WO2013144825A1

WO2013144825A1 - Unit for the digestion of organic wastes and plant for treating organic wastes comprising the unit

Info

Publication number: WO2013144825A1
Application number: PCT/IB2013/052378
Authority: WO
Inventors: Loris Bressan
Original assignee: Ambientalia S.R.L.
Priority date: 2012-03-27
Filing date: 2013-03-26
Publication date: 2013-10-03
Also published as: ITBO20120164A1; EP2831218A1

Abstract

A unit for the digestion of mixtures of organic wastes and biomasses comprises a base (2), a member (3) for containing a mass (50) of organic wastes, rising from the base (2) along a vertical axis of extension (A) and comprising at least one perimeter wall (4) equipped, at its lower end adjacent to the base (2), with a reclosable mouth (4a) for picking up the mass (50). The containment member also comprises a roof (5) having an openable door (5a) to allow organic wastes to be fed into the containment member (3). The unit also comprises means for feeding (7) the organic wastes operatively associated with the door (5a) and configured to gravity feed the organic wastes into the containment member (3) through said door (5a) and mixing means (9) accommodated at least partly inside the containment member (3) and configured to move the mass (50) in order to distribute it.

Description

DESCRIPTION

UNIT FOR THE DIGESTION OF ORGANIC WASTES AND PLANT FOR THE TREATMENT OF ORGANIC WASTES COMPRISING SAID UNIT

Technical field

This invention relates to a unit for the digestion of organic wastes and a plant for treating organic wastes comprising the unit.

More precisely, this invention relates to a unit for the anaerobic digestion of organic wastes and a plant for the aerobic treatment of organic wastes comprising the unit.

The invention is therefore applicable to the sector of recycling and the eco- efficient transformation of urban wastes, of organic biomasses including energy crops and animal faeces.

The expression "organic wastes" means a mixture combining both organic wastes and biomasses.

The digestion unit can be used both in anaerobic digestion processes and in aerobic digestion processes, after the modification of the characteristic features of each of the treatments.

Anaerobic digestion is a biochemical type conversion process which occurs in the absence of oxygen and consists in micro-organisms breaking down the complex organic substances (lipids, proteins, glucosides) contained in the organic wastes, which produces biogas normally consisting of approximately 50-70% natural gas and, for the remaining part, C02 and other components. The biogas produced in this way is treated, accumulated and can be used as renewable energy fuel for powering internal combustion engines for the cogeneration of electrical and thermal energy or, after purification, for the production of biomethane (usable as a replacement for natural gas). Background art

There are various types of prior art dry anaerobic digestion units (or digestors) defined by a longitudinal tunnel extending horizontally and comprising an inlet portal.

The inlet portal is configured to hermetically occlude an inlet opening to the tunnel, through which, in an open configuration of the portal, an operator can feed or extract the organic material into the digestor by means of suitable loading/unloading means, such as for example mechanical arms and graders.

Thus, known digestors comprise a single access opening through which the material is both fed into and removed from the tunnel downstream of the decomposition process.

Disadvantageously, in light of the length of the tunnel, each operator is forced to go into the tunnel for long intervals of time with significant wasted time and health risks.

Alternatively, continuous type digestors are known, extending horizontally, and comprising pusher means positioned in succession along the direction of extension of the tunnel and configured to allow the material to continuously advance from the access opening to an outlet opening located at the opposite end.

Disadvantageously, in this configuration the pusher means must be high- powered because they must move within the dry mass with the precise aim of moving it forwards. The energy consumption and possibility of blockages due to deposits and sediments are therefore extremely high. It should also be noted that the digestion processes are for the most part performed at controlled temperature, so that fermentation occurs uniformly throughout the organic mass.

To keep the temperature constant (and high), the known art comprises conduction heating by placing a series of heating coils in the base of the tunnel and, if necessary, sprinkling high-temperature fluids.

Disadvantageously, however, when the volume of the mass to be heated is high, the efficiency of these types of heating systems decreases since the "core" of the organic mass cannot be reached thus being limited to exchanging heat with the peripheral zones of it.

Moreover, it should be noted that the difficulty in uniformly heating the mass inside the digestor prevents thermophilic digestion (at a temperature greater than 50 °C), which is the most efficient, because too much power must be lost in heating in order ensure that all the zones of the mass are at the proper temperature. Disclosure of the invention

The aim of this invention is to provide a unit for the digestion of organic wastes that overcomes the above mentioned drawbacks of the prior art. More specifically, the aim of this invention is to provide a highly efficient unit for the digestion of organic wastes which can be installed in small spaces.

Another aim of this invention is to provide a unit for the digestion of organic wastes which minimizes operator interventions inside it.

The aim of this invention is also to provide a plant for treating organic wastes which is self-sufficient in terms of power and is capable of minimizing dissipation.

