Boiler deep waste heat recovery and anti-corrosion and anti-blocking system based on heat pipe-heat pump combination

Abstract

The invention relates to the technical field of boiler energy conservation and environmental protection, in particular to a boiler deep waste heat recovery, corrosion prevention and blockage prevention system based on heat pipe-heat pump compounding, which comprises a high-temperature-stage heat pipe heat exchange section and a deep cooling-stage heat pump evaporation section which are sequentially arranged along the flow direction of flue gas, and further comprises an ash removal and corrosion prevention system, the ash removal and corrosion prevention system comprises a high-frequency sound wave ash blower used for cleaning the fluoroplastic heat exchange tube bundle and a liquid collecting and neutralizing device used for collecting and treating acid condensate. A high-temperature section uses a conventional metal material but works in a safe area; the system can safely work in a strong acid condensation environment for a long time by utilizing the natural extreme acid corrosion resistance characteristic of fluoroplastic; and in combination with four anti-blocking designs of non-adhesion of the fluoroplastic light pipes, large-interval arrangement without bridging, high-frequency sound wave soot blowing and online spraying and flushing, the heat exchange surface is ensured to be clean for a long time, the efficient heat exchange performance is maintained, and the maintenance intensity and cost are greatly reduced.

Description

Technical Field

[0001] This invention relates to the field of boiler energy conservation and environmental protection technology, specifically to a deep waste heat recovery and anti-corrosion and anti-clogging system for boilers based on a heat pipe-heat pump composite. Background Technology

[0002] Flue gas heat loss is one of the most significant heat losses in boiler operation, accounting for over 60% of the total heat loss. Effectively reducing flue gas temperature is crucial for improving boiler thermal efficiency and achieving energy conservation and emission reduction. Traditional economizers or ordinary metal heat exchangers can typically reduce flue gas temperature to 120℃ to 150℃, but further significant temperature reduction faces three insurmountable technical bottlenecks:

[0003] Low-temperature corrosion problem: When the wall temperature of the heat exchange surface is lower than the acid dew point of the flue gas, especially the sulfuric acid dew point, which is usually between 90°C and 150°C, water vapor and acidic gases such as SO3 in the flue gas condense into corrosive liquids such as sulfuric acid and sulfurous acid, causing severe electrochemical corrosion to metal heat exchangers such as carbon steel, and rapidly shortening the service life of the equipment.

[0004] Ash accumulation and blockage issues: In low-temperature zones, ash in the flue gas adheres more easily to the heat exchange surface. If condensate is also present, the ash and acid mix to form a hard, cement-like scale, severely clogging the flue, increasing system resistance, increasing fan energy consumption, and making cleaning and maintenance extremely difficult.

[0005] Energy grade and economic issues: The lower the flue gas temperature, the lower the grade (quality) of the waste heat. Conventional heat exchange methods require a huge heat exchange area due to the small heat transfer temperature difference, leading to a surge in initial equipment investment and poor economic efficiency.

[0006] In existing technologies, there are solutions that use heat pipe heat exchangers or heat pumps alone. Although heat pipe heat exchangers can transfer heat efficiently and effectively isolate hot and cold fluids, they still cannot avoid metal corrosion problems in their low-temperature range. Although using a heat pump alone can achieve deep cooling, having an expensive and precision heat pump evaporator directly handle highly polluting and corrosive flue gas poses a very high risk of blockage, corrosion and damage. The system is complex and the return on investment is uncertain.

[0007] Therefore, there is an urgent need in this field for an integrated system that can safely, efficiently, and reliably achieve deep waste heat recovery from flue gas, and can fundamentally solve low-temperature corrosion and ash blockage from the perspectives of structural design and materials science. Summary of the Invention

[0008] To overcome the shortcomings of existing technologies, the present invention aims to provide a boiler deep waste heat recovery and anti-corrosion and anti-clogging system based on heat pipe-heat pump composite, which reduces the boiler flue gas temperature to below the acid dew point, down to 25-40℃, close to the ambient temperature, maximizing the recovery of sensible heat and a large amount of latent heat of vaporization in the flue gas; secondly, through graded treatment and material innovation, it completely solves the problems of low-temperature corrosion and ash accumulation and blockage in the process, ensuring that the system can operate stably and efficiently for a long time.

