Method and apparatus for reusing a medium in a process, and the use thereof

Abstract

The present invention relates to a method for reusing medium in a process in which, by means of the medium, materials with different densities are separated into a floating fraction and a sinking fraction, comprising separating the floating fraction and the sinking fraction in a density separator; separating the medium from the floating fraction and the sinking fraction by means of a screen, wherein at least a part of the separated medium is transported to a separator and is separated into density agent and water; mixing, in a medium tank, the density agent and the water with each other in a ratio according to a desired density of the medium, wherein the ratio for obtaining the desired density is determined from density measurements in the medium tank; adding the separated medium from the medium tank and optionally from a suspension tank to the density separator; and determining an amount of medium to be added from the medium tank and / or the suspension tank by density measurement in the density separator.

Description

[0001] METHOD AND APPARATUS FOR REUSING A MEDIUM IN A PROCESS, AND THE USE THEREOF

[0002] TECHNICAL FIELD

[0003] The invention relates to a method and an apparatus for reusing a medium in a process wherein, by means of the medium, materials with different densities are separated into a floating fraction and a sinking fraction.

[0004] PRIOR ART

[0005] An apparatus and method for separating materials into a floating and a sinking fraction is known, inter alia, from BE 1027787 (BE ’787). BE '787 describes a method for separating materials, such as metals and plastics, with different densities into two separate fractions: a lighter floating fraction and a heavier sinking fraction, in a medium in a density separator. Herein, the medium that is entrained during the discharge of the fractions from the density separator is collected and dewatered. The measured average density of the collected and dewatered medium corresponds to the desired average density of the medium in the density separator. The invention also relates to an apparatus suitable for carrying out this method. The medium is an aqueous suspension comprising water and a density agent. Density of the medium is measured in the density separator by means of a non-nuclear density meter and is to take place at regular intervals. Thereafter the density of the medium can be adjusted if necessary. This is highly dependent on the density of the density agent in order to be able to adjust the density of the medium accurately and quickly. Additionally, it is challenging to separate different plastics on the basis of their densities since these lie within a narrow range of densities. This is not possible with the apparatus and method of BE '787. The apparatus of BE '787 requires a density agent having a sufficiently high density such that the settling velocity is sufficiently high to achieve a separation between the water and the density agent in the funnel- shaped body. Since the densities of plastics are much closer to each other, it is necessary to use a density agent with a much lower density to create a more stable medium. In addition, a flotation drum is less suitable due to the turbulence in the medium, which reduces the separation efficiency.

[0006] US 2429436 discloses a process for separating particles with different densities by making use of successive hydraulic classification steps. Here, the mixture is immersed in an upwardly flowing high-density aqueous solution formed by a suspension of fine solid particles, wherein in each classification chamber heavier particles of decreasing particle size settle, while lighter fractions are carried over. The mixtures thus obtained are then split up into heavy and light fractions via screening steps. Further, the document describes the use of a magnetizable heavy medium that, after separation, is recovered via magnetic separation and reintroduced into the cycle. In that case it is necessary to use magnets to efficiently remove the fine solid particles of the heavy medium from the process streams, wherein this heavy medium is present in both the floating (light) and the settled (heavy) fraction and therefore must be separated from both fractions. This means that this process is only applicable to processes with particles having magnetic properties.

[0007] The present invention aims to find at least a solution for some of the above- mentioned problems or disadvantages.

[0008] SUMMARY OF THE INVENTION

[0009] In a first aspect, the present invention relates to a method according to claim 1.

[0010] The combination of the density separator, the screen, the separator and the medium tank are advantageous for the reuse of a medium in a process for separating materials with different densities. In the method, the separated medium is separated, by means of a screen, from the floating fraction and the sinking fraction, in combination with the settling of the density agent in the separator, the addition of the settled density agent and the water to the medium tank in a ratio of the water and the settled density agent according to a desired density determined by density measurements in the medium tank, and the addition of the medium from the medium tank and optionally from the suspension tank to the density separator according to the desired density of the medium in the density separator, determined from density measurements in the density separator. Additionally, the combination enables flexible deployment of the process for separating materials with different densities by means of the medium, in that the desired density of the density separator can be easily and accurately adjusted by adding more or less water or settled density agent to the medium tank, or optionally by adding fresh density agent to the suspension tank. Additionally advantageous is the accurate / efficient adjustment of the density of the medium within a narrow range, such as for separating different plastics on the basis of their densities. Preferred embodiments of the apparatus are shown in claims 2 to 9.

[0011] In a second aspect, the present invention relates to an The apparatus according to claim 10.

[0012] The apparatus is the density separator combined with the screen, the separator and the medium tank and optionally the suspension tank. This combination of components is advantageous in that it can provide the possibility of flexibly deploying the process for separating materials with different densities by means of the medium, in that the desired density of the density separator can be easily adjusted by adding more or less water or settled density agent to the medium tank, or optionally by adding fresh density agent to the suspension tank. For this purpose sensors are preferably present in the density separator and the medium tank which can generate electronic signals and serve for actuating valves on outlets of components of the apparatus. Additionally different plastics can be separated on the basis of their densities since these lie in a narrow range of densities and the apparatus can be efficiently adjusted for obtaining the desired density of the medium in the density separator. The apparatus is particularly advantageous for reusing medium.

[0013] Preferred embodiments of the method are described in the dependent claims 11 to 18.

[0014] In a third aspect, the present invention relates to a use according to claim 19.

[0015] This use results in a separation with reuse of the medium for automotive shredder residue or waste from electrical and electronic equipment.

[0016] DESCRIPTION OF THE FIGURES

[0017] Figure 1 shows a schematic overview of steps in a method according to an embodiment of the present invention.

[0018] DETAILED DESCRIPTION

[0019] Unless defined otherwise, all terms used in the description of the invention, including technical and scientific terms, have the meaning as commonly understood by a person skilled in the technical field of the invention. For a better assessment of the description of the invention, the following terms are explicitly explained.

[0020] As used in this document, the articles "a", "an" and "the" refer to both the singular and the plural, unless the context clearly dictates otherwise. For example, "a segment" means one or more than one segment.

[0021] The terms "comprise," "comprising," "consist of," "consisting of," "provided with," "include," "including," "contain," "containing," are synonyms and are inclusive or open terms that indicate the presence of what follows, and which do not exclude or prevent the presence of other components, characteristics, elements, members, steps, as known from or disclosed in the prior art.

