A subcritical hydrothermal system based on a loop-tube group reactor

Abstract

This invention belongs to the fields of chemical engineering, hydrometallurgy, and materials preparation technology, specifically relating to a subcritical hydrothermal system based on a circulating tubular reactor group. This subcritical hydrothermal system includes a feeding unit, a closed-loop reaction unit, and a product separation unit. The closed-loop reaction unit consists of a high-temperature shielded circulating pump, a gas-liquid mixer, a parallel multi-channel tubular reactor group, and a high-pressure gas-liquid separator. The core of this system lies in using a forced circulation loop and an "online detection-selective extraction" control strategy to ensure that the material circulates and reacts within the system until the target is reached. The average residence time h is determined by the total system volume V and the target product flow rate F. out Precise control. This invention solves the problems of solid-phase deposition, uneven gas-liquid mixing, and inaccurate reaction time control in subcritical hydrothermal processes, and realizes the enhancement and precise programming control of the reaction process. It is particularly suitable for complex gas-liquid-solid multiphase reaction systems such as waste catalyst resource utilization and battery material repair.

Description

Technical Field

[0001] This invention belongs to the fields of chemical engineering, hydrometallurgy and materials preparation technology, and specifically relates to a subcritical hydrothermal system based on a circulating tubular reactor. Background Technology

[0002] Subcritical water, with its unique high-temperature, high-pressure liquid physicochemical properties, demonstrates key value in multiple fields. The significantly increased ion product of subcritical water creates an autocatalytic reaction environment; its dielectric constant decreases significantly, broadening the range of substance dissolution and transport. This characteristic makes subcritical water a powerful tool for the efficient degradation and resource utilization of organic waste, enabling the rapid conversion of stubborn organic matter. In the green leaching of mineral resources, it achieves highly selective extraction of metals. In the field of advanced materials, it provides a precisely controllable reaction medium for nanotechnology synthesis and battery repair. Simultaneously, it serves as an efficient platform for the targeted conversion of biomass into high-value chemicals. Therefore, subcritical water technology is evolving from a reaction method into a core technology driving the upgrading of green and low-carbon industries.

[0003] In current subcritical hydrothermal technology applications, the common reactor configurations are mainly divided into two categories: batch reactors and continuous tubular reactors. However, both of these traditional reactor designs have significant engineering limitations. While batch reactors are simple in structure, their operation is discontinuous, batch-to-batch quality control is difficult, production efficiency is low, and large-scale continuous production is difficult to achieve. Conventional continuous tubular reactors, while possessing continuous production potential, often suffer from limited flow velocity and uneven flow field distribution within the system, making it difficult to effectively suppress the deposition and accumulation of solid materials. Long-term operation is prone to local blockage and decreased mass transfer efficiency, severely limiting their industrial applicability for processing high-solids-content, easily agglomerated materials. Furthermore, for reactions involving the gas phase (such as oxygen), there are problems such as uneven mixing of the gas, liquid, and solid phases, low oxygen utilization, and poor reaction selectivity. In addition, existing technologies struggle to precisely control the actual residence time of materials in the reaction zone, especially when reaction kinetics are complex and require specific reaction processes, lacking flexible and precise control methods. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a subcritical hydrothermal system based on a circulating tubular reactor that combines high-efficiency mass transfer, continuous operation, anti-clogging, and precise control capabilities.

[0005] This invention, by constructing a closed-loop high-speed circulation and intelligent control system, achieves fully suspended material transport and programmable control of reaction time, thus breaking through the bottlenecks of traditional reactor engineering and promoting the development of subcritical hydrothermal technology towards efficient, stable, and intelligent industrial applications. This invention enables efficient, uniform, and cyclical reactions of slurry systems under subcritical hydrothermal conditions, with precisely programmable control over the residence time.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows.

