ITUD20110173A1 - ANAEROBIC DIGESTION SYSTEM FOR THE PRODUCTION OF AGRICULTURAL BIOMASS BIOGAS, LETAME, ZOOTECHNIC WASTE AND SOLID ORGANIC WASTE - Google Patents

Description

"ANAEROBIC DIGESTION SYSTEM FOR THE PRODUCTION OF BIOGAS FROM AGRICULTURAL BIOMASS, MANURE, ZOOTECHNICAL WASTE AND ORGANIC SOLID WASTE"

Application sector

This invention refers to an anaerobic digestion system for the production of biogas from various organic substances, such as agricultural biomass, sludge and solid waste.

The anaerobic treatment of biomass and waste has recently become very important, because it allows to produce energy without creating a negative impact on the environment. Biogas is a very valuable form of energy, because it contains methane, a combustible gas whose combustion produces two chemical compounds that are absolutely harmless for the environment: water and carbon dioxide from renewable sources.

It is therefore understandable how the production of biogas in specialized plants is today a valid tool in the fight against terrestrial overheating due to the accumulation in the atmosphere of carbon dioxide deriving from the use of fossil fuels and to the <uncontrolled fermentation of organic waste.>

11 biogas is also extremely practical and versatile, in fact it can be used directly in internal combustion engines and gas turbines for the cogeneration of electricity and heat, or, after an appropriate refining treatment, it can be introduced into the networks of distribution of fossil methane. Methane can be compressed and stored in cylinders and used to fuel gas vehicles.

The latter application appears particularly interesting for biogas derived from the treatment of solid urban waste, as the availability of organic matter occurs in the urban area, precisely where the need to use a non-polluting fuel is particularly felt.

A further advantage of biogas production plants is the possibility of treating the material coming out of anaerobic digestion by means of an aerobic composting process, which makes it possible to produce an organic fertilizer (compost) that can be used in agriculture. Of course, for the use of compost in the food chain, no toxic substances must be present in the material entering the anaerobic digestion system.

The state of the art

In the current state of the art, the use of horizontal cylindrical digesters for the production of biogas, with "batch" or continuous process is known. For example, the patent EP 0 476 217 describes a cylindrical horizontal digester heated by forced circulation of hot water inside cavities integrated in the shell. This solution requires a much more complex and heavier construction standard than the system object of the present invention, where the weight of the material inside the digester is uniformly supported by the tank liquid and the buoyancy thrust, present above all during the phases of loading / unloading, it is balanced by tie rods fixed to the bottom of the tank, or by other simple fixing systems. moreover, the aforementioned European patent has highlighted other disadvantages as it is equipped with a stirring system for the material being treated which, in addition to being very demanding from the construction point of view, has a high consumption of electricity and requires expensive maintenance.

In another system known and called "a garage", such as the one described in patent W 0 02131104, the heat is transmitted by the percolation liquid (heated in special exchangers) and by the surface of the heated floor. It is evident that the heating through the walls of the "garage" is not very efficient due to the discontinuity of contact. For these reasons, the "garage" systems all work with a mesophilic process at a temperature of about 35 - 40 "C, while the thermophilic systems, which use bacteria that grow around 55" C, have higher biogas production yields. and they also ensure more efficient sanitation. Another disadvantage of this system is that it cannot treat material with limited porosity: in fact it is necessary to treat the material by mixing it with structural materials such as shredded wood, in order to increase the porosity of the mass.

The process described in US patent 4,735,724 relates to an unstirred vertical digester, designed to favor the concentration of the solid substance in the upper part, while the digestate is removed from the lower part: it has disadvantages from an operational point of view and drawbacks in the phase to replace the material being treated.

Another known system, as described in US patent 200210192810, in which the reactor is cylindrical, horizontal, rotating, immersed in a liquid and used for the aerobic composting of the sludge already digested anaerobically in a particular "U" -shaped digester. This type of system does not provide for anaerobic digestion: it includes pipes for the entry of the air required by the composting process, and moreover the rotation system is much more complex and expensive, which significantly affects production and production costs. depreciation.

Even more complex and costly from a construction and management point of view is the system proposed in US patent 5,427,947, which provides for a rotating cylindrical reactor for composting.

