Paper machine drying part heat recovery device based on gas-steam double circulation

Abstract

The utility model discloses a paper machine drying part heat recovery device based on gas-steam double circulation, and relates to the technical field of energy conservation in the papermaking industry. The utility model provides a gas-steam double-circulation waste heat recovery device aiming at the problems that high-temperature wet waste gas of a drying part of a paper machine is directly discharged and energy consumption is large. The device is sequentially composed of a waste gas outlet vertical pipe, a cyclone dust remover, an evaporation heat exchange pipe, a compressor, an oil separator, a condenser, a connecting pipe, a flash tank, a waste heat recovery pipe, a preheater, a circulating air pipeline and the like, latent heat of waste gas is converted into 0.2 MPa secondary steam and 70 DEG C circulating hot air through a closed circuit of dust removal, evaporation, compression, condensation and flash evaporation, and fresh air and cooling water are synchronously preheated.

Description

Technical Field

[0001] This utility model relates to the field of energy-saving technology in the papermaking industry, specifically a heat recovery device for the drying section of a paper machine based on a dual gas-steam circulation system. Background Technology

[0002] In modern high-speed paper machines, the drying section uses saturated steam to heat the drying cylinders to evaporate moisture from the paper web. Steam consumption accounts for more than 60% of the total energy consumption of the entire production line. The high-temperature, humid waste gas carried out with the paper web is directly discharged into the workshop or discharged outdoors through simple ducts, resulting in a significant waste of sensible and latent heat, while also increasing the humidity and corrosion risk in the production workshop. An existing drying cylinder structure device for a paper machine drying section (publication number: CN207047604U) has the following drawbacks and requires further improvement.

[0003] Traditional heat recovery in drying sections often employs a single gas heat exchanger or heat pump system: gas heat exchangers can only utilize the high-temperature sensible heat of the waste gas, making it difficult to recover latent heat.

[0004] Although single-cycle heat pumps can raise the temperature and provide heat, they suffer from low efficiency and frequent operation and maintenance due to the small temperature difference on the evaporator side and the tendency for condensation and scaling on the heat exchanger. Furthermore, they are difficult to output low-pressure steam suitable for the drying cylinder and fresh hot air suitable for the hood simultaneously, thus failing to meet the dual requirements of significantly reducing steam consumption and improving the workshop environment. Utility Model Content

[0005] The main objective of this invention is to provide a heat recovery device for the drying section of a paper machine based on a dual gas-steam circulation system, which can effectively solve the problems in the background art.

[0006] To achieve the above objectives, the technical solution adopted by this utility model is as follows: a heat recovery device for the drying section of a paper machine based on a dual air-steam circulation system. The cyclone dust collector is located downstream of the exhaust gas outlet riser and is connected to the exhaust gas outlet riser via a flange. The bottom of the cyclone dust collector is equipped with a ash discharge valve. The side wall of the cyclone dust collector is connected to a heat exchange tube via a sealed pipeline. The lower end of the heat exchange tube is connected to a compressor via a suction pipe. The exhaust end of the compressor is connected to a condenser via a high-pressure pipeline. The water outlet of the condenser is connected to a flash tank via a connecting pipe. The outlet of the flash tank is connected to a waste heat recovery pipe via a horizontal pipeline. The lower end of the waste heat recovery pipe is fixedly connected to a preheater, and its middle section is connected to the air inlet of the paper machine drying hood via a circulating air pipeline. The top of the waste heat recovery pipe is equipped with a pressure relief valve and an exhaust port. The top of the flash tank is equipped with two pulse jet cleaning devices, and a motor and a pressure gauge are respectively installed above the pulse jet cleaning devices.

[0007] Preferably, the cyclone dust collector is integrally formed from an upper cylindrical section and a lower conical bucket section. The inner diameter of the upper cylindrical section is φ450mm, and the cone angle of the lower conical bucket section is 50°±2°. The lower conical bucket section is connected to the cylindrical section by an annular butt weld.

