A method for removing impurities from coal descaling alkali and a method for descaling coal

Abstract

The application provides a coal descaling alkali liquor impurity removal and regeneration method and a coal descaling method. The technical scheme provided by the application can effectively remove impurities in the coal descaling alkali liquor, effectively regenerates the alkali in the coal descaling alkali liquor, can be recycled, and is beneficial to improving the economy of coal descaling. The impurity removal and regeneration method comprises the following steps: 1) adjusting the alkali content in the coal descaling alkali liquor; 2a) when the ratio of the sum of the molar amounts of Al and Fe elements to the molar amount of Si element in the coal descaling alkali liquor in step 1) is greater than or equal to 5, preferably greater than or equal to 10, the following low-temperature impurity removal operation is performed; 2b) when the ratio of the sum of the molar amounts of Al and Fe elements to the molar amount of Si element in the coal descaling alkali liquor in step 1) is less than 10, preferably less than 5, the low-temperature impurity removal and high-temperature impurity removal operations are performed.

Description

Technical Field

[0001] This invention relates to the field of coal acid-alkali ash removal technology, specifically to a method for removing impurities and regenerating alkaline solutions for coal ash removal, and a method for coal ash removal. Background Technology

[0002] Traditional coal ash removal methods mainly include jigging, heavy media, and flotation, which have relatively low ash removal efficiency, typically achieving only 10-30% ash content. This ash is generally unusable as a carbon material, except in small quantities for high-ash carbon materials such as electrode paste and high-ash carbon blocks. Refining ash removal based on traditional methods can be divided into two main categories: physical and chemical methods. Chemical methods are mainly divided into four types: hydrofluoric acid method, conventional acid-base method, molten alkali leaching method, and chemical coal method. The conventional acid-base method involves reacting alkali with the mineral ash in the coal to generate acid-soluble products, which then react with acid and enter the liquid phase. After filtration and washing, these products are separated from the organic matter in the coal. Conventional acid-base chemical ash removal has comprehensive advantages in terms of ash removal efficiency, economic benefits, and environmental benefits. Ash removal using conventional chemical methods can yield coal with an ash content of less than 1% or lower, which can largely replace petroleum coke in the preparation of carbon anodes and other carbon materials, such as supercapacitor electrodes, high-quality activated carbon, and advanced carbon materials like graphene.

[0003] In conventional acid-alkali ash removal, the alkali solution needs to react with the coal and its contained minerals. Minerals dissolved in the alkali solution consume the solution, reducing the effective alkali content. Accumulation of this alkali will render the alkali solution unusable, reducing the economic efficiency of coal ash removal. Alkali is the most significant reagent consumed in conventional coal ash removal and constitutes a major cost component.

[0004] The monograph "Practical Technology for Coal Washing and Processing" (pp. 86-87) outlines some possible chemical reactions in conventional chemical coal ash removal methods and the mechanism of action of adding calcium oxide to the alkaline solution used in coal ash removal. However, the relevant theories lack experimental support, and the complex effects of the inorganic components in the ash removal alkaline solution are not discussed in depth. Patent CN200380102494.4 (Method for Demineralizing Coal) proposes adding calcium oxide, calcium hydroxide, magnesium oxide, or magnesium hydroxide, etc., to regenerate and reuse the alkali lost from ash dissolution in the alkaline solution through a causticizing reaction. However, the conditions for alkaline solution regeneration are not clearly defined. Therefore, mature technical solutions are currently lacking for the removal of inorganic mineral components and the regeneration of alkaline solutions in coal ash removal. Summary of the Invention

[0005] The inventors have discovered that the inorganic minerals soluble in alkaline solutions in coal mainly consist of aluminum, silicon, and iron, which are the primary target impurities for the regeneration of coal ash removal alkaline solutions. This invention aims to provide a method for the regeneration of coal ash removal alkaline solutions and a method for coal ash removal. The technical solution provided by this invention achieves a high impurity removal rate, effectively removing aluminum, silicon, and iron from coal ash removal alkaline solutions, thus enabling effective regeneration of the alkali in the solutions, allowing for recycling, and improving the economic efficiency of coal ash removal.

