Step liquefaction method and system for high-activity coal

Abstract

The invention discloses a step liquefaction method and system for high-activity coal, and relates to the technical field of coal chemical industry. The method comprises the following steps: preparing coal slurry; the method comprises the following steps: mixing preheated coal slurry with preheated hydrogen, preheating again, introducing the mixture into a first-stage reactor for a first-stage liquefaction reaction, and carrying out gas-liquid separation on a material obtained by the reaction in a first-stage separation unit to obtain a first hot high-pressure separation gas phase part and a first hot high-pressure separation liquid phase part; the liquid phase part of the first hot high-pressure separator enters a second-stage liquefaction reaction and is separated through a second-stage separation unit; a gas phase part obtained by the two-stage separation unit is depressurized and cooled and then is subjected to hydrofining together with flash oil; and feeding the crude oil hydrogenation pretreatment product into a product fractionating tower for normal-pressure fractionation to obtain components in different temperature intervals. According to the invention, the process path is redesigned, and after two-stage reaction, the high-activity material can be completely lightened, and meanwhile, the light component is prevented from being excessively lightened and cracked into more gas.

Description

Technical Field

[0001] The invention relates to the technical field of coal chemical industry, and in particular to a cascade liquefaction method and system for high-activity coal. Background Art

[0002] Coal direct liquefaction technology originated in the early 20th century. The coal direct liquefaction process is mainly divided into the German IGOR process, the Japanese NEDOL liquefaction process, the American H-Coal process and the Chinese Shenhua HTI liquefaction process. Among them, the reaction operating pressure of the German IGOR process is 30MPa, the reaction temperature is 470℃, and the circulating solvent is separated by vacuum distillation. At the same time, the technology uses red mud catalyst. Due to the low activity of red mud catalyst, in order to obtain a higher oil yield, the control of reaction operating conditions is more stringent. The reaction conditions of the Japanese NEDOL liquefaction process are 17MPa and the reaction temperature is 450℃. The technology uses vacuum distillation to separate the circulating solvent, and the catalyst used is ultrafinely crushed natural pyrite. Ultrafine pyrite has good catalytic performance, but the ore is hard, the ultrafine crushing is difficult, and the production cost is high. The reaction pressure of the American H-Coal process is 20MPa, the reaction temperature is 455℃, and the circulating solvent is separated by hydrocyclone separation and vacuum distillation. Since this technology uses a petroleum-based catalyst, which is easily deactivated in the coal liquefaction reaction system, the catalyst needs to be replaced frequently, resulting in a high cost for liquefied oil production.

[0003] At present, the research progress of domestic coal direct liquefaction is reported as follows:

[0004] China Shenhua HTI liquefaction process mainly uses two reactors. The reaction temperature of the two reactors is 430-465℃, the reaction pressure is 15-19MPa, and the coal slurry space velocity is 0.7-1.0t / m 3 .h. The catalyst used in this process is γ-hydrated iron oxide, and the co-catalyst is S. The solid-liquid separation adopts the vacuum distillation method, and the circulating solvent adopts the boiling bed hydrogenation process technology. This technology is difficult to operate due to the complex internal components of the reactor and the difficulty in controlling the circulating pump.

[0005] CN101643660A provides a coal liquefaction method, which is to subject the coal to solvent extraction treatment, remove the ash in the coal, reduce the inert components and oxygen content in the raw coal, and then carry out hydrogenation liquefaction. In fact, it is a combined process technology of thermal extraction process and liquefaction process, wherein the reaction temperature of the liquefaction process is 420-470°C, the reaction pressure is 10-30MPa, and the coal slurry space velocity is 0.6-1.4t / m 3.h. This technology can only process lignite or low-rank coal with a metamorphic degree similar to lignite. At the same time, the thermal extraction process will remove inert components while also entraining some components that can be converted into light hydrocarbon compounds under high temperature and high pressure conditions. Therefore, there are problems such as low raw material utilization efficiency and weak raw material adaptability.

[0006] CN103074097A A method and system for direct liquefaction of coal, which introduces a method of mixing coal slurry with hydrogen, reacting in two series reactors, obtaining a liquefied reaction product at the outlet of the second liquefaction reactor, wherein a portion of the liquefied reaction product is returned to the inlet of the first liquefaction reactor for recycling. The reaction temperature of the liquefaction reaction is 400-480°C, the reaction pressure is 10-30MPa, the gas-liquid ratio is 600-2000NL / kg, and the coal slurry space velocity is 0.5-4.5h -1 This technology can effectively balance the reaction load of the reactor, but it will cause the light materials produced by the liquefaction reaction to be repeatedly hydrogenated and cracked in the reactor, reducing the utilization efficiency of the reactor and leading to a higher gas yield, making the materials excessively light.

