Resource recycling method for coal gasification slag

Abstract

The invention provides a coal gasification slag resource recycling method which comprises the following steps: screening coal gasification slag according to the particle size to obtain coarse particle ash and fine particle ash; the fine-particle ash is subjected to slurry preparation and then reselection, and first underflow and first overflow are obtained; and treating the first underflow to obtain carbon fine powder, decarburized tailings and to-be-treated ash. And the to-be-treated ash and the first overflow are subjected to slurry preparation and then reselection, and flotation ash meeting the flotation condition and to-be-floated ash not meeting the flotation condition are obtained. And the flotation ash meeting the flotation conditions is subjected to flotation, and carbon fine powder and decarburized tailings are obtained through treatment. By carrying out particle size grading, reselection and flotation on the coal gasification slag, the combined process realizes efficient carbon-ash separation of the coal gasification slag while saving the operating cost. The method has the advantages of mild conditions, simple and easily available equipment requirements, low energy consumption, high recovery rate and good market prospect.

Description

Technical Field

[0001] The present application relates to the technical field of resource recovery of coal gasification slag, and in particular to a resource recovery method of coal gasification slag. Background Art

[0002] In my country's energy structure, coal has always occupied a dominant position and is an important cornerstone for ensuring national energy security. Based on the current situation of my country's relatively scarce oil and natural gas resources, coal gasification technology, as an efficient means of coal conversion, has vital strategic significance for achieving clean and efficient use of coal.

[0003] Gasifiers are key processes and technical units in coal chemical industry, which will produce a large amount of coal gasification slag. At present, the annual production of coal gasification slag in my country is as high as 70 million tons, with hundreds of millions of tons of slag stored in the stockpile. The comprehensive utilization rate is low, and it is mainly disposed of by landfill or slag dump, which not only occupies a large amount of land, pollutes soil and water, but also causes waste of resources and energy. Summary of the invention

[0004] The present application provides a method for recycling coal gasification slag to solve at least some of the problems in the related art.

[0005] The embodiment of the present application provides a method for recycling coal gasification slag, comprising:

[0006] The coal gasification slag is screened according to the particle size to obtain coarse ash particles and fine ash particles;

[0007] The fine-grained ash is mixed with slurry and then re-selected to obtain a first underflow and a first overflow;

[0008] Processing the first underflow to obtain carbon concentrate, decarbonized tailings and ash to be processed;

[0009] The ash to be treated and the first overflow are mixed and then re-selected to obtain flotation ash that meets flotation conditions and ash to be floated that does not meet flotation conditions;

[0010] The flotation ash that meets the flotation conditions is floated and processed to obtain carbon concentrate and decarbonized tailings.

[0011] Optionally, the first underflow is processed to obtain carbon concentrate, decarbonized tailings and ash to be processed, including:

[0012] reselecting the first underflow to obtain a second underflow and a second overflow;

[0013] The second overflow is processed to obtain carbon concentrate and a first ash, the second underflow is processed to obtain a decarbonized tailing and a second ash, and the first ash and the second ash are used as the ash to be processed.

[0014] Optionally, the step of processing the second overflow to obtain carbon concentrate and first ash comprises:

[0015] Screening the second overflow according to particle size to obtain first ash of coarse particles and third ash of fine particles;

[0016] The third ash is centrifuged to obtain carbon powder.

[0017] Optionally, the step of processing the second underflow to obtain decarbonized tailings and second ash includes:

[0018] Screening the second underflow according to particle size to obtain coarse-grained second ash and fine-grained fourth ash;

[0019] The second ash is dehydrated to obtain decarbonized tailings.

[0020] Optionally, the step of mixing the ash to be treated and the first overflow for gravity separation to obtain flotation ash that meets flotation conditions and ash to be floated that does not meet flotation conditions includes:

[0021] grinding the first overflow;

[0022] The ash to be treated and the first overflow after grinding are mixed and then re-selected to obtain the flotation ash and the ash to be floated.

