FR2668398A1 - Method and device for extracting the organic material contained in household waste - Google Patents

Abstract

The invention relates to a method and device for extracting the organic material contained in household waste, with a view to composting it. The method is characterised in that the said waste is introduced into a primary screen, the mesh dimension of which is between approximately 100 and 200 mm, at least on one of its parts, in that the fines from the primary screen are subjected successively to a magnetic extraction, to a possible manual sorting, to a grinding and to a screening, and in that the fines from the latter are subjected to a densimetric sorting which supplies, on the one hand, the final impurities and, on the other hand, the organic material to be composted. Application to the manufacture of compost.

Description

 The present invention relates to a method and a device for extracting the organic matter contained in household waste with a view to its composting.

 We know that household waste is a heterogeneous product whose characteristics are very variable over time, which makes its treatment particularly complex when it comes to extracting one or more components. Among these, compostable organic matter represents approximately 50 to 60% of raw waste, and it is of definite interest in agriculture when it has been properly fermented and stabilized.

 Also, the main object of the present invention is to provide a method and a device which make it possible to efficiently and economically extract the compostable organic material contained in household waste.

 Another object is to provide a process and a device of this kind which can be easily adapted to the composition of the waste to be treated and to the quality sought for the organic matter to be extracted.

 According to the invention, these aims, as well as others which will appear subsequently, are achieved by means of a process of the kind specified above which is characterized by the fact that the waste to be treated is introduced into a primary trommel, the mesh size of which is between approximately 100 and 200 mm, at least on one of its parts, which the passers-by of this primary trommel are successively subjected to magnetic extraction, to possible manual sorting, to grinding and screening, and that the passers-by of the latter is subjected to a densimetric sorting which supplies, on the one hand, the last impurities, and, on the other hand, the organic matter to be composted.

 While it is true that some of the steps in this process are well known to specialists, it is their combination in the order specified above which, surprisingly, makes it possible to achieve the aims of the invention, such as that they have been specified above.

 Advantageously, this process can comprise an additional screening carried out in a secondary trommel between the magnetic separation and the grinding specified above, however the possible manual sorting which was mentioned above can be carried out on the refusals of the secondary trommel in question. The presence of the latter facilitates the sorting of glasses, non-ferrous metals and heavy plastics.

 In the general process specified above, the paper and cardboard contained in the refusals of the primary trommel are recovered by incineration. However, in the event that these products cannot be recovered by energy vote, and to avoid landfill shorts, it may be advantageous to extract them and mix them with fermentable organic matter to make compost, since these products have a high cellulose content and are therefore perfectly campostable.

 In this case, the method according to the invention further comprises a paper and cardboard processing path in which the refusals of the primary trommel are successively subjected to magnetic extraction, to possible manual sorting, to grinding, to screening. and vacuum treatment, the paper and cardboard extracted during these last two operations are sent to the densimetric sorting specified above.

 According to a variant which makes it possible to use only one shredder, the paper and cardboard processing path is a path in which the refusals of the primary trommel are successively subjected to magnetic extraction and to possible manual sorting before they are refer to the grinding specified above, and in which the refusals of the screening of the general process are successively subjected to another screening and to a treatment by aspiration, the passers-by of these two operations being returned to the densimetric sorting of the general process.

 In the most general form, the device used for implementing the method according to the invention is characterized in that it successively comprises a primary trommel whose mesh size is between approximately 100 and 200 mm, an apparatus magnetic extraction, a possible manual sorting station, a grinder, a screen and a densimetric sorting device.

 If it is desired to make a compost of excellent quality, it is advantageous to separate from the household waste the fines which they contain, and, for this purpose, the primary trommel of the device according to the invention preferably comprises a part located in lover whose mesh size is between 20 and 50 mm approximately.

 To avoid installing upstream of the primary trommel devices for opening bags of household waste, or to resort to lifters arranged in the trommel which are the cause of a very significant breakage of glass, the side wall of the primary trommel of the device according to the invention is preferably provided internally with laceration points constituted by two plates crossed in an isosceles triangle, the base of which is integral with the side wall of the trommel and the vertices of which are opposite one another the other on their common axis of symmetry.

 Advantageously, the angle at the base of the isosceles triangles which constitute these laceration points is between approximately 60 and 70, and the distance between their vertices is between approximately 5 and 10 cm.

 For the reasons which have been indicated above, the device according to the invention also advantageously comprises a secondary trommel inserted functionally between the magnetic extraction device and the mill of the installation.

 According to an advantageous embodiment, the side wall of the secondary trommel specified above is internally covered with an elastic coating, and it has oblong holes crossed in staggered rows, these provisions being intended to limit the breakage of the glass and to make optimal efficiency of the trommel in question.

