Flue gas deep waste heat recovery system with humidification type air heater for gas heating furnace

Abstract

The utility model discloses a flue gas deep waste heat recovery system with a humidification type air heater for a gas heating furnace, and belongs to the technical field of waste heat recovery of industrial heating furnaces. According to the system, high-temperature and high-humidity flue gas of a heating furnace is sequentially fed into a front energy saver and a flue gas deep waste heat recovery tower for heat exchange, and the flue gas deep waste heat recovery tower is discharged after being subjected to more than two stages of spraying heat exchange from bottom to top; a waste heat water inlet and a waste heat water outlet of the front energy saver are respectively connected with a water outlet and a water inlet of a high-temperature sensible heat air heater of the heating furnace; a waste heat water outlet of the flue gas deep waste heat recovery tower is respectively connected with high-temperature side inlets of the process water heater and the low-temperature sensible heat air heater; the high-temperature side outlets of the two are connected, are connected with the water inlet of a medium-temperature spraying device of the flue gas deep waste heat recovery tower and are connected with the inlet of a humidifying spraying device of the humidifying type air heater, and the water outlet of the humidifying type air heater is connected with the water inlet of a low-temperature spraying device of the flue gas deep waste heat recovery tower; and the air outlet is connected with an air inlet of the low-temperature sensible heat air heater.

Description

Technical Field

[0001] This utility model relates to a deep waste heat recovery system for flue gas from a gas-fired heating furnace with a humidifying air heater, belonging to the field of waste heat recovery technology for industrial heating furnaces. Background Technology

[0002] Many industrial enterprises, such as chemical plants and steel mills, have gas-fired furnaces used to heat liquid, gaseous, or solid materials. The exhaust gas temperature of these furnaces is often high (e.g., 100–300°C) and contains a large amount of water vapor, resulting in significant loss of both latent and sensible heat. To deeply recover this high-temperature, high-humidity waste heat from the flue gas, commonly used methods include: indirect-contact low-temperature economizers or energy-saving devices, and flue gas condensation heat recovery devices based on absorption heat pumps. However, the former suffers from corrosion problems and high costs of heat exchange materials; the latter has drawbacks such as the need for large heat sources to drive the absorption heat pump, high costs leading to long investment recovery periods.

[0003] Heating furnace air intake, other in-plant process air intake, process water intake, or return water from the heating network of the town's centralized heating outside the plant requires a lot of high-grade heat energy such as steam. If waste heat from flue gas is used for heating, a lot of high-grade heat energy can be saved.

[0004] In addition, the flue gas contains a large amount of pollutants such as water vapor, escaped hydrogen chloride, and soluble fine particulate matter, and is also considered to be one of the important potential sources of atmospheric haze. Therefore, it is necessary to carry out in-depth purification, or even achieve near-zero emissions of flue gas pollutants, and achieve substantial "fairing of flue gas". Utility Model Content

[0005] The purpose and task of this utility model is to use a multi-stage heat exchange method to perform graded waste heat recovery of high-temperature and high-humidity flue gas from a gas-fired heating furnace, which is then used to heat the gas-fired heating furnace's intake air, other process intake air or process water, and heat network return water, thereby achieving deep waste heat recovery and substantial whitening treatment of the flue gas.

[0006] The specific description of this utility model is as follows: A deep waste heat recovery system for flue gas from a gas-fired heating furnace with a humidifying air heater, comprising two parts: a gas-fired heating furnace and its auxiliary subsystem, and a deep waste heat recovery heating and process heating subsystem. The gas-fired heating furnace and its auxiliary subsystem includes a gas-fired heating furnace 101, a material heating module 102, a flue gas treatment device 103, an induced draft fan 104, and a forced draft fan 105. The deep waste heat recovery heating and process heating subsystem includes a pre-energy saver 1, an energy saver circulation pump 2, a high-temperature sensible heat air heater 3, a low-temperature sensible heat air heater 4, a deep waste heat recovery tower 5, a medium-temperature waste water pump 9, and connecting pipes and components. The air inlet pipe of the low-temperature sensible heat air heater 4 is connected to ambient air A through a bypass air inlet. The air outlet of the low-temperature sensible heat air heater 4 is connected to the air inlet of the forced draft fan 105 through a pipe of low-temperature superheated air C. The air outlet of the forced draft fan 105 is connected to the air outlet of the forced draft fan 105 through a pipe of high-temperature superheated air D. The gas-fired heating furnace 101 is connected to the air inlet. The flue gas outlet of the gas-fired heating furnace 101 is connected to the flue gas inlet of the downstream flue gas treatment equipment 103 via a high-temperature flue gas E pipe. The flue gas outlet of the downstream flue gas treatment equipment 103 is connected to the flue gas inlet of the pre-energy saver 1. The flue gas outlet of the pre-energy saver 1 is connected to the flue gas inlet of the induced draft fan 104 via a medium-temperature flue gas F pipe. The flue gas outlet of the induced draft fan 104 is connected to the flue gas deep waste heat recovery tower 5. The top of the deep waste heat recovery tower 5... The section is a smoke outlet section 26, which has a smoke outlet for low-temperature ultra-clean flue gas Q; the waste water outlet of the flue gas deep waste heat recovery tower 5 is connected to the inlet of the medium-temperature waste water pump 9 through the waste heat outlet pipe 17, and the outlet of the medium-temperature waste water pump 9 is connected to the heating water inlet of the low-temperature sensible heat heater 4; the outlet of the pre-energy saver 1 is connected to the heating water inlet of the high-temperature sensible heat heater 3 through the energy saver circulation pump 2, and the heating water outlet of the high-temperature sensible heat heater 3 is connected to the inlet of the pre-energy saver 1.

