Agricultural and forestry waste grading raw liquid circulating water heat treatment system and method for saving water and reducing consumption

Abstract

The application belongs to the technical field of agricultural and forestry waste treatment, and particularly relates to a water-saving and consumption-reducing agricultural and forestry waste grading raw solution circulating hydrothermal treatment system and method. The system comprises a feeding unit, a circulating hydrothermal reaction unit and a primary hydrothermal reaction device in communication with one discharge port of the feeding unit, wherein the primary hydrothermal reaction device is provided with a water inlet; the circulating hydrothermal reaction unit comprises a liquid storage device and a circulating hydrothermal reaction device in sequence communication, and another discharge port of the feeding unit is in communication with the circulating hydrothermal reaction device; a hydrothermal liquid outlet of the primary hydrothermal reaction device is in communication with the liquid storage device through a liquid conveying pipeline, and a suction filter pump is arranged on the liquid conveying pipeline, and the suction filter pump is used to convey the hydrothermal liquid generated in the primary hydrothermal reaction device to the liquid storage device through the liquid conveying pipeline. The system can treat agricultural and forestry waste, reduce water consumption, sewage and additive consumption, and improve the quality of hydrothermal liquid products.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of resource utilization of agricultural and forestry wastes, and particularly to a water-saving and consumption-reducing agricultural and forestry waste grading raw liquid circulating hydrothermal treatment system and method. BACKGROUND

[0002] The sustainable development of society cannot be achieved without the rational use of resources and the effective protection of the environment. The resource utilization of agricultural and forestry wastes can alleviate the dual pressures of resource depletion and environmental pollution. The use of hydrothermal reaction is a feasible strategy for converting agricultural and forestry wastes into high-quality products. The organic matter in agricultural and forestry wastes is hydrolyzed during the hydrothermal reaction process, and the hydrolysis products are transferred to the liquid phase, thereby reducing the greenhouse gas emissions during the treatment of agricultural and forestry wastes and achieving significant environmental benefits. Through hydrothermal reaction, agricultural and forestry wastes can be fully converted into three high-value-added products: hydrothermal gas, hydrothermal liquid, and hydrothermal carbon. The hydrothermal gas can be used as fuel gas; the hydrothermal liquid can be used to prepare nano-carbon materials, biogas fermentation, or liquid fertilizer; and the hydrothermal carbon can be used as fuel or, after modification, as a soil conditioner or for the preparation of porous carbon materials. The comprehensive application of hydrothermal products is conducive to the resource utilization and value-added utilization of agricultural and forestry wastes. This makes the development of hydrothermal technology for treating agricultural and forestry wastes promising.

[0003] The hydrothermal reaction treatment of agricultural and forestry wastes relies on a specific working reaction system. Patent CN 201611270675.3 discloses a biomass hydrothermal liquefaction method and system for continuous feeding and continuous discharging, but this system cannot improve the problem of difficult recovery of hydrothermal liquid products in CN 113801669 A. Patents CN 212669610 U, CN 216005693 U, CN 219724080 U, and CN 116514365 A all use a waste heat recovery unit to recover the waste heat after hydrothermal reaction, improving the energy utilization efficiency of hydrothermal carbonization and the entire system, but none of them can achieve the recovery and utilization of hydrothermal liquid products. The utility model patent CN 217677380 U designs a circulating loop of hydrothermal liquefaction working medium, which couples the hydrothermal reaction treatment system with a microgrid, fully recovers the waste heat of hydrothermal reaction, and recovers the hydrothermal liquid and biomass for further reaction, which also recovers the active components of the hydrothermal liquid to some extent. However, the hydrothermal liquefaction reactor and the fluid treatment loop in this system are connected in series, and the loss of hydrothermal liquid will reduce the amount of waste treated in a single cycle or require additional water to meet the reaction needs of hydrothermal liquid and biomass, which will reduce the self-catalytic effect brought by the reuse of hydrothermal products, and the improvement of hydrothermal product quality is very limited. SUMMARY

[0004] The purpose of this invention is to address the problems of high water consumption, difficulty in recycling additives, and large wastewater volumes in the existing hydrothermal treatment of agricultural and forestry waste. Therefore, it proposes a water-saving and energy-reducing graded raw material circulating hydrothermal treatment system and method for agricultural and forestry waste. This system effectively separates the hydrothermal reaction products and uses the separated hydrothermal liquid as a hydrothermal medium, which is then pumped back to the hydrothermal reactor for the next round of hydrothermal reaction. Using the system described in this invention to treat agricultural and forestry waste can reduce water consumption, wastewater volume, and additive usage, while simultaneously improving the quality of the hydrothermal liquid product.

[0005] The first aspect of this invention proposes a water-saving and energy-reducing graded raw material circulating hydrothermal treatment system for agricultural and forestry waste. The system includes a feeding unit, a primary hydrothermal reactor, and a circulating hydrothermal reactor. One agricultural and forestry waste outlet of the feeding unit is connected to the inlet of the primary hydrothermal reactor. The primary hydrothermal reactor has a water inlet for supplying a water medium to the primary hydrothermal reactor. The circulating hydrothermal reactor includes a liquid storage device and a circulating hydrothermal reactor connected in sequence. Another agricultural and forestry waste outlet of the feeding unit is connected to the circulating hydrothermal reactor. The feed inlet is connected; the hydrothermal liquid outlet of the primary hydrothermal reactor is connected to the liquid storage device through a liquid delivery pipeline. A filtration pump is installed on the liquid delivery pipeline. The filtration pump is used to transport the primary hydrothermal liquid produced by the hydrothermal reaction of the water medium and agricultural and forestry waste in the primary hydrothermal reactor to the liquid storage device through the liquid delivery pipeline. The liquid storage device is used to transport the primary hydrothermal liquid to the circulating hydrothermal reactor. The hydrothermal liquid outlet of the circulating hydrothermal reactor is used to discharge the secondary hydrothermal liquid produced by the hydrothermal reaction of the primary hydrothermal liquid and agricultural and forestry waste.

[0006] Preferably, a first solid-liquid separation device is installed at the lower part of the primary hydrothermal reaction device to separate the primary hydrothermal liquid and hydrothermal char produced by the hydrothermal reaction of water medium and agricultural and forestry waste, and retain the hydrothermal char in the first solid-liquid separation device. The primary hydrothermal liquid is then transported to the storage device through the liquid delivery pipeline. A second solid-liquid separation device is installed at the lower part of the circulating hydrothermal reaction device to separate the secondary hydrothermal liquid and hydrothermal char produced by the hydrothermal reaction of primary hydrothermal liquid and agricultural and forestry waste, and retain the hydrothermal char in the second solid-liquid separation device. The secondary hydrothermal liquid is collected through the drain port at the bottom of the circulating hydrothermal reaction device. Both the first and second solid-liquid separation devices have a material inlet for collecting the hydrothermal char retained in the first and second solid-liquid separation devices.