[0022] The citation of numerical ranges by their end points includes all integers, fractions, and / or real numbers between the end points, including the end points themselves.

[0023] In a first aspect the invention relates to a method for reusing medium in a process wherein by means of the medium materials with different densities are separated into a floating fraction and a sinking fraction.

[0024] The method comprises the steps of: introducing the materials to be separated into the medium in a density separator, comprising an aqueous suspension of a density agent, discharging the floating fraction and the sinking fraction of the materials, separating the medium from the floating fraction and the sinking fraction, and adding the separated medium to the medium into which the materials to be separated are introduced.

[0025] In an embodiment, the method comprises separating the medium from the floating fraction and the sinking fraction. The separation of the medium results in the medium being reusable after removal of the floating fraction and the sinking fraction from the density separator. The medium is separated by means of a screen. The screen is advantageous for separating the medium from the floating and the sinking fraction in that it is simple to design, use and maintain. Moreover, the screen provides a direct separation on the basis of the size of the density agent, and the floating and sinking fraction. Alternatively, the separating of the medium can be carried out by means of a cyclone or a decanter centrifuge. The cyclone has as an advantage that the cyclone attains a high efficiency and requires minimal maintenance due to the absence of moving components. The decanter centrifuge is highly efficient for solid-liquid separation on the basis of the size of solid matter in the medium; furthermore, the decanter centrifuge can process large volumes and automatically discharge separated materials.

[0026] In an embodiment, at least a part of the separated medium is transported to a separator. The said portion of the separated medium is separated in the separator into the density agent and water. The separation of the said portion of the separated medium is effected by settling of the density agent in the separator. By the settling of the density agent a separation can simply take place on the basis of density differences. Furthermore, settling requires no energy.

[0027] Alternatively, the separation can be carried out by means of decanter centrifugation, filtration, or cyclonic separation. Decanter centrifugation is highly efficient for solidliquid separation on the basis of size of solid matter in the medium; furthermore, a decanter centrifuge can process large volumes and automatically discharge separated materials. Filtration is suitable for separating solids and liquids, it is simple to use, and it is not necessary to use chemical additives for the separation, making it an environmentally friendly choice. Cyclonic separation offers high efficiency, minimal maintenance due to the absence of moving parts and a compact design that is useful for limited installation space.

[0028] In an embodiment, the settled density agent is transported from the separator to a medium tank. In the medium tank the settled density agent and water are mixed with each other in a ratio according to a desired density of the medium. The said ratio for obtaining the desired density of the medium is determined from density measurements in the medium tank. Preferably, there is feedback of the density measurements in the medium tank to a control of supply valves of the settled density agent and the water. The addition of the density agent and the water in the ratio according to the desired density of the medium tank provides the possibility to regulate and adjust the density of the medium in the medium tank.

[0029] In an embodiment, the separated medium is added from the medium tank and optionally from a suspension tank to the density separator, wherein an amount of medium to be added from the medium tank and / or the suspension tank is determined by density measurement in the density separator. Preferably, there is a feedback of density measurements in the density separator to a control of a supply of medium from the medium tank and / or the suspension tank. The addition of the medium from the medium tank according to the desired density in the density separator provides the possibility to regulate and adjust the density of the medium in the density separator.

[0030] In a preferred embodiment, the separated medium is separated, by means of a screen, from the floating fraction and the sinking fraction, in combination with the settling of the density agent in the separator, the addition of the settled density agent and the water to the medium tank in a ratio of the water and the settled density agent according to a desired density determined by density measurements in the medium tank, and the addition of medium from the medium tank and optionally from the suspension tank to the density separator according to the desired density of the medium in the density separator, determined from density measurements in the density separator. This combination of steps is advantageous in view of the above advantages. Additionally, the combination allows the flexible deployment of the process for the separation of materials with different densities by means of the medium, in that the desired density of the density separator can be easily and accurately adjusted by adding more or less water or settled density agent to the medium tank or optionally by adding fresh density agent to the suspension tank. Additionally advantageous is the adjusting of the density of the medium in the medium tank within a narrow range, such as for separating different plastics on the basis of their densities. This narrow range often lies between 0.80 kg / L and 2.15 kg / L.

[0031] In an embodiment, the method comprises the additional step of decanting the water from the separator. This occurs during the separation of the separated medium in the separator. The water is collected in a water tank after decanting. The decanting of water from the separator provides an efficient separation of solid density agent. The collecting of water in a water tank after decanting facilitates collection and storage for reuse. Decanting is energy-efficient, can be carried out continuously, and requires little maintenance.

[0032] In a further embodiment, the method comprises the additional step of settling the density agent on the bottom of the separator. The settled density agent is collected on the bottom of the separator. The density agent can be simply collected on the bottom of the separator, as a result of which no additional storage device is necessary. Moreover, the density agent remains partially in suspension, which makes the transport between different installations for carrying out the method simpler. This is possible with frequent removal of the density agent from the separator. Due to the frequent removal, the separator does not become oversaturated with density agent and the medium in the density separator is replenished in time. Preferably, the separator comprises a mixer for keeping the density agent in suspension in the medium.

[0033] In an embodiment, the density agent settles on the bottom of the separator and the settled density agent is stored in a suspension tank. Preferably, the suspension tank is replenished with fresh and undissolved density agent. Storing the density agent in the suspension tank prevents oversaturation of the separator with density agent. Moreover, the suspension tank is easily replenished with fresh and undissolved density agent when the suspension has a lower density than the medium in the medium tank. This ensures that the density of the suspension remains consistent and that the efficiency of the separation process in the density separator can be maintained.

[0034] In an embodiment, the method comprises the additional step of separating the separated medium by decanting the water in the discharged medium over lamellae to adjacent lamellae. The separator is a lamella separator. The density agent is retained by the lamellae and settles along the lamellae to the bottom of the lamella separator. The lamella separator has an increased separation surface in a compact design. Furthermore, the lamella separator increases the efficiency of sedimentation whereby the separation of solids and liquids proceeds more quickly and more effectively. This leads to a higher processing capacity without the need for a large installation.

