Anaerobic digestion plant

Abstract

The present invention relates to a methanation plant in which the digestate outlet (40) comprises a solid matter outlet (42) and a seepage juice outlet (60) distinct from each other, the peripheral wall (14) of the digester (10) having at the seepage juice outlet (60) a masonry support (62) provided with an orifice (64) through which a tubular filter screen (66) is placed, the filter screen (66) being movable between a working position, in which the filter screen (66) closes the orifice (64) and is internal to the digester (10), and a cleaning position, in which the filter screen (66) is external to the digester (10) and accessible by a cleaning device (70) while closing the orifice (64) of the masonry support (62). The invention also relates to a continuous biomass methanization process using such a methanization plant (1). Figure 1 of the abstract: Figure 1

Description

Title of the invention: Methanization installation

[0001] The present invention relates to a methanization installation. Prior art

[0002] In a context of need to increase the production of renewable energies, methanization offers many advantages. It allows the production of biogas, for its direct use or for the production of electricity, by the degradation by microorganisms of organic waste such as cereal residues or animal droppings, particularly from cattle. Biogas is composed mainly of methane, but also of carbon dioxide and other gases such as hydrogen sulfide. Methanization also makes it possible to limit greenhouse gas emissions compared to the use of fossil fuels.

[0003] EP 2 449 085 discloses a reactor for the methanization of biomass comprising a gas-tight tank, access to which is permitted by a sealed door designed for the admission of the biomass, said tank being designed in the form of a garage, and an installation for draining part of the seepage juice, consisting of a drainage pipe opening into an opening made in a side wall of the reactor. At the end of methanization, the mixture of solid matter and the remainder of the seepage juice can be loaded out of the reactor into a vehicle.

[0004] However, such a drainage installation can become clogged with solid matter, requiring regular maintenance to unclog the installation.

[0005] One of the aims of the present invention is to propose a methanization installation whose production costs are reduced and whose maintenance is easy during methanization. Summary

[0006] To this end, the present invention relates to a methanization installation comprising:

[0007] a digester for converting biomass into biogas and a digestate comprising solids and seepage juice,

[0008] the digester comprising in particular:

[0009] a biomass inlet towards the interior of the digester,

[0010] a base on which the biomass rests during digestion during a methanization process,

[0011] a peripheral wall,

[0012] a digestate outlet to the outside of the digester,

[0013] the digestate outlet comprising a solids outlet and a seepage juice outlet distinct from each other, the peripheral wall of the digester having at least at the level of the seepage juice outlet a masonry support provided with an orifice through which a tubular filter grid is placed, the filter grid being movable between a working position, in which the filter grid is internal to the digester and recovers the seepage juice while closing the orifice of the masonry support, and a cleaning position, in which the filter grid is external to the digester and accessible by a cleaning device while closing the orifice of the masonry support.

[0014] Thanks to this embodiment, the seepage juice can be extracted separately from the solid materials and continuously when the grid is in the working position, the seepage juice being able to be reused to reseed the inlet biomass without intermediate treatment. The digester does not require complex maintenance to unblock the solid and liquid material discharges by stopping the methanization process. When the grid is in the cleaning position, maintenance is carried out to unclog the grid without stopping the methanization in progress in the digester.

[0015] The movement of the filter grid between the working position and the cleaning position can be motorized.

[0016] The filter grid can be operated by a jack.

[0017] The device for unclogging the filter grid may comprise at least one nozzle for projecting a fluid onto the filter grid.

[0018] The peripheral wall of the digester may comprise, in sectors remote from the seepage juice outlet, a slope covered with a gas-tight sheet.

[0019] The installation may comprise a device for recirculating the seepage juice recovered at the outlet of the digester to a biomass watering device arranged inside the digester in the vicinity of the biomass inlet.

[0020] The digester may be devoid of mechanical means for driving the biomass along the bottom of the digester.

[0021] The solids outlet may comprise a conveying system inclined relative to the bottom of the digester so as to evacuate the solids outside the digester by making them rise along the conveying system, and to allow the seepage juice carried by the conveying system to flow by gravity towards the inside of the digester, the peripheral wall of the digester having at the level of the solids outlet a masonry support supporting the conveying system.