Further systems are known in which digestion includes several stages of biological treatment. The one of the two-phase type indicated in US patent 6,342,378, and the three-phase type described in US 5,269,634 which uses three reactors, containing material with different treatment times, which reactors are connected to each other by a system of conduits suitable for pumping the liquid process from one reactor to another.

The present patent starts from these known technical solutions to overcome the disadvantages and drawbacks listed, creating a new system that focuses on construction simplicity and low construction and management costs.

Essence of the invention

The objects of the invention are achieved according to the characteristics of the main claim and / or of any other claim reported in this patent text.

The main purpose of the present invention is to provide an anaerobic digestion system for the production of biogas from agricultural biomass, manure, livestock waste and solid organic waste, substantially characterized by one or more horizontal digesters, parallel and / or side by side, immersed in a heated liquid, usually water.

The digesters have the shape of a cylinder whose ends are fixed to two opposite walls of the tank containing heated liquid. Another type of embodiment provides that the digesters, always of horizontal cylindrical shape, can float in the liquid contained by the tank.

The system with the digesters fixed to the walls of the tank is suitable for treating with a "batch" process (infomata) materials with a high content of dry matter, which are loaded by pushing through the loading opening made on the wall of the tank. The digested material is discharged through the opposite opening of the digester, from which the digestate comes out pushed by the fresh material which is loaded on the other opposite side.

In the case of biomass or agricultural waste collected in bales, preferably cylindrical "round bales", the fresh material is loaded in a very simple way by means of a forklift or an agricultural tractor equipped with lifting forks. To allow for loading operations, the round bales have a smaller diameter than the internal diameter of the digester. The difference in diameter also serves to facilitate the internal circulation of the priming liquid and its absorption by the round bales.

In the case of bulk materials, on the other hand, these are loaded by means of a special push loader, which can be moved by means of a trolley to position itself in correspondence with the mouth of each digester.

Once the digester has been loaded with fresh material, and at the same time the digestate has been unloaded, digested material, the two ends of the cylinder are closed by means of two hermetic gas and liquid-tight lids.

The biological digestion process is triggered by the total or partial filling of the digester with liquid deriving from a previous digestion treatment, such as that resulting from the pressing of the digestate, or with zootechnical waste. It is also possible to trigger the process through the partial recirculation of already digested solid material.

The biogas produced inside the digester is collected by special outlets made in the upper part and sent, possibly with the aid of a blower, to an accumulation system, such as a gasometer, from which it is taken for use. in generating sets, after dehumidification and desulphurization, or to be sent to a refining system capable of absorbing carbon dioxide and raising the methane content for subsequent introduction into the network or compression in cylinders.

At the end of the digestion process, which lasts approximately two or three weeks, the liquid is drained from the digester and collected in its tank. The liquid is discharged through a series of openings located in the lower part of the digester or end covers, preferably on the discharge cover. After draining the liquid the drain cover is removed. In correspondence with the digester discharge mouth there is a tank for collecting the solid material and the liquid left in the digester. The collection tank is equipped with a liquid drainage system, which is sent to a special container waiting to be recycled in the digester for a new cycle or recovered in another way. The shovelable material accumulated in the collection tank is removed by mechanical shovel and used according to the planned scheme, recirculation in the digester, pressing, composting or spreading on agricultural land.

When the liquid contained in the digester has been drained, the loading lid is also removed.

The heating and sanitation of the fresh material loaded into the digester take place through heat exchange between the cylindrical wall of the digester and the liquid contained in the tank containing the digester. The tank can be made of reinforced concrete or any other waterproof material, while the cylindrical body of the digester, fixed to the bottom of the tank with anti-floating tie rods, is made of corrosion resistant materials, such as plastic, fiberglass or stainless steel. . The heat exchange takes place with the tank liquid through the digester wall, which is therefore not insulated. Instead, the walls of the tank and the two end covers of the digesters can be insulated.

The heat necessary for heating the liquid in the tank can be provided by the <biogas fueled cogeneration unit, or by the solar radiation of the tank,> which in this case is equipped with a transparent cover to obtain the greenhouse effect, and in the at the same time reducing heat losses through the free surface of the liquid.

