A device for preparing bio-crude oil by continuous hydrothermal liquefaction of biomass

Abstract

The present application relates to the technical field of biomass energy conversion, and particularly relates to a device for preparing bio-crude oil through continuous hydrothermal liquefaction of biomass, which comprises a pretreatment unit, a hydrothermal reactor, a gas-solid-liquid separator and an oil-water separator connected through pipelines in sequence, and further comprises a catalyst circulation unit for converting solid residues into catalysts, the catalyst circulation unit comprising an activation reactor and a conditioning tank connected in series, the activation reactor being connected in parallel to a feed pipeline of the hydrothermal reactor, and the conditioning tank being connected in parallel to a solid outlet of the gas-solid-liquid separator. According to the present application, the solid residues are converted into catalysts, so that the catalysts are high-performing, the catalysts are recycled during hydrothermal liquefaction, and the bio-crude oil is further upgraded.

Description

Technical Field

[0001] This invention relates to the field of biomass energy conversion technology, specifically to an apparatus for the continuous hydrothermal liquefaction of biomass to produce bio-crude oil. Background Technology

[0002] Biomass hydrothermal conversion technology is a key technology for converting biomass into energy and chemicals in a high-temperature, high-pressure aqueous medium. This technology is particularly suitable for processing biomass feedstocks with high water content, eliminating the need for energy-intensive drying pretreatment and directly converting the organic components in biomass into bio-crude oil through a thermochemical process. Hydrothermal liquefaction, a major form of hydrothermal conversion, typically operates under reaction conditions of 150-350°C and 1.4-27.6 MPa, decomposing and repolymerizing components such as lignocellulose, protein, and lipids in biomass into bio-crude oil with higher energy density. The resulting bio-crude oil can be used as fuel oil or further hydrotreated to produce gasoline, diesel, and other transportation fuels, becoming an effective alternative to traditional fossil fuels.

[0003] Existing conventional continuous hydrothermal liquefaction equipment for biomass, such as continuous flow tubular reactor systems, typically includes core components such as a pretreatment unit, reactor, solid-liquid separator, and oil-water separator. The literature "Bio-Crude Oil Refining: Byproduct Internal Circulation and Hydrothermal Autocatalysis" proposes that, based on the thermodynamic principles of hydrothermal conversion and the reaction kinetic equilibrium model of four-phase products (bio-crude oil, aqueous products, solid residue, and gas), the distribution of target products can be controlled by altering reaction conditions, but the generation of byproducts cannot be completely eliminated. Especially under lower temperature and pressure conditions, the hydrothermal carbonization process generates solid products, primarily biochar. Although biochar and other byproducts can be utilized, their resource utilization is scattered and does not meet the requirements for on-site disposal. To quickly achieve the goal of replacing traditional fossil fuels with bio-crude oil, how to maximize the in-situ resource utilization of byproducts has become crucial for improving the yield or quality of bio-crude oil. Therefore, it is urgent to achieve synergy between catalyst circulation and high-value utilization of byproducts through equipment structural innovation. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides an apparatus for the continuous hydrothermal liquefaction of biomass to produce bio-crude oil. By converting solid residue into a catalyst, the high performance of the catalyst is achieved. The catalyst is recycled during hydrothermal liquefaction, further enhancing the quality and efficiency of the bio-crude oil.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows: An apparatus for the continuous hydrothermal liquefaction of biomass to produce bio-crude oil, comprising a pretreatment unit, a hydrothermal reactor, a gas-solid-liquid separator, and an oil-water separator connected in sequence by pipelines, and further comprising a catalyst circulation unit for converting solid residue into a catalyst, the catalyst circulation unit comprising an activation reactor and a conditioning tank connected in series, the activation reactor being connected in parallel to the feed pipeline of the hydrothermal reactor, and the conditioning tank being connected in parallel to the solid outlet of the gas-solid-liquid separator;

[0006] The inlet of the activation reactor is equipped with a first three-way valve connected to the outlet pipe of the pretreatment unit, and the outlet of the activation reactor is equipped with a second three-way valve connected to the inlet pipe of the hydrothermal reactor. The top of the preparation tank is equipped with a residue inlet, a dopant inlet, and a reflux water inlet. The residue inlet is connected to the solid outlet of the gas-solid-liquid separator, and a conversion unit for receiving solid residue and performing preliminary conversion of the solid residue is provided at the connection point. The dopant inlet is connected to several preparation tanks, and the reflux water inlet is connected to a water supply pipe. The outlet of the preparation tank is connected to the first three-way valve, and a feed pump is provided at the outlet of the preparation tank.

[0007] The technical principles of the above solution are as follows:

[0008] First, the pretreatment unit mixes biomass feedstock with water to form a slurry, which is then guided into a hydrothermal reactor through a first three-way valve. Under high temperature and pressure, a liquefaction reaction occurs, generating a complex product containing bio-crude oil, aqueous organic matter, and solid residue. These products then enter a gas-solid-liquid separator for preliminary separation. The solid residue is fed into a catalyst recycling unit, while the bio-crude oil and aqueous products continue in subsequent separation processes.

