Method and device for improving heat exchange efficiency of heat pipe heat exchanger

Abstract

The invention discloses a method and device for improving the heat exchange efficiency of a heat pipe heat exchanger, relates to the technical field of heat pipe heat exchangers, and is particularly suitable for a heat pipe low-temperature economizer in a boiler flue gas waste heat recovery system. The technical problems that the boiling point of circulating cooling water is limited, the temperature difference between inlet water and outlet water is small, and the heat exchange efficiency is low due to the fact that an existing heat pipe low-temperature economizer adopts an open water tank are solved. The water tank is designed to be of a closed structure, the upper portion of the water tank is connected with the expansion balance water tank located above the water tank through the communicating pipeline, static pressure is formed through the height difference between the water tank and the water tank to improve the internal pressure of the water tank, the boiling point of circulating cooling water is increased, the temperature of water flowing out of the water tank exceeds 100 DEG C, and the water inlet and outlet temperature difference is remarkably increased; the heat exchange efficiency and the heat exchange amount of the heat pipe exchanger are improved; the device is simple in structure and reliable in operation, existing equipment can be easily transformed, and economical efficiency and practicability are both achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of heat pipe heat exchangers, in particular to a method and device for improving the heat exchange efficiency of a heat pipe heat exchanger, which is especially suitable for a heat pipe low-temperature economizer in a boiler flue gas waste heat recovery system and can be widely applied to boiler flue gas waste heat recovery scenes in the power, metallurgy, chemical and other industries. BACKGROUND

[0002] During the operation of a boiler, excessively high exhaust gas temperature will cause a large amount of high-temperature flue gas heat to be directly discharged into the atmosphere, resulting in serious heat waste, and also increasing the evaporation capacity of the desulfurization tower and consuming a large amount of water resources, which does not meet the industry demand for energy saving and consumption reduction. To solve this problem, flue gas waste heat recovery technology is widely used. Traditional flue gas waste heat recovery equipment mostly uses a metal coil water pipe low-temperature economizer, which realizes heat exchange between flue gas and cooling water by inserting a water pipe into a flue. However, in actual operation, such economizers generally have problems such as water leakage and ash accumulation due to factors such as erosion and abrasion of dust-containing airflow, low-temperature corrosion, alternating stress damage, and water impact. Once the water pipe is perforated and leaks, high-pressure water injection into the electric dust removal system will seriously threaten the safe operation of the equipment.

[0003] In recent years, heat pipe low-temperature economizers have gradually replaced traditional metal coil water pipe low-temperature economizers due to their advantages of high-efficiency heat exchange and compact structure. The core structure of a heat pipe low-temperature economizer includes a heat pipe vacuum pipe, which is a sealed shell and contains an evaporation medium inside. The lower section of the vacuum pipe is placed in a flue, and the upper section is placed in a water tank filled with circulating cooling water. The heat transfer from flue gas to cooling water is realized through the vaporization-condensation cycle of the evaporation medium. However, to prevent the expansion of the circulating cooling water in the water tank from causing the tank to crack, the water tank is usually designed as an open structure. This design limits the boiling point of the circulating cooling water to 100℃ (standard atmospheric pressure), and in actual operation, to avoid boiling of the cooling water, the water temperature is usually controlled at a lower level, resulting in a small temperature difference between the cold water entering the water tank and the hot water flowing out of the water tank, which severely limits the heat exchange efficiency and heat exchange capacity of the heat pipe heat exchanger, and the waste heat resources in the boiler flue gas cannot be fully recovered, leaving a large energy-saving improvement space.

[0004] Therefore, how to break through the temperature limitation of the open water tank on the cooling water and increase the inlet and outlet water temperature difference to improve the heat exchange efficiency of the heat pipe heat exchanger has become a technical problem to be solved in the field. SUMMARY

[0005] The present application aims to overcome the deficiencies of the prior art, and provide a method and device for improving the heat exchange efficiency of a heat pipe heat exchanger, the core purpose of which is to improve the internal pressure of a water tank by optimizing the structural design of the water tank, to increase the boiling point of circulating cooling water, to break the temperature limit of the existing open water tank, to increase the temperature difference of the circulating cooling water at the inlet and outlet, and thus to significantly improve the heat exchange efficiency and heat exchange capacity of the heat pipe heat exchanger, while solving the problems of leakage and blockage of traditional coal economizers and the low heat exchange efficiency of existing heat pipe coal economizers, and the device is simple in structure, easy to modify, and suitable for industrial actual application requirements.

