purpose, has so far hardly been used in agricultural biogas plants due to high acquisition costs, high operating costs and the high effort required for the regeneration of the material used.

The invention is based on the problem of providing a device for desulfurizing biogas which overcomes the disadvantages of the prior art, in particular is inexpensive to manufacture and operate and yet has a high degree of efficiency in desulfurization. Preferably, the device should also be easy to operate, in particular be largely automatable, be permanently reliable to operate and produce waste materials that are easy to dispose of.

The invention is solved by the device defined in the main claim. Particular embodiments of the invention are defined in the subclaims. ,

The invention relates to a device for desulfurizing biogas with microorganisms, in particular bacteria, in which a settlement surface for the microorganisms is arranged between a gas inlet and a gas outlet and is overflowed by the biogas to be desulfurized and the hydrogen sulfide contained in the biogas is removed by the

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Microorganisms are broken down and the settlement surface is wetted with a liquid containing microorganisms at predetermined intervals.

The microorganisms or bacteria that break down the hydrogen sulphide contained in the biogas can be found, for example, in the digested liquid manure that is created in the actual biogas reactor through anaerobic processes, or in sewage sludge. The microorganisms that are created in agricultural biogas reactors through anaerobic processes are particularly suitable for desulfurizing the biogas in the desulfurization reactor. They are present in liquid solution or in a liquid/solid mixture that is preferably sprayed onto the settlement area. Wetting with liquid containing microorganisms takes place relatively frequently, for example several times a day.

In addition, the settlement area is moistened at longer intervals, for example once a week, with a liquid that contains nutrients for the microorganisms, in particular with fresh liquid manure, as is also used in the biogas reactor. The liquid is also used to adjust the pH value of the liquid used in the desulfurization reactor. In particular, fresh liquid manure has typical pH values between 7 and , while the pH value of the liquid contained in the desulfurization reactor drops due to the breakdown of the hydrogen sulfide and in particular due to the resulting elemental sulfur or sulfate. By adding the fresh liquid manure, the pH value can be adjusted to the range between 6.5 and 8, in particular between 6.5 and 7.5, which is favorable for the process.

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The liquid collected in a collecting chamber of the reactor is tempered by a heating device, in particular a heat exchanger, for example to a value above 20° Celsius. Good results can be achieved, for example, at a temperature between 28 and 37° Celsius. The humidity in the reactor should be as high as possible, in particular more than 75% relative humidity, preferably close to 100%. The temperature, humidity and/or the pH value of the liquid are measured in the reactor and adjusted using the heating device, by wetting the settlement area and/or by adding fresh liquid manure.

The addition of oxygen to the reactor promotes the desulfurization process. For this purpose, oxygen is preferably added to the biogas taken from the biogas reactor, in particular by adding ambient air. The microorganisms oxidize the hydrogen sulfide according to the reaction

H ₂ S + 2O ₂ -> H ₂ SO ₄
directly converted into sulfate, or according to

2H ₂ S + O ₂ ^ 2S +2H ₂ O
first into elemental sulphur and then according to

2S + 2H ₂ O + 3O ₂ -» 2H ₂ SO ₄

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converted into sulphate. The sulphate also partially accumulates on the settlement area and thereby hinders the further desulfurization process. For this purpose, the settlement area is rinsed at predetermined intervals, preferably by wetting the settlement area with liquid containing the microorganisms and/or fresh liquid manure.

The wetting device of the device according to the invention preferably has a line arranged above the settlement surface with outlet openings for the liquid containing microorganisms. Wetting takes place on the one hand by spraying and on the other hand by dripping the liquid from top to bottom due to gravity. The gas inlet is preferably below or at least in the lower area of the settlement surface, with the inflowing gas flowing from bottom to top due to a pressure difference between the gas inlet and gas outlet and/or due to convection and thereby sweeping over the settlement surface. The gas outlet is preferably arranged above or at least in the upper area of the settlement surface. The settlement surface fills the space between the gas inlet and gas outlet, at least completely in some areas, so that it is guaranteed that the gas flow between the gas inlet and gas outlet flows over the settlement surface.

