CN116099280A - Method for separating fines in a slurry - Google Patents

Abstract

The present invention relates to a method for separating fines in a slurry, the method comprising: passing the slurry comprising fines through a pressure separation screen for preliminary separation, returning the filtrate fraction of the slurry under the pressure separation screen to the fiber washing step; the portion of the slurry located on the pressure separation screen is passed into a holding tank of a vacuum rotary filtration system for filtration, the fines in the slurry forming a cake on the outer surface of the flexible filter medium of the vacuum rotary filtration system, wherein in a discharge section the filter medium is vibrated or at least locally deformed such that the cake formed on its outer surface is detached.

Description

Method for separating fines in a slurry

Technical Field

The present invention relates generally to a method for separating fines in a slurry. More particularly, the present invention relates to a process for filtering and separating fines present in chemical, wastewater treatment, paper, fuel, wastewater treatment, power plant desulfurization, and zein dehydration. More precisely, the invention is applicable to the separation of fines produced in a corn wet milling process.

Background

Today, there are problems in separating fines from pulp in a number of processes, including in chemical, sewage treatment, paper making, fuel, sewage treatment, power station desulfurization, and zein dewatering. The following is described by way of example, but the application of the present invention is not limited thereto. Common methods for preparing corn starch in the corn starch preparation process include a corn starch wet milling method, which mainly comprises: the corn kernels are first steeped and then coarsely ground and finely ground to initially separate the starch, fiber and other components. In addition, the use of oven dried corn or corn steep times can result in more fines. The resulting fibers are then subjected to a preliminary wash separation in which a portion of the fines are entrained with coarser fibers, thereby being separated together and subsequently extruded into a fiber extruder and/or dried into a dryer. However, due to the extremely small size, another portion of the fines may be entrained with the wash fluid and cannot be separated as the wash fluid is returned to the fiber wash separation system. The presence of fines in the fiber washing system can result in accumulation in the washing system, reducing the washing efficiency and allowing the water content of the dewatered fiber cake to remain high. Another portion of fines can accumulate in various parts of the system, clog filter media or lines, or increase the viscosity of the material to be filtered, greatly reducing the separation effect, resulting in a reduction in the throughput of the overall system. On the other hand, the fine fibers carry more bound starch, and the fine fibers are easy to flow out along with the filtrate in the rapid extrusion process, so that the loss of active ingredients is caused, and the yield of the whole process is reduced.

Some methods for separating or discharging fines have been proposed in the prior art, such as CN102174759B. One common way is to achieve the discharge of fines by reducing the rotational speed of the fibre press dewaterer. As mentioned above, for example, in a corn wet milling process, the fibers are free from starch particles under the action of a fine grinding impact and washed through a fiber washing station to screen out free starch adhering to the fibers and then dewatered in a fiber press dehydrator. The normal operating speed of the fibre press dewaterer is typically 12 rpm, at which most of the fines will be returned to the washing step as the washing liquid leaves the press dewaterer, so that the fines accumulate in the fibre washing station, thereby increasing the viscosity of the system and reducing the capacity of the system. In order to avoid and/or reduce the amount of fines carried by the wash liquid leaving the press dewaterer, the dewatering time is increased by reducing the rotational speed of the fiber press dewaterer, allowing to slow down the extrusion speed of the slurry into the extruder, avoiding that the fines leave the extruder at the large pore size screen in the early stages of extrusion. As the extrusion proceeds, the moisture of the material gradually decreases, and the mesh size becomes smaller, so that the possibility that the fine fibers flow out with the filtrate is reduced, and the possibility that the fine fibers are carried to the discharge end by the large fibers and enter the drying section is increased.

Such a solution reduces the amount of fines carried by the wash liquor to a certain extent, but still does not completely solve the problem that fines flow out or accumulate with the wash liquor, and the extrusion dewatering time is prolonged due to the reduced rotational speed, resulting in a low system throughput. If most of the fine fibers are required to be discharged, a plurality of fiber extrusion dehydrators are required to achieve the ideal effect, and the cost and the space requirement are greatly increased.

