Anaerobic digestion plant

Abstract

The invention relates to a biogas plant comprising a digester for converting biomass into biogas and digestate comprising solid matter and seepage juice. The digester includes an outlet to the outside. The plant includes a conveying system (44) for discharging digestate through the outlet. The conveying system includes a drawer (200) having a bottom and side edges, and a scraper element configured to perform reciprocating movements in a horizontal direction towards the outlet (40) between a filling position and an emptying position. The scraper element (204) includes a nose (210) configured to push the digestate towards the outlet (40) by a first surface in a first direction of translation outwards from the digester, and to slide under the digestate by a second surface in a direction of translation inwards. Abstract figure: Figure 7A

Description

Title of the invention: Methanization plant

[0001] The present invention relates to a methanization plant. Previous technique

[0002] In a context of needing to increase renewable energy production, the methanization of biomass offers numerous advantages. It enables the production of biogas, for direct use or for electricity generation, through the breakdown of organic waste such as cereal residues or animal manure, particularly from cattle, by microorganisms. Biogas is composed mainly of methane, but also of carbon dioxide and other gases such as hydrogen sulfide. Methanization also helps to limit greenhouse gas emissions compared to the use of fossil fuels. After a methanation reaction, the biomass is transformed into biogas and a digestate comprising solid matter and leachate.

[0003] EP 2 449 085 is known a reactor for the methanation of biomass comprising a gas-tight tank, the access to which is permitted by a sealed door designed for the admission of biomass, said tank being designed in the form of a garage, and a drainage system for a portion of the seepage liquid, consisting of a drainage pipe opening into an opening in a side wall of the reactor. At the end of the methanation process, the mixture of solid matter and the remaining seepage liquid can be loaded out of the reactor into a vehicle.

[0004] However, such removal by vehicle requires significant logistical planning and a shutdown of the methanation process. The removed materials must be air-dried, resulting in the release of hydrogen sulfide, a gas toxic to the environment and living organisms.

[0005] Furthermore, existing drainage facilities may present a risk that material may accumulate until it obstructs the outlet of the digester, requiring intervention to unblock it.

[0006] One of the aims of the present invention is to provide a simple methanization plant with reduced production costs and less labor requirements than prior art plants. Summary

[0007] For this purpose, the present disclosure relates to a methanization plant comprising a digester for transforming biomass into biogas and digestate, the digestate comprising solid matter and seepage juice, the digester comprising an outlet to the outside of the digester, the plant comprising a conveying system for evacuating a quantity of digestate through the outlet, the conveying system comprising a drawer having a bottom and side edges, the conveying system being provided with a scraper element configured to perform back-and-forth movements along the bottom and between the edges of the drawer in a horizontal translation direction towards the outlet, under the action of an actuator, between a filling position and an emptying position, said scraper element comprising a nose configured to push the digestate towards the outlet by a first surface in a first translation direction going outwards from the digester, and to slide under the digestate by a second surface in a translation direction towards the inside of the digester.

[0008] Particularly advantageously, the methanization plant according to the present disclosure greatly reduces the risk of digestate outlet blockage compared to known solutions. Furthermore, the proposed solution has a very small footprint compared to other solutions and operates efficiently even with a very short back-and-forth movement of the nozzle.

[0009] The features described in the following paragraphs may optionally be implemented independently of each other or in combination with each other:

[0010] According to an improvement, the first surface of the nose of the scraping element extends in a vertical plane, substantially perpendicular to the horizontal translation direction, so as to push the solid material towards the outlet, and in which the second surface is at least partly inclined downwards, so as to be able to slide under the digestate.

[0011] According to an improvement, the outlet is provided in a concrete support, and a bottom of the digester comprises a masonry slab, the drawer and the scraping element are provided below the level of the bottom of the digester in a trench provided in the masonry slab.

[0012] According to an improvement, the installation includes a first evacuation line for juices, and a second evacuation line for solids, the drawer including a gutter for evacuating seepage juices provided in the bottom of the drawer and including an orifice for conveying the juices to the first line outside the digester, the installation including, outside the digester, a recovery pit configured to convey the solids to the second line, the second line being separate from the first line.

[0013] According to an improvement, the installation includes two drainage channels, each located at a junction between the bottom of the drawer and a rim of the drawer.

[0014] According to an improvement, the nose comprises a cover configured to slide in the channel, the cover having a U-shaped cross-section reversed, the lid being movable in translation with the nose, in the gutter below the level of the bottom of the drawer.

[0015] According to an improvement, each cover has a length such that it is configured to always cover the orifice, regardless of the position of the scraper element between the drain position and the fill position. Thus, solid matter cannot reach, and potentially obstruct, the gutter orifice.

[0016] According to an improvement, a distal end of the lid opposite the nose has a push face configured to push the solid matter present in the channel in a direction oriented outwards from the digester. In this way, the back-and-forth movement of the push face allows the channel to be cleared of solid matter with each pass, preventing it from becoming clogged.

[0017] According to an improvement, the drawer includes, between the bottom of the drawer and the pit, a portion inclined downwards suitable for allowing the solid material to fall towards the pit.

[0018] According to an improvement, the installation includes a casing covering a portion of the drawer extending outside the digester.

[0019] According to an improvement, the drawer is provided with a piston outside the digester, the piston being movable in translation along a vertical direction substantially perpendicular to the direction of translation of the nose, the piston comprising, at one end of the rod, a head configured to compress the solid materials inside the pit.

[0020] According to an improvement, the drawer has two slides, attached to the nose, extending along the direction of translation, configured respectively to slide along two guide grooves formed in the two edges of the drawer, the two guide grooves projecting outwards from the two edges.

[0021] This disclosure also relates to a process for the methanization of biomass using a methanization plant as described above, comprising: - the incorporation of biomass through the biomass inlet of the digester, - watering the biomass, preferably at the digester inlet, 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 biomass transport, - the digestion of biomass by microorganisms to form biogas and digestate comprising solid matter and seepage juice, the removal of solid matter and seepage juice via the conveying system to the outside of the digester during which the digestate is removed by back-and-forth movements of the scraping element comprising, sequentially: - a movement of said scraping element from the filling position to the emptying position, during which the first surface of the nose pushes the digestate, located in a hollow volume between the edges of the drawer, towards the outlet, - a movement of said scraping element from the emptying position to the filling position, during which the second surface of the nose slides under the digestate, the hollow volume filling with digestate.

