Micro-fine coal dewatering process and system based on filter aid pre-coating and gradient dewatering

Abstract

The present application relates to the technical field of fine coal slime dewatering, and discloses a fine coal dewatering process and system based on filter aid pre-coating and gradient dewatering, which is used to solve the problems of filter material blockage and filter cake densification in the existing vacuum filtration of fine coal.The process adopts a strategy of "physical isolation-in-situ grading-structure protection".Firstly, a diatomite / pearlite composite rigid pre-coating layer is constructed on the filter cloth.Then, the flocculated coal slurry is transported to the pre-coating layer and left to stand, and a self-filtration structure with "coarse at the bottom and fine at the top" is constructed in situ by gravity settling.During the dewatering stage, a low vacuum degree is used to maintain the flow channel of the coarse particle layer from being blocked by fine mud, and then a high vacuum degree is switched to for deep dewatering after the skeleton is stable.Through the cooperation of each step, the present application effectively prevents the penetration and blockage of fine particles, significantly reduces the moisture content of the filter cake, and improves the dewatering efficiency.

Description

Technical Field

[0001] This invention belongs to the field of fine coal slime dewatering technology, specifically relating to a fine coal dewatering process and system based on filter aid pre-coating and gradient dewatering. Background Technology

[0002] Coal, as a primary energy source, has always held a vital position in strategic resource reserves. With the in-depth development of coal resources and the widespread application of mechanized mining, the proportion of fine coal particles is increasing, posing significant challenges to coal preparation plants. In coal preparation plants, flotation concentrate and coal slurry typically contain a large amount of fine coal particles. Dewatering these materials is a crucial step in the coal preparation process, and filter presses are commonly used dewatering equipment.

[0003] The characteristics of fine coal particles are mainly reflected in their small particle size, large specific surface area, and strong surface electronegativity. Therefore, several inherent challenges exist in the dewatering process: ① Filter pore clogging: Fine particles easily penetrate or embed themselves in the pores of the filter cloth with the water flow, causing deep clogging, leading to a sharp increase in filtration resistance and a rapid decrease in dewatering rate. ② Filter cake density: The filter cake formed by fine particles is too dense, with low porosity and poor air and water permeability, greatly weakening the subsequent vacuum suction effect. These two points together result in long dewatering cycles, low processing capacity, and high moisture content in the product filter cake, seriously affecting production efficiency and economic benefits. Existing technologies also employ chemical dosing sedimentation concentration and positive pressure dewatering using plate and frame filter presses, but most face intractable technical challenges such as filter cloth / filter cloth clogging and the inability to retain the pore structure of the filter cake due to its density. Some attempts have tried to solve this problem by improving the filter cloth material or simply increasing the vacuum level. However, improving the filter cloth is costly and only addresses the symptoms, not the root cause. Simply increasing the vacuum level can exacerbate the penetration and clogging of fine particles in the initial stages, often with the opposite effect. Therefore, there is an urgent need for a dehydration method that innovates from the perspective of process principles. Summary of the Invention

[0004] In response to the above situation, the present invention provides a dewatering process and system for fine coal based on filter aid pre-coating and gradient dewatering. It utilizes "static layering" to construct a "second adaptive filter layer" above the filter cloth and protects this loose structure from instantaneous destruction through "low vacuum", thereby solving the technical problem of "surface blockage" of fine coal.

[0005] To achieve the above objectives, this invention employs a fine-particle coal dewatering process based on filter aid pre-coating and gradient dewatering. By employing two main strategies—"physical isolation" and "structural reconstruction"—the initial conditions of the filtration process are altered, thereby solving the problem of filter cloth clogging in fine-particle coal dewatering and significantly improving the dewatering efficiency and quality. The process includes the following steps:

[0006] S1. Construction of Composite Pre-coating: Before filtering the coal slurry, a rigid, porous, coarse-particle pre-coating of a composite filter aid consisting of diatomaceous earth and perlite is uniformly pre-coated onto the clean filter cloth of the vacuum filter as a "protective layer." The particle size is larger than the pore size of the filter cloth, forming a true filtration layer on the filter cloth surface, preventing fine coal particles from directly contacting the filter cloth. Diatomaceous earth itself has high rigidity and an irregular shape, forming a high-porosity, high-permeability support structure. Perlite reduces the cost of the filter aid, and the mixed ratio of the two ensures unobstructed vacuum channels.

