A hot drying and dewatering process based on air separation of raw coal particles

Abstract

A kind of hot drying dewatering process based on raw coal particle air separation, the raw coal drying technical field, including the following steps: step one: raw coal crushing and air separation pretreatment based on dust concentration safety threshold. Obtain the dust dispersion degree detection data of the raw coal to be processed, when the dust dispersion degree detection data does not exceed threshold, directly enter step two for drying;When dust dispersion degree detection data exceeds the preset safety threshold, the following air separation pretreatment operation is performed: the raw coal mined in open pit is crushed to the preset particle size, then sent into raw coal particle air separation system, through the classification effect of airflow air separation, separate out primary dust and micro-particles prone to secondary dust, to obtain clean coal.The dust concentration of clean coal powder into the dryer is strictly controlled below 30g / m³ by air separation, the fine particles prone to dust in raw coal are peeled off in advance, the amount of secondary dust generated in high-temperature drying process is reduced from the source, the problems of dust exceeding standard and equipment ash wear are effectively avoided, and dust classification control and source dust suppression are realized.

Description

Technical Field

[0001] This invention belongs to the field of raw coal drying technology, specifically relating to a thermal drying and dehydration process based on air classification of raw coal particles. Background Technology

[0002] Raw coal mined from open-pit mines first needs to be crushed and then dehydrated in a dryer according to particle size requirements. However, the mining and crushing processes generate a large amount of primary dust, which typically accounts for about 5% of the total raw coal content. Secondary dust is also generated during the hot drying process. When drying and dehydration operations are carried out in a high-temperature environment, the coal dust accumulated inside the dryer poses a significant safety hazard of dust explosion.

[0003] Chinese patent CN100422677C discloses a coal drying process and equipment, which uses nitrogen to inertize the rotary dryer and rotary cooler, and a bag filter dust collector for dust removal. While the above-mentioned existing process reduces the risk of explosion to some extent, its equipment structure is complex, nitrogen consumption is high, system operating costs are high, and the extensive use of inert gas to control oxygen content during the drying process does not fundamentally eliminate the source of dust.

[0004] Furthermore, the existing processes lack an intelligent pretreatment mechanism based on a safe dust concentration threshold, cannot dynamically adjust the air separation conditions according to the dust state of the raw coal, have uncontrollable dust concentration at the raw coal feed, and generate large amounts of secondary dust during the drying process, resulting in a high risk of dust exceeding standards. Therefore, there is an urgent need to develop a drying and dehydration process that can effectively remove dust before the raw coal enters the dryer, has adaptive adjustment capabilities for the safe threshold, and enables dust recycling. Summary of the Invention

[0005] To address the problem of uncontrollable dust explosion risks during the drying and dehydration of raw coal in open-pit mines due to excessively high dust content in the feed material, this invention provides a thermal drying and dehydration process based on air classification of raw coal particles. This process incorporates an air classification pretreatment stage before the raw coal enters the dryer. Air classification parameters are dynamically adjusted based on dust concentration detection data to achieve quantitative control of the safe dust concentration threshold. The separated dust and coal powder recovered from the drying tail gas are uniformly collected in the finished product silo, forming a complete process system from dust source elimination to product resource recovery. The specific technical solution is as follows:

[0006] A thermal drying and dewatering process based on air classification of raw coal particles includes the following steps:

[0007] Step 1: Raw coal crushing and air separation pretreatment based on dust concentration safety threshold

[0008] Obtain dust dispersion detection data of the raw coal to be processed. If the dust dispersion detection data does not exceed the threshold, proceed directly to step two for drying. If the dust dispersion detection data exceeds the preset safety threshold, perform the following air classification pretreatment operation:

[0009] After the raw coal mined from the open-pit mine is crushed to the preset particle size, it is sent to the raw coal particle air separation system. Through airflow classification, primary dust and microparticles that are prone to generating secondary dust are separated to obtain clean coal. The separated primary dust is collected and temporarily stored by the first dust removal system.

[0010] In this process, based on the raw coal dust dispersion detection data, the air volume and air speed of the raw coal particle air separation system are dynamically adjusted to pre-separate primary dust of different particle sizes and micro particles that are prone to generating secondary dust, so that the dust concentration in the clean coal entering the subsequent drying step is reduced to below the preset safety threshold.

[0011] Step 2: Drying the clean coal

[0012] The clean coal obtained in step one is fed into a rotary dryer via a conveying device. The clean coal is dried and dehydrated using a drying heat source to obtain the dried finished coal.

[0013] Step 3: Exhaust Gas Treatment and Particulate Matter Treatment

[0014] The dust separated in the first step of the air separation process is processed by the first dust removal system to separate the exhaust gas, dust and air-separated particles.

[0015] The exhaust gas and particles generated by the rotary dryer during the drying process in step two are treated separately by the second dust removal system.

[0016] Step 4: Product Collection and Co-processing

[0017] The dried coal from step two, the air-separated particles from the first dust removal system, and the dried particles from the second dust removal system are all incorporated into the finished product silo.

[0018] The exhaust gas generated by the first dust removal system and the exhaust gas generated by the second dust removal system are purified and then discharged.

[0019] Dust generated by the first dust removal system and dust generated by the second dust removal system are collected in the pulverized coal storage silo.