[0008] Preferably, the high-pressure pipeline also includes an oil separator with a nominal diameter of DN65. One end of the oil separator is connected to the compressor exhaust port via a DN65, PN2.5 raised face flange, and the other end is connected to the condenser inlet via a flange of the same specification.

[0009] Preferably, the flash tank is a vertical cylindrical structure with an inner diameter of φ600mm and a height of 1600mm. Two internally threaded spray ports G1-1 / 2″ are symmetrically arranged on the top, and the pulse spray device is sealed to the spray ports through the threaded opening.

[0010] Preferably, the waste heat recovery pipe is welded with several short pipes for temperature measurement and pressure tapping at 500mm intervals along the axial direction. Each short pipe has an external thread specification of M20×1.5 and is embedded with a K-type thermocouple sheath.

[0011] Preferably, the preheater is a U-shaped tube bundle heat exchanger with a shell diameter of φ350mm. Its shell is connected to the lower end of the waste heat recovery tube through a 45° steel elbow and a DN150, PN1.6 flat welding flange. The tube bundle is made of copper U-shaped tubes with an outer diameter of φ19mm and a tube spacing of 25mm.

[0012] Compared with the prior art, the present invention has the following beneficial effects:

[0013] This invention utilizes a "waste gas side loop" constructed by connecting cyclone dust collector heat exchanger preheaters in series. Without altering the paper machine's drying conditions, it recovers the sensible and latent heat of the originally directly emitted 90℃~120℃ humid waste gas in stages and converts it into secondary steam at approximately 0.2MPa and circulating hot air at 70℃~90℃. This reduces steam consumption per ton of paper by 10%~20%, while simultaneously lowering the exhaust temperature to below 50℃ and reducing absolute humidity by approximately 40%, thereby reducing energy waste and workshop moisture load.

[0014] This invention adopts a dual-circulation structure of air and steam: the air circulation side first passes through a cyclone dust collector to separate droplets / fibers before entering the refrigerant evaporator, avoiding scaling on the heat exchange surface; the steam circulation side utilizes the high-pressure condensation heat of the heat pump to flash evaporate into low-pressure steam and preheat the fresh air for parallel output, taking into account both the steam supply needs of the drying cylinder and the air supply needs of the hood. The overall performance coefficient of the system can reach more than 3.5, which not only solves the problems of single air-to-air heat exchange not being able to utilize latent heat and the low condensation efficiency of traditional heat pumps, but also reduces the frequency of maintenance downtime, achieving dual optimization of energy saving and environmental improvement. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the overall structure of this utility model;

[0016] Figure 2 This is an enlarged view of part A of this utility model.

[0017] In the diagram: 1. Cyclone dust collector; 2. Exhaust gas outlet; 3. Ash discharge valve; 4. Compressor; 5. Condenser; 6. Heat exchange tube; 7. Connecting pipe; 8. Flash tank; 9. Waste heat recovery pipe; 10. Preheater; 11. Circulating air duct; 12. Pressure relief valve; 13. Exhaust port; 14. Pulse jet cleaning device; 15. Motor; 16. Pressure gauge. Detailed Implementation

[0018] To make the technical means, creative features, objectives and effects of this utility model easier to understand, the present utility model will be further described below in conjunction with specific embodiments.

