Coal liquefaction pitch deferrization system and method based on high gradient magnetic separation

Abstract

This invention discloses a coal liquefaction pitch de-ironization system and method based on high-gradient magnetic separation. The method includes (1) heating the coal liquefaction pitch to reduce its viscosity; (2) feeding the reduced-viscosity coal liquefaction pitch into a high-shear homogenizer for forced shear dispersion; and (3) feeding the forced-shear dispersed coal liquefaction pitch into a high-gradient magnetic separation device, where Fe2O3 particles are selectively adsorbed and removed under the action of a magnetic field, and then the de-ironized pitch is discharged. The de-ironized pitch obtained by this invention can be directly fed into a POX reactor. Because the Fe2O3 impurities have been deeply removed, problems such as nozzle wear, furnace wall erosion, and pipeline blockage in the POX reactor are effectively avoided, which is conducive to improving the carbon conversion rate of the POX process and ensuring the long-term stable operation of the device.

Description

Technical Field

[0001] This invention belongs to the field of deep processing technology of coal liquefaction pitch, specifically involving a coal liquefaction pitch iron removal system and method based on high gradient magnetic separation. It is mainly used to remove ferric oxide (Fe2O3) impurities from coal liquefaction pitch, realize the pretreatment of coal liquefaction pitch, and provide qualified raw materials for subsequent partial oxidation process (POX process) to ensure the stable and efficient operation of POX process. Background Technology

[0002] Coal liquefaction pitch is a heavy byproduct of direct coal liquefaction that has not been fully cracked and hydrogenated, accounting for 10%-30% of the products. Liquefied pitch is a complex substance containing unreacted coal, heavy oil, catalyst, and inorganic ash, making downstream utilization difficult and necessitating the development of technologies for large-scale utilization. Currently, direct gasification of coal liquefaction pitch to produce hydrogen (POX) is a suitable method, converting it into high-value syngas (CO+H2) to supply hydrogen for coal-to-oil production, reducing coal consumption and carbon emissions.

[0003] Coal liquefaction bitumen has a high ash content (some bitumen ash can reach 15%-30wt%), with Fe2O3 accounting for 30%-40wt% of the total ash. The presence of Fe2O3 impurities seriously affects the stable operation of the POX process, resulting in the following significant problems: First, it exacerbates equipment wear and corrosion: Fe2O3 particles have high hardness and, during the bitumen process, cause severe erosion and wear on nozzles, furnace walls, and conveying pipelines, shortening equipment lifespan. Second, it poses safety hazards: Fe2O3 results in a relatively low ash melting point for bitumen components, leading to problems such as slag buildup on furnace walls and blockage of the slag removal system; furthermore, Fe2O3 readily reacts with gases such as H2S, producing corrosive byproducts, further increasing the risk of equipment damage and subsequent system failures. Third, it increases process energy consumption and operating costs: The presence of Fe2O3 reduces bitumen fluidity, requiring higher feed temperatures to meet the atomization requirements of the subsequent POX process, thus increasing energy consumption; simultaneously, equipment maintenance, system cleaning, and syngas purification all significantly increase the overall operating cost of the POX process. Therefore, iron removal pretreatment of coal liquefaction pitch is a prerequisite for the efficient operation of the POX process.

[0004] Currently, the main deashing technologies for coal liquefaction pitch include centrifugal sedimentation, filtration, and extraction, which are mostly used for pitch modification and the preparation of high-end carbon materials, but none of them can meet the requirements of POX process for selective removal of Fe2O3.

[0005] The research paper "Study on Influencing Factors of Centrifugal Deashing Behavior of Coal Liquefaction Asphalt in Shenhua" and CN 116376593 A disclose a method for deashing coal liquefaction asphalt using coking wash oil as an extractant, followed by centrifugal extraction. While adding solvents to reduce the viscosity of the asphalt system and utilizing centrifugal sedimentation to remove ash, the separation efficiency is low. The micron-sized particle size distribution of ash in the asphalt is the main reason limiting its deep removal. Furthermore, the long sedimentation time makes continuous production impossible, and increased solvent consumption raises operating costs; solvent recovery also increases process complexity.

[0006] CN117531293A discloses a deashing method using ceramic membrane filtration and circulating rinsing. First, coal liquefaction residue is extracted with solvent oil to obtain an extract. The extract is then separated by sedimentation to obtain a precipitate, which is mixed with circulating materials in a circulating pump and passed through a ceramic membrane filter to obtain a purified liquid. This patented method achieves good filtration results, but the accumulation of high-viscosity asphaltene and micron-sized particles easily clogs the ceramic membrane, leading to significant flux attenuation.

[0007] CN 117363374 A discloses a deashing agent and removal method for alkali-catalyzed oil slurry. By compounding a charge neutralizer, a demulsifier and a dimer acid polyamide, the alkaline catalyst solid particles in the oil slurry are efficiently removed by sedimentation. This technology focuses on oil slurry deashing, relies on reagent sedimentation separation, has a high cost, does not combine magnetic field-enhanced separation, and has limited effect on sedimentation of micron-sized Fe2O3 particles in high-viscosity asphalt.

[0008] CN 119776024 A discloses a method for preparing mesophase asphalt from aromatic-rich heavy oil. Using catalytic cracking slurry as raw material, appropriate amounts of initiator and magnetic organic iron macromolecular complexes are added. Under certain conditions, a two-phase coexisting asphalt is prepared through a thermal polycondensation reaction. Then, nitrogen stripping is used to remove the light components from the asphalt, and a weak magnetic field-assisted microwave heating sedimentation process is used to separate and settle the asphalt containing the mesophase components. Finally, the heavy components in the lower layer of the mesophase components are taken out and iron-containing impurities are induced to settle and removed under a strong magnetic field, thereby obtaining high-purity, low-softening-point mesophase asphalt. However, this method can only be used for batch processing, has low sedimentation efficiency, especially for micron-sized Fe2O3 particles, and does not solve the problem of the difficulty in capturing weakly magnetic metal oxides in high-viscosity systems. Furthermore, the addition of additives is detrimental to cost control and may introduce new undesirable impurities into subsequent processes.

