WO2014183804A1

WO2014183804A1 - A separator and a method for separating solid particles from liquids

Info

Publication number: WO2014183804A1
Application number: PCT/EP2013/060300
Authority: WO
Inventors: Åke STIGEBRANDT
Original assignee: Stigebrandt Hydroteknik Ab
Priority date: 2013-05-17
Filing date: 2013-05-17
Publication date: 2014-11-20

Abstract

The present invention relates to a separator arrangement 1 and a method for separating solid particles from liquids in a wastewater suspension. The present invention also relates to a method of controlling the discharge rate of a separator 1. The separator 1 hasa vessel 2, which comprises a separation compartment3 for receiving the wastewater suspensionand for separating the solid particles from liquids by means of gravity, a sedimentation compartment 4 located below the separation compartment and provided with downwardly tapered wallportions4', a compaction compartment 5, 105comprising an upper section 5a, 105aand a lower section 5b, 105b. The upper section is provided with wallportionsforming an angle α with the centre axis of the vessel 2, and wherein the lower section 5b of the compaction compartment 5is provided with downwardly tapered wall portions5b', forming an angle θ with the centre axis of the vessel. (Elected for publication: Fig. 1)

Description

A SEPARATOR AND A METHOD FOR SEPARATING SOLID PARTICLES

FROM LIQUIDS

Field of the Invention

The present invention relates to the field of separating solid particles from liquids by sedimentation, and in particular relates to a separator arrangement, a method for separating and a method for controlling the discharge density in a separator.

Background of the Invention

The mining industry uses large volumes of process water for many purposes, such as cooling machinery, cleaning surfaces and refining materials. As a result, the process water is polluted by contaminants and particles, such as oil and various chemicals used in the mining processes, as well as rock particles and minerals/metals from the extraction (such as zinc, copper, arsenic etc.). These residual particles which are left over from a mining process are commonly referred to as "tailings". On the one hand this polluted process water, i.e. wastewater, may contain valuable material such as minerals and metals, but on the other hand it may also contain hazardous particles.

Wastewater from mining operations is often challenging to manage because of the large volumes that are produced. Large sedimentation ponds are often excavated in the ground, into which the wastewater is conducted, so that the particles suspended in the wastewater can separate from the liquids under influence from the gravitational force. In dry and desert type environments, the access of water is often limited and the sedimentation ponds are thus not an optimal solution. Another problem with the sedimentation ponds is that the wastewater contains minerals and metals, which are of a significant value, but often too difficult to collect from the bottom a pond. An additional problem with ponds is their environmental impact due to the potential contaminants suspended in the wastewater as well as the fact that they often need maintenance or even need to be replaced by new ponds, which also lead to high impact on the environment and the surroundings.

Hence, there exists a need for an arrangement that is capable of cleaning large volumes of wastewater directly at the source, while also improving the extraction valorization of the mining operations and reducing the environmental impact.

Summary of the Invention

In view of the above mentioned problems and other drawbacks of the prior art, it is an object of the present invention to provide a separator arrangement and separation method. This and other objects are achieved by a separator arrangement and a method for separating according to the appended claims.

According to a first aspect of the present invention, it relates to a separator arrangement for separating solid particles from liquids in a wastewater suspension, comprising:

- a separation compartment for receiving the wastewater suspension and for separating the solid particles from liquids by means of gravity,

a sedimentation compartment located below the separation compartment and provided with downwardly tapered wall portions adapted to receive a sediment of solid particles,

a compaction compartment comprising an upper section and a lower section, wherein the upper section of the compaction compartment is adapted to receive the sediment from the sedimentation compartment, the upper section being provided with wall portions forming an angle with the tapered walls of the sedimentation compartment, and wherein the lower section of the compaction compartment is provided with downwardly tapered wall portions. The present invention is based on the realization that a mechanical separator arrangement can be improved, by providing a compaction compartment with a lower section with downwardly sloping wall portions, the pressure increases at the lower end of the compaction compartment, which further increases the density of the sediment.

Specifically, the solid particles are further separated from the liquid portion of the wastewater suspension, as the sediment is subjected to a compressing force from an overlying material (i.e. wastewater and solid particles) in combination with the increased retention time caused by the additional compaction compartment. Additionally, the shape of the compaction compartment with a decreasing cross section in the direction towards the bottom of the separator, forces the sediment into a smaller space, while the liquid portion of the wastewater suspension is forced upwards.

Advantages with the present invention include that it provides an adequate compaction rate and dryness of the sediment. The present separator can advantageously be used for the separation of many different types of wastewater suspensions, in which the solid particles are heavier than the liquid portion (and thus possible to be separated by a sedimentation process). As a specific example, the present invention is capable of separating tailings (the residual particles in mining operations), from a wastewater suspension. Additional examples include cooling water from iron and steel manufacturing processes, as well as the separation of wastewater that contains organic material, such as potato starch. The definition of wastewater should in the context of this application be interpreted in a broad sense. It should be seen as starting material in a process, which is in a liquid state and contains suspended solid particles. Moreover, the wastewater may consist of different types of liquids and solids particles. For instance, the liquid may comprise more than one type, such as a combination of water and oil. Wastewater may also be defined as any type of liquid containing solid particles, whereby the term "waste" does not solely or necessary imply an impurity based on environmental aspects, but may also include that the task of separating the wastewater may be performed for other reasons, such as a desire to extract valuable materials, such as metals and minerals suspended therein.