[0023] Optionally, a cyclic processing step is further included, and the cyclic processing step includes:

[0024] The ash to be floated that does not meet the flotation conditions is repeatedly ground and re-selected, and the flotation ash that meets the flotation conditions obtained after each grinding and re-selection is floated and processed to obtain carbon concentrate and decarbonized tailings.

[0025] Optionally, the flotation ash that meets the flotation conditions is floated and processed to obtain carbon concentrate and decarbonized tailings, including:

[0026] The flotation ash that meets the flotation conditions is subjected to bubble flotation to obtain carbonaceous matter and tailings;

[0027] The carbonaceous material is collected and filtered to obtain carbon powder;

[0028] The tailings are concentrated and filtered to obtain decarbonized tailings.

[0029] Optionally, the coal gasification slag is screened according to particle size to obtain coarse ash particles and fine ash particles, including:

[0030] Adding liquid to coal gasification slag to form a first mixed slurry with a concentration of 35% to 65%;

[0031] The first mixed slurry is screened according to the particle size to obtain coarse ash particles and fine ash particles.

[0032] Optionally, the step of preparing a slurry for the fine-grained ash and performing gravity separation to obtain a first underflow and a first overflow comprises:

[0033] Adding liquid to the fine-grained ash to form a second mixed slurry with a concentration of 10% to 30%;

[0034] The second mixed slurry is subjected to gravity selection to obtain a first underflow and a first overflow.

[0035] Optionally, the grading aperture range for screening the coal gasification slag is 0.5 mm to 1 mm; and / or

[0036] The classification aperture range for reselecting the fine ash particles is 0.074 mm to 0.15 mm; and / or

[0037] The frother used for flotation includes one of 2-octanol and methyl isobutyl carbinol, with a dosage of 1 to 15 kg; and / or

[0038] The collector used for flotation includes one of diesel, kerosene, waste diesel and waste engine oil, and the dosage is 1.5 to 18 kg.

[0039] The coal gasification slag resource recovery method provided in this application performs particle size classification, gravity separation and flotation on the coal gasification slag. The combined process saves operating costs and realizes efficient carbon ash separation of the coal gasification slag. The above methods all have mild conditions, simple and easy-to-obtain equipment requirements, low energy consumption, high recovery rate, and good market prospects.

[0040] It should be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0042] Figure 1 Shown is a flow chart of a method for recycling coal gasification slag according to an exemplary embodiment of the present application;

[0043] Figures 2 to 6 Shown is a detailed flow chart of each step of the coal gasification slag resource recovery method of the present application;

[0044] Figure 7 Shown is a flow chart of a method for recycling coal gasification slag resources according to another exemplary embodiment of the present application. DETAILED DESCRIPTION

[0045] Exemplary embodiments will be described in detail herein, examples of which are shown in the accompanying drawings. When the following description refers to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The implementations described in the following exemplary embodiments do not represent all implementations consistent with the present application. Instead, they are merely examples of devices and methods consistent with some aspects of the present application as detailed in the appended claims.

[0046] In order to better understand the technical solution of the present application, the coal gasification slag resource recovery method of the present application is described in detail below in conjunction with the accompanying drawings. In the absence of conflict, the features of the following embodiments and implementations can be combined with each other.

[0047] The embodiment of the present application provides a method for recycling coal gasification slag, which can be applied to gasification fine slag. Gasification slag is generally divided into gasification fine slag and gasification coarse slag. Fine slag is a water-containing slag obtained by carrying out the coarse coal gas flow from the top of the gasifier and undergoing preliminary washing, purification and precipitation, and has the characteristics of high carbon (18% to 50%) and high water content (40% to 65%).

[0048] See also Figure 1 As shown, the method for recycling coal gasification slag includes steps S1-S5:

[0049] Step S1, sieving the coal gasification slag according to the particle size to obtain coarse ash particles (+a mm) and fine ash particles (-a mm). It can be understood that the coarse ash particles have a high ash content, a low carbon content, and a diameter greater than a mm. The fine ash particles have a high carbon content, a low ash content, and a diameter less than a mm. In this embodiment, the grading aperture range for sieving the coal gasification slag is a=0.5mm~1mm.

