Coal gasification fine slag-oily sludge combined reselection treatment method

Abstract

The invention discloses a coal gasification fine slag-oily sludge combined reselection treatment method which comprises the following steps: 1) carrying out reselection separation on fine slag ore pulp, collecting light-component ore pulp, and filtering to obtain low-ash coal gasification fine slag; (2) carrying out acid leaching reaction on the low-ash coal gasification fine slag and the oily sludge; and (3) the acid leaching slurry is subjected to gravity separation, and concentrate products and tailing products are collected. According to the method, the oily sludge and the low-ash coal gasification fine slag are innovatively mixed and then subjected to synergistic acid leaching, and high-selectivity redistribution of components and reconstruction adjustment of a microstructure are achieved through mechanical-chemical action, adsorption and other actions, so that recycling of the coal gasification fine slag and the oily sludge is achieved. The method is easy to implement, the medicament treatment cost and the equipment cost can be greatly reduced, the clean coal product can be extracted from the coal gasification fine slag and the oil-containing sludge, clean and value-added utilization of the coal gasification fine slag and the oil-containing sludge is realized, and the economic benefit, the resource benefit and the environmental benefit are remarkable.

Description

Technical Field

[0001] The invention belongs to the technical field of waste resource utilization, and specifically relates to a method for combined gravity separation of coal gasification fine residue and oily sludge. Background Art

[0002] Oilfield oily sludge is an oily solid waste generated during oil extraction, transportation, refining and oily wastewater treatment. As a large-equivalent hazardous waste, oily sludge must be treated harmlessly.

[0003] The composition of oily sludge in oilfields is complex. It is a three-phase mixture of oil, solid and water. It contains a high amount of water and often contains insoluble solids such as mud, scale, and gravel. It may also contain aged crude oil, wax, asphaltene, colloids, suspended solids, salts, etc. Some also contain flocculants, corrosion inhibitors, scale inhibitors, bactericides, etc. added during the production process. The complex components combined with mechanical action make the oily sludge become a stable suspended emulsion, which is difficult to achieve multiphase separation.

[0004] The treatment technology of oily sludge in oil fields can be divided into reduction treatment technology, harmless disposal technology and resource utilization technology according to the purpose. According to the treatment method, it can be mainly divided into sludge dehydration landfill, biological treatment and thermal treatment technology. At present, there are more than a dozen technologies for treating oily sludge, including landfill, injection into formation profile adjustment, solidification of oily sludge to inert solidified substrate, solvent extraction and other physical and chemical technologies, co-combustion, direct incineration, catalytic pyrolysis, microwave pyrolysis and other thermal treatment technologies, as well as land cultivation, composting and other biological technologies. These technologies can be used in combination to treat various oily sludges, but they all have certain problems, such as land pollution and secondary pollution caused by landfill and other technologies; for example, after some physical and chemical methods are used to treat oily sludge with high oil content, although most of the oil is recovered, a larger equivalent of low oil content oily sludge is produced; for example, the biological method for treating oily sludge is technically difficult and has high maintenance costs; in addition, when treating low oil content oily sludge, no matter which technology is used, it is often economical, costly and has poor deoiling effect. In summary, the existing technologies for treating oily pollution have poor universality, and it is difficult to ensure harmless and reduced-volume treatment while recycling oily sludge.

[0005] Coal gasification slag is a major byproduct of the entrained-bed coal gasification production process. As a large equivalent solid waste produced by coal chemical industry, domestic and foreign scholars have proposed many technical solutions for the recovery and utilization of coal gasification coal slime components in recent years, which can be roughly divided into two categories, namely resource utilization and harmless utilization. Resource utilization mainly refers to the separation of carbonaceous and inorganic components in coal gasification slag by physical and chemical methods (such as flotation and leaching), and then the recovery of carbonaceous and inorganic components. For example, some scholars use foam flotation to separate coal gasification slag into carbon-rich concentrate (loss on ignition can reach 88.86%) and high-ash tailings (loss on ignition less than 10%). According to the national standard "Fly ash for cement and concrete" (GB / T 1596-2017), if the loss on ignition is less than 15%, it can be used directly as Class III fly ash in roadbed and other building materials. Therefore, coal gasification slag carbon ash is widely used in building materials after separation. The lower the loss on ignition, the higher the value of high-ash tailings and the wider its application. At the same time, because the ash of coal gasification fine slag contains rich silicon and aluminum elements, the separated ash can be used to produce ceramic or glass materials, such as microcrystalline glass, ceramic glaze, etc.; harmless utilization mainly refers to stacking, landfilling, solidification, or mixed burning treatment. Stacking and landfilling are currently the main means of treating coal gasification fine slag, occupying land resources, and bringing huge pressure to enterprise development and land use. At present, there are few companies and means that can treat coal gasification fine slag on a large scale. Economic efficiency restricts the treatment of coal gasification fine slag. Although existing research has achieved certain results, there are still problems such as poor economy, poor universality, and poor environmental protection. Research on more thorough carbon ash separation methods and utilization after separation of coal gasification fine slag is a research hotspot of coal gasification fine slag. Summary of the invention

