Heat pump system based on natural gas flue gas waste heat recovery and white smoke purification

Abstract

The invention discloses a heat pump system based on natural gas flue gas waste heat recovery and white smoke purification, and relates to the technical field of heat pumps. Aiming at the characteristics of high water vapor content and high latent heat value in flue gas after natural gas combustion, a heat pump circulation principle is utilized, a deep cooling environment is constructed through a gradient refrigerant dehumidifying tower serving as an evaporation end to forcibly condense water, and double efficient recovery of sensible heat and a huge amount of latent heat in the flue gas is realized. The temperature of the flue gas is reduced to be far lower than the dew point of the flue gas by utilizing a deep cooling environment constructed by the gradient refrigerant dehumidifying tower, so that water vapor is separated, and low-temperature condensation latent heat which is generally difficult to recover is released. The energy is effectively captured by the heat pump system and upgraded, and the recovery rate and the economic benefit of the system on the low-grade waste heat of the natural gas are improved. According to the invention, a set of self-cleaning circulation system without external heat source input is constructed, the operation cost is reduced, the process flow is simplified, and the equipment layout is optimized.

Description

Technical Field

[0001] This invention relates to the field of heat pump technology, and specifically to a heat pump system based on natural gas flue gas waste heat recovery and white smoke purification. Background Technology

[0002] Natural gas, as a clean energy source, is widely used in heating and industrial production. Its main component, methane, has a high hydrogen content, and its combustion produces hot, humid flue gas containing a very high proportion of water vapor. Existing conventional heat pump systems struggle to directly utilize natural gas flue gas with its high water content as a low-grade heat source, leading to problems such as evaporator corrosion and low heat exchange efficiency. However, heat pump systems utilizing natural gas as a low-grade heat source can improve natural gas utilization and are a growing industry trend. The core challenge lies in the fact that natural gas flue gas contains not only sensible heat but also a huge amount of latent heat of vaporization carried by a large amount of water vapor. Furthermore, because the exhaust temperature of natural gas boilers is relatively low, direct emission not only results in significant energy waste but also causes rapid condensation in cold environments, forming visible "white smoke" and causing visual pollution.

[0003] Faced with this challenge, the industry's commonly adopted solution is usually a step-by-step approach. For waste heat recovery, conventional economizers can only recover a portion of the high-temperature sensible heat, making it difficult to effectively recover the low-temperature latent heat. For eliminating white smoke, mainstream technologies often rely on external energy sources such as steam turbine extraction or electric heating to reheat the flue gas. These methods, due to their inability to match the low-temperature, high-humidity characteristics of natural gas flue gas, result in high energy consumption and system complexity. In particular, existing technologies are often mistakenly considered to require reliance on power plant turbine systems, limiting their application in independent heating stations or distributed natural gas energy stations.

[0004] The drawbacks of traditional methods are obvious. Waste heat recovery is inefficient; because the flue gas is not cooled below the water vapor dew point, a huge amount of latent heat of condensation is directly wasted. Secondly, eliminating white smoke is costly, relying on external heat sources to reheat the flue gas, which not only consumes a large amount of valuable energy and increases the company's operating costs but also generates additional carbon emissions, contradicting the principles of energy conservation and emission reduction. The combination of multiple independent treatment units results in a large footprint, complex processes, and high investment and maintenance costs for the entire flue gas treatment system, leading to unsatisfactory overall energy efficiency and economic performance. Summary of the Invention

[0005] The purpose of this invention is to provide a heat pump system based on natural gas flue gas waste heat recovery and white smoke purification to solve the problems existing in the background art.

[0006] To solve the above technical problems, the present invention adopts the following technical solution: The present invention provides a heat pump system based on natural gas flue gas waste heat recovery and white smoke purification, comprising: a gas pre-generation module, used to obtain raw hot and humid natural gas flue gas and low-pressure liquid refrigerant, supply the low-pressure liquid refrigerant to a gradient refrigerant dehumidification tower serving as the evaporation end of the heat pump, and cause the raw hot and humid natural gas flue gas to flow counter-currently through the gradient refrigerant dehumidification tower to generate dry and cold flue gas flow and low-pressure gaseous refrigerant.

[0007] The flue gas and gaseous refrigerant extraction module is used to extract dry and cold flue gas flow and simultaneously collect low-pressure gaseous refrigerant to generate a low-pressure gaseous refrigerant flow that carries the low-temperature heat recovered from the flue gas.

[0008] The refrigerant compression and quality enhancement module is used to compress a low-pressure gaseous refrigerant stream to generate high-grade, high-temperature, and high-pressure refrigerant vapor.

[0009] The superheated steam preheating module is used to introduce high-grade, high-temperature, and high-pressure refrigerant vapor into the heat transfer zone of the heat collection carrier, where it preheats with the original hot and humid natural gas flue gas entering the system to generate cooled saturated refrigerant vapor.

[0010] The main condenser waste heat recovery module is used to transport the cooled saturated refrigerant vapor to the main condenser zone of the heat collection heat carrier, release the latent heat of condensation to the external circulating water to recover the medium-grade waste heat, and generate standby high-pressure liquid refrigerant.

[0011] The flue gas self-reheating whitening module is used to guide the standby high-pressure liquid refrigerant through the self-whitening drive zone of the heat collection heat carrier, and use its remaining sensible heat to reheat the dry and cold flue gas flow, generating a clean exhaust gas flow with qualified temperature rise and the cooled high-pressure liquid refrigerant.

[0012] The emission and refrigerant throttling circulation module is used to discharge clean exhaust gas with qualified temperature rise, and simultaneously throttle and reduce the pressure of the cooled high-pressure liquid refrigerant to generate low-pressure liquid refrigerant for the gas pre-generation module, thus completing the internal closed-loop self-circulation of system energy.

[0013] The beneficial effects of this invention are as follows: Addressing the characteristic of natural gas combustion producing a large amount of water vapor, this invention achieves efficient dual recovery of both sensible and latent heat from flue gas through deep cooling and forced condensation of water. The deep cooling environment constructed using a gradient refrigerant dehumidification tower ensures that the flue gas temperature is far below its dew point, thereby physically separating the large amount of water vapor it contains and releasing the latent heat of condensation. This low-temperature energy, which is difficult to utilize using traditional methods, is effectively captured and upgraded by the heat pump system, significantly improving the overall energy recovery rate and economic benefits of the system.