[0006] To achieve its objective, the present invention provides the following technical solution:

[0007] The first aspect of this invention provides a method for removing impurities and regenerating coal ash removal alkaline solution, the method comprising the following steps:

[0008] 1) Adjust the alkali content in the coal ash removal alkaline solution to make the alkali content ≤35wt%, preferably ≤25wt%;

[0009] 2a) When the ratio of the sum of the molar amounts of Al and Fe elements in the coal ash removal alkaline solution in step 1) to the molar amount of Si element is ≥5, preferably ≥10, the following steps are performed: the coal ash removal alkaline solution is mixed with the impurity removal agent and reacted at low temperature, and then filtered to obtain the regenerated alkaline solution.

[0010] 2b) When the ratio of the sum of the molar amounts of Al and Fe elements in the coal deashing alkaline solution described in step 1) to the molar amount of Si element is <10, preferably <5, then the following steps are performed:

[0011] First, the coal ash removal alkaline solution is mixed with a cleaning agent and reacted at a low temperature, then filtered. The resulting filtrate is then mixed with the cleaning agent again and reacted at a high temperature. After filtration, a regenerated alkaline solution is obtained. Alternatively, the coal ash removal alkaline solution is first mixed with a cleaning agent and reacted at a high temperature, then filtered. The resulting filtrate is then mixed with the cleaning agent again and reacted at a low temperature. After filtration, a regenerated alkaline solution is obtained.

[0012] The reaction temperature for the low-temperature reaction is 10-99℃, and the reaction temperature for the high-temperature reaction is 120-220℃.

[0013] In this invention, the "alkali content in the coal ash removal alkaline solution" refers to the mass content of sodium hydroxide and potassium hydroxide in the coal ash removal alkaline solution; if the agent used in the alkaline ash removal process of coal is sodium hydroxide, then the above-mentioned alkali content refers to the content of sodium hydroxide; if the agent used is potassium hydroxide, then the above-mentioned alkali content refers to the content of potassium hydroxide; if the agent used is a mixture of sodium hydroxide and potassium hydroxide, then the above-mentioned alkali content refers to the total content of potassium hydroxide and the hydroxide agent.

[0014] In this invention, the alkali content of the coal ash removal alkaline solution is controlled to ≤35wt%, preferably ≤25wt%, beforehand. Then, different impurity removal operations are performed on the coal ash removal alkaline solution according to the ratio of the sum of the molar amounts of Al and Fe elements to the molar amount of Si element in the coal ash removal alkaline solution. When the ratio is ≥5, preferably ≥10, a one-step low-temperature impurity removal is performed at 10-99℃. When the ratio is <10, preferably <5, a two-step impurity removal is performed by low temperature at 10-99℃ + high temperature at 120-220℃. This can effectively remove mineral components from the coal ash removal alkaline solution and has a high impurity removal rate. In particular, it can efficiently remove inorganic elements such as silicon, aluminum, and iron from the coal ash removal alkaline solution simultaneously. This allows the alkali lost due to the dissolution of minerals in the coal into the alkaline solution to be efficiently regenerated. The resulting regenerated alkaline solution can be reused, improving the economic efficiency of coal ash removal.

[0015] In some embodiments, in step 1), the alkali content in the coal ash removal alkaline solution is adjusted by dilution. Specific dilution methods include, for example, dilution with water, or dilution by adding the filter cake washing liquid generated during the coal alkali ash removal process.

[0016] In some embodiments, the impurity removal agents mentioned in each step of step 2a) or 2b) are independently selected from one or more of calcium and magnesium agents. Only one of the calcium and magnesium agents may be used, or they may be mixed in any proportion. In some embodiments, the calcium agent is selected from one or more of calcium oxide, calcium hydroxide, and lime slurry; the magnesium agent is selected from one or more of magnesium oxide, magnesium hydroxide, and magnesium hydroxide emulsion. The lime slurry may be formulated based on calcium oxide or calcium hydroxide, and the magnesium hydroxide emulsion may be formulated based on magnesium oxide or magnesium hydroxide.

[0017] In some preferred embodiments, during the low-temperature reaction in step 2a) or 2b), the amount of the impurity-removing agent, calculated as the sum of the molar amounts of calcium and magnesium, is in a ratio of 1-3 to the sum of the molar amounts of aluminum and iron in the reaction solution. The inventors have discovered that adding the impurity-removing agent according to this ratio during the low-temperature reaction can thoroughly and efficiently remove aluminum, iron, etc., at a low temperature of 10-99°C. Simultaneously, the generated insoluble substances (such as aluminum-iron-calcium-magnesium compounds) can carry a small amount of silica, thus simultaneously promoting the removal of silica. Furthermore, the inventors have discovered that when the ratio of the sum of the molar amounts of Al and Fe to the molar amount of Si in the coal ash removal alkaline solution in step 1) is ≥5, particularly ≥10, adding the impurity-removing agent at a low temperature of 10-99°C according to the above-mentioned preferred ratio can achieve simultaneous and efficient removal of aluminum, silicon, and iron through a one-step low-temperature impurity removal process.

