Leaf filter for filtering alumina slurry and control method thereof

Abstract

The invention belongs to the technical field of aluminum oxide production, and particularly provides a leaf filter for filtering aluminum oxide slurry and a control method thereof.The method comprises the steps that a flocculating agent is added into the aluminum oxide slurry, the temperature of the aluminum oxide slurry is adjusted to a preset temperature interval, and the pH value of the aluminum oxide slurry is adjusted to a preset pH value interval; determining the viscosity and the suspended matter content of the aluminum oxide slurry, and adjusting the filtering parameters of the leaf filter based on the viscosity and the suspended matter content so as to filter the aluminum oxide slurry; in the aluminum oxide slurry filtering process, a pulse type backwashing device in the leaf filter is started to wash a composite filtering medium in the leaf filter every first time interval; and in the first time interval, based on the inlet pressure, the outlet pressure and the outlet filtrate flow of a filter chamber in the leaf filter, judging whether to start a pulse type backwashing device to wash the composite filter medium or not. According to the technical scheme provided by the invention, the stability of the leaf filter for filtering the aluminum oxide slurry can be improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of alumina production, and particularly relates to a leaf filter for filtering alumina slurry and a control method thereof. BACKGROUND

[0002] In the alumina production process, filtering and refining of alumina slurry is a key link, and the effect of refining directly affects the quality and yield of alumina products. However, in the prior art, the filtering precision of the traditional leaf filter is insufficient, and it is difficult to effectively intercept alumina slurry with fine particles, colloids and many impurity ions, resulting in high content of solid suspended matter in the refined alumina slurry and low colloidal removal rate. In addition, the filtering efficiency is also low, and it is difficult to match the processing capacity and filtering speed of the leaf filter in high-load production, often causing alumina slurry to accumulate in the leaf filter, thereby causing the production to slow down. The adaptability of the traditional leaf filter is also poor, and swelling or hardening phenomenon is easy to occur when the pH value and temperature of the alumina slurry change, resulting in increased filtering resistance, frequent parameter adjustment, and poor production stability. Therefore, how to improve the stability of the leaf filter in filtering alumina slurry is a technical problem to be solved. SUMMARY

[0003] Embodiments of the application provide a leaf filter for filtering alumina slurry and a control method thereof, thereby improving the stability of the leaf filter in filtering alumina slurry.

[0004] Other characteristics and advantages of the application will become apparent from the detailed description that follows, or can be learned by practice of the application.

[0005] According to a first aspect of the embodiments of the application, a leaf filter for filtering alumina slurry is provided, characterized in that the leaf filter comprises: a filtering chamber for prolonging the residence time of alumina slurry in the leaf filter; a composite filter medium arranged in the filtering chamber for filtering impurities in the alumina slurry; and a backwashing system connected with the filtering chamber for washing impurities attached to the composite filter medium.

[0006] In some embodiments of the application, based on the foregoing scheme, the leaf filter further comprises: a plurality of filtering units arranged inside the filtering chamber for carrying the composite filter medium; and a deflector arranged at the bottom of the filtering chamber for guiding the flow of the alumina slurry to prevent the alumina slurry from being retained in the filtering chamber.

[0007] In some embodiments of the application, based on the foregoing scheme, a sealing element is arranged between each adjacent filtering unit, and the sealing element is used to prevent the alumina slurry from channeling.

[0008] In some embodiments of the present application, based on the foregoing scheme, the composite filter medium comprises: a coarse filter layer composed of high-strength polyester fiber woven mesh, used for preliminarily filtering particulate impurities in the alumina slurry; a fine filter adsorption layer composed of nano-titanium dioxide and activated carbon, used for removing colloidal and ionic impurities in the alumina slurry; and a support layer composed of a support material with pores, used for supporting the coarse filter layer and the fine filter adsorption layer.

[0009] In some embodiments of the present application, based on the foregoing scheme, the composite filter medium further comprises: a first transition layer arranged between the coarse filter layer and the fine filter adsorption layer, used for providing a transition for the change in pore size between the coarse filter layer and the fine filter adsorption layer; and a second transition layer arranged between the fine filter adsorption layer and the support layer, used for providing a transition for the change in pore size between the fine filter adsorption layer and the support layer.

[0010] In some embodiments of the present application, based on the foregoing scheme, the backwashing system comprises: a pulse backwashing device used for controlling deionized water or compressed air to flush the composite filter medium; pressure sensors respectively arranged at the inlet and outlet of the filter chamber, used for detecting the inlet pressure and outlet pressure of the filter chamber; and a flow sensor arranged at the outlet of the filter chamber, used for detecting the outlet filtrate flow of the filter chamber.