These aims are fully achieved by the unit for the digestion of organic wastes according to this invention, comprising a base, a member for containing a mixed mass of organic wastes and biomasses, rising from the base along a vertical direction of extension and comprising at least one perimeter wall (that is a perimeter enclosure) equipped, at its bottom end adjacent to the base, with a closable mouth for picking up the mass. It should be noted that the containment member also comprises an upper roof having a door which is movable between an open configuration and a closed configuration to allow mixtures of organic wastes and biomasses to be fed into the containment member.

In this regard, the digestion unit also comprises means for feeding the organic wastes which are operatively associated with the door and configured to gravity feed the organic wastes into the containment member through the door and mixing means accommodated at least partly inside the containment member and configured to move the mass in order to distribute it (and render uniform its state of decomposition).

Advantageously, that way, the digestion unit is automatically fed without any operator having to go into the space defined by the containment member.

Moreover, the movement of the mass of wastes, obtained by the combined operation of the mixing means and gravity, allows both the percolate (that is the catalyst liquid) and the temperature inside the containment member to be evenly distributed.

In particular, the possibility of moving the material from the top downwards also facilitates the absorption of the percolate sprinkled from the roof of the containment member to the bottom zones, thus combating the formation of deposits which might block the functionality of the digestor.

Brief description of the drawings

These and other features of the invention will become more apparent from the following detailed description of a preferred, non-limiting embodiment of it, with reference to the accompanying drawings, in which:

- figure 1 is a perspective view of a first embodiment of a unit for the digestion of organic wastes according to this invention, with some parts cut away in order to better illustrate others;

- figure 2 is a view from the side in cross section of a second embodiment of a unit for the digestion of organic wastes according to this invention;

- figure 2a shows a detail P from figure 2;

- figures 2b and 2c show a detail P1 from figure 2 in two different embodiments;

- figures 3a and 3b show a component of the digestion unit of figure 1 ;

- figure 4 shows a schematic view of a plant for treating organic wastes according to this invention.

Detailed description of the preferred embodiments of the invention

With reference to the accompanying drawings, the numeral 1 denotes a unit for the digestion of organic wastes according to this invention.

In particular, this invention relates to a "dry" digestion unit 1 (or digestor 1 ), that is a unit for treating a mass 50 of organic wastes in which the dry substance is greater than 15%-20% by weight.

Moreover, the digestor 1 according to this invention is of the discontinuous type, that is once loaded, it is left to operate without interruptions for a predetermined interval of time (preferably 25-30 days) before being reopened for unloading.

It should be noted that the digestion unit 1 according to this invention is placed, in use, within a plant 100 for treating organic wastes.

The expression organic wastes preferably defines a mixture of organic wastes and biomasses.

Thus, the digestion unit 1 can be both of "aerobic" and of "anaerobic" type, according to the needs of the place of installation and the specifications of the plant 100.

Whatever the case, the characteristic features of the aerobic configuration of digestion unit 1 and those of the anaerobic configuration of the digestion unit 1 are specified below, where necessary.

The digestion unit 1 comprises a base 2, from which a containment member 3 rises up, defining inside it a space "V" for receiving the mass 50 of organic wastes.

The containment member 3 is at least defined by a perimeter wall 4 and by a roof 5, which delimit the aforesaid receiving space "V".

More precisely, said at least one perimeter wall 4 is a perimeter enclosure which laterally delimits (the top surface area of) the receiving space "V". The perimeter enclosure can consist of a plurality of walls adjacent and successive to each other (for example polygonal) or of a single curved wall (for example circular or elliptical).

Reference will hereinafter be made to the perimeter wall and to the perimeter enclosure 4 without distinction.

Preferably, the perimeter enclosure 4 (and hence the containment member 3) rises up from the base 2 along a vertical axis of extension "A", which preferably corresponds to a main direction of extension of the digestion unit 1.

In the preferred embodiment, the containment member 3 has a substantially axisymmetric geometry about the vertical axis of extension "A".

With reference to the accompanying drawings, the containment member 3 has a substantially cylindrical geometry. Thus, the roof 5 has a substantially circular geometry and the perimeter enclosure 4 is defined by a single cylindrical wall.

Alternatively, however, the containment member 3 might have a different geometry, such as for example parallelepiped (or even cubic).

To allow the "digested" mass 50 to be picked up, the perimeter enclosure 4 has at least one closable pickup mouth 4a, located at a bottom end, adjacent to the base 2.

In other words, the closable pickup mouth 4a is located at ground level to allow specific collection means (not illustrated) to go into the containment member 3 to remove a portion of digested mass 50 and transport it to the successive treatment stage.