[0006] The main purpose of the present invention is to provide a method for reselection of coal gasification fine slag, aiming to achieve adsorption carbon enrichment of coal gasification fine slag and improve the subsequent adsorption effect of coal gasification fine slag on oil-containing sludge;

[0007] The main purpose of the present invention is to also provide a coal gasification fine slag-oil-containing sludge synergistic acid leaching method, aiming to achieve synergistic activation of coal gasification fine slag-oil-containing sludge and improve the subsequent reselectivity of coal and ash.

[0008] The main purpose of the present invention is to provide a method for achieving the reselection and separation of coal and ash in coal gasification fine slag-oil-containing sludge based on the collaborative acid leaching method.

[0009] The objective of the present invention is achieved through the following technical solutions:

[0010] The present invention utilizes the porous adsorption properties of coal gasification fine slag to adsorb oil substances in oily sludge, and then utilizes the density difference of carbonaceous and inorganic ash minerals for gravity separation. However, studies have found that untreated coal gasification fine slag is difficult to completely adsorb the oil in oily sludge. Simply mixing coal gasification fine slag with oily sludge not only fails to achieve coordinated consumption, but makes it more difficult to separate, increasing the burden of joint treatment. In response to the difficulties faced by joint treatment, it is necessary to solve the problems of insufficient adsorption of gasification fine slag and difficulty in separating oil, solid and liquid in oily sludge. Not only is it necessary to provide a suitable site for competitive adsorption of gasification fine slag and solid-liquid two phases in oily sludge, but it is also necessary to promote the separation of oil from the solid-liquid phase of oily sludge. Therefore, a suitable modification method is needed. Conventional alkaline treatment demulsification effect is not ideal and costly. Therefore, the present invention innovatively changes the method of alkaline oil washing, utilizing the property that both coal gasification fine slag and oily sludge solid phase contain a large amount of alkaline minerals, and uses acid leaching to treat both. In this way, the chemical and physical synergy of the components can be achieved, the solid phase structure of the oily sludge is destroyed, the oil is precipitated from the solid phase, and the fine slag of coal gasification is activated, with a larger specific surface area and stronger adsorption, thereby achieving synergistic treatment. On this basis, further based on the combined control of the blending ratio, the amount of mixed acid added, and the stirring leaching time and other parameters, the sorting effect of the gravity separation stage after the combined acid leaching can be further improved, and the problems faced by the combined treatment can be further solved, the sorting selectivity of coal and ash can be improved, and the synergistic disposal of the two solid wastes can be achieved. Specifically:

[0011] A method for treating coal gasification fine residue-oil-containing sludge by combined gravity separation comprises the following steps:

[0012] 1) Gravity separation of the fine slag slurry, collection of light component slurry, and filtration to obtain low-ash coal gasification fine slag;

[0013] 2) subjecting the low-ash coal gasification fine slag and the oily sludge to an acid leaching reaction to obtain an acid leaching slurry;

[0014] 3) The acid leaching slurry is subjected to gravity separation to collect the concentrate product and tailings product.

[0015] In some specific embodiments, the concentration of the fine slag slurry in step 1) is 15-35%.

[0016] Furthermore, the concentration of the fine slag slurry in step 1) is 25%.

[0017] In some specific embodiments, the fine slag slurry in step 1) is prepared by mixing coal gasification fine slag and water, stirring and dispersing the mixture evenly, and then preparing the fine slag slurry with a slurry concentration of 15-35%.