Additional solutions include the use of plate and frame filters to separate and reject fines. The working principle of the plate-and-frame filter press is filter pressing dehydration, namely, a slurry consisting of solid and liquid phases is filtered by a filter medium to realize solid and liquid separation. The slurry to be filtered enters each filter chamber from a feed hole of a rear top plate under a certain pressure by a delivery pump, and solids are trapped in the filter chambers through filter cloth and gradually form filter cakes; the filtrate is discharged out of the machine through the water outlet holes on the plate frame. The fiber which is washed by the fiber washing station and is free of starch enters a fiber extrusion dehydrator to be dehydrated, and then the dehydrated fiber enters a subsequent dryer to be dried; and the discharged liquid carrying the fine fibers is separated by a pressure screen, so that the fine fibers with 90% of water on the pressure screen enter a plate-and-frame filter, filter cakes of the fine fibers are obtained by filter pressing and dehydration of the plate-and-frame filter, and the generated filtrate is returned to a fiber washing station or subjected to acid preparation and needs further treatment to prevent environmental pollution. The filter cake of the thus obtained fines has a water content of up to about 70% and is mixed with the fibres discharged from the press dehydrator and fed to a dryer for drying.

Although the proposal of adopting the plate-and-frame filter can separate out the fine fibers, the separated fine fibers have higher water content, and a great deal of steam is consumed for drying in the subsequent operation. In addition, the plate and frame filter has complex operation and high labor intensity. Moreover, the fine fibers are easy to block the filter cloth, especially the pores of the filter cloth are blocked and cannot be separated from the filter cloth, so that the filtering efficiency is greatly reduced. Therefore, the filter cloth needs to be replaced after a certain time, otherwise, the filtering effect cannot be achieved.

In the prior art, a horizontal decanter centrifuge is also used to centrifugally separate out fine fibers. The principle of the horizontal decanter centrifuge is that the sedimentation velocity of particles in liquid is accelerated by using the strong centrifugal force generated by the high-speed rotation of a centrifuge rotor, and substances with different sedimentation coefficients and buoyancy densities in materials are separated. Therefore, a strong centrifugal force is required to force the particles to overcome the diffusion and create a settling motion. Such decanter centrifuges comprise a cylinder, called a bowl, which rotates at high speed about its own axis, typically driven by an electric motor. After entering the rotary drum, the suspension (or emulsion) is quickly driven to rotate at the same speed as the rotary drum, and the components are separated from each other under the action of centrifugal force and are discharged respectively. In general, the higher the rotation speed of the drum, the better the separation effect.

The slurry carrying the fine fibers enters a decanter centrifuge, the slurry is separated and dehydrated by the decanter centrifuge, the generated filtrate is returned to a fiber washing station, or the filtrate is subjected to acid making and further treatment is needed to prevent environmental pollution, and the generated solid is the fine fibers. The resulting fine fiber solids have a water content of up to about 70% and are mixed with the fibers discharged from the press dehydrator and dried in a dryer.

However, the current use of such centrifugal devices is not ideal, mainly because of the very small amount that can be handled and the very high costs, and the water content of the filter cake obtained is also up to about 70%.

Disclosure of Invention

The present invention has been made to solve the above-mentioned problems occurring in the prior art, and provides a method for separating fine fibers in slurry, which allows to obtain a fine fiber cake having a low water content, and is capable of preventing clogging of a filter medium, improving filtration and separation efficiency, and stably operating with low operation strength, thereby greatly reducing costs and achieving high production efficiency.

The present invention relates to a method for separating fines in a slurry, the method comprising:

passing the slurry comprising fines through a pressure separation screen for preliminary separation, returning the filtrate fraction of the slurry under the pressure separation screen to the fiber washing step;

the portion of the slurry located on the pressure separation screen is passed into a holding tank of a vacuum rotary filtration system for filtration, the fines in the slurry forming a cake on the outer surface of the flexible filter medium of the vacuum rotary filtration system, wherein in a discharge section the filter medium is vibrated or at least locally deformed such that the cake formed on its outer surface is detached.

By means of the method of the invention, the fine fibers in the slurry can be effectively separated with lower cost and smaller space, the loss of effective components is prevented, the filter cake with reduced water content is allowed to be obtained, and the cost and the energy consumption are saved.

