Coal gasification slag harmless disposal system and method

Abstract

The application discloses a coal gasification residue harmless treatment system and method in the technical field of solid waste treatment, which comprises the following steps: a screening device is used for screening treatment of the coal gasification residue to obtain oversize material and undersize material; a grinding device is used for grinding treatment of the oversize material to obtain ground oversize material; a sorting device is used for residual carbon sorting treatment of the undersize material to obtain concentrate and gasification tail residue, wherein the concentrate is used as a residual carbon product after dehydration, and the gasification tail residue is used as mixed material with the ground oversize material after dehydration and enters a compound leaching device; the compound leaching device is used for compound leaching and dehydration treatment of the mixed material; a chemical oxidation device is used for chemical oxidation and dehydration treatment of the mixed material after the compound leaching and dehydration treatment; and a water washing adjusting device is used for water washing adjustment and dehydration treatment of the mixed material after the chemical oxidation and dehydration treatment. The coal gasification residue generated by the coal chemical industry is subjected to systematic harmless treatment, and the effect of turning waste into treasure is realized.

Description

Technical Field

[0001] This invention relates to a harmless disposal system and method for coal gasification slag, belonging to the field of solid waste treatment technology. Background Technology

[0002] Coal gasification, a technology for the clean utilization of coal, produces syngas through the reaction of coal with oxygen or steam at high temperatures. However, the gasification process generates solid waste such as gasification slag. Currently, the national output of gasification slag exceeds 60 million tons and is showing an increasing trend year by year. There is no effective comprehensive utilization method for gasification slag, and the main disposal method is slag yard storage. Gasification slag contains a large amount of unreacted solid residue, various heavy metals such as copper (Cu), lead (Pb), and chromium (Cr), COD, etc. The large amount of gasification slag stored on land causes serious combined pollution of water, soil, and air, and large-scale disposal is urgently needed.

[0003] Elemental analysis of coal gasification slag revealed that it contains significant amounts of SiO2 (45-55%), Al2O3 (approximately 20%), Fe2O3 (approximately 10%), and unburned carbon (approximately 15-25%). Due to the formation of a glassy state, some inorganic metal elements may be encapsulated within the aluminosilicate lattice structure. Some metals may exist in the slag in exchangeable, carbonate-bound, iron-manganese-bound, organic matter and sulfide-bound, and residual forms, posing a risk of heavy metal leaching. Some organic matter may leach from unburned carbon into the medium, causing an increase in COD in the water, which also requires attention. Given the high proportion of unburned carbon in the slag, researching and utilizing residual carbon for high-value recovery can save resources and create significant economic value.

[0004] The physicochemical properties of coal gasification slag vary depending on the type of coal and the gasification process, exhibiting characteristics such as complex composition, uneven heavy metal content, and variable physicochemical properties. To date, the harmless disposal and resource utilization rates of coal gasification slag have remained low. In recent years, researchers have attempted to develop more effective and environmentally friendly technologies to address the issues of meeting standards for residual carbon, heavy metals, and COD in coal gasification slag. Common treatment methods mainly include physical, chemical, and biological methods. Physical methods, primarily mechanical and gravity separation, can separate some large particles and carbon, but their effectiveness in removing heavy metals is limited and cannot meet environmental protection requirements. Chemical methods, including solidification / stabilization treatment and chemical precipitation, can effectively reduce the migration and bioavailability of heavy metals, but may generate new pollutants. These methods are often limited to extracting valuable elements or removing individual harmful elements and cannot systematically achieve the harmless disposal of coal gasification slag. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a harmless treatment system and method for coal gasification slag. This system performs a series of treatments on the coal gasification slag generated in the coal chemical industry, systematically realizing the harmless treatment of coal gasification slag and turning waste into treasure.

