Coal direct liquefaction method of differentiating and segmenting supply of circulating solvent

Abstract

The present application relates to the technical field of coal direct liquefaction, and provides a coal direct liquefaction method for differentiating and segmenting the supply of circulating solvents, which can improve the conversion rate and oil yield of coal direct liquefaction by differentiating and segmenting the supply of circulating solvents for different stages of coal direct liquefaction. The coal direct liquefaction method comprises the following steps: (1) preparing oil coal slurry by using materials comprising coal and circulating solvent I; (2) feeding circulating solvent II and the oil coal slurry into a first liquefaction reactor to perform first liquefaction reaction; then feeding the reaction materials and circulating solvent III into a second liquefaction reactor to continue second liquefaction reaction, and separating coal liquefaction oil from the post-reaction materials obtained from the second liquefaction reaction; the circulating solvent I, the circulating solvent II and the circulating solvent III are respectively prepared by using one or more of light fraction, medium temperature fraction and heavy fraction.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of coal direct liquefaction, and particularly relates to a coal direct liquefaction method with different segmented supply of circulating solvents. BACKGROUND

[0002] Coal direct liquefaction technology is mainly a process of destroying coal molecular structure under high temperature and high pressure and further converting it into small molecule liquid fuel through hydrogenation. Generally speaking, in the coal direct liquefaction technology, coal, catalyst and hydrogen-donating solvent are first mixed together to prepare oil coal slurry, and then the oil coal slurry enters a reactor for pyrolysis, and the broken coal free radical fragments are constantly stabilized by active hydrogen from the gas phase and the hydrogen-donating solvent, thereby generating small molecule products.

[0003] The hydrogen-donating solvent used in industry is generally the circulating oil produced by the coal direct liquefaction reaction, for example, the circulating solvent used in the China Shenhua process (patent CN1257252C) is the fraction segment of 220-450℃ distillation range of the coal liquefaction oil after hydrogenation and is used for coal slurry preparation at one time. At present, the research on the circulating solvent for coal direct liquefaction mainly focuses on the composition and preparation method of the circulating solvent: patent application CN103468315A and patent application CN101333448A both use coal direct liquefaction oil plus coal tar, petroleum / petroleum refining by-products to prepare coal liquefaction circulating solvent, and patent application CN107118799A, CN106479564A and CN105925304A all use different distillation methods to prepare coal liquefaction circulating solvent.

[0004] However, in the existing coal direct liquefaction process, the circulating solvent is added at one time in the oil coal slurry preparation stage, and with the transportation and reaction of the oil coal slurry, local hydrogen deficiency may occur in some areas at the bottom of the reactor, which leads to insufficient hydrogen supply performance of the solvent in the coal direct liquefaction reaction stage and coking, etc., thereby reducing the oil yield and conversion rate of the coal direct liquefaction. SUMMARY

[0005] The present application provides a coal direct liquefaction method with different segmented supply of circulating solvents. In the scheme of the present application, the coal liquefaction oil after hydrogenation is fractionated to obtain light fraction, medium temperature fraction and heavy fraction of different fraction segments, and based on the differences of these fractions, a plurality of circulating solvents are prepared and supplied to the preparation link of the oil coal slurry and different liquefaction reaction stages, respectively. By using the method of the present application, the circulating solvents are provided for different stages of the coal direct liquefaction through differentiation, which can improve the conversion rate and oil yield of the coal direct liquefaction and improve the overall coal direct liquefaction efficiency.

[0006] In order to achieve the purpose of the present application, the following technical scheme is provided:

[0007] The present application provides a coal direct liquefaction method of differentiating segmented supply of circulating solvents, comprising the following steps:

[0008] (1) preparing oil coal slurry by using materials comprising coal and circulating solvent I;

[0009] (2) feeding circulating solvent II and the oil coal slurry into a first liquefaction reactor for first liquefaction reaction, and then feeding the reaction materials and circulating solvent III into a second liquefaction reactor for second liquefaction reaction, and separating coal liquefied oil from the post-reaction materials obtained from the second liquefaction reaction;

[0010] The circulating solvent I, the circulating solvent II and the circulating solvent III are respectively prepared by using one or more of light fraction, medium temperature fraction and heavy fraction, and the light fraction, the medium temperature fraction and the heavy fraction are obtained by fractionating hydrogenated post-reaction liquefied oil obtained by hydrogenating coal liquefied oil; wherein the distillation range of the light fraction is 220- X1 ℃, the distillation range of the medium temperature fraction is X1-X2 ℃, and the distillation range of the heavy fraction is > X2 ℃; the value of X1 is between 240-280 ℃, preferably between 250-270 ℃; the value of X2 is between 300-360 ℃, preferably between 310-350 ℃;

[0011] The circulating solvent I at least comprises the medium temperature fraction and the heavy fraction, the circulating solvent II at least comprises the medium temperature fraction, and the circulating solvent III at least comprises one or more of the light fraction and the medium temperature fraction.

[0012] Another aspect of the present application provides a circulating solvent system used in a coal direct liquefaction process, wherein the coal direct liquefaction process comprises the steps of preparing oil coal slurry by using coal and performing liquefaction reaction on the oil coal slurry to obtain coal liquefied oil, and the circulating solvent system comprises circulating solvent I, circulating solvent II and circulating solvent III;

[0013] The circulating solvent I, II and III are respectively prepared by using solvents comprising one or more of light fraction, medium temperature fraction and heavy fraction;

[0014] The circulating solvent I at least comprises the medium temperature fraction and the heavy fraction, the circulating solvent II at least comprises the medium temperature fraction, and the circulating solvent III at least comprises one or more of the light fraction and the medium temperature fraction.

[0015] The distillation range of the light fraction is 220- X1 ℃, the distillation range of the medium temperature fraction is X1-X2 ℃, and the distillation range of the heavy fraction is > X2 ℃, wherein the value of X1 is between 240-280 ℃, preferably between 250-270 ℃, and the value of X2 is between 300-360 ℃, preferably between 310-350 ℃.

[0016] The circulating solvent I is used as a solvent required for preparing the oil slurry; the circulating solvent II and the circulating solvent III are used as hydrogen-donating solvents required for the liquefaction reaction;

[0017] Preferably, the liquefaction reaction of the oil slurry comprises a first liquefaction reaction and a second liquefaction reaction performed in sequence, the circulating solvent II is used for supplying to the first liquefaction reaction, and the circulating solvent III is used for supplying to the second liquefaction reaction.

[0018] Preferably, the light fraction, the medium-temperature fraction and the heavy fraction are obtained by fractionating a hydrogenated liquefied oil obtained by hydrogenation reaction of the coal liquefied oil.

