GR1009957B - Anaerobic digestion arrangement - Google Patents

Abstract

The invention relates to an arrangement of intermittently working anaerobic digestion reactors designed to treat the organic fraction of solid dry waste. The design of the system increases the durability of the construction and improves its functionality, in particular, the management of leachate and air discharge. Each reactor is a closed airtight tank having a fully airtight door on its only open side. The reactor has a ventilation network which is installed on the reactor’s floor and consists of a piping network and an air supply air pump. The leachate is collected through nozzles and ventilation ducts. The leachate recirculation and maceration system consists of a network of pipes, the recirculation pump and the spraying nozzles. In addition, it has a suitable underfloor heating system consisting of a network of pipes encased in the concrete of the reactors’ floor. The biogas produced by the anaerobic digestion process is conducted, through a duct, to the biogas transport and storage network.

Description

ANAEROBIC DIGESTION ARRANGEMENT

DESCRIPTION

Technical field of invention

The invention refers to a device for the anaerobic digestion of solid waste of the "intermittent project" type (batch processing) in order to achieve the breakdown of their organic components and the production of biogas, which is mostly composed of methane and can be used as fuel for the production thermal, mechanical or electrical energy. The device consists of specially designed closed reactors, intermittent work, in which the anaerobic digestion of the organic fraction of the solid waste in dry form takes place.

Particular features of the innovative device presented by the present invention are its construction in such a way that it does not appear vulnerable to corrosive components produced during digestion, the improved management of the digestion components in order to promote the performance of the device ( fuel gas production in a given time) and the formation of the appropriate innovative infrastructure, so that the produced active ingredients (which promote methanation) are more efficiently collected in order to be reused in the methanation process.

State of the Art and Evaluation

The Anaerobic Digestion (ANA) process is a well-known and proven technology for the treatment of organic waste. The AX process is based on the decomposition of the organic matter of the waste in a suitable digester, in specific conditions of temperature, pH and substrate, by a combination of bacteria and in the absence of oxygen, to produce a gas mixture -called biogas- and the digested residue ( digestate slurry).

Anaerobic digestion technologies are distinguished based on the moisture content of the incoming raw material, into wet and dry digestion. Specifically, digestion is wet, where the substrate, in the form of liquid sludge, has a dry mass content of 10% to 15%. Accordingly, dry digestion is where the substrate, in the form of stable solid material, has a dry mass content of 20% to 50%.

Liquid AX is the first form in which the method was developed. The first application of liquid AC was carried out by Donald Cameron in Exeter in England in 1895 and in particular the lamps of the city's municipal lighting operated by burning biogas that came from municipal sewage. In Denmark, the first biogas plants from municipal wastewater date back to 1920.

The dry anaerobic digestion method has been applied in the last two decades for the treatment of solid waste, with the aim of stabilizing the organic fraction of the waste and producing biogas. To achieve the above, the usual dry anaerobic digestion systems apply provisions for biogas collection and management, leachate collection, soaking and heating.

Advantages of the present invention

Taking into account the state of the art as described above, the purpose of the present invention is the development of dry anaerobic digestion systems, in such a way as to improve leachate runoff, optimize process efficiency, while at the same time increasing system durability, by limiting the metal and mechanical parts that come into direct contact with the waste. In addition, the combination of the required networks is achieved with saving materials, reducing energy consumption and improving safety.

Detailed description

Figure 1 shows, indicatively, a vertical longitudinal section of the proposed configuration of the elements that make up the present invention.

Figure 2 shows, in top view, the configuration of the ventilation device before its encasement in the concrete of the reactor floor.

Figure 3 shows a longitudinal vertical section of the reactor with an emphasis on the leachate collection elements, near the port.

Figure 4 shows a detail of the innovative combination of ventilation and leachate collection systems.

Figure 5 shows a top view of the underfloor heating system before its embedment in the floor.

