A process for beneficiating scarce coking coal by dense medium separation with enhanced liberation and recovery of middlings

Abstract

The present application relates to the technical field of coal preparation, especially relates to a rare coking coal heavy medium washing process for strengthening middling coal dissociation and recovery. The process comprises the steps of fine raw coal separation, fine clean coal medium removal, fine middling coal medium removal, fine gangue medium removal, fine middling coal crushing, fine coal dilute medium dehydration, dilute medium magnetic separation, coal slime heavy medium separation, coarse clean coal medium removal, coarse middling coal medium removal, coarse tailing coal magnetic separation, grinding operation, coarse clean coal magnetic separation, fine coal mixed medium allocation, and coal slime mixed allocation. The present application uses a coal slime heavy medium system completely independent of the fine coal heavy medium system to complete high-precision separation and tailing throwing of coarse coal slime and crushed fine middling coal. In the present method, the coarse middling coal is fully dissociated but not excessively dissociated, the coarse coal slime has high separation precision, the process flow is simple, the separation is efficient, and the economic benefit is remarkable.

Description

Technical Field

[0001] This invention relates to the field of coal preparation technology, and in particular to a heavy media washing process for scarce coking coal that enhances middlings separation and recovery. Technical Background

[0002] Coking coal is an indispensable raw material for steel manufacturing and plays a vital role in the industrial economy. However, major coking coal types such as coking coal and fat coal account for less than 15% of my country's total coal resources. This scarce coking coal often yields 20%–30% middlings after washing, which, due to their high ash content and poor caking properties, can only be used as fuel, further reducing its resource utilization rate. How to recover and extract clean coal resources from middlings to improve the washing recovery rate of scarce coking coal has always been an important research topic in the industry.

[0003] The difficulty in middlings reprocessing lies in the presence of associated minerals embedded between coal particles. Currently, there are two main approaches to middlings recovery: improving the precision of sorting equipment – ​​multiple sorting and grinding followed by gravity / flotation. With the continuous improvement in the sorting precision of coal preparation equipment in recent years, middlings from coking coal processing can be further sorted using jigs, hydrocyclones, and spiral separators, achieving a certain level of clean coal recovery. Although high-precision sorting equipment can recover qualified clean coal from coking coal processing, the clean coal yield is relatively low because organic combustibles and gangue remain closely intertwined. Therefore, achieving effective dissociation of scarce coking middlings followed by high-precision sorting to improve clean coal recovery is imperative.

[0004] Patent CN102861663A provides a two-stage recovery process for scarce coking middlings, involving crushing, grinding, and dissociation, as well as gravity flotation. It focuses on the crushing and grinding of middlings >6mm and 6-0.5mm, and the two-stage isodense heavy medium cyclone separation and flotation control of the dissociated material, achieving the goal of middlings dissociation and efficient separation. However, this invention has the following problems: ① The separate heavy medium system and flotation system for middlings products in coal preparation plants are not considered in conjunction with existing gravity separation and flotation processes, resulting in redundant investment, high operating costs, and poor economic efficiency; ② After separation, 6-0.5mm middlings and <0.5mm coal slime are subjected to open-circuit grinding followed by flotation, making it difficult to control the process in a single grinding operation to achieve sufficient dissociation without over-dissociation. If the grinding particle size is too fine, not only will energy consumption be high and production costs be high, but the large amount of high-ash fine mud produced will also contaminate the flotation clean coal and reduce the quality of the clean coal. If the grinding particle size is too coarse, the middlings will not be fully liberated. The unliberated middlings will either lead to excessive ash content in the clean coal or be lost in the tailings, resulting in a waste of resources.

[0005] Patent CN113877717A discloses a combined method of heavy medium separation and flotation for fine coal, achieving efficient separation of 50(80)~1mm fine coal and 1~0.25mm coarse coal slime. However, in the separation of scarce coking coal, this process cannot meet the separation density requirements of different particle sizes. 1~0.25mm coarse coal slime and 80~1mm fine raw coal cannot achieve equal elementary ash separation in the same medium density. Therefore, this method suffers from poor separation accuracy and high ash content of coarse coal slime, resulting in a loss of clean coal yield due to back ash from gravity separation.