The system is completed by the containers of the priming liquid, zootechnical waste and leachate, and of the waste liquid and by the system of pumps, valves and pipes necessary to convey this liquid into the digester and to discharge it. The loading and unloading of the liquid can take place through openings and drains made on the wall of the digester, or on the discharge cover. In any case, there are grid devices to avoid clogging of the liquid discharge openings.

The loading lid is only opened after the liquid has completely flowed out of the opposite opening. The digester is slightly inclined towards the discharge side to facilitate drainage.

The system, according to the present invention, is completed by the filling devices of the tank containing the heating liquid and by the relative heating systems, such as for example the boiler cogenerator, heat exchanger, pumps, valves, etc.

In the case of treatment of non-pumpable materials, the "batch" type process can also include two or more phases.

The treatments carried out in the digesters of the present invention can all be of the biological type, hydrolysis and biomethanization, or a chemical pre-treatment of hydrolysis can be provided, which can be particularly useful in the digestion of agricultural waste, for example rice straw.

The system described above is suitable for the treatment of material with a high content of dry matter, while the variant with floating digester can only accept pumpable material as input, therefore in the case of organic waste it is required to grind and pulp it. The floating digester can easily rotate on itself, driven by two pairs of upper motorized wheels which counteract its buoyancy, or the rotation can take place by means of a belt or rope system, wound on the digester and operated by two rotating winding drums. In the case of the belt drive system, the rotation is necessarily alternated in both directions. Depending on the needs of the process, the rotation can be continuous or intermittent.

Floating digesters lend themselves to various system configurations as the liquid can be transferred from one to another, according to a series, parallel or combined series and parallel scheme. This system includes pumps, piping and valves necessary for operation. To allow vertical displacement of the digester during the loading and unloading phases, flexible pipes supported by suitable accompanying means are used. The same pipes can follow the alternating rotation movement of the digester, if foreseen, while in the case of one-way rotation, quick coupling pipes are preferred, which are disconnected once the unloading and loading operations have been carried out.

In a further variant of the present invention, in order to avoid the introduction of oxygen into the digester, the emptying of the digested liquid can be carried out by sending compressed biogas, or inert gas, into the digester, so as to obtain the complete escape of the fluid from one or more openings obtained in the lower part of the digester or in its end covers.

Furthermore, the digester can be easily inspected and its interior can be easily cleaned after having removed the two end covers.

Finally, according to another characteristic of the invention, the tank containing the heating liquid contains floating bodies, such as hollow plastic spheres or expanded polystyrene elements, in order to limit heat dispersion across the free surface of the liquid.

The present invention is particularly advantageous even in the case where the production capacity is not high and the use of other known systems is not economically interesting, as in the case of small farms, or when it is intended to produce biogas with the organic waste produced. from small communities.

Drawings illustrations

These and other characteristics of the present invention will appear evident from the following description by way of preferential example of construction, however not limiting, and in the eight attached drawing tables, where:

Fig. 1 shows, in longitudinal section view, a cylindrical digester blocked in the structure of the tank, immersed in the heated liquid;

Fig.2 shows, in plan view, a system comprising four parallel digesters immersed in the same tank containing heated liquid;

<-> Fig. 3 shows, in side view, the loading side of the system represented in the previous figure;

Fig. 4 shows, in partial longitudinal section view, a digester during the loading phase of round bales with a suitable forklift truck;

<-> Fig. 5 shows, in partial longitudinal section view, a digester fixed to the tank with a push loading 1 unloading system for loose materials;

Fig. 6 shows, in partial longitudinal section view, the previous figure in the subsequent phase of pushing the bulk material inside the digester;

Fig. 7 shows, in front view of the cylindrical digester, the trolley loads bulk material with a pusher;

<-> Fig. 8 shows, in front view, the tank with the four cylindrical digesters highlighting the upper transparent covers used to obtain the greenhouse effect;

<-> Fig. 9 shows, in longitudinal section, a cylindrical digester of the floating type for the treatment of fluids, it is represented as a discharge for which it floats and protrudes above the tank;

<-> Fig. 10 shows, in front view, the previous figure;

