A method for reducing ash and dehydrating coarse clean coal

Abstract

This invention proposes a method for desliming and dewatering coarse coal, comprising the following steps: After TBS overflow clean coal is screened (I), the +0.5mm particle size product is combined with the oversize from the clean coal desliming screen and dewatered to obtain heavy medium lump concentrate and centrifugal liquid; after -0.5mm particle size product is screened (II), the +0.25mm particle size product, centrifugal liquid, and clean coal dilute medium magnetic tailings are combined and classified by a fine-dilute hydrocyclone; the underflow product from the classification is screened (III), and the undersize, -0.25mm particle size product, and classification overflow product are combined and subjected to flotation to obtain flotation clean coal; a portion of the oversize is sent to a lump coal dewatering system for dewatering, and the other portion is combined with the flotation clean coal, filtered, and dewatered to obtain the flotation clean coal product. This invention enhances the desliming and ash reduction effect of coarse clean coal slime and improves the dewatering effect of coarse clean coal slime; at the same time, it shortens the process flow, reduces the number of equipment to be operated, and significantly reduces the production cost per ton of coal.

Description

Technical Field

[0001] This invention relates to the field of coal preparation technology, and in particular to a method for reducing ash and dewatering coarse and refined coal. Background Technology

[0002] In existing technology, raw coal with a particle size of 1mm-50mm is deslimed by a desliming screen to obtain oversize lump coal and undersize coal slime. The oversize lump coal is then separated using a three-product heavy medium hydrocyclone to obtain heavy medium lump clean coal, middlings, and gangue products. The heavy medium lump clean coal is deslimed by a desliming screen, and the oversize material from the desliming screen enters a lump coal dewatering system (such as a horizontal vibrating discharge centrifuge) for recovery, yielding heavy medium lump clean coal products and centrifugal liquid. The undersize material from the desliming screen is then processed by a magnetic separator to recover magnetite powder, resulting in clean coal dilute medium magnetic tailings.

[0003] The undersize coal slime is classified by a classifying hydrocyclone to obtain coal slime overflow product and coal slime underflow product. The coal slime overflow product enters the flotation system for flotation, and the coal slime underflow product with a particle size of 1mm-0.25mm enters the TBS for separation to obtain TBS overflow clean coal; Figure 1 As shown, the TBS overflow clean coal undergoes pre-dewatering and ash reduction via a two-stage stacked screen (screen gap 0.35mm). The oversize product enters a horizontal scraper discharge centrifuge for dewatering, becoming TBS coarse clean coal and centrifugal liquid. The undersize product flows by gravity into the flotation system. The clean coal dilute medium magnetic tail and centrifugal liquid are combined and concentrated and classified by a fine dilute hydrocyclone. The underflow undergoes pre-dewatering and ash reduction via an arc screen (screen gap 0.75mm) and a linear vibrating screen (screen gap 0.50mm). The oversize material enters a vertical scraper discharge centrifuge for dewatering, becoming fine magnetic tail coarse clean coal and centrifugal liquid. The centrifugal liquid is incorporated into the clean coal dilute medium magnetic tail, and the undersize material enters the flotation system. The coal slime entering the flotation system undergoes flotation, filtration, and dewatering to obtain the flotation clean coal product.

[0004] The above process has the following problems:

[0005] 1. After the dilute medium magnetic tail and centrifugal liquid of the clean coal are combined, the concentration is low and the flow rate is large, which cannot meet the feed concentration of the clean dilute hydrocyclone, resulting in serious underflow entrainment of fine particles, which seriously pollutes the coarse clean coal after recovery.

[0006] 2. The grading accuracy of the arc screen + linear vibrating screen is poor, and the ash content of the product on the screen is too high. After long-term production, the screen gaps are severely worn, and the coarse material under the screen is seriously lost, which puts great pressure on the subsequent flotation operation.