Preferably, the collection means are defined by specific blades (telescopic arms) or graders (such as bobcats® or the like) for finding their way into the housing space "V" without the need for the driving operator to physically go into the containment member 3.

In order to keep the pick-up aperture 4a tightly closed during the bacterial action (in particular, the anaerobic process), the containment member 3 comprises closing means 6 which are movable between a first position, in which they completely occlude the aperture 4a, and a second position, in which they leave the passageway free for the collection means.

Preferably, the closing means 6 are of the sealing type, to allow the digestor 1 to be tightly sealed during the anaerobic digestion processes. In the embodiment illustrated, the closing means 6 are defined by a portal 6a, preferably swinging, pivoted at an upper edge of the pick-up aperture 4a.

It should be noted that since a dry plant is involved, the portal 6a has a single function of opening/closing the containment member 3, without any structural function, such as for example sealing against hydrostatic pressure.

To simplify the movement of opening and closing the portal, actuating means (hydraulic, pneumatic or electrical) are associated with it which are designed to impart rotational (or swinging) movement to it.

It should be noted that the containment member 3 for larger digestors (that is with surface width or diameter greater than 5 metres) can comprise two pick-up apertures 4a, which are opposite each other.

In this regard, said larger digestors 1 can have a central support pillar 3a for reinforcing the structure.

Advantageously, this allows reaching the mass 50 to be removed from both sides of the containment member 3 without requiring crossing the housing space "V" from side to side.

It should also be noted that the base 2 in smaller digestors 1 (diameter less than 5 metres) is made of concrete, while the containment member 3 is preferably made of metal.

On the other hand, both the base 2 and the containment member 3 in larger digestors 1 (diameter greater than 5-6 metres) are preferably made of (reinforced) concrete.

Preferably, the containment member 3 also comprises an openable door 5a which is formed in the roof 5 and which is movable between a closed configuration and an open configuration to allow mixtures of organic wastes and biomasses to be fed into the housing space "V". Advantageously, the door 5a allows gravity feeding the mass 50 from above, thus simplifying and speeding up the procedures for filling the digestion unit 1.

In other words, filling occurs by simply taking advantage of the gravity and vertical nature of the silo (containment member 3).

Preferably, the door 5a is openable by tilting, that is it is pivoted on one of the edges to rotate between the open configuration and the closed configuration.

Alternatively, however, the door might be a sliding or other type of door. Similarly to the portal 6, the door 5a is preferably tightly sealed.

In this case too, the door 5a is associated with a movement unit (hydraulic, pneumatic or electrical) configured to selectively move it between the two configurations according to a command given from a panel or control unit (not illustrated).

To increase the safety of the digestion unit 1 , a plurality of inner door panels are envisaged (not illustrated) which are designed to prevent the wastes (that is the mass) from creating sealing problems (that is leaks) by pushing against the portal 6 and/or the door 5a.

Thus, the housing space "V" is substantially partly delimited by the inner door panels.

To supply the containment member 3 with the organic wastes, the digestion unit 1 comprises feeding means 7 which are operatively associated with the door 5a and configured to gravity feed the organic wastes into the containment member 3 through the door 5a.

Thus, the feeding means 7 comprise a release portion 7a facing the door 5a, at least when it is in the open configuration, for releasing a predetermined quantity of mixture (wastes and/or biomasses) inside the door 5a.

Preferably, the means 7 for feeding the organic wastes comprise at least one conveyor belt 8 (or conveyor) having an unloading portion 8a above the door (5a) and facing it. Advantageously, that way, the wastes are gravity released through the door 5a in a simple, precise and quick manner.

To stop filling, it is therefore sufficient to stop the conveyor belt 8.

If, for treating organic wastes, the plant 100 has a plurality of digestion units 1 , the conveyor belt 8 has a corresponding plurality of elements (defining the unloading portions 8a) which are movable between an alignment position, in which they define a sliding plane of the organic wastes, and a release position, in which each movable element defines a tilted plane relative to the sliding one and oriented towards the door 5a. That way, it is possible to bring the respective movable element to the release position, according to which digestion unit 1 is to be fed.

It should be noted that the conveyor belt 8 has a loading portion 8b located at a zone for loading the wastes.

The digestion unit 1 also comprises mixing means 9 accommodated at least partly inside the containment member 3 and configured to move the mass 50 in order to distribute it.

In use, the mixing means 9 are submerged in the mass 50 inside the containment member 3.

Preferably, the mixing means 9 are active along a vertical direction, oriented towards the base 2 in such a manner as to act in conjunction with the force of gravity to move the mass 50 from the top downwards.

In this regard, the mixing means 9 comprise at least one elongate element 0 extending along a main axis "B" of it.

Preferably, the main axis "B" is oriented towards the base 2.

More preferably, the elongate element 10 extends from the roof 5 towards the base 2.