[0006] Patent CN111167594A discloses an improved process for heavy medium separation of 1-0.25mm coarse coal slime based on constant-low flow pressure, which enhances the heavy medium separation effect and effectively reduces medium consumption. Patent CN115318429A discloses a non-desliming heavy medium separation process for fine coal based on dilute medium grading and separation. This process involves precisely controlling the flow of the combined medium containing 1-0.25mm coarse coal slime in the fine coal heavy medium system, then feeding it into a three-product coal slime heavy medium cyclone separator group for grading and separation, ensuring controllable, adjustable, high-precision, and low-medium-consumption separation of coarse coal slime. Both patents achieve efficient separation of 80-1mm fine coal and 1-0.25mm coarse coal slime by adding a coarse coal slime heavy medium separation system and by addressing issues such as stable flow fluctuations and density control. However, the following problems still exist: ① The incoming material for coarse coal slime heavy medium separation is mainly the combined and diverted flow of the fine coal heavy medium system, which makes it impossible to independently control the separation density of coarse coal slime heavy medium. It is always affected by the separation density of fine coal heavy medium, thus failing to fully achieve the requirement of maximizing the clean coal yield while separating different particle sizes and elementary ash content. ② The higher requirements for the fineness of the heavy medium and the stability of the suspension in coarse coal slime separation are ignored. The fineness of the medium determines the stability of the suspension, which in turn affects the separation accuracy and product recovery rate. As the medium is continuously consumed, fine magnetite is gradually lost in the magnetite tail and product, and the content of -0.074mm decreases from 90% to 70%. The fineness and stability of the heavy medium deteriorate, making it difficult to meet the needs of high-precision separation of coarse coal slime.

[0007] The above analysis shows that although many coal dissociation and coarse coal slime heavy media separation methods have been proposed in the existing technology, there are still problems of poor separation accuracy and low recovery rate for coal dissociation and re-separation in scarce coking processes. Summary of the Invention

[0008] To address the aforementioned issues, this invention provides a rare coking coal heavy media washing process that enhances the dissociation and recovery of middlings. This process utilizes completely independent heavy media systems for fine coal and coal slime to achieve high-precision separation of fine raw coal and coarse coal slime. After dissociation, the fine and middlings coal enter the coal slime heavy media system, avoiding mutual interference between the two systems and redundant investment in separate middlings re-selection. The oversize material from the desliming screen of the coarse and middlings coal after heavy media separation is ground together with the underflow magnetic separator in a closed-loop cycle, ensuring sufficient but not excessive dissociation of the coarse and middlings coal and meeting the fineness requirements of the heavy media, thereby enhancing the dissociation and recovery of middlings.

[0009] The present invention adopts the following technical solution:

[0010] A heavy media washing process for scarce coking coal that enhances middlings dissociation and recovery includes the following steps:

[0011] Step a, raw coal sorting: raw coal with a particle size of no more than 50mm is sorted in a three-product heavy medium cyclone separator under the action of a qualified medium to obtain fine coal, middlings coal and gangue.

[0012] Step b1, desliming of fine coal: The fine coal in step a passes through an arc screen and a desliming screen to obtain arc screen combined medium, desliming screen combined medium, desliming screen dilute medium and oversize material; wherein, the arc screen combined medium is divided into two parts by a diverter, arc screen combined medium 1 and desliming screen combined medium go to the fine coal combined medium barrel together, arc screen combined medium 2 and desliming screen dilute medium go to the dilute medium barrel together, and the oversize material is dewatered and used as the fine coal product;

[0013] Step b2, medium removal of fine coal: The fine coal in step a passes through an arc screen and a medium removal screen to obtain arc screen combined medium, medium removal screen combined medium and oversize material; wherein, the arc screen combined medium and the medium removal screen combined medium go to the combined medium tank together, and the oversize material is fed into the coal slime mixing tank.

[0014] Step b3, Desliming of the final gangue: The final gangue from step a passes through an arc screen and a desliming screen to obtain arc screen combined medium, desliming screen combined medium, desliming screen dilute medium and oversize material; wherein, the arc screen combined medium and the desliming screen combined medium are sent to the combined medium barrel together; the desliming screen dilute medium is sent to the dilute medium barrel, and the oversize material is used as the final gangue product.