[0006] To achieve the above-mentioned application purposes, the present application provides the following technical solutions, which are divided into two parts of device and method: 1. Device technical solution A device for improving the heat exchange efficiency of a heat pipe heat exchanger, suitable for a boiler flue gas waste heat recovery system, comprising a flue (1), a heat pipe vacuum tube (2), a closed water tank (3), a connecting pipeline (4), and an expansion balance water tank (5), the specific structures and connection relationships of the various components are as follows: - Flue (1): a flow channel for boiler flue gas, used for transporting high-temperature boiler flue gas to provide a heat source for heat pipe heat exchange; - Heat pipe vacuum tube (2): a conventional heat pipe structure, a closed tube shell is filled with an evaporation medium (such as distilled water, heat-conducting oil, etc.), the lower section is placed in the flue (1) to absorb the heat of high-temperature flue gas to vaporize the evaporation medium, and the upper section is placed in the water tank (3) to condense the vaporized medium to release heat and transfer the heat to the circulating cooling water in the water tank (3); - Water tank (3): a closed structure made of pressure-resistant materials (such as carbon steel, stainless steel) to ensure that it can withstand a certain pressure without leaking, the water tank (3) is filled with circulating cooling water to absorb the heat released by the upper section of the heat pipe vacuum tube (2); the water tank (3) is provided with a water inlet and a water outlet, the water inlet is used to introduce low-temperature circulating cooling water (such as normal-temperature tap water or industrial waste water), and the water outlet is used to discharge high-temperature circulating cooling water after heating, and valves are provided at the water inlet and the water outlet to adjust the flow of the cooling water in and out according to the heat exchange requirements; - Connecting pipeline (4): a connecting channel between the water tank (3) and the expansion balance water tank (5), made of pressure-resistant stainless steel pipe, with good sealing and pressure resistance, one end of which is connected to the upper part of the water tank (3), and the other end is connected to the expansion balance water tank (5), and sealing structures (such as sealing pads, welded seals) are provided at the connection positions to prevent air and water leakage and ensure stable system pressure; - Expansion balance tank (5): placed above the water tank (3), maintaining a preset height difference of 2-10 meters between the water tank (3), which can be flexibly adjusted according to the required water tank pressure (the higher the height difference, the greater the static pressure, and the higher the pressure in the water tank); The core role of the expansion balance tank (5) has two, one is to form a static pressure through the height difference with the water tank (3), to increase the pressure inside the water tank (3), and then to increase the boiling point of the circulating cooling water; Two is to accommodate the volume change of the circulating cooling water when it is heated and expanded, to avoid the water tank (3) from cracking due to excessive pressure, and to maintain the stability of the pressure in the entire system; Preferably, the expansion balance tank (5) is equipped with a liquid level meter and a pressure gauge on the top, respectively for real-time monitoring of the liquid level in the tank and the system pressure, facilitating timely adjustment and maintenance by staff, and ensuring safe and stable operation of the device.

[0007] In addition, in order to reduce the heat loss inside the system and further improve the heat exchange efficiency, the outer walls of the water tank (3) and the expansion balance tank (5) are wrapped with a thermal insulation layer (such as rock wool, polyurethane insulation layer), and the thickness of the thermal insulation layer is determined according to the actual working condition, preferably ≥50mm.

[0008] 2. Method technical scheme A method for improving the heat exchange efficiency of a heat pipe heat exchanger, which is implemented by using the above device, and specifically includes the following steps: S1. Device assembly: First, fix the lower section of the heat pipe vacuum tube (2) in the flue (1) to ensure that the vacuum tube is in full contact with the flue gas and can absorb the heat of the flue gas; Insert the upper section of the heat pipe vacuum tube (2) into the closed water tank (3) to ensure that the upper section is in full contact with the circulating cooling water in the water tank (3); Connect the upper part of the water tank (3) with the expansion balance tank (5) through the connecting pipeline (4), and seal the connection between the connecting pipeline (4) and the water tank (3) and the expansion balance tank (5) to ensure that the system is leak-proof; According to the required water tank pressure, adjust the installation height of the expansion balance tank (5) to maintain a height difference of 2-10 meters between the water tank (3) and the water tank (3); At the same time, wrap the outer walls of the water tank (3) and the expansion balance tank (5) with a thermal insulation layer to reduce heat loss.