The elongate element 10 is associated with a movement member 1 1 , or actuator, which is configured to cyclically move the elongate element 10 in order to blend the mass 50.

It should be noted that, preferably, the elongate element 10 is operative along a direction parallel to the main axis "B" to move the mass thus allowing a part of the mass 50 at an upper height to be mixed with a part of the mass 50 at a lower height.

Preferably, the mixing means 9 comprise a plurality of elongate elements 10 all located internally within the containment member 3 and active in conjunction with each other on different zones of the mass 50.

Advantageously, that way, the state of decomposition of the mass 50 is rendered uniform in all the zones of it thus speeding up the digestion process.

Preferably, the elongate elements 10 are distributed substantially uniformly in the section of the containment member 3.

In the preferred embodiment, each elongate element 10 is defined by a spiral blade 12 extending around the main axis "B".

Thus, the blade 12 extends along a curved trajectory wound around the main axis "B".

In other words, the main axis "B" substantially defines a direction of extension of the longitudinal member 10.

The blade 12 is thus substantially wound in a helical fashion around the main axis "B" (figure 3) so that a rotation of it about the main axis "B" corresponds with a thrust action on the mass 50 parallel to said axis.

In light of this, the movement members 1 1 are preferably rotary actuators rigidly connected to the elongate element 0 to set it in rotation around the main axis "B".

In the embodiment illustrated, the mixing means comprise a plurality of electric motors 11 a, each connected to a respective elongate element 10. Alternatively, it is in any case possible to envisage the presence of drive means (reduction gears) interposed between the motors 1 1a (or more generally, the movement members) and the elongate elements 10.

It should be noted that the movement speed of the blades 12 is extremely limited, because the digestion process requires lengthy time scales (days). In particular, the rotation speed of the blades is between 50 and 60 rotations/hour. Thus, it should be noted that the blades would substantially not have any mixing effect if the mass were liquid, as they only perform a slow-speed mixing function on "dry" mass, such as the one treated by the plant according to this invention.

It should be noted that the winding does not necessarily have to be regular, but can comprise the presence of turns of a different diameter and with variable step. That way, the action of the mixing means 9 is made more irregular and is better distributed.

In the embodiment illustrated, the blade 12 substantially defines the elongate element 10.

In an alternative embodiment, the elongate element 10 on the other hand comprises a central core (substantially rectilinear) and a screw (defining the blade).

Preferably, the main axis "B" of the elongate elements 10 is substantially vertical, that is mainly extends from the roof 5 of the containment member 3 to the base 2.

Thus, the movement members are located at the roof 5 of the containment member 3 (outside of it).

In the embodiment illustrated in figure 1 , the mixing means 9 comprise a plurality of elongate elements 10 extending from the roof 5 towards the base 2.

Consequently, each elongate element 10 extends between a first end 10a adjacent to the roof 5 and a second end 10b, opposite to the first 10a and spaced from the base 2.

The distance between the base 2 and the second end 10b of the elongate element 10 is sized to allow the passage of the collection means, so that the mixing means 9 are not involved in the unloading procedures of the containment member 3.

In other words, between the base 2 and the second end 10b of each elongate element 10 there is at least one free manoeuvring space "V1" in which the collection means are free to move. In alternative embodiments (figure 2), the main axis "B" is not vertical, rather inclined relative to the vertical.

In these embodiments, at least one longitudinal member extends starting from one side of the perimeter enclosure 4 to the opposite side.

In this case, the movement members 11 (that is the motor 11a or the motors 11a) are located along the perimeter enclosure 4.

Preferably (at least in the anaerobic configuration), the digestion unit 1 also comprises vacuum generating means 13 which are associated with the containment member 3, to extract the air (oxygen) from the inside of it to allow the anaerobic digestion of the mass 50.

The vacuum generating means 13 can be of different kinds, but in the preferred embodiment are defined by a pump 13a which, as soon as the portal 6 and the door 5a are closed, extracts the air (in particular the oxygen) from inside the containment member 3 thus generating the vacuum, so that the process starts immediately.

Moreover, in this regard, the digestion unit 1 also comprises a duct 14 for delivering the biogas which forms inside the containment member 3 during the bacterial action.

The delivery duct 14 is connected to an upper portion of the containment member to intercept the biogas formed and send the aforesaid biogas to an accumulation tank or to other operating units, as will become clearer as this description continues.

Moreover, the digestion unit 1 is equipped with heating means 15 associated with the containment member 3 and configured to keep the temperature in it at a predetermined temperature interval (range).

Preferably, the heating means 15 are used in anaerobic digestion units 1 in which the heating means 15 are configured (regulated) to keep the temperature inside the containment member 3 at values greater than 40 °C, preferably in an interval of between 50 and 55 °C, in order to obtain digestion by "thermophilia" (that is, by means of thermophilic bacteria).

