A flow guide, an apparatus and a method for processing a suspension

Abstract

The present invention is directed to a flow guide (110), an apparatus (100) and a method (400) for processing a suspension inside a processing apparatus (100). The apparatus (100) has at least one reject outlet (108a, 108b) located at the surface level (109) of suspension and a rotor (102) equipped to flush the suspension wherein the flow guide (HO) located at proximity of wing of a rotor diverts at least a part of a flow at the proximity of wing (103) of a rotor (102) to the reject outlet (108a, 108b).

Description

[0001]A FLOW GUIDE, AN APPARATUS AND A METHOD FOR PROCESSING A SUSPENSION Background An invention relating to an apparatus, a method, and a flow guide for processing a suspension inside an apparatus, for example a pulper, is presented. A screening process is an important step in several industrial processes. Screening is a process where impurities are separated from the wanted material. For example, in the paper recycling process screening is a key process used for enhancing the quality of products. In the screening process the suspension is fed to the screening apparatus, e.g. a pulper. A typical pulper comprises a vessel on bottom of which a wing of a rotor is rotating on top of a screening plate. The flow passing through the screen plate is called an accept flow. The part of the flow not being able to pass through the screen plate, i.e. a rejected flow, is removed from the pulper through a reject outlet. Publications US4938423A, US2007114311A1, GB713501A and CN216193633U show examples of known pulpers. One of the problems of the prior art solutions is an accumulation of material unable neither to pass through a screening plate nor reaching a reject outlet. Because of this prior art pulpers need frequently to be shut down and cleaned. The present invention is directed to solve the problems of the prior art. Summary This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. A flow guide for suspension processing apparatus and an apparatus comprising a flow guide to be installed inside a vessel of an apparatus is provided. The apparatus can be for example a pulper arranged to screen a suspension containing fibrous material, such as recycled paper, carton or cardboard. In some embodiments the flow guide comprising a first flow divert element equipped to divert at least a part of a flow at a proximity of a wing of a rotor, or at the residual accumulation zone, of the apparatus to a direction increasing the diverted flow’s radial distance from the rotor, a second flow divert element equipped to divert at least a part of the flow from the first flow divert element towards the surface of the suspension and a third flow divert element equipped to divert at least a part of the flow from the second flow divert element towards a reject outlet. In some embodiments the width of the second flow divert element in the radial direction of the rotor is greater than 0.1 of a diameter of the vessel, preferably 0.15±0.05 of the diameter of the vessel. The flow guide may comprise also a fourth flow divert element fitted on a rotor facing side of the second flow divert element, the fourth divert element being equipped to reduce the interaction between the flow guided by the second flow divert element and the flow closer to the rotor. In another embodiment the flow guide comprises at least one opening to allow heavier material in the flow diverted by the third flow divert element to fall towards the bottom of the vessel before such heavier material reaches the reject outlet. The apparatus can also comprise a harvesting device partially submerged to the suspension for mechanical removal of unwanted solid objects present at the surface or near the surface of the suspension. Also presented is a method for processing a suspension in an apparatus having a vessel with at least one reject outlet located at the surface level of suspension and a rotor equipped to flush the suspension. The method comprising diverting, by a flow guide located inside the vessel at the proximity of wing of a rotor, or at the residual accumulation zone, at least a part of a flow at proximity of wing of the rotor to the reject outlet. Some embodiments of the method further comprising diverting, by a first flow divert element, at least a part of the flow at the proximity of wing of a rotor to a direction increasing the radial distance of the diverted flow from the rotor, diverting, by a second flow divert element, at least a part of the flow from the first flow divert element towards the surface of the suspension and diverting, by a third flow divert element, at least a part of the flow from the second flow divert element towards the reject outlet. In some embodiments the method further comprising diverting heavier material in the flow diverted by the third flow divert element to fall towards the bottom of the vessel before such heavier material reaching the reject outlet and / or the unwanted solid objects may be removed from the suspension by a harvesting device partially submerged to the suspension. The processing suspension may contain fibrous material, such as recycled paper, carton or cardboard. The following detailed description and accompanying figures will further explain these features. The embodiments described below are not limited to implementations which solve any or all of disadvantages of the prior art. Short description of the figures: Fig. 1: A pulper according to the invention with several pulping sections Fig. 2: An embodiment of apparatus according to the invention Fig. 3: An embodiment of a flow guide according to the invention Fig. 4a: A side view of an embodiment of an apparatus according to the invention Fig. 4b: A top view of an embodiment of an apparatus according to the invention Fig. 5: An embodiment of a method according to the invention Fig. 6a: A side view of a multistage embodiment of an apparatus according to the invention Fig. 6b: A view of an embodiment of an apparatus according to the invention along longitudinal axis of a multistage apparatus Detailed