[0009] S2. Inject cooling water: inject circulating cooling water into the water tank (3) through the water inlet of the water tank (3), and at the same time, the cooling water flows into the expansion balance tank (5) through the connecting pipeline (4), until the circulating cooling water fills the water tank (3), and the preset liquid level (the liquid level height is not less than the connection port of the connecting pipeline (4) and the water tank) is maintained in the expansion balance tank (5), and the water inlet valve is closed.

[0010] S3. Start running: start the boiler, high-temperature flue gas (temperature usually 400-600℃) flows through the flue (1), the high-temperature flue gas contacts the lower section of the heat pipe vacuum tube (2), transfers heat to the evaporation medium in the vacuum tube, and makes the evaporation medium vaporize; the vaporized evaporation medium (gas state) rises to the upper section of the heat pipe vacuum tube (2) under the action of pressure difference, exchanges heat with the circulating cooling water in the water tank (3), and the gaseous medium condenses into liquid state, releasing a large amount of heat to heat the circulating cooling water in the water tank (3).

[0011] S4. Pressure regulation and heat exchange enhancement: since the water tank (3) is a closed structure and is connected to the expansion balance water tank (5) located above through the communication pipeline (4), the cooling water in the expansion balance water tank (5) generates static pressure due to gravity, which is transmitted to the water tank (3) through the communication pipeline (4), so that the internal pressure of the water tank (3) increases; according to the physical principle, the boiling point of water increases by about 10℃ for every 0.1MPa increase in pressure, and by adjusting the height difference between the expansion balance water tank (5) and the water tank (3), the pressure in the water tank (3) can be adjusted to the required value, so that the boiling point of the circulating cooling water exceeds 100℃ (for example, when the height difference is 5 meters, the static pressure is about 0.05MPa, and the boiling point of the cooling water can be raised to about 105℃; when the height difference is 10 meters, the static pressure is about 0.1MPa, and the boiling point of the cooling water can be raised to about 110℃); at this time, the circulating cooling water in the water tank (3) can be heated to more than 100℃ and discharged from the water outlet, forming a large temperature difference with the low-temperature cooling water entering the water tank (compared with the existing open water tank, the temperature difference can be increased by 30-50℃), significantly improving the heat exchange efficiency and heat exchange capacity of the heat pipe heat exchanger; at the same time, the volume change of the circulating cooling water caused by heating and expansion flows into the expansion balance water tank (5) through the communication pipeline (4) and is accommodated by the water tank, avoiding damage to the water tank (3) due to excessive pressure and maintaining stable system pressure.

[0012] S5. Continuous monitoring and maintenance: during operation, the liquid level in the water tank is monitored in real time through the liquid level meter on the expansion balance water tank (5), if the liquid level is too high, part of the cooling water can be discharged through the blowdown valve at the bottom of the water tank; if the liquid level is too low, the cooling water can be supplemented through the water inlet; the system pressure is monitored in real time through the pressure gauge, if the pressure is too high, the height of the expansion balance water tank (5) can be adjusted or part of the cooling water can be discharged, if the pressure is too low, the cooling water can be supplemented or the height difference between the water tank and the water tank can be increased; the sealing performance, insulation layer integrity and operating state of each part of the device are checked regularly, and the ash deposited on the lower section of the heat pipe vacuum tube (2) is cleaned in time to ensure long-term stable operation of the device.