[0007] This invention provides a subcritical hydrothermal system based on a circulating tubular reactor group, comprising a feed unit, a closed-loop reaction unit, and a product separation unit connected in sequence. The feed unit includes a slurry supply unit and a reaction gas supply unit. The closed-loop reaction unit includes a high-temperature shielded circulating pump, a gas-liquid mixer, a parallel multi-channel tubular reactor group, and a high-pressure gas-liquid separator connected in sequence. The liquid phase outlet of the high-pressure gas-liquid separator is connected to the inlet of the high-temperature shielded circulating pump through a liquid phase reflux pipeline to form a closed loop in a turbulent material flow state. The raw material inlet of the high-temperature shielded circulating pump is connected through a feed... The feed pipelines are connected to the slurry supply unit and the reaction gas supply unit, respectively, to provide preheated slurry and supercritical or near-supercritical reaction gas to the gas-liquid mixer to form a gas-liquid mixture, which then undergoes a subcritical hydrothermal reaction in the parallel multi-channel tubular reactor group. The liquid phase outlet of the high-pressure gas-liquid separator is connected to the product separation unit through a liquid phase extraction pipeline for material extraction and separation. A first flow control module is provided on the liquid phase extraction pipeline to acquire and adjust the extraction flow rate of the liquid phase extraction pipeline to control the average residence time of the material in the closed loop.

[0008] Preferably, the subcritical hydrothermal system includes a control unit, and the liquid phase extraction pipeline is equipped with an online analysis module for real-time monitoring of the concentration of the target component in the extracted material; the control unit is electrically connected to the online analysis module and the first flow control module respectively, for acquiring the concentration feedback signal of the target component, and dynamically adjusting the extraction flow rate according to the concentration feedback signal.

[0009] Preferably, a second flow control module is provided on the liquid phase reflux pipeline for acquiring and adjusting the circulation flow rate of the liquid phase reflux pipeline; a third flow control module is provided on the feed pipeline for acquiring and adjusting the feed flow rate of the liquid phase feed pipeline; the ratio of the circulation flow rate to the feed flow rate is 5 to 50; and the output flow rate accounts for 0.5% to 10% of the circulation flow rate.

[0010] Preferably, the parallel multi-channel tubular reactor group includes multiple tubular reaction modules connected in parallel. The inlets of the multiple tubular reaction modules are connected in parallel through a distributor to ensure that the absolute value of the deviation of the material flow rate entering the multiple tubular reaction modules is less than 5%. The outlets of the multiple tubular reaction modules are connected in parallel through a collector.

[0011] Preferably, the gas outlet of the high-pressure gas-liquid separator is connected to a gas processing module, which has a first processing mode and a second processing mode. When the gas processing module switches to the first processing mode, it is used to connect the separated gas to the reaction gas supply unit through a gas return pipeline. Alternatively, when the gas processing module switches to the second processing mode, it is used to connect the separated gas to the waste gas discharge module through a gas extraction pipeline.

[0012] Preferably, the slurry supply unit includes a raw material storage module, a ball mill, a high-pressure feed pump, and a preheating module connected in sequence; the slurry outlet of the preheating module is connected to the raw material inlet of the high-temperature shielded circulation pump through a slurry feed pipeline, for providing slurry preheated to near the subcritical hydrothermal reaction temperature; the inlet of the high-pressure feed pump is connected to the online pH adjustment module, for adjusting the pH of the slurry in the high-pressure feed pump.

[0013] Preferably, the outlet pressure of the high-pressure feed pump is higher than the operating pressure of the closed reaction cycle unit.

[0014] Preferably, the reaction gas supply unit includes high-pressure gas tanks connected in sequence; the high-pressure gas tanks are connected to the raw material inlet of the high-temperature shielded circulation pump through a gas feed pipeline.

[0015] Preferably, the parallel multi-channel tubular reactor group is used to provide the main volume and temperature environment for the subcritical hydrothermal reaction; the operating pressure of the parallel multi-channel tubular reactor group is 15MPa~25MPa, and the operating temperature is 200℃~350℃.

