DE3228895A1 - Process for obtaining biogas and apparatus for carrying out this process - Google Patents

Abstract

In order to be able to dispose of refuse and sewage sludge together, and to obtain organic substances therein in a form suitable for the production of energy, a continuous process for obtaining biogas from refuse and sewage sludge comprises comminuting the refuse to a maximum particle size of less than 1 cm and mixing this with sewage sludge in a weight ratio such that the water content of the mixture is 45 to 79% by weight, continuously feeding the mixture thus obtained having a pH between 6.5 and 9.5 into a reactor having a feed opening and a discharge opening separate from this and rotting the material in the reactor with external heating and exclusion of oxygen, removing the rotten material from the discharge opening of the reactor, returning 5 to 25% by weight of the rotten material to the feed opening of the reactor and withdrawing from the reactor the biogas formed during rotting. The apparatus for carrying out this process is a suitable rotating tube reactor having a feed end and a discharge end for solids, a gas-tight closed interior, a gas withdrawal device, a heating device and heat insulation for the tube shell.

Description

Process for obtaining

Biogas and device for carrying out this process The invention relates to a continuous process for the production of biogas from waste and sewage sludge, industrial waste or preferably household waste being used as garbage. if Biogas is mentioned here, it is a mixture of essentially consist of methane and carbon dioxide with a methane content of usually 50 to 65%.

It is known to start rotting rubbish in stationary bins, whereby biogas is created and sometimes also collected and used to generate energy will. Such processes, which have a relatively long lazy period, cannot, however to be used for waste disposal by municipalities, as the throughput of such processes is low. In addition, these methods are laborious because after the completion of the Digestion of one approach the digester can be emptied for the next approach got to.

In municipalities, larger amounts of garbage fall continuously, especially Household waste and sewage sludge, which are usually brought to the landfill as such will. The landfill process is laborious and therefore expensive and does not allow any recovery of valuable organic matter that is used in energy can be converted.

The object on which the invention is based now consisted of continuously To dispose of garbage and sewage sludge together and thereby at least part of the contained organic substances in a form suitable for energy generation to win. Another object of the invention was to remove garbage and sewage sludge to reduce in terms of volume so that the amount to be dumped is considerable reduced will. Finally, another object of the invention was to provide a treated Obtain material with a consistency suitable for direct landfill.

The continuous process according to the invention for the production of biogas from garbage and sewage sludge is characterized by the fact that you take the garbage to a maximum Grain size of less than 1 cm crushed and in such a quantitative ratio with sewage sludge mixed so that the water content of the mixture is 45 to 70% by weight, the so obtained mixture continuously with a pH between 6.5 and 9.5 in one Feeds the reactor with an inlet opening and a discharge opening which is separate therefrom and the putrefaction rots in the reactor with external heating and the exclusion of oxygen Material from the discharge opening of the reactor decreases, 5 to 25% by weight of the digested Material returned to the inlet opening of the reactor and that formed during the digestion Removes biogas from the reactor.

In order to be able to carry out the process continuously in this way, it is necessary to adhere to the specified reaction conditions.

This method is suitable for the first time, waste, preferably household waste, but also industrial waste and commercial waste to be disposed of together with sewage sludge and the volume of waste to be dumped by partially removing organic matter Material and by achieving a higher degree of compaction by up to 50 volume% to reduce. The putrefactive material resulting from this process has a Consistency and a water content, due to which the material without further drainage through filter presses, which would be labor and energy consuming, to be deposited immediately.

At the same time, a significant part of the contained organic Materials are converted into the valuable biogas, from which with the help of gas engines or decentralized energy through direct introduction into industrial process heating systems can be won. In addition, the mobilization of heavy metals is used in this process Avoided from garbage or sewage sludge.

It is particularly expedient to use garbage in the method according to the invention with the highest possible carbon content to be used, for example by pre-sorting or sieving separates certain waste fractions. In the usual way, the Household waste also eliminates plastics, glass and metal parts, especially since these are for one Are suitable for recycling. If necessary, plastics can also be reused because they are not available landfilled or incinerated.

It is important that the garbage to increase the reaction rate is crushed to a favorable grain size. As stated, the maximum grain size should be be less than 1 cm. It is cheaper to reduce the maximum grain size to less than 5 mm, preferably less than 3 mm, especially less than 2 mm and especially set to less than 1.5 mm. A lower grain size is not critical, since the reaction speed is greater, the smaller the garbage is crushed became. The comminution can be carried out, for example, with the help of hammer mills, ball mills or other conventional waste shredding devices.