Frequently, the wastewater from the mining industry may contain 15 - 30% particulate/solid matter with a grading curve including particles from 1 nanometer up to approximately 0,3 microns.

The separator according to the present invention comprises a separation compartment, a sedimentation compartment and a compaction compartment, which together may be referred to as a vessel. Consequently, each compartment of the vessel has a certain geometric shape, whereby the expression wall portions refers to the geometry of the vessel wall for each individual compartment or section.

As previously stated, the upper section of the compaction compartment is provided with wall portions forming an angle (other than 180°) with the tapered wall portions of the sedimentation compartment, which is located above. It should be understood that, in this context, an angle implies divergent wall portions. Thus, an angle of 180° is excluded from the angle formed by the inner surface of the sedimentation compartment and the inner surface of the upper section of the compaction compartment. In other words, there should be a relative flaring or tapering between the two sections. In addition the angle should be larger than 180°. To further describe and define these angles, the inner surface of the vessel is taken as a reference surface.

Starting off from the top of the separator and moving towards the bottom of the separator, the angle of the inner surfaces can be defined. Specifically, the inner surface of the downwardly tapered wall portions of the separation compartment is thus provided at a downward sloping angle, i.e. a grade or a slope, which can be converted to an angle. This angle can be measured as the angle between the inner surface of the compartment and the centre axis of the separator.

According to an exemplary embodiment, the downwardly tapered wall portions of the lower section of the compaction compartment form an angle with said wall portions of the upper section. The wall portions of the upper and lower section of the compaction compartment are arranged such that they form an angle with each other. It should be understood that an angle implies divergent wall portions. Thus, an angle of 180° is excluded from said angle formed by the upper and lower section of the compaction compartment. In other words, there should be a relative flaring or tapering between the two sections. In addition, the angle should be larger than 180°.

According to an exemplary embodiment, the inner surface of the wall portions of the sedimentation compartment are downward sloping at an angle of between 10^°and 75^° relative to the center axis of the vessel. A downwardly sloping angle of between 30^°and 70^° provides a suitable surface, which satisfies both the need of providing a sedimentation surface and ensuring an efficient transfer/flow of solid sediment further downwards in the separator vessel.

According to an exemplary embodiment, the wall portions of the upper section of the compaction compartment are essentially vertical .

According to another exemplary embodiment, the wall portions of the upper portion of the compaction compartment are provided at an angle in the range between 0^° and 30^° relative to the center axis of the vessel, suitably between 0^° and 10. The wall portions of the upper section of the compaction compartment enhance the transfer of sediment from the sedimentation compartment to the compaction compartment. The downwardly sloping wall portions of the sedimentation compartment transit into the wall portions of the upper section of the compaction compartment.

According to an exemplary embodiment, the wall portions of the lower portion of the compaction compartment are downward sloping and provided at an angle of between 5^° and 30^° relative to the center axis of the vessel. Such an angle increases pressure at the lower end of the compaction compartment, which improves the compression and increases the density of the sediment. In addition, the size of the compaction compartment may be dimensioned to promote desired compatction, while at the same time providing a transition to the discharge arrangement is achieved. The wall portions of the upper section of the compaction compartment transit into the downwardly sloping wall portions of the lower portion of the compaction compartment.

According to an exemplary embodiment, the wall portions of the upper section of the compaction compartment are downwardly tapered in relation to the center axis of the vessel. Additionally, the wall portions of the lower section of the compaction compartment and the wall portions of the upper section of the compaction compartment may form continuous wall portions which are arranged at the same downwardly tapered angle in relation to the center axis of the vessel. According to an exemplary embodiment, the downwardly tapered angle is between 5^° and 30^° relative to the center axis of the vessel.

To sum up, the wall portions of the lower portion of the compaction compartment are always downwardly tapered, while the wall portions of the upper section of the compaction compartment may be either vertical or provided with a tapering which is the same tapering as the lower section of the compaction compartment or different. According to an exmplary

embodiment, the separation vessel has an essentially circular cross-section. Alternatively, the separation vessel may have a different shape, which does not include a circular cross section. For instance, the separation vessel may have a shape wherein the distance from one point on the wall of the

separation vessel to the center axis of the separation vessel is of a different length than the distance from another point on the wall of the separation vessel to the center axis of the separation vessel. Examples may e.g. include cross sections with a rectangular shape or a rectangular shape with rounded edges. Advantages include that by giving the separation vessel a certain horizontal elongation, the vessel volume can be increased.

According to an exemplary embodiment, the scraper arrangment extends to or close to the junction between the sedimentation compartment and the compaction compartment. Thus, the compaction compartment does not house the scraper arrangement, which is therefore located above the compaction compartion. According to another exemplary embodiment, the scraper arrangement can extend into the compaction compartment.

According to an exemplary embodiment, the volume of the compaction compartment is smaller than the volume of the sedimentation compartment, and wherein the volumetric relationship between the compaction compartment and the sedimentation compartment is in the range between 10% and 75%, suitably between 10% and 40%. Advantages include that the separation process may be improved by optimizing the retention time in each compartment.

According to an exemplary embodiment, the volume of the lower section of the compaction compartment is smaller than the volume of the upper section of the compaction compartment, and wherein the volumetric relationship between the lower section and the upper section of the compaction compartment is in the range between 15% and 80%. By providing a certain volumetric capacity to the compression compartment, the density of the material can be regulated to present a consistent value.

