A method for removing alkali metal elements from high-alkali coal

Abstract

The application discloses a method for removing alkali metal elements from high-alkali coal, which comprises the following steps: 1) obtaining coarse crushing particles by coarsely crushing the high-alkali coal; 2) obtaining a swelling slurry by mixing and stirring the coarse crushing particles with a swelling agent and a promoter; 3) obtaining a grinding slurry by mixing and grinding the swelling slurry with water and a grinding aid; and 4) obtaining low-alkali coal and waste liquid by performing solid-liquid separation on the grinding slurry. 5) passing the waste liquid into a solar evaporation pond to obtain alkali metal salt and circulating liquid. The application can achieve the effect of deep alkali removal, and the coal obtained after alkali removal by the method of the application has an alkali metal content lower than 0.5% and meets the requirements of MT / T1074-2008.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of coal pretreatment, and particularly relates to a method for removing alkali metal elements from high-alkali coal. BACKGROUND

[0002] High-alkali coal refers to coal with a content of alkali metals (Na and K) in coal ash higher than 2%. High-alkali coal is widely distributed in the world, has a shallow burial depth, a high mining value, a low sulfur content, a low ash content, and a high content of fusinite, and is a high-quality coal chemical raw material and a thermal power generation fuel with a high development value. However, due to the high content of alkali metals, the high-alkali coal will cause a problem of burning toward the fire side in the utilization process, thereby affecting the safe and stable operation of equipment and the economy of the whole plant. Therefore, how to remove the alkali metals from the coal is a key technology for the utilization of high-alkali coal.

[0003] However, at present, by mixing low-alkali coal or minerals with an alkali metal capturing effect, the problem of burning toward the fire side in the combustion process of high-alkali coal can be effectively alleviated. However, the local reserves of low-alkali coal are low, and the price of low-alkali coal is much higher than that of high-alkali coal. In addition, the minerals do not have a calorific value, thereby increasing the utilization cost of high-alkali coal. In addition, the methods such as high-temperature pressurization or high-temperature stirring for removing alkali before combustion have high requirements for equipment and have a high water content.

[0004] Chinese patent CN 106090976 A (China Shenhua Energy Co., Ltd., authorized in 2018) discloses a pretreatment system for high-sodium coal. The high-sodium coal is subjected to hot water washing to remove sodium, and is dried and then pulverized.

[0005] Chinese patent CN 105238488 A (Huazhong University of Science and Technology, authorized in 2018) discloses a method for removing alkali from coal. Carbon dioxide is introduced into an aqueous solution of a water-soluble organic solvent as an eluent, and is mixed with the coal. Through the synergistic effect of carbon dioxide, water and the water-soluble organic solvent, the alkali metal compounds and organic alkali metal compounds in the coal can be effectively removed in a short time, and the effect of removing alkali is close to that of acid washing. The application mainly relates to a water washing method for removing alkali, and also needs to use carbon dioxide, which is not conducive to actual implementation.

[0006] Therefore, it is necessary to develop a process for removing alkali from high-alkali coal according to local conditions.

[0007] In order to solve the above problems, the present application is proposed. SUMMARY

[0008] In view of the above problems, the present application provides a method for removing alkali from high-alkali coal, which can solve the technical problems in the prior art.

[0009] The present application mainly removes the alkali metal elements in high-alkali coal through three steps. Specifically, the steps are as follows:

[0010] Firstly, the high-alkali coal is swelled by a swelling agent to destroy the cross-linking structure of the high-alkali coal, so that small molecules in the structure of the high-alkali coal are leached out, and the side chain weak bond groups are broken, thereby promoting the removal of organic alkali in the high-alkali coal. On the other hand, after swelling, the high-alkali coal particles become loose, and the large pore structure is increased, which is beneficial to the diffusion of the solvent in the particles and promotes the removal of soluble alkali and organic alkali.

[0011] Secondly, the high-alkali coal particle size is reduced by the way of swelling and superfine grinding, which promotes the contact between the particles and the solvent, destroys the blind hole, and removes the alkali metal in the blind hole, thereby increasing the alkali metal removal efficiency.

[0012] Finally, after the waste liquid is evaporated by solar energy, the alkali metal salt is collected, and the liquid resource is recycled.