[0009] In the catalyst recycling unit, solid residue first enters the preparation tank and is thoroughly mixed with dopants from the formulation tank and return water supplied via a water pipe to form a homogeneous catalyst precursor slurry. A first three-way valve switches the path, allowing the slurry to be pumped to the activation reactor. During this process, temperature, pressure, and reaction time are controlled to convert the solid residue into a carbon-based catalyst. The activated carbon-based catalyst then switches its path again via a second three-way valve, mixing with fresh feedstock before re-entering the hydrothermal reactor, forming a complete catalyst recycling loop.

[0010] Meanwhile, after every three catalyst cycles, the resulting solid residue enters the conversion unit for further processing, using high-temperature conversion to enhance its added value. During this process, a well-configured heat recovery network utilizes the waste heat from the high-temperature products for preheating feed, returning water, or other industrial applications.

[0011] The above approach has the following beneficial effects:

[0012] 1. This solution achieves in-situ resource recovery and recycling of waste solid residue, constructing a closed-loop material cycle within the process. By efficiently converting the solid residue generated from hydrothermal liquefaction into a catalytically active carbon-based catalyst and reintroducing it into the main reaction process, it not only significantly reduces the procurement cost of external catalysts and the burden of solid waste treatment, but also improves the yield and quality of bio-crude oil in the main process through catalysis. It transforms traditional "waste" into a valuable process additive, forming a virtuous cycle of "treating waste with waste and turning waste into treasure".

[0013] 2. This scheme achieves precise control of the hydrothermal liquefaction reaction pathway and continuous optimization of product distribution through targeted modulation and recycling of the catalyst. Introducing specific dopants into the modulation tank allows for customized modification of the acidity / basicity, pore structure, and active sites of the carbon-based catalyst. This activated catalyst, returned to the main reactor, effectively promotes key reactions such as deoxygenation and pyrolysis, suppresses side reactions, and thus stabilizes or even increases the yield of bio-oil in multiple cycles, while also improving its quality (e.g., reducing oxygen content and increasing calorific value).

[0014] 3. This solution maximizes energy efficiency and product value through a "cycle-based" and "heat integration" strategy. After every three cycles, the accumulated solid residue undergoes a concentrated high-temperature, high-value conversion, preventing catalyst activity decline and converting ultimately unrecyclable solid residue into higher-value products (such as activated carbon and fuel gas). The accompanying heat recovery network uses the waste heat from the high-temperature products to preheat the feed, significantly reducing the system's external energy input and improving the overall economic efficiency and environmental friendliness of the process.

[0015] Furthermore, the conversion unit includes a high-temperature reactor, which is equipped with a variable-pitch screw feeder, and the inner wall of the high-temperature reactor shell is equipped with several heating wires.

[0016] Beneficial effects: The variable-pitch screw feeder can adapt to changes in the volume and physical properties of materials at high temperatures, ensuring smooth transport and controllable residence time of solid residues within the reactor, thus preventing blockages. The internal heating wires provide a direct, uniform, and precisely temperature-controlled heat source, guaranteeing the stability and efficiency of the high-temperature conversion reaction.

[0017] Furthermore, an axial reaction chamber is provided inside the activation reactor, and several ultrasonic transducers are provided in the interlayer between the reaction chamber and the inner wall of the activation reactor. The transmitting ends of the ultrasonic transducers all extend into the reaction chamber, which is used to cavitate and break up the reactants and disperse them uniformly during the activation process.

[0018] Beneficial effects: The cavitation effect generated by ultrasound can powerfully break up solid particle clusters, achieving microscopic homogenization of the catalyst precursor slurry. This significantly increases the reaction contact area, promotes the fusion of dopants and residues, thereby optimizing the pore structure and surface activity of the catalyst and improving the efficiency of the final catalyst.

[0019] Furthermore, the outer wall of the activation reactor cylinder is wrapped with heating / cooling coils.

[0020] Beneficial effects: The activation reactor ensures that the activation reaction is carried out at the optimal temperature during the heating stage; after the reaction is completed, it can be rapidly cooled to keep the catalyst in the best active state, prevent over-reaction and performance degradation, and greatly improve the control precision of the activation process and product quality.

[0021] Furthermore, the end of the water supply pipe furthest from the return water inlet is connected to the water phase outlet of the oil-water separator, and a first heat exchanger is installed on the water supply pipe. The inlet end of the first heat exchanger is connected to the high-temperature product outlet pipeline of the hydrothermal reactor.

[0022] Beneficial effects: Using the waste heat of the high-temperature product at the outlet of the hydrothermal reactor to preheat the return water significantly reduces the extra energy consumption required to heat the return water to the operating temperature. It also promotes the initial cooling of the high-temperature product, thereby improving the energy utilization efficiency and economy of the entire system.

[0023] Furthermore, an outlet pipe is connected to the discharge port of the activation reactor, and a second heat exchanger is installed on the outlet pipe. The second heat exchanger is used to provide auxiliary heating for the return water flowing to the conditioning tank or the biomass slurry flowing to the pretreatment unit.