[0019] The technical solution provided by the present application has the following beneficial effects:

[0020] The present application obtains the light fraction, the medium-temperature fraction and the heavy fraction having the distillation range characteristics required by the present application by fractionating the hydrogenated liquefied oil obtained by hydrogenation of the coal liquefied oil, and provides the circulating solvents I / II / III based on the differentiation of these fractions, recycles the circulating solvent I comprising at least the medium-temperature fraction and the heavy fraction for preparation of the oil slurry, recycles the circulating solvent II comprising at least the medium-temperature fraction for the first liquefaction reactor, and recycles the circulating solvent III comprising at least one or more of the light fraction, the medium-temperature fraction and the heavy fraction for the second liquefaction reactor, so that the coal direct liquefaction is performed in this way, the differentiated effects of the circulating solvents of different fractions can be fully played, and the problems such as coking of the products caused by insufficient hydrogen-donating performance of the solvents in the coal direct liquefaction reaction stage in the prior art can be effectively overcome, which is beneficial to improving the oil yield and the conversion rate. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 It is a process flow diagram in one embodiment. DETAILED DESCRIPTION

[0022] In order to facilitate the understanding of the present application, the present application will be further described below in conjunction with examples. It should be understood that the following examples are only for better understanding of the present application, and do not mean that the present application is limited to the following examples only.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items. The terms "first", "second", "I", "II", "III", etc. are only used for descriptive purposes and should not be construed as indicating or implying relative importance.

[0024] When the specific experimental steps or conditions are not mentioned in the examples, the conventional experimental steps or conditions corresponding thereto can be used. When the reagents or instruments are not mentioned by the manufacturer, they are conventional products that can be obtained from the market.

[0025] In one aspect, the present application provides a coal direct liquefaction method using different segments of recycled solvents, comprising the following steps:

[0026] (1) preparing an oil coal slurry using a material comprising coal and recycled solvent I;

[0027] (2) feeding recycled solvent II and the oil coal slurry into a first liquefaction reactor for a first liquefaction reaction, and then feeding the reaction material and recycled solvent III into a second liquefaction reactor for a second liquefaction reaction, and separating coal liquefied oil from the reaction material obtained from the second liquefaction reaction;

[0028] The recycled solvent I, the recycled solvent II and the recycled solvent III are prepared using one or more of a light fraction, a medium temperature fraction and a heavy fraction, and the light fraction, the medium temperature fraction and the heavy fraction are obtained by fractionating hydrogenated liquefied oil obtained by hydrogenation of coal liquefied oil; wherein the distillation range of the light fraction is 220℃-X1℃, the distillation range of the medium temperature fraction is X1-X2℃, and the distillation range of the heavy fraction is >X2℃; the value of X1 is between 240-280℃, preferably between 250-270℃; the value of X2 is between 300-360℃, preferably between 310-350℃;

[0029] The recycled solvent I at least comprises the medium temperature fraction and the heavy fraction, the recycled solvent II at least comprises the medium temperature fraction, and the recycled solvent III at least comprises one or more of the light fraction, the medium temperature fraction.

[0030] Further, the coal direct liquefaction method further comprises the following steps (3) and (4):

[0031] Step (3): hydrogenating the coal liquefied oil obtained from step (2) to obtain hydrogenated liquefied oil, and fractionating the hydrogenated liquefied oil to obtain product oil fraction segments, the light fraction, the medium temperature fraction and the heavy fraction;

[0032] Step (4): preparing the recycled solvent I, II, III using one or more of the light fraction, the medium temperature fraction and the heavy fraction obtained from step (3), recycling the recycled solvent I to step (1), recycling the recycled solvent II to the first liquefaction reactor, and recycling the recycled solvent III to the second liquefaction reactor.

[0033] In the present application, the light fraction with a distillation range of 220℃ to X1℃, the medium temperature fraction with a distillation range of X1 to X2℃, and the heavy fraction with a distillation range of >X2℃, wherein the value of X1 is between 240 and 280℃, for example, 240℃, 250℃, 260℃, 270℃, 280℃, etc., and preferably between 250 and 270℃; and the value of X2 is between 300 and 360℃, for example, 300℃, 310℃, 320℃, 330℃, 340℃, 350℃, 360℃, etc., and preferably between 310 and 350℃.

[0034] The present inventors have found through long-term research that, by subjecting the hydrogenated coal liquefaction oil obtained by hydrogenation to fractionation (e.g., distillation cutting) to obtain light, medium temperature, and heavy fractions having the distillation range characteristics required by the present application, and providing circulating solvents I / II / III based on the differentiation of these fractions, using the circulating solvent I comprising at least the medium temperature fraction and the heavy fraction for the preparation of the oil coal slurry, the circulating solvent II comprising at least the medium temperature fraction for the first liquefaction reactor, and the circulating solvent III comprising at least one or more of the light fraction, the medium temperature fraction, for the second liquefaction reactor, the coal direct liquefaction is carried out in this way, the differentiated effects of the different fraction segments of the circulating solvent can be fully utilized, the characteristics of the different fraction segments in the wide distillation range of the circulating solvent and the characteristics of different stages of the coal liquefaction process can be well matched, and the problems of coking and low oil yield caused by insufficient hydrogen supply performance of the solvent in the coal direct liquefaction reaction stage in the prior art can be effectively overcome.

[0035] The present inventors have found that the light fraction with a distillation range of 220℃ to X1℃ (the value of X1 is between 240 and 280℃, and preferably between 250 and 270℃) obtained by distillation cutting of the hydrogenated coal liquefaction oil can effectively reduce the viscosity of the oil coal slurry and improve the flowability of the oil coal slurry; the medium temperature fraction with a distillation range of X1 to X2℃ (the value of X1 is between 240 and 280℃, and preferably between 250 and 270℃, and the value of X2 is between 300 and 360℃, and preferably between 310 and 350℃) obtained by distillation cutting has good hydrogen supply performance, which is conducive to the transfer and provision of active hydrogen and the stabilization of coal pyrolysis free radicals; and the heavy fraction with a distillation range of >X2℃ (the value of X2 is between 300 and 360℃, and preferably between 310 and 350℃) obtained by distillation cutting can well preliminarily dissolve coal and the coal pyrolysis macromolecules in the initial stage of coal direct liquefaction and has a good stabilizing effect on the medium-sized coal molecular fragments generated by the fragmentation of coal macromolecules. The present application adds different fraction segments of the circulating solvent or the mixed solvent in different stages of coal direct liquefaction, which provides hydrogen-donating solvents for coal direct liquefaction in a differentiated manner, promotes the transportation of the oil coal slurry and the coal liquefaction conversion, reduces the hydrogen-poor coking in the coal direct liquefaction process, effectively improves the coal direct liquefaction conversion rate and the oil yield, and improves the overall efficiency of coal direct liquefaction.

