Gas-fired boiler deep condensation waste heat recovery device and recovery control method

Abstract

The present application relates to waste heat recovery and flue gas treatment technical field, especially to a kind of gas boiler deep condensation waste heat recovery device and recovery control method.The device includes compressor, brazed plate condenser, drying filter, liquid transfer line, evaporation device, discharge line and gas-liquid separator, compressor is communicated with brazed plate condenser, brazed plate condenser is communicated with drying filter, drying filter is communicated with evaporation device liquid inlet end by liquid transfer line, and evaporation device is connected to compressor gas inlet end by discharge line through gas-liquid separator;Evaporation device includes parallel chimney core evaporator and water tank immersion evaporator, chimney core evaporator is installed in chimney, and water tank immersion evaporator receives condensate to carry out heat exchange.The present application recovers flue gas sensible heat, latent heat and condensate sensible heat by chimney core evaporator and water tank immersion evaporator, and overall waste heat recovery rate is about 15% higher than single-stage evaporator scheme.

Description

Technical Field

[0001] This invention belongs to the field of waste heat recovery and flue gas treatment technology of gas-fired boilers, and particularly relates to a deep condensation waste heat recovery device and recovery control method for gas-fired boilers. Background Technology

[0002] With the full implementation of the "coal-to-gas" project in northern China, gas-fired boilers have achieved large-scale popularization in urban heating, commercial and industrial settings across the country.

[0003] Gas-fired boilers, as a common energy conversion device, are widely used in heating, industrial production, and domestic hot water supply. During operation, the high-temperature flue gas emitted carries a large amount of sensible heat and latent heat of water vapor; direct emission of these gases would result in significant energy waste. With increasingly stringent requirements for energy conservation and emission reduction, efficient recovery of flue gas waste heat, especially deep recovery of condensation heat below the flue gas acid dew point temperature, has become crucial for improving boiler thermal efficiency.

[0004] In existing waste heat recovery technologies for gas-fired boilers, common measures include installing flue gas condensers or economizers in the flue to cool the flue gas using water or air, recovering some sensible heat. However, conventional heat exchange equipment is limited by the heat exchange temperature difference and the thermal properties of the medium, typically only able to reduce the flue gas temperature to 60–80℃, which is insufficient to break through the dew point temperature of water vapor (approximately 55–60℃). Therefore, it cannot fully recover the large amount of latent heat released by the condensation of water vapor in the flue gas. Some improved devices use heat pump systems for auxiliary cooling, but these mostly employ a single-stage evaporator structure, which suffers from limitations such as limited heat exchange capacity, inadequate utilization of condensate, complex and conflict-prone control, and significant acid corrosion and scaling problems. Based on engineering practice and research analysis, the existing technical solutions mainly have the following technical defects in specific applications: 1. Due to the limitation of return water temperature, the deep condensation capacity is insufficient, making it difficult to improve the gas-saving rate; In frigid northern regions, the boiler return water temperature in heating systems remains consistently above 60°C year-round, far exceeding the dew point temperature of natural gas flue gas (approximately 55–60°C). Conventional integrated condensing boilers and external flue gas heat exchangers rely on boiler return water as a cooling source. The high return water temperature results in minimal or even negative heat exchange temperature differences, making it impossible to stably lower the flue gas temperature below the dew point. Such solutions can only recover sensible heat from the flue gas, with actual operating thermal efficiency only maintained at 88%–92%, latent heat recovery rate less than 20%, and actual gas savings of only 3%–5%. The economic benefits are not significant, leading to a lack of incentive for end-users to upgrade.

[0005] 2. External structures require a large footprint and are poorly adaptable to existing boiler rooms; Existing deep condensing solutions generally employ an external heat exchanger layout, requiring the addition of a separate equipment room, circulation pipelines, and supporting electrical systems between the boiler and the chimney. This approach is costly to implement and has a long construction period. Furthermore, most existing boiler rooms that are over 10 years old do not have reserved space for new equipment, making on-site implementation extremely difficult and severely hindering the large-scale promotion and application of waste heat recovery technology. In addition, the existing external heat exchanger layout requires long-term boiler shutdowns for modification.

[0006] 3. The whitening of flue gas requires secondary heating, and the additional energy consumption offsets the energy-saving benefits; To eliminate white smoke from chimneys in winter, current mainstream flue gas whitening technologies all adopt a "condensation first, then heating" process. The condensed flue gas needs to be reheated using natural gas, electricity, or steam to reduce its relative humidity to below 60%. This approach not only increases equipment investment but also consumes a significant amount of additional energy, meaning that the gas cost savings from condensation recovery are almost entirely offset by the energy consumption in the whitening process, failing to balance energy savings with environmental compliance requirements.

[0007] 4. The sensible heat of condensate is not effectively recovered, resulting in a waste of secondary energy; Existing flue gas waste heat recovery systems only focus on the sensible heat in the flue gas and the latent heat released by water vapor condensation. The sensible heat carried by the low-temperature condensate generated during the condensation process is generally not given sufficient attention or recovery in the industry. In actual engineering projects, condensate with a temperature of 20℃–35℃ is usually discharged directly through drainage pipes, constituting a significant waste of secondary energy and further reducing the overall energy efficiency of the waste heat recovery system. Summary of the Invention

[0008] In view of this, the present invention aims to provide a deep condensation waste heat recovery device and recovery control method for gas-fired boilers, in order to solve the prominent problems such as the difficulty of deep condensation due to the high return water temperature of heating systems in northern regions, the limited space of existing boiler rooms making it difficult to adapt to external equipment, the need for long-term boiler shutdown for renovation, the need for secondary heating in existing flue gas whitening solutions to consume additional energy, and the general waste of sensible heat in condensate.

[0009] To achieve the above objectives, the technical solution created by this invention is implemented as follows: A deep condensing waste heat recovery device for a gas-fired boiler includes a compressor, a brazed plate condenser, a liquid receiver, a dryer filter, a liquid delivery pipeline, an evaporator, a discharge pipeline, and a gas-liquid separator. The outlet of the compressor is connected to the refrigerant inlet of the brazed plate condenser via a pipeline. The liquid outlet of the brazed plate condenser is connected to the inlet of the liquid receiver and the dryer filter via pipelines. The outlet of the dryer filter is connected to the inlet of the liquid delivery pipeline via a pipeline. The liquid delivery pipeline is connected to the inlet of the evaporator. The outlet of the evaporator is connected to the inlet of the gas-liquid separator via a discharge pipeline. The outlet of the gas-liquid separator is connected to the inlet of the compressor via a pipeline. The compressor and the main controller are connected via a line or wireless device. The evaporation unit includes a chimney-core evaporator and a water-tank submerged evaporator connected in parallel. The chimney-core evaporator is installed inside the chimney of the gas-fired boiler and exchanges heat with the flue gas. The water-tank submerged evaporator is used to receive the condensate inside the chimney. There are two liquid delivery lines. The inlet ends of the two liquid delivery lines are connected to the outlet end of the dryer filter. The outlet ends of the two liquid delivery lines are connected to the inlet ends of the chimney-core evaporator and the water-tank submerged evaporator, respectively. There are two discharge lines. One end of the two discharge lines is connected to the discharge end of the chimney-core evaporator and the water-tank submerged evaporator, respectively. The other end of the two discharge lines is connected to the inlet end of the gas-liquid separator.

[0010] Furthermore, the water tank submersible evaporator includes a liquid collection tank, a first refrigerant coil, a condensate collection pipe, a condensate overflow pipe, and a condensate discharge pipe. The first refrigerant coil is installed inside the liquid collection tank, with its refrigerant inlet and outlet ends extending out of the tank. The refrigerant inlet end is connected to the outlet end of the corresponding liquid delivery pipeline, and the refrigerant outlet end is connected to the inlet end of the gas-liquid separator via the corresponding discharge pipeline. The condensate collection pipe is connected to one end of the top plate of the liquid collection tank, the condensate overflow pipe is connected to the other end of the top plate, and the condensate discharge pipe is connected to the bottom plate of the liquid collection tank and located below the condensate overflow pipe.

[0011] Furthermore, the water tank submersible evaporator also includes flow guide plates, with at least three flow guide plates arranged in parallel within the liquid collection tank. The at least three flow guide plates are perpendicular to the coiling plane of the first refrigerant coil, which passes through the flow guide plates. Adjacent flow guide plates are staggered vertically. The top of the upper flow guide plate is connected to the top plate of the liquid collection tank, and the bottom of the upper flow guide plate is suspended. The bottom of the lower flow guide plate is connected to the bottom plate of the liquid collection tank, and the top of the lower flow guide plate is suspended.