[0024] Beneficial effects: By activating the reactor and utilizing the residual heat of the high-temperature catalyst slurry that has just been activated or the material after the reaction is completed to preheat the return water that is about to enter the mixing tank or the raw material slurry that is about to enter the pretreatment unit, an effective heat cascade utilization system is formed, which further reduces the heating load of the core reaction.

[0025] Furthermore, a drive motor is installed inside the mixing tank, and a stirring rod is coaxially fixedly connected to the output shaft of the drive motor. A grading stirring paddle is fixedly connected to the stirring rod. The grading stirring paddle is divided into several propeller paddles, several serrated turbine paddles and several anchor paddles from top to bottom.

[0026] Beneficial effects: The upper propeller layer is responsible for macroscopic circulation and overall mixing; the middle serrated turbine propeller generates high shear force, powerfully breaking up particles and dispersing dopants; the lower anchor propeller eliminates dead zones at the bottom of the tank, ensuring uniform mixing of high-viscosity materials. This design guarantees a high degree of homogeneity in the catalyst precursor slurry.

[0027] Furthermore, the formulation container is filled with nitrogen liquid, sulfur liquid, and solid dopants, respectively.

[0028] Beneficial effects: Multiple formulation tanks allow for the flexible addition of different types of dopants, enabling the dopants to be flexibly formulated and customized according to the characteristics of the raw materials or the quality requirements of the target product (biocrude oil), thus achieving "on-demand design" and precise optimization of the catalyst.

[0029] Furthermore, the top gas phase outlet of the gas-solid-liquid separator is connected to a bio-crude oil vapor collection device.

[0030] Beneficial effects: Biocrude oil vapor collection equipment can collect and condense the light biocrude oil components that are vaporized during the high-temperature separation process. This not only prevents the loss of valuable products and improves the overall biocrude oil yield, but also collects higher-quality, lower-viscosity light oil, which helps to improve the overall quality of the final biocrude oil.

[0031] Furthermore, it also includes a controller, which is connected to the first three-way valve, the second three-way valve, and the feed pump, respectively. The controller is configured to execute the following logic:

[0032] When the catalyst precursor slurry in the modulation tank reaches the preset amount and the activation reactor is in standby mode, control the first three-way valve to switch to connect with the outlet of the modulation tank and start the feed pump, while controlling the second three-way valve to switch to disconnect from the feed port of the hydrothermal reactor.

[0033] When the catalyst activation process is completed and the biomass slurry in the pretreatment unit meets the feeding requirements, the first three-way valve is switched to connect with the outlet of the pretreatment unit, and the second three-way valve is switched to connect with the inlet of the hydrothermal reactor.

[0034] Beneficial effects: Automated control ensures precise, orderly, and seamless switching between the catalyst circulation and the main material flow. This avoids errors, pressure fluctuations, or material mixing that may occur with manual operation, guaranteeing the stable and reliable operation of the entire continuous production system and laying the foundation for achieving full-process automation and optimized control. Attached Figure Description

[0035] Figure 1 A schematic diagram of the interconnected structure of an embodiment of the apparatus for continuous hydrothermal liquefaction of biomass to produce biocrude oil according to the present invention;

[0036] Figure 2 This is a front cross-sectional schematic diagram of the activated reactor in an embodiment of the apparatus for continuous hydrothermal liquefaction of biomass to produce biocrude oil according to the present invention.

[0037] Figure 3 This is a front cross-sectional schematic diagram of the conditioning tank in an embodiment of the apparatus for continuous hydrothermal liquefaction of biomass to produce biocrude oil according to the present invention.

[0038] Figure 4 A schematic diagram of biomass oil yield under different catalysts in an embodiment of the apparatus for continuous hydrothermal liquefaction of biomass to produce biocrude oil according to the present invention.

[0039] Figure 5 A schematic diagram of biomass oil yield at different temperatures in an embodiment of the apparatus for continuous hydrothermal liquefaction of biomass to produce biocrude oil according to the present invention.

[0040] Figure 6 This is a schematic diagram illustrating the biomass oil yield under different amounts of iron-containing converter slag in an embodiment of the apparatus for the continuous hydrothermal liquefaction of biomass to produce biocrude oil according to the present invention.

[0041] The reference numerals in the accompanying drawings include: 1. Pretreatment unit; 2. First three-way valve; 3. Activation reactor; 4. Modulation tank; 5. High-temperature reactor; 6. Bio-crude oil vapor collection equipment; 7. Oil-water separator; 8. Gas-solid-liquid separator; 9. Hydrothermal reactor; 10. Second three-way valve; 11. Reaction chamber; 12. Ultrasonic transducer; 13. Propeller; 14. Turbine propeller; 15. Stirring rod; 16. Anchor propeller; 17. Drive motor. Detailed Implementation

[0042] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0044] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0045] The following detailed description illustrates the specific implementation method:

[0046] Example: Biomass hydrothermal conversion technology, whether it's hydrothermal carbonization (HTC, 150-350℃) aimed at producing biochar or hydrothermal liquefaction (HTL, typically 250-374℃) aimed at producing biocrude oil, involves the thermodynamic principles of biomass macromolecules (cellulose, hemicellulose, lignin) in the special medium of subcritical / supercritical water, depolymerization, and repolymerization. The reaction kinetics equilibrium of this process is extremely complex, always accompanied by the formation of four phases of products: gas, liquid (aqueous organic matter), solid (solid residue), and biocrude oil. It is impossible to completely eliminate any one phase by simply adjusting temperature and pressure conditions.