[0011] According to a second aspect of the embodiments of the present application, a control method of the leaf filter machine is provided, and the method is characterized in that the method comprises: adding a flocculating agent to the alumina slurry, adjusting the temperature of the alumina slurry to a preset temperature range, and adjusting the pH value of the alumina slurry to a preset pH value range; determining the viscosity and suspended matter content of the alumina slurry, and adjusting the filtration parameters of the leaf filter machine based on the viscosity and suspended matter content of the alumina slurry, so as to filter the alumina slurry according to the filtration parameters; during the filtering of the alumina slurry, every interval of a first time interval, starting the pulse backwashing device in the leaf filter machine to flush the composite filter medium in the leaf filter machine; and within the first time interval, based on the inlet pressure, outlet pressure, and outlet filtrate flow of the filter chamber in the leaf filter machine, determining whether to start the pulse backwashing device to flush the composite filter medium.

[0012] In some embodiments of the present application, based on the foregoing scheme, the filtration parameters comprise the filtration pressure and filtration speed of the leaf filter machine, and the adjusting of the filtration parameters of the leaf filter machine based on the viscosity and suspended matter content of the alumina slurry comprises: if the viscosity of the alumina slurry is greater than a preset viscosity threshold, then the filtration pressure of the leaf filter machine is adjusted to be lower; and if the suspended matter content of the alumina slurry is greater than a preset suspended matter content, then the filtration speed of the leaf filter machine is adjusted to be lower.

[0013] In some embodiments of the present application, based on the foregoing scheme, the determining whether to start the pulse backwash device to wash the composite filter medium based on the inlet pressure, the outlet pressure and the outlet filtrate flow of the filter chamber in the leaf filter comprises: determining the pressure difference between the inlet pressure and the outlet pressure, if the absolute value of the pressure difference is greater than a preset pressure difference, then starting the pulse backwash device to wash the composite filter medium; if the outlet filtrate flow is less than a preset flow threshold, then starting the pulse backwash device to wash the composite filter medium.

[0014] In some embodiments of the present application, based on the foregoing scheme, the method further comprises: if the number of times of starting the pulse backwash device to wash the composite filter medium in the first time interval is greater than a first preset number of times, then adjusting the first time interval to be lower; if the number of times of starting the pulse backwash device to wash the composite filter medium in the first time interval is less than a second preset number of times, then adjusting the first time interval to be higher, the first preset number of times being greater than the second preset number of times.

[0015] In some embodiments of the present application, based on the foregoing scheme, the flocculating agent comprises polyaluminum chloride and polyacrylamide, the preset temperature range is 60-80℃, and the preset pH value range is 9-11.

[0016] Based on the technical scheme provided in the present application, firstly, the residence time of the alumina slurry in the leaf filter is prolonged through the filter chamber, so that the fine particles, colloids and impurity ions in the slurry have more sufficient time to contact the composite filter medium, increasing the chances of impurities being intercepted and adsorbed, thereby being able to solve the problem of insufficient filtering precision of the traditional leaf filter and difficulty in effectively removing impurities, and further being able to improve the stability of alumina slurry filtration. Secondly, through the backwash system, the accumulated impurities on the composite filter medium are cleaned, which can avoid the filter medium from being frequently clogged, reduce the interruption of the filtration process caused by cleaning the clogging, enable the filtration process to continue and proceed stably, thereby being able to improve the filtration efficiency, solve the problem of mismatch between the processing capacity and the filtration speed during high-load production, and the problem of slurry backlog, and further being able to guarantee the continuity and stability of production.

[0017] It should be understood that the foregoing general description and the following detailed description are only exemplary and explanatory, and cannot limit the present application. BRIEF DESCRIPTION OF DRAWINGS

[0018] The accompanying drawings, which are incorporated herein and constitute part of the specification, illustrate embodiments consistent with the application and, together with the description, further serve to explain the principles of the application. It is to be understood that the drawings are only schematic, and that they do not necessarily correspond to the actual relative sizes of the components. In the drawings: Figure 1 A schematic block diagram of a filter chamber in one embodiment of the application is shown; Figure 2 A schematic block diagram of a composite filter medium in one embodiment of the application is shown; Figure 3 A flow chart of a leaf filter machine control method in one embodiment of the application is shown. DETAILED DESCRIPTION

[0019] The technical solutions in the embodiments of the application will be described clearly and completely below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are only some of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by a person of ordinary skill in the art without creative effort are within the protection scope of the application.

[0020] In addition, the described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided to give a thorough understanding of embodiments of the application. However, one of ordinary skill in the related art will recognize that the application can be practiced without one or more of the specific details, or with other methods, components, devices, steps, etc. In other instances, well-known methods, devices, implementations, or operations are not shown or described in detail to avoid obscuring aspects of the application.

[0021] The block diagrams shown in the drawings are only functional entities, and do not necessarily correspond to physically independent entities. That is, the functional entities can be implemented in the form of software, or in one or more hardware modules or integrated circuits, or in different network and / or processor devices and / or microcontroller devices.