[0007] More preferably, the system further includes a multi-stage circulating hydrothermal reaction unit. The hydrothermal liquid outlet of the circulating hydrothermal reaction device in the upper-stage circulating hydrothermal reaction unit is connected to the liquid storage device in the lower-stage circulating hydrothermal reaction unit, for conveying the circulating secondary hydrothermal liquid generated by the circulating hydrothermal reaction device in the upper-stage circulating hydrothermal reaction unit to the liquid storage device in the lower-stage circulating hydrothermal reaction unit. The other agricultural and forestry waste outlet of the feeding unit is connected to the feed inlet of the circulating hydrothermal reaction device in each stage of the circulating hydrothermal reaction unit through a conveying pipeline. The circulating hydrothermal reaction device in each stage of the circulating hydrothermal reaction unit is used to perform a hydrothermal reaction between the received secondary hydrothermal liquid and the agricultural and forestry waste to produce hydrothermal char and circulating secondary hydrothermal liquid.

[0008] Preferably, a first valve is provided on the connecting pipe between one agricultural and forestry waste outlet of the feeding unit and the inlet of the primary hydrothermal reactor, a second valve is provided on the connecting pipe between the other agricultural and forestry waste outlet of the feeding unit and the inlet of the circulating hydrothermal reactor, and a third valve is provided on the connecting pipe between the liquid storage device and the circulating hydrothermal reactor.

[0009] Preferably, the top of the primary hydrothermal reactor is equipped with a movable first top sealing layer for sealing the feed inlet of the primary hydrothermal reactor; the bottom of the primary hydrothermal reactor is equipped with a movable first bottom sealing layer for sealing the first solid-liquid separation device and the feed outlet in the primary hydrothermal reactor.

[0010] Preferably, a movable second top sealing layer is installed on the top of the circulating hydrothermal reactor to seal the feed inlet of the circulating hydrothermal reactor; a movable second bottom sealing layer is installed on the bottom of the circulating hydrothermal reactor to seal the second solid-liquid separation device and the feed outlet in the circulating hydrothermal reactor.

[0011] Preferably, the feeding unit includes a screw feeder and a crushing device connected in sequence. The discharge port of the crushing device is connected to the inlet of the primary hydrothermal reaction device and the circulating hydrothermal reaction device, respectively. The screw feeder is provided with a feeding port and a screw pusher handle.

[0012] A second aspect of this invention proposes a method for the circulating hydrothermal treatment of graded raw materials for agricultural and forestry waste based on the system described above, the method comprising the following steps:

[0013] Step S1: Agricultural and forestry waste is transported from one of the agricultural and forestry waste outlets of the feeding unit to the primary hydrothermal reactor. At the same time, water medium is injected into the primary hydrothermal reactor through the water inlet. The agricultural and forestry waste and the water medium undergo a hydrothermal reaction in the primary hydrothermal reactor to produce hydrothermal carbon and primary hydrothermal liquid.

[0014] Step S2: The primary hydrothermal liquid generated in step S1 is stored in the liquid storage device through the liquid delivery pipeline under the action of the filtration pump. At the same time, agricultural and forestry waste is transported from another agricultural and forestry waste outlet of the feeding unit to the circulating hydrothermal reaction device.

[0015] Step S3: The primary hydrothermal liquid in the storage device is input into the circulating hydrothermal reactor. Agricultural and forestry waste reacts with the primary hydrothermal liquid in the circulating hydrothermal reactor to produce hydrothermal carbon and secondary hydrothermal liquid.

[0016] Preferably, the secondary hydrothermal liquid generated in step S3 is transported through the hydrothermal liquid outlet to the storage device in the next-stage circulating hydrothermal reaction unit for storage. At the same time, the other agricultural and forestry waste outlet of the feeding unit transports agricultural and forestry waste to the circulating hydrothermal reaction device in the next-stage circulating hydrothermal reaction unit through the conveying pipeline. The secondary hydrothermal liquid and the agricultural and forestry waste undergo a hydrothermal reaction in the circulating hydrothermal reaction device to produce hydrothermal char and the first-stage circulating secondary hydrothermal liquid. Then, each time, the N-1th stage circulating secondary hydrothermal liquid generated in the previous stage is transported to the circulating hydrothermal reaction device in the next-stage circulating hydrothermal reaction unit for hydrothermal reaction to obtain the Nth stage circulating secondary hydrothermal liquid, where N is 2-10.

[0017] Preferably, the volume of the secondary hydrothermal liquid is reduced by 20-60 vol% compared to the primary hydrothermal liquid; the volume of the first-stage circulating secondary hydrothermal liquid is reduced by 20-60 vol% compared to the secondary hydrothermal liquid; and the volume of the Nth-stage circulating secondary hydrothermal liquid is reduced by 20-60 vol% compared to the (N-1)th-stage circulating secondary hydrothermal liquid.

[0018] Preferably, in step S1, the solid-liquid ratio of the agricultural and forestry waste to the aqueous medium is 50-200 kg / m³. 3 .

[0019] Preferably, in step S3, the solid-liquid ratio of the agricultural and forestry waste to the primary hydrothermal liquid is 50-200 kg / m³. 3 .

[0020] Preferably, the conditions for the hydrothermal reaction in steps S1 and S3 include: a reaction temperature of 140-220℃ and a reaction time of 15-195 min.

[0021] Preferably, the agricultural and forestry waste includes materials such as straw, sludge, manure, fallen leaves, weeds, and dead branches. More preferably, the particle size of the agricultural and forestry waste is 40-100 mesh.

[0022] The water-saving and energy-saving agricultural and forestry waste graded raw liquid circulating hydrothermal treatment system and method described in this invention has the following beneficial effects:

[0023] (1) The graded raw liquid circulating hydrothermal reaction system constructed in this invention includes key components such as a liquid storage device, a filtration pump and a liquid delivery pipeline. Under the action of the filtration pump, the hydrothermal liquid enters the liquid storage device through the liquid delivery pipeline and is stored therein. It is then used to continue to react with agricultural and forestry waste in a hydrothermal reaction, which reduces the amount of water used to treat agricultural and forestry waste in a hydrothermal reaction and reduces the discharge volume of the hydrothermal liquid (99.85 vol%), which reduces the difficulty of treating the hydrothermal liquid and has significant environmental benefits.

[0024] (2) The graded raw liquid circulating hydrothermal reaction system constructed in this invention is used to treat agricultural and forestry waste, which significantly improves the concentration of organic matter and nutrient ions in the hydrothermal liquid, such as increasing the concentration of organic matter by 3.70 times; the highest yield (76.24wt%) and the maximum higher heating value (24.36MJ / kg) of the circulating hydrothermal carbon are also greatly improved, which is conducive to realizing the resource utilization and high-value utilization of agricultural and forestry waste;

[0025] (3) Agricultural and forestry waste can continuously complete a series of steps such as feeding, crushing, conveying, reaction, product separation and collection in the graded raw liquid circulation hydrothermal reaction system constructed in this invention. Hydrothermal carbon is recovered through the feeding port, and hydrothermal liquid is directly collected by the liquid storage device, which reduces additional manpower input. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of a water-saving and energy-reducing agricultural and forestry waste graded raw liquid circulating hydrothermal treatment system according to one embodiment of the present invention.