Primary sewage sludge is expediently used as sewage sludge, such as Excess sludge from a biological treatment stage or not yet digested sewage sludge a primary clarification, although the method according to the invention does not apply to the use such a primary sewage sludge is limited. Usually contains such primary sewage sludge used 80 to 96, preferably 90 to 95% water.

The mixing ratio of garbage and sewage sludge depends on the water content of these two mixture components, as the water content of the mixture 45 to 70% by weight, preferably 50 to 65% by weight.

For example, a final water content is achieved with normal water contents of the mixture within the claimed range when blending from about 50 to 60% shredded household waste with 40 to 50% primary sewage sludge.

In many cases it is advantageous to use the crushed mixture To precondition garbage and sewage sludge prior to introduction into the reactor by this mixture is composted in an aerobic compost or an anaerobic acidic one Undergoes fermentation.

If the pH of the mixture to be introduced into the reactor is with or does not have the specified pH value without preconditioning, such as after a preconditioning through acid fermentation, the pH value must be adjusted, such as by adding lime.

It is therefore important for the process according to the invention that the mixture to be fed into the reactor has a certain water content and a Has a certain pH that is not adjusted during the digestion in the reactor will. With a water content of the mixture before it is fed into the reactor below 45% the microbiological processes necessary for digestion end so that little or no biogas is produced and the desired effect is not achieved will. With a water content over 70%, on the other hand, you get the after digestion Discharge opening of the reactor a material that is too liquid to be dumped directly to become, and therefore has to be subjected to post-drainage. Should the water content of the mixture, for example due to the preconditioning, below the stressed area it must be readjusted by adding water.

The mixture is continuously or intermittently with the exclusion of oxygen fed into the reactor and withdrawn from it, thus seen as a whole a continuous process is created.

In the Reaktpr can under mesophilic conditions preferably with a temperature of 30 to 400 C or under thermophilic conditions preferably be worked at a temperature of 50 to 70 "C. For this purpose, the material heated in the reactor by appropriate heating devices, such as with the help of a heating jacket or with the help of heating coils inside the reactor.

An inclined rotary tube reactor is expediently used as the reactor, as this is particularly suitable for fully continuous operation. There come but also differently constructed reactors into consideration, such as vertical standing reactors with an upper inlet opening and a lower discharge opening as well as with stationary floors inside, the digested material about with Help of crow rakes through openings. in the floors from floor to floor from above is conveyed down through the reactor.

When using mesophilic conditions in the reactor, one needs a longer residence time, but gets more stable conditions. Thermophilic conditions are more sensitive to excessive temperatures, but allow shorter dwell times. Favorable residence times in the reactor are 5 to 20 days.

The one preferably used as a device for the method according to the invention The inclined rotary tube reactor has a different one from conventional rotary tube reactors Construction.

In the usual way, he has an importer and an exporter for Solids, but it must have a gas-tight interior with a gas extraction device as well as a heating device. In addition, it is expedient to have thermal insulation for the pipe jacket.

The inclination of the rotary tube reactor is expediently 5 to 150, preferably a maximum of 100 against the horizontal.

That resulting from the rotting of the mixture of garbage and sewage sludge Biogas is drawn off under pressure control, for example at the front of the reactor. It is essential in the method according to the invention that part of the digested material, which is removed at the discharge end of the reactor, to the inlet opening of the reactor is returned, such as with the help of a thick matter pump. With the material return the microorganisms required for the rotting processes become the entrance of the reactor recycled, which accelerates the methane phase, so that the residence times in the Reactor can expediently be about 4 to 40 days, which is considerably shorter than in the case of stationary, discontinuous processes. The reduction of the residence time and thus increasing the throughput rate is an essential consideration for economic exploitation on a larger scale.

In the mesophilic operating mode, residence times of 8 to 20 days, with thermophilic operation, count on dwell times of 4 to 10 days.

In the drawing, FIG. 1 is a side view of a rotary tube reactor according to the invention, Fig. 2 is an enlarged view of the discharge end of the in 1 and FIG. 3 shows a cross section of the tubular reactor shown in FIG. 1 shown rotary tube reactor along the line III-III in Fig. 1 from the introductory part seen from.

The rotary tube reactor shown in the drawing has an angle d against the horizontal inclined tube 1, which is supported by an insulating jacket made of foam 2 is surrounded. The tube 1 rests, as can be seen in particular in FIG. light is on rollers 3 and 4, the latter of which is driven by a motor 5 and generates the rotary motion of the reactor.

The reactor has an inlet end 6 and an outlet end 7 with the aid a special discharge device, which will be explained in more detail, as well as a pressure-controlled one Gas sampling device 8.