[0014] This invention constructs a self-extinguishing flue gas system without relying on external steam networks or turbine extraction, significantly reducing operating costs and carbon emissions. The system cleverly utilizes the residual sensible heat carried by the high-pressure liquid refrigerant in the heat pump cycle to precisely reheat the dehydrated, dry flue gas. The heat for the entire extinguishing process comes from the system's internal cascade utilization, eliminating dependence on external steam, hot water, or electric heating and conserving resources.

[0015] This invention highly integrates flue gas purification and energy recovery processes into a closed-loop self-circulating system, simplifying the process flow and optimizing equipment layout. By integrating multiple functional links such as deep dehumidification, gas collection, compression and quality enhancement, waste heat recovery, and flue gas reheating around the heat pump cycle, a compact system with coupled functions and self-sufficiency in energy is formed. Compared with traditional decentralized treatment solutions, this effectively reduces equipment footprint, lowers initial investment, and improves system stability and automation. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the system structure connection of the present invention.

[0018] Figure 2 This is a schematic diagram of the gas pre-generation module of the present invention. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Reference Figure 1 As shown, the present invention provides a heat pump system based on natural gas flue gas waste heat recovery and white smoke purification, comprising: a gas pre-generation module for obtaining raw hot and humid natural gas flue gas and low-pressure liquid refrigerant, supplying the low-pressure liquid refrigerant to a gradient refrigerant dehumidification tower serving as the evaporation end of the heat pump, and causing the raw hot and humid natural gas flue gas to flow counter-currently through the gradient refrigerant dehumidification tower to generate dry and cold flue gas flow and low-pressure gaseous refrigerant.

[0021] In a specific embodiment of the present invention, the gas pre-generation module specifically includes: inputting a low-pressure gaseous refrigerant stream as the sole working medium into the compressor's suction port.

[0022] The compressor is started to mechanically compress the low-pressure gaseous refrigerant flow, converting the mechanical work input by the compressor into heat energy and adding it to the internal energy of the low-pressure gaseous refrigerant flow, generating high-grade, high-temperature, and high-pressure refrigerant vapor at the compressor discharge port.

[0023] Reference Figure 2 As shown, specifically, this invention first obtains the natural gas combustion exhaust gas to be treated, i.e., the raw hot and humid flue gas, and then uses a gradient refrigerant dehumidification tower to deeply remove the moisture, ultimately obtaining a dry and cooled flue gas stream. The entire process begins with starting the supply system, which uses an induced draft fan to force the raw hot and humid flue gas generated by the natural gas boiler into the gradient refrigerant dehumidification tower from the inlet located at the bottom or middle. Simultaneously with the entry of the raw hot and humid flue gas, a refrigerant circulation system delivers low-temperature, low-pressure liquid refrigerant to the refrigerant inlet at the top of the gradient refrigerant dehumidification tower, and distributes it evenly to the top of the vertically arranged built-in tube bundles inside the tower via a spray or distribution device. Under the influence of gravity, the low-pressure liquid refrigerant flows downwards along the outer wall of the built-in tube bundles, simultaneously absorbing heat and beginning to evaporate. Because the temperature of the initially hot and humid flue gas, forced to flow upwards, decreases from bottom to top, the refrigerant flowing along the tube bundle absorbs a large amount of heat and evaporates rapidly in the lower part of the tower, while absorbing less heat and evaporating more slowly but at extremely low temperatures in the upper part. This creates a continuously varying temperature gradient field inside the tower, with the upper part being extremely cold and the lower part being moderately cold. The initially hot and humid flue gas, forced to move upwards, first comes into contact with the relatively warmer lower tube bundle, where some water vapor condenses into water droplets and is collected. As the flue gas continues to rise, its temperature continues to decrease, and when it comes into contact with the even cooler upper tube bundle, the remaining water vapor in the flue gas is further forced to condense deeply. All the condensed water flows down the tube wall or collection tray and is collected and removed from the drain outlet at the bottom of the tower. After such a complete process of gradual cooling and forced dehydration in layers, most of the moisture in the original hot and humid flue gas is physically separated, forming a dry and cold flue gas flow with significantly reduced temperature and extremely low humidity at the gas outlet at the top of the tower, which prepares for subsequent reheating and whitening.

[0024] This invention highly integrates flue gas purification and energy recovery processes into a closed-loop self-circulating system, simplifying the process flow and optimizing equipment layout. By integrating multiple functional links such as deep dehumidification, gas collection, compression and quality enhancement, waste heat recovery, and flue gas reheating around the heat pump cycle, a compact system with coupled functions and self-sufficiency in energy is formed. Compared with traditional decentralized treatment solutions, this effectively reduces equipment footprint, lowers initial investment, and improves system stability and automation.

[0025] Raw hot and humid flue gas refers to the untreated high-temperature and high-humidity waste gas directly generated during the natural gas combustion process. Its data structure includes physical parameters such as temperature and humidity. Due to the high cleanliness of natural gas and the absence of ash accumulation risk, it is more suitable for deep condensation waste heat recovery. Its temperature is typically set between 50 and 120 degrees Celsius, and the relative humidity is set at the high humidity level generated during combustion. These settings are based on actual measurements of the outlet parameters of typical gas-fired boilers. The gradient refrigerant dehumidification tower is a specially designed heat exchange device. Its function is to establish a stable temperature gradient field from extremely low to moderately cold within the tower. Its structural feature is the integration of multiple sets of vertically or spirally arranged internal tube bundles. Dry and cold flue gas flow is the product generated after the raw hot and humid flue gas has been treated by the gradient refrigerant dehumidification tower. Its characteristic properties are extremely low moisture content and low temperature. Data shows that its absolute moisture content is controlled below 5 grams per cubic meter, and the temperature drops to 20 to 30 degrees Celsius. This setting standard is based on the engineering requirement to ensure that the subsequent reheating step can economically and effectively eliminate the visual white smoke phenomenon. The supply system is a conveying device consisting of an induced draft fan, pipelines, and control valves. Its function is to provide a stable flow rate of raw hot and humid flue gas for the entire processing flow. Low-pressure liquid refrigerant is the working medium in the heat pump cycle system after throttling and pressure reduction. Here, it specifically refers to environmentally friendly refrigerants such as R134a or R410A, characterized by low temperature and low pressure liquid properties. Its pressure is set according to the type of refrigerant. For example, when using R134a, the pressure entering the gradient refrigerant dehumidification tower is set to 0.1 MPa to 0.2 MPa to ensure evaporation within the target temperature range of 5°C to -10°C. The built-in tube bundle is a collection of metal pipes installed inside the gradient refrigerant dehumidification tower, typically made of corrosion-resistant and thermally conductive materials such as titanium alloys. Its function is to provide channels for refrigerant flow and serve as a heat exchange interface between the refrigerant and the flue gas. The temperature gradient field refers to the non-uniform temperature distribution formed along the height direction inside the gradient refrigerant dehumidification tower. Its characteristic property is that the temperature is lowest at the top of the tower and gradually increases downwards. The establishment of this temperature gradient field is the core basis for realizing the staged condensation of moisture in flue gas.

