Coal-to-liquids desolidification purification process

Abstract

The application discloses a coal-to-oil desolidification and purification process, and belongs to the technical field of coal-to-oil treatment. The process aims to solve the problems of difficult efficient removal of fine solid particles in coal-to-oil products, easy plugging of filters and insufficient resource recovery. The technical scheme mainly comprises the following steps: separating gas phase and liquid phase of the product after hydrogenation reaction of coal slurry through flash separation; performing solid-liquid separation on the liquid phase through a high-precision filter, and regenerating the filter by adopting two-stage online washing (including washing oil replacement and nitrogen pulse backwashing); finally, distilling the filtered liquid to obtain products, and performing sedimentation separation and drying on the filter residue, so that the solvent can be recycled. The method is mainly used for purification treatment of coal-to-oil products, and can effectively improve the oil quality and reduce the operation cost.

Description

Technical Field

[0001] This invention relates to the field of coal-to-oil processing technology, specifically to a coal-to-oil desolidification and purification process. Background Technology

[0002] In the field of coal-to-oil technology, the removal of solid particles is always a crucial step in the entire process, from coal slurry preparation and hydrogenation to product separation. The reaction products contain unreacted coal powder, catalyst particles, and ash, among other solid impurities with a wide particle size distribution. Some micron- and submicron-sized particles are difficult to remove effectively using conventional separation methods. Traditional centrifugal separation and ordinary filtration technologies have limited efficiency in capturing small particles. These residual solid impurities directly affect the quality of subsequent oil products and lead to scaling and clogging in downstream distillation towers, heat exchangers, and other equipment, impacting the long-term stable operation of the unit.

[0003] To achieve more efficient solid-liquid separation, high-precision filters have been used in industry. However, the coal-to-oil product system is complex, and its heavy components such as asphaltenes and colloids easily combine with fine solid particles. During filtration, these components not only form a surface filter cake but also gradually penetrate and clog the internal pores of the filter media. Conventional regeneration methods such as backwashing or simple air blowing mainly remove surface deposits and are ineffective at removing complex contaminants retained deep within the filter media. As operating time increases, the transmembrane pressure difference of the filter grows rapidly, requiring frequent cleaning or filter element replacement, which not only increases operating costs but also affects the continuity of production. How to achieve effective online cleaning and regeneration of filters and maintain their long-term stable separation performance is a pressing problem that needs to be solved.

[0004] In the filtration and washing process, the selection of washing media and the recycling method directly affect the operational economy and efficiency. A certain amount of solid waste liquid is generated during production, containing recyclable solvent oil components. Direct disposal leads to resource waste and increased treatment costs; simple recycling, however, may result in the accumulation of solid impurities within the system, especially when used for rinsing precision filters, where inferior washing media can potentially cause secondary contamination of the filter element. Therefore, a reasonable separation and recycling strategy is needed to achieve high-quality recovery and utilization of the effective components in the waste liquid.

[0005] Furthermore, the parameter control of multiple operating units in the process is interconnected, collectively affecting the final overall solidification effect. For example, the coal slurry formulation directly affects its transportability and reaction efficiency; the temperature and pressure conditions of the hydrogenation reaction determine the oil conversion rate and impurity morphology; and the operational stability of flash separation affects the feed state of subsequent filtration units. Improper control of these parameters can exacerbate the refinement, emulsification, or tight binding of solid particles with the oil, thus creating greater difficulties for subsequent separation steps. The stable operation of the entire system depends on the coordinated optimization of each unit's operation.

[0006] In summary, existing technologies face multiple challenges in addressing the solidification issue in coal-to-oil conversion, including insufficient removal efficiency of fine particles, irreversible deep clogging of high-precision filters with difficulties in regeneration, challenges in the efficient separation and resource recovery of washing media and solid waste, and complex multi-process collaborative control. These problems restrict the technical and economic viability and long-term operational reliability of coal-to-oil plants. Summary of the Invention

[0007] This invention provides a solids removal and purification process for coal-to-oil, aiming to solve the problems of difficulty in removing micron-sized solids, easy clogging of filters, high energy consumption, and difficulty in recovering effective components from waste liquid in coal-to-oil.

[0008] This addresses the problem of inconsistent properties of recycled solvent oils and the resulting poor backflushing effect or resource waste due to mixing.

[0009] This addresses the problem of poor fluidity and low reaction efficiency caused by an improper solid-liquid ratio in coal slurry preparation.

[0010] This addresses the problem of low conversion rate, excessive byproducts, or excessive energy consumption caused by improper control of hydrogenation reaction conditions.

[0011] This solves the problems of inaccurate fixed threshold triggering for washing and poor nitrogen backflushing effect at room temperature.

[0012] This addresses the problem of incomplete removal of stubborn organic residues by hot nitrogen.

[0013] This solves the problem of large pressure fluctuations in pipeline nitrogen, which leads to unstable backflushing pressure and unreliable results when using it directly.

[0014] This solves the problem of the buffer tank being unable to maintain the set backflush pressure due to insufficient air supply pressure.