Preferably, the settlement surface is formed by a plurality of settlement elements which are designed in a brush-like manner with a plurality of bristles, wherein the bristles are preferably designed in a rag-like manner with a large surface area. Brushes and bristles are made of a material which is resistant to sulfur, for example polyvinyl chloride (PVC) or polypropylene (PP).

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The collecting space arranged below the settlement area is connected to the part of the wetting device arranged above the settlement area via a pumping device. The gas inlet and/or outlet preferably occur continuously. In contrast, the pumping of the liquid from the collecting space into the wetting device preferably occurs intermittently, for example once an hour for a few minutes.

Further advantages, features and details of the invention emerge from the subclaims and the following description, in which an embodiment is described in detail with reference to the drawings. The features disclosed in the claims and in the description can each be essential to the invention individually or in any combination.

Fig. 1 shows a state-of-the-art biogas plant,

Fig. 2 shows a cross-section through the desulfurization reactor in side view,

Fig. 3 shows part of the wetting device,

Fig. 4 shows a top view of the settlement elements, and

Fig. 5 shows a plan view of the gas supply and gas extraction in the upper part of the desulfurization reactor. ,

Fig. 1 shows a state-of-the-art agricultural biogas plant. First, the raw substrate is fed to a shredder 1

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fed, then introduced into a pre-pit 2, in which the ^fresh slurry is made pumpable or kept by means of an agitator 3. The fresh slurry is then fed by means of the pump 4 into the actual biogas reactor 5, in which an anaerobic process takes place and the resulting biogas collects in the gas chamber 6. The digested slurry is collected in a storage tank 7 and can be removed from the storage tank 7 and used, for example, as fertilizer on agricultural land. The biogas is removed from the gas chamber 6 and fed to a cogeneration plant 8, which supplies heat and electrical energy. For many applications it is necessary to arrange a desulfurization device or a desulfurization reactor 9, shown only schematically in Fig. 1, between the biogas reactor 5 and the cogeneration plant 8, which is only shown as an example.

Fig. 2 shows a cross-section through the desulfurization device or reactor 9 according to the invention in a side view. The reactor 9 is essentially cylindrical, in particular circular-cylindrical, and sealed from the environment. In particular, the reactor 9 is closed with a lid 10 which has sealed passages for the gas inlet 11, the gas outlet 12 and the feed 13 of the wetting device. In the lower area, the reactor 9 forms a collecting chamber 14 for the liquid in the reactor 9. In the collecting chamber 14, a heating device in the form of a heat-exchanging hose 15 is arranged, which is fed from the outside via sealed passages 16, for example with heating water or heating steam. The heat can come from the combined heat and power plant 8, in particular from its waste heat.

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Furthermore, the tempered liquid can be removed from the collecting chamber 14 via a corresponding sealed passage through a removal line 17, which is part of the wetting device. In addition, the reactor 9 has a sealed passage for an overflow 18 near the upper edge of the collecting chamber 14, which is bent inside the collecting chamber 14 up to almost its lower end. The overflow 18 has a siphon-like connection outside the collecting chamber 14, via which the used liquid, in particular liquid containing sulfate, can be removed from the reactor 9, in particular pumped out.

The actual reaction chamber for desulfurization is penetrated by a plurality of brush-like settling elements 19, the main axes of which are essentially parallel to one another and preferably aligned vertically. Each settling element 19 has a plurality of lobe-like bristles 20 providing a large surface area, which protrude essentially radially from the respective main axis 21 and hang downwards as a result of gravity. The settling elements 19 are fixed at their lower end in a first perforated grid 22 separating the actual reaction chamber from the collecting chamber 14, and at their upper end to bars arranged in a corresponding grid-like manner or a second perforated grid 23. Above the settling elements 19, as part of the wetting device, a ring line 24 is arranged, which is fed by the supply 13. As shown in Fig. 5, the ring line 24 has spray nozzles 25 directed at the settling elements 19, preferably at equal intervals. The course and in particular the diameter of the ring line 24 are adapted to the geometry of the reactor 9 in such a way that the settling elements 19 are wetted as evenly as possible. The liquid drips from top to bottom due to gravity and therefore wets the settling elements 19 over a large area. The lobes or threads of the

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Settlement elements 19 can be angled, roughened and/or porous in order to provide the largest possible surface as a settlement area.