[0022] The flow charts shown in the drawings are only exemplary illustrations, and do not necessarily include all contents and operations / steps, nor are they necessarily executed in the described order. For example, some operations / steps can be further divided, and some operations / steps can be combined or partially combined, so that the actual execution order can be changed according to actual conditions.

[0023] It should also be noted that the terms "first", "second", etc. in the specification and claims of the present application and in the above drawings are used to distinguish similar objects, and do not necessarily have to be used to describe a specific order or sequence. It should be understood that the objects thus used can be interchanged under appropriate circumstances, so that the embodiments of the present application described herein can be implemented in an order other than that illustrated or described.

[0024] In the alumina production process, filtering and refining of alumina slurry is a key link, and the effect of refining will directly affect the quality and yield of alumina products, but in the prior art, the filtering precision of the traditional leaf filter is insufficient, it is difficult to effectively intercept the alumina slurry with fine particles, colloids and many impurity ions, so that the solid suspended matter content of the refined alumina slurry is high, and the colloidal removal rate is low; in addition, the filtering efficiency is also low, and the processing capacity and filtering speed of the leaf filter are difficult to match during high-load production, often causing alumina slurry to accumulate in the leaf filter, thereby causing the production to slow down; the adaptability of the traditional leaf filter is also poor, and swelling or hardening phenomenon is easy to occur when the pH value and temperature of the alumina slurry change, resulting in increased filtering resistance, frequent parameter adjustment is required, and the production stability is poor. Based on this, the present application proposes a leaf filter for filtering alumina slurry and a control method thereof to improve the stability of the leaf filter for filtering alumina slurry.

[0025] Next, the leaf filter for filtering alumina slurry proposed in the present application will be described in detail. Figure 1 The leaf filter for filtering alumina slurry proposed in the present application will be described in detail.

[0026] Referring to Figure 1 , a schematic block diagram of a filtering chamber in an embodiment of the present application is shown, the leaf filter can at least include a filtering chamber, a composite filter medium and a backwashing system, wherein the filtering chamber can be used to prolong the residence time of the alumina slurry in the leaf filter, the composite filter medium is arranged inside the filtering chamber and can be used to filter impurities in the alumina slurry; the backwashing system is connected with the filtering chamber and is used to flush the impurities attached to the composite filter medium.

[0027] In the present application, the backwashing system can specifically include a pulse backwashing device, a pressure sensor and a flow sensor, wherein the pulse backwashing device can be used to control deionized water or compressed air to flush the composite filter medium; the pressure sensor is arranged at the inlet and outlet of the filtering chamber respectively and can be used to detect the inlet pressure and outlet pressure of the filtering chamber; the flow sensor is arranged at the outlet of the filtering chamber and can be used to detect the outlet filtrate flow of the filtering chamber.

[0028] In the present application, the impurities accumulated on the composite filter medium are cleaned through the backwashing system, which can avoid the frequent clogging of the filter medium, reduce the interruption of the filtration process caused by cleaning the clogging, and enable the filtration process to continue stably, thereby improving the filtration efficiency, solving the problem of mismatch between the processing capacity and the filtration speed during high-load production, and avoiding the accumulation of slurry, and further ensuring the continuity and stability of production.

[0029] In the present application, the residence time of the alumina slurry in the leaf filter is prolonged by the filter chamber, so that the fine particles, colloids and impurity ions in the slurry have more sufficient time to contact the composite filter medium, increasing the opportunity for impurities to be trapped and adsorbed, thereby solving the problem of insufficient filtration precision of the traditional leaf filter and difficulty in effectively removing impurities, and further improving the stability of the alumina slurry filtration.

[0030] In addition, the leaf filter can further include a plurality of filter units and a flow guide plate, the plurality of filter units are arranged inside the filter chamber and can be used to carry the composite filter medium; the flow guide plate is arranged at the bottom of the filter chamber and can be used to guide the flow of the alumina slurry to prevent the alumina slurry from being retained in the filter chamber.

[0031] In the present application, the filter chamber is provided with a quick-release clamp and a filter chamber top cover with a sealing groove, which can be used to open the filter chamber and replace the damaged composite filter medium in time, and can also be used to seal the filter chamber to avoid leakage of filtration pressure during the filtration process, resulting in reduced filtration effect.

[0032] In the present application, the width of the flow guide plate is 50mm at the inlet of the filter chamber and 20mm at the outlet end of the filter chamber, forming a gradually narrowing wedge-shaped structure, and the flow guide plate is further provided with an inclination angle of 15° to 20°, so that the flow rate of the alumina slurry in the flow guide plate gradually increases, thereby avoiding the alumina slurry from being retained in the filter chamber, and further avoiding the deposition of impurities in the filter chamber to cause clogging of the filter chamber.