[0022] According to an improvement, the installation includes a first evacuation line for the juices, and a second evacuation line for the solids, the drawer including a seepage juice evacuation channel cut into the bottom of the drawer and including an orifice to convey the juices to the first line outside the digester, the installation including, outside the digester, a recovery pit configured to convey the solids to the second line, the second line being separate from the first line, and the process includes the separation of the solid matter and the seepage juices during the back-and-forth movements.

[0023] According to an improvement, in which the drawer is provided with a piston outside the digester, the piston comprising a rod movable in translation along a vertical direction substantially perpendicular to the direction of translation of the nose, the piston comprising, at one end of the rod, a head configured to compress the solids inside the pit, the vertical translational movement of the piston being a reciprocating movement between a high position and a low position, out of phase with the reciprocating movement of the nose, so that the piston is in the low position when the nose is in the filling position, and the piston is in the high position when the nose is in the emptying position.

[0024] According to examples, the methanization installation may include one or more drawers. Brief description of the drawings

[0025] Other features, details and advantages will become apparent from reading the detailed description below, and from analyzing the accompanying drawings, which are not to scale, on which:

[0026] [Fig. 1] shows a longitudinal and vertical cross-sectional view of an installation of methanization according to a method of implementation.

[0027] [Fig.2] shows a cross-sectional view of the digester of the installation of the [Fig.1] at the biomass inlet.

[0028] [Fig.3] shows a longitudinal cross-sectional view of the solid material outlet of the methanization installation of [Fig.1] according to a first embodiment.

[0029] [Fig.4] shows a longitudinal cross-sectional view of the seepage juice outlet of the methanization plant of [Fig.1] according to a second embodiment.

[0030] [Fig.5] shows a longitudinal cross-sectional view of the solid material outlet of the methanization plant of [Fig.1] according to a variant of the first embodiment, the nose being in the filling position.

[0031] [Fig.6] shows a longitudinal cross-sectional view of the solid material outlet of the methanization plant of [Fig.1] according to the variant of [Fig.5], the nose being in the emptying position.

[0032] [Fig. 7] shows a schematic perspective view of a conveying system according to an example, the nose being in the filling position in a view 7A and in the emptying position in a view 7B.

[0033] [Fig.8] shows a schematic perspective view of a drawer and an evacuation pit according to an example, the drawer being in particular equipped with a formwork according to a particular example.

[0034] [Fig. 9] shows a schematic perspective view of a drawer according to an example,

[0035] [Fig. 10] shows a schematic perspective view of a drawer and a discharge pit according to an example, in which the inclined portion of the drawer towards the pit is particularly visible,

[0036] [Fig. 11] shows a schematic perspective view of a nose according to an example,

[0037] [Fig. 12] shows a detailed schematic view of a channel in which slides a lid, as shown in this example, with the end of the lid left open here to visualize the cavity,

[0038] [Fig. 13] schematically illustrates an example of a conveying system equipped with a piston, and shows on a first view 13A the piston in the high position, and on a second view 13B the piston in the low position. Description of the implementation methods

[0039] Reference is now made to [Fig. 1]. [Fig. 1] represents a methanization plant 1 according to an example of the invention.

[0040] The methanization plant 1 includes a digester 10 for transforming biomass 11 into biogas and digestate comprising solid matter and seepage juice.

[0041] The biomass 11 to be methanized by the present installation 1 may include, for example, any type of manure, straw, corn stalks, sunflower stalks, a straw / slurry mixture, a manure / slurry mixture, a straw / silage mixture or a manure / silage mixture, or even bio-waste straw or bio-waste manure.

[0042] The digester 10 includes a base 12 on which the biomass 11 being digested during a methanation process rests. The base 12 may include a A masonry slab, for example in concrete. The base 12 can also be made of earth covered with a gas-impermeable membrane. The gas-impermeable membrane is made, for example, of plastic, in particular high-density polyethylene (HDPE).

[0043] The digester 10 comprises a peripheral wall 14. The peripheral wall 14 delimits the interior of the digester 10 from the exterior of the digester 10. According to the example shown, the digester 10, viewed from above, has a rectangular shape. However, the digester 10 can have any other technically feasible shape.

[0044] The peripheral wall 14 may include a masonry support and / or a slope 18 covered with a gas-impermeable sheet 20 which may be surmounted by a slab as will be detailed below.

[0045] The digester 10 further includes a biomass inlet 22 11 into the interior of the digester 10. The biomass inlet 22 11 includes, for example, a pipe 24 through an orifice 26 through the peripheral wall 14. The installation 1 may include a pump 25, for example a piston pump, or a screw conveyor for introducing the biomass 11 into the digester 10.

[0046] The bottom 12 of the digester 10 is preferably substantially flat.

[0047] The digester 10 preferably includes a watering device 28 comprising at least one watering ramp 28 disposed inside the digester 10 in the vicinity of the biomass inlet 11. As will be described later, watering the biomass 11 at the inlet of the digester 10 allows the biomass 11 to be spread out and moved along the bottom of the digester 10. Thanks to this device, the digester 10 is free of mechanical means of driving the biomass 11, it is therefore of simple construction, and this results in a considerable energy saving compared to a digester having a conveyor inside.

[0048] The spraying ramp 28 includes, for example, a plurality of nozzles 30 for projecting fluid over the biomass 11 that 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.

[0049] The digester 10 is advantageously covered with a gas-impermeable tarpaulin 32 to recover the biogas produced during a methanization process.

[0050] The digester 10 has a digestate outlet 40 to the outside of the digester 10. Preferably, the digestate outlet 40 is located opposite the biomass inlet 22 11. For example, when the digester 10 has a rectangular shape in top view, the biomass inlet 22 11 and the digestate outlet 40 are each located on a distinct short side of the rectangle.