[0035] In an alternative embodiment, the separator is a decanter centrifuge. The separation of the separated medium takes place by allowing the water in the discharged medium to flow off along a rotating screw. The water flows out of the decanter centrifuge in the opposite direction to the transport direction of the rotating screw. The rotating screw carries the density agent along in the transport direction of the screw. The decanter centrifuge is highly efficient for solid-liquid separation on the basis of size of solid matter in the medium. Furthermore, the decanter centrifuge can process large volumes and automatically discharge separated materials. In an embodiment, the method comprises the additional step of flowing a part of the separated medium through a filter, this prior to the separator. Coarse particles are separated on the filter and filtered medium is pumped to the separator.

[0036] In a further embodiment, the filter is a belt filter. At least a portion of the separated medium is conveyed onto a belt in the belt filter, where the medium passes through the belt and coarse particles comprising agglomerated density agent are separated. The coarse particles are carried along with the belt. The medium that passes through the belt is transported to the separator. Preferably, the coarse particles are scraped off the belt and collected. Preferably, water that is used for cleaning the filter, more specifically the belt of the belt filter, is collected and added to an inlet stream of the filter.

[0037] Filtering with a belt filter provides an efficient separation of the coarse particles from the medium, including the agglomerated density agent or fine pieces of the floating or the sinking fraction being removed from the medium. As a result the purity of the separated medium increases. Additionally, it is advantageous that the purity of the water also increases, whereby blockages of pumps and valves are avoided. Preferably, the water for cleaning the filter is returned to a supply of the filter. This recirculation reduces the water consumption and consequently contributes to a more sustainable and more environmentally friendly method. By this combination of advantages the use of a belt filter improves the efficiency, quality and sustainability of the separation process.

[0038] In an embodiment, the method comprises the additional step of the direct transporting of the separated medium through a first part of the screen to the medium tank. The screen is split into at least two parts. The separated medium originating from the first part of the screen is collected and / or stored in the medium tank. Due to the direct flow-through of the medium, originating from the first part of the screen, to the medium tank, there is sufficient medium available to add to the density separator. By the pumping of the medium from the medium tank, a sufficiently high level of the medium in the density separator is maintained. Preferably, the separated medium from the first part of the screen is first collected in a first tank under the first part of the screen. The first part of the screen is directly coupled to the first tank. More preferably, the separated medium from the first part of the screen is pumped over to the medium tank upon reaching a maximum level of the first tank. This prevents the first tank from overflowing. In a further embodiment, the separated medium is transported through a second part of the screen to the separator. As a result at least a part of the medium can be collected for reuse in the medium. Consequently, the separated medium can again be adjusted to the desired density of the medium. Preferably, the separated medium is transported through the second part of the screen to the filter prior to being supplied to the separator.

[0039] In a further embodiment, the method comprises the additional step of rinsing off adhering medium from the floating fraction or from the sinking fraction after the passing of the floating fraction or the sinking fraction along the first part of the screen. The rinsed-off medium is transported through the second part of the screen to the separator. Preferably, the separated medium is conveyed through the second part of the screen to the filter prior to supply to the separator. As a result adhering density agent on the floating or sinking fraction can be rinsed off and collected for reuse in the medium with the desired density. Preferably, the separated medium from the second part of the screen is first collected in a second tank under the second part of the screen. The second part of the screen is directly coupled to the second tank. Preferably, the separated medium from the second part of the screen is pumped over to the separator upon reaching a maximum level of the second tank. This prevents the second tank from overflowing.

[0040] In an embodiment, the method comprises pumping medium from the medium tank to the filter. As a result, in the event of too high a level of the medium in the medium tank, the medium can be transported to the filter. Furthermore, pumping the medium from the medium tank to the filter can be used to restore the desired density in the medium tank to the required level. As a result there is volume free in the medium tank that can be filled with density agent from the separator or from the suspension tank.

[0041] In an embodiment, the method comprises the additional step of adding water to the medium tank to lower the desired density of the medium. Small fluctuations in the amount of water that during the separating of the materials into a floating fraction and a sinking fraction are added to the medium are averaged out and have no substantial influence on the average density of the medium in the medium tank.

[0042] It is, however, possible that over a longer period less water is added to the medium. This can for example be because a throughput rate of the materials to be separated is reduced, whereby together with the materials to be separated less water is introduced into the density separator and whereby the density of the medium decreases less quickly.

[0043] Another possibility is that a different separation of materials is desired. The floating fraction must for example comprise only lighter materials. For that purpose it is necessary to lower the desired density of the medium in the density separator. A part of the materials that previously was discharged with the floating fraction will now sink to the bottom of the density separator.

[0044] The density of the medium can be lowered by adding water to the medium tank until the desired density is reached. Because the medium that leaves the density separator is compensated by the medium from the medium tank, the medium in the density separator will also reach the desired average density. This step of the method is suitable for gradually lowering the average density of the medium during the separating of materials.

[0045] A rapid lowering of the desired density is possible in an embodiment wherein water is added directly to the density separator.

[0046] In an embodiment, the method comprises the additional step of adding density agent to the medium tank to increase the average density of the medium.

[0047] It is also possible that over a longer period more water is added to the medium. This can for example be because the throughput rate of the materials to be separated is increased, whereby together with the materials to be separated more water is introduced into the density separator, whereby the density of the medium decreases more quickly. If the density of the medium in the medium tank is not adjusted, the density of the medium in the density separator will gradually decrease and after a period of time a correction is required.

[0048] It is likewise possible that, with a different desired separation of materials, the sinking fraction must comprise only the heaviest materials. For that purpose it is necessary to increase the desired density of the medium in the density separator. A part of the materials that previously sank to the bottom of the density separator will now be discharged with the floating fraction.

[0049] The average density of the medium can be increased by adding density agent to the medium tank until the desired average density is reached. Again, because the medium that leaves the density separator is compensated by the medium from the medium tank, the medium in the density separator will also reach the desired higher average density.

[0050] This step of the method is suitable for gradually increasing the average density of the medium during the separating of materials.

[0051] Preferably this step of the method is applied to obtain a rapid increase of the average density of the medium in the density separator in the event that a different separation of materials is desired.

[0052] In a further embodiment, the density agent is added from the bottom of the separator. Preferably, the addition of an amount of density agent to the medium tank is controlled by density measurements in the separator. Preferably, the opening and closing of the supply valve from the separator to the medium tank is controlled by the density measurements in the separator and optionally controlled by the density measurements in the medium tank. As a result, the desired density in the medium tank can be obtained quickly.