[0036] In the preferred embodiment, when the liquefied oil after hydrogenation is subjected to fractionation, the value of X1 is between 250-270°C; the value of X2 is between 310-350°C; the preferred fractionation cut point is used in the present application, and under the condition that other conditions are basically the same, it is beneficial to further improve the liquefaction effect.

[0037] Further, the coal direct liquefaction method further comprises the following steps (3) and (4):

[0038] Step (3): subjecting the coal liquefied oil obtained in step (2) to hydrogenation reaction to obtain the liquefied oil after hydrogenation, and subjecting the liquefied oil after hydrogenation to fractionation to obtain product oil fraction segments, the light fraction, the medium temperature fraction, and the heavy fraction;

[0039] Step (4): using one or more of the light fraction, the medium temperature fraction, and the heavy fraction obtained in step (3) to prepare the circulating solvent I, the circulating solvent II, and the circulating solvent III, circulating the circulating solvent I to step (1), circulating the circulating solvent II to the first liquefaction reactor, and circulating the circulating solvent III to the second liquefaction reactor. That is, in the coal direct liquefaction method, the coal liquefied oil obtained in step (2) can be subjected to hydrogenation to obtain the liquefied oil after hydrogenation, and the light fraction, the medium temperature fraction, and the heavy fraction required for preparing the circulating solvent I, the circulating solvent II, and the circulating solvent III are obtained by fractionation, thereby providing each circulating solvent required in different stages of the process.

[0040] Further, the circulating solvent I comprises the medium temperature fraction and the heavy fraction, and optionally comprises the light fraction. In some examples, the circulating solvent I comprises the medium temperature fraction and the heavy fraction; in some examples, the circulating solvent I comprises the medium temperature fraction, the heavy fraction, and the light fraction. In some embodiments, in the circulating solvent I, the mass percentage of the light fraction is 0-40% (such as 0, 10%, 20%, 30%, 40%, etc.), the mass percentage of the medium temperature fraction is 20-80% (such as 20%, 30%, 40%, 50%, 60%, 70%, 80%, etc.), and the mass percentage of the heavy fraction is 10-80% (such as 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, etc.). The circulating solvent I can be prepared from the medium temperature fraction and the heavy fraction, and optionally the light fraction.

[0041] In a preferred embodiment, in the circulating solvent I, the mass percentage of the light fraction is 0-20%, the mass percentage of the medium-temperature fraction is 40-60%, and the mass percentage of the heavy fraction is 20-60%. The use of the preferred circulating solvent I is conducive to improving the dissolution effect of the macromolecular coal structure and has good coal slurry transportability, which is conducive to further improving the coal direct liquefaction efficiency.

[0042] Preferably, in step (1), the mass ratio of the circulating solvent I to the coal is (0.5-4):1, for example, 0.5:1, 1:1, 2:1, 3:1, 4:1, etc.

[0043] Further, the circulating solvent II at least includes a medium-temperature fraction and optionally includes one or more of a light fraction and a heavy fraction. Preferably, the circulating solvent II includes a medium-temperature fraction and a light fraction and optionally includes a heavy fraction. In some examples, the circulating solvent II is prepared from a medium-temperature fraction and a light fraction. In some examples, the circulating solvent is prepared from a medium-temperature fraction, a light fraction, and a heavy fraction. In some examples, the circulating solvent II is a medium-temperature fraction, for example, the distillation range of the medium-temperature fraction is 280-340°C.

[0044] Preferably, in the circulating solvent II, the mass percentage of the light fraction is 0-80% (for example, 0, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, etc.), for example, 10-80%, for example, 10-30%; the mass percentage of the medium-temperature fraction is 20-100% (for example, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, etc.), for example, 20-90%, for example, 60-90%; and the mass percentage of the heavy fraction is 0-20% (for example, 0, 10%, 20%), for example, 0-10%. In some preferred examples, in the circulating solvent II, the mass percentage of the light fraction is 10-30%, the mass percentage of the medium-temperature fraction is 60-90%, and the mass percentage of the heavy fraction is 0-10%; the use of the preferred circulating solvent II is conducive to reducing the gasification of the light fraction, playing the roles of the medium-temperature solvent in hydrogen supply and the heavy fraction in hydrogen transfer, and being conducive to further improving the coal direct liquefaction efficiency.

[0045] More preferably, in the circulating solvent II, the mass percentage of the medium-temperature solvent is 50-100% (for example, 50%, 60%, 70%, 80%, 90%, 100%, etc.), and the sum of the mass percentages of the light fraction and the heavy fraction is 0-50% (for example, 0, 10%, 20%, 30%, 40%, 50%, etc.), which is conducive to further improving the coal direct liquefaction effect and further improving the conversion rate and oil yield.

[0046] Further, in step (2), the circulating solvent III comprises at least one or more of the light fraction, the medium-temperature fraction, and optionally the heavy fraction. Preferably, the circulating solvent III comprises at least the medium-temperature fraction, which enhances the hydrogen supply and hydrogen transfer, and is conducive to further improving the direct coal liquefaction efficiency. In some examples, the circulating solvent III is a mixture of the light fraction and the medium-temperature fraction. In some examples, the circulating solvent III is a mixture of the medium-temperature fraction and the heavy fraction. In some examples, the circulating solvent III is a mixture of the light fraction, the medium-temperature fraction, and the heavy fraction. In some examples, the circulating solvent III is the light fraction, for example, the distillation range of the light fraction is 220-280°C. In some examples, the circulating solvent III is the medium-temperature fraction, for example, the distillation range of the medium-temperature fraction is 270-350°C.

[0047] Preferably, in the circulating solvent III, the mass fraction of the light fraction is 0-100% (e.g., 0, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, etc.), preferably 0-40%; the mass fraction of the medium-temperature fraction is 0-100% (e.g., 0, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, etc.), preferably 40-100%; the mass fraction of the heavy fraction is 0-20% (e.g., 0, 10%, 20%, etc.); and the sum of the mass fractions of the light fraction and the medium-temperature fraction is not 0. More preferably, in the circulating solvent III, the mass fraction of the medium-temperature fraction is 60-90% (e.g., 60%, 70%, 80%, 90%, etc.), and the remaining components are the light fraction and / or the heavy fraction, and the mass fraction of the remaining components is 10-40% (e.g., 10%, 20%, 30%, 40%, etc.); using the preferred circulating solvent III is conducive to further improving the direct coal liquefaction efficiency.