[0018] In some specific embodiments, the gravity separation in step 1) is specifically to mix the fine slag slurry evenly and then use a spiral chute to gravity separate, control the gravity separation feed rate to 0.5-3 t / h, preferably 1-2 t / h; the opening of the light component discharge port is 10%-45%, preferably 15%-25%, to obtain the light component, heavy component and intermediate component of the first gravity separation, wherein the light component is collected as the product, and the intermediate component is subjected to the second gravity separation, the opening is the same as the first gravity separation, the obtained light component is collected as the product, and the light component obtained by the two gravity separations is filtered and dried to obtain low-ash coal gasification fine slag;

[0019] Furthermore, the water content of the low-ash coal gasification fine slag in step 1) is less than 30%;

[0020] In some specific embodiments, the leaching acid used in the acid leaching reaction in step 2) is at least one of sulfuric acid or hydrochloric acid.

[0021] In certain specific embodiments, the hydrogen ion molar concentration of the leaching acid in step 2) is 1-5 mol / L, and the total amount of the leaching acid added is 20-120 wt % of the total ash mass of the low-ash coal gasification fine slag and the oily sludge.

[0022] Furthermore, in step 2), the concentration of the leaching acid is 1-2 mol / L, and the total amount of the leaching acid added is 50-120 wt% of the total ash mass of the low-ash coal gasification fine slag and the oily sludge.

[0023] In some specific embodiments, the oil content of the oily sludge in step 2) is 3-30%, the water content is 30-80%, and the solid content is 5-20%. The oily sludge is gray-black oily sludge with less asphaltene, higher fluidity, and a calorific value of 5-13 MJ / kg.

[0024] In certain specific embodiments, the process conditions of the acid leaching reaction in step 2) are: stirring at room temperature for 12-24 hours, and adding the mixed acid three times in equal amounts every 4-8 hours.

[0025] In certain specific embodiments, the wet weight ratio of the low-ash coal gasification fine slag to the oily sludge in step 3) is 1:1-8.

[0026] In certain specific embodiments, the mass concentration of the acid leaching slurry in step 3) is 15-35%, and the feed rate of the gravity separation is 0.5-3 t / h.

[0027] Furthermore, in step 3), the mass concentration of the acid leaching slurry is 15-35%, and the feed rate of the gravity separation is 1-2 t / h.

[0028] In some specific embodiments, during the gravity separation process in step 3), the opening of the light component discharge port is 10% to 45%, preferably 15% to 25%, and the opening of the heavy component discharge port is 5% to 10%. In the second gravity separation of the intermediate component, the opening of the light component discharge port is 10% to 20%, preferably 15% to 20%, and the opening of the heavy component discharge port is 5% to 10%. The first light component and the second light component are mixed and filtered to obtain a low-ash and high-oil content concentrate product, and the first heavy component and the second heavy component are mixed and filtered to obtain a high-ash and low-oil content tailings product.

[0029] Compared with the prior art, the present invention has at least the following advantages:

[0030] The combined gravity treatment method of coal gasification fine slag and oily sludge provided by the present invention innovatively blends oily sludge and low-ash coal gasification fine slag and then conducts synergistic acid leaching, and realizes highly selective redistribution of components and reconstruction and adjustment of microstructure through mechanical-chemical action, adsorption and other effects, so that the oily sludge can be recycled and utilized; it is beneficial to obtain low-ash flotation clean coal products and high-ash tailings. Clean coal is directly used as high calorific value fuel, and high-ash tailings can be used for building materials. The present invention is easy to implement, and can greatly reduce the cost of chemical treatment and equipment, and can extract clean coal products from coal gasification fine slag and oily sludge, so as to realize the clean and value-added utilization of coal gasification fine slag and oily sludge, with significant economic benefits, resource benefits and environmental benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the specific embodiments of the present invention, the drawings required for use in the specific embodiments or the description of the prior art will be briefly introduced below.

[0032] Figure 1 The present invention provides a process flow chart of a coal gasification fine residue-oil-containing sludge combined gravity treatment method. DETAILED DESCRIPTION

[0033] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. The following embodiments are only illustrative and not restrictive, and the protection scope of the present invention cannot be limited thereto.

[0034] When a certain amount, concentration or other value or parameter is expressed in the form of a range, a preferred range, or a preferred upper and lower numerical limit, it should be understood that it is equivalent to specifically revealing any range by combining any pair of upper range limits or preferred numerical values ​​with any lower range limit or preferred numerical value, regardless of whether the range is specifically disclosed. Unless otherwise indicated, the numerical range values ​​listed herein include the endpoints of the range, and all integers and fractions within the range.