The description which follows, and which does not present any limiting character, will make it possible to understand as well as the present invention can be put into practice. Blle should be read against the accompanying drawings, among which:
FIG. 1 represents a general flow diagram of the method according to the invention
Figure 2 shows a schematic perspective view of a tip with which the primary trommel used in this process can be fitted in order to open the waste bags
Figure 3A shows an embodiment of the supposedly unwound side wall of a secondary trommel which can be used in this process; and
FIG. 3B is similar to FIG. 3A, but it represents another embodiment of this side wall.

 We will first describe a basic process which is shown in solid lines in Figure 1 and in which the raw waste 1 is first introduced into a primary trommel 2 equipped with large meshes between 100 and 200 mm about.

 Due to the fact that the waste 1 is generally contained in plastic bags, the invention provides for optimizing this primary screening by providing the trommel 2 with spikes which allow the bags to be opened and lacerated better and an advantageous embodiment of which is shown schematically in the perspective view of Figure 2.

 As shown in this figure, each point designated as a whole by the reference 3 consists of two triangular plates a and 4b which intersect at right angles along an axis X, the latter being perpendicular to the side wall of the trommel - or, more exactly, at its tangent plane - at the point where point 3 is located. The plates a and 4b have the form of isosceles triangles whose base angle, a and oc ', respectively, is between approximately 60 and 70. The vertices 5a and 5b, respectively, of these triangles which is opposite their base, are distant from each other on the axis X with a length h which is preferably between 5 and 10 cm.

 The screening refusals 6 of the trommel 2 consist essentially of plastics, certain metals, paper and cardboard, and they are brought to a magnetic separation device 7 which extracts the ferrous metals which the it is recovered in 8, while the rest, composed of combustible elements, is preferably incinerated in 9 to produce energy in an appropriate boiler.

 For their part, the passers-by 10 of the screening which is carried out in the trommel 2 are composed of glass, metals, fines, certain heavy plastics such as bottles and fermentable organic matter. A magnetic separation device 11 makes it possible to eliminate the ferrous metals which will join in 8 those coming from the screen refusals 6, then they are subjected to a manual sorting 12 by means of which the non-ferrous metals, the materials are recovered in 13 heavy plastics and glass.

 The remaining fraction is mainly composed of fermentable organic matter and fines, and it is sent to a grinder 14 so as to give it a texture which will favor fermentation and to give the finished product a particle size suitable for the intended use, in the agriculture for example.

 The ground product obtained is sent to a screen 15 so as to eliminate certain elements, such as - the plastics, which could still be present despite the manual sorting operation 12, the screen refusals can also be incinerated in @ 9 thus being valued in the form of energy.

 The pass-through fraction of the screening 15 is treated in a densimetric sorting apparatus 16 to remove the last impurities 17 and thus to perfect the extraction of the organic matter which is sent to a composting unit 18 which constitutes the final stage of the process.

 The basic process which has just been described is susceptible of several variants, which will be used depending on the type of waste to be treated and the product which it is desired to obtain.

 Thus, in the case where one wishes to make a very high quality compost, it is necessary to remove raw waste 1 the fines which are dense, which therefore weigh down the compost, which is disadvantageous, and which, on the other hand , have a fairly low content of fermentable organic matter (for example 20 to 30X on the dry product), this being disadvantageous when it comes to producing a very good quality compost.

 To this end, the primary trommel 2 can be replaced by a double drum, the first part, 2a, is fitted with small meshes ranging for example from 20 to 50 mm approximately, while its next part, 2b, has meshes larger dimensions, for example between 100 and 200 mm. The fines 19 which pass through the meshes of the first part 2a of the trommel are eliminated, while the fraction 10 which crosses its second part with large meshes 2b, as well as the refusal 6, are treated as explained above.

On the other hand, the sorting of glasses, non-ferrous metals, and heavy plastics can between facilitated by the establishment of a secondary trommel which is shown in broken lines at 20 in Figure 1 and in which arrive the waste from the magnetic separation device 11. The finer organic material passes through the meshes of this secondary trommel 20, and it joins the crusher 14 to be then subjected to the treatments described above. The
refusal is sent for its part to the sorting step 12 which makes it possible to recover in 13, as has been said, glasses, heavy plastics and non-ferrous metals.

 As the secondary trommel 20 is mainly intended for concentrating the glass, its side wall is before constituted by a perforated sheet protected by a rubber or plastic coating intended to limit the breakage of the glass, while the effectiveness of this trommel is optimal when its meshes are formed by oblong, oval or elliptical holes for example, which are preferably staggered, like those, 21a, of FIG. 3A, or even crossed, like those, 21b, of FIG. 3B.