[0020] In the above technical solution, the preset safety threshold is 50g / m³, and the raw coal particle air separation system achieves the classification and separation of particles ≥1mm and <1mm by adjusting the airflow speed. After air separation pretreatment, the dust concentration in the clean coal entering the rotary dryer is reduced to below 30g / m³.

[0021] In the above technical solution, the first dust removal system includes an air separation and purification module and an air separation particle conveying module; the air separation and purification module includes a cyclone collector and a bag filter, and the dust separated in step one is purified in two stages by the air separation and purification module; the air separation particle conveying module includes a first processing channel connected to the cyclone collector and a second processing channel connected to the bag filter, the first processing channel includes a coal powder receiving screw conveyor, a closed airlock, a transfer screw conveyor and a belt conveyor, the second processing channel includes a closed airlock, a coal powder receiving screw conveyor, a transfer screw conveyor and a belt conveyor, and the air separation coal powder particles produced by the cyclone collector and the bag filter are uniformly conveyed to the coal powder storage bin for temporary storage.

[0022] In the above technical solution, the conveying device in step two includes a belt conveyor and a feed buffer conveying bin, and the drying heat source is a hot air furnace.

[0023] In the above technical solution, the second dust removal system in step two includes a drying and purification module and a dried particle conveying module; the drying and purification module includes a cyclone collector and a bag filter, and the exhaust gas discharged from the rotary dryer in step two undergoes two-stage purification treatment through the drying and purification module; the dried particle conveying module includes a third processing channel connected to the cyclone collector and a fourth processing channel connected to the bag filter, the third processing channel includes a coal powder receiving screw conveyor, a closed air valve, a transfer screw conveyor, and a belt conveyor, and the fourth processing channel includes a closed air valve, a coal powder receiving screw conveyor, a transfer screw conveyor, and a belt conveyor. The dried coal powder particles produced by the cyclone collector and the bag filter are uniformly conveyed to the coal powder storage silo for temporary storage.

[0024] In the above technical solution, the raw coal particle air separation system is a vertical cylindrical structure, and the cylinder is equipped with multi-layered symmetrical guide plates arranged at intervals along the height direction; the raw coal enters from the top of the cylinder and falls under the action of gravity; the air source at the bottom of the cylinder generates an upward counterflow airflow, which, together with the multi-layered symmetrical guide plates, causes light dust to be separated upward, while heavy particles fall under the action of gravity and are discharged from the bottom.

[0025] In the above technical solution, the preset particle size is 0-20mm; the raw coal particle air separation system is a three-stage composite grading structure. The three-stage composite grading structure is provided with a first-stage spiral airflow grading zone, a second-stage tangential jet centrifugal grading zone, and a third-stage conical airflow screening and selection zone connected sequentially along the material conveying direction. The first-stage grading zone separates the raw coal into coarse particles with a particle size ≥1mm and fine powder <1mm. The second-stage grading zone separates the 0.5-1mm coarse particles in the <1mm fine powder and returns them to the first-stage grading zone for re-grading. The third-stage grading zone is equipped with an air distribution plate and a grading impeller. By adjusting the inclination angle of the air distribution plate (5°-15°) and the rotation speed of the grading impeller (600-2400rpm), the fine powder is separated into ultrafine powder <0.1mm and microfine powder 0.1-0.5mm. After the three-stage grading, the ≥1mm coarse particles and the 0.1-0.5mm microfine powder are combined to obtain clean coal.

[0026] In the above technical solution, the processing capacity of the raw coal particle air separation system is 300 tons / hour or more, and its installed power is no more than 150KW.

[0027] The above technical solution also includes a step for verifying the effect of wind separation:

[0028] After step one is completed, a sample is taken from the clean coal obtained after air separation pretreatment, and the same batch of raw coal that has not undergone air separation pretreatment is taken as a control. The two samples are lifted in the same manner under the same environmental conditions, and the degree of dust dispersion is observed and compared. If no visible dust is dispersed when the clean coal sample is lifted, the air separation effect is judged to be qualified, and step two is continued. If there is still obvious dust dispersion when the clean coal sample is lifted, the air separation parameters in step one are adjusted and air separation pretreatment is repeated until the verification is qualified.

[0029] In the above technical solution, the dried finished coal, the air-separated particles separated during the air separation process, and the dried particles recovered from the drying exhaust gas are all sent into the finished product silo. The air separation dust removal stage and the drying exhaust gas dust removal stage form a synergistic recovery system by merging and collecting the products, so that the original air-separated particles separated before drying and the dried particles recovered from the drying exhaust gas are combined in the finished product silo.

[0030] The thermal drying and dehydration process based on air classification of raw coal particles of the present invention has the following advantages compared with the prior art:

[0031] I. This invention uses 50g / m³ as the dust safety threshold for judgment. Adaptive air classification pretreatment is only initiated when the dust dispersion of raw coal exceeds the standard. Raw coal that does not exceed the standard is directly dried, balancing dust removal effect and production efficiency. Through precise air classification, the dust concentration of clean coal entering the dryer is strictly controlled below 30g / m³, removing 0-1mm dust-generating fine particles from the raw coal in advance. This reduces the amount of secondary dust generated during high-temperature drying from the source, effectively avoiding the problems of excessive dust and equipment wear and tear. It achieves graded dust control and source dust suppression, solving the problem of excessive secondary dust during drying from the source.

