Technological method for preparing nanoscale ultra-pure coal through one-step method

Abstract

The invention provides a process method for preparing nanoscale ultra-pure coal by a one-step method, which comprises the following steps: (1) feeding raw material coal into a steam mill, introducing superheated steam into the steam mill in the presence of an agglomeration agent, performing high-speed collision crushing on the superheated steam and the raw material coal, and then separating; (2) the separated materials are separated through a cyclone separator, mineral substances are discharged from the top of the cyclone separator along with steam, coal granules are obtained at the bottom of the cyclone separator, and after the coal granules are dried through hot steam, nanoscale ultra-pure coal powder and an agglomeration agent are obtained; wherein the temperature of the superheated steam ranges from 280 DEG C to 350 DEG C, and the temperature of an outlet of the steam mill ranges from 130 DEG C to 180 DEG C; the boiling point of the agglomeration agent is 180-300 DEG C. According to the method, the temperature difference of the inlet and the outlet of the steam mill is utilized, combination and separation of the superfine pulverized coal and the agglomeration agent are achieved, the technological process is simplified, meanwhile, direct heat exchange is achieved in the evaporation and condensation processes of the agglomeration agent, and the heat efficiency of the whole process is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of preparing ultra-pure coal, and in particular relates to a process for preparing nano-level ultra-pure coal in one step. Background Art

[0002] The current situation of my country's production and consumption of energy, which is mainly coal, determines that the application scope of coal should be further expanded in China, and the preparation of coal-based activated carbon should be vigorously promoted. Developing high-end and differentiated coal utilization technologies, focusing on high-end industries, selectively developing high-end new material projects, and realizing the transformation and upgrading of traditional fuels to materials is not only the only choice for my country, but also an urgent need of the coal industry.

[0003] Coal is mainly composed of organic carbon-hydrogen skeleton structure and inorganic minerals. Coal-based carbon materials are high-carbon materials made from coal as the main raw material, such as coal-based activated carbon, graphene, etc. These coal-based high-end carbon materials have certain requirements for coal particle size, ash content, etc. However, the ash content in coal will have an adverse effect on the preparation of high-end carbon materials and the performance of products. For example, the ash content in raw coal will inhibit the action of the activator in the carbonization process, increase the amount of activator, and increase the cost. The residual ash in the activated carbon will agglomerate with the electrolyte ions under the action of the electric field to inhibit the formation of the double electric layer, and a large number of studies have shown that the electrochemical performance of coal-based capacitors made by deashing is better than that of capacitors without deashing. Therefore, how to provide ultra-fine and ultra-pure raw coal powder is a prerequisite for the preparation of high-end carbon materials from coal. Generally, ultra-pure coal refers to low-sulfur, low-ash clean coal with an ash content of 0.1% to 1% and a particle size of less than 10μm. Ultra-pure coal is a high value-added coal resource with advantages such as low ash content, high calorific value and low environmental impact. It is one of the main ways to achieve efficient and clean utilization of coal resources. Therefore, the preparation technology of ultra-pure coal has also become a hot spot and difficulty in research at home and abroad.

[0004] The preparation methods of ultra-pure coal are usually divided into three categories: chemical method, physical method and physicochemical method. Among them, the chemical method can generally prepare ultra-pure coal with an ash content of less than 1%, but its production process has problems such as high cost, high pollution, low production efficiency, and serious reagent corrosion. In addition, the use of this process will also remove inorganic mineral components such as sodium and potassium in the raw coal that contain catalytic activity, resulting in a decrease in the activation rate of activated carbon. The physical ash removal method has the advantages of low pollution, high efficiency, low cost, and little impact on coal quality. It is generally used to prepare clean coal with an ash content of less than 3%. Some methods can obtain low-ash clean coal with an ash content of 1% to 2%. If you want to get a lower ash content, the process flow will also become complicated. The physical and chemical method is a deashing method that uses the difference in surface chemical properties between minerals and coal for separation. It has great advantages in deashing ultrafine coal powder. Conventional physical and chemical methods, such as oil cluster-screening method, oil cluster-flotation method, etc., generally use short-chain hydrocarbon pentane as a flocculant, which has a low ignition point, is volatile, and has the risk of explosion. In addition, the entire production process is long, which limits its industrial application.

