Energy-saving system for horizontal tube continuous cooking and waste heat recovery method

Abstract

The application discloses a kind of transverse tube continuous cooking energy-saving system and waste heat recovery method, the transverse tube continuous cooking energy-saving system of the present application includes preheating spiral, feeder, T-shaped pipe, cooking pipe, unloader, spray pipe, spray pot, black liquor tank, cooking medicine liquor tank, pressure-reducing unloading cyclone separator, flash vapor compression device, injection absorption heat pump and pressure cooking medicine liquor heating tank.The present application aims to solve the problems of high energy consumption, low waste heat utilization rate, low spray pulp concentration and low flash vapor heat energy grade in traditional transverse tube continuous cooking process;reduce factory area white mist thermal pollution, without changing the quality of fiber and finished pulp, can be low-cost reformed in existing production line, with short payback period, suitable for reed, wheat straw, bagasse, bamboo pulp and eucalyptus broad-leaved wood pulp transverse tube cooking process, in line with the green and low-carbon development requirements of pulp industry.

Description

Technical Field

[0001] This invention belongs to the field of energy-saving technology in pulp and paper making, specifically relating to an energy-saving system for continuous cooking in a horizontal tube and a method for waste heat recovery. Background Technology

[0002] Continuous cooking in horizontal tubes is the mainstream core process in the non-wood pulping industry. It has advantages such as continuous operation, uniform pulp quality, high production efficiency, and controllable pollutants, and is widely used in the large-scale production of straw pulps such as reeds, wheat straw, bagasse, and bamboo chips. Traditional continuous cooking in horizontal tubes generally adopts a cold spray process, which has technical shortcomings: the high-temperature cooked pulp (around 160°C) is directly mixed and heated with cold black liquor (around 85°C), causing the pulp temperature to drop sharply to 105°C. This results in a significant drop in the system's heat energy grade, and a large amount of high-temperature waste heat is directly degraded into low-grade heat energy, which is difficult to recover by conventional methods. The flash steam generated in the spray boiler under normal pressure is directly discharged, forming a large area of ​​"white fog" thermal pollution in the plant area, while also causing a huge amount of ineffective heat energy loss. Based on GB / T1927.1 "General Rules for Energy Balance Calculation of Pulp and Paper Equipment", on-site measurements and calculations of the production line show that the total heat input of the traditional system is approximately 31.15 GJ / h, with steam accounting for as much as 90.36%. The three core waste points are steam loss during spraying, heating of raw materials with high moisture content, and heat exchange loss during unloading, accounting for more than 60% of the total heat input. The steam consumption per ton of pulp in traditional horizontal tube cooking of reed pulp is as high as 5.0–5.5 GJ / t, with older production lines exceeding 6.0 GJ / t, far exceeding the levels of advanced cooking processes such as DDS. Taking a 50,000-ton-per-year air-dried reed pulp production line as an example, for every 0.1 GJ increase in steam consumption per ton of pulp, the annual increase in steam cost exceeds 1 million yuan. At the same time, the traditional process relies on manual control of the cold black liquor dosage and steam supply, resulting in large fluctuations in process parameters, easily leading to lignin aggregation and unstable pulp consistency, with the overall system thermal energy utilization rate being less than 60%. Existing energy-saving technologies lack waste heat recovery and utilization solutions adapted to the entire horizontal tube continuous steaming process. They cannot simultaneously achieve significant reductions in steam consumption, elimination of "white fog," and stable operation under adaptive conditions without replacing large main equipment, reducing slurry quality, or incurring low retrofit costs. Therefore, realizing waste heat recovery in horizontal tube continuous steaming energy-saving systems has significant engineering application value. Summary of the Invention

[0003] The technical problem to be solved by this invention is as follows: Addressing the aforementioned problems in existing technologies, this invention provides an energy-saving system and waste heat recovery method for continuous horizontal tube cooking. The invention aims to solve the problems of high energy consumption, low waste heat utilization, low pulp concentration, and low flash steam heat energy grade in traditional continuous horizontal tube cooking processes. It reduces white fog heat pollution in the plant area, does not alter the quality of fibers and finished pulp, can be implemented in existing production lines at low cost, has a short investment payback period, and is suitable for horizontal tube cooking processes of reed, wheat straw, bagasse, bamboo pulp, and eucalyptus hardwood pulp, aligning with the green and low-carbon development requirements of the pulping industry.

[0004] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A horizontal tube continuous cooking energy-saving system includes a preheating screw, a feeder, a T-tube, a cooking tube, a discharger, a spray pipe, a spray pan, a black liquor tank, a cooking liquid tank, a pressure-reducing discharge cyclone separator, a flash vapor compression device, a jet-type absorption heat pump, and a pressure cooking liquid heating tank. The raw material sequentially passes through the preheating screw, feeder, T-tube, cooking tube, discharger, and spray pipe before entering the pressure-reducing discharge cyclone separator. The high-temperature slurry is separated from the flash vapor by the pressure-reducing discharge cyclone separator. The separated low-grade flash vapor is then... After being pressurized and upgraded into high-quality cooking steam by the flash steam compression device, the steam is sent into the T-tube. The black liquor supplied by the black liquor tank and the high-temperature slurry separated by the pressure relief unloading cyclone separator are sent together into the discharge pot. The cooking liquid in the cooking liquid tank is pressurized by the liquid pump and then the flash steam from the discharge pot is drawn through the nozzle and sent into the jet absorption heat pump to use the waste heat of the flash steam from the pressure relief unloading cyclone separator and the waste heat of the slurry recovered by the jet absorption heat pump to prepare high-temperature cooking liquid. The high-temperature cooking liquid is then sent into the T-tube by the circulation pump.