Fig. 11 shows, in longitudinal section view, a cylindrical digester partially immersed since it is partially filled with the fluid to be treated;

<-> Fig. 12 shows, in front view, the previous figure;

Fig. 13 shows, in longitudinal section view, the same digester of the four previous figures, completely immersed in the liquid of the tank as it is completely filled with the fluid to be treated;

Fig. 14 shows, in front view, the previous figure;

<-> Fig. 15 shows, in longitudinal section view, a cylindrical digester of the floating type equipped with a belt device that partially wraps the external lateral surface which has the purpose of making the digester roll on itself in the liquid of the tank . Here it is represented empty, so it floats on liquid;

<-> Fig. 16 shows, in front view, the previous figure, highlighting the two tape winding units;

Fig. 17 shows, in longitudinal section view, the same digester of the two previous figures, partially loaded with the treatment fluid, so that it is partially immersed in the tank liquid;

<-> Fig. 18 shows, in front view, the previous figure;

<-> Fig. 19 shows, in longitudinal section, the same floating digester of the four previous figures, but fully loaded and immersed in the heated liquid of the tank, with the belt device suitable for making the digester roll on itself ; <-> Fig. 20 shows, in front view, the previous figure.

<As can be seen from the attached figures, this is a new modular system of> anaerobic digestion essentially characterized by being formed by one or more horizontal digesters immersed in a heated liquid; the example shows four parallel digesters side by side. The digester substantially consists of a cylindrical container 1 whose two ends are closed by removable lids 2, which are fixed to the two opposite walls of the tank 3 containing the heated liquid 4. The digester is made of liquid and gas tightness, and It is equipped with suitable seals 5 provided during the construction phase to prevent the liquid from escaping from the tank. Furthermore, these digesters being immersed in the liquid undergo a buoyancy thrust especially when they are unloaded or during the loading phase, for which there are several tie rods 6 anchored to the floor of the tank that partially envelop the lateral surface, and 10 other equivalent means,

This digester can be used to anaerobically treat both pumpable materials (wet digestion) and shovelable materials (dry digestion). The pumpable materials are introduced into the digester through one or more openings made on the shell or on the lids and are discharged through openings made in the lower part of the digester. In the case of treating pumpable materials, it is also possible to discharge the digester by introducing pressurized gas, preferably biogas, and opening one or more discharge openings. On the other hand, when handling non-pumpable materials, the loading / unloading system of the digester 1 is pushed. In a first case in which solid material in round bales 7 is used, it is simply possible to use a lift truck 8 equipped with forks 9 which lifts and directs the cylinder and pushes it towards the inside of the digester. Obviously, on the other hand, the cover 2 must be open to allow the contents of the digester to escape, otherwise it is not possible to load with new material. The material in round bales is made to slide on a tooth 19, on the lower part of the inlet, so that the last loaded bale cannot move backwards during the extraction of the forks. The material treated inside the digester is pushed out, from the loading step, and dropped into an external shallow collection tank 15 from where the material is removed.

On the other hand, in the case of use of solid bulk materials, in Figures 5, 6 and 7, a possible solution is represented with the use of an appropriate machine 11, for the collection with top loading of the bulk material 13, and horizontal thrust and longitudinal inside the digester 1 with a press 12. When there are several digesters side by side, this machine can move by means of a trolley 10 to position itself in correspondence with the loading mouth of each digester. The front and upper part of the machine 11, where the loose material 13 is collected, provides two semi-lids with an arc of circumference 14 which close in such a way as to form a circular channel during the phase of pushing the material inside the digester. Once the thrust has been carried out, the piston returns to the retracted position and the two covers are opened to allow the compression chamber to be loaded. The movements of the loader carriage and the operating phases of the machine are obtained with known technical means.

Once the digester has been loaded with fresh material and the digestate has been discharged at the same time, the two ends of the digester are closed by means of the two gas and liquid-tight lids. The biological digestion process is therefore triggered by filling the digester, totally or partially, with liquid deriving from a previous digestion treatment, or with zootechnical wastewater to be exploited for the production of biogas. The introduction of the liquid takes place through openings made in the shell or in the lids with suitable systems known in the sector. During the insertion of the liquid, the air present in the digester escapes through a valve which is open during this phase. It is also possible to trigger the process by recirculating already digested material which is mixed with the fresh organic material before being loaded into the digester.