[0051] According to one example, the digestate outlet 40 comprises a solids outlet 42 and a seepage juice outlet 60, distinct from each other.

[0052] The outlet 40 can be equipped with a conveying system 44 intended to convey, or even separate, the digestate and seepage juice out of the digester 10.

[0053] The recirculation device 80 may include a lift pump 82 for moving the seepage juice conveyed by the conveying system 44 along a first discharge pipe 71 to a storage container 84. The storage container 84 includes a seepage juice inlet 86 connected to the discharge pipe 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 biomass irrigation device 28 11.

[0054] Recirculating the seepage juice allows it to be reused, thus enabling operation in a closed loop without generating additional waste, and limiting water consumption for spraying the biomass 11 at the inlet of the digester 10. Spraying the biomass 11 spreads it out and moves it along the bottom of the digester 10 without the use of mechanical means. Spraying the biomass 11 with seepage juice helps maintain the temperature around 37°C inside the digester and re-inoculates the biomass 11 with microorganisms.

[0055] The installation 1 may include a pump 53, for example a piston pump, connected to the conveying system 44 to discharge the conveyed solids to a storage tank 54 by means of a second conduit 56, such as a pipe.

[0056] According to one example, the second pipe 56 can be connected to a pit 310 for the recovery of solid materials, itself placed at the outlet of the conveying system 44.

[0057] The masonry support 46 includes, for example, a concrete slab through which an opening is provided for the passage of the conveying system 44. The peripheral wall 14 of the digester 10 then includes, in areas 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.

[0058] In the example of Figures 1 and 2, the peripheral wall 14 includes a slope 18 at areas distant from the solid material outlet 42 and the seepage juice outlet 60. In particular, the peripheral wall 14 includes a masonry support 46, 62 at the solid material outlet 42 and the seepage juice outlet 60, and a slope 18 elsewhere.

[0059] Various examples of the embodiment of a conveyor system 44 according to the invention will now be described. The characteristics of the installation presented above can be combined, unless otherwise stated, with the various examples of conveyor system 44.

[0060] According to a first embodiment, the solid matter outlet 42 comprises a conveying system 44 inclined relative to the bottom 12 of the digester so as to evacuate the solid matter outside the digester by raising it along the conveying system 44, and to allow the seepage juice carried by the conveying system 44 to flow by gravity into the inside of the digester 10, the peripheral wall 14 of the digester having at the level of the solid matter outlet 42 a masonry support 46 supporting the conveying system 44.

[0061] To this end, the conveying system 44 may include, for example, a worm screw 48.

[0062] As shown in [Fig. 3], the auger 48 can be provided with a solid outer shell 50. The auger 48 can be provided with a perforated inner shell 52, coaxial with the outer shell 50. The inner shell 52 improves the phase separation between the solid matter of the digestate and the seepage juice, the seepage juice flowing along the outer shell 50 inside it.

[0063] The screw 48 is for example inclined at an angle between 20° and 60° relative to the bottom 12 of the digester 10.

[0064] Alternatively, the conveying system 44 could be different and could include any technically feasible means such as a conveyor belt, in place of or in addition to a screw conveyor 48.

[0065] According to one embodiment, and as represented in [Fig.4], 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 unclogging device 70 while closing the orifice 64 of the masonry support 62.

[0066] Outside the digester 10, the orifice 64 opens, for example, into a conduit 71 for draining the seepage juice. In the cleaning position, the filter screen 66 is inside the conduit 71 for draining the seepage juice.

[0067] 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.

[0068] The filter screen 66 is, for example, actuated by a cylinder. In the example of [Fig. 4], a rod 72 is attached to one end of the filter screen 66 from outside the digester 10. The rod 72 is itself connected to a cylinder which, when activated In operation, it 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.

[0069] The filter screen cleaning device 70 includes, for example, at least one nozzle 74 for projecting a fluid onto the filter screen 66. The nozzle(s) 74 are, for example, placed in the duct 71 for draining the seepage juice.

[0070] It is understood that any other suitable unclogging device may be considered.

[0071] According to yet another embodiment shown in [Fig. 5] and 6, the system 44 of The conveying system includes a drawer 100. The drawer 100 extends partially inside the digester 10 and partially outside the digester 10 to allow the evacuation of solid materials.

[0072] Drawer 100, for example, is made of metal.

[0073] The drawer 100 includes in particular a bottom 102 and a scraper element 104. According to the example shown, the bottom 102 is fixed and the scraper element 104 is mobile in translation along the bottom 102 of the drawer 100.

[0074] The base 102 has for example a U-shaped form with a central part 106 and two rims 108 extending on either side of the central part 106. In particular, the central part 106 is flat.

[0075] The drawer 100, for example, has a width, defined as the shortest distance from one edge 108 to the other edge 108, which may be greater than 50 centimeters.

[0076] According to one embodiment, the drawer 100 can be inclined so that the scraping element 104 is movable between a low point inside the digester 10 and a high point outside the digester 10. The inside and outside of the digester 10 are thus defined by a first side and a second side of the masonry support 46. The drawer 100 can be inclined at an angle between 20° and 60° with respect to the bottom 12 of the digester 10.

[0077] The scraping element 104 has, for example, a nose 110 perpendicular to the bottom 102 of the drawer 100. The nose 110 preferably extends over the entire width of the bottom 102 of the drawer 100. The nose 110 is movable between a first extreme filling position where the nose 110 is inside the digester 10, and a second extreme emptying position where the nose 110 is outside the digester 10. The nose 110 typically has a first flat surface 112 oriented towards the top of the drawer 100 and a second surface 114 inclined relative to the first surface 112 and intersecting with the first surface 112.