[0005] Optionally, the pressure-reducing unloading cyclone separator consists of an upper separation cylinder and a lower slurry storage tank. The separation cylinder has a pulp and flash steam inlet on one side, a drive device and a steam outlet at the top, and a rotatable separation scraper inside. The separation scraper is connected to the drive device to separate the high-temperature pulp from the inner wall of the separation cylinder. Inspection ports are provided on the side walls of both the separation cylinder and the slurry storage tank. A black liquor inlet is provided at the bottom of the separation cylinder for inputting black liquor supplied from the black liquor tank. A rotatable stirring impeller is provided inside the slurry storage tank and is connected to the drive device. Multiple transmitter mounting ports and a slurry outlet are provided on the side wall of the slurry storage tank. The transmitter mounting ports are used to install sensors and transmitters for detecting the internal working status of the slurry storage tank.

[0006] Optionally, both the separation cylinder and the pulp storage tank are cylindrical structures, the separation scraper is a spiral structure, and the pulp and flash steam inlets are arranged on the outside of the separation scraper to achieve tangential feeding.

[0007] Optionally, the pressure-reducing unloading cyclone separator is equipped with a discharge pressure control valve for controlling the discharge pressure of the pressure-reducing unloading cyclone separator.

[0008] Optionally, the discharge pressure of the pressure-reducing unloading cyclone separator is 0.3 to 0.4 MPa, and the steam outlet of the pressure-reducing unloading cyclone separator separates and produces low-grade flash steam with a temperature of 115 to 125°C.

[0009] Optionally, the flash steam compression device includes a steam compressor, a wire mesh demister, and a steam buffer tank. The low-grade flash steam at 115-125°C produced by the steam outlet of the pressure-reducing unloading cyclone separator is demisted by the wire mesh demister and then enters the steam buffer tank. The low-grade flash steam stored in the steam buffer tank is then pressurized and heated to 165-168°C and 0.68-0.7MPa by the steam compressor to obtain high-quality steam that matches the cooking conditions.

[0010] Optionally, the jet-type absorption heat pump uses the cooking liquid in the cooking liquid tank as the ejector power medium. After being pressurized by the liquid pump, the cooking liquid in the cooking liquid tank is drawn from the flash steam from the discharge pot through the nozzle and sent to the jet-type absorption heat pump. Then, it is sent to the T-tube through the circulation pump to stably control the slurry in the discharge pot at 105-115°C at 85-90°C.

[0011] Optionally, the pressure cooking liquid heating tank is a closed pressure vessel structure used to preheat the 80°C cooking liquid to 115-125°C.

[0012] A waste heat recovery method for the aforementioned horizontal tube continuous cooking energy-saving system includes the following steps: S1, Raw material cooking: After wet preparation and metering, the pulping raw materials are preheated by a preheating screw and fed into a T-tube by a feeder. In the T-tube, they are mixed with fresh steam, recovered steam from the flash steam compression device and cooking liquid and then enter the cooking tube. The cooking temperature, cooking pressure and cooking time are controlled according to the cooking process requirements to complete the delignification and fiber dissociation. S2, depressurization spraying and steam-slurry separation: The high-temperature slurry after cooking is sent to the depressurization discharge cyclone separator through the unloader, the spray valve on the unloader, and the spray pipe to be steadily depressurized to 0.3-0.4MPa, so as to separate the slurry from the 115-125℃ flash steam. After separation, the slurry is sent to the spraying pot through the discharge valve. S3, Flash Steam Diversion and Utilization: The flash steam discharged from the pressure-reducing unloading cyclone separator is divided into two paths. The first path is directly fed into the pressure cooking liquid heating tank for heat exchange and temperature increase of the cooking liquid. The second path enters the flash steam compression device to upgrade it into steam suitable for the cooking conditions, and is sent back to the cooking process through the T-tube to replace fresh steam. S4, Deep recovery of slurry waste heat: Using a jet absorption heat pump to draw the waste heat of slurry from the spraying pot under negative pressure with cooking liquid as the driving force, a high-calorific-value cooking liquid is obtained and introduced into the pressure cooking liquid heating tank. The temperature of slurry exiting the spraying pot is kept stable at 88-90℃ by regulating the jet absorption heat pump. S5, intelligent steady-state operation of the whole system: By monitoring temperature, pressure and flow rate online, it automatically adjusts the load of the flash steam compressor, the flash steam distribution ratio of the pressure-reducing unloading cyclone separator and the heat pump operation of the jet absorption heat pump to strictly control heat loss and realize waste heat recycling.

[0013] Optionally, the pulping raw materials are some or all of reed pulp, wheat straw pulp, bagasse pulp, bamboo pulp (non-wood pulp), and hardwood pulp.

[0014] Compared with existing technologies, this invention mainly achieves the following beneficial effects: This invention abandons the traditional cold black liquor mixing and cold spraying process, adopting a reduced-pressure hot spraying process to improve the quality of the flash steam. The flash steam directly heats the cooking liquor, and the upgraded flash steam is compressed and reused in the cooking process. A jet-type absorption heat pump deeply recovers the waste heat from the high-temperature pulp in the spraying pot, constructing a "flash steam upgrading - multi-stage waste heat recovery" thermal energy recycling system. This invention solves the problems of high energy consumption, low waste heat utilization, low pulp concentration, and low flash steam thermal energy quality in traditional horizontal tube continuous cooking processes. It reduces white fog thermal pollution in the plant area, does not change the quality of fiber and finished pulp, can be retrofitted to existing production lines at low cost, has a short investment payback period, and is suitable for horizontal tube cooking processes of reed, wheat straw, bagasse, bamboo pulp, and eucalyptus hardwood pulp, meeting the green and low-carbon development requirements of the pulping industry. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the existing horizontal tube continuous cooking system.

[0016] Figure 2 This is a schematic diagram of the heat flow in an existing horizontal tube continuous cooking system.

[0017] Figure 3 This is a schematic diagram of the structure of the horizontal tube continuous cooking system in an embodiment of the present invention.

[0018] Figure 4 The diagrams show the closed-loop heat flow of waste heat recovery in the horizontal tube continuous cooking system and the existing horizontal tube continuous cooking system in this embodiment of the invention. (a) is the closed-loop heat flow diagram of waste heat recovery in the existing horizontal tube continuous cooking system, and (b) is the closed-loop heat flow diagram of waste heat recovery in the horizontal tube continuous cooking system in this embodiment of the invention.