[0053] In an embodiment, the method comprises the mixing of the medium tank by one or more mixing elements. As a result, the composition of the medium in the medium tank is kept consistent. Preferably, one mixing element rotates in the medium tank.

[0054] In an embodiment, water is added externally to the method to the water tank. The adding of external water helps to keep the amount of water in the water tank at level, and additionally in the medium tank and the suspension tank. This contributes to the stability and continuity of the method.

[0055] In an embodiment, water is added to the separator. Preferably, the water is added to the separator at the bottom of the separator for sufficiently keeping the density agent in suspension at the bottom of the separator. Preferably, the said water originates from the water tank. Adding water to the separator helps to keep the density agent in suspension, which increases the efficiency of the separation process.

[0056] In an embodiment, water is added to the screen for the cleaning of the screen. Preferably, the said water originates from the water tank. In an embodiment water is sprayed on the filter for the cleaning of the filter.

[0057] Preferably, the said water originates from the water tank.

[0058] The adding of water facilitates the cleaning of filters and screens, whereby blockages are prevented and maintenance of the screens and filters is reduced.

[0059] In an embodiment, the method comprises the step of homogenizing the medium in the density separator by means of a transport screw. The transport screw is used for the removal of the sinking fraction from the density separator. Preferably, there are no additional mixing elements present in the density separator so that sinking and floating of the material to be separated is not disturbed.

[0060] In an embodiment, the medium is a suspension of water with an additive. The additive is preferably calcium carbonate or kaolin, more preferably the additive is calcium carbonate. Alternatively, magnesium carbonate, barium sulfate, zinc sulfide or strontium sulfate can be used. An advantage of these additives, and more specifically salts, is that they are poorly soluble to insoluble in water, whereby a suspension of the density agent and water is possible. As a result, the density agent can be separated from the medium by simple and energy-efficient methods, such as settling or screening. This is in contrast with soluble salts which can only be recovered by reverse osmosis or evaporation.

[0061] In a preferred embodiment, the additive has a density less than 5.0 kg / L, preferably the density of the additive is less than 4.0 kg / L, more preferably less than 3.0 kg / L. Due to their low density it is simpler to adjust small variations in desired density of the medium in the density separator or in the medium tank. Other options for the additives would be ferrite or ferrosilicon, because of their advantage that both density agents can be separated from the medium due to their magnetic properties. But these are less suitable for adjusting small fluctuations in the medium.

[0062] In an embodiment, the density agent is present in the medium in a ratio of 2 wt% to 30 wt% relative to the total weight of the medium, preferably from 3 wt% to 25 wt%, more preferably from 4 wt% to 25 wt%. The weight percentage of the density agent that is added to the water is low, so that the flow behavior of the suspension does not differ greatly from that of water. As a result, the transport and the pumping of the medium are simple and energy-efficient. Moreover, there is sufficient wetting of the materials to be separated possible with the medium in the density separator. In a second aspect, the invention relates to an apparatus for reusing medium in a process wherein by means of the medium materials with different densities are separated into a floating fraction and a sinking fraction.

[0063] The apparatus comprises a density separator for separating materials to be separated in a medium, a separation installation for separating the medium from the floating and the sinking fraction, a separator for separating the medium into density agent and water, and a medium tank for the mixing of the medium.

[0064] In an embodiment, the density separator comprises a first inlet, a second inlet, a first outlet and a second outlet. The first inlet serves for introducing the materials to be separated. The second inlet serves for introducing a medium. The first outlet serves for discharging the floating fraction. The second outlet serves for discharging the sinking fraction.

[0065] In an embodiment, the separation installation is a screen. The screen comprises an inlet, a first outlet and a second outlet. The inlet of the screen serves for introducing the floating or the sinking fraction from the density separator. The first outlet serves for discharging the medium. The second outlet serves for discharging a screened floating or a screened sinking fraction. Preferably, the apparatus comprises two screens. A first screen serves for separating the medium from the floating fraction. A second screen serves for separating the medium from the sinking fraction. The screen, or each of the two screens, is advantageous for separating the medium from the floating or the sinking fraction in that it is simple to design, use and maintain and works without electricity. Moreover, the screen provides direct separation on the basis of the size of the density agent, and the floating and the sinking fraction.

[0066] Alternatively, the separation installation is a cyclone or a decanter centrifuge. The cyclone has as an advantage that it attains a high efficiency and requires minimal maintenance due to the absence of moving components. The decanter centrifuge is highly efficient for solid-liquid separation on the basis of the size of solid matter in the medium; furthermore, the decanter centrifuge can process large volumes and automatically discharge separated materials.

[0067] In an embodiment, the separator comprises an inlet, a first outlet and a second outlet. The inlet serves for introducing at least a part of the medium from the separation installation, preferably the screen. The first outlet serves for decanting water. The decanting of the water from the said part of the separated medium in the separator allows a simple separation on the basis of density differences.

[0068] Furthermore, decanting requires only minimal energy.

[0069] The second outlet serves for discharging the density agent. Preferably, the second outlet is positioned at the bottom of the separator. The second outlet allows the density agent to be removed separately from the separator. As a result the density agent can form a separate stream and that stream can be added to water in a desired ratio. Preferably, the water originates from the separator. As a result, optimal reuse of density agent and water from the medium originating from the density separator can be pursued.

[0070] In an embodiment, the medium tank comprises a first inlet, a second inlet and an outlet. The first inlet serves for introducing water, preferably from the water tank. The second inlet serves for introducing density agent from the separator and / or the suspension tank. Preferably, the medium tank comprises a third inlet for introducing density agent from the suspension tank. The outlet serves for discharging the medium to the density separator. The medium tank is a buffer to absorb fluctuations in the level of the density separator. The medium tank likewise serves to absorb fluctuations in measured density in the density separator.

[0071] In an embodiment, the medium tank comprises a sensor for measuring the density. The said sensor serves for measuring the density in the medium tank. Preferably, there is a feedback system of density measurements by the density sensor for controlling a supply valve of the medium tank to the density separator. The supply valve is encompassed on the outlet of the medium tank. This is advantageous for controlling and regulating the addition of medium from the medium tank in an amount according to the desired density of the density separator.