[0012] Furthermore, the water tank submersible evaporator also includes a pH monitor and a level gauge, which are respectively installed on both sides of the top plate of the collection tank, with the pH monitor located near the condensate collection pipe.

[0013] Furthermore, the water tank submerged evaporator also includes a sodium hydroxide solution tank. The outlet of the sodium hydroxide solution tank is connected to the part of the condensate collection pipe near the collection tank via a dosing pipeline. An electric regulating valve is installed on the dosing pipeline.

[0014] Furthermore, this application also includes a water collection device, which is installed at the flue gas inlet of the chimney and located below the chimney core evaporator. The water collection device includes an annular water collection pan, a liquid collection pan, and a condensate conduit. Both the annular water collection pan and the liquid collection pan are installed on the inner wall of the chimney. The annular water collection pan is located above the flue gas inlet of the chimney, and the liquid collection pan is located below the flue gas inlet of the chimney. The annular water collection pan and the liquid collection pan are connected through a condensate conduit, and the bottom end of the liquid collection pan is connected to the condensate collection pipe.

[0015] Furthermore, the chimney-core evaporator includes an evaporator body, a flue gas duct, a second refrigerant coil, fins, and a flange. The evaporator body is installed inside the chimney and located above the flue gas inlet. The flue gas duct is located inside the evaporator body and divides the evaporator body into an inner cavity and an outer cavity along the height of the chimney. The bottom ends of both the inner and outer cavities are connected to the chimney, and the top ends of the inner and outer cavities are connected through an inner-outer cavity connection port. The flue gas is finally discharged from the top of the evaporator body into the upper part of the chimney. The inner-outer cavity connection port is located on the flue gas duct. The refrigerant coil is installed along the height of the flue gas duct. During the process of flue gas being discharged through the chimney, the flue gas passes through the second refrigerant coil for heat exchange. There are two flanges, which are fixed to the top and bottom of the evaporator body respectively. The two flanges are connected to the flanges on the inner wall of the chimney, realizing factory production, rapid on-site installation, and minimal space occupation. Fins are set on the inner wall of the evaporator body, and / or, fins are set on the inner and outer walls of the flue gas duct. The fins are used to reduce drag and increase efficiency.

[0016] Furthermore, each infusion line is equipped with an electronic expansion valve, and both the infusion line and the discharge line are equipped with integrated temperature and pressure sensors. The integrated temperature and pressure sensors are located close to the corresponding collection tank and evaporator body. The electronic expansion valves are located upstream of the corresponding integrated temperature and pressure sensors. The two electronic expansion valves are respectively connected to the corresponding first PID controller and second PID controller via lines or wireless devices.

[0017] Furthermore, the inlet end of the brazed plate condenser is connected to the water source through an inlet pipe, and the outlet end of the brazed plate condenser is connected to the external heat system through an outlet pipe. The external heat system includes boiler return water, heating water supply or domestic hot water system. An electronic descaling device, a Y-shaped filter and an electric valve are installed in sequence on the inlet pipe, with the electric valve located close to the brazed plate condenser.

[0018] Based on the above-mentioned deep condensing waste heat recovery device for gas-fired boilers, the present invention also provides a control method for deep condensing waste heat recovery of gas-fired boilers, comprising the following steps: S1: Obtain the flue gas outlet temperature of the chimney core evaporator; S11: When the flue gas temperature is greater than the preset value, the main controller calculates and outputs instructions through the PID algorithm. The compressor receives the instructions to increase the operating frequency, reduce the pressure and temperature of the chimney core evaporator, increase the heat exchange temperature difference between the liquid refrigerant and the flue gas, and reduce the flue gas temperature to the target value. S12: When the flue gas temperature stabilizes at the preset value, the main controller stops outputting commands, and the compressor continues to operate at the current frequency; S13: The main controller adopts a combined feedforward control strategy and closed-loop control strategy; S131: Feedforward control strategy: The boiler's rated load is P N The main controller divides the boiler's operating load range into three sections: the first load section, the second load section, and the third load section. The first load section is 20% P. N To less than 40% P N The second load segment is 40% P. N To less than 70% P N The third load segment is 70% P. N Up to 110%P N The main controller uses a PID algorithm and configures corresponding integral and derivative parameters for each load segment to control the dynamic characteristics of the compressor to adapt to the boiler under the first, second, and third load segments, thereby improving regulation stability. Within the full load range of 20%-110% of the boiler, a matching relationship between the boiler load command and the compressor reference frequency is established, and interpolation is used to obtain the corresponding reference frequency for non-calibrated intermediate load points. When the boiler load changes abruptly, the feedforward unit can respond quickly and pre-adjust the frequency. S132: Closed-loop composite control strategy: Based on the reference frequency determined in step S131, closed-loop PID regulation is performed according to the measured temperature of the flue gas outlet of the chimney core evaporator to achieve precise control of the compressor operating frequency. S2: Obtain the superheat of the refrigerant at the discharge end of the chimney core evaporator; When the superheat exceeds the preset value, it indicates that the liquid refrigerant supply is insufficient and the heat exchange area is not fully utilized. The first PID controller obtains the information to increase the opening degree through the PID algorithm. The corresponding electronic expansion valve increases the opening degree according to the received information to increase the liquid refrigerant flow and reduce the temperature of the chimney core evaporator. When the superheat is less than the preset value, it indicates that the liquid refrigerant supply is excessive and there is a risk of liquid returning to gas. The first PID controller obtains the information to reduce the opening degree through the PID algorithm. The corresponding electronic expansion valve reduces the opening degree according to the received information to reduce the liquid refrigerant flow and increase the temperature of the chimney core evaporator. S3: Obtain the superheat of the refrigerant at the discharge end of the water tank submerged evaporator; When the superheat exceeds the preset value, it indicates that the liquid refrigerant supply is insufficient and the heat exchange area is not fully utilized. The second PID controller obtains the information to increase the opening degree through the PID algorithm. The corresponding electronic expansion valve increases the opening degree according to the received information to increase the liquid refrigerant flow and reduce the temperature of the water tank submerged evaporator. When the superheat is less than the preset value, it indicates that the liquid refrigerant supply is excessive, and there is a risk of liquid returning to gas. The second PID controller obtains the information to reduce the opening degree through the PID algorithm. The corresponding electronic expansion valve reduces the opening degree according to the received information to reduce the liquid refrigerant flow and increase the temperature of the water tank submerged evaporator.

[0019] Compared with the prior art, the present invention can achieve the following beneficial effects: (1) The present invention creates a chimney core evaporator and a water tank submerged evaporator connected in parallel. The chimney core evaporator prioritizes the recovery of sensible heat and latent heat in the flue gas, while the water tank submerged evaporator further recovers the sensible heat carried in the condensate. The chimney core evaporator and the water tank submerged evaporator can operate completely independently at their respective optimal evaporation temperatures without interfering with each other, thus maximizing heat exchange efficiency.

[0020] (2) The present invention creates a stable control of flue gas outlet temperature at 30±1℃ through deep condensation, which greatly reduces the relative humidity of flue gas. When directly emitted, no white smoke will be generated in winter environment. There is no need to adopt the traditional whitening process route of "condensation first, then heating", which avoids the extra energy consumption caused by secondary heating, ensures that the energy-saving benefits of condensation recovery are not offset by the whitening energy consumption, and meets environmental compliance requirements.

[0021] (3) This invention incorporates a pH monitor and a sodium hydroxide solution tank. When the pH value of the condensate is detected to be below 6.5, sodium hydroxide solution is automatically added to the collection tank via an electric regulating valve for neutralization. The addition is stopped when the pH value is above 7.5. The neutralized condensate can be directly recycled for boiler feedwater, which not only prevents acidic condensate from corroding subsequent pipes and equipment, but also realizes the recycling of water resources.

[0022] (4) The present invention creates a water collection device at the flue gas inlet of the chimney to directly collect the condensate dripping from the chimney core evaporator, thereby preventing the condensate from wetting the core material below or splashing upward with the flue gas, and ensuring the long-term stable and efficient operation of the chimney core evaporator.