[0013] Compared with the prior art, the advantages and positive effects of the present application are that, The heat exchange efficiency is greatly improved: through the structural design of the closed water tank + expansion balance water tank, the static pressure is generated by using the height difference to improve the internal pressure of the water tank, the boiling point of the circulating cooling water is effectively improved, the water temperature flowing out of the water tank exceeds 100 DEG C, the inlet and outlet water temperature difference of the circulating cooling water is significantly increased (compared with the existing open water tank, the temperature difference is increased by 30-50 DEG C), and under the same heat pipe heat exchange area, the heat exchange amount can be increased by 20%-40%, the waste heat resource in the boiler flue gas can be fully recovered, and the energy saving effect is remarkable. Solve the pain points of the prior art: on the one hand, compared with the traditional metal coil water pipe low-temperature economizer, the heat pipe vacuum pipe structure is adopted, the problems of water pipe leakage, ash accumulation and blockage are avoided, and the equipment operation safety is improved; on the other hand, compared with the existing open water tank heat pipe economizer, the cooling water temperature limit is broken, the problem of low heat exchange efficiency is solved, and the safety and efficiency are unified; Simple structure and reliable operation: the present application only increases the closed water tank, the connecting pipeline and the expansion balance water tank on the basis of the existing heat pipe low-temperature economizer, without changing the heat pipe vacuum pipe, flue and other core equipment, the structure is simple, the manufacturing cost is low; at the same time, the expansion balance water tank can effectively accommodate the cooling water thermal expansion volume, maintain the system pressure stable, prevent the water tank from cracking, prolong the service life of the equipment, and no complex operation is needed in the running process, the reliability is high; Easy to transform, strong universality: the present application is not only suitable for new boiler flue gas waste heat recovery system, but also can directly transform the existing heat pipe low-temperature economizer, only the original open water tank is replaced by the closed water tank, and the connecting pipeline and the expansion balance water tank are added, the transformation period is short, the engineering quantity is small, and it is suitable for boiler flue gas waste heat recovery scenes in power, metallurgy, chemical industry and other industries, and has wide application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0014] In order to more clearly illustrate the technical scheme of the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creating labor intensity.

[0015] Figure 1 It is a structural schematic diagram of the device of the present application. In the figure: 1-flue, 2-heat pipe vacuum pipe, 3-water tank, 4-connecting pipeline, 5-expansion balance water tank. DETAILED DESCRIPTION

[0016] In order to more clearly illustrate the above-mentioned purposes, features and advantages of the present application, the present application will be further described below in combination with the drawings and embodiments. It should be noted that the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

[0017] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application. However, the present application can be practiced without the specific details described herein. In other instances, well-known methods have not been described in detail in order not to unnecessarily obscure aspects of the present application. Embodiment

[0018] The embodiment provides a device and method for improving the heat exchange efficiency of a heat pipe heat exchanger, which is suitable for a small and medium-sized boiler flue gas waste heat recovery system (boiler rated evaporation capacity is 10-20t / h), and specifically as follows. I. Device specific structure 1. Flue (1): made of carbon steel, the cross-sectional size is 1.2m x 1.0m, used for conveying high-temperature flue gas (flue gas temperature is 400-500℃) discharged from the boiler; 2. Heat pipe vacuum tube (2): made of stainless steel tube, distilled water is filled in the tube as evaporation medium, the vacuum tube diameter is 50mm, the length is 3.0m, 100 are arranged, the lower section of all vacuum tubes is uniformly fixed in the flue (1), and the upper section is inserted into the water tank (3) with an insertion depth of 1.0m; 3. Water tank (3): made of a closed box body of 304 stainless steel, the volume is 5m³, a DN50 water inlet and a DN65 water outlet are arranged on the water tank (3), and stainless steel ball valves are arranged at the water inlet and the water outlet, used for adjusting the cooling water flow; the design pressure of the water tank (3) is 0.3MPa, which can ensure that the static pressure generated by the expansion balance water tank can be borne; 4. Connecting pipeline (4): made of a DN40 pressure-resistant stainless steel pipe, the length is 15m, one end of the pipe is welded in communication with the upper part of the water tank (3), the welding position is sealed by argon arc welding, and the other end is welded in communication with the bottom of the expansion balance water tank (5), and a graphite sealing gasket is additionally arranged at the connecting position, so that no leakage is caused; 5. Expansion balance water tank (5): made of 304 stainless steel, the volume is 1m³, and the water tank is installed 5m above the water tank (3), so that a height difference of 5m is formed between the water tank (3) and the expansion balance water tank (5), and about 0.05MPa static pressure can be generated; the water tank is provided with a glass tube liquid level meter (measurement range 0-1.0m) and a pressure gauge (measurement range 0-0.5MPa), which are used for monitoring the liquid level and pressure in real time; 6. Heat preservation layer: the outer walls of the water tank (3) and the expansion balance water tank (5) are wrapped with a 60mm-thick rock wool heat preservation layer, and an iron sheet protective layer is additionally wrapped outside the heat preservation layer, so that heat loss is reduced.