[0072] In a preferred embodiment of the apparatus, the density separator is combined with the screen, the separator and the medium tank. This combination of parts is advantageous in view of the above advantages. Additionally, the combination enables flexible deployment of the process for separating materials with different densities by means of the medium, in that the desired density of the density separator can be easily adjusted by adding more or less water or density agent to the medium tank. For this purpose sensors are preferably present in the density separator and the medium tank which can generate electronic signals and serve for actuating valves on outlets of components of the apparatus. The valves can be supply valves. Additionally, different plastics can be separated on the basis of their densities since these are in a narrow range of densities. The apparatus can be efficiently adjusted for obtaining the desired density of the medium in the density separator.

[0073] In an embodiment, the apparatus comprises a water tank for storing water. The water tank comprises an inlet which serves for introducing water from the separator. The water tank comprises an outlet for discharging water to the medium tank.

[0074] In a further embodiment, the water tank comprises a second outlet for discharging water from the water tank to other components in the installation, such as for example the density separator, the screen, the filter and the separator. Alternatively, the second outlet can serve for adding water to other installations outside this apparatus.

[0075] In an embodiment, the apparatus comprises a second inlet for adding water externally to the apparatus.

[0076] The water tank is advantageous as a buffer for regulating the desired densities in the density separator and / or the medium tank. Furthermore, the water tank is advantageous for being able to employ water for rinsing and for cleaning components of the apparatus, such as filters or screens. Moreover, by means of the water tank the level of the density separator can be kept at level so that there is sufficient medium in the density separator for the optimal separation of the materials to be separated.

[0077] In an embodiment, the separator is a lamella separator. The lamella separator comprises lamellae. The lamellae form an angle of at least 45° and at most 75° relative to a horizontal plane. The lamellae serve for the settling of the density agent against the lamellae and the decanting of water and the medium over the lamellae. Preferably, the lamellae form an angle of at least 50° relative to a horizontal plane, more preferably an angle of at least 55°, more preferably an angle of at least 57°. Preferably, the lamellae form an angle of at most 70° relative to a horizontal plane, more preferably an angle of at most 65°, more preferably an angle of at least 63°. The lamella separator has an increased separation surface in a compact design. Furthermore, the lamella separator increases the efficiency of sedimentation whereby the separation of solids and liquids proceeds more quickly and more effectively. This leads to a higher processing capacity without the need for a large installation. In an embodiment, the apparatus comprises a filter for the removal of coarse particles. The filter comprises an inlet, a first outlet and a second outlet. The inlet serves for introducing the medium from the screen and / or the medium tank. The first outlet serves for discharging the medium, preferably to the separator. The second outlet serves for discharging coarse particles. Coarse particles comprise agglomerated density agent and / or small material particles originating from the floating or the sinking fraction.

[0078] In an embodiment, the filter has a pore size of at least 600 pm, preferably at least 400 pm, more preferably at least 200 pm, more preferably at least 100 pm.

[0079] In an embodiment, the filter is a belt filter, a screw filter, a chamber filter press, a belt filter press, a rotary filter or a vibrating filter. Preferably, the filter is a belt filter so that the filter has a simple and low-maintenance design and the coarse particles can be scraped off easily.

[0080] The presence of the filter can increase the purity of the medium. In addition, water for cleaning the filter can be returned to a filter supply, which allows for ecological operation.

[0081] In an embodiment, the screen is a vibrating screen. The vibrating screen a has a pore size of at most 1 mm, preferably at most 750 pm, more preferably 500 pm, more preferably 250 pm. As a result, the floating and the sinking fraction are retained, but the density agent can move through the screen. Consequently, recovery of the medium is possible.

[0082] In an embodiment, the screen comprises a first part and a second part. A spray head is placed between the first and second parts to rinse off the medium from the sinking or floating fraction. The screen comprises in the second part of the screen the first outlet. Preferably both parts of the screen are vibrating screens. As a result adhering density agent can be rinsed off from the floating or the sinking fraction by the spray head and collected for reuse in the medium with the desired density.

[0083] In a further embodiment, the screen comprises a second tank. The second tank serves for collecting the medium separated in the second part of the screen. The second part of the screen is preferably directly coupled to the second tank. Preferably, the second tank comprises a pump for pumping over separated medium from the second part of the screen to the separator upon reaching a maximum level of the second tank. This prevents the second tank from overflowing.

[0084] In an embodiment, the screen comprises in the first part a third outlet. The third outlet serves for discharging the medium to the medium tank. Preferably, the third outlet is coupled to a first tank. The first tank serves for collecting the medium separated in the first part of the screen. The first part of the screen is preferably directly coupled to the first tank. Preferably, the first tank comprises a pump for pumping over separated medium from the first part of the screen to the medium tank upon reaching a maximum level of the first tank. This prevents the first tank from overflowing. Preferably, the third outlet comprises a split valve for the controlled discharging of the medium to the medium tank or the separator. Preferably, the split valve is electronically controllable.

[0085] In an embodiment, the medium tank comprises one or more sensors for determining a density of the medium in the medium tank. Preferably, the number of sensors for determining the density in the medium tank is two. Preferably, the one or more sensors are positioned at a fixed depth in the medium tank. Preferably, the medium tank comprises a level sensor for measuring the level of the medium in the medium tank.

[0086] In an embodiment a bottom part of the separator comprises one or more sensors for determining a density of sediment in the separator. The sediment is settled density agent separated from water originating from the medium. As a result the density agent is present in a more concentrated form than in the medium tank or the density separator. Preferably a number of sensors in the medium tank is at most six, more preferably four sensors, more preferably two sensors. Preferably, the one or more sensors are positioned at a fixed depth in the medium tank. More preferably, the multiple sensors are positioned at different depths of the separator. More preferably, two of the plurality of sensors are positioned near a bottom of the separator. "Near the bottom" means that those two sensors are positioned in a zone of the separator where the density agent can accumulate. More preferably, those two sensors are positioned where no lamellae are present in the lamella separator and near the second outlet of the lamella separator.

[0087] In an embodiment, the density separator comprises one or more sensors for determining a density of the medium in the medium tank. Preferably, a number of sensors in the density separator is at most four, more preferably three sensors, more preferably two sensors. Preferably, the one or more sensors are positioned at a fixed depth in the density separator. Multiple sensors positioned preferably at different depths of the density separator has as an advantage that a variation in concentration over depth of the density separator can be monitored. The degree of settling of density agent in the density separator is thereby monitored. More concentrated medium than the desired density of the medium in the density separator can then be added at the top in the density separator. As a result the desired density of the medium in the density separator can be maintained for correct separation into the floating and the sinking fractions. Preferably, the one or more sensors are positioned at one or more depths of the density separator such that density measurements can be measured in a non-turbulent zone. As a result measuring can be performed accurately. The non-turbulent zone is a zone of the density separator that is located sufficiently far from the first and the second inlet and the first and second outlet, such that no turbulent flows are present in the medium due to the introduction and discharge of materials.