Description Fig. 1 shows an embodiment of a pulper (10) according to the invention with several pulping sections (11,12,13). The material to be processed is fed to a primary pulper section (11) as indicated by an arrow (31). A first rotor (21) shredders the suspension in the primary pulper section (11) and part of the material passes through a screen plate to the accept inlet (neither shown in Fig.1). At least part of the suspension from the primary pulper section (11) is flowing to a secondary pulper section (12). This is indicated in Fig. 1 by an arrow (41) from the primary pulper (11) to the secondary pulper (12). This flow can be simple overflow over the wall (61) separating the primary (11) and secondary (12) pulper sections. This overflow can happen either over the whole length of the wall (61) or just certain section of the wall (61) where the height of the wall is lower than in other parts of the wall (61) and preferable lower than the internal height (H) of the vessel containing the primary pulper section (11). The second rotor (22) in the secondary pulper section (12) shredders the suspension in the secondary pulper section (12) and part of the material passes through a screen plate to the accept inlet (neither shown in Fig. 1). At least part of the suspension from the secondary pulper section (12) is flowing to the tertiary pulper section (13) over the wall (71). This is indicated in Fig. 1 by an arrow (51) from the secondary pulper section (12) to the tertiary pulper section (13) where the third rotor (23) shreds the suspension in the tertiary pulper section (13). The overflow from the secondary pulper section (12) to the tertiary pulper section (13) can happen similarly like the overflow from the primary pulping section (11) to the secondary pulping section (12). In some embodiments the rotor is located on the wall of a pulper section. In Fig. 1 the first rotor (21) in the primary pulper section (11) and the second rotor (22) in the secondary pulper section (12) are located at the walls of the respective pulper sections. In other embodiments the rotor is located at the bottom of the pulper section, like the third rotor (23) in the tertiary pulper section (13). Even if the pulper in Fig. 1 has multiple pulping sections in some embodiments according to the invention the pulper might have only one pulper section. In Fig. 1 both the primary pulper (11) and the secondary pulper (12) have flow guides (110) inside them directing the flow from the proximity of the rotors (21, 22) towards the top of the walls (61, 71), from where a part the suspension overflows to the next pulper section. From the point view of the pulper sections where the suspension flows from these overflow areas can be understood as reject outlets and from the point view of the pulper sections to which the suspension flows to these overflow areas can be understood as inlet ports. The function of the flow guides (110) is explained in more detail later. In some embodiments the apparatus can comprise several sections inside a single vessel like shown in Fig. 1. In other embodiments a system of separate apparatuses could be implemented by having several apparatuses containing one or more rotors and a flow of suspension between different apparatuses would be arranged via like pumps or gravity induced flow or other means know as such to a person skilled in the art. Fig.2 shows one embodiment of an apparatus (100) according to the invention, preferably an apparatus for processing a suspension with fibrous material in it, e.g. a pulper. The suspension could contain for example pulp content, paperboards, cartons, fiberboards, packing material or bio waste. In some embodiments the pulper is a tank-type open topped pulper, in some other embodiments the pulper could be a closed vessel. In some embodiments the pulper is used in a continuous mode, where the material to be processed is continuously added to the pulper, while in other embodiments the pulper is used in batch or semi batch mode. The apparatus (100) consists of a vessel (101), which is filled by a suspension to be processed, for example screened. In some embodiments the suspension has a consistency of 3-8%. The suspension can be fed to the vessel via inlet ports (104, 105). In the most basic form, an inlet port is just an opening in a vessel (101) via which the material can be poured to the vessel, e.g. manually or via a conveyer belt. In some embodiment two or more inlet ports can be used. An overflow to a pulper as explained in connection of Fig. 1 can also understood as one type of inlet port. The first inlet port (104) could be used to feed the vessel (101) with the material to be processed, e.g. pulp content, paperboards, cartons, fiberboards, packing material or bio waste and the second inlet port (105) can be used to provide the carrier fluid, e.g. water, for the suspension. In such an embodiment the suspension is formed inside the vessel when the material to be processed is torn or shredded, e.g. by a rotating wing of a rotor, to smaller pieces and mixed with the carrier fluid. In another embodiments the material to be processed and the fluid can be provided to the vessel (101) already in a form of suspension. In such a case only one inlet port can be used. In Fig. 2 the apparatus is an open topped, but as mentioned above it could also be close topped, in which case the inlet ports (104, 105) could be holes in the walls or at the top or bottom of the vessel (101) or even an overflow over the walls as explained in connection to Fig 1. In some embodiments the vessel contains a rotor (102). The rotor can have a rotating wing or wings (103) for flushing the suspension. In Fig. 2 the rotor (102) is located at the bottom of the vessel (101) where it rotates on top of a screen plate (111), but as explained in connection to Fig. 1 the rotor could also be located at the wall of the vessel (101). A screen plate (111) screens the material by allowing the accepted material to flow through the screen plate (111) and to exit via the accept port (106). In order to prevent clogging of the apparatus, the vessel (101) consists of at least one reject port (108a, 107) to allow the material which can’t pass the screen plate (111), e.g. the rejected material, to exit the vessel (101). In Fig. 2 the upper reject port (108a) located in the wall of the vessel (101) is seen behind the flow guide (110). As explained in connection to Fig 1, in some embodiments according to the invention areas where the suspension overflows from one pulper section to another can be understood as one type of reject ports or outlets from the point view of the pulper section from which the suspension flows from. In some embodiments of the invention the suspension consists of carrier liquid, preferred material, and unwanted material. The unwanted material can consist of material or objects which have density lower than the carrier liquid and material or objects which have higher density than the carried liquid. In this application the former is called heavier unwanted material and latter lighter unwanted material. In some embodiments of the invention the invention the suspension fills up the vessel (11) to the level of the upper reject outlet (108a), i.e. the surface level (109) of the suspension reaches the upper reject outlet (108a) allowing the rejected material and excess fluid to exit the vessel (101). In some embodiments the vessel (101) has a lower reject port (107) at the bottom of the vessel (101). Due the flow patterns caused by the rotating rotor wings, in some embodiments a significant part the of the lighter unwanted material, or at least more than exits via the lower reject port (107), exits the vessel (101) via upper reject port (108a) and a significant part of the heavier unwanted material exists the vessel (101) via the lower reject (107). In some embodiments the vessel (101) has multiple upper reject ports (108a) and / or multiple lower reject ports (107). In some embodiments of the invention a flow guide (110) is installed inside the vessel (101). The flow guide (110) diverts part of the flow close to, or in proximity of, the rotor (102) and its wings (103) towards the upper reject port (108a). Fig. 3 shows a detail of the apparatus (100) with two embodiments of the flow guide according to the invention. One flow guide in Fig.3 consists of four different flow control, or flow divert, elements (201, 202, 203, 204) for diverting the flows inside the vessel (101). These elements can be separate elements or some or all of them can be combined to a single physical element. In some embodiments some or all of these elements are made of stainless steel. The other flow guide in Fig. 3 shows only two divert elements (201, 202). The rotating rotor (no rotor or its wings are shown in Fig. 3 for clarity reasons) flushes the suspension. The rotation direction is indicated by the arrow (220) in Fig. 3. In some embodiments the first flow divert element (201) is placed on the proximity, or vicinity, of a rotating rotor wing. In some embodiments the first flow diver element (201) can be located at or close to a space identified as a residual accumulation zone. The concept of residual accumulation zone is explained in more detail later. A first flow divert element (201) diverts at least a part of a flow at the proximity of the rotor wing or at a residual accumulation zone of a rotor to a direction increasing the diverted flow’s radial distance from the rotor. In some embodiments this means that the first divert element (201) diverts at least a part of the flow towards the walls of the vessel (101). This flow is marked in Fig.3 by the first black arrow (211). In some embodiments the first flow divert element (201) is attached on the bottom of the vessel (101) so that its height is lower closer to the rotor and higher further away from the rotor. For example, the height of the first flow divert element could be 100-600mm closer to the wall and at the closest point to the rotor wing the tip of the element can fuse with bottom of the vessel. In some embodiments the diameter of the vessel is D and thus the radius is D / 2. In some embodiments the rotor’s wings reach can be up to D / 4 or D / 8 from the axis of the rotor. The tip of the first divert element (201) can be at close proximity of the rotor wing. In some embodiments the radial distance between the tip of the first diver element (201) and the wing of the rotor is less than 10mm and in other embodiments the tip of the first divert element (201) can even reach under the wing of the rotor. In some embodiments according to the invention at least part of the flow diverted by the first divert element (201) is diverted by a second divert element (202). The second divert element (202) diverts at least a part of the flow (211) from the first flow divert element (201) towards the surface of the suspension. This flow is marked in Fig. 3 by the second black arrow (212). In some embodiments the second flow divert element (202) is fitted to the wall of the vessel (101). The width of the second flow divert element (202) can vary, but in some embodiments the width of the second flow divert element in radial direction of the rotor is greater than 0.1 of a diameter of the vessel, preferably 0.15±0.05 of the diameter of the vessel. In some embodiments the second divert element (202) is fitted with a blocking element (204) which reduces the interaction between the flow (212) directed by the second divert element (202) and the suspension flowing on the other side of the blocking element (204). This blocking element (204) can act as a fourth divert element by guiding the flow (212) diverted by the second divert element (202) towards the surface of the suspension and simultaneously reducing the interference and contamination from the other flows present in the suspension. In some embodiments a third divert, of flow control, element (203) diverts at least part of the flow (212) from the second flow divert element (202) towards the reject outlet (108a). This flow is marked in Fig. 3 by the third black arrow (213). In some embodiment the third flow control element (203) is attached to wall on a level where the surface of the suspension is