[0005] At present, the prior art has studied the preparation of ultra-pure coal: Patent CN 113930268 A discloses a method for preparing ultra-pure coal. The method comprises the following steps: (1) roasting coal in a protective gas; (2) treating the roasted coal with alkali to obtain secondary coal; (3) adding acid to the secondary coal for leaching, washing and drying to obtain ultra-pure coal with an ash content of less than 0.3wt%. The invention adopts conventional acid-base method for ash removal, and the chemical reagents are highly polluting and corrosive to the equipment. In addition, the invention only discloses the laboratory pilot study process, and has not formed a process flow for continuous industrial production.

[0006] Patent CN 110003965 A discloses a method for preparing ultrafine clean coal by ball milling pretreatment and chemical method. The patent includes the following steps: (1) crushing anthracite and roasting it in a protective atmosphere to obtain coal particles; adding a dispersant to the obtained coal particles, controlling the ball gradation for ball milling and drying to obtain ultrafine coal powder; (2) mixing the ultrafine coal powder with a surfactant, adding it to a mixed leaching solution of acid and fluoride salt, filtering, washing and drying after heating and leaching to obtain ultrafine coal powder with an ash content of less than 0.5wt%. This invention uses acid and fluoride salt for ash removal, which is similar to the hydrofluoric acid method and also has problems such as pollution and corrosion.

[0007] Patent CN107626438A discloses a process for preparing ultra-pure coal by physical method using anthracite, which includes the following steps: grinding anthracite through a 200-mesh sieve to obtain a coal sample, conducting a flotation test on the coal sample, and obtaining flotation clean coal. Sodium silicate is added to the flotation clean coal, and the step-by-step release is performed to obtain the step-by-step release clean coal. After stirring evenly, it is poured into a spiral chute to obtain spiral-sorted clean coal; wherein, the middling obtained after one spiral sorting should be returned to the spiral chute for another spiral sorting, sodium silicate and water are added to the spiral-sorted clean coal, stirred for a period of time, kerosene is added, stirring is continued for a period of time, sifted and dried, and the sieved material is ultra-pure coal, and the obtained ultra-pure coal has coarse particles and a high impurity content (ash content <2%).

[0008] In summary, although the existing technology has conducted some research on ultra-pure coal, there are still problems such as high impurity content and environmental unfriendliness. It is urgent to develop an ultra-pure coal preparation technology that has a simple process, is environmentally friendly, and has little impact on coal quality. Summary of the invention

[0009] In order to overcome the deficiencies in the prior art, the present invention provides a one-step process for preparing nano-level ultra-pure coal, which utilizes the temperature difference between the inlet and outlet of the steam mill to achieve the combination and separation of ultra-fine coal powder and agglomerating agent, thereby simplifying the entire process flow. At the same time, the evaporation and condensation processes of the agglomerating agent in the present invention are direct heat exchange, thereby improving the thermal efficiency of the entire process.

[0010] In order to achieve the purpose of the present invention, the present invention adopts the following technical solutions:

[0011] The present invention provides a one-step process for preparing nano-grade ultrapure coal, which comprises:

[0012] 1) In the presence of an agglomerating agent, the raw coal is sent to a steam mill and superheated steam is introduced into the steam mill to cause high-speed collision and crushing with the raw coal before sorting;

[0013] 2) The sorted materials are separated by a cyclone separator, and the separated minerals are discharged from the top of the cyclone separator along with the steam, and coal agglomerates are obtained at the bottom of the cyclone separator. The coal agglomerates are dried by hot steam to obtain nano-scale ultra-pure coal powder and agglomerating agent;

[0014] Wherein, the temperature of the superheated steam is 300-350°C, and the outlet temperature of the steam mill is controlled to be 130-180°C;

[0015] The boiling point of the agglomerating agent is 180-300°C.

[0016] The process method of the present invention utilizes low-grade superheated steam to perform steam pneumatic grinding on raw coal. The agglomerated agent steam enters the steam mill together with the superheated steam. The raw coal can be fully mixed and collided with the agglomerated agent steam while being ground, and is "agglomerated" into very small coal particle agglomerates by the agglomeration oil, thereby achieving a "one-step" method for grinding the raw coal and mixing it with the agglomerated agent in the steam mill. At the same time, the prepared ultrafine coal powder and minerals can be well separated.