According to an exemplary embodiment, the separator arrangement further comprises a scraper arrangement adapted to rotate along the downwardly tapered wall portions inside the sedimentation compartment. A scraper arrangement may improve the transfer of sediment in the separation vessel by mechanically moving the sediment deposited on the tapered wall portions. A rotatable scraper arrangement is suitable for a sedimentation compartment with a cylindrical cross section and curved surfaces. However, if the sedimentation compartment comprises straight surfaces, a reciprocating scraper arrangement with a "to-and-from" motion may be used instead or in combination with a rotating scraper.

According to an exemplary embodiment, the axial extension, i.e. the height, of the upper section of the compaction compartment is equal or longer than the axial extension of the lower section of the compaction compartment. According to an exemplary embodiment, the axial extension of the upper section is in the range of 100% and 200% of the extension of the lower section. According to an exemplary embodiment, the separator arrangement further comprises a mixing compartment, which is connected to a supply of a flocculating agent and a supply of the wastewater suspension, such that the flocculating agent is added to the wastewater suspension before the wastewater suspension enters the sedimentation compartment. The flocculating agent is able to form agglomerates of solid particles, whereby the size of the solid particles increase, which in turn makes them more susceptible to the gravitational force and speeds up the separation process.

Although it would be conceivable to discharge the compacted sediment from the separator arrangement directly from the compaction compartment onto a transport band or the like, according to an exemplary embodiment the compacted sediment is suitably discharged from the separator arrangement via a discharge arrangement forming part of the separator arrangement. Suitably, the discharge arrangement is connected to the lower section of the compaction compartment.

According to an exemplary embodiment, the separator arrangement further comprises a discharge arrangement located at the lower section of the compaction compartment, wherein the discharge arrangement comprises:

- a housing which defines a discharge compartment, the discharge compartment being adapted to receive sediment from the compaction compartment, and

- at least one axle-free spiral conveyor located inside said housing. The discharge arrangement feeds out the sediment from the separator and in cooperation with the compaction compartment, the retention time for the sediment in the compaction compartment may be controlled. Advantages include that the discharge arrangement further improves the capacity of the separator by efficiently feeding the sediment out of the separator. The discharge compartment provides a certain volume ready for discharge so that the axle-free spiral conveyor has a continuous supply of sediment to feed. Moreover, the open center of the axle-free spiral conveyor reduces the risk of material becoming blocked inside the discharge compartment, as some material in the open center is allowed. In addition, the open center in the axle- free spiral conveyor reduces the vacuum forces behind the blades, opposite to the feeding direction of the axle-free spiral conveyor

According to an exemplary embodiment, the housing is in open communication with the lower section of the compaction compartment such that an opening between the compaction compartment and the discharge compartment is created.

According to an exemplary embodiment, the housing of the compaction compartment comprises an openable hatch for emptying the separator. A hatch provides for an accessible opening for discharging the sediment in a vertical direction, which may be beneficial for rapidly emptying the whole separator vessel, for instance in case of a dysfunction in the discharge arrangement.

According to an exemplary embodiment, the housing is further connected to a transporting means for transporting the sediment away from the separator, wherein the transporting means is located after the axle-free spiral conveyor and adapted to receive and transport the sediment away from the axle-free spiral conveyor. Transporting means may be advantageously adapted to transport the sediment to a deposit/storage area, a receptacle or directly to a transporting vehicle.

According to an exemplary embodiment, the transporting means comprises a spiral conveyor (with axle or axle-free) and/or a belt conveyor or a membrane pump or a peristaltic pump. A spiral conveyor may be easily enclosed in a housing, such that the sediment is transported without risk for leaks or spill-over along the transportation path. A belt conveyor provides another possible transporting means, which provides for a flexibil ity to combine and transport the material over long distances, with little risk for material getting blocked and less potential downtime in the transportation. A membrane pump or a peristaltic pump provides a suitable arrangement for discharging the sediment into a duct or a tube. In particular, a membrane pump or a peristaltic pump are suitable for feeding out sediment containing small particles (of e.g. the size of less than 50 μιτι) and which has a "pastelike" consistency. The inventor has realized that it is possible to control the amount of sediment that is discharged from the separator arrangement based on measurements of the amount and/or weight of sediment present inside the compaction compartment and/or discharge compartment. For instance, an upper and a lower limit value linked to the sediment density may be set. When the upper limit value is reached the discharging of sediment is started, and when the lower limit value is reached the discharging of sediment is stopped. Another possibility is to continuously control and adapt the discharge speed based on measurements of the amount and/or weight of sediment present inside the compaction compartment and/or discharge compartment. There are numerous ways of how to implement such measurement-based discharge control, some exemplary embodiments being presented in the following description.

According to an exemplary embodiment, the separator arrangement further comprises a pressure measuring arrangement for measuring pressure inside the compaction compartment and/or inside the discharge compartment, wherein the pressure measuring arrangement comprises a pressure sensor located inside the compaction compartment and/or inside the discharge compartment. Suitably, the measuring arrangement is located inside a membrane, so that it is protected from mechanical and chemical impact from the material inside the vessel. The measured pressure is indicative of the weight and density of the sediment inside the compaction compartment and/or inside the discharge compartment. Thus, in the above exemplary embodiment the weight may be determined indirectly. However, in other exemplary embodiments the weight may be determined directly.