[0018] The inventors have discovered that when the ratio of the sum of the molar amounts of Al and Fe elements to the molar amount of Si element in the coal ash removal alkaline solution described in step 1) is <10, particularly <5, a two-step purification scheme of low temperature + high temperature can achieve a significantly improved purification effect. Specifically, low temperature purification can be performed first, followed by high temperature purification, or vice versa. As mentioned above, preferably, in step 2b), during the low-temperature purification reaction, the amount of the purification agent, calculated as the sum of the molar amounts of calcium and magnesium elements, is in a ratio of 1-3 to the sum of the molar amounts of aluminum and iron elements in the reaction solution; while during the high-temperature purification reaction, preferably, the amount of the purification agent, calculated as the sum of the molar amounts of calcium and magnesium elements, is in a ratio of 0.8-2.2 to the molar amount of silicon element in the reaction solution. The inventors have discovered that adding the impurity removal agent in the above-mentioned preferred proportions during both the low-temperature and high-temperature reactions has several advantages. First, in the low-temperature reaction, aluminum and iron can be removed more thoroughly and efficiently simultaneously. The insoluble substances generated (such as aluminum-iron-calcium-magnesium compounds) can carry a small amount of silica, thus also promoting silica removal. Second, in the high-temperature reaction, silica in the ash solution can be removed more thoroughly, resulting in the formation of insoluble silicon-calcium-magnesium compounds. Overall, this method can efficiently and thoroughly remove inorganic mineral elements such as aluminum, iron, and silicon (mainly the mineral components soluble in the alkali solution removed from coal during the coal alkali-alkali ash removal process), promoting efficient regeneration of the alkali solution.

[0019] In some embodiments, the reaction time of the low-temperature reaction in step 2a) or step 2b) is 0.1-6h; in some preferred embodiments, the reaction time of the high-temperature reaction in step 2b) is 0.1-6h.

[0020] In some preferred embodiments, in step 2b), the reaction temperature of the high-temperature reaction is 140-180°C, and the reaction time is preferably 0.25-3 hours. Using these preferred high-temperature reaction conditions further improves the removal effect of impurities in the coal ash removal alkaline solution, and can significantly increase the impurity removal rate.

[0021] In some embodiments, in step 1), when the ratio of the sum of the molar amounts of Al and Fe elements to the molar amount of Si element in the coal ash removal alkaline solution is <10, preferably <5, an iron agent and / or an aluminum agent is added to make this ratio ≥5, preferably ≥10. It should be noted that this scheme is only an optional scheme and it is not necessary to adjust the above ratio by adding additional iron or aluminum agents. If the above ratio is <10, preferably <5, the low-temperature + high-temperature two-step impurity removal scheme of step 2b) can be directly adopted.

[0022] Preferably, the iron agent is selected from ferric chloride, ferric sulfate, ferric nitrate, sodium ferrate, or other iron-containing substances that can be converted or generate ferric hydroxide in alkaline solution; the aluminum agent is selected from aluminum chloride, aluminum sulfate, aluminum nitrate, sodium aluminate, or other aluminum-containing substances that can be dissolved in alkaline solution.

[0023] A second aspect of this invention also provides a method for coal ash removal, wherein the regenerated alkali solution obtained from the coal ash removal alkali solution described above through a regeneration method is used for alkaline ash removal of coal. The specific operation of the alkaline ash removal can employ existing processes known in the art, and there are no particular limitations thereto.

[0024] In some preferred embodiments, the coal ash removal method includes the following steps:

[0025] 1) Crush the coal, preferably to a particle size of less than 3mm;

[0026] 2) The coal from step 1) is subjected to alkaline deashing at 100-250℃, and the coal is filtered to obtain coal deashing alkaline solution and filter cake.

[0027] 3) The filter cake is acid-washed to remove ash, resulting in low-ash coal and filter cake washing liquid; the coal ash removal alkaline solution is treated according to the impurity removal and regeneration method described above to obtain regenerated alkaline solution;

[0028] 4) Use the regenerated alkali solution in step 2) to perform the alkali descaling.