[0017] In a specific embodiment of the process of the present invention, the superheated steam used in step 1) and step 2) can be low-pressure superheated steam from a steam generator or a thermal power plant; in some preferred embodiments, the pressure of the selected low-pressure superheated steam is 0.5-1.2MPa, for example, 0.6MPa, 0.9MPa, 1.2MPa. In some specific embodiments, the agglomerating agent enters the inner grinding chamber of the steam mill from the bottom through the laval nozzle of the steam mill along with the superheated steam, driving the raw coal transported by the screw conveyor to collide and crush at high speed to achieve the purpose of grinding.

[0018] The process of the present invention selects one or more of kerosene, light diesel oil or edible oil with a boiling point (180-300°C) between the inlet and outlet temperatures of the steam mill as agglomerating agents, and simultaneously introduces superheated steam into the steam mill so that the agglomerating agent exists in the form of steam in the steam mill. The raw coal is sheared and collided with each other under the drive of high-speed steam to achieve the purpose of grinding, and is fully mixed with the agglomerating agent steam while being ground. The agglomerating agent wets the hydrophobic raw coal particles, and is "agglomerated" into very small coal particles and separated from the minerals therein.

[0019] Specifically, in the process method of the present invention, the temperature at the steam mill inlet is determined by the temperature of the superheated steam. The temperature at the steam mill outlet after the superheated steam and coal powder are fully mixed in the steam mill is the outlet temperature, which can be adjusted by the inlet superheated steam temperature. If the outlet temperature is too low, the inlet superheated steam temperature can be appropriately increased so that the outlet temperature is controlled between 130 and 180°C.

[0020] In some preferred embodiments, the present invention uses light oil products such as light diesel oil and kerosene with higher boiling points as agglomerating agents instead of short-chain alkanes used in traditional agglomerating agents, thereby avoiding unsafe factors such as spontaneous combustion and explosion during the grinding process.

[0021] In some preferred embodiments, in step 1), the agglomerating agent is added to the superheated steam and then gasified before being introduced into the steam mill. Specifically, during the initial start-up, the agglomerating agent is added to the superheated steam pipeline via a metering pump, and then enters the steam mill with the superheated steam after being gasified. In some preferred embodiments, the amount of agglomerating agent added is 10% to 15% of the mass of the raw coal, for example, 12%, 13%, 14%.

[0022] In the process of the present invention, the raw coal is fully mixed with the agglomerator steam while being ground. Under the suction of the induced draft fan, the coarse and fine uneven coal powder after grinding is sorted by the classifier, and the ultrafine coal powder that meets the particle size requirements leaves the top of the steam mill together with the steam and the agglomerator. The temperature of the gas-solid mixture coming out of the top of the steam mill is reduced to below the boiling point of the agglomerator. The agglomerator forms coal agglomerates with a certain particle size and strength with the hydrophobic ultrafine coal powder during the condensation process, and the minerals continue to be dispersed in the steam.

[0023] In some specific implementations, the mixture of sorted coal agglomerates, minerals and steam is pressurized to 90 kPa by a fan and then sent to a cyclone separator for separation.

[0024] In step 2) of the process of the present invention, the coal agglomerates obtained at the bottom of the cyclone separator enter the interior of the dryer, where the coal agglomerates are heated and dried using superheated steam, thereby achieving separation of the ultra-pure coal and the agglomerating agent. The agglomerating agent vapor leaves the top of the dryer along with the superheated steam and returns to the steam mill, thereby also achieving recycling of the agglomerating agent vapor.

[0025] In some specific embodiments, after the minerals are discharged from the top of the cyclone separator along with the steam, they enter the jacket of the dryer to further recover heat and are discharged from the bottom of the jacket of the dryer in the form of waste condensate.

[0026] The nano-scale ultra-pure coal powder obtained by the process of the present invention has an ash content of 0.1-1%, such as 0.3%, 0.6%, 0.9%, and a particle size of less than 1 μm, such as 0.5 μm, 0.8 μm.