[0015] This addresses the issue of potential contamination of the clean backflushing nitrogen system when using factory compressed air as a power source.

[0016] To achieve these and other advantages according to the present invention, a coal-to-oil desolidification and purification process is provided, comprising the following steps:

[0017] S1. After the raw coal is processed in the coal preparation process, coal powder is used as raw material, a catalyst is added, and it is mixed with solvent oil to make coal slurry.

[0018] S2. After the coal slurry is mixed with hydrogen, it enters the reactor to react and produce coal-to-oil containing unreacted coal powder, catalyst and ash.

[0019] S3. After the coal-to-oil process is depressurized to 1.8–2.2 MPa by a pressure reducing valve, it is fed into a flash tank. The gas and liquid phases are separated by a spiral guide plate. The gas phase is discharged from the top of the tank, and after the light oil is recovered by the condenser, the non-condensable gas is returned to the reactor for recycling. At the same time, the liquid phase is maintained at 50–70% of the height of the flash tank.

[0020] S4. The liquid in the flash tank is output to a high-precision filter, which uses a filter element with a filtration accuracy of 0.05–0.15 μm for solid-liquid separation. Simultaneously, the feed time (set threshold 120–180 min; if the coal slurry throughput increases by 10%, this can be shortened to 100–160 min; if the throughput decreases by 10%, it can be extended to 140–200 min) or the pressure difference between the inlet and outlet of the filter element (triggered by a pressure difference change rate of 0.5–1.0 kPa / min) is monitored in real time. When either the feed time or the pressure difference reaches the set threshold (if the feed time reaches the threshold first but the pressure difference change rate does not exceed the limit, washing can be delayed by 10–15 min before initiating (observing the pressure difference change); if the pressure difference change rate exceeds the limit first but the feed time has not yet arrived, washing should be initiated immediately to ensure the filter element does not become deeply clogged), a secondary online washing process is initiated, ensuring the filter contains only washing oil and solids.

[0021] First-stage washing involves adding washing oil (cyclohexane can be added, at a rate of 5-8% of the washing oil's mass, cyclohexane purity ≥99.5%, industrial grade) at a concentration of 1.8-2.2... MPa pressure enters from the filter feed side. The filter volume V1 and the injected washing oil volume V2 are related in the order V1≤V2≤2V1, displacing residual coal-derived oil. Cyclohexane dissolves the colloidal complexes on the filter element surface and in the pores. Cyclohexane is miscible with coal-derived oil and solvent oil, so it does not need to be separated separately and can be recycled with the solvent oil. If cyclohexane is lost during the recycling process (loss rate is about 0-2% / cycle), it can be replenished to the washing oil storage tank with fresh cyclohexane. The distillation range of cyclohexane is 80.7℃, which is significantly different from the distillation range of light oil and solvent oil in coal-derived oil. During the S5 atmospheric distillation process (top temperature 180-200℃), cyclohexane is distilled out with light oil and separated from solvent oil after condensation. No additional separation equipment is needed, and it can be directly recycled to the washing oil storage tank.

[0022] Secondary washing involves introducing nitrogen gas at a pressure of 2.2–2.6 MPa from the outlet side of the filter (nitrogen preheating method: using an electric heater or a steam heater, with the preheating temperature controlled at 80–120℃ and the preheating time at 5–10 min, ensuring that the temperature fluctuation when the nitrogen enters the filter is ≤±5℃), with a pulse duration of 15–40 s, to backflush all the sludge and liquid in the filter to the sludge and liquid tank;

[0023] The primary and secondary washing processes work together to form a deep cleaning mechanism. The primary washing replaces residual oil and dissolves colloids on the surface, while the secondary washing removes deep blockages.

[0024] S5. The filtrate is transferred to a distillation tower for atmospheric and vacuum distillation to obtain light oil and asphalt products. Simultaneously, the filter residue is transferred to a settling tank and allowed to stand for 30–90 minutes. The settling time is adjusted according to the solid content of the filter residue: 30–60 minutes for solids ≤10%, and 60–90 minutes for solids >10%, ensuring the solid content of the upper solvent oil is ≤1%.

[0025] S6. Extract the solvent oil with a solid content ≤1% from the top of the settling tank and transfer it to a dedicated backflushing storage tank (volume 0.3~0.8 m³). 3 It is connected in series with the washing oil storage tank and is equipped with a liquid level interlock: when the liquid level in the backflushing tank is lower than 1 / 3, oil is automatically replenished from the washing oil storage tank. It is dedicated to the first-level washing operation of S4. At the same time, the high solid content liquid at the bottom of the settling tank is heated and then transported to the drying equipment. The solid phase is made into dry powder product, and the gas phase is cooled and then enters the coal slurry raw material tank for recycling and raw material preparation. Among them, the backflushing tank needs to be equipped with a pre-filter with a filtration accuracy of 0.01 μm to avoid trace solids from entering the washing oil and causing secondary pollution of the filter element.