[0007] 3. After the TBS overflow passes through the stacked high-frequency vibrating fine screen for dewatering and desliming, the coarse coal slime enters the centrifuge for dewatering. Due to the low concentration and large flow rate of the TBS overflow, although the stacked screen has a high classification accuracy, the screen plate with small screen openings has poor drainage capacity, which easily causes water to run off the screen surface and cannot effectively carry out dewatering and desliming operations. At the same time, the fine particles carried by the TBS overflow block the screen openings, which further aggravates the problem of excessive ash and moisture content in the product on the screen.

[0008] The above problems will cause the coal washing and beneficiation system to have poor ash reduction and dewatering effect on coarse and clean coal, poor classification effect of fine and rare cyclones, excessive ash in coarse and clean coal magnetic tails, high moisture content in flotation clean coal, low efficiency of flotation clean coal dewatering system, and complex coarse and clean coal dewatering system with poor adaptability. Summary of the Invention

[0009] This invention proposes a method for reducing ash and water in coarse coal, which enhances the desliming and ash reduction effect of coarse coal slime, improves the dewatering effect of coarse coal slime, and increases the dewatering efficiency of the equipment; at the same time, it shortens the process flow, reduces the number of equipment to be started, and greatly reduces the production cost per ton of coal.

[0010] The technical solution of this invention is implemented as follows: 1. A method for reducing ash and dewatering crude coal, characterized by comprising the following steps:

[0011] (1) Raw coal is processed to obtain clean coal desliming screen oversize, clean coal dilute medium magnetic tail and TBS overflow clean coal. The TBS overflow clean coal is screened by I to obtain +0.5mm particle size product and -0.5mm particle size product. The +0.5mm particle size product is combined with the clean coal desliming screen oversize and then passed through the lump coal dewatering system to obtain heavy medium lump concentrate product and centrifugal liquid.

[0012] (2) The -0.5mm particle size product is screened II to obtain the +0.25mm particle size product and the -0.25mm particle size product. The +0.25mm particle size product is combined with the centrifugal liquid and the fine coal dilute medium magnetic tail in step (1), and then classified by a fine dilute hydrocyclone to obtain the graded underflow product and the graded overflow product. The high concentration of the +0.25mm particle size product is combined with the centrifugal liquid and the fine coal dilute medium magnetic tail in step (1) to ensure the feed concentration of the fine dilute hydrocyclone.

[0013] (3) The graded underflow product of step (2) is screened into III to obtain the oversize and undersize. The undersize, the -0.25mm particle size product of step (2) and the graded overflow product are combined and then floated to obtain flotation clean coal.

[0014] (4) Part of the material on the screen in step (3) is sent to the lump coal dewatering system for dewatering, and the other part is combined with the flotation clean coal in step (3), filtered and dewatered to obtain the flotation clean coal product.

[0015] Furthermore, in step (3), screening III adopts a three-stage stacked screen, which includes multiple stacks, each of which includes a first-stage screen, a second-stage screen, and a third-stage screen. A slurry adjustment tank is provided between the first-stage screen and the second-stage screen, and high-pressure water spray pipes are provided on the screen surfaces of the second-stage screen and the third-stage screen.

[0016] Furthermore, in step (1), the screening method I uses a section of coarse arc screen.

[0017] Furthermore, in step (2), screening II adopts a two-stage drainage arc screen.

[0018] Furthermore, in step (1), the lump coal dewatering system adopts a horizontal vibrating unloading centrifuge.

[0019] Furthermore, in step (4), the filtration and dewatering are performed using a pressure filter and an air-flow filter press.

[0020] Furthermore, in step (4), the filtrate obtained after filtration and dehydration is returned to the flotation operation in step (3).

[0021] The beneficial effects of this invention are:

[0022] This invention performs coarse removal and recovery of +0.5mm particles in the TBS overflow product, allowing the +0.5mm particles to enter the lump coal dewatering system and be combined with lump clean coal for dewatering. The -0.5mm particles are secondary-classified using an arc screen, while the -0.25mm particles directly enter the flotation process. The +0.25mm particles are combined with the clean coal dilute medium magnetic tail and centrifugal liquid to increase the concentration of the clean coal magnetic tail, thereby ensuring the feed concentration of the dilute hydrocyclone and solving the problem of severe fine entrainment in the underflow. After concentration in the dilute hydrocyclone, the graded underflow product is obtained, which is then dewatered and ash-reduced by a three-stage stacked screen to obtain the oversize and undersize products.

