GREEN WASTE PROCESSING PROCESSES

Abstract

The invention relates to a process for treating green waste (D), characterized in that it comprises at least the following steps: - a) shredding (1) the green waste (D) to a first defined size, - b) screening (2) the woody elements obtained in step a) to obtain a size smaller than that of step a) and to remove non-woody elements (20), - c) separation (5) of the solid elements obtained in the previous step by density difference in a liquid medium, only the woody solid elements without impurities being retained for the next step, - d) shredding (6) the woody elements obtained in the previous step to the desired final size, - e) storage (8) before use of the woody elements obtained in the previous step in a process for manufacturing wood-based heating products.

Description

[0001] The present invention relates to a method for treating green waste.

[0002] Green waste is plant waste originating from agricultural, forestry, or private or public green space maintenance activities. It includes a woody component, such as branches or tree trunks, and a non-woody component, such as leaves and grass clippings. Hereafter, the term "green waste" will also encompass any woody waste such as timber, planks, crates, boxes, and pallets, provided that this woody waste has not been treated with chemicals.

[0003] Generally, this waste is used as a substrate for making compost. Currently, other uses for woody green waste are being considered, as compost production is sufficient to meet demand. On the other hand, the need for woody material is significant for various applications, including heating.

[0004] It is in this context that the applicant developed a process for treating green waste, enabling the use of the woody part of the green waste in the production of raw material for the production of wood pellets or kindling for heating. Such pellets are also referred to by the English term "pellet."

[0005] To this end, the invention relates to a process for treating green waste, characterized in that it comprises at least the following steps: a) shredding of green waste to a first defined size, b) screening of the woody elements obtained in step a) to obtain a size lower than that of step a) and to remove non-woody elements, c) separation of the solid elements obtained in the previous step by density difference in liquid medium, only the woody solid elements without impurities being kept for the next step, d) shredding of the woody elements obtained in the previous step to the desired final size, e) storage before use of the woody elements obtained in the previous step in a wood-based heating product manufacturing process.

[0006] Thus, the process which is the subject of the invention makes it possible, from green waste comprising in addition to a woody part, a non-woody fraction which includes leaves, grass, non-vegetable materials such as metal, plastic, to keep only the woody part and to prepare it for use, as a raw material, for other recovery processes, in particular the production of wood pellets, briquettes or more generally of fuels intended to power heating, electricity production, steam or other appliances.

[0007] According to advantageous but not mandatory aspects of the invention, such a process may comprise one or more of the following steps: After step b) and before step c), the elements obtained in step b are dried in an additional step f). After step f), in step g), the smaller particles, called fines, are sieved to remove them. During sieving, non-woody and non-ferrous metal solids are removed. After step c) and before step d), the non-woody ferrous metals are removed. After step d) and before step e), the smaller particles, called fines, are sieved to remove them. During sieving, the woody particles are dried.

[0008] The invention will be better understood and other advantages thereof will become more apparent upon reading the following description of several embodiments of the invention, given by way of non-limiting example and with reference to the following drawings in which: Figure 1 is a simplified diagram of the process according to one embodiment of the invention.

[0009] The diagram in Figure 1 illustrates an embodiment of the process according to the invention.

[0010] Green waste, designated by the letter D, comes from various activities, whether private, industrial, or public. Here, this term refers to waste derived from plants and containing woody material. Examples include forestry or pruning waste (D1), maintenance of private or public green spaces (D2), and the collection of waste (D3) such as wooden crates, wooden boxes, wooden pallets, planks, or more generally, waste from the wood industry. These various types of green waste (D) are collected using established methods.

[0011] It is understood that these green waste materials (D) come in various shapes and sizes and frequently contain a non-woody component. This non-woody component can originate either from the green waste collection process or from the initial origin and use of the woody component. Thus, non-woody components include polymers, metal, grass, ceramics, terracotta, stones, organic waste, and other materials.

