Preparation and preheating method of oil-coal slurry and direct coal liquefaction process

Abstract

The present invention provides a method for preparing and preheating an oil-coal slurry and a direct coal liquefaction process. The method of the present invention can achieve stable preheating of high-concentration oil-coal slurry, and can improve the operational stability and effective utilization rate of the device. The method comprises the following steps: (1) stirring and mixing materials including a heavy fraction and raw coal in an oil-coal slurry preparation tank to obtain an oil-coal slurry premix; (2) feeding the oil-coal slurry premix, a first light fraction, and hydrogen into a coal slurry heater I and heating them to 250-300°C to obtain an oil-coal slurry intermediate material; (3) feeding the oil-coal slurry intermediate material and the second light fraction obtained in step (2) into a coal slurry heater II and heating them to 350-400°C to obtain an oil-coal slurry to be liquefied, and the oil-coal slurry to be liquefied is used to be transported to a liquefaction reactor of the direct coal liquefaction process.

Description

Technical Field

[0001] The present invention relates to the technical field of direct coal liquefaction, in particular to a method for preparing and preheating oil-coal slurry in a direct coal liquefaction process, and also to a direct coal liquefaction process. Background Art

[0002] Direct coal liquefaction technology involves using high temperature and high pressure to break down the macromolecular structure of coal and then hydrogenate it, converting it into a small-molecule liquid fuel. In this process, pulverized coal, a catalyst, and a hydrogen-donating solvent are mixed into a coal-oil slurry, heated as needed, and then transported to the liquefaction reaction unit.

[0003] During the long-term operation of the direct coal liquefaction process, the solvent is typically a direct coal liquefaction oil that is hydrogenated and then cut and recycled. This solvent, also known as a circulating solvent, has a wide distillation range. Current research on direct coal liquefaction circulating solvents primarily focuses on adding external solvents or using different cutting and hydrogenation methods. For example, patents CN103468315A and CN101333448A both use direct coal liquefaction oil with coal tar and petroleum / petroleum refining byproducts to prepare the coal liquefaction circulating solvent. Patents CN107118799A, CN106479564A, and CN105925304A use different distillation and cutting methods to prepare the coal liquefaction circulating solvent. Chinese patent CN1257252C uses a circulating solvent that is a fraction of coal liquefaction oil with a distillation range of 220-450°C after hydrogenation, and is used once to prepare an oil-coal slurry with a concentration of no more than 45%. The State Energy Group's world's first million-ton coal direct liquefaction demonstration unit uses a high-temperature solvent (>350°C) and a medium-temperature solvent (220-350°C) cut from the full-fraction coal direct liquefaction oil to prepare a circulating hydrogen supply solvent, which is then mixed with coal powder to prepare an oil-coal slurry with a concentration of no more than 45%. However, all of the above patents use a wide-fraction solvent once to prepare the oil-coal slurry, and the prepared oil-coal slurry has a low concentration.

[0004] In the industrial production equipment of direct coal liquefaction, increasing the coal slurry concentration is conducive to increasing the raw coal processing capacity and increasing the utilization rate of the reactor, thereby improving the overall economic benefits of the equipment. On the one hand, the concentration of the oil-coal slurry is related to the properties of the solvent, and on the other hand, the viscosity of the oil-coal slurry is closely related to its concentration. At present, the preheating of the oil-coal slurry in the direct coal liquefaction process mainly adopts a coal slurry heating furnace to heat the oil-coal slurry to 350-400℃ in one step. This process has a sharp increase in viscosity many times in the oil-coal slurry heating section, which increases the system resistance, resulting in the deterioration of local mass transfer and heat transfer conditions, uneven heating, and increased coal powder deposition and coking risks, reducing operational flexibility and affecting the safety and stability of oil-coal slurry preheating and transportation. Therefore, how to use a new method to configure the oil-coal slurry for direct coal liquefaction and have high operational flexibility during the heating process, and not easily cause operational risks due to the sharp increase in oil-coal slurry viscosity, is a key technical problem that needs to be solved urgently. Summary of the Invention

[0005] To address the problems existing in the prior art, the present invention provides a method for preparing and preheating an oil-coal slurry in a direct coal liquefaction process, as well as a direct coal liquefaction process. The method of the present invention enables stable preheating of high-concentration oil-coal slurries, improving the operational stability and effective utilization of the device.

[0006] To achieve its purpose, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing and preheating an oil-coal slurry in a direct coal liquefaction process, comprising the following steps:

[0008] (1) mixing the heavy fraction and the raw coal in an oil-coal slurry preparation tank to obtain an oil-coal slurry premix;

[0009] (2) feeding the oil-coal slurry premix, the first light fraction, and hydrogen into a coal slurry heater I and heating them to 250-300° C. to obtain an oil-coal slurry intermediate material;

[0010] (3) feeding the intermediate oil-coal slurry and the second light fraction obtained in step (2) into a coal slurry heater II and heating them to 350-400° C. to obtain an oil-coal slurry to be liquefied, and the oil-coal slurry to be liquefied is used to be fed to a liquefaction reactor of the direct coal liquefaction process;

[0011] The first light fraction is a light fraction I having a distillation range of 220-T1°C, and the second light fraction is the light fraction I or the light fraction II;

[0012] When the second light fraction is the light fraction I, T1 = 260-300°C, and the heavy fraction is a fraction with a distillation range of > T1°C;

[0013] When the second light fraction is the light fraction II, the light fraction II is a fraction section with a distillation range of T1-T2°C, and T1 = 250-270°C, T2 = 270-300°C, and T2 > T1; the heavy fraction is a fraction section with a distillation range > T2°C.