[0022] According to another aspect of the invention, there is provided a process for continuous methanization of biomass using a methanization installation as described above, the process comprising:

[0023] the incorporation of biomass through the biomass inlet of the digester,

[0024] watering the biomass, preferably at the inlet of the digester to spread the biomass and move it along the bottom of the digester towards the digestate outlet, the digester being devoid of mechanical means of driving the biomass,

[0025] digestion of biomass by microorganisms to form biogas and digestate comprising solids and seepage juice,

[0026] the separate outlet of solid matter and seepage juice, the evacuation of the seepage juice being done through the filter grid towards the outside of the digester.

[0027] The evacuation of the seepage juice can thus take place continuously, without requiring conveying or mixing means inside the digester.

[0028] According to a variant of the method, the filter grid is placed in the cleaning position, the method comprising a step of unclogging the filter grid during methanization, the filter grid closing the orifice of the masonry support.

[0029] It is thus possible to carry out maintenance without stopping the methanization in progress in the digester.

[0030] According to another aspect of the invention, there is provided a methanization installation comprising:

[0031] a digester for converting biomass into biogas and a digestate comprising solids and seepage juice,

[0032] the digester comprising in particular:

[0033] a biomass inlet towards the interior of the digester,

[0034] a base on which the biomass rests during digestion during a methanization process,

[0035] a peripheral wall,

[0036] a digestate outlet to the outside of the digester,

[0037] the digestate outlet comprising a solids outlet and a seepage juice outlet distinct from each other, the solids outlet comprising a conveying system inclined relative to the bottom of the digester so as to evacuate the solids outside the digester by making them rise along the conveying system, and to allow the seepage juice carried by the conveying system to flow by gravity towards the inside of the digester, the peripheral wall of the digester having at the level of the solids outlet a masonry support supporting the conveying system.

[0038] By this embodiment, solids can be efficiently separated from the seepage juice and extracted from the digester, and they can be stored for reuse for other purposes. The conveyor system is supported by the masonry support.

[0039] The features set out in the following paragraphs may, optionally, be implemented, independently of one another or in combination with one another:

[0040] The conveying system may comprise a worm screw.

[0041] The worm screw may be provided with a solid outer shell. The worm screw may be provided with an openwork inner shell, coaxial with the outer shell.

[0042] The installation may include a pump connected to the conveying system for discharging the conveyed solid materials to a storage tank.

[0043] The peripheral wall of the digester may comprise, in sectors remote from the solid materials outlet, a slope covered with a gas-tight sheet.

[0044] The digester may be devoid of mechanical means for driving the biomass along the bottom of the digester.

[0045] The digestate outlet may comprise a solids outlet and a seepage juice outlet distinct from each other, the peripheral wall of the digester having at the seepage juice outlet a masonry support provided with an orifice through which a tubular filter grid is placed, the filter grid being movable between a working position, in which the filter grid closes the orifice and is internal to the digester, and a cleaning position, in which the filter grid is external to the digester and accessible by a cleaning device while closing the orifice of the masonry support.

[0046] The movement of the filter grid between the working position and the cleaning position can be motorized.

[0047] The filter grid can be operated by a jack.

[0048] The device for unclogging the filter grid may comprise at least one nozzle for projecting a fluid onto the filter grid.

[0049] The invention also relates to a process for the methanization of biomass using a methanization installation as described above, comprising:

[0050] the incorporation of biomass through the digester biomass inlet,

[0051] watering the biomass, preferably at the inlet of the digester, to spread the biomass and make it advance along the bottom of the digester towards the digestate outlet, the digester being devoid of mechanical means for driving the biomass,

[0052] digestion of biomass by microorganisms to form biogas and digestate comprising solids and seepage juice,

[0053] the separate outlet of solids and seepage juice, the solids being evacuated by the conveying system to the outside of the digester.