[0007] S2. Coal slurry flocculation conditioning: This step can also be called coal slurry pretreatment. An appropriate amount of flocculant is added to the fine coal slurry to be dewatered. Through gentle stirring, the fine particles are bridging with polymers to form larger, loosely structured flocs. This increases the apparent particle size and reduces the possibility of them clogging the pores of the pre-coating layer. It also improves the filter cake structure. The filter cake composed of flocs has larger and more numerous pores and better connectivity, which is very conducive to the rapid discharge of water.

[0008] S3. Conveying and In-situ Classification Deposition: The conditioned coal slurry is conveyed to the pre-coated layer of the filter cloth and allowed to stand for a settling time. The pre-coating layer forms a self-filtering structure with a gradient particle distribution of "coarse at the bottom and fine at the top" in situ through gravity settling; when left to stand, the coarse particles settle first and come into contact with the pre-coating layer; the fine particles settle later and are located in the upper layer.

[0009] S4. Structural protection gradient dewatering: The self-filtration structure formed on the pre-coated filter cloth is subjected to gradient dewatering treatment in two stages: low vacuum stabilization and high vacuum deep dewatering. The two steps S3 and S4 above are the key control strategies of this invention. The dehydration process no longer uses a constant high vacuum, but is divided into three stages: Settling stage of coal slurry: Before filtration, the coal slurry is allowed to settle, allowing larger coal particles to settle first, which can reduce the clogging of the filter cloth by fine coal particles to a certain extent.

[0010] Low vacuum forming stage: In the initial stage of filtration, a lower vacuum level is used. At this point, the flocculated coal slurry slowly and steadily deposits on the pre-coating layer under gentle suction, forming the initial filter cake. This stage avoids strong suction forcibly drawing in unflocculated fine particles or small flocs and damaging the pre-coating structure, ensuring the uniformity and permeability of the initial filter cake.

[0011] High vacuum dehydration stage: After the initial filter cake has formed and stabilized, switch to high vacuum. At this point, the main structure of the filter cake is finalized, the internal pore channels are stable, and the powerful vacuum suction can efficiently extract the water from the pores, achieving deep dehydration without causing the filter cake to compact or the channels to close.

[0012] S5. Dry coal slime filter cake removal: After the high vacuum deep dewatering is completed, the dry coal slime filter cake with reduced moisture content is removed, and the dewatering process is now complete.

[0013] Furthermore, the gradient dehydration treatment in the two stages of step S4 is as follows: S41, Low Vacuum Stabilization Stage: Apply the first vacuum level Duration ;in, The system is designed to maintain the filtrate flow rate below the critical seepage velocity of the lower coarse coal seam, preventing fine particles from penetrating into the lower voids or pre-coated pores under high flow rate. The low vacuum stage is not only for shaping, but also to match the permeability of the coarse particle layer, preventing the fine mud from being pulled into the gaps between coarse particles by strong suction, causing "self-clogging". S42, High Vacuum Deep Dehydration Stage: After the filter cake skeleton has set, the vacuum level is increased to the second vacuum level. Intensive dehydration, duration .

[0014] Furthermore, in step S1, the composite filter aid used is a mixture of diatomaceous earth and perlite, wherein the mass percentage of diatomaceous earth is 60%-80% and that of perlite is 20%-40%.

[0015] Furthermore, in step S2, the flocculant used is anionic polyacrylamide, and the amount of flocculant added is 100-500 grams per ton of dry coal slime.

[0016] Furthermore, in step S3, the settling time of the coal slurry... The time is 30-120 seconds, allowing the coarse coal seam formed by the sedimentation of the coarse particles to directly cover the pre-coated layer as a secondary filter cloth.

[0017] Furthermore, in step S4, the first vacuum level during the low vacuum stabilization stage... The range is to The second vacuum level in the high vacuum deep dehydration stage The range is to Duration of the low vacuum steady-flow phase The duration of the high-vacuum deep dehydration stage is 30-90 seconds. It lasts 60-180 seconds.

[0018] Furthermore, in step S42, during the middle or later stages of the high vacuum deep dehydration stage, after the filter cake skeleton has been shaped, the process also includes spraying and washing the filter cake with a detergent to replace the high-salt interstitial water in the filter cake.

[0019] This invention also provides a dewatering system for implementing the above-mentioned fine coal dewatering process. The system includes a vacuum filter for vacuum filtering the coal slurry. The lower part of the filter cylinder of the vacuum filter is provided with a filter plate covered with filter cloth. The bottom outlet of the filter cylinder is connected to a vacuum system via a negative pressure conduit. The vacuum system is a gradient vacuum system capable of automatically switching between high and low vacuum levels according to a PLC control program. It also includes a filter aid pre-coating device for uniformly coating a composite filter aid onto the filter cloth; a flocculant adding and mixing device for quantitatively adding flocculant to the coal slurry and stirring it; and a coal slurry settling zone is provided inside the filter cylinder to allow the coarse particles in the coal slurry to settle.