[0078] The first surface 112 and the edges 108 of the central part 106 define a hollow volume inside the drawer 100, configured to receive solid materials and discharge them to the outside of the digester 10. The first surface 112, facing upwards, forms a pushing surface for the material when the scraping element 104 is actuated in the upward direction. The first surface 112 can be inclined at a right angle to the bottom 102, for example, at an angle between 75° and 105° to the bottom 102 of the central part 106. The second surface 114, inclined downwards, is designed to slide under the material when the scraping element 104 is actuated in its downward motion. For this purpose, the second surface 114 can be inclined at an angle less than or equal to 45° to the bottom 102, and for example, less than or equal to 35°, preferably at an angle of 30° to the central part 106 of the bottom 102.

[0079] The scraping element 104 may further include a third surface 116 connecting lower edges of the first surface 112 and the second surface 114 by extending parallel to the bottom 102 of the drawer 100. The nose 110 then has a general triangular shape.

[0080] A preferred embodiment of a conveying system according to the invention will now be described, in particular with reference to Figures 7 to 13.

[0081] According to this embodiment, the conveying system 44 includes a drawer 200 extending partially inside the digester 10 and partially outside the digester 10 to allow the evacuation of solid materials through the outlet 40.

[0082] Drawer 200, for example, is made of plastic. In particular, it can be made of HDPE.

[0083] The drawer 200 includes in particular a bottom 202 and a scraper element 204. According to the example shown, the bottom 202 is fixed and the scraper element 204 is mobile in translation along the bottom 202 of the drawer 200.

[0084] The base 202, for example, has a U-shaped form with a central portion 206 and two edges 208 extending on either side of the central portion 206. In particular, the central portion 206 is flat. The scraping element 204 is movable along the base 202 of the drawer in the space between the two edges 208.

[0085] The drawer 200 has, for example, a width, defined as the shortest distance from one edge 208 to the other edge 208, which may be greater than 50 centimeters.

[0086] In such an example, the bottom 202 of the drawer 200 is substantially parallel to the bottom 12 of the digester 10. By "substantially parallel," it is understood that the bottom 202 of the drawer 200 forms an angle with the bottom 12 of the digester 10 of less than + / -5°. In particular, the drawer 200 is substantially horizontal.

[0087] In one example, the drawer 200 can be housed in a trench 240 in the bottom 12 of the digester 10, the trench extending horizontally from the inside of the digester, through the concrete support 46, to the outside of the digester via the outlet 40. Thus, in the case of such a trench, the scraping element operates below the level of the bottom 12 of the digester. In other examples, the drawer can be housed at the level of the bottom 12 of the digester, for example, resting on the concrete slab that forms the bottom 12.

[0088] The scraping element 204 can be movable between an extreme filling position represented by an example in view 7A of [Fig. 7], and an extreme emptying position represented in view 7B. Such a back-and-forth movement defines a substantially horizontal translational direction, along the drawer which extends horizontally.

[0089] The drawer 200 may include a folded sheet metal forming the central part 206, and two edges 208 so as to give it a general U-shaped form, the edges 208 projecting upwards. Such a shape can be obtained by folding the sheet metal along parallel fold lines.

[0090] The channels 300 and the guide grooves 220 which will be described in more detail below can also be obtained by bending the sheet metal forming the drawer 200.

[0091] The scraping element 204 has a nose 210 configured to, in one direction, pass in or under the solid material so as to make it rise over the scraping element, and in another opposite direction, push solid material that has fallen into the drawer 200 towards the outlet 40.

[0092] According to one example, the nose can be made of stainless steel. Alternatively, the nose can be made of another metallic material, or even of a plastic material.

[0093] To this end, the nose 210 typically has a first surface 212 suitable for pushing the material. Such a first surface 212 can be flat and extend substantially perpendicular to the direction of translation of the nose 210.

[0094] The nose 210 further comprises a second surface 214 inclined downwards towards the bottom 202 and intersecting with the first surface 212. Typically, this second surface 214 extends from a high end of the first surface 212, and descends extending along the direction of translation in a direction from the outside to the inside of the digester, preferably down to the level of the bottom 202 of the drawer 200.

[0095] The first surface 212, the bottom 202 of the drawer and the edges 208 delimit between them a hollow volume inside the drawer 200 configured to receive solid materials and evacuate them to the outside of the digester 10 through the outlet 40.

[0096] The first surface 212 forms a pushing surface for the material, when the scraping element 204 is actuated in translation from the extreme filling position to the extreme emptying position.

[0097] According to the example shown in [Fig. 7], the nose 210 remains inside the digester throughout its back-and-forth movement. According to other examples, it is possible to provide for the nose to exit at least partially outside the digester through the outlet 40.

[0098] According to a preferred example, and as shown in [Fig. 7], the stroke of the nose 210 does not extend beyond the plane formed by an opening in the outlet 40. Indeed, the stroke of the nose stops and it resumes its movement in the opposite direction towards the interior of the digester when The first surface 212 coincided with the opening of the outlet 40. In other words, a limit of the stroke of the nose 210 can be defined as when the first surface 212 reached and obstructed the outlet 40.

[0099] As described previously, the first surface 212 can form a right angle with respect to the bottom 202, or more generally form an angle between 75° and 105° with respect to the bottom 202. The second surface 214, inclined downwards, has the function of sliding under the material when the scraping element 204 is actuated towards the inside of the digester 10. The second surface 214 can for this purpose be inclined at an angle less than or equal to 45° with respect to the bottom 202, and for example less than or equal to 35° such that 30° with respect to the bottom 202. The angle can be chosen according to the rheology of the digestate.

[0100] The scraping element 204 may further include a third lower surface 216 connecting the first surface 212 and the second surface 214 and extending parallel to the bottom 202 of the drawer 200. Such an arrangement makes it possible to form a scraping edge 217 common to the second downward-inclined surface 214 and the third surface 216. According to one example, the scraping edge 217 extends parallel to the bottom 202 of the drawer and transversely to the translational direction of the scraping element, in particular from one edge 208 to the other of the drawer. In one example, the scraper edge 217 extends close to the bottom 202 of the drawer; preferably, the scraper edge 217 and the third surface 216 are in continuous contact, throughout the back-and-forth movement of the scraper element, with the bottom 202 of the drawer, and / or, where applicable, with the bottom of the trench 240, and / or with the bottom 12 of the digester. The nozzle 210 may in this case have a generally triangular shape.Such an edge makes it possible in particular to pass efficiently under the solid material so that very little solid material passes under the nose 210 or remains in the trench 240.