[0009] In summary, there is an urgent need for an efficient, continuous, low-cost coal liquefaction pitch iron removal technology that is adapted to the pretreatment requirements of the POX process. The key focus should be on solving the problem of efficient removal of Fe2O3 particles (especially micron-sized particles), reducing the Fe2O3 content in pitch to the allowable range of the POX process (e.g., below 0.3 wt%), and ensuring the stable, efficient, and safe operation of the subsequent POX process. Summary of the Invention

[0010] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a coal liquefaction pitch iron removal system and method based on high gradient magnetic separation, so as to achieve efficient and selective removal of weakly magnetic Fe2O3 from high-viscosity coal liquefaction pitch to meet the feed requirements of POX process.

[0011] To achieve one aspect of the above-mentioned objectives, the present invention adopts the following technical solution: A high-gradient magnetic separation method for de-ironizing coal liquefaction pitch includes the following steps: (1) heating the coal liquefaction pitch to increase the temperature and reduce viscosity; (2) sending the reduced viscosity coal liquefaction pitch into a high-shear homogenizer for forced shear dispersion; (3) sending the forced shear dispersion coal liquefaction pitch into a high-gradient magnetic separation device, selectively adsorbing and removing Fe2O3 particles from the coal liquefaction pitch under the action of a magnetic field, and then discharging the de-ironized pitch.

[0012] Preferably, in step (1), the coal liquefaction pitch is heated to 280℃-320℃; Preferably, the viscosity of the coal liquefaction pitch is reduced to 200-1500 mPa·s after heating, more preferably 400-600 mPa·s.

[0013] Preferably, the viscosity of the coal liquefaction pitch at room temperature is not less than 8000 mPa·s, for example, 10000-12000 mPa·s; and the Fe2O3 content in the coal liquefaction pitch is above 5wt%, for example, 8wt%-12wt%.

[0014] Preferably, the high-shear homogenizer rotates at a speed higher than 2500 rpm, and more preferably between 3000-30000 rpm.

[0015] Preferably, the high-shear homogenizer is a pipeline high-shear homogenizer with a single-channel design. The coal liquefaction pitch after heating and viscosity reduction directly enters the pipeline high-shear homogenizer for forced shearing and dispersion before being output.

[0016] Preferably, the residence time of the coal liquefaction pitch in the high-shear homogenizer is not less than 0.5 s, and more preferably 1-4 s.

[0017] Preferably, the magnetic field strength at the center of the magnet in the high-gradient magnetic separation device is not less than 5T, and more preferably 8-15T, with a magnetic field gradient of 6×10⁻⁶. 6 - 2x10 7 A / m 2 8×10 is preferred 6 -1.5×10 7 A / m².

[0018] Preferably, the method for removing iron from coal liquefaction pitch further includes step (4): using hot nitrogen to perform pulse backflushing regeneration on the magnetic separator in order to recover Fe2O3 residue; Preferably, during backflushing, nitrogen is preheated to 280-320°C to prevent the asphalt from cooling and solidifying during backflushing. Then, it is introduced from the backflushing port on the side of the high gradient magnetic separator at a pressure of 0.8-1.0 MPa. The backflushing time is controlled at 5-10 minutes to peel off the Fe2O3 particles and residual asphalt adsorbed on the surface of the magnetic medium. The gas-liquid-solid mixture of nitrogen, Fe2O3 particles and asphalt droplets is then conveyed out of the high gradient magnetic separator in the form of airflow for recovery.

[0019] Preferably, during backflushing, nitrogen gas is introduced from the backflushing port on the side of the high gradient magnetic separation device in a pulse mode.

[0020] Preferably, after backflushing and regeneration are completed, the high-gradient magnetic separation device is restarted to continue the magnetic separation and iron removal process.

[0021] Preferably, after the gas-liquid-solid mixture of nitrogen, Fe2O3 particles, and asphalt droplets is sent out of the high-gradient magnetic separation device by nitrogen backflushing in the form of gas flow, the gas-liquid-solid mixture enters a cyclone separator to separate Fe2O3 particles and nitrogen containing asphalt droplets; wherein, the Fe2O3 particles are reused as a precursor for coal liquefaction catalyst; the nitrogen containing asphalt droplets is recycled back into the system after gas-liquid separation to recover asphalt; the separated nitrogen is reused for backflushing.

[0022] Preferably, the Fe2O3 content in the deferroasphalt is ≤0.08wt%, and the deferroasphalt removal rate is ≥96%.

[0023] To achieve one aspect of the above-mentioned objectives, the present invention adopts the following technical solution: A coal liquefaction pitch de-ironization system based on high gradient magnetic separation, the coal liquefaction pitch de-ironization system comprising a heat exchanger, a high shear homogenizer, a high gradient magnetic separation device and pipelines connected in series; The heat exchanger is used to heat the coal liquefaction pitch that is being transported to increase its temperature and decrease its viscosity. The high-shear homogenizer is used to perform forced shear dispersion on the viscosity-reduced coal liquefaction pitch. The high-gradient magnetic separation device is used to selectively adsorb and remove Fe2O3 particles from coal liquefaction pitch after forced shear dispersion under the action of a magnetic field, so as to discharge iron-free pitch.

[0024] Preferably, the pipeline is equipped with a pipeline insulation and heat tracing design.