[0023] A portion of the oversize material (fine-grained coarse coal slime) is used as coarse material in the flotation of coarse coal. The coarse particles of the coarse coal slime form a skeleton in the filter cake, creating a loose filter cake and reducing the damping of the filter cake, thereby improving the efficiency of the flotation dewatering equipment. Since the addition of fine-grained coarse coal slime needs to be adjusted according to the amount of flotation concentrate and the operating conditions of the flotation equipment, the excess fine-grained coarse coal slime is introduced to the lump coal dewatering system, using lump coal as a skeleton to improve the dewatering effect of the fine-grained coarse coal slime. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of the coal preparation process for coarse and fine coal in the existing technology;

[0026] Figure 2 This is a schematic diagram of the process for ash reduction and dewatering of coarse and clean coal according to the present invention. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Example 1

[0029] like Figure 2 As shown, a method for reducing ash and dewatering crude coal includes the following steps:

[0030] (1) 1mm-50mm raw coal is deslimed by a desliming screen to obtain oversize lump raw coal and undersize coal slime. The oversize lump raw coal is separated by heavy media coal separation to obtain heavy media lump clean coal, middlings coal and gangue products. The heavy media lump clean coal is deslimed by a desliming screen to obtain clean coal deslimed oversize and clean coal deslimed undersize. The clean coal deslimed undersize is then separated by a magnetic separator to recover magnetite powder to obtain clean coal dilute medium magnetic tailings.

[0031] The undersize coal slime is classified by a classifying hydrocyclone to obtain coal slime overflow product and coal slime underflow product. The coal slime overflow product enters the flotation system for flotation. The coal slime underflow product with a particle size of 1mm-0.25mm is separated by a TBS separator to obtain TBS overflow clean coal. The TBS overflow clean coal product is screened by screening I to obtain +0.5mm particle size product and -0.5mm particle size product. The +0.5mm particle size product and the oversize of the clean coal desliming screen are combined and then enter the lump coal dewatering system for recovery. The lump coal dewatering system uses four horizontal vibrating discharge centrifuges for dewatering and recovery to obtain heavy medium lump clean coal product and centrifugal liquid.

[0032] (2) The -0.5mm particle size product is screened II to obtain the +0.25mm particle size product and the -0.25mm particle size product. The +0.25mm particle size product, the centrifugal liquid in step (1) and the fine coal dilute medium magnetic tail are combined and then classified by a fine dilute hydrocyclone to obtain the graded underflow product and the graded overflow product.

[0033] (3) The graded underflow product from step (2) is screened into III to obtain the oversize and undersize. The undersize, the -0.25mm particle size product from step (2), and the graded overflow product are combined and then floated to obtain flotation clean coal.

[0034] (4) Part of the material on the screen in step (3) is sent to the lump coal dewatering system for dewatering, and the other part is combined with the flotation clean coal in step (3) and enters the filtration dewatering system to obtain flotation clean coal product. The filtrate obtained in the filtration dewatering system is returned to the flotation operation in step (4). The filtration dewatering system includes a pressure filter and an air-flow filter press connected in sequence.

[0035] In step (1), screening I uses a single-stage coarse-cutting arc screen, which is a vibrating arc screen with a screen gap of 0.75mm; in step (2), screening II uses a two-stage drainage arc screen, which is a vibrating arc screen with a screen gap of 0.35mm.

[0036] In step (3), screening III uses a five-layer, three-section stacked screen. The five-layer, three-section stacked screen consists of five parallel stacks, each layer including a first-stage screen, a second-stage screen, and a third-stage screen. Flexible polyurethane screens with a screen gap of 0.35mm are used. A slurry adjustment tank is installed between the first-stage and second-stage screens to further dilute and wash the fine-grained high-ash particles on the surface of the coarse particles. High-pressure water spray pipes are installed on the screen surfaces of both the second-stage and third-stage screens to flush and wash the particle surfaces, reducing the adsorption of fine-grained high-ash particles on the coarse coal particles. The five-layer, three-section stacked screen is a high-frequency vibrating fine screen, model ZKJ-1007D5 / 3.