[0009] To achieve the above objectives, this invention provides a boiler deep waste heat recovery and anti-corrosion / anti-clogging system based on a heat pipe-heat pump composite, comprising a high-temperature stage heat pipe heat exchange section and a deep cooling stage heat pump evaporation section arranged sequentially along the flue gas flow direction.

[0010] The high-temperature heat pipe heat exchange section is used to cool the flue gas to above the acid dew point temperature.

[0011] The deep cooling stage heat pump evaporation section uses a heat exchange tube bundle made of fluoroplastics to deeply cool the flue gas to below the acid dew point and up to near the ambient temperature.

[0012] The system also includes a dust removal and corrosion prevention system, which includes a high-frequency acoustic soot blower for cleaning the fluoroplastic heat exchanger tube bundle and a liquid collection and neutralization device for collecting and treating acidic condensate.

[0013] The aforementioned high-temperature flue gas first enters the high-temperature stage heat pipe heat exchange section, where it exchanges heat with boiler feedwater / makeup water, lowering its temperature to above the acid dew point. Subsequently, the flue gas enters the deep cooling stage heat pump evaporation section, where it undergoes deep heat exchange with the low-temperature heat pump working fluid within the fluoroplastic tube bundle, further reducing its temperature to near ambient temperature. The condensed acid produced during this process flows into the bottom collection and neutralization device. The heat pump working fluid, having absorbed the waste heat from the flue gas, becomes low-temperature, low-pressure steam. After being compressed by the compressor, it becomes high-temperature, high-pressure steam, which enters the condenser for condensation and heat release, transferring the heat to end users such as heating water. The refrigerant, after releasing heat, is depressurized and cooled by a throttling valve before returning to the evaporator to complete the cycle. The intelligent control system monitors the entire process and controls the periodic operation of the acoustic soot blower and spray system.

[0014] As a further improvement to this technical solution, the dust removal and corrosion prevention system also includes an online spraying device for the fluoroplastic heat exchanger tube bundle.

[0015] As a further improvement to this technical solution, the fluoroplastic is polytetrafluoroethylene or perfluoroalkoxy resin.

[0016] As a further improvement to this technical solution, the fluoroplastic heat exchange tube bundle adopts smooth tubes with a smooth outer surface and is arranged in a sequential, large-spacing manner, with the tube spacing not less than twice the outer diameter of the tube.

[0017] As a further improvement to this technical solution, the high-temperature heat pipe heat exchange section adopts a carbon steel gravity heat pipe, with its evaporation section placed in the flue and its condensation section placed in the boiler feedwater or makeup water pipeline.

[0018] As a further improvement to this technical solution, a heat pump circulation loop is also included. This loop is composed of the deep cooling stage heat pump evaporator section, compressor, condenser and throttling valve connected by pipelines. The condenser is used to heat boiler feedwater, heating water or process water.

[0019] As a further improvement to this technical solution, an intelligent control system is also included, which is used to monitor the exhaust gas temperature and composition in real time, and has a built-in dew point temperature calculation model. Based on the monitoring results, the system automatically adjusts the operating power of the heat pump system and controls the start and stop of the acoustic soot blower and spray device.

[0020] As a further improvement to this technical solution, the intelligent control system is configured to ensure that the flue gas temperature at the outlet of the high-temperature stage heat pipe heat exchange section is always higher than the acid dew point temperature calculated based on the real-time flue gas composition by adjusting the heat pump evaporation temperature.