[0019] II. Method implementation steps S1. Device assembly: 100 lower sections of heat pipe vacuum tubes (2) are evenly fixed in the flue (1), ensuring that the axis of the vacuum tube is perpendicular to the direction of the flue gas flow, so as to facilitate the full absorption of the heat of the flue gas; the upper sections of the vacuum tubes are inserted into the closed water tank (3), ensuring that the tube wall of the upper section is in full contact with the cooling water in the water tank; the upper part of the water tank (3) is connected with the expansion balance water tank (5) through a DN40 stainless steel pipe, and the welding part is well sealed; the expansion balance water tank (5) is fixedly installed on the steel frame 5 meters above the water tank (3); the water tank (3) and the water tank are wrapped with rock wool insulation layer and fixed; S2. Inject cooling water: open the water inlet valve of the water tank (3), inject normal temperature circulating cooling water (temperature is 25℃) into the water tank (3), the cooling water flows into the expansion balance water tank (5) through the connecting pipeline (4), until the water tank (3) is filled with cooling water, the liquid level in the expansion balance water tank (5) reaches 0.5m, and the water inlet valve is closed; S3. Start running: start the boiler, adjust the boiler load to the rated load, high-temperature flue gas (temperature is about 450℃) flows through the flue (1) and contacts the lower section of the heat pipe vacuum tube (2), transfers heat to the distilled water in the tube, and makes the distilled water vaporize (vaporization temperature is about 100℃); the gaseous distilled water rises to the upper section of the vacuum tube and exchanges heat with the cooling water in the water tank (3), and is condensed into liquid and releases heat to heat the cooling water; S4. Pressure regulation and heat exchange strengthening: due to the 5-meter height difference between the expansion balance water tank (5) and the water tank (3), a static pressure of 0.05MPa is generated, the internal pressure of the water tank (3) rises to 0.05MPa, and the boiling point of the cooling water rises to about 105℃; after running for 30 minutes, the temperature of the cooling water in the water tank (3) stabilizes at 102℃, and the temperature difference between the outlet water temperature (25℃) and the inlet water temperature (25℃) is 77℃; compared with the existing open water tank (temperature difference is about 40℃), the temperature difference is increased by 92.5%; at the same time, the volume change (about 5%) of the cooling water caused by heating expansion flows into the expansion balance water tank (5) through the connecting pipeline (4), the liquid level in the water tank rises to 0.52m, and the system pressure stabilizes at 0.05MPa, without leakage; S5. Continuous monitoring: during the operation, the liquid level meter and pressure gauge data are recorded once an hour, ensuring that the water tank liquid level is maintained at 0.4-0.6m and the system pressure is maintained at 0.04-0.06MPa; the sealing performance of the device and the integrity of the insulation layer are checked once a day, and the accumulated ash on the lower section of the heat pipe vacuum tube (2) is cleaned once a week, to ensure the stability of the heat exchange efficiency. Implementation effect

[0020] The embodiment runs stably, has no leakage and no failure, the heat exchange efficiency of the heat pipe heat exchanger is improved by 35% compared with the existing open water tank structure, about 120kW of flue gas waste heat can be recovered per hour, about 80 tons of standard coal can be saved per year, the leakage problem of the traditional economizer is avoided, the equipment operation safety is improved, and the waste heat recovery demand of the small and medium-sized boiler is met. Embodiment

[0022] The embodiment provides a device and a method for improving the heat exchange efficiency of a heat pipe heat exchanger, and is suitable for a large boiler flue gas waste heat recovery system (the rated evaporation capacity of the boiler is 100-200t / h), and specifically as follows: I. Device specific structure 1. Flue (1): made of carbon steel, the cross-sectional size is 3.0m*2.5m, and is used for conveying high-temperature flue gas (the flue gas temperature is 500-600℃) discharged from the boiler; 2. Heat pipe vacuum tube (2): made of a stainless steel tube, the tube is filled with heat-conducting oil as an evaporation medium (the vaporization temperature is about 120℃), the vacuum tube has a diameter of 80mm, a length of 4.0m, and a total of 300 vacuum tubes are arranged, the lower sections of all the vacuum tubes are uniformly fixed in the flue (1), and the upper sections are inserted into the water tank (3) with an insertion depth of 1.5m; 3. Water tank (3): made of a closed box body made of carbon steel, and has a volume of 20m³; a DN100 water inlet and a DN125 water outlet are arranged on the water tank (3); electric regulating valves are arranged at the water inlet and the water outlet, and the flow of cooling water can be automatically adjusted through a control system; and the water tank (3) is designed to withstand a pressure of 0.5MPa; 4. Connecting pipeline (4): made of a DN80 pressure-resistant stainless steel pipe, has a length of 25m, one end of the pipe is welded in communication with the upper portion of the water tank (3), and the other end of the pipe is welded in communication with the bottom of the expansion balance water tank (5), and double sealing (welding sealing+sealing gasket sealing) is adopted at the connection positions; 5. Expansion balance water tank (5): made of carbon steel, has a volume of 5m³, and is installed 10m above the water tank (3) to form a height difference of 10m with the water tank (3), so that a static pressure of about 0.1MPa can be generated; the water tank is provided with an electronic liquid level meter (transmits a liquid level signal to a control system in real time) and a pressure transmitter (transmits a pressure signal to the control system in real time), so that the liquid level and the pressure can be automatically monitored; 6. Insulation layer: the outer walls of the water tank (3) and the expansion balance water tank (5) are wrapped with a polyurethane insulation layer with a thickness of 80mm, and the insulation layer is further wrapped with a color steel plate protective layer, so that the insulation effect is better.