[0033] In the present application, a sealing element is arranged between each adjacent filter unit, which can be a fluororubber sealing ring with a size of 500mm x 500mm x 100mm, which can be used to prevent the alumina slurry from flowing, and specifically, the leakage rate of the alumina slurry in the filter unit can be less than 0.1%; in addition, the filter units are arranged in a cross-flow manner along the flow guide plate, so that the alumina slurry can flow along the flow guide plate in an "S" shape, thereby prolonging the residence time of the alumina slurry in the filter chamber to some extent, and improving the filtration effect and stability of the alumina slurry.

[0034] In the present application, the composite filter medium is carried by multiple filter units, which can make the distribution of the filter medium more uniform, and also can increase the filtering area, thereby improving the retention capacity of impurities in the alumina slurry, and helping to further reduce the impurity content in the slurry. In addition, by modularizing the filter units, the number of filter units can be flexibly adjusted according to the processing capacity of the alumina slurry in actual production, thereby improving the adaptability of the leaf filter to different processing capacities of the slurry and the filtering efficiency.

[0035] Further, please refer to Figure 2 , which shows a schematic block diagram of the composite filter medium in an embodiment of the present application, as Figure 2 shown, the composite filter medium can at least include a coarse filter layer, a fine filter adsorption layer and a support layer, wherein the fine filter adsorption layer is composed of a high-strength polyester fiber woven mesh with a pore size of 50 μm to 100 μm, a thickness of 2 mm to 3 mm, and a surface treated by hydrophobic treatment, which can be used to preliminarily filter particle impurities with a particle size greater than or equal to 20 μm.

[0036] Continuing to refer to Figure 2 , the fine filter adsorption layer is a porous membrane composed of nano-titanium dioxide (particle size of 20 mm to 50 nm) and activated carbon (specific surface area of 1500 m² / g to 2000 m² / g), with a thickness of 0.5 mm to 1 mm, which can remove colloidal and ionic impurities in the alumina slurry by physical retention and chemical adsorption. Specifically, the physical retention method is to throttle part of the colloidal impurities by a pore size of 1 μm to 5 μm, and the chemical adsorption method is to degrade organic impurities by nano-titanium dioxide and to adsorb ionic impurities by activated carbon. In some specific embodiments of the present application, the adsorption capacity of the composite filter medium for silica colloids can reach 50 mg / g to 80 mg / g, and the removal rate of impurity ions such as iron ions and lead ions can reach more than 95%.

[0037] Continuing to refer to Figure 2 , the support layer is composed of porous ceramic (alumina content greater than 95%, porosity 40% to 50%, compressive strength greater than or equal to 100 MPa), with a thickness of 5 mm to 8 mm, which can be used to provide structural support for the coarse filter layer and the fine filter adsorption layer to ensure that the coarse filter layer and the fine filter adsorption layer do not deform under a filtering pressure of 0.5-1.0 MPa.

[0038] In the present application, by setting the coarse filter layer, the larger particle impurities in the alumina slurry are preliminarily filtered, and then the colloidal and ionic impurities are removed by the fine filter adsorption layer, and finally the support layer supports the coarse filter layer and the fine filter adsorption layer to prevent them from deforming due to the filtration pressure. In this way, by the three-layer composite filter medium, most of the impurities in the alumina slurry can be effectively filtered, the filtering effect is improved, and at the same time, the deformation or damage of the filter medium under high pressure filtration can be prevented, thereby improving the stability of the alumina slurry filtration.

[0039] With reference to the foregoing Figure 2 , the composite filter medium can further include a first transition layer and a second transition layer, wherein the first transition layer can be composed of a fiber material coated with 5-10 microns, which can be used to provide a transition for the pore size change between the coarse filter layer and the fine filter adsorption layer, so as to avoid the excessive pore size change between the coarse filter layer and the fine filter adsorption layer, which can cause the decrease of the filtering efficiency, and the second transition layer can be composed of a transition slurry sprayed, the transition slurry is composed of Al2O3, SiO2 and ZrO2, and the specific composition ratio is Al2O3:SiO2:ZrO2=6:3:1, which can be used to provide a transition for the pore size change between the fine filter adsorption layer and the support layer.

[0040] In the present application, by setting the first transition layer and the second transition layer, a smooth transition is provided for the pore size change between the layers of the composite filter medium, which can avoid the blocking of the slurry flow or the excessive local filtration pressure caused by the sudden change of the pore size, so that the slurry can flow more smoothly through the composite filter medium, thereby improving the filtering efficiency and stability of the alumina slurry, and ensuring that the tiny impurities can be effectively filtered.