[0013] Preferably, before the solar evaporation, there is also an electric alkali removal step, specifically, the grinding slurry is fed into an electric alkali removal device to obtain a low-alkali slurry under a certain voltage, and then the low-alkali slurry is subjected to solid-liquid separation, thereby further removing the alkali metal elements.

[0014] The technical scheme of the present application is as follows:

[0015] The first aspect of the present application provides a method for removing alkali metal elements from high-alkali coal, which comprises the following steps:

[0016] 1) After the high-alkali coal is coarsely crushed, the coarsely crushed particles with a certain particle size are obtained by screening, and the coarse particles not meeting the feeding particle size are sent back to the coarse crushing step;

[0017] 2) The coarsely crushed particles are mixed with a swelling agent at a certain mass ratio and stirred for a certain time to obtain a swelling slurry;

[0018] 3) The swelling slurry is mixed with water and grinding aids at a certain mass ratio, and then ground for a certain time to obtain a grinding slurry;

[0019] 4) The grinding slurry is subjected to solid-liquid separation to obtain low-alkali coal and waste liquid.

[0020] 5) The waste liquid is fed into a solar evaporation pool to evaporate the waste liquid, and the steam is collected and condensed during the evaporation process to obtain alkali metal salt and recycled liquid.

[0021] Preferably, there is also an electric alkali removal step in steps (3) and (4), specifically, the grinding slurry is fed into an electric alkali removal device to obtain a low-alkali slurry under a certain voltage, and then the low-alkali slurry is subjected to solid-liquid separation.

[0022] Preferably, the certain voltage is 1-30V.

[0023] Preferably, the certain particle size in step (1) is 20-300um.

[0024] Preferably, the swelling agent in step (2) is one or more of water, methanol, ethanol, propionaldehyde or ether; the certain mass ratio is: coarse crushed particles: swelling agent = 100:0-3000; and the certain stirring time is 30 seconds to 7 days.

[0025] Preferably, step (2) further includes a promoter, that is, the coarsely crushed particles are mixed with a swelling agent and a promoter in a certain mass ratio, and the promoter is one or more of hydrogen peroxide, n-hexane, urea, isopropanol, N-methylpyrrolidone or an ionic liquid; the certain mass ratio is: coarsely crushed particles: swelling agent: promoter = 100:0~3000:0~100.

[0026] Preferably, the circulating liquid obtained after evaporation in step (5) can be used as the circulating swelling liquid of the next process in step (3), and the circulating water obtained after evaporation in step (5) can be used as the swelling liquid, that is, in step (2), the coarsely crushed particles are mixed with the swelling agent and the circulating swelling liquid in a certain mass ratio, wherein the certain mass ratio is: coarsely crushed particles: swelling agent: circulating swelling liquid = 100:0~3000:0~3000.

[0027] In a more preferred embodiment of step (2), both the accelerator and the circulating swelling agent are present. That is, in step (2), the coarsely crushed particles are mixed with the swelling agent, the accelerator, and the circulating swelling liquid in a certain proportion and stirred for a certain period of time to obtain a swelling slurry. The certain proportion is: coarsely crushed particles: swelling agent: accelerator: circulating swelling liquid = 100:0-3000:0-100:0-3000.

[0028] Preferably, the grinding aid described in step (3) is one or more of sorbitan oleate, sorbitan trioleate, oleic acid, fatty acid ammonium salt, anionic fatty ester, modified polyurethane polymer, paraffin wax, low molecular weight wax, polyacrylic acid, polycarboxylate, humic acid, polyolefin, rosin, polyoxyethylene, polyether, Tween or Span;

[0029] Preferably, the certain mass ratio described in step (3) is: swelling slurry: water: grinding aid = 100: 0-3000: 0-100; the grinding method is selected from but not limited to a medium stirred mill, a ball mill, a planetary mill, a high-speed rotary mill or a colloid mill; and the total grinding time is 3 seconds to 12 hours.

[0030] Preferably, the circulating liquid obtained after evaporation in step (5) can be used as the circulating water in step (3) in the next process, the circulating water obtained after evaporation in step (5), and water needs to be added in step (3) for grinding, that is, in step (3), the swelling slurry is mixed with water, grinding aids, and the circulating liquid in a certain mass ratio, and then grinding is performed, wherein the certain mass ratio is: swelling slurry: water: circulating liquid: grinding aid = 100: 0-3000: 0-3000: 0-100.