[0012] Starting with these heterogeneous green waste materials (D), the first step is to reduce their size to achieve a uniform size. In this case, step 1 is a primary shredding process, also known as slow shredding. It is understood that step 1 is carried out using at least one shredder. Such shredding is generally performed at a speed of less than 50 rpm. Alternatively, another type of shredding may be used, depending on the nature of the green waste to be shredded. This step 1 reduces the initial dimensions of the green waste to obtain, for example, G150 size particles according to the European standard EN14961 and the Austrian standard ÖNORM M7133 for wood chips. In this case, the G150 size particles have a surface area of ​​less than 15 cm².

[0013] Subsequently, reference will be made to these normative documents concerning the definition of sizes for wood chips. If necessary, other normative documents or regulatory references are used, as required, provided that the principle of defining a surface area, and therefore dimensions, in order to have a dimensionally homogeneous product type is respected.

[0014] Next, a second screening is carried out to reduce the size of the particles to G80, resulting in a surface area of ​​less than 8 cm². Alternatively, as shown, depending on the requirements, the reduction is performed to a different, defined size, either smaller than G80 or between G80 and G150.

[0015] As a reminder, screening is a process of separating elements according to their size. Screening is generally carried out by passing materials through sieving screens of a defined passage diameter.

[0016] Here, screening 2 separates any leaves and / or grass present, as well as certain inorganic elements such as metals. All of these non-woody elements are removed for further processing, which may be final treatment or another use, for example, composting in the case of leaves and / or grass.

[0017] Following screening, the G80 size particles are, if necessary, dried in an optional step 3. Drying is carried out either naturally in the air or in at least one heated chamber, the method for which is well-established. The purpose of this step 3 is to reduce the moisture content of the G80 size particles to a defined level. Here, the defined moisture content is approximately 20%. Alternatively, the defined moisture content may be different.

[0018] It is easy to understand that this step 3 is only necessary if the moisture content is higher than the defined level. To determine this, it is advantageous to measure the moisture content of the screened elements.

[0019] The G80 size elements, either after drying in step 3 or directly from the screening unit 2 if they are dry, are, as illustrated in Figure 1, advantageously directed towards at least one internally fed rotary cylindrical screen 4. Such a screen is commonly referred to by the German term trommel. This term will be used preferentially hereafter.

[0020] The purpose of this step is to separate the previously obtained G80 particles and, using a series of appropriate sieving screens, remove smaller G10 particles with a maximum surface area of ​​1 cm², referred to as fines. These fine particles are present alongside the G80 particles but are not bonded to them. Therefore, step 4 is optional if the G80 particles from the screening are the only ones present, or if the G10 particles are negligible in quantity. These G10 particles are then removed, as indicated by arrow 40, to storage, final waste treatment, or another use.

[0021] Advantageously, the trommel 4 is equipped with a device adapted to also remove non-woody materials such as small plastics or non-ferrous metals. For this purpose, the trommel is, for example, equipped with an electrostatic filter and / or a suction system.

[0022] The G80 graded material, once freed of fines, is directed to a solids separation stage using density difference in a liquid medium. This stage is carried out with at least one separator 5. Such a separator 5 is designed to ensure the advancement and mixing of the G80 graded solids in the liquid, for example, water, in order to remove any impurities from the woody material. In other words, soil, sand, stones, and more generally all small non-woody elements with a density greater than that of the liquid, which are still present on and physically bound to the G80 graded material, are separated from it by flotation, thus effectively washing the material, and removed, as indicated by arrow 50, for further processing, storage, or other use.

[0023] Separator 5 is designed to ensure continuous separation and cleaning with the shortest possible residence time for the elements within the separator, while maintaining maximum efficiency. For example, the residence time is less than 30 seconds. This minimizes wetting of the elements as they pass through the separator liquid. Typically, the moisture content of G80-sized elements exiting Separator 5, once they have been freed of impurities, is a maximum of 35%. In other words, the passage of the G80-sized elements through the liquid only results in surface wetting, not deep penetration, as the liquid does not have time to penetrate the core of the woody material.