[0041] Next, the control method of the leaf filter proposed in the present application will be described in detail. Figure 3

[0042] Please refer to Figure 3 , a flow chart of the leaf filter control method in an embodiment of the present application is shown, wherein the control method can be executed on the leaf filter as described above, and the method can specifically include the following S1-S4: S1, a flocculating agent is added to the alumina slurry, and the temperature of the alumina slurry is adjusted to a preset temperature range, and the pH value of the alumina slurry is adjusted to a preset pH value range.

[0043] S2, the viscosity and suspended matter content of the alumina slurry are determined, and the filtering parameters of the leaf filter are adjusted based on the viscosity and suspended matter content of the alumina slurry, so that the alumina slurry is filtered according to the filtering parameters.

[0044] ​S3, during the filtering of the alumina slurry, every first time interval, start the pulse backwash device in the leaf filter to wash the composite filter medium in the leaf filter.

[0045] S4, during the first time interval, based on the inlet pressure, outlet pressure, and outlet filtrate flow of the filtering chamber in the leaf filter, determine whether to start the pulse backwash device to wash the composite filter medium.

[0046] In the present application, the preset temperature range can be 50-80℃, the preset pH value range can be 9-11, the flocculant can be polyaluminum chloride (PAC), polyacrylamide (PAM), etc., and can be determined according to actual needs, which is not limited in the present application.

[0047] In the present application, the composite filter medium in the leaf filter is washed by the pulse backwash device, which can be gas backwash, i.e. using 0.8-1.2 MPa compressed air, pulse frequency 5-10 Hz, single backwash time 0.5-1 second, which can strip more than 90% of the filter cake attached to the surface of the filter medium, or liquid backwash, i.e. using deionized water or recycled filtrate to wash, pressure 0.3-0.5 MPa, using a rotating spray head (speed 200-300 r / min) to spray deionized water or recycled filtrate, which can cover an area of 100%.

[0048] In the present application, the flocculant can make the small particles and colloidal substances in the alumina slurry coagulate into larger flocs, so as to facilitate subsequent filtration, and adjusting the alumina slurry to the preset temperature range and preset pH value range can make the alumina slurry be in a more favorable condition for filtration, for example, a suitable temperature can reduce the viscosity of the alumina slurry, so that it has good fluidity to facilitate filtration, and a suitable pH value can make the flocculant be in the best action environment, improve the effect of the flocculant, and also can avoid part of the impurities to precipitate or dissolve at a specific pH value, thereby ensuring the stability of the filtration process and the consistency of the filtration effect.

[0049] In the present application, viscosity and suspended solids content are important physical property indicators of alumina slurry, which can directly affect the ease and effect of alumina slurry filtration, and by measuring the viscosity and suspended solids content of the alumina slurry, the current state of the slurry can be comprehensively understood, providing data support for subsequent adjustment of filtration parameters.

[0050] In the present application, the filtration parameters such as filtration pressure, filtration speed, filtration time, etc. are adjusted according to the viscosity and the content of suspended solids of the slurry, so that the filtration process can be more suitable for the characteristics of the slurry; reasonable adjustment of the filtration parameters can ensure that stable filtration effects can be obtained for the slurry under different conditions, ensure that the quality of the refined alumina slurry meets the production requirements, and avoid problems such as incomplete filtration or damage to the filtration medium caused by unreasonable filtration parameters.

[0051] In the present application, during the filtration process, the composite filtration medium will be gradually blocked by impurities in the alumina slurry, resulting in increased filtration resistance and decreased filtration efficiency, and regular backwashing can reduce the accumulation and adhesion of impurities on the filtration medium, thereby avoiding damage to the filtration medium caused by impurities, prolonging the service life of the filtration medium, reducing the operating cost of the equipment, and improving the stability of the alumina slurry filtration.

[0052] In the present application, by monitoring the inlet pressure, outlet pressure and outlet filtrate flow of the filtration chamber in real time, the working state of the filtration medium and the change of the filtration process can be understood in time, and when these parameters change abnormally, it indicates that the filtration medium may have been blocked by impurities, at which time the pulse backwashing device is started in time to flush the filtration medium, which can avoid further increase of the filtration resistance and further decrease of the filtration efficiency, and ensure the stable operation of the filtration process of the alumina slurry.

[0053] In the above S2, the filtration parameters of the leaf filter are adjusted based on the viscosity and the content of suspended solids of the alumina slurry, which can be performed according to the following S21 to S22: S21, if the viscosity of the alumina slurry is greater than a preset viscosity threshold, the filtration pressure of the leaf filter is adjusted to be lower.

[0054] S22, if the content of suspended solids of the alumina slurry is greater than a preset content of suspended solids, the filtration speed of the leaf filter is adjusted to be lower.

[0055] In the present application, when the viscosity of the alumina slurry is greater than the preset viscosity threshold, the filtration pressure of the leaf filter can be adjusted to 0.1 MPa to 0.15 MPa, so as to avoid rapid clogging of the filter holes of the filtration medium caused by excessive pressure, and as the filtration proceeds, if the filtrate flow decreases significantly, the pressure is gradually increased to 0.3 MPa to 0.3 MPa.