[0054] The method according to the invention is particularly advantageous. Indeed, it makes it possible to carry out methanization without requiring conveying or mixing means inside the digester, and to efficiently extract the solid materials separately from the seepage juice. Brief description of the drawings

[0055] Other characteristics, details and advantages will appear on reading the detailed description below, and on analyzing the attached drawings which are not drawn to scale, in which: Fig. 1

[0056] [Fig-1] shows a longitudinal and vertical sectional view of a mechanization installation thanization according to one embodiment. Fig. 2

[0057] [Fig.2] shows a cross-sectional view of the digester of the installation of [Fig.l] at the level of the biomass inlet. Fig. 3

[0058] [Fig.3] shows a longitudinal sectional view of the solids outlet of the methanization installation of [Fig.l] according to a first embodiment. Fig. 4

[0059] [Fig.4] shows a longitudinal sectional view of the seepage juice outlet of the methanization plant of [Fig.l] according to a second embodiment. Description of the embodiments

[0060] Reference is now made to [Fig.l]. [Fig.l] represents a methanization installation 1 according to one embodiment of the invention.

[0061] The methanization installation 1 comprises a digester 10 for transforming biomass 11 into biogas and into a digestate comprising solid matter and seepage juice.

[0062] The biomass 11 to be methanized by the present installation 1 may comprise, for example, any type of manure, straw, corn stover, sunflower stover, a straw / slurry mixture, a manure / slurry mixture, a straw / silage mixture or a manure / silage mixture, or even biowaste straw or biowaste manure.

[0063] The digester 10 comprises a bottom 12 on which the biomass 11 rests during digestion during a methanization process. The bottom 12 may comprise a masonry slab, for example made of concrete. The bottom 12 may also be made using earth covered with a gas-impermeable sheet. The gas-impermeable sheet is for example made of plastic, in particular high-density polyethylene (HDPE).

[0064] The digester 10 comprises a peripheral wall 14. The peripheral wall 14 delimits the interior of the digester 10 and the exterior of the digester 10. According to the example shown, the digester 10 in top view has a rectangular shape. However, the digester 10 may have any other technically conceivable shape.

[0065] The peripheral wall 14 may comprise a masonry support and / or a slope 18 covered with a gas-impermeable sheet 20 which can be topped with a slab as will be detailed below.

[0066] The digester 10 further comprises an inlet 22 for biomass 11 towards the interior of the digester 10. The inlet 22 for biomass 11 comprises, for example, a pipe 24 through an orifice 26 passing through the peripheral wall 14. The installation 1 may comprise a pump 25, for example a piston pump, or an endless screw for introducing the biomass 11 into the interior of the digester 10.

[0067] The bottom 12 of the digester 10 is preferably substantially flat.

[0068] The digester 10 preferably comprises a watering device 28 comprising at least one watering ramp 28 arranged inside the digester 10 in the vicinity of the inlet of the biomass 11. As will be described later, watering the biomass 11 at the inlet of the digester 10 makes it possible to spread the biomass 11 and advance it along the bottom of the digester 10. Thanks to this device, the digester 10 is devoid of mechanical means for driving the biomass 11, it is therefore of simple construction, and this results in a considerable energy saving compared to a digester comprising a conveyor inside.

[0069] The watering ramp 28 comprises, for example, a plurality of nozzles 30 for spraying fluid above the biomass 11 which has just been introduced into the digester 10. Preferably, a plurality of ramps 28, for example four ramps 28, are arranged perpendicular to the direction of advance of the biomass 11 along the bottom of the digester 10.

[0070] The digester 10 is advantageously covered with a gas-impermeable tarpaulin 32 to recover the biogas produced during a methanization process.

[0071] The digester 10 has a digestate outlet 40 towards the outside of the digester 10. Preferably, the digestate outlet 40 is placed opposite the biomass 11 inlet 22. For example, when the digester 10 has a rectangular shape in top view, the biomass 11 inlet 22 and the digestate outlet 40 are each located on a separate short side of the rectangle.

[0072] According to the present invention, the digestate outlet 40 comprises a solids outlet 42 and a seepage juice outlet 60 which are separate from each other.

[0073] According to a first embodiment, the solid materials outlet 42 comprises a conveying system 44 inclined relative to the bottom 12 of the digester so as to evacuate the solid materials outside the digester by making them rise along the conveying system 44, and to allow the seepage juice carried by the conveying system 44 to flow by gravity towards the inside of the digester 10, the peripheral wall 14 of the digester having at the level of the solid materials outlet 42 a masonry support 46 supporting the conveying system 44.

[0074] The conveying system 44 comprises, for example, an endless screw 48.