The gas inlet 11 has a pipe 26 inside the reactor 9, in which the biogas to be desulfurized is guided to the lower end of the settlement elements 19 and only enters the reactor 9 in this area. The biogas then flows from bottom to top past the settlement surface of the settlement elements 19 as a result of convection, different gas densities and/or a pressure difference between the gas inlet 11 and gas outlet 12, where the desulfurization takes place. The residence time of the gas in the reactor 9 can be regulated, for example, by the arrangement of the settlement elements 19 and/or by the adjustable pressure difference between the gas inlet 11 and gas outlet 12. There is usually a slight excess pressure in the reactor 9 compared to the atmosphere, for example less than 50 hPa.

Temperature, humidity and/or pressure in the reactor 9 can be measured, for example, using a corresponding sensor 27, the signal from which is passed on to a central control device. The temperature and/or the pH value of the liquid in the collecting chamber 14 is measured in a corresponding manner. The beads 28 embossed into the outer shell of the reactor 9 and running in a ring shape also serve to force the inflowing biogas to flow over the settlement area. It is advantageous that the gas flow in the reactor is from bottom to top and thus in the opposite direction to the liquid flowing from top to bottom.

In the line to the gas inlet 11, oxygen is added to the biogas to be desulfurized, preferably continuously or at predeterminable intervals.

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supplied, in particular by adding ambient air. In the embodiment shown, for example, the volume flow of the biogas is determined by a corresponding flow meter 35 and evaluated by a control unit 36. The control unit 36 controls an air pump 37, possibly just a simple air inlet valve, through which the biogas to be desulfurized is enriched with ambient air.

Fig. 3 shows a part of the wetting device which follows the representation in Fig. 2 on the left side of the picture. On the right edge of Fig. 3, a part of the reactor 9 or a settling element 19 is also shown. Liquid can be removed from the collecting chamber 14 via a first shut-off valve 29 which can optionally be controlled by a motor from a central control device and fed to the ring line 24 (Fig. 2) by means of a circulation pump 30. The circulation pump 30 is controlled by the central control device and/or by a timer 31 via a relay 32. A filter 33 which can preferably be regenerated, for example backwashed or washed out, is connected to the line upstream of the circulation pump 30. This is intended to prevent undesired entry of solids into the reactor 9 and in particular to prevent clogging of the spray nozzles 25.

Nutrients for the microorganisms, in particular fresh liquid manure, can be fed to the reactor 9 via a second shut-off valve 34, which can optionally be controlled by the central control device. This takes place at relatively long intervals, for example once a week. In contrast, the pumping of the liquid in the collecting chamber 14 takes place at shorter intervals, for example once an hour for 2 to 10 minutes. In addition,

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If the pH value of the liquid in the collection chamber 14 falls below a predeterminable value, for example between 6 and 6.5, fresh liquid manure is added in sufficient quantity to adjust the pH value back to a value of, for example, 7 to 7.5. The drop in the pH value is a consequence of the sulphur enrichment in the liquid in the collection chamber 14 or on the settlement elements 19. In addition to rinsing the sulphate from the settlement surfaces, in particular by spraying the settlement elements 19, the settlement elements 19 can also be cleaned at relatively long intervals, for example with water, optionally mixed with a cleaning liquid. For this purpose, the settlement elements 19 can also be removed from the reactor 9 and, if necessary, replaced with new settlement elements 19. .

Fig. 4 shows the top view of the arrangement of the settlement elements 19 in the reactor 9. As can only be partially seen from the illustration, the bristles of adjacent settlement elements 19 touch one another or even engage with one another. It is important that the biogas to be desulfurized flows past as large a surface as possible of the settlement elements 19. If necessary, the individual settlement elements 19 may not have a circular cylindrical outer peripheral surface as in the embodiment shown, but instead have, for example, a hexagonal honeycomb cylindrical outer peripheral surface and/or conical outer peripheral surfaces that correspond to one another.