[0026] The backflushing tank and the washing oil tank are connected in series and a liquid level interlock is set up: when the liquid level in the backflushing tank is lower than 1 / 3, the solvent oil recovered from the settling tank in the washing oil tank is used to replenish the oil first; if the amount of solvent oil recovered from the settling tank is insufficient, then the reduced-pressure distillation oil produced is added.

[0027] In this technical solution, the two-stage online washing forms a step-by-step deep cleaning mechanism: the first stage washing (mechanical peeling + solvent dissolution) is: high-pressure washing oil impacts the filter cake on the surface of the filter element, while cyclohexane penetrates and dissolves the colloidal complex; the second stage washing (gas expansion) is: the impact force of the adiabatic expansion of hot nitrogen gas is used to peel off and break up the deep blockage, so as to achieve complete regeneration of the filter element.

[0028] Preferably, the coal-to-oil desolidification and purification process of the present invention further includes the step of:

[0029] S7. The reduced-pressure distillation oil with a distillation range of 260℃ to 320℃ obtained from S5 is recycled as washing oil and used for the first-stage washing of S4.

[0030] Preferably, in the coal-to-oil desolidification and purification process of the present invention, in S6, the upper solvent oil with a solid content ≤1% obtained by separation is mixed with the reduced-pressure distillation oil obtained by vacuum distillation, and the solid content of the washing oil obtained after mixing does not exceed 1.5%. The washing oil obtained after mixing is directly transported to a dedicated backflushing storage tank for the primary washing operation in S4, and the lower high-solid-content liquid is spray-dried and then transported to a coal slurry preparation storage tank. The dedicated backflushing storage tank is a branch tank of the washing oil storage tank, which is specifically used to store the high-purity solvent oil after sedimentation separation and pre-filtration, and is only used for the primary washing of the filter.

[0031] Preferably, in the coal-to-oil desolidification and purification process of the present invention, in S1, coal powder and solvent oil are mixed at a mass ratio of 1:1.5 to 1:2.

[0032] Preferably, in the coal-to-oil desolidification and purification process of the present invention, the reactor reaction conditions in S2 are: reaction temperature of 425–450°C, reaction pressure of 10–14 MPa, and reaction time of 30–100 min. The parameter range of 425–450°C, 10–14 MPa, and 30–100 min is based on a balance optimization between coal powder hydrogenation conversion efficiency and side reaction suppression: below 425°C, the coal powder conversion rate is less than 85%; above 450°C, the coking side reaction rate increases significantly; below 10 MPa, hydrogen solubility is insufficient; above 14 MPa, equipment investment costs surge; a time shorter than 30 min results in insufficient reaction, while a time longer than 100 min leads to excessive energy consumption. This range can achieve a conversion rate ≥90% and a side reaction rate ≤5%.

[0033] Preferably, in the coal-to-oil desolidification and purification process of the present invention, in S4, "when the pressure difference reaches the set threshold" specifically means: real-time monitoring of the rate of change of the pressure difference between the inlet and outlet of the filter element (continuous monitoring cycle of 5-10 min, taking the average value as the judgment basis), when the rate of change exceeds the preset rate threshold, the online washing program is triggered; and in the secondary washing, the nitrogen gas introduced is hot nitrogen gas preheated to 80-120°C by a heater; wherein, the preset rate threshold is 0.5-1.0 kPa / min; the nitrogen pulse duration is dynamically adjusted based on the rate of change of the pressure difference between the inlet and outlet of the filter element: when the rate of change is equal to or higher than 0.75 kPa / min, the pulse duration is 30-40 s; when the rate of change of the pressure difference is lower than 0.75 kPa / min, the pulse duration is 15-25 s.

[0034] Preferably, in the coal-to-oil desolidification and purification process of the present invention, a nitrogen buffer tank is connected in parallel for each filter or each group of filters on the nitrogen pipeline of the secondary washing stage in S4, wherein the volume of the nitrogen buffer tank is 0.5 to 1.0 m³. 3 ;

[0035] The inlet of the nitrogen buffer tank is connected to the main nitrogen pipe through a branch line equipped with a self-regulating pressure regulating valve. The set pressure of the self-regulating pressure regulating valve is the same as the nitrogen pressure required for the secondary washing.

[0036] The outlet of the nitrogen buffer tank is directly connected to the backflush port on the liquid outlet side of the filter.

[0037] Preferably, in the coal-to-oil desolidification and purification process of the present invention, a pneumatic booster pump is installed in parallel before the inlet of the self-regulating pressure regulating valve on the branch connecting the nitrogen main pipe and the nitrogen buffer tank.

[0038] The start and stop of the pneumatic booster pump are controlled by a pressure sensor installed on the nitrogen buffer tank: when the pressure inside the tank is detected to be lower than 101% to 102% of the lower limit of the pressure required for secondary washing, the pneumatic booster pump automatically starts; when the pressure reaches 99% to 100% of the upper limit of the required pressure, it automatically stops (a 5 to 10 second delay start / stop protection is set to avoid frequent switching); the rated flow rate of the pneumatic booster pump is 5 to 10 Nm³. 3 / h.