On the other hand, the heating means 15 can be configured to keep the temperature inside the containment member 3 at higher values of between 20 and 45 °C, preferably in an interval of between 37 and 41 °C, in order to obtain digestion by "mesophilia" (that is, by means of mesophilic bacteria).

Alternatively, the digestion unit 1 might operate by "psychrophilia", that is at a low temperature for which the presence of heating means is not required.

Preferably, the heating means 15 are associated with the perimeter enclosure 4 and with the roof 5 of the containment member 3 (that is the walls) to exchange heat with the mass 50 inside the containment member 3.

Moreover, in addition or alternatively, the heating means 15 are associated with the base 2.

More precisely, the perimeter enclosure 4 and/or the roof 5 and/or the base 2 are preferably crossed by a plurality of heat exchange pipes 16 in which a super-heated carrier fluid flows (preferably water).

Preferably, the pipes 16 define a series of exchange coils in which the carrier fluid flows (in recirculation).

In one embodiment, the heating means 15 comprise a plurality of elongate members 17 (heated) connected to the roof 5 and protruding from it towards the base 2. More precisely, the elongate members 17 are substantially vertical.

The elongate members 17 are distributed inside the section of the containment member 3, in particular at a central zone.

Advantageously, that way, it is possible to transfer heat uniformly throughout the mass 50, even in those central zones which are difficult to heat by means of the sole peripheral coils (pipes 16 of the containment member 3 and of the base 2).

Preferably, the elongate members 17 are also crossed by respective exchange pipes 16 (similar to the ones above).

More preferably, the heating means 15 are also associated with the elongate elements 10 of the mixing means 9.

More precisely, the elongate elements 10 are crossed by respective heat exchange pipes 16.

In light of this, the elongate element 10 acts both as a mixer, by means of the rotary movement, and as a heater, by means of the circulation of a carrier fluid.

In other words, the elongate element 10 is both a mixing means 9 and a heating means 15.

Preferably, the digestion unit 1 comprises sprinkling means 18 located inside the containment member 3, near the roof 5, and configured to release a catalyst fluid inside the containment member 3 in order to speed up the decomposition of the mass 50.

The sprinkling means 18 are defined by a plurality of sprinklers 18a positioned in an upper zone of the containment member 3, near the roof 2. That way, the catalyst fluid is gravity distributed inside the containment member 3.

Preferably, the sprinkling means 18 are also associated with the elongate elements 10 of the mixing means 9.

Thus, the elongate elements 10 are crossed by respective channels 10c and comprise apertures 10d, preferably with a function of inoculation, and configured to release the carrier fluid into the mass 50.

Consequently, the elongate elements 10 are both mixing means 9 and sprinkling means 18.

Similarly, the elongate members 17 of the heating means 15 can also be associated with the sprinkling means 18 by fitting them with specific channels (not illustrated) leading into corresponding nozzles.

Advantageously, this also allows the mass 50 to be moistened in points which are difficult to reach with a static system in which the catalyst fluid is sprinkled only at the upper part (that is at the roof 5).

Preferably, the catalyst fluid is percolate, that is a liquid which mainly originates from the infiltration of water into the mass 50 of wastes or from the decomposed wastes.

In this regard, the base 2 comprises one or more traps 2a shaped to channel the percolate formed during the fermentation, and to send it to a tank 102 for storing it, which is then recovered and sprinkled inside the containment member 3.

To promote the channelling of the percolate, the base 2 of the digestion unit 1 is joined with a slope, in order to drain the percolate, which is easily formed, into one or more traps 102.

It should be noted that the heating means 15 preferably comprise a heat exchange unit 15a associated with the percolate tank 102.

That way, it is possible to sprinkle percolate inside the containment member 3 (that is inside the mass 50).

Advantageously, such a solution allows the mixing means 9, and in particular the elongate elements 0, to perform a triple function, that is: - mixers for rendering the mass 50 uniform and preventing deposits;

- heaters for rendering the temperature uniform in all the zones of the mass 50;

- sprinklers for keeping the mass 50 moist and for reaching, with the catalyst percolate, even zones which are difficult to reach with the sole gravity sprinkling of the percolate.

Clearly, this solution allows greatly speeding up the anaerobic digestion process.

In other words, the elongate elements 10 are mixing means 9, heating means 15 and sprinkling means 18.

If the digestion unit is of aerobic type, means 19 for blowing air into the containment member 3 are provided (in place of the heating 15 and sprinkling means 18).

Thus, in this embodiment, the unit 1 comprises an air treatment unit designed to produce an air flow.

Preferably, the air treatment unit is positioned outside the containment member 3. The air treatment unit is associated with specific ducts 20 (preferably made of PVC) for transferring the fluid from the outside to the inside of the containment member 3.