[0023] (5) The present invention creates an integrated temperature and pressure sensor at the position near the evaporator on each infusion pipeline and discharge pipeline to collect temperature and pressure data in real time. The first PID controller and the second PID controller calculate the superheat and adjust the opening of the electronic expansion valve with a high-speed cycle of 100ms. It can complete the rapid response to boiler load fluctuations or condensate water level changes within 10 seconds and maintain stable operation. Attached Figure Description

[0024] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 A schematic diagram of the principle of a deep condensing waste heat recovery device for a gas-fired boiler, as described in an embodiment of the present invention; Figure 2 for Figure 1 Schematic diagram of a submersible evaporator with a middle water tank; Figure 3 for Figure 1 Schematic diagram of the internal structure of a chimney-type evaporator; Figure 4 for Figure 1 Schematic diagram of the internal structure of a chimney-type evaporator; Figure 5 for Figure 1 Top view of the connection structure of the second refrigerant coil and liquid delivery pipeline of the central chimney core evaporator; Figure 6 for Figure 1 Schematic diagram of the connection structure between the central water collection unit and the chimney; Figure 7 A reference diagram showing the usage status of a deep condensing waste heat recovery device for a gas-fired boiler, as described in an embodiment of the present invention.

[0025] Explanation of reference numerals in the attached figures: 10. Compressor; 11. Brazed plate condenser; 12. Liquid receiver; 13. Dryer filter; 14. Liquid delivery line; 15. Evaporator; 16. Discharge line; 17. Gas-liquid separator; 18. Water collection device; 19. Skid-mounted container; 110. Inlet water pipe; 111. Outlet water pipe; 112. Electronic descaling device; 113. Y-type filter; 114. Electric valve; 115. Water source; 116. External heating system; 141. Electronic expansion valve; 142. Integrated temperature and pressure sensor; 151. Chimney-type evaporator; 152. Water tank submerged evaporator; 1520. Collection tank; 1521. First refrigerant coil; 1522. Condensate collection pipe; 1523. Condensate overflow pipe; 1524. Condensate discharge pipe; 1525. Flow guide plate; 1526. pH monitor; 1527. Level gauge; 1528. Sodium hydroxide solution tank; 1529. Electric regulating valve; 1510. Evaporator body; 1511. Flue gas duct; 1512. Second refrigerant coil; 1513. Fins; 1514. Flange; 1515. Inner cavity; 1516. Outer cavity; 1517. Inner and outer cavity connection port; 15211, Refrigerant inlet; 15212, Refrigerant outlet; 181. Annular water collection tray; 182. Liquid collection tray; 183. Condensate conduit; 20. Gas-fired boiler; 21. Chimney; 22. Flue gas inlet; 30. Main controller; 31. First PID controller; 32. Second PID controller. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not constitute a limitation thereof.

[0027] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0028] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0029] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0030] The invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0031] like Figure 1 As shown, a deep condensing waste heat recovery device for a gas-fired boiler includes a compressor 10, a brazed plate condenser 11, a liquid receiver 12, a dryer filter 13, a liquid delivery pipeline 14, an evaporator 15, a discharge pipeline 16, and a gas-liquid separator 17. The outlet of the compressor 10 is connected to the refrigerant inlet of the brazed plate condenser 11 via a pipeline. The liquid outlet of the brazed plate condenser 11 is connected to the liquid receiver 12 and the liquid inlet of the dryer filter 13 via pipelines. The liquid outlet of the dryer filter 13 is connected to the liquid inlet of the liquid delivery pipeline 14 via a pipeline. The liquid delivery end of the liquid delivery pipeline 14 is connected to the liquid inlet of the evaporator 15. The liquid outlet of the evaporator 15 is connected to the inlet of the gas-liquid separator 17 via the discharge pipeline 16. The outlet of the gas-liquid separator 17 is connected to the inlet of the compressor 10 via a pipeline. The compressor 10 is connected to the main controller 30 via a line or wireless device. The main controller 30 is responsible for controlling the operating frequency of the compressor 10. The evaporation device 15 includes a chimney core evaporator 151 and a water tank submerged evaporator 152 connected in parallel. The chimney core evaporator 151 is installed inside the chimney 21 of the gas boiler 20 and exchanges heat with the flue gas. The water tank submerged evaporator 152 receives the condensate in the chimney 21 and exchanges heat. There are two liquid delivery pipes 14. The inlet end of both liquid delivery pipes 14 is connected to the outlet end of the dryer filter 13. The outlet end of the two liquid delivery pipes 14 is connected to the inlet end of the chimney core evaporator 151 and the inlet end of the water tank submerged evaporator 152, respectively. There are two discharge pipes 16. One end of the two discharge pipes 16 is connected to the discharge end of the chimney core evaporator 151 and the discharge end of the water tank submerged evaporator 152, respectively. The other end of the two discharge pipes 16 is connected to the inlet end of the gas-liquid separator 17.

[0032] In operation, the low-temperature, low-pressure gaseous refrigerant from the gas-liquid separator 17 is drawn into the compressor 10, which compresses it into high-temperature, high-pressure superheated vapor and sends it through pipelines to the refrigerant inlet of the brazed plate condenser 11. In the brazed plate condenser 11, the refrigerant vapor exchanges heat with water on the other side, releasing heat and condensing into high-pressure, medium-temperature liquid refrigerant. The condensed liquid refrigerant can enter the liquid receiver 12 to balance and store the amount of refrigerant required under different operating conditions. Meanwhile, the liquid refrigerant can also flow into the dryer filter 13 to remove moisture and impurities. The clean liquid refrigerant after passing through the dryer filter 13 is divided into two paths through the pipeline and enters two liquid delivery pipelines 14 respectively. The liquid delivery pipelines 14 send the liquid refrigerant into the chimney core evaporator 151 and the water tank submerged evaporator 152 respectively. The liquid refrigerant absorbs heat from its respective heat source in the chimney core evaporator 151 and the water tank submerged evaporator 152 and evaporates from liquid to gas. The refrigerant (gase refrigerant or containing incompletely evaporated liquid refrigerant) coming out of the chimney core evaporator 151 and the water tank submerged evaporator 152 enters the gas-liquid separator 17 through the discharge pipeline 16 respectively. Both discharge pipelines 16 are equipped with one-way valves. The gas-liquid separator 17 separates the gaseous and liquid refrigerant. The gaseous refrigerant returns from the outlet to the inlet of the compressor 10 to start the next cycle, thus preventing the liquid refrigerant from entering the compressor 10 and thus preventing damage to the compressor.

[0033] This application uses a chimney core evaporator 151 and a water tank submerged evaporator 152 to stably reduce the flue gas temperature from 150℃ to 30℃, thereby increasing the actual operating thermal efficiency of the boiler from 90% to over 98%, and the gas saving rate is expected to reach 8%-10%.

[0034] This application can also replenish refrigerant to the dryer filter 13 through the liquid receiver 12 to ensure that the amount of refrigerant in the device meets the usage requirements.

[0035] like Figures 1-2 As shown, the submersible evaporator 152 further includes a liquid collection tank 1520, a first refrigerant coil 1521, a condensate collection pipe 1522, a condensate overflow pipe 1523, and a condensate discharge pipe 1524. The first refrigerant coil 1521 is disposed within the liquid collection tank 1520, and the refrigerant inlet end 15211 and the refrigerant outlet end 15212 of the first refrigerant coil 1521 extend out of the liquid collection tank 1520, respectively. 11 is connected to the outlet end of the corresponding infusion pipeline 14, and the refrigerant outlet end 15212 is connected to the inlet end of the gas-liquid separator 17 through the corresponding discharge pipeline 16; the condensate collection pipe 1522 is connected to one end of the top plate of the collection tank 1520, the condensate overflow pipe 1523 is connected to the other end of the top plate of the collection tank 1520, and the condensate discharge pipe 1524 is connected to the bottom plate of the collection tank 1520 and is located below the condensate overflow pipe 1523.

[0036] Valves are installed on the condensate collection pipe 1522, condensate overflow pipe 1523 and condensate discharge pipe 1524 near the collection tank.

[0037] The condensate collection pipe 1522 transports the condensate in the chimney 21 to the collection tank 1520. The first refrigerant coil 1521 absorbs the heat of the condensate in the collection tank 1520, causing the low-temperature, low-pressure liquid refrigerant in the first refrigerant coil 1521 to evaporate into a gaseous state. At the same time, based on the water level and the amount of condensate generated, the liquid level is controlled and discharged through the condensate overflow pipe 1523, the condensate discharge pipe 1524, and the corresponding valves.