[0019] Figure 5 This is a schematic diagram of the structure of the pressure-reducing unloading cyclone separator in an embodiment of the present invention.

[0020] Figure 6 This is a schematic diagram of the heat flow direction of the horizontal tube continuous cooking system in an embodiment of the present invention.

[0021] Legend: 1. Preheating spiral; 2. Feeder; 3. T-tube; 4. Cooking tube; 5. Unloader; 6. Discharge pipe; 7. Discharge pot; 8. Black liquor tank; 9. Cooking solution tank; 10. Pressure-reducing unloading cyclone separator; 101. Flash steam inlet; 1010. Transmitter mounting port; 1011. Slurry outlet; 102. Steam outlet; 103. Separation cylinder; 104. Separation scraper; 105. Inspection port; 106. Drive unit; 107. Black liquor inlet; 108. Agitator impeller; 109. Slurry storage tank; 11. Flash steam compression device; 12. Jet absorption heat pump; 13. Pressure cooking solution heating tank. Detailed Implementation

[0022] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be further described in detail below with reference to the accompanying drawings in the embodiments of the present invention.

[0023] like Figure 1 As shown, the improved horizontal tube continuous cooking energy-saving system in this embodiment includes a preheating screw 1, a feeder 2, a T-tube 3, a cooking tube 4, a discharger 5, a spray pipe 6, a spray pot 7, a black liquor tank 8, and a cooking liquid tank 9. After wet preparation, the pulping raw materials are preheated by the preheating screw 1, extruded and pushed by the feeder 2, and then fed into the T-tube 3. They are mixed with the steam and cooking liquid fed into the T-tube 3 and then fed into the cooking tube 4, realizing rapid heating of the pulping raw materials, water, and cooking liquid, providing a stable temperature environment for the delignification reaction. A spiral stirring device is installed in the cooking tube 4 to ensure uniform mixing of materials and sufficient heat transfer, avoiding uneven pulp quality caused by excessively high or low local temperatures. The unloader 5, serving as the connecting hub between the cooking tube 4 and the spray pan 7, has the core function of cooling the cooked high-temperature slurry (160°C) to a suitable spray temperature, while simultaneously transporting the slurry to the spray pan 7 via the spray pipe 6. In traditional processes, a large amount of 85°C cold black liquor (diluted black liquor from the washing and screening section) is introduced into the unloader 5 to directly mix with the high-temperature slurry, utilizing the low-temperature characteristics of the cold black liquor to cool the slurry. This process is also a key step in the significant heat loss. The spray pan 7 is an atmospheric pressure device, and its core function is to temporarily store the slurry. After the high-temperature slurry (around 105°C) enters the spray pan 7, the pressure drops sharply, and some of the water evaporates to form flash steam. This flash steam is directly discharged outdoors, which is the primary cause of heat waste. The previous horizontal tube continuous cooking system used a "cold spray" mode. Its core principle was to utilize the direct mixing and heat exchange between cold black liquor and high-temperature slurry to rapidly reduce the slurry temperature, avoiding equipment damage, slurry splashing, and safety hazards caused by direct spraying of high-temperature slurry. Simultaneously, the black liquor diluted the slurry, creating conditions for subsequent production stages. The heat flow was as follows: Figure 2 As shown, the main components include the cooking tube 4, the unloader 5, and the spray tank 7, wherein: Q0 - Heat supplied by steam, kJ / h; Q1 - The heat introduced by the cooking liquid, kJ / h; Q2 - Heat consumption for heating the oven-dry raw material, kJ / h; Q3 - Heat consumption for heating the moisture introduced by the raw material, kJ / h; Q4 - Heat consumption for heating the medicinal solution, kJ / h; Q5 - Heat loss of cooking equipment, kJ / h; Q6 - Heat loss from auxiliary equipment, kJ / h; Q7 - Heat loss of non-insulated equipment, kJ / h; Q8 - Heat loss in the pipeline, kJ / h; Q9 - Heat loss due to cooking unloading and steam evaporation, kJ / h; Q 10 -Energy consumption for cooking activation, kJ / h; Q 11 -Heat carried by the cold black liquor during unloading into the unloader, kJ / h; Q 12 - Total heat entering the discharge pan, kJ / h; Q 13 - The heat carried away by the black liquid in the spraying pan, kJ / h; Q 14 - The heat carried away by the slurry in the spraying pan, kJ / h; Q 15 -Heat loss of the spraying boiler equipment, kJ / h; Q 16 - The heat discharged with the ejected steam, kJ / h.