[0027] Figure Labels

[0028] 1. Feeding unit; 2. Primary hydrothermal reaction device; 3. Circulating hydrothermal reaction unit; 4. Liquid storage device; 5. Circulating hydrothermal reaction device; 6. Liquid delivery pipeline; 7. Filter pump; 8. First solid-liquid separation device; 9. Material delivery pipeline; 10. First valve; 11. First top sealing layer; 12. First bottom sealing layer; 13. Screw feeder; 14. Crushing device; 15. Feed inlet; 16. Screw pusher handle; 17. Discharge port; 18. Second valve; 19. Second valve; 20. Second top sealing layer; 21. Second bottom sealing layer; 22. Second solid-liquid separation device; 23. Drain port; 24. Water inlet. Detailed Implementation

[0029] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0030] In the hydrothermal treatment of agricultural and forestry waste, organic matter undergoes hydrolysis, generating small molecule products that dissolve and enter the hydrothermal reaction system. These small molecules include organic matter such as organic acids and polysaccharides, as well as inorganic metal minerals such as potassium, calcium, and magnesium, and nutrients such as nitrogen and phosphorus. These dissolved substances serve two purposes: firstly, they are hydrolysis products of straw, possessing recycling value and can be effectively accumulated during the cyclic hydrothermal reaction; secondly, during the hydrothermal reaction, these substances act as active agents, providing autocatalysis and significantly improving the quality of the hydrothermal products. Furthermore, when the reaction temperature is 140-220℃ and the reaction time is 15-195 min, the hydrolyzed organic matter is well retained in the liquid phase, thus maximizing the catalytic effect of the hydrothermal reaction of agricultural and forestry waste and facilitating its resource utilization.

[0031] The first aspect of this invention proposes a water-saving and energy-reducing graded raw material circulating hydrothermal treatment system for agricultural and forestry waste. The system includes a feeding unit 1, a primary hydrothermal reaction device 2, and a circulating hydrothermal reaction unit 3. One agricultural and forestry waste outlet of the feeding unit 1 is connected to the inlet of the primary hydrothermal reaction device 2. The primary hydrothermal reaction device 2 has a water inlet 24 on its side wall for supplying a water medium to the primary hydrothermal reaction device 2. The circulating hydrothermal reaction unit 3 includes a liquid storage device 4 and a circulating hydrothermal reaction device 5 connected in sequence. Another agricultural and forestry waste outlet of the feeding unit 1 is connected to the circulating hydrothermal reaction unit 3. The feed inlet of device 5 is connected; the hydrothermal liquid outlet of the primary hydrothermal reaction device 2 is connected to the liquid storage device 4 through the liquid delivery pipeline 6. The liquid delivery pipeline 6 is equipped with a filtration pump 7. The filtration pump 7 is used to transport the primary hydrothermal liquid produced by the hydrothermal reaction of the water medium and agricultural and forestry waste in the primary hydrothermal reaction device 2 to the liquid storage device 4 through the liquid delivery pipeline 6. The liquid storage device 4 is used to transport the primary hydrothermal liquid to the circulating hydrothermal reaction device 5. The hydrothermal liquid outlet of the circulating hydrothermal reaction device 5 is used to discharge the secondary hydrothermal liquid produced by the hydrothermal reaction of the primary hydrothermal liquid and agricultural and forestry waste.

[0032] In a specific embodiment, both the primary hydrothermal reaction device 2 and the circulating hydrothermal reaction device 5 are hydrothermal reaction vessels, and the liquid storage device 4 is a liquid storage tank.

[0033] In the processing system described in this invention, in a specific embodiment, the feeding unit 1 includes a screw feeder 13 and a crushing device 14 connected in sequence. The discharge port of the crushing device 14 is connected to the inlet of the primary hydrothermal reactor 2 and the circulating hydrothermal reactor 5, respectively. The screw feeder 13 is provided with a feeding port 15 and a screw pusher handle 16. In the specific operation process, agricultural and forestry waste enters from the feeding port 15 and enters the screw feeder 13 at a uniform speed with the assistance of the screw pusher handle 16. Then, it continues to be conveyed to the crushing device 14 for crushing to 40-100 mesh. Then, under the action of high-pressure nitrogen, it is conveyed through the discharge port of the crushing device 14 to the primary hydrothermal reactor 2 and the circulating hydrothermal reactor 5 for hydrothermal reaction treatment.

[0034] In the processing system of the present invention, in a specific embodiment, a first valve 10 is installed on the connecting pipe between one agricultural and forestry waste outlet of the feeding unit 1 and the inlet of the primary hydrothermal reactor 2; a second valve 18 is installed on the connecting pipe between the other agricultural and forestry waste outlet of the feeding unit 1 and the inlet of the circulating hydrothermal reactor 5; and a third valve 19 is installed on the connecting pipe between the liquid storage device 4 and the circulating hydrothermal reactor 5. During implementation, the processing system of the present invention is started, the first valve 10 is opened, and the second valve 18 and the third valve 19 are closed. Agricultural and forestry waste enters the primary hydrothermal reactor 2 from one agricultural and forestry waste outlet of the feeding unit 1, while water medium is simultaneously supplied to the primary hydrothermal reactor 2 through the water inlet 24.

[0035] In a preferred embodiment, a first valve 10 is provided on the connecting pipe between one agricultural and forestry waste outlet of the crushing device 14 and the feed inlet of the primary hydrothermal reaction device 2; a second valve 18 is provided on the connecting pipe between the other agricultural and forestry waste outlet of the crushing device 14 and the feed inlet of the circulating hydrothermal reaction device 5; and a third valve 19 is provided on the connecting pipe between the liquid storage device 4 and the circulating hydrothermal reaction device 5.

[0036] In the processing system described in this invention, in a specific embodiment, a movable first top sealing layer 11 is installed on the top of the primary hydrothermal reactor 2 to seal the feed inlet of the primary hydrothermal reactor 2; a movable first bottom sealing layer 12 is installed on the bottom of the primary hydrothermal reactor 2 to seal the first solid-liquid separation device 8 and the feed outlet 17 in the primary hydrothermal reactor 2. After agricultural and forestry waste and water medium are both transported into the primary hydrothermal reactor 2, the first valve 10 is closed, and both the first top sealing layer 11 and the first bottom sealing layer 12 are kept sealed to ensure a sealed environment for the primary hydrothermal reactor 2. Hydrothermal reaction parameters are set, and the primary hydrothermal reactor 2 begins the hydrothermal reaction.

[0037] In the processing system described in this invention, in a specific embodiment, a first solid-liquid separation device 8 is installed at the lower part of the primary hydrothermal reaction device 2. This device separates the primary hydrothermal liquid and hydrothermal char produced by the hydrothermal reaction of water medium and agricultural and forestry waste, and retains the hydrothermal char in the first solid-liquid separation device 8. The primary hydrothermal liquid is then transported to the storage device 4 through the liquid delivery pipeline 6. The first solid-liquid separation device 8 has a material inlet 17 for collecting the hydrothermal char retained in the first solid-liquid separation device 8. Specifically, the first solid-liquid separation device 8 is a sieve plate with a pore size of less than 50 μm.