[0038] The liquid collection tank 1520 is welded from 316L stainless steel and has a volume 1.5 times the rated evaporation capacity of boiler 20. It is wrapped with a 50mm thick polyurethane insulation layer and is completely sealed without leakage. It is used to temporarily store the acidic condensate generated by flue gas condensation to ensure the stability of the heat exchange process. The insulation layer prevents heat loss from the condensate and ensures the efficiency of waste heat recovery. The sealed structure avoids the volatilization of acidic condensate and corrosion of surrounding equipment. The first refrigerant coil 1521 is made of φ20mm 316L stainless steel tube wound into a multi-layer spiral coil and is completely immersed in the liquid collection tank 1520. The first refrigerant coil 1521 is designed with a 20% area margin.

[0039] The water tank submersible evaporator 152 also includes three guide plates 1525. The three guide plates 1525 are arranged in parallel inside the liquid collection tank 1520 and are perpendicular to the coiling plane of the first refrigerant coil 1521. The first refrigerant coil 1521 passes through the guide plates 1525. Adjacent guide plates 1525 are arranged alternately. The top of the upper guide plate 1525 is connected to the top plate of the liquid collection tank 1520 and the bottom of the upper guide plate 1525 is suspended. The bottom of the lower guide plate 1525 is connected to the bottom plate of the liquid collection tank 1520 and the top of the lower guide plate 1525 is suspended.

[0040] The condensate in the collection tank 1520 is longitudinally flushed along the first refrigerant coil 1521 by three guide plates 1525, which greatly improves the flow rate, turbulence and heat exchange efficiency.

[0041] The water tank submersible evaporator 152 also includes a pH monitor 1526 and a level gauge 1527. The pH monitor 1526 and the level gauge 1527 are respectively installed on both sides of the top plate of the liquid collection tank 1520. The pH monitor 1526 is installed near the condensate collection pipe 1522.

[0042] The liquid level gauge 1527 is used to detect the height of the condensate inside the collection tank 1520, between the guide plate 1525 located near the condensate overflow pipe 1523 and the side wall of the collection tank 1520; the pH value of the condensate entering the collection tank 1520 is detected by inserting the detection end of the pH monitor 1526 into the bottom of the collection tank 1520. The liquid level gauge 1527 is an ultrasonic liquid level gauge.

[0043] The water tank submerged evaporator 152 also includes a sodium hydroxide solution tank 1528. The outlet of the sodium hydroxide solution tank 1528 is connected to the part of the condensate collection pipe 1522 near the collection tank 1520 through a dosing pipeline. An electric regulating valve 1529 is installed on the dosing pipeline.

[0044] The pH monitor collects the pH value of the condensate in the collection tank 1520 every 10 seconds. When the pH is below 6.5, the electric regulating valve 1529 opens, and the sodium hydroxide solution is mixed with the condensate and added to the collection tank 1520 to adjust the pH value of the condensate in the collection tank 1520, preventing the acidic condensate from corroding subsequent pipes and equipment. At the same time, the neutralized condensate can be directly recycled for boiler 20 makeup water. When the pH value is above 7.5, the electric regulating valve 1529 closes, and the addition of sodium hydroxide solution stops.

[0045] like Figure 6 As shown, this application also includes a water collection device 18, which is installed at the flue gas inlet 22 of the chimney 21 and located below the chimney core evaporator 151. The water collection device 18 includes an annular water collection plate 181, a liquid collection plate 182, and a condensate conduit 183. Both the annular water collection plate 181 and the liquid collection plate 182 are installed on the inner wall of the chimney 21. The annular water collection plate 181 is located 100 mm above the flue gas inlet 22 of the chimney 21 in the vertical direction, and the liquid collection plate 182 is located below the flue gas inlet 22 of the chimney 21 in the vertical direction. The annular water collection plate 181 and the liquid collection plate 182 are connected through the condensate conduit 183, and the bottom end of the liquid collection plate 182 is connected to the condensate collection pipe 1522.

[0046] When the chimney-core evaporator 151 is in operation, the flue gas (or humid hot air) cools as it rises, causing condensation to form on the inner wall of the chimney 21 or the surface of the core. The annular water collection tray 181 directly collects the condensate dripping from the chimney-core evaporator 151, preventing it from dripping directly into the flue gas channel below and avoiding water droplets splashing upwards with the flue gas, affecting stability, or flowing into the flue along the chimney inlet. The liquid collection tray 182 receives the condensate flowing down from the annular water collection tray 181 through the condensate conduit 183, as well as the condensate dripping from the inner wall below the flue gas inlet 22 of the chimney 21 and from the core. After collecting all the condensate, it is transported to the liquid collection tank 1520 through the condensate collection pipe 1522.

[0047] The chimney-core evaporator 151 includes an evaporator body 1510, a flue 1511, a second refrigerant coil 1512, fins 1513, and a flange 1514. The evaporator body 1510 is installed inside the chimney 21 and located above the flue gas inlet 22. The flue 1510 is disposed inside the evaporator body 1510 and divides the evaporator body 1510 into an inner cavity 1515 and an outer cavity 1516 along the height direction of the chimney 21. The bottom ends of both the inner cavity 1515 and the outer cavity 1516 are connected to the chimney 21, and the top ends of the inner cavity 1515 and the outer cavity 1516 are connected through an inner and outer cavity connection port 1517. The flue gas is finally discharged from the top of the evaporator body 1510 into the upper part of the chimney 21. The inner and outer cavity connection port 1517 is opened on the flue gas duct 1511. The second refrigerant coil 1512 is set along the height direction of the flue gas duct 1511. During the process of the flue gas being discharged through the chimney 21, the flue gas passes through the second refrigerant coil 1512 to exchange heat with the flue gas. There are two flanges 1514. The two flanges 1514 are fixed at the top and bottom of the evaporator body 1510 respectively. The two flanges 1514 are connected to the flanges on the inner wall of the chimney 21 respectively. The fins 1513 are used to achieve drag reduction and efficiency improvement.

[0048] Specifically, when the second refrigerant coil 1512 is installed on the inner wall of the flue duct 1511, and the fins 1513 are installed on the inner wall of the flue duct 1511, the fins 1513 can also be installed on both the inner and outer walls, with the fins 1513 offset from the second refrigerant coil 1512 (e.g., Figure 3 (As shown); when the second refrigerant coil 1512 is disposed on the inner wall of the evaporator body 1510, and the fins 1513 are disposed on the inner wall of the evaporator body 1510, the fins 1513 and the second refrigerant coil 1512 are offset (as shown). Figure 4 (As shown); when the second refrigerant coil 1512 is disposed on the inner wall of the flue duct 1511 and the inner wall of the evaporator body 1510, and the fins 1513 are disposed on the inner wall of the flue duct 1511 and the inner wall of the evaporator body 1510, the fins 1513 are offset from the second refrigerant coil 1512 (e.g.) Figure 5 As shown), the top end of the second refrigerant coil 1512 is connected to the liquid outlet of the corresponding liquid delivery line 14, and the liquid outlet of the second refrigerant coil 1512 is connected to the inlet of the corresponding discharge line 16.

[0049] The evaporator body 1510 can also adopt multi-cavity simultaneous heat exchange. Each cavity is equipped with a second refrigerant coil 1512. The top end of each second refrigerant coil 1512 is connected to the corresponding liquid supply line 14, and the bottom end of each second refrigerant coil 1512 is connected to the corresponding discharge line 16. Multiple liquid supply lines 14 and multiple discharge lines 16 form a pipe bundle. By lengthening the evaporator body 1510, the flue gas temperature can be stably reduced to below 30°C, which not only ensures heat exchange efficiency but also minimizes the impact on the chimney flow cross section, making it suitable for various positive pressure combustion gas boilers.

[0050] When installing the chimney core evaporator 151, a straight section of the original chimney 21 can be cut off, and the installation can be completed by connecting the chimney core evaporator 151 to the flange of the cut part of the chimney 21 through the flange 1514.

