AU2014285729A1

AU2014285729A1 - A waste treatment process and plant with oscillating screening

Info

Publication number: AU2014285729A1
Application number: AU2014285729A
Authority: AU
Inventors: Arnaud SOMMAIN
Original assignee: Suez Environnement SAS
Current assignee: Suez International SAS
Priority date: 2013-07-05
Filing date: 2014-07-03
Publication date: 2016-01-28
Anticipated expiration: 2034-07-03
Also published as: CN105555411B; HK1222598A1; PL3016745T3; AU2014285729B2; EP3016745A1; EP3016745B1; FR3008007B1; WO2015001514A1; CN105555411A; FR3008007A1

Abstract

Process for treating waste, in particular municipal waste, containing organic matter mixed with undesirables, especially metals, mineral materials, plastics, glass, according to which process: - the waste is subjected to a first sorting by screening, - the fraction of waste passing through the screening is subjected to a pre-fermentation treatment in a rotating tube with supply at one end and extraction at the other end, - at least one portion of the material exiting the pre-fermentation treatment tube is subjected to a methanization treatment in a digester, the waste, without prior grinding, being subjected to sorting by screening through a screen comprising a grid (2) located in a plane inclined by an angle α with respect to the horizontal, the grid (2) being subjected to vibrations in a transverse direction substantially orthogonal to the direction of flow of the waste on top of the inclined screen.

Description

WO 2015/001514 PCT/IB2014/062832 A WASTE TREATMENT PROCESS AND PLANT WITH OSCILLATING SCREENING 5 The present invention relates to a process for treating waste, in particular household refuse, containing organic matter mixed with undesirable products, especially metals, mineral matter, plastics, and glass, according to which 10 process: - the waste is subjected to a first sorting by screening, - the fraction of waste passing through the screening is subjected to a prefermentation treatment in a rotating 15 tube with feed at one end and extraction at the other end, - at least one portion of the material leaving the prefermentation treatment tube is subjected to a methanization treatment in a digester. 20 The household waste resulting from non-selective collections contains different categories of material such as putrescible waste (food waste, glass waste), paper, cardboard, glass, plastic, ferrous or non-ferrous metals, 25 fabrics, sanitary textiles, toxic products (batteries, pots of paint, etc.). The methanization and composting of this household waste with a view to converting it to reusable biogas and compost 30 generally comprises four main steps: - a mechanical preparation of the waste which aims to separate the biodegradable organic matter from the other fractions that cannot be upgraded to biogas or to compost; a prefermentation rotating tube, generally 35 that is essentially horizontal, constitutes a means for such a preparation; WO 2015/001514 PCT/IB2014/062832 -2 - methanization, which aims to produce renewable energy and is carried out in horizontal or vertical chambers, which may or may not be mechanically stirred; - composting, or aerobic maturation, which generally 5 involves a prior operation of pressing the digestate originating from the methanization, in order to achieve a level of solids content and a porosity that enable the self-composting of the digestate, or then which requires the provision of a structuring agent 10 and the mixing thereof with the digestate in order to obtain a compostable substrate; - final refining which aims to additionally remove the contaminants remaining after the preceding two opera tions, and to prepare the compost to a particle size 15 that enables the agronomical upgrading thereof. The treatment of this waste therefore requires a sorting that will make it possible in particular to separate the biodegradable organic matter from the other fractions that 20 cannot be upgraded to biogas or to compost. The particular technical field of the invention therefore lies within the particular context of this first step of mechanical preparation of the waste. 25 Screening makes it possible to select the materials according to their particle size and to separate organic matter and mineral matter. 30 Fine screening using a fine mesh makes it possible to optimize the collection of the organic material that will be able to be reused. Unfortunately, currently, it is difficult to use a fine 35 mesh without encountering clogging problems. The existing devices therefore use meshes of relatively large size that prevent the loss of organic matter but that do not offer the selectivity necessary for the purification thereof.