[0006] To achieve the above objectives, the present invention is implemented using the following technical solution:

[0007] In a first aspect, the present invention provides a system for the harmless disposal of coal gasification slag, comprising:

[0008] Screening device: screens the coal gasification slag to obtain oversize and undersize materials;

[0009] Grinding device: Grinds the material on the sieve to obtain the ground material on the sieve;

[0010] Sorting device: The undersize material is sorted for residual carbon to obtain concentrate and gasification tailings. The concentrate is dewatered and used as residual carbon product. The gasification tailings are dewatered and mixed with the ground oversize material as a mixture and fed into the compound washing device.

[0011] Compound washing device: performs compound washing and dehydration treatment on the mixed materials;

[0012] Chemical oxidation unit: performs chemical oxidation and dehydration treatment on the mixture after compound washing and dehydration;

[0013] Water washing and conditioning device: performs water washing and conditioning and dehydration treatment on the mixture after chemical oxidation and dehydration;

[0014] Heavy metal curing device: performs heavy metal curing treatment on the mixture after water washing, conditioning and dehydration.

[0015] Furthermore, it also includes a wastewater treatment and reuse device, which recovers the wastewater from the dehydration treatment of each device in the coal gasification slag harmless treatment system, removes organic matter and heavy metals, and then returns it to each device in the coal gasification slag harmless treatment system.

[0016] Furthermore, the screening device includes a screening machine, and the screening machine uses a screen with a mesh size of 0.5mm-3.0mm.

[0017] Furthermore, the sorting device includes a separator, and the separator may be a spiral separator, a TBS, a flotation machine, or a flotation column.

[0018] Furthermore, the grinding device includes a ball mill, and the output particle size of the ball mill is ≤2.0mm.

[0019] Furthermore, the compound rinsing device includes a rinsing tank and a rinsing agent adding device, and the rinsing agent adding device adds rinsing agent to the rinsing tank through a dosing pump. The rinsing tank is equipped with a pH detection port, and the rinsing agent includes at least one of organic acid, inorganic acid, organic chelating agent and surfactant.

[0020] Furthermore, the chemical oxidation device includes a chemical oxidation tank and an oxidant addition device, and the oxidant addition device adds an oxidant to the chemical oxidation tank through a dosing pump. The oxidant is selected from hydrogen peroxide (H2O2), ozone, or persulfate.

[0021] Furthermore, the water washing and conditioning device includes a water washing tank and a conditioning agent adding device, wherein the conditioning agent adding device adds pH conditioning agent or water to the water washing tank through a dosing pump.

[0022] Furthermore, the heavy metal curing device includes a curing tank and a curing agent adding device. The curing agent adding device adds curing agent to the curing tank through a dosing pump. The curing tank adopts bioleaching technology and / or multi-stage passivation method. The bioleaching uses a composite strain. The curing agent is selected from cement, quicklime, Ca(OH)2, Na2S or Na2S2O3.

[0023] Secondly, the present invention provides a method for the harmless disposal of coal gasification slag, comprising the following steps:

[0024] The coal gasification slag is screened to obtain oversize and undersize materials;

[0025] The material on the sieve is ground to obtain the ground material on the sieve.

[0026] The undersize material is subjected to residual carbon separation treatment to obtain concentrate and gasification tailings. The concentrate is dewatered and used as residual carbon product, while the gasification tailings are dewatered and mixed with the ground oversize material as a compound washing device.

[0027] The mixture is subjected to compounding, rinsing, and dehydration treatment;

[0028] Chemical oxidation and dehydration treatment are carried out on the mixture after compounding, rinsing and dehydration;

[0029] The mixture after chemical oxidation and dehydration is then subjected to water washing and dehydration treatment;

[0030] Heavy metal solidification treatment is carried out on the mixture after water washing, conditioning and dehydration.

[0031] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0032] I. This invention provides a method for harmlessly treating coal gasification slag generated in the coal chemical industry. It systematically realizes the harmless disposal of coal gasification slag, turning waste into treasure. It can not only solve the solid waste treatment problem in the coal chemical industry, but also bring certain economic benefits to enterprises. It completely solves the problem that coal gasification slag in the coal chemical industry cannot be treated except by slag yard storage.