[0016] Preferably, the inlet of the gas-liquid mixer is connected to a gas injection unit, which includes a gas compressor and a supercritical injection device for pressurizing the reaction gas to a supercritical or near-supercritical state before injecting it into the gas-liquid mixer.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Enhanced Reaction and High Efficiency: This invention utilizes a high-temperature shielded circulating pump to drive high-speed material circulation within a closed loop, generating intense turbulence. This completely solves the problems of solid particle settling and wall scaling in high-solids-content slurries, achieving ultimate mixing and mass transfer of the gas-liquid-solid three phases. The parallel pipe assembly design ensures high throughput while maintaining high flow rates and a narrow residence time distribution.

[0018] 2. Precise and controllable residence time: This invention employs a control logic of "forced circulation + online detection + selective extraction." Materials circulate and react within the system, and only products reaching the set parameters can be extracted. This is achieved by simply adjusting the extraction flow rate F. outThis allows for precise and linear control of the average total reaction time of materials within the system (h = V / F). out This enables "programmable" control of complex reaction processes, resulting in excellent product consistency.

[0019] 3. Flexible and Safe Gas Handling: This invention features switchable gas handling modules designed for different reaction types, such as oxidation and reduction. For oxidation reactions, it enables supercritical oxygen injection and closed-loop circulation of excess oxygen, achieving a utilization rate exceeding 95%. For reduction reactions that produce combustible gases, it allows for the safe extraction and treatment of exhaust gases, eliminating the risk of gas accumulation within the system.

[0020] 4. Intrinsic Safety and Reliability: The system of this invention adopts a fully pipelined design, eliminating the need for large pressure vessel cavities; the core moving equipment uses leak-free shielded pumps; the parallel modular design allows for isolated maintenance in case of individual module failure, ensuring continuous system operation. Multi-parameter online monitoring and SIL-level safety interlocks guarantee long-term stable operation of the device.

[0021] 5. Adaptability: By adjusting parameters such as temperature gradient, gas atmosphere (oxidation / inert / reduction), and circulation ratio, the same device can be flexibly applied to various subcritical hydrothermal processes such as aerobic leaching of waste catalysts and anaerobic remediation of lithium battery black powder. The equipment has high utilization rate and good investment benefits. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the overall process flow of the subcritical hydrothermal system based on a circulating tubular reactor in an embodiment of the present invention.

[0023] Figure 2 This is a schematic diagram of the segmented temperature control structure of a parallel multi-channel tubular reactor group in an embodiment of the present invention.

[0024] Explanation of reference numerals in the attached figures: I. Feeding Unit; II. Closed-Loop Reaction Cycle Unit; III. Product Separation Unit; 1. Raw Material Storage Module; 2. Ball Mill; 3. High-Pressure Feed Pump; 4. Preheating Module; 5. High-Pressure Gas Tank; 6. Online pH Adjustment Module; 7. High-Temperature Shielded Circulation Pump; 8. Gas-Liquid Mixer; 9. Parallel Multi-Channel Tubular Reactor Group; 10. High-Pressure Gas-Liquid Separator; 11. Back Pressure Valve; 12. Flash Tank; 13. Solid-Liquid Separator; 14. Liquid Phase Collection Container; 15. Solid Phase Collection Container; 71. Flow Meter; 72. Second Flow Control Module; 73. Pressure Gauge; 101. Concentration Detection Module; 102. Waste Gas Discharge Module; 91. Slurry Inlet; 92. Preheating Section; 93. Reaction Section; 94. Cooling Section; 95. Product Collection End. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0026] The technical solution of the present invention will be further described below through specific embodiments. Unless otherwise specified, the methods described in the following embodiments are conventional methods; the reagents and materials described are commercially available unless otherwise specified.