[0025] Preferably, the high gradient magnetic separation device includes a body for accommodating the iron removal process of coal liquefaction pitch, wherein the top of the body is provided with a coal liquefaction pitch inlet and the bottom is provided with an iron removal pitch outlet; The high gradient magnetic separation device also includes a superconducting electromagnetic coil disposed outside the main body, a magnetic concentrating medium disposed inside the main body, and a dispersion and equalization structure disposed inside the main body, so that the incoming coal liquefaction pitch flows uniformly through the magnetic concentrating medium.

[0026] Preferably, the lower side of the body is provided with a backflushing nitrogen inlet and the upper side is provided with a backflushing nitrogen outlet.

[0027] Preferably, the coal liquefaction pitch de-ironization system further includes a backflushing and separation unit, wherein the backflushing and recovery unit includes: A backflush pipe is connected to the backflush nitrogen inlet and is used to introduce backflush nitrogen into the body to backflush and remove iron oxide particles and residual asphalt adsorbed on the magnetic medium. The gas-liquid-solid mixture containing nitrogen, Fe2O3 particles and asphalt droplets is sent out from the backflush nitrogen outlet in the form of airflow. An electric heater, installed on the backflush pipe, is used to heat the nitrogen gas to be introduced into the body. A cyclone separator, the inlet of which is connected to the backflushing nitrogen outlet, is used to perform cyclone separation on the gas-liquid-solid mixture to separate Fe2O3 particle residue and nitrogen containing asphalt droplets.

[0028] Preferably, the coal liquefaction pitch de-ironization system further includes a de-ironized pitch delivery pump for sending the de-ironized pitch from the de-ironized pitch outlet into the POX unit for partial oxidation to produce syngas.

[0029] Compared with the prior art, the present invention has the following advantages: (1) Due to the high ash content and high viscosity of coal liquefaction pitch, there is a technological gap in the pretreatment of coal liquefaction pitch POX process. In response to the pretreatment requirements of coal liquefaction pitch POX process, this solution proposes for the first time the idea of ​​"temperature control + high speed shear + ultra-strong magnetic gradient" to synergistically remove Fe2O3 from pitch, which can effectively remove iron oxide particles from coal liquefaction pitch. The Fe2O3 content in the iron-removed pitch can be ≤0.08wt%, and the iron removal rate can be as high as 97% or more. Unlike conventional mixing, high-speed shearing breaks larger iron oxide particles into finer fragments, such as those at the micron level. Initially, this might seem contrary to the expectation of easy removal by magnetic adsorption or magnetic sedimentation. However, the study unexpectedly found that after heating and reducing the viscosity of coal liquefaction pitch, forced shearing dispersion treatment using a mechanical high-shear device can effectively peel off the heavy pitch layer on the surface of iron oxide particles (the heavier the portion of the pitch, the easier it is to adsorb and coat the iron oxide particles). This prevents the magnetic induction intensity from being shielded, and effectively enhances the magnetic response of even micron-sized weakly magnetic iron oxide particles. This is also an important prerequisite for the subsequent effective iron removal using a high-gradient magnetic separation device.

[0030] (2) Existing asphalt deashing technologies employ filtration and extraction methods that use solvent oil for dilution. This consumes a large amount of solvent oil, increasing operating costs. Furthermore, solvent recycling also increases the complexity of the process system. In addition, existing asphalt deashing technologies typically require the addition of additional agents, such as auxiliaries or additives. This not only increases costs but may also introduce unnecessary impurities into subsequent processes. For example, the agents may contain metal ions, silicon, or phosphorus, which could lead to furnace lining corrosion after entering the POX gasifier. In contrast, in this invention, solvent oil and auxiliaries / additives are not necessary. Excellent iron removal can be achieved without solvent oil and auxiliaries / additives. Of course, it is also understood in the art that, without excessive consideration of cost, further addition of solvent oil and auxiliaries / additives, such as demulsifiers, is not excluded in this invention to further reduce viscosity. This is only to emphasize that based on the synergistic effect of "temperature control + high-speed shearing + ultra-strong magnetic gradient" of this invention, excellent iron removal can be achieved even without adding solvent oil and auxiliaries / additives.

[0031] (3) Existing asphalt deashing technology cannot selectively remove Fe2O3, and other ash residues are mixed in. If the iron oxide in it is to be reused, it needs to undergo further treatment, which has no practical economic value. Existing magnetic gravity sedimentation technology for asphalt can remove iron oxide with a certain degree of selectivity, but on the one hand, the pretreatment cost of asphalt to achieve sedimentation is high, and on the other hand, it is more suitable for the sedimentation and removal of slightly larger iron-containing impurities. It has poor sedimentation effect on micron-sized weak magnetic iron oxide particles. Furthermore, the iron-containing impurities that are settled out are still seriously mixed with heavy asphalt, making it difficult to separate and utilize. In contrast, in this invention, the selectively recovered iron oxide has a low asphalt content, a very light coating degree, and a lower ash residue content. It does not require further treatment such as coking and can be directly reused as an iron oxide catalyst. Moreover, the de-ironized asphalt can also be directly sent to the POX unit reaction, which is conducive to extending the life of downstream POX equipment and ensuring the safe and efficient operation of the POX process. It achieves multiple directly usable products in one separation, which is more cost-effective. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of one embodiment of the coal liquefaction pitch de-ironization system of the present invention; The following are the labels in the diagram: 1-Asphalt raw material conveying pump; 2-Heat exchanger; 3-High shear homogenizer; 4-High gradient magnetic separator; 5-Electromagnetic coil; 6-Magnetic medium; 7-External cooling system; 8-Electric heater; 9-Iron-removing asphalt conveying pump; 10-Cyclone separator; 11-Backflush pipe; 12-Body. Detailed Implementation

[0033] To enable those skilled in the art to better understand the present invention, the technical solution of the present invention will be clearly and completely described below with reference to the embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0034] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and should be understood to include values ​​close to these ranges or values, such as values ​​±10% of the endpoint values. For numerical ranges, endpoint values ​​of various ranges, endpoint values ​​of various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. Without conflict, the embodiments and features described in this application can be combined with each other.