[0014] Furthermore, the heavy fraction, the light fraction I and the light fraction II are obtained by fractionating the coal liquefaction oil obtained in the liquefaction reactor after hydrogenation.

[0015] Furthermore, in step (1), the mass concentration of the oil-coal slurry premix is ​​55-60%.

[0016] In some embodiments, in step (2), based on the total mass of the heavy fraction used in step (1), the first light fraction used in step (2) and the second light fraction used in step (3), the mass percentage of the first light fraction is 4-10%, preferably 5-10%; the mass percentage of the second light fraction is 4-20%, preferably 5-20%.

[0017] In some embodiments, based on the total mass of the oil-coal slurry to be liquefied, the mass proportion of the first light fraction and the second light fraction is 5-20%, preferably 7-20%.

[0018] In some embodiments, in step (1), the temperature of the oil-coal slurry preparation tank is 70-100° C., preferably 75-85° C.; and the stirring and mixing time is, for example, 4 h to 10 h, preferably 6-8 h.

[0019] In some embodiments, in step (1), a catalyst is added when preparing the oil-coal slurry premix, and the catalyst accounts for 1-3 wt% of the mass of the dry coal.

[0020] In a preferred embodiment, when the second light fraction is the light fraction II, T2-T1>10°C;

[0021] In a preferred embodiment, in step (2), the coal is heated to 250-280° C. in the coal slurry heater I, and in step (3), the coal is heated to 350-380° C. in the coal slurry heater II.

[0022] The present invention also provides a direct coal liquefaction process, comprising the following steps:

[0023] (a) preparing the oil-coal slurry to be liquefied by the method described above;

[0024] (b) feeding the coal-oil slurry to be liquefied into a liquefaction reactor for liquefaction reaction to obtain coal liquefied oil;

[0025] (c) subjecting the coal liquefaction oil to a hydrogenation reaction and then fractionating it to obtain the light fraction I, the heavy fraction, and optionally the light fraction II; recycling a portion of the light fraction I as the first light fraction, recycling a portion of the light fraction I or the light fraction II as the second light fraction, and recycling the heavy fraction for preparing the oil-coal slurry premix.

[0026] In some embodiments, in step (b), the liquefaction reaction temperature is 430-460° C., the pressure is 13-22 MPa, and the residence time is 0.5-2 h;

[0027] In step (c), the temperature of the hydrogenation reaction is 360-400°C, the pressure is 13-22 MPa, and the volume space velocity is 0.5-2h -1 , hydrogen-to-oil ratio 400-1000.

[0028] The technical solution provided by the present invention has the following beneficial effects:

[0029] The present invention introduces heavy fractions and light fractions of specific distillation ranges at different stages during the preparation and preheating of the oil-coal slurry. The method of the present invention is used to prepare and preheat the oil-coal slurry, which helps to avoid coking and clogging during the preheating process and can effectively improve the operating cycle and operating stability of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Shown is a schematic diagram of a direct coal liquefaction process in one embodiment.

[0031] Description of some reference numerals:

[0032] 101: Oil-coal slurry preparation tank; 102: Coal slurry heater I; 103: Coal slurry heater II; 104: Liquefaction reactor; 105: Liquefaction separation unit; 106: Hydrogenation reaction unit; 107: Distillation cutting unit. DETAILED DESCRIPTION

[0033] In order to facilitate the understanding of the present invention, the present invention will be further described below in conjunction with examples. It should be understood that the following examples are only for a better understanding of the present invention and do not mean that the present invention is limited to the following examples.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one skilled in the art to which this invention belongs. The term "and / or" as may be used herein includes any and all combinations of one or more of the associated listed items. The terms "first," "second," etc., are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.

[0035] The present invention provides a method for preparing and preheating an oil-coal slurry in a direct coal liquefaction process, comprising the following steps:

[0036] (1) mixing the heavy fraction and the raw coal in an oil-coal slurry preparation tank to obtain an oil-coal slurry premix;

[0037] (2) feeding the oil-coal slurry premix, the first light fraction, and hydrogen into a coal slurry heater I and heating them to 250-300° C. to obtain an oil-coal slurry intermediate material;

[0038] (3) feeding the intermediate oil-coal slurry and the second light fraction obtained in step (2) into a coal slurry heater II and heating them to 350-400° C. to obtain an oil-coal slurry to be liquefied, and the oil-coal slurry to be liquefied is used to be fed to a liquefaction reactor of the direct coal liquefaction process;

[0039] The first light fraction is a light fraction I having a distillation range of 220-T1°C, and the second light fraction is the light fraction I or the light fraction II;

[0040] When the second light fraction is the light fraction I, T1 = 260-300°C (e.g., 260°C, 270°C, 280°C, 300°C, etc.), the heavy fraction is a fraction segment with a distillation range > T1°C;

[0041] When the second light fraction is the light fraction II, the light fraction II is a fraction segment with a distillation range of T1-T2°C, and T1 = 250-270°C (for example, 250°C, 260°C, 270°C, etc.), T2 = 270-300°C (for example, 270°C, 280°C, 300°C, etc.), and T2>T1; the heavy fraction is a fraction segment with a distillation range>T2°C.