[0027] like Figure 1 A subcritical hydrothermal system based on a circulating tubular reactor group includes a feed unit I, a closed-loop reaction circulation unit II, and a product separation unit III connected in sequence. Feed unit I includes a slurry supply unit and a reactant gas supply unit. Closed-loop reaction circulation unit II includes a high-temperature shielded circulating pump 7, a gas-liquid mixer 8, a parallel multi-channel tubular reactor group 9, and a high-pressure gas-liquid separator 10 connected in sequence. The liquid phase outlet of the high-pressure gas-liquid separator 10 is connected to the inlet of the high-temperature shielded circulating pump 7 via a liquid phase reflux pipeline to form a closed loop in a turbulent material flow state. The raw material inlet of the circulating pump 7 is connected to the slurry supply unit and the reaction gas supply unit through the feed pipeline, respectively, to provide preheated slurry and reaction gas to the gas-liquid mixer 8 to form a gas-liquid mixture, and to carry out a subcritical hydrothermal reaction in the parallel multi-channel tubular reactor group 9; the liquid phase outlet of the high-pressure gas-liquid separator 10 is connected to the product separation unit III through the liquid phase extraction pipeline, to extract and separate the material; a first flow control module is installed on the liquid phase extraction pipeline to obtain and adjust the extraction flow rate of the liquid phase extraction pipeline, so as to control the average residence time of the material in the closed loop.

[0028] In this embodiment of the invention, the closed-loop reaction unit II is a closed forced circulation loop, wherein the high-temperature shielded circulation pump 7 is used to provide circulation power for the reactants within the closed loop and maintain them in a high-velocity turbulent state. The parallel multi-channel tubular reactor group 9 consists of multiple parallel tubular reaction modules with a total volume of V, used to provide the main volume and temperature environment required for the subcritical hydrothermal reaction. The high-pressure gas-liquid separator 10 has its liquid phase outlet connected to the inlet of the high-temperature shielded circulation pump 7 via a return pipeline, and is equipped with a liquid phase sampling outlet and a gas outlet.

[0029] Based on the above implementation method, the subcritical hydrothermal system includes a control unit, and the liquid phase extraction pipeline is equipped with an online analysis module for real-time monitoring of the concentration of the target component in the extracted material; the control unit is electrically connected to the online analysis module and the first flow control module respectively, for obtaining the concentration feedback signal of the target component, and dynamically adjusting the extraction flow rate according to the concentration feedback signal.

[0030] Specifically, the control unit is configured to: regulate the flow rate of the qualified product exiting the liquid phase outlet through the first flow control module, thereby controlling the average residence time of the material in the closed loop; the formula for calculating the average residence time is: h = V / F out Where h is the average residence time in the closed loop; V is the total volume of the parallel multi-channel tubular reactor group; F out The circulating flow rate of the closed loop.

[0031] Based on the above implementation method, a flow meter 71, a second flow control module 72, and a concentration detection module 101 are installed on the liquid phase reflux pipeline to acquire and adjust the circulation flow rate of the liquid phase reflux pipeline; a third flow control module is installed on the feed pipeline to acquire and adjust the feed flow rate of the liquid phase feed pipeline; the ratio of circulation flow rate to feed flow rate is 5 to 50; the volume percentage of the outflow rate to the circulation flow rate is 0.5% to 10%. The concentration detection module 101 is used to detect the concentration of the target component in the liquid phase reflux pipeline.

[0032] Based on the above embodiments, the parallel multi-channel tubular reactor group 9 includes multiple tubular reaction modules connected in parallel. The inlets of the multiple tubular reaction modules are connected in parallel through a distributor to ensure that the absolute value of the deviation of the material flow rate entering the multiple tubular reaction modules is less than 5%. The outlets of the multiple tubular reaction modules are connected in parallel through a collector.

[0033] Based on the above embodiments, the gas outlet of the high-pressure gas-liquid separator 10 is connected to a gas processing module, which has a first processing mode and a second processing mode. When the gas processing module switches to the first processing mode, it is used to connect the separated gas to the reaction gas supply unit through a gas return pipeline; or, when the gas processing module switches to the second processing mode, it is used to connect the separated gas to the waste gas discharge module 102 through a gas extraction pipeline. In this embodiment of the invention, the first processing mode and the second processing mode can be switched as needed.

[0034] Specifically, the gas processing module includes a switchable first processing mode and a second processing mode; the first processing mode includes a circulation loop for compressing and purifying the separated gas and returning it to the gas injection unit; the second processing mode includes an exhaust gas treatment device for exporting the separated gas and performing safe treatment.