[0032] Second, this invention dynamically adjusts the air volume and air speed of the air separation system based on real-time dust dispersion data of raw coal, which can adapt to the dust fluctuation characteristics of raw coal from different origins, with different moisture contents and in different seasons. It overcomes the defects of poor adaptability and unstable separation effect of traditional fixed parameter air separation process, greatly improves the versatility and stability of raw coal drying treatment under complex mining conditions, has adaptive working condition adjustment capability, and has stronger process adaptability.

[0033] Third, this invention sets up independent first and second dust removal systems for the two dust-generating processes of air separation and drying, realizing separate and specialized treatment of exhaust gas, dust, and particles; at the same time, it constructs a differentiated product recovery system, with finished coal, air-separated particles, and dried particles uniformly collected in the finished product silo, and fine dust separately collected in the coal powder storage silo, realizing the fine classification and recovery of coarse and fine materials, avoiding the waste of high-quality raw coal and the mixing of materials. Through the dual-process separate treatment and the coordinated collection and recovery of materials, the utilization rate of coal resources is improved.

[0034] IV. This invention offers two configuration options: a vertical counter-current airflow guide structure and a three-stage composite airflow classification structure, to suit different production scenarios. The vertical structure is simple to operate and has low maintenance costs, making it suitable for small and medium-sized production lines. The three-stage classification structure offers precise stratification and high fine powder removal rate, making it suitable for large-scale, high-capacity production lines. The appropriate configuration can be selected flexibly according to production needs, covering all production conditions.

[0035] Fifth, this invention includes a process for verifying the effectiveness of air separation. By conducting comparative tests on raw coal from the same batch, the quality of air separation pretreatment is determined. If the quality is not up to standard, the air separation parameters are adjusted in real time and the process is reprocessed. Standardized air separation effectiveness verification steps are set up to solve the problems of traditional processes lacking quality verification and inconsistent batch production effects. This ensures that the pretreatment quality of each batch of raw coal is stable and controllable, and achieves closed-loop process management.

[0036] VI. The air separation system of this invention can achieve a large flow rate processing capacity of 300 tons / hour and above, which can be adapted to the large-scale production needs of raw coal in large open-pit mines. At the same time, the installed power of the equipment is no more than 150KW. Compared with traditional multi-stage separation equipment, energy consumption is significantly reduced. It has the advantages of high output, energy saving and low cost, and has stronger industrial adaptability, which can meet the drying needs of high output and low energy consumption.

[0037] VII. Both dust removal systems of this invention adopt a two-stage purification mode of cyclone collector and bag filter, which thoroughly purifies the exhaust gas and can stably meet emission standards; they are equipped with an independent four-channel material conveying structure, each material is conveyed independently and without interference, and equipped with airlocks, screw conveyors and other equipment to effectively prevent material backflow and blockage, and improve the stability of continuous system operation. Attached Figure Description

[0038] Figure 1 The flowcharts for the thermal drying and dehydration process based on air classification of raw coal particles in Embodiments 1 and 2 of the present invention are shown below.

[0039] Figure 2 This is a top view of the vertical cylindrical structure of Embodiment 1 of the present invention;

[0040] Figure 3 This is a front view of the vertical cylindrical structure of Embodiment 1 of the present invention;

[0041] Figure 4 This is a flowchart of the three-level composite hierarchical structure in Embodiment 2 of the present invention;

[0042] Figures 1 to 4 In the middle, 1. Deflector plate. Detailed Implementation

[0043] The following are specific implementation cases and appendices. Figures 1 to 4 The present invention will be further described, but the present invention is not limited to these embodiments.

[0044] During the cold-state commissioning of a rotary forced fluidized bed dryer at an open-pit mine in Xinjiang, the measured dust concentration reached 110 g / m³ at a processing capacity of 200 tons per hour. This far exceeds the 50 g / m³ limit for coal dust explosion and the 30-50 g / m³ normal production safety value, confirming that the existing drying process poses a serious safety hazard when raw coal is directly fed into the machine.

[0045] In response to the above situation, this invention proposes a thermal drying and dehydration process based on air classification of raw coal particles.

[0046] The overall process flow of this invention is as follows: dust detection threshold determination, differentiated air separation pretreatment, clean coal hot air drying, dual-process separate dust removal treatment, product collaborative collection and recycling, and closed-loop verification of air separation effect. It can realize threshold linkage adaptive air separation, dual-process collaborative recycling, and closed-loop quality verification. It also configures two differentiated air separation equipment structures to form two independent and complete implementation processes.

[0047] Example 1

[0048] like Figures 1 to 3As shown, this embodiment uses a counter-current air separation system for raw coal pretreatment. This method is suitable for small and medium-sized raw coal drying production lines. The equipment has a simple structure, is easy to operate and maintain, has an installed power of 150KW, and consumes less energy. It can process 300 tons of raw coal per hour. The specific process steps are as follows:

[0049] Step 1: Raw coal crushing and air separation pretreatment based on dust concentration safety threshold: Collect raw coal from open-pit mines, crush the raw coal, and monitor the dust dispersion of the raw coal to be treated in real time. The preset safety threshold is 50g / m³. When the dust dispersion test data exceeds 50g / m³, the crushed raw coal is sent into the raw coal particle air separation system with a vertical cylindrical structure through the raw coal conveyor and raw coal airlock. The air separation system is a vertical cylindrical structure with multiple layers of symmetrical guide plates 1 arranged at intervals along the height direction inside the cylinder. The angle between the guide plates 1 and the horizontal direction can be adjusted within the range of 15°-60°. The raw coal is fed evenly from the top of the cylinder and falls at a constant speed under its own gravity. The air source at the bottom of the cylinder continuously generates an upward countercurrent airflow. The rising airflow comes into full contact with the falling raw coal. Combined with the turbulence and guiding effect of the multiple layers of symmetrical guide plates 1, the light and easily dusty primary dust and secondary microparticles <1mm in the raw coal are separated upward, while the heavy raw coal particles ≥1mm fall stably under the action of gravity and are discharged from the bottom of the cylinder to obtain clean coal. During operation, the system dynamically adjusts the airflow and velocity of the air separation system in real time based on the raw coal dust dispersion data. The higher the dust dispersion, the greater the corresponding increase in airflow and velocity, enhancing the removal effect of fine dust and ultimately reducing the dust concentration of the pretreated clean coal to below 30g / m³. The raw dust that rises during the air separation process enters the first dust removal system with the airflow, achieving separate treatment of exhaust gas, dust, and air-separated particles.

[0050] After treatment, the dust concentration in the clean coal decreased from 110 g / m³ to approximately 28 g / m³, which is below the upper explosive limit of 50 g / m³ for coal dust, meeting the requirements for safe production. The classification efficiency was approximately 58.2%, and the lower limit of the classification particle size was approximately 0.3 mm.

[0051] In the above process, this technology can achieve on-demand grading and air separation of raw coal with a preset particle size range of 0-20mm. For example, by adjusting the raw coal particle air separation system to a higher wind speed, coal powder particles larger than 1mm can be effectively separated and removed, significantly reducing the powder content of the raw coal entering the dryer, and reducing the amount of secondary dust generated during the high-temperature drying and dehydration process of raw coal from the source, further strengthening dust control and production safety assurance capabilities.

[0052] Therefore, in this process, pretreatment can be completed before the raw coal enters the dryer. The air volume and speed can be controlled by the raw coal particle air separation system to separate the primary dust on the raw coal in advance and control the amount of secondary dust generated. The raw coal after dust removal is then sent to the dryer for dehydration treatment, thus avoiding the safety hazard of explosion caused by dust accumulation under high temperature drying conditions.

[0053] Step Two: Clean Coal Drying: The low-dust clean coal obtained from the pretreatment in Step One is evenly fed into a rotary dryer via a conveyor belt system combined with a feed buffer hopper. A hot air furnace is used as the heat source for continuous thermal drying and dehydration of the clean coal, removing surface and internal moisture to obtain the dried finished coal. The rotary dryer has a three-circle structure. Its internal rotors forcefully disperse the material through mechanical movement, causing the material to be fluidized and suspended in different drying chambers, ensuring full contact with the hot air. The feed buffer hopper buffers and distributes the material evenly, preventing uneven drying and sudden changes in equipment load caused by fluctuations in the instantaneous feed rate, thus ensuring continuous and stable operation of the drying process.

[0054] Step 3: Exhaust Gas and Particle Treatment: The exhaust gas, dust, and air-classified particles generated in the air separation process are sent to the first dust removal system for separate treatment. The first dust removal system includes an air separation purification module and an air-classified particle conveying module. The air separation purification module consists of a cyclone collector and a bag filter, achieving two-stage purification of the exhaust gas and effectively intercepting fine dust to ensure that the exhaust gas meets standards. The air-classified particle conveying module has independent first and second processing channels. The first processing channel is connected to the cyclone collector and sequentially conveys coarse particles through a coal powder collecting screw conveyor, an airlock, a transfer screw conveyor, and a belt conveyor. The second processing channel is connected to the bag filter and sequentially conveys fine dust through an airlock, a coal powder collecting screw conveyor, a transfer screw conveyor, and a belt conveyor. Finally, all air-classified coal powder particles are transported to the coal powder storage silo for temporary storage. Meanwhile, the high-temperature exhaust gas and dried particles generated during the drying process of the rotary dryer are sent to the second dust removal system for treatment. The structure of the second dust removal system is matched with that of the first dust removal system. It achieves two-stage purification of exhaust gas through the second cyclone collector and the second bag filter. It is equipped with the third and fourth independent conveying channels to complete the conveying and collection of dried coal powder particles, which are then uniformly sent to the coal powder storage silo.

[0055] This process employs rotary dryer technology, relying on direct contact between the material and the heat medium and the formation of a dispersed fluidized state to complete the drying process. This type of dryer has a fast heat and moisture exchange rate, high dehydration efficiency, and low operating costs. It can effectively reduce the moisture content of raw coal, reduce the weight and cost of coal transportation, and at the same time increase the calorific value of raw coal combustion.

[0056] Step 4: Product Collection and Co-processing Recycling: The exhaust gases purified by the first and second dust removal systems are uniformly discharged in compliance with standards; all fine dust collected by the two dust removal systems is collected in the coal powder storage silo; the dried finished coal, the air-classified particles produced by the first dust removal system, and the dried particles produced by the second dust removal system are uniformly sent to the finished product silo for collection and storage, forming a co-processing recycling system of air-classification dust removal and drying dust removal, realizing the fine classification and recycling of coarse and fine materials.