[0039] Preferably, in the coal-to-oil desolidification and purification process of the present invention, the power source of the pneumatic booster pump is not the factory compressed air, but a line of clean high-pressure nitrogen drawn from the secondary washing nitrogen main pipe (the power source pressure is not less than 1.2 times the pressure required for secondary washing).

[0040] The nitrogen branch pipe, which serves as the power source, is equipped with a two-position three-way solenoid valve or pneumatic directional valve controlled by a pressure sensor signal from the nitrogen buffer tank.

[0041] When the pressure sensor sends a start signal, the valve switches to introduce clean, high-pressure nitrogen into the pneumatic booster pump as the power source; when a stop signal is sent, the valve resets and cuts off the power source supply.

[0042] The present invention has at least the following beneficial effects:

[0043] 1. This invention provides a complete and continuous coal-to-oil desolidification and purification process. Initial gas-liquid separation is achieved through flash evaporation, followed by micron-level solid-liquid separation using a high-precision filter, effectively removing the vast majority of solid particles. An innovative two-stage online washing mechanism ensures the long-term stable operation of the filter. Finally, the settling and drying of the filter residue enables the recycling of washing oil and solvent, significantly reducing the consumption of fresh solvent and the emission of solid waste, thus achieving energy conservation, emission reduction, and resource utilization.

[0044] 2. This invention achieves graded and high-quality utilization of recovered solvents. The clean washing oil from the upper part is dedicated to backwashing filters with extremely high cleanliness requirements, ensuring the purity of the backwashing medium, effectively avoiding secondary contamination of the filter element, and extending the filter element's service life. Simultaneously, the dried and recovered solvent from the lower part is used for the preparation of coal slurry with relatively lower requirements, achieving tiered utilization of materials and minimizing material consumption and operating costs while ensuring process effectiveness.

[0045] 3. By limiting the optimal mass ratio of coal powder to solvent oil, this invention ensures that the prepared coal slurry has good fluidity and stability, which facilitates transportation and atomization. At the same time, it ensures a suitable raw material concentration in the subsequent hydrogenation reaction, which is conducive to improving reaction efficiency and oil yield, and lays a solid foundation for the stable and efficient operation of the entire process.

[0046] 4. By optimizing the operating range of reaction temperature, pressure and time, this invention can effectively suppress the occurrence of side reactions such as excessive cracking and coking while ensuring full conversion of pulverized coal and improving oil yield. This reduces the load on subsequent process units and ensures the economy, safety and stability of the reaction process.

[0047] 5. This invention, by monitoring the dynamic parameter of differential pressure change rate, can more sensitively and earlier predict the clogging trend of the filter element, achieving precise triggering of washing. This avoids blind washing based on fixed time or delayed washing based on absolute pressure difference, saving washing media and effectively preventing deep clogging. Using hot nitrogen backflushing reduces the viscosity of residues, improves their fluidity, and makes them easier to purge and peel off, thus significantly improving the effect and efficiency of backflushing cleaning. 6. In this invention, the nitrogen buffer tank acts as a local pressure stabilizing container, effectively absorbing pressure fluctuations in the nitrogen pipeline network, providing stable pressure and sufficient nitrogen for each backflushing pulse. Combined with a self-regulating pressure regulating valve, it ensures that the operating pressure of each backflushing operation is precisely and stably within the set range, guaranteeing the consistency, reliability, and repeatability of the backflushing effect, and protecting the filter element from pressure shock damage.

[0048] 7. The introduction of the pneumatic booster pump in this invention provides a backup pressure source for the system. When the main pipeline pressure decreases, it can automatically start and increase the pressure to the required range, ensuring that the backflush pressure of the secondary washing can be reliably guaranteed under any operating conditions. This greatly enhances the anti-interference capability and operational reliability of the entire backflush system and avoids washing failures due to insufficient pressure.

[0049] 8. This invention uses clean high-pressure nitrogen from the same source as the power source, which completely eliminates the possibility of introducing contaminants such as oil and water due to the use of factory compressed air, ensuring the cleanliness of the power air circuit, thereby maintaining the purity of the medium in the entire backflushing nitrogen system, avoiding the risk of secondary contamination of the precision filter element, and improving the safety of the system and the stability of product quality.

[0050] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0051] Figure 1 This is a flow chart of the coal-to-oil desolidification and purification process in one of the technical solutions of the present invention. Detailed Implementation

[0052] The present invention will now be described in further detail with reference to specific embodiments, so that those skilled in the art can implement it based on the description.

[0053] It should be understood that terms such as “having,” “comprising,” and “including” as used herein do not exclude the presence or addition of one or more other elements or combinations thereof.

[0054] Example 1

[0055] The solidification and purification process for coal-to-oil includes the following steps:

[0056] S1. After the raw coal is processed in the coal preparation process, coal powder is used as raw material, a catalyst is added, and it is mixed with solvent oil to make coal slurry; the coal powder and solvent oil are mixed at a mass ratio of 1:1.8.