[0038] In the specific implementation process, after the hydrothermal reaction in the primary hydrothermal reactor 2 is completed and cooled to room temperature, the first bottom sealing layer 12, the second valve 18, and the third valve 19 are opened, and the filtration pump 7 is turned on. The primary hydrothermal liquid and hydrothermal carbon produced in the primary hydrothermal reactor 2 are separated in the first solid-liquid separation device 8. The hydrothermal carbon is retained in the first solid-liquid separation device 8, while the primary hydrothermal liquid is transported to the storage device 4 through the liquid delivery pipeline 6 under the action of the filtration pump 7. After filtration is completed, the hydrothermal carbon in the first solid-liquid separation device 8 is collected from the feed port 17. Then, according to the volume of primary hydrothermal liquid stored in the storage device 4, an appropriate amount of agricultural and forestry waste is transported to the circulating hydrothermal reactor 5.

[0039] In the processing system described in this invention, in a specific embodiment, a movable second top sealing layer 20 is installed on the top of the circulating hydrothermal reactor 5 to seal the feed inlet of the circulating hydrothermal reactor 5; a movable second bottom sealing layer 21 is installed on the bottom of the circulating hydrothermal reactor 5 to seal the second solid-liquid separation device 22 and the feed outlet 17 in the circulating hydrothermal reactor 5. During specific operation, after the hydrothermal liquid stored in the liquid storage device 4 and a certain amount of agricultural and forestry waste are transported to the circulating hydrothermal reactor 5, the second valve 18 and the third valve 19 are closed, while the second top sealing layer 20 and the second bottom sealing layer 21 are kept sealed to ensure a sealed environment for the circulating hydrothermal reactor 5. Hydrothermal reaction parameters are then set, and the circulating hydrothermal reactor 5 begins the circulating hydrothermal reaction.

[0040] In the processing system described in this invention, in a specific embodiment, a second solid-liquid separation device 22 is installed at the lower part of the circulating hydrothermal reaction device 5. This device separates the secondary hydrothermal liquid and hydrothermal char produced by the hydrothermal reaction of the primary hydrothermal liquid and agricultural and forestry waste, and retains the hydrothermal char in the second solid-liquid separation device 22. The secondary hydrothermal liquid is collected through the drain port 23 at the bottom of the circulating hydrothermal reaction device 5. The second solid-liquid separation device 22 has a feed port 17 for collecting the hydrothermal char retained in the second solid-liquid separation device 22.

[0041] In the specific implementation process, after the hydrothermal reaction in the circulating hydrothermal reactor 5 ends and the circulating hydrothermal reactor 5 cools to room temperature, the second bottom sealing layer 21 is opened. The secondary hydrothermal liquid and hydrothermal carbon generated in the circulating hydrothermal reactor 5 are separated in the second solid-liquid separation device 22. The hydrothermal carbon is retained in the second solid-liquid separation device 22, while the secondary hydrothermal liquid is collected through the drain port 23. The hydrothermal carbon in the second solid-liquid separation device 22 is collected from the feed port 17. Specifically, the second solid-liquid separation device 22 is a sieve plate.

[0042] In the processing system described in this invention, in order to minimize water consumption and additive usage in the hydrothermal reaction, while reducing wastewater treatment volume, lowering production costs, and improving the quality of the hydrothermal liquid, in a preferred embodiment, the system further includes a multi-stage circulating hydrothermal reaction unit 3. Specifically, it may include 2-9 stages of circulating hydrothermal reaction units 3. Each stage of the circulating hydrothermal reaction unit 3 includes a liquid storage device 4 and a circulating hydrothermal reaction device 5. Specifically, the hydrothermal liquid outlet of the circulating hydrothermal reaction device 5 in the previous stage of the circulating hydrothermal reaction unit 3 is connected to the next stage of the circulating hydrothermal reaction unit 5. The storage device 4 in reaction unit 3 is connected, and each connecting pipe is equipped with a filtration pump 7, used to transport the circulating secondary hydrothermal liquid generated by the circulating hydrothermal reactor 5 in the previous stage of circulating hydrothermal reaction unit 3 to the storage device 4 in the next stage of circulating hydrothermal reaction unit 3. The other agricultural and forestry waste outlet of the feeding unit 1 is connected to the inlet of the circulating hydrothermal reactor 5 in each stage of circulating hydrothermal reaction unit 3 via a conveying pipe 9. Specifically, the agricultural and forestry waste enters the circulating hydrothermal reactor 5 in each stage of circulating hydrothermal reaction unit 3 under the action of high-pressure nitrogen gas. The circulating hydrothermal reactor 5 in each stage of circulating hydrothermal reaction unit 3 is used to perform a hydrothermal reaction between the received secondary hydrothermal liquid and the agricultural and forestry waste to form a circulating secondary hydrothermal liquid containing hydrothermal carbon.

[0043] In the specific operation process, the primary hydrothermal liquid generated by the primary hydrothermal reactor 2 is stored in the primary storage device 4. According to the volume of the primary hydrothermal liquid stored in the primary storage device 4, an appropriate mass of agricultural and forestry waste is transported to the primary circulating hydrothermal reactor 5 for the first circulating hydrothermal reaction. Then, the secondary hydrothermal liquid generated by the primary circulating hydrothermal reactor 5 is stored in the secondary storage device 4. Then, according to the volume of the secondary hydrothermal liquid stored in the secondary storage device 4, an appropriate mass of agricultural and forestry waste is transported to the secondary circulating hydrothermal reactor 5 for the second circulating hydrothermal reaction. This process is repeated until it enters the final circulating hydrothermal reactor unit 3. The circulating secondary hydrothermal liquid generated by the final circulating hydrothermal reactor 5 is collected through the drain port 23.

[0044] In the processing system described in this invention, in a specific embodiment, each level of circulating hydrothermal reaction unit 3 can work simultaneously in sequence, thereby improving work efficiency.