[0026] For example, to process a stream of raw hot and humid flue gas with a temperature of 120 degrees Celsius and an absolute moisture content of 100 grams per cubic meter, the supply system is first started, pumping this raw hot and humid flue gas into the lower part of a gradient refrigerant dehumidification tower at a flow rate of 5000 cubic meters per hour. Simultaneously, low-pressure liquid refrigerant R134a at a pressure of 0.15 MPa is injected from the top of the gradient refrigerant dehumidification tower, allowing it to flow downwards along the built-in tube bundle. Inside the tower, the refrigerant evaporates and absorbs heat, forming a stable temperature gradient field on the outer wall of the built-in tube bundle, ranging from -5 degrees Celsius at the top of the tower to 15 degrees Celsius at the bottom. The raw hot and humid flue gas flows counter-currently upwards, and as it flows through the lower region at 15 degrees Celsius and the upper region at -5 degrees Celsius, its water vapor is forcibly condensed and separated, ultimately generating a stream of dry and cold flue gas at a temperature of 25 degrees Celsius and an absolute moisture content of 4.5 grams per cubic meter at the top outlet of the tower.

[0027] This invention addresses the issue of large amounts of water vapor produced during natural gas combustion by employing deep cooling to force condensation of moisture, achieving efficient dual recovery of both sensible and latent heat from flue gas. The deep cooling environment created using a gradient refrigerant dehumidification tower ensures that the flue gas temperature is significantly lower than its dew point, thereby physically separating the large amount of water vapor and releasing its latent heat of condensation. This low-temperature energy, which is difficult to utilize using traditional methods, is effectively captured and upgraded by the heat pump system, significantly improving the overall energy recovery rate and economic benefits of the system.

[0028] The flue gas and gaseous refrigerant extraction module is used to extract dry and cold flue gas flow and simultaneously collect low-pressure gaseous refrigerant to generate a low-pressure gaseous refrigerant flow that carries the low-temperature heat recovered from the flue gas.

[0029] Specifically, this step follows immediately after the products generated in the previous stage. It extracts the dry, cold flue gas flow from the top of the gradient refrigerant dehumidification tower and simultaneously collects the low-pressure refrigerant that has vaporized due to heat absorption within the tower, ultimately integrating it into a low-pressure vapor stream carrying the residual heat of the flue gas. The process begins by activating an induced draft fan located in a pipe downstream of the outlet at the top of the gradient refrigerant dehumidification tower. This fan generates negative pressure, stably drawing the dry, cold flue gas flow accumulated at the top of the tower out through this outlet and delivering it to a designated flue gas duct to prepare for the subsequent reheat treatment stage. Simultaneously with the extraction of the dry, cold flue gas flow, the compressor in the heat pump system begins operation. The strong negative pressure generated at its suction port is connected through pipelines to the final outlet of the evaporation pipe inside the gradient refrigerant dehumidification tower. In the previous stage, the low-pressure liquid refrigerant, having absorbed the sensible heat of the original hot and humid flue gas and the latent heat of a large amount of moisture condensation, has completely transformed into a gaseous low-pressure refrigerant. The compressor's suction function efficiently extracts this low-pressure refrigerant from the end of the evaporator pipe. All the refrigerant extracted from the end of the built-in tube bundle is collected in a main pipe, thus forming a low-pressure refrigerant stream with a stable flow rate and state, carrying a large amount of heat energy recovered from the flue gas. This stream will serve as the sole working medium for the next compression and heating stage.

[0030] The induced draft device refers to a centrifugal or axial fan, whose function is to perform work on the gas through impeller rotation, generating a pressure difference to achieve forced gas flow. The designated pipeline is a dedicated channel for transporting dry, cold flue gas, typically made of corrosion-resistant metal or non-metal materials. The low-pressure refrigerant refers to the low-temperature, low-pressure gaseous state formed after the refrigerant completes evaporation and heat absorption in the gradient refrigerant dehumidification tower; its characteristic property is that it carries the latent heat recovered from the natural gas flue gas. It should be noted that this gas is entirely the internal working fluid of the heat pump system, not the exhaust gas from the external turbine; this gas flow will serve as the sole working medium for the next compression and quality enhancement stage.

[0031] For example, following the previous example, after a dry, cold flue gas flow at a temperature of 25 degrees Celsius is generated at the top of the gradient refrigerant dehumidification tower, a 15-kilowatt induced draft fan is activated to extract the gas from the top of the tower and send it into a designated pipe with a diameter of 0.8 meters. Simultaneously, the compressor in the heat pump circuit starts operating, creating a suction pressure of 0.18 MPa at its suction port. This negative pressure extracts all the low-pressure R134a refrigerant at a temperature of 12 degrees Celsius from the outlet ends of all the built-in tube bundles within the gradient refrigerant dehumidification tower, converging it into a stable low-pressure vapor flow. This vapor flow carries all the heat recovered from the original hot and humid flue gas and is ready to enter the compressor.

[0032] The refrigerant compression and quality enhancement module is used to compress a low-pressure gaseous refrigerant stream to generate high-grade, high-temperature, and high-pressure refrigerant vapor.

[0033] In a specific embodiment of the present invention, generating high-grade high-temperature and high-pressure refrigerant vapor includes: inputting low-pressure vapor flow as the sole working medium into the suction port of the compressor.

[0034] The compressor is started to mechanically compress the low-pressure vapor flow, converting the mechanical work input by the compressor into heat energy and adding it to the internal energy of the low-pressure vapor flow, generating high-grade, high-temperature, and high-pressure refrigerant vapor at the compressor exhaust port.

[0035] Specifically, the low-pressure vapor stream received from the previous stage is compressed, converting the recovered heat from the flue gas, along with the mechanical energy input during compression, into higher temperature and pressure heat energy—a process of pressurization and quality enhancement—to generate a high-temperature, high-pressure refrigerant vapor with a higher heat energy grade. The entire process begins by continuously guiding the low-pressure vapor stream, the sole working medium from the previous stage, to the suction port of a compressor. The compressor is then started, and through its internal mechanical structure, such as the meshing motion of a scroll plate or the rotational compression of a screw, it forcibly compresses the low-pressure vapor stream entering its cavity. During this mechanical compression, the work done by the external electrical energy driving the compressor is almost entirely converted and added to the internal energy of the refrigerant vapor, according to the laws of thermodynamics. This energy injection directly leads to increased molecular motion in the gas, macroscopically manifested as a rapid and simultaneous increase in both pressure and temperature. Finally, at the compressor's exhaust port, a completely new fluid, with its energy grade enhanced, can be stably obtained—high-grade, high-temperature, high-pressure refrigerant vapor. This vapor not only carries all the heat initially recovered from the original hot and humid flue gas but also contains additional heat converted from the compressor's work. Therefore, its temperature and pressure are much higher than before, enabling it to effectively exchange and transfer heat to the outside.