[0101] According to one example, the second surface 214 and the third surface 216 form at the level of the scraping edge 217 an acute angle of between 10 and 45°.

[0102] According to examples, it is possible that the second surface forms a curve, for example convex, in the manner of a snow shovel.

[0103] Other nose shapes 210 can be considered as long as they have at least a first surface 212 for pushing material and a second surface 214 directed downwards, in particular towards a bottom of the trench 240 of the bottom 12 of the digester 10, capable of penetrating into or under the solid material present in the digester 10.

[0104] The scraping element 204 may include two slides 218, integral with the nose 210, extending horizontally, configured respectively to slide along guide grooves 220 formed in the two edges 208 of the drawer 200.

[0105] According to one example, the two slides 218 extend at least partially outside the drawer 200 so as to be connected to the actuator that causes the reciprocating movement of the scraper element 204. The slides 218 may, in particular, include a rack portion so as to cooperate with a toothed wheel connected to the actuator. Other known transmission mechanisms enabling reciprocating movement of the nose 210 may be considered.

[0106] For example, the slides 218 can be assembled to the nose 210 by welding, or gluing, or come from the same material as the nose 210 which can for example be molded.

[0107] The drawer 200 includes, for example, a channel 300 for draining seepage juices to the outside of the digester 10. In the example shown, the drawer 200 has a channel 300 on either side of the bottom 202 of the drawer 200. Each channel 300 may have a U-shape.

[0108] According to one example, the drawer 200 has two drainage channels 300 arranged laterally at the bottom 202 of the drawer, each located at a junction between the bottom 202 of the drawer and a rim 208 of the drawer 200.

[0109] In another example, the drawer 200 includes a single channel 300, for example on one side of the drawer or along a central line of the drawer equidistant from the two edges 208.

[0110] An orifice 302 can be drilled in each channel 300 to evacuate seepage juices out of the digester 10. During the movement of the nose 210 from the filling position to the emptying position, seepage juices can flow out of the digester 10 from the bottom 202 of the drawer 200 through the channel(s) 300. Such an arrangement is illustrated by an example in [Fig.9].

[0111] According to one example, each orifice 302 can be fluidly connected to a means of evacuation 304 such as a pipe, or a channel, allowing the seepage juices to be conveyed to a first conduit 71 of the juices out of the conveying system 44. The first conduit 71 can optionally be connected to a juice recirculation system, or allow the evacuation of the juices.

[0112] According to one example, the nose 210 is provided with covers 232 extending lengthwise from the nose 210 parallel to the direction of translation of the nose 210. The covers 232 can advantageously be shaped in relief from the lower surface 216 of the nose, so as to slide inside the channels 300 cut into the bottom 202 of the drawer. Such covers are shown, in particular, in an example in [Fig. 11]. Thus, the covers 232 slide below the level of the bottom 202 of the drawer, inside the volume of the channels 300. The covers 232 can advantageously have an inverted U-shaped cross-section, in particular inverted with respect to the U-shape of the channels. Thus, the covers can comprise two profiles, substantially parallel to each other, which extend lengthwise respectively in the Two channels, following the sliding direction of the scraper element 204. In this way, only the two projecting edges of the inverted U of each cover 232 are in contact with the bottom of a channel 300, leaving a cavity 234 inside the inverted U of the cover 232, closed by the bottom of the channel 300. Advantageously, this cavity is in fluidic communication with the orifice 302 of the channel. The inverted U-shaped covers 232 can prevent the orifices 302 from becoming clogged by solid matter.

[0113] According to one example, the lids 232 have at their end portion 233 a thrust face 235 capable of pushing, in a direction outwards from the digester, the solid matter which could have reached the channel 300.

[0114] According to examples, such a thrust face 235 can be provided substantially perpendicular to the direction of back and forth, or inclined with respect to it.

[0115] According to one example, drawer 200 further includes, outside digester 10, a pit 310 for the recovery of solid materials.

[0116] According to one example, the solid material pit 310 can be arranged at a lower level than the bottom 202 of the drawer 200, so that an inclined portion 270 of the drawer connects the bottom of the drawer to the solid material pit. Such an inclined portion 270 can, for example, form an angle of approximately 45° with the horizontal. The inclined portion 270 will have a sufficient slope to allow the solid material to fall into the pit 310.

[0117] According to one example, the drawer 200 is covered, at least over a portion of its length, by a casing 250 in the shape of an inverted U relative to that of the drawer 200. Such a casing 250 allows the evacuation of solid materials by the scraping element 204 to be encapsulated. Such a casing is shown according to an example in [Fig.8].

[0118] The formwork 250 may be of a narrower U-shape than the drawer, so that the formwork 250 has side walls 251 positioned inside the edges 208 of the drawer, opposite the edges 208 of the drawer. In [Fig. 10], only the side walls of the formwork 250 are shown, and are particularly visible.

[0119] According to one example, the conveying system 44 can be designed so that the casing 250 covers a portion located outside the digester 10. In this case, it can be provided that the nose 210 has its stroke limited so that the first surface 212 of the nose 210, in its extreme emptying position, just reaches the beginning of the portion covered by the casing 250.

[0120] According to one example, the inclined portion 270 begins, at its highest point, just back from the limit of the stroke of the nose 210 towards the inside of the digester, for example 5mm back, or more, so that the first surface 212 exceeds at least slightly the highest point of the inclined portion 270. In other examples, the highest point of the inclined portion 270 is positioned at the level of the limit of the stroke of the nose 210.

[0121] According to one example, the recovery pit 310 is provided under the portion of the drawer covered by the formwork 250. In such an example, the bottom of the drawer may not extend to the portion covered by the formwork, and the inclined portion 270 which connects the bottom of the drawer to the recovery pit 310 may extend at least partially under the formwork 250, and / or at least partially outside the portion covered by the formwork 250.