[0024] In step 6, the cleaned G80 woody material is then ground to the desired size, for example, G20, which corresponds to a maximum surface area of ​​2 cm² for producing wood chips, kindling, wood pellets, or other fuels for heating appliances. This grinding process in step 6 can be either slow or fast, using appropriate sizing screens.

[0025] Advantageously, between separator 5 and crushing stage 6, the components pass over a conveyor belt (not shown) equipped with an electromagnet to collect any remaining ferrous metal residue. It should be noted that if staples, nails, or screws are embedded in the component, the entire component will be removed by this device.

[0026] Following the crushing in step 6, the material of the desired size, in this case G20, is directed to at least one rotary circular screen or trommel 7. This step is optional. It may happen that the material obtained after crushing in step 6 is usable as is, either by design or because there is little or no fines present.

[0027] In this example, trommel 7 differs from trommel 4 in that it has more than two sieving elements. Alternatively, trommels 4 and 7 are similar. Trommel 7 separates the fines, i.e., particles smaller than G10, just like trommel 4, and recovers not only G20-sized particles (such as chips) but also potentially particles of other sizes, between G10 and G20, and / or of a different type than chips, depending on the requirements.

[0028] In all cases, elements with a size greater than G20 are returned, according to arrow 70, to crushing 6, while the fines below the G10 size are removed, according to arrow 71, for storage, final treatment or other use.

[0029] Advantageously, the trommel 7 is equipped, in one or more areas of the trommel 7, with at least one hot air injection device, in order to obtain a humidity level as close as possible to that desired for the use of G20 grade wood elements.

[0030] The next step, referenced as step 8, consists of either storage in a silo or a skip, before the woody elements thus obtained are used in a manufacturing process for heating pellets, kindling, wood chips, or other fuels. It is understood that, if necessary, an additional drying step is carried out during storage, in order to reduce and / or maintain the moisture content at the desired value for the subsequent processing and / or use of the woody elements.

[0031] Similarly, storage time can be close to zero when G20 grade wood elements are directly introduced into a manufacturing process for wood pellets, briquettes, chips or other similar products.

[0032] During the various stages, measurements of the humidity level and other physico-chemical parameters, for example temperature, pH, are carried out.

[0033] The transfer of components between the devices performing the various stages is advantageously carried out automatically by belt or bucket conveyors. The different stages are managed from a control module. This module can be located remotely from the installation and is advantageously controllable remotely, for example, via a computer or smartphone. Alternatively, all stages of the process can be automated.

[0034] In another embodiment, several devices performing the various steps are arranged either in parallel or in series, as required.

[0035] Alternatively, the different stages of the process are carried out in a mobile installation, either mounted on a self-propelled vehicle or not, or adapted to be transported by container.

Claims

1. A process for treating green waste (D), characterized in that it comprises at least the following steps: - a) shredding (1) of green waste (D) down to a first defined size, - b) screening (2) of the woody elements obtained in step a) to obtain a sizing lower than that of step a) and to remove non-woody elements (20), - c) separation (5) of the solid elements obtained in the previous step by density difference in a liquid medium, only the woody solid elements without impurities being retained for the next step, - d) grinding (6) of the woody elements obtained in the previous step to the desired final size, - e) storage (8) prior to use of the woody elements obtained in the previous step in a process for manufacturing wood-based heating products.

2. A process according to claim 1, characterized in that after step b) and before step c), in an additional step f) drying (3) of the elements obtained in step b).

3. A method according to claim 2, characterized in that after step f), a further step g) is carried out by sieving (4) to remove the smaller caliber elements called fines.

4. A method according to claim 3, characterized in that during sieving (4) non-woody and non-ferrous metal solids are removed.

5. A method according to claim 1, characterized in that after step c) and before step d), the non-woody elements are removed in ferrous metal.

6. A method according to claim 1, characterized in that after step d) and before step e), a sieving (7) is carried out to remove the smaller caliber elements called fines.

7. A method according to claim 6, characterized in that during sieving (7) the woody elements are dried.