[0020] Furthermore, the system also includes a filter cake washing device, which includes a movable spray pipe disposed above the filter cake for uniformly spraying washing liquid onto the filter cake.

[0021] The present invention also includes other components that enable its normal use, all of which are conventional means in the art. In addition, devices or components not limited in the present invention, such as: vacuum filter and its matching filter cloth, PLC control program automatically switching high and low vacuum gradient vacuum system, filter aid pre-coating device, flocculant addition and mixing device, filter cake washing device, etc., all adopt the prior art in the art.

[0022] The beneficial effects of this invention are as follows: 1. High efficiency in preventing clogging: The pre-coating of the mixed filter aid acts as a sacrificial layer, solving the major problem of fine particles clogging the filter cloth.

[0023] 2. High dehydration rate: The porous filter cake structure formed by flocculation, combined with the gradient vacuum dehydration process, minimizes overall dehydration resistance and increases the dehydration rate compared to traditional methods. above.

[0024] 3. Low filter cake moisture: The deep dewatering stage is carried out under high vacuum, which can more effectively remove capillary water from the filter cake and effectively reduce the moisture content of the final filter cake.

[0025] 4. Flexible process: The type of filter aid, the amount of flocculant and the vacuum parameters can be flexibly adjusted according to different coal quality and particle size composition, making it highly adaptable.

[0026] 5. Good economic benefits: Compared with traditional single filter aids, mixed filter aids reduce the cost of reagents, improve the dewatering efficiency of fine coal slime, reduce energy consumption, and optimize the overall operating cost. Attached Figure Description

[0027] Figure 1 This is a flowchart of the dehydration process in this invention; Figure 2 This is a schematic diagram of the coal slurry settling device for the filter press in this invention; Figure 3 This is a schematic diagram of the filter cake structure formed by gradient dehydration in this invention. Detailed Implementation

[0028] The present invention will now be clearly described in conjunction with the accompanying drawings and specific embodiments. Any modifications, equivalent substitutions, improvements, etc., made by those skilled in the art based on the embodiments of the present invention without inventive effort to obtain all other embodiments should be included within the scope of protection of the present invention.

[0029] Example 1 like Figure 1 As shown, a dewatering process for fine coal particles based on filter aid pre-coating and gradient dewatering includes the following steps: S1. Construction of composite pre-coating: Before starting to filter coal slurry, a composite filter aid consisting of 60% diatomaceous earth and 40% perlite is uniformly pre-coated on the clean filter cloth of the vacuum filter. The average particle size of the composite filter aid is larger than the maximum pore size of the filter cloth. A rigid porous coarse particle filter aid pre-coating layer with a thickness of about 2mm is formed on the filter cloth of the vacuum filter through the pre-coating device.

[0030] S2. Coal slurry flocculation and conditioning: Before the coal slurry is transported to the filter press, an appropriate amount of anionic polyacrylamide flocculant is added to it, with an addition amount of 250 grams per ton of dry coal slurry. The mixture is then stirred and sheared for about 2 minutes, so that the fine particles can form larger, loosely structured flocs through polymer bridging.

[0031] S3. Conveying and In-situ Classification and Sedimentation: The conditioned coal slurry is conveyed to the settling area above the pre-coated filter cloth of the filter press, and the settling time is... In about 1 minute, coarse particles settle first and come into contact with the pre-coating layer; fine particles settle later and are located on the upper layer; a self-filtration structure with a gradient particle distribution of "coarse at the bottom and fine at the top" is formed in situ on the pre-coating layer, which serves as a secondary filter cloth.

[0032] S4. Structurally Protective Gradient Dewatering: After the coal slurry enters the filter plate of the filter press, a low-vacuum forming stage is initiated first, with the first vacuum degree... Controlled Duration After approximately 40 seconds, the filter cake surface was observed to be smooth and free of cracks. The principle is to maintain the filtrate flow rate below the critical seepage velocity of the underlying coarse-particle coal seam while preventing fine particles from the upper layer from penetrating into the voids or pre-coated pores of the lower layer under high flow velocity.

[0033] After 40 seconds, the system automatically switches to the high-vacuum dehydration stage, raising the vacuum level to the second vacuum level. Controlled Duration Approximately 60 seconds.

[0034] In addition, during the middle stage of high vacuum deep dehydration, after the filter cake skeleton has been shaped, the filter cake needs to be sprayed and washed with detergent.