[0024] from Figure 2From the perspective of heat flow: The heat transfer characteristics of this process directly lead to a large amount of heat waste, specifically manifested as: (1) The heat transfer method is simple and inefficient: The heat exchange method between cold black liquor and high temperature slurry is direct mixing heat exchange. Although the cooling speed is fast, there are no effective recovery measures in the heat transfer process. A large amount of heat energy released by high temperature slurry is directly absorbed by black liquor, causing the system heat energy grade to drop sharply from 160℃ to about 105℃. The high temperature waste heat that could originally be recovered and utilized is converted into medium and low temperature waste heat, which greatly reduces the recovery value and utilization efficiency of waste heat. (2) Disconnection between heat recovery and utilization: After the black liquor heats up, the cold black liquor absorbs heat and rises to 95-100℃, and the generated warm water is used for production. However, in actual production, the amount of this part of warm water far exceeds the production demand. The heat of the excess warm water cannot be effectively utilized and can only be cooled naturally, resulting in idle and wasted heat energy. At the same time, the flash steam generated by the spray boiler 7 (the steam generated by the rapid vaporization of some hot water due to overheating when saturated water at high temperature and high pressure enters the low-pressure environment due to the sudden drop in pressure, around 100℃) is directly discharged without any recovery measures, further aggravating the waste of heat. (3) Uncontrollable heat transfer process: The amount of cold black liquor added mainly relies on manual experience for control, which makes it difficult to accurately match the temperature and flow rate of the high-temperature pulp, resulting in large fluctuations in the discharge pulp temperature (usually between 100-110℃). This not only affects the stability of subsequent pulp washing production, but also leads to unstable flash steam volume. The flash steam emission forms a steaming "white fog", which seriously affects the plant environment and causes safety hazards such as difficulty in treating waste gas emissions. Combining the process flow and heat transfer characteristics of the cold spray process, the core defects of the traditional horizontal tube continuous cooking process directly lead to a large amount of heat waste, which is also a key issue to be focused on in subsequent heat balance accounting. The specific defects and their correlation with heat waste are as follows: (1) Cold black liquor mixing and cooling leads to a sharp drop in heat energy grade: This is the core defect of the traditional process. When 160℃ high-temperature slurry is directly mixed with 85℃ cold black liquor, the slurry temperature drops to about 105℃ instantly, and the heat energy grade of the system drops significantly, making it difficult to efficiently recover the medium and low temperature waste heat through conventional technology. It can only be wasted in the form of flash steam, idle warm water, etc., which is also one of the main sources of heat waste. (2) Flash steam direct discharge causes a large amount of heat loss: Because the discharge slurry temperature is difficult to control stably below 100℃, after the slurry enters the spraying pot 7, a large amount of flash steam will be generated under normal pressure. This part of the exhaust steam (low-pressure steam after completing the work or heat transfer task) carries a large amount of heat, which not only wastes heat energy, but also forms a "white fog" phenomenon, polluting the plant environment. At the same time, the high temperature slurry is prone to heat loss in subsequent production processes, which is an important link in heat waste.(3) Low thermal efficiency and lack of closed-loop recovery system: In traditional processes, the heat provided by steam is only used for heating raw materials and providing energy for the reaction. After the reaction is completed, the residual heat carried by the slurry is not effectively recovered, but is directly lost through cold black liquor mixing, flash steam discharge, etc., forming a one-way cycle of "energy supply-waste". There is no residual heat recovery and recycling system, resulting in a system thermal efficiency of less than 60%. (4) Coarse process parameter control, increasing additional heat consumption: Process parameters such as the amount of cold black liquor added and the amount of steam supplied mainly rely on manual control. There is a lack of precise monitoring and control methods, which easily leads to problems such as excessive steam supply and excessive cold black liquor addition. This not only increases steam consumption, but also aggravates heat waste and affects the stability of slurry quality. In summary, the cold spray mode, equipment operation characteristics and process defects of the traditional horizontal tube continuous cooking process determine its technical problems of heat consumption and waste.

[0025] Addressing the technical pain points of traditional continuous horizontal tube cooking systems, such as high energy consumption, low flash steam quality, poor waste heat utilization, devaluation of cold spray heat, white fog pollution in the plant area, and extensive manual control, this embodiment of the energy-saving system for continuous horizontal tube cooking retains the original main equipment (preheating spiral 1, feeder 2, T-tube 3, cooking tube 4, spray pan 7), without altering the cooking reaction mechanism or damaging fiber quality. It constructs a closed-loop heat energy cycle system of "improving flash steam quality - deep recovery and utilization of waste heat," achieving a significant reduction in steam consumption per ton of pulp, full recovery of flash steam, reduction of white fog, adaptive and stable operation, and a short investment payback period. Specifically, as follows... Figure 3As shown, the horizontal tube continuous cooking energy-saving system in this embodiment includes a preheating screw 1, a feeder 2, a T-tube 3, a cooking tube 4, a discharger 5, a spray pipe 6, a spray pan 7, a black liquor tank 8, a cooking liquid tank 9, a pressure-reducing unloading cyclone separator 10, a flash vapor compression device 11, a jet-type absorption heat pump 12, and a pressure cooking liquid heating tank 13. The raw material passes through the preheating screw 1, feeder 2, T-tube 3, cooking tube 4, discharger 5, and spray pipe 6 in sequence before entering the pressure-reducing unloading cyclone separator 10 to separate the high-temperature slurry from the flash vapor. The separated low-temperature slurry... The flash steam is pressurized and upgraded into high-quality cooking steam that can be recycled after passing through the flash steam compressor 11, and then sent into the T-tube 3. The black liquor supplied by the black liquor tank 8 and the high-temperature slurry separated by the pressure relief unloading cyclone separator 10 are sent together into the spraying pot 7. The cooking liquid in the cooking liquid tank 9 is pressurized by the liquid pump and then the flash steam from the spraying pot 7 is drawn through the nozzle and sent into the jet absorption heat pump 12 to use the waste heat of the flash steam from the pressure relief unloading cyclone separator 10 and the waste heat of the slurry recovered by the jet absorption heat pump 12 to prepare high-temperature cooking liquid. The high-temperature cooking liquid is then sent into the T-tube 3 through the circulation pump. The horizontal tube continuous cooking energy-saving system in this embodiment is based on the traditional horizontal tube continuous cooking production line, and is equipped with four core energy-saving equipment and technologies: a pressure-reducing unloading cyclone separator 10, a flash steam compression device 11, a jet absorption heat pump 12, and a pressure cooking liquid heating tank 13. It can be combined with supporting pipelines, regulating valves, temperature, pressure and flow sensors, DCS / PLC intelligent control system, etc. to realize the reuse of cooking heat energy.

[0026] Figure 4The diagrams show the closed-loop heat flow of waste heat recovery in the horizontal tube continuous cooking system of this embodiment and the existing horizontal tube continuous cooking system. (a) is the closed-loop heat flow diagram of waste heat recovery in the existing horizontal tube continuous cooking system, which includes multiple stages such as feeding, cooking, cold spraying, spraying pot 7, cooking liquid, and dilute black liquor. However, its heat transfer is only sequential between feeding, cooking, cold spraying, and spraying pot 7, without effective closed-loop waste heat recovery. (b) is the closed-loop heat flow diagram of waste heat recovery in the horizontal tube continuous cooking system of this embodiment, which includes heat transfer in two stages: depressurized spraying (through depressurized discharge cyclone separator 10), recovery / discharge, and spraying pot 7. The object of heat transfer is the cooking liquid. The discharge end of the cooking tube 4 is connected to the pressure-reducing unloading cyclone separator 10 via the unloader 5, the discharge valve of the unloader 5, and the discharge pipe 6. The gas phase outlet of the pressure-reducing unloading cyclone separator 10 is split into two paths: one path is connected to the pressure cooking liquid heating tank 13, and the other path is connected to the flash steam compression device 11. After the upgrading steam is stabilized, it is connected to the steam inlet of the T-tube 3. The slurry outlet of the pressure-reducing unloading cyclone separator 10 is connected to the discharge pot 7 via the discharge valve. The flash evaporation chamber at the top of the discharge pot 7 is connected to the suction port of the jet absorption heat pump 12. The heat exchange liquid outlet of the jet absorption heat pump 12 is connected to the pressure cooking liquid heating tank 13. The entire system is controlled by an automated control system to achieve fully automatic linkage regulation.