The dry anaerobic digestion reactor of the present invention is a closed airtight (rectangular, preferably, without excluding any other geometric configuration) concrete tank, which on one side has a door for loading and unloading organic solid waste. To implement dry anaerobic digestion processes, a reactor is equipped with biogas management, aeration, venting, leachate collection, recirculation and soaking, heating, safety, monitoring and control systems. In-reactor digestion is carried out discontinuously in batches. To complete a dry anaerobic digestion cycle within the reactor, the following takes place:

1. Inside the reactor, the solid organic waste to be digested is deposited in a pile, through the door that closes and seals hermetically.

2. The waste aeration phase through the aeration network begins. The aeration lasts until the temperature rises to the appropriate levels, to then carry out the digestion of the waste. The increase in temperature is achieved by the release of heat from the aerobic biodegradation reactions of organic waste. When the target temperature is reached, the fans are stopped, so within a few hours the aerobic microorganisms consume the remaining oxygen inside the reactor.

3. Anaerobic digestion then begins by inoculating the waste with leachates from previous treatment cycles through the soaking network. Wetting the waste with leachate ensures that moisture is maintained at the required levels and inoculates the waste with organic acids and anaerobic microorganisms to carry out the anaerobic digestion reactions. In addition, the temperature of the waste is maintained at the desired levels for the realization of the anaerobic reactions with the help of an underfloor heating system.

4. Completion of anaerobic digestion is noted when a decrease in the amount of biogas produced is recorded and is achieved by stopping soaking and starting final aeration. The air supply to the waste allows the biogas to be completely removed from the waste pile and the reactor, for the safe opening of the door. This is followed by the unloading of the waste, for its implementation.

Figure 1 shows an indicative and non-binding embodiment of the present invention. The illustrated dry anaerobic digestion reactor (1) of the present invention is composed of a closed airtight rectangular concrete tank of special specifications (of suitable strength for the process conditions) and of the peripheral process management systems. On the only open side of the tank, a completely airtight door (2) is installed, from which the organic solid waste for digestion is loaded and unloaded. Within the tank, the organic waste is deposited in a pile (3). The style of the waste pile placed inside the reactor ensures the uniform progress of operations and the exit of gases from the waste mass. A thermal insulation system is placed on the floor (6) and/or on the walls of the reactor to seamlessly control the temperature of the processes and reduce energy costs.

The most essential innovation of the present invention lies in the special design of the reactor for carrying out the processes of aeration and collection of the produced leachates. As can be seen in figure 2, the ventilation and collection of leachates is carried out through a common network of ducts (4) and nozzles (5) integrated in the floor (6) of the reactor. The ducts are boxed along the floor (6), following its slope, and start from a common duct, hereinafter called the distributor (7), which is connected to the air supply air pump depression (8) of explosion-proof type. Along the ducts (4), nozzles (5) of a suitable cross-section are installed, the tip of which reaches the crown of the floor, so that the outlet of the nozzles (5) is "face-to-face" with the floor (6). During the aeration operation, in the initial and final phase of the overall treatment cycle, the air pump (8) supplies air, which is transported through the aeration ducts (4) and exits through the nozzles (5) to the pile of organic waste. The air supply network allows the mixing of fresh, but also recirculated air from the reactor at the inlet of the air pump (8), automatically through diaphragms.

During the operation of anaerobic digestion, in the intermediate and main phase of the overall cycle, leachates are produced which run through the heap and, by gravity, are directed towards the floor (6) of the reactor. The innovation of the present invention lies in the fact that the collection of leachates is done through the nozzles (5) and the ducts (4) of the single ventilation-leachate collection network, significantly simplifying the construction. The ventilation ducts (4) extend along the length of the reactor (1) and terminate in a transverse collector (10) which, in turn, terminates in a final collection well (11) located near the feed port (2), as, illustratively , is also depicted in figure 2.

Figure 4 shows the two phases of the innovative use of the above-mentioned "duct-nozzle" system both for heap aeration and leachate removal.