[0035] S5. Dry coal slime filter cake removal: After the high vacuum deep dewatering is completed, the dry coal slime filter cake with reduced moisture content is removed, and the dewatering process is now complete.

[0036] A comparison of the dewatering process provided in this embodiment with the traditional fine coal dewatering process: Compared with the original constant high vacuum degree Compared with dehydration processes, the method of this invention improves the processing capacity per unit area. The filter cake moisture content was significantly reduced, and the time required for dewatering fine coal slime was significantly shortened. Compared with the pre-coated filter aid + constant high vacuum (simulating ordinary modified vacuum filtration) process and the no-pre-coating + standing + gradient vacuum process, the dewatering efficiency was significantly improved, proving that only the combination of "pre-coating" + "standing" + "gradient vacuum" can achieve the lowest filter cake moisture content and the highest dewatering rate.

[0037] Example 2 The difference from Example 1 is that, in step S1, the composite filter aid used is a pre-coated slurry made by mixing 70% diatomaceous earth and 30% perlite; in step S2, the amount of anionic polyacrylamide flocculant added is 100 grams per ton of dry coal slime; and in step S3, the coal slurry settling time is... The duration is 120 seconds; in step S4, the first vacuum level during the low vacuum stabilization phase... for Duration The second vacuum level is 90 seconds; this is the second vacuum level during the high-vacuum deep dehydration stage. for Duration It lasts for 180 seconds.

[0038] Example 3 The difference from Example 1 is that, in step S1, the composite filter aid used is a pre-coated slurry made by mixing 80% diatomaceous earth and 20% perlite; in step S2, the amount of anionic polyacrylamide flocculant added is 500 grams per ton of dry coal slime; and in step S3, the coal slurry settling time is... The duration is 30 seconds; in step S4, the first vacuum level during the low vacuum stabilization phase... for Duration The second vacuum level is 30 seconds; this is the second vacuum level during the high-vacuum deep dehydration stage. for Duration It lasts for 100 seconds.

[0039] Example 4 Based on any of the above embodiments, the present invention also provides a dewatering system for implementing the fine coal dewatering process in the above embodiments, such as... Figure 2 As shown, the dewatering system includes a vacuum filter for vacuum filtering coal slurry. The lower part of the filter cylinder 1 of the vacuum filter is provided with a filter plate 3 covered with filter cloth 2. The bottom outlet of the filter cylinder is connected to a vacuum system (not shown in the figure) through a negative pressure conduit 4. The vacuum system is a gradient vacuum system that can automatically switch between high and low vacuum levels according to a PLC control program. It also includes a filter aid pre-coating device (not shown in the figure) for uniformly coating a composite filter aid on the filter cloth; a flocculant adding and mixing device (not shown in the figure) for quantitatively adding flocculant to the coal slurry and stirring it; and a coal slurry settling zone 5 is provided inside the filter cylinder for settling the coarse particles in the coal slurry. The filter press is a vertical cylindrical structure with an open inlet at the top and a constricted outlet at the bottom. A supernatant outlet valve 6 is installed on the side wall of the coal slurry settling zone at the top of the filter press for discharging supernatant. A supernatant granular coal slurry outlet valve 7 is installed on the side wall of the filter press corresponding to the middle supernatant granular coal slurry layer for pumping out the fine granular coal slurry that has settled. A large granular coal slurry outlet valve 8 is installed on the lower side wall of the filter press for pumping out the large granular particles that have settled first. A bottom outlet valve 9 connected to a negative pressure conduit is installed at the bottom outlet of the filter press.

[0040] Example 5 Based on Example 4, the dehydration system further includes a filter cake washing device, which includes a movable spray pipe disposed above the filter cake for uniformly spraying washing liquid onto the filter cake to replace the high-salt interstitial water in the filter cake, thereby reducing the ash content of the product.

[0041] The aforementioned vacuum filter and its supporting filter cloth, PLC control program automatically switching between high and low vacuum gradient vacuum system, as well as filter aid pre-coating device, flocculant addition and mixing device, filter cake washing device, etc., all adopt existing technologies, and the specific settings will not be described in detail here.

[0042] The basic working mechanism of gradient dehydration in this invention is as follows: like Figure 3As shown, the settling time T1 of the coal slurry in the filter press must be selected to ensure that a coarse particle layer of at least 5-10 mm thickness is formed at the bottom; the end point of the low vacuum steady flow stage T2 should be determined by monitoring the filtrate flow rate or the surface condition of the filter cake; if high vacuum is turned on before the coarse particle skeleton is stable, the upper fine mud will instantly "seal off" the flow channel. This process "induces" water flow through the coarse particle layer through low vacuum, essentially using coarse coal particles as a "secondary filter aid".