According to one embodiment of the invention, wherein the vacuum rotary filter system comprises a rotatable body and a cake removing device for removing a cake from the filter medium mounted on the rotatable body, the cake removing device comprising:

an actuation mechanism for actuating at least a portion of the filter media, the actuation mechanism configured to actuate at least a portion of the filter media in a discharge section during at least one cycle such that the at least a portion of the filter media protrudes outwardly, and to cease actuating the filter media after the cycle, causing the filter media to quickly resume shape such that the cake on the filter media is detached from an outer surface of the filter media by vibration or deformation of the filter media.

By actuating the filter media to disengage the filter cake, the discharge can be effectively performed without additional washing or corrective action, and damage or clogging of the filter media is avoided.

According to one embodiment of the invention, wherein the actuation mechanism comprises:

a gas supply for supplying a gas, operatively fluidly connected to an inner side of the filter medium facing an outer surface of the rotatable body;

a control mechanism for controlling the supply of gas from the gas supply source;

wherein when the filter medium is rotated to a discharge section, gas is supplied to the inside of the filter medium during at least one period and is stopped at the end of the period, causing the filter medium to bulge outwardly during the period and to rapidly resume deformation after the period, thereby causing the filter cake to disengage from the outer surface of the filter medium, wherein the period does not exceed 10 seconds, or is between 5 seconds and 10 seconds, even below 5 seconds.

By supplying gas to the inside of the filter medium, the filter medium is caused to bulge slightly outwards, while the filter cake still tends to remain in place, so that the filter cake is easily detached from the filter medium. With the cake removing device in the present invention, even a material having a relatively high viscosity can be applied to the vacuum rotary filter system because it is dried during the filtration process and the gas is blown from inside to outside toward the pores of the filter medium, forcing the material out of the pores of the filter medium, and even a viscous material or a material including very fine fibers does not cause clogging of the pores of the filter medium, thereby achieving good filtration and separation effects.

In addition, the filter medium from which the filter cake has been removed does not need to undergo a washing operation by the action of the gas, thereby omitting the mechanism and process associated with the washing operation, simplifying the mechanism, saving the cost, and not causing pollution to the environment due to the discharge of the washing residual liquid.

According to one embodiment of the invention, the gas is supplied to the inner side of the filter medium in a radially outward direction of the rotatable body.

According to one embodiment of the invention, the gas is supplied to the inside of the filter medium intermittently two or more times, so that the filter medium in the discharge section vibrates two or more times, the amplitude of the filter medium in the radial direction being at most 5 cm. Preferably, the amplitude of the filter medium is at most 2 cm, or even more preferably 1 cm.

According to one embodiment of the invention, the method further comprises further drying the filter cake detached from the filter medium.

According to one embodiment of the invention, the method comprises feeding filtrate produced in the vacuum rotary filtration system to a gas-liquid separator for gas-liquid separation.

According to one embodiment of the invention, the size of the fines is less than 1.8 mm.

According to one embodiment of the invention, the size of the fines is between 75 micrometers and 1.8 millimeters.

According to one embodiment of the invention, the size of the fines is between 50 and 75 microns.

According to one embodiment of the invention, the method is used in a corn wet milling process to treat pulp after treatment by an extrusion dewaterer.

According to one embodiment of the invention, the water content of the filter cake formed by the vacuum rotary filter system is below 54%, and the thickness of the filter cake is between 1 and 2.2 mm.

According to one embodiment of the invention, the water content of the filter cake formed by the vacuum rotary filter system is between 39% and 48%.

According to another aspect, the invention also relates to a corn wet milling process comprising a method as described above, wherein the pulp comprising fines is a pulp produced by passing through a fibre press dewaterer.

The process of the invention allows fine fibers in slurry to be separated, thus obtaining a product with better quality, greatly reducing the problems caused by the fine fibers on a system, reducing the water content in a filter cake, obviously saving the cost and improving the economic benefit.

Other forms, objects, features, aspects, advantages, and other embodiments of the present invention will become apparent from the detailed description and the accompanying drawings provided herein.

Drawings

The disclosure of the present invention will become more apparent with reference to the accompanying drawings. It is to be understood that these drawings are solely for purposes of illustration and are not intended as a definition of the limits of the invention. In the drawings:

fig. 1 is a schematic block diagram of a corn starch wet milling process according to the prior art.