[0042] In the prior art, the preparation of oil-coal slurry usually uses the entire distillation range >350°C of the coal direct liquefaction hydrogenation stabilized oil as the hydrogen supply solvent, and the insufficient part is supplemented by the solvent of the 220-350°C distillation range. The oil-coal slurry is mixed and prepared in a coal slurry tank at a concentration not exceeding 45%. When preparing oil-coal slurry in the prior art, if the coal slurry concentration is increased, it is very easy to cause coal powder precipitation and local blockage and coking during the heating process of the oil-coal slurry. The solvent distillation range used in the preparation of the oil-coal slurry is relatively wide, and the oil-coal slurry concentration is relatively low. After extensive research, the inventor's team found that different distillate segments in the range of 220°C-350°C have different effects on direct coal liquefaction. The lower temperature distillate segment has an efficient viscosity reduction effect, but in the longer high-concentration oil-coal slurry preparation stage, the low-temperature distillate segment has a significant swelling effect on the coal, and its swelling and viscosity-increasing effect is greater than its dissolution and viscosity-reducing effect; the middle distillate segment has a strong initial hydrogen supply effect, and the higher temperature distillate segment has a similar structure to the coal and has good solubility, and has the ability to efficiently dissolve and disperse the macromolecular structure of the coal and a strong hydrogen transfer effect under high temperature and high pressure. The inventors discovered that, during the preparation and preheating process of the oil-coal slurry, a high-concentration oil-coal slurry premix is ​​first prepared using a heavy fraction, and then a two-stage preheating is performed. First, a first light fraction is added to the oil-coal slurry premix and preheated to 250-300°C, which can reduce the viscosity of the oil-coal slurry and alleviate the initial preheating viscosity peak; the obtained oil-coal slurry intermediate material is mixed with the second light fraction and then preheated to 350-400°C, which can, on the one hand, reduce the second viscosity peak and, at the same time, preliminarily stabilize the small amount of free radical fragments produced by the pyrolysis of the coal at elevated temperature.

[0043] The present invention introduces heavy and light fractions of specific distillation ranges at different stages during the preparation and preheating of the oil-coal slurry. The heavy fraction can dissolve and disperse macromolecular coal structures, which is conducive to the preparation of a high-concentration oil-coal slurry. It has a strong hydrogen transfer effect under high temperature and high hydrogen pressure conditions, which has a significant effect on improving the direct coal liquefaction conversion rate and oil yield. The light fraction segment has a significant viscosity reduction effect on the oil-coal slurry, and because it contains partially saturated hydrogenated aromatic rings, it can provide hydrogen to stabilize the initial pyrolysis free radicals of coal in the early stage of coal liquefaction. The preparation and preheating of the oil-coal slurry using the method of the present invention is conducive to avoiding coking and clogging during the preheating process, and can effectively improve the operating cycle and operational stability of the device.

[0044] The inventors have found that if a heavy fraction is directly used to prepare a high-concentration oil-coal slurry without introducing a light fraction in the subsequent preheating stage, a sharp increase in viscosity will occur in the coal slurry heating furnace, affecting transportation and device stability; and if a light fraction is directly mixed with a heavy fraction and added once during the coal slurry preparation process to prepare a high-concentration oil-coal slurry, the low-temperature fraction will swell with the coal for a long time, and its swelling and viscosity-increasing effect will be greater than its dissolving and viscosity-reducing effect, and clogging and coking will still occur during the coal slurry heating process; in addition, if the oil-coal slurry concentration is reduced, the effective processing capacity of the device will be reduced. The present invention, through ingenious design, uses a heavy fraction segment solvent to prepare a high-concentration oil-coal slurry, and combines it with two-stage preheating. A small amount of light fraction segment solvent is added in each of the two preheating stages of the oil-coal slurry. While ensuring the effective utilization rate of the device, it can slow down the sharp increase in viscosity of the oil-coal slurry as it heats up, thereby achieving the purpose of smoothly preheating the high-concentration oil-coal slurry. The method of the present invention can give full play to the role of different fraction segments of the direct coal liquefaction circulating solvent, and significantly improve the stability and efficiency of the device.

[0045] Furthermore, the heavy fraction, the light fraction I and the light fraction II are obtained by fractionating the coal liquefaction oil obtained in the liquefaction reactor after hydrogenation.

[0046] The method of the present invention can prepare a high-concentration oil-coal slurry, and can smoothly preheat the high-concentration oil-coal slurry without causing problems such as equipment clogging and coking. Preferably, in step (1), the mass concentration of the oil-coal slurry premix is ​​55-60%. The method of the present invention can alleviate the problem of a sharp increase in viscosity of the high-concentration oil-coal slurry during the two preheating and reheating processes (i.e., the two preheating stages), avoiding coking and clogging problems.