[0088] In an embodiment, the first and / or the second tank comprises one or more sensors for determining a density of the medium in the first and / or the second tank. Preferably, the number of sensors in the first and / or the second tank for determining the density is two. Preferably, the one or more sensors are positioned at a fixed depth in the first and / or the second tank. Because the sensors can measure a density it can be decided whether the medium in the first and / or the second tank can flow to the medium tank or to the separator for further reuse or separation of water and density agent. Preferably, the first and / or the second tank comprises a level sensor for measuring the level of the medium in the first and / or second tank.

[0089] In an embodiment, at least a part of the one or more sensors are pressure sensors for determining the density of the medium. Preferably, all of the one or more sensors are pressure sensors. The pressure sensors can determine the density of the medium accurately, simply and also for a non-transparent medium. Alternatively optical sensors, sensors based on the measuring of sound waves, or other sensors can also be used. Sensors based on sound waves are advantageous due to the high accuracy and wide applicability in medium composition. Optical sensors can perform rapid measurements, but these sensors are limited to a transparent medium.

[0090] In an embodiment, the one or more sensors are pressure sensors and the pressure sensors have a measuring range between 0 kPa and 100 kPa, preferably between 0 kPa and 85 kPa, more preferably between 0 kPa and 70 kPa. As a result pressures can be measured accurately, whereby density of the medium in the density separator, in the medium tank, in the first or in the second tank can be efficiently adjusted. Or the density of the density agent in suspension in the separator can be determined.

[0091] In an embodiment, the density separator is a flotation tank. The flotation tank comprises a transport screw and carriers. The transport screw serves for removing the sinking fraction from the flotation tank. The carriers serve for removing the floating fraction from the flotation tank. As a result, the floating and the sinking fraction can each be transported to an end of the flotation tank for the efficient removal of both fractions from the flotation tank. Alternatively, the density separator is a rotatable drum, preferably a rotatable flotation drum.

[0092] In an embodiment, the apparatus comprises a suspension tank for storing the density agent in a concentrated suspension. The concentrated suspension is a suspension with a density, wherein the difference between the density of the concentrated suspension and the density of water at standard atmospheric pressure and at a temperature of 4°C is at least twice as great as the difference between the density of the medium in the medium tank and the density of water at standard atmospheric pressure and at a temperature of 4°C. Preferably, the suspension tank comprises a first inlet, a second inlet and an outlet. The first inlet serves for introducing the settled density agent originating from the bottom of the separator. The second inlet serves for supplementing fresh and undissolved density agent to the suspension tank. The outlet serves for discharging the concentrated suspension from the suspension tank, preferably to the medium tank. Being able to store the density agent in the suspension tank prevents oversaturation of the separator with density agent. Moreover, the suspension tank can be easily supplemented with fresh and undissolved density agent when the suspension has a lower density than the medium in the medium tank, preferably the suspension tank can be supplemented with fresh and undissolved density agent if the difference between the density in the suspension tank and the density of water at standard atmospheric pressure and at a temperature of 4°C is smaller than twice the difference between the density of the medium tank and the density of water at standard atmospheric pressure and at a temperature of 4°C. This ensures that the density of the suspension remains consistent and that the efficiency of the separation process in the density separator can be maintained. and the density of water at standard atmospheric pressure and at a temperature of 4°C

[0093] In an embodiment, the medium tank comprises one or more mixing elements. As a result the composition and density of the medium in the medium tank is kept consistent. Preferably, one mixing element rotates in the medium tank.

[0094] In an embodiment, the suspension tank comprises one or more mixing elements. As a result, the composition and density of the medium in the suspension tank is kept consistent. Preferably, one mixing element rotates in the suspension tank.

[0095] In an embodiment, a ratio of a volume of the medium tank relative to a volume of the first or the second tank is at least three, preferably at least four, more preferably at least five. This is advantageous so that adjustment and supplementation of the medium to the medium tank or a throughput to the separator can be carried out of the floating or the sinking fraction from the density separator.

[0096] In an embodiment, a ratio of a volume of the medium tank relative to a volume of the density separator is at least a quarter, preferably at least a third, more preferably at least a half. This is advantageous so that a sufficiently large buffer can be present for the adjusting and / or supplementing of the medium in the density separator.

[0097] In a third aspect the invention relates to a use of a method according to the first aspect and / or an apparatus according to the second aspect for separating materials with different densities into a floating fraction and a sinking fraction.

[0098] This use results in a separation with reuse of the medium for automotive shredder residue or waste from electrical and electronic equipment.

[0099] It is advantageous that the method and the apparatus allow efficiently and accurately adjusting the density of the medium within a narrow range, such as for separating different plastics on the basis of their densities. This narrow range is generally between 0.80 kg / L and 2.15 kg / L, preferably between 0.85 kg / L and 1.75 kg / L.

[0100] A person skilled in the art will appreciate that an apparatus according to the second aspect is preferably configured for carrying out a method according to the first aspect and that a method according to the first aspect is preferably carried out with an apparatus according to the second aspect. Each feature described in this document, above as well as below, can consequently relate to each of the three aspects of the present invention.

[0101] The present invention will now be described in more detail, with reference to figures that are not limiting.

[0102] FIGURE DESCRIPTION

[0103] Figure 1: shows a schematic overview of steps in a method according to an embodiment of the present invention.

[0104] Figure 1 provides a schematic overview of a method for reusing medium in a process wherein by means of the medium, materials (1) with different densities are separated into a floating fraction and a sinking fraction.

[0105] The materials (1) are added to the density separator (2). By means of the medium in the density separator (2) materials (1) are separated according to their different densities into the floating fraction (5) and the sinking fraction (4). The medium is an aqueous suspension of a density agent.

[0106] Subsequently, the floating fraction (5) and the sinking fraction (4) of the materials

[0107] (I) are separated from the medium, this by screening by means of screens (3a, 3b). The screening leads to the medium being able to be reused after the removal of the floating fraction (5) and the sinking fraction (4) from the density separator (2). Alternatively, the separating of the medium can be carried out by separating by means of a cyclone or decanting by means of a centrifuge.