[0057] S2. After the coal slurry and hydrogen are mixed, they enter the reactor for reaction. The reaction conditions are: reaction temperature of 435℃, reaction pressure of 12 MPa, and reaction time of 60 min, producing coal-to-oil containing unreacted coal powder, catalyst and ash.

[0058] S3. After the coal-to-oil mixture is depressurized to 2.0 MPa by a pressure reducing valve, it is fed into the flash tank. The gas phase and liquid phase are separated by a spiral guide plate. The gas phase is discharged from the top of the tank, and after the light oil is recovered by the condenser, the non-condensable gas is returned to the reactor for recycling. At the same time, the liquid phase level is maintained at 60% of the total height of the flash tank by interlocking control between the liquid level sensor installed on the flash tank and the outlet regulating valve.

[0059] S4. The liquid in the flash tank is output to a high-precision filter, which uses a filter element with a filtration accuracy of 0.10 μm for solid-liquid separation; at the same time, the feeding time is monitored in real time (the threshold is set at 150 min, and the coal slurry processing capacity in this embodiment is 5 m³). 3 / h) The pressure difference change rate at the inlet and outlet of the filter element (set threshold 0.7 kPa / min) reaches 0.7 kPa / min after 120 min of feeding, triggering the secondary online washing. Therefore, the secondary online washing is started to ensure that the filter contains only washing oil and solids.

[0060] First-stage washing: 5% (by mass) industrial-grade cyclohexane (99.8% purity) is added to the washing oil and injected from the feed side at a pressure of 2.0 MPa; filter volume V1 = 0.2 m³. 3 The volume of washing oil injected is V2 = 0.3m. 3 (Saving V1≤V2≤2V1), the residual coal is replaced with oil; cyclohexane is recycled in subsequent processes along with the residual coal, and the concentration after recycling is 4.8%, with a loss rate of 0.2%, and no need to add fresh cyclohexane;

[0061] Secondary washing involves introducing room temperature nitrogen gas at a pressure of 2.4 MPa into the filter outlet side for 25 seconds to backflush all the sludge and liquid in the filter into the sludge and liquid tank.

[0062] S5. The filtrate is sent to a distillation tower for atmospheric distillation and vacuum distillation in sequence to obtain light oil and asphalt products; at the same time, the filter residue is sent to a settling tank and left to stand for 60 min.

[0063] S6. Extract the solvent oil with a solid content of 0.8% from the top of the settling tank, filter it through a 0.01 μm pre-filter, and then transport it to a 0.5 m... 3 Backflushing dedicated storage tank (volume 0.5 m³) 3 In this embodiment, the liquid level is maintained at 2 / 3 (and the interlock for replenishing oil from the washing oil storage tank is not triggered), which is dedicated to the first-level washing operation of S4. At the same time, the high solid content liquid with a solid content of 30% in the lower part of the settling tank is heated to 120°C and then transported to the spray drying equipment. The solid phase is made into a dry powder product (moisture content ≤5%), and the gas phase is cooled to 40°C and then enters the coal slurry raw material tank for recycling and raw material preparation. No solid residue was detected in the pre-filter of the backflushing tank, which proves that the cleanliness of the solvent oil meets the requirements.

[0064] S7. The reduced-pressure distillation oil with a distillation range of 260℃~320℃ obtained from S5 is recycled as washing oil and used for the first-stage washing of S4.

[0065] The solvent oil with a solid content of ≤1% obtained from the upper part of S6 is directly transported to the backflushing tank for the first-stage washing operation of S4. The cyclohexane contained in the solvent oil with a solid content of ≤1% in the upper part of the settling tank does not need to be separated separately and can be directly transported with the solvent oil to the washing oil storage tank for reuse in the first-stage washing. The lower high-solids liquid is spray-dried and then transported to the coal slurry preparation storage tank. In S4, cyclohexane can be added to the washing oil used in the first-stage washing (the amount added is 5-8% of the mass of the washing oil) to enhance the dissolution effect on the colloidal complex. The washing oil containing cyclohexane enters the subsequent settling separation step with the residual coal oil and is recycled together with the solvent oil. The washing oil (i.e., the displacement oil) preferably uses the solvent oil with a solid content of ≤1% in the upper part of the settling tank. When the supply of this solvent oil is insufficient, the reduced-pressure oil (boiling range 260℃-320℃) produced by the vacuum tower is added. There is no strict limit to the mixing ratio of the two, but it must be ensured that the solid content of the washing oil (displacement oil) after mixing is ≤1.5%.

[0066] Solvent oil: refers to the base oil mixed with pulverized coal during coal slurry preparation, as well as the recyclable oil recovered through sedimentation, separation, and drying. It is the basic raw material for washing oil and displacement oil. Washing oil: refers to the oil-phase medium used for primary filter washing, including solvent oil recovered from the settling tank and reduced-pressure oil produced by the vacuum distillation tower; the two can be mixed. Displacement oil: is the same substance as washing oil. Filtrate / Filter residue: refers to the solid-containing liquid discharged from the secondary filter washing backflushing; both are the same substance and subsequently enter the settling tank for further processing. Backflushing dedicated storage tank: refers to a dedicated storage tank for storing solvent oil recovered from the settling tank, used only for primary filter washing, and is a branch tank of the "washing oil storage tank".