[0007] The above-mentioned prior art has made certain progress in the research of direct coal liquefaction, but there are still the following technical problems:

[0008] (1) The temperatures of the reactors in the system are all controlled at the same temperature, and the temperature control range is uniformly between 400 and 480°C. The reaction pressure of the system is between 10 and 30 MPa. The reaction temperature and reaction pressure of the overall system are relatively demanding.

[0009] (2) The technical applicability of existing coal direct liquefaction technology to liquefied coal is too broad and cannot effectively adapt to the graded conversion of the typical active components in coal that are easy to convert - vitrinite, the intermediate active components - exinite, and the components that are more difficult to crack and hydrogenate - inertin.

[0010] (3) The liquefied products produced by the existing coal direct liquefaction technology have the problem of insufficient hydrogenation depth, especially the problem that the olefin substances generated in the reaction system are difficult to be fully saturated, which leads to poor stability of the oil products. On the other hand, it is easy to cause the light components to be over-lightened and the gas yield to be too high.

[0011] This shows that the prior art needs to be further improved. Summary of the invention

[0012] One of the purposes of the present invention is to provide a cascade liquefaction method for high-activity coal. By redesigning the process path, after two-stage reaction, all high-activity materials can be lightweight, while also avoiding excessive lightweighting of lightweight components and cracking into more gas.

[0013] In order to achieve the above object, the present invention adopts the following technical solutions:

[0014] A cascade liquefaction method for high-activity coal comprises the following steps:

[0015] S1. preparing coal slurry;

[0016] S2, mixing the coal slurry obtained in step S1 with the preheated hydrogen and preheating it again, and then passing it into a primary reactor for a primary liquefaction reaction, and sending the material obtained after the reaction to a first-stage separation unit, and obtaining a first hot high-fraction gas phase part and a first hot high-fraction liquid phase part after separation by the first-stage separation unit; the temperature of the first-stage reactor is 320-400°C, and the pressure is 10-18MPa;

[0017] S3, passing the first hot high-fraction liquid phase into a secondary reactor for secondary liquefaction reaction, and sending the resulting material after the reaction into a second-stage separation unit, and obtaining a second hot high-fraction gas phase and a second hot high-fraction liquid phase after separation in the second-stage separation unit; the temperature of the secondary reactor is 420-460° C., and the pressure is 10-18 MPa;

[0018] S4, subjecting the second hot high-fraction liquid phase to vacuum distillation through a vacuum distillation tower to obtain flash oil and coal liquefaction pitch;

[0019] S5, sending the first hot high-fraction gas phase part and the second hot high-fraction gas phase part into an atmospheric distillation tower after depressurization and temperature reduction, and the flash oil is also sent into the atmospheric distillation tower; performing a hydrorefining step in a hydrogenation reactor connected to the atmospheric distillation tower to obtain a crude oil hydrogenation pretreatment product;

[0020] S6. The crude oil hydrogenation pretreatment product is sent to a product fractionation tower for atmospheric pressure fractionation to obtain components in different temperature ranges.

[0021] In the above-mentioned cascade liquefaction method of high-activity coal, in step S1, the coal slurry is prepared from coal powder, catalyst, co-catalyst and circulating solvent, the particle size of the coal powder is less than 100 mesh, the catalyst is an iron-based catalyst or a powdered catalyst containing nickel and molybdenum elements; the co-catalyst is an organic compound rich in sulfur; the circulating solvent is an aromatic hydrocarbon or partially saturated aromatic hydrocarbon compound containing 2 to 4 rings, and the mass fraction of the aromatic hydrocarbon and partially saturated aromatic hydrocarbon compound is ≥40%; the mass fraction of the coal powder in the coal slurry is 30 to 55%; the amount of the catalyst added is 0.1 to 2.0% of the mass of the coal powder.

[0022] In the above-mentioned cascade liquefaction method of high-activity coal, in step S2, the coal slurry and the preheated hydrogen are mixed and preheated at a temperature of 200 to 300°C; the temperature of the primary reactor is 350 to 400°C, and the temperature of the secondary reactor is 440 to 455°C; the pressure of the primary reactor and the secondary reactor is 13 to 15 MPa; the gas-liquid ratio in the primary reactor and the secondary reactor is 600 to 2000 NL / kg, and the coal slurry space velocity is 0.2 to 3 -1 .

[0023] In the above-mentioned cascade liquefaction method of high-activity coal, the iron-based catalyst is natural ore, industrial waste slag, iron compound or synthetic nano-scale hydrated iron oxide; and the powdered catalyst is ground mineral powder.