The reactor (1) has been loaded with biodegradable material which has been deposited on the floor (2), forming a pile (3). Inside the floor (6) - made of concrete, the ducts (4) are embedded along which there are - likewise embedded in the concrete - nozzles (5) which end on the surface of the floor (2) without protruding above it.

Figure 4A shows the situation in which air is fed into the distributor (7) and distributed to the boxed ducts (4). Then this air ends up in the nozzles (5) from where it escapes to run through the mass of the pile (3).

Figure 4B shows the situation in which the aeration phase has been completed and the aqueous leachates (3A) fall from the pile (1) and, through the nozzles (5), end up in the ducts (4) from where they are removed by gravity. It should be noted that, as shown in the figure, both the floor (6) and the ducts (4) have the appropriate slope to facilitate the drains (3A) to move in the desired direction.

Figure 2 shows maintenance wells (9) through which the periodic cleaning of the ventilation ducts (4) is facilitated from solid transported materials that have been carried away by the flow of leachates.

From the collection well (11) starts a pipe (12) that leads the leachate to the storage tank (not shown) which is located outside the reactor.

It is obvious that a part of the leachates will remain on the floor (6) of the reactor (1) and will not follow the intended path of their channeling to the ducts (4) through the nozzles (5). To collect the leachates that collect on the floor (6) of the reactor and do not go through the nozzles (5) and ducts (4), the floor of the reactor is designed with suitable slopes, which ensure the uninterrupted flow of the leachates so that they end up in the secondary channel (14) and, from there, to the collecting well (11) which is located near the port (2) and parallel to it.

In particular, as illustrated in Figure 3, the floor (6) has a special configuration of slopes both lengthwise and widthwise. The slope (13) of the floor is formed along the reactor in the direction of the leachate concentration channel (14). From the feed port (2) to the leachate collection channel, the slope is reversed (15) so as to avoid accumulation of leachate at the bottom of the port (2)

In the same figure 3, a siphon device is depicted in the collection well (11) into which (and below the surface of the collected leachates) the transverse collector (10) discharges. In this way, the leakage of gases from the reactor to the leachate storage tank and vice versa is excluded. In the well (11), there is also the final retention of any possible transported materials moving through the pipelines (4).

The innovative design of the unified aeration and leachate collection network of the present invention increases the functionality of the processes and the performance of the anaerobic digestion, improving the performance of the processes of aeration and concentration of the leachates. Effective diffusion of air throughout the mass of the waste pile is achieved in the initial and final phases of the treatment cycle, as well as optimal and faster removal of leachates for their concentration, storage and recirculation. A very important advantage is that the design of the reactor networks ensures absolute tightness to avoid biogas leaks. In addition, the innovative design of the networks, compared to the dry anaerobic digestion systems of the existing state of the art, achieves the avoidance of contact of any metal element or other part of the equipment with the mass of organic waste to be digested. In this way, the durability of the installation and the lifetime of the installed equipment are increased. It should be noted that, in known applications of the technical level, there is contact of metal elements of the reactor with the pile, resulting in their unwanted corrosion by the corrosive components of the waste.

The leachate storage tank is underground and is made of reinforced concrete of suitable strength for the operating conditions. The tank is thermally insulated and has a suitable heating network embedded in the bottom of the tank to maintain the temperature of the leachates at the desired levels. For the uniform distribution of heat in the total mass of leachates, a stainless steel, explosion-proof type stirrer is installed.

The leachate recirculation and wetting system (Figure 1) consists of the recirculation pump (not shown) which feeds the wetting pipe (16) which runs inside the reactor, above the stack (3), fixed to the reactor roof (1 ). Along its length, this wetting conduit (16) carries multiple wetting nozzles (17) each of which shoots down a bundle (17A) of leachate in the shape of an "umbrella" so as to ensure wetting of the exposed surface of the pile (3 ) in its entire extent. The recirculation system has a suitable arrangement of valves (not shown) to regulate the flow of leachates.