[0033] Second, the raw materials processed by this invention are suitable for gasification coarse slag and gasification fine slag. The coal gasification slag after harmless treatment can meet the general industrial solid waste Class I parameter standards and can be used as raw materials for underground filling, cement, building materials and other high value-added products, thereby realizing the harmless treatment and resource utilization of coal gasification slag.

[0034] Third, the leaching agents used in this invention preferentially include organic acids, inorganic acids, organic chelating agents, surfactants, etc., to remove heavy metals from coal gasification slag through acidic, alkaline, or compound leaching agents. When oxalic acid and citric acid are used as leaching agents, the leaching agents are biodegradable, reducing environmental impact and having greater environmental advantages than traditional methods. In addition, by optimizing the treatment conditions, the amount of chemical reagents used and the treatment cost are reduced. At the same time, the coal gasification slag after harmless treatment can be recycled as a resource, increasing economic benefits. Attached Figure Description

[0035] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0036] Figure 1 This is a schematic diagram of the processing flow of a coal gasification slag harmless disposal system provided in Embodiment 1 of the present invention;

[0037] Figure 2 This is a schematic diagram of the process for removing heavy metals from coal gasification slag by residual carbon sorting, rinsing, and oxidation, according to a harmless treatment system for coal gasification slag provided in Embodiment 1 of the present invention.

[0038] In the diagram: 1. Screening device; 2. Sorting device; 3. Grinding device; 4. Compound rinsing device; 5. Chemical oxidation device; 6. Water washing and conditioning device; 7. Heavy metal solidification device; 8. Wastewater treatment and reuse device; 9. Rinsing agent addition device; 10. Oxidant addition device; 11. Conditioner addition device; 12. Solidifying agent addition device. Detailed Implementation

[0039] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other.

[0040] The following detailed description is exemplary and intended to provide further detailed explanation of the invention. Unless otherwise specified, all technical terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used in this invention is for describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention.

[0041] Example 1:

[0042] This embodiment provides a harmless treatment system for coal gasification slag. The core of the solution is the removal and stabilization of residual carbon, COD, and heavy metals. (Refer to...) Figure 1 The process includes: screening device 1, sorting device 2, grinding device 3, compound washing device 4, chemical oxidation device 5, water washing and conditioning device 6, heavy metal solidification device 7, and wastewater treatment and reuse device 8. The coal gasification slag is first classified by screening device 1. The undersize material enters sorting device 2, and the oversize material enters grinding device 3. The sorted gasification tailings and the ground undersize material are mixed and then sequentially fed into compound washing device 4, chemical oxidation device 5, water washing and conditioning device 6, and heavy metal solidification device 7 to remove residual carbon, heavy metals, COD, and ensure the pH value meets standards. This process is suitable for treating both coarse and fine gasification slag. The harmlessly treated coal gasification slag meets the Class I parameter standards for general industrial solid waste and can be used as raw material for underground filling, cement, building materials, and high-value-added products, achieving harmless treatment and resource utilization of coal gasification slag. Specifically:

[0043] The screening device 1 includes a screening machine with a coal gasification slag inlet, an oversize material outlet, and an undersize material outlet. It screens the coal gasification slag to separate the material into large oversize particles and small undersize particles. When the organic matter content in the large oversize particles is ≤2.0%, pre-screening helps to reduce the load on the next sorting unit. In this embodiment, the screen mesh size used in the screening machine is 0.5mm-3.0mm.

[0044] The sorting device 2 includes a pre-slurry mixer with an inlet and a separator. The inlet of the pre-slurry mixer is connected to the undersize material outlet of the screening machine, and the outlet of the pre-slurry mixer is connected to the feed inlet of the separator. The separator separates two or more products, including light products and heavy products. The light products (residual carbon) are discharged from the light product outlet of the separator, and the other products are collectively referred to as heavy products (gasification tailings) and are discharged from the heavy product outlet of the separator. The separator is preferably a spiral separator, TBS, flotation machine or flotation column, which can achieve an organic content of <2.0% in the gasification tailings. In this embodiment, the dry basis residual carbon content in the gasification tailings is ≤2.0%.