[0021] As a further improvement to this technical solution, the acid dew point of flue gas is calculated in real time by an intelligent control system, and the operating conditions of the heat pump system are controlled in reverse based on this.

[0022] As a further improvement to this technical solution, the method for deep recovery of waste heat from boiler flue gas and for corrosion and clogging prevention of this invention includes the following steps:

[0023] S1. The high-temperature flue gas first passes through the high-temperature heat pipe heat exchange section to recover the high-temperature sensible heat and use the heat directly to heat the boiler feedwater, while cooling the flue gas to above the acid dew point.

[0024] S2. The cooled flue gas is then passed through the deep cooling stage heat pump evaporation section composed of fluoroplastic heat exchange tube bundles for deep cooling to release latent heat and a large amount of sensible heat.

[0025] S3. The low-grade heat absorbed by the evaporation section is upgraded by a heat pump system and then used for external heating.

[0026] S4. High-frequency sonic blowing and regular online spraying are used to prevent blockage of the fluoroplastic evaporation section, and the generated acidic condensate is treated by the liquid collection and neutralization system.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] 1. This boiler deep waste heat recovery and anti-corrosion and anti-clogging system based on heat pipe-heat pump composite uses conventional metal materials in the high-temperature section but operates in a safe zone; in the low-temperature section, it revolutionarily adopts "plastic instead of steel", utilizing the inherent extreme acid corrosion resistance of fluoroplastics, enabling the system to work safely in a strong acid condensation environment for a long time; combined with the quadruple anti-clogging design of fluoroplastic tubes that do not adhere, large spacing that does not bridge, high-frequency soot blowing and online spray flushing, it ensures long-term cleanliness of the heat exchange surface, maintains high-efficiency heat exchange performance, and greatly reduces maintenance intensity and cost.

[0029] 2. This boiler deep waste heat recovery and anti-corrosion and anti-clogging system based on heat pipe-heat pump composite technology realizes energy recovery by coupling heat pipe and heat pump technologies. The heat pipe efficiently recovers medium and high temperature sensible heat, while the heat pump focuses on tapping deep latent heat and low temperature sensible heat. Finally, the flue gas temperature can approach the ambient temperature, thus improving the waste heat recovery rate and boiler thermal efficiency. Attached Figure Description

[0030] The accompanying drawings described herein are for illustrative purposes only and are not intended to limit the scope of the invention in any way. Furthermore, the shapes and proportions of the components in the drawings are merely illustrative to aid in understanding the invention and do not specifically limit the shapes and proportions of the components. Those skilled in the art, guided by the teachings of this invention, will select various possible shapes and proportions to implement the invention according to specific circumstances.

[0031] Figure 1 This is a flowchart illustrating the overall process flow of the system of the present invention.

[0032] Figure 2 This is a flow chart of the heat pump cycle of the present invention; Detailed Implementation

[0033] The details of the present invention can be more clearly understood by referring to the accompanying drawings and the description of specific embodiments. However, the specific embodiments of the present invention described herein are for illustrative purposes only and should not be construed as limiting the invention in any way. Under the teachings of this invention, those skilled in the art will conceive of any possible variations of the invention, all of which should be considered within the scope of the invention. The terms "installation" and "connection" should be interpreted broadly, referring to direct connection as well as indirect connection through an intermediate medium.

[0034] The terms "central axis," "vertical," "horizontal," "front," "rear," "upper," "lower," "left," "right," "top," "bottom," "inner," and "outer" used herein to indicate orientation or positional relationships are based on the orientation or positional relationships shown in the accompanying drawings and are used only for the convenience of describing the invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, in the description of the invention, "a number" means two or more, unless otherwise explicitly specified.