<Once the digestion process is complete, the liquid is drained from the digester and collected in its tank. The liquid is discharged through a series of openings with> valves which are located in the lower part of the digester or on the discharge cover, which is subsequently removed for discharging the material into the appropriate external tank 15.

The heating and sanitation of the fresh material take place by means of heat exchange between the walls of the digester and the liquid 4 contained in the tank 3 which houses the digester. Both tanks 3 and 15 can be made of reinforced concrete or any other waterproof material, while the cylindrical body of the digester, fixed to the bottom of the tank with anti-floating tie rods, is made of corrosion resistant materials, such as plastic, fiberglass or stainless steel. The heat exchange between the treated material and the hot liquid of the tank takes place through the digester wall, which is therefore not insulated. The walls of the tank and the covers of the digesters which are not in contact with the heating liquid can be insulated. The heat needed to heat the tank liquid can conveniently be supplied by the cogeneration unit fueled by biogas.

As shown in Fig.8, to favor solar radiation the tank can be equipped with a transparent cover in order to obtain the greenhouse effect. The system is completed by the graft liquid tank (zootechnical waste and leachate) and by the system of tanks, pumps, valves and ducts necessary to convey this liquid into the digester and to discharge it. The pre-heating of the priming liquid is generally not necessary due to the high heating capacity of the digester by the tank liquid.

Digester 1 needs to be heated to operate efficiently and this happens through the liquid in which it is immersed. This liquid 4 can be heated by means of various known means, such as boilers and burners, also using the same biogas produced by the anaerobic digestion system. To maintain this liquid at the temperature, upper covers 20 are provided for the containment tank 3, preferably transparent in order also to obtain heat due to the greenhouse effect.

The digester described is particularly suitable for the treatment of material with a high content of dry matter, while the variant with floating digester can only accept pumpable material as input, therefore in the case of organic waste it is required to grind and pulp it.

Now, as in Figures 9 to 20, a second version of the digester is shown, again with a horizontal cylindrical shape, which, however, can float in the heated liquid contained in the tank 3, where the hydrostatic thrust and therefore the thickness of the mantle is not opposed. of the cylindrical digester can be even thinner, resulting in savings in construction cost. The floating digester 16 only needs to be guided in its vertical movements, which are shown in Figures 9 - 10 empty digester, Figures 11 - 12 digester in the loading or unloading phase, and Figures 13 - 14 full digester. Furthermore, flexible pipes are provided for the digester loading and unloading operations.

To agitate the contained liquid, the floating digester 16 according to the present invention can rotate on itself, operated by two pairs of upper wheels which oppose the buoyancy, or as in Figures 15 - 20 by means of one or more belt devices 17 wound on motorized rotating drums 18. In the case of the belt or cable rotation system, the rotation is necessarily alternated in both directions. Depending on the needs of the process, the rotation can be continuous or intermittent. Compared to known agitated systems, the digester of the present invention has the advantage that the agitation system is not located inside the digester, a position that makes its maintenance very difficult because the agitator is accessible only after having completely emptied the digester.

The floating digesters are also suitable for embodiments in the various configurations of the system as the liquid contained by the digesters can be transferred from one to the other according to a series, parallel or combined series / parallel scheme. To allow vertical displacement of the digester during the loading or unloading phases, suitable flexible pipes supported by suitable accompanying means are used. When the digester rotation is foreseen, suitable systems using idle wheels are provided to counteract any axial thrusts and avoid longitudinal movement in both directions. The rotation of the digester is basically aimed at preventing the loss of organic substance through the discharge in the mode of use with a continuous process, but the agitation also serves to favor the release of the biogas from the bath and to prevent the sedimentation of solid substances on the bottom. of the digester.

The invention, of course, is not limited to the example of embodiment described above, starting from which other forms (for example digesters with non-circular section) and other methods of realization can be provided, and the details of execution may in any case without thereby varying from the essence of the invention as stated and claimed hereinafter.