[0050] Step S2, after the fine-particle ash is mixed with slurry, it is re-selected (gravity separation) to obtain a first underflow (bmm-amm) and a first overflow (-b mm). Optionally, the fine-particle ash can be fed into a classification cyclone for re-selection. It can be understood that the classification cyclone is a kind of re-selection equipment. When the mixed slurry enters tangentially from the periphery of the cyclone at a certain pressure, a high-speed rotating flow field will be generated in the cylindrical cavity. Due to the action of centrifugal force, particles with higher density or coarser particle size are thrown to the wall of the device, and move downward in the axial and radial directions, and finally discharged through the underflow port. The obtained first underflow has high ash content, low carbon content, high density, large weight, and a diameter between ba mm. Particles with lower density or finer particle size move toward the central axis and form an upward inner vortex at the center of the axis, and then are discharged through the overflow port. The obtained first overflow has high carbon content, low ash content, low density, small weight, and a diameter less than b mm. Efficient separation of light and heavy phases in the mixed slurry is achieved; wherein b is less than a. In this embodiment, the classification aperture range for reselecting the fine particle ash is b=0.074mm~0.15mm.

[0051] Step S3, processing the first underflow to obtain carbon concentrate, decarbonized tailings and ash to be processed, so as to achieve efficient carbon-ash separation.

[0052] Step S4, the ash to be treated and the first overflow are mixed and then re-selected to obtain flotation ash that meets the flotation conditions and ash to be floated that does not meet the flotation conditions. Optionally, a grading cyclone can be used for the re-selection operation.

[0053] Step S5, float the flotation ash that meets the flotation conditions, and process it to obtain carbon powder and decarbonized tailings. It can be understood that the cost of screening and re-selection is low, and the carbon extraction efficiency of flotation is high, but the reagent consumption is large and the production cost is high. Therefore, the present application first processes most of the gasification slag to obtain carbon powder and decarbonized tailings through the previous screening and re-selection steps, saving operating costs. The remaining small part of the gasification slag is then floated and processed to obtain carbon powder and decarbonized tailings, thereby achieving efficient carbon ash separation and reducing production costs, while meeting product quality requirements and taking into account economic benefits.

[0054] Through the above method, the coal gasification slag resource recovery method provided in the present application is a coal gasification fine slag classification-gravity selection-flotation combined carbon ash separation process, which belongs to the technical field of high-value component resource recovery of coal-based solid waste. By subjecting the coal gasification slag to particle size classification, gravity selection and flotation, large-size coal gasification slag is separated by gravity, and small-size coal gasification slag is separated by bubble flotation to obtain carbon concentrate and decarbonized tailings products. The combined process saves operating costs while achieving efficient carbon ash separation of coal gasification slag. The above methods all have mild conditions, simple and easy-to-obtain equipment requirements, low energy consumption, high recovery rate, and good market prospects.

[0055] The coal gasification slag resource recovery method provided in this application can achieve dual benefits by implementing the carbon ash separation project of coal gasification fine slag: on the one hand, carbon concentrate with high calorific value can be recovered as a substitute for thermal coal, pulverized coal injection or to prepare carbon-based adsorbents; on the other hand, the tailings after decarbonization can be used as building materials for resource disposal. Therefore, the coal gasification slag carbon ash separation technology can not only effectively solve the problem of coal gasification fine slag treatment, but also promote the recycling of resources and improve energy efficiency.

[0056] See also Figure 2 As shown, in some optional embodiments, the above step S1, screening the coal gasification slag according to the particle size to obtain coarse ash particles and fine ash particles, may include steps S11-S12:

[0057] Step S11, adding liquid to coal gasification slag to form a first mixed slurry with a concentration of 35% to 65%. Optionally, the coal gasification slag can be fed into a slurry preparation barrel, and the supernatant of gasification ash water can be used for slurry preparation to form a first mixed slurry with a concentration of 35% to 65%.