In this embodiment, too, the walls of the containment member 3 and/or the base 2 are associated with the ducts 20 for transferring the air, which comprise specific air vent nozzles 20a.

In particular, the ducts 20 are embedded in the base 2 and/or in the walls of the containment member 3 which comprise apertures for feeding (pressurized) air into the housing space "V". To improve the aeration of the mass 50, the elongate elements 10 of the mixing means also comprise (calibrated) blow holes 21 (that is, for delivery of the pressurized air).

It should be noted that the blades 12 (that is the elongate elements 10) in said embodiment are internally hollow to allow the air to be fed, and have the aforesaid holes 21 on the outer surface of them.

The digestion unit can also comprise air ducts 20 extending downwards from the roof 5 and preferably, equipped with an inspection cap at the end part, to allow any material to be unloaded which would create blockages inside the tube.

An anaerobic configuration of the digestion unit 1 (that is with the heating means 15 and the sprinkling means 18) can be associated with a corresponding aerobic configuration of the digestion unit 1 in order to treat the mass 50 in successive fermentation steps.

The digestion unit 1 is thus placed within a plant 100 for treating organic wastes, which is also an object of this invention.

The plant 100 comprises an anaerobic digestion unit 1 , as described up to here, connected to a cogenerator 101 , that is an apparatus capable of generating energy in different forms (electricity/heat).

More precisely, the plant 100 comprises at least one digestion unit 1 in which the containment member 3 is hermetically sealed to prevent the leakage of the biogas generated by the digestion, at least one cogenerator

101 in fluid connection with the digestion unit 1 , to receive the biogas generated by the fermentation of the mass 50.

Preferably, the cogenerator 101 is configured to provide heat to the heating means 15 of the digestion unit 1.

Advantageously, that way, it is possible to produce, with a single energy source (the mass 50, mixture of organic wastes and biomasses), both the energy required for the operation of the mechanical/electrical members of the plant and the heat useful for achieving thermophilic digestion. More preferably, the cogenerator 101 is also configured to exchange heat with the sprinkling means 16, and in particular with the percolate tank 102. In other words, the plant 100 is self-sufficient. However, it should be noted that the energy produced by the plant is only used in minimal part for auto- feeding and for the most part (up to 95%), it is fed into the grid and sold. The same holds true for the heat produced, which is only used in a small part to heat the digestion unit 1 and for the most part, is reutilized for other purposes.

To allow the heat exchange between the cogenerator 101 and the heating means 15, the ducts 16 of the heating means have a portion of heat exchange 16a located at the cogenerator, in such a manner as to recover the heat needed to heat the digestion unit 1.

Preferably, the plant 100 also comprises means 13 for regulating the inflow of biogas to the cogenerator 01.

The means 103 are configured to regulate the flow rate of biogas into the cogenerator 101 according to the pressure inside the containment member 3 of the digestion unit 1.

In other words, the regulating means 03 comprise a valve located in the upper part (top) of the digestion unit 1 (in particular of the containment member 3) which is designed to block or release the passage of the biogas.

The digestion unit 1 is preferably designed to operate at an overpressure up to 50 mbar. It can in any case also operate at ambient pressure or negative pressure. There are several advantages to operating at overpressure. The first is that, in the event of natural disasters such as for example earthquakes, should fractures (cracks) be created in the structure, a biogas leakage would be created without the risk of the entry of oxygen into the containment member (which might cause an explosion!).

The second advantage is similar to the one above, and is that the possibility of the gaskets (preferably of inflatable type) being damaged in the doors (door 5a and portal 6a) is unlikely, if operating at overpressure, to cause air to be sucked in from the outside.

Another advantage is that a pressurized plant shortens the material transformation times and reduces the operating times while extracting the maximum biogas.

The presence of a cooling system (not illustrated in detail) and possibly a gasometer 104 is may be provided downstream of the valve.

The biogas is purified in a specific purifier or filter (not illustrated in detail) before reaching the cogenerator 101 , and in particular the combustion engines. That way, the biogas fed into the cogenerator is free of pollutants (sulphur compounds, etc.) which are harmful for the cogenerator.

Preferably, the plant 100 also comprises a disposal unit 105 in fluid connection with the digestion unit 1.

The disposal unit 105 is designed to receive the biogas produced in the initial transients of the treatment (that is the digestion) in which the biogas produced has a low concentration of natural gas (and hence is not very functional to the combustion in the motor of the cogenerator).

In light of this, the plant 100 comprises a control unit 106 configured to selectively direct the biogas to the cogenerator 101 or to the disposal unit 105 according to the concentration of natural gas in the containment member 3.