[0024] In the above-mentioned cascade liquefaction method of high-activity coal, the mass fraction of coal powder in the coal slurry is 40-50%; the added amount of catalyst is 0.5-1% of the mass of coal powder; the molar ratio of effective sulfur contained in the promoter to the active metal of the catalyst is 0.2-4:1.

[0025] In the above-mentioned method for cascade liquefaction of highly active coal, in step S4, the vacuum distillation system controls its vacuum degree to be less than 1000 Pa, and controls the softening point of the coal liquefaction pitch to be 150-210°C.

[0026] In the above-mentioned cascade liquefaction method of high-activity coal, in step S5, the hydrogenation reactor required for the hydrorefining step is a fixed bed or an ebullating bed reactor, the hydrogenation catalyst is a supported catalyst, the carrier of the supported catalyst is one or a mixture of aluminum oxide, silicon oxide, magnesium oxide, and clay, and the active metal is one or more of nickel, molybdenum, and cobalt; the hydrogenation reaction temperature is 250-350°C, the reaction pressure is 10-18MPa, the gas-liquid ratio is 7001600, and the space velocity is 0.3-2h -1 .

[0027] In the above-mentioned cascade liquefaction method of high-activity coal, in step S6, the different temperature ranges are: T<170°C, 170°C≤T﹤220~260°C, T≥220~260°C.

[0028] Another object of the present invention is to provide a cascade liquefaction system for high-activity coal, which includes a coal slurry preparation tank, a coal slurry preheater, a primary reactor, a first-stage separation unit, a secondary reactor, a second-stage separation unit, an atmospheric distillation tower, a pressure distillation tower, a hydrogenation reactor, an oil-gas separator and a product fractionation tower;

[0029] The coal slurry preparation tank is used to mix coal powder, catalyst, co-catalyst and circulating solvent to prepare coal slurry;

[0030] The coal slurry preheater is used to preheat the coal slurry and hydrogen;

[0031] The primary reactor is used to generate a primary liquefaction reaction, and the material after the primary liquefaction reaction enters a first-stage separation unit connected to the primary liquefier;

[0032] The first-stage separation unit is used to separate the material to obtain a first hot high-fraction gas phase part and a first hot high-fraction liquid phase part;

[0033] The second stage separation unit is used to perform secondary liquefaction on the first hot high fraction liquid phase portion, and obtain a second hot high fraction gas phase portion and a second hot high fraction liquid phase portion;

[0034] The vacuum distillation tower is used to perform vacuum distillation on the second hot high-fraction liquid phase to prepare flash oil and coal liquefaction pitch;

[0035] The hydrogenation reactor is used to perform hydrogenation refining on the first hot high-fraction gas phase part and the second hot high-fraction gas phase part after flash oil is evaporated, cooled and depressurized;

[0036] The oil-gas separator is used to separate the materials after hydrofining, and the fractionation tower is used to obtain components in different temperature ranges.

[0037] The above-mentioned coal slurry preheater, primary reactor and secondary reactor are all bubbling bed reactors without internal components.

[0038] Compared with the prior art, the present invention brings the following beneficial technical effects:

[0039] The present invention provides a cascade liquefaction method for highly active coal, by improving the process, such as the material after the reaction in the primary reactor enters the first separation unit, the first hot high-fraction gas phase part and the first hot high-fraction liquid phase part are separated in the first separation unit, wherein the first hot high-fraction gas phase part is subjected to deep hydrogenation after cooling and depressurization to obtain the product, and the first hot high-fraction liquid phase part is then introduced into the secondary reactor for reaction, and separated by the second separation unit; the reaction temperatures of the primary reactor and the secondary reactor of the present invention are significantly lower than the liquefaction temperature in the prior art, considering the overall control of the reaction system, so the reaction pressures of the primary reactor and the secondary reactor are equal, the temperature difference between the two is 50-90°C, the components that are easy to react can start to react at lower temperatures and pressures, and the components that are difficult to react require more harsh reaction conditions, so the present invention sets the reaction temperatures of the primary reactor and the secondary reactor in a targeted manner. Such a design method can prevent light components from being over-lightened and cracked into more gases.

[0040] The primary reactor and the secondary reactor in the present invention can separate the gas from the system, thus avoiding further cracking of the low-hydrocarbon gas and consumption of hydrogen, and improving the processing efficiency of the reactor.

[0041] The vacuum distillation in the present invention can better retain the solid phase material in the coal liquefaction pitch, thereby ensuring the long-term operation of the crude oil hydrogenation catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The present invention will be further described below in conjunction with the accompanying drawings:

[0043] Figure 1 The figure is a process flow chart of the cascade liquefaction of highly active coal according to the present invention. DETAILED DESCRIPTION

[0044] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application.

[0045] In the description of this application, words such as "first" and "second" are only used to distinguish different objects, and do not limit the quantity and execution order, and words such as "first" and "second" do not necessarily limit differences. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions.