[0045] In the processing system described in this invention, during the solid-liquid separation of hydrothermal products, the hydrothermal carbon carries away a portion of the liquid, resulting in a decrease in the hydrothermal liquid recovery rate, which is 20-60 vol%. As the number of cyclic reactions increases, the degree of carbonization of the hydrothermal carbon increases, its hydrophilicity decreases, and the reduction in hydrothermal liquid gradually decreases. To ensure the airtightness of the reaction environment and to avoid wasting space, in a preferred embodiment, the volume of the circulating hydrothermal reaction device 5 in the next-stage circulating hydrothermal reaction unit 3 is smaller than that in the previous-stage circulating hydrothermal reaction unit 3. Specifically, when the average reduction in hydrothermal liquid entering each stage of the circulating hydrothermal reaction device 5 is 20 vol%, and the circulating hydrothermal reaction unit 3 has eight stages, with the volume of the primary hydrothermal reaction device 2 as 1, the volumes of each stage of the circulating hydrothermal reaction device 5 increase sequentially as follows: 0.8000, 0.6400, 0.5120, 0.4096, 0.3277, 0.2621, 0.2097, and 0.1678. Specifically, when the average amount of hydrothermal liquid entering each stage of the circulating hydrothermal reactor 5 decreases by 40 vol%, and the circulating hydrothermal reactor unit 3 has eight stages, with the volume of the primary hydrothermal reactor 2 as 1, the volumes of each stage of the circulating hydrothermal reactor 5 increase sequentially to 0.6000, 0.3600, 0.2160, 0.1296, 0.0778, 0.0467, 0.0280, and 0.0168. Specifically, when the average amount of hydrothermal liquid entering each stage of the circulating hydrothermal reactor 5 decreases by 60 vol%, and the circulating hydrothermal reactor unit 3 has eight stages, with the volume of the primary hydrothermal reactor 2 as 1, the volumes of each stage of the circulating hydrothermal reactor 5 increase sequentially to 0.4000, 0.1600, 0.0640, 0.0256, 0.0102, 0.0041, 0.0016, and 0.0007.

[0046] In the specific operation, agricultural and forestry waste enters through the feeding port 15 and, with the assistance of the spiral push handle 16, enters the spiral feeding device 13 at a uniform speed. It continues to be conveyed to the crushing device 14 for crushing to 40-100 mesh. Then, the first valve 10 is opened, and the agricultural and forestry waste is conveyed to the primary hydrothermal reactor 2 under the action of high-pressure nitrogen. Simultaneously, a certain volume of water medium is conveyed into the primary hydrothermal reactor 2 through the water inlet 24. Then, the first valve 10 is closed, keeping both the first top sealing layer 11 and the first bottom sealing layer 12 sealed. The hydrothermal reaction parameters are set (reaction temperature 140-220°C). The primary hydrothermal reaction device 2 begins hydrothermal reaction at ℃ (reaction time is 15-195 min). When the hydrothermal reaction in the primary hydrothermal reaction device 2 ends, the primary hydrothermal liquid and hydrothermal carbon produced are separated in the first solid-liquid separation device 8. The hydrothermal carbon is retained in the first solid-liquid separation device 8. After the primary hydrothermal reaction device 2 cools to room temperature, the first bottom sealing layer 12 and the filtration pump 7 are opened. The primary hydrothermal liquid is then transported to the liquid storage device 4 through the liquid delivery pipeline 6 under the action of the filtration pump 7. After filtration ends, the hydrothermal carbon in the first solid-liquid separation device 8 is collected from the feed port 17.

[0047] Next, the third valve 19 is opened, and the primary hydrothermal liquid stored in the liquid storage device 4 enters the circulating hydrothermal reactor 5. At the same time, a certain mass of agricultural and forestry waste is fed into the feed port 15 and fed into the screw feeder 13 at a uniform speed with the assistance of the screw pusher handle 16. It is then conveyed to the crushing device 14 for crushing to 40-100 mesh. The second valve 18 is then opened, and the crushed agricultural and forestry waste is conveyed to the circulating hydrothermal reactor 5 under the action of high-pressure nitrogen. Then, the second valve 18 and the third valve 19 are closed, and the second top sealing layer 20 and the second bottom sealing layer 21 are kept in a sealed state. The hydrothermal reaction parameters are set (reaction temperature is 140-220℃, reaction time is 15-195min), and the circulating hydrothermal reactor 5 begins to carry out the circulating hydrothermal reaction. When the circulating hydrothermal reaction in the circulating hydrothermal reactor 5 ends, the secondary hydrothermal liquid and hydrothermal carbon produced are separated in the second solid-liquid separation device 22, and the hydrothermal carbon is retained in the second solid-liquid separation device 22.

[0048] Then, the second bottom sealing layer 21 is opened, allowing the secondary hydrothermal liquid separated from the second solid-liquid separation device 22 to be transported to the next-stage circulating hydrothermal reactor 5. At the same time, a certain mass of crushed agricultural and forestry waste continues to be transported to the next-stage circulating hydrothermal reactor 5 through the conveying pipeline 9 for circulating hydrothermal reaction. This cycle is repeated until the last circulating hydrothermal reaction ends, and the resulting hydrothermal liquid is collected through the drain port 23.

[0049] A second aspect of this invention proposes a method for the circulating hydrothermal treatment of graded raw materials for agricultural and forestry waste based on the system described above, the method comprising the following:

[0050] Step S1: Agricultural and forestry waste is transported from one of the agricultural and forestry waste outlets of the feeding unit 1 to the primary hydrothermal reactor 2. At the same time, water medium is injected into the primary hydrothermal reactor 2 through the water inlet 24. The agricultural and forestry waste and the water medium undergo a hydrothermal reaction in the primary hydrothermal reactor 2 to produce hydrothermal carbon and primary hydrothermal liquid.

[0051] Step S2: The primary hydrothermal liquid generated in step S1 is stored in the liquid storage device 4 through the liquid delivery pipeline 6 under the action of the filtration pump 7. At the same time, agricultural and forestry waste is transported from another agricultural and forestry waste outlet of the feeding unit 1 to the circulating hydrothermal reaction device 5.

[0052] Step S3: The primary hydrothermal liquid in the storage device 4 is input into the circulating hydrothermal reactor 5. Agricultural and forestry waste and the primary hydrothermal liquid undergo a hydrothermal reaction in the circulating hydrothermal reactor 5 to produce hydrothermal carbon and secondary hydrothermal liquid.

[0053] In the method described in this invention, in a preferred embodiment, the secondary hydrothermal liquid generated in step S3 is transported through the hydrothermal liquid outlet to the storage device 4 in the next-stage circulating hydrothermal reaction unit 3 for storage. At the same time, another agricultural and forestry waste outlet of the feeding unit 1 is transported through the conveying pipeline 9 to the circulating hydrothermal reaction device 5 in the next-stage circulating hydrothermal reaction unit 3. The secondary hydrothermal liquid and the agricultural and forestry waste undergo a hydrothermal reaction in the circulating hydrothermal reaction device 5 to produce hydrothermal char and the first-stage circulating secondary hydrothermal liquid. Then, each time, the N-1th stage circulating secondary hydrothermal liquid generated in the previous stage is transported to the circulating hydrothermal reaction device 5 in the next-stage circulating hydrothermal reaction unit 3 for hydrothermal reaction to obtain the Nth stage circulating secondary hydrothermal liquid, where N is 2-10.

[0054] In the method described in this invention, in a specific embodiment, the agricultural and forestry waste includes materials such as straw, sludge, manure, fallen leaves, weeds, and dead branches.