[0031] The second aspect of the present application provides a low-alkali coal obtained by the method of the first aspect of the present application, wherein the content of alkali metal in the low-alkali coal is less than 0.5% based on the mass percentage, which meets the requirements of MT / T1074-2008.

[0032] The third aspect of the present application provides a method for improving the removal depth of alkali metal elements in high-alkali coal. First, the high-alkali coal is swelled by a swelling agent to destroy the cross-linking structure of the high-alkali coal, so that small molecules in the structure of the high-alkali coal are leached out, and the side chain weak bond groups are broken, promoting the removal of organic alkali in the high-alkali coal. On the other hand, after swelling, the high-alkali coal particles become loose, and the large pore structure increases, which is beneficial to the diffusion of the solvent in the particles, promoting the removal of soluble alkali and organic alkali. Second, the high-alkali coal particles are reduced in size by the method of swelling and superfine grinding, promoting the contact between the particles and the solvent, destroying the blind holes, so that the alkali metal in the blind holes is removed, and the removal efficiency of the alkali metal is increased. Finally, the waste liquid is evaporated by solar energy, and the alkali metal salt is collected, and the liquid resource is recycled.

[0033] Preferably, before solar evaporation, there is also an electric alkali removal step, specifically, the grinding slurry is introduced into an electric alkali removal device to obtain a low-alkali slurry under a certain voltage, and then the low-alkali slurry is subjected to solid-liquid separation to further remove the alkali metal elements.

[0034] In the present application, it is called superfine grinding because the degree of grinding can be finer. The first step of pre-swelling process makes the high-alkali coal particles swell fully, become loose, and have increased large pore structure, which increases the stress points.

[0035] In the present application, the "blind hole" in the "destroying the blind hole to remove the alkali metal in the blind hole" refers to the exposed pore channel before the high-alkali coal particles become new small particle size particles after grinding.

[0036] Compared with the prior art, the present application has the following beneficial effects:

[0037] 1. The present application can achieve the effect of deep alkali removal. After alkali removal by the process of the present application, the content of alkali metal in the low-alkali coal is less than 0.5% based on the mass percentage, which meets the requirements of MT / T1074-2008.

[0038] 2、The reason that the present application can realize deep dealkalization lies in the following three points:

[0039] Firstly, the high-alkali coal is swelled by the swelling agent, the cross-linking structure of the high-alkali coal is destroyed, the small molecules in the structure of the high-alkali coal are leached out, and the side chain weak bond groups are broken, thereby promoting the removal of the organic alkali in the high-alkali coal. On the other hand, after swelling, the high-alkali coal particles become loose, the large pore structure is increased, which is beneficial to the diffusion of the solvent in the particles and promotes the removal of the soluble alkali and the organic alkali.

[0040] Secondly, the high-alkali coal particle size is reduced by the way of superfine grinding after swelling, which promotes the contact between the particles and the solvent, destroys the blind hole, and removes the alkali metal in the blind hole, thereby increasing the alkali metal removal efficiency.

[0041] Finally, the ground slurry is introduced into the electric dealkalization device to prepare a low-alkali slurry under a certain voltage, and then the low-alkali slurry is subjected to solid-liquid separation, thereby further removing the alkali metal elements.

[0042] 3、After the three-step dealkalization, the waste liquid is introduced into a solar evaporation pond, the waste liquid is evaporated, the steam is collected and condensed during the evaporation process, and alkali metal salt and circulating liquid are prepared. The waste liquid is recycled by the method of solar evaporation.

[0043] 4、The swelling process is very crucial in the present application. The high-alkali coal is swelled with the swelling agent, so that the high-alkali coal is fully swelled, becomes loose, and the large pore structure is increased, which is beneficial to the diffusion of the solvent in the particles and promotes the removal of the soluble alkali and the organic alkali. In addition, the swelling is beneficial to the subsequent superfine grinding, which reduces the high-alkali coal particle size, promotes the contact between the particles and the solvent, destroys the blind hole, removes the alkali metal in the blind hole, and increases the alkali metal removal efficiency.