[0058] Step S12, screening the first mixed slurry according to the particle size to obtain coarse ash particles and fine ash particles. Optionally, the first mixed slurry can be screened according to the particle size using a coarse-cutting screen to obtain coarse ash particles and fine ash particles. In this embodiment, the optional aperture of the coarse-cutting screen is 0.5 mm-1 mm.

[0059] See also Figure 3 As shown, in some optional embodiments, the above step S2, after mixing the fine-grained ash with slurry and performing gravity separation to obtain the first underflow and the first overflow, may include steps S21-S22:

[0060] Step S21, adding liquid to the fine ash to form a second mixed slurry with a concentration of 10% to 30%. Optionally, the coarse ash on the sieve can be discharged, and the fine ash under the sieve can be collected into a slurry mixing bucket, and the supernatant of gasified ash water can be used to mix the slurry to form a second mixed slurry with a concentration of 10% to 30%.

[0061] Step S22, re-select the second mixed slurry to obtain a first underflow and a first overflow. Optionally, the second mixed slurry can be fed into a classification cyclone for re-selection to obtain a first underflow and a first overflow.

[0062] See also Figure 4 As shown, in some optional embodiments, the above step S3, treating the first underflow to obtain carbon concentrate, decarbonized tailings and ash to be treated, may include steps S31-S32:

[0063] Step S31, re-select the first underflow to obtain a second underflow and a second overflow. It can be understood that the second underflow has a high ash content, a low carbon content, a high density and a large weight. The second overflow has a high carbon content, a low ash content, a low density and a small weight. Optionally, the first underflow can be fed into a fluidized bed separator for re-selection. The fluidized bed separator is also a re-selection equipment, and its working principle is similar to that of a grading cyclone. The fluidized bed separator can also be replaced by a shaking table re-selection machine, a spiral chute re-selection machine and other re-selection equipment.

[0064] Step S32, the second overflow is processed to obtain carbon fine powder and first ash. Optionally, the second overflow can be firstly screened by an arc-shaped grading screen according to the particle size to obtain coarse particles of the first ash and fine particles of the third ash. The third ash is then centrifuged by a centrifuge to obtain a carbon fine powder product after dehydration and desliming.

[0065] The second underflow is processed to obtain decarbonized tailings and second ash. Optionally, the second underflow can be screened according to particle size using an arc-shaped grading screen to obtain coarse particles of the second ash and fine particles of the fourth ash. The fourth ash is then dehydrated using a vibrating screen to obtain a decarbonized tailings product. This achieves efficient carbon-ash separation.

[0066] The first ash and the second ash are used as the ash to be treated. Optionally, the first ash and the second ash can be fed into a slurry mixing barrel, and the supernatant of gasified ash water can be used to mix the slurry to form a mixed slurry for standby use.

[0067] See also Figure 5 As shown, in some optional embodiments, the above step S4, after the ash to be treated and the first overflow are mixed and then re-selected to obtain the flotation ash that meets the flotation conditions and the ash to be floated that does not meet the flotation conditions, may include steps S41-S42:

[0068] Step S41, grinding the first overflow to further reduce the particle size of the first overflow. Optionally, a grinding machine may be used to grind the first overflow. The grinding machine may be a wet ball mill, a rod mill, etc.

[0069] Step S42, the ash to be treated and the first overflow after grinding are mixed and then re-selected to obtain the flotation ash and the ash to be flotated. Optionally, the slurry after the first overflow grinding and the ash to be treated can be fed into a mixing barrel together, and the gasified ash water supernatant is used to mix the slurry to form a mixed slurry, and the mixed slurry is fed into a classifying cyclone for re-selection.