[0027] The above technical solution has the following technical effects:

[0028] The process method of the present invention makes full use of the temperature difference between the inlet and outlet of the steam mill, and uses a "one-step method" to achieve the combination and separation of ultrafine coal powder and agglomerating agent, thereby simplifying the entire process flow. At the same time, the evaporation and condensation processes of the agglomerating agent are both direct heat exchange, thereby improving the thermal efficiency of the entire process.

[0029] The process method of the invention selects agglomerating agents with a specific boiling point, prepares nano-level ultrafine coal powder with a particle size D50 less than 1 μm and an ash content less than 1%, and achieves the purpose of ultrafine grinding and deep ash removal.

[0030] The process of the present invention avoids the corrosion problem of equipment caused by the traditional use of chemical agents such as acids and alkalis, as well as the environmental problems caused by waste liquid. In addition, the agglomerating agent steam can directly enter the steam mill and be fully mixed with the raw coal to achieve the one-step preparation of ultra-pure coal. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 : A specific implementation method of the process of the present invention;

[0032] Figure 2 : Process flow chart of conventional oil agglomeration (OTP). DETAILED DESCRIPTION

[0033] In order to facilitate the understanding of the present invention, the present invention will be further described below in conjunction with examples. It should be understood that the following examples are only for a better understanding of the present invention and do not mean that the present invention is limited to the following examples.

[0034] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0035] In the following examples, the following methods were used to determine the performance indicators of pulverized coal:

[0036] (1) Particle size determination: using a laser particle size analyzer;

[0037] (2) Ash content determination: GBT212-2008 Industrial analysis method of coal;

[0038] Example 1

[0039] This embodiment uses Taixi anthracite according to Figure 1 The method shown prepares ultra-pure coal;

[0040] 1) Raw coal with a particle size of ≤1mm (feed rate of 5kg / h) is fed into the steam mill by gravity from the raw coal powder bin, and light diesel is selected as the agglomerating agent. When the agglomerating agent is initially started, the metering pump pressurizes the agglomerating agent to about 1.1MPa and then enters the steam mill together with the low-pressure superheated steam; the feed rate of light diesel is 0.6kg / h, the boiling point range is 180℃~300℃, the pressure of the low-pressure superheated steam is 1.0MPa, the temperature is 320℃, and the gas velocity of the superheated steam entering the steam mill is 700~1200m / s.

[0041] In the grinding chamber of the steam mill, the raw coal is fully mixed with the agglomerator and crushed by high-speed collision under the drive of high-speed steam. After being sorted by the classifier inside the steam mill to obtain coal powder with a particle size D50 of 0.309μm, it leaves the steam mill from the top outlet together with the steam and agglomerator. The top outlet temperature of the steam mill is 150℃. During this condensation process, the agglomerator forms agglomerates with a certain particle size and strength with the hydrophobic ultrafine coal powder. The diameter of the coal agglomerates is about 1mm, while the minerals continue to be dispersed in the steam.

[0042] 2) The mixture of coal agglomerates, minerals and steam is pressurized to 90 kPa by a fan and then sent to a cyclone separator for separation. In the cyclone separation, high-speed rotation is used to separate coal agglomerates and minerals. The minerals are discharged from the top of the cyclone separator together with the steam. The temperature of the steam mixture is about 130°C. After entering the dryer jacket for further heat recovery, it is discharged from the bottom of the dryer jacket in the form of waste condensate. The coal agglomerates discharged from the bottom of the cyclone separator enter the dryer and are heated by fresh low-pressure superheated steam. The agglomerating agent steam is discharged from the top of the dryer with the superheated steam and enters the steam mill for recycling again. Nano-level ultra-pure coal powder is obtained at the bottom of the dryer.

[0043] It has been determined that the particle size of the nano-level ultra-pure coal powder is D50=0.309μm, the ash content is 0.6%, the output of the nano-level ultra-pure coal powder is 4.75kg / h, and the yield is as high as 95%.