[0035] Based on the above implementation, the slurry supply unit includes a raw material storage module 1, a ball mill 2, a high-pressure feed pump 3, and a preheating module 4 connected in sequence. The slurry outlet of the preheating module 4 is connected to the raw material inlet of the high-temperature shielded circulation pump 7 via a slurry feed pipeline, for providing slurry preheated to near the subcritical hydrothermal reaction temperature. The inlet of the high-pressure feed pump 3 is connected to both the online pH adjustment module 6 and the outlet of the ball mill 2. The online pH adjustment module 6 is used to adjust the pH of the slurry in the high-pressure feed pump 3. Specifically, the outlet pressure of the high-pressure feed pump 3 is higher than the working pressure of the closed reaction circulation unit II. After being heated by the preheater 4, the feed slurry is injected into the inlet of the high-temperature shielded circulation pump 7 or the liquid phase reflux pipeline. The reaction gas supply unit includes a high-pressure gas tank 5 connected in sequence. The high-pressure gas tank 5 is connected to the raw material inlet of the high-temperature shielded circulation pump 7 via a gas feed pipeline.

[0036] The high-temperature shielded circulating pump 7 is connected to the gas-liquid mixer 8 via a discharge pipe, and a pressure gauge 73 is connected to the discharge pipe for monitoring pressure. Specifically, the high-temperature shielded circulating pump 7 is made of titanium alloy or nickel-based alloy, its bearings are made of silicon carbide, and it is equipped with an online monitoring system for vibration, temperature, and axial displacement.

[0037] Based on the above embodiments, the parallel multi-channel tubular reactor group 9 is used to provide the main volume and temperature environment for the subcritical hydrothermal reaction; the operating pressure of the parallel multi-channel tubular reactor group 9 is 15MPa~25MPa, and the operating temperature is 200℃~350℃. Specifically, the parallel multi-channel tubular reactor group 9 has a segmented temperature control structure on its exterior, which can realize temperature gradient control along the material flow direction. Each tubular reaction module in the parallel multi-channel tubular reactor group 9 is a coil or tube structure, and the inlets of all tubular reaction modules are connected in parallel to a distributor, and the outlets of all tubular reaction modules are connected in parallel to a collector. The distributor ensures that the absolute value of the deviation of the material flow rate entering each tubular reaction module is less than 5%. Multiple tubular reaction modules are formed by connecting multiple reaction tubes in parallel to form the parallel multi-channel tubular reactor group 9.

[0038] In this embodiment of the invention, a parallel multi-channel tubular reactor group 9, combined with a segmented temperature control structure, constitutes a segmented temperature-controlled tubular reactor. The segmented temperature-controlled tubular reactor includes the parallel multi-channel tubular reactor group 9, the segmented temperature control structure, and slurry inlets 91 and product collection ends 95 located at both ends of the parallel multi-channel tubular reactor group 9. The parallel multi-channel tubular reactor group 9 includes multiple reaction tubes connected in parallel. The inlets of the multiple reaction tubes are connected to a distributor, which is located at the slurry inlet 91 at one end of the parallel multi-channel tubular reactor group 9. The distributor ensures that the absolute value of the deviation in the material flow rate entering each reaction tube is less than 5%.

[0039] The segmented temperature control structure includes multiple independent heating jacket sections arranged along the axial direction of the reaction tubes, namely a preheating section 92, a reaction section 93, and a cooling section 94. By arranging multiple independent heating jacket sections along the axial direction of the reaction tubes, the temperature at different locations can be controlled separately. In the parallel multi-channel configuration, multiple reaction tubes simultaneously pass through heating jacket sections of the same temperature range, ensuring that the channels of each reaction tube experience a consistent thermal environment in the axial direction, thereby spatially dividing the reaction process into different functional sections.