[0056] In the present application, if the content of suspended solids of the alumina slurry is greater than a preset content of suspended solids, the filtration speed of the leaf filter can be adjusted to 0.5 L / (m²·min) to 1 L / (m²·min), and the flocculation time can also be appropriately prolonged before filtration to enhance the flocculation effect.

[0057] In the present application, when the viscosity of the alumina slurry is greater than the preset viscosity threshold value, the flowability of the slurry becomes poor, and under a higher filtration pressure, the slurry may not pass through the filter medium smoothly, easily causing the formation of an excessively thick filter cake on the surface of the filter medium, and even a local blockage phenomenon. Reducing the filtration pressure can reduce the resistance of the slurry passing through the filter medium, making the filtration process more stable, avoiding interruption of the filtration or equipment failure due to excessive pressure, and ensuring the continuity and stability of the filtration process.

[0058] In the present application, when the suspended solids content in the alumina slurry is greater than the preset suspended solids content, it means that there are more impurities in the slurry. If the filtration speed is too fast, the impurity particles do not have enough time to contact the filter medium, and part of the impurities may pass through the filter medium with the filtrate, causing incomplete filtration. Reducing the filtration speed can make the slurry stay on the surface of the filter medium for a longer time, increase the contact opportunity of impurities with the filter medium, improve the retention capacity of the filter medium for impurities, ensure that more impurities are removed, and improve the filtration effect. At the same time, in the process of rapid filtration of high-suspended solids content slurry, impurities are easily quickly accumulated on the surface of the filter medium, forming a dense filter cake layer, causing the filtration resistance to increase sharply, and even causing the filter medium to be completely blocked. Therefore, reducing the filtration speed can slow down the accumulation speed of impurities on the surface of the filter medium, which is beneficial to the discharge of the filtrate and reduces the risk of filter medium blockage, prolonging the service life of the filter medium.

[0059] In the above S4, the inlet pressure, outlet pressure, and outlet filtrate flow of the filtration chamber in the leaf filter are used to determine whether to start the pulse backwash device to wash the composite filter medium, which can be performed according to the following S41 to S42: S41, determine the pressure difference between the inlet pressure and the outlet pressure, if the absolute value of the pressure difference is greater than the preset pressure difference, then start the pulse backwash device to wash the composite filter medium.

[0060] S42, if the outlet filtrate flow is less than the preset flow threshold value, then start the pulse backwash device to wash the composite filter medium.

[0061] In the present application, the preset pressure difference can be 1.5 to 2 times the pressure difference when starting to run, for example, when the pressure difference when starting to run is 0.05 MPa, the preset pressure difference can be 0.075 MPa to 0.1 MPa, and the present application does not make specific limitations.

[0062] In the present application, the preset flow threshold value can be 70% to 80% of the filtrate flow when starting to run, for example, when the filtrate flow when starting to run is 50 m³ / h, the preset flow threshold value can be 35 m³ / h to 40 m³ / h, and the present application does not make specific limitations.

[0063] In the present application, when the filter medium is gradually blocked by impurities in the alumina slurry, the resistance of the slurry through the filter medium increases, and the difference between the inlet pressure and the outlet pressure (absolute value of pressure difference) also increases. By setting a preset pressure difference, when the absolute value of the pressure difference is greater than the preset value, the pulse backwash device is started in time to quickly remove the impurities blocked in the pores of the filter medium, restore the permeability of the filter medium, and ensure that the filtration process continues stably.

[0064] In the present application, the outlet filtrate flow should be maintained within a relatively stable range under normal operation. When the filter medium is blocked or the filtration process is abnormal, the outlet filtrate flow will decrease significantly. If the outlet filtrate flow is less than a preset flow threshold, the pulse backwash device is started to remove the impurities blocked in the pores of the filter medium in time, restore the permeability of the filter medium, and ensure that the filtration process continues stably.

[0065] Further, the control method of the leaf filter according to the present application can also be executed as follows S5 to S6: S5, if the number of times of starting the pulse backwash device to flush the composite filter medium is greater than a first preset number of times within the first time interval, the first time interval is adjusted to be lower.

[0066] S6, if the number of times of starting the pulse backwash device to flush the composite filter medium is less than a second preset number of times within the first time interval, the first time interval is adjusted to be higher, and the first preset number of times is greater than the second preset number of times. In the present application, the first time interval can be 8 hours or 7 hours, and the specific value can be determined according to actual production requirements. The present application does not make specific limitations on this.

[0067] In the present application, the first preset number of times can be 5 times or 6 times, and the second preset number of times can be 2 times or 1 time. The specific value can be determined according to actual production requirements. The present application does not make specific limitations on this.