[0029] In step 1), preferably, the coal is crushed and screened to a size of less than 3 mm, such as less than 3 mm, less than 2 mm, less than 1 mm, less than 0.5 mm, or less than 0.1 mm. This is to ensure that the ash in the coal can fully contact the alkaline solution in subsequent steps and be removed after reaction and conversion.

[0030] In step 2), the alkali used for alkaline deashing can be sodium hydroxide and / or potassium hydroxide. The specific operation of alkaline deashing in step 2) can be carried out with reference to existing processes in the field, such as the corresponding process operations and reaction conditions in patent applications CN201710999565.9 (A process for preparing ultrapure coal using a physicochemical method from anthracite), CN201710999573.3 (A process for preparing ultrapure coal using a chemical method from anthracite), and CN200380102494.4 (Methods for demineralizing coal), etc.

[0031] In step 3), the acid used for acid washing and ash removal of the filter cake can be, for example, sulfuric acid, hydrochloric acid, or nitric acid, and the concentration of the acid used is, for example, 1-50 wt%, preferably 3-30 wt%, more preferably 5-20 wt%. For specific acid washing and ash removal operations and process conditions, existing processes in the field can be referred to, for example, the corresponding processes in patent applications CN201710999565.9 (A process for preparing ultrapure coal using a physicochemical method of anthracite), CN201710999573.3 (A process for preparing ultrapure coal using a chemical method of anthracite), and CN200380102494.4 (Methods for demineralizing coal), etc.

[0032] The technical solution provided by this invention has the following beneficial effects:

[0033] The method of this invention for regenerating alkaline solutions used in coal ash removal can efficiently remove impurities, particularly inorganic mineral elements such as aluminum, silicon, and iron. This allows for efficient regeneration of the alkaline solution, resulting in recyclable alkaline solutions and improving the economic efficiency of coal ash removal. Furthermore, this invention allows for flexible selection of impurity removal schemes based on the composition of the coal ash removal alkaline solution, balancing both efficiency and economy in alkaline solution regeneration. Detailed Implementation

[0034] To facilitate understanding of the present invention, the following description, in conjunction with embodiments, will further illustrate the invention. It should be understood that the following embodiments are merely for a better understanding of the invention and do not imply that the invention is limited to these embodiments.

[0035] Where specific experimental steps or conditions are not specified in the examples, the corresponding conventional experimental steps or conditions in this technical field can be followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0036] The concentrations of alkali, aluminum, silicon, and iron in the coal ash removal alkaline solution, as well as the concentrations of aluminum, silicon, and iron in the intermediate impurity removal alkaline solution and the regenerated alkaline solution, were all detected using ICP.

[0037] The impurity removal rates of the intermediate and regenerated alkaline solutions mentioned below are calculated using the following formula:

[0038] Impurity removal rate (%) = (1-(C) Al除杂 +C Si除杂 +C Fe除杂 ) / (C Al碱液 +C Si碱液 +C Fe碱液 ))×100%

[0039] Among them, C Al除杂C represents the mass concentration of aluminum in the alkaline solution after impurity removal using a purification agent. Al碱液 The mass concentration of aluminum in the original coal ash removal alkaline solution;

[0040] C Si除杂 C represents the mass concentration of silicon in the alkaline solution after impurity removal using a purification agent. Si碱液 The mass concentration of silicon in the original coal ash removal alkaline solution;

[0041] C Fe除杂 C represents the mass concentration of iron in the alkaline solution after impurity removal using a purification agent. Fe碱液 The mass concentration of iron in the original coal ash removal alkaline solution;

[0042] Coal samples A and B were taken, and the industrial analysis results are shown in Table 1 below. In Table 1, M... ad A ad V ad and FC ad These are the moisture content, ash content, volatile matter content, and fixed carbon content of the air-dried coal.

[0043] Table 1. Industrial analysis of coal samples (wt%)

[0044]

[0045] Example 1

[0046] (1) Obtain coal ash removal alkaline solution

[0047] Take 400g of coal sample A, crush it to a particle size of less than 1mm, mix it with 600g of sodium hydroxide and 400ml of water, and knead and react at 150℃ for 3 hours. Dilute with 1500mL of water, cool, filter, and wash to obtain coal ash removal alkaline solution and filter cake (i.e., coal ash removed by alkaline method). The concentration of alkali (i.e., sodium hydroxide) in the coal ash removal alkaline solution is determined to be 25wt%, C. Al碱液 The concentration was 3496 ppm, C Si碱液 The concentration was 1215 ppm, C Fe碱液 The concentration was 435 ppm. 10 wt% dilute hydrochloric acid was added to the filter cake at an acid-to-coal ratio of 1.5:1 (by mass), and the mixture was leached at 60°C for 30 minutes. After filtration and washing, ultrapure coal was obtained with an ash content of 0.45%.