[0015] Step d, fine coal dilute medium dewatering: the arc screen diverting medium 2 in step b1 and the dilute medium of the dewatering screen in step b3 are buffered by the dilute medium tank and then pumped to the dewatering screen for dewatering and demediation, to obtain the oversize material and undersize water.

[0016] Step e, dilute medium magnetic separation: The screened water from step d is fed into the magnetic separator for the first magnetic separation to obtain magnetic concentrate and magnetic tailings; the magnetic concentrate is returned to the fine coal mixing tank, and the magnetic tailings are used as coal slurry water for subsequent flotation operations;

[0017] Step f, coal slime heavy medium separation: The material oversize from the screen in step d and the material oversize from the desliming screen in step b2 are buffered in the mixing tank and then pumped to the three-product coal slime heavy medium cyclone separator for separation to obtain coarse clean coal, coarse medium coal and coarse tailings.

[0018] Step g1, coarse and fine coal desliming: In step f, coarse and fine coal is fed into a double-layer arc screen for desliming to obtain the oversize and undersize mixture; the undersize mixture is set to be diverted, undersize mixture divert 1 goes to the coal slime mixing tank, and undersize mixture divert 2 goes to the coarse and fine coal magnetic separation operation together with the oversize.

[0019] Step g2, desliming of coarse and medium coal: The coarse and medium coal in step f are fed into a double-layer arc screen for desliming to obtain the oversize and undersize mixture; the oversize is sent to the grinding operation, and the undersize mixture is sent to the coal slime mixing tank.

[0020] Step g3, coarse tailings magnetic separation: The coarse tailings from step f are fed into a magnetic separator for a second magnetic separation to obtain magnetic concentrate and magnetic tailings; the magnetic concentrate is then ground, and the magnetic tailings are classified and dewatered to become coarse tailings slime products.

[0021] Step i, coarse and fine coal magnetic separation: The material oversize and undersize in step g1 are fed into the fine coal magnetic separator for the third magnetic separation to obtain magnetic fine coal and magnetic tailings; the magnetic tailings are used as coarse and fine coal products after being graded and dewatered; the magnetic fine coal is set to be divided, magnetic fine coal diversion 1 goes to the fine coal mixing tank, and magnetic fine coal diversion 2 goes to the coal slime mixing tank.

[0022] Step j, Coal mixing: The arc-shaped screen mixing media 1 and the desliming screen mixing media in step b1, the arc-shaped screen mixing media and the desliming screen mixing media in step b2, the arc-shaped screen mixing media and the desliming screen mixing media in step b3, and the magnetic fine mixing media 1 in step i are returned to step a as qualified media after being buffered in the coal mixing media barrel.

[0023] Step k, coal slime mixing and preparation: the material overseen by the desliming screen in step b2, the material overseen by the screen in step d, the underseen medium diversion 1 in step g1, the underseen medium diversion 2 in step g2, the material after grinding in step h, and the magnetic fine diversion 2 in step i are mixed and fed into the coal slime mixing tank, and after buffering, returned to step f.

[0024] Preferably, it also includes step c, which is the crushing of fine coal: the material from the desliming screen in step b2 is crushed by a crusher before being fed into the coal slime mixing tank. The crusher is a reversible impact hammer crusher, which crushes the material to a particle size of less than 2 mm.

[0025] Preferably, it also includes step h, which is a grinding operation in which the oversize material from step g2, the magnetic concentrate from step g3, and the supplementary magnetite powder and water are ground and dissociated together, and the ground material is then fed into the coal slime mixing tank.

[0026] Preferably, in step h, the grinding operation uses a rod mill, and the added magnetite powder and water control the feed mass concentration at 45-55 wt%. After grinding, the mineral particles with a particle size of less than 0.074 mm account for more than 80% of the total material mass content.

[0027] Preferably, in steps b1 and b3, the desliming screen is configured in two sections. The first section is located near the feed end, occupying 1 / 3 of the total length of the desliming screen, with a screen aperture of 0.5 mm; the second section is located near the discharge end, occupying 2 / 3 of the total length of the desliming screen, with a screen aperture of 1.0 mm. The second section is also equipped with a water spray system, with a spray volume of 1.2–2.0 m³ / h. 3 / t.