[0070] See also Figure 6 As shown, in some optional embodiments, the above step S5, flotation ash that meets the flotation conditions, and processing to obtain carbon concentrate and decarbonized tailings, may include steps S51-S53:

[0071] Step S51, the flotation ash that meets the flotation conditions is subjected to bubble flotation to obtain carbonaceous substances and tailings. Optionally, the flotation ash that meets the flotation conditions can be subjected to bubble flotation by a flotation system. It can be understood that in the flotation operation, a surfactant-foaming agent that can generate a large number of bubbles is used. When air is introduced into the water or air enters the water due to the agitation of the water, the hydrophobic end of the surfactant is oriented toward the air side of the bubble at the gas-liquid interface, and the hydrophilic end is still in the solution, forming bubbles. Another surfactant-collector that plays a capturing role is adsorbed on the surface of the solid mineral powder. This adsorption has a certain selectivity depending on the nature of the mineral. Its basic principle is to use the lattice defects on the crystal surface, and the outward hydrophobic end is partially inserted into the bubble, so that during the flotation process, the bubble may take away the specified mineral powder (that is, the carbonaceous substance) to achieve the purpose of mineral processing. In this embodiment, the flotation system can select a flotation cell or a flotation column. The foaming agent includes one of sec-octanol and methyl isobutyl carbinol, that is, the foaming agent can be selected from sec-octanol, methyl isobutyl carbinol (MIBC), etc., and the dosage is 1 to 15 kg. The collector includes one of diesel, kerosene, waste diesel, and waste engine oil, that is, the collector can be selected from diesel, kerosene, waste diesel, waste engine oil and other organic matter, and the dosage is 1.5 to 18 kg.

[0072] Step S52, collecting and filtering the carbonaceous material to obtain carbon fine powder. Optionally, a scraper can be used to collect the carbonaceous material, and the carbonaceous material can be sent to a filter press for dehydration and recovery to obtain carbon fine powder.

[0073] Step S53, the tailings are concentrated and filtered to obtain decarbonized tailings. Optionally, the tailings can be collected in a bucket, and the collected slurry flows to the concentration tank for concentration, and the concentrated tailings are recovered by a filter press to obtain decarbonized tailings. The overflow of the concentration tank and the filtrate of the filter press can be purified by the sedimentation tank and returned to the circulating water pool for recycling, and there is no wastewater discharge during the entire production cycle.

[0074] It is understandable that after the previous screening and re-selection steps, most of the coal gasification slag can be processed to obtain carbon concentrate and decarbonized tailings. The remaining first ash, second ash and first overflow may contain ash that can be screened and re-selected to obtain carbon concentrate and decarbonized tailings. In order to separate this part of ash, in some optional embodiments, the coal gasification slag resource recovery method of the present application may also include a recycling process for separating this part of ash, thereby reducing the proportion of ash that is finally floated, which can further reduce costs.

[0075] The cyclic treatment process includes: repeatedly grinding and re-selecting the ash to be floated that does not meet the flotation conditions, flotating the flotation ash that meets the flotation conditions after each grinding and re-selection, and processing to obtain carbon concentrate and decarbonized tailings. It can be understood that grinding the ash to be floated can further reduce the particle size of the ash to be floated. The ash to be floated that has been ground and re-selected can be re-selected to separate the flotation ash that meets the flotation conditions, so that this part of the flotation ash is subsequently floated and processed to obtain carbon concentrate and decarbonized tailings. Repeating the cyclic treatment process can separate carbon concentrate and decarbonized tailings in a more refined and efficient manner.

[0076] See also Figure 7 As shown, the embodiment of the coal gasification slag resource recovery method provided in the embodiment of the present application is as follows:

[0077] Laboratory simulation: The coal gasification slag is fed into a slurry mixing barrel, and the supernatant of the gasification ash water is used to form a first mixed slurry with a concentration of 50%. The first mixed slurry is fed into a coarse-cutting screen for screening. The grading aperture of the coarse-cutting screen is 0.5 mm, and the samples are divided into coarse-grained ash slag with a low carbon content (greater than 0.5 mm) and fine-grained ash slag with a high carbon content (less than 0.5 mm).