[0036] Compression work refers to the physical process of using mechanical equipment to consume external energy to compress a gaseous working fluid, thereby increasing its pressure and temperature. High-grade, high-temperature, high-pressure refrigerant vapor refers to a superheated vapor state reached by the refrigerant after it has undergone work in the compressor. Its characteristic attribute is that it simultaneously possesses high pressure and high temperature, allowing its contained thermal energy to drive a high-temperature heat exchange process, hence it is called high-grade energy. Taking R134a refrigerant as an example, its pressure is usually set between 1.0 MPa and 2.0 MPa, and its temperature is set between 80 degrees Celsius and 120 degrees Celsius. This setting is based on ensuring that its heat can be effectively used to produce domestic hot water or meet industrial heating needs. The compressor is the core component of a heat pump system. It is a fluid machine that converts input mechanical work into gas pressure energy. Its function is to provide power for the entire heat pump cycle and to raise the heat absorbed by the low-grade heat source to a high-grade level. Its type can be selected according to the processing capacity and pressure requirements, such as scroll, screw, or centrifugal.

[0037] For example, following the previous step, the incoming low-pressure R134a vapor stream, at a temperature of 12 degrees Celsius and a pressure of 0.18 MPa, is entirely fed into the suction port of a scroll compressor. The compressor is started to perform compression work, consuming 40 kilowatts of electrical power. After compression, at the compressor's discharge port, a high-grade, high-temperature, high-pressure refrigerant vapor with a pressure increased to 1.5 MPa and a temperature increased to 95 degrees Celsius is generated. This vapor carries sufficient high-quality heat energy to produce industrial hot water and is ready to enter the next stage for heat release.

[0038] The superheated steam preheating module is used to introduce high-grade, high-temperature, and high-pressure refrigerant vapor into the heat transfer zone of the heat collection carrier, where it preheats with the original hot and humid natural gas flue gas entering the system to generate cooled saturated refrigerant vapor.

[0039] In a specific embodiment of the present invention, while generating cooled saturated refrigerant vapor, the superheated heat released by the high-temperature and high-pressure refrigerant vapor is used to preheat the original hot and humid natural gas flue gas entering the heat transfer zone, generating preheated flue gas before entering the gradient refrigerant dehumidification tower.

[0040] Specifically, the high-grade, high-temperature, and high-pressure refrigerant vapor generated in the previous stage is adjusted and first guided into a specific area within a special device called a heat collection heat carrier—the heat transfer zone. This allows it to undergo a pre-heat exchange with the untreated raw hot and humid flue gas that has just entered the system. Through this heat exchange, the high-temperature, high-pressure refrigerant vapor releases some heat, achieving cooling, and ultimately transforms into cooled, saturated refrigerant vapor that remains at high pressure but has slightly decreased in temperature. The process begins by guiding all the high-temperature, high-pressure refrigerant vapor discharged from the compressor exhaust port in the previous stage through a piping system, allowing it to first flow into the heat transfer zone within the heat collection heat carrier. This heat transfer zone contains an independent heat exchange channel. Simultaneously, the raw hot and humid flue gas from outside, about to enter the gradient refrigerant dehumidification tower, is guided to flow through the heat exchange channel on the other side of the heat transfer zone before entering the main treatment process. High-temperature, high-pressure refrigerant vapor flows within its own channel, while the relatively cooler, raw hot and humid flue gas flows in an adjacent channel. The two exchange heat non-contactly through shared heat exchange walls. Due to the significant temperature difference, the superheated heat carried by the high-temperature, high-pressure refrigerant vapor is efficiently transferred to the raw hot and humid flue gas, thus preheating or pre-treating the flue gas. As the superheated heat is continuously released, the temperature of the refrigerant vapor decreases until it reaches or exactly equals its saturation temperature at its current pressure. After this cooling process, the refrigerant vapor changes from superheated vapor to saturated vapor, forming cooled saturated refrigerant vapor, ready to be transported to the next heat recovery area.

[0041] In this context, "allocation" refers to arranging and guiding the flow and application of high-temperature, high-pressure refrigerant vapor according to the system's operating logic. The heat collection heat exchanger is a composite heat exchange device integrating multiple heat exchange functions. Its interior is divided into functionally distinct zones, including a heat transfer zone, a main condensation zone, and a self-extinguishing zone. Its function is to uniformly manage and efficiently utilize the heat energy released by the refrigerant at different stages. The heat transfer zone is a sub-functional area within the heat collection heat exchanger, structured as an independent shell-and-tube or plate heat exchanger, specifically designed for pre-heat exchange between the high-temperature, high-pressure refrigerant vapor and the original hot, humid flue gas. Pre-heat exchange refers to a preliminary heat exchange performed before the main process occurs. Its purpose is to recover and utilize the superheated heat of the high-temperature refrigerant, while simultaneously pre-treating the materials entering the system to improve the overall system's energy efficiency. Cooled saturated refrigerant vapor refers to the state of high-temperature, high-pressure superheated refrigerant vapor after releasing its superheated portion of heat, when its temperature drops to the saturation point but before large-scale condensation occurs. Its characteristic property is that it is at the critical point of the gas-liquid two phases, carrying a large amount of latent heat of condensation waiting to be released, and its pressure is basically the same as when it enters this step.

[0042] For example, following the previous example, high-grade, high-temperature, high-pressure refrigerant vapor at a pressure of 1.5 MPa and a temperature of 95 degrees Celsius is entirely guided into the heat transfer zone inside the heat collection carrier. Simultaneously, a stream of raw hot and humid flue gas at a temperature of 120 degrees Celsius is also introduced into this heat transfer zone for pre-heat exchange with the refrigerant vapor. During the heat exchange process, the refrigerant vapor transfers its superheated heat to the flue gas, and its own temperature drops from 95 degrees Celsius to its saturation temperature at 1.5 MPa, i.e., 88 degrees Celsius. After this process is completed, at the outlet of the heat transfer zone, a cooled saturated refrigerant vapor, still at a pressure of 1.5 MPa and a temperature of 88 degrees Celsius, is generated, preparing for the subsequent release of the main condensation heat.