located in typical operation conditions and / or at the level of the reject outlet (108a). In other embodiments the upper edge of the third control element (203) is on the same level as the wall on the vessel (101) and / or the bottom edge of the third flow control element (203) in under the surface level of the suspension in typical operation condition. To allow some operation flexibility the third flow control element (203) be constructed so that in normal operational conditions a part of it is submersed in the suspension and part is above the surface of the suspension. In some embodiments the shape of the third flow control element is such that it comprises at least one sub element (203a, 203b) which reduces the interaction between the rotating flow (220) with the flow (213) directed by the third flow control element (203). In some embodiments of these sub elements (203a, 203b) are integrated parts of the third flow control element (203) in other embodiments they are physically separate, but still functionally operate together with other elements of the third flow control element (203). In some embodiments the first sub element (203a) is a closed end of the third flow control element (203) facing the rotating flow (220) and thus blocking the circular suspension flow (220) rotating at the surface and / or close to the surface of the suspension, from directly encountering the flow (213) diverted by the third flow control element (203). Similarly, the second sub element (203b) can be a closed end of the other side of the third flow control element (203), the second sub element(203b) blocking the flow (213) diverted by the third flow control element (203) from directly flowing to the circular suspension flow (220) rotating outside the third flow control element (203) at the surface and / or close to the surface of the suspension. In some embodiments the shape of the second sub element could be such that it directs a significant part of the flow (213) diverted by the third flow control element (203) to the reject outlet (108a), from where the reject flow marked by the forth black arrow (214) in Fig. 3 exits the vessel (101). In some embodiments the bottom or part of the bottom of the third flow control element (203) is open, or having one or multiple openings, allowing part of the flow (213) diverted by the third flow control element (203) to be separated from the main diverted flow (213). Such an opening (303) can also be seen in Figs. 4a & 4b. In Fig. 3 the separated, or diverted, flow is marked by the white arrow (215). This separated flow (215) could for example consist of preferred material wanted to the accept flow as such material is typically heavier than carrier liquid. In some embodiments the gravitational forces effect the preferred material more than the lighter unwanted material in the flow (213) diverted by the third flow control element (203), causing higher share of the heavier material compared to the lighter elements to be separated from the flow (213) diverted by the third flow control element (203). This in turn increases the share of lighter unwanted material in the flow reaching the reject outlet (108a). In some embodiments the flow to the reject outlet (108a) is smaller than the diverted flow (215). In such a case the effects of gravitational forces are negligible and the movement of the material in suspension if mainly determined by the flow patterns within the flows (213, 215). The amount of the flow (214) through the reject outlet (108a) can be controlled e.g. by the pumps connected to the reject outlet (108a) or controlling the amount of suspension inside the vessel (101), i.e. by controlling how high the surface level of the suspension raises. In some embodiment according to the invention the third flow control element (203) blocks the material added to the vessel for reaching the reject outlet (108a) without first being directed close to the rotor at least once. The strong downward flow patterns and the solid wall of the third flow control element (203) prevents the flow from the surface, to which the new material in fed, from reaching the side of the third flow control element (203) where the flow (213) diverted by the third flow control element (203) flows and directs the newly fed material toward the rotor. Fig.4a shows a side and Fig.4b a top view of one embodiment of an apparatus according to the invention. The different elements and their numbering are the same as in earlier figures. When a processing apparatus, like a pulper, is operated it processes a suspension typically containing a carried liquid and the material to be processed, which typically is in solid form. In some embodiments the material to be processed consists of the preferred material and unwanted material. Further, the unwanted material can consist of many different types of unwanted material. Some of the unwanted material, like pieces of metal, could be heavier than the carried liquid and some, like plastics, lighter than the carried liquid. For example, in the process of screening recycled paper or cardboard the unwanted material could consist metallic staples, pieces of plastic tapes, plastic envelope windows and / or other pieces of plastic. In some embodiments the suspension contains pieces of plastic which can be just a few micrometers thin but have relatively large surface area. In some embodiments the surface area of such plastic pieces can vary from several square millimeters to several square centimeters or even square meter range if big plastic bags or sheets to packing wrappings are included in the material. The target of a screening process is to maximize the share of preferred material in the accept flow exiting the apparatus via the accept outlet (106) and maximize the share of unwanted material in the reject flow exiting the apparatus via the reject outlet or outlets (107, 108a, 108b). In some embodiments the reject outlet consists of a harvesting device (108b) for mechanical removal of the unwanted material. The harvesting device (108b) can be for example a step screen, a conveyor belt or a tool with rotating or