[0028] Preferably, in step b2, the desliming screen is set in two sections. The first section is close to the feed end and accounts for 1 / 3 of the total length of the desliming screen, and the second section is close to the discharge end and accounts for 2 / 3 of the total length of the desliming screen. The screen holes of the desliming screen are all 0.5mm. No water spraying is set in this step.

[0029] Preferably, in step d, the particle size retained by the dewatering screen is 0.2 mm.

[0030] Preferably, in steps g1 and g2, the sieve aperture of the double-layer arc sieve is 0.35 mm, and the particle size is between 0.2 and 0.25 mm.

[0031] Preferably, in the second and third magnetic separation processes, water is added to adjust the feed concentration of the magnetic separator to between 15 and 25 wt%.

[0032] Preferably, in step j, the density of each material fed into the coal slurry mixing tank is adjusted to between 1.35 and 1.45 kg / L, with the goal of separation in the first stage of the three-product coal slime heavy medium cyclone separator.

[0033] Preferably, in step k, the density of each material fed into the coal slime mixing tank is adjusted to between 1.40 and 1.50 kg / L, with the goal of separation in the first stage of the three-product coal slime heavy medium cyclone separator.

[0034] Preferably, in step b1, the arc-shaped screen medium is divided into two parts by a diverter, wherein the arc-shaped screen medium diverter 2 accounts for 20% to 30% of the arc-shaped screen medium flow rate; in step g1, the under-screen medium is diverted, wherein the under-screen medium diverter 2 accounts for 25% to 35% of the under-screen medium flow rate; in step i, the diversion ratio of the magnetic fine diverter 1 and the magnetic fine diverter 2 is adjusted according to the control density of the fine coal medium barrel.

[0035] The beneficial effects of this invention are as follows:

[0036] In this invention, both fine coal (-2mm) and coarse coal slime (1-0.2mm) undergo strict demediuming or dewatering before entering the coal slime heavy medium system. The density of the coal slime heavy medium suspension is no longer affected by the combined and separated media in the fine coal heavy medium. The fine coal and coarse coal slime media systems are completely independent and do not interfere with each other. The separation density can be flexibly adjusted according to the coal quality and ash content of the clean coal, which helps to maximize the yield and improve the total clean coal recovery rate.

[0037] The raw coal's coarse slime (1-0.2mm) and the crushed middlings (-2mm) are separated in a three-product heavy medium cyclone to obtain coarse clean coal, coarse middlings, and tailings slime. The undissociated coarse middlings (2-0.2mm) are ground in heavy medium and then returned to the separation process. The coarse middlings are re-separated through closed-circuit grinding to ensure sufficient dissociation, and are discharged from the clean coal or tailings or dissociated to -0.2mm and discharged through the desliming screen. Under the protection of magnetite, which has higher hardness and wear resistance, the adverse effects of excessively fine dissociated particles on subsequent processes are avoided.

[0038] In the coal slime heavy medium system, coarse magnetite particles are discharged from the underflow magnetic flux after being classified by the heavy medium hydrocyclone and enter the grinding stage together with the coarse and medium coal. The heavy medium completes the preparation from coarse to fine while grinding and dissociating the coarse and medium coal, and realizes closed-loop circulation, which significantly improves the fineness of the heavy medium, the stability of the suspension, and the separation accuracy of the coarse coal slime.

[0039] This invention fully integrates the middlings separation and recovery process into the heavy media separation process of coking coal and coarse coal slime, eliminating the need for a separate middlings recovery and separation process. It has outstanding advantages such as simple process, high separation efficiency, high clean coal recovery rate, low energy consumption, low operating cost, and significant economic benefits. Attached Figure Description

[0040] Figure 1 This is a flow chart of a rare coking coal heavy media washing process for enhancing middlings dissociation and recovery according to the present invention.

[0041] Figure 2 This is an enlarged process flow diagram of the heavy medium system for fine coal in this invention;

[0042] Figure 3 This is an enlarged process flow diagram of the coal slime heavy media system in this invention. Detailed Implementation

[0043] The technical solution of the present invention will be described in more detail below with reference to the embodiments.