[0037] Comparative Example 1

[0038] like Figure 1 As shown, a method for reducing ash and dewatering crude coal includes the following steps:

[0039] (1) 1mm-50mm raw coal is deslimed by a desliming screen to obtain oversize lump raw coal and undersize coal slime. The oversize lump raw coal is separated by heavy media coal separation to obtain heavy media lump clean coal, middlings coal and gangue products. The heavy media lump clean coal is deslimed by a desliming screen to obtain clean coal desliming screen oversize and clean coal desliming screen undersize. The clean coal desliming screen undersize is then processed by a magnetic separator to recover magnetite powder to obtain clean coal dilute medium magnetic tailings. The clean coal desliming screen oversize is then fed into the lump coal dewatering system for recovery. The lump coal dewatering system uses four horizontal vibrating unloading centrifuges for dewatering and recovery to obtain heavy media lump clean coal products and centrifugal liquid.

[0040] (2) The undersize coal slime is classified by a classifying hydrocyclone to obtain coal slime overflow product and coal slime underflow product. The coal slime overflow product enters the flotation system for flotation. The coal slime underflow product with a particle size of 1mm-0.25mm is separated by a TBS separator to obtain TBS overflow clean coal. The TBS overflow clean coal is pre-dehydrated and ash-reduced by four two-stage stacked screens (screen mesh gap is 0.35mm) to obtain oversize product and undersize product. The oversize product is dehydrated by two horizontal scraper discharge centrifuges to obtain TBS coarse clean coal and centrifugal liquid.

[0041] (3) The centrifugal liquid from steps (1) and (2) is incorporated into the fine coal dilute medium magnetic tail, and then classified by a fine dilute hydrocyclone to obtain the graded underflow product and the graded overflow product. The graded underflow product is dewatered and ash-reduced by a set of vibrating arc screen (screen mesh gap 0.75mm) + linear vibrating screen (screen mesh gap 0.50mm) to obtain the oversize and undersize products. The oversize product is dewatered by a vertical scraper unloading centrifuge to obtain the fine magnetic tail coarse fine coal and centrifugal liquid. The centrifugal liquid is incorporated into the fine coal dilute medium magnetic tail.

[0042] (4) The undersize product from step (2), the graded overflow product from step (3), and the undersize material are all fed into the flotation machine for flotation to obtain flotation clean coal. The flotation clean coal is recycled and dewatered by four pressure filters and four air-flow filters to become flotation clean coal products. The dewatered filtrate is returned to the flotation system.

[0043] The crude and refined coal includes TBS crude and refined coal and fine magnetic tailings crude and refined coal. Using the method of Comparative Example 1, the ash content of the crude and refined coal exceeds 11%, which is more than 2.0% higher than that of heavy medium lump coal. The crude and refined coal dewatering system has been operating at full load for a long time, resulting in excessive moisture content in the crude and refined coal products. As a result, the total moisture content of the refined coal products is 0.23% higher than the target moisture content, which is 13%. The moisture content of various refined coal products is shown in Table 1.

[0044] Table 1. Moisture content of various refined coal products in Comparative Example 1

[0045]

[0046]

[0047] Using the method of Example 1, the moisture content of various clean coal products is shown in Table 2. As can be seen from Table 2, the total moisture content of the clean coal is 12.79%, which is lower than the target moisture content of 13%.

[0048] Table 2. Moisture content of various refined coal products in Example 1

[0049] product Yield / % Moisture / % Heavy medium lump coal products 55.00 8.70 Flotation clean coal products 45.00 17.8 Total coking coal 100.00 12.79

[0050] As shown in Tables 1 and 2, the total moisture content of the clean coal decreased by 0.44%, keeping it below 13%, thus reducing the occurrence of excessive moisture content in transported clean coal. Based on the coal preparation plant's annual production of 2.9 million tons of marketable coal, this translates to an annual saving of approximately 1.6 million yuan in transportation costs. The total power consumption of the clean coal dewatering system decreased by 197.9 kW, resulting in annual electricity savings of over 912,000 yuan. Furthermore, the problems of coarse flotation runoff and screen clogging were effectively resolved, significantly reducing reagent consumption and maintenance costs, saving approximately 3.108 million yuan. In conclusion, the coal preparation plant can increase revenue and reduce costs by approximately 5.62 million yuan annually, achieving considerable economic benefits.