[0044] The performance comparison of pulverized coal before and after treatment by the above method is shown in the following table:

[0045] project Raw coal Nano-grade ultra-pure coal Ash content (Ad,%) 2.95 0.60 Particle size (μm) 1000 0.309 Yield (%) - 95

[0046] Example 2

[0047] This embodiment uses Shendong bituminous coal to prepare ultra-pure coal;

[0048] 1) Feed coal with particle size ≤ 1mm (feed rate 5kg / h) from the raw coal powder bin into the steam mill by gravity, and select kerosene as agglomerating agent. When initially started, after being pressurized to about 1.1MPa by a metering pump, it enters the steam mill together with low-pressure superheated steam. The feed rate of kerosene is 0.6kg / h, and the boiling point range is 180℃~300℃; the pressure of low-pressure superheated steam is 1.2MPa, the temperature is 340℃, and the gas velocity of superheated steam entering the steam mill is 700~1200m / s;

[0049] In the grinding chamber of the steam mill, the raw coal is fully mixed and crushed by high-speed steam, and then sorted by the classifier inside the steam mill to obtain coal powder with a particle size D50 of 0.504μm, which leaves the steam mill from the top outlet together with the steam and agglomerator; the outlet temperature at the top of the steam mill is reduced to 170℃, and the agglomerator forms agglomerates with a certain particle size and strength with the hydrophobic ultrafine coal powder during the condensation process. The diameter of the coal agglomerates is about 1mm, while the minerals continue to be dispersed in the steam.

[0050] 2) The mixture of coal agglomerates, minerals and steam is pressurized to 90 kPa by a fan and then sent to a cyclone separator. The minerals are discharged from the top of the cyclone separator together with the steam. The steam mixture has a temperature of about 130°C and enters the dryer jacket for further heat recovery. It is discharged from the bottom of the dryer jacket in the form of waste condensate. The coal agglomerates discharged from the bottom of the cyclone separator enter the dryer and are heated by fresh low-pressure superheated steam. The agglomerating agent steam is discharged from the top of the dryer along with the superheated steam and enters the steam mill for recycling again, and nano-level ultra-pure coal powder is obtained at the bottom of the dryer.

[0051] It has been determined that the particle size of the nano-level ultra-pure coal powder is D50=0.504μm, the ash content is 0.89%, the output of the nano-level ultra-pure coal powder is 4.75kg / h, and the yield is as high as 95%.

[0052] The performance comparison of pulverized coal before and after treatment by the above method is shown in the following table:

[0053] project Raw coal Nano-grade ultra-pure coal Ash content (Ad,%) 3.25 0.89 Particle size (μm) 1000 0.504 Yield (%) - 95

[0054] Comparative Example 1

[0055] This comparative example uses Shenhua bituminous coal to prepare ultra-pure coal.

[0056] 1) Raw coal with a particle size of ≤1mm (feed rate of 5kg / h) is fed into the steam mill by gravity from the raw coal powder bin, and kerosene is selected as the agglomerating agent. When initially started, it is pressurized to about 1.1MPa by a metering pump and then enters the steam mill together with low-pressure superheated steam. The amount of kerosene added is 0.6kg / h, and the boiling point range is 180℃~300℃; the pressure of low-pressure superheated steam is 1.2MPa, the temperature is 340℃, and the gas velocity of superheated steam entering the steam mill is 700~1200m / s;

[0057] In the grinding chamber of the steam mill, the raw coal is crushed by high-speed collision driven by high-speed steam, and then sorted by the classifier inside the steam mill to obtain coal powder with a particle size D50 of 0.504μm, which leaves the steam mill from the top outlet together with the steam and agglomerated agent; the top outlet temperature of the steam mill is reduced to 190℃, and the agglomerated agent forms agglomerates with a certain particle size and strength during the condensation process with the hydrophobic ultrafine coal powder. The diameter of the coal agglomerates is about 1mm, while the minerals continue to be dispersed in the steam.

[0058] 2) The mixture of coal agglomerates, minerals and steam is pressurized to 90 kPa by a fan and then sent to a cyclone separator. The minerals are discharged from the top of the cyclone separator together with the steam. The steam mixture has a temperature of about 130°C and enters the dryer jacket for further heat recovery. It is discharged from the bottom of the dryer jacket in the form of waste condensate. The coal agglomerates discharged from the bottom of the cyclone separator enter the dryer and are heated by fresh low-pressure superheated steam. The agglomerating agent steam is discharged from the top of the dryer along with the superheated steam and enters the steam mill for recycling again, and nano-level ultra-pure coal powder is obtained at the bottom of the dryer.