[0027] like Figure 5As shown, the pressure-reducing unloading cyclone separator 10 consists of an upper separation cylinder 103 and a lower pulp storage tank 109. The separation cylinder 103 has a pulp and flash steam inlet 101 on one side, a drive device 106 and a steam outlet 102 on the top, and a rotatable separation scraper 104 inside. The separation scraper 104 is connected to the drive device 106 to separate the high-temperature pulp from the inner wall of the separation cylinder 103. The separation cylinder 103 and the pulp storage tank 109... Each side wall is provided with an inspection port 105. The bottom of the separation cylinder 103 is provided with a black liquor inlet 107 for inputting black liquor supplied by the black liquor tank 8. The slurry storage tank 109 is provided with a rotatable stirring impeller 108, which is connected to the drive device 106. The side wall of the slurry storage tank 109 is provided with multiple transmitter mounting ports 1010 and slurry outlets 1011. The transmitter mounting ports 1010 are used to install sensors and transmitters for detecting the internal working status of the slurry storage tank 109. High-temperature pulp and flash steam generated by pressure reduction enter the separation cylinder 103 tangentially through the pulp and flash steam inlets 101. Under the combined action of centrifugal force and the separation scraper 104, pulp-gas separation is accelerated. The pulp falls from the edge of the cylinder to the bottom of the separator, where it mixes with the black liquor entering through the black liquor inlet 107 under the action of the stirring impeller 108, enters the pulp storage tank 109, and finally exits the separator from the pulp outlet 1011. The flash steam swirls into the center of the cylinder, gathers upwards to the top, and exits the separator from the steam outlet. The development and use of the pressure-reducing unloading cyclone separator 10 replaces the traditional high-pressure unloading mode that is directly connected to the blowdown boiler. By controlling the unloading pressure difference, the high-temperature pulp is slowly released under pressure reduction, avoiding fiber damage caused by a sudden drop in high temperature and pressure. At the same time, it effectively improves the quality of flash steam and creates conditions for the recovery and utilization of blowdown boiler flash steam.

[0028] In this embodiment, both the separation cylinder 103 and the pulp storage tank 109 are cylindrical structures, and the separation scraper 104 has a spiral structure. The pulp and flash steam inlets 101 are arranged on the outside of the separation scraper 104 to achieve tangential feeding. The pressure-reducing unloading cyclone separator 10 adopts a vertical cylindrical pressure-bearing cylinder, tangential lateral feeding, an inner wall with an annular power guide plate, and a pulp tank structure of the pulp storage tank 109. It is equipped with a separation scraper 104 to prevent wall adhesion and an agitator impeller 108 for stirring and mixing, and can be equipped with a flash steam demisting component for demisting. The pressure-reducing unloading cyclone separator 10 can accurately and steadily reduce the cooking pressure from 0.68 to 0.7 MPa to 0.3 to 0.4 MPa, releasing high-quality clean flash steam at 115 to 125°C. Through secondary slow gradient pressure reduction and spraying, and control of black liquor reduction, fiber breakage and lignin precipitation are avoided, while improving the recoverable grade of steam. In this embodiment, the separation cylinder 103 and the slurry storage tank 109 are independent of each other, and the discharge pipe at the bottom of the separation cylinder 103 is inserted into the inside of the slurry storage tank 109. The stirring shaft of the stirring impeller 108 is inserted into the discharge pipe at the bottom of the separation cylinder 103, and the impeller body of the stirring impeller 108 is located below the discharge pipe at the bottom of the separation cylinder 103. This allows the slurry in the separation cylinder 103 to directly enter the impeller body of the stirring impeller 108 through the discharge pipe at the bottom of the separation cylinder 103. Under the centrifugal action of the impeller body of the stirring impeller 108, the slurry is dispersed to the surrounding area, making the stirring of the stirring impeller 108 more uniform.

[0029] In this embodiment, the pressure-reducing unloading cyclone separator 10 is equipped with a discharge pressure control valve to control the discharge pressure of the pressure-reducing unloading cyclone separator 10. In this embodiment, the discharge pressure of the pressure-reducing unloading cyclone separator 10 is 0.3 to 0.4 MPa, and the steam outlet 102 of the pressure-reducing unloading cyclone separator 10 separates and produces low-grade flash steam with a temperature of 115 to 125°C.

[0030] In this embodiment, the flash steam compression device 11 includes a steam compressor, a wire mesh demister, and a steam buffer tank. The low-grade flash steam (115-125°C) produced by the steam outlet 102 of the pressure-reducing unloading cyclone separator 10 is demisted by the wire mesh demister and then enters the steam buffer tank, effectively removing black liquor droplets and fine fibers to prevent corrosion and scaling of the unit. Then, the low-grade flash steam stored in the steam buffer tank is pressurized and heated to 165-168°C and 0.68-0.7MPa by the steam compressor to obtain high-quality steam that matches the cooking conditions. After pressure stabilization, it is connected to the cooking steam pipeline to replace fresh steam. The flash steam compression device 11 innovatively applies steam compression technology to the horizontal tube continuous cooking energy-saving system, solving the problem of low-grade (approximately 120°C) flash steam that cannot be directly reused in the cooking process for heat energy recycling.