[0007] The deep waste heat recovery heating and process heating subsystem also includes a humidifying air heater 6, a process water heater 7, and a low-temperature waste heat pump 10. The bottom of the humidifying air heater 6 is a fresh air tower bottom water tank 11. Above the liquid surface of the fresh air tower bottom water tank 11 is an air inlet section 12. An air inlet for ambient air A is opened on the side of the air inlet section 12. The upper part of the air inlet section 12 consists of a spray humidification section 13, a humidification spray device 14, a fresh air humidity regulating device 15, and an air outlet section 16. The air outlet section 16 has an air outlet for saturated humid air B, which is connected to the air inlet of the low-temperature sensible heat air heater 4. The waste heat circulating water outlet of the fresh air tower bottom water tank 11 is connected to the inlet of the low-temperature spray device 24 of the deep waste heat recovery tower 5 via the low-temperature waste heat pump 10. The inlet of the humidifying spray device 14 of the deep waste heat recovery tower 5 is connected to... The high-temperature outlet of the process water heater 7, the heating water outlet of the low-temperature sensible heat heater 4, and the inlet of the medium-temperature spray device 22 of the flue gas deep waste heat recovery tower 5 are connected. The high-temperature inlet of the process water heater 7 is connected to the outlet of the medium-temperature waste water pump 9. The low-temperature inlet of the process water heater 7 is connected to the main pipe of the process water inlet G. The low-temperature outlet of the process water heater 7 is connected to the main pipe of the process water outlet H. A flue gas tower bottom water pool 19 is provided at the bottom of the flue gas deep waste heat recovery tower 5. The flue gas tower bottom water pool 19 has a waste heat circulating water outlet connected to the waste heat outlet water pipe 17. Above the liquid surface of the flue gas tower bottom water pool 19 is the flue gas inlet section 20. The upper part of the flue gas inlet section 20 consists of a medium-temperature heat exchange section 21, a medium-temperature spray device 22, a low-temperature heat exchange section 23, a low-temperature spray device 24, a flue gas humidity regulating device 25, and a flue gas outlet section 26.

[0008] The humidifying air heater 6 and the flue gas deep waste heat recovery tower 5 are either set up separately or as an integrated unit. If they are set up as an integrated unit, a tower partition plate 18 is set between the humidifying air heater 6 and the flue gas deep waste heat recovery tower 5, and the waste heat outlet water pipe 17 is set inside or outside the humidifying air heater 6.

[0009] The inlet of the medium-temperature waste water pump 9 is also connected to the outlet of the water quality conditioning device 8, which is also equipped with an inlet for the water quality conditioning agent K.

[0010] The main pipe of the process water inlet G is connected to the main pipe of the heating network water return, or to the main pipe of the demineralized water makeup water or the main pipe of the steam condensate water.

[0011] The material heating module 102 is located inside the shell of the gas heating furnace 101 and has an inlet for feeding I and an outlet for discharging O.

[0012] The spray humidification section 13, the medium-temperature heat exchange section 21, and the low-temperature heat exchange section 23 are vertically arranged counter-current heat exchange structures composed of fresh air or flue gas and spray water, with the interior using hollow sections or packing structures.

[0013] The spray humidification section 13, the medium-temperature heat exchange section 21 and the low-temperature heat exchange section 23 adopt a single-layer trough-type water distribution structure, a trough-type structure or a water distribution structure composed of N layers of nozzles, where N is greater than or equal to 1.