[0046] The "highly active coal" mentioned in the present invention refers to coal that meets the primary coal index and volatile matter (V daf >40%), and low-rank coal with inertin content less than 15%.

[0047] The technical solution of the present application is further described in detail below in conjunction with the accompanying drawings.

[0048] like Figure 1 As shown, the present invention provides a cascade liquefaction method for high-activity coal, which specifically comprises the following steps:

[0049] Step 1: Preparation of coal slurry: Dry and crush the high-activity lump coal into dry coal powder under vacuum conditions, and then prepare the dry coal powder with catalyst, co-catalyst and circulating solvent into coal slurry.

[0050] Step 2, primary liquefaction reaction and gas-liquid separation of primary coal liquefaction product: the preheated coal slurry is mixed with the preheated hydrogen and preheated again, and then introduced into the primary reactor for primary liquefaction reaction; the liquefied reaction product obtained at the outlet of the primary reactor enters the first-stage separation unit under high temperature and high pressure conditions for gas-liquid separation to obtain a first hot high-fraction gas phase portion and a first hot high-fraction liquid phase portion.

[0051] Step three, secondary liquefaction reaction and gas-liquid separation of secondary coal liquefaction reaction products: pump the first hot high-fraction liquid phase portion into the secondary reactor for secondary liquefaction reaction; the liquefied reaction product obtained at the outlet of the secondary reactor enters the second-stage classification unit for gas-liquid separation to obtain a second hot high-fraction gas phase portion and a second hot high-fraction liquid phase portion.

[0052] Step 4: Distillation separation: distill the second hot high-fraction liquid phase obtained by separation in the secondary reactor to obtain flash oil and residue.

[0053] Step 5, crude oil hydrogenation: The liquefied crude oil obtained after the first hot high-fraction gas phase part and the second hot high-fraction gas phase part are cooled and depressurized and then hydrogenated and refined together with the flash oil to remove the sulfur, nitrogen, oxygen and other heteroatoms in the crude oil, and at the same time saturate the olefins and the aromatics to obtain the crude oil hydrogenation pretreatment product.

[0054] Step 6, product fractionation: Separate the crude oil hydrogenation pretreatment product to obtain light oil, middle distillate oil and heavy oil, wherein the middle distillate oil and heavy oil are mixed in a certain proportion and used as a circulating solvent for coal slurry preparation in the coal liquefaction process, and the light oil and the remaining middle distillate oil are used as feedstock oil for subsequent deep processing of oil products.

[0055] Preferably, the above catalyst is an iron catalyst or a multi-metal composite catalyst. More preferably, the iron catalyst is a natural ore (such as pyrite), industrial waste slag (blast furnace tailings), an iron compound (iron oxide or sulfide) or a synthetic nano-scale hydrated iron oxide. The multi-metal composite catalyst is a mineral containing elements such as nickel and molybdenum, preferably nano-scale hydrated iron oxide, ground ultrafine mineral powder, etc. The ultrafine mineral powder is a graded catalyst with a particle size of 10 nanometers to 100 microns; the co-catalyst is sulfur or other sulfur-rich organic compounds. The above circulating solvent is an aromatic hydrocarbon containing 2 to 4 rings and or partially saturated compounds, and the content of aromatic hydrocarbons and partially saturated aromatic hydrocarbon compounds is higher than 40% (mass fraction).

[0056] Preferably, the amount of catalyst added is 0.1-2% by weight of dry coal powder, preferably 0.5-1%; the molar ratio of effective sulfur in the promoter to active metal of the catalyst is 0.2-4:1, preferably 0.5-2.5:1; the mass fraction of dry coal in the coal slurry is 30-55%, preferably 40-50%.

[0057] Furthermore, in the above method, the temperature of the coal slurry preheater for preheating the coal slurry is 200-300°C, preferably 250-280°C; the core temperature of the primary reactor is controlled between 320-400°C, preferably 350-400°C; the core temperature of the secondary reactor is controlled between 420-460°C, preferably 440-455°C; the system pressure is controlled between 10-18MPa, preferably 13-15MPa; the gas-liquid ratio is 600-2000NL / kg, preferably 800-1200NL / kg; the coal slurry space velocity is 0.2-3 -1 The preferred air velocity is 0.8 to 2 -1 .

[0058] Furthermore, in the above method, the weight flow ratio of the first hot high-fraction gas phase portion and the first hot high-fraction liquid phase portion separated by the first-stage separation unit is controlled to be 0.05 to 1:1, preferably 0.25 to 0.8:1.