[0122] The formwork 250 or the drawer 200 may include, at the level of the portion of the drawer covered by the formwork 250 oriented towards the interior of the digester 10, guidance portions 260 for the solid material provided laterally on either side of the formwork 250. The expression "oriented towards the interior of the digester" is to be interpreted in the sense that the nose 210, during its translational movement from the filling position, reaches the vicinity of the guidance portions 260 before reaching the portion of the drawer covered by the formwork 250.

[0123] The guide portions 260 can be arranged to form, on either side of the formwork 250, two inclined surfaces connecting, on each side of the formwork, the edge 208 of the drawer 200 to the corresponding side wall 251. The inclined surfaces move closer together along the direction of translation of the nose from the filling position to the emptying position. In this way, the two inclined surfaces of the guide portions 260 allow the solid material pushed by the nose 210 to be guided inside the formwork 250, which is designed to be narrower than the drawer, to reach the pit 310, and prevent material from accumulating on either side outside the formwork 250.

[0124] According to one example, the nose 210 has a limited stroke at the level of these guide portions 260, so that the first surface 212, in the extreme emptying position, stops at the junction between the guide walls 260 and the edges 208. Indeed, the nose being of a width substantially equal to that which separates the two edges 208, it cannot continue to translate between the guide walls 260, which, according to one example, move closer together towards the formwork 250.

[0125] The guide portions 260 can be formed from the same material as the formwork 250. The formwork can be made by folding a single sheet of metal. The guide portions 260 can also be obtained by folding this same sheet.

[0126] The guide portions 260, at their distal end relative to the formwork 250, can be welded to the edges 208 of the drawer.

[0127] In other examples, the guide portions can be attached to the drawer and / or to the formwork, for example by welding or gluing, or by screwing or riveting.

[0128] According to one example, the covers 232 can be designed so as to extend over a sufficient length for, and for all positions of, the scraping element 204 between the extreme filling position and the extreme emptying position, present at least a distal portion 233 of their length beyond the orifice 302. In this way, the orifice 302 is continuously covered by the cover 232, over the entire reciprocating stroke of the nose 210. This ensures that the orifice 302 is never accessible to solid matter, protected by the sliding cover 232.

[0129] Here, "covered" means that the solid materials are blocked, but that, of course, some clearance remains so that the seepage fluids can flow between the cover 232 and the walls of the channel 300, reaching the orifice 302 and flowing towards the first pipe 71. Such clearances are particularly visible in [Fig. 12]. Recesses (not shown) may also be provided in the cover to facilitate the flow of fluids.

[0130] Advantageously, the outer end 304 of the channel 300 can be closed by a closing wall 305, so as to prevent the solid material pushed by the distal portion 233 of the cover from falling out of the pit 310. Indeed, the solid material can thus accumulate against this closing wall 305 and fall naturally, tipping over an upper edge 306 of the channel 300, towards the inside of the drawer in the direction of the pit 310. The closing walls 305 are shown schematically and by way of a non-limiting example in [Fig. 10] and 13. By one example, the closing walls 305 are portions of a larger wall covering together each outer end 304 of each channel 300.

[0131] According to one example, the guide portions 260 include a lower edge 261, which extends to the level of the plane formed by the bottom 202 of the drawer. The term "at the level" means that the lower edge 261 extends to a height substantially equal to that of the bottom 202. Thus, given that the channel or each channel 300 extends below the level of the bottom 202 of the drawer, the lower edges 261 form with the channels 300 passage openings 262 through which the cover or each cover 232 can slide. Thus, the passage openings 262 form a connection between a front section 301 of the channels 300, positioned on the side of the guide walls 260 oriented towards the inside of the digester, and a rear section 303 of the channels 300, positioned on the side of the guide walls 260 oriented towards the outside of the digester.

[0132] According to one embodiment, the drawer 200 does not include a casing 250, side walls 251, or guide walls 260. This is the case in particular in the example of [Fig.10].

[0133] According to one example, the orifices 302 are positioned, in each channel 300, behind each guide portion 260, in the rear sections of the channels 300. In this way, the stroke of the nose being limited to the vicinity of the guide walls 260, the orifices 302 are never crossed, nor even reached, by the first surface 212 of the nose 210 which only moves along the front sections of the channels 300.

[0134] The conveying system may further be provided with a piston 252 capable of compressing solid materials inside the recovery pit 310. If applicable, the piston 252 may slide through an opening 254 in the casing 250, or the piston may slide on a structure fixed to the masonry support 46, or outside the digester 10. The piston 252 thus has a stroke in a vertical direction, substantially perpendicular to the direction of translation of the nozzle. The piston 252 is provided with a rod and a head, the head being dimensioned to substantially correspond to the surface area of ​​an opening in the pit 310, so as to push and / or compress a maximum quantity of solid material pushed by the nozzle 210 towards the pit 310.

[0135] According to one example, the respective back-and-forth movements of the piston 252 and the nozzle 210 can be phased out. In particular, such a phase shift can be provided so that when the nozzle 210 is in the filling position, the piston 252 lowers to a low position to push the solid material towards the pit 202, and when the nozzle has moved into its emptying position, the piston has first risen to a high position to clear the passage to the pit 202 for the solid material, possibly via the inclined portion 270 of the spool. The successive high and low positions of the piston are shown respectively in views 13A and 13B of [Fig. 13]. Other configurations are also possible, according to other examples. In particular, the piston can be configured to perform its compression operation while the nozzle 210 is not moving, or independently of the position of the nozzle 210.

[0136] According to one embodiment, the piston 252 can move from the upper position, particularly as illustrated in [Fig. 13A], to the lower position, particularly as illustrated in [Fig. 13B], while the nozzle 210 is in the discharge position. In this discharge position, the first surface 212 closes the outlet 40, preventing the material discharged by the piston from being forced back into the digester.

[0137] When the installation 1 includes a seepage juice recirculation device 80 as shown in [Fig. 1], and a conveying system as described in Figures 7 to 13, the seepage juice collected by the channels 300 and, where applicable, the discharge means 304, is conveyed to the first pipe 71. The lift pump 82 moves the seepage juice along the discharge pipe 71 to the storage container 84. The seepage juice is stored inside the storage container 84 for a predetermined period, and then recirculated to the biomass irrigation device 28 11 via the pipe 90.