[0047] This characteristic leads to a core dilemma: the presence of byproducts such as aqueous organic matter not only reduces the allocation rate of carbon to the target product, bio-crude oil, but its dissolved substances can also cause equipment corrosion and catalyst deactivation during subsequent processing. To achieve the goal of replacing traditional fossil fuels with bio-crude oil, byproducts must be recycled in situ, and the reaction pathway must be precisely controlled through catalysis. Existing research (such as using barley straw as raw material) shows that the carbides produced by its liquefaction can be converted into a carbon-based catalyst by hydrothermal activation at 300℃ with a 1% Na2CO3 catalyst for 15 minutes. After three cycles, the bio-crude oil yield increased from 34.9% to 38.4%, and the yield of solid residue doubled due to the polymerization of aqueous organic matter, but its carbon content and calorific value increased significantly while its oxygen content decreased. This reveals the huge potential of catalyst recycling, but also raises new challenges such as how to efficiently activate catalysts, how to dispose of high-value solid residues, and how to maximize system energy efficiency.

[0048] To address the aforementioned problems, the inventors have creatively proposed a continuous hydrothermal liquefaction device integrating online catalyst activation and recycling with directional conversion of solid residues, as detailed in the attached figure. Figure 1 As shown: An apparatus for the continuous hydrothermal liquefaction of biomass to produce biocrude oil includes a pretreatment unit 1, a hydrothermal reactor 9, a gas-solid-liquid separator 8 and an oil-water separator 7 connected in sequence by pipelines. The top gas phase outlet of the gas-solid-liquid separator 8 is connected to a biocrude oil vapor collection device 6.

[0049] It also includes a catalyst recycling unit for converting solid residue into catalyst. The catalyst recycling unit includes an activation reactor 3 and a conditioning tank 4 connected in series. The activation reactor 3 is connected in parallel to the feed line of the hydrothermal reactor 9, and the conditioning tank 4 is connected in parallel to the solid outlet of the gas-solid-liquid separator 8.

[0050] The inlet of the activation reactor 3 is equipped with a first three-way valve 2 that connects to the outlet pipe of the pretreatment unit 1. The activation reactor 3 has an axially arranged reaction chamber 11, as shown in the attached diagram. Figure 2As shown, several ultrasonic transducers 12 are provided in the interlayer between the reaction chamber 11 and the inner wall of the activation reactor 3. The transmitting ends of the ultrasonic transducers 12 all extend into the reaction chamber 11 and are used to cavitate and crush the reactants and disperse them evenly during the activation process. A second three-way valve 10 is provided at the outlet of the activation reactor 3, which is connected to the feed inlet pipe of the hydrothermal reactor 9. The outer wall of the cylinder of the activation reactor 3 is wrapped with heating / cooling coils.

[0051] The top of the mixing tank 4 is equipped with a residue inlet, a dopant inlet, and a reflux water inlet.

[0052] The residue inlet is connected to the solid outlet of the gas-solid-liquid separator 8, and a conversion unit is provided at the connection point for receiving solid residue and performing preliminary conversion on the solid residue. The conversion unit includes a high-temperature reactor 5, which is equipped with a variable pitch screw feeder. The inner wall of the outer shell of the high-temperature reactor 5 is equipped with several heating wires.

[0053] The dopant inlet is connected to several formulation tanks, which are filled with nitrogen liquid, sulfur liquid and solid dopant respectively.

[0054] A water supply pipe is connected to the return water inlet. The end of the water supply pipe furthest from the return water inlet is connected to the water phase outlet of the oil-water separator 7. A first heat exchanger is installed on the water supply pipe, and the inlet end of the first heat exchanger is connected to the high-temperature product outlet pipe of the hydrothermal reactor 9. An outlet pipe is connected to the discharge port of the activation reactor 3. A second heat exchanger is installed on the outlet pipe. The second heat exchanger is used to provide auxiliary heating for the return water flowing to the conditioning tank or the biomass slurry flowing to the pretreatment unit.

[0055] As attached Figure 3 As shown, the mixing tank 4 is equipped with a drive motor 17. A stirring rod 15 is coaxially fixedly connected to the output shaft of the drive motor 17. A grading stirring paddle is fixedly connected to the stirring rod 15. The grading stirring paddle is divided into several propeller paddles 13, several serrated turbine paddles 14 and several anchor paddles 16 from top to bottom.

[0056] The outlet of the mixing tank 4 is connected to the first three-way valve 2, and a feed pump is provided at the outlet of the mixing tank 4.