[0078] The coarse particles on the screen are discharged, and the fine particles under the screen are collected in the slurry mixing barrel and further liquid is added to form a second mixed slurry with a concentration of about 20%. The second mixed slurry is fed into a grading cyclone for further classification. The grading aperture is 0.15mm, and it is divided into the first underflow (0.15mm-0.5mm) and the first overflow (less than 0.15mm).

[0079] The first underflow is fed into the fluidized bed separator for reselection to obtain the second underflow and the second overflow. The second overflow is screened by an arc-shaped grading screen to obtain the first ash of coarse particles and the third ash of fine particles. The third ash is then centrifuged by a centrifuge, and the carbon concentrate product is obtained after dehydration and desliming. The second underflow is screened by an arc-shaped grading screen to obtain the second ash of coarse particles and the fourth ash of fine particles. The fourth ash is dehydrated by a vibrating screen to obtain a decarbonized tailings product.

[0080] The first overflow is ground by a grinding machine, and the ash to be treated and the first overflow after grinding are mixed and fed into a classification cyclone for gravity separation to obtain flotation ash and ash to be floated. The ash to be floated is repeatedly ground and gravity separated, and the flotation ash obtained after each grinding and gravity separation is fed into a flotation system for bubble flotation to obtain carbonaceous matter and tailings.

[0081] The scraper is used to collect carbonaceous materials and sent to the filter press for dehydration and recovery to obtain carbon concentrate. The tailings are collected in buckets, and the collected slurry flows to the concentration tank for concentration. The concentrated tailings are then recovered by the filter press to obtain decarbonized tailings. The overflow of the concentration tank and the filtrate of the filter press can be returned to the circulating water pool for recycling.

[0082] Example 1: The foaming agent is selected as 2-octanol and the collector is selected as diesel. When the foaming agent (2-octanol) is added in an amount of 4 kg / t and the collector (diesel) is added in an amount of 8 kg / t, the yield of carbon concentrate is 45% and the ash content is 28%; the yield of decarbonized tailings is 49% and the ash content is 95%.

[0083] Example 2: Methyl isobutyl carbinol (MIBC) is selected as the foaming agent, and diesel is selected as the collector. When the dosage of the foaming agent (MIBC) is 4 kg / t and the dosage of the collector (diesel) is 8 kg / t, the yield of carbon concentrate is 47%, and the ash content is 29%; the yield of carbon extraction tailings is 45%, and the ash content is 97%.

[0084] Example 3: The foaming agent is selected as 2-octanol and the collector is selected as kerosene. When the foaming agent (2-octanol) is added in an amount of 4 kg / t and the collector (kerosene) is added in an amount of 8 kg / t, the yield of carbon concentrate is 53% and the ash content is 35%; the yield of carbon tailings is 40% and the ash content is 93%.

[0085] The coal gasification slag resource recovery method of the present application can achieve the following beneficial effects:

[0086] (1) A combined process of coal gasification slag screening and grading, gravity separation and bubble flotation to extract carbon concentrate was designed. The process parameters such as the amount of reagents added can be dynamically adjusted according to the product quality requirements of carbon concentrate and carbon extraction tailings, so as to meet the product quality requirements while taking into account economic benefits.

[0087] (2) It can realize the resource utilization of nearly all coal gasification slag. The recovered carbon concentrate can be used for circulating gasification, boiler blending or preparation of carbon-based adsorption materials; the ignition loss of carbon-extracting tailings can be controlled within 5%, and it is rich in inorganic components such as SiO2 and Al2O3, meeting the first-level fly ash standards in the "Management Measures for the Comprehensive Utilization of Fly Ash", and can be used to produce cementitious materials, building materials, etc.

[0088] (3) The production process achieves near-zero wastewater discharge. The water used in the process can be prepared with the supernatant of gasification ash water, without the need to add additional fresh water. The water used in the gasification slag sorting stage can be recycled after purification in the sedimentation tank, and there is no wastewater discharge during the entire production cycle.

[0089] It should be understood that the present application is not limited to the precise structures that have been described above and shown in the drawings, and that various modifications and changes may be made without departing from the scope thereof. The scope of the present application is limited only by the appended claims.