[0051] The liquid delivery pipeline 14 located inside the chimney 21 is a φ25mm stainless steel pipe. The bottom of the stainless steel pipe is the refrigerant inlet, and the top is connected to the second refrigerant coil 1512. The refrigerant flows upward from the center, preferentially cooling the core area of ​​the flue gas with the highest temperature at the center of the chimney 21. The second refrigerant coil 1512 is a spiral coil with a spiral pitch of 150mm. The spiral flow channel prolongs the contact time between the refrigerant and the flue gas, enhancing the heat exchange effect. 8-12 pieces of 3-layer steel, 50mm high and 2mm thick, are welded to the inner wall of the evaporator body 1510 or the inner wall 1515 and outer wall 1516 of the flue gas duct. 16L stainless steel sheets are used as fins 1513, which are evenly distributed along the circumference. Fins 1513 can also be welded to the inner and outer walls of the flue duct 1511 and the inner wall of the evaporator body 1510. Under the premise that the flow cross-sectional loss is less than 15%, the heat exchange area is increased by 40%, and the flue gas resistance is less than 150Pa. The fins 1513 are set vertically, so that the flue gas rises evenly along the axial direction of the chimney 21, reducing local turbulence and flow resistance, and significantly reducing the flue gas resistance. Water vapor can be condensed on the surface of the fins 1513, increasing the condensate collection surface. A 50mm thick rock wool insulation layer can be laid on the outer wall of the chimney 21 to prevent heat loss and avoid condensation corrosion of the outer wall coils.

[0052] Each infusion line 14 is equipped with an electronic expansion valve 141. Both the infusion line 14 and the discharge line 16 are equipped with integrated temperature and pressure sensors 142. The integrated temperature and pressure sensors 142 are located near the corresponding collection tank 1520 and evaporator body 1510. The electronic expansion valve 141 is located upstream of the corresponding integrated temperature and pressure sensor 142. The two electronic expansion valves 141 are respectively connected to the corresponding first PID controller 31 and second PID controller 32 via lines or wireless devices.

[0053] Based on the temperature and pressure data collected by the corresponding integrated temperature and pressure sensor 142, the first PID controller 31 calculates the superheat of the refrigerant passing through the chimney core evaporator 151, and the second PID controller 32 calculates the superheat of the refrigerant passing through the water tank submerged evaporator 152. According to the superheat of the refrigerant, the PID algorithm is used to adjust the opening of each electronic expansion valve 141 respectively.

[0054] The inlet of the brazed plate condenser 11 is connected to the water source 115 through the inlet pipe 110, and the outlet of the brazed plate condenser 11 is connected to the external heat system 116 through the outlet pipe 111. The external heat system 116 includes a boiler return water system, a heating water supply system, or a domestic hot water system. An electronic descaling device 112, a Y-shaped filter 113, and an electric valve 114 are sequentially installed on the inlet pipe 110. The electric valve 114 is located close to the brazed plate condenser 11.

[0055] Water from water source 115 flows through brazed plate condenser 11, exchanging heat with the high-temperature, high-pressure gaseous refrigerant inside. This causes the gaseous refrigerant to condense and release heat, becoming liquid refrigerant. Simultaneously, the absorbed heat is transferred to an external heating system. An electronic descaling device 112, a Y-shaped filter 113, and an electric valve 114 installed on the inlet pipe 110 jointly ensure the efficient, stable, and safe operation of the device. The electronic descaling device 112 generates a high-frequency electromagnetic field or pulsed electric field, altering the crystallization habits of calcium, magnesium, and carbonate ions in the water, causing them to form loose aragonite-like scale. Instead of dense calcite-like scale, it is flushed away by the water flow, preventing scale buildup in the plate channels of the brazed plate condenser 11 and maintaining high heat exchange efficiency. The Y-shaped filter 113 has a built-in stainless steel filter screen to intercept mechanical impurities in the water (mud, rust, welding slag, biological slime, etc.), preventing impurities from entering the narrow channels between the plates of the brazed plate condenser and causing blockage or wear. The electric valve 114 automatically adjusts its opening or performs switching actions according to the corresponding first PID controller 31 and second PID controller 32 (such as water temperature, pressure, flow rate, or external heat demand) (using PID algorithm). The electric valve 114 is located close to the brazed plate condenser 11 to reduce the impact of pipe volume, enabling precise and rapid water flow cutoff or flow regulation, and preventing abnormal overheating or icing of the brazed plate condenser 11 due to thermosiphon effect when it is shut down.

[0056] The refrigerant used in this application is R134a (1,1,1,2-tetrafluoroethane). By adjusting the opening of the corresponding electronic expansion valve 141, the refrigerant evaporation temperature in the chimney-core evaporator 151 can be stably controlled at 15-20℃ (corresponding to a saturation pressure of 0.49-0.57MPa), which can directly reduce the boiler flue gas temperature from 130-180℃ to 20-30℃. By adjusting the opening of the corresponding electronic expansion valve 141, the refrigerant evaporation temperature in the water tank submerged evaporator 152 can be stably controlled at 3-8℃ (corresponding to a saturation pressure of 0.32-0.38MPa), with a heat exchange temperature difference of only 2-3℃. This can further cool the flue gas condensate from 40-50℃ to 5-10℃, deeply recovering about 2% of the waste heat, significantly improving the gas saving rate and energy efficiency. The gas saving rate is 8%-10%. The water tank submerged evaporator 152 adopts a flooded heat exchange, with a heat transfer coefficient ≥3000W / (㎡). (℃). The chimney core evaporator 151 and the water tank submerged evaporator 152 can operate completely independently at their respective set evaporation temperatures without interfering with each other. When the heat load of the chimney core evaporator 151 or the water tank submerged evaporator 152 changes drastically (such as boiler load fluctuations or changes in condensate tank water level), the first PID controller 31 and the second PID controller 32 can also complete the adjustment within 10 seconds to maintain stable operation.

[0057] The compressor 10, brazed plate condenser 11, liquid receiver 12, dryer filter 13, water tank submerged evaporator 152, and gas-liquid separator 17 of this application are all integrated into a steel skid-mounted enclosure 19, such as Figure 7 As shown.

[0058] Taking a gas-fired boiler with a rated evaporation capacity of 2 t / h as an example, the initial flue gas temperature of this boiler under normal non-condensing conditions is about 150℃, the dew point temperature of water vapor in the flue gas is about 54℃, and the acid dew point temperature of low-sulfur pipeline natural gas is about 58℃. This device is designed for such operating conditions, aiming to reduce the flue gas temperature below the water dew point to achieve deep condensation.

[0059] In actual operation, through the aforementioned control strategy, this device can stably control the flue gas outlet temperature of the chimney core evaporator 151 at 30±1℃, making the flue gas temperature far below the acid dew point and water dew point, thereby achieving efficient waste heat recovery. At the same time, the outlet suction superheat of the chimney core evaporator 151 and the water tank submerged evaporator 152 is stably controlled at 5±1℃, ensuring the safe and efficient operation of the compressor 10.

[0060] To prevent the equipment from operating in hazardous areas, safety protection logic is in place. The inviolable safety red line parameters are set as follows: 1. The flue gas outlet temperature of the chimney core evaporator 151 shall not be lower than 25°C to prevent excessive cooling from causing a sharp drop in the coefficient of performance (COP) and exacerbating low-temperature acid corrosion. 2. The condensate outlet temperature of the water tank submersible evaporator 152 shall not be lower than 5℃ to prevent the condensate from freezing and clogging the pipes; 3. The outlet superheat of both evaporators shall not be lower than 2°C. This temperature is the warning line to prevent liquid slugging in compressor 10.