[0045] The grinding device 3 includes a ball mill with a feed inlet, a discharge outlet, and a water inlet. The feed inlet of the ball mill is connected to the oversize material outlet of the screening machine. The ball mill grinds the oversize material. Its function is to expose the sealed heavy metals and residual carbon by grinding the coal gasification slag particles, which is beneficial to improving the harmless treatment effect. In this embodiment, the discharge particle size of the ball mill is ≤2.0mm.

[0046] The compound leaching device 4 includes a leaching tank with an inlet, an outlet, and a water supply inlet, a leaching agent addition device 9, and a dewatering device. The inlet of the leaching tank is connected to the ball mill outlet of the grinding device 3 and the heavy product outlet of the separator of the sorting device 2. The outlet of the leaching tank is connected to the inlet of the matching dewatering device. The leaching agent addition device 9 adds leaching agent to the leaching tank through a dosing pump. The leaching tank is equipped with a pH detection port, and the leaching agent in the leaching tank contains one or more leaching agents. The preferred leaching agents are organic acids, inorganic acids, organic chelating agents, surfactants, etc. The heavy metals are leached from the coal gasification slag by acidic, alkaline, or compound leaching agents. In this embodiment, oxalic acid and citric acid are used as leaching agents. These leaching agents are biodegradable, reducing environmental impact and having a greater environmental advantage than traditional methods, thus being environmentally friendly. By optimizing the processing conditions, the amount of chemical reagents used and the processing cost are reduced. At the same time, the coal gasification slag after harmless treatment can be recycled as a resource, increasing economic benefits. The scrubbing tank is equipped with a pH detection port, and the type of scrubbing agent added is adjusted by detecting the pH value of the scrubbing liquid. The dewatering equipment of the compound scrubbing device 4 is preferably a linear vibrating screen, slag-water separator or dewatering chute, etc., to remove water and scrubbing agent from the coal gasification slag after scrubbing.

[0047] The chemical oxidation unit 5 includes a chemical oxidation tank with an inlet, an outlet, and a water inlet, an oxidant addition device 10, and a dewatering device. The inlet of the chemical oxidation tank is connected to the outlet of the dewatering device of the compound washing device 4, and the outlet of the chemical oxidation tank is connected to the inlet of the dewatering device. The oxidant addition device 10 adds oxidant to the chemical oxidation tank through a dosing pump. The preferred oxidants are hydrogen peroxide (H2O2), ozone, and persulfate. The advanced oxidation process of the chemical oxidation unit 5 can remove soluble organic matter, volatile organic matter, and semi-volatile organic matter leached from the coal gasification slag. The oxidant can also convert heavy metals in the coal gasification slag from low valence states to high valence states, making them easier to remove by water washing. The dewatering device of the chemical oxidation unit 5 preferably uses a linear vibrating screen, a slag-water separator, or a dewatering chute to remove water and oxidant from the coal gasification slag after chemical oxidation.

[0048] The water washing and conditioning device 6 includes a water washing tank with an inlet, an outlet, and a water replenishment inlet, a conditioning agent addition device 11, and a dewatering device. The inlet of the water washing tank is connected to the outlet of the dewatering device of the compound leaching device 5, and the outlet of the water washing tank is connected to the inlet of the dewatering device of the water washing and conditioning device 6. The conditioning agent addition device 11 adds pH conditioning agent or water to the water washing tank through a dosing pump. The functions of the water washing and conditioning device 6 are: first, to remove residual oxidants and leaching agents from the coal gasification slag; and second, to adjust the pH value of the material by adding pH conditioning agents. The dewatering device of the water washing and conditioning device 6 preferably uses a linear vibrating screen, a slag-water separator, or a dewatering chute to remove moisture, residual oxidants, and leaching agents from the coal gasification slag.