WO 2015/001514 PCT/IB2014/062832 -3 The objective of the invention is therefore above all to propose a waste treatment process such as is presented in the preamble, and that comprises in particular screening 5 using fine meshes while minimizing the clogging problems. According to the invention, a process for treating waste, in particular household refuse, containing organic matter mixed with undesirable products, especially metals, mineral 10 matter, plastics, and glass, according to which process: - the waste is subjected to a first sorting by screening, - the fraction of waste passing through the screening is subjected to a prefermentation treatment in a rotating 15 tube with feed at one end and extraction at the other end, - at least one portion of the material leaving the prefermentation treatment tube is subjected to a methanization treatment in a digester, 20 is characterized in that the waste, after pre-fermentation treatment, is subjected to a sorting by screening through a screen comprising a grate located in a plane inclined by an angle a with respect to the horizontal, the grate being subjected to vibrations in a transverse direction 25 substantially orthogonal to the flow direction of the waste above the inclined screen. The invention also relates to a plant for carrying out the process, this plant comprising: 30 - a first primary screen, - a prefermentation rotating tube, - and a digester for a fine fraction resulting from the prefermentation tube, the grate possibly comprising a series of wires, the center 35 line of each wire having an orientation similar to the flow direction of the waste above the screen, the wires being located in one and the same plane, the distance between one wire and its neighboring wires varying between a maximum WO 2015/001514 PCT/IB2014/062832 -4 and a minimum, the minimum distance being non-zero. The wires may have a substantially sinusoidal shape. Advantageously, the grate comprises at least one crossbar, 5 positioned perpendicularly to the center line of the wires and firmly attached to the wires so as to maintain a constant spacing between the wires. The vibrations may be transmitted to the screen by means of the crossbar. An electromagnetic hammer may hit one end of the crossbar. 10 Advantageously, the mesh L of the grate is less than or equal to 5 mm. The mesh L of the grate may also be less than or equal to 2 mm. 15 The angle a may be between 30 and 600. Preferably the angle a is 420. A brushing means may be capable of exerting a back-and forth movement over the screen. 20 The brushing means may comprise at least one roller having an axis substantially orthogonal to the flow direction of the waste. The roller may be mounted on a movable frame. 25 The brushing means may comprise an articulated arm equipped with a brush. Other features and advantages of the invention will appear in the following description of one embodiment with 30 reference to the appended drawings, but which has no limiting nature. In these drawings: fig. 1 is a diagram representing the operation of the process according to the invention, fig. 2 is a schematic perspective view of a screen 35 used in the process according to the invention, fig. 3 is a schematic top view of the grate of the screen from fig.2, WO 2015/001514 PCT/IB2014/062832 -5 fig. 4 is a schematic view, on a larger scale, of a detail from fig. 3, fig. 5 is a schematic perspective view of a screen used in the process according to the invention, equipped 5 with a roller brushing device, fig. 6 is a side elevation view of the screen from fig. 5, fig. 7 is a view similar to fig. 6, a retractable support being deployed, 10 fig. 8 and fig. 9 are views similar to fig. 7, the retractable support being moved in order to carry out the cleaning, fig. 10 is a view similar to fig. 6, at the end of cleaning, 15 fig. 11 and fig. 12 are views similar to fig. 5, illustrating the position of the carriage above one grate and another neighboring grate, and fig. 13 is a view similar to figs. 11 and 12, the carriage being in the standby position. 20 Fig. 1 makes it possible to contextualize the invention. The line inlet where the waste to be treated is introduced can be seen at the top left. After a first screen referred to as a primary screen, the fine fraction having a particle 25 size of less than 450 mm passes through a prefermentation rotating tube then through a trommel screen where the finest fraction, having a particle size of less than 80 mm, is recovered and passes through a second trommel screen where the finest fraction, having a particle size of less 30 than 20 mm, is recovered in order to be passed through a screen, that is to say the sieve screen according to the invention, which makes it possible to separate a first very fine fraction, having a particle size of less than 5 mm, from a second fraction having a particle size of between 5 35 and 20 mm.