[0035] Please see Figures 1-2 As shown, the present invention provides a boiler deep waste heat recovery and anti-corrosion and anti-clogging system based on heat pipe-heat pump composite, including a high-temperature stage heat pipe heat exchange section and a deep cooling stage heat pump evaporation section arranged sequentially along the flue gas flow direction. The high-temperature stage heat pipe heat exchange section is used to cool the flue gas to above the acid dew point temperature; the deep cooling stage heat pump evaporation section adopts a heat exchange tube bundle made of fluoroplastics to deeply cool the flue gas to below the acid dew point until close to the ambient temperature.

[0036] The high-temperature heat pipe heat exchange section is located at the front end of the flue, using gravity heat pipes made of metal such as carbon steel. Its evaporation section is placed inside the flue to absorb heat from the flue gas, while the condensation section is placed inside the boiler feedwater or makeup water pipe. This section is responsible for safely cooling the high-temperature flue gas (above 140°C) to a safe temperature above the acid dew point, such as 90-100°C, efficiently recovering high-grade sensible heat. Simultaneously, because its wall temperature is always above the dew point, acid corrosion is completely avoided.

[0037] Fluoroplastics are made of polytetrafluoroethylene (PTFE) or perfluoroalkoxy resins. The deep-cooling stage evaporator section of the heat pump is located at the rear end of the flue, serving as the evaporator for the heat pump system. It utilizes heat exchange tube bundles made of corrosion-resistant, flexible extruded fluoroplastics such as PTFE and PFA. This section is responsible for further cooling the flue gas from the upstream section from a safe temperature to a target low temperature, such as 25-40°C. Fluoroplastics possess excellent hydrophobicity, anti-sticking properties, and resistance to strong acid corrosion, fundamentally preventing low-temperature corrosion and significantly reducing ash adhesion.

[0038] Specifically, the system also includes a dust removal and corrosion prevention system, which includes a high-frequency acoustic soot blower for cleaning the fluoroplastic heat exchanger tube bundles and a liquid collection and neutralization device for collecting and treating acidic condensate. The dust removal and corrosion prevention system also includes an online spray system specifically designed for the fluoroplastic heat exchanger tube bundles.

[0039] The fluoroplastic heat exchanger tube bundles are made of smooth, bare tubes arranged in a wide-spaced configuration, with the tube spacing not less than twice the outer diameter of the tubes, to physically prevent ash bridging. In addition, a high-frequency acoustic sootblower and an online spray system are installed. The acoustic sootblower operates periodically, using vibration waves to dislodge loose ash; the spray system can be activated during furnace shutdown or low load to thoroughly rinse the tube bundles with water.

[0040] Furthermore, the drainage design includes a collection tank and a neutralization discharge device at the bottom of the deep cooling stage flue to collect the acidic liquid generated by condensation, neutralize it, and then discharge it into the wastewater system to avoid secondary pollution.

[0041] In addition, it includes a heat pump circulation loop, which consists of a deep cooling stage heat pump evaporator, compressor, condenser, and expansion valve connected by pipelines. The condenser is used to heat boiler feedwater, heating water, or process water. The evaporator absorbs low-grade waste heat from the flue gas and transfers it to the heat pump working fluid. After the working fluid is upgraded by the compressor consuming electricity, it releases high-grade heat energy in the condenser, which is used to heat boiler feedwater, heating water, or process water, greatly improving the value and flexibility of waste heat utilization.

[0042] In addition, it includes an intelligent control system for real-time monitoring of flue gas temperature and composition, and a built-in dew point temperature calculation model. Based on the monitoring results, it automatically adjusts the operating power of the heat pump system and controls the start and stop of the acoustic soot blower and spray device. The intelligent control system is configured to ensure that the flue gas temperature at the outlet of the high-temperature stage heat pipe heat exchange section is always higher than the acid dew point temperature calculated based on the real-time flue gas composition by a safety margin by adjusting the heat pump evaporation temperature. The intelligent control system calculates the flue gas acid dew point in real time and uses this as a basis to control the operating conditions of the heat pump system.

[0043] Example:

[0044] Taking a gas-fired steam boiler with a rated evaporation capacity of 10t / h as an example, its original flue gas temperature is 140℃.