[0044] Example 1

[0045] like Figures 1-3 As shown, a heavy media washing process for scarce coking coal that enhances middlings dissociation and recovery includes the following steps:

[0046] Step a, raw coal sorting: raw coal with a particle size of no more than 50mm is sorted in a three-product heavy medium cyclone separator under the action of a qualified medium to obtain fine coal, middlings coal and gangue.

[0047] Step b1, desliming of fine coal: The fine coal in step a passes through an arc screen and a desliming screen to obtain arc screen combined medium, desliming screen combined medium, desliming screen dilute medium and oversize material; wherein, the arc screen combined medium is divided into two parts by a diverter. Arc screen combined medium diverter 1 goes to the fine coal combined medium tank together with the desliming screen combined medium, and arc screen combined medium diverter 2 goes to the dilute medium tank together with the desliming screen dilute medium. Arc screen combined medium diverter 2 is generally 20% to 30% of the arc screen combined medium flow rate. The oversize material is dewatered and used as the fine coal product.

[0048] Step b2, medium removal of fine coal: The fine coal in step a passes through an arc screen and a medium removal screen to obtain arc screen combined medium, medium removal screen combined medium and oversize material; wherein, the arc screen combined medium and the medium removal screen combined medium go to the combined medium tank together, and the oversize material is fed into the coal slime mixing tank.

[0049] Step b3, Desliming of the final gangue: The final gangue from step a passes through an arc screen and a desliming screen to obtain arc screen combined medium, desliming screen combined medium, desliming screen dilute medium and oversize material; wherein, the arc screen combined medium and the desliming screen combined medium are sent to the combined medium barrel together; the desliming screen dilute medium is sent to the dilute medium barrel, and the oversize material is used as the final gangue product.

[0050] In the above-mentioned desliming process, the desliming screen used in steps b1 and b3 is configured in two sections. The first section is located near the feed end, accounting for 1 / 3 of the total length of the desliming screen, with a screen aperture of 0.5 mm; the second section is located near the discharge end, accounting for 2 / 3 of the total length of the desliming screen, with a screen aperture of 1.0 mm. The second section is also equipped with a water spray, with a spray volume of 1.2–2.0 m³ / h. 3 / t. The desliming screen used in step b2 is set in two sections. The first section is close to the feed end and accounts for 1 / 3 of the total length of the desliming screen. The second section is close to the discharge end and accounts for 2 / 3 of the total length of the desliming screen. The screen holes of the desliming screen are all 0.5mm. No water spray is set. The discharge moisture content is controlled within 10%.

[0051] Step c, middlings coal crushing: The material overseen by the desliming screen in step b2 is fed into the hammer crusher and crushed to below 2mm. The crushed material is then fed into the coal slime mixing tank for coal slime heavy media separation.

[0052] Step d, fine coal dilute medium dewatering: the dilute medium of the arc screen in step b1 and the dilute medium of the dewatering screen in step b3 are buffered by the dilute medium tank and then pumped to the dewatering screen for 0.2mm dewatering and demediation to obtain the oversize material and undersize water.

[0053] Step e, dilute medium magnetic separation: The screened water from step d is fed into the magnetic separator for the first magnetic separation to obtain magnetic concentrate and magnetic tailings; the magnetic concentrate is returned to the fine coal mixing tank, and the magnetic tailings are used as coal slurry water for subsequent flotation operations;

[0054] Step f, coal slime heavy media separation: The material oversize in step d and the crushed material in step c are buffered in the mixing tank and then pumped to the three-product coal slime heavy media hydrocyclone group for separation to obtain coarse clean coal, coarse medium coal and coarse tailings.