[0040] In this embodiment of the invention, the temperature gradient formation mechanism is as follows: the axial temperature gradient is actively constructed by setting different target temperatures in adjacent temperature zones. During the flow of the reaction stream, it is affected by convective heat transfer and heat capacity effects, resulting in a continuous rather than abrupt temperature change along the axial direction. The gradient shape is determined by parameters such as temperature difference between temperature zones, section length, and flow velocity, ensuring that the temperature distribution matches the reaction process. This embodiment of the invention achieves "spatialization" of the reaction through segmented temperature control, actively setting temperature gradients to form different regions, such as preheating zones, reaction zones, and cooling zones, thereby causing the temperature gradient in each heating jacket section to change gradually from 200℃ to 350℃. For example, along the preheating section 92 to the reaction section 93, the temperature gradient transitions from 200℃~250℃ to 250℃~350℃; along the reaction section 93 to the cooling section 94, the temperature gradient transitions from 350℃~250℃ to 200℃.

[0041] Based on the above embodiments, the gas-liquid mixer 8 is connected to a gas injection unit at its inlet. The gas injection unit includes a gas compressor and a supercritical injection device, which is used to pressurize the reaction gas to a supercritical or near-supercritical state and then inject it into the gas-liquid mixer 8.

[0042] Based on the above embodiments, the product separation unit III includes a back pressure valve 11, a flash tank 12, a solid-liquid separator 13, a liquid phase collection container 14, and a solid phase collection container 15. The outlet of the flash tank 12 is connected to the inlets of the liquid phase collection container 14 and the solid phase collection container 15, respectively, for collecting and recovering the separated liquid and solid phases.

[0043] Specifically, the back pressure valve 11 is used to maintain and precisely control the system pressure, and to achieve controlled pressure reduction at the outlet; the flash tank 12 utilizes the sudden pressure drop to induce a change in the physical state of the fluid, thereby achieving energy recovery, gas-liquid separation and product cooling.

[0044] The specific application scenarios of the subcritical hydrothermal system based on a circulating tubular reactor of the present invention are described in detail below through specific embodiments. Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0045] Example 1 A subcritical hydrothermal system based on a circulating tubular reactor is used to recover molybdenum from waste catalysts in diesel hydrotreating, which contain residual valuable metals such as molybdenum, nickel, and cobalt, supported by alumina. The feedstock is wet-milled into a slurry with a solid content of approximately 20%, and a 1 mol / L sodium hydroxide solution is added to adjust the pH to be greater than 12. After preheating in preheater 4, the slurry is pressurized by a high-pressure plunger feed pump and injected into the reflux line of closed reaction cycle unit II.

[0046] Closed-loop reaction unit II forms a closed circuit. A high-temperature shielded circulation pump 7 made of titanium alloy drives the slurry circulation. Oxygen from the oxygen storage tank is pressurized to a supercritical state (pressure > 38 MPa) by a compressor and injected into the outlet pipeline of the circulation pump through a static mixer, instantly mixing and dissolving with the high-temperature slurry. The gas-liquid mixture then enters the parallel multi-channel tubular reactor group 9, controlling the absolute value of the material flow deviation entering the multiple tubular reaction modules to be less than 5%. This parallel multi-channel tubular reactor group 9 is composed of multiple titanium alloy coil modules connected in parallel. The coils are equipped with three jackets, and the temperature of the three jackets is controlled near the set temperature, so that the temperature gradient of each heating jacket section varies from 200℃ to 350℃. The specific setting method is: the temperature of the preheating section 92 is controlled at 200℃, the temperature of the reaction section 93 is controlled at 300℃, and the temperature of the cooling section 94 is reduced to 200℃.

[0047] After the reaction, the material enters the high-pressure gas-liquid separator 10. The excess oxygen separated is compressed by a compressor, condensed, and dehydrated before being returned to the oxygen injection end for recycling, with an oxygen utilization rate >98%. The vast majority of the slurry at the bottom of the separator (approximately 97%) is returned to the inlet of the circulation pump via a return pipeline to continue the reaction. An online X-ray fluorescence analyzer is installed in the separator bypass to monitor the molybdenum concentration in the slurry in real time. When the molybdenum concentration reaches a preset value (e.g., leaching rate >95%), the control system adjusts the discharge valve to discharge compliant slurry at a certain flow rate. At this time, the system's fresh feed flow rate is F. in The circulating flow rate is F cycle The cycle ratio is R, and the average residence time is h = V / F out The extracted molybdenum-rich leachate is sent to subsequent processes for molybdenum recovery, and the residue is treated separately. In this embodiment of the invention, the circulation flow rate F... cycle With feed flow rate F in The ratio is 10 to 100; the extracted flow rate accounts for the circulating flow rate F cycle The volume percentage is 0.5% to 10%. The average residence time of the material in the closed loop is controlled to be about 4 hours.