[0035] Unless otherwise indicated, all percentages, parts, ratios, etc. herein are by weight.

[0036] The materials, methods, and examples herein are illustrative and are not to be construed as limiting unless specifically stated.

[0037] In the following examples, the mixed acid is a solution of 98% concentrated sulfuric acid: water = 1:10 (mass ratio), and its hydrogen ion molar concentration is 1.82 mol / L;

[0038] The coal gasification fine slag used comes from a coal gasification chemical plant in Yunnan with smokeless feed, with an ash content of 39.74% and a calorific value of 18.6 MJ / kg; the oily sludge used comes from a factory in Chongqing, with an oil content of 8.11%, a water content of 65.47%, a solid content of 26.42%, and a calorific value of 11.81 MJ / kg.

[0039] The test methods used in the following embodiments include:

[0040] 1) Ash content test;

[0041] The ash content was determined according to the slow ashing method in accordance with the national standard GB / T 212-2008 "Industrial Analysis Methods of Coal". About 1 g of sample was weighed into an ash dish using an analytical balance, and placed in a muffle furnace. The furnace temperature was slowly raised to 500°C within 30 min, maintained for 30 min, and then slowly raised to 815±10°C. The temperature was burned until the mass was constant, and the mass fraction of the residue to the original sample was taken as the ash content.

[0042] 2) Calorific value test of clean coal products

[0043] According to the national standard GB / T 213-2008 "Method for determining the calorific value of coal", the calorific value is determined according to the principle of oxygen bomb calorimetry;

[0044] The yield is calculated based on the total dry weight of low-ash coal gasification fine slag and oily sludge before acid leaching = dry weight of low-ash coal gasification fine slag + solid dry weight of oily sludge + oil content of oily sludge.

[0045] The total amount of leaching acid added = [wet weight of low-ash coal gasification fine slag × ash content of low-ash coal gasification fine slag × (1-water content of low-ash coal gasification fine slag) + wet weight of oily sludge × solid content of oily sludge] × 50-120%;

[0046] Example 1

[0047] This embodiment provides a method for combined gravity separation of coal gasification fine slag and oily sludge, which comprises the following steps:

[0048] 1) Premixing coal gasification fine slag and water, diluting the slurry to a concentration of 25wt% and stirring evenly to obtain fine slag slurry; controlling the light component discharge port opening of the spiral chute to 15-25%, the feed rate to 1.5t / h, reselecting the fine slag slurry to obtain light components, intermediate components and heavy components, returning the intermediate components to the spiral chute for a second reselection separation under the same conditions, collecting the light components from the two reselections, filtering and drying in the shade (the negative pressure of the filtration is 0.1MPa), and mixing to obtain low-ash coal gasification fine slag (water content is 11.33%);

[0049] 2) The collected light component (i.e., low-ash coal gasification fine slag) is mixed with the oily sludge at a wet weight ratio of 1:6, and one-third of the sulfuric acid solution (concentration of 1.82 mol / L) is added, and the reaction is stirred for 5 hours. The operation is repeated twice (i.e., after stirring for 5 hours, one-third of the sulfuric acid solution is then added, stirred for 5 hours, and the remaining one-third of the sulfuric acid solution is added), and the slurry concentration is diluted to 20% according to the original solid content to obtain an acid leaching slurry; wherein the acid solution is 106.5% of the ash mineral (taking the light component discharge port opening of 22.5% in step 1) as an example); that is, the total mass of the sulfuric acid solution: the low-ash coal gasification fine slag: the oily sludge = 1.8:1:6, in which the ash content of the oily sludge is calculated according to the solid content, and the total ash mineral: the mass of the sulfuric acid solution = 1.69:1.8.

[0050] 3) The obtained acid leaching slurry is subjected to two gravity separations according to the process, the gravity separation feed rate is 1.5t / h, the opening of the first light component discharge port is 20%, and the opening of the heavy component discharge port is 10%, so as to obtain the light component, heavy component and intermediate component of the first gravity separation; the intermediate component and heavy component obtained by the first gravity separation are re-gravitated in the second gravity separation, the opening of the light component discharge port is 15%, and the opening of the heavy component discharge port is 8%; the light components separated by the two gravity separations are combined, and after suction filtration and drying, a low-ash and high-oil content refined carbon product is obtained; the heavy components separated by the two gravity separations are combined, and after suction filtration and drying, a high-ash and low-oil content tailings product is obtained.