[0031] In this embodiment, the jet-type absorption heat pump 12 uses the cooking liquid in the cooking liquid tank 9 as the ejector power medium. After being pressurized by the liquid pump, the cooking liquid in the cooking liquid tank 9 is drawn through the nozzle from the flash steam of the discharge pot 7 and sent to the jet-type absorption heat pump 12. Then, it is sent to the T-tube 3 through the circulation pump to stabilize the slurry in the discharge pot 7 at 85-90°C, which is 105-115°C. This allows the waste heat of the high-temperature slurry to be converted into the cooking liquid for recycling. The jet-type absorption heat pump 12 adopts a corrosion-resistant special alloy structure and uses the cooking liquid as its self-ejector power, requiring no external energy consumption. It draws flash steam generated by the waste heat of the slurry in the discharge pot under negative pressure. After absorbing heat, the cooking liquid is sent to the pressure liquid heating tank. The jet-type absorption heat pump 12 automatically controls the discharge temperature of the slurry at 85-90°C, eliminating the direct discharge of flash steam and white fog pollution at the source. The innovative application of ejector heat pump technology to the waste heat recovery of the horizontal tube continuous cooking energy-saving system scientifically solves the problem of difficult waste heat recovery from the spray pan slurry.

[0032] In this embodiment, the pressure cooking liquid heating tank 13 is a closed pressure vessel structure used to preheat the 80℃ cooking liquid to 115-125℃. Specifically, the closed pressure vessel structure is a stainless steel closed tank with a flame-retardant insulation layer on the outer wall and an internal annular jet direct heater. The pressure cooking liquid heating tank 13 can simultaneously recover the high-grade waste heat of flash steam and the low-temperature waste heat of the spray pan 7. The application of the new process and equipment for pressure preparation of cooking liquid breaks the traditional operation mode of preparing cooking liquid at a temperature not exceeding 100℃, directly heating the 80℃ liquid to 115-125℃, significantly reducing the consumption of fresh steam for heating the liquid during the cooking process.

[0033] Figure 6 To illustrate the heat flow of the horizontal tube continuous cooking system in this embodiment, the main components include cooking tube 4, unloader 5, spray pan 7, cooking liquid tank 9, and steam compressor, wherein: Q0 - Heat supplied by steam, kJ / h; Q1 - The heat introduced by the cooking liquid, kJ / h; Q2 - Heat consumption for heating the oven-dry raw material, kJ / h; Q3 - Heat consumption for heating the moisture introduced by the raw material, kJ / h; Q4 - Heat consumption for heating the medicinal solution, kJ / h; Q5 - Heat loss of cooking equipment, kJ / h; Q6 - Heat loss from auxiliary equipment, kJ / h; Q7 - Heat loss of non-insulated equipment, kJ / h; Q8 - Heat loss in the pipeline, kJ / h; Q 10 -Energy consumption for cooking activation, kJ / h; Q 11-Heat carried by the cold black liquor during unloading into the unloader, kJ / h; Q 12 - Total heat entering the discharge pan, kJ / h; Q 13 - The heat carried away by the black liquid in the spraying pan, kJ / h; Q 14 - The heat carried away by the slurry in the spraying pan, kJ / h; Q 15 -Heat loss of the spraying boiler equipment, kJ / h; Q 17 -Heat from unloading steam, kJ / h; Q 18 - The heat of the hot boiled medicinal liquid, kJ / h; Q 19 -Recover the heat of steam, kJ / h; Q 20 -Heat of exhaust steam from the spray boiler, kJ / h.

[0034] In addition, this embodiment also provides a waste heat recovery method for a horizontal tube continuous cooking energy-saving system, including the following steps: S1, Raw material cooking: After wet preparation and metering, the pulping raw materials are preheated by the preheating screw 1 and fed into the T-tube 3 by the feeder 2. In the T-tube 3, they are mixed with fresh steam, recovered steam from the flash steam compression device 11 and cooking liquid and then enter the cooking tube. The cooking temperature, cooking pressure and cooking time are controlled according to the cooking process requirements to complete the delignification and fiber dissociation. S2, depressurization and steam-slurry separation: The high-temperature slurry after cooking is sent to the depressurization cyclone separator 10 through the unloader 5, the discharge valve on the unloader 5, and the discharge pipe 6 to stabilize the pressure to 0.3-0.4MPa, so as to separate the slurry from the 115-125℃ flash steam. After separation, the slurry is sent to the discharge pot 7 through the discharge valve. S3, Flash Steam Diversion and Utilization: The flash steam discharged from the pressure-reducing unloading cyclone separator 10 is divided into two paths. The first path is directly fed into the pressure cooking liquid heating tank 13 for heat exchange and temperature increase of the cooking liquid. The second path enters the flash steam compression device 11 to upgrade it into steam suitable for the cooking conditions, and is sent back to the cooking process through the T-tube 3 to replace fresh steam. S4, Deep recovery of slurry waste heat: The jet absorption heat pump 12 is used to draw the waste heat of the slurry in the spraying pot 7 under negative pressure with the cooking liquid as the driving force to obtain high calorific value cooking liquid, which is introduced into the pressure cooking liquid heating tank 13, and the slurry outlet temperature of the spraying pot 7 is stably maintained at 88-90℃ by regulating the jet absorption heat pump 12. S5, intelligent steady-state operation of the whole system: By monitoring temperature, pressure and flow rate online, the system automatically adjusts the load of flash steam compressor 11, the flash steam distribution ratio of pressure relief unloading cyclone separator 10 and the heat pump operation of jet absorption heat pump 12 to strictly control heat loss and realize waste heat recycling.

[0035] In this embodiment, the waste heat recovery method of the horizontal tube continuous cooking energy-saving system adopts reduced pressure thermal discharge to replace the traditional cold black liquor cooling and high-pressure unloading mode. Pulp-vapor separation is achieved through cyclone separation. The flash steam is utilized in two paths: one directly heats the cooking liquor, and the other is recycled back to the cooking process through upgrading flash cooking. The recovery ratio of the two paths can be controlled by valves. As an optional implementation method, the energy consumption of the horizontal tube continuous cooking energy-saving system under different recovery ratios under the same operating conditions can be calculated separately, and the recovery ratio with the lowest energy consumption of the horizontal tube continuous cooking energy-saving system can be selected as the optimal recovery ratio. The waste heat of the high-temperature pulp in the discharge pot is deeply recovered through a jet-type absorption heat pump to preheat the cooking liquor. The entire system is automatically controlled and regulated, without altering the cooking reaction or affecting the quality of the finished product, forming a complete waste heat recovery and thermal energy recycling system. In this embodiment, the pulping raw materials can be some or all of reed pulp, wheat straw pulp, bagasse pulp, bamboo pulp (non-wood pulp), and hardwood pulp.