[0043] The main condensing waste heat recovery module is used to transport the cooled saturated refrigerant vapor to the main condensing zone of the heat collection heat carrier, release the latent heat of condensation to the external circulating water to recover the medium-grade waste heat, and generate standby high-pressure liquid refrigerant.

[0044] In a specific embodiment of the present invention, the generation of high-pressure liquid refrigerant for use includes: introducing cooled saturated refrigerant vapor into the main condensing zone, and simultaneously introducing external circulating water into the main condensing zone.

[0045] The cooled saturated refrigerant vapor exchanges heat with the external circulating water, and uses the released latent heat of condensation to heat the external circulating water, generating medium-grade hot water and standby high-pressure liquid refrigerant.

[0046] Specifically, the cooled saturated refrigerant vapor generated in the previous stage, ready to release a large amount of heat energy, is transported and utilized. It undergoes a phase change in the main condensing zone of the heat collection carrier, releasing its main energy, namely latent heat of condensation, to recover medium-grade waste heat for external use. Ultimately, a high-pressure liquid refrigerant is generated, ready for use. The process begins by guiding the cooled saturated refrigerant vapor flowing from the heat transfer zone in the previous stage through internal piping to the main condensing zone of the heat collection carrier, specifically designed for external heating. The main condensing zone is essentially a highly efficient heat exchanger, also equipped with two isolated fluid channels. The cooled saturated refrigerant vapor flows in one channel, while the external medium to be heated, such as external circulating water used for producing domestic hot water, flows in the other channel in a counter-current or cross-flow manner. Because the temperature of the saturated refrigerant vapor is higher than that of the external circulating water, heat is transferred from the refrigerant side to the water side. During this heat transfer process, the temperature of the refrigerant vapor remains essentially constant, but its state continuously changes from gaseous to liquid. This phase change process releases a massive amount of latent heat of condensation. This energy is the main output after being recovered from the original hot and humid flue gas and upgraded by the heat pump system. It raises the temperature of the external circulating water from ambient temperature to a set temperature suitable for bathing, heating, or industrial production, thus completing the external output and effective utilization of medium-grade waste heat. Once the refrigerant vapor completely condenses into liquid in the main condensing zone, it transforms into a ready-to-use high-pressure liquid refrigerant, which then flows out from the outlet of the main condensing zone, preparing for the next heat exchange step.

[0047] The main condensing zone is the functional area inside the heat exchanger used for the main heat output. Its structure is typically a high-efficiency plate heat exchanger or shell-and-tube heat exchanger, providing a site for large-scale latent heat exchange between saturated refrigerant vapor and the external heat-using medium. Latent heat of condensation refers to the heat released when a unit mass of a substance completely transforms from a gaseous state to a liquid state at constant temperature and pressure; it is the main form of energy recovered in this step. Medium-grade waste heat refers to thermal energy with a temperature in an intermediate range, typically between 60°C and 120°C. This grade of thermal energy has wide applications and is very suitable for hot water preparation or process heating. Standby high-pressure liquid refrigerant is the state formed after the saturated refrigerant vapor has released its latent heat of condensation and completely liquefied in the main condensing zone. Its characteristics are high pressure, medium temperature liquid, and it still carries some usable sensible heat. External circulating water is a water circulation loop independent of the heat pump system. Its function is to absorb the heat released from the main condensing zone and transport it to the user end.

[0048] For example, continuing from the previous step, cooled saturated refrigerant vapor at a pressure of 1.5 MPa and a temperature of 88 degrees Celsius is introduced into the main condensing zone of the heat collection carrier. Within this zone, it exchanges heat with external circulating water at an initial temperature of 20 degrees Celsius. The refrigerant vapor condenses at 88 degrees Celsius, releasing a large amount of latent heat of condensation, heating the external circulating water to 75 degrees Celsius for subsequent industrial insulation. During this process, the refrigerant vapor completely transforms into a liquid state, ultimately generating a fully liquefied, slightly subcooled, high-pressure liquid refrigerant at a pressure of approximately 1.48 MPa and a temperature of 86 degrees Celsius at the outlet of the main condensing zone.

[0049] The flue gas self-reheating whitening module is used to guide the standby high-pressure liquid refrigerant through the self-whitening drive zone of the heat collection heat carrier, and use its remaining sensible heat to reheat the dry and cold flue gas flow, generating a clean exhaust gas flow with qualified temperature rise and the cooled high-pressure liquid refrigerant.

[0050] In a specific embodiment of the present invention, the generation of clean exhaust gas with qualified temperature rise and cooled high-pressure liquid refrigerant specifically involves guiding the high-pressure liquid refrigerant to be used to the refrigerant channel of the self-whitening drive zone.

[0051] The extracted dry and cold flue gas is used as the sole object to be heated and introduced into the flue gas channel of the self-whitening drive zone.

[0052] The remaining sensible heat carried by the standby high-pressure liquid refrigerant is transferred to the dry and cold flue gas flow, generating a clean exhaust gas flow with a qualified temperature rise.

[0053] Specifically, the high-pressure liquid refrigerant generated in the previous stage, still carrying some residual heat, is guided to flow through the last functional area inside the heat collection carrier, namely the self-whitening drive zone. In this area, the remaining sensible heat of the high-pressure liquid refrigerant is used to precisely raise the temperature of the dry, cold flue gas stream previously extracted from the gradient refrigerant dehumidification tower and subjected to deep dehydration treatment—a reheat process—ultimately generating a clean emission gas stream with a temperature that meets environmental emission requirements and will not form visual white smoke. The process begins by guiding the high-pressure liquid refrigerant flowing from the main condensation zone in the previous stage through internal pipes to the self-whitening drive zone inside the heat collection carrier. The self-whitening drive zone is also an independent heat exchanger structure with two isolated flow channels. In one of these channels flows high-temperature, high-pressure liquid refrigerant. Simultaneously, the dry, cold flue gas stream previously extracted from the top of the gradient refrigerant dehumidification tower in the second step, which is the sole object of heating, is also guided to the other adjacent flow channel in the self-whitening drive zone. As these two fluids pass each other, heat is naturally transferred from the refrigerant side to the flue gas side because the temperature of the liquid refrigerant is significantly higher than that of the dry, cold flue gas. The high-pressure liquid refrigerant releases its sensible heat during this process, and its temperature continues to decrease while remaining liquid. The dry, cold flue gas, after absorbing this heat, experiences a significant temperature increase. This reheating process fully utilizes the waste heat within the heat pump cycle system, requiring no external energy consumption, thus achieving cascaded energy utilization and internal circulation. Finally, when the temperature of the dry, cold flue gas is raised to a preset safety threshold sufficiently high above its dew point temperature, it transforms into a clean emission gas with a qualified temperature rise, which can be directly discharged without forming a visible white plume in a low-temperature environment.