[0035] It should be noted that the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion, for example, a process, method, system, product, or device that includes a series of steps or units is not necessarily limited to those steps or units that are explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such process, method, product, or device.

[0036] like Figure 1 As shown, the coal liquefaction pitch de-ironization system of the present invention includes a heat exchanger 2, a high-shear homogenizer 3, a high-gradient magnetic separation device 4 connected in series, and pipes for connecting them.

[0037] The heat exchanger 2 is used to heat the coal liquefaction pitch that is being transported to increase its temperature and decrease its viscosity. For example, steam can be used for heating in the heat exchanger. The specific heating process is well known in the art and will not be described in detail here.

[0038] The high-shear homogenizer 3 is used to perform forced shear dispersion on the viscosity-reduced coal liquefaction pitch. The high-shear homogenizer 3 is well known in the art and can be a commercially available mature high-shear homogenizer product. In one embodiment, the high-shear homogenizer 3 is a pipeline high-shear homogenizer with a single-channel design. One end of the channel is connected to a heat exchanger and the other end is connected to a high-gradient magnetic separation device. The heated and viscosity-reduced coal liquefaction pitch directly enters the pipeline high-shear homogenizer for forced shear dispersion during transportation and is then output to the downstream high-gradient magnetic separation device. This reduces intermediate dwell time and helps reduce the risk of coking and blockage. For example, the pipeline high-shear homogenizer of German IKA DISPAX-REACTOR® DR is an example.

[0039] The high-gradient magnetic separation device 4 is used to selectively adsorb and remove Fe2O3 particles from coal liquefaction pitch after forced shear dispersion under the action of a magnetic field, so as to discharge iron-removed pitch. In one embodiment, the high-gradient magnetic separation device 4 includes a body 12 for accommodating the iron removal process of coal liquefaction pitch. The top of the body 12 is provided with a coal liquefaction pitch inlet and the bottom is provided with an iron-removed pitch outlet. The high-gradient magnetic separation device also includes a superconducting electromagnetic coil 5 disposed outside the body 12 to provide a background magnetic field, a magnetically concentrated medium 6 disposed inside the body 12 to provide a strong magnetic field gradient, and a dispersion and equalization structure disposed inside the body 12 to ensure that the incoming coal liquefaction pitch flows uniformly through the magnetically concentrated medium. Specifically, the coal liquefaction pitch raw material after forced homogeneous dispersion enters the top of the high-gradient magnetic separation device. The dispersion and equalization structure disposed inside the device achieves uniform distribution of the pitch, avoiding biased flow, short circuit, and wall-attached flow, and ensuring that all the pitch passes through the magnetically concentrated medium area uniformly. The pitch after dispersion and equalization can flow uniformly through the magnetically concentrated medium cavity for iron adsorption and removal. The dispersion and flow equalization structure can be configured as a two-stage dispersion and flow equalization structure. The first-stage dispersion uses a disc-type baffle distributor, installed on the top of the magnetic separation device and directly below the feed inlet. It consists of a central baffle plate, a porous annular diffuser plate, and an outer annular guide ring. The diameter of the baffle plate is approximately 1 / 3 of the diameter of the magnetic medium cavity, and the porous annular diffuser plate has an opening rate of 30%-40% and a hole diameter of 5-8mm. Its function is to force the coal liquefaction pitch to spread radially from the center to the surrounding area, preventing the pitch from directly impacting the magnetic medium and achieving initial uniform dispersion of the pitch. The second-stage dispersion uses an interlayer guide grid, set inside the magnetic medium cavity. The magnetic medium (iron-chromium-aluminum fiber) is filled in 2-4 sections, with radial flow dividers set between the layers. The upper and lower ends of the magnetic medium are supported by stainless steel slotted grids. Its function is to prevent the magnetic medium from being compacted by the pitch and the flow channel from being blocked, to guide the pitch to permeate and flow evenly inside the magnetic medium, and to ensure uniform airflow distribution during subsequent nitrogen backflushing, thereby improving the regeneration effect of the magnetic medium.

[0040] The background magnetic field of the high-gradient magnetic separation device 4 is generated by a superconducting magnet, which can be selected from low-temperature superconducting magnets or high-temperature superconducting magnets, and is equipped with an external cooling system 7; for example, when using a low-temperature superconducting magnet, the coil can be kept in a 4.2K working environment by circulating liquid helium cooling; when using a high-temperature superconducting magnet, the coil can be kept in a 20K working environment by a refrigerator or liquid nitrogen cooling. The magnetic focusing medium can be high-temperature resistant iron-chromium-aluminum fiber with a diameter of 20-80μm and a filling rate of 5%-10%. The high-gradient magnetic separation device is specifically well-known in the art and can be a commercially available mature high-shear homogenizer product, such as the Eriez HGMS series high-gradient magnetic separation device.

[0041] It is understood in the art that, in this invention, the relevant pipelines used for conveying heated asphalt may be equipped with pipeline insulation and heat tracing design to prevent cooling and blockage.

[0042] In this invention, the lower side of the main body 12 may be provided with a backflushing nitrogen inlet, and the upper side may be provided with a backflushing nitrogen outlet, so as to backflush the inside of the equipment. The coal liquefaction pitch de-ironization system may also include a backflushing and separation unit, which includes a backflushing pipe 11, an electric heater 8, and a cyclone separator 10.