[0059] It has been determined that the particle size of the nano-level ultra-pure coal powder is D50=0.504μm, the ash content is 2.49%, the output of the nano-level ultra-pure coal powder is 4.75kg / h, and the yield is as high as 95%.

[0060] The performance comparison of pulverized coal before and after treatment by the above method is shown in the following table:

[0061]

[0062]

[0063] It can be seen from the coal powder performance data obtained in Comparative Example 1 that when the outlet temperature at the top of the steam mill is increased to 190°C, it is not reduced to below the boiling point of the agglomerator, so that most of the agglomerator still exists in the coal powder, greatly reducing the ash removal effect.

[0064] Comparative Example 2

[0065] This comparative example adopts conventional Figure 2 The oil agglomeration method (OTP) process shown;

[0066] The raw coal with a particle size of less than 10 cm is crushed into coal powder with a hammer crusher less than 250 μm, and then mixed with water to form a slurry with a concentration of 50% as the feed of the stirred ball mill. When the average particle size is 7 μm, it is further diluted to a concentration of 15% using a circulation machine, and then sent into a high shear mixer together with agglomerating agents (selected short-chain hydrocarbons such as pentane, hexane, and heptane), wherein the volume ratio of agglomerating agent to coal powder is 1:1.

[0067] After high-speed shearing, particles of about 3 mm are formed, and the minerals are dispersed in the water. They are dehydrated and washed by a screening machine, and the water under the screen is clarified and reused; the material on the screen is sent to a heating jacket and heated with 60°C water to evaporate the agglomerating agent, obtaining high-purity clean coal with an ash content of less than 1% and a yield of 95%. The agglomerating agent vapor is then compressed and cooled for recovery and reuse.

[0068] The performance comparison of pulverized coal before and after treatment by the above method is shown in the following table:

[0069] project Raw coal High purity clean coal Ash content (Ad,%) 3.25 0.92 Particle size (μm) 250 7 Yield (%) - 95

Claims

1. A one-step process for preparing nano-grade ultrapure coal, characterized in that: The process method includes: 1) In the presence of an agglomerating agent, the raw coal is sent to a steam mill and superheated steam is introduced into the steam mill to cause high-speed collision and crushing with the raw coal before sorting; 2) The sorted materials are separated by a cyclone separator, and the separated minerals are discharged from the top of the cyclone separator along with the steam, and coal agglomerates are obtained at the bottom of the cyclone separator. The coal agglomerates are dried by hot steam to obtain nano-scale ultra-pure coal powder and agglomerating agent; Wherein, the temperature of the superheated steam is 300-350°C, and the outlet temperature of the steam mill is controlled to be 130-180°C; The boiling point of the agglomerating agent is 180-300°C.

2. The process according to claim 1, characterized in that: The agglomerating agent is selected from one or more of kerosene, light diesel oil or edible oil.

3. The process according to claim 1 or 2, characterized in that: The superheated steam in step 1) and step 2) is low-pressure superheated steam from a steam generator or a thermal power plant; The pressure of the low-pressure superheated steam is preferably 0.5-1.2 MPa.

4. The process according to claim 3, characterized in that: In step 1), the speed of superheated steam introduced into the steam mill is 700-1200 m / s.

5. The process according to any one of claims 1 to 4, characterized in that: In step 1), the agglomerating agent is added into the superheated steam to be gasified and then introduced into the steam mill.

6. The process according to claim 5, characterized in that: The added amount of the agglomerating agent is 10% to 15% of the raw coal.

7. The process according to claim 6, characterized in that: The material sorted in step 2) is pressurized to 90 kPa and then sent to a cyclone separator for separation.

8. The process according to claim 7, characterized in that: In step 2), the agglomerating agent obtained after drying is recycled into the steam mill as feed.

9. The process according to claim 8, characterized in that: The coal agglomerates in step 2) are dried with superheated steam in a dryer; After being discharged from the top of the cyclone separator along with the steam, the minerals enter the jacket of the dryer to recover heat and obtain waste condensate.

10. The process according to claim 9, characterized in that: The nano-scale ultra-pure coal powder has an ash content of 0.1-1% and a particle size of less than 1 μm.

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