[0048] (2) Low-temperature chemical removal

[0049] Using calcium oxide as the impurity removal agent, the required amount of calcium oxide to be added to the coal ash removal alkaline solution is calculated based on a molar ratio of 2 (the sum of the molar amounts of Ca in the impurity removal agent and Al and Fe in the coal ash removal alkaline solution). After adding calcium oxide, the mixture is heated to 75°C and reacted for 1 hour. After filtration, an intermediate impurity-removed alkaline solution is obtained. Upon testing, C... Al除杂 It is 206 ppm, C Si除杂It is 1057 ppm, C Fe除杂 The value is 23 ppm. Based on the formula for calculating the impurity removal rate (%), the impurity removal rate of the intermediate alkali solution can be calculated to be 75%.

[0050] (3) High-temperature chemical removal

[0051] Using calcium oxide as the impurity removal agent, the required amount of calcium oxide to be added to the intermediate impurity removal alkaline solution was calculated based on 1.2 times the molar amount of silicon in the solution. After adding calcium oxide, the mixture was heated to 160°C and reacted for 1 hour. After cooling, the precipitate was removed by filtration, yielding a regenerated alkaline solution. The C content was then tested. Al除杂 It was 56 ppm, C Si除杂 The concentration was 31 ppm, C Fe除杂 The value is 16 ppm. Based on the formula for calculating the impurity removal rate (%), the impurity removal rate of the regenerated alkali solution is calculated to be 98%.

[0052] Example 2

[0053] (1) Obtain coal deashing alkaline solution according to step (1) of Example 1.

[0054] (2) High-temperature chemical removal

[0055] Using calcium oxide as the impurity removal agent, the amount of calcium oxide to be added to the coal ash removal alkaline solution was calculated based on 1.2 times the molar amount of silicon in the solution. After adding calcium oxide, the solution was heated to 160°C and reacted for 1 hour. After cooling, the precipitate was removed by filtration, yielding an intermediate impurity removal alkaline solution. Testing and calculations showed that the impurity removal rate was 25%.

[0056] (3) Low-temperature chemical removal

[0057] Using calcium oxide as the impurity removal agent, the required amount of calcium oxide to be added to the intermediate ash removal alkaline solution is calculated based on a molar ratio of 2 (the sum of the molar amounts of the impurity removal agent Ca and the molar amounts of Al and Fe in the intermediate ash removal alkaline solution). After adding calcium oxide, the solution is heated to 75°C and reacted for 1 hour. The resulting regenerated alkaline solution, after filtration, shows an impurity removal rate of 98% according to testing and calculation.

[0058] Example 3

[0059] The coal ash removal alkaline solution was obtained according to step (1) of Example 1. Ferric sulfate was added, ensuring that the sum of the molar amounts of Al and Fe in the coal ash removal alkaline solution was 10 times the molar amount of Si. Simultaneously, calcium oxide was used as the impurity removal agent. The required amount of calcium oxide to be added was calculated and determined based on a molar ratio of Ca in the impurity removal agent to the sum of the molar amounts of Al and Fe in the coal ash removal alkaline solution of 2. Calcium oxide was added according to this amount. After adding the above-mentioned calcium oxide and ferric hydroxide, the mixture was heated to 90°C and reacted for 3 hours. After filtration, a regenerated alkaline solution was obtained, and the impurity removal rate was found to be 98% after testing and calculation.

[0060] Example 4

[0061] (1) Obtain coal ash removal alkaline solution

[0062] Referring to CN200380102494.4, 100g of coal sample B was crushed to a particle size of less than 3mm, mixed with 80g of potassium hydroxide and 320ml of water, and reacted in a high-pressure reactor at 220℃ for 3 hours with stirring. After cooling, filtration, and washing, coal after alkaline ash removal (i.e., filter cake) and coal ash removal alkaline solution were obtained. The concentration of alkali (potassium hydroxide) in the coal ash removal alkaline solution was determined to be 20wt%, C. Al碱液 It was 521 ppm, C Si碱液 It was 1765 ppm, C Fe碱液 The ash content was 326 ppm. 10 wt% dilute nitric acid was added to the filter cake at an acid-to-coal ratio of 0.4:1 (by mass), and the mixture was leached at 75°C for 30 minutes. After filtration and washing, ultrapure coal was obtained with an ash content of 0.19%.