otherwise moving pikes or hooks. In the embodiment shown in Fig. 4a the reject outlet (108b) consists of a step screen partially submerged to the suspension, which removes the solid objects present at the surface (109) or near the surface (109) of the suspension. The step screen (108b) drops the reject to a waste removal system, which for clarity reasons not shown in Fig.4a. In some embodiments the harvesting device (108a) is located before the opening (303), i.e. the flow diverted by the third divert element encounters the harvesting device (108b) before encountering the opening (303). In some other embodiments the harvesting device (108b) is located on top the opening (303) or after the opening (303). In some embodiments the apparatus has at least one reject outlet consisting of at least one reject port (108a) and in others the apparatus has at least one reject outlet consisting of at least one harvesting device (108b). In some embodiments the apparatus has at least two reject outlets consisting of at least one reject port (108a) and at least one harvesting device (108b). Construction of a reject port (108a) can be simple and very reliable. They can be simple holes on the wall of the vessel (101), or they can be areas of wall of the vessel (101) where the height of the wall is lower and thus allowing the reject to flow over the wall in predetermined locations. A step screen (108b) and other mechanical harvesting devices, can have more complex contraction than simple reject ports (108a), but they have other advantages like minimizing the amount of carrier liquid removed with the unwanted material as majority of the carrier liquid flows back down to the vessel (101) during the mechanical removal process. In some embodiments a significant part or majority of the bigger pieces of light unwanted material are removed by a harvesting device (108b) and smaller pieces are mainly removed via the reject port (108a). In one embodiment according to the invention the apparatus consists of at least two reject outlets, a lower reject outlet (107) for the heavier unwanted material as heavier material tend to accumulate on the bottom of the vessel and a upper reject outlet, either at least one reject port (108a) and / or at least one harvesting device (108b) for removing the lighter unwanted material which raise on the surface of the suspension due the buoyant, and / or the flow patterns presents at the suspension, especially if the density of the lighter material is smaller than the density of the carrier liquid. The inventors have found that in the prior art systems a significant part of the lighter unwanted material won’t rise to the surface of the suspension. As the rotating rotor wings flush the suspension eventually the content of the vessel starts rotating, especially on the surface of the suspension in the direction of rotation of the wings. The rotation direction of the rotor is indicated by the white arrow (220) in Fig.3. This rotation causes centrifugal forces which can cause, outside the immediate vicinity of the rotating wings, the heavier material in the suspension to move towards the walls of the vessel and thus causing accumulation of heavier material closer to the walls and accumulation of lighter material closer to the rotor. It is also possible that other forces contribute to the accumulation of the heavier material toward the wall of the vessel. There can for example be other flow patterns present in the suspension, e.g. the upwards and down circular flow caused by the rotor wings, indicated by the white arrows (307) in Fig. 4a. These distortions can affect the distribution of material inside the vessel. The inventors have found out that because of these and / or some other still unknown effects a part of the lighter unwanted material in prior art solutions will not reach the reject outlets, but start to accumulate in certain areas, indicated by the gray areas (301) in figures 4a and 4b. In this application those areas are called residual accumulation zones. Accumulation of unwanted material in the called residual accumulation zones can hinder the operation of the apparatus. For example, the concentration of plastic in the suspension, can reach such a high level that it starts hindering the operation of the apparatus, requiring the apparatus to be stopped and cleaned. This cleanup can require emptying the vessel and manually removing the excess material, e.g. with a high-pressure water spray. In some embodiments of the invention the accumulation of the lighter material in the residual accumulation zones is reduced or even totally prevented by a flow guide (110) according to the invention. For example, a tip of the flow guide (110) can be placed at the proximity of the wing (103) of the rotor (102) so that a part of the suspension flow is, as described in connection to Fig. 3, first diverted toward the walls of the vessel (101), then upwards towards the surface (109) of the suspension and finally towards the upper reject outlet (108a, 108b). In some embodiments the distance is between the first flow guide (110) and the wing of the rotor is less than 50mm, preferably less than 10mm and in other embodiments the tip the first divert element can even reach under the wing of the rotor. Directing part of the flow from the proximity of rotor (102) disturbs the flow patterns forming of the residual accumulation zone and thus hinders accumulation of unwanted material to the residual accumulation zones or in some embodiments even preventing the residual accumulation zone from forming in the first place. This greatly reduces the accumulation of unwanted light material in the suspension, which in turn increases the operation effectiveness of the apparatus. Some embodiments according to the invention utilize the detailed structure of explained in this application to A) reduce or even prevent the accumulation of material in the residual accumulation zone or zones (301), B) increase the share of lighter unwanted material at the reject flow exiting via the upper reject outlet (108a, 108b) and / or C) reduce the share of the preferred