[0054] The self-whitening drive zone is a dedicated functional area within the heat collection heat exchanger for flue gas reheating. Its structure is a compact liquid-gas heat exchanger. Its function is to utilize the residual sensible heat of the high-pressure liquid refrigerant to heat the dehydrated, dry, and cold flue gas, eliminating the visual pollution of "white smoke" formed when the flue gas is released into the atmosphere. Residual sensible heat refers to the portion of the heat energy that the high-pressure liquid refrigerant retains after releasing its main latent heat, when its temperature is higher than the ambient temperature. This portion of heat energy is typically wasted in traditional refrigeration cycles. The dry, cold flue gas flow is introduced as the sole object to be heated, meaning that the heat source for this reheat process comes entirely from within the refrigerant cycle system, without the introduction of external heat sources such as steam or electric heating. This reheat process fully utilizes the recovered waste heat within the heat pump cycle system, eliminating the need for any external energy sources such as external grid steam or electric heating, perfectly matching the current situation where natural gas heating stations typically lack high-grade heat sources. Clean exhaust gas with acceptable temperature rise refers to gas that has been reheated to a sufficiently high temperature to ensure that, after mixing with cold ambient air, the mixing temperature remains above the dew point temperature of water vapor, thus preventing condensation and resulting in a visually clean and transparent airflow. The acceptable temperature standard is typically set at 15 to 25 degrees Celsius higher than the flue gas dew point temperature. This setting is based on extensive environmental engineering practice to ensure effective whitening reduction under varying atmospheric humidity and temperature conditions.

[0055] For example, continuing from the previous step, the standby high-pressure liquid refrigerant with a pressure of approximately 1.48 MPa and a temperature of 86 degrees Celsius is guided to the self-whitening drive zone of the heat collection heat carrier. Simultaneously, the dry, cold flue gas stream previously extracted from the gradient refrigerant dehumidification tower, with a temperature of 25 degrees Celsius and a dew point temperature of 5 degrees Celsius, is introduced into the flue gas passage side of this zone as the sole object to be heated. After heat exchange between the two fluids, the temperature of the standby high-pressure liquid refrigerant drops to 40 degrees Celsius. The dry, cold flue gas stream, after absorbing heat, is precisely reheated from 25 degrees Celsius to 45 degrees Celsius. Because 45 degrees Celsius is far higher than its dew point temperature of 5 degrees Celsius, the resulting exhaust gas stream is now clean and has met the required temperature rise, allowing for safe direct discharge.

[0056] This invention constructs a self-extinguishing flue gas system without relying on external steam networks or turbine extraction, significantly reducing operating costs and carbon emissions. The system cleverly utilizes the residual sensible heat carried by the high-pressure liquid refrigerant in the heat pump cycle to precisely reheat the dehydrated, dry flue gas. The heat for the entire extinguishing process comes from the system's internal cascade utilization, eliminating dependence on external steam, hot water, or electric heating and conserving resources.

[0057] The emission and refrigerant throttling circulation module is used to discharge clean exhaust gas with qualified temperature rise, and simultaneously throttle and reduce the pressure of the cooled high-pressure liquid refrigerant to generate low-pressure liquid refrigerant for the gas pre-generation module, thus completing the internal closed-loop self-circulation of system energy.

[0058] In a specific embodiment of the present invention, the generation of low-pressure liquid refrigerant for the gas pre-generation module specifically involves guiding the cooled high-pressure liquid refrigerant through a throttling device.

[0059] By utilizing the adiabatic expansion effect of the throttling device, the pressure and temperature of the high-pressure liquid refrigerant after cooling are reduced simultaneously, generating a low-temperature, low-pressure liquid refrigerant.

[0060] Specifically, as the final stage of the integrated approach, this stage is responsible for safely releasing the clean exhaust gas, which has passed the temperature rise test in the previous stage, into the atmosphere. Simultaneously, it performs final treatment on the refrigerant, which has completed its reheat mission and whose temperature has decreased, namely, throttling and depressurization, restoring it to its initial state—low-pressure liquid refrigerant—suitable for further flue gas cooling and dehumidification. This completely completes the closed-loop self-circulation of energy and working fluid within the system. The implementation process begins by releasing the clean exhaust gas, which has passed the temperature rise test at the outlet of the self-extinguishing white plume drive zone in the previous stage, directly into the surrounding atmosphere through the exhaust pipes and outlets at the end of the system. Because its temperature and humidity are precisely controlled, no visual white plume pollution is generated after emission. Simultaneously, on another flow path, the liquid refrigerant, which has released its remaining sensible heat in the self-extinguishing white plume drive zone in the previous stage and whose temperature has significantly decreased but whose pressure is still high, is guided and flows through a key throttling device. This throttling device can be a thermostatic expansion valve, an electronic expansion valve, or a capillary tube. When the high-pressure liquid refrigerant flows through the narrow channel inside the throttling device, a violent resistance effect and adiabatic expansion occur. In this almost instantaneous process, the refrigerant pressure drops sharply, and simultaneously, according to the Joule-Thomson effect, its temperature also decreases significantly. After passing through the throttling device, the high-temperature, high-pressure liquid refrigerant transforms into a low-temperature, low-pressure liquid mixed with some flash gas—the very low-pressure liquid refrigerant required initially. This refrigerant, restored to its low-temperature, low-pressure state, is directly transported back to the top inlet of the gradient refrigerant dehumidification tower, ready to begin the next cycle, again cooling and dehumidifying the original hot and humid flue gas entering the system. Thus, an integrated self-circulating system, relying solely on external electrical power to drive the compressor without any additional heat or cold sources, is fully constructed, enabling continuous waste heat recovery and deep purification of white smoke from flue gas.