[0108] The screens (3a, 3b) are split into two parts. A first part of the separated medium is separated through a first part (3a', 3b') of the screens (3a, 3b) to a medium tank

[0109] (II). The first part of the separated medium originating from the first part (3a', 3b') of the screen (3a, 3b) is stored in a first tank (7), after which the first part of the separated medium from the first tank (7) is collected and / or stored in the medium tank (11). The first part of the separated medium in the first tank (7) is pumped to the medium tank (11) or brought by gravity to the medium tank when a maximum level of the first tank is reached. This is measured with a pressure sensor at the bottom of the first tank (7). Adhering medium on the floating fraction (5) or on the sinking fraction (4) is rinsed off from the floating fraction (5) or from the sinking fraction (4) prior to a second part (3a", 3b") of the screen (3a, 3b). The said floating fraction (5) and the said sinking fraction (4) originate from the first part (3a', 3b') of the screen (3a, 3b). A second part of the separated medium is collected and / or stored in a second tank (6). Prior to this the second part of the separated medium originating from the second tank (6) is pumped over to a filter (8) upon reaching a maximum level of the second tank (6). This is measured with a pressure sensor at the bottom of the second tank (6).

[0110] From the second part of the separated medium originating from the second tank (6) coarse particles are separated on the filter (8) and filtered medium is pumped to a separator (9). The filter (8) is for example a belt filter. It is clear that the filter can also be of another type, as described above. On a belt encompassed in the belt filter through which the second part of the separated medium passes, the belt ensures that the coarse particles are separated. The coarse particles comprise agglomerated density agent and / or fine pieces of the floating or the sinking fraction. Optionally, at a too high level of the medium in the medium tank (11), the medium can be transported to the filter (8). The level of the medium in the medium tank (11) is determined by a level sensor.

[0111] After the passage of the second part of the separated medium through the belt filter, the second part of the separated medium is separated in the separator (9) into the density agent and water. The separator (9) is a lamella separator. Alternatively, the separating of at least a part of the separated medium can be carried out by means of decanter centrifugation, filtering or cyclonic separation. The separating of the second part of the separated medium is by means of the settling of the density agent to a bottom of the separator (9) along lamellae comprised in the separator (9). As a result water is decanted over the lamellae. The said water is decanted from the lamella separator (9) into a water tank (10).

[0112] Subsequently the settled density agent is transported from the separator (9) to the medium tank (11). In the medium tank (11) the settled density agent and water are mixed with each other in a ratio according to a desired density of the medium. The water originates from the water tank (10). The said ratio for obtaining the desired density of the medium is determined from density measurements measured in the medium tank (11). Feedback from the density measurements in the medium tank (11) is sent to control the supply valves of the settled density agent and the water. As a result supply valves are opened or closed. To measure the density of the density agent there are two pressure sensors present in the lamella separator (9) at a fixed depth in the separator (9).

[0113] The separated medium is added from the medium tank (11) to the density separator (2), wherein an amount of medium to be added from the medium tank (11) is determined by density measurement in the density separator (2). Optionally there is a feedback of density measurements in the density separator (2) to a control of a supply valve of the medium tank (11). The density measurements in the density separator (2) are carried out by two pressure sensors at different fixedly determined depths of the density separator (2).

[0114] Furthermore, the addition of water or of density agent to the medium tank (11) can compensate for small fluctuations in order to lower or, respectively, increase the desired density of the medium.

[0115] Settled density agent, originating from the bottom of the separator (9), is introduced via a first inlet into a suspension tank (12). The suspension tank (12) serves for storing the density agent in a concentrated suspension. The concentrated suspension is a suspension with a density, wherein the difference between the density of the concentrated suspension and the density of water at standard atmospheric pressure and at a temperature of 4°C is at least twice as great as the difference between the density of the medium in the medium tank (11) and the density of water at standard atmospheric pressure and at a temperature of 4°C. Via a second inlet, fresh and undissolved density agent (13) can be supplemented to the suspension tank (12). Via an outlet concentrated suspension is fed from the suspension tank (12) to the medium tank (11).

[0116] Optionally, water can be added to the separator (9) at the bottom of the lamella separator. Optionally, water can be added to the screens (3a, 3b) for the cleaning of the screens (3a, 3b). Optionally, water can be sprayed onto the filter (8) for the cleaning of the filter (8). The said water originates from the water tank (10).

[0117] The medium is a suspension of water with an additive. The additive is preferably calcium carbonate or kaolin, more preferably the additive is a salt such as calcium carbonate. Alternatively, magnesium carbonate, barium sulfate, zinc sulfide or strontium sulfate can be used. The additive has a density less than 5.0 kg / L, more specifically less than 3.0 kg / L. The density agent is present in a ratio of 3 wt% to 30 wt% to the total weight of the medium in the medium.

Claims

CLAIMS1. Method for reusing medium in a process wherein by means of the medium materials (1) with different densities are separated into a floating fraction (5) and a sinking fraction (4), comprising the steps of:- the introduction of the materials to be separated into a medium in a density separator (2), comprising an aqueous suspension of a density agent (13),- the discharge of the floating fraction (5) and the sinking fraction (4) of the materials (1),- the separation of the medium from the floating fraction (5) and the sinking fraction (4),- the addition of the separated medium to the medium into which the materials to be separated are introduced, characterized in that, the medium is separated from the floating fraction (5) and the sinking fraction (4) by means of a screen (3a, 3b), wherein at least a portion of the separated medium is transported to a separator (9), wherein the said portion of the separated medium is separated into the density agent and water, wherein the separation of the said portion of the separated medium is effected by settling of the density agent in the separator (9), wherein the settled density agent is transported from the separator (9) to a medium tank (11), wherein in the medium tank (11) density agent and water are mixed with one another in a ratio according to a desired density of the medium, wherein the ratio for obtaining the desired density is determined from density measurements in the medium tank (11), wherein the separated medium is supplied from the medium tank (11) and optionally from a suspension tank (12) to the density separator (2), wherein an amount of medium to be supplied from the medium tank (11) and / or the suspension tank (12) is determined by density measurements in the density separator (2).

2. The method according to claim 1, characterized in that in the separator (9) the separating of the separated medium takes place by the decanting of the water from the separator (9), wherein the water is collected in a water tank (10), and wherein the density agent settles and is collected on a bottom of the separator (9).