According to an exemplary embodiment, the separator further comprises a weight measuring arrangement for measuring the weight of the separator, wherein the weight measuring arrangement comprises at least one weight meter located on or under or inside a supporting structure of the separator. The supporting structure may, for instance, be a support frame holding the vessel (which contains the separation, sedimentation and compaction compartments). In a more particular example, the weight measuring arrangement may be located on or under or inside a support frame which consists of a leg of the separator. A pressure sensor or weight gauge provides means for capturing actual weight or pressure data, from which the density of the material can be derived from. As the volumes of the different compartments inside the vessel are known parameters, the amount of solid particles in the vessel can be calculated.

According to an exemplary embodiment, at least two pressure sensors are arranged at a vertical distance from each other in the compaction compartment. At least two pressure sensors provide pressure data on at least two levels, whereby the weight and distribution in terms of compaction rate of the material inside the compaction compartment can be determined.

According to an exemplary embodiment, the separator arrangement further comprises a control unit connected to the axle-free spiral conveyor and an actuating means, wherein the control unit controls the speed and/or torque of the axle-free spiral conveyor based on input from the measuring arrangement. The inter-connection between the axle-free spiral conveyor, the control unit and the measuring unit provides an automated system for controlling/regulating the density of the sediment inside the separator based on the actual/measured value so that a desired density of the material can be obtained, in order to achieve a discharged sediment with a high density, but at the same time ensuring that the density of the material is at a manageable level so as to enable a hassle-free discharge operation which is operating at the desired speed. Although the controlling may be fully automated, it is also conceivable to have a measurement arrangement which indicates the density to an operator, who will, based on the measurements, manually start or stop the operation of the discharge arrangement.

According to a second aspect of the present invention, it relates to a method for separating solid particles from liquids in a wastewater suspension by using a separator arrangement according to the first aspect of the invention, wherein the method comprises the steps of:

- filling a separation compartment with a wastewater suspension, whereby a sediment of solid particles is deposited on the tapered wall portions of the sedimentation compartment,

- moving the sediment of solid particles to the compaction compartment,

- receiving the sediment of solid particles in the discharge compartment,

- discharging the sediment of solid particles from the discharge compartment.

Advantages include that an improved separation method is achieved by moving the sediment to a compaction compartment. It is thus possible to provide a higher density and an increased dryness of the sediment.

According to an exemplary embodiment, the step of discharging the sediment is effectuated by rotating at least one axle-free spiral conveyor. The open center of the axle-free spiral conveyor reduces the risk for material to become blocked inside the discharge compartment, as a certain material in the open center is allowed. In addition, the open center in the axle-free spiral conveyor reduces the vacuum forces behind the blades, opposite to the feeding direction of the axle-free spiral conveyor.

According to an exemplary embodiment, the method is further comprising a step of measuring the pressure inside the compaction compartment and/or inside the discharge compartment.

According to an exemplary embodiment, the method is further comprising a step of measuring the weight of the separator. The use of a pressure sensor or weight gauge provides the advantage that a weight or a pressure value may be captured, from which the density of the material can be derived from. As the volumes of the different compartments inside the vessel are known parameters, the amount of solid particles in the vessel can be calculated. Also, based on experimental data, the distribution relationship of sediment between the compartments is known.

According to an exemplary embodiment, the method is further comprising the steps of:

- calculating the density of the sediment located in the compaction compartment by using input from pressure measurements and/or weight measurements,

- regulating the discharge rate and/or timing based on input of the density of the sediment.

Advantageously, by capturing actual values of the sediment density in the compaction compartment, the density of the discharged sediment can be regulated.

According to a third aspect of the present invention, it relates to a method for controlling the discharge rate of a separator arrangement, comprising the steps of:

- capturing the density value of the wastewater before introduction in the separator,

- capturing pressure and/or weight measurement data of sediment in a compaction compartment and/or a discharge compartment,

- comparing the measurement data to the captured density value, - calculating the required discharge rate based on said data,

- modifying the speed and/or torque of a drive motor arrangement such that the desired discharge rate is achieved.

The method for controlling the discharge rate of the separator provides for an automated controlling/regulating operation of the density of the sediment inside the separator based on the actual/measured value so that the a desired density of the material can be obtained, in order to achieve a discharged sediment with a high density, but at the same time enabling the density of the material to be at a manageable level so as to enable a hassle- free discharge operation which is operating at the desired speed.

Brief description of the drawings

The invention will now be described with reference to the appended drawings, which by way of example illustrate embodiments of the present invention and in which:

Fig. 1 a is a schematic side view, partly cut-away, of a separator arrangement according to at least one exemplary embodiment of the present invention, Fig. 1 b is a schematic side view, partly cut-away, of a separator arrangement according to another exemplary embodiment of the present invention,

Fig. 2 is a schematic perspective view of a discharge arrangement in the separator according to an exemplary embodiment,

Fig. 3 is a flow chart of an exemplary method for separating solids from liquids.

Detailed Description

In the following description, a separator arrangement according to at least one exemplary embodiment of the present invention is described in the context of separation of wastewater from a mining operation. It should be noted that this by no means limits the scope of the present invention, which is equally applicable to other types of industrial applications, such as cleaning process water from various refining processes in the iron and steel industry, food industry as well as cleaning surface water (from e.g. sand, sediment and dirt). Fig. 1 a is a schematic side view of a separator arrangement according to at least one exemplary embodiment of the present invention, parts of the separator being shown in a cut-away view disclosing interior features of the separator. Fig. 1 a shows a separator arrangement 1 (in the following referred to as "separator"), comprising a separation vessel 2 and auxiliary process equipment. In order to provide an efficient separation process and a high density sediment material, the vessel 2 is provided with a separation compartment 3, a sedimentation compartment 4 and a compaction

compartment 5, which are separate compartments arranged in vertical extension in relation to each other. Suitably, the separator 1 also comprises a discharge compartment 6.