 According to another variant of the method according to the invention which is shown in dashed lines in FIG. 1, it may be advantageous to extract the paper and cardboard contained in the refusal 6 from the primary trommel 2, insofar as they do not cannot be recovered as energy, since this avoids landfill costs. Indeed, these products have a high cellulose content, so that it is perfectly possible to compost them.

 In this case, the refusals 6 are sent to the magnetic separator 7, as before, but they are then subjected to a possible manual sorting 22 intended to recover the papers and / or the cardboards which are more or less intact, in the case of 'an attractive redemption price of such products, then they are sent to a grinder 23.

As the particle size distribution after crushing of the plastics is coarser than that of the rest of the treated waste, it is easy to concentrate them in the rejects 24 of a second screen 25 whose passer 26 joins the fermentable organic matter before the aforementioned densimetric sorting 16 where the last impurities are eliminated.

 Refusals 24 of the second screen 25 can then undergo a suction treatment 27, such as that described in French patent application No. 90-1.i98 of the Applicant, in order to recover the plastics at 28, on the one hand, and paper and cardboard on the other hand, these joining the passer 26 of the second screening 25.

 In another variant which is shown in double lines in FIG. 1, and which has the advantage of using only one mill, the rejects 6 are sent as previously to a magnetic separation device 7 and, where appropriate , subjected to manual sorting 22, but it is here immediately upstream of the crusher 14 that they join the basic process which has been described above. The refusal of the trommel 15, whose mesh is of the order of 20 to 30 mm, is sent, no longer to the incineration operation 9, but to a second trommel 29 which is equipped with larger meshes and which serves to concentrate plastics in refusals. This facilitates the following operation which is a suction 30 practiced on the refusals of the trommel 29, which is analogous to step 27 of the previous variant and which makes it possible to separate the plastics 31. The passers-by of the two trommels 15 and 29 join the densimetric sorting 16 of the basic processing.

Claims (10)

- CLAIMS 1. A method of extracting the organic material contained in household waste with a view to its composting, characterized by the fact that said waste is introduced into a primary trommel whose mesh size is between approximately 100 and 200 mm, at least on one of its parts, that the passers-by of said primary trommel is successively subjected to magnetic extraction, to possible manual sorting, to crushing and to screening, and that the passer-by is subjected to this the latter to a densimetric sorting which provides, on the one hand, the last impurities, and, on the other hand, the organic matter to be composted. 2. Method according to claim 1, characterized in that it comprises an additional screening in a secondary trommel between said magnetic separation and said grinding, said possible manual sorting being carried out on the refusals of said secondary trommel. 3. Method according to any one of claims 1 and 2, characterized in that it further comprises a vole for processing paper and cardboard in which the refusals of said primary trommel are successively subjected to magnetic extraction, to a possible manual sorting, crushing, screening and vacuum treatment, the paper and cardboard extracted during these last two operations being sent to said densimetric sorting. 4. Method according to any one of claims 1 and 2, characterized in that it further comprises a paper and cardboard processing path in which the refusals of said primary trommel are successively subjected to magnetic extraction and to a possible manual sorting before sending them back to said grinding, and by the fact that the refusals of said screening are successively subjected to another screening and to a suction treatment, 14z bystanders of these two operations being sent back to said denhimetric sorting. 5. Device for implementing the method according to any one of claims 1 to 4, characterized in that it successively comprises a primary trommel (2) whose mesh size is between 100 and 200 mm approximately, a magnetic extraction device (11), a possible manual sorting station (12), a crusher (14), a screen (15) and a densimetric sorting device <16). 6. Device according to claim 5, characterized in that said primary trommel (2) comprises a part located upstream (2a) whose mesh size is between 20 and 50 mm-approximately. 7. Device according to any one of claims 5 and 6, characterized in that the side wall of said primary trommel is internally provided with laceration points (3) constituted by two plates crossed in an isosceles triangle (4a, 4b), the base is integral with said side wall and the vertices (5a, 5b) opposite to said base are distant from each other on their common axis of symmetry (X). 8. Device according to claim 7, characterized in that the angle at the base (oye) of said isosceles triangles (4a, 4b) is between approximately 60 and 70, and that the distance (h) between said vertices (5a , 5b) is between approximately 5 and 10 cm.  9. Device according to any one of claims 5 and 6, characterized in that it further comprises a secondary trommel C20) inserted functionally between said magnetic extraction device (11) and said grinder (14). 10. Device according to claim 9, characterized in that the side wall of said secondary trommel (20) is covered internally with an elastic coating and that it has oblong crossed holes (21b) or staggered <21a).