[0023] II. Method implementation steps S1. Device assembly: 300 lower sections of heat pipe vacuum tubes (2) are evenly fixed in the flue (1), the distance between the vacuum tubes is 100 mm, ensuring smooth flue gas flow and full contact with the vacuum tubes; the upper sections of the vacuum tubes are inserted into the closed water tank (3); the upper part of the water tank (3) is connected with the expansion balance water tank (5) through a DN80 stainless steel pipe, and double sealing is done at the welding position; the expansion balance water tank (5) is installed on the concrete support 10 meters above the water tank (3); the outer walls of the water tank (3) and the water tank are wrapped with polyurethane insulation layer and fixed; the electronic liquid level meter, pressure transmitter and control system are connected to realize automatic monitoring; S2. Inject cooling water: open the water inlet electric regulating valve of the water tank (3), inject normal temperature circulating cooling water (temperature is 20℃) into the water tank (3), the cooling water flows into the expansion balance water tank (5), until the water tank (3) is filled with cooling water, and the liquid level in the expansion balance water tank (5) reaches 3.0m, then close the water inlet electric regulating valve; S3. Start running: start the boiler, adjust the boiler load to the rated load, high temperature flue gas (temperature is about 550℃) flows through the flue (1), heats the lower section of the heat pipe vacuum tube (2), and makes the heat conducting oil in the tube vaporize; the gaseous heat conducting oil rises to the upper section of the vacuum tube, exchanges heat with the cooling water in the water tank (3), condenses and releases heat, and heats the cooling water; S4. Pressure regulation and heat exchange intensification: the 10-meter height difference between the expansion balance water tank (5) and the water tank (3) generates a static pressure of 0.1MPa, the internal pressure of the water tank (3) rises to 0.1MPa, and the boiling point of the cooling water rises to about 110℃; after running for 1 hour, the temperature of the cooling water in the water tank (3) stabilizes at 108℃, and the temperature difference between the outlet temperature and the inlet temperature (20℃) is 88℃; compared with the existing open water tank (temperature difference is about 45℃), the temperature difference is increased by 95.6%; the volume change of the heated and expanded cooling water flows into the expansion balance water tank (5) through the connecting pipeline (4), and the system pressure stabilizes at 0.1MPa; the control system monitors the liquid level and pressure in real time, and if the pressure exceeds 0.12MPa, the water tank blowdown valve is automatically opened to discharge part of the cooling water, ensuring stable pressure; S5. Continuous monitoring and maintenance: the control system monitors the liquid level and pressure in real time for 24 hours, and automatically adjusts the cooling water inflow and outflow; the device is checked once a week, focusing on the sealing, insulation layer and running state of the heat pipe vacuum tube; the lower section of the heat pipe vacuum tube (2) is blown with high pressure air once a month to remove ash; the water quality of the water tank (3) and the expansion balance water tank (5) is detected and discharged once a quarter to prevent scaling from affecting heat exchange efficiency. Implementation effect

[0024] This embodiment is applicable to large boiler flue gas waste heat recovery systems. It operates stably and reliably, and its heat exchange efficiency is 38% higher than that of the existing open water tank structure. It can recover about 500kW more flue gas waste heat per hour and save about 350 tons of standard coal per year. At the same time, it effectively avoids the leakage and blockage problems of traditional economizers, reduces equipment operation and maintenance costs, and combines energy saving, safety and economy.