[0048] In some embodiments, in step (2), the mass ratio of the circulating solvent II to the coal is (0.1-5):1 (e.g., 0.1:1, 0.2:1, 0.5:1, 0.8:1, 1:1, 2:1, 3:1, 4:1, 5:1, etc.), preferably (0.2-5):1, more preferably (0.2-2):1; and in step (3), the mass ratio of the circulating solvent III to the coal is (0.1-5):1 (e.g., 0.1:1, 0.2:1, 0.5:1, 0.8:1, 1:1, 2:1, 3:1, 4:1, 5:1, etc.), preferably (0.2-5):1, more preferably (0.2-2):1. Preferably, the mass ratio of the circulating solvent III to the coal is greater than the mass ratio of the circulating solvent II to the coal.

[0049] Preferably, in step (2), the mass ratio of the circulating solvent II to the coal is (0.2-5):1; in step (3), the mass ratio of the circulating solvent III to the coal is (0.2-5):1; using the preferred mass ratio, the liquefaction effect can be further improved, and the conversion rate and oil yield can be further increased. More preferably, the mass ratio of the circulating solvent II to the coal is (0.2-2):1; in step (3), the mass ratio of the circulating solvent III to the coal is (0.2-2):1; using the preferred ratio, the relatively better conversion rate and oil yield can be obtained, and the effective utilization rate of the device will not be greatly reduced.

[0050] In the present application, in the coal direct liquefaction stage, the medium-temperature component distillate oil with high hydrogen supply performance is added differentially, the hydrogen supply performance of the solvent in the coal direct liquefaction process is improved, the gasification loss of the medium-temperature component in the oil coal slurry preheating process is reduced, and the coal direct liquefaction conversion rate and oil yield can be improved.

[0051] In some embodiments, in step (2), the oil coal slurry is preheated before being fed into the first liquefaction reactor, and is preferably preheated to 340-400℃ (for example, 340℃, 370℃, 400℃, etc.), and after preheating, is fed into the first liquefaction reactor together with the circulating solvent II.

[0052] In some embodiments, in step (2), the operating temperature of the first liquefaction reactor is 430-480℃, the hydrogen partial pressure is controlled to be 12-25 MPa, and the residence time is 20-120 min.

[0053] In some embodiments, in step (2), the operating temperature of the second liquefaction reactor is 430-480℃, the hydrogen partial pressure is controlled to be 12-25 MPa, and the residence time is 20-120 min. Specifically, after the liquefaction reaction in the second liquefaction reactor, the reaction material is separated by a separator to separate gas, water and solid liquefaction residue, and coal liquefaction oil is obtained.

[0054] In some embodiments, in step (3), the product oil fraction is a distillate oil with a distillation range <220℃, for example, all distillate oils with a distillation range <220℃.

[0055] Further, in step (1), the material for preparing the oil coal slurry further comprises a catalyst. In some embodiments, the mass ratio of the catalyst to the coal is 1:(20-120), such as 1:20, 1:50, 1:70, 1:100, 1:120, etc. The catalyst used can be any catalyst commonly used in the art, and is not particularly limited, and specifically, for example, the catalyst is selected from one or more of water-soluble or oil-soluble catalysts; further specifically, the catalyst is, for example, selected from one or more of iron-containing catalysts, nickel-containing catalysts, cobalt-containing catalysts, molybdenum-containing catalysts, tungsten-containing catalysts, and alkali metal catalysts. Among them, the iron-containing catalyst is, for example, iron oxide (such as hydrated iron oxide), etc., the nickel-containing catalyst is, for example, nickel sulfide, etc., the cobalt-containing catalyst is, for example, cobalt oxide, etc., the molybdenum-containing catalyst is, for example, molybdenum sulfide, etc., the tungsten-containing catalyst is, for example, tungsten oxide, etc., and the alkali metal catalyst is, for example, sodium carbonate, etc., or a composite of one or more of the above catalysts. For example, in step (1), the coal, the catalyst, and the recycled solvent I can be mixed, and stirred for 200-500 min to uniformly mix the components, to obtain the oil coal slurry.

[0056] In the present application, the hydrogenation reaction of the coal liquefaction oil and the fractionation (such as distillation cutting) of the hydrogenated liquefaction oil can be carried out by conventional operations in the art, and are not particularly limited, and can be directly carried out by existing process operations, which will not be described herein. Among them, the hydrogenation reaction of the coal liquefaction oil is, for example, full-range hydrogenation, which is carried out in a hydrogenation reactor; for example, the hydrogenation reaction conditions are as follows: temperature 350-390°C, pressure 12-20 MPa, volume space velocity 0.5-2 h -1 ; the hydrogenation catalyst used is, for example, a hydrogenation catalyst (such as HRK658, etc. from Axens) well known in the art.

[0057] In some embodiments, the product oil fractions obtained in step (3) and the remaining other fractions (such as the light fraction and / or the medium-temperature fraction remaining after the preparation of the recycled solvent) are sent to a downstream hydro-upgrading unit for further treatment to obtain a target product oil.

[0058] In some preferred embodiments, in step (2), the mass ratio of the recycled solvent II to the coal is (0.2-5):1, and more preferably (0.2-2):1; in step (3), the mass ratio of the recycled solvent III to the coal is (0.2-5):1, and more preferably (0.2-2):1; and in the recycled solvent II, the mass percentage of the medium-temperature solvent is 50-100%, and the sum of the mass percentages of the light fraction and the heavy fraction is 0-50%. The coal direct liquefaction process of the present application is carried out by using the preferred mode, which is beneficial to taking into account better oil yield and conversion rate.

[0059] The mass ratio of the other materials to the coal is based on dry coal.

[0060] In the present application, the coal includes, but is not limited to, coal of different metamorphic degrees or different macerals.

[0061] Another aspect of the present application provides a circulating solvent system for use in a coal direct liquefaction process, the coal direct liquefaction process including a step of preparing coal into an oil coal slurry and a step of subjecting the oil coal slurry to a liquefaction reaction to obtain a coal liquefaction oil, the circulating solvent system including a circulating solvent I, a circulating solvent II and a circulating solvent III;

[0062] The circulating solvent I, II and III are respectively prepared by using a solvent containing one or more of a light fraction, a medium temperature fraction and a heavy fraction;

[0063] The circulating solvent I includes at least the medium temperature fraction and the heavy fraction, the circulating solvent II includes at least the medium temperature fraction, and the circulating solvent III includes at least one or more of the light fraction and the medium temperature fraction;

[0064] The distillation range of the light fraction is 220℃-X1℃, the distillation range of the medium temperature fraction is X1-X2℃, and the distillation range of the heavy fraction is >X2℃, wherein X1 is between 240-280℃, preferably between 250-270℃, and X2 is between 300-360℃, preferably between 310-350℃;

[0065] The circulating solvent I is used as a solvent required for preparing the oil coal slurry, and the circulating solvent II and the circulating solvent III are used as hydrogen-donating solvents required for the liquefaction reaction.