[0036] In summary, the waste heat recovery method of the horizontal tube continuous cooking energy-saving system in this embodiment, through process innovation and technology application such as the pressure-reducing unloading cyclone separator 10, the steam compression of the flash steam compression device 11, the waste heat absorption of the jet absorption heat pump 12, and the pharmaceutical preparation of the pressure cooking liquid heating tank 13, constructs an energy-saving system of "pressure reduction and quality improvement - waste heat recovery - recycling". Compared with the traditional horizontal tube continuous cooking system technology, it has the following significant beneficial effects: (1) Significant energy-saving effect and greatly reduced steam consumption: The present invention greatly reduces the consumption of fresh steam through a dual waste heat recovery mechanism. Compared with the traditional horizontal tube continuous cooking pulping process, the steam consumption per ton of pulp in this system can be reduced by 0.8 to 0.9 tons, and the energy saving rate reaches 35 to 40%. The main features are: the flash steam compression device 11 upgrades the low-grade flash steam into high-quality steam required for cooking, and directly sends it back to the horizontal cooking tube to replace part of the fresh steam; the pressure cooking liquid heating tank 13 uses the jet absorption heat pump 12 to achieve negative pressure flash steaming of the discharge pot 7, recovering the waste heat of the slurry to the cooking liquid, reducing the consumption of fresh steam for heating the cooking liquid. (2) High waste heat utilization rate, realizing closed-loop heat energy circulation: In response to the serious waste heat waste problem in traditional processes, this invention constructs a tiered waste heat recovery system with a high total waste heat recovery rate in the unloading and discharge links, completely changing the traditional process's "energy supply-cost" unidirectional heat energy flow mode, forming a complete closed-loop heat energy circulation. The high-quality flash steam separated by the pressure-reducing unloading cyclone separator is used to heat the cooking liquid on-site, and the other part is compressed by the steam compressor and reused for cooking heating; the low-temperature waste heat carried by the slurry in the discharge pot is deeply recovered to the pressure cooking liquid heating tank by the jet absorption heat pump, realizing efficient utilization of low-temperature waste heat and maximizing the system's heat energy utilization efficiency. (3) Outstanding environmental benefits and reduced white fog pollution: Traditional process spraying boiler flash steam is directly discharged into the air, which not only wastes heat, but also forms "white fog" that pollutes the factory environment and poses a risk of thermal pollution. This invention recovers all flash steam through the whole process of waste heat recovery, and there is no direct discharge of flash steam, which reduces "white fog" emissions and thermal pollution by more than 95%, improves the factory working environment, and is in line with the national green, low-carbon, energy-saving and emission-reduction industrial policy. (4) Stable process operation and guaranteed pulp quality: This invention adopts a depressurized hot spraying mode. The depressurized unloading cyclone separator accurately controls the unloading pressure difference, so that the high temperature pulp is slowly depressurized and released, and the pulp characteristics are almost unchanged. This avoids the problem of lignin possibly agglomerating fibers caused by the direct mixing of high temperature pulp and cold black liquor in traditional cold spraying, and ensures the integrity of pulp fiber morphology; at the same time, the key parameters are adjusted in real time through online monitoring and control components to keep the cooking temperature, pressure and pulp temperature stable, avoid parameter fluctuations affecting pulp quality, and produce pulp with stable quality. (5) Good economic performance and short investment return period: This invention can be directly optimized and modified on the existing horizontal tube continuous cooking production line without large-scale replacement of cooking equipment. The modification is easy and the construction period is short, which greatly reduces the equipment investment cost.Taking a production line with an annual output of 50,000 tons of air-dried pulp as an example, after adopting this invention, approximately 40,000 tons of steam will be saved annually. Considering the comprehensive benefits of steam procurement costs, water resource recovery, and energy consumption reduction, the annual comprehensive energy-saving benefits can reach 6 million to 8 million yuan. The investment payback period is only 1.0 to 1.5 years, with a high rate of return on investment. It can quickly reduce the production costs of enterprises and enhance their market competitiveness. (6) Strong adaptability and high application value: This invention is not only applicable to non-wood pulp horizontal tube continuous cooking systems, but also to the horizontal tube continuous cooking process of eucalyptus and other hardwood pulps. It is not only suitable for the transformation of traditional production lines, but also for the design of new production lines. There is no need to make significant adjustments for different raw materials or production scales. It is in line with the green and low-carbon development direction of the pulp industry and can promote energy conservation, consumption reduction, transformation and upgrading of the pulp industry. It has significant industrial promotion value and social significance.