[0043] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A dewatering process for fine coal particles based on filter aid pre-coating and gradient dewatering, characterized in that, Includes the following steps: S1. Pre-coating construction: First, a composite filter aid is pre-coated on the filter cloth of the vacuum filter to form a rigid porous pre-coating. S2, Coal slurry flocculation conditioning: Add flocculant to coal slurry and stir to form flocs; S3. Conveying and In-situ Classification Deposition: The conditioned coal slurry is conveyed to the pre-coated layer of the filter cloth and allowed to stand for a settling time. Through gravity settling, a self-filtering structure with a gradient particle distribution of "coarse at the bottom and fine at the top" is formed in situ on the pre-coated layer; S4. Structural protection gradient dewatering: The self-filtration structure formed on the pre-coated filter cloth is subjected to gradient dewatering treatment in two stages: low vacuum stabilization and high vacuum deep dewatering. S5. Dry coal slime filter cake removal: After the high vacuum deep dewatering is completed, the dry coal slime filter cake with reduced moisture content is removed, and the dewatering process is now complete.

2. The micro-fine coal dewatering process based on filter aid pre-coating and gradient dewatering according to claim 1, characterized in that, Step S4, the gradient dehydration process consisting of two stages—low vacuum stabilization and high vacuum deep dehydration—is as follows: S41, Low Vacuum Stabilization Stage: Apply the first vacuum level Duration ;in, The flow rate of the filtrate is set to be less than the critical seepage velocity of the lower coarse coal seam to prevent fine particles from the upper layer from penetrating into the voids or pores of the lower layer under high flow rate. S42, High Vacuum Deep Dehydration Stage: After the filter cake skeleton has set, the vacuum level is increased to the second vacuum level. Intensive dehydration, duration .

3. The micro-fine coal dewatering process based on filter aid pre-coating and gradient dewatering according to claim 1, characterized in that: In step S1, the composite filter aid used is a mixture of diatomaceous earth and perlite, wherein the mass percentage of diatomaceous earth is 60%-80% and the remainder is perlite; and the average particle size of the composite filter aid is larger than the maximum pore size of the filter cloth.

4. The micro-fine coal dewatering process based on filter aid pre-coating and gradient dewatering according to claim 1, characterized in that: In step S2, the flocculant used is anionic polyacrylamide, and the amount of flocculant added is 100-500 grams per ton of dry coal slime.

5. The micro-fine coal dewatering process based on filter aid pre-coating and gradient dewatering according to claim 1, characterized in that: In step S3, the settling time of the coal slurry The time is 30-120 seconds, allowing the coarse coal seam formed by the sedimentation of the coarse particles to directly cover the pre-coated layer as a secondary filter cloth.

6. The micro-fine coal dewatering process based on filter aid pre-coating and gradient dewatering according to claim 2, characterized in that: In step S4, the first vacuum level during the low vacuum stabilization stage... The range is to The second vacuum level in the high vacuum deep dehydration stage The range is to Duration of the low vacuum steady-flow phase The duration of the high-vacuum deep dehydration stage is 30-90 seconds. It lasts 60-180 seconds.

7. The micro-fine coal dewatering process based on filter aid pre-coating and gradient dewatering according to claim 2, characterized in that: In step S42, after the filter cake skeleton is shaped in the high vacuum deep dehydration stage, the filter cake is also sprayed and washed with detergent to replace the high-salt interstitial water in the filter cake.

8. A system for implementing the fine coal dewatering process based on filter aid pre-coating and gradient dewatering as described in any one of claims 1-7, characterized in that: The system includes a vacuum filter for vacuum filtering coal slurry, wherein the lower part of the filter cylinder of the vacuum filter is provided with a filter plate covered with filter cloth; the bottom outlet of the filter cylinder is connected to a vacuum system through a negative pressure conduit, and the vacuum system is a gradient vacuum system capable of automatically switching between high and low vacuum levels according to a PLC control program; it also includes a filter aid pre-coating device and a flocculant adding and mixing device, wherein the filter aid pre-coating device is used to uniformly coat the filter cloth with a composite filter aid, and the flocculant adding and mixing device is used to quantitatively add flocculant to the coal slurry and stir it; a coal slurry settling zone is provided inside the filter cylinder to allow the coarse particles in the conditioned coal slurry to settle.

9. The system according to claim 8, characterized in that: The system also includes a filter cake washing device, which includes a movable spray pipe disposed above the filter cake for uniformly spraying washing liquid onto the filter cake.

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