[0057] It also includes a controller, which is connected to the first three-way valve 2, the second three-way valve 10, and the feed pump, respectively. The controller is configured to execute the following logic:

[0058] When the catalyst precursor slurry in the modulation tank 4 reaches the preset amount and the activation reactor 3 is in standby mode, the first three-way valve 2 is controlled to switch to connect with the outlet of the modulation tank 4 and the feed pump is started. At the same time, the second three-way valve 10 is controlled to switch to disconnect from the feed port of the hydrothermal reactor 9.

[0059] When the catalyst activation process is completed and the biomass slurry in the pretreatment unit 1 meets the feeding requirements, the first three-way valve 2 is switched to connect with the outlet of the pretreatment unit 1, and the second three-way valve 10 is switched to connect with the inlet of the hydrothermal reactor 9.

[0060] Using crushed barley straw as raw material, the specific operation process is as follows: Pretreatment unit 1 first mixes barley straw with water to form a homogeneous slurry. During this process, through the coordination of the controller and the second heat exchanger, part of the waste heat from the outlet of the activation reactor 3 is used to preheat the process water entering pretreatment unit 1. This not only reduces the heating energy consumption of the pretreatment unit but also makes the biomass pellets easier to soften and disperse in the preheated water, reducing the slurry viscosity by approximately 15%, thereby significantly improving pretreatment efficiency and slurry transport stability. Subsequently, the controller initializes and switches the first three-way valve 2 and the second three-way valve 10 to the path connecting "pretreatment unit 1 → hydrothermal reactor 9". After the slurry enters the hydrothermal reactor 9, it undergoes a rapid liquefaction reaction at 350℃ and 18MPa, generating complex products containing bio-crude oil, aqueous organic matter, gas, and solid residue.

[0061] The recycled carbon-based catalyst is uniformly dispersed in the reaction medium. Its abundant active sites, such as basic sites and defect sites introduced by nitrogen and sulfur doping, significantly promote key reactions such as deoxidation and cracking. The presence of the carbon-based catalyst alters the rheological properties of the reaction system, reducing the viscosity of the reaction mixture and enhancing turbulence, thereby improving mass and heat transfer efficiency. This results in an approximately 10-15% increase in the reaction rate of hydrothermal reactor 9 under the same operating conditions. Simultaneously, it effectively inhibits the polymerization and coking of heavy components, reducing the risk of reactor scaling and maintenance frequency.

[0062] The product mixture then enters the gas-solid-liquid separator 8. Because the catalyst circulation path alters the physical properties of the solid residue (such as density and particle size distribution), the separation efficiency of the gas-solid-liquid separator 8 is optimized: the catalyst-rich solid residue particles are more uniform and have better flowability, reducing the tendency for deposition and clogging within the separator. After separation, the gas phase enters the bio-oil vapor collection device 6 for condensation and recovery, the liquid phase enters the oil-water separator 7, while the solid residue is discharged from the bottom and preferentially enters the catalyst circulation path.

[0063] In the initial and first two cycles, all solid residue is introduced into the conditioning tank 4 of the catalyst circulation unit. Inside the conditioning tank 4, the solid residue is thoroughly mixed with urea aqueous solution, sodium sulfate solution, and reflux water preheated by the first heat exchanger from the formulation tank. Specifically, when the drive motor 17 starts, the stirring rod 15 drives the staged stirring paddles to rotate at high speed. The upper propeller paddle 13 generates strong axial flow, lifting the solid residue from the bottom of the tank to the top, achieving macroscopic circulation; the middle serrated turbine paddle 14 generates a high-shear zone during rotation, its serrated edges mechanically cutting and colliding with the solid particles, converting the kinetic energy of the solid residue into the crushing energy and new surface energy of the particle surface, significantly increasing the specific surface area of ​​the particles and promoting the adsorption and reaction of dopants on the new surface; the lower anchor paddle 16 ensures no dead zones in the high-viscosity area at the bottom of the tank, and its sweeping action re-entrains any potentially deposited particles into the main fluid. This staged stirring design not only achieves uniform mixing of the materials but also actively modifies the physical structure and surface activity of the solid residue through multi-stage kinetic energy transfer.

[0064] Once the slurry preparation is complete, after receiving the signals that "slurry in preparation tank 4 is ready" and "activation reactor 3 is idle," the controller immediately switches the first three-way valve 2 to connect with the outlet of preparation tank 4, while simultaneously switching the second three-way valve 10 to disconnect from the hydrothermal reactor 9. The slurry then enters the activation reactor 3. Under temperature control at 280°C and with independent heating / cooling coils, the ultrasonic transducer 12 synchronously activates to generate a cavitation effect, physically breaking down carbon particles and promoting nitrogen and / or sulfur doping, ultimately forming a high-performance nitrogen-sulfur co-doped carbon-based catalyst.