[0019] In the description of this utility model, it should be noted that the terms "upper," "lower," "inner," "outer," "front end," "rear end," "both ends," "one end," and "the other end," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this utility model. In addition, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0020] In the description of this utility model, it should be noted that, unless otherwise explicitly specified and limited, the terms "installed," "equipped with," "connected," etc., should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model based on the specific circumstances. Example

[0021] Please see Figure 1-2 This utility model provides a technical solution:

[0022] A heat recovery device for the drying section of a paper machine based on a dual air-steam circulation system is disclosed. A cyclone dust collector 1 is located downstream of the exhaust gas outlet riser 2 and connected to it via a flange. A ash discharge valve 3 is located at the bottom of the cyclone dust collector 1. A heat exchange tube 6 is connected to the side wall of the cyclone dust collector 1 via a sealed pipe. The lower end of the heat exchange tube 6 is connected to a compressor 4 via a suction pipe. The exhaust end of the compressor 4 is connected to a condenser 5 via a high-pressure pipe. The water outlet of the condenser 5 is connected to a flash tank 8 via a connecting pipe 7. The outlet of the flash tank 8 is connected to a waste heat recovery pipe 9 via a horizontal pipe. The lower end of the waste heat recovery pipe 9 is fixedly connected to a preheater 10, and its middle section is connected to the air inlet of the paper machine drying hood via a circulating air pipe 11. A pressure relief valve 12 and an exhaust port 13 are respectively located at the top of the waste heat recovery pipe 9. Two pulse jet cleaning devices 14 are located at the top of the flash tank 8, and a motor 15 and a pressure gauge 16 are respectively located above the pulse jet cleaning devices 14.

[0023] The hot and humid exhaust gas discharged from the paper machine drying section has a high enthalpy due to its high moisture content and temperature, and can carry approximately 90% of the heat consumed during drying. To efficiently recover this waste heat, this embodiment provides a drying section heat recovery device based on a dual-cycle air-steam system. This device utilizes processes such as cyclone dust removal, evaporation flash evaporation, and compression condensation to transfer the heat from the exhaust gas to the circulating air and cooling water, significantly reducing steam consumption and improving energy efficiency. The device mainly includes: a cyclone dust collector, heat exchange pipelines, a compressor, an oil separator, a condenser, a flash tank, waste heat recovery pipes, a preheater, circulating air ducts, and related valves and actuators.

[0024] Cyclone dust collector: Installed downstream of the exhaust gas outlet riser, it is sealed via a flange connection. The cyclone dust collector is integrally formed from an upper cylindrical section and a lower conical bucket section. The inner diameter of the upper cylindrical section is φ450mm, and the cone angle of the lower bucket section is 50°±2°. The cyclone utilizes centrifugal force to remove large particles of fiber and dust from the exhaust gas, improving the stability of the subsequent heat exchanger. A ash discharge valve is located at the bottom of the dust collector for periodically discharging the separated dust. Sealed pipes are opened on the side wall of the cyclone dust collector, connecting to the downstream heat exchange pipes to guide the exhaust gas towards the heat exchange section.

[0025] Heat exchange tubes and compressor: After cyclone dust removal, some of the exhaust gas enters the heat exchange tubes along sealed pipes. The heat exchange tubes act as evaporators, transferring the heat energy of the exhaust gas to the working fluid inside the tubes, and are connected to the compressor's suction port through the lower suction pipe. The compressor pressurizes the suction vapor to produce high-temperature, high-pressure gas.

[0026] Oil separator and condenser: The compressor discharge end first passes through a DN65 nominal diameter oil separator to remove the carried lubricating oil, and then is transported to the condenser via a flanged connection pipeline of the same specification. Inside the condenser, the high-temperature gas releases heat to the cooling medium, causing the vapor to condense into liquid. The water outlet of the condenser is connected to the flash tank via a connecting pipe, introducing the condensed hot water into the flash tank.

[0027] Flash Tank: The flash tank is a vertical cylindrical structure with an inner diameter of φ600mm and a height of 1600mm. Two internally threaded G1-1 / 2″ injection ports are symmetrically located on the top of the tank. Each injection port is threadedly connected to a pulse jet cleaning device. A motor and pressure gauge are installed above the injection device for timed jet cleaning and monitoring of the tank's internal pressure. Hot water entering the flash tank undergoes flash evaporation under low pressure, forming high-temperature secondary steam that is released from the top of the tank. Simultaneously, the flashed liquid continues to flow out. This flash evaporation process effectively utilizes the high potential energy of the hot water and recovers steam heat.