[0061] Based on the above-mentioned deep condensing waste heat recovery device for gas-fired boilers, the present invention also provides a control method for deep condensing waste heat recovery of gas-fired boilers, comprising the following steps: S1: Obtain the flue gas outlet temperature of the chimney core evaporator 151; S11: When the flue gas temperature is greater than the preset value, the main controller 30 calculates and outputs instructions through the PID algorithm. The compressor 10 receives the instructions to increase the operating frequency, reduce the pressure and temperature of the chimney core evaporator 151, increase the heat exchange temperature difference between the liquid refrigerant and the flue gas, and reduce the flue gas temperature to the target value. S12: When the flue gas temperature stabilizes at the preset value, the main controller 30 stops outputting commands, and the compressor 10 continues to operate at the current frequency; S13: The main controller 30 adopts a combined feedforward control strategy and closed-loop control strategy; S131: Feedforward control strategy: The boiler's rated load is P N The main controller 30 divides the boiler's operating load range into a first load segment, a second load segment, and a third load segment; wherein, the first load segment is 20%P. N To less than 40% P N In this stage, combustion is incomplete, resulting in small flue gas volume, low flue gas temperature, high inertia, and strong hysteresis, making it prone to oscillation and liquid carryover risks; the second load stage is 40% P. N To less than 70% P N The boiler operates in its economical zone, with stable combustion, consistent flue gas parameters, and optimal linearity in heat transfer characteristics, representing the baseline operating condition. The third load range is 70% P. N Up to 110%P N When the boiler operates at full load or overload, the flue gas volume is large, the flue gas temperature is high, the heat exchange is large, and the load change rate is fast, requiring high response speed. The main controller 30 adopts the PID algorithm and configures the corresponding integral and derivative parameters for each load segment to control the compressor 10 to adapt to the dynamic characteristics of the boiler under the first load segment, the second load segment, and the third load segment, thereby improving the regulation stability. Within the full load range of 20%-110% of the boiler, a matching relationship between the boiler load command and the compressor reference frequency is established, and the corresponding reference frequency is obtained by interpolation calculation for non-range fixed-point loads. The matching relationship between boiler load commands and compressor reference frequencies can be obtained through conventional field calibration methods in this field, requiring no creative effort. For example, during the commissioning phase, at least three load points can be selected within the boiler's full-load operating range. These load points include the endpoints of each load segment and at least one intermediate point, allowing the boiler to operate stably at each load point. After the main controller 30 stabilizes through closed-loop regulation of the outlet flue gas temperature, the operating frequency of the compressor 10 at this time is recorded; this is the reference frequency corresponding to that load point. By fitting all the calibrated load-frequency correspondence points, the matching relationship within the full-load range can be obtained. For uncalibrated intermediate load points, the corresponding reference frequency can be calculated using linear interpolation or other conventional interpolation methods.

[0062] When the boiler load changes abruptly, the feedforward unit can respond quickly and pre-adjust the frequency. S132: Closed-loop composite control strategy: Based on the reference frequency determined in step S131, closed-loop PID regulation is performed according to the measured temperature of the flue gas outlet of the chimney core evaporator 151 to achieve precise control of the compressor operating frequency. The PID control module built into the main controller 30 uses the target temperature at the flue gas outlet (preset value, e.g., 30℃) as the control objective and the actual measured temperature at the flue gas outlet as the process feedback value. The main controller 30 uses the deviation between the measured temperature and the target temperature as the input to the PID algorithm, and after proportional, integral, and derivative operations, outputs a frequency correction value. The final compressor operating frequency value is the sum of the reference frequency and the frequency correction value.

[0063] To ensure stability, the frequency correction of the PID adjustment is limited to within ±10% of the reference frequency. The main controller 30 performs PID calculations once per second to ensure response speed while avoiding oscillations caused by excessively rapid adjustments.

[0064] In order to achieve the best control effect across the full load range, the PID parameters (proportional P, integral time I, derivative time D) of the main controller 30 are segmented and automatically switched according to the load range of the boiler (first load segment, second load segment, third load segment). The specific parameters are pre-calibrated through factory bench testing and fixed in the controller.

[0065] Through factory bench testing, four sets of core parameters were calibrated for each section: 1. PID parameters of the main controller: In the first load segment, the proportional gain P is increased, the integral time I is lengthened, and the derivative D is disabled to match the large inertia characteristics; in the second load segment, the optimal reference parameters for all operating conditions are adopted; in the third load segment, the proportional gain P is reduced, the integral time I is shortened, and the micro derivative D is enabled to improve the response speed. The specific calibration uses the second load section of the boiler as the baseline operating condition, and the critical proportional gain method is used to tune the optimal parameters for the entire operating condition (e.g., proportional gain P=1.5, integral time I=1.0 min, derivative time D=0.1 min). To address the characteristics of high flue gas inertia and strong hysteresis in the first load section, the proportional gain is reduced to 0.8, the integral time is lengthened to 3.0 min, and the derivative is disabled. To meet the requirement of fast response in the third load section, the proportional gain is increased to 2.0, the integral time is shortened to 0.5 min, and the micro-derivative is enabled (0.2 min). Through factory bench testing, the PID parameters and frequency variation limits are calibrated and solidified in each load range. During operation, the main controller automatically switches parameter groups according to the real-time boiler load rate, thereby stably controlling the flue gas outlet temperature at 30±1℃ across the entire load range, while ensuring priority intervention at the safety red line, achieving the optimal balance between safety and efficiency. 2. Feedforward compensation coefficient: The first load segment uses a small coefficient for fine-tuning, the second load segment uses a base coefficient, and the third load segment uses a large coefficient to increase the pre-adjustment range.

[0066] To overcome the lag of simple PID control during sudden changes in boiler load, the main controller 30 introduces load feedforward compensation. The feedforward compensation coefficient is dimensionless, and the coefficient for the second load segment is calibrated to 1.0 (baseline coefficient) based on the steady-state response characteristics of the second load segment. Due to the large inertia and strong lag in the first load segment, a small coefficient of 0.3-0.6 is used for fine-tuning to avoid excessive feedforward causing oscillations. Due to the high flue gas velocity and drastic changes in heat exchange in the third load segment, a large coefficient of 1.5-2.0 is used to increase the pre-adjustment range.

[0067] 3. Flue gas target temperature: The first load section is set at 32℃ to avoid energy efficiency deterioration due to excessively low evaporation temperature; the second load section is set at 30℃ (baseline value); the third load section is set at 28℃ to utilize high flue gas temperature conditions for deep cooling and efficiency improvement. 4. Preset values ​​for superheat of the first PID controller and the second PID controller (set according to the boiler's operating load range into the first load segment, the second load segment and the third load segment): The first load segment is set to 6℃ to increase the safety margin and prevent liquid carryover; the second load segment is set to 5℃ as the baseline value; the third load segment is set to 4℃ to maximize the utilization rate of the heat exchange area.

[0068] To avoid repeated parameter switching due to load fluctuations at the critical point of the interval, a ±5% hysteresis rule is adopted: the switch from the first load segment to the second load segment is triggered when the load continues to rise to 45%; the switch from the second load segment to the first load segment is triggered when the load continues to fall to 35%; the switch from the second load segment to the third load segment is triggered when the load continues to rise to 75%; and the switch from the third load segment to the second load segment is triggered when the load continues to fall to 65%.

[0069] The boiler's own static load feedforward control system collects two pre-load signals in real time: the first signal is the boiler operating load command output by the boiler burner PLC, and its range corresponds to 0%-110% of the boiler's rated load; the second signal is the measured flue gas temperature at the inlet of the chimney core evaporator (151); both signals are connected to the boiler's own programmable logic controller (PLC) in the form of a 4-20mA standard current loop. Within the boiler's full load range of 20%-110%, a 1:1 linear correspondence is established between the boiler load command and the reference frequency of compressor 10. The reference frequency of compressor 10 is its standard operating frequency under rated conditions. A pre-calibration matrix is ​​formed, with 20% load corresponding to 10Hz. Typical calibration points in this embodiment are: 100% load corresponding to 55Hz, 70% load corresponding to 40Hz, and 30% load corresponding to 25Hz. For intermediate loads outside the calibration points, a linear interpolation method is used to calculate the corresponding reference frequency. Under the same load conditions, the inlet flue gas temperature of the chimney core evaporator 151 is introduced to correct the reference frequency. The correction rule is: based on the deviation between the measured inlet flue gas temperature and the target flue gas temperature, a fine adjustment of no more than ±5% is applied to the reference frequency.

[0070] When the boiler load changes abruptly, the feedforward unit does not need to wait for feedback on the flue gas outlet temperature change. The feedforward unit can respond quickly and pre-adjust the frequency by about 90% of the amplitude.

[0071] To ensure operational safety, the reference frequency output by the feedforward unit is locked within the safe operating range of 30Hz-50Hz. When the calculated reference frequency exceeds this range, or when a preset safety threshold (such as exceeding flue gas temperature limits or abnormal pressure) is triggered, the following actions are immediately executed: the feedforward output signal is blocked; and the system seamlessly switches to the pure feedback control mode where the main controller operates independently. When a boiler load signal malfunctions (such as signal loss, over-range operation, or sudden abnormal changes), the feedforward unit automatically exits operation, maintaining the basic control functions unaffected, and the main controller continues to complete the closed-loop regulation.

[0072] Liquid carryover refers to liquid refrigerant entering the compressor 10 without being completely evaporated, which may cause liquid slugging damage.