[0057] By integrating the processes of air classification pretreatment, rotary dryer drying, and two-stage series dust removal of the dryer exhaust gas, the exhaust gas from the rotary dryer is treated in series by a cyclone collector and a bag filter. The dust emission concentration at the dust removal outlet can be controlled at about 28 mg / m³, which is significantly lower than the 150 mg / m³ dust emission concentration allowed in the national industrial waste emission standards. This achieves the dual effect of dust reduction and safe operation.

[0058] In the above steps, the coal yield is high after the raw coal is dried and processed. The separated coal powder particles enter the finished product silo together with the dried raw coal. After the raw coal is dried and processed, there is no loss of raw coal quantity except for the evaporated water.

[0059] Step 5: Verification of Air Classification Effect: After air classification pretreatment, randomly select pretreated clean coal samples and use raw coal from the same batch that has not undergone air classification pretreatment as a control sample. Under the same temperature, humidity, and ventilation conditions, both sets of samples are lifted to the same height and vibrated in the same manner to visually compare the degree of dust dispersion. If no visible dust is dispersed in the clean coal sample, the air classification effect is deemed qualified, and the sample proceeds normally to the drying process. If significant dust dispersion is observed, the air volume and velocity of the air classification system are increased in real time, and air classification pretreatment is repeated until the verification is qualified, ensuring closed-loop control of pretreatment quality.

[0060] In this embodiment, the air separation system equipment parameters are: processing capacity of 300 tons / hour and installed power of 145KW, which meets the production needs of large capacity and low energy consumption and is suitable for large-scale raw coal pretreatment operations in open-pit mines.

[0061] This invention employs a precise air classification pretreatment process for raw coal particles, reconstructing the raw coal processing flow and constructing a novel open-pit mine raw coal drying and dewatering process system that integrates raw coal crushing, fine particle air classification and dust removal, and fluidized bed thermal drying. This process, by adding a controllable air classification and dust removal stage before the thermal drying process, removes fine particles that easily generate primary and secondary dust from the particle source, effectively avoiding the safety hazards of excessive dust and dust explosions caused by the large-scale precipitation and aggregation of fine dust under high-temperature drying conditions. This effectively solves the long-standing problem restricting the large-scale drying and quality improvement of raw coal in open-pit mines.

[0062] Example 2

[0063] Main references Figure 1 and Figure 4 As shown, the main difference between this embodiment and Embodiment 1 is that the internal structure of the raw coal particle air separation system is different, while the operation of the drying and dust removal system is the same as in Embodiment 1.

[0064] This embodiment employs a three-stage composite classification structure: a primary spiral airflow classification zone, a secondary tangential jet centrifugal classification zone, and a tertiary conical airflow screening and selection zone. This results in more classification stages, higher particle size classification accuracy, and superior removal of 0.1-1mm fine particles. It is suitable for processing raw coal with high dust and fine powder content. The specific process steps are as follows:

[0065] Step 1: Raw coal crushing and air classification pretreatment based on dust concentration safety threshold: After crushing the raw coal from the open-pit mine, the dust dispersion of the raw coal is monitored in real time. A safety threshold of 50 g / m³ is used; if this threshold is exceeded, a three-stage composite airflow classification operation is initiated. The air classification system sequentially connects the primary spiral airflow classification zone, the secondary tangential jet centrifugal classification zone, and the tertiary conical airflow screening and selection zone along the material conveying direction.

[0066] In the primary spiral airflow classification zone, raw coal descends in a swirling manner within the spiral airflow conveying channel. The combined effect of the spiral centrifugal force and the airflow conveying force performs coarse classification, separating the material into coarse particles ≥1mm and fine powder <1mm. The airflow velocity in this classification zone is controlled within a range that allows the fine powder to rise while permitting the settling of coarse particles.

[0067] The fine powder <1mm separated in the primary classification zone enters the secondary tangential jet centrifugal classification zone. This zone introduces downward negative pressure under tangential airflow conditions, with the pressure difference controlled within the range of 500-1500Pa. This causes the fine powder to undergo secondary centrifugal classification in a high-speed rotating airflow field, separating out the 0.5-1mm coarse particles entrained within. These coarse particles are returned to the primary classification zone for reclassification via a reflux channel. The remaining fine powder, mainly 0.1-0.5mm, enters the tertiary conical airflow screening and refining zone through the outlet.

[0068] The three-stage conical airflow screening and refining zone has a conical structure, wider at the bottom and narrower at the top. The lower part of the cylinder contains an adjustable-tapered air distribution plate, the inclination angle of which can be adjusted within the range of 5°-15°. The upper part of the cylinder features an adjustable-speed classifying impeller, with a rotational speed range of 600-2400 rpm. During operation, the rising airflow enters from below the air distribution plate and forms a fluidized bed within the conical cylinder. The thickness of the fluidized bed is adjusted by combining the inclination angle and the taper of the air distribution plate. The fine powder is suspended in the fluidized bed and moves upward. When it passes through the classifying impeller, it undergoes a third classification under the combined action of centrifugal force and airflow drag: ultrafine powder with a particle size <0.1mm passes through the impeller gap and enters the cyclone separator or bag filter for collection with the airflow; fine powder with a particle size of 0.1-0.5mm is thrown towards the outer edge of the conical cylinder by centrifugal force and falls along the cylinder wall and is discharged from the fine powder outlet at the bottom; particles with a particle size of 0.5-1mm have been separated in the secondary classification zone and return to the primary classification zone for reclassification, and do not enter the tertiary classification zone.