WO 2015/001514 PCT/IB2014/062832 -6 Subsequently, the first fraction passes through a mechanically stirred horizontal digester with an at least partial recirculation by means of a mixing hopper. 5 It is during this digestion phase that biogas is extracted. The digestat is i4tcself composted. The second fraction hen passes at first through a ballistic separator which makes it possible to remove heavy 10 waste before passing through a digester in a manner similar to the first fraction. The digestate undergoes a maturation phase by drainage or dehydration in order to stabilize it or convert it into fuel. 15 Fig. 2 shows the screening device used in the process according to the invention. The screening device comprises a frame 1 holding an inclined grate 2. The grate 2 is located in a plane 20 inclined by an angle a( with respect to the horizontal. Advantageously, the grate 2 is mounted on a static grate support having an inclination that can be adjusted from 30 to 60 degrees. In this embodiment, the inclination is 420 25 with respect to the horizontal. This steep inclination enables the product to be treated to rush down the slope without being forced to pass through a mesh. Clogging is thus much less frequent. 30 The grate 2 has an elongated shape, a lower end and an upper end being firmly attached to tension systems 3 that make it possible to transmit a permanent tension to the grate 2 in order to keep it substantially flat. 35 Electromagnetic hammers 4 that make it possible to laterally hit the grate are mounted on the sides of the grate, firmly attached to the frame 1.

WO 2015/001514 PCT/IB2014/062832 -7 The grate 2 (fig. 4) is in the form of a series of longitudinal wires 5 having a substantially sinusoidal profile organized in a rectangular shape. 5 The wires 5 are located in one and the same plane, the distance between one wire 5 and its neighboring wires varying between a maximum and a minimum. But, even when the distance between one wire and its adjoining wire is 10 minimum, no welding is present between the two wires. This particular arrangement has been adopted after numerous tests. It minimizes clogging and facilitates the cleaning of the grate. 15 Stiffening crossbars 6 are provided at regular intervals in order to maintain a constant spacing between the wires 5. The electromagnetic hammers 4 are positioned opposite the stiffening bars. The frequencies used are generally between 20 10 and 60 Hz. The case of the use of several screening stages, it is possible to use different frequencies for each stage. In order to guarantee the operation of the process, a 25 cleaning step is provided. Fig. 5 shows a metal framework 7 placed above the grate 2. A carriage 8 is suspended beneath the framework 7 by means of rails so as to be able to slide transversely with 30 respect to the grate 2. The carriage 8 consists of metal sections assembled together in order to delimit in particular an upper surface 8a, attached to which are wheels that cooperate with the rails provided on the framework 7, and an inclined lower surface 8b, parallel to 35 the surface of the grate 2, mounted beneath which is a retractable support 9 that supports cleaning rollers 10. Means (not shown) are provided for rotating the rollers about their axis.

WO 2015/001514 PCT/IB2014/062832 -8 The retractable support 9 comprises two parallel faces 9a and 9b connected by connecting rods 9c. The first face 9a is slidably mounted beneath the carriage 8 whereas the 5 second face 9b supports the cleaning rollers 10. Two grates 2 are provided (of 1 m 75 cm x 3 m 60 cm), positioned side-by-side and fed by a V-shaped chute (not shown) . This chute makes it possible to feed the two grates 10 2 simultaneously or else simply one thereof. In this way, it becomes possible to temporarily decrease the flow rate of waste arriving at the screening station while directing all of the flow to one of the two grates in 15 order to allow the cleaning of the other grate under continuous flow but without the presence of waste. The carriage 8 may therefore be found above one or the other of the grates or else move to the side, in the 20 standby position. In operation, the carriage 8 is positioned in the standby position as in fig. 13. 25 When a cleaning operation is considered to be necessary, the carriage 8 is moved above one of the grates 2, the cleaning of which will be carried out (figs. 11 and 12). The retractable support 9 is then in the folded away position as illustrated in fig. 6. 30 Once the carriage 8 arrives in position above the grate 2 to be cleaned, the retractable support 9 is folded down (fig. 7) in order to bring the rollers 10 into contact with the grate 2. 35 The retractable support 9 then moves downward relative to the carriage 8, parallel to the grate 2 in order to carry out the cleaning thereof (figs. 8 and 9).