The working principle of the separator is to receive wastewater from an inlet duct 7 and to separate solid particles suspended in the wastewater from the liquid portion of the wastewater. The separation process works by the principle of gravity, and the process is further improved at low fluid velocites in the separation compartment 3. Wastewater is first introduced into the separation compartment 3 in the vessel 2. For this purpose, the wastewater inlet duct 7 is in

communication with the separation compartment 3. Suitably, the duct 7 has a nozzle 8 with a large oriface, such that the flow velocity of the wastewater is reduced as it is being introduced into the separation compartment 3, which in turn maintains a low fluid velocity in the separation compartment 3.

The liquid inside the separation compartment 3 is essentially still. As the wastewater enters the separation compartment 3, the velocity of the solid particles suspended in the wastewater suspension is drastically reduced, and provided that their density is higher than the fluid portion of the wastewater, the solid particles migrate downwards in the separation

compartment 3 of the separator 1 , while the fluid portion of the wastewater migrates upwards in the separation compartment 3. Typically, the fluid portion of the wastewater, i.e. the clear liquid, may be collected at the upper part of the separator 1 , wherefore a duct 9 may be arranged in this upper part in order to receive the clear liquid and transport it further away to a drain 10.

Additionally, the separator 1 may be provided with a top scraper arrangement (not shown) for collecting floating sludge on the liquid surface in the separator 1 . Floating sludge may for instance occur when metal particles in the wastewater create low-density chemical compounds together with other materials. Furthermore, a sludge pocket 12 may be arranged to collect the floating sludge from the scraper arrangement in order to store or move the sludge further away from the separator 1 . Suitably, the outlet duct 9 is connected to a pump that is adapted to transport the sludge away from the sludge pocket 12.

The sedimentation compartment 4 is arranged vertically below the separation compartment 3 and is provided with downwardly tapered wall portions 4', which provide a surface for solid particles to be deposited on. The downwardly tapered wall portions 4' of the sedimentation compartment 4 form an angle a with the center axis C of the vessel 2. Suitably, a scraper arrangement 13 is arranged inside the sedimentation compartment 4. The blades of the scraper arrangement are rotable and adapted to scrape off the sediment from the tapered wall portions 4', such that the sed iment is transported further down into the compaction compartment 5. In particular, the scraper arrangement 13 may be connected to an acuating arrangement 14, s u ch as a drive-motor arrangement that provides for an automatic operation. Furthermore, the acuating arrangement 14 may also be connected to a control unit, which may regulate the speed and timing of the drive-motor arrangement 14. The control unit may be a separate control unit or be constitued by a control unit 40, which may also control other functions, such as a discharge arrangement 21 .

The compaction compartment 5 is arranged vertically below the sedimentation compartment 4 and is adapted to receive the sediment from the sedimentation compartment 4 and to accommodate the sediment for a certain retention time, during which the sediment is further separated from the liquids. The compaction compartment 5 comprises an upper section 5a and a lower section 5b. The upper section 5a of the compaction compartment is adapted to receive the sediment from the sedimentation compartment 4. Furthermore, the wall portions of the upper section 5a are forming an angle with the tapered wall portions 4' of the sedimentation compartment 4. Typically, this implies that the sedimentation compartment 4 is provided with downwardly tapered wall portions 4', while the wall portions 5' of the upper section 5a of the compaction compartment 5 are more vertical/closer to the vertical plane than the former. The wall portions 5a' of the upper section of the compaction compartment 5a form an angle β with the center axis C of the vessel 2. (In the illustrated example, the angle β is 0). The wall portions 5b' of the lower section of the compaction compartment 5b form an angle Θ with the center axis C of the vessel 2.

As illustrated in fig. 1 b, the compaction compartment 105 may be designed such that the wall portions 105a' of the upper section 105a and the wall portions 105b' of the lower section 105b form continuous and downwardly tapered wall portions 105a', 105b', which are arranged at the same downwardly tapered angle Θ in relation to the center axis C of the vessel 2. Now referring back to fig. 1 a, in order to enhance the separation process and to improve the process speed for the separation of small solid particles (in particular of the size between 1 nanometer to 0.3 microns.) which are suspended in the wastewater, the separator may be provided with a mixing compartment 16 for mixing the wastewater with a flocculating agent. The flocculating agent stimulates the cohesion of the small particles, such that they agglomerate and form larger solid particles, also called "floes". The agglomerated/composed weight of the particles may thus be larger than the weight of the individual particles, wherefore they separate faster from the liquid. However, depending on the density of the flocculated particles, they may either be separated by sedimentation and collected in the discharge compartment 6 at the lower end of the separator 1 , or by floatation and thus collected as floating sludge in the upper part of the separator 1 . Examples of flocculating agents include polyacrylamide or natural products such as starch. .Additionally, a valve 28 may be arranged on the inlet duct 7 so that when the valve is open, wastewater fluid can be collected at a drain 29 for e.g. analysis. The valve 28 may also be used for emptying the mixing compartment 16. The mixing compartment 16 is suitably dimensioned based on the required reaction time for the flocculation process and the desired wastewater flow to the separator 1 . The d i mensions such as the vol u me of the m ixi ng compartment 16 and the inlet and outlet flows to/from the compartment 16 may be calculated therefrom.