[0055] In the method described in this invention, the surface of the hydrothermal carbon contains abundant functional groups and has good wettability. During solid-liquid separation, it can carry a considerable amount of water, resulting in a reduction in hydrothermal liquid. As the number of cyclic hydrothermal reactions increases, the degree of carbonization of the hydrothermal carbon increases, its hydrophobicity decreases, and the liquid reduction rate decreases. In a specific embodiment, the volume of the secondary hydrothermal liquid is reduced by 20-60 vol% compared to the primary hydrothermal liquid; the volume of the first-stage cyclic secondary hydrothermal liquid is reduced by 20-60 vol% compared to the secondary hydrothermal liquid; and the volume of the Nth-stage cyclic secondary hydrothermal liquid is reduced by 20-60 vol% compared to the (N-1)th-stage cyclic secondary hydrothermal liquid.

[0056] In the method described in this invention, in a specific embodiment, the particle size of the agricultural and forestry waste is 40-100 mesh to ensure sufficient contact between the material and the water medium and to reduce the resistance during pneumatic conveying.

[0057] In the method described in this invention, in a specific embodiment, in step S1, the solid-liquid ratio of the agricultural and forestry waste to the aqueous medium is 50-200 kg / m³. 3 .

[0058] In the method described in this invention, in a specific embodiment, in step S3, the solid-liquid ratio of the agricultural and forestry waste to the primary hydrothermal liquid is 50-200 kg / m³. 3 .

[0059] In the method described in this invention, in a specific embodiment, the conditions for the hydrothermal reaction in steps S1 and S3 include: a reaction temperature of 140-220°C and a reaction time of 15-195 min.

[0060] The following examples further illustrate the water-saving and energy-reducing agricultural and forestry waste graded raw liquid circulating hydrothermal treatment system and method of the present invention. These examples are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures; however, the scope of protection of the present invention is not limited to the following examples.

[0061] The water-saving and energy-reducing methods for the graded raw liquid recycling hydrothermal treatment of agricultural and forestry waste in Examples 1-3 and Comparative Example 1 are all implemented in the system described below, such as... Figure 1As shown, the system includes a feeding unit 1, a primary hydrothermal reaction device 2, and an eight-stage circulating hydrothermal reaction unit 3. The feeding unit 1 includes a screw feeder 13 and a crushing device 14 connected in sequence. The screw feeder 13 is equipped with a feeding port 15 and a screw pusher handle 16. One discharge port of the crushing device 14 is connected to the feed port of the primary hydrothermal reaction device 2. A first valve 10 is installed on the connecting pipe between the discharge port of the crushing device 14 and the feed port of the primary hydrothermal reaction device 2. The eight circulating hydrothermal reaction units 3 are respectively primary, secondary, and tertiary hydrothermal reaction units 3. The system comprises eight stages of circulating hydrothermal reaction units 3, each including a liquid storage device 4 and a circulating hydrothermal reaction device 5 connected in sequence. A third valve 19 is installed on the connecting pipe between the liquid storage device 4 and the circulating hydrothermal reaction device 5. The other outlet of the pulverizing device 14 is connected to the inlet of the circulating hydrothermal reaction device 5 in each stage of the circulating hydrothermal reaction unit 3. A second valve 18 is installed on the connecting pipe between the other outlet of the pulverizing device 14 and the inlet of the circulating hydrothermal reaction device 5 in each stage. The primary hydrothermal reactor 2 has a water inlet 24 on its side wall for supplying water medium to the primary hydrothermal reactor 2; a movable first top sealing layer 11 is installed on the top of the primary hydrothermal reactor 2, and a movable first bottom sealing layer 12 is installed on the bottom of the primary hydrothermal reactor 2; a first solid-liquid separation device 8 (sieve plate) is installed at the lower part of the primary hydrothermal reactor 2 for separating the primary hydrothermal liquid produced by the hydrothermal reaction from the hydrothermal carbon, and retaining the hydrothermal carbon in the first solid-liquid separation device 8; the primary hydrothermal reactor 2 The bottom (hydrothermal liquid outlet) of the device is connected to the primary storage device 4 via a liquid delivery pipeline 6. A filtration pump 7 is installed on the liquid delivery pipeline 6. The filtration pump 7 is used to transport the primary hydrothermal liquid generated in the primary hydrothermal reactor 2 to the primary storage device 4 via the liquid delivery pipeline 6. The primary storage device 4 is used to transport the primary hydrothermal liquid to the primary circulating hydrothermal reactor 5. A movable second top sealing layer 20 is installed on the top of each circulating hydrothermal reactor 5, and a movable second bottom sealing layer 21 is installed on the bottom of each circulating hydrothermal reactor 5.Each stage of the circulating hydrothermal reactor 5 is equipped with a second solid-liquid separation device 22 at its lower part. This device separates the secondary hydrothermal liquid produced by the circulating hydrothermal reaction from the hydrothermal carbon, retaining the hydrothermal carbon in the second solid-liquid separation device 22. Simultaneously, the generated secondary hydrothermal liquid is transported by the suction pump 7 through the liquid delivery pipeline 6 to the next stage storage device 4 for storage and then to the next stage of the circulating hydrothermal reactor 5 for the next round of circulating hydrothermal reaction. This process continues until the circulating hydrothermal reaction in the eight-stage circulating hydrothermal reactor 5 is completed. The separated secondary hydrothermal liquid is collected from the drain port 23, while the generated hydrothermal carbon is collected from the primary hydrothermal reactor 2 and the feed inlet 17 of each stage of the circulating hydrothermal reactor 5.

[0062] Rice straw raw material: from the experimental base of Huazhong Agricultural University, crushed through a 40-mesh sieve, with a moisture content of 9.23 wt%.

[0063] Example 1

[0064] Step S1: 10 tons of dried rice straw are fed into the feed inlet 15 and, with the assistance of the screw pusher handle 16, are fed into the screw feeder 13 at a uniform speed. The straw is then conveyed to the crushing device 14 for crushing to 40 mesh. The first valve 10 is then opened, and the agricultural and forestry waste is conveyed to the primary hydrothermal reactor 2 under high-pressure nitrogen. Simultaneously, a certain volume of magnesium acetate at a concentration of 8 kg / m³ is fed into the primary hydrothermal reactor 2 through the water inlet 24. 3 The aqueous medium results in a solid-liquid ratio of 80 kg / m³. 3 Then, the first valve 10 is closed to keep the first top sealing layer 11 and the first bottom sealing layer 12 sealed. The hydrothermal reaction parameters are set (reaction temperature is 180℃, reaction time is 120min), and the primary hydrothermal reaction device 2 starts to carry out the hydrothermal reaction. When the hydrothermal reaction in the primary hydrothermal reaction device 2 ends, the primary hydrothermal liquid and hydrothermal carbon produced are separated in the first solid-liquid separation device 8. The hydrothermal carbon is retained in the first solid-liquid separation device 8. After the primary hydrothermal reaction device 2 cools to room temperature, the first bottom sealing layer 12 and the filtration pump 7 are opened. The primary hydrothermal liquid is then transported to the storage device 4 of the first-stage circulating hydrothermal reaction unit 3 through the liquid delivery pipeline 6 under the action of the filtration pump 7. After the filtration ends, the hydrothermal carbon in the first solid-liquid separation device 8 is collected from the feed port 17.