Fig. 2 is a schematic diagram of a corn starch wet milling process including a method for separating fines according to the present invention.

Fig. 3 is a schematic block diagram of a method for separating fines according to the invention.

FIG. 4 is a schematic diagram of a vacuum rotary filtration system according to one embodiment of the invention.

Detailed Description

In the drawings, like reference numerals designate identical or functionally equivalent elements unless otherwise indicated. The various elements shown in the drawings are not necessarily drawn to scale and are intended to clearly illustrate the principles of the invention. Although the method for separating fine fibers is described in the present invention by way of example of a corn wet milling process, the scope of the present invention is not limited to this process. The invention is applicable to any application where it is desired to separate fines.

Fig. 1 is a general schematic of a corn starch wet milling process according to the prior art. In general, the corn starch wet milling process mainly comprises: the corn kernels are first steeped S1, then coarsely ground S2 and finely ground S3 to initially separate the starch, fiber and other components, and then the ground product is fiber washed S4. Fines are produced during both the rough grinding S2 and the fine grinding S3. The fibers produced during the coarse and fine grinding include coarser fibers and fines, wherein the size of the fines may even reach less than 1.8 mm, or between 75 and 1.8 mm, or even between 50 and 75 microns.

The washed product is then fed to a press dehydrator for dewatering S5, the separated slurry L is returned to the washing system, and the solids S resulting from the press dewatering are fed to a dryer for drying S6 to further reduce the water content thereof. Finally the resulting product is packaged S7. Some existing processes also include feeding the slurry L produced by dewatering S5 to a plate and frame filter or centrifuge to separate out fines from the slurry, however, the effect is not ideal and there are still problems.

To this end, the invention proposes a method for separating fines in a slurry. As shown in fig. 2-3, for the dewatered slurry L described above, it is first passed through a pressure separation screen, which may be a 50 micron pressure separation screen or a suitable pressure separation screen selected as desired, for preliminary pressure screen separation S8. The filtrate fraction of the slurry L, which is located under the pressure separation screen, is returned to the fiber washing system for washing S4. At the same time, the portion of slurry L (material to be filtered 300) located on the pressure separation screen is passed into a holding tank 102 of a vacuum rotary filtration system 100 (as shown in fig. 4) for further filtration S9. The fines in this section form a filter cake 301 on the outer surface of the flexible filter medium 105 of the vacuum rotary filter system. In the discharge section, the filter medium is vibrated or at least locally deformed, so that the filter cake 301 formed on its outer surface is detached. The formed cake 301 is dried again after being detached from the filter medium S6. Preferably, the filter cake 301 may be dried together with the solids S previously produced in the press dehydrator after mixing. The water content of the filter cake 301 produced by the method of the present invention is significantly reduced. The filtrate 302 of the vacuum rotary filtration system is sent to a gas-liquid separator for gas-liquid separation S10, the separated gas may be pumped out via a vacuum pump 111, and the resulting liquid fraction may be entered into a washing system via a filtrate pump 112 or subjected to an acid making operation.

The present invention also proposes an improved vacuum rotary filtration system. A vacuum rotary filter system 100 according to the invention is described in detail below in connection with fig. 4, and mainly comprises a rotatable body 101, a drive mechanism (not shown in the figure) for driving the rotatable body in rotation in a direction of rotation R, a reservoir 102 for receiving a material to be filtered and a corresponding pipe system. The rotatable body 101 is typically provided in the form of a drum or drum. The rotatable body 101 is divided in the radial direction D into several filter sectors 103, each of which may be arranged as desired to perform different functions, e.g. in the direction of rotation a cake forming section, a washing section, a dewatering drying section, a vacuum releasing section, a discharging section etc. Each sector may be provided with a separate channel and a distribution head in communication with the channel. As the rotatable body 101 rotates in the direction of rotation R, these channels can be in turn in fluid communication with the vacuum tube and the compressed air tube by means of the dispensing head, so that each sector surface can be subjected to the operating steps of filtering, washing, drying, blowing loose, unloading, etc. in turn during one revolution.