[0049] The heavy metal solidification device 7 includes a solidification tank with an inlet, an outlet, and a water inlet, a solidifying agent addition device 12, and a dewatering device. The inlet of the solidification tank is connected to the outlet of the dewatering device of the water washing and regulating device 6, and the outlet of the solidification tank is connected to the inlet of the dewatering device of the heavy metal solidification device 7. The solidifying agent addition device 12 adds solidifying agent to the solidification tank via a dosing pump. The solidification tank employs bioleaching technology and / or multi-stage passivation. For bioleaching, a combination of bacterial strains such as *Thiobacillus ferrooxidans* and *Thiobacillus thiooxidans* is preferred. Preferred solidifying agents include cement, quicklime, Ca(OH)₂, Na₂S, and Na₂S₂O₃. The heavy metal solidification device 7 can solidify heavy metals in coal gasification slag after chemical oxidation and chemical leaching to ensure that heavy metals in the coal gasification slag do not enter the groundwater during long-term leaching. The dewatering equipment of the heavy metal solidification unit 7 shall preferably be a linear vibrating screen, a slag-water separator or a dewatering chute, etc., to remove moisture and solidifying agent from the solidified coal gasification slag.

[0050] The wastewater treatment and reuse device 8 includes an inlet, an outlet, a makeup inlet, and an overflow outlet. The inlet of the wastewater reuse device 8 is connected to the outlets of the dewatering equipment in the compound rinsing device 4, the chemical oxidation device 5, the water washing and conditioning device 6, and the heavy metal solidification device 7. The outlet of the wastewater reuse device 8 is connected to the inlet of the pre-mixing machine, the inlet of the ball mill, the makeup inlet of the chemical oxidation tank, the makeup inlet of the compound rinsing tank, the makeup inlet of the water washing tank, and the makeup inlet of the solidification tank. The wastewater treatment and reuse device 8 is a complete set of wastewater treatment and circulating water reuse devices for washing, chemical oxidation, and rinsing processes. It removes organic matter and heavy metals from the rinsing wastewater generated during the harmless treatment of coal gasification slag, ultimately achieving effluent quality that meets reuse standards.

[0051] It should be noted that the chemical oxidation tank, rinsing tank, water washing tank, and solidification tank (collectively referred to as reaction tanks) are all equipped with reflux pumps. The inlet of the reflux pump is connected to the outlet of the corresponding dewatering equipment, and the outlet of the reflux pump is connected to the inlet of each reaction tank.

[0052] Because the physicochemical properties of coal gasification slag vary depending on the type of coal and the gasification process, any general-purpose processing technology must possess sufficient flexibility and adaptability. Therefore, some embodiments of this invention exhibit the following flexibility, for example:

[0053] (i) Without pre-screening, the coal gasification slag directly enters the residual carbon separation-chemical oxidation-composite rinsing-heavy metal solidification process to obtain harmlessly treated coal gasification slag;

[0054] (ii) If the oversize material after pre-screening meets the standards for heavy metals and other indicators, and has other uses, it can be used directly as a product and will not be mixed with the undersize gasification tailings after sorting before entering the subsequent harmless treatment unit.

[0055] (iii) Based on the test results of heavy metal content and form of existence, gasification tailings and oversize materials can directly enter the subsequent harmless treatment unit without going through the grinding unit.

[0056] (iv) The material after water washing and conditioning can be directly obtained as harmless coal gasification slag without going through the heavy metal solidification unit.