[0043] The backflush pipe 11 is connected to the backflush nitrogen inlet, which is used to introduce backflush nitrogen into the body 12 to backflush off iron oxide particles and residual asphalt adsorbed on the magnetic medium, and to send out the gas-liquid-solid mixture containing nitrogen, Fe2O3 particles and asphalt droplets from the backflush nitrogen outlet in the form of airflow.

[0044] The electric heater 8 is installed on the backflush pipe 11 and is used to heat the nitrogen gas to be introduced into the body 12. Of course, it is understood in the art that other heating devices that can effectively heat nitrogen gas can also be used.

[0045] The feed inlet of the cyclone separator 10 is connected to the backflushing nitrogen outlet, and is used to perform cyclone separation on the gas-liquid-solid mixture to separate Fe2O3 particles and nitrogen containing asphalt droplets.

[0046] In one embodiment, the coal liquefaction pitch de-ironization system further includes a de-ironized pitch delivery pump 9, used to send the de-ironized pitch from the de-ironized pitch outlet into the POX unit for partial oxidation to produce syngas.

[0047] During operation, the coal liquefaction pitch (asphalt raw material, with a room temperature viscosity of not less than 8000 mPa·s, for example 10000-12000 mPa·s; wherein the Fe2O3 content is usually above 5wt%, for example 8wt%-12wt%) is first subjected to a temperature-raising and viscosity-reducing pretreatment in heat exchanger 2. The asphalt raw material is sent to the heat exchanger by asphalt raw material conveying pump 1. Steam can be used as the heat source. The steam in the heat exchanger exchanges heat with the asphalt raw material through the indirect wall. The asphalt raw material can be continuously heated to 280-320℃, for example 300℃. This temperature range is between the softening point temperature and the thermal decomposition temperature. This can reduce the viscosity (for example, the asphalt viscosity is reduced to 200-1500 mPa·s, preferably 400-600 mPa·s, for example 450 mPa·s) while avoiding coking of the coal liquefaction pitch, so as to better facilitate subsequent forced dispersion and magnetic separation.

[0048] The heated and viscosity-reduced asphalt raw material is transported to the high-shear homogenizer 3 via a pipeline. The pipeline needs to be insulated and heated to maintain the temperature of the coal liquefaction asphalt. The high-shear homogenizer can adopt a single-channel design (only one inlet and one outlet, such as the pipeline-type high-shear homogenizer of the German IKA DISPAX-REACTOR® DR series). The heated and viscosity-reduced asphalt can directly enter the high-shear homogenizer 3 connected in series with the pipeline. To better ensure the forced shearing effect, the rotation speed of the high-shear homogenizer 3 can be appropriately higher, such as above 2500 rpm, preferably 3000-30000 rpm, such as 3000, 3500, 5000 or 10000 rpm. The specific speed can also be determined by comprehensively considering factors such as the number of layers, tooth shape, size of the rotor and stator, and the residence time of the asphalt. For example, it is understood in the art that a longer residence time may be more beneficial to ensuring the forced shearing effect. In some embodiments, the residence time of the coal liquefaction asphalt in the high-shear homogenizer can be not less than 0.5s, such as 1-4s, such as 2 or 3s, and is controlled according to the actual situation.

[0049] Under high-intensity shear force, the asphalt coating structure of Fe2O3 particles is broken instantly, allowing the micron-sized Fe2O3 particles to be fully exposed and uniformly dispersed, while also preventing particle agglomeration and sedimentation, thus laying the foundation for subsequent efficient magnetic separation and iron removal.

[0050] The homogeneous and dispersed asphalt material enters the high-gradient magnetic separation device 4, and the superconducting electromagnetic coil is turned on. The background magnetic field strength can be set to not less than 5T, preferably 8-15T, such as 10 or 12T. A high-gradient magnetic concentrating medium (gradient can be 6×10⁻⁶) is used. 6 -2x10 7 A / m 2 8×10 is preferred 6 - 1.5x10 7 A / m 2This invention selectively adsorbs weakly paramagnetic Fe2O3 particles. Based on the high-gradient magnetic dipole force theory, it utilizes the strong background magnetic field generated by a superconducting coil to perform high-order polarization on the weakly magnetic Fe2O3 particles, coupled with the high magnetic field gradient generated by the magnetically concentrated medium, overcoming the flow resistance in high viscosity, and achieving the directional capture of micron-sized particles. The iron-removed pitch after iron removal treatment can be sent to the POX unit via iron-removed pitch delivery pump 9 for partial oxidation to produce syngas; the Fe2O3 content in the iron-removed pitch can be ≤0.2wt%, such as 0.08wt%, 0.06wt%, 0.04wt%, or even 0.02wt%, and the iron removal rate ≥82%, such as 90%, 94%, 96%, or 98%. Because the iron oxide particles have been deeply removed, problems such as nozzle wear, furnace wall erosion, and pipeline blockage in the subsequent POX reactor are effectively avoided, which is conducive to improving the carbon conversion rate of the POX process and ensuring the long-term stable operation of the unit.

[0051] Because the iron content in coal liquefaction pitch raw materials is high, an iron removal cycle can be set every 20-45 minutes, such as 25, 30 or 35 minutes, to allow for shutdown to clean up the adsorbed iron oxide and prevent the iron oxide adsorbed on the magnetic medium from becoming saturated and weakening the iron removal effect of the subsequent pitch. Of course, it is understood in the art that the specific time can be reasonably determined according to the iron oxide content in the pitch and the feeding rate.