[0059] Furthermore, in the above method, the second hot high-fraction liquid phase is separated into flash oil and coal liquefaction pitch by vacuum distillation, and the vacuum distillation system controls its vacuum degree to be less than 1000Pa, preferably 10-300Pa, and controls the softening point of coal liquefaction pitch to be between 150 and 210°C, preferably 160-190°C.

[0060] Furthermore, in the above method, the crude oil hydrogenation is a mixture of the light liquid phase material from the first hot high-fraction gas phase after decompression and cooling, the light liquid phase material from the second hot high-fraction gas phase after decompression and cooling, and the flash oil obtained by vacuum distillation, and then sent to the hydrogenation system. The reactor of the hydrogenation system is a fixed bed reactor or an ebullating bed reactor, and the hydrogenation catalyst is a supported catalyst. The carrier is a mixture of one or more of aluminum oxide, silicon oxide, magnesium oxide, or clay, and its active metal is one or more of nickel, molybdenum, cobalt and other metals. The reaction temperature is 250-350°C, preferably 260-300°C, the reaction pressure is 10-18MPa, preferably 12-15MPa, the gas-liquid ratio is 7001600, and the air velocity is 0.3-2h -1 .

[0061] Furthermore, in the above method, the product after hydrogenation of the crude oil is sent to a product distillation tower for atmospheric distillation, and components in different temperature ranges are collected, namely, components when T<170°C, components when 170°C≤T﹤220~260°C, and components when T≥220~260°C.

[0062] Combine the following Figure 1 A cascade liquefaction system for high-activity coal according to the present invention is described in detail.

[0063] A cascade liquefaction system for high-activity coal includes a coal slurry preparation tank, a coal slurry preheater, a primary reactor, a first-stage separation unit, a secondary reactor, a second-stage separation unit, an atmospheric distillation tower, a pressurized distillation tower, a hydrogenation reactor, an oil-gas separator and a product fractionation tower.

[0064] The above-mentioned coal slurry preparation tank is used to mix coal powder, catalyst, co-catalyst and circulating solvent and prepare coal slurry;

[0065] The coal slurry preheater is used to preheat coal slurry and hydrogen; the outlet of the coal slurry preparation tank is connected to the inlet of the coal slurry preheater, the prepared coal slurry enters the coal slurry preheater, and is mixed with the hydrogen entering the coal slurry preheater for preheating.

[0066] The primary reactor is used for a primary liquefaction reaction. An outlet is arranged at the top of the primary reactor. The material after the primary liquefaction reaction enters a first-stage separation unit connected to the primary liquefier from the outlet at the top. The first-stage separation unit has a gas phase outlet at the top and a liquid phase outlet at the bottom. The material is separated in the first-stage separation unit, and the obtained first hot high-fraction gas phase part is discharged from the gas phase outlet and enters an atmospheric distillation tower connected to the first-stage separation unit; and the first hot high-fraction liquid phase part is discharged from the liquid phase outlet at the bottom.

[0067] The liquid phase outlet at the bottom of the first-stage separation unit is connected to the inlet of the secondary reactor, the first hot high-fraction liquid phase portion is pumped into the secondary reactor for secondary liquefaction reaction, and the reacted material enters the second-stage separation unit connected to the secondary reactor, and the second-stage separation unit is used to perform secondary liquefaction on the first hot high-fraction liquid phase portion, and obtain a second hot high-fraction gas phase portion and a second hot high-fraction liquid phase portion;

[0068] The vacuum distillation tower is used to carry out vacuum distillation on the second hot high-fraction liquid phase to prepare flash oil and coal liquefaction asphalt; the hydrogenation reactor is used to carry out hydrogenation refining on the flash oil, the first hot high-fraction gas phase after cooling and pressure reduction, and the second hot high-fraction gas phase; the oil-gas separator is used to separate the materials after hydrogenation refining, and the oil-gas separator is connected to the product distillation tower to obtain components in different temperature ranges through the product distillation tower.

[0069] Preferably, the coal slurry preheater, primary reactor and secondary reactor are all bubbling bed reactors without internal components.

[0070] The present invention will be further described below in conjunction with specific embodiments.

[0071] Embodiment 1:

[0072] The system used in this embodiment is a 0.1t / d coal direct liquefaction continuous test system, a cascade liquefaction method for high-activity coal, comprising the following steps:

[0073] Step 1: Make coal slurry

[0074] High-activity long flame coal from Xinjiang (with an inert group content of 89% and a Vdaf content of 45%) is crushed into dry coal powder under a vacuum system, and then the dry coal powder is mixed with a catalyst, a co-catalyst and a circulating solvent to form a coal slurry.