[0069] After three-stage classification, coarse particles ≥1mm and fine powders of 0.1-0.5mm are combined to obtain clean coal. After treatment, the dust concentration in the clean coal decreases from 110g / m³ to approximately 22g / m³, which is below the lower limit of the coal dust explosion safety threshold of 30g / m³. The classification efficiency is approximately 80.0%, and the lower limit of the classified particle size is precisely controlled at approximately 0.1mm. Under conditions of an airflow of 140-180m³ / h and a classifying impeller speed of 1800rpm, the recovery rate of the 0.1-0.5mm particle size product is higher than 95%.

[0070] During the operation, the air supply speed and volume of the three-level classification zone are dynamically matched based on the real-time dust dispersion data of raw coal, adapting to the fluctuations of raw coal dust and ensuring stable classification accuracy.

[0071] The cleaned coal obtained after three-stage grading is sent to a rotary dryer for drying and dehydration.

[0072] Step 2, Clean Coal Drying: The process is the same as in Example 1. Qualified clean coal is sent to a rotary dryer via a belt conveyor and a feed buffer conveyor hopper. Hot air furnace is used to heat the dryer to complete the drying and dehydration process, resulting in dried finished coal.

[0073] Step 3, Exhaust Gas and Particle Treatment: Consistent with the dust removal system in Example 1, exhaust gas and particles from the air separation process are treated by two-stage purification and dual-channel conveying through the first dust removal system; exhaust gas and particles from the drying process are treated by two-stage purification and dual-channel conveying through the second dust removal system. Each channel operates independently to avoid material mixing and pipeline blockage, ensuring stable system operation.

[0074] Step 4, Product Collection and Collaborative Recycling: Following the unified recycling logic of this invention, the exhaust gas is purified to meet emission standards, fine dust is collected in the coal powder storage bin, and finished coal, air-separated particles, and dried particles are uniformly collected in the finished product bin to maximize resource recycling.

[0075] Step 5: Verification of air classification effect: Using the same comparative verification method as in Example 1, complete the closed-loop verification of air classification quality. If it fails, dynamically adjust the impeller speed, air distribution plate angle, and air supply parameters of the three-level classification zone, and re-classify and pre-treat until the dust removal effect meets the standard.

[0076] This embodiment achieves precise tiered sorting of raw coal particles through a three-level gradient classification structure. Compared with a single air separation structure, the removal rate of fine dust is increased by more than 20%, and the amount of secondary dust generated during the drying process is greatly reduced. It is especially suitable for the processing of inferior raw coal with high fine powder content and easy dust generation, as well as surface raw coal from open-pit mines.

[0077] Comparison of comparative experimental data:

[0078] To fully verify the advanced nature and practicality of the process of this invention, comparative experiments were conducted between Examples 1 and 2 of this invention and traditional direct drying process for raw coal and conventional fixed-parameter air separation drying process. The raw coal used in the experiments was from the same batch mined in the same open-pit mine, and the experimental environment, drying temperature, equipment capacity, and operating time were completely consistent. The comparison data of the core performance parameters are shown in the table below:

[0079] Experimental group Feed dust concentration (g / m³) Dust concentration of clean coal entering the dryer (g / m³) Secondary dust generation during drying (mg / m³) Coal powder recovery rate (%) Continuous operating time of the equipment (h) Energy consumption per unit (kWh / t) Comparative Example 1 (Traditional Direct Drying Process) 68.5 68.5 42.6 82.3 18 8.6 Comparative Example 2 (Conventional fixed-parameter air separation process) 67.8 42.5 25.3 89.6 24 7.2 Example 1 (Vertical Countercurrent Air Separation Process of the Invention) 68.2 28.6 12.8 95.2 32 6.1 Example 2 (Three-stage composite grading process of the present invention) 67.9 25.3 9.5 97.8 32 6.5

[0080] The above experimental data clearly demonstrate that both embodiments of the present invention can stably control the dust concentration of the clean coal entering the dryer to below 30 g / m³, which is far superior to traditional processes and conventional air classification processes; the amount of secondary dust generated during drying is significantly reduced, resulting in significant dust control effects; the coal powder recovery rate is increased by more than 5%, significantly optimizing resource utilization; the continuous operating time of the equipment is significantly extended, and the system stability is higher; the energy consumption per unit product is significantly reduced, combining the comprehensive advantages of environmental protection, high efficiency, and energy saving. Among them, Embodiment 2 with three-stage composite grading has the best dust removal accuracy and resource recovery rate, while Embodiment 1 with a vertical counter-flow structure has lower energy consumption and simpler operation and maintenance, and can be flexibly selected according to actual production needs.

[0081] Furthermore, to verify the source control mechanism of the 1mm critical classification particle size defined in this embodiment on primary and secondary dust, and to explore the impact of different air classification particle sizes on dust generation during raw coal drying, dust accumulation risk, and production safety, this invention conducts a multi-gradient particle size air classification control experiment. Four classification thresholds of 0.1mm, 0.5mm, 1.0mm, and 1.5mm are used to pre-treat the same batch of 0-20mm open-pit mine raw coal. Subsequently, the same rotary drying process, the same hot air temperature, and the same wind speed are used for drying operations. The primary dust removal effect, the concentration of secondary dust generated during the drying process, and the safety risks are monitored under each particle size classification condition, thereby verifying the necessity of selecting a 1mm classification particle size in this invention.