WO 2015/001514 PCT/IB2014/062832 -9 Once the grate 2 has been cleaned, the retractable support 9 is folded away (fig. 10) before the carriage 8 returns to the standby position (fig. 13). 5

Claims

1. A process for treating waste, in particular household refuse, containing organic matter mixed 5 with undesirable products, especially metals, mineral matter, plastics, and glass, according to which process: - the waste is subjected to a first sorting by screening, 10 - the fraction of waste passing through the screening is subjected to a prefermentation treat ment in a rotating tube with feed at one end and extraction at the other end, - at least one portion of the material leaving 15 the prefermentation treatment tube is subjected to a methanization treatment in a digester, characterized in that the waste, after pre fermentation treatment, is subjected to a sorting by screening through a screen comprising a grate 20 (2) located in a plane inclined by an angle a with respect to the horizontal, the grate (2) being subjected to vibrations in a transverse direction substantially orthogonal to the flow direction of the waste above the inclined screen. 25

2. A plant for carrying out the process as claimed in claim 1, comprising: - a first primary screen, - a prefermentation rotating tube, 30 - and a digester for a fine fraction resulting from the prefermentation tube, characterized in that the grate (2) comprises a series of wires (5), the center line of each wire (5) having an orientation similar to the flow 35 direction of the waste above the screen, the wires (5) being located in one and the same plane, the distance between one wire (5) and its neighboring WO 2015/001514 PCT/IB2014/062832 11 wires varying between a maximum and a minimum, the minimum distance being non-zero.

3. The waste treatment plant as claimed in claim 2, 5 characterized in that the wires (5) have a substantially sinusoidal shape.

4. The waste treatment plant as claimed in claim 2 or 3, characterized in that the grate (2) comprises 10 at least one crossbar (6), positioned perpendicularly to the wires (5) and firmly attached to the wires (5) so as to maintain a constant spacing between the wires (5). 15

5. The waste treatment plant as claimed in claim 4, characterized in that the vibrations are transmitted to the screen by means of the crossbar (6). 20

6. The waste treatment plant as claimed in claim 5, characterized in that an electromagnetic hammer (4) hits one end of the crossbar (6).

7. The waste treatment plant as claimed in any one of 25 claims 2 to 6, characterized in that the mesh L of the grate (2) is less than or equal to 5 mm.

8. The waste treatment plant as claimed in claim 7, characterized in that the mesh L of the grate (2) 30 is less than or equal to 2 mm.

9. The waste treatment plant as claimed in any one of claims 2 to 8, characterized in that the angle a is between 300 and 600. 35

10. The waste treatment plant as claimed in claim 9, characterized in that the angle a is 420. WO 2015/001514 PCT/IB2014/062832 12

11. The waste treatment plant as claimed in any one of claims 2 to 10, characterized in that a brushing means (9, 10) is capable of exerting a back-and forth movement over the grate (2). 5

12. The waste treatment plant as claimed in claim 11, characterized in that the brushing means comprises at least one roller (10) having an axis substantially orthogonal to the flow direction of 10 the waste.

13. The waste treatment plant as claimed in claim 12, characterized in that the roller (10) is mounted on a movable frame (8, 9). 15

14. The waste treatment plant as claimed in claim 11, characterized in that the brushing means comprises an articulated arm equipped with a brush.