[0067] Example 2

[0068] Same as Example 1, except that:

[0069] S4. The liquid in the flash tank is output to a high-precision filter, which uses a filter element with a filtration accuracy of 0.10 μm for solid-liquid separation. Simultaneously, the rate of change of the pressure difference between the inlet and outlet of the filter element is monitored in real time (set threshold 0.8 kPa / min). When the pressure difference change rate reaches 0.8 kPa / min after 140 minutes of feeding, a secondary online washing is triggered.

[0070] The first stage of washing involves adding washing oil (in this embodiment, 5% industrial-grade cyclohexane by mass, 99.8% purity) at a pressure of 2.0 MPa from the filter feed side. The filter volume V1 is 0.2 m³. 3 The volume of washing oil injected, V2, is 0.3 m³. 3(Consisting to V1≤V2≤2V1), the residual coal-to-oil is displaced; cyclohexane enters the subsequent sedimentation and separation step along with the residual coal-to-oil and is recovered together with the solvent oil (the concentration of cyclohexane after recovery is about 4.8%, and the loss rate is 0.2%). No separate purification is required, and it is directly recovered for the next primary washing; in this embodiment, no additional fresh cyclohexane is added because the loss is less than 1%, which does not affect the dissolution effect.

[0071] Secondary washing involves preheating nitrogen to 100℃ via a steam heater (preheating time 8 min, temperature fluctuation ≤ ±5℃), then introducing it from the liquid outlet side at a pressure of 2.4 MPa with a pulse duration of 30 s (selecting the midpoint of the 30-40 s range due to the pressure difference change rate ≥ 0.75 kPa / min), and backflushing the sludge liquid to the sludge liquid tank.

[0072] Example 3

[0073] Including all the steps of Example 2, only S4 is optimized as follows:

[0074] S4. High-precision filtration and two-stage online washing:

[0075] In the secondary scrubbing nitrogen pipeline, a single filter is connected in parallel at a length of 0.8 m. 3 Nitrogen buffer tank;

[0076] The inlet of the nitrogen buffer tank is connected to the main nitrogen pipe through a branch equipped with a self-regulating pressure regulating valve (set pressure 2.4 MPa), and the outlet is directly connected to the backflush port on the liquid outlet side of the filter.

[0077] The remaining parameters are the same as in Example 2: nitrogen preheating to 100°C, pressure 2.4 MPa, pulse duration 30s.

[0078] Example 4

[0079] Including all the steps of Example 3, only S4 is optimized as follows:

[0080] S4. High-precision filtration and two-stage online washing:

[0081] On the branch line connecting the main nitrogen pipeline and the buffer tank, a pneumatic booster pump (rated flow rate 8 Nm³) is installed in parallel before the inlet of the self-regulating pressure regulating valve. 3 / h);

[0082] The booster pump is controlled by a pressure sensor on the buffer tank: it starts automatically when the pressure inside the tank is lower than 2.4 MPa × 101.5% = 2.436 MPa, and stops automatically when it reaches 2.4 MPa × 99.5% = 2.388 MPa.

[0083] The remaining parameters are the same as in Example 3: nitrogen preheating to 100°C, pressure 2.4 MPa, pulse duration 30 s.

[0084] Example 5

[0085] Includes all the steps of Examples 1 to 4.

[0086] Comparative Example 1-1

[0087] Similar to Example 1, the difference is that in step S3, the coal-to-oil is introduced into the flash tank after being depressurized by a pressure reducing valve. Instead of controlling the liquid level to be maintained at 50-70% of the height of the flash tank, the liquid level is allowed to fluctuate freely. At the same time, the pressure difference between the inlet and outlet of the filter element is not monitored in real time; instead, the secondary online washing program is started every 60 minutes of filtration.

[0088] Comparative Examples 1-2

[0089] Same as Example 1, except that in step S4, the nitrogen gas introduced for the secondary washing is unheated room temperature nitrogen gas with a pressure of 1.8 MPa and a pulse duration of 60 s.

[0090] Comparative Example 2

[0091] Similar to Example 2, the difference is that in S4, the online washing program is triggered only based on a fixed feed time threshold (90 min), and the rate of pressure difference change is not monitored. Furthermore, in the secondary washing process, the nitrogen gas introduced is room temperature nitrogen.

[0092] Comparative Example 3

[0093] Similar to Example 3, the difference is that in S4, no nitrogen buffer tank is set for each filter. The main nitrogen pipe is directly connected to the backflush port of the filter through a normal pipeline, and only a manual shut-off valve is installed in the pipeline.

[0094] Comparative Example 4

[0095] Similar to Example 4, except that a pneumatic booster pump is not installed in parallel on the branch connecting the nitrogen main pipe and the nitrogen buffer tank, and the pressure is maintained only by a self-regulating pressure regulating valve.