The wastewater enters the mixing compartment 16 through a duct 17. The duct 17 may be provided with a valve 1 1 that controls the supply rate of the wastewater. The flocculating agent may be supplied directly through a branched connection 18 to the duct or be supplied directly to the mixing compartment 16 through a separate inlet 19. Suitably, the velocity of the wastewater gives rise to a vortex inside the compartment 16, such that the flocculating agent is thoroughly mixed with the wastewater. There are several possibilities embodiments of arrangements for creating a vortex, for instance, the process/wastewater may be introduced into the mixing compartment 16 with a high velocity, such that a turbulent flow regime is created. Other examples of embodiments may include mechanical devices such as turning blades/propellers 20 (as illustrated in fig. 1 ) or pumps.

A discharge arrangement 21 is located vertically below the compaction compartment 5, 105. The discharge arrangement 21 comprises a discharge compartment 6. Furthermore, a discharge mechanism such as an axle-free spiral conveyor 22 is mounted inside the discharge compartment 6 and is adapted to feed the sediment towards an outlet 23 in the discharge compartment 6. In connection to the outlet 23, a transport arrangement 25 such as a spiral conveyor is arranged to transport the sediment away from the separator. Alternatively to the spiral conveyor, a conduit or a belt conveyor may serve as a transport arrangement. Also, a combination of transport arrangements is possible. The discharge compartment 6 may be connected to a water inlet duct 24 with a valve 24A, through which water can be introduced into the discharge compartment 6 in order to break up and reduce the compactness of the sediment material such that clogs in the axle-free spiral conveyor can be removed. The compaction compartment 5, 105 may also be provided with a hatch 26, through which sediment and wastewater can be extracted.

The details on the connection between the compaction compartment 5, 105 and the discharge compartment 6 are further illustrated in fig. 2. The end portions of the axle-free spiral conveyor 22 are received and ratably arranged in a housing 31 of the discharge compartment 6. The axle-free spiral conveyor 22 is adapted to feed sediment towards an outlet 23, while enabling a recirculation/back flow of sediment through the open center of the axle-free spiral conveyor 22. Consequently, a recirculation/back flow of sediment reduces the risk for clogging of the discharge arrangement 21 . In addition, the open center of the axle-free spiral conveyor 22 relieves vacuum behind the blades of the spiral opposite to the feeding direction. The discharge arrangement 21 is adapted to transport the sediment from the outlet 23 to a duct/passage 33, which may be regulated by a valve 34. A transport arrangement 25 may be connected the duct/passage 33 and adapted to feed the sediment further away from the separator 1 . Particularly, in fig. 2, the transport arrangement 25 is illustrated as a membrane pump or a peristaltic pump. The lower section 5b, 105b of the compression compartment has downwardly tapered wall portions 5b', 105b', which provide for a smaller dimension in the opening 32 to the discharge arrangement 21 , such that a snug fit between the compression compartment 5, 1 05 and the discharge arrangement 21 is achieved.

Turning back to fig. 1 , a measuring unit 30 may be provided inside or adjacent to the compaction compartment 5, 105 or the discharge compartment 6. The measuring unit 30 may be located inside a membrane, such that it is protected from the wastewater. The measuring unit 30 may consist of a pressure transmitter (as illustrated) or a weight gauge. The measuring unit 30 is thus adapted to provide sufficient measurement data for calculating the density of the sediment material located in the compaction compartment 5, 105.

The discharge arrangement 21 may further comprise a drive motor arrangement 27 providing for an automatic operation of the axle-free spiral conveyor 22, such that the axle-free spiral 22 conveyor rotates around its center axis. Furthermore, the drive motor arrangement 27 may be connected to a control unit 40 which is adapted to perform automatic regulating operations to the drive motor arrangement 27, such as controll ing the rotational speed and/or torque of the axle-free spiral conveyor 22. The control unit 40 may be adapted to receive input signals from the measuring unit 30, perform calculations and send control signals to the drive motor arrangement 27.

In use of the separator 1 , wastewater is supplied from an inlet duct 7 to the separation compartment 3 inside the separator 1 . The velocity of the wastewater drastically slows down as it enters the separation compartment 3 with essentially still liquid. In the still liquid conditions inside the separation compartment 3, solid particles contained in the wastewater migrate downwards and settle on the downwardly tapered wall portions 4' of the sedimentation compartment 4. Sediment of solid particles gradually builds up in the sedimentation compartment 4, whereafter the sediment is further transported downwards to a compaction compartment 5, 105. Suitably, a scraper arrangement 13 is arranged inside the sedimentation compartment 4 and scrapes the sediment off the downwardly tapered wall portions 4' of the sedimentation compartment 4.

Following, the sediment is moved further downwards, first to the lower section 5b, 105b of the compaction compartment 5, 105, then to the discharge compartment 6. The tapering of the lower section 5b relative to the upper section 5a, 105a increases the compaction of the sediment. The overlying material (wastewater and sediment) is exercising a force/pressure on the sediment in the compaction compartment 5, 105 and the discharge compartment 6, which force in combination with the outflow from the discharge arrangement 21 move the sediment out from the compaction compartment 5, 105 and the discharge compartment 6. The shape of the compaction compartment 5, 105, with a decreasing cross section in the direction towards the bottom of the separator 1 , forces the sediment into a smaller space while the liquid portion of the wastewater suspension is forced upwards. In combination with weight of the overlying material, a compression of the solid material is achieved.