Claims

1. A method for recycling coal gasification slag, characterized in that: include: The coal gasification slag is screened according to the particle size to obtain coarse ash particles and fine ash particles; The fine-grained ash is mixed with slurry and then re-selected to obtain a first underflow and a first overflow; Processing the first underflow to obtain carbon concentrate, decarbonized tailings and ash to be processed; The ash to be treated and the first overflow are mixed and then re-selected to obtain flotation ash that meets flotation conditions and ash to be floated that does not meet flotation conditions; The flotation ash that meets the flotation conditions is floated and processed to obtain carbon concentrate and decarbonized tailings.

2. The method for recycling coal gasification slag according to claim 1, characterized in that: The step of processing the first underflow to obtain carbon concentrate, decarbonized tailings and ash to be processed comprises: reselecting the first underflow to obtain a second underflow and a second overflow; The second overflow is processed to obtain carbon concentrate and a first ash, the second underflow is processed to obtain a decarbonized tailing and a second ash, and the first ash and the second ash are used as the ash to be processed.

3. The method for recycling coal gasification slag according to claim 2, characterized in that: The method of treating the second overflow to obtain carbon concentrate and first ash comprises: Screening the second overflow according to particle size to obtain first ash of coarse particles and third ash of fine particles; The third ash is centrifuged to obtain carbon powder.

4. The method for recycling coal gasification slag according to claim 2, characterized in that: The step of processing the second underflow to obtain decarbonized tailings and second ash comprises: Screening the second underflow according to particle size to obtain coarse-grained second ash and fine-grained fourth ash; The second ash is dehydrated to obtain decarbonized tailings.

5. The method for recycling coal gasification slag according to claim 1, characterized in that: The method of re-selecting the ash to be treated and the first overflow after slurry mixing to obtain flotation ash that meets flotation conditions and ash to be floated that does not meet flotation conditions includes: grinding the first overflow; The ash to be treated and the first overflow after grinding are mixed and then re-selected to obtain the flotation ash and the ash to be floated.

6. The method for recycling coal gasification slag according to claim 1, characterized in that: It also includes a recycling process, which includes: The ash to be floated that does not meet the flotation conditions is repeatedly ground and re-selected, and the flotation ash that meets the flotation conditions obtained after each grinding and re-selection is floated and processed to obtain carbon concentrate and decarbonized tailings.

7. The method for recycling coal gasification slag according to claim 1 or 6, characterized in that: The flotation ash that meets the flotation conditions is floated and processed to obtain carbon concentrate and decarbonized tailings, including: The flotation ash that meets the flotation conditions is subjected to bubble flotation to obtain carbonaceous matter and tailings; The carbonaceous material is collected and filtered to obtain carbon powder; The tailings are concentrated and filtered to obtain decarbonized tailings.

8. The method for recycling coal gasification slag according to claim 1, characterized in that: The coal gasification slag is screened according to the particle size to obtain coarse ash particles and fine ash particles, including: Adding liquid to coal gasification slag to form a first mixed slurry with a concentration of 35% to 65%; The first mixed slurry is screened according to the particle size to obtain coarse ash particles and fine ash particles.

9. The method for recycling coal gasification slag according to claim 1, characterized in that: The step of preparing the fine ash slurry for gravity separation to obtain a first underflow and a first overflow comprises: Adding liquid to the fine-grained ash to form a second mixed slurry with a concentration of 10% to 30%; The second mixed slurry is subjected to gravity selection to obtain a first underflow and a first overflow.

10. The method for recycling coal gasification slag according to claim 1, characterized in that: The grading aperture range for screening coal gasification slag is 0.5 mm to 1 mm; and / or The classification aperture range for reselecting the fine ash particles is 0.074 mm to 0.15 mm; and / or The frother used for flotation includes one of 2-octanol and methyl isobutyl carbinol, with a dosage of 1 to 15 kg; and / or The collector used for flotation includes one of diesel, kerosene, waste diesel and waste engine oil, and the dosage is 1.5 to 18 kg.

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