[0138] Solid materials, once conveyed out of the digester 10, can be discharged by means of a pump 53 linked for example to the recovery pit 310, to a storage tank 54 for their subsequent use.

[0139] According to one example, the second conduit 56 is separate from the first conduit 71. In this way, the conveying system 44 allows a separation of the solid matter and the seepage juices.

[0140] A first method of biomass methanization using a methanization plant 1 as described above, independent of the type of conveying system 44, will now be described.

[0141] The first process includes the incorporation of biomass 11 by the biomass 11 inlet 22 of the digester 10. As discussed above, the incorporated biomass 11 may include, for example, any type of manure, straw, corn stalks, sunflower stalks, a straw / slurry mixture, a manure / slurry mixture, a straw / silage mixture or a manure / silage mixture, or biowaste straw or biowaste manure.

[0142] The biomass 11 advantageously comprises between 15% and 99% by weight of dry matter. The biomass 11 has, for example, a density between 0.25 and 1.

[0143] The biomass 11 is in particular introduced into the digester 10 through the pipe 24 by means of a pump or a screw conveyor.

[0144] The biomass 11 is introduced into the digester 10 and tends to create a mound.

[0145] The first process then includes a step of watering the biomass 11 at the inlet 22 of the digester 10 to spread the biomass 10 and move it along the bottom 12 of the digester 10 towards the digestate outlet 40, the digester 10 being devoid of mechanical means of driving the biomass 11.

[0146] Irrigation is preferably carried out intermittently. In one embodiment, for a digester 10 with a capacity of 200 m3, the irrigation flow rate is between 10 m3 and 100 m3 per day.

[0147] The biomass mound 11 formed at the entrance of the digester collapses under the watering, and is carried along the bottom 12 of the digester 10.

[0148] The first process includes 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.

[0149] Biomass is preferably introduced as regularly as possible, preferably several times a day, to allow the most stable gas production possible.

[0150] The seepage juice flows towards the bottom 12 of the digester 10 and the solid matter floats on the surface of the juice.

[0151] The residence time of the materials between the entry of the biomass 11 and the exit 40 of the digestate is for example between 20 days and 60 days to extract biogas in sufficient quantity.

[0152] The first process then includes the separate discharge of solids and seepage juice, the solids being discharged by the conveying system 44 to the outside of the digester 10.

[0153] The solid materials at the outlet of digester 10 have, for example, a density between 0.9 and 1.

[0154] The evacuation of solid materials is for example triggered by a level sensor in the digester 10.

[0155] When the conveying system 44 includes a scraper element 104, 204, the actuator which causes the back-and-forth movement of the scraper element 104, 204 can be controlled by a processor in communication with such a level sensor.

[0156] The solid materials, once conveyed out of the digester, can be discharged by means of a pump 53 into a storage tank 54 for their subsequent use.

[0157] A second continuous biomass methanization process using a methanization plant 1 equipped with a conveying system of the type shown in [Fig.4] will now be described.

[0158] The second process includes the same first steps as the first process, as well as the separate discharge of solids and seepage juice, the seepage juice being discharged through the filter screen 66 to the outside of the digester 10.

[0159] In particular, the filter screen 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 screen 66 is placed in the working position, the seepage juice that has percolated to the bottom of the digester 10 is drawn towards the filter screen 66 and passes inside this filter screen 66 through the orifice 64 of the masonry support 62. The solid matter remains outside the filter screen 66.

[0160] The seepage juice is notably evacuated into the seepage juice evacuation conduit 71.

[0161] The drainage of seepage juice takes place continuously, except during the cleaning period of the filter grid 66.

[0162] When the installation 1 includes a seepage juice recirculation device 80 as shown in [Fig. 1], the lift 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 put back into circulation towards the biomass irrigation device 28 11 via the pipeline 90.

[0163] If maintenance is desired, the filter grid 66 is moved to the cleaning position, the filter grid 66 then being external to the digester 10 and accessible by a cleaning device 70 while blocking the orifice 64 of the masonry support 62.

[0164] The movement of the filter grid 66 can be achieved by a cylinder which moves the rod 72 and consequently the filter grid 66 towards the outside of the digester 10.

[0165] The process then includes a step of unclogging the filter grid 66 during methanation.

[0166] Unclogging can be manual or automated, for example by projecting a fluid onto the filter grid 66 using at least one projection nozzle 74.

[0167] When unclogging is complete, the filter screen 66 can again be moved into working position inside the digester 10.

[0168] The first process and the second process can be carried out separately, or concurrently, in which case the solids are removed by a conveying system and the seepage juice is removed through the filter screen 66 to the outside of the digester 10.

[0169] The evacuation of solid matter and seepage juice can take place simultaneously.

[0170] Considering an installation equipped with a conveying system 44 of the type shown in figures 7 to 13, a third methanization process will be described.

[0171] For clarity of description, the nose 210 of the scraping element 204 is initially considered to be in the extreme filling position, for example as shown in [Fig. 7A]. The inclined shape of the second surface 214 allows the nose 210 to penetrate into / under the solid material, possibly by the action of the scraping edge 217. The hollow volume delimited by the first surface 212, the bottom 202 of the drawer and the edges 208 is then filled with solid material. The nose 210 is then moved horizontally to the extreme emptying position where the nose 210 is close to the outlet 40. The contents of the hollow volume are then pushed by the first surface 212 so as to be conveyed outside the digester 10. The scraping element 204 is then moved again in a direction oriented towards the inside of the digester 10 to allow further filling of the hollow volume.By performing a repeated back-and-forth movement along the bottom 202 of the drawer 200, the scraping element 204 allows a certain quantity of solid matter to be pushed out of the digester, for example in several stages.

[0172] By gravity, the seepage juices flow through the channels 300 on the sides of the drawer, and, when the installation 1 includes a seepage juice recirculation device 80 as shown in [Fig. 1], are conveyed to a first pipe 71. Then, the lift pump 82 moves the seepage juice along the discharge pipe 71 to the storage container 84. The seepage juice is stored inside the storage container 84 for a predetermined period, then recirculated to the biomass watering device 28 11 via the pipe 90.