Now referring to fig. 3, which illustrates an exemplary method for controlling the discharge rate of the separator 1 according to the present invention. In order to determine the density of the sediment in the vessel 2, and in particular in the compaction compartment 5, 105, some parameters are measured, while others may be of constant or known values or based on known relationships and behavior which depend on the characteristics of the wastewater.

The illustrated method related to fig. 3 comprises a set of steps, which hereafter are described in a certain order. Nevertheless, the method should not be limited to this specific order, which on the contrary mainly serves the purpose of listing included and suitable steps in a clear and concise way.

A first step S1 in the method, the density of the wastewater is captured before its introduction into the separator 1 . This measurement may be performed by simply measuring the weight of the wastewater for a predetermined volume. Alternatively, the separator 1 may comprise a measuring arrangement for automatically measuring the wastewater density prior to its introduction into the separator. Such an automatic measuring arrangement may be continuously or instantaneously operable.

In a step S2, a desired density of the d ischarged sed iment is determined. The desired density of the discharge sediment may for instance be determined from the particle sizes and or other characteristics of the wastewater suspension.

In step S3 actual pressure data is captured inside the compaction compartment 5, 105 and/or the discharge compartment 6. The pressure is captured by a pressure meter 30, which is suitably located inside the compression 5, 105 and/or the discharge compartment6. Additionally or alternatively, the weight of the separator 1 may be measured by a weight meter/sensor, suitably arranged in the supporting and load bearing structure of the separator. Suitably, such a weight sensor is located inside, on or under the supporting structure.

A further step S4 includes comparing the measured data containing pressure and/or weight values to the desired discharge density.

Another step S5 includes calculating the desired discharge rate from the discharge arrangement 6. Typically, if the density of the sediment in the compaction compartment 5, 105 is lower than the desired discharge density, the discharge rate of the discharge arrangement 21 may be set to a minimum, or even stopped. On the other hand, by continuously measuring the density, or by an experience-based function, the measured density in the compaction compartment 5, 105 is not likely to exceed the desired value. However, in case the measured value/actual density value is higher than the desired value, the discharge speed will be increased to a maximum.

A further step S6 includes calculating the required speed and/or torque of the rotation of a discharge mechanism 22 inside the discharge compartment 6.

A step S7 includes implementing the required speed and/or torque of the discharge mechanism 22, which suitably includes an axle-free spiral conveyor inside the discharge compartment 6, and thus discharging the sediment from the discharge compartment 6, which may suitable involve a rotation of an axle-free spiral conveyor 22.

The skilled person will realize that the present invention by no means is limited to the described exemplary embodiments. The separator may also comprise means for regulating the wastewater supply prior to its introduction into the vessel. For instance, if the wastewater supply is too high and the risk of overfilling the vessel occurs, a valve mechanism may be arranged on the supply duct. The wastewater may also be diverted into a buffer container/receptacle in case of peaks in the wastewater supply. The measurement of pressure and weight has been described as performed by a pressure and/or a weight meter. The sensing parts and the measuring technology will not be further elaborated on within the context of this application, but may be performed by any known measuring technique, such as infra-red, radar or any other suitable measuring units.

The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Moreover, the expression "comprising" does not exclude other elements or steps. Other non-limiting expressions include that "a" or "an" does not exclude a plurality and that a single unit may fulfill the functions of several means. Any reference signs in the claims should not be construed as limiting the scope. Finally, while the invention has been illustrated in detail in the drawings and in the foregoing description, such illustration and description is considered to be illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments.

Claims

C L A I M S

1 . A separator arrangement (1 ) for separating solid particles from liquids in a wastewater suspension, comprising:

a separation compartment (3) for receiving the wastewater suspension and for separating the solid particles from liquids by means of gravity,

- a sedimentation compartment (4) located below the separation compartment and provided with downwardly tapered wall portions (4') adapted to receive a sediment of solid particles,

a compaction compartment (5, 105) comprising an upper section (5a, 105a) and a lower section (5b, 105b), wherein the upper section (5a, 105a) of the compaction compartment (5, 105) is adapted to receive the sediment from the sedimentation compartment (4), said upper section (5a, 105a) being provided with wall portions (5a', 105a') forming an angle with said tapered wall portions (4') of the sedimentation compartment (4), and wherein the lower section of the compaction compartment (5b, 105b) is provided with downwardly tapered wall portions (5b', 105b').

2. The separator arrangement according to claim 1 , wherein the downwardly tapered wall portions (5b') of the lower section (5b) of the compaction compartment (5) form an angle with said wall portions (5a') of the upper section (5a).

3. The separator arrangement according to claim 2, wherein the wall portions (5a') of the upper portion (5a) of the compaction compartment (5) are provided at an angle (β) in the range between 0^° and 30^° relative to the center axis (C) of the vessel (2), suitably between 0^° and 10^°.

4. The separator arrangement according to claim 3, wherein the wall portions (5b') of the lower portion (5b) of the compaction compartment (5) are downward-sloping and are provided at an (Θ) angle of between 5^° and 30^° relative to the center axis (C) of the vessel (2).

5. The separator arrangement according to claim 1 , wherein the wall portions (105a' ) of th e u pper section (105a) of the compaction compartment (105) are downwardly tapered in relation to the center axis (C) of the vessel (2).