[0051] In this example, the performance indicators of the low-ash coal gasification fine slag prepared in step 1) were tested, and the results were as follows:

[0052]

[0053]

[0054] From the data in the table, it can be seen that when the light component opening degree in this application is 22.5%, its comprehensive performance is the best, so this opening degree is used in the following implementations to conduct tests, and the moisture content of the low-ash coal gasification fine slag after shade drying is measured to be 11.33%.

[0055] In this example, the performance of the refined carbon product and tailings product prepared in step 3) was tested, and the results were as follows:

[0056]

[0057] It can be seen from the table that after gravity separation, a high-yield, low-ash, and high-calorific value clean coal product is obtained. At the same time, the tailings have a high ash content, which meets the ash content standard for building materials.

[0058] Example 2

[0059] This embodiment provides a method for combined gravity treatment of coal gasification fine slag and oily sludge, which is basically the same as Example 1, except that the mass ratios of low-ash coal gasification fine slag and oily sludge in step 2) are 1:2, 1:3, 1:4 and 1:7.

[0060] In this example, the performance of the refined carbon product and tailings product prepared in step 3) was tested, and the results were as follows:

[0061]

[0062] It can be seen from the table that as the ratio increases, the ash content of the clean coal product decreases and the calorific value increases, but the yield decreases, and the calorific value does not increase much as the ash content further decreases. It can be seen that the influence of ash on the calorific value decreases after oil absorption, and the ash content of the tailings has reached 87.62% at 1:7. It can be seen that further increasing the ratio will make it impossible to discard the tailings.

[0063] Example 3

[0064] The present embodiment provides a method for combined gravity treatment of coal gasification fine slag and oily sludge, which is basically the same as Example 1, except that: Group (one): total mass of acid solution: low-ash coal gasification fine slag: oily sludge = 1.5:1:6; Group (two), total mass of acid solution: low-ash coal gasification fine slag: oily sludge = 2:1:6.

[0065] In this example, the performance of the refined carbon product and tailings product prepared in step 3) was tested, and the results were as follows:

[0066]

[0067] It can be seen from the table that when less acid is added, the ash content of the refined carbon increases, the calorific value decreases, the ability of the gasified fine slag to adsorb oil decreases, and the tailings cannot be discarded; when the acid is excessive, the quality of the refined carbon does not change much, the ash content of the tailings decreases, and the quality decreases. It can be seen that excessive acid leaching is not suitable.

[0068] Example 4

[0069] This embodiment provides a method for treating coal gasification fine slag-oil-containing sludge combined gravity separation, which is basically the same as Example 1, except that: Group (I): each acid leaching interval is 4 hours; Group II: each acid leaching interval is 6 hours.

[0070] In this example, the performance of the refined carbon product and tailings product prepared in step 3) was tested, and the results were as follows:

[0071]

[0072] It can be seen from the table that when the acid leaching time interval is 4 hours, the yield of refined carbon product is larger, but the quality is worse than that in Example 1. There is no significant change at 6 hours, which shows that the 5-hour interval is more appropriate.

[0073] Comparative Example 1

[0074] This comparative example provides a combined gravity separation method for coal gasification fine slag and oily sludge, which is basically the same as Example 1, except that the coal gasification fine slag is not subjected to gravity separation, but is directly subjected to acid leaching with the oily sludge, specifically:

[0075] 1) The moisture content of coal gasification fine slag was determined to be 20.51%;

[0076] 2) The coal gasification fine slag and the oily sludge were mixed at a wet weight ratio of 1.12:6 to make the dry weight the same as that in Example 1, and one-third of the sulfuric acid solution (concentration of 1.82 mol / L) was added, and the reaction was stirred for 5 hours. The operation was repeated twice (i.e., after stirring for 5 hours, one-third of the sulfuric acid solution was added, and the reaction was stirred for 5 hours, and the remaining one-third of the sulfuric acid solution was added). The slurry concentration was diluted to 20% according to the original solid content to obtain an acid leaching slurry; wherein the total mass of the acid solution: coal gasification fine slag: oily sludge = 1.8:1.12:6.