3. The method according to claim 2, characterized in that the separator (9) is a lamella separator, wherein the separating of the separated medium takes place by the water in the discharged medium being decanted over lamellae to adjacent lamellae, and wherein the density agent is retained by the lamellae and settles along the lamellae to the bottom of the separator (9).

4. The method according to any one of the preceding claims 1-3, characterized in that prior to the separator (9) a part of the separated medium flows through a filter (8), whereby coarse particles are separated on the filter (8) and filtered medium is pumped to the separator (9).

5. The method according to any one of the preceding claims 1-4, characterized in that the screen (3) is split into at least two parts, wherein the separated medium is transported through a first part of the screen (3a' & 3b') directly to the medium tank (11) and is collected in the medium tank (11), and wherein the separated medium is transported through a second part of the screen (3a" & 3b") to the separator (9).

6. The method according to claim 5, characterized in that the method comprises the additional step of rinsing off adhering medium from the floating fraction (5) or from the sinking fraction (4) after the passing of the floating fraction (5) or sinking fraction (4) along the first part of the screen (3a' & 3b'), wherein the rinsed-off medium is transported through the second part of the screen (3a" & 3b") to the separator (9).

7. The method according to any one of the preceding claims 1-6, characterized in that the method comprises the additional step of adding water to the medium tank (11) to lower the average density of the medium.

8. The method according to any one of the preceding claims 1-7, characterized in that the method comprises the additional step of adding density agent to the medium tank (11) to increase the average density of the medium.

9. The method according to one of claims 1-8, characterized in that the medium is a suspension of water with an additive, wherein the additive is calcium carbonate or kaolin, wherein the additive is present in the medium in a ratio of 5 wt% to 30 wt% relative to the total weight of the medium.

10. Apparatus for reusing a medium in a process wherein, by means of the medium, materials having different densities are separated into a floating fraction (5) and a sinking fraction (5), characterized in that the apparatus comprises a density separator (2) for separating, in a medium, the materials into the floating fraction (5) and the sinking fraction (4), a screen (3a & 3b) for separating the medium from the floating fraction (5) and the sinking fraction (4), a separator (9) for separating the medium into density agent and water, a medium tank (11) for mixing the medium, and optionally a suspension tank (12), wherein the density separator (2) comprises a first inlet, a second inlet, a first outlet, and a second outlet, wherein the first inlet serves for introducing materials to be separated, the second inlet serves for introducing a medium, wherein the first outlet serves for discharging the floating fraction (5) and the second outlet serves for discharging the sinking fraction (4), wherein the screen comprises an inlet, a first outlet, and a second outlet, wherein the inlet of the screen (3a & 3b) serves for introducing the floating fraction (5) or the sinking fraction (4) from the density separator (2), wherein the first outlet serves for discharging the medium, and wherein the second outlet serves for discharging a screened floating or sinking fraction, wherein the separator (9) comprises an inlet, a first outlet, and a second outlet, wherein the inlet serves for introducing at least a portion of the medium from the screen, wherein the first outlet serves for decanting water, and wherein the second outlet serves for discharging density agent, wherein the second outlet is positioned at a bottom of the separator (9), wherein the medium tank (11) comprises a first inlet, a second inlet, and an outlet, wherein the first inlet serves for introducing water, wherein the second inlet serves for introducing density agent from the separator (9), and wherein the outlet serves for discharging the medium to the density separator (2), wherein the suspension tank (12) comprises a first inlet, a second inlet, and an outlet, wherein the first inlet serves for introducing the density agent originating from the bottom of the separator (9), wherein the second inlet serves for replenishing the suspension tank (12) with fresh and undissolved density agent, and wherein the outlet serves for discharging concentrated suspension from the suspension tank (12).

11. The apparatus according to claim 10, characterized in that the apparatus comprises a water tank (10) for storing water, wherein the water tank (10) comprises an inlet which serves for introducing water from the separator (9),wherein the water tank (10) comprises an outlet for discharging water to the medium tank (11).

12. The apparatus according to claim 10 or 11, characterized in that the separator (9) is a lamella separator, wherein the lamella separator comprises lamellae, wherein the lamellae form an angle of at least 45° and at most 75° relative to a horizontal plane.

13. The apparatus according to any one of the preceding claims 10-12, characterized in that the apparatus comprises a filter (8) for the removal of coarse particles, wherein the filter (8) comprises an inlet, a first outlet and a second outlet, wherein the inlet serves for introducing medium, wherein the first outlet serves for discharging medium, wherein a second outlet is suitable for discharging coarse particles; wherein the filter (8) has a pore size of at least 100 pm, wherein the filter (8) is a belt filter, a screw filter, a chamber filter press, a belt filter press, a rotary filter or a vibrating filter.

14. The apparatus according to any one of the preceding claims 10-13, characterized in that the screen (3a & 3b) is a vibrating screen, wherein the vibrating screen has a pore size of at most 1 mm.

15. The apparatus according to any one of the preceding claims 10-14, characterized in that the screen (3a & 3b) comprises a first part and a second part, wherein between the first part (3a' & 3b') and the second part (3a" & 3b") a spray head for rinsing off medium from the sinking or floating fraction is placed, wherein the first outlet of the screen (3a & 3b) is in the second part of the screen (3a" & 3b"), wherein the screen in the first part (3a' & 3b') comprises a third outlet and wherein the third outlet serves for discharging medium to the medium tank (11).

16. The apparatus according to any one of the preceding claims 10-15, characterized in that the medium tank (11) comprises one or more sensors for determining a density of medium in the medium tank (11).

17. The apparatus according to any one of the preceding claims 10-16, characterized in that one or more sensors for determining a density of sediment in the separator (9) are arranged in a bottom part of the separator (9).

18. The apparatus according to any one of the preceding claims 10-17, characterized in that the density separator (2) is a flotation tank, wherein the flotation tank comprises a transport screw and carriers, wherein the transport screw serves for removing the sinking fraction from the flotation tank, wherein the carriers serve to remove the floating fraction from the flotation tank.

19. The use of a method according to any one of the preceding claims 1-9 and / or an apparatus according to any one of the preceding claims 10-18 for separating materials with different densities into a floating fraction and a sinking fraction, wherein the materials is automotive shredder residue or waste of electrical and electronic equipment.

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