[0096] Comparative Example 5-1

[0097] Similar to Example 5, except that step S6 is omitted, i.e. the liquid in the settling tank is not separated and recycled, but all the filter residue liquid is directly transported to the drying equipment.

[0098] Comparative Example 5-2

[0099] Similar to Example 5, except that in the secondary washing of step S4, the nitrogen pulse duration is fixed at 5 seconds and is not optimized within the range of 15 to 40 seconds.

[0100] To evaluate the process effects of each embodiment and comparative example, the following test methods were used for effect testing:

[0101] Solid content of filtrate (ppm): Take a sample of the filtrate from the outlet of the S4 high-precision filter and determine the solid content by gravimetric method according to GB / T2293-2019 "Test Method for Quinoline Insoluble Matter in Coking Pitch Products". After centrifugation, filtration, washing, drying and constant weight, weigh the sample and calculate the mass percentage of solid impurities.

[0102] Filter backwash cycle (minutes): Records the continuous operating time of the high-precision filter from the end of this backwash to the next automatic backwash starting due to pressure difference or time reaching a threshold. The longer this time, the slower the filter element clogs and the better the process stability.

[0103] Nitrogen consumption per unit (Nm 3 / ton of filtrate): The volume of nitrogen (standard cubic meters) consumed in the S4 secondary washing step for producing one ton of qualified filtrate product.

[0104] Initial pressure difference of the filter: The pressure difference (kPa) between the inlet and outlet of the filter when it is put back into operation after primary and secondary washing, backflushing and regeneration. The higher the initial pressure difference, the worse the regeneration effect of the filter.

[0105] Washing oil usage (m) 3 / ton of filtrate): This counts the volume of fresh washing oil consumed in the S4 primary washing step for producing one ton of qualified filtrate product. The washing oil can be separated and reused through subsequent processes.

[0106] Comprehensive energy consumption (kWh / ton of product): This refers to the total electrical energy consumed by the entire process system (from coal slurry preparation to product output) to produce one ton of filtrate.

[0107] Each embodiment and comparative example were run three times and the average value was taken to ensure data repeatability. The test results are shown in Table 1.

[0108] Table 1

[0109]

[0110] Analysis of results from comparison of performance data:

[0111] Comparative Example 1-1, due to the lack of control over the flash tank liquid level and the use of fixed-time backflushing, resulted in a short online filtration time, a thinner filter cake, and an increased liquid-to-solid content in the filtrate to 58 ppm. The shortened backflushing cycle also increased energy consumption. Comparative Example 1-2, using ambient temperature and low-pressure nitrogen, exhibited a weakened backflushing effect, requiring more nitrogen to achieve a certain cleaning effect, increasing nitrogen consumption to 12.0 Nm³. 3The filter initially had a high differential pressure. Example 2, by monitoring the rate of change of differential pressure in real time, could trigger backflushing more accurately, avoiding premature or delayed cleaning. Therefore, the filtrate solids content (18 ppm) was better than that of Example 1 (25 ppm), and the backflushing cycle was longer. Comparative Example 2 used a fixed-time trigger, which was not intelligent enough, resulting in untimely or excessive cleaning, with the solids content rising to 38 ppm, the backflushing cycle shortened, and nitrogen consumption increased.

[0112] Example 5, as an integrated solution, combines the aforementioned optimizations and achieves higher efficiency in washing oil recycling, thus obtaining the best overall effect (solid content 17 ppm, energy consumption 170 kWh / ton of product). Comparative Example 5-1 completely omits solvent recycling, resulting in a significant increase in fresh washing oil consumption to 1.25 m³. 3 Energy consumption also increased significantly per ton of product. Comparative Example 5-2 used an unoptimized nitrogen pulse duration, which may have resulted in incomplete backflushing or energy waste, affecting the backflushing effect and nitrogen consumption.

[0113] Each embodiment, by progressively introducing key technologies, demonstrates superior performance compared to Basic Embodiment 1 and its corresponding comparative embodiments in terms of filtrate purity, operational stability, filter regeneration efficiency, and energy consumption. The comparative embodiments effectively highlight the practical benefits brought by each technical feature.

[0114] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and embodiments shown and described herein.