material at the reject flow exiting via the upper reject outlet (108a, 108b). Note that the locations of the residual accumulation zones (301), circular flows (307) as well as the shape and orientation of the flow guide (110) depends on the induvial para- meters of the apparatus in use and thus in some embodiment of the invention their shape and position might differ on what is presented in any of the figures. Fig. 6a shows a side view of a primary pulper (524) in a multistage embodiment of a pulper according to the invention and Fig. 6b shows a view along longitudinal axis of a primary pulper in a multistage embodiment of a pulper according to the invention. For clarity purposes all the elements presented in the previously explained embodiments are not shown in Figs 6a and 6b. It is however understood that in some embodiments those elements can be included to the embodiments shown in Figs 6a and 6b. In embodiments shown in Figs 6a and 6b a rotor (521) is located at a wall of the cylindrically shaped vessel (506) of the primary pulper (524). The radius of the cylindrical cross section is marked as D / 2, where the D is diameter of the vessel. In some embodiments the vessel can be of different shapes, for example elliptical, rectangle or even irregular shape. The rotor (521) is rotating in a direction indicated by a white arrow (520). This rotation causes the suspension inside the vessel (506) to rotate in the same direction. In Figs 6a and 6b the primary pulper (524) is separated from a secondary pulper (505) by a partition wall (561). In some embodiment the partition wall (561) does not block the whole area of the cross section of the primary pulper (524) but leaves a section of the upper part of the partition wall (561) open allowing a suspension to flow, if the surface (509) of the suspension is higher than at least some part of the partition wall (561), from the primary pulper (524) to the secondary pulper (505) as explained earlier. In some embodiments a first flow divert or diverting element (501) diverts, as explained earlier, a part of the suspension from the proximity of the rotor wings, or the residual accumulation zone, away from the rotor (521). In the embodiments shown in Figs 6a and 6b the first diverted flow is indicated by a black arrow (511). In embodiment where the pulper has a round cross section, like in Fig 6b, the first diverted flow (511) can, due the curvature of the wall, be directed partly towards the surface (509) of the suspension. In some embodiments a second divert or diverting element (502) diverts at least part of the first diverted flow (511) further towards the surface (509) of the suspension, creating a second diverted flow identified in Figs 6a and 6b by a black arrow (512). In some embodiments a fourth flow divert or diverting element (504) is fitted on the side facing the circular rotation (520) motion of the suspension of the first (501) and / or the second (502) flow divert element. In some embodiments a third divert of diverting element (503) diverts at least part of the second diverted flow (512) at the level of the surface (509) of the suspension towards a reject outlet (507, 508). In Figs 6a and 6b this third diverted flow is marked with a black arrow (513). In some embodiments the third flow divert element (503) has an open bottom or a significant section, or sections, of its bottom open, allowing part of the suspension in the third diverted flow (513) to separate, or descent, towards the bottom of the primary pulper (524) and thus being removed from the third diverted flow (513) before it reaches the reject outlet (507, 508). This separated flow is marked in Fig 6a and 6b with white arrow (515). The reject flow from the primary pulper (524) to the secondary pulper (505) via the reject outlet (507, 508) is marked in Figs 6a and 6b with a black arrow (514). In Figs 6a and 6b the distance which the diverted flows (511, 512, 513) travel before reaching the reject outlet (507, 508) is marked with dashed lines (S1, S2, S3). In some embodiments it is beneficial to increase this total distance (S1+S2+S3). In some embodiments only a specific part or parts of the diverted flow distance is optimized. In some embodiments the distance (S1) the first diverted flow (511) travels is optimized, in other embodiments the distance (S2) the second diverted flow (512) travels is optimized and some embodiments the distance (S3) the third diverted flow (513) travels is optimized. In some embodiments each of the distances is optimized. In some embodiments the distance the first diverted flow travels (S1) is 6-17% of the total perimeter of the vessel (506) which in embodiments where the vessel (506) has a round cross section and the diverted flow is diverted along the round wall the circular section, the first distance (S1) would be 20° - 60° of the whole 360° circumference of a circle. In other embodiments the distance the second diverted flow travels (S2) is 6-17% of the total perimeter of the vessel (506), or 20° - 60° in case of round cross section with circular divert direction and in some embodiments the distance the third diverted flow travels (S3) is 6-33% of the total perimeter of the vessel (506) or in case of round cross section with circular divert direction, 20° - 120°. In some embodiments the total distance (S) is 22-67% of the total perimeter of the vessel (506) or in case round cross section with circular divert direction, 80° - 240°. The angle and percentage values describe the distance the flow diverting elements divert the flow along the circumferential length of the pulper (524, 505, 11, 12) or vessel (101). At the same time, the flow divert elements (501, 502) can also divert the flow in the direction of the axis of the horizontal pulper (524, 505, 11, 12). First and second flow divert elements (501, 502) can be made of one plate or two separate plates. Especially in horizontally aligned cylindrical pulper both the first and the second flow divert elements (501, 502) are beneficially made of integrally one plate. In some embodiments the first (S1) and second (S2) the travelling distances of