[0044] 5、The dealkalization process of the present application does not involve high temperature and high pressure operating conditions, has good environmental protection, and has simple and easy preparation process. BRIEF DESCRIPTION OF DRAWINGS

[0045] Figure 1 The electric dealkalization process flow chart of the present application;

[0046] Figure 2 The electric dealkalization process flow chart of the present application;

[0047] Figure 3 The material flow chart in the dealkalization process of the present application. DETAILED DESCRIPTION

[0048] The present invention is described below with reference to specific examples, but the embodiments of the present invention are not limited thereto. Experimental methods in the examples where specific conditions are not specified generally follow conventional conditions and those described in manuals, or according to conditions recommended by the manufacturer. The general equipment, materials, and reagents used are all commercially available unless otherwise specified. The raw materials required in the following examples and comparative examples are all commercially available.

[0049] Comparative Example:

[0050] Coal particles (sodium content 3.2%, potassium content 0.7%) are coarsely crushed and screened to obtain coarse particles of 75-150 μm. Coarse particles that do not meet the feed particle size are returned to the coarse crushing step. The coarse particles are mixed with methanol, water, and oleic acid in a ratio of 100:300:1 and fed into a medium stirred mill. After grinding for 3 hours, the mill is discharged to produce a grinding slurry. The grinding slurry is mechanically filtered to produce low-alkali coal. The resulting low-alkali coal has a sodium content of 1% and a potassium content of 0.4%.

[0051] Implementation Case 1:

[0052] After the coarse crushing, the coal particles (sodium content 3.2%, potassium content 0.7%) were screened to obtain coarse particles of 75-150 μm. The coarse particles that did not meet the feed particle size were sent back to the coarse crushing step. The coarse particles and methanol were stirred at a ratio of 100:400 for 20 hours, and then the swelling slurry was mixed with water and oleic acid at a ratio of 100:300:1 and fed into a medium stirred mill. After grinding for 3 hours, the material was discharged to obtain a grinding slurry. The grinding slurry was mechanically filtered to obtain low-alkali coal. The sodium content of the obtained low-alkali coal was 0.6%, and the potassium content was undetectable.

[0053] Implementation Case 2

[0054] Compared with Case 1, an accelerator was added;

[0055] After coarse crushing, the coal particles (sodium content 3.2%, potassium content 0.7%) are screened to obtain coarse particles of 75-150 μm. The coarse particles that do not meet the feed particle size are sent back to the coarse crushing step. The coarse particles: methanol: N-methylpyrrolidone are stirred at a ratio of 100:400:20 for 20 hours. The swelling slurry is mixed with water and oleic acid at a ratio of 100:300:1 and then fed into a medium stirred mill. After grinding for 3 hours, the material is discharged to obtain a grinding slurry. The grinding slurry is mechanically filtered to obtain low-alkali coal. The sodium content of the obtained low-alkali coal is 0.06%, and the potassium content is undetectable.

[0056] Implementation Case 3:

[0057] Compared with Case 2, an electric dealkalization unit was added;

[0058] After the coal particles (sodium content 3.2%, potassium content 0.7%) are coarsely crushed, they are screened to obtain coarse particles of 75 to 150 μm, and the coarse particles that do not meet the feed particle size are sent back to the coarse crushing step. The coarse particles: methanol: N-methylpyrrolidone are stirred at a ratio of 100:400:20 for 20 hours, and the swelling slurry is mixed with water and oleic acid at a ratio of 100:300:1 and input into a medium stirred mill. After grinding for 3 hours, the material is discharged to obtain a grinding slurry. The grinding slurry is input into an electric dealkalization cell, a voltage of 3V is applied, and then mechanical filtration is performed to obtain low-alkali coal. The sodium content of the obtained low-alkali coal is 0.03%, and the potassium content is undetectable.

[0059] Implementation Case 4:

[0060] Compared with Case 2, the circulating fluid prepared in Case 2 was used

[0061] After coarse crushing, the coal particles (sodium content 3.2%, potassium content 0.7%) are screened to obtain coarse particles of 75-150 μm. The coarse particles that do not meet the feed particle size are sent back to the coarse crushing step. After stirring the coarse particles: methanol: circulating swelling liquid: N-methylpyrrolidone at a ratio of 100:300:100:20 for 20 hours, the swelling slurry is mixed with water, circulating liquid, and oleic acid at a ratio of 100:50:250:1 and input into a medium stirred mill. After grinding for 3 hours, the material is discharged to obtain a grinding slurry. The grinding slurry is mechanically filtered to obtain low-alkali coal. The sodium content of the obtained low-alkali coal is 0.08%, and the potassium content is undetectable.