[0073] Closed-loop composite control strategy: Obtain the flue gas outlet temperature of the chimney core evaporator 151; when the flue gas temperature is greater than 30℃ (preset value), the waste heat recovery is insufficient. The main controller 30 calculates and outputs instructions through the PID algorithm. The compressor 10 receives the instructions to increase the operating frequency, reduce the pressure and temperature of the refrigerant, increase the heat exchange temperature difference between the liquid refrigerant and the flue gas, and reduce the flue gas temperature to the target value (30℃). When the flue gas temperature stabilizes at 30℃ (preset value), the main controller 30 stops outputting commands, and the compressor 10 maintains the current frequency to keep the current operating conditions stable. When the safety red line is triggered, such as when the condensate temperature drops to 6℃ or the flue gas temperature drops to 26℃, the main controller 30 outputs a command to stop increasing the frequency of the compressor 10 or slightly decrease the frequency. Slightly decreasing means that the main controller 30 adjusts the compressor 10 based on the current operating frequency of the compressor 10 by a smaller value of no more than 5% or 3Hz, and after each adjustment, the compressor 10 runs stably for no less than 30 seconds before making the next judgment. The main controller 30 is only responsible for controlling the operating frequency of the compressor 10 and does not interfere with the adjustment of the electronic expansion valve 141. It is completely decoupled from the first PID controller 31 and the second PID controller 32, thus eliminating control conflicts from the architecture. The control parameters of the main controller 30 include: Preset value (SP): Target outlet temperature of flue gas for chimney core evaporator 151 is 30℃; Process value (PV): Measured flue gas temperature at the outlet of the 151-type chimney evaporator; Output value (MV): Target operating frequency of compressor 10; Control method: Direct drive compressor 10; Cycle time: 1 second (medium-speed cycle, balancing response speed and stability); S2: Obtain the superheat of the refrigerant at the discharge end of the chimney core evaporator 151; When the superheat exceeds the preset value, it indicates that the liquid refrigerant supply is insufficient and the heat exchange area is not fully utilized. The first PID controller 31 obtains the information to increase the opening degree through the PID algorithm. The corresponding electronic expansion valve 141 increases the opening degree according to the received information to increase the liquid refrigerant flow and reduce the superheat of the refrigerant in the chimney core evaporator 151 to 3-5℃. When the superheat is less than the preset value, it indicates that the liquid refrigerant supply is excessive and there is a risk of liquid returning to gas. The first PID controller 31 obtains the information to reduce the opening degree through the PID algorithm. The corresponding electronic expansion valve 141 reduces the opening degree according to the received information to reduce the liquid refrigerant flow and increase the superheat of the refrigerant in the chimney core evaporator 151 to 3-5℃. The preset values ​​are set based on the superheat of the first load segment, the second load segment, and the third load segment; When the detected superheat is below 2℃ (liquid hammer red line), the forced valve shut-off interlock is immediately triggered (controlling the corresponding electronic expansion valve 141 to close), the first PID controller 31 stops working, and directly forces the corresponding electronic expansion valve 141 to close until the superheat recovers to above 3℃; S3: Obtain the superheat of the refrigerant at the discharge end of the water tank submersible evaporator 152; When the superheat exceeds the preset value, it indicates that the liquid refrigerant supply is insufficient and the heat exchange area is not fully utilized. The second PID controller 32 obtains the opening information through the PID algorithm, and the corresponding electronic expansion valve 141 increases the opening according to the received opening information, increases the liquid refrigerant flow, and reduces the superheat of the refrigerant in the water tank submerged evaporator 152 to 3-5℃. When the superheat is less than 3℃ (preset value), it indicates that the liquid refrigerant supply is excessive and there is a risk of liquid returning to gas. The second PID controller 32 obtains the information to reduce the opening degree through the PID algorithm. The corresponding electronic expansion valve 141 reduces the opening degree according to the received information to reduce the liquid refrigerant flow and increase the superheat of the refrigerant in the water tank submerged evaporator 152 to 3-5℃. The preset values ​​are set based on the superheat of the first load segment, the second load segment, and the third load segment; When the detected superheat is below 2°C (liquid hammer red line), the forced valve shut-off interlock is immediately triggered, the second PID controller 32 stops working, and the corresponding electronic expansion valve 141 is directly forced to close through the PID algorithm until the superheat recovers to above 3°C.

[0074] The control parameters of the first PID controller 31 and the second PID controller 32 include: Preset value (SP): Target superheat of 4°C at the outlet of the chimney core evaporator 151 and the water tank submerged evaporator 152; Process value (PV): corresponds to the suction superheat. The superheat is the difference between the outlet suction temperature (measured by the corresponding integrated temperature and pressure sensor 142) and the reference evaporation temperature. The reference evaporation temperature can be converted from the compressor suction pressure. Output value (MV): corresponds to the opening command of the electronic expansion valve (0-100%). Control method: Direct drive electronic expansion valve 141; Cycle time: 100ms (high-speed loop to ensure anti-interference capability and safe response speed).

[0075] The main controller 30 adjusts the frequency of the compressor 10 to change the evaporation pressure; the first PID controller 31 and the second PID controller 32 independently adjust the opening of the corresponding electronic expansion valve 141 according to the change in evaporation pressure and the superheating requirements of the chimney core evaporator 151 and the water tank submerged evaporator 152.

[0076] The main controller 30, the first PID controller 31, and the second PID controller are all proportional-integral-derivative controllers.

[0077] The first PID controller 31 and the second PID controller 32 operate completely independently, automatically adapting to heat exchange capacity and load demand. The flue gas side heat exchange capacity of the chimney core evaporator 151 is strong and the heat exchange capacity is large (accounting for 80-85% of the total heat exchange). The first PID controller 31 automatically maintains the corresponding electronic expansion valve 141 at a large opening according to the load ratio through the PID algorithm to match the large flow rate of refrigerant. The heat exchange capacity of the water tank submerged evaporator 152 is relatively small (accounting for 15-20% of the total heat exchange). The second PID controller 32 automatically maintains the corresponding electronic expansion valve 141 at a small opening according to the load ratio through the PID algorithm to match the small flow rate of refrigerant. The sum of the load ratios of the two is 100%. The entire process does not require manual setting of the load distribution ratio, automatically achieving the optimal flow distribution between the chimney core evaporator 151 and the water tank submerged evaporator 152, fundamentally eliminating problems such as liquid grabbing, flow deviation, and liquid-carrying back gas.

[0078] It should be understood that the various forms of processes shown above can be used to reorder, add, or delete steps. For example, the steps described in this invention disclosure can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution disclosed in this invention can be achieved, and this is not limited herein.

[0079] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A deep condensing waste heat recovery device for a gas-fired boiler, characterized in that: The system includes a compressor (10), a brazed plate condenser (11), a liquid receiver (12), a dryer filter (13), a liquid delivery line (14), an evaporator (15), a discharge line (16), and a gas-liquid separator (17). The outlet of the compressor (10) is connected to the refrigerant inlet of the brazed plate condenser (11) via a pipeline. The liquid outlet of the brazed plate condenser (11) is connected to the liquid receiver (12) and the dryer filter via pipelines. The inlet end of (13) is connected, the outlet end of the dryer filter (13) is connected to the inlet end of the infusion pipeline (14) through a pipeline, the infusion end of the infusion pipeline (14) is connected to the inlet end of the evaporator (15), the outlet end of the evaporator (15) is connected to the inlet end of the gas-liquid separator (17) through the discharge pipeline (16), and the outlet end of the gas-liquid separator (17) is connected to the inlet end of the compressor (10) through a pipeline. The evaporation device (15) includes a chimney-core evaporator (151) and a water tank submerged evaporator (152) connected in parallel. The chimney-core evaporator (151) is installed inside the chimney (21) of the gas boiler (20). The water tank submerged evaporator (152) is used to receive the condensate inside the chimney (21). There are two liquid delivery pipelines (14), and the inlet ends of both liquid delivery pipelines (14) are connected to the outlet end of the dryer filter (13). The outlet end of the infusion pipeline (14) is connected to the inlet end of the chimney core evaporator (151) and the inlet end of the water tank submerged evaporator (152), respectively. There are two discharge pipelines (16). One end of the two discharge pipelines (16) is connected to the discharge end of the chimney core evaporator (151) and the discharge end of the water tank submerged evaporator (152), respectively. The other end of the two discharge pipelines (16) is connected to the inlet end of the gas-liquid separator (17).