[0173] The solid materials discharged into the recovery pit 310 can then be discharged by means of a pump 53 to a storage tank 54 for their subsequent use, as shown in [Fig.1].

Claims

Demands

1. A methanation plant (1) comprising a digester (10) for converting biomass (11) into biogas and digestate, the digestate comprising solid matter and seepage juice, the digester (10) comprising an outlet (40) to the outside of the digester (10), the plant comprising a conveying system (44) for discharging a quantity of digestate through the outlet (40), the conveying system comprising a drawer (200) having a bottom (202) and lateral edges (208), the conveying system (44) being provided with a scraper element (204) configured to perform reciprocating movements along the bottom (202) and between the edges (208) of the drawer in a horizontal translation direction towards the outlet (40), under the action of an actuator, between a filling position and an emptying position,said scraping element (204) comprising a nose (210) configured to push the digestate towards the outlet (40) by a first surface (212) in a first direction of translation towards the outside of the digester, and to slide under the digestate by a second surface (214) in a direction of translation towards the inside of the digester (10).

2. Installation (1) according to claim 1, wherein the first surface (212) of the nose (210) of the scraping element (204) extends in a vertical plane, substantially perpendicular to the horizontal translation direction, so as to push the solid material towards the outlet (40), and wherein the second surface (214) is at least partly inclined downwards, so as to be able to slide under the digestate.

3. Installation (1) according to any one of the preceding claims, wherein the outlet (40) is provided in a concrete support (46), and a bottom of the digester (10) comprises a masonry slab (12), the drawer (200) and the scraping element (204) are provided below the level of the bottom of the digester (10) in a trench (240) provided in the masonry slab (12).

4. Installation (1) according to any one of claims 1 to 3, wherein it comprises a first juice drainage conduit (71) and a second solids drainage conduit (56), the drawer (200) comprising a seepage juice drainage channel (300) cut into the bottom (202) of the drawer (200) and comprising an orifice (302) for conveying the juices to the first pipe (71) outside the digester (10), the installation (1) comprising, outside the digester (10), a recovery pit (310) configured to convey the solid matter to the second pipe (56), the second pipe (56) being separate from the first pipe (71).

5. Installation (1) according to the preceding claim, comprising two drainage channels (300), each located at a junction between the bottom (202) of the drawer and a rim (208) of the drawer (200).

6. Installation (1) according to any one of claims 4 or 5, the nose (210) comprising a cover (232) configured to slide in the channel (300), the cover (232) having an inverted U-shaped cross-section, the cover (232) being movable in translation with the nose (210), in the channel (300) below the level of the bottom (202) of the drawer (200), each cover (232) having a length such that it is configured to always cover the orifice (302), and this at any position of said scraper element (204) between the emptying position and the filling position.

7. Installation (1) according to the preceding claim, wherein a distal end (233) of the cover (232) opposite the nose (210) has a push face (235) configured to push the solid material present in the channel (300) in a direction oriented outwards from the digester (10).

8. Installation (1) according to any one of claims 1 to 7, wherein the drawer (200) comprises, between the bottom (202) of the drawer and the pit (310), a downward inclined portion (270) suitable for allowing the solid material to fall into the pit (310).

9. Installation (1) according to any one of the preceding claims, comprising a casing (250) covering a portion of the drawer (200) extending outside the digester (10).

10. Installation (1) according to any one of the preceding claims in combination with claim 4, wherein the drawer (200) is provided with a piston (252) outside the digester (10), the piston (252) comprising a rod movable in translation along a vertical direction substantially perpendicular to the direction of translation of the nose (210), the piston (252) comprising, at one end of the rod, a head configured to compress the solids inside the pit (310).

11. Installation (1) according to any one of the preceding claims, wherein the drawer (200) has two slides (218), integral with the nose (210), extending in the direction of translation, configured respectively to slide along two guide grooves (220) formed in the two rims (208) of the drawer, the two guide grooves (220) projecting outwards from the two rims (208).

12. A method for the methanization of biomass (11) using a methanization plant (1) according to any one of the preceding claims, comprising: - the incorporation of biomass (11) through the biomass inlet (11) of the digester (10), - the spraying of the biomass (11), preferably at the inlet of the digester (10), to spread the biomass (11) and move it along the bottom (12) of the digester (10) towards the digestate outlet (40), the digester (10) being devoid of mechanical means for conveying the biomass (11), - the digestion of the biomass (11) by microorganisms to form biogas and digestate comprising solids and seepage, the removal of the solids and seepage by the conveying system (44) to the outside of the digester (10) during which the digestate is discharged by back-and-forth movements of the scraping element (204) comprising,sequentially: - a movement of said scraping element (204) from the filling position to the emptying position, during which the first surface (212) of the nose pushes the digestate, located in a hollow volume between the edges (208) of the drawer (200), towards the outlet (40), - a movement of said scraping element (204) from the emptying position to the filling position, during which the second surface (214) of the nose slides under the digestate, the hollow volume filling with digestate.

13. A method according to the preceding claim, wherein the installation (1) comprises a first juice discharge pipe (71), and a second solids discharge pipe (56), the drawer (200) including a seepage channel (300) cut into the bottom (202) of the drawer (200) and including an orifice (302) for conveying the juices to the first pipe (71) outside the digester (10), the installation (1) including, outside the digester (10), a recovery pit (310) configured to convey the solid matter to the second pipe (56), the second pipe (56) being separate from the first pipe (71), the process including the separation of the solid matter and the seepage juices during the back-and-forth movements.

14. A method according to the preceding claim, wherein the installation (1) is according to claim 10, the vertical translational movement of the piston (252) being a reciprocating movement between a high position and a low position, out of phase with the reciprocating movement of the nose (210), so that the piston (252) is in the low position when the nose (210) is in the filling position, and the piston (252) is in the high position when the nose (210) is in the emptying position.

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