[0055] Step g1, Coarse and clean coal desliming: The coarse and clean coal in step f is fed into a double-layer arc screen for desliming, resulting in oversize and undersize media; the undersize media is divided into two streams, and the proportion of the undersize media to the coal slime mixing tank or the coarse and clean coal magnetic separator is adjusted according to the coal quality, separation density, suspension characteristics, etc. The undersize media diversion 2 is generally 25% to 35% of the total flow of the undersize media, of which undersize media diversion 1 goes to the coal slime mixing tank, and undersize media diversion 2 goes to the coarse and clean coal magnetic separation operation together with the oversize;

[0056] Step g2, desliming of coarse and medium coal: The coarse and medium coal in step f are fed into a double-layer arc screen for desliming to obtain the oversize and undersize mixture; the oversize is sent to the grinding operation, and the undersize mixture is sent to the coal slime mixing tank.

[0057] Step g3, coarse tailings magnetic separation: The coarse tailings from step f are fed into a magnetic separator for a second magnetic separation. Water is added to adjust the feed concentration of the magnetic separator to between 15 and 25 wt%, resulting in magnetic concentrate and magnetic tailings. The magnetic concentrate is then used for grinding, and the magnetic tailings are classified and dewatered to become coarse tailings slime.

[0058] The double-layer arc screen used in steps g1 and g2 above has a screen aperture of 0.35 mm and a particle size of 0.2 to 0.25 mm.

[0059] Step h, grinding operation: The material screened in step g2, the magnetic concentrate and the supplemented magnetite powder and water in step g3 are ground and dissociated together. The ground material is then fed into the coal slime mixing tank.

[0060] In this step, a rod mill is used for grinding. The feed mass concentration is controlled at 45-55 wt%, and after grinding, mineral particles with a diameter less than 0.074 mm account for more than 80% of the total material mass content. The amount of magnetite powder and water added is determined based on the amount lost from tailings and products in the media system to maintain the dynamic balance and stability of the media system.

[0061] Step i, coarse and fine coal magnetic separation: The material oversize and undersize material from step g1 are fed into the fine coal magnetic separator for the third magnetic separation. Water is added to adjust the feed concentration of the magnetic separator to between 15 and 25 wt%, resulting in magnetic concentrate and magnetic tailings. The magnetic tailings are graded and dewatered to become the coarse and fine coal product. The magnetic concentrate is set to be split, and the split ratio is adjusted according to the control density of the fine coal mixing tank. Magnetic concentrate split 1 goes to the fine coal mixing tank, and magnetic concentrate split 2 goes to the coal slime mixing tank.

[0062] Step j, fine coal mixing media preparation: the arc-shaped screen mixing media 1 and the desliming screen mixing media in step b1, the arc-shaped screen mixing media and the desliming screen mixing media in step b2, the arc-shaped screen mixing media and the desliming screen mixing media in step b3, and the magnetic fine mixing media 1 in step i, after being buffered in the fine coal mixing media barrel, are returned to step a as qualified media; the buffering includes density control, which is aimed at the first stage of separation of the three-product coal slime heavy medium cyclone, and is determined according to the ash content and coal quality of the fine coal, generally controlled between 1.35 and 1.45 kg / L.

[0063] Step k, coal slime mixing and preparation: The material from the desliming screen in step b2, the material from the screen in step d, the under-screen mixed medium diversion 1 in step g1, the under-screen mixed medium in step g2, the material after grinding in step h, and the magnetic fine diversion 2 in step i are mixed and fed into the coal slime mixing tank, and after buffering, returned to step f; the buffering includes density control, which is determined based on the ash content and coal quality of the three-product coal slime heavy medium hydrocyclone, and is generally controlled between 1.40 and 1.50 kg / L, with the target being the separation of the first stage of the three-product coal slime heavy medium hydrocyclone.

[0064] Example 2

[0065] The experimental method was compared with the conventional process. The main characteristics are shown in Table 1, and the sorting indicators are shown in Table 2.

[0066] Table 1 Comparison of main characteristics of different processes

[0067]

[0068] Table 2 Comparison of sorting indicators for different processes

[0069]

[0070]

[0071] The heavy media washing process provided by this invention significantly improves the separation accuracy (E value) and flotation perfection index of coarse coal slime compared to traditional processes. Regarding the separation volume of coarse coal slime and flotation, the feed volume for coarse coal slime separation is increased while the feed volume for flotation is decreased. Since flotation costs are significantly higher than coarse coal slime costs, this method results in lower production costs. In terms of total clean coal yield, this method increases the yield by 0.52% compared to traditional processes, representing a significant improvement for the industry and substantially increasing economic benefits.