2. The deep condensing waste heat recovery device for a gas-fired boiler according to claim 1, characterized in that: The water tank submersible evaporator (152) includes a liquid collection tank (1520), a first refrigerant coil (1521), a condensate collection pipe (1522), a condensate overflow pipe (1523), and a condensate discharge pipe (1524). The first refrigerant coil (1521) is disposed inside the liquid collection tank (1520). The refrigerant inlet end (15211) and the refrigerant outlet end (15212) of the first refrigerant coil (1521) extend out of the liquid collection tank (1520), respectively. The refrigerant inlet end (15211) is connected to the corresponding... The outlet end of the infusion pipeline (14) is connected, and the refrigerant outlet end (15212) is connected to the inlet end of the gas-liquid separator (17) through the corresponding discharge pipeline (16); the condensate collection pipe (1522) is connected to one end of the top plate of the collection tank (1520), the condensate overflow pipe (1523) is connected to the other end of the top plate of the collection tank (1520), and the condensate discharge pipe (1524) is connected to the bottom plate of the collection tank (1520) and located below the condensate overflow pipe (1523).

3. The deep condensing waste heat recovery device for a gas-fired boiler according to claim 2, characterized in that: The water tank submersible evaporator (152) further includes at least three guide plates (1525), which are arranged parallel to each other inside the liquid collection tank (1520). The at least three guide plates (1525) are perpendicular to the coiling plane of the first refrigerant coil (1521), and the first refrigerant coil (1521) passes through the at least three guide plates (1525). 25) The two adjacent flow guide plates (1525) are staggered vertically. The top of the upper flow guide plate (1525) is connected to the top plate of the liquid collection tank (1520). The bottom of the upper flow guide plate (1525) is suspended. The bottom of the lower flow guide plate (1525) is connected to the bottom plate of the liquid collection tank (1520). The top of the lower flow guide plate (1525) is suspended.

4. The deep condensing waste heat recovery device for a gas-fired boiler according to claim 3, characterized in that: The water tank submersible evaporator (152) also includes a pH monitor (1526) and a level gauge (1527). The pH monitor (1526) and the level gauge (1527) are respectively installed on both sides of the top plate of the liquid collection tank (1520). The pH monitor (1526) is installed close to the condensate collection pipe (1522).

5. The deep condensing waste heat recovery device for a gas-fired boiler according to claim 4, characterized in that: The water tank submerged evaporator (152) also includes a sodium hydroxide solution tank (1528). The outlet of the sodium hydroxide solution tank (1528) is connected to the part of the condensate collection pipe (1522) near the collection tank (1520) through a dosing pipeline. An electric regulating valve (1529) is installed on the dosing pipeline.

6. The deep condensing waste heat recovery device for a gas-fired boiler according to claim 2, characterized in that: It also includes a water collection device (18), which is installed at the flue gas inlet (22) of the chimney (21) and below the chimney core evaporator (151). The water collection device (18) includes an annular water collection plate (181), a liquid collection plate (182) and a condensate conduit (183). The annular water collection plate (181) and the liquid collection plate (182) are both installed on the inner wall of the chimney (21). The annular water collection plate (181) is located above the flue gas inlet (22), and the liquid collection plate (182) is located below the flue gas inlet (22). The annular water collection plate (181) and the liquid collection plate (182) are connected through the condensate conduit (183). The bottom end of the liquid collection plate (182) is connected to the condensate collection pipe (1522).

7. The deep condensing waste heat recovery device for a gas-fired boiler according to claim 2, characterized in that: The chimney-core evaporator (151) includes an evaporator body (1510), a flue (1511), a second refrigerant coil (1512), fins (1513), and a flange (1514). The evaporator body (1510) is installed inside the chimney (21) and located above the flue gas inlet (22). The flue (1511) is disposed inside the evaporator body (1510) and divides the evaporator body (1510) into an inner cavity (1515) and an outer cavity (1516) along the height direction of the chimney (21). The bottom ends of the inner cavity (1515) and the outer cavity (1516) are connected to the chimney (21). The top ends of the inner cavity (1515) and the outer cavity (1516) are connected through the inner and outer cavity communication port (1514). 7) The flue gas is finally discharged from the top of the evaporator body (1510) into the upper part of the chimney (21). The inner and outer cavity connection port (1517) is opened on the flue gas duct (1511). The second refrigerant coil (1512) is arranged along the height direction of the flue gas duct (1511). There are two flanges (1514). The two flanges (1514) are respectively fixed at the top and bottom of the evaporator body (1510). The two flanges (1514) are respectively connected to the flange on the inner wall of the chimney (21). The fins (1513) are arranged on the inner wall of the evaporator body (1510) and / or the fins (1513) are arranged on the inner and outer walls of the flue gas duct (1511).

8. The deep condensing waste heat recovery device for a gas-fired boiler according to claim 7, characterized in that: Each of the infusion lines (14) is equipped with an electronic expansion valve (141), and both the infusion lines (14) and the discharge lines (16) are equipped with integrated temperature and pressure sensors (142). The integrated temperature and pressure sensors (142) are located close to the corresponding collection tank (1520) and the evaporator body (1510), and the electronic expansion valve (141) is located upstream of the corresponding integrated temperature and pressure sensor (142).

9. The deep condensing waste heat recovery device for a gas-fired boiler according to claim 1, characterized in that: The inlet end of the brazed plate condenser (11) is connected to the water source (115) through the inlet pipe (110), and the outlet end of the brazed plate condenser (11) is connected to the external heating system (116) through the outlet pipe (111). An electronic descaling device (112), a Y-shaped filter (113) and an electric valve (114) are sequentially arranged on the inlet pipe (110), and the electric valve (114) is located close to the brazed plate condenser (11).

10. A method for controlling deep condensing waste heat recovery in a gas-fired boiler, applied to the deep condensing waste heat recovery device for a gas-fired boiler as described in claims 1 to 9, characterized in that: S1: Obtain the flue gas outlet temperature of the chimney core evaporator (151); S11: When the flue gas temperature is greater than the preset value, the main controller (30) calculates and outputs instructions through the PID algorithm. The compressor (10) receives the instructions to increase the operating frequency, reduce the pressure and temperature of the chimney core evaporator (151), increase the heat exchange temperature difference between the liquid refrigerant and the flue gas, and reduce the flue gas temperature to the target value. S12: When the flue gas temperature stabilizes at the preset value, the main controller (30) stops outputting commands, and the compressor (10) continues to operate at the current frequency; S13: The main controller (30) adopts a feedforward control strategy and a closed-loop composite control strategy; S131: Feedforward control strategy: The boiler's rated load is P N The main controller (30) divides the boiler's operating load range into at least three load ranges. The main controller (30) uses a PID algorithm and configures corresponding integral and derivative parameters for each load range to control the compressor (10) to adapt to the dynamic characteristics of the boiler under different load ranges and improve regulation stability. Within the full load range of 20%-110% of the boiler, a matching relationship between the boiler load command and the compressor reference frequency is established, and interpolation is used to obtain the corresponding reference frequency for non-calibrated intermediate load points. When the boiler load changes abruptly, the feedforward unit in the main controller (30) can respond quickly and pre-adjust the frequency in advance; S132: Closed-loop composite control strategy: Based on the reference frequency determined in step S131, closed-loop PID regulation is performed according to the measured temperature of the flue gas outlet of the chimney core evaporator (151) to achieve precise control of the compressor operating frequency. S2: Obtain the superheat of the refrigerant at the discharge end of the chimney core evaporator (151); When the superheat is greater than the preset value, the first PID controller (31) obtains the opening information through the PID algorithm, and the corresponding electronic expansion valve (141) increases the opening according to the received opening information, thereby reducing the temperature of the chimney core evaporator (151). When the superheat is less than the preset value, the first PID controller (31) obtains the information to reduce the opening degree through the PID algorithm, and the corresponding electronic expansion valve (141) reduces the opening degree according to the received information to increase the temperature of the chimney core evaporator (151). S3: Obtain the superheat of the refrigerant at the discharge end of the water tank submersible evaporator (152); When the superheat exceeds the preset value, the second PID controller (32) obtains the opening information through the PID algorithm, and the corresponding electronic expansion valve (141) increases the opening according to the received opening information, thereby reducing the temperature of the water tank submerged evaporator (152). When the superheat is less than the preset value, the second PID controller (32) obtains the information to reduce the opening degree through the PID algorithm. The corresponding electronic expansion valve (141) reduces the opening degree according to the received information to increase the temperature of the water tank submerged evaporator (152).

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