[0082] The following is an analysis of the experimental process and mechanism for different air-classified particle size gradients:

[0083] 1. Air classification test with a particle size of 0.1mm: Initial air classification of raw coal using a 0.1mm ultrafine classification mode removes only a very small amount of ultrafine free dust. The vast majority of easily dust-generating particles (0.1-1mm) remain inside the clean coal. Under this condition, while some surface dust appears to be removed, potential dust-generating particles trapped between the raw coal particles are not removed. Upon entering the high-temperature dryer, these hidden particles are precipitated out in large quantities due to the hot air scouring and the friction of the tumbling particles, generating high-intensity secondary dust. This has almost no source dust suppression effect and cannot solve the problem of excessive dust during the drying process.

[0084] 2. Air classification test with a particle size of 0.5mm: Increasing the air classification particle size to 0.5mm can remove some ultrafine dust, but a large amount of highly reactive and dust-generating particles in the 0.5-1mm range still remain. Tests showed that the instantaneous dust concentration in the drying chamber could reach 48-52 g / m³, and the dust accumulation per cubic meter was close to the critical concentration threshold for coal mine dust explosions, posing a significant safety hazard. Furthermore, under this particle size classification mode, the drying process generates a large amount of continuous dust, resulting in a dust-filled working environment and severe dust accumulation in the equipment's air ducts and heat exchange structures, failing to meet safety production and environmental emission standards.

[0085] 3. Air classification test with a particle size of 1.0mm, which is the core critical particle size of this invention: By precisely setting the air classification threshold to 1mm, all primary dust, adhering microparticles, and potential secondary dust parent particles <1mm in the raw coal can be selectively removed, leaving only structurally stable and non-dust-prone main particles of raw coal ≥1mm for the drying process. Test results show that after 1mm precise classification pretreatment, the dust concentration of the incoming clean coal can be stably reduced to below 30g / m³, with no significant secondary dust precipitation during the drying process. The dust concentration in the drying chamber is maintained at a safe low value, completely avoiding the risk of dust accumulation and explosion, and thoroughly cutting off the source of secondary dust generation at the physical particle level.

[0086] 4. Test under the condition of 1.5mm particle size for air classification: Further expanding the classification particle size to 1.5mm can completely remove fine particles that are prone to dust generation, but the power cost and time cost of air classification separation are increased.

[0087] Comprehensive comparative experiments, conducted through multi-gradient particle size comparison tests, demonstrate that: grading with excessively small particle sizes of 0.1mm and 0.5mm cannot effectively eliminate secondary dust generated during drying and poses significant safety hazards; grading with excessively large particle sizes of 1.5mm, while suppressing dust, results in resource waste; the 1mm precise grading threshold defined in this invention is the optimal critical parameter that balances safe production, zero secondary dust, and high finished product recovery rate. Combined with the dust concentration threshold-linked adaptive air classification, three-stage composite grading or vertical counter-current air classification structure, and dual-process collaborative recovery system of this invention, safer, more refined, and more efficient production of raw coal thermal drying processes can be achieved, solving the long-standing technical pain points in the industry of being unable to accurately match air classification particle sizes and being unable to eradicate secondary dust generated during drying at its source.

[0088] The comparison data of the overall process described above further confirms that: the processes of both embodiments of the present invention can stably control the dust concentration of the clean coal entering the dryer to below 30g / m³, which is superior to the traditional process and the conventional air classification process; the amount of secondary dust generated during drying is greatly reduced, and the dust control effect is significant; the coal powder recovery and utilization rate is increased by more than 5%, and the resource utilization rate is optimized; the continuous operation time of the equipment is significantly extended, and the system stability is higher.

[0089] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A thermal drying and dewatering process based on air classification of raw coal particles, characterized in that: Includes the following steps: Step 1: Raw coal crushing and air separation pretreatment based on dust concentration safety threshold Obtain dust dispersion detection data of the raw coal to be processed. If the dust dispersion detection data does not exceed the threshold, proceed directly to step two for drying. If the dust dispersion detection data exceeds the preset safety threshold, perform the following air classification pretreatment operation: After the raw coal mined from the open-pit mine is crushed to the preset particle size, it is sent to the raw coal particle air separation system. Through airflow classification, primary dust and microparticles that are prone to generating secondary dust are separated to obtain clean coal. The separated primary dust is collected and temporarily stored by the first dust removal system. In this process, based on the raw coal dust dispersion detection data, the air volume and air speed of the raw coal particle air separation system are dynamically adjusted to pre-separate primary dust of different particle sizes and micro particles that are prone to generating secondary dust, so that the dust concentration in the clean coal entering the subsequent drying step is reduced to below the preset safety threshold. Step 2: Drying the clean coal The clean coal obtained in step one is fed into a rotary dryer via a conveying device. The clean coal is dried and dehydrated using a drying heat source to obtain the dried finished coal. Step 3: Exhaust Gas Treatment and Particulate Matter Treatment The dust separated in the first step of the air separation process is processed by the first dust removal system to separate the exhaust gas, dust and air-separated particles. The exhaust gas and particles generated by the rotary dryer during the drying process in step two are treated separately by the second dust removal system. Step 4: Product Collection and Co-processing The dried coal from step two, the air-separated particles from the first dust removal system, and the dried particles from the second dust removal system are all incorporated into the finished product silo. The exhaust gas generated by the first dust removal system and the exhaust gas generated by the second dust removal system are purified and then discharged. Dust generated by the first dust removal system and dust generated by the second dust removal system are collected into the pulverized coal storage silo.