[0077] 3) The obtained acid leaching slurry is subjected to two gravity separations according to the process, the gravity separation feed rate is 1.5t / h, the opening of the first light component discharge port is 20%, and the opening of the heavy component discharge port is 10%, so as to obtain the light component, heavy component and intermediate component of the first gravity separation; the intermediate component and heavy component obtained by the first gravity separation are re-gravitated in the second gravity separation, the opening of the light component discharge port is 15%, and the opening of the heavy component discharge port is 8%; the light components separated by the two gravity separations are combined, and after suction filtration and drying, a low-ash and high-oil content refined carbon product is obtained; the heavy components separated by the two gravity separations are combined, and after suction filtration and drying, a high-ash and low-oil content tailings product is obtained.

[0078] In this example, the performance of the refined carbon product and tailings product prepared in step 3) was tested, and the results were as follows:

[0079]

[0080] It can be seen from the table that if the coal gasification fine slag is not pre-treated by gravity separation, although the concentrate has a certain calorific value, the ash content is too high. In addition, due to the excessive amount of ash material, there are more carbonaceous ash and undissociated minerals in the tailings, resulting in the tailings ash content not meeting the disposal standard.

[0081] Comparative Example 2

[0082] This comparative example provides a method for combined gravity treatment of coal gasification fine residue and oily sludge, which is basically the same as Example 1, except that the acid solution is replaced with water of equal mass.

[0083] In this example, the performance of the refined carbon product and tailings product prepared in step 3) was tested, and the results were as follows:

[0084]

[0085] It can be seen from the table that although direct water treatment can obtain a higher yield of concentrate, the quality is not high, and the tailings do not meet the standards and cannot be discarded.

[0086] In summary, the low-ash coal gasification fine slag after gravity separation and the oily sludge after acid leaching have a synergistic disposal effect. Under certain conditions, low-ash and high calorific value clean coal products and high-ash tailings can be obtained, achieving waste treatment, turning waste into treasure, and realizing resource utilization.

[0087] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. These modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in the scope of the claims and specification of the present invention.

Claims

1. A method for treating coal gasification fine residue and oily sludge by combined gravity separation, characterized in that: The steps include: 1) Gravity separation of the fine slag slurry, collection of light component slurry, and filtration to obtain low-ash coal gasification fine slag; 2) subjecting the low-ash coal gasification fine slag and the oily sludge to an acid leaching reaction to obtain an acid leaching slurry; 3) The acid leaching slurry is subjected to gravity separation to collect the concentrate product and tailings product.

2. The method for combined gravity separation of coal gasification fine residue and oily sludge according to claim 1, characterized in that: The concentration of the fine slag slurry in step 1) is 15-35%.

3. The method for combined gravity separation of coal gasification fine slag and oily sludge according to claim 1, characterized in that: The intermediate components obtained after the gravity separation in step 1) are subjected to multiple gravity separations.

4. The method for combined gravity separation of coal gasification fine residue and oily sludge according to claim 1, characterized in that: The leaching acid used in the acid leaching reaction in step 2) is at least one of sulfuric acid or hydrochloric acid.

5. The method for combined gravity separation of coal gasification fine slag and oily sludge according to claim 4, characterized in that: The concentration of the leaching acid in step 2) is 1-5 mol / L, and the total amount of the leaching acid added is 20-120 wt% of the total ash mass of the low-ash coal gasification fine slag and the oily sludge.

6. The method for combined gravity separation of coal gasification fine slag and oily sludge according to claim 1, characterized in that: The oily sludge in step 2) has an oil content of 3-30%, a water content of 30-80%, and a solid content of 5-20%.

7. The method for combined gravity separation of coal gasification fine residue and oily sludge according to claim 4, characterized in that: The process conditions of the acid leaching reaction in step 2) are: stirring at room temperature for 12-24 hours, and adding the mixed acid three times in equal amounts every 4-8 hours.

8. The method for combined gravity separation of coal gasification fine slag and oily sludge according to claim 4, characterized in that: In step 3), the wet weight ratio of the low-ash coal gasification fine slag to the oily sludge is 1:1-8.

9. The method for combined gravity separation of coal gasification fine residue and oily sludge according to claim 1, characterized in that: The mass concentration of the acid leaching slurry in step 3) is 15-35%, and the feed rate of the gravity separation is 0.5-3 t / h.

10. The method for combined gravity separation of coal gasification fine residue and oily sludge according to claim 4, characterized in that: The intermediate components and heavy components obtained after the gravity separation in step 3) are subjected to multiple gravity separations.

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