[0047] In some embodiments, in step (2), based on the total mass of the heavy fraction used in step (1), the first light fraction used in step (2), and the second light fraction used in step (3), the mass percentage of the first light fraction is 4-10%, for example, 4%, 5%, 7%, 8%, 10%, etc., preferably 5-10%; the mass percentage of the second light fraction is 4-20%, for example, 4%, 5%, 10%, 15%, 20%, etc., preferably 5-20%. Adding the first and second light fractions in the above preferred amounts at two different stages of preheating is beneficial to further improve the smooth preheating effect of the oil-coal slurry, further improve the operating stability of the device, etc. In some examples, the mass percentage of the second light fraction is higher than the mass percentage of the first light fraction, which is beneficial to further improve the smooth preheating effect and further improve the operating stability of the device.

[0048] The inventors found in their research that during the preheating temperature rise process, the oil-coal slurry will have two temperature ranges where the viscosity increases sharply, resulting in a significant increase in the transport resistance. At the same time, a too fast heating rate will also cause the oil-coal slurry to have poor local heat and mass transfer in the heating furnace, increasing the risk of coking and clogging. The temperature range of the first viscosity peak is between 140-230°C, and the second viscosity peak is between 280-350°C. The inventors found that during the preparation and preheating process of the oil-coal slurry, two stages of preheating are carried out in the coal slurry heaters I and II according to a certain temperature span, and solvents with specific distillation characteristics are added at different stages, which can effectively avoid the coking and clogging problem during the preheating process and improve the preheating stability. Moreover, the method of the present invention is easy to stably prepare a high-concentration oil-coal slurry, for example, the mass concentration of the oil-coal slurry to be liquefied is above 47%, for example, 47-54%, for example, about 47-48%. The present invention cleverly designs the preheating as a stage preheating with a specific temperature span, and introduces solvents with different distillation characteristics during the preparation of the oil-coal slurry and in different preheating stages. This can effectively slow down the sharp increase in viscosity of the oil-coal slurry during preheating, preheat the oil-coal slurry smoothly, and improve the stability of the device and the operational flexibility.

[0049] In a preferred embodiment, based on the total mass of the oil-coal slurry to be liquefied, the sum of the mass proportions of the first light fraction and the second light fraction is 5-20%, preferably 7-20%.

[0050] Furthermore, in step (1), a catalyst is added when preparing the oil-coal slurry premix. The catalyst can be any catalyst type known in the art of direct coal liquefaction, without particular limitation. The catalyst can be used in an amount conventionally used in the art, for example, the catalyst accounts for 1-3 wt % of the mass of the dry coal. In the present invention, the "mass concentration of the oil-coal slurry premix," "mass concentration of the oil-coal slurry to be liquefied," and "oil-coal slurry concentration" are all based on the total content of coal and catalyst in the corresponding slurry.

[0051] In some embodiments, in step (1), the temperature of the oil-coal slurry preparation tank is 70-100° C., preferably 75-85° C.; and the stirring and mixing time is, for example, 4 h to 10 h, preferably 6-8 h.

[0052] In the present invention, when the second light fraction is the light fraction II, the light fraction II is a fraction with a distillation range of T1-T2°C, and T1 = 250-270°C, T2 = 270-300°C, and T2>T1; preferably, T2-T1>10°C.

[0053] In a preferred embodiment, in step (2), the temperature is heated to 250-280° C. in the coal slurry heater I, and in step (3), the temperature is heated to 350-380° C. in the coal slurry heater II.

[0054] In some examples, the oil-coal slurry premix obtained in step (1) can be fed into the inlet of the coal slurry heater I in step (2) via a high-pressure delivery pump, and the first light fraction is mixed with the oil-coal slurry premix at the inlet; the oil-coal slurry intermediate material and the second light fraction are mixed at the inlet of the coal slurry heater II.

[0055] In step (2), the amount of hydrogen introduced is determined according to the corresponding pressure required by the liquefaction reactor of the downstream coal direct liquefaction process, and the amount of hydrogen corresponds to the pressure of the downstream liquefaction reactor.

[0056] The present invention also provides a direct coal liquefaction process, comprising the following steps:

[0057] (a) preparing the oil-coal slurry to be liquefied by the preparation method described above;

[0058] (b) feeding the coal-oil slurry to be liquefied into a liquefaction reactor for liquefaction reaction to obtain coal liquefied oil;

[0059] (c) subjecting the coal liquefaction oil to a hydrogenation reaction and then fractionating (e.g., distillation cutting) to obtain the light fraction I, the heavy fraction, and optionally the light fraction II; recycling a portion of the light fraction I as the first light fraction, recycling a portion of the light fraction I or the light fraction II as the second light fraction, and recycling the heavy fraction for preparing the oil-coal slurry premix.

[0060] During the fractionation process in step (c), a low-temperature fraction, i.e., a fraction with a temperature less than 220°C, is also cut to obtain. In some examples, the entire heavy fraction obtained by fractionation is used to prepare the coal-oil slurry premix, and portions of light fraction I and optional light fraction II are used as the first and second light fractions, respectively. The remaining portion is mixed with the low-temperature fraction to form the coal liquefaction product oil.