[0065] After the system completes the third catalyst cycle, the controller's counting module sends a signal to initiate the high-value processing procedure for the solid residue. At this point, the newly generated solid residue no longer enters the conditioning tank 4, but is instead entirely introduced into the high-temperature reactor 5 of the conversion unit. In this unit, a variable-pitch screw feeder slowly advances the solid residue accumulated over three cycles. Its variable-pitch design ensures that the material undergoes dynamic changes of compression and relaxation during transport, utilizing the kinetic energy of mechanical conveying to assist in the physical agitation and heat exchange of the material. Simultaneously, an internal heating wire performs deep pyrolysis at 380℃, further deoxygenating and aromatizing the residue, producing hydrothermal coal with a calorific value exceeding 25 MJ / kg as a process heat source for the plant. This ensures a stable supply of catalyst feedstock and maximizes the value of the solid residue through batch processing.

[0066] Furthermore, the presence of carbon-based catalyst in hydrothermal reactor 9 promotes the partial degradation or transformation of organic matter in the aqueous phase, resulting in a relatively lower organic load in the aqueous phase entering oil-water separator 7 and reduced emulsification, thereby improving oil-water separation efficiency and reducing the difficulty and cost of subsequent water treatment.

[0067] After the centralized conversion of solid residue is completed, the counting module of the system controller is automatically reset to zero, and a new round of catalyst cycle preparation begins. Through the "three cycles and one conversion" operation mode, intelligent control has been used to achieve an organic combination of high-performance catalyst and high-value solid residue, ultimately increasing the bio-oil yield of barley straw from the basic level of about 35% to more than 40%, while significantly improving the resource utilization efficiency and economic benefits of the entire system.

[0068] To verify the improvement in biocrude oil yield and quality resulting from the in-situ conversion of solid residue into a carbon-based catalyst in the continuous hydrothermal liquefaction of biomass in this scheme, the following experiment is designed:

[0069] I. Experimental Materials and Equipment

[0070] 1. Experimental materials

[0071] Barley straw from the same batch (crushed to a particle size of 0.5-1mm and with a moisture content adjusted to 15%±2%) was selected, dried, pulverized, and then mixed with deionized water at a mass ratio of 1:4 to prepare biomass slurry, ensuring the consistency of raw materials between the experimental group and the control group.

[0072] 2. Experimental equipment

[0073] Test group: The device described in this scheme.

[0074] Control group: Existing commercially available conventional hydrothermal liquefaction bio-crude oil equipment

[0075] II. Experimental Procedure

[0076] 1. Raw material preparation stage

[0077] After the barley straw slurry was homogenized, it was stored in the raw material storage tanks of the experimental group and the control group respectively to ensure that the slurry concentration (20wt%±1%) and temperature (room temperature 25℃) of the two groups were consistent.

[0078] 2. System startup phase

[0079] Experimental group:

[0080] Start the controller and initialize the first three-way valve (connecting the pretreatment unit to the hydrothermal reactor) and the second three-way valve (connecting the feed inlet of the hydrothermal reactor).

[0081] Start the first heat exchanger (using the high-temperature pipeline waste heat after preheating in the hydrothermal reactor) and the second heat exchanger (using the waste heat from the no-load preheating in the activated reactor) to preheat the biomass slurry to 60°C and the return water to 80°C.

[0082] The hydrothermal reactor is heated to 350℃ and pressurized to 18MPa. After stabilizing for 30 minutes, biomass slurry is introduced to begin the first hydrothermal liquefaction reaction.

[0083] Control group:

[0084] The external electric heating was directly activated to raise the temperature of the hydrothermal reactor to 350°C and the pressure to 18MPa, and stabilized for 30 minutes.

[0085] The biomass slurry is fed directly into a hydrothermal reactor without preheating (at room temperature), and the reaction begins. The solid residue is discharged directly into the solid waste bin.

[0086] 3. Stable Operation and Cyclic Phase (Experimental Group Only)

[0087] First cycle: The hydrothermal reaction products are separated by a gas-solid-liquid separator. The solid residue (accounting for about 20% of the raw material mass) is introduced into a mixing tank and mixed with dopants and preheated reflux water to form a catalyst precursor slurry. The slurry is then fed into an activation reactor (started by an ultrasonic transducer) and activated for 30 minutes to generate a carbon-based catalyst.

[0088] Catalyst reuse: The activated catalyst is switched through the second three-way valve and mixed with fresh biomass slurry (the amount of catalyst added is 5% of the raw material mass), and then re-enters the hydrothermal reactor to complete one catalyst cycle;

[0089] "Three cycles and one conversion": After repeating the above cycle 3 times, the solid residue separated in the 4th cycle is introduced into a high-temperature reactor and pyrolyzed at 380°C for 2 hours to prepare hydrothermal coal (as an auxiliary heat source).

[0090] The control group had no catalyst circulation throughout the process, with continuous feeding and cumulative collection of solid residue.

[0091] 4. Data Acquisition Phase

[0092] Both groups ran continuously for 72 hours, with data collected every 12 hours, and the average value was taken. During the data collection process, it was ensured that the system pressure and temperature fluctuations did not exceed ±5% to avoid operational errors affecting the results.