[0045] System installation: Install this system sequentially in the flue at the tail end of the boiler.

[0046] Operation process: Flue gas at 140℃ first enters the high-temperature carbon steel heat pipe section and is cooled to 95℃, above its sulfuric acid dew point. The recovered heat is directly used to heat the boiler softened water from 20℃ to 70℃.

[0047] The 95°C flue gas then enters a deep cooling stage composed of PTFE tube bundles. Here, it is deeply cooled to 30°C by the heat pump working fluid, releasing a large amount of latent heat and sensible heat.

[0048] The heat pump refrigerant, such as R134a, absorbs heat and evaporates, then is compressed to 80°C by the compressor and enters the condenser to heat the heating circulating water from 40°C to 60°C for user use.

[0049] The condensed acid produced by flue gas cooling is collected, neutralized, and then discharged.

[0050] The high-frequency soot blower operates once every 4 hours for 2 minutes each time; the online spray system automatically rinses for 10 minutes every weekend morning.

[0051] Results: This system stabilized the flue gas temperature at 30°C, reducing it from 140°C to 30°C, increasing boiler thermal efficiency by approximately 12%, and saving over 60,000 cubic meters of natural gas annually. After one heating season of continuous operation, a shutdown inspection revealed that the fluoroplastic evaporator tubes were as clean as new, showing no signs of corrosion, minimal ash accumulation, and no significant change in flue gas resistance. Through these methods, this invention successfully achieves deep, safe, efficient, and reliable recovery of waste heat from boiler flue gas.

[0052] The method for deep recovery of waste heat from boiler flue gas and for corrosion and clogging prevention of the present invention includes the following steps:

[0053] S1. The high-temperature flue gas first passes through the high-temperature heat pipe heat exchange section to recover the high-temperature sensible heat and use the heat directly to heat the boiler feedwater, while cooling the flue gas to above the acid dew point.

[0054] S2. The cooled flue gas is then passed through the deep cooling stage heat pump evaporation section composed of fluoroplastic heat exchange tube bundles for deep cooling to release latent heat and a large amount of sensible heat.

[0055] S3. The low-grade heat absorbed by the evaporation section is upgraded by a heat pump system and then used for external heating.

[0056] S4. High-frequency sonic blowing and regular online spraying are used to prevent blockage of the fluoroplastic evaporation section, and the generated acidic condensate is treated by the liquid collection and neutralization system.

[0057] The three core processes of this invention are:

[0058] Flue gas path: This shows the stepped cooling process of the flue gas temperature from high to low, and the corresponding heat exchange equipment. This is the main flow of the system.

[0059] Heat pump cycle path: This demonstrates the circulation of the heat pump working fluid from liquid to gas and back to liquid, as well as the energy enhancement process from low-grade heat to high-grade heat. This is the core technical principle of the system.

[0060] Heat utilization path: This shows the final destination of the recovered heat. Part of it is used to directly heat the boiler feedwater through heat pipes, and the other part is used to heat the heating water through a heat pump, demonstrating the efficient use of energy.

[0061] The auxiliary systems (intelligent control, dust removal, and liquid drainage) are presented in a modular form, indicating that they provide support and assurance for the entire main process.

[0062] It should be noted that the fixed connections and fixing methods of the present invention are achieved using conventional fixing means such as bolt connections or welding. The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly, and should not be used to limit the scope of protection of the present invention. All equivalent changes or modifications made according to the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A boiler deep waste heat recovery and anti-corrosion / anti-clogging system based on heat pipe-heat pump composite, comprising a high-temperature stage heat pipe heat exchange section and a deep cooling stage heat pump evaporation section arranged sequentially along the flue gas flow direction, characterized in that: The high-temperature heat pipe heat exchange section is used to cool the flue gas to above the acid dew point temperature. The deep cooling stage heat pump evaporation section uses a heat exchange tube bundle made of fluoroplastics to deeply cool the flue gas to below the acid dew point and up to near the ambient temperature. The system also includes a dust removal and corrosion prevention system, which includes a high-frequency acoustic soot blower for cleaning the fluoroplastic heat exchanger tube bundle and a liquid collection and neutralization device for collecting and treating acidic condensate.