Inside the tube 1 is along its length in the upper area a scraper 9 and a heater with heating coils 10 are arranged. The rotary tube reactor rotates clockwise as indicated by the arrow in FIG.

The reference number 11 indicates the degree of filling or the level of solids Shown in the rotary tube reactor in the resting state.

The discharge device shown enlarged in FIG. 2 consists of a bent tube 12 protruding into the discharge end of the tube 1, in which a discharge screw 14 driven by the motor 13 is located. Since the discharge takes place in the form of a plug, an additional pressure control is to avoid this a leakage of biogas is not required. That emerging from the pipe 12 Digested material 15 is taken directly to the landfill, for example with the aid of trolleys 16 brought.

The entry device can be designed similarly to the discharge device and contain a corresponding driven screw. This is in the Drawing perpendicular to the plane of the paper and has the reference number 17.

Of course, many of the features of the rotary tube reactor according to the invention can be modified without the inventive concept is left. For example, instead of the heating coils inside the reactor one through which heating fluid flows Heating jacket can be used. Warm combustion gases from the combustion of a part can be used as a heating medium of the resulting biogas can be used. Other design modifications are available for the professional at hand.

Example One of plastics, glass and metal by pre-sorting and sieving of the freed household waste fraction with a carbon content of about 20%, based on the dry matter, a hammer mill was used to reduce the grain size crushed by a maximum of 3 mm. The shredded household garbage was made with primary sewage sludge with a water content of 90% in a mixing ratio of 60% household waste 40% sewage sludge mixed.

This mixture was acid anaerobic in the usual manner for 5 days Fermentation preconditioned, after which the water content to 60% and the pH through Addition of lime was adjusted to 7.5.

The mixture treated in this way was now shown in the drawing The rotary tube reactor shown is fed in continuously with the exclusion of oxygen. Thermophilic conditions were kept at 550 ° C. in the rotary tube reactor. The length of stay of the material during digestion in the Rehrohr reactor was 12 days. The resulting Biogas was drawn off under pressure control via the front of the reactor. Of the Digested material withdrawn at the discharge end became 10% with the aid of a nitrogen pump returned to the inlet of the rotary tube reactor.

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Claims (12)

Process for the production of biogas and device for. Implementation of this method Patent claims 1. Continuous Process for the production of biogas from garbage and sewage sludge, characterized in that, that the garbage is crushed to a maximum grain size of less than 1 cm and mixed with sewage sludge in such a proportion that the water content of the Mixture is 45 to 79% by weight, the mixture thus obtained is continuous with a pH between 6.5 and 9.5 in a reactor with an inlet opening a discharge opening separate therefrom and in the reactor under the outside Warming and exclusion of oxygen rots the putrefactive material the end the discharge opening of the reactor decreases, 5 to 25% by weight of the digested material zur.Einführöffnung the reactor and the biogas formed during the digestion withdraws from the reactor. 2. The method according to claim 1, characterized in that the Garbage to a maximum grain size of less than 5 mm, preferably less than 3 mm, especially less than 2 mm, especially less than 1.5 mm crushed. 3. The method according to claim 1 and 2, characterized in that one as sewage sludge, primary sewage sludge, preferably one with a water content between 80 and 96% by weight is used. 4. The method according to claim 1 to 3, characterized in that one using the mixture of garbage and sewage sludge prior to introduction into the reactor an aerobic rot or an acidic one. anaerobic fermentation preconditioned. 5. The method according to claim 1 to 4, characterized in that one adjusts the water content of the mixture to 50 to 65% by weight. 6. The method according to claim 1 to 5, characterized in that one adjust the pH of the mixture to 7-8.5. 7. The method according to claim 1 to 6, characterized in that one in the reactor under mesophilic conditions at 30 to 400 C or under thermophilic conditions Conditions heated to 50 to 700 C. 8. The method according to claim 1 to 7, characterized in that one used an inclined rotary tube reactor as the reactor. 9. The method according to claim 1 to 8, characterized in that one 1 to 20% by weight of the digested material as returned to the inlet opening of the reactor. 10. The method according to claim 1 to 9, characterized in that one adjusts the residence time to 4 to 40 days, preferably 4 to 20 days. 11. Device for performing the method according to claim 1 to 9, characterized in that it is an inclined rotary tube reactor with an inlet end (6) and a discharge end (7) for solids, a gas-tight interior, a gas extraction device (8), a heating device (10) and a thermal insulation (2) for the pipe jacket (1). 12. The device according to claim 11, characterized in that the Rotary tubular reactor 5 to 150 (angle d) is inclined to the horizontal.