[0061] In the direct coal liquefaction process of the present invention, the liquefaction reaction of step (b) and the hydrogenation reaction of step (c) can be carried out using corresponding process operations, conditions and catalysts well known in the art, and there are no special restrictions on this. In some embodiments, in step (b), the temperature of the liquefaction reaction is 430-460°C, the pressure is 13-22MPa, and the residence time is 0.5-2h. The hydrogenation reaction of step (c) is, for example, full-fraction hydrogenation; in some embodiments, in step (c), the temperature of the hydrogenation reaction is 360-400°C, the pressure is 13-22MPa, and the volume space velocity is 0.5-2h -1 , a hydrogen-to-oil ratio of 400-1000. Specifically, in step (b), the product obtained from the liquefaction reaction is separated in a liquefaction separation unit to separate water, gas, and residue to obtain coal liquefied oil for subsequent hydrogenation reaction; the above separation treatment of the product obtained from the liquefaction reaction is a conventional technique in the art and will not be described in detail here.

[0062] In the present invention, the coal includes but is not limited to coals of various metamorphic degrees or different microscopic components.

[0063] At the beginning of the coal direct liquefaction process, before the circulation is established, a mixed solvent of anthracene oil and wash oil in a mass ratio of 1:1 can be used as the starting solvent to prepare the oil-coal slurry. As the coal direct liquefaction process proceeds, the coal liquefaction oil obtained subsequently is hydrogenated and fractionated to obtain a light fraction I, a heavy fraction and an optional light fraction II of the corresponding distillation range, and these fractions are used as solvents to carry out direct coal liquefaction according to the process of the present invention. Unless otherwise specified in the embodiments below, at the beginning of the coal direct liquefaction process, the mixed solvent of anthracene oil and wash oil in the mass ratio of 1:1 is used as the starting solvent to replace the solvent in each link. After the circulation is established, it is replaced with the corresponding fraction of the corresponding distillation range.

[0064] After extensive research, the inventors found that the coal liquefaction oil obtained in the coal direct liquefaction process is subjected to full-fraction hydrogenation and then cut into specific light fractions and heavy fractions. The heavy fraction can effectively disperse the small molecular products of direct coal liquefaction at high temperature, has the effect of efficiently transferring hydrogen, and significantly improves the coal liquefaction performance; the light fraction has a significant effect on reducing the viscosity of the oil-coal slurry, but it is easily gasified in the high-temperature section of direct coal liquefaction, which reduces the hydrogen partial pressure and is not conducive to the liquefaction reaction; in the present invention, a high-concentration oil-coal slurry premix is ​​prepared using heavy fractions, which is then preheated in two stages, and a small amount of light solvent of a specific distillation range is added in each preheating stage to slow down the sharp increase in viscosity of the oil-coal slurry during the preheating process, while reducing the excessive addition of light solvent, which causes the light solvent to enter the liquefaction reactor and reduce the hydrogen partial pressure due to gasification, resulting in hydrogen transfer that is not conducive to the liquefaction reaction; in addition, the remaining light fraction can be further used as a product for downstream hydrogenation and quality improvement, which can increase the yield of the liquefied product and improve the overall efficiency of the device.

[0065] The present invention is further illustrated below by examples and comparative examples, but it should not be understood that the present invention is limited to these examples.

[0066] Where specific experimental steps or conditions are not specified in the examples, the corresponding conventional experimental steps or conditions in the art can be used. Reagents or instruments used without specifying the manufacturer are all commercially available conventional products.

[0067] Coal quality of Shendong coal—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.

[0068] In the following examples, the amount of hydrogen introduced in step S2 is determined according to the pressure required by the downstream liquefaction reactor.

[0069] Example 1

[0070] See the process flow diagram for Figure 1 The following steps are included:

[0071] S1: Shenhua coal, iron oxide catalyst (1 wt% of dry coal mass) and heavy fraction with a distillation range of >270°C are stirred and mixed in an oil-coal slurry preparation tank to prepare an oil-coal slurry premix. The temperature of the oil-coal slurry preparation tank is controlled at 70°C and the stirring time is 4 hours. The mass concentration of the obtained oil-coal slurry premix is ​​55%.

[0072] S2: The prepared oil-coal slurry premix, light fraction I with a distillation range of 220-250°C, and hydrogen are pressurized as needed and fed into the coal slurry heater I, where the temperature is raised to 250°C to obtain an oil-coal slurry intermediate material;

[0073] S3: The intermediate oil-coal slurry is mixed with the light fraction II having a distillation range of 250-270°C, and the mixture is heated to 350°C in the coal slurry heater II to obtain the oil-coal slurry to be liquefied;

[0074] Wherein, based on the total mass of the heavy fraction in step S1, the light fraction I in step S2 and the light fraction II in step S3, the addition amount of the light fraction I in step S2 accounts for 5%, and the addition amount of the light fraction II in step S3 accounts for 5%.

[0075] The mass concentration of the oil-coal slurry to be liquefied is 52%.