[0066] The circulating solvent system provided by the present application, in which the circulating solvent I is used as a solvent required for preparing the oil coal slurry, and the circulating solvent II and the circulating solvent III are used as hydrogen-donating solvents required for the liquefaction reaction, differentiates and adjusts the light fraction, the medium temperature fraction and the heavy fraction with specific distillation range requirements into a plurality of circulating solvents, and uses them as solvents for different stages of coal direct liquefaction, which can effectively overcome the problems of coking of products, low oil yield and the like caused by insufficient hydrogen-donating performance of solvents in the coal direct liquefaction reaction stage in the prior art.

[0067] Preferably, the oil coal slurry is subjected to a liquefaction reaction, which includes a first liquefaction reaction and a second liquefaction reaction performed in sequence, the circulating solvent II is used for supplying to the first liquefaction reaction, and the circulating solvent III is used for supplying to the second liquefaction reaction; the different circulating solvents are supplied to different stages of the liquefaction reaction, which can further improve the direct coal liquefaction conversion rate and oil yield, and improve the overall direct coal liquefaction efficiency. For the first liquefaction reaction, it can be specifically performed in a first liquefaction reactor, the operating temperature is for example 430-480°C, the hydrogen partial pressure control is for example 12-25 MPa, and the residence time is for example 20-120 min. For the second liquefaction reaction, it can be specifically performed in a second liquefaction reactor, the operating temperature is for example 430-480°C, the hydrogen partial pressure control is for example 12-25 MPa, and the residence time is for example 20-120 min.

[0068] Preferably, the light fraction, the medium-temperature fraction and the heavy fraction are obtained by subjecting the coal liquefied oil to a hydrogenation reaction.

[0069] Further, the circulating solvent I includes the medium-temperature fraction and the heavy fraction, and optionally includes the light fraction. In some examples, the circulating solvent I includes the medium-temperature fraction and the heavy fraction; in some examples, the circulating solvent I includes the medium-temperature fraction, the heavy fraction and the light fraction. In some embodiments, in the circulating solvent I, the mass percentage of the light fraction is 0-40%, the mass percentage of the medium-temperature fraction is 20-80%, and the mass percentage of the heavy fraction is 10-80%. The circulating solvent I can be prepared from the medium-temperature fraction and the heavy fraction, and optionally the light fraction.

[0070] In a preferred embodiment, in the circulating solvent I, the mass percentage of the light fraction is 0-20%, the mass percentage of the medium-temperature fraction is 40-60%, and the mass percentage of the heavy fraction is 20-60%. The use of the preferred circulating solvent I is beneficial to improve the dissolution effect of macromolecular coal structure and has good coal slurry transportability, which is beneficial to further improve the direct coal liquefaction efficiency.

[0071] Further, the circulating solvent II includes at least the medium-temperature fraction, and optionally includes one or more of the light fraction and the heavy fraction. Preferably, the circulating solvent II includes the medium-temperature fraction and the light fraction, and optionally includes the heavy fraction. In some examples, the circulating solvent II is prepared from the medium-temperature fraction and the light fraction. In some examples, the circulating solvent is prepared from the medium-temperature fraction, the light fraction and the heavy fraction. In some examples, the circulating solvent II is the medium-temperature fraction, for example, the distillation range of the medium-temperature fraction is 280-340°C.

[0072] Preferably, in the circulating solvent II, the mass percentage of the light fraction is 0-80%, for example 10-80%; the mass percentage of the medium temperature fraction is 20-100%, for example 20-90%; and the mass percentage of the heavy fraction is 0-20%. In some preferred examples, in the circulating solvent II, the mass percentage of the light fraction is 10-30%, the mass percentage of the medium temperature fraction is 60-90%, and the mass percentage of the heavy fraction is 0-10%; the preferred circulating solvent II is conducive to further improving the efficiency of direct coal liquefaction.

[0073] More preferably, in the circulating solvent II, the mass percentage of the medium temperature fraction is 50-100%, and the sum of the mass percentages of the light fraction and the heavy fraction is 0-50%.

[0074] Further, the circulating solvent III comprises at least one or more of the light fraction, the medium temperature fraction, and optionally the heavy fraction. Preferably, the circulating solvent III comprises at least the medium temperature fraction, which is conducive to further improving the efficiency of direct coal liquefaction. In some examples, the circulating solvent III is a mixture of the light fraction and the medium temperature fraction. In some examples, the circulating solvent III is a mixture of the medium temperature fraction and the heavy fraction. In some examples, the circulating solvent is a mixture of the light fraction, the medium temperature fraction, and the heavy fraction. In some examples, the circulating solvent III is the light fraction, for example, the distillation range of the light fraction is 220-280°C. In some examples, the circulating solvent III is the medium temperature fraction, for example, the distillation range of the medium temperature fraction is 270-350°C.

[0075] Preferably, in the circulating solvent III, the mass percentage of the light fraction is 0-100%, preferably 0-40%; the mass percentage of the medium temperature fraction is 0-100%, preferably 40-100%; the mass percentage of the heavy fraction is 0-20%; and the sum of the mass percentages of the light fraction and the medium temperature fraction is not 0. More preferably, in the circulating solvent III, the mass percentage of the medium temperature fraction is 60-90%, the rest of the components are the light fraction and / or the heavy fraction, and the mass percentage of the rest of the components is 10-40%; the preferred circulating solvent III is conducive to further improving the efficiency of direct coal liquefaction.

[0076] Regarding the circulating solvent system provided by the present application, the contents corresponding to the direct coal liquefaction method of different segmented supply of circulating solvent provided by the present application are described in the foregoing direct coal liquefaction method, and will not be described one by one.

[0077] In still another aspect of the present application, the circulating solvent system described above is applied in the direct coal liquefaction process.

[0078] The raw materials used in the examples and comparative examples are described as follows:

[0079] Shendong coal quality situation - M ad : 9.42% wt; A d : 4.88% wt; V daf : 35.93% wt; C daf : 81.11% wt; H daf : 4.82% wt; N daf : 0.95% wt; S td : 0.29% wt.

[0080] Hydrated iron oxide catalyst: FeOOH.