The control unit 106 is thus associated with the sensor means configured to detect the concentration of the gas inside the housing space "V" and possibly to detect its pressure. In particular, gas samples are extracted from the containment member, through several sampling points, positioned in the upper part of the digestor 1 , and sent to a gas analyser which determines the concentration of different gases, preferably CH4, C02, 02, H2S.

The control unit 106, in use, is designed to receive one or more signals correlated with the concentration of natural gas in the containment member 3 and is configured to operate the regulating means 104 (even manually by means of a control panel) in such a manner as to direct the biogas to the cogenerator or to the disposal unit 05.

Preferably, the disposal unit 105 comprises a burning unit 107 configured to burn the biogas sent to it.

The burning unit 107 also comprises a unit 08 for recovering the carbon dioxide generated in the combustion.

Advantageously, said recovery unit 108 is connected to the containment member 3 of the digestion unit 1 to emit the carbon dioxide (acting as inert gas) into the containment member 3 (that is into the housing space "V") before opening the door 5a and/or the portal 6.

This improves the safety of the plant and speeds up the processes of opening/closing the digestion unit.

Alternatively, a container can be provided for collecting the carbon dioxide (CO2) produced in the initial transients of the digestion. This stored carbon dioxide is then reutilized, as described above, as an inert gas to be emitted into the containment member 3 before an opening of the door 5a and/or of the portal 6.

In this embodiment, the digestion unit 1 is equipped with a vacuum pump or turbine (not illustrated) configured to extract the gas in the step of hydrolysis (when only CO2 is produced) and to send it to a tank/gasometer.

Thus, this invention also relates to a method for treating organic wastes, comprising a first step of preparing a member 3 for containing the mass 50 of organic wastes, rising from the base 2 along a vertical axis of extension "A" and comprising at least one perimeter wall 4 equipped, at its lower end adjacent to the base 2, with a reclosable mouth 4a for picking up the mass 50.

As described above, the containment member 3 also comprises a roof 5 having an openable door 5a to allow organic wastes to be fed into the containment member 3.

The method also comprises a step of opening the door 5a, preferably by means of specific actuating means.

The organic wastes defining the mass 50 are then gravity fed into the containment member 3 through the door 5a (by means of the feeding means 7) until the containment member 3 is full.

Once a predetermined filling volume is achieved, the door 5a is closed

(hermetically) for a predetermined interval of time (digestion time).

The predetermined interval of time is between 20 and 35 days, preferably between 25 and 30 days.

At this point, a catalyst fluid (preferably percolate) is sprinkled inside the containment member 3 to speed up the decomposition of the mass 50. Moreover, during said interval of time, the mass 50 is mixed inside the containment member 3 through the aforementioned mixing means 9 for a predetermined interval of time.

During the digestion, the mass 50 produces biogas, which is preferably extracted with the extraction means described above.

Once the fermentation (digestion) is complete, that is at the end of the predetermined interval of time, the reclosable mouth 4a is opened to allow the digested mass 50 to be picked up through the reclosable mouth 4a (preferably by using specific picking up means).

The invention achieves the preset aims and brings important advantages. In effect, the use of the mixing means in conjunction with the force of gravity for moving and rendering the mass uniform allows reducing the times the material remains inside the digestor and operating with a percentage of dry substance greater than 20% without blockage problems for pumps and moving members.

The presence of heating means submerged in the material facilitates the distribution of temperature and allows operating by thermophilia, that is at temperatures over 45 °C without an excessive consumption of energy. Moreover, the presence of ducts for inoculating the percolate into the blade of the mixing means greatly speeds up the digestion process by also distributing the substance into zones which are difficult to reach by means of roof sprayers alone.

The presence is particularly advantageous, in the plant according to this invention, of means for recovering the carbon dioxide, with or without the burner, which increase the safety of the plant while taking advantage of the waste fluids which are thus reused and recycled.

Claims

1. A unit for the digestion of wastes, characterized in that it comprises:

- a base (2);

- a member (3) for containing a dry mass (50) of organic wastes, emerging from the base (2) along a vertical axis of extension (A) and comprising at least one perimeter wall (4) equipped, at its lower end adjacent to the base

(2) , with a reclosable mouth (4a) for picking up the dry mass (50); the containment member (3) also comprising a roof (5) having an openable door (5a) to allow organic wastes to be fed into the containment member

(3) ;

- means for feeding (7) the organic wastes operatively associated with the door (5a) and configured to gravity feed the organic wastes into the containment member (3) through the door (5a);

- mixing means (9) accommodated at least partly inside the containment member (3) and configured to move the dry mass (50) in order to distribute it.

2. A digestion unit according to claim 1 , characterized in that the containment member (3) has a substantially axisymmetric geometry relative to the vertical direction of extension (A).