[0072] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A heavy media washing process for scarce coking coal that enhances middlings dissociation and recovery, characterized in that, Includes the following steps: Step a, raw coal sorting: raw coal with a particle size of no more than 50mm is sorted in a three-product heavy medium cyclone separator under the action of a qualified medium to obtain fine coal, middlings coal and gangue. Step b1, desliming of fine coal: The fine coal in step a passes through an arc screen and a desliming screen to obtain arc screen combined medium, desliming screen combined medium, desliming screen dilute medium and oversize material; wherein, the arc screen combined medium is divided into two parts by a diverter, arc screen combined medium 1 and desliming screen combined medium go to the fine coal combined medium barrel together, arc screen combined medium 2 and desliming screen dilute medium go to the dilute medium barrel together, and the oversize material is dewatered and used as the fine coal product; Step b2, medium removal of fine coal: The fine coal in step a passes through an arc screen and a medium removal screen to obtain arc screen combined medium, medium removal screen combined medium and oversize material; wherein, the arc screen combined medium and the medium removal screen combined medium go to the combined medium tank together, and the oversize material is fed into the coal slime mixing tank. Step b3, Desliming of the final gangue: The final gangue from step a passes through an arc screen and a desliming screen to obtain arc screen combined medium, desliming screen combined medium, desliming screen dilute medium and oversize material; wherein, the arc screen combined medium and the desliming screen combined medium are sent to the combined medium barrel together; the desliming screen dilute medium is sent to the dilute medium barrel, and the oversize material is used as the final gangue product. Step d, fine coal dilute medium dewatering: the arc screen diverting medium 2 in step b1 and the dilute medium of the dewatering screen in step b3 are buffered by the dilute medium tank and then pumped to the dewatering screen for dewatering and demediation, to obtain the oversize material and undersize water. Step e, dilute medium magnetic separation: The screened water from step d is fed into the magnetic separator for the first magnetic separation to obtain magnetic concentrate and magnetic tailings; the magnetic concentrate is returned to the fine coal mixing tank, and the magnetic tailings are used as coal slurry water for subsequent flotation operations; Step f, coal slime heavy medium separation: The material oversize from the screen in step d and the material oversize from the desliming screen in step b2 are buffered in the mixing tank and then pumped to the three-product coal slime heavy medium cyclone separator for separation to obtain coarse clean coal, coarse medium coal and coarse tailings. Step g1, coarse and fine coal desliming: In step f, coarse and fine coal is fed into a double-layer arc screen for desliming to obtain the oversize and undersize mixture; the undersize mixture is set to be diverted, undersize mixture divert 1 goes to the coal slime mixing tank, and undersize mixture divert 2 goes to the coarse and fine coal magnetic separation operation together with the oversize. Step g2, desliming of coarse and medium coal: The coarse and medium coal in step f are fed into a double-layer arc screen for desliming to obtain the oversize and undersize mixture; the oversize is sent to the grinding operation, and the undersize mixture is sent to the coal slime mixing tank. Step g3, coarse tailings magnetic separation: The coarse tailings from step f are fed into a magnetic separator for a second magnetic separation to obtain magnetic concentrate and magnetic tailings; the magnetic concentrate is then ground, and the magnetic tailings are classified and dewatered to become coarse tailings slime products. Step i, coarse and fine coal magnetic separation: The material oversize and undersize in step g1 are fed into the fine coal magnetic separator for the third magnetic separation to obtain magnetic fine coal and magnetic tailings; the magnetic tailings are used as coarse and fine coal products after being graded and dewatered; the magnetic fine coal is set to be divided, magnetic fine coal diversion 1 goes to the fine coal mixing tank, and magnetic fine coal diversion 2 goes to the coal slime mixing tank. Step j, Coal mixing: The arc-shaped screen mixing media 1 and the desliming screen mixing media in step b1, the arc-shaped screen mixing media and the desliming screen mixing media in step b2, the arc-shaped screen mixing media and the desliming screen mixing media in step b3, and the magnetic fine mixing media 1 in step i are returned to step a as qualified media after being buffered in the coal mixing media barrel. Step k, coal slime mixing and preparation: the material overseen by the desliming screen in step b2, the material overseen by the screen in step d, the underseen medium diversion 1 in step g1, the underseen medium diversion 2 in step g2, the material after grinding in step h, and the magnetic fine diversion 2 in step i are mixed and fed into the coal slime mixing tank, and after buffering, returned to step f.