The outer surface of the rotatable body 101 is provided with a support member for securing the filter medium 105, which may be in the form of a grid or mesh and made of metal, plastic or any other suitable material. The filter medium 105 covers and is fixed on the outer side of the support member to rotate together with the rotatable body 101. The filter media 105 may generally be any suitable flexible filter media such as a filter cloth, screen, or membrane. When rotated to be positioned in the holding tank 102, the filter medium 105 draws the material 300 to be filtered, typically a slurry comprising particles or fibers, from the holding tank 102 and in a subsequent sector is separated into a cake 301 and filtrate 302 by a vacuum, drying operation, or the like. The filter cake 301 formed on the outer surface of the filter media 105 is released from the filter media 105 at the discharge section 104 for subsequent processing. Filtrate 302 is drawn from rotatable body 101 via tubing and filtrate pump 112 for gas-liquid separation by gas-liquid separator 110.

The prior art generally uses a doctor blade or flexible pleated filter cloth discharge to remove the formed filter cake. A scraper 106 is provided near the discharge section 104 so that the resulting filter cake 301 is scraped off the filter medium 105. The flexible pleated filter cloth discharge mode mainly consists in arranging several discharge rollers 107 near the discharge section 104 to achieve the detachment of the filter cake 301 by changing the direction of movement of the filter medium.

As mentioned above, such doctor blades and flexible flaps have a number of disadvantages. The invention aims to improve the discharging mode in the prior art and provide a more environment-friendly, more efficient and simpler full-automatic discharging mode.

A schematic of a vacuum rotary filtration system 100 capable of continuous filtration according to the present invention is shown in fig. 4, comprising a cake removal device 200 according to the present invention and a device for treating filtrate 302. The filtrate 302 filtered by the filter medium 105 is sent to a gas-liquid separator for gas-liquid separation, and then sent to a processing apparatus of the next step via a filtrate pump 112.

The cake removal device 200 comprises an actuation mechanism 201 for actuating at least a portion of the filter medium 105, which is configured to actuate at least a portion of the filter medium 105 or even all of the filter medium located in the discharge section 104 during at least one period T, such that the filter medium 105 may protrude outwardly, e.g. in the radial direction D, and immediately after that period T, to stop actuating at least a portion of the filter medium 105, such that the filter medium may resume its shape rapidly. By virtue of the inertia of the filter cake 301 itself and the sudden small amplitude of vibration of the filter media 105 during this period T, the filter cake 301 is allowed to disengage from the outer surface of the filter media into the adjustable cake guide rail 205 to continue with subsequent processing steps. The cake guide rail 205 is used to guide the filter cloth away from the rotatable body and its angle can be adjusted to obtain a desired cake exit direction.

Preferably, after an interval t from stopping the last actuation, the actuation mechanism 201 may again repeatedly actuate at least a portion or even all of the filter media 105 to facilitate complete disengagement of the filter cake. The actuation mechanism 201 may be actuated once, twice or more as needed to ensure that the filter cake 301 is effectively disengaged from the filter media. The interval t may be not more than 10 seconds, for example in the range of 2-5 seconds.

The actuation mechanism 201 may actuate at least a portion or even all of the filter media 105 in any suitable manner, including pneumatically, mechanically, etc. An embodiment employing pneumatic means is shown in fig. 4, wherein the actuation mechanism 201 comprises a gas supply 202 for supplying a gas, which may be a compressed gas or any suitable fluid. The gas supply 202 is operably fluidly connected to the inside of the filter medium 105, i.e., the side facing the outer surface of the rotatable body 101. The actuation mechanism 201 further includes a control mechanism 203 for controlling the supply of gas from the gas supply source to start or stop the supply of gas from the gas supply source 202, control the amount of gas supplied, and the like. When the filter medium is rotated to the discharge section, the control mechanism 203 is configured to supply gas to the inside of the filter medium 105 during a period T, causing deformation of the filter medium, in particular a radially outward protrusion, and to stop the supply of gas at the end of the period T, so that the filter medium 105 quickly resumes its shape. The amplitude of the filter medium in the radial direction D during deformation is at most 5 cm, typically 2 cm or 1 cm. The filter cake 301 breaks away from the outer surface of the filter media during this period T and enters the filter cake guide rail 205. The period T may be very short, for example not exceeding 10 seconds, or preferably between 5 seconds and 10 seconds, even below 5 seconds. The period T may be adjusted according to specific needs. The control mechanism 203 may also be configured to intermittently repeat the gas supply two or more times such that the filter medium is actuated or at least partially deformed two or more times to facilitate rapid and efficient separation of the filter cake.