[0075] The catalyst is pyrite with an iron content greater than 45%, which is ground into ultrafine powder with a particle size distribution of 500nm to 1 micron; the added amount of the catalyst is 0.1% to 2.0% (mass fraction) of the mass of dry coal powder, and the molar ratio of sulfur to catalyst active metal components in the promoter is 2:1; the mass fraction of coal powder in the coal slurry is 43%, and the circulating solvent is aromatic hydrocarbons or partially saturated aromatic hydrocarbon compounds containing 2 to 4 rings, and the mass fraction of aromatic hydrocarbons and partially saturated aromatic hydrocarbon compounds is higher than 40%.

[0076] The particle size of the dry coal powder is less than 100 mesh, the water content is 4.8% (mass fraction), and the ash content is 5.3%.

[0077] The initial solvent is an external solvent of aromatic hydrocarbons and hydrogenated aromatic hydrocarbon compounds with a mass fraction of 62%, which is then gradually replaced by a solvent generated during the conversion of the coal itself, that is, a circulating solvent.

[0078] Step 2: Liquefaction reaction

[0079] The prepared coal slurry and hydrogen are sent into a coal slurry preheater without internal components. The temperature of the coal slurry preheater is controlled at 260-280°C. Then, the coal slurry is sent into a primary reactor. The core temperature of the primary reactor is controlled at 370-380°C. The pressure of the reaction system is controlled at 14-15MPa, the gas-liquid ratio is 800NL / kg, and the coal slurry space velocity is 0.8h -1 ; The materials after reaction are sent to the first-stage separation unit, and the first hot high-fraction liquid phase separated by the first-stage separation unit is pumped into the secondary reactor. The core temperature of the secondary reactor is controlled at 445-455°C; the system pressure is still controlled at 14-15MPa, the gas-liquid ratio is 1200NL / kg, and the space velocity is 1.2h -1 ; The weight flow ratio of the first hot high-fraction gas phase and the first hot high-fraction liquid phase separated from the first-stage separation unit is controlled to be 1:4.

[0080] Step 3: Product Separation

[0081] The first hot high-fraction gas phase separated by the first-stage separation unit is sent to the atmospheric distillation tower after pressure reduction and temperature reduction, and the temperature of the first-stage separation unit is controlled at 380℃±10℃; the second hot high-fraction gas phase separated by the second-stage separation unit is also sent to the atmospheric distillation tower after pressure reduction and temperature reduction, and the temperature of the second-stage separation unit is controlled at 430℃±10℃; the first-stage separation unit and the second-stage separation unit have the same structure, both of which are composed of a high-temperature separator, a medium-temperature separator, a low-temperature separator, a condenser, a pressure reducing valve and other equipment. Part of the gas phase obtained by step-by-step separation is discharged into the exhaust gas system, and the other part is used as circulating gas.

[0082] Step 4: Distillation separation

[0083] The second hot high-fraction liquid phase obtained by the second-stage separation unit is separated into flash oil and coal liquefied pitch by vacuum distillation. The vacuum distillation system controls the vacuum degree to 50-100Ka and the softening point of coal liquefied pitch to 180°C.

[0084] Step 5: Crude Oil Hydrogenation

[0085] The liquefied crude oil obtained by separation of the two-stage separation unit and the flash oil obtained by vacuum distillation are hydrotreated together to remove the sulfur, nitrogen, oxygen and other heteroatoms in the crude oil, and at the same time saturate the olefins and partially saturate the aromatics to obtain the crude oil hydrogenation pretreatment product. The reactor used for crude oil hydrogenation is a fixed bed reactor, and the hydrogenation catalyst is a carrier catalyst loaded with two active metals of nickel and molybdenum, and the carrier is prepared by mixing alumina and clay. The main control process conditions of the hydrogenation reactor are: reaction temperature of 260-300℃, reaction pressure of 14MPa, gas-liquid ratio of 1200, and space velocity of 1.0h-1.

[0086] Step 6: Product fractionation

[0087] The product after hydrogenation of crude oil is sent to the product distillation tower for atmospheric pressure fractionation, and is fractionated into components when T<170℃, components when 170℃≤T﹤220~260℃, and components when T≥220~260℃; the components when T≥220~260℃ are used as circulating solvent for coal slurry preparation, and the components when T<170℃ and components when 170℃≤T﹤220~260℃ are used as products as raw materials for further quality improvement and deep processing of subsequent oil products.

[0088] Comparative Example 1:

[0089] The same high activity long flame coal as in Example 1 was used.

[0090] The process adopts Japan's NEDOL coal liquefaction process.

[0091] The liquefaction performance indicators of Example 1 and Comparative Example 1 are compared, as shown in Table 1. Table 1 shows the properties of coal powder and the liquefaction performance indicators.

[0092] Table 1 Properties and liquefaction performance indicators of raw coal powder used in Example 1 and Comparative Example 1

[0093]

[0094]

[0095] Embodiment 2:

[0096] The system used in this embodiment is a 0.1 t / d coal direct liquefaction continuous test system.