[0063] (2) Low-temperature chemical removal

[0064] Using calcium oxide (50 wt%) and magnesium oxide (50 wt%) as impurity removal agents, the required amount of impurity removal agent to be added to the coal ash removal alkaline solution was determined by calculating a ratio of 3:1 between the sum of the molar amounts of Ca and Mg in the impurity removal agent and the sum of the molar amounts of Al and Fe in the coal ash removal alkaline solution. After adding the impurity removal agent to the coal ash removal alkaline solution, the mixture was heated to 45°C and reacted for 3 hours.

[0065] After filtration, an intermediate alkaline solution was obtained. Upon testing, C... Al除杂 It is 98 ppm, C Si除杂 It was 1593 ppm, C Fe除杂 The value is 28 ppm. Based on the formula for calculating the impurity removal rate (%), the impurity removal rate of the intermediate impurity removal alkaline solution is calculated to be 34%.

[0066] (3) High-temperature chemical removal

[0067] In the intermediate impurity removal alkaline solution, the amount of calcium oxide to be added is calculated and determined based on 0.8 times the molar amount of silicon in the intermediate ash removal alkaline solution, and the amount of magnesium oxide to be added is calculated and determined based on 0.8 times the molar amount of silicon. Calcium oxide and magnesium oxide are added to the intermediate impurity removal alkaline solution as impurity removal agents according to the above amounts, and the solution is heated to 180°C and reacted for 0.5 hours.

[0068] After cooling, the precipitate was removed by filtration, yielding a regenerated alkali solution. Analysis showed that C... Al除杂 39 ppm, C Si除杂 The concentration was 21 ppm, C Fe除杂 The value is 15 ppm. Based on the formula for calculating the impurity removal rate (%), the impurity removal rate of the regenerated alkali solution is calculated to be 97%.

[0069] Comparative Example 1

[0070] The procedure was carried out in accordance with Example 1. The difference lies in the impurity removal operation of the coal ash removal alkaline solution, which is explained below:

[0071] Using calcium oxide as the impurity removal agent, the dosage of the impurity removal agent in the coal ash removal alkaline solution was calculated by molar ratio I, based on the ratio of the molar amount of Ca in the impurity removal agent to the sum of the molar amounts of Al and Fe in the coal ash removal alkaline solution, which is 2. The dosage II was calculated by molar ratio of the molar amount of Ca in the impurity removal agent to 1.2 times the molar amount of silicon in the coal ash removal alkaline solution. The sum of the dosages I and II was taken as the amount of calcium oxide added. After adding calcium oxide to the coal ash removal alkaline solution, the mixture was heated to 75°C and reacted for 1 hour. After cooling, the solution was filtered to obtain a regenerated alkaline solution. Testing and calculation showed that the impurity removal rate was 76%.

[0072] Comparative Example 2

[0073] The reaction was carried out in accordance with Comparative Example 1. The difference was that after adding calcium oxide, the mixture was heated to 160°C and reacted for 1 hour. After cooling, the regenerated alkali solution was obtained by filtration, and the impurity removal rate was found to be 28% after testing and calculation.

[0074] Comparative Example 3

[0075] (1) Obtain coal ash removal alkaline solution

[0076] 400g of coal sample A was crushed to a particle size of 2mm, mixed with 600g of sodium hydroxide and 300ml of water, and kneaded at 120℃ for 3 hours. After dilution with 800mL of water and cooling, the mixture was filtered and washed to obtain coal ash removal alkaline solution and filter cake (i.e., coal ash removal by alkaline method). The alkali concentration of the coal ash removal alkaline solution was determined to be 37%, and C... Al碱液 It was 5496 ppm, C Si碱液 It was 1538 ppm, C Fe碱液The concentration was 573 ppm. 10 wt% dilute hydrochloric acid was added to the filter cake at an acid-to-coal ratio (mass) of 1.5:1. The mixture was leached at 60°C for 30 minutes, filtered, and washed to obtain ultrapure coal with an ash content of 0.46%.

[0077] (2) Low-temperature chemical removal

[0078] Following step (2) of Example 1, an intermediate impurity removal alkaline solution was obtained, and the impurity removal rate was found to be 35% after testing and calculation.