[0061] In this step, the clean exhaust gas that meets the temperature rise requirements is the final substance treated and discharged, and its characteristics have been described in detail in the previous step. The flue gas outlet is the final outlet connecting the treated flue gas to the atmosphere. Throttling and pressure reduction is a thermodynamic process, referring to the process by which the pressure of a high-pressure fluid decreases after passing through a valve or narrow channel. For refrigerants, this process is usually accompanied by a significant drop in temperature. The throttling device is the core component for realizing the throttling and pressure reduction process. Its function is to control the flow rate of the refrigerant and reduce its pressure by generating local resistance. Its structure can range from a simple capillary tube to a complex electronic expansion valve. Low-pressure liquid refrigerant is the final product of the throttling and pressure reduction process. Its characteristic properties are low temperature and low pressure, which enables it to absorb heat in the next cycle. Its state is completely consistent with the refrigerant injected into the gradient refrigerant dehumidification tower at the beginning of the first step. The internal closed-loop self-circulation of system energy refers to the circulation of the working medium, i.e., the refrigerant, in a closed loop throughout the entire system. Energy is transferred, converted, and utilized in stages between different devices within the system. Apart from the electrical energy input to drive the compressor, there is no other form of energy exchange with the outside world to complete its main function, thus achieving a high degree of energy self-sufficiency.

[0062] For example, following the previous example, clean exhaust gas with a temperature rise of 45 degrees Celsius, meeting the requirements, is directly discharged into the atmosphere through a 0.8-meter diameter exhaust port. Simultaneously, high-pressure liquid R134a refrigerant flowing from the self-whitening drive zone, with a pressure of approximately 1.45 MPa and a temperature of 40 degrees Celsius, is guided through an electronic expansion valve for throttling and pressure reduction. After passing through the expansion valve, the refrigerant pressure drops sharply to 0.15 MPa, and the temperature correspondingly decreases to 5 degrees Celsius, forming a low-temperature, low-pressure liquid refrigerant containing a small amount of flash vapor. This generated low-pressure liquid refrigerant is transported back to the top of the gradient refrigerant dehumidification tower to cool the next batch of raw hot and humid flue gas entering the system, thus completing the entire self-circulation process of the integrated heat pump-assisted flue gas waste heat recovery and white smoke purification method.

[0063] In a specific embodiment of the present invention, after the gas pre-generation module, the method further includes: collecting the water condensed and precipitated in the gradient refrigerant dehumidification tower to generate natural gas combustion condensate.

[0064] The condensate from natural gas combustion is directed to a water treatment unit for purification, producing reusable purified water.

[0065] The outlet of the water treatment unit is connected to the reuse pipeline, and the other end of the reuse pipeline is selectively connected to the water inlet of the gradient refrigerant dehumidification tower and the water inlet of the external circulating water system, respectively, for the purpose of reusing the purified water for system water replenishment or supplementing the external circulating water.

[0066] In a specific embodiment of the present invention, the preheated flue gas generated before entering the gradient refrigerant dehumidification tower is supplied to the gradient refrigerant dehumidification tower, which serves as the evaporation end of the heat pump, so as to utilize the recovered superheated heat to increase the evaporation rate of the subsequent low-pressure liquid refrigerant in the gas pre-generation module.

[0067] In a specific embodiment of the present invention, the flue gas self-reheating whitening module, through a control unit, collects the dew point temperature of the dry and cold flue gas flow in real time at the flue gas inlet end located in the self-whitening driving zone, and transmits the temperature signal to the control unit. The dew point temperature of the dry and cold flue gas flow and the preset safe temperature rise threshold are used to adjust the flow rate of the standby high-pressure liquid refrigerant in the self-whitening driving zone, so as to control the remaining sensible heat transferred to the dry and cold flue gas flow, thereby generating a clean emission gas flow with a temperature rise that just meets the emission conditions.

[0068] The flow rate of the standby high-pressure liquid refrigerant in the self-whitening drive zone specifically includes: calculating the target exhaust temperature of the real-time dew point temperature plus the safe temperature rise threshold, then comparing it with the actual outlet temperature of the dry and cold flue gas to obtain the difference between the actual outlet temperature of the dry and cold flue gas and the target exhaust temperature, and then combining it with the preset temperature difference-adjustment amplitude correlation logic to match and obtain the adjusted flow rate of the standby high-pressure liquid refrigerant in the self-whitening drive zone.

[0069] It should be noted that the temperature difference-adjustment range correlation logic is pre-established based on system thermal performance tests. The specific process is as follows: 1. First, collect key system parameters, including the dew point temperature range of dry cold flue gas under different operating conditions, the pressure / temperature of the standby high-pressure liquid refrigerant, and the heat exchange coefficient of the self-whitening drive zone; 2. Design multiple sets of experiments to simulate the target flue gas temperature corresponding to different dew point temperatures plus safe temperature rise thresholds, adjust the opening of the flow control valve, and record the corresponding data of the temperature difference (actual outlet temperature - target temperature) and the opening adjustment range; 3. Analyze the experimental data, screen the parameter range that makes the system heat exchange stable and the flue gas temperature fluctuate the least, and determine the temperature difference threshold and the corresponding opening adjustment range; 4. Pre-set this correlation into the control unit to form automatic adjustment logic, ensuring that the adjustment is accurate according to the experimentally verified rules during actual operation.

[0070] The above embodiments can be implemented, in whole or in part, by software, hardware, firmware, or any other combination thereof. When implemented in software, the above embodiments can be implemented, in whole or in part, as a computer program product. Those skilled in the art will recognize that the algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0071] In addition, the functional modules in the various embodiments of this application can be integrated into one processing module, or each module can exist physically separately, or two or more modules can be integrated into one module.

[0072] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of protection of the claims.

[0073] The above content is merely an example and illustration of the concept of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the concept of the invention or exceed the scope defined by the present invention, and all such modifications and additions should fall within the protection scope of the present invention.

Claims

1. A heat pump system based on natural gas flue gas waste heat recovery and white smoke purification, characterized in that, include: The gas pre-generation module is used to obtain raw hot and humid natural gas flue gas and low-pressure liquid refrigerant, supply the low-pressure liquid refrigerant to the gradient refrigerant dehumidification tower which serves as the evaporation end of the heat pump, and make the raw hot and humid natural gas flue gas flow counter-currently through the gradient refrigerant dehumidification tower to generate dry and cold flue gas flow and low-pressure gaseous refrigerant. The flue gas and gaseous refrigerant extraction module is used to extract dry and cold flue gas flow and simultaneously collect low-pressure gaseous refrigerant to generate a low-pressure gaseous refrigerant flow that carries the flue gas to recover low-temperature heat. The refrigerant compression and quality enhancement module is used to perform compression work on a low-pressure gaseous refrigerant stream to generate high-grade, high-temperature, and high-pressure refrigerant vapor. The superheated steam preheat exchange module is used to introduce high-grade, high-temperature and high-pressure refrigerant vapor into the heat transfer zone of the heat collection heat carrier, and preheat it with the original hot and humid natural gas flue gas entering the system to generate cooled saturated refrigerant vapor. The main condensing waste heat recovery module is used to transport the cooled saturated refrigerant vapor to the main condensing zone of the heat collection heat carrier, release the latent heat of condensation to the external circulating water to recover the medium-grade waste heat, and generate standby high-pressure liquid refrigerant. The flue gas self-reheating whitening module is used to guide the high-pressure liquid refrigerant to flow through the self-whitening drive zone of the heat collection heat carrier, and use its remaining sensible heat to reheat the dry and cold flue gas flow to generate a clean exhaust gas flow with qualified temperature rise and the cooled high-pressure liquid refrigerant. The emission and refrigerant throttling circulation module is used to discharge clean exhaust gas with qualified temperature rise, and simultaneously throttle and reduce the pressure of the cooled high-pressure liquid refrigerant to generate low-pressure liquid refrigerant for the gas pre-generation module, thus completing the internal closed-loop self-circulation of system energy.