[0048] Example 2 Similar to Example 1 above, the subcritical hydrothermal system based on the circulating tubular reactor can also be used to repair graphite in lithium battery recycled black powder.

[0049] After the lithium battery recycled black powder is made into a slurry, the system is first thoroughly purged with high-purity nitrogen until the oxygen content is <10 ppm. Under an absolutely oxygen-free environment, the slurry enters the reaction circulation unit. At this point, oxygen injection is turned off, and the gas treatment module switches to exhaust gas treatment mode (second mode). The reaction is carried out in subcritical water at 300℃ and 25 MPa to repair the graphite structure and remove impurities.

[0050] Small amounts of hydrogen and methane produced during the reaction are separated in a high-pressure gas-liquid separator, stabilized, and then safely discharged to the catalytic oxidation furnace. The slurry is circulated during the reaction, and the degree of graphite structure repair is monitored using online Raman spectroscopy. When the ID / IG value of the graphite reaches the battery-grade requirement, the control system extracts the slurry at a extraction ratio of approximately 3%. After solid-liquid separation, washing, and drying, the repaired graphite product is obtained. The extraction ratio is the extraction flow rate as a percentage of the circulating flow rate F. cycle Volume percentage.

[0051] Comparative Example 1 According to existing technology (Meng Xiangbin, Gao Shanbin, Hu Sheng, et al. Pre-sulfurization process of hydrogenation catalyst in batch reactor with elemental sulfur as sulfidation medium [J]. Chemical Industry and Engineering Progress, 2015, 34(7): 1877-1881.), a traditional batch high-pressure reactor was used to treat the same batch of diesel hydrogenation waste catalyst with alumina as support and residual valuable metals such as molybdenum, nickel, and cobalt as in Example 1. The single reactor volume is 5m³. 3 Heating to 300℃ takes 2 hours, holding the reaction at that temperature takes 4 hours, and cooling and unloading takes 2 hours, for a total cycle of 8 hours, with the effective reaction time accounting for only 50%. The molybdenum leaching rate fluctuates between batches between 88% and 94% (RSD > 3%), and solid deposits are present at the bottom of the reactor. Oxygen is introduced only once, with a utilization rate of less than 60%.

[0052] Analysis of the results of Comparative Example 1 and Examples 1-2 shows that, compared with Comparative Example 1, Examples 1-2 of the present invention have more precise control of reaction time, higher product consistency (RSD<2%), oxygen utilization rate increased to over 98%, unit volume processing efficiency increased by about 3 times, and continuous automated production was achieved, significantly reducing safety risks.

[0053] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A subcritical hydrothermal system based on a circulating tubular reactor, comprising a feed unit (I), a closed-loop reaction circulation unit (II), and a product separation unit (III) connected in sequence, characterized in that, The feeding unit (I) includes a slurry supply unit and a reaction gas supply unit; The closed reaction cycle unit (II) includes a high-temperature shielded circulation pump (7), a gas-liquid mixer (8), a parallel multi-channel tubular reactor group (9), and a high-pressure gas-liquid separator (10) connected in sequence; the liquid phase outlet of the high-pressure gas-liquid separator (10) is connected to the inlet of the high-temperature shielded circulation pump (7) through a liquid phase reflux pipeline to form a closed loop in the turbulent operation state of the material. The raw material inlet of the high-temperature shielded circulating pump (7) is connected to the slurry supply unit and the reaction gas supply unit respectively through the feed pipeline, and is used to provide preheated slurry and reaction gas to the gas-liquid mixer (8) to form a gas-liquid mixture and carry out subcritical hydrothermal reaction in the parallel multi-channel tubular reactor group (9); The liquid phase outlet of the high-pressure gas-liquid separator (10) is connected to the product separation unit (III) through a liquid phase extraction pipeline for extracting and separating materials; a first flow control module is provided on the liquid phase extraction pipeline for acquiring and adjusting the extraction flow rate of the liquid phase extraction pipeline to control the average residence time of materials in the closed loop.