[0075] As shown in [Fig. 3], the auger 48 may be provided with a solid outer shell 50. The auger 48 may be provided with an openwork inner shell 52, coaxial with the outer shell 50. The inner shell 52 improves the phase separation between the solids of the digestate and the seepage juice, the seepage juice flowing along the outer shell 50 inside it.

[0076] The endless screw 48 is for example inclined at an angle of between 20° and 60° relative to the bottom 12 of the digester 10.

[0077] Alternatively, the conveyor system 44 could be different and could include any technically feasible means such as a belt.

[0078] The installation 1 may comprise a pump 53, for example a piston pump, connected to the conveying system 44 to discharge the solid materials conveyed to a storage tank 54 by means of piping 56.

[0079] The masonry support 46 comprises, for example, a concrete slab through which an orifice is provided to allow the conveying system 44 to pass. The peripheral wall 14 of the digester 10 then comprises, in sectors remote from the solid materials outlet 42, a slope 18 covered with a gas-tight sheet 20.

[0080] According to a second embodiment shown in more detail in [Fig. 4], which can be implemented alone or in addition to the first embodiment, the peripheral wall 14 of the digester has at the level of the seepage juice outlet 60 a masonry support 62 provided with an orifice 64 through which a tubular filter grid 66 is placed, the filter grid 66 being movable between a working position, in which the filter grid 66 closes the orifice 64 and is internal to the digester 10, and a cleaning position, in which the filter grid 66 is external to the digester 10 and accessible by a declogging device 70 while closing the orifice 64 of the masonry support 62.

[0081] Outside the digester 10, the orifice 64 opens for example into a conduit 71 for discharging the seepage juice. In the cleaning position, the filter grid 66 is inside the conduit 71 for discharging the seepage juice.

[0082] The movement of the filter grid 66 between the working position and the cleaning position can be motorized. In this way, the movement of the filter grid 66 requires little or no human intervention.

[0083] The filter grid 66 is for example actuated by a jack. In the example of [Fig.4], a rod 72 is fixed to one end of the filter grid 66 from outside the digester 10. The rod 72 is itself connected to a jack which, when put into operation, moves the rod 72 and consequently the filter grid 66 towards the inside of the digester 10 or towards the outside of the digester 10. The filter grid 66 is thus movable in translation through the orifice 64 of the masonry support 62.

[0084] The device 70 for unclogging the filter grid comprises, for example, at least a nozzle 74 for projecting a fluid onto the filter grid 66. The nozzle(s) 74 are for example placed in the conduit 71 for discharging the seepage juice.

[0085] Of course, any other suitable unclogging device can be considered.

[0086] The masonry support 62 comprises, for example, a concrete slab.

[0087] The peripheral wall 14 of the digester 10 then comprises, in sectors distant from the seepage juice outlet 60, a slope 18 covered with a gas-tight sheet 20. The gas-tight sheet 20 is for example made of plastic, in particular high-density polyethylene.

[0088] As can be seen in [Fig.l], the installation 1 may comprise a device 80 for recirculating the seepage juice recovered at the outlet of the digester 10 to the device 28 for watering the biomass 11 arranged inside the digester 10 in the vicinity of the inlet 22 of the biomass 11.

[0089] The recirculation device 80 may comprise a lift pump 82 for moving the seepage juice along the discharge conduit 71 to a storage container 84. The storage container 84 comprises a seepage juice inlet 86 connected to the discharge conduit 71 and a seepage juice outlet 88. The storage container 84 may be a heated basin or a heated tank. A pipe 90 connects the seepage juice outlet 88 to the device 28 for watering the biomass 11.

[0090] Recirculating the seepage juice allows it to be reused and thus to operate in a closed circuit without generating additional waste, and to limit the consumption of water for watering the biomass 11 at the inlet of the digester 10. Watering the biomass 11 allows the biomass 11 to be spread and moved along the bottom of the digester 10 without using mechanical means. Watering the biomass 11 with seepage juice allows the temperature to be maintained around 37°C inside the digester, and the biomass 11 to be reseeded with microorganisms.

[0091] In the example of Figures 1 and 2, the peripheral wall 14 comprises a slope 18 at sectors distant from the solids outlet 42 and the seepage juice outlet 60. In particular, the peripheral wall 14 comprises a masonry support 46, 62 at the solids outlet 42 and the seepage juice outlet 60, and a slope 18 elsewhere.