2. The thermal drying and dehydration process based on air classification of raw coal particles according to claim 1, characterized in that: The preset safety threshold is 50g / m³. The raw coal particle air separation system achieves the classification and separation of particles ≥1mm and <1mm by adjusting the airflow speed. After air separation pretreatment, the dust concentration in the clean coal entering the rotary dryer is reduced to below 30g / m³.

3. The thermal drying and dewatering process based on raw coal particle air classification according to claim 1, characterized in that: The first dust removal system includes an air separation and purification module and an air separation particle conveying module. The air separation and purification module includes a cyclone collector and a bag filter. The dust separated in step one undergoes two-stage purification treatment via the air separation and purification module. The air separation particle conveying module includes a first processing channel connected to the cyclone collector and a second processing channel connected to the bag filter. The first processing channel includes a coal powder receiving screw conveyor, a closed-loop conveyor, a transfer screw conveyor, and a belt conveyor. The second processing channel includes a closed-loop conveyor, a coal powder receiving screw conveyor, a transfer screw conveyor, and a belt conveyor. The air-separated coal powder particles produced by the cyclone collector and the bag filter are uniformly conveyed to a coal powder storage silo for temporary storage.

4. The thermal drying and dehydration process based on air classification of raw coal particles according to claim 1, characterized in that: The conveying device in step two includes a belt conveyor and a feed buffer conveying bin, and the drying heat source is a hot air furnace.

5. The thermal drying and dehydration process based on air classification of raw coal particles according to claim 1, characterized in that: In step two, the second dust removal system includes a drying and purification module and a dried particle conveying module. The drying and purification module includes a cyclone collector and a bag filter. The exhaust gas discharged from the rotary dryer in step two undergoes two-stage purification treatment via the drying and purification module. The dried particle conveying module includes a third processing channel connected to the cyclone collector and a fourth processing channel connected to the bag filter. The third processing channel includes a coal powder receiving screw conveyor, a closed-loop fan, a transfer screw conveyor, and a belt conveyor. The fourth processing channel includes a closed-loop fan, a coal powder receiving screw conveyor, a transfer screw conveyor, and a belt conveyor. The dried coal powder particles produced by the cyclone collector and the bag filter are uniformly conveyed to the coal powder storage silo for temporary storage.

6. The thermal drying and dewatering process based on air classification of raw coal particles according to claim 1, characterized in that: The raw coal particle air separation system is a vertical cylindrical structure with multiple layers of symmetrical herringbone baffles arranged at intervals along the height direction inside the cylinder. Raw coal enters from the top of the cylinder and falls under the action of gravity. The air source at the bottom of the cylinder generates an upward counterflow airflow, which, together with the multiple herringbone baffles, causes light dust to be separated upwards, while heavy particles fall under the action of gravity and are discharged from the bottom.

7. The thermal drying and dewatering process based on air classification of raw coal particles according to claim 1, characterized in that: The preset particle size is 0-20mm; the raw coal particle air separation system is a three-stage composite grading structure. The three-stage composite grading structure is provided with a first-stage spiral airflow grading zone, a second-stage tangential jet centrifugal grading zone, and a third-stage conical airflow screening and selection zone connected sequentially along the material conveying direction. The first-stage grading zone separates the raw coal into coarse particles with a particle size ≥1mm and fine powder <1mm. The second-stage grading zone separates the 0.5-1mm coarse particles in the <1mm fine powder and returns them to the first-stage grading zone for re-grading. The third-stage grading zone is equipped with an air distribution plate and a grading impeller. By adjusting the inclination angle of the air distribution plate from 5° to 15° and the rotation speed of the grading impeller from 600 to 2400 rpm, the fine powder is separated into ultrafine powder <0.1mm and microfine powder 0.1-0.5mm. After the three-stage grading, the ≥1mm coarse particles and the 0.1-0.5mm microfine powder are combined to obtain clean coal.

8. The thermal drying and dewatering process based on air classification of raw coal particles according to claim 1, characterized in that: The raw coal particle air separation system has a processing capacity of 300 tons / hour or more, and its installed power is no more than 150KW.

9. The thermal drying and dewatering process based on air classification of raw coal particles according to claim 1, characterized in that: It also includes a wind sorting effect verification step: After step one is completed, a sample is taken from the clean coal obtained after air separation pretreatment, and the same batch of raw coal that has not undergone air separation pretreatment is taken as a control. The two samples are lifted in the same manner under the same environmental conditions, and the degree of dust dispersion is observed and compared. If no visible dust is dispersed when the clean coal sample is lifted, the air separation effect is judged to be qualified, and step two is continued. If there is still obvious dust dispersion when the clean coal sample is lifted, the air separation parameters in step one are adjusted and air separation pretreatment is repeated until the verification is qualified.

10. The thermal drying and dewatering process based on air classification of raw coal particles according to claim 1, characterized in that: The dried finished coal, the air-separated particles separated during the air separation process, and the dried particles recovered from the drying exhaust gas are all sent into the finished product silo. The air separation dust removal process and the drying exhaust gas dust removal process form a synergistic recovery system by merging and collecting the products, so that the original air-separated particles separated before drying and the dried particles recovered from the drying exhaust gas are combined in the finished product silo.

Images