Filter cake removal device 200 may include an on-off valve for controlling the supply of gas. Gas from the gas supply 202 may be delivered to the gas port 108 on the rotatable body via the on-off valve 204 and tube and then through the suction filter tube 109 to the inside of the filter media 105. Fig. 4 schematically illustrates a portion of rotatable body 101 and filter media 105 on its outer surface. The gas may be delivered to the holes 113 on the outside of the rotatable body in the direction indicated by the arrows in fig. 4, although only one hole is shown, one or more holes may be arranged as desired. Through this aperture 113, the gas may act in a radially outward direction on the filter medium 105 to deform it, e.g., to create a "bulge" effect. Then, when the gas supply is stopped, the filter medium 105 resumes its shape and returns to the original position.

In addition, during the supply of gas, the gas flow may act radially outward against the pores of the filter medium 105 such that even if the pores of the filter medium are plugged with fibers or particles in the filter material, the continuous gas flow forces those particles or fibers present in the pores out of the filter medium, thereby unblocking the pores of the filter medium, enabling good filtration and separation efficiency to be achieved. Accordingly, the cake removing device 200 according to the present invention can be well adapted to viscous materials that easily clog filter media, without additional washing and cleaning operations of the filter media, as compared to a doctor blade or flexible pleated filter cloth discharge mode.

By treating the slurry L by means of the vacuum rotary filter system disclosed by the invention, fine fibers in the slurry can be effectively separated, and meanwhile, the loss of active ingredients is greatly reduced. By separating out the fines in the slurry, the clogging in the system, which may be caused by the fines, is also greatly improved, especially because the fines clog the pores of the filter cloth, so that the service life of the filter cloth is significantly prolonged. On the other hand, the present invention also allows to obtain a fine filter cake with a significantly reduced water content compared to the solutions of the prior art, thereby reducing the steam required in the subsequent drying operations, greatly reducing the costs and increasing the production efficiency.

In addition, the fiber washing effect in the fiber washing station can be improved by using the method for separating fine fibers in the present invention. The experimental data of the applicant prove that the fiber washing temperature can be reduced by 2-3 ℃, and the content of fibrin and starch in washing liquid is respectively reduced from 12% and 18% before to below 10% and 16%, so that the product yield is effectively increased, and considerable benefits are obtained. Conventionally, in order to improve the fiber washing effect, an enzyme preparation is usually added to a washing station. In the present invention, however, by improving the fiber washing effect, the use of an enzyme preparation can be allowed to be omitted or reduced, thereby further saving costs.

In particular, the water content of the fine fiber filter cake produced according to the method of the invention may reach below 54% or below 50% compared to the water content of 70% in the prior art, more preferably between 43% and 48%.

Further description will be provided below in connection with specific examples of the present invention.

Example 1

The laboratory experimental device is adopted to simulate the operation of a vacuum drum filter to filter and separate fine fibers, wherein the vacuum degree is-0.08 MPa, the suction filtration time is 120 seconds, and the dehydration time is 120 seconds. The thickness of the filtered fine fiber filter cake is 1.5-2 mm, the water content is reduced to 43% -60%, and the water content of about 70% can be only realized under the same condition by using a plate-frame filter or a horizontal decanter centrifuge in the prior art.

Example 2

The pulp containing fine fibers is filtered by a vacuum drum filter with a filtering area of 1 square meter, wherein the rotating speed of the drum is 0.1 rpm, and the vacuum degree is-0.08 MPa. The thickness of the filtered fine fiber filter cake is 1.5-2.5-mm, the water content is reduced to 43% -48%, and the water content of about 70% can be only realized under the same condition by using a plate-frame filter or a horizontal decanter centrifuge in the prior art.

Example 3

The pulp containing fine fibers is filtered by a vacuum rotary drum filter with the filtering area of 1 square meter, the rotating speed of the rotary drum is 0.15 rpm, and the vacuum degree is-0.05 MPa. The thickness of the filtered fine fiber filter cake is 1.25-2.25 mm, the water content is reduced to 46% -51%, and the water content of about 70% can be only realized under the same condition by using a plate-frame filter or a horizontal decanter centrifuge in the prior art.