[0052] After the magnetic separator has been running continuously for one iron removal cycle, the Fe2O3 particles adsorbed on the surface of the magnetic medium may be close to saturation. At this time, nitrogen backflushing can be started and the magnetic field generator can be turned off. The nitrogen is preheated by the electric heater to a temperature that is basically the same as that of the asphalt raw material, such as 280-320℃ or 300℃, to avoid the asphalt cooling and solidification. The nitrogen is introduced from the backflushing nitrogen inlet on the side of the magnetic separator at a pressure of 0.8-1.0MPa, such as 0.9MPa, preferably in pulse mode (e.g., the pulse jet time is controlled at 0.3-0.5s, the interval between each jet is 2-5s, and about 5-7 consecutive pulses are performed in one recovery cycle). The backflushing time can be controlled according to the actual situation, such as 5-10min, to completely remove the Fe2O3 particles and a small amount of residual asphalt adsorbed on the surface of the magnetic medium. The gas-liquid-solid mixture of nitrogen, Fe2O3 particles and asphalt droplets is sent out of the high gradient magnetic separator from the backflushing nitrogen outlet in the form of airflow.

[0053] The gas-solid mixture then enters a cyclone separator for cyclone separation. Fe2O3 particles are discharged from the bottom, while nitrogen containing a small amount of asphalt droplets is discharged from the top. The discharged Fe2O3 particles, due to their low solid impurity content (e.g., below 15 wt%, such as 12 wt%, 10 wt%, or 8 wt%) and low asphalt residue (e.g., below 10 wt%, such as 8 wt%, 6 wt%, or 4 wt%), can be directly reused as a precursor for coal liquefaction catalysts in direct coal liquefaction reactions. The nitrogen containing asphalt droplets is condensed and separated into gas and liquid phases; the recovered asphalt can be reintroduced into the system for recycling, and the purified nitrogen can be returned for backflushing, achieving closed-loop resource utilization. After backflushing regeneration is completed, the magnetic field generator is restarted to continue magnetic separation and iron removal.

[0054] The present invention will be further illustrated below with examples / comparative examples, but it should not be construed as the present invention being limited to these.

[0055] Where specific experimental steps or conditions are not specified in the examples, they can be performed according to the corresponding conventional experimental steps or conditions in this technical field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products. All examples employ a process of temperature-induced viscosity reduction, dispersion using a pipeline-type online high-shear homogenizer, a high-gradient magnetic separation device, and nitrogen backflushing regeneration. The parameters of the coal liquefaction pitch raw material used are: ash content 20%, Fe2O3 content accounting for 30% of the ash content, and a room temperature viscosity of 10000 mPa·s.

[0056] Explanation of the method for calculating iron removal rate: The iron content in asphalt was rapidly determined using XRF (X-ray fluorescence spectrometry) and calculated using the following formula: ×100% Iron removal rate (%), Cin: Total iron mass percentage in the inlet fluid of the magnetic separator (%), Cout: Total iron mass percentage in the outlet fluid of the magnetic separator (%) Example 1 First, a temperature-heating and viscosity-reducing pretreatment process is performed. The asphalt is heated to 300℃ using a heat exchanger, significantly reducing its viscosity to 450 mPa·s. It then enters a tubular high-shear homogenizer, where the rotation speed is increased to 3500 rpm. Under conditions of high iron content, the heavy asphalt coating layer on the surface of the Fe2O3 particles is peeled off by strong mechanical shear force (residence time approximately 1.2 s).

[0057] High-gradient magnetic separation process: The broken-up asphalt slurry enters the high-gradient magnetic separation device. The superconducting electromagnetic coil is turned on, and the background magnetic field strength is set to 12.0T. A high-gradient magnetic concentrating medium (gradient 1.5 x 10⁻⁶) is used. 7 A / m2 Selective adsorption of weakly paramagnetic Fe2O3 particles was performed. Due to the high iron content, a working cycle of 30 minutes was set to prevent the magnetic medium from becoming saturated too quickly.

[0058] High-temperature nitrogen backflushing and iron residue recovery: After power failure and demagnetization, high-temperature nitrogen at 0.9 MPa is introduced for pulse backflushing. Fe2O3 particles (10wt% solid impurities, 6wt% asphalt residue) are recovered by a cyclone separator, achieving a total iron removal rate of 97.2% for the asphalt. See Table 1 below for details. The viscosity and flowability of the feed liquid meet the atomization requirements of the subsequent POX process nozzles.

[0059] Example 2 First, a temperature-heating and viscosity-reducing pretreatment process is performed. The asphalt is heated to 280℃ using a heat exchanger, reducing its viscosity to 1500 mPa·s. It then enters a pipeline high-shear homogenizer, with the rotation speed increased to 3000 rpm. Under conditions of high iron content, the heavy asphalt coating layer on the surface of the Fe2O3 particles is peeled off through intense mechanical shear force.

[0060] High-gradient magnetic separation process: The broken-up asphalt slurry enters the high-gradient magnetic separation device. The superconducting electromagnetic coil is turned on, and the background magnetic field strength is set to 10.0T. A high-gradient magnetic concentrating medium (gradient 1.2 x 10⁻⁶) is used. 7 A / m 2 Selective adsorption of weakly paramagnetic Fe2O3 particles was performed. Due to the high iron content, a working cycle of 30 minutes was set to prevent the magnetic medium from becoming saturated too quickly.

[0061] High-temperature nitrogen backflushing and iron residue recovery: After power failure and demagnetization, high-temperature nitrogen at 0.9 MPa was introduced for pulse backflushing. Fe2O3 particles (12wt% solid impurities, 8.5wt% asphalt residue) were recovered by a cyclone separator, achieving a total iron removal rate of 86.4% for the asphalt. See Table 1 below for details. This verified that despite the relatively high viscosity, efficient iron removal was still achieved through compensation with an ultra-high-intensity magnetic field. The viscosity and flowability of the feed liquid met the atomization requirements of the subsequent POX process nozzles.