[0092] A first method for continuous biomass methanization using a methanization installation 1 according to the first embodiment will now be described.

[0093] The first method comprises incorporating biomass 11 through the biomass 11 inlet 22 of the digester 10. As discussed above, the incorporated biomass 11 may comprise, for example, any type of manure, straw, corn stover, sunflower stover, a straw / slurry mixture, a manure / slurry mixture, a straw / silage or a manure / silage mixture, or biowaste straw or biowaste manure.

[0094] The biomass 11 advantageously comprises between 15% and 99% by weight of dry matter. The biomass 11 has, for example, a density of between 0.25 and 1.

[0095] The biomass 11 is in particular introduced inside the digester 10 through the pipe 24 by means of a pump or an endless screw.

[0096] The biomass 11 is introduced into the digester 10 and tends to create a mound.

[0097] The first method then comprises a step of watering the biomass 11, preferably entially at the inlet 22 of the digester 10, to spread the biomass 10 and advance it along the bottom 12 of the digester 10 towards the digestate outlet 40, the digester 10 being devoid of mechanical means for driving the biomass 11.

[0098] The watering is preferably implemented intermittently. In an exemplary embodiment, for a digester 10 having a capacity of 200 m3, the watering flow rate is between 10 m3 and 100 m3 per day.

[0099] The mound of biomass 11 formed at the inlet of the digester collapses under watering, and is carried along the bottom 12 of the digester 10.

[0100] The first method comprises a step of digesting the biomass 11 by microorganisms to form biogas and a digestate comprising solid matter and seepage juice. We will not go into detail about the digestion of the biomass 11 which is not the subject of the present invention.

[0101] The biomass is preferably introduced as regularly as possible, preferably several times per day, to allow the most stable gas production possible.

[0102] The seepage juice flows towards the bottom 12 of the digester 10 and the solid materials float on the surface of the juice.

[0103] The residence time of the materials between the inlet of the biomass 11 and the outlet 40 of the digestate is for example between 20 days and 60 days to extract biogas in sufficient quantity.

[0104] The first method then comprises the separate discharge of the solids and the seepage juice, the solids being discharged by the conveying system 44 to the outside of the digester 10.

[0105] The solid materials leaving the digester 10 have, for example, a density of between 0.9 and 1.

[0106] The evacuation of solid materials is for example triggered by a level sensor in the digester 10.

[0107] In the example shown, the conveying system 44 comprises a worm screw 48. The worm screw 48 may be provided with a solid outer shell 50 and an openwork inner shell 52, coaxial with the outer shell 50. The inner shell 52 plays the role of phase separator, and the seepage juice which may have been entrained in the endless screw 48 flows along the external shell 50 inside the latter and returns by gravity to the inside of the digester 10.

[0108] The conveyed solid materials can be discharged by means of a pump 53 to a storage tank 54 for their subsequent use.

[0109] A second method for continuous biomass methanization using a methanization installation 1 according to the second embodiment of the invention will now be described.

[0110] The second method comprises the same first steps as the first method, as well as the separate outlet of the solids and the seepage juice, the evacuation of the seepage juice being done through the filter grid 66 towards the outside of the digester 10.

[0111] In particular, the filter grid 66 is placed transversely to the masonry support 62 in the vicinity of the bottom 12 of the digester 10. In this way, when the filter grid 66 is placed in the working position, the seepage juice having percolated at the bottom of the digester 10 is entrained towards the filter grid 66 and passes inside this filter grid 66 through the orifice 64 of the masonry support 62. The solid materials remain outside the filter grid 66.

[0112] The seepage juice is in particular discharged into the seepage juice discharge conduit 71.

[0113] The evacuation of the seepage juice takes place continuously, outside the period of cleaning of the filter grid 66.

[0114] When the installation 1 comprises a device 80 for recirculating the seepage juice as shown in [Fig.l], the lifting pump 82 moves the seepage juice along the discharge conduit 71 to the storage container 84. The seepage juice is stored inside the storage container 84 for a predetermined duration, then is recirculated to the device 28 for watering the biomass 11 via the pipe 90.

[0115] If maintenance is desired, the filter grid 66 is moved towards the cleaning position, the filter grid 66 then being external to the digester 10 and accessible by a cleaning device 70 while closing the orifice 64 of the masonry support 62.