[0068] In the present application, the clogging of the filter medium during the filtration of the alumina slurry varies with factors such as time and slurry composition. When the number of times of starting the pulse backwashing device in the first time interval is greater than the first preset number of times, it indicates that the clogging speed of the filter medium is relatively fast, and the existing backwashing time interval is insufficient to effectively maintain the permeability of the filter medium. Therefore, the first time interval can be adjusted to be lower, and the backwashing frequency can be increased, so that the impurities clogging in the filter medium can be removed more timely, the excessive accumulation of impurities can be prevented to cause a significant decrease in the filtration effect, and the quality of the refined alumina slurry can be ensured to be stable. In the first time interval, if the number of times of starting the backwashing system is less than the second preset number of times, it indicates that the clogging of the filter medium is relatively light, and the current backwashing frequency can be too high. The first time interval can be adjusted to be higher, and the number of times of backwashing can be appropriately reduced, so that the filtration effect can be ensured to be unaffected, and unnecessary wear of the filter medium caused by excessive backwashing can be avoided.

[0069] Next, the leaf filter for filtering alumina slurry and the control method thereof proposed in the present application will be described in combination with some specific embodiments.

[0070] Embodiment 1: A new type of leaf filter with a filtration area of 100 m² is adopted. The initial parameters of the alumina slurry used in the experiment are as follows: solid suspended substance (SS) content 80 mg / L, colloid content 30 ppm, pH value 10.2, temperature 75 °C, and sodium aluminate concentration 120 g / L.

[0071] Slurry pretreatment: polyaluminum chloride (PAC) with a concentration of 600 mg / L and polyacrylamide (PAM) with a concentration of 80 mg / L are added to the slurry, and the slurry is stirred for 15 minutes. The temperature of the slurry is adjusted to 70 °C, and the pH value is adjusted to 10.

[0072] Filtration process: The filtration pressure is set to 0.1 MPa and the filtration speed is 1.2 L / (m²·min) at the beginning of the filtration. As the filtration proceeds, the pressure is increased by 0.05 MPa every 20 minutes until it reaches 0.3 MPa. The intelligent control system monitors the filtrate flow, pressure, and solid suspended substance (SS) concentration in real time, and dynamically adjusts the parameters.

[0073] Filtration precision: After refinement, the solid suspended substance (SS) content in the slurry is reduced to 4.8 mg / L, the colloid content is reduced to 8 ppm, and the Fe³⁺ concentration is reduced from 0.15 mg / L to 0.06 mg / L, reaching the expected precision improvement target.

[0074] Filtration efficiency: The average filtration speed reaches 3.8 L / (m²·min), and the processing time for each ton of slurry is 0.42 hours, which is much higher than the efficiency of traditional leaf filters.

[0075] Operating cost: After single filtration, the performance of the filter medium does not decrease obviously; the water consumption of backwashing is 4.2% of the filtration amount, which is reduced by more than 60% compared with the traditional equipment.

[0076] Example 2: Two kinds of alumina slurry with different properties are selected, and the same new leaf filter with a filtration area of 50 m² is used to carry out a comparative experiment, and the specific parameters are as follows: Table 1 Parameters of alumina slurry with different properties Slurry A treatment: Because the SS and colloidal content are high, the initial filtration pressure is set to 0.1 MPa, the filtration speed is 0.8 L / (m²·min), and the backwashing time interval is shortened to 6 hours. The final filtration speed is stabilized at 1.5 L / (m²·min), the SS of the refined slurry is reduced to 7.2 mg / L, the colloidal content is reduced to 10 ppm, and the requirements of the subsequent process are met. Slurry B treatment: The conventional parameters are used, the initial pressure is 0.12 MPa, and the speed is 1.2 L / (m²·min). The filtration process is smooth, the average filtration speed reaches 2.2 L / (m²·min), the SS of the refined slurry is reduced to 3.5 mg / L, the colloidal content is reduced to 6 ppm, and the requirements of the subsequent process are met. Through the experiment, it can be concluded that the leaf filter and the control method thereof can improve the adaptability of the filter press to alumina slurry with different parameters, and thus the stability of the alumina slurry filtration can be improved.

[0077] Example 3: In the same alumina slurry treatment scenario, a new leaf filter (filtration area 100 m²) and a traditional plate and frame leaf filter (filtration area 100 m²) are used for comparison, the initial SS content of the slurry is 75 mg / L, the colloidal content is 28 ppm, and the temperature is 70°C. Comparison of experimental results Table 2 Comparison of filtration parameters of the new leaf filter and the traditional plate and frame leaf filter As can be seen from Table 2, first, the filtration speed and the processing time per ton of slurry of the new leaf filter are better than those of the traditional plate and frame leaf filter, which indicates that the new leaf filter has high filtration efficiency. Second, the SS content and colloidal removal rate of the refined slurry of the new leaf filter are higher than those of the traditional plate and frame leaf filter, which indicates that the new leaf filter has better filtration effect. Finally, the filter material life and the water consumption of backwashing of the new leaf filter are better than those of the traditional plate and frame leaf filter, which indicates that the new leaf filter has lower filtration loss.