[0025] Example 3 (Existing Equipment Retrofit Example) This embodiment addresses the modification of an existing heat pipe low-temperature economizer (open water tank structure) in a power plant, employing the device and method of this invention, as detailed below: I. Current Status Before Renovation The existing heat pipe low-temperature economizer is equipped with an open water tank (volume of 10m³) and heat pipe vacuum tubes (diameter of 60mm, length of 3.5m, 200 in total). During operation, the maximum cooling water outlet temperature is 95℃, the temperature difference between the inlet and outlet water is about 42℃, the heat exchange efficiency is low, and there is a problem of large cooling water evaporation loss.

[0026] II. Modification Scheme (using the device of this invention) 1. Replace the water tank: Replace the original open water tank with a closed water tank (3) (carbon steel material, volume 10m³, design pressure resistance 0.3MPa), add a DN80 inlet and a DN100 outlet to the water tank, and install an electric regulating valve; 2. Add connecting pipeline and expansion balance tank: Use DN60 pressure-resistant stainless steel pipe as connecting pipeline (4), with a length of 20m. One end is welded to the upper part of the closed water tank (3), and the other end is welded to the expansion balance tank (5) (carbon steel material, volume 3m³). Install the expansion balance tank (5) 8 meters above the water tank (3) to form an 8-meter height difference and generate a static pressure of about 0.08MPa. The tank is equipped with a level gauge and a pressure gauge. 3. Add insulation layer: Wrap the outer wall of the closed water tank (3) and expansion balance water tank (5) with a 70mm rock wool insulation layer; 4. Other modifications: The original heat pipe vacuum tube (2) and flue (1) are retained. Only the water tank and supporting equipment are modified. There is no need to change the core heat exchange components.

[0027] III. Operational Results After Modification After the modification is completed, the boiler flue gas temperature is about 480℃, the pressure in the water tank (3) is stable at 0.08MPa, the boiling point of the cooling water is raised to about 108℃, the outlet temperature of the cooling water is stable at 105℃, the temperature difference between the inlet and outlet water is increased to 83℃ (inlet water temperature 22℃), the heat exchange efficiency is increased by 39% compared with before the modification, about 280kW of waste heat from the flue gas can be recovered every year, saving about 200 tons of standard coal, while avoiding the evaporation loss of cooling water, reducing water consumption, and the investment payback period of the modification is only 8 months, with significant economic benefits.

[0028] General Precautions 1. During installation, the water tank (3) and expansion balance tank (5) must be sealed. The welded joints must be subjected to a water pressure test (the test pressure is 1.5 times the design pressure) to ensure no leakage. 2. During operation, the height difference between the expansion balance tank (5) and the water tank (3) must be strictly controlled. The height of the water tank must not be changed arbitrarily to avoid excessively high or low system pressure affecting heat exchange efficiency and equipment safety. 3. Regularly clean the ash accumulation in the lower section of the heat pipe vacuum tube (2) to avoid excessive ash accumulation affecting the heat transfer of flue gas; regularly check the cooling water quality to prevent scaling, and add descaling agent if necessary; 4. When the boiler load changes, adjust the cooling water flow rate by adjusting the opening of the inlet and outlet valves of the water tank (3) to ensure stable heat exchange efficiency; 5. When the system is shut down, first close the boiler flue gas passage, and after the cooling water temperature in the water tank (3) drops to normal temperature, drain the cooling water and clean and maintain the device.

[0029] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments for application in other fields. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A device for improving the heat exchange efficiency of a heat pipe heat exchanger, suitable for a boiler flue gas waste heat recovery system, comprising a flue (1) and a heat pipe vacuum tube (2), wherein the lower section of the heat pipe vacuum tube (2) is placed inside the flue (1), characterized in that, It also includes a closed water tank (3), connecting pipelines (4) and an expansion balance tank (5); The upper section of the heat pipe vacuum tube (2) is placed in a water tank (3), which is filled with circulating cooling water to absorb the heat released by the condensation of the upper section of the heat pipe vacuum tube (2). One end of the connecting pipe (4) is connected to the upper part of the water tank (3), and the other end is connected to the expansion balance water tank (5); The expansion balance tank (5) is located above the water tank (3) and forms a preset height difference with the water tank (3). It is used to generate static pressure through the height difference to increase the internal pressure of the water tank (3) and to accommodate the volume change of the circulating cooling water during thermal expansion, so as to maintain the stability of the system pressure.