[0065] Step S2: Next, open the third valve 19, and the primary hydrothermal liquid stored in the primary liquid storage device 4 of the primary circulating hydrothermal reaction unit 3 enters the primary circulating hydrothermal reaction unit 5. At the same time, a certain mass of agricultural and forestry waste is introduced from the feed port 15, so that the solid-liquid ratio is 80 kg / m³. 3With the assistance of the spiral push handle 16, the waste enters the spiral feeding device 13 at a uniform speed and continues to be conveyed to the crushing device 14 for crushing. After crushing to 40 mesh, the second valve 18 is opened, and the crushed agricultural and forestry waste is conveyed to the first-stage circulating hydrothermal reactor 5 under the action of high-pressure nitrogen. Then, the second valve 18 and the third valve 19 are closed, and the second top sealing layer 20 and the second bottom sealing layer 21 are kept in a sealed state. The hydrothermal reaction parameters are set (reaction temperature is 200℃, reaction time is 100min), and the first-stage circulating hydrothermal reactor 5 begins the first circulating hydrothermal reaction. When the circulating hydrothermal reaction in the first-stage circulating hydrothermal reactor 5 ends, the secondary hydrothermal liquid and hydrothermal carbon produced are separated in the second solid-liquid separation device 22, and the hydrothermal carbon is retained in the second solid-liquid separation device 22.

[0066] Step S3: Then open the second bottom sealing layer 21 to transport the secondary hydrothermal liquid separated from the second solid-liquid separation device 22 to the next-stage circulating hydrothermal reactor 5. At the same time, a certain mass of crushed agricultural and forestry waste is transported to the next-stage circulating hydrothermal reactor 5 through the conveying pipeline 9 to carry out circulating hydrothermal reaction, forming circulating secondary hydrothermal liquid with hydrothermal carbon. The circulating secondary hydrothermal liquid is then transported to the circulating hydrothermal reactor 5 of the next-stage circulating hydrothermal reaction unit 3 for reaction, and the cycle is repeated until the eighth stage of circulating hydrothermal reaction is completed. The final generated circulating secondary hydrothermal liquid is collected through the drain port 23.

[0067] Example 2

[0068] The procedure is carried out in accordance with Example 1, except that in step S2, the hydrothermal liquid in the storage device 4 is replenished with magnesium acetate at a concentration of 8 kg / m³. 3 The water medium is used to maintain a consistent volume of aqueous solution each time, and the same amount of material is added in each reaction.

[0069] Example 3

[0070] The process is carried out in accordance with Example 1, except that an appropriate amount of water is added to the hydrothermal liquid in the storage device 4 to maintain the consistency of the aqueous solution volume each time, and the same amount of material is added for each reaction.

[0071] Comparative Example 1

[0072] The implementation follows the method of Example 1, except that steps S2 and S3 are omitted, and the hydrothermal carbon and hydrothermal liquid separated by the first solid-liquid separation device 8 in step S1 are directly collected.

[0073] Test case

[0074] Examples 1-3 and Comparative Example 1 were evaluated based on water consumption, hydrothermal liquid production, product benefits, and product properties. According to the current "General Rules for Calculating Comprehensive Energy Consumption" (GB / T2589–2020), the calorific value of standard coal is 29.27 MJ / kg, and the results are shown in Table 1.

[0075] Assuming all hydrothermal carbon is used as fuel and the liquid products are treated as wastewater, estimate the product benefits based on the average calorific value, yield, water consumption, and hydrothermal liquid production of the aforementioned hydrothermal carbon. When estimating water supply and wastewater treatment fees, the current non-residential water supply fee in Wuhan (starting August 1, 2014) of 2.35 yuan / m³ will be used. 3 ) and wastewater treatment (1.37 yuan / m³) 3 The pricing standards are as follows: coal price is calculated at 950 yuan / ton; additives are calculated at an average of 800 yuan / ton. The benefit assessment results are shown in Table 2.

[0076] The quality of the hydrothermal liquids prepared in Examples 1-3 and Comparative Example 1 was determined, and the results are shown in Table 3.

[0077] Table 1 Hydrothermal Product Yield and Material Input

[0078]

[0079]

[0080] Table 2 Material Costs and Values ​​of Hydrothermal Products

[0081]

[0082] Table 3. Composition and properties of hydrothermal fluids

[0083]

[0084] As can be seen from the above data, compared with Comparative Example 1, the water-saving and energy-saving agricultural and forestry waste grading raw liquid circulating hydrothermal treatment system of the present invention can significantly improve the quality of hydrothermal char and hydrothermal liquid. Compared with Comparative Example 1, in Example 1 of the present invention, the value of hydrothermal char is increased by 1.15 times, and the costs of additives, water supply, and wastewater treatment are reduced by 44.91%, 44.78%, and 99.85%, respectively, effectively improving product value and efficiency while reducing energy consumption. The water-saving and energy-saving agricultural and forestry waste grading raw liquid circulating hydrothermal treatment system and method of the present invention can significantly reduce the water consumption and liquid discharge for treating agricultural and forestry waste, thereby reducing the cost of straw hydrothermal treatment. Compared to Comparative Example 1, the system of the present invention produces a hydrothermal liquid volume of only 0.15 vol% of that in Comparative Example 1, greatly reducing storage capacity. At the same time, the concentration of organic matter in the hydrothermal liquid is increased. The total organic carbon concentration in the hydrothermal liquid of Example 1 is 3.70 times that in the hydrothermal liquid of Comparative Example 1. This shows that the present invention not only saves energy and reduces consumption in the treatment of agricultural and forestry waste, but also facilitates the production of high-quality hydrothermal products, thereby greatly promoting the resource utilization and value-added utilization of agricultural and forestry waste.