the diverted flows are optimized by placing divert elements on the opposite sides of the pulper vessel either or both in the longitudinal and axial direction. In some embodiments the reject outlet from the primary pulper (524) to the secondary pulper (505) is one or more holes (507) in a partition wall (561) separating the primary pulper (524) and the secondary pulper (505). In some embodiments the hole is created by cutting off a segment of the partition wall (561) or by using a partition wall (561) element with a specific segment missing when the apparatus is manufactured. In some embodiments the total area of reject outlet hole or holes (507) is 2-10% of the total area of the cross section in primary pulper (524) in a longitudinal direction. Above some embodiments of the invention is described using the flow from the primary pulper (524) to a secondary pulper (505) as an example, but it is understood that similar approach can be used also in context for any consecutive pulpers, e.g. from a secondary pulper to a tertiary pulper. Fig.5 shows a flowchart of an embodiment of a method (400) according to the invention for processing a suspension. The detailed behavior of the flows and possible different embodiment options are not described in detail in the context of method as those have been already explained in context of the apparatus. It is clear for a person skilled in the art that the described method can be modified according to what is presented in the context of the apparatus. In one embodiment of an invention a suspension in an apparatus comprising a vessel with at least one reject outlet located at the surface level of suspension and a rotor equipped to flush the suspension is processed by diverting, by a flow guide located at the proximity of the wing of a rotor, at least a part of a flow to the reject outlet. In some embodiment of a method according to the invention the method (400) is divided into the steps explained below. It is noted that some embodiments might not comprise all the steps and in some embodiments some of the steps are in different order than presented below. In the first step (401) at least part of a flow at a proximity of a wing of a rotor is diverted by a flow guide, for example by a tip of the first divert element. This interferes with the flow patterns at the residual accumulation zone and thus reduces the accumulation of the lighter unwanted material in the residual accumulation zone and allows parts of the lighter material already at the residual accumulation zone to exit the residual accumulation zone. In the second step (402) the flow diverted in the first step (401) is further diverted, by the first divert element, away from the rotor at least in the radial direction. In some embodiments this direction is towards the walls of the vessels, rather than towards top or bottom of the vessel, but depending on the orientation of the rotor in relation to the vessel, radial direction could also be toward top or bottom of the vessel. The direction does not need to be only to the radial direction as the direction might have also have two other directional components. In some embodiments the diverted flow will move also in the direction of the rotation of the rotor, e.g. to tangential direction, and / or in the direction of the rotors rotational axis. In some embodiments the flow in the axis direction is towards the surface of the suspension, but for example in embodiments where the wings of the rotors are significantly above the bottom of the vessel the flow could also be towards the bottom of the vessel. In the third step (403) the diverted flow is further diverted, by a second divert element, towards the surface of the suspension. As described in the connection of the Fig. 3, in some embodiment the flow directed towards the surface of the suspension can be further guided by directing it with an additional element or elements limiting its possibilities to move towards the rotor in a radial direction. These additional elements could also limit the interaction between the diverted flow and the general suspension flow. In the fourth step (404) the diverted flow is further diverted or directed by a third divert element towards the reject outlet. As described in the connection of the Fig. 3, in some embodiment a part of the flow directed in the direction of the reject outlet, preferably the heavier material in the diverted flow, are diverted (405) towards the bottom of the vessel via opening or opening in the third divert element. In the fifth step (406) the diverted flow reaching the reject outlet, or a significant part of it is diverted to the reject outlet and via it outside the vessel. The flow exiting the vessel preferably comprising of significant amounts of lighter unwanted material. Thus, this method results in increased operation efficiency of the apparatus as the accumulation of the lighter unwanted material at the residual accumulation zones is reduced. Even though explained above in specific order, the different steps could also be carried out in a different order. In some embodiments the process is continuous, meaning that all the steps are carried out repeatedly and continuously. The foregoing description has provided by way of non-limiting examples of particular implementations and embodiments of the invention a full and informative description of the best mode presently contemplated by the inventors for carrying out the invention. It is however clear to a person skilled in the art that the invention is not restricted to details of the embodiments presented above, but that it can be implemented in other embodiments using equivalent means without deviating from the characteristics of the invention. Furthermore, some of the features of the above-disclosed embodiments of this invention may be used to advantage without the corresponding use of other features. As such, the foregoing description should be considered as merely illustrative of the principles of the present invention, and not in limitation thereof. Hence, the scope of the invention is only restricted by the appended patent claims.