6. The separator arrangement according to claim 5, wherein the wal l portions (1 05b') of the lower section (105b) of the compaction compartment (105) and the wall portions (105a') of the upper section (105a) of the compaction compartment (105) form continuous wall portions (105a', 105b') which are arranged at the same downwardly tapered angle in relation to the center axis (C) of the vessel (2).

7. The separator arrangement according to claim 6, wherein said downwardly tapered angle (Θ) is between 5^° and 30^° relative to the center axis (C) of the vessel (2).

8. The separator arrangement according to any one of the preceding claims, wherein the volume of the compaction compartment (5, 105) is smaller than the volume of the sedimentation compartment (4), and wherein the volumetric relationship between the compaction compartment (5, 105) and the sedimentation compartment (4) is in the range between 10% and 75%, suitably between 10% and 40%.

9. The separator arrangement according to any one of the preceding claims 5-8, wherein the volume of the lower section (5b, 105b) of the compaction compartment (5, 105) is smaller than the volume of the upper section (5a) of the compaction compartment (5, 105), and wherein the volumetric relationship between the lower section (5b, 105b) and the upper section (5a, 105a) of the compaction compartment (5, 105) is in the range between 15% and 80%.

10. The separator arrangement according to any one of the preceding claims, further comprising a scraper arrangement (13) adapted to rotate along the downwardly tapered walls portions (4') inside the

sedimentation compartment (4).

1 1 . The separator arrangement according to any of the preceding claims, further comprising a mixing compartment (16), which is connected to a supply (18,19) of a flocculating agent and a supply (17) of the wastewater suspension, such that the flocculating agent is added to the wastewater suspension before the wastewater suspension enters the separation compartment (3).

12. The separator arrangement according to any one of the preceding claims, further comprising a discharge arrangement (21 ) located after and/or below the compaction compartment (5, 105), wherein said discharge arrangement (21 ) comprises:

- a housing (31 ) which defines a discharge compartment (6), said discharge compartment (6) being adapted to receive sediment from the compaction compartment (5, 105), and

- at least one axle-free spiral conveyor (22) located inside said housing (6).

13. The separator arrangement (1 ) according to claim 12, wherein said housing (31 ) is in open communication with the compaction compartment (5) such that an opening (32) between the compaction compartment (5, 105) and the discharge compartment (6) is created.

14. The separator arrangement according to claim 12 or 13, wherein the housing of the compaction compartment (5, 105) comprises an openable hatch (26) for emptying the separator (1 ).

15. The separator arrangement (1 ) according to any one of claims 12- 14, wherein said housing (31 ) is further connected to a transporting means (25) for transporting the sediment away from the separator (1 ), wherein the transporting means (25) is located after the axle-free spiral conveyor (22) and adapted to receive and transport the sediment away from the discharge arrangement (21 ).

16. The separator arrangement (1 ) according to claim 15, wherein said transporting means (25) comprises a spiral conveyor and/or a belt conveyor and/or a membrane pump and/or a peristaltic pump.

17. The separator arrangement (1 ) according to any one of the preceding claims, further comprising a pressure measuring arrangement (30) for measuring pressure inside the compaction compartment (5, 105) and/or inside the discharge compartment (6), wherein the pressure measuring arrangement (30) comprises at least one pressure sensor located inside the compaction compartment (5) and/or inside the discharge compartment (6).

18. The separator arrangement (1 ) according to any one of the preceding claims, further comprising a weight measuring arrangement for measuring the weight of the separator, wherein the weight measuring arrangement comprises at least one weight meter located on or under or, inside a supporting structure of the separator (1 ).

19. The separator arrangement according to claim 17 or 18, further comprising a control unit (40) connected to the axle-free spiral conveyor (22) and an actuating means (27), wherein the control unit (40) controls the speed and/or torque of the axle-free spiral conveyor (22) based on input from the pressure measuring arrangement (30) and/or weight measuring arrangement.

20. A method for separating solid particles from liquids in a wastewater suspension by using a separator arrangement (1 ) according to claim 12 or any one of claims 13-19 when dependent on claim 12, wherein the method comprises the steps of:

- filling the separation compartment (3) with a wastewater suspension, whereby a sed iment of sol id particles is deposited on the downwardly tapered wall portions (4') of the sedimentation compartment (4),

- moving the sediment of solid particles to the compaction compartment (5, 105),

- receiving the sediment of solid particles in the discharge compartment (6),

- discharging the sediment of solid particles from the discharge compartment (6).

21 . A method according to claim 20, wherein the step of discharging the sediment is effectuated by rotating at least one axle-free spiral conveyor

(22).

22. A method according to claim 20 or 21 , further comprising a step of measuring the pressure inside the compaction compartment (5, 105) and/or inside the discharge compartment (6).

23. A method according to claim 20 or 21 , further comprising a step of measuring the weight of the separator (1 ).

24. A method according to any one of claims 20-23, further comprising the steps of:

- calculating the density of the sediment located in the compaction compartment (5, 105) by using input from pressure measurements and/or weight measurements,

25. A method for controlling the discharge rate of a separator arrangement (1 ) according to any of one of claims 1 - 19, comprising the steps of:

- capturing the density value of the wastewater before introduction in the separator (1 ),

- capturing pressure and/or weight measurement data of sediment in a compaction compartment (5, 105) and/or a discharge compartment (6),

- comparing the measurement data to the captured density value,

- calculating the required discharge rate based on said data,

- modifying the speed and/or torque of a drive motor arrangement (27) such that the desired discharge rate is achieved.