2. The subcritical hydrothermal system based on a circulating tubular reactor as described in claim 1, characterized in that, The subcritical hydrothermal system includes a control unit, and the liquid phase extraction pipeline is equipped with an online analysis module for real-time monitoring of the concentration of the target component in the extracted material. The control unit is electrically connected to the online analysis module and the first flow control module, respectively, for acquiring the concentration feedback signal of the target component and dynamically adjusting the extraction flow rate according to the concentration feedback signal.

3. The subcritical hydrothermal system based on a circulating tubular reactor as described in claim 2, characterized in that, A second flow control module (72) is provided on the liquid phase reflux pipeline to acquire and adjust the circulation flow rate of the liquid phase reflux pipeline; a third flow control module is provided on the feed pipeline to acquire and adjust the feed flow rate of the liquid phase feed pipeline. The ratio of the circulating flow rate to the feed flow rate is 5 to 50; the volume percentage of the output flow rate to the circulating flow rate is 0.5% to 10%.

4. The subcritical hydrothermal system based on a circulating tubular reactor as described in claim 1, characterized in that, The parallel multi-channel tubular reactor group (9) includes multiple tubular reaction modules connected in parallel. The inlets of the multiple tubular reaction modules are connected in parallel through a distributor to ensure that the absolute value of the deviation of the material flow rate entering the multiple tubular reaction modules is less than 5%. The outlets of the multiple tubular reaction modules are connected in parallel through a collector.

5. The subcritical hydrothermal system based on a circulating tubular reactor as described in claim 1, characterized in that, The gas outlet of the high-pressure gas-liquid separator (10) is connected to a gas processing module, which has a first processing mode and a second processing mode. When the gas processing module is switched to the first processing mode, it is used to connect the separated gas to the reaction gas supply unit through a gas return pipeline. Alternatively, when the gas processing module is switched to the second processing mode, it is used to connect the separated gas to the waste gas discharge module (102) through a gas extraction pipeline.

6. The subcritical hydrothermal system based on a circulating tubular reactor as described in claim 1, characterized in that, The slurry supply unit includes a raw material storage module (1), a ball mill (2), a high-pressure feed pump (3), and a preheating module (4) connected in sequence. The slurry outlet of the preheating module (4) is connected to the raw material inlet of the high-temperature shielded circulation pump (7) through a slurry feed pipeline, and is used to provide slurry preheated to near the subcritical hydrothermal reaction temperature. The inlet of the high-pressure feed pump (3) is connected to the online pH adjustment module (6), and is used to adjust the pH of the slurry in the high-pressure feed pump (3).

7. The subcritical hydrothermal system based on a circulating tubular reactor as described in claim 6, characterized in that, The outlet pressure of the high-pressure feed pump (3) is higher than the working pressure of the closed reaction cycle unit (II).

8. The subcritical hydrothermal system based on a circulating tubular reactor according to claim 6, characterized in that, The reaction gas supply unit includes a high-pressure gas tank (5) connected in sequence; the high-pressure gas tank (5) is connected to the raw material inlet of the high-temperature shielded circulation pump (7) through a gas feed pipeline.

9. The subcritical hydrothermal system based on a circulating tubular reactor as described in claim 1, characterized in that, The parallel multi-channel tubular reactor group (9) is used to provide the main volume and temperature environment for the subcritical hydrothermal reaction; the working pressure of the parallel multi-channel tubular reactor group (9) is 15MPa~25MPa, and the working temperature is 200℃~350℃.

10. The subcritical hydrothermal system based on a circulating tubular reactor according to claim 1, characterized in that, The gas-liquid mixer (8) is connected to a gas injection unit at its inlet. The gas injection unit includes a gas compressor and a supercritical injection device, which is used to pressurize the reaction gas to a supercritical or near-supercritical state and then inject it into the gas-liquid mixer (8).

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