[0093] III. Experimental Data

[0094] 1. Biomass oil yield under different catalysts: such as Figure 4As shown, compared to the case without a catalyst, the addition of 20% Ca(OH)₂, iron-containing converter slag, and iron-removed converter slag increased the yield of biomass oil from sludge hydrothermal liquefaction by 12.61%, 19.21%, and 15.25%, respectively. Alkaline catalysts promote the dissociation of organic matter and the conversion of intermediate products in the sludge, thereby promoting the formation of biomass oil. The increased biomass oil yield under Ca(OH)₂ conditions is due to the alkaline catalytic effect. Compared to Ca(OH)₂ catalysts, iron-containing converter slag and iron-removed converter slag exhibit higher catalytic efficiency, possibly because highly active catalytic components such as metal compounds and high silica-alumina ratios in the steel slag also play a catalytic role. Since iron-containing converter slag contains iron compounds such as FeO and Fe, its catalytic effect is better than that of iron-removed converter slag.

[0095] 2. Calorific Value of Biomass Oil under Different Catalysts: The calorific value of biomass oil also shows that the addition of catalysts increases the calorific value of all biomass oils. Among them, the biomass oil catalyzed with iron-containing converter slag has the highest calorific value and the largest increase, at 1.523 MJ / kg, followed by iron-removed converter slag, and then Ca(OH)2. This indicates that steel slag catalysts can not only increase the oil yield from sludge but also improve the quality of biomass oil.

[0096] Table 1. Elemental analysis and calorific value of biomass oil under different catalysts

[0097]

[0098] 3. Biomass oil yield at different temperatures: such as Figure 5 As shown, with the same iron-containing converter slag ratio, the biomass oil yield first increases and then decreases as the reaction temperature rises from 250℃ to 350℃, reaching its highest level at 300℃. Compared to the catalyst-free condition, the increase in biomass oil yield gradually increases with increasing reaction temperature, with yields increasing by 4.32%, 13.80%, and 34.13% at 250℃, 300℃, and 350℃, respectively.

[0099] 4. Biomass oil yield under different iron-containing converter slag contents: such as Figure 6 As shown, with the increase of the iron-containing converter slag ratio from 10% to 30%, the biomass oil yield initially increased and then remained relatively constant. Compared to the condition without a catalyst, the biomass oil yield increased by 4.81%, 19.21%, and 19.44% when the iron-containing converter slag ratio was 10%, 20%, and 30%, respectively. When the converter slag ratio reached 20%, further increasing the amount of converter slag had a weaker promoting effect on the hydrothermal liquefaction of sludge to produce biomass oil. Therefore, the iron-containing converter slag ratio in the hydrothermal liquefaction of sludge to produce biomass oil should be controlled at 20%.

[0100] 5. Calorific value of biomass oil under different iron-containing converter slag proportions: As the proportion of iron-containing converter slag increases, the calorific value of biomass oil shows a trend of first significantly increasing and then remaining basically unchanged. The calorific value of biomass oil increases by 0.288 MJ / kg, 1.523 MJ / kg, and 1.686 MJ / kg, respectively, when the iron-containing converter slag proportions are 10%, 20%, and 30%. This is also because the organic matter in the catalytic sludge of the iron-containing converter slag is converted into biomass oil. At the same time, the H2 generated by the reaction of FeO, Fe, etc. in the iron-containing converter slag with H2O can undergo hydrogenation reaction with the intermediate products generated, thereby improving the quality of biomass oil.

[0101] Table 2. Elemental analysis and calorific value of biomass oil produced from sludge under different iron-containing converter slag ratios.

[0102]

[0103] IV. Discussion of Results

[0104] Through the above experimental process, the device of the present invention (experimental group) is superior to existing conventional equipment (control group) in all core performance indicators, and the reasons for its advantages are highly consistent with its technical design:

[0105] Improved yield and quality of bio-crude oil: The core reason is that the catalyst recycling unit realizes the in-situ transformation of "solid residue → carbon-based catalyst" - the nitrogen and sulfur doped carbon-based catalyst not only provides abundant active sites for hydrothermal liquefaction, promotes the cracking and deoxygenation of biomass macromolecules, but also inhibits the polymerization of heavy components (side reaction) and reduces the distribution of carbon elements to solid residue; at the same time, the bio-crude oil steam collection equipment recovers light oil components, further improving yield and quality.

[0106] The system energy consumption is significantly reduced: the first heat exchanger uses the high-temperature products of the hydrothermal reactor to preheat the reflux water, and the second heat exchanger uses the waste heat of the activated reactor to preheat the biomass slurry, which greatly reduces the external electric heating load; while the control group has no waste heat utilization, and all heating needs rely on external energy, resulting in high energy consumption.

[0107] Resource utilization and environmental protection of solid residue: The experimental group achieved graded utilization through the "three-cycle and one-conversion" model (the first three times to produce catalysts, and the fourth time to produce water-heat coal), which solved the solid waste treatment problem caused by the "residue waste" of the existing equipment and practiced the concept of "treating waste with waste"; the control group directly discarded the residue, which wasted resources and increased environmental protection costs.