[0076] S4: The obtained oil-coal slurry to be liquefied is fed into the liquefaction reactor of the liquefaction unit for liquefaction reaction. The liquefaction reaction temperature is 455.0°C, the pressure is 19.0 MPa, and the residence time is 1.0 h.

[0077] The product obtained from the liquefaction reaction is separated (in the liquefaction separation unit) to separate the water, gas and residue. The obtained coal liquefaction oil is subjected to full fraction hydrogenation in the hydrogenation reaction unit. The hydrogenation reaction temperature is 375°C, the pressure is 19 MPa, and the volume space velocity is 1.1 h -1 , the hydrogen-to-oil ratio is 400, and the hydrogenation catalyst is commercial Ni-Mo / Al2O3 (HRK658 from Axens); the resulting product is then distilled and cut in a distillation cutting unit into a low-temperature distillate section <220°C, a light distillate I (distillation range 220-250°C), a light distillate II (distillation range 250-270°C) and a heavy distillate (distillation range >270°C); wherein the heavy distillate is entirely recycled for preparing the oil-coal slurry premix in step S1, part of the light distillate I is conveyed to the coal slurry heater I, part of the light distillate II is conveyed to the coal slurry heater II, and the remaining light distillates I and II are mixed with the low-temperature distillate section as coal liquefaction product oil.

[0078] Example 2

[0079] S1: Shenhua coal, iron oxide catalyst (1 wt% of dry coal mass) and heavy fraction with a distillation range of >300°C are stirred and mixed in an oil-coal slurry preparation tank to prepare an oil-coal slurry premix. The temperature of the oil-coal slurry preparation tank is controlled at 100°C and the stirring time is 10 hours. The mass concentration of the obtained oil-coal slurry premix is ​​60%.

[0080] S2: The prepared oil-coal slurry premix, light fraction I with a distillation range of 220-270°C, and hydrogen are pressurized as needed and fed into the coal slurry heater I, where the temperature is raised to 280°C to obtain an oil-coal slurry intermediate material;

[0081] S3: The intermediate oil-coal slurry is mixed with the light fraction II having a distillation range of 270-300°C, and the mixture is heated to 400°C in the coal slurry heater II to obtain the oil-coal slurry to be liquefied;

[0082] Wherein, based on the total mass of the heavy fraction in step S1, the light fraction I in step S2 and the light fraction II in step S3, the addition amount of the light fraction I in step S2 accounts for 10%, and the addition amount of the light fraction II in step S3 accounts for 15%.

[0083] The mass concentration of the oil-coal slurry to be liquefied is 48%.

[0084] S4: The obtained oil-coal slurry to be liquefied is fed into the liquefaction reactor of the liquefaction unit for liquefaction reaction (reaction conditions refer to Example 1); water, gas and residue are separated from the product obtained by the liquefaction reaction, and the obtained coal liquefaction oil is subjected to full-fraction hydrogenation (reaction conditions refer to Example 1) and then distilled and cut into a low-temperature distillate section <220°C, a light distillate I (distillation range 220-270°C), a light distillate II (distillation range 270-300°C) and a heavy distillate (distillation range >300°C); wherein the heavy distillate is entirely recycled for preparing the oil-coal slurry premix in step S1, part of the light distillate I is fed to the coal slurry heater I, part of the light distillate II is fed to the coal slurry heater II, and the remaining light distillates I and II are mixed with the low-temperature distillate section as the coal liquefaction product oil.

[0085] Example 3

[0086] S1: Shenhua coal, iron oxide catalyst (1 wt% of the dry coal mass) and heavy fraction with a distillation range of >280°C are stirred and mixed in an oil-coal slurry preparation tank to prepare an oil-coal slurry premix. The temperature of the oil-coal slurry preparation tank is controlled at 85°C, and the stirring time is 6 hours. The mass concentration of the obtained oil-coal slurry premix is ​​58%.

[0087] S2: The prepared coal-oil slurry premix, light fraction I with a distillation range of 220-280°C, and hydrogen are pressurized as needed and fed into the coal slurry heater I, where the temperature is raised to 250°C to obtain an intermediate coal-oil slurry material;

[0088] S3: The intermediate oil-coal slurry is mixed with the light fraction I with a distillation range of 220-280°C, and the mixture is heated to 350°C in the coal slurry heater II to obtain the oil-coal slurry to be liquefied;

[0089] Among them, based on the total mass of the heavy fraction in step S1, the light fraction I in step S2 and the light fraction I in step S3, the addition amount of the light fraction I in step S2 accounts for 8%, and the addition amount of the light fraction I in step S3 accounts for 15%.

[0090] The mass concentration of the oil-coal slurry to be liquefied is 47.2%.

[0091] S4: The obtained oil-coal slurry to be liquefied is fed into the liquefaction reactor of the liquefaction unit for liquefaction reaction (reaction conditions refer to Example 1); water, gas and residue are separated from the product obtained from the liquefaction reaction, and the obtained coal liquefaction oil is subjected to full-fraction hydrogenation (reaction conditions refer to Example 1) and then distilled and cut into a low-temperature fraction section <220°C, a light fraction I (distillation range 220-280°C) and a heavy fraction (distillation range >280°C); wherein the heavy fraction is entirely recycled for the preparation of the oil-coal slurry premix in step S1, and part of the light fraction I is fed to the coal slurry heater I and the coal slurry heater II, and the remaining light fraction I is mixed with the low-temperature fraction section as the coal liquefaction product oil.