[0079] (3) High-temperature chemical removal

[0080] Following step (3) of Example 1, a regenerated alkali solution was obtained, and the impurity removal rate was found to be 49% after testing and calculation.

[0081] Example 5

[0082] The procedure was carried out with reference to Comparative Example 3, except that the coal ash removal alkaline solution in step (1) of Comparative Example 3 was diluted with water to make the alkaline concentration 30%; the operations in steps (2) and (3) were carried out with reference to Comparative Example 3.

[0083] Results: After step (2), the impurity removal rate was 65%; after step (3), the impurity removal rate was 89%.

[0084] Example 6

[0085] The procedure was carried out in accordance with Example 3, except that sodium aluminate was added, and the sum of the molar amounts of Al and Fe in the coal ash removal alkaline solution was made to be 5 times the molar amount of Si.

[0086] Result: The impurity removal rate was 93%.

[0087] Example 7

[0088] The procedure was carried out in accordance with Example 1, except that the reaction temperature in step (3) was 120°C. Result: The impurity removal rate was 93%.

[0089] Example 8

[0090] The regenerated alkaline solution obtained in Example 1 was used for alkaline deashing of coal. Specifically, the regenerated alkaline solution obtained in Example 1 was concentrated to an alkaline concentration of 60 wt% (consistent with the concentration of the alkaline solution obtained in Example 1, which was a mixture of 600 g sodium hydroxide and 400 ml water). Then, alkaline deashing of coal sample A was performed according to step (1) of Example 1, except that "600 g sodium hydroxide and 400 ml water" in step (1) of Example 1 was replaced with the above-mentioned concentrated regenerated alkaline solution.

[0091] Experimental results: The impurity removal rate was 98%.

[0092] As seen in Examples 1 and 2, the two-step addition of reagents at low and high temperatures can remove inorganic components from the coal ash removal alkaline solution, and the low-temperature and high-temperature removal steps can be interchanged without affecting the removal effect. As seen in Examples 3 and 6, by adding an iron agent that can be converted or generate ferric hydroxide and an aluminum agent soluble in the alkaline solution to the coal ash removal alkaline solution, making the sum of the molar amounts of Al and Fe in the solution more than 5 times, especially more than 10 times, the molar amount of Si, efficient one-step removal of impurities can be achieved at low temperatures. As seen in Example 4, when silicon content is predominant in the coal ash removal alkaline solution, the solution of this invention can also achieve efficient removal of impurities. As seen in Comparative Examples 1 and 2, neither high-temperature nor low-temperature treatment alone can achieve efficient removal of impurities. As can be seen from Comparative Example 3 and Example 5, when the concentration of the coal ash removal alkali solution is too high, for example, exceeding 35%, the removal efficiency at both high and low temperatures is significantly affected. Adjusting the alkali concentration to below 35% can significantly improve the removal efficiency of the alkali solution. Compared with Example 1, controlling the alkali concentration to below 25% is beneficial to further significantly improve the removal efficiency of the alkali solution, and can more significantly improve the impurity removal rate. The coal ash removal alkali solution regeneration process proposed in this invention, by controlling the alkali concentration of the coal ash removal alkali solution and according to the composition characteristics of the coal ash removal alkali solution, can flexibly carry out impurity removal by one-step low-temperature removal or by two-step low-temperature and high-temperature removal, achieving efficient regeneration of the alkali solution and significantly improving the economy of coal ash removal.

[0093] It is readily understood that the above embodiments are merely illustrative examples for clear explanation and do not imply that the invention is limited thereto. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for removing impurities and regenerating coal ash removal alkaline solution, characterized in that, The method includes the following steps: 1) Adjust the alkali content in the coal ash removal alkaline solution to ensure that the alkali content is ≤35wt%; 2a) When the ratio of the sum of the molar amounts of Al and Fe elements in the coal ash removal alkaline solution in step 1) to the molar amount of Si element is ≥5, the following steps are performed: the coal ash removal alkaline solution is mixed with the impurity removal agent and reacted at low temperature, and then filtered to obtain the regenerated alkaline solution. 2b) When the ratio of the sum of the molar amounts of Al and Fe elements in the coal deashing alkaline solution described in step 1) to the molar amount of Si element is less than 5, then the following steps are performed: First, the coal ash removal alkaline solution is mixed with a cleaning agent and reacted at a low temperature, then filtered. The resulting filtrate is then mixed with the cleaning agent again and reacted at a high temperature. After filtration, a regenerated alkaline solution is obtained. Alternatively, the coal ash removal alkaline solution is first mixed with a cleaning agent and reacted at a high temperature, then filtered. The resulting filtrate is then mixed with the cleaning agent again and reacted at a low temperature. After filtration, a regenerated alkaline solution is obtained. The reaction temperature for the low-temperature reaction is 10-99℃, and the reaction temperature for the high-temperature reaction is 120-220℃.