[0078] The above merely provides an example of the present application, and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present application shall fall into the scope of claims of the present application.

Claims

1. A leaf filter for filtering alumina slurry, characterized in that: The leaf filter comprises: a filter chamber for extending the residence time of the alumina slurry in the leaf filter; A composite filter medium is disposed in the filter chamber and is used to filter impurities in the alumina slurry; A backwashing system is connected to the filter chamber and is used to flush impurities attached to the composite filter medium.

2. The leaf filter according to claim 1, characterized in that The leaf filter also includes: a plurality of filter units disposed inside the filter chamber and configured to carry the composite filter medium; The guide plate is arranged at the bottom of the filter chamber and is used to guide the flow of the aluminum oxide slurry to prevent the aluminum oxide slurry from being retained in the filter chamber.

3. The leaf filter according to claim 2, characterized in that A seal is provided between each adjacent filter unit, and the seal is used to prevent the aluminum oxide slurry from flowing across.

4. The leaf filter according to claim 1, characterized in that The composite filter medium comprises: A coarse filter layer, composed of a high-strength polyester fiber woven mesh, for preliminarily filtering particulate impurities in the alumina slurry; A fine filtration adsorption layer, composed of nano-titanium dioxide and activated carbon, for removing colloidal and ionic impurities in the alumina slurry; The support layer is composed of a support material with pores and is used to support the coarse filtration layer and the fine filtration adsorption layer.

5. The leaf filter according to claim 4, characterized in that The composite filter medium further comprises: A first transition layer is provided between the coarse filter layer and the fine filter adsorption layer, and is used to provide a transition for the pore size change between the coarse filter layer and the fine filter adsorption layer; The second transition layer is arranged between the fine filtration adsorption layer and the support layer, and is used to provide a transition for the pore size change between the fine filtration adsorption layer and the support layer.

6. The leaf filter according to claim 1, characterized in that The backwash system comprises: A pulse backwashing device for controlling deionized water or compressed air to flush the composite filter medium; pressure sensors, respectively disposed at the inlet and outlet of the filter chamber, for detecting the inlet pressure and outlet pressure of the filter chamber; The flow sensor is arranged at the outlet of the filter chamber and is used to detect the outlet filtrate flow of the filter chamber.

7. A control method for a leaf filter according to any one of claims 1 to 6, characterized in that: The method comprises: S1, adding a flocculant to the alumina slurry, adjusting the temperature of the alumina slurry to a preset temperature range, and adjusting the pH value of the alumina slurry to a preset pH range; S2, determining the viscosity and suspended matter content of the alumina slurry, and adjusting the filtration parameters of the leaf filter based on the viscosity and suspended matter content of the alumina slurry to filter the alumina slurry according to the filtration parameters; S3, during the filtering of the alumina slurry, starting the pulse backwashing device in the leaf filter at every first time interval to flush the composite filter medium in the leaf filter; S4, within the first time interval, based on the inlet pressure, outlet pressure, and outlet filtrate flow rate of the filter chamber in the leaf filter, determining whether to start the pulse backwashing device to flush the composite filter medium.

8. The method according to claim 7, characterized in that The filtration parameters include the filtration pressure and filtration speed of the leaf filter, and the filtration parameters of the leaf filter are adjusted based on the viscosity and suspended matter content of the alumina slurry, including: S21, if the viscosity of the alumina slurry is greater than a preset viscosity threshold, lowering the filtration pressure of the leaf filter; S22: If the suspended matter content of the alumina slurry is greater than a preset suspended matter content, the filtration speed of the leaf filter is reduced.

9. The method according to claim 7, characterized in that The determining whether to start the pulse backwashing device to flush the composite filter medium based on the inlet pressure, outlet pressure, and outlet filtrate flow of the filter chamber in the leaf filter includes: S41, determining a pressure difference between the inlet pressure and the outlet pressure, and if the absolute value of the pressure difference is greater than a preset pressure difference, starting the pulse backwashing device to flush the composite filter medium; S42: If the outlet filtrate flow rate is less than a preset flow rate threshold, start the pulse backwashing device to flush the composite filter medium.

10. The method according to claim 7, characterized in that The method further comprises: S5, within the first time interval, if the number of times the pulse backwashing device is activated to flush the composite filter medium is greater than a first preset number, reducing the first time interval; S6. Within the first time interval, if the number of times the pulse backwashing device is started to flush the composite filter medium is less than a second preset number, increase the first time interval, and the first preset number is greater than the second preset number.

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