2. A heat pump system based on natural gas flue gas waste heat recovery and white smoke purification according to claim 1, characterized in that, The gas pre-generation module specifically includes: Low-pressure liquid refrigerant is injected from the top of the gradient refrigerant dehumidification tower, allowing it to flow and evaporate from top to bottom along the built-in tube bundle, forming a temperature gradient field inside the gradient refrigerant dehumidification tower with an extremely cold upper part and a moderately cold lower part. The raw hot and humid natural gas flue gas is fed into the middle and lower part of the gradient refrigerant dehumidification tower and forced to flow counter-currently from bottom to top through the temperature gradient field. This causes the water vapor generated by combustion in the flue gas to be condensed and precipitated in stages, generating a dry and cold flue gas flow at the top of the gradient refrigerant dehumidification tower.

3. A heat pump system based on natural gas flue gas waste heat recovery and white smoke purification according to claim 1, characterized in that, The generation of high-grade, high-temperature, high-pressure refrigerant vapor includes: The low-pressure gaseous refrigerant stream is input into the compressor's suction port as the sole working medium; The compressor is started to mechanically compress the low-pressure gaseous refrigerant flow, converting the mechanical work input by the compressor into heat energy and adding it to the internal energy of the low-pressure gaseous refrigerant flow, generating high-grade, high-temperature, and high-pressure refrigerant vapor at the compressor discharge port.

4. A heat pump system based on natural gas flue gas waste heat recovery and white smoke purification according to claim 1, characterized in that, While generating cooled saturated refrigerant vapor, the superheated heat released by the high-temperature and high-pressure refrigerant vapor is used to preheat the original hot and humid natural gas flue gas entering the heat transfer zone, generating preheated flue gas before entering the gradient refrigerant dehumidification tower.

5. A heat pump system based on natural gas flue gas waste heat recovery and white smoke purification according to claim 1, characterized in that, The specific steps of generating the high-pressure liquid refrigerant to be used include: introducing the cooled saturated refrigerant vapor into the main condensing zone, and simultaneously introducing external circulating water into the main condensing zone; The cooled saturated refrigerant vapor exchanges heat with the external circulating water, and uses the released latent heat of condensation to heat the external circulating water, generating medium-grade hot water and standby high-pressure liquid refrigerant.

6. A heat pump system based on natural gas flue gas waste heat recovery and white smoke purification according to claim 1, characterized in that, The specific details of generating a clean exhaust gas flow with a qualified temperature rise and a cooled high-pressure liquid refrigerant are as follows: Guide the high-pressure liquid refrigerant to the refrigerant channel of the self-whitening drive zone; The extracted dry and cold flue gas is used as the sole object to be heated and introduced into the flue gas channel of the self-whitening drive zone. The remaining sensible heat carried by the standby high-pressure liquid refrigerant is transferred to the dry and cold flue gas flow, generating a clean exhaust gas flow with a qualified temperature rise.

7. A heat pump system based on natural gas flue gas waste heat recovery and white smoke purification according to claim 1, characterized in that, The specific details of generating the low-pressure liquid refrigerant for the gas pre-generation module are as follows: The cooled, high-pressure liquid refrigerant is guided through a throttling device; By utilizing the adiabatic expansion effect of the throttling device, the pressure and temperature of the high-pressure liquid refrigerant after cooling are reduced simultaneously, generating a low-temperature, low-pressure liquid refrigerant.

8. A heat pump system based on natural gas flue gas waste heat recovery and white smoke purification according to claim 1, characterized in that, Following the gas pre-generation module, the system further includes: The water condensed and precipitated in the gradient refrigerant dehumidification tower is collected to generate natural gas combustion condensate; The condensate from natural gas combustion is directed to a water treatment unit for purification, producing reusable purified water. The outlet of the water treatment unit is connected to the reuse pipeline, and the other end of the reuse pipeline is selectively connected to the water inlet of the gradient refrigerant dehumidification tower and the water inlet of the external circulating water system, respectively, for the purpose of reusing the purified water for system water replenishment or supplementing the external circulating water.

9. A heat pump system based on natural gas flue gas waste heat recovery and white smoke purification according to claim 4, characterized in that, The preheated flue gas generated before entering the gradient refrigerant dehumidification tower is supplied to the gradient refrigerant dehumidification tower, which serves as the evaporation end of the heat pump, so as to utilize the recovered superheated heat to increase the evaporation rate of the subsequent low-pressure liquid refrigerant in the gas pre-generation module.

10. A heat pump system based on natural gas flue gas waste heat recovery and white smoke purification according to claim 1, characterized in that, The flue gas self-reheating whitening module uses a control unit to collect the dew point temperature of the dry and cold flue gas flow in real time at the flue gas inlet located in the self-whitening driving zone, and transmits the temperature signal to the control unit. The dew point temperature of the dry and cold flue gas flow is compared with the preset safe temperature rise threshold. The flow rate of the standby high-pressure liquid refrigerant in the self-whitening driving zone is adjusted to control the remaining sensible heat transferred to the dry and cold flue gas flow, thereby generating a clean emission gas flow with a temperature rise that just meets the emission conditions. The flow rate of the standby high-pressure liquid refrigerant in the self-whitening drive zone specifically includes: calculating the target exhaust temperature of the real-time dew point temperature plus the safe temperature rise threshold, then comparing it with the actual outlet temperature of the dry and cold flue gas to obtain the difference between the actual outlet temperature of the dry and cold flue gas and the target exhaust temperature, and then combining it with the preset temperature difference-adjustment amplitude correlation logic to match and obtain the adjusted flow rate of the standby high-pressure liquid refrigerant in the self-whitening drive zone.

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