2. The boiler deep waste heat recovery and anti-corrosion / anti-clogging system based on heat pipe-heat pump composite as described in claim 1, characterized in that: The dust removal and corrosion prevention system also includes an online spraying device for the fluoroplastic heat exchanger tube bundle.

3. The boiler deep waste heat recovery and anti-corrosion / anti-clogging system based on heat pipe-heat pump composite as described in claim 2, characterized in that: The fluoroplastic is polytetrafluoroethylene or perfluoroalkoxy resin.

4. The boiler deep waste heat recovery and anti-corrosion / anti-clogging system based on heat pipe-heat pump composite as described in claim 3, characterized in that: The fluoroplastic heat exchange tube bundle uses smooth tubes with a flat outer surface and is arranged in a straight line with a large spacing, with the tube spacing not less than twice the outer diameter of the tube.

5. The boiler deep waste heat recovery and anti-corrosion / anti-clogging system based on heat pipe-heat pump composite as described in claim 4, characterized in that: The high-temperature heat pipe heat exchange section uses a carbon steel gravity heat pipe, with its evaporation section placed in the flue and its condensation section placed in the boiler feedwater or makeup water pipeline.

6. The boiler deep waste heat recovery and anti-corrosion / anti-clogging system based on heat pipe-heat pump composite as described in claim 5, characterized in that: It also includes a heat pump circulation loop, which is composed of the deep cooling stage heat pump evaporator section, compressor, condenser and throttling valve connected by pipelines. The condenser is used to heat boiler feedwater, heating water or process water.

7. The boiler deep waste heat recovery and anti-corrosion / anti-clogging system based on heat pipe-heat pump composite as described in claim 6, characterized in that: It also includes an intelligent control system for real-time monitoring of exhaust gas temperature and composition, and has a built-in dew point temperature calculation model to automatically adjust the operating power of the heat pump system and control the start and stop of the sonic soot blower and spray device based on the monitoring results.

8. The boiler deep waste heat recovery and anti-corrosion / anti-clogging system based on heat pipe-heat pump composite as described in claim 7, characterized in that: The intelligent control system is configured to ensure that the flue gas temperature at the outlet of the high-temperature stage heat pipe heat exchange section is always higher than the acid dew point temperature calculated based on the real-time flue gas composition by adjusting the heat pump evaporation temperature.

9. The boiler deep waste heat recovery and anti-corrosion / anti-clogging system based on heat pipe-heat pump composite as described in claim 8, characterized in that: The intelligent control system calculates the acid dew point of the flue gas in real time and uses this as a basis to control the operating conditions of the heat pump system.

10. The boiler deep waste heat recovery and anti-corrosion / anti-clogging system based on heat pipe-heat pump composite as described in claim 9, characterized in that: The method for deep recovery of waste heat from boiler flue gas and for corrosion and clogging prevention of the present invention includes the following steps: S1. The high-temperature flue gas first passes through the high-temperature heat pipe heat exchange section to recover the high-temperature sensible heat and use the heat directly to heat the boiler feedwater, while cooling the flue gas to above the acid dew point. S2. The cooled flue gas is then passed through the deep cooling stage heat pump evaporation section composed of fluoroplastic heat exchange tube bundles for deep cooling to release latent heat and a large amount of sensible heat. S3. The low-grade heat absorbed by the evaporation section is upgraded by a heat pump system and then used for external heating. S4. High-frequency sonic blowing and regular online spraying are used to prevent blockage of the fluoroplastic evaporation section, and the generated acidic condensate is treated by the liquid collection and neutralization system.

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