[0085] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A water-saving and energy-reducing graded raw liquid circulating hydrothermal treatment system for agricultural and forestry waste, characterized in that, The system includes a feeding unit (1), a primary hydrothermal reaction device (2) and a circulating hydrothermal reaction unit (3). One of the agricultural and forestry waste discharge ports of the feeding unit (1) is connected to the feed port of the primary hydrothermal reaction device (2). The primary hydrothermal reaction device (2) has a water inlet (24) for supplying water medium to the primary hydrothermal reaction device (2). The circulating hydrothermal reaction unit (3) includes a liquid storage device (4) and a circulating hydrothermal reaction device (5) connected in sequence. The other agricultural and forestry waste discharge port of the feeding unit (1) is connected to the feed port of the circulating hydrothermal reaction device (5). The hydrothermal liquid outlet of the primary hydrothermal reaction device (2) is connected to the storage device (4) through a liquid delivery pipeline (6). A filtration pump (7) is installed on the liquid delivery pipeline (6). The filtration pump (7) is used to transport the primary hydrothermal liquid generated after the hydrothermal reaction of the water medium in the primary hydrothermal reaction device (2) with agricultural and forestry waste to the storage device (4) through the liquid delivery pipeline (6). The storage device (4) is used to transport the primary hydrothermal liquid to the circulating hydrothermal reaction device (5). The hydrothermal liquid outlet of the circulating hydrothermal reaction device (5) is used to discharge the secondary hydrothermal liquid generated after the hydrothermal reaction of the primary hydrothermal liquid with agricultural and forestry waste. The lower part of the primary hydrothermal reaction device (2) is equipped with a first solid-liquid separation device (8), which is used to separate the primary hydrothermal liquid and hydrothermal carbon generated by the hydrothermal reaction of water medium and agricultural and forestry waste, and retain the hydrothermal carbon in the first solid-liquid separation device (8), while the primary hydrothermal liquid is transported to the liquid storage device (4) through the liquid delivery pipeline (6). The lower part of the circulating hydrothermal reactor (5) is equipped with a second solid-liquid separation device (22) for separating the secondary hydrothermal liquid and hydrothermal carbon produced by the hydrothermal reaction of primary hydrothermal liquid and agricultural and forestry waste, and retaining the hydrothermal carbon in the second solid-liquid separation device (22). The secondary hydrothermal liquid is collected through the drain port (23) at the bottom of the circulating hydrothermal reactor (5). The first solid-liquid separation device (8) and the second solid-liquid separation device (22) are both equipped with a feed port (17) for collecting the hydrothermal carbon retained in the first solid-liquid separation device (8) and the second solid-liquid separation device (22). The top of the primary hydrothermal reactor (2) is equipped with a movable first top sealing layer (11) for sealing the feed port of the primary hydrothermal reactor (2). The bottom of the primary hydrothermal reactor (2) is equipped with a movable first bottom sealing layer (12) for sealing the first solid-liquid separation device (8) and the feed port (17) in the primary hydrothermal reactor (2). The top of the circulating hydrothermal reactor (5) is equipped with a movable second top sealing layer (20) for sealing the feed inlet of the circulating hydrothermal reactor (5); the bottom of the circulating hydrothermal reactor (5) is equipped with a movable second bottom sealing layer (21) for sealing the second solid-liquid separation device (22) and the feed outlet (17) in the circulating hydrothermal reactor (5).

2. The system according to claim 1, characterized in that, The system also includes a multi-stage circulating hydrothermal reaction unit (3). The hydrothermal liquid outlet of the circulating hydrothermal reaction device (5) in the upper-stage circulating hydrothermal reaction unit (3) is connected to the liquid storage device (4) in the lower-stage circulating hydrothermal reaction unit (3) to transport the circulating secondary hydrothermal liquid generated by the circulating hydrothermal reaction device (5) in the upper-stage circulating hydrothermal reaction unit (3) to the liquid storage device (4) in the lower-stage circulating hydrothermal reaction unit (3). Another agricultural and forestry waste outlet of the feeding unit (1) is connected to the inlet of the circulating hydrothermal reaction device (5) in the circulating hydrothermal reaction unit (3) at each level through the conveying pipeline (9). The circulating hydrothermal reaction device (5) in the circulating hydrothermal reaction unit (3) at each level is used to perform hydrothermal reaction between the received secondary hydrothermal liquid and agricultural and forestry waste to produce hydrothermal carbon and circulating secondary hydrothermal liquid.

3. The system according to claim 1, characterized in that, A first valve (10) is installed on the connecting pipe between one agricultural and forestry waste outlet of the feeding unit (1) and the inlet of the primary hydrothermal reactor (2). A second valve (18) is installed on the connecting pipe between the other agricultural and forestry waste outlet of the feeding unit (1) and the inlet of the circulating hydrothermal reactor (5). A third valve (19) is installed on the connecting pipe between the liquid storage device (4) and the circulating hydrothermal reactor (5).

4. The system according to claim 1, characterized in that, The feeding unit (1) includes a screw feeder (13) and a crushing device (14) connected in sequence. The discharge port of the crushing device (14) is connected to the feed ports of the primary hydrothermal reaction device (2) and the circulating hydrothermal reaction device (5). The screw feeder (13) is provided with a feeding port (15) and a screw pusher handle (16).

5. A method for circulating hydrothermal treatment of graded raw materials of agricultural and forestry waste based on the system described in any one of claims 1-4, characterized in that, The method includes the following steps: Step S1: Agricultural and forestry waste is transported from one of the agricultural and forestry waste outlets of the feeding unit (1) to the primary hydrothermal reaction device (2), and water medium is injected into the primary hydrothermal reaction device (2) through the water inlet (24). The agricultural and forestry waste and the water medium undergo hydrothermal reaction in the primary hydrothermal reaction device (2) to produce hydrothermal carbon and primary hydrothermal liquid. Step S2: The primary hydrothermal liquid generated in step S1 is stored in the liquid storage device (4) through the liquid delivery pipeline (6) under the action of the filtration pump (7). At the same time, agricultural and forestry waste is transported from another agricultural and forestry waste outlet of the feeding unit (1) to the circulating hydrothermal reaction device (5). Step S3: The primary hydrothermal liquid in the storage device (4) is input into the circulating hydrothermal reaction device (5). Agricultural and forestry waste and primary hydrothermal liquid undergo hydrothermal reaction in the circulating hydrothermal reaction device (5) to produce hydrothermal carbon and secondary hydrothermal liquid.

6. The method according to claim 5, characterized in that, The secondary hydrothermal liquid generated in step S3 is transported through the hydrothermal liquid outlet to the storage device (4) in the next-level circulating hydrothermal reaction unit (3) for storage. At the same time, the other agricultural and forestry waste outlet of the feeding unit (1) is transported through the conveying pipeline (9) to the circulating hydrothermal reaction device (5) in the next-level circulating hydrothermal reaction unit (3). The secondary hydrothermal liquid and the agricultural and forestry waste undergo hydrothermal reaction in the circulating hydrothermal reaction device (5) to produce hydrothermal carbon and the first-level circulating secondary hydrothermal liquid. Then, each time, the N-1th level circulating secondary hydrothermal liquid generated in the previous stage is transported to the circulating hydrothermal reaction device (5) of the next level circulating hydrothermal reaction unit (3) for hydrothermal reaction to obtain the Nth level circulating secondary hydrothermal liquid, where N is 2-10.

7. The method according to claim 6, characterized in that, The secondary hydrothermal fluid has a volume reduction of 20-60 vol% compared to the primary hydrothermal fluid. The volume of the first-stage circulating secondary hydrothermal liquid is reduced by 20-60 vol% compared to the secondary hydrothermal liquid. The volume of the secondary hydrothermal liquid in the Nth stage circulation is reduced by 20-60 vol compared to that in the (N-1)th stage circulation.

8. The method according to claim 5, characterized in that, In step S1, the solid-liquid ratio of the agricultural and forestry waste to the aqueous medium is 50-200 kg / m³. 3 ; In step S3, the solid-liquid ratio of the agricultural and forestry waste to the primary hydrothermal liquid is 50-200 kg / m³. 3 ; The conditions for the hydrothermal reaction in steps S1 and S3 include: a reaction temperature of 140-220°C and a reaction time of 15-195 min; The agricultural and forestry waste includes straw, sludge, manure, fallen leaves, weeds, and dead branches; The particle size of the agricultural and forestry waste is 40-100 mesh.

Images