[0097] The difference from Example 1 is that the raw coal used is Yunnan Pioneer lignite, and its coal quality data is shown in Table 2; the catalyst used is synthetic hydrated iron oxide (FeOOH), the co-catalyst is sulfur, and the starting solvent is an additional solvent containing 62% aromatic hydrocarbons and hydrogenated aromatic hydrocarbon compounds, which is gradually replaced by the solvent generated during the conversion process of the coal itself, that is, the circulating solvent.

[0098] Comparative Example 2:

[0099] The difference from Example 2 is that the China Shenhua coal liquefaction process is used, and the data in the table are calculated based on a dry ash-free basis. The liquefaction performance indicators of Example 2 and Comparative Example 2 are compared, as shown in Table 2, which shows the properties of coal powder and liquefaction performance indicators.

[0100] Table 2 Properties and liquefaction performance indicators of raw coal powder used in Example 2 and Comparative Example 2

[0101]

[0102] Embodiment 3:

[0103] The system used in this embodiment is a 0.1 t / d coal direct liquefaction continuous test system.

[0104] The difference from Example 1 is that the raw coal used is Xinjiang high-activity long flame coal, and its coal quality data is shown in Table 3; the catalyst used is industrial waste slag, the co-catalyst is sulfur, and the starting solvent is an external solvent containing 65% aromatic hydrocarbons and hydrogenated aromatic hydrocarbon compounds, which is gradually replaced by the solvent generated during the conversion process of the coal itself, that is, the circulating solvent.

[0105] Comparative Example 3:

[0106] The raw coal used in Example 3 is the same, but the system and liquefaction process are completely different. This comparative example adopts a coal direct liquefaction method disclosed in CN103074097A, and compares the liquefaction performance indicators of Example 3 and Comparative Example 3, as shown in Table 3, which shows the properties of coal powder and liquefaction performance indicators.

[0107] Table 3 Properties and liquefaction performance indicators of raw coal powder used in Example 3 and Comparative Example 3

[0108]

[0109] The main process differences and process conditions of the liquefaction reaction unit are shown in Table 4.

[0110] Table 4 Main process differences and process conditions of liquefaction reaction unit

[0111]

[0112]

[0113] It can be seen from the embodiments and comparative examples that, compared with the coal liquefaction processes of Japan's NEDOL and China's Shenhua, the direct coal liquefaction method provided by the present invention can effectively reduce the excessive lightness of light materials in the reaction process when using the same high-activity coal as raw material, which is manifested in a significantly reduced gas yield. At the same time, the reaction of heavy components is more sufficient, that is, the conversion rate is higher, and the yield of asphaltene is lower. Under the combined effect, the yield of liquefied oil, the main product of coal liquefaction, is significantly higher.

[0114] In the description of this application, the words "primary", "secondary", etc. are only used to distinguish different objects, and do not limit the quantity and execution order, and the words "primary", "secondary", etc. do not necessarily limit the difference. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions.

[0115] Parts not described in the present invention can be implemented by those skilled in the art by referring to the existing technology.

[0116] Those skilled in the art should recognize that the above embodiments are only used to illustrate the present application and are not intended to be limiting of the present application. As long as they are within the spirit of the present application, appropriate changes and modifications to the above embodiments should fall within the scope of protection of the claims of the present application.

Claims

1. A cascade liquefaction method for high-activity coal, characterized in that: The following steps are involved: S1. preparing coal slurry; S2, mixing the coal slurry obtained in step S1 with the preheated hydrogen and preheating it again, and then passing it into a primary reactor for a primary liquefaction reaction, and sending the material obtained after the reaction to a first-stage separation unit, and obtaining a first hot high-fraction gas phase part and a first hot high-fraction liquid phase part after separation by the first-stage separation unit; the temperature of the first-stage reactor is 320-400°C, and the pressure is 10-18MPa; S3, passing the first hot high-fraction liquid phase portion into a secondary reactor for secondary liquefaction reaction, and sending the resulting material after the reaction into a second-stage separation unit, and obtaining a second hot high-fraction gas phase portion and a second hot high-fraction liquid phase portion after separation in the second-stage separation unit; The temperature of the secondary reactor is 420-460°C and the pressure is 10-18MPa; S4, subjecting the second hot high-fraction liquid phase to vacuum distillation through a vacuum distillation tower to obtain flash oil and coal liquefaction pitch; S5, sending the first hot high-fraction gas phase part and the second hot high-fraction gas phase part into an atmospheric distillation tower after depressurization and temperature reduction, and the flash oil is also sent into the atmospheric distillation tower; performing a hydrorefining step in a hydrogenation reactor connected to the atmospheric distillation tower to obtain a crude oil hydrogenation pretreatment product; S6. The crude oil hydrogenation pretreatment product is sent to a product fractionation tower for atmospheric pressure fractionation to obtain components in different temperature ranges.