[0092] Example 4

[0093] The same method as in Example 1 was used, except that, based on the total mass of the heavy fraction in step S1, the light fraction I in step S2, and the light fraction II in step S3, the light fraction I in step S2 was added in an amount of 4%, and the light fraction II in step S3 was added in an amount of 4%. The mass concentration of the oil-coal slurry to be liquefied was 50.9%.

[0094] Comparative Example 1

[0095] S1: Shenhua coal, iron oxide catalyst (1wt% of dry coal mass) and circulating solvent are prepared into an oil-coal slurry in an oil-coal slurry preparation tank. The circulating solvent is a mixture of a distillation range of 220-350°C fraction and a distillation range of >350°C fraction in a mass ratio of 3:1. The temperature of the oil-coal slurry preparation tank is controlled at 70°C, the stirring time is 4h, and the mass concentration of the obtained oil-coal slurry is 50%.

[0096] S2: The prepared oil-coal slurry and hydrogen are directly pressurized as needed and enter the coal slurry preheater to be heated to 350°C;

[0097] S3: After heating, the coal-oil slurry enters the liquefaction reactor of the liquefaction unit for liquefaction reaction (reaction conditions refer to Example 1). Water, gas, and residue are separated from the liquefaction reaction product. The resulting coal liquefaction oil is subjected to full-fraction hydrogenation (reaction conditions refer to Example 1) and then distilled to form a low-temperature distillate segment with a distillation range of <220°C, a medium-temperature distillate segment with a distillation range of 220-350°C, and a heavy distillate segment with a distillation range of >350°C. The medium-temperature distillate segment and the heavy distillate segment are recycled to prepare the circulating solvent in step S1.

[0098] Comparative Example 2

[0099] S1: Shenhua coal, iron oxide catalyst (1 wt% of dry coal mass) and circulating solvent are prepared into an oil-coal slurry preparation tank. The circulating solvent has a distillation range of >260°C. The temperature of the oil-coal slurry preparation tank is controlled at 70°C. The stirring time is 4 hours. The mass concentration of the oil-coal slurry is 55%.

[0100] S2: The prepared oil-coal slurry and hydrogen are pressurized as needed and enter the coal slurry preheater to be heated to 350°C;

[0101] S3: After heating, the oil-coal slurry enters the liquefaction reactor of the liquefaction unit for liquefaction reaction (reaction conditions refer to Example 1), and the water, gas and residue in the liquefaction reaction product are separated. The obtained coal liquefaction oil is subjected to full-fraction hydrogenation (reaction conditions refer to Example 1) and then cut into a fraction segment with a distillation range of ≤260°C and a fraction segment with a distillation range of >260°C. The fraction segment with a distillation range of >260°C is recycled for preparing the circulating solvent in step S1.

[0102] Comparative Example 3

[0103] The process was carried out with reference to Example 1. The difference from Example 1 was that the light fraction I and the light fraction II were added when preparing the oil-coal slurry premix in step S1; the light fraction I was not added in step S2, and the light fraction II was not added in step S3.

[0104] Comparative Example 4

[0105] The process is carried out with reference to Example 1. The difference from Example 1 is that the light fraction I is added when preparing the oil-coal slurry premix in step S1; and the light fraction I is not added in step S2.

[0106] Comparative Example 5

[0107] The process was carried out with reference to Example 1, except that the order of adding the light fraction I and the light fraction II was reversed.

[0108] Comparative Example 6

[0109] The process was carried out with reference to Example 1, except that the light fraction II was not added in step S3.

[0110] Comparative Example 7

[0111] The process is carried out with reference to Example 3. The difference from Example 3 is that the corresponding amount of light fraction I added in step S3 is adjusted to be added to S2, and the corresponding amount of light fraction I is no longer added in step S3.

[0112] Comparative Example 8

[0113] The process was carried out with reference to Example 1, except that the distillation range of the light fraction I was 220-230°C, the distillation range of the light fraction II was 230-330°C, the distillation range of the heavy fraction was >330°C, and the distillation range of the low temperature fraction was <220°C.

[0114] By comparing the oil-coal slurry concentrations, the coking conditions of the oil-coal slurry preheater and the oil-coal slurry reheater prepared in the test devices of the embodiments and comparative examples, the following results were obtained:

[0115] Table 1 Device operation results

[0116]

[0117] Note: In Table 1, "Operation Time" refers to the duration of the process operation in each Example or Comparative Example. "Coal Slurry Heater I Operation Status" and "Coal Slurry Heater II Operation Status" refer to the corresponding operating status of the equipment at the corresponding "Operation Time". "Stable" means that the corresponding equipment can operate normally.