[0028] Waste heat recovery pipe and circulating air duct: The output at the bottom of the flash tank is connected to the waste heat recovery pipe via a horizontal pipe. The waste heat recovery pipe has two functions: its lower end is fixedly connected to a preheater, used to preheat the incoming air or process water using high-temperature steam inside the pipe; the middle of the pipe is connected to the air inlet of the paper machine drying hood via a circulating air duct, sending the waste heat back into the drying hood in the form of air to circulate and heat the drying airflow. To ensure the safe operation of the system, the top of the waste heat recovery pipe is equipped with a safety pressure relief valve and an exhaust port, which can automatically relieve pressure or exhaust air when the pressure is too high.

[0029] Preheater: The preheater is a U-shaped tube bundle heat exchanger with a shell diameter of φ350mm. It is connected to the lower end of the waste heat recovery tube using 45° steel elbows and DN150, PN1.6 flat-welded flanges. The tube bundle is constructed of copper tubes with an outer diameter of φ19mm and a tube spacing of 25mm. During system operation, hot water / steam from the waste heat recovery tube enters the shell side of the preheater, while cold air or process water flows and heats up within the tube side, preheating the fresh air and water and improving heat exchange efficiency.

[0030] Monitoring and execution components: Two pulse jet cleaning devices at the top of the flash tank, each driven by a motor, periodically spray air to remove impurities deposited on the tank walls and bottom. Pressure gauges above the cleaning devices monitor the tank pressure in real time, ensuring stable flash evaporation operation. Valves such as drain valves, ash discharge valves, and pressure relief valves in the system provide valve control and safety protection.

[0031] Work process

[0032] Exhaust gas introduction and dust removal: Hot and humid exhaust gas from the paper machine's drying section enters this unit through the exhaust pipe, first flowing into a cyclone dust collector. Inside the cyclone dust collector, the exhaust gas is separated by rotational motion, with most of the fibers and dust settling at the bottom of the cone and being discharged through the ash discharge valve. This process effectively reduces the risk of blockage in subsequent pipelines.

[0033] Vapor compression cycle: High-temperature exhaust gas after dust removal enters the heat exchange tube through sidewall pipes. Inside the heat exchange tube, the exhaust gas transfers some heat to the medium inside the tube, causing the gas temperature to decrease. Subsequently, this portion of vapor is introduced into the compressor through the suction pipe and compressed to a high-pressure, high-temperature state. The compressed vapor then passes through an oil separator to remove lubricating oil before entering the condenser.

[0034] Condensation and Flash Evaporation: In the condenser, high-temperature steam exchanges heat with cooling water, with most of the heat being carried away, and the steam condenses into hot water. The hot water produced by condensation enters the flash tank through the connecting pipe. The pressure inside the flash tank is lower than the pressure during condensation, so some of the hot water immediately flashes into high-temperature secondary steam. This secondary steam can be used in other heating processes or discharged to the low-pressure side through a pressure regulating valve. The remaining liquid after flash evaporation continues to flow into the waste heat recovery pipe.

[0035] Waste heat recovery and circulation: The flash evaporation products flowing in the waste heat recovery pipe carry heat. Its lower end connects to a preheater, which heats external fresh air or process water. The hot air is then sent to the paper machine drying hood via a circulating air duct for secondary utilization. In this way, the heat energy of the waste gas is recovered and utilized through multiple pathways, synergistically heating the drying section's supply air and workshop air, significantly improving energy efficiency. The pressure relief valve and exhaust port at the top of the system ensure timely release of pressure fluctuations, guaranteeing stable operation of the unit.