[0081] Hydrogenation catalyst: commercial Ni-Mo / Al203(HRK658 from Axens).

[0082] In the following examples and comparative examples, a mixture of anthracene oil and wash oil (mass ratio 1:1) was used as the solvent for each step at the initial start-up of the process; during the process operation, the corresponding circulating solvents prepared were used as the solvents for the corresponding steps as the subsequent hydrogenation and distillation cutting were carried out.

[0083] Example 1

[0084] (1) Shendong coal, hydrated iron oxide catalyst and circulating solvent I were mixed, the mass ratio of catalyst to dry coal was 1:100, and the mass ratio of circulating solvent I to dry coal was 1:1; the components were uniformly mixed by stirring for 240 min to obtain an oil coal slurry;

[0085] (2) The oil coal slurry was heated to 380°C by a heater and then entered the first liquefaction reactor together with circulating solvent II; the mass ratio of circulating solvent II to dry coal was 0.8:1; the operating temperature of the first liquefaction reactor was 450°C, the hydrogen partial pressure was controlled at 18 MPa, and the residence time was 60 min. The reaction material discharged from the first liquefaction reactor entered the second liquefaction reactor together with circulating solvent III; the mass ratio of circulating solvent III to dry coal was 1.2:1, the operating temperature of the second liquefaction reactor was 455°C, the hydrogen partial pressure was controlled at 19 MPa, and the residence time was 60 min; the reaction material obtained from the second liquefaction reactor was separated by a separator to separate out gas, water and solid liquefaction residue, and a liquid coal liquefaction oil was obtained;

[0086] (3) The coal liquefaction oil entered a solvent hydrogenation reactor for full fraction hydrogenation to obtain hydrogenated liquefaction oil; the hydrogenation reaction conditions were: temperature 375-385°C, pressure 14 MPa-19 MPa; volume space velocity 0.75-1.2 h -1The catalyst used in hydrogenation is commercial Ni-Mo / Al203. After hydrogenation, the liquefied oil is subjected to distillation cutting, and product oil fractions with distillation ranges of <220 ℃, fraction A (with a distillation range of 220-250 ℃), fraction B (with a distillation range of 250-310 ℃) and fraction C (with a distillation range of >310 ℃) are obtained in sequence.

[0087] Circulating solvent I is prepared by mixing fractions A, B and C in a mass ratio of A:B:C = 5%:55%:40%; circulating solvent II is prepared by mixing fractions A, B and C in a mass ratio of A:B:C = 20%:75%:5%; and circulating solvent III is prepared by mixing fractions A, B and C in a mass ratio of A:B:C = 15%:80%:5%. Circulating solvent I is used in step (1), circulating solvent II is used in the first liquefaction reactor, and circulating solvent III is used in the second liquefaction reactor.

[0088] Analysis of the solid liquefaction residue (containing liquefaction residue and asphaltene), gas and water separated from the second liquefaction reactor in step (2) can obtain the yield of coal direct liquefaction products (based on the mass of dry and ash-free raw coal): the mass fraction of liquefaction residue is 11.5% (corresponding to a coal direct liquefaction conversion rate of 88.5%), the oil yield is 54.8%, the water yield is 10.2%, the gas yield is 13.1%, and the asphaltene yield is 10.4%.

[0089] Example 2

[0090] (1) Shendong coal, hydrated iron oxide catalyst and circulating solvent I are mixed, the mass ratio of catalyst to dry coal is 1:100, and the mass ratio of circulating solvent I to dry coal is 1:1; the components are uniformly mixed by stirring for 240 min to obtain an oil coal slurry;

[0091] (2) The oil coal slurry is heated to 380 ℃ by a heater and then enters the first liquefaction reactor together with circulating solvent II; the mass ratio of circulating solvent II to dry coal is 1:1; the operating temperature of the first liquefaction reactor is 450 ℃, the hydrogen partial pressure is controlled at 18 MPa, and the residence time is 60 min. The reaction material is discharged from the first liquefaction reactor and then enters the second liquefaction reactor together with circulating solvent III; the mass ratio of circulating solvent III to dry coal is 1:1, the operating temperature of the second liquefaction reactor is 455 ℃, the hydrogen partial pressure is controlled at 19 MPa, and the residence time is 60 min; the reaction material obtained from the second liquefaction reactor is separated by a separator to obtain gas, water and solid liquefaction residue, and a liquid coal liquefied oil is obtained;

[0092] (3) The coal liquefaction oil enters a solvent hydrogenation reactor to be fully fractionated and hydrogenated to obtain hydrogenated liquefaction oil. The hydrogenation reaction conditions are the same as those in Example 1. The hydrogenated liquefaction oil is subjected to distillation cutting to sequentially obtain product oil fractions with distillation ranges <220°C, fraction A (with a distillation range of 220-270°C), fraction B (with a distillation range of 270-330°C), and fraction C (with a distillation range >330°C).

[0093] The circulating solvent I is prepared by mixing fraction B and C at a mass ratio of B:C = 60:40; the circulating solvent II is prepared by mixing fraction A and B at a mass ratio of A:B = 50:50; and the circulating solvent III is prepared by mixing fraction A and B at a mass ratio of A:B = 30:70. The circulating solvent I is used in step (1), the circulating solvent II is used in the first liquefaction reactor, and the circulating solvent III is used in the second liquefaction reactor.

[0094] The solid liquefaction residue (containing liquefaction residue and asphaltene), gas, and water separated from the second liquefaction reactor in step (2) are analyzed to obtain the yield of coal direct liquefaction products (based on the mass of dry and ash-free raw coal): the mass of liquefaction residue accounts for 9.8% (corresponding to a coal direct liquefaction conversion rate of 90.2%), the oil yield is 56.6%, the water yield is 10.6%, the gas yield is 14.1%, and the asphaltene yield is 8.9%.