Claims

1. A coal-to-oil desolidification and purification process, characterized in that, Includes the following steps: S1. After the raw coal is processed in the coal preparation process, coal powder is used as raw material, a catalyst is added, and it is mixed with solvent oil to make coal slurry. S2. Coal slurry and hydrogen enter the reactor to react and produce coal-to-oil containing unreacted coal powder, catalyst and ash. S3. After the coal-to-oil mixture is depressurized by a pressure reducing valve, it is fed into a flash tank. A spiral guide plate separates the gas phase and the liquid phase. The gas phase is discharged from the top of the tank, and after the light oil is recovered by the condenser, the non-condensable gas is returned to the reactor for recycling. At the same time, the liquid phase is maintained at 50-70% of the height of the flash tank. S4. The liquid in the flash tank is output to the filter, where a filter element with a filtration accuracy of 0.05–0.15 μm is used for solid-liquid separation. The feed time and the pressure difference between the inlet and outlet of the filter element are monitored in real time. When the feed time or pressure difference reaches the set threshold, the secondary online washing is initiated to ensure that the filter contains only washing oil and solids. In the first stage of washing, washing oil is introduced from the feed side of the filter at a pressure of 1.8 to 2.2 MPa. The relationship between the filter volume V1 and the injected volume V2 of washing oil is V1≤V2≤2V1, which displaces the residual coal-to-oil. Secondary washing involves introducing nitrogen gas at a pressure of 2.2–2.6 MPa from the outlet side of the filter. The introduced nitrogen gas is hot nitrogen gas preheated to 80–120°C by a heater. The pulse duration is 15–40 seconds, which backflush all the sludge and liquid in the filter into the sludge and liquid tank. S5. The filtrate is sent to a distillation tower for atmospheric distillation and vacuum distillation in sequence to obtain light oil and asphalt products; the filter residue is sent to a settling tank and allowed to stand for 30-90 minutes. S6. Extract the solvent oil with a solid content of ≤1% from the upper part of the settling tank and transport it to the washing oil storage tank for recycling; at the same time, heat the high solid content liquid in the lower part of the settling tank and transport it to the drying equipment. The solid phase is made into dry powder product, and the gas phase is cooled and then entered into the coal slurry raw material tank for recycling. In the secondary scrubbing nitrogen pipeline, a nitrogen buffer tank is installed in parallel for each filter or each group of filters, with a volume of 0.5–1.0 m³. 3 ; The inlet of the nitrogen buffer tank is connected to the main nitrogen pipe through a branch line equipped with a self-regulating pressure regulating valve. The set pressure of the self-regulating pressure regulating valve is the same as the nitrogen pressure required for the secondary washing. The outlet of the nitrogen buffer tank is directly connected to the backflush port on the liquid outlet side of the filter; On the branch line connecting the main nitrogen pipeline and the nitrogen buffer tank, a pneumatic booster pump is installed in parallel before the inlet of the self-regulating pressure regulating valve. The start and stop of the pneumatic booster pump are controlled by a pressure sensor installed on the nitrogen buffer tank: when the pressure inside the tank is detected to be lower than 101% to 102% of the lower limit of the pressure required for secondary washing, the pneumatic booster pump automatically starts; when the pressure reaches 99% to 100% of the upper limit of the required pressure, it automatically stops; the rated flow rate of the pneumatic booster pump is 5 to 10 Nm³. 3 / h.

2. The coal-to-oil desolidification and purification process as described in claim 1, characterized in that, It also includes the following steps: S7. The reduced-pressure distillation oil with a distillation range of 260℃ to 320℃ obtained from S5 is recycled as washing oil and used for the first-stage washing of S4.

3. The coal-to-oil desolidification and purification process as described in claim 2, characterized in that, The solvent oil with a solid content of ≤1% obtained from the upper part of S6 is mixed with the reduced-pressure distillation oil obtained from vacuum distillation, and the solid content of the washing oil obtained after mixing does not exceed 1.5%. The washing oil obtained after mixing is directly transported to a special backflushing storage tank for the first-stage washing operation of S4. The lower high-solids liquid is spray-dried and then transported to a coal slurry preparation storage tank.

4. The coal-to-oil desolidification and purification process as described in claim 1, characterized in that, In S1, pulverized coal and solvent oil are mixed at a mass ratio of 1:1.5 to 1:

2.

5. The coal-to-oil desolidification and purification process as described in claim 1, characterized in that, In S2, the reactor reaction conditions are: reaction temperature of 425–450℃, reaction pressure of 10–14 MPa, and reaction time of 30–100 min.

6. The coal-to-oil desolidification and purification process as described in claim 1, characterized in that, In S4, "when the differential pressure reaches the set threshold" specifically means: real-time monitoring of the rate of change of the differential pressure between the filter element inlet and outlet; when the rate of change exceeds the preset rate threshold, the online washing program is triggered; the preset rate threshold is 0.5 to 1.0 kPa / min; the nitrogen pulse duration is dynamically adjusted based on the rate of change of the differential pressure between the filter element inlet and outlet: when the rate of change is equal to or higher than 0.75 kPa / min, the pulse duration is 30 to 40 s; when the rate of change of differential pressure is lower than 0.75 kPa / min, the pulse duration is 15 to 25 s.

7. The coal-to-oil desolidification and purification process as described in claim 1, characterized in that, The power source of the pneumatic booster pump is a clean high-pressure nitrogen gas from the secondary scrubbing nitrogen main pipe; the nitrogen branch pipe that serves as the power source is equipped with a two-position three-way solenoid valve or pneumatic reversing valve controlled by the pressure sensor signal on the nitrogen buffer tank. When the pressure sensor sends a start signal, the valve switches to introduce clean, high-pressure nitrogen into the pneumatic booster pump as the power source; when a stop signal is sent, the valve resets and cuts off the power source supply.

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