Claims (1)

R I V E N D I C A Z I O N I 1 "Anaerobic digestion system for the production of biogas from manure, livestock manure and solid organic waste, characterized by the fact that it includes the following process elements operating in coordination and cooperation with each other: - a tank 3 for containing the liquid 4 as a means of uniform heat transmission to the digester immersed in it, of the fixed type 1, made of reinforced concrete and 10 other equivalent material. Said hermetically sealed, tennicarnent insulated tank, of a size suitable for receiving one or more digesters, connected to an external tank 15 for the collection of the materials that are discharged from the digesters, possibly equipped with a top cover 20, to contain the resulting heat dispersions from the liquid mass 4, also of the transparent type in order to create a greenhouse effect; means for heating the liquid 4 contained by the tank 3; <-> one or more digesters, of fixed type 1. These digesters are cylindrical in shape and positioned horizontally, operating individually and 10 connected together in parallel and 10 in series. The two ends of the digesters can be opened and closed by means of suitable removable lids 2 fixed to the digesters in correspondence with the opposite walls of the tank 3. Said cylindrical digesters have a large diameter (for example greater than 1.5 m), sufficient to comfortably contain the round bales 7 of solid biomass and at the same time allowing easy cleaning maintenance by operators; - handling means suitable for loading the materials, from which to obtain the biogas, inside the digesters, such as forklifts 8 equipped with appropriate forks 9 to push the material in the form of cylindrical round bales inside the digester, and 10 suitable trolleys 10 mobile and suitable for feeding several digesters, equipped with a collection compartment for the loose material 13 conveyed from above, equipped with two closing lids 14 and with an automatic pushing unit 12 of the same collected material able to insert it inside the digester. Loading can take place when the digester is full only if the lid of the discharge ends is opened, so by pushing new dead material into the loading end, the material contained in the digester is pushed out of the discharge opening and is collected in the evacuation tank. 15; suitable means for anchoring 6 of the digesters 1 to the bottom of the tank or to other parts of the tank to cope with the hydrostatic thrust suffered; <-> automatic means and equipment for loading and discharging the fluids and evacuating the gases generated in said digesters. The anaerobic digestion process can be mesophilic, thermophilic or mixed. 2 "Anaerobic digestion system for the production of biogas, according to the first claim, characterized in that it uses horizontal cylindrical digesters of the floating type 16, immersed inside the tank 3. They are hermetic and are fed with pumpable fluid material, and then they are unloaded with appropriate automatic equipment and are guided and kept in position inside the tank by means of one or more devices. 3 "Anaerobic digestion system for the production of biogas, according to the first and second claims, characterized by the fact that in the case of solid and fluid material being treated, biological and finally close the digester hermetically.> <4 "Anaerobic digestion system for the production of biogas, according to the first and second claims>, characterized in that the digesters are fed by pumpable fluid materials and therefore also the biological primer liquid can be mixed with the liquid pumped into the dig - estore. 5 "Anaerobic digestion system for the production of biogas, according to the first and second claims, characterized by the fact that several digesters can be organized for single-phase and multi-phase, increasing the biogas production efficiency. 6 "Anaerobic digestion system for the production of biogas, according to the second claim, characterized by the fact that they are floating digesters in the liquid 4 contained in the tank 3 and they are equipped with suitable connections with flexible or quick-connect pipes in order to load e10 discharge the fluid being treated e10 to evacuate the biogas produced. 7 "Anaerobic digestion system for the production of biogas, according to the first and second claims, characterized by the fact that the loading of the liquid containing the organic substance to be digested can be carried out in continuous, discontinuous (" batch "process) or semi-continuous (intermittent process ). SA Anaerobic digestion system for the production of biogas, according to the second claim, characterized in that the floating digesters 16 can rotate on themselves, alternately in both directions, by means of appropriate upper drive wheels in direct contact with the lateral surface of the digester e10 with tape winding devices 17, 1S or rope which act directly on said external surface. The rotation can be continuous or intermittent, and has the purpose of mixing the materials contained in the digester. 9 "Anaerobic digestion system for the production of biogas, according to the first and second claims, characterized in that the tank 3 of the heating liquid 4 contains floating bodies, such as for example hollow plastic spheres or elements in expanded polystyrene, suitable to limit the dispersion of heat through the free surface of the liquid.