[0095] Example 3

[0096] (1) The Shendong coal, hydrated iron oxide catalyst, and circulating solvent I are mixed, the mass ratio of catalyst to dry coal is 1:100, and the mass ratio of circulating solvent I to dry coal is 1.5:1. After stirring for 240 min, the components are uniformly mixed to obtain an oil coal slurry;

[0097] (2) The oil coal slurry is heated to 380°C by a heater and then enters the first liquefaction reactor together with the circulating solvent II. The mass ratio of circulating solvent II to dry coal is 1.4:1. The operating temperature of the first liquefaction reactor is 450°C, the hydrogen partial pressure is controlled at 18 MPa, and the residence time is 60 min. The reaction material is discharged from the first liquefaction reactor and then enters the second liquefaction reactor together with the circulating solvent III. The mass ratio of circulating solvent III to dry coal is 0.6:1, the operating temperature of the second liquefaction reactor is 455°C, the hydrogen partial pressure is controlled at 19 MPa, and the residence time is 60 min. The reaction material obtained from the second liquefaction reactor is separated by a separator to obtain gas, water, and solid liquefaction residue, and then liquid coal liquefaction oil is obtained;

[0098] (3) The coal liquefaction oil enters the solvent hydrogenation reactor to be fully fractionated and hydrogenated to obtain hydrogenated liquefaction oil. The hydrogenation reaction conditions are the same as those in Example 1. The hydrogenated liquefaction oil is subjected to distillation cutting to sequentially obtain product oil fractions of distillation range <220°C, fraction A (distillation range 220-280°C), fraction B (distillation range 280-340°C), and fraction C (distillation range >340°C).

[0099] Circulating solvent I is prepared by mixing fraction B and C at a mass ratio of B:C = 50:50; circulating solvent II is fraction B with a mass ratio of 100%; and circulating solvent III is prepared by mixing fraction B and C at a mass ratio of B:C = 90:10. Circulating solvent I is used in step (1), circulating solvent II is used in the first liquefaction reactor, and circulating solvent III is used in the second liquefaction reactor.

[0100] The solid liquefaction residue (containing liquefaction residue and asphaltene), gas, and water separated from the second liquefaction reactor in step (2) are analyzed to obtain the yield of coal direct liquefaction products (based on the mass of dry and ash-free raw coal): liquefaction residue mass ratio 11.9% (corresponding to a coal direct liquefaction conversion rate of 88.1%), oil yield 55.4%, water yield 9.8%, gas yield 12.8%, and asphaltene yield 10.1%.

[0101] Example 4

[0102] The procedure of Example 1 is followed, except that in step (2), the mass ratio of circulating solvent II to dry coal is 0.1:1, and the mass ratio of circulating solvent III to dry coal is 0.1:1.

[0103] Example 5

[0104] The procedure of Example 1 is followed, except that in step (2), the mass ratio of circulating solvent II to dry coal is 3:1, and the mass ratio of circulating solvent III to dry coal is 3:1.

[0105] Example 6

[0106] The procedure of Example 3 is followed, except that fraction A (distillation range 220-260°C), fraction B (distillation range 260-330°C), and fraction C (distillation range >330°C) are used.

[0107] Example 7

[0108] The procedure of Example 1 is followed, except that in circulating solvent I, the mass ratio of fraction A:B:C is 25:65:10.

[0109] Example 8

[0110] The procedure of Example 1 was followed except that in the circulating solvent III, the fraction segments A:B:C = 40%:40%:20% by mass ratio.

[0111] Example 9

[0112] The procedure of Example 1 was followed except that in the circulating solvent II, the fraction segments A:B:C = 60%:20%:20% by mass ratio.

[0113] Comparative Example 1

[0114] (1) The Shendong coal, hydrated iron oxide catalyst and circulating solvent IV were mixed, the mass ratio of catalyst to dry coal was 1:100, and the mass ratio of circulating solvent to dry coal was 1:1; the components were uniformly mixed by stirring for 240 min to obtain an oil slurry;

[0115] (2) The oil slurry was heated to 380℃ by a heater and then entered the first liquefaction reactor, the operating temperature of the first liquefaction reactor was 450℃, the hydrogen partial pressure was controlled at 18 MPa, and the residence time was 60 min. The reaction material discharged from the first liquefaction reactor entered the second liquefaction reactor, the operating temperature of the second liquefaction reactor was 455℃, the hydrogen partial pressure was controlled at 19 MPa, and the residence time was 60 min; the reaction material obtained from the second liquefaction reactor was separated by a separator to separate gas, water and solid liquefaction residue, and liquid coal liquefaction oil was obtained.

[0116] (3) The liquid coal liquefaction oil entered the solvent hydrogenation reactor for full-range hydrogenation to obtain hydrogenated liquefaction oil, and the hydrogenation reaction conditions were the same as those in Example 1; the hydrogenated liquefaction oil was subjected to distillation cutting, and product oil fractions with a distillation range <220℃, fraction segment E (with a distillation range of 220-350℃) and fraction segment F (with a distillation range >350℃) were obtained in sequence, and the fraction segments E and F were prepared to obtain the circulating solvent IV (fraction segment E: F = 80%:20% by mass ratio). The obtained circulating solvent IV was recycled to step (1).

[0117] The analysis of the solid liquefaction residue, gas and water separated in the second liquefaction reactor in step (2) can obtain the yield of coal direct liquefaction products (based on the mass ratio of dry ash-free raw coal): the mass ratio of liquefaction residue is 13.3% (corresponding to a coal direct liquefaction conversion rate of 86.7%), the oil yield is 51.5%, the water yield is 9.5%, the gas yield is 12.5%, and the asphaltene yield is 13.2%.

[0118] Comparative Example 2

[0119] The procedure of Example 1 was followed except that in step (3), X1 was 230℃ and X2 was 280℃; that is, the distillation range of fraction segment A was 220-230℃, the distillation range of fraction segment B was 230-280℃, and the distillation range of fraction segment C was >280℃.

[0120] Comparative Example 3

[0121] Reference is made to Example 1, except that the circulating solvent I (fraction A: C = 40%:60%, mass ratio), the circulating solvent II (fraction A: C = 80%:20%, mass ratio).

[0122] Table 1 Summary of experimental results

[0123] No. Liquefaction residue, % Conversion, % Oil yield, % Water yield, % Gas yield, % Asphaltene yield, % Example 1 11.5 88.5 54.8 10.2 13.1 10.4 Example 2 9.8 90.2 56.6 10.6 14.1 8.9 Example 3 11.9 88.1 55.4 9.8 12.8 10.1 Example 4 13.1 86.9 51.8 11.2 14.5 9.4 Example 5 12.4 87.6 53.9 10.8 12.7 10.2 Example 6 10.7 89.3 56.2 10.1 12.4 10.6 Example 7 12.5 87.5 53.2 10.9 13.3 10.1 Example 8 12.1 87.9 53.5 10.7 13.2 10.5 Example 9 12.7 87.3 52.9 10.6 13.5 10.3 Comparative Example 1 13.3 86.7 51.5 9.5 12.5 13.2 Comparative Example 2 14.6 85.4 50.8 9.7 12.1 12.8 Comparative Example 3 13.8 86.2 51.1 10.2 12.7 12.2

[0124] From the above experimental results, compared with the comparative examples, the oil yield and conversion rate of the examples using the method of the present application can be significantly improved.