2. The apparatus for improving the heat exchange efficiency of a heat pipe heat exchanger according to claim 1, characterized in that, The preset height difference between the expansion balance tank (5) and the water tank (3) is 2-10 meters, which is used to provide static pressure that makes the boiling point of the circulating cooling water exceed 100°C.

3. The apparatus for improving the heat exchange efficiency of a heat pipe heat exchanger according to claim 1, characterized in that, The expansion balance tank (5) is equipped with a level gauge and a pressure gauge, which are used to monitor the liquid level and system pressure in the expansion balance tank (5) in real time.

4. The apparatus for improving the heat exchange efficiency of a heat pipe heat exchanger according to claim 1, characterized in that, The connecting pipeline (4) is made of pressure-resistant stainless steel pipe, and the connection between the connecting pipeline (4) and the water tank (3) and the expansion balance water tank (5) is equipped with a sealing structure to ensure the system's airtightness.

5. The apparatus for improving the heat exchange efficiency of a heat pipe heat exchanger according to claim 1, characterized in that, The outer walls of the water tank (3) and the expansion balance tank (5) are both covered with an insulation layer to reduce heat loss inside the system.

6. The apparatus for improving the heat exchange efficiency of a heat pipe heat exchanger according to claim 1, characterized in that, The water tank (3) is provided with an inlet and an outlet. The inlet is used to introduce low-temperature circulating cooling water, and the outlet is used to discharge high-temperature circulating cooling water after heating. Valves are provided at both the inlet and outlet to control the flow rate of the circulating cooling water.

7. A method for improving the heat exchange efficiency of a heat pipe heat exchanger, using the apparatus according to any one of claims 1-6, characterized in that, Includes the following steps: S1. Assembly device: Fix the lower section of the heat pipe vacuum tube (2) inside the flue (1), insert the upper section into the closed water tank (3), and connect the upper part of the water tank (3) to the expansion balance water tank (5) located above it through the connecting pipe (4) to ensure that the system is well sealed and that the expansion balance water tank (5) and the water tank (3) maintain a height difference of 2-10 meters. S2. Inject cooling water: Inject circulating cooling water into the water tank (3) and the expansion balance tank (5) so that the circulating cooling water fills the water tank (3) and maintains the preset liquid level in the expansion balance tank (5); S3. Start-up and operation: Boiler flue gas flows through flue (1) and heats the lower section of heat pipe vacuum tube (2), causing the evaporation medium in heat pipe vacuum tube (2) to vaporize; the vaporized evaporation medium rises to the upper section of heat pipe vacuum tube (2) and exchanges heat with the circulating cooling water in water tank (3), condenses and releases heat and heats the circulating cooling water; S4. Pressure regulation and heat exchange enhancement: Static pressure is formed by the height difference between the expansion balance tank (5) and the water tank (3), which increases the internal pressure of the water tank (3), raises the boiling point of the circulating cooling water, and makes the temperature of the circulating cooling water flowing out of the water tank (3) after heating exceed 100°C, increases the temperature difference between the inlet and outlet of the circulating cooling water, and improves the heat exchange efficiency; at the same time, the expansion balance tank (5) accommodates the volume change caused by the thermal expansion of the circulating cooling water, maintains the stability of the system pressure, and prevents the water tank (3) from being damaged due to excessive pressure; S5. Continuous monitoring: The system level and pressure are monitored in real time by using the level gauge and pressure gauge on the expansion balance tank (5) to ensure stable operation of the device.

8. The method for improving the heat exchange efficiency of a heat pipe heat exchanger according to claim 7, characterized in that, In step S4, the internal pressure of the water tank (3) is adjusted according to the height difference between the expansion balance water tank (5) and the water tank (3). For every 0.1 MPa increase in pressure, the boiling point of the circulating cooling water increases by about 10°C.

9. The method for improving the heat exchange efficiency of a heat pipe heat exchanger according to claim 7, characterized in that, In step S3, the evaporating medium inside the heat pipe vacuum tube (2) vaporizes and rises to the upper section for condensation. The condensed medium then flows back to the lower section of the heat pipe vacuum tube (2) by gravity, completing the circulating heat exchange.

10. The method for improving the heat exchange efficiency of a heat pipe heat exchanger according to claim 7, characterized in that, It also includes the step of heat preservation treatment of water tank (3) and expansion balance water tank (5) to reduce heat loss inside the system and further improve heat exchange efficiency.

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