[0116] The movement of the filter grid 66 can be carried out by a jack which moves the rod 72 and consequently the filter grid 66 towards the outside of the digester 10.

[0117] The method then comprises a step of unclogging the filter grid 66 during methanization.

[0118] Unclogging can be manual or automated, for example by projecting a fluid onto the filter grid 66 using at least one projection nozzle 74.

[0119] When the unclogging is finished, the filter grid 66 can again be moved into the working position inside the digester 10.

[0120] The first method and the second method can be implemented separately, or concomitantly, in which case the solid materials are evacuated by a conveying system and the seepage juice is evacuated through the filter grid 66 to the outside of the digester 10.

[0121] The evacuation of solid matter and seepage juice can take place simultaneously.

Claims

Claims

1. Methanization installation (1) comprising: a digester (10) for transforming biomass (11) into biogas and into a digestate comprising solid matter and seepage juice, the digester (10) comprising in particular: - an inlet (22) for biomass (11) towards the inside of the digester (10), - a bottom (12) on which the biomass (11) rests during digestion during a methanization process, - a peripheral wall (14), - a digestate outlet (40) towards the outside of the digester (10), the installation (1) being characterized in that the digestate outlet (40) comprises a solid matter outlet (42) and a seepage juice outlet (60) distinct from each other, in which the peripheral wall (14) of the digester (10) has at the seepage juice outlet (60) a masonry support (62) provided of an orifice (64) through which a tubular filter grid (66) is placed,the filter grid (66) being movable between a working position, in which the filter grid (66) closes the orifice (64) and is internal to the digester (10), and a cleaning position, in which the filter grid (66) is external to the digester (10) and accessible by a cleaning device (70) while closing the orifice (64) of the masonry support (62).,

2. Installation (1) according to claim 1, in which the movement of the filter grid (66) between the working position and the cleaning position is motorized.

3. Installation (1) according to claim 2, in which the filter grid (66) is actuated by a jack.

4. Installation (1) according to claim 1 or 2, in which the unclogging device (70) of the filter grid (66) comprises at least one nozzle (74) for projecting a fluid onto the filter grid (66).

5. Installation (1) according to any one of claims 1 to 3, in which the peripheral wall (14) of the digester (10) comprises, in sectors remote from the seepage juice outlet (60), a slope (18) covered with a gas-tight sheet (20).

6. Installation (1) according to any one of claims 1 to 4, comprising a device (80) for recirculating the seepage juice recovered at the outlet of the digester (10) to a device (28) for watering the biomass (11) arranged inside the digester (10) in the vicinity of the inlet (22) of the biomass (11).

7. Installation (1) according to any one of claims 1 to 5, in which the digester (10) is devoid of mechanical means for driving the biomass (11) along the bottom (12) of the digester (10).

8. Installation (1) according to any one of claims 1 to 6, in the outlet (42) of solid materials comprises a conveying system (44) inclined relative to the bottom (12) of the digester (10) so as to evacuate the solid materials outside the digester (10) by making them rise along the conveying system (44), and to allow the seepage juice carried by the conveying system (44) to flow by gravity towards the inside of the digester (10), the peripheral wall (14) of the digester (10) having at the level of the outlet (42) of solid materials a masonry support (46) supporting the conveying system (44).

9. A method for the continuous methanization of biomass (11) using a methanization installation (1) according to any one of the preceding claims, comprising: - the incorporation of biomass (11) via the biomass inlet (11) of the digester (10), - the watering of the biomass (11), preferably at the inlet of the digester (10), to spread the biomass (11) and advance it along the bottom (12) of the digester (10) towards the digestate outlet (40), the digester (10) being devoid of mechanical means for driving the biomass (11), - the digestion of the biomass (11) by microorganisms to form biogas and a digestate comprising solid matter and seepage juice, - the separate outlet of the solid matter and the seepage juice, the evacuation of the seepage juice being carried out through the filter grid (66) towards outside the digester (10).

10. Methanization method according to the preceding claim, in which the filter grid (66) is placed in the cleaning position, the method comprising a step of unclogging the filter grid (66) in progress of methanization, the filter grid (66) closing the orifice (64) of the masonry support (62).

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