[0125] From the comparison of Example 4 and other examples, in step (2) of Example 4, the mass ratio of circulating solvent II to dry coal is not controlled to be (0.2-5):1, and the mass ratio of circulating solvent III to dry coal is not controlled to be (0.2-5):1, and the direct coal liquefaction effect of Example 4 is poorer than that of other examples, and the conversion rate and oil conversion rate are lower than those of other examples.

[0126] From the comparison of Example 1 and Example 9, in Example 9, the mass ratio of the medium-temperature solvent in the circulating solvent II is not within the preferred range of 50-100%, and the direct coal liquefaction effect of Example 9 is poorer than that of Example 1, and the conversion rate and oil conversion rate are lower than those of Example 1.

[0127] It is easily understood that the above examples are only examples for clarity and do not mean that the present application is limited to this. For ordinary skilled persons in the art, other different forms of changes or variations can be made on the basis of the above description. Here, it is not necessary and impossible to exhaust all the embodiments. The obvious changes or variations derived therefrom are still within the protection scope of the present application.

Claims

1. A coal direct liquefaction method of differential segmented feed of a circulating solvent, characterized by, The method comprises the following steps: (1) preparing oil slurry with coal and circulating solvent I; (2) feeding circulating solvent II and the oil slurry into a first liquefaction reactor for first liquefaction reaction, and then feeding the reaction product and circulating solvent III into a second liquefaction reactor for second liquefaction reaction, and separating coal liquefied oil from the reaction product obtained from the second liquefaction reaction; in step (2), the mass ratio of the circulating solvent II to the coal is (0.1-5):1, and the mass ratio of the circulating solvent III to the coal is (0.1-5):1; The coal liquefied oil is subjected to hydrogenation to obtain hydrogenated liquefied oil, and the hydrogenated liquefied oil is subjected to fractionation to obtain a light fraction, a medium-temperature fraction and a heavy fraction; wherein the distillation range of the light fraction is 220 ℃-X1 ℃, the distillation range of the medium-temperature fraction is X1-X2 ℃, and the distillation range of the heavy fraction is >X2 ℃; X1 is 240-280 ℃; X2 is 300-360 ℃; In the circulating solvent I, the mass fraction of the light fraction is 0-40%, the mass fraction of the medium-temperature fraction is 20-80%, and the mass fraction of the heavy fraction is 10-80%; in the circulating solvent II, the mass fraction of the medium-temperature fraction is 50-100%, and the sum of the mass fractions of the light fraction and the heavy fraction is 0-50%; the circulating solvent III comprises at least the light fraction and / or the medium-temperature fraction.

2. The direct coal liquefaction method according to claim 1, characterized by, The direct coal liquefaction method further comprises the following step (3): The coal liquefied oil obtained in step (2) is subjected to hydrogenation to obtain hydrogenated liquefied oil, and the hydrogenated liquefied oil is subjected to fractionation to obtain product oil fraction, the light fraction, the medium-temperature fraction and the heavy fraction.

3. The direct coal liquefaction method according to claim 1, characterized by, X1 is 250-270 ℃.

4. The direct coal liquefaction method according to claim 1, characterized by, X2 is 310-350 ℃.

5. The direct coal liquefaction method according to any one of claims 1-4, wherein In the circulating solvent I, the mass fraction of the light fraction is 0-20%, the mass fraction of the medium-temperature fraction is 40-60%, and the mass fraction of the heavy fraction is 20-60%.

6. The direct coal liquefaction method according to claim 5, wherein In step (1), the mass ratio of the circulating solvent I to the coal is (0.5-4):

1.

7. The direct coal liquefaction method according to any one of claims 1 to 4, characterized by, In step (2), the circulating solvent III optionally comprises the heavy fraction.

8. The direct coal liquefaction method according to claim 7, wherein In step (2), the circulating solvent III comprises at least the medium-temperature fraction.

9. The direct coal liquefaction method according to claim 7, wherein In the circulating solvent III, the mass fraction of the light fraction is 0-100%, the mass fraction of the medium-temperature fraction is 0-100%, the mass fraction of the heavy fraction is 0-20%, and the sum of the mass fractions of the light fraction and the medium-temperature fraction is not 0.

10. The direct coal liquefaction method according to claim 9, wherein In the circulating solvent III, the mass fraction of the light fraction is 0-40%, and the mass fraction of the medium-temperature fraction is 40-100%.

11. The direct coal liquefaction method according to claim 9, characterized by, In the circulating solvent III, the mass fraction of the medium-temperature fraction is 60-90%, and the remaining components are the light fraction and / or the heavy fraction, and the mass fraction of the remaining components is 10-40%.

12. The direct coal liquefaction method according to any one of claims 1 to 4, characterized by, The mass ratio of the circulating solvent II to the coal in step (2) is (0.2-5):

1. The mass ratio of the circulating solvent III to the coal in step (2) is (0.2-5):

1.

13. The direct coal liquefaction method according to claim 12, characterized by, The mass ratio of the circulating solvent III to the coal is greater than the mass ratio of the circulating solvent II to the coal.

14. The direct coal liquefaction method according to claim 12, characterized by, The mass ratio of the circulating solvent II to the coal in step (2) is (0.2-2):

1.

15. The direct coal liquefaction method according to claim 12, wherein The mass ratio of the circulating solvent III to the coal in step (2) is (0.2-2):

1.

16. The direct coal liquefaction method according to any one of claims 1 to 4, characterized by, The oil slurry in step (2) is preheated before being fed into the first liquefaction reactor. The operating temperature of the first liquefaction reactor in step (2) is 430-480℃, the hydrogen partial pressure is controlled to be 12-25MPa, and the residence time is 20-120min. The operating temperature of the second liquefaction reactor in step (2) is 430-480℃, the hydrogen partial pressure is controlled to be 12-25MPa, and the residence time is 20-120min. The material for preparing the oil slurry in step (1) further comprises a catalyst.

17. The direct coal liquefaction method according to claim 16, wherein The oil slurry in step (2) is preheated to 340-400℃ before being fed into the first liquefaction reactor. The mass ratio of the catalyst to the coal in step (1) is 1:(20-120), and the catalyst is selected from one or more of water-soluble or oil-soluble catalysts.

18. The direct coal liquefaction method according to claim 16, wherein The catalyst is selected from one or more of iron-containing catalysts, nickel-containing catalysts, cobalt-containing catalysts, molybdenum-containing catalysts, tungsten-containing catalysts, and alkali metal-containing catalysts.

19. The direct coal liquefaction method according to claim 2, wherein The product oil fraction in step (3) is distillate oil with a distillation range <220℃.

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