3. A digestion unit according to either claim 1 or 2, characterized in that the means (7) for feeding the organic wastes comprise at least one conveyor belt (8) having a release portion (8a) above the door (5a) and facing the door, to allow the organic wastes to fall by gravity through the door (5a).

4. A digestion unit according to any one of the preceding claims, characterized in that the mixing means (9) comprise at least one elongate element (10) with a main axis of extension (B) and cyclically movable, for moving the mass thus allowing a part of the mass (50) at an upper height to be mixed with a part of the mass (50) at a lower height.

5. A digestion unit according to claim 4, characterized in that the elongate element (10) is crossed by at least one pipe (16) for recirculating a carrier fluid to exchange heat with the mass (50) near the elongate element ( 0).

6. A digestion unit according to either claim 4 or 5, characterized in that the elongate element (10) has, on an outer surface of it, a plurality of apertures (10d) for sprinkling a catalyst fluid used to speed up the decomposition of the mass (50).

7. A digestion unit according to any one of the claims form 4 to 6, characterized in that the at least one elongate element (10) is defined by a spiral blade (12) extending around the main axis (B); the mixing means (9) comprising at least one movement member (11) associated with the blade (12) to set it in rotation around the main axis (B) to move the mass (50) located near the blade ( 2).

8. A digestion unit according to any one of the preceding claims, characterized in that it comprises vacuum generating means (13) which are associated with the containment member (3), to extract the air from the inside of the containment member (3) to allow the anaerobic digestion of the mass (50).

9. A digestion unit according to any one of the preceding claims, characterized in that it comprises sprinkling means (18) located inside the containment member (3), near the roof (5), and configured to release a catalyst fluid inside the containment member in order to speed up the decomposition of the mass (50).

10. A digestion unit according to any one of the preceding claims, characterized in that it comprises heating means (15) associated with the walls (4, 5) of the containment member (3) and/or with the base (3), for exchanging heat with the mass (50) inside the containment body (3), and which are configured to keep the temperature inside the containment member (3) within a predetermined interval of values.

1 1. A digestion unit according to claim 0, characterized in that the heating means (15) comprise a plurality of elongate members (17) connected to the roof (5) and protruding from it towards the base (2); the elongate members being crossed by at least one recirculating channel (16) containing a heating fluid.

12. A digestion unit according to any one of the preceding claims, characterized in that it comprises means (19) for blowing air into the containment member (3), to allow the aerobic digestion of the mass (50).

13. A plant for treating organic wastes, comprising:

- at least one digestion unit (1) according to any one of the preceding claims, wherein the containment member (3) is hermetically closed to prevent the leakage of the biogas generated by the digestion;

- at least one cogenerator (101 ) in fluid connection with the at least one digestion unit (1), for receiving the biogas generated; the cogenerator (101 ) being configured to supply heat to means (15) for heating the digestion unit (1 );

- means (103) for regulating the inflow of the biogas into the cogenerator (101 ), which are configured to regulate the flow rate of the biogas into the cogenerator (101 ) according to the pressure inside the containment member (3) of the digestion unit (1).

14. A plant according to claim 3, characterized in that it comprises a unit (105) for disposing of the biogas with a low natural gas concentration, which is in fluid connection with the digestion unit (1); the plant comprising a control unit (106) configured to selectively direct the biogas inside the cogenerator (101) or inside the disposal unit (105) according to the natural gas concentration in the biogas.

15. A plant according to claim 13, characterized in that the disposal unit (105) comprises a burning unit (107) configured to burn the biogas sent to the disposal unit (105); the burning unit (107) also comprising a unit (108) for recovering the carbon dioxide generated in the combustion, which is connected to the containment member (3) of the digestion unit (1) to emit the carbon dioxide inside the containment member (3) before the door (5a) and/or the reclosable pick-up mouth (4a) is opened.

16. A method for treating organic wastes, comprising the following steps:

- preparing a member (3) for containing a dry mass (50) of organic wastes, emerging from a base (2) along a vertical axis of extension (A) and comprising at least one perimeter wall (4) equipped, at its lower end adjacent to the base (2), with a reclosable mouth (4a) for picking up the dry mass (50); the containment member (3) also comprising a roof (5) having an openable door (5a) to allow organic wastes to be fed into the containment member (3);

- opening the door (5a);

- gravity feeding the organic wastes defining the mass (50) into the containment member (3) through the door (5a) until the containment member (3) is full;

- hermetically closing the door (5a);

- sprinkling a catalyst fluid inside the containment member (3), to speed up the decomposition of the dry mass (50);

- mixing, for a predetermined interval of time, the dry mass (50) inside the containment member (3) through mixing means (9); - extracting the biogas generated during the decomposition of the mass (50) inside the containment member (3);

- opening the reciosable mouth (4a) at the end of the predetermined interval of time;

- picking up the digested dry mass (50) through the reciosable mouth (4a).