[0057] In this embodiment, after the coal gasification slag is screened and graded by a Φ2.0mm screen, the oversize material is fed into a ball mill via a chute and ground to a size smaller than 2.0mm. The undersize material smaller than 2.0mm is fed into a slurry preparer for slurry preparation (the slurry-to-liquid ratio is between 5-30% depending on the actual separation requirements). The mixed slurry is pumped into a separator for residual carbon separation. After separation, two materials are selected: concentrate and gasification tailings. These materials are fed into a concentrate tank and a tailings tank, respectively. The concentrate slurry is pumped to a linear vibrating screen for dewatering and is used as the residual carbon product. The gasification tailings are dewatered using a slag-water separator. The dewatered tailings and the ground material are mixed and fed into a compound washing tank for washing. The compound washing tank is equipped with a pH detection port. Based on the feedback pH value, a dosing pump is used to selectively add a leaching agent to the leaching tank, maintaining the leaching solution concentration at optimal conditions. The slag-water mixture after passing through the compound leaching tank is dewatered by a slag-water separator and then enters a chemical oxidation tank. An oxidant is added to the oxidation tank via a dosing device to degrade the organic matter in the coal gasification slag, promoting the release of organically bound heavy metals. The slag-water mixture after passing through the chemical oxidation tank is dewatered by a slag-water separator and then enters a water washing and conditioning tank to remove residual oxidant and leaching agent. After passing through the water washing and conditioning tank, the slag-water mixture is dewatered again by a slag-water separator and then enters a solidification tank. A solidifying agent is added to the solidification tank to solidify and stabilize the residual heavy metals in the coal gasification slag. The process technology route of wastewater treatment and reuse device 8 is: pH adjustment, coagulation and sedimentation, catalytic oxidation treatment, and biological treatment to ultimately achieve the recycled water standard. After treatment by the above-mentioned harmless disposal device, the residual carbon product can be used as a boiler co-firing feedstock, and the various parameters of the gasification tailings meet the general industrial solid waste Class I parameter standards. It should be noted that there are no restrictions on the order of the screening device, grinding device, sorting device, compound washing device, and chemical oxidation device in the application, and the addition or deletion of some device units are allowed in this invention.

[0058] Example 2:

[0059] According to the system for harmless treatment of coal gasification slag of the present invention, reference is made to Figure 2 It is understood that a combined treatment method involving sorting pretreatment, chemical oxidation, and rinsing in the laboratory can efficiently remove residual organic matter, COD, and heavy metals from coal gasification slag, ultimately achieving the harmless and resource-based utilization of the slag and effectively improving treatment efficiency and economic benefits. The specific implementation steps are as follows:

[0060] Residual carbon pre-treatment: Residual carbon pre-sorting is performed to reduce the amount of coal gasification slag to be processed and improve processing efficiency. This method is suitable for coal gasification slag with high carbon content. Utilizing the density difference between residual carbon and tailings, ZnCl2 solution is used to sort the coal gasification slag, recover residual carbon, reduce the amount of coal gasification slag entering subsequent units, and improve the efficiency of subsequent processing. See Table 1 for the results of the small-scale flotation and settling test of coal gasification slag. After residual carbon recovery, coal gasification tailings with a density ≥2.0 g / cm3 enter the next oxidation treatment unit.

[0061] Chemical oxidation treatment: Under reaction conditions of 2 hours of oxidation, a solid-liquid ratio of 1:5, and an oxidant concentration of 0.5 M, the COD of the gasification tailings leachate can be reduced from 40 mg / L to 10 mg / L (Class IV groundwater standard).

[0062] Compound leaching: Hydrochloric acid, citric acid and oxalic acid all have good leaching and removal effects on excessive metals (mercury, arsenic and antimony) in gasification tailings leachate. Among them, citric acid has a higher removal rate for antimony (97.8%) and oxalic acid has a higher removal rate for arsenic (80.9%). The compound leaching experiment shows that after leaching with a specific compound ratio and number of times, the concentration of heavy metals in the gasification tailings leachate can be reduced to below the Class IV standard of groundwater.

[0063] In this embodiment, a combination of chemical oxidation and rinsing is used to achieve a high heavy metal removal rate, especially for Cu, Pb and Cr, which are significantly effective in removing them, thus meeting the standards of resource recovery and harmlessness.