2. The method for removing impurities and regenerating coal ash-removing alkaline solution according to claim 1, characterized in that, In step 1), the alkali content in the coal ash removal alkaline solution is adjusted to be ≤25wt%.

3. The method for removing impurities and regenerating coal ash removal alkaline solution according to claim 1, characterized in that, In step 1), the alkali content in the coal ash removal alkaline solution is adjusted by dilution.

4. The method for removing impurities and regenerating coal ash-removing alkaline solution according to claim 1, characterized in that, The impurity removal agents mentioned in each step of step 2a) or step 2b) are independently selected from one or more of calcium agents and magnesium agents.

5. The method for removing impurities and regenerating coal ash removal alkaline solution according to claim 4, characterized in that, The calcium agent is selected from one or more of calcium oxide, calcium hydroxide, and lime milk; the magnesium agent is selected from one or more of magnesium oxide, magnesium hydroxide, and magnesium hydroxide emulsion.

6. The method for removing impurities and regenerating coal ash removal alkaline solution according to claim 4, characterized in that, In step 2a) or step 2b), when the low-temperature reaction is carried out, the amount of the impurity removal agent, calculated as the sum of the molar amounts of calcium and magnesium, is in a ratio of 1-3 to the sum of the molar amounts of aluminum and iron in the reaction solution.

7. The method for removing impurities and regenerating coal ash removal alkaline solution according to claim 4, characterized in that, In step 2b), when the high-temperature reaction is carried out, the amount of the impurity removal agent, calculated as the sum of the molar amounts of calcium and magnesium, is in a ratio of 0.8 to 2.2 to the molar amount of silicon in the reaction solution.

8. The method for removing impurities and regenerating coal ash removal alkaline solution according to any one of claims 1-7, characterized in that, In step 2a) or step 2b), the reaction time of the low-temperature reaction is 0.1-6 hours; And / or, in step 2b), the reaction time of the high-temperature reaction is 0.1-6 h.

9. The method for removing impurities and regenerating coal ash removal alkaline solution according to any one of claims 1-7, characterized in that, In step 2b), the reaction temperature of the high-temperature reaction is 140-180℃.

10. The method for removing impurities and regenerating coal ash removal alkaline solution according to claim 9, characterized in that, In step 2b), the reaction time of the high-temperature reaction is 0.25-3h.

11. The method for removing impurities and regenerating coal ash removal alkaline solution according to any one of claims 1-7, characterized in that, In step 2b), when the ratio of the sum of the molar amounts of Al and Fe elements to the molar amount of Si element in the coal ash removal alkaline solution is <5, iron and / or aluminum agents are added to make the ratio ≥5.

12. The method for removing impurities and regenerating coal ash removal alkaline solution according to claim 11, characterized in that, The iron agent is selected from one or more of ferric chloride, ferric sulfate, ferric nitrate, sodium ferrate, or other substances that can be converted or generated into ferric hydroxide in alkaline solution; the aluminum agent is selected from one or more of aluminum chloride, aluminum sulfate, aluminum nitrate, sodium aluminate, or other aluminum-containing substances that can be dissolved in alkaline solution.

13. A method for removing ash from coal, characterized in that, The regenerated alkaline solution obtained from the impurity removal and regeneration method according to any one of claims 1-12 is used for alkaline ash removal from coal.

14. The coal ash removal method according to claim 13, characterized in that, The coal ash removal method includes the following steps: 1) Crush the coal; 2) The coal from step 1) is subjected to alkaline deashing at 100-250℃, and the coal is filtered to obtain coal deashing alkaline solution and filter cake. 3) The filter cake is acid-washed to remove ash, resulting in low-ash coal and filter cake washing liquid; the coal ash removal alkaline solution is treated according to the impurity removal and regeneration method according to any one of claims 1-12 to obtain regenerated alkaline solution; 4) Use the regenerated alkali solution in step 2) to perform the alkali descaling.

15. The coal ash removal method according to claim 14, characterized in that, The crushing refers to crushing to a particle size of less than 3 mm.

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