Example 4

The pulp containing fine fibers is filtered by a vacuum rotary drum filter with the filtering area of 1 square meter, the rotating speed of the rotary drum is 0.2 rpm, and the vacuum degree is-0.05 MPa. The thickness of the filtered fine fiber filter cake is 1-2 mm, the water content is reduced to between 50% and 54%, and the water content of about 70% can be only realized under the same condition by using a plate-frame filter or a horizontal decanter centrifuge in the prior art.

Example 5

The pulp containing fine fibers is filtered by a vacuum rotary drum filter with a filtering area of 1 square meter, the rotating speed of the rotary drum is 0.25 rpm, and the vacuum degree is-0.05 MPa. The thickness of the filtered fine fiber filter cake is 1-1.8 mm, the water content is reduced to 52% -54%, and the water content of about 70% can be only realized under the same condition by using a plate-frame filter or a horizontal decanter centrifuge in the prior art.

While the invention has been described in detail with reference to the preferred embodiments, it will be understood that the invention is not limited by the examples disclosed and that many additional modifications and variations may be made thereto by those skilled in the art without departing from the scope of the invention. It should be noted that the use of "a" or "an" throughout this disclosure does not exclude a plurality, and "comprising" does not exclude other elements. Furthermore, elements described in association with different embodiments may be combined.

Claims (10)

1. A method for separating fines in a slurry, the method comprising:

passing the slurry comprising fines through a pressure separation screen for preliminary separation, returning the filtrate fraction of the slurry under the pressure separation screen to the fiber washing step;

the portion of the slurry located on the pressure separation screen is passed into a holding tank of a vacuum rotary filtration system for filtration, the fines in the slurry forming a cake on the outer surface of the flexible filter medium of the vacuum rotary filtration system, wherein in a discharge section the filter medium is vibrated or at least locally deformed such that the cake formed on its outer surface is detached.

2. A method as claimed in claim 1, wherein the vacuum rotary filtration system comprises a rotatable body and a cake removal device for removing cake from the filtration media mounted on the rotatable body, the cake removal device comprising:

an actuation mechanism for actuating at least a portion of the filter media, the actuation mechanism configured to actuate at least a portion of the filter media in a discharge section during at least one cycle such that the at least a portion of the filter media protrudes outwardly, and to cease actuating the filter media after the cycle, causing the filter media to quickly resume shape such that the cake on the filter media is detached from an outer surface of the filter media by vibration or deformation of the filter media.

3. The method of claim 2, wherein the actuation mechanism comprises:

a gas supply for supplying a gas, operatively fluidly connected to an inner side of the filter medium facing an outer surface of the rotatable body;

a control mechanism for controlling the supply of gas from the gas supply source;

wherein, upon rotation of the filter medium to a discharge section, gas is supplied to the inside of the filter medium during at least one cycle and is stopped at the end of the cycle, causing the filter medium to bulge outwardly during the cycle and to rapidly resume deformation after the cycle, thereby causing the filter cake to disengage from the outer surface of the filter medium, wherein the cycle does not exceed 10 seconds.

4. A method as claimed in claim 3, wherein the gas is supplied to the inside of the filter medium in a radially outward direction of the rotatable body.

5. A method as claimed in claim 3, wherein gas is supplied to the inside of the filter medium intermittently two or more times, so that the filter medium in the discharge section is vibrated two or more times, the amplitude of the filter medium in the radial direction being at most 5 cm.

6. The method of any of claims 1-5, wherein the method further comprises:

further drying the cake released from the filter medium, and/or

And conveying the filtrate generated in the vacuum rotary filtering system to a gas-liquid separator for gas-liquid separation.

7. The method of any of claims 1-5, wherein the size of the fines is less than 1.8 millimeters.

8. A chemical process comprising the method according to any one of claims 1-7.

9. A corn wet milling process comprising the method according to any one of claims 1-7, wherein the slurry comprising fines is a slurry produced by a fiber press dewaterer.

10. A vacuum rotary filtration system for use in the method of any one of claims 1-7.

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