[0037] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A horizontal tube continuous cooking energy-saving system, characterized in that, The system includes a preheating spiral (1), a feeder (2), a T-tube (3), a cooking tube (4), a discharger (5), a spray pipe (6), a spray pan (7), a black liquor tank (8), a cooking liquid tank (9), a pressure-reducing unloading cyclone separator (10), a flash steam compressor (11), a jet-type absorption heat pump (12), and a pressure cooking liquid heating tank (13). The raw material passes through the preheating spiral (1), feeder (2), T-tube (3), cooking tube (4), discharger (5), and spray pipe (6) in sequence before entering the pressure-reducing unloading cyclone separator (10) to separate the slurry from the flash steam. The low-grade flash steam after separation is pressurized and upgraded to high grade by the flash steam compressor (11). After the quality cooking steam is sent into the T-tube (3), the black liquor supplied by the black liquor tank (8) and the slurry separated by the pressure relief unloading cyclone separator (10) are sent into the spray pot (7). The cooking liquid in the cooking liquid tank (9) is pressurized by the liquid pump and then the flash steam from the spray pot (7) is drawn through the nozzle and sent into the jet absorption heat pump (12) to use the waste heat of the flash steam from the pressure relief unloading cyclone separator (10) and the waste heat of the slurry recovered by the jet absorption heat pump (12) to prepare the cooking liquid. The cooking liquid is then sent into the T-tube (3) through the circulation pump. The gas phase outlet of the pressure relief unloading cyclone separator (10) is divided into two paths, one of which is connected to the pressure cooking liquid heating tank (13) and the other of which is connected to the flash steam compression device (11). The pressure-reducing unloading cyclone separator (10) consists of an upper separation cylinder (103) and a lower pulp storage tank (109). The separation cylinder (103) has a pulp and flash steam inlet (101) on one side, a drive device (106) and a steam outlet (102) on the top. The separation cylinder (103) has a separation scraper (104) inside, which is connected to the drive device (106) to separate the pulp from the inner wall of the separation cylinder (103). Both the separation cylinder (103) and the pulp storage tank (109) have inspection ports (105) on their side walls. The bottom of the separation cylinder (103) has a black liquor inlet (107) for input. The black liquor is supplied by the black liquor tank (8); the storage tank (109) is equipped with an agitator (108) inside, and the agitator (108) is connected to the drive device (106); the side wall of the storage tank (109) is provided with multiple transmitter mounting ports (1010) and pulp outlets (1011), and the transmitter mounting ports (1010) are used to install sensors and transmitters for detecting the working status inside the storage tank (109); the separation cylinder (103) and the storage tank (109) are both cylindrical structures, the separation scraper (104) is a spiral structure, and the pulp and flash steam inlets (101) are arranged on the outside of the separation scraper (104) to achieve tangential feeding.

2. The energy-saving horizontal tube continuous cooking system according to claim 1, characterized in that, The pressure-reducing unloading cyclone separator (10) is equipped with a discharge pressure control valve for controlling the discharge pressure of the pressure-reducing unloading cyclone separator (10).

3. The energy-saving horizontal tube continuous cooking system according to claim 2, characterized in that, The discharge pressure of the pressure-reducing unloading cyclone separator (10) is 0.3 to 0.4 MPa, and the steam outlet (102) of the pressure-reducing unloading cyclone separator (10) separates and produces low-grade flash steam with a temperature of 115 to 125°C.

4. The energy-saving horizontal tube continuous cooking system according to claim 1, characterized in that, The flash steam compression device (11) includes a steam compressor, a wire mesh demister and a steam buffer tank. The low-grade flash steam of 115-125℃ produced by the steam outlet (102) of the pressure-reducing unloading cyclone separator (10) is demisted by the wire mesh demister and then enters the steam buffer tank. The low-grade flash steam stored in the steam buffer tank is then pressurized and heated to 165-168℃ and 0.68-0.7MPa by the steam compressor to obtain high-quality steam that matches the cooking conditions.

5. The energy-saving horizontal tube continuous cooking system according to claim 1, characterized in that, The jet-type absorption heat pump (12) uses the cooking liquid in the cooking liquid tank (9) as the ejector power medium. After being pressurized by the liquid pump, the cooking liquid in the cooking liquid tank (9) is drawn from the flash steam from the discharge pot (7) through the nozzle and sent into the jet-type absorption heat pump (12). Then, it is sent into the T-tube (3) through the circulation pump to stably control the 105-115℃ slurry in the discharge pot (7) at 85-90℃.

6. The energy-saving horizontal tube continuous cooking system according to claim 1, characterized in that, The pressure cooking liquid heating tank (13) is a closed pressure vessel structure used to preheat the 80℃ cooking liquid to 115~125℃.

7. A method for waste heat recovery in a horizontal tube continuous cooking energy-saving system according to any one of claims 1 to 6, characterized in that, Includes the following steps: S1, Raw material cooking: After wet preparation and metering, the pulping raw material is preheated by the preheating screw (1) and fed into the T-tube (3) by the feeder (2). In the T-tube (3), it is mixed with fresh steam, the recovered steam from the flash steam compression device (11) and the cooking liquid and enters the cooking tube. The cooking temperature, cooking pressure and cooking time are controlled according to the cooking process requirements to complete the delignification and fiber dissociation. S2, depressurization and steam-slurry separation: The cooked slurry is sent to the depressurization cyclone separator (10) through the unloader (5), the discharge valve on the unloader (5), and the discharge pipe (6) to achieve stable depressurization to 0.3-0.4MPa, so as to separate the slurry from the 115-125℃ flash steam. After separation, the slurry is sent to the discharge pot (7) through the discharge valve. S3, Flash Steam Diversion and Utilization: The flash steam separated and discharged by the pressure-reducing unloading cyclone separator (10) is divided into two paths. The first path is directly fed into the pressure cooking liquid heating tank (13) to exchange heat and raise the temperature of the cooking liquid. The second path enters the flash steam compression device (11) to upgrade the steam into steam suitable for the cooking conditions. It is then sent back to the cooking process through the T-tube (3) to replace fresh steam. S4, Deep recovery of residual heat of slurry: Using a jet-type absorption heat pump (12) to draw the residual heat of slurry from the spraying pot (7) under negative pressure with the cooking liquid as the driving force to obtain high-calorific-value cooking liquid, and introduce it into the pressure cooking liquid heating tank (13), and by regulating the jet-type absorption heat pump (12), the slurry outlet temperature of the spraying pot (7) is stably maintained at 88-90℃. S5, Intelligent steady-state operation of the whole system: By monitoring temperature, pressure and flow rate online, the load of the flash steam compressor (11), the flash steam distribution ratio of the pressure relief unloading cyclone separator (10) and the heat pump operation of the jet absorption heat pump (12) are automatically adjusted to strictly control heat loss and realize waste heat recycling.

8. The waste heat recovery method of the horizontal tube continuous cooking energy-saving system according to claim 7, characterized in that, The pulping raw materials are some or all of reed pulp, wheat straw pulp, bagasse pulp, bamboo pulp (non-wood pulp), and hardwood pulp.

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