[0064] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0065] As is known from common technical knowledge, this invention can be implemented through other embodiments that do not depart from its spirit or essential characteristics. Therefore, the disclosed embodiments described above are merely illustrative and not exhaustive. All modifications within the scope of this invention or its equivalents are included in this invention.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A harmless treatment system for coal gasification slag, characterized in that, include: Screening device: screens the coal gasification slag to obtain oversize and undersize materials; Grinding device: Grinds the material on the sieve to obtain the ground material on the sieve; Sorting device: The undersize material is sorted for residual carbon to obtain concentrate and gasification tailings. The concentrate is dewatered and used as residual carbon product. The gasification tailings are dewatered and mixed with the ground oversize material as a mixture and fed into the compound washing device. Compound rinsing device: for compound rinsing and dehydration treatment of mixed materials, the compound rinsing device includes a rinsing tank and a rinsing agent adding device, and the rinsing agent adding device adds rinsing agent to the rinsing tank through a dosing pump. The rinsing tank is equipped with a pH detection port. The rinsing agent includes at least one of organic acid, inorganic acid, organic chelating agent and surfactant. Chemical oxidation device: chemically oxidizes and dehydrates the mixture after compound washing and dehydration treatment. The chemical oxidation device includes a chemical oxidation tank and an oxidant addition device. The oxidant addition device adds oxidant to the chemical oxidation tank through a dosing pump. The oxidant is selected from hydrogen peroxide (H2O2), ozone or persulfate. Water washing and conditioning device: performs water washing and conditioning and dehydration treatment on the mixture after chemical oxidation and dehydration; Heavy metal curing device: performs heavy metal curing treatment on the mixture after water washing, conditioning and dehydration.

2. The coal gasification slag harmless treatment system according to claim 1, characterized in that, It also includes a wastewater treatment and reuse device, which recovers the wastewater from the dewatering treatment of each device in the coal gasification slag harmless treatment system, removes organic matter and heavy metals, and then returns it to each device in the coal gasification slag harmless treatment system.

3. The coal gasification slag harmless treatment system according to claim 1, characterized in that, The screening device includes a screening machine, and the screening machine uses a screen with a mesh size of 0.5mm-3.0mm.

4. The coal gasification slag harmless treatment system according to claim 1, characterized in that, The sorting device includes a separator, and the separator may be a spiral separator, a TBS, a flotation machine, or a flotation column.

5. The coal gasification slag harmless treatment system according to claim 1, characterized in that, The grinding device includes a ball mill, and the output particle size of the ball mill is ≤2.0mm.

6. The coal gasification slag harmless treatment system according to claim 1, characterized in that, The water washing and conditioning device includes a water washing tank and a conditioning agent adding device. The conditioning agent adding device adds pH conditioning agent or water to the water washing tank through a dosing pump.

7. The coal gasification slag harmless treatment system according to claim 1, characterized in that, The heavy metal curing device includes a curing tank and a curing agent adding device. The curing agent adding device adds curing agent to the curing tank through a dosing pump. The curing tank adopts bioleaching technology and / or multi-stage passivation. The bioleaching uses a composite strain. The curing agent is selected from cement, quicklime, Ca(OH)2, Na2S or Na2S2O3.

8. A method for the harmless disposal of coal gasification slag, characterized in that, The coal gasification slag harmless treatment system according to any one of claims 1-7 includes the following steps: The coal gasification slag is screened to obtain oversize and undersize materials; The material on the sieve is ground to obtain the ground material on the sieve. The undersize material is subjected to residual carbon separation treatment to obtain concentrate and gasification tailings. The concentrate is dewatered and used as residual carbon product, while the gasification tailings are dewatered and mixed with the ground oversize material as a compound washing device. The mixture is subjected to compounding, rinsing, and dehydration treatment; Chemical oxidation and dehydration treatment are carried out on the mixture after compounding, rinsing and dehydration; The mixture after chemical oxidation and dehydration is then subjected to water washing and dehydration treatment; Heavy metal solidification treatment is carried out on the mixture after water washing, conditioning and dehydration.

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