[0051] In Example 1 and Comparative Example 1, the particle size composition of the graded underflow product of the fine hydrocyclone is shown in Table 3. As can be seen from Table 3, the content of +0.5mm particle size material in Example 1 is significantly reduced, and the content of -0.125mm particle size material is reduced from 14.78% to 6.10%, and the fineness of the underflow material is significantly improved.

[0052] Table 3. Particle size distribution of graded underflow products

[0053]

[0054] The oversize materials from the three-stage stacked screen of Example 1 and the two-stage stacked screen of Comparative Example 1 were sampled and analyzed. The results are shown in Table 4. Table 4 shows that the content of -0.25 particle size in the oversize material decreased from 18.67% in Comparative Example 1 to 6.05% in Example 1. The change in the content of -0.125 particle size was the most significant, decreasing from 12.45% in Comparative Example 1 to 2.81% in Example 1. The total ash content of the oversize material in Example 1 was 9.97%, a decrease of 2.31 percentage points compared to 12.01% in Comparative Example 1, indicating a significant improvement in desliming effect.

[0055] In Example 1, the feed concentration and flow rate were within a suitable range, which fully utilized the performance advantages of the three-stage stacked screen and effectively achieved the purpose of desliming and ash reduction.

[0056] Table 4 Comparison of particle size distribution of material oversize material on stacked screens in Example 1 and Comparative Example 1

[0057]

[0058] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for reducing ash and dewatering crude coal, characterized in that, The following steps are involved: (1) Raw coal is processed to obtain clean coal desliming screen oversize, clean coal dilute medium magnetic tail and TBS overflow clean coal. The TBS overflow clean coal is screened by I to obtain +0.5mm particle size product and -0.5mm particle size product. The +0.5mm particle size product is combined with the clean coal desliming screen oversize and then passed through the lump coal dewatering system to obtain heavy medium lump concentrate product and centrifugal liquid. (2) The -0.5mm particle size product is screened II to obtain the +0.25mm particle size product and the -0.25mm particle size product. The +0.25mm particle size product is combined with the centrifugal liquid and the fine coal dilute medium magnetic tail in step (1), and then classified by a fine dilute hydrocyclone to obtain the graded underflow product and the graded overflow product. (3) The graded underflow product of step (2) is screened into III to obtain the oversize and undersize. The undersize, the -0.25mm particle size product of step (2) and the graded overflow product are combined and then floated to obtain flotation clean coal. (4) Part of the material on the screen in step (3) is sent to the lump coal dewatering system for dewatering, and the other part is combined with the flotation clean coal in step (3), filtered and dewatered to obtain the flotation clean coal product.

2. The method for reducing ash and dewatering crude coal according to claim 1, characterized in that, In step (3), screening III uses a three-stage stacked screen.

3. The method for reducing ash and dewatering crude coal according to claim 1, characterized in that, In step (1), a section of coarse arc screen is used for screening I.

4. The method for reducing ash and dewatering crude coal according to claim 1, characterized in that, In step (2), screening II uses a two-stage drainage arc screen.

5. The method for reducing ash and dewatering crude coal according to claim 1, characterized in that, In step (1), the lump coal dewatering system uses a horizontal vibrating unloading centrifuge.

6. The method for reducing ash and dewatering crude coal according to claim 1, characterized in that, In step (4), the filtration and dewatering are performed using a pressure filter and an air-flow filter press.

7. The method for reducing ash and dewatering crude coal according to claim 1, characterized in that, In step (4), the filtrate obtained after filtration and dehydration is returned to the flotation operation in step (3).

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