[0118] From the above examples and comparative examples, it can be seen that:

[0119] 1) If light fraction I and light fraction II are added during the preparation of the oil-coal slurry premix, the operating conditions of coal slurry heaters I and II are both poor, with a large amount of coal powder deposited and blocked coking areas;

[0120] 2) If the light fraction I is added during the preparation of the oil-coal slurry premix, the coal slurry heater I may not operate for a long time due to the prolonged swelling of the light solvent and the coal.

[0121] 3) If the order of adding light fraction I and light fraction II is swapped, the second heater will be operated in a poor condition and cannot be operated for a long time due to the serious gasification of light fraction I in coal slurry heater II.

[0122] It will be readily understood that the above embodiments are merely examples for clarity of description and are not intended to limit the present invention to these examples. Those skilled in the art will readily appreciate that other variations or modifications based on the above description are possible. It is not necessary and impossible to provide an exhaustive list of all possible implementations. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A method for preparing and preheating coal-oil slurry in a direct coal liquefaction process, characterized in that: The steps include: (1) mixing the heavy fraction and the raw coal in an oil-coal slurry preparation tank to obtain an oil-coal slurry premix; (2) feeding the oil-coal slurry premix, the first light fraction, and hydrogen into a coal slurry heater I and heating them to 250-300° C. to obtain an oil-coal slurry intermediate material; (3) feeding the intermediate oil-coal slurry and the second light fraction obtained in step (2) into a coal slurry heater II and heating them to 350-400° C. to obtain an oil-coal slurry to be liquefied, and the oil-coal slurry to be liquefied is used to be fed to a liquefaction reactor of the direct coal liquefaction process; The first light fraction is a light fraction I having a distillation range of 220-T1°C, and the second light fraction is the light fraction I or the light fraction II; When the second light fraction is the light fraction I, T1 = 260-300°C, and the heavy fraction is a fraction with a distillation range of > T1°C; When the second light fraction is the light fraction II, the light fraction II is a fraction section with a distillation range of T1-T2°C, and T1 = 250-270°C, T2 = 270-300°C, and T2 > T1; the heavy fraction is a fraction section with a distillation range > T2°C.

2. The method according to claim 1, characterized in that The heavy fraction, the light fraction I and the light fraction II are obtained by fractionating the coal liquefaction oil obtained in the liquefaction reactor after hydrogenation.

3. The method according to any one of claims 1-2, characterized in that In step (1), the mass concentration of the oil-coal slurry premix is ​​55-60%.

4. The method according to any one of claims 1 to 2, characterized in that In step (2), based on the total mass of the heavy fraction used in step (1), the first light fraction used in step (2) and the second light fraction used in step (3), the mass percentage of the first light fraction is 4-10%; the mass percentage of the second light fraction is 4-20%.

5. The method according to claim 4, characterized in that In step (2), based on the total mass of the heavy fraction used in step (1), the first light fraction used in step (2) and the second light fraction used in step (3), the mass percentage of the first light fraction is 5-10%; the mass percentage of the second light fraction is 5-20%.

6. The method according to claim 4, characterized in that Based on the total mass of the oil-coal slurry to be liquefied, the total mass proportion of the first light fraction and the second light fraction is 5-20%.

7. The method according to claim 6, characterized in that Based on the total mass of the oil-coal slurry to be liquefied, the total mass proportion of the first light fraction and the second light fraction is 7-20%.

8. The method according to any one of claims 1-2, characterized in that In step (1), the temperature of the oil-coal slurry preparation tank is 70-100°C.

9. The method according to claim 8, characterized in that In step (1), the temperature of the oil-coal slurry preparation tank is 75-85°C.

10. The method according to claim 8, characterized in that In step (1), the stirring and mixing time is 4h-10h.

11. The method according to claim 10, characterized in that In step (1), the stirring and mixing time is 6-8 hours.

12. The method according to any one of claims 1-2, characterized in that In step (1), a catalyst is added when preparing the oil-coal slurry premix, and the catalyst accounts for 1-3 wt% of the mass of the dry coal.

13. The method according to any one of claims 1-2, characterized in that When the second light fraction is the light fraction II, T2-T1>10°C; And / or, in step (2), the coal is heated to 250-280° C. in the coal slurry heater I, and in step (3), the coal is heated to 350-380° C. in the coal slurry heater II.

14. A direct coal liquefaction process, characterized in that: The steps include: (a) preparing the oil-coal slurry to be liquefied by the method according to any one of claims 1 to 13; (b) feeding the coal-oil slurry to be liquefied into a liquefaction reactor for liquefaction reaction to obtain coal liquefied oil; (c) subjecting the coal liquefaction oil to a hydrogenation reaction and then fractionating it to obtain the light fraction I, the heavy fraction, and optionally the light fraction II; recycling a portion of the light fraction I as the first light fraction, recycling a portion of the light fraction I or the light fraction II as the second light fraction, and recycling the heavy fraction for preparing the oil-coal slurry premix.

15. The direct coal liquefaction process according to claim 14, characterized in that: In step (b), the liquefaction reaction temperature is 430-460° C., the pressure is 13-22 MPa, and the residence time is 0.5-2 h; In step (c), the temperature of the hydrogenation reaction is 360-400°C, the pressure is 13-22 MPa, and the volume space velocity is 0.5-2h -1 , hydrogen-to-oil ratio 400-1000.

Images