Fig. 5 shows a plan view of the upper area of the reactor 9 with the openings for the gas inlet 11 and the gas outlet 12. In addition to a central opening for the gas inlet 11 or the gas supply, further openings for the gas inlet 11 are provided on a surface facing the outer circumference of the reactor.

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9 concentric circular line. In the present case, a total of six further openings are provided for the gas inlet 11, each at an angular distance of 60 °.

A first opening for the gas outlet 12 or gas extraction is provided somewhat eccentrically. Further openings for the gas outlet 12 are also arranged on a concentric circular line; in the embodiment shown, there are three further openings at an angular distance of 120° each. The openings for the gas outlet 12 are arranged closer to the edge of the reactor 9 than the openings for the gas inlet 11. The gas outlet 12 could in principle also occur via a single opening. In contrast, a gas supply to the reactor 9 that is distributed as evenly as possible is advantageous because this ensures an even flow over the settlement area in the reactor 9. The ring line 24 is also arranged concentrically in relation to the circumference of the reactor 9, the diameter of the ring line 24 preferably being somewhat smaller than the diameter of the circular line of the openings for the gas inlet 1.1.

The method or device according to the invention enables a high degree of desulfurization to be achieved with low acquisition and operating costs. If required, several of the devices according to the invention can be connected in series or in parallel in a modular manner. In a typical embodiment, the reactor 9 has a volume of about 1 to 5 m ³ , in particular 3 m ³ . The essentially circular-cylindrical reactor 9 has a diameter of about 1.50 m and a height of about 2 m. Such a reactor 9 is sufficient for desulfurizing about 500 m ³ of biogas per day. A particularly advantageous feature of the invention is that

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no waste is produced during disposal and in particular no chemical additives are required for desulfurization. This not only results in low operating costs, but also avoids any environmental pollution. The device according to the invention can in particular be controlled and operated automatically and can be manufactured or set up in a short time using simple means. The microorganisms or bacteria that are produced in the biogas plant through the anaerobic processes and are contained in the digested liquid manure are used to desulfurize the biogas from an agricultural biogas plant.

Claims (10)

1. Device for desulfurizing biogas with microorganisms, in particular bacteria, with a settlement surface for the microorganisms arranged between a gas inlet ( 11 ) and a gas outlet ( 12 ), which can be overflowed by the biogas to be desulfurized and the hydrogen sulfide contained in the biogas can be broken down by the microorganisms, and a wetting device for wetting the settlement surface with a liquid containing microorganisms at predetermined time intervals. 2. Device according to claim 1, characterized in that the wetting device has a line arranged above the settlement surface with outlet openings for the liquid containing microorganisms. 3. Device according to claim 1 or 2, characterized in that the wetting device has a ring line ( 24 ) with spray nozzles ( 25 ) directed towards the settlement area. 4. Device according to one of claims 1 to 3, characterized in that the settlement surface completely fills the space between the gas inlet ( 11 ) and the gas outlet ( 12 ) at least in some regions. 5. Device according to one of claims 1 to 4, characterized in that the settlement surface is formed by a plurality of settlement elements ( 19 ) whose main axes 21 are aligned substantially parallel to one another and preferably in the vertical. 6. Device according to claim 5, characterized in that the settling elements are designed like a brush with a plurality of bristles ( 20 ) which protrude substantially radially from the main axis ( 21 ) and are preferably designed like tabs with a large surface area. 7. Device according to claim 5 or 6, characterized in that the settlement elements ( 19 ) consist of a material resistant to sulfur, in particular a polymer plastic. 8. Device according to one of claims 1 to 7, characterized in that a collecting space ( 14 ) for the liquid dripping from the settlement surface is arranged below the settlement surface, which liquid can be tempered in the collecting space ( 14 ). 9. Device according to claim 8, characterized in that the wetting device further comprises a pump ( 30 ) with which liquid can be removed from the collecting space ( 14 ) and thus the settlement surface can be wetted. 10. Device according to one of claims 1 to 9, characterized in that the temperature, humidity and/or the pH value in the reactor ( 9 ) can be measured by means of at least one measuring device ( 27 ).