Claims

Claims 1. A flow guide (110) for a suspension processing apparatus (100), characterized in that the flow guide (110) comprising: a first flow divert element (201) located inside a vessel (101) of the apparatus (100) equipped to divert at least a part of a flow at a residual accumulation zone (301) of a rotor (102) of the apparatus (100) to a direction increasing the diverted flow’s radial distance from the rotor (102), a second flow divert element (202) equipped to divert at least a part of the flow (211) from the first flow divert element (201) towards the surface (109) of the suspension and a third flow divert element (203) equipped to divert at least a part of the flow (212) from the second flow divert element (202) towards a reject outlet (108a, 108b).

2. The flow guide (110) according to the claim 1, characterized in that the flow guide further comprising: a fourth flow divert element (204) fitted on a rotor facing side of the second flow divert element (202).

3. The flow guide (110) according to any of the claims 1 to 2 characterized in that the flow guide further comprising: At least one opening (303) to allow heavier material in the flow (213) diverted by the third flow divert element (203) to fall towards the bottom of the vessel (101) of the processing apparatus (100) before such heavier material reaches the reject outlet (108a, 108b).

4. The flow guide (110) according to any of the claims 1 to 3 characterized in that the width of the second flow divert element (202) in the radial direction of the rotor is greater than 0.1 of a diameter of the vessel (101) of the processing apparatus (100), preferably 0.15±0.05 of the diameter of the vessel (101).

5. An apparatus (100) for processing a suspension, characterized in that the apparatus comprising: a vessel (101) with at least one reject outlet (108a, 108b) located at least at the surface level (109) of the suspension when the apparatus (101) is operational, a rotor (102) equipped to flush the suspension and at least one flow guide (110) located inside the vessel (101) at a residual accumulation zone (301) of the rotor (102) and the flow guide (110) being equipped to divert at least a part of a flow at the residual accumulation zone (301) of the rotor to the reject outlet (108a, 108b).

6. The apparatus (100) according to the claim 5 characterized in that the flow guide (110) comprising: a first flow divert element (201) located inside a vessel (101) of the apparatus (100) equipped to divert at least a part of a flow at the residual accumulation zone (301) of the rotor (102) to a direction increasing the radial distance of the diverted flow from the rotor (102), a second flow divert element (202) equipped to divert at least a part of the flow from the first flow divert element (201) towards the surface (109) of the suspension and a third flow divert element (203) equipped to divert at least a part of the flow from the second flow divert element (202) towards the reject outlet (108a, 108b).

7. The apparatus (100) according to the claims 5 or 6 characterized in that the flow guide (110) further comprising: a fourth flow divert element (204) fitted on a rotor facing side of the second flow divert element (202).

8. The apparatus (100) according to any of the claims 5 to 7 characterized in that the apparatus (100) is equipped with at least one opening (303) to allow the heavier material in the flow diverted by the third flow divert element (203) to fall towards the bottom of the vessel (101) before such heavier material reaches the reject outlet (108a, 108b).

9. The apparatus (100) according to any of the claims 5 to 8 characterized in thatthe apparatus (100) is a pulper arranged to screen a suspension containing fibrous material, such as recycled paper, carton or cardboard.

10. The apparatus (100) according to any of the claims 5 to 9 characterized in that the apparatus further comprising a harvesting device (108b) partially submerged to the suspension for mechanical removal of unwanted objects present at the surface (109) or near the surface (109) of the suspension.

11. A method (400) for processing a suspension in an apparatus comprising a vessel with at least one reject outlet located at the surface level of the suspension and a rotor equipped to flush the suspension characterized in that the method comprising diverting by a flow guide located inside the vessel at the residual accumulation zone of a rotor at least a part of a flow at the residual accumulation zone of a rotor to the reject outlet.

12. The method (400) according to the claim 11 characterized in that the method further comprising: diverting (401, 402) by a first flow divert element at least a part of the flow at the residual accumulation zone of a rotor to a direction increasing the radial distance of the diverted flow from the rotor, diverting (403) by a second flow divert element at least a part of the flow from the first flow divert element towards the surface of the suspension and diverting (404) by a third flow divert element at least a part of the flow from the second flow divert element towards the reject outlet.

13. The method (400) according to any of the claims 11 to 12 characterized in that the method further comprising: diverting (405) heavier material in the flow diverted by the third flow divert element to fall towards the bottom of the vessel before such heavier material reaching the reject outlet.

14. The method (400) according to any of the claims 11 to 13 characterized in that the method further comprising: processing a suspension containing fibrous material, such as recycled paper, carton or cardboard.

15. The method (400) according to any of the claims 11 to 14 characterized in that the method further comprising: mechanically removing unwanted objects by a harvesting device partially submerged to the suspension.

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