[0036] Soot blowing and safety control: A pulse jet cleaning device installed at the top of the flash tank periodically injects high-pressure airflow into the tank, blowing the sediment to the bottom and discharging it through the drain valve, thus maintaining flash evaporation efficiency. A pressure gauge monitors the tank pressure in real time, and the pressure is regulated by adjusting the pressure control valve when necessary to ensure the system pressure difference remains within the design range. Through coordinated operation, the entire system achieves efficient recovery and reuse of waste steam and heat from the paper machine drying section.

[0037] The foregoing has shown and described the basic principles, main features, and advantages of this utility model. Those skilled in the art should understand that this utility model is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of this utility model. Various changes and modifications can be made to this utility model without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claims. The scope of protection of this utility model is defined by the appended claims and their equivalents.

Claims

1. A heat recovery device for the drying section of a paper machine based on a dual gas-steam cycle, comprising a cyclone dust collector (1), a compressor (4), a flash tank (8), and a waste heat recovery pipe (9), characterized in that: The cyclone dust collector (1) is located downstream of the exhaust gas outlet riser (2) and is connected to the exhaust gas outlet riser (2) via a flange. The bottom of the cyclone dust collector (1) is equipped with a ash discharge valve (3). The side wall of the cyclone dust collector (1) is connected to a heat exchange tube (6) via a sealed pipeline. The lower end of the heat exchange tube (6) is connected to a compressor (4) via a suction pipe. The exhaust end of the compressor (4) is connected to a condenser (5) via a high-pressure pipeline. The water outlet end of the condenser (5) is connected to a flash tank (8) via a connecting pipe (7). The outlet of the flash tank (8) is connected to the waste heat recovery pipe (9) via a horizontal pipe. The lower end of the waste heat recovery pipe (9) is fixedly connected to the preheater (10), and the middle section is connected to the air inlet of the paper machine drying hood via a circulating air pipe (11). The top of the waste heat recovery pipe (9) is provided with a pressure relief valve (12) and an exhaust port (13). The top of the flash tank (8) is provided with two pulse jet devices (14). The pulse jet devices (14) are provided with a motor (15) and a pressure gauge (16) above them.

2. The heat recovery device for the drying section of a paper machine based on a dual gas-steam circulation system according to claim 1, characterized in that: The cyclone dust collector (1) is integrally formed from an upper cylindrical section and a lower conical bucket section. The inner diameter of the upper cylindrical section is φ450mm, and the cone angle of the lower conical bucket section is 50°±2°. It is connected to the cylindrical section by an annular butt weld.

3. The heat recovery device for the drying section of a paper machine based on a dual gas-steam circulation system according to claim 1, characterized in that: The high-pressure pipeline also includes an oil separator with a nominal diameter of DN65. One end of the oil separator is connected to the exhaust port of the compressor (4) through a DN65 or PN2.5 raised face flange, and the other end is connected to the inlet of the condenser (5) through a flange of the same specification.

4. A heat recovery device for a paper machine drying section based on a dual gas-steam circulation system according to claim 1, characterized in that: The flash tank (8) is a vertical cylindrical structure with an inner diameter of φ600mm and a height of 1600mm. Two internally threaded spray ports G1-1 / 2″ are symmetrically arranged on the top. The pulse spray device (14) is sealed to the spray port through the threaded port.

5. A heat recovery device for a paper machine drying section based on a dual gas-steam circulation system according to claim 1, characterized in that: The waste heat recovery pipe (9) is welded with several short pipes for temperature measurement and pressure tapping at 500mm intervals along the axial direction. Each short pipe has an external thread specification of M20×1.5 and is embedded with a K-type thermocouple sleeve.

6. A heat recovery device for a paper machine drying section based on a dual gas-steam circulation system according to claim 1, characterized in that: The preheater (10) is a U-shaped tube bundle heat exchanger with a shell diameter of φ350mm. Its shell is connected to the lower end of the waste heat recovery tube (9) through a 45° steel elbow and a DN150, PN1.6 flat welding flange. The tube bundle is made of copper U-shaped tube with an outer diameter of φ19mm and a tube spacing of 25mm.

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