[0062] Example 3 First, the asphalt undergoes a temperature-raising and viscosity-reducing pretreatment process. A heat exchanger is used to raise the temperature to 320℃, significantly reducing the viscosity to 200 mPa·s. It then enters a pipeline high-shear homogenizer, with the rotation speed increased to 3500 rpm. Under conditions of high iron particle content, strong mechanical shear force is used to peel away the heavy asphalt coating layer from the surface of the Fe2O3 particles.

[0063] High-gradient magnetic separation process: The broken-up asphalt slurry enters the high-gradient magnetic separation device. The superconducting electromagnetic coil is turned on, and the background magnetic field strength is set to 5.0T. High-gradient magnetic media (gradient 8x10) are used.6 A / m 2 Selective adsorption of weakly paramagnetic Fe2O3 particles was performed. Due to the high iron content, a working cycle of 30 minutes was set to prevent the magnetic medium from becoming saturated too quickly.

[0064] High-temperature nitrogen backflushing and iron residue recovery: After power failure and demagnetization, high-temperature nitrogen at 0.9 MPa was introduced for pulse backflushing. Fe2O3 particles (14wt% solid impurities, 10wt% asphalt residue) were recovered via a cyclone separator, achieving a total iron removal rate of 82.1% for the asphalt. See Table 1 below for details. This verifies that the required magnetic field strength can be appropriately reduced with low-viscosity media. The viscosity and flowability of the feed liquid meet the atomization requirements of the subsequent POX process nozzles.

[0065] Comparative Example 1 First, a temperature-heating and viscosity-reducing pretreatment process is performed. The asphalt is heated to 300℃ using a heat exchanger, significantly reducing its viscosity to 450 mPa·s. It then directly enters the high-gradient magnetic separation device. The superconducting electromagnetic coil is activated, and the background magnetic field strength is set to 12.0 T. A high-gradient magnetic media (gradient 1.5 x 10⁻⁶) is used for this process. 7 A / m 2 Selective adsorption of weakly paramagnetic Fe2O3 particles was performed. Due to the high iron content, a working cycle of 30 minutes was set to prevent the magnetic medium from becoming saturated too quickly.

[0066] High-temperature nitrogen backflushing and iron residue recovery: After power failure and demagnetization, high-temperature nitrogen at 0.9 MPa was introduced for pulse backflushing. Fe2O3 particles (solid impurity content 22.5 wt%, asphalt residue 30 wt%) were recovered by a cyclone separator, and the total iron removal rate of asphalt reached 54.5%. See Table 1 below for details. The results show that despite the extremely strong magnetic field, the fluid resistance increased significantly due to the increased volume of agglomerates, resulting in a lower iron removal rate. Subsequent POX process nozzles showed obvious signs of wear.

[0067] Comparative Example 2 First, the asphalt undergoes a temperature-raising and viscosity-reducing pretreatment process. A heat exchanger is used to raise the temperature to 300℃, significantly reducing the viscosity to 450 mPa·s. It then enters a pipeline high-shear homogenizer, where the rotation speed is increased to 3500 rpm. Under conditions of high iron content, strong mechanical shear force is used to peel away the heavy asphalt coating layer from the surface of the Fe2O3 particles.

[0068] The asphalt slurry, after being heated, viscosity reduced, and sheared homogenized, then enters a high-gradient magnetic separation device. The superconducting electromagnetic coil is activated, and the background magnetic field strength is set to 1.5T. A weak-gradient magnetic focusing medium (gradient 1.5 x 10⁻⁶) is used. 5 A / m 2Selective adsorption of weakly paramagnetic Fe2O3 particles was performed. Due to the high iron content, a working cycle of 30 minutes was set to prevent the magnetic medium from becoming saturated too quickly.

[0069] High-temperature nitrogen backflushing and iron residue recovery: After power failure and demagnetization, high-temperature nitrogen at 0.9 MPa was introduced for pulse backflushing. Fe2O3 particles (solid impurity content >30wt%, asphalt residue >45wt%) were recovered by a cyclone separator, with a total iron removal rate of 19.2% for the asphalt. The results show that conventional low-field-strength methods cannot effectively capture weakly paramagnetic Fe2O3 particles. See Table 1 below for details.

[0070] Table 1

[0071] This invention addresses the high viscosity of coal liquefaction pitch by employing a heat exchanger to raise the temperature and reduce the viscosity of the pitch feed. Combined with a high-shear homogenizer, it forcibly breaks down the asphalt's encapsulation of Fe2O3 particles, fully exposing and uniformly dispersing the micron-sized Fe2O3 particles. After forced shear dispersion, the pitch enters a high-gradient magnetic separation device. An electromagnetic coil generates a magnetic field, and a magnetic medium enhances the magnetic field strength to selectively adsorb weakly paramagnetic Fe2O3. After power is cut off and the magnetism is lost, nitrogen backflushing is used to transport the Fe2O3 particles to a cyclone separator. The recovered Fe2O3 can be reused as a precursor for coal liquefaction catalysts. After iron removal, the coal liquefaction pitch can enter the subsequent POX process.

Claims

1. A method for iron removal from coal liquefaction pitch based on high-gradient magnetic separation, characterized in that, Includes the following steps: (1) Heating coal liquefaction pitch to increase temperature and reduce viscosity; (2) The viscosity-reduced coal liquefaction pitch is fed into a high-shear homogenizer for forced shear dispersion. (3) The coal liquefaction pitch after forced shear dispersion is sent to a high gradient magnetic separation device. Under the action of a magnetic field, Fe2O3 particles in the coal liquefaction pitch are selectively adsorbed and removed, and then the de-iron pitch is discharged.