2. The heavy media washing process for scarce coking coal with enhanced middlings dissociation and recovery as described in claim 1, characterized in that, It also includes step c, which is the crushing of fine coal: the material from the desliming screen in step b2 is crushed by a crusher before being fed into the coal slime mixing tank. The crusher is a reversible impact hammer crusher, which crushes the material to a particle size of less than 2mm.

3. The heavy media washing process for scarce coking coal with enhanced middlings dissociation and recovery as described in claim 1, characterized in that, It also includes step h, which is a grinding operation. The oversize material from step g2, the magnetic concentrate from step g3, and the supplementary magnetite powder and water are ground and dissociated together. After grinding, the material is fed into the coal slime mixing tank.

4. The heavy media washing process for scarce coking coal with enhanced middlings dissociation and recovery as described in claim 3, characterized in that, In step h, a rod mill is used for grinding, and the feed mass concentration is controlled at 45-55 wt%. After grinding, the mineral particles with a diameter of less than 0.074 mm account for more than 80% of the total material mass content. The amount of magnetite powder and water added is determined according to the amount of loss from tailings and products in the media system in order to maintain the dynamic balance and stability of the media system.

5. The heavy media washing process for scarce coking coal with enhanced middlings dissociation and recovery as described in claim 1, characterized in that, In steps b1 and b3, the desliming screen is configured in two sections. The first section, located near the feed end, occupies 1 / 3 of the total length of the screen and has a screen aperture of 0.5 mm. The second section, located near the discharge end, occupies 2 / 3 of the total length and has a screen aperture of 1.0 mm. The second section is also equipped with a water spray system with a spray volume of 1.2–2.0 m³ / h. 3 / t; In step b2, the desliming screen is set in two sections. The first section is close to the feed end and accounts for 1 / 3 of the total length of the desliming screen. The second section is close to the discharge end and accounts for 2 / 3 of the total length of the desliming screen. The screen holes of the desliming screen are all 0.5mm.

6. The heavy media washing process for scarce coking coal with enhanced middlings dissociation and recovery as described in claim 2, characterized in that, In step d, the particle size retained by the dewatering screen is 0.2 mm.

7. The heavy media washing process for scarce coking coal with enhanced middlings dissociation and recovery as described in claim 1, characterized in that, In steps g1 and g2, the sieve aperture of the double-layer arc sieve is 0.35 mm, and the particle size is between 0.2 and 0.25 mm.

8. The heavy media washing process for scarce coking coal with enhanced middlings dissociation and recovery as described in claim 1, characterized in that, In the second and third magnetic separation processes, water is added to adjust the feed concentration of the magnetic separator to between 15 and 25 wt%.

9. The heavy media washing process for scarce coking coal with enhanced middlings dissociation and recovery as described in claim 1, characterized in that, In step j, the density of each material fed into the coal slurry mixing tank is adjusted to between 1.35 and 1.45 kg / L, with the goal of separation by the first stage of the three-product coal slime heavy medium cyclone separator. In step k, the density of each material fed into the coal slime mixing tank is adjusted to between 1.40 and 1.50 kg / L, with the goal of separation by the first stage of the three-product coal slime heavy medium cyclone separator.

10. The heavy media washing process for scarce coking coal with enhanced middlings dissociation and recovery as described in claim 1, characterized in that, In step b1, the arc-shaped screen medium is divided into two parts by a diverter, wherein the arc-shaped screen medium diverter 2 accounts for 20% to 30% of the arc-shaped screen medium flow rate; in step g1, the under-screen medium is diverted, wherein the under-screen medium diverter 2 accounts for 25% to 35% of the under-screen medium flow rate; in step i, the diversion ratio of the magnetic fine diverter 1 and the magnetic fine diverter 2 is adjusted according to the control density of the fine coal medium barrel.

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