[0062] The above embodiments illustrate the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention and are not intended to limit the scope of the present invention in any way. Various changes and modifications may be made to the present invention without departing from the scope of the present invention, and all such changes and modifications fall within the scope of the claims.

Claims

1. A method for removing alkali metal elements from high-alkali coal, characterized in that: It includes the following steps: 1) After the high-alkali coal is coarsely crushed, it is screened to obtain coarse particles with a certain particle size; 2) mixing the coarsely crushed particles with a swelling agent in a certain mass ratio and stirring for a certain period of time to obtain a swelling slurry; 3) mixing the swelling slurry with water and a grinding aid in a certain mass ratio and grinding for a certain time to obtain a grinding slurry; 4) performing solid-liquid separation on the ground slurry to obtain low-alkali coal and waste liquid; 5) passing the waste liquid into a solar evaporation pool to evaporate the waste liquid, collecting and condensing steam during the evaporation process to produce alkali metal salts and circulating liquid; The swelling agent in step (2) is one or more of water, methanol, ethanol, propionaldehyde or ether; the certain mass ratio is: coarse crushed particles: swelling agent = 100: 0-3000, wherein the mass value of the swelling agent is not 0; the certain stirring time is 30 seconds to 7 days; Step (2) also includes a promoter, that is, the coarsely crushed particles are mixed with a swelling agent and a promoter in a certain mass ratio, and the promoter is one or more of hydrogen peroxide, n-hexane, urea, isopropanol, N-methylpyrrolidone or an ionic liquid; the certain mass ratio is: coarsely crushed particles: swelling agent: promoter = 100: 0~3000: 0~100, wherein the mass values ​​of the swelling agent and the promoter are not 0.

2. The method according to claim 1, characterized in that Step (3) and step (4) also include an electro-dealkalization step, specifically, the grinding slurry is passed into the electro-dealkalization device to obtain a low-alkali slurry at a certain voltage, and then the low-alkali slurry is subjected to solid-liquid separation; the certain voltage is: 1~30V.

3. The method according to claim 1, characterized in that The certain particle size described in step (1) is 20-300 μm.

4. The method according to claim 1, wherein The circulating liquid obtained after evaporation in step (5) can be used as the circulating swelling liquid of the next process in step (3). The circulating water obtained after evaporation in step (5) can be used as the swelling liquid. That is, in step (2), the coarsely crushed particles are mixed with the swelling agent and the circulating swelling liquid in a certain mass ratio, wherein the certain mass ratio is: coarsely crushed particles: swelling agent: circulating swelling liquid = 100: 0~3000: 0~3000; wherein the mass values ​​of the swelling agent and the circulating swelling liquid are not 0.

5. The method according to claim 1, wherein The grinding aid described in step (3) is one or more of sorbitan oleate, sorbitan trioleate, oleic acid, fatty acid ammonium salt, anionic fatty ester, modified polyurethane polymer, paraffin wax, low molecular weight wax, polyacrylic acid, polycarboxylate, humic acid, polyolefin, rosin, polyoxyethylene, polyether, Tween or Span; the certain mass ratio is: swelling slurry: water: grinding aid = 100: 0~3000: 0~100; wherein the mass values ​​of water and grinding aid are not 0; the grinding method is a medium stirred mill, a ball mill, a planetary mill, a high-speed rotary mill or a colloid mill; and the grinding time is 3 seconds to 12 hours.

6. The method according to claim 1, characterized in that The circulating liquid obtained after evaporation in step (5) can be used as circulating water for the next process in step (3). The circulating water obtained after evaporation in step (5) requires water to be added for grinding in step (3), that is, in step (3), the swelling slurry is mixed with water, a grinding aid, and a circulating liquid in a certain mass ratio and then ground, wherein the certain mass ratio is: swelling slurry: water: circulating liquid: grinding aid = 100: 0~3000: 0~3000: 0~100; wherein the mass values ​​of water, circulating liquid, and grinding aid are not 0.

7. A low-alkali coal obtained by the method according to any one of claims 1 to 6, characterized in that: Based on mass percentage, the alkali metal content in low-alkali coal is less than 0.5%.

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