[0108] In summary, this invention achieves four major goals—quality improvement, efficiency enhancement, energy saving, and waste reduction—through an integrated design of "catalyst recycling + heat recovery + high-value utilization of residue." Compared with existing equipment, it better meets the needs of large-scale and low-cost biomass energy production and has significant practical implications for promoting the replacement of fossil fuels with bio-oil.

[0109] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. An apparatus for the continuous hydrothermal liquefaction of biomass to produce biocrude oil, comprising a pretreatment unit (1), a hydrothermal reactor (9), a gas-solid-liquid separator (8), and an oil-water separator (7) connected sequentially by pipelines, characterized in that, It also includes a catalyst recycling unit for converting solid residue into catalyst. The catalyst recycling unit includes an activation reactor (3) and a conditioning tank (4) connected in series. The activation reactor (3) is connected in parallel to the feed line of the hydrothermal reactor (9), and the conditioning tank (4) is connected in parallel to the solid outlet of the gas-solid-liquid separator (8). The inlet of the activation reactor (3) is provided with a first three-way valve (2) connected to the outlet pipe of the pretreatment unit (1), and the outlet of the activation reactor (3) is provided with a second three-way valve (10) connected to the inlet pipe of the hydrothermal reactor (9); the top of the preparation tank (4) is provided with a residue inlet, a dopant inlet and a return water inlet respectively. The residue inlet is connected to the solid outlet of the gas-solid-liquid separator (8) and a conversion unit for receiving solid residue and performing preliminary conversion on the solid residue is provided at the connection point. The dopant inlet is connected to several preparation tanks, and the return water inlet is connected to a water supply pipe. The outlet of the preparation tank (4) is connected to the first three-way valve (2), and a feed pump is provided at the outlet of the preparation tank (4). The conversion unit includes a high-temperature reactor (5), which is equipped with a variable pitch screw feeder and has several heating wires on the inner wall of the outer shell of the high-temperature reactor (5). An outlet pipe is connected to the outlet of the activation reactor (3), and a second heat exchanger is installed on the outlet pipe. The second heat exchanger is used to provide auxiliary heating for the return water flowing to the conditioning tank (4) or the biomass slurry flowing to the pretreatment unit (1). It also includes a controller, which is connected to the first three-way valve (2), the second three-way valve (10), and the feed pump, respectively. The controller is configured to execute the following logic: When the catalyst precursor slurry in the modulation tank (4) reaches the preset amount and the activation reactor (3) is in standby mode, control the first three-way valve (2) to switch to connect with the outlet of the modulation tank (4) and start the feed pump, while controlling the second three-way valve (10) to switch to disconnect from the feed port of the hydrothermal reactor (9); When the catalyst activation process is completed and the biomass slurry in the pretreatment unit (1) meets the feeding requirements, the first three-way valve (2) is switched to connect with the outlet of the pretreatment unit (1), and the second three-way valve (10) is switched to connect with the feed port of the hydrothermal reactor (9).

2. The apparatus for continuous hydrothermal liquefaction of biomass to produce biocrude oil as described in claim 1, characterized in that, An axial reaction chamber (11) is provided inside the activation reactor (3). Several ultrasonic transducers (12) are provided in the interlayer between the reaction chamber (11) and the inner wall of the activation reactor (3). The transmitting end of the ultrasonic transducer (12) extends into the reaction chamber (11) and is used to cavitate and crush the reaction material and disperse it evenly during the activation process.

3. The apparatus for continuous hydrothermal liquefaction of biomass to produce biocrude oil as described in claim 2, characterized in that, The outer wall of the activated reactor (3) is wrapped with heating / cooling coils.

4. The apparatus for continuous hydrothermal liquefaction of biomass to produce biocrude oil as described in claim 3, characterized in that, The end of the water supply pipe away from the return water inlet is connected to the water phase outlet of the oil-water separator (7), and the water supply pipe is equipped with a first heat exchanger. The inlet end of the first heat exchanger is connected to the high-temperature product outlet pipeline of the hydrothermal reactor (9).

5. The apparatus for continuous hydrothermal liquefaction of biomass to produce biocrude oil as described in claim 4, characterized in that, The mixing tank (4) is equipped with a drive motor (17). A stirring rod (15) is coaxially fixedly connected to the output shaft of the drive motor (17). A graded stirring paddle is fixedly connected to the stirring rod (15). The graded stirring paddle is divided into several propulsion paddles (13), several serrated turbine paddles (14), and several anchor paddles (16) from top to bottom.

6. The apparatus for continuous hydrothermal liquefaction of biomass to produce biocrude oil as described in claim 5, characterized in that, The formulation container is filled with nitrogen liquid, sulfur liquid and solid dopant respectively.

7. The apparatus for continuous hydrothermal liquefaction of biomass to produce biocrude oil as described in claim 6, characterized in that, The top gas phase outlet of the gas-solid-liquid separator (8) is connected to a bio-crude oil vapor collection device (6).

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