As shown in Figure 5, the anaerobic digestion reactor has a suitable in-floor heating system consisting of a network of ducts (18) encased in the concrete in the reactor floor to help maintain the temperature at desired levels. Accordingly, the leachate storage tank has a heating system consisting of a network of pipes encased in the concrete at the bottom of the tank. The system comes with the required heat exchangers, circulators and everything required for its proper operation. The heat supply to the reactor is regulated according to the phase of the digestion process in which it is located.

The gases released from above the pile (3) throughout the anaerobic digestion cycle exit through an outlet pipe (19) and are channeled to the corresponding treatment or disposal system. Without deviating from the existing state of the art, the waste gases produced in the initial and final phases of the treatment cycle (venting) are directed to the gaseous emissions treatment system or to the flare (not shown) depending on their methane content. The biogas produced in the anaerobic digestion phase is received from the outlet pipe (19) and is directed to the storage airlock or to the flare, depending on their methane content. The outlet and routing of the waste gases and biogas is achieved automatically, based on the measurements (via suitable sensors - not shown) of the composition of the reactor atmosphere and through the actuation of an appropriate valve arrangement, as dictated by the existing state of the art.

The reactor is equipped with multiple systems and protection devices intended for use in explosive atmospheres. Thus, overpressure and underpressure safety valves (20), as well as flame arresters (21), are placed in specially selected places. Special measures are taken to make it impossible to open the reactor door before it is ensured that the concentrations of explosive gases inside the reactor are at safe levels.

Claims (6)

1. A system for anaerobic digestion of the biodegradable material of the organic fraction of solid waste, and said system consists of at least one batch dry anaerobic digestion reactor (1) and which reactor (1) is a closed airtight tank, having a watertight port (2) and provisions for biogas collection and management, leachate collection and recirculation, ventilation, ventilation and heating and is characterized by that in the floor (6) of the aforementioned reactor (1) at least one aeration duct (4) is integrated, which supplies nozzles (5), integrated in the aforementioned floor (6), through which air is directed to the overlying pile (3) of biodegradable material and from that a part, at least, of the aqueous leachates (3A) flowing, by gravity, from the aforesaid pile (3) enter the aforesaid nozzles (5) and end up in the aforesaid aeration ducts (4). 2. Anaerobic digestion system according to claim 1, characterized by that the floor (6) of the aforementioned reactor (1) has a channel, hereinafter referred to as the secondary channel (14) and which is located near the port (2) and extends parallel to it, from that the floor (6) of the aforementioned reactor (1), on which the biodegradable pile (3) is deposited, is formed with a slope along the reactor (1) such that the leachates (3A) that have not flowed into the aforementioned nozzles (5 ) to move, by gravity, on the floor (6) until they reach the aforementioned secondary channel (14) and from that the part of the floor (6), extending between the port (2) and the aforementioned secondary channel (14), is inclined opposite to that of the floor (6) of the rest of the reactor (1) so as to prevent the accumulation of leachate at the bottom part of the port (2). 3. Anaerobic digestion system according to claim 1 or 2, characterized by that the pile ventilation network (3) consists of multiple parallel ducts (4), which are integrated into the floor (6) of the reactor (1), and which ducts (4) are placed at an angle so that the aqueous leachates (3A ) that penetrate inside them, to flow by gravity until they end up outside them. 4. Anaerobic digestion system according to claim 3, characterized by that all of the aforementioned ducts (4) end in a transverse collector (10) which discharges into a final collection well (11). 5. Anaerobic digestion system according to claims 2 or 4, characterized by that the aforementioned secondary channel (14) discharges into a final collecting well (11). 6. Anaerobic digestion system according to claims 1-5 characterized by that the leachates (3A) that end up in the final collection well (11) are collected and re-directed to the pile (3), through wetting and that the aforementioned wetting is achieved by spraying from multiple wetting nozzles (17) located above the pile (3) and fed by at least one wetting pipe (16).