2. The method for liquefaction of highly active coal according to claim 1, characterized in that: In step S1, the coal slurry is prepared from coal powder, a catalyst, a promoter and a circulating solvent. The particle size of the coal powder is less than 100 meshes. The catalyst is an iron-based catalyst or a powdered catalyst containing nickel and molybdenum elements; the promoter is an organic compound rich in sulfur; the circulating solvent is an aromatic hydrocarbon or a partially saturated aromatic hydrocarbon compound containing 2 to 4 rings, and the mass fraction of the aromatic hydrocarbon and the partially saturated aromatic hydrocarbon compound is ≥40%; the mass fraction of the coal powder in the coal slurry is 30 to 55%; and the amount of the catalyst added is 0.1 to 2.0% of the mass of the coal powder.

3. The method for liquefaction of highly active coal according to claim 1, characterized in that: In step S2, the preheating temperature of the coal slurry and the preheated hydrogen mixture is 200-300°C; the temperature of the primary reactor is 350-400°C, and the temperature of the secondary reactor is 440-455°C; the pressure of the primary reactor and the secondary reactor is 13-15MPa; the gas-liquid ratio in the primary reactor and the secondary reactor is 600-2000NL / kg, and the coal slurry space velocity is 0.2-3 -1 .

4. The method for liquefaction of highly active coal according to claim 2, characterized in that: The iron-based catalyst is natural ore, industrial waste residue, iron compound or synthetic nano-scale hydrated iron oxide; the powdered catalyst is ground mineral powder.

5. The method for liquefaction of highly active coal according to claim 2, characterized in that: The mass fraction of coal powder in the coal slurry is 40-50%; the added amount of catalyst is 0.5-1% of the mass of coal powder; the molar ratio of effective sulfur contained in the promoter to active metal of the catalyst is 0.2-4:

1.

6. The method for liquefaction of highly active coal according to claim 1, characterized in that: In step S4, the vacuum distillation system controls the vacuum degree to be less than 1000 Pa, and controls the softening point of the coal liquefaction pitch to be 150-210°C.

7. The method for liquefaction of highly active coal according to claim 1, characterized in that: In step S5, the hydrogenation reactor required for the hydrorefining step is a fixed bed or an ebullating bed reactor, the hydrogenation catalyst is a supported catalyst, the carrier of the supported catalyst is one or a mixture of aluminum oxide, silicon oxide, magnesium oxide, and clay, and the active metal is one or more of nickel, molybdenum, and cobalt; the hydrogenation reaction temperature is 250-350° C., the reaction pressure is 10-18 MPa, the gas-liquid ratio is 700-1600, and the space velocity is 0.3-2 h -1 .

8. The method for liquefaction of highly active coal according to claim 1, characterized in that: In step S6, the different temperature ranges are: T<170°C, 170°C≤T﹤220~260°C, T≥220~260°C.

9. A cascade liquefaction system for high-activity coal, comprising a coal slurry preparation tank and a coal slurry preheater, characterized in that: It also includes a primary reactor, a first-stage separation unit, a secondary reactor, a second-stage separation unit, an atmospheric distillation tower, a pressure distillation tower, a hydrogenation reactor, an oil-gas separator, and a product fractionation tower; The coal slurry preparation tank is used to mix coal powder, catalyst, co-catalyst and circulating solvent to prepare coal slurry; The coal slurry preheater is used to preheat the coal slurry and hydrogen; The primary reactor is used to generate a primary liquefaction reaction, and the material after the primary liquefaction reaction enters a first-stage separation unit connected to the primary liquefier; The first-stage separation unit is used to separate the material to obtain a first hot high-fraction gas phase part and a first hot high-fraction liquid phase part; The second stage separation unit is used to perform secondary liquefaction on the first hot high fraction liquid phase portion, and obtain a second hot high fraction gas phase portion and a second hot high fraction liquid phase portion; The vacuum distillation tower is used to perform vacuum distillation on the second hot high-fraction liquid phase to prepare flash oil and coal liquefaction pitch; The hydrogenation reactor is used to perform hydrogenation refining on the first hot high-fraction gas phase part and the second hot high-fraction gas phase part after flash oil is evaporated, cooled and depressurized; The oil-gas separator is used to separate the materials after hydrofining, and the fractionation tower is used to obtain components in different temperature ranges.

10. A high-activity coal liquefaction system according to claim 9, characterized in that: The coal slurry preheater, the primary reactor and the secondary reactor are all bubbling bed reactors without internal components.

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