2. The method for iron removal from coal liquefaction pitch according to claim 1, characterized in that, In step (1), the coal liquefaction pitch is heated to 280℃-320℃; Preferably, the viscosity of the coal liquefaction pitch is reduced to 200-1500 mPa·s after heating, more preferably 400-600 mPa·s; Preferably, the viscosity of the coal liquefaction pitch at room temperature is not less than 8000 mPa·s, more preferably 10000-12000 mPa·s; the Fe2O3 content in the coal liquefaction pitch is above 5wt%, more preferably 8wt%-12wt%.

3. The method for iron removal from coal liquefaction pitch according to claim 1 or 2, characterized in that, The rotational speed of the high-shear homogenizer is higher than 2500 rpm, preferably 3000-30000 rpm; Preferably, the high-shear homogenizer is a pipeline high-shear homogenizer with a single-channel design. The coal liquefaction pitch after heating and viscosity reduction directly enters the pipeline high-shear homogenizer for forced shearing and dispersion before being output during the transportation process. Preferably, the residence time of the coal liquefaction pitch in the high-shear homogenizer is not less than 0.5 s, and more preferably 1-4 s.

4. The method for iron removal from coal liquefaction pitch according to any one of claims 1-3, characterized in that, The magnetic field strength at the center of the magnet in the high-gradient magnetic separation device is not less than 5T, preferably 8-15T, and the magnetic field gradient is 6×10⁻⁶. 6 - 2x10 7 A / m 2 8×10 is preferred 6 -1.5×10 7 A / m².

5. The method for iron removal from coal liquefaction pitch according to any one of claims 1-4, characterized in that, The method for removing iron from coal liquefaction pitch also includes step (4): using hot nitrogen to pulse backflush the magnetic separator to regenerate it in order to recover Fe2O3 residue; Preferably, during backflushing, nitrogen is preheated to 280-320°C to prevent the asphalt from cooling and solidifying during backflushing. Then, it is introduced from the backflushing port on the side of the high-gradient magnetic separator at a pressure of 0.8-1.0 MPa to peel off the Fe2O3 particles and residual asphalt adsorbed on the surface of the magnetic medium. The gas-liquid-solid mixture of nitrogen, Fe2O3 particles, and asphalt droplets is then conveyed out of the high-gradient magnetic separator in the form of airflow for recovery. Preferably, nitrogen is introduced from the backflushing port on the side of the high-gradient magnetic separator in a pulse mode. After backflushing and regeneration are completed, the high-gradient magnetic separation device is restarted to continue the magnetic separation and iron removal process.

6. The method for iron removal from coal liquefaction pitch according to claim 5, characterized in that, After a gas-liquid-solid mixture of nitrogen, Fe2O3 particles, and asphalt droplets is conveyed out of the high-gradient magnetic separation device via nitrogen backflushing and pneumatic conveying, the mixture enters a cyclone separator to separate Fe2O3 particles and nitrogen containing asphalt droplets. The Fe2O3 particles are reused as a precursor for coal liquefaction catalysts. The nitrogen containing asphalt droplets is recycled back into the system after gas-liquid separation to recover asphalt. The separated nitrogen is reused for backflushing.

7. A coal liquefaction pitch iron removal system based on high-gradient magnetic separation, characterized in that, The coal liquefaction pitch de-ironization system includes a heat exchanger, a high-shear homogenizer, a high-gradient magnetic separator connected in series, and pipelines used for connection. The heat exchanger is used to heat the coal liquefaction pitch that is being transported to increase its temperature and decrease its viscosity. The high-shear homogenizer is used to perform forced shear dispersion on the viscosity-reduced coal liquefaction pitch. The high-gradient magnetic separation device is used to selectively adsorb and remove Fe2O3 particles from coal liquefaction pitch after forced shearing and dispersion under the action of a magnetic field, so as to discharge iron-free pitch. The pipeline is equipped with a pipeline insulation and heat tracing design.

8. The system according to claim 7, characterized in that, The high gradient magnetic separation device includes a body for accommodating the iron removal process of coal liquefaction pitch, with a coal liquefaction pitch inlet at the top and an iron removal pitch outlet at the bottom. The high gradient magnetic separation device also includes a superconducting electromagnetic coil disposed outside the main body, a magnetic concentrating medium disposed inside the main body, and a dispersion and equalization structure disposed inside the main body, so that the incoming coal liquefaction pitch flows uniformly through the magnetic concentrating medium.

9. The system according to claim 8, characterized in that, The lower side of the body is provided with a backflush nitrogen inlet, and the upper side is provided with a backflush nitrogen outlet; The coal liquefaction pitch de-ironization system further includes a backflushing and separation unit, which includes: A backflush pipe is connected to the backflush nitrogen inlet and is used to introduce backflush nitrogen into the body to backflush and remove iron oxide particles and residual asphalt adsorbed on the magnetic medium. The gas-liquid-solid mixture containing nitrogen, Fe2O3 particles and asphalt droplets is sent out from the backflush nitrogen outlet in the form of airflow. An electric heater, installed on the backflush pipe, is used to heat the nitrogen gas to be introduced into the body. A cyclone separator, the inlet of which is connected to the backflushing nitrogen outlet, is used to perform cyclone separation on the gas-liquid-solid mixture to separate Fe2O3 particle residue and nitrogen containing asphalt droplets.

10. The system according to any one of claims 7-9, characterized in that, Preferably, the coal liquefaction pitch de-ironization system further includes a de-ironized pitch delivery pump for sending the de-ironized pitch from the de-ironized pitch outlet into the POX unit for partial oxidation to produce syngas.

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