[0014] The pre-energy saver 1 and the low-temperature sensible heat heater 4 adopt the structure of a fluoroplastic coil heat exchanger, a carbon-based material coil heat exchanger, a fluoroplastic steel coil heat exchanger, a stainless steel heat exchanger, or an ND steel heat exchanger with corrosion resistance on the smoke and flue side.

[0015] This invention achieves graded heat recovery and utilization of high-temperature, high-humidity flue gas from a gas-fired boiler. The waste heat from the higher-temperature flue gas is preferentially used for preheating the boiler's intake air to save fuel consumption. The waste heat can also be used to heat process water, including heating return water or demineralized water, steam condensate, and other process water requiring heating within the plant, typically to 50–70°C or higher, before being sent to downstream supplementary heating equipment. Using this invention, the overall system heat utilization efficiency of the gas-fired boiler can be increased from the usual 80%–90% to 105%–110% (calculated based on the lower heating value of the fuel). Furthermore, this patent can ultimately reduce the flue gas temperature to 7–35°C, achieving deep waste heat recovery and near-zero pollutant emissions. Attached Figure Description

[0016] Figure 1 This is a system schematic diagram of this utility model.

[0017] Figure 1 The component numbers and names are as follows.

[0018] 1. Pre-energy saver; 2. Energy saver circulation pump; 3. High-temperature sensible heat heater; 4. Low-temperature sensible heat heater; 5. Flue gas deep waste heat recovery tower; 6. Humidifying heater; 7. Process water heater; 8. Water quality conditioning device; 9. Medium-temperature waste water pump; 10. Low-temperature waste water pump; 11. Fresh air tower bottom water tank; 12. Air inlet section; 13. Spray humidification section; 14. Humidification spray device; 15. Fresh air humidity conditioning device; 16. Air outlet section; 17. Waste heat outlet pipe; 18. Tower partition; 19. Flue gas tower bottom water tank; 20. Flue gas inlet section; 21. Medium-temperature heat exchange section. 21. Medium-temperature spray device 22. Low-temperature heat exchange section 23. Low-temperature spray device 24. Flue gas humidity control device 25. Smoke outlet section 26. Gas-fired heating furnace 101. Material heating module 102. Post-furnace flue gas treatment equipment 103. Exhaust fan 104. Forced fan 105. Ambient air A. Saturated humid air B. Low-temperature superheated air C. High-temperature superheated air D. High-temperature flue gas E. Medium-temperature flue gas F. Process water inlet G. Process water outlet H. Water quality conditioner K. Feed I. Discharge O. Low-temperature ultra-clean flue gas Q. Detailed Implementation

[0019] Figure 1 This is a system schematic diagram and embodiment of the present invention.

[0020] The specific embodiment 1 of this utility model is as follows.

[0021] The specific description of this utility model is as follows: A deep waste heat recovery system for flue gas from a gas-fired heating furnace with a humidifying air heater, comprising two parts: a gas-fired heating furnace and its auxiliary subsystem, and a deep waste heat recovery heating and process heating subsystem. The gas-fired heating furnace and its auxiliary subsystem includes a gas-fired heating furnace 101, a material heating module 102, a flue gas treatment device 103, an induced draft fan 104, and a forced draft fan 105. The deep waste heat recovery heating and process heating subsystem includes a pre-energy saver 1, an energy saver circulation pump 2, a high-temperature sensible heat air heater 3, a low-temperature sensible heat air heater 4, a deep waste heat recovery tower 5, a medium-temperature waste water pump 9, and connecting pipes and components. The air inlet pipe of the low-temperature sensible heat air heater 4 is connected to ambient air A through a bypass air inlet. The air outlet of the low-temperature sensible heat air heater 4 is connected to the air inlet of the forced draft fan 105 through a pipe of low-temperature superheated air C. The air outlet of the forced draft fan 105 is connected to the air outlet of the forced draft fan 105 through a pipe of high-temperature superheated air D. The gas-fired heating furnace 101 is connected to the air inlet. The flue gas outlet of the gas-fired heating furnace 101 is connected to the flue gas inlet of the downstream flue gas treatment equipment 103 via a high-temperature flue gas E pipe. The flue gas outlet of the downstream flue gas treatment equipment 103 is connected to the flue gas inlet of the pre-energy saver 1. The flue gas outlet of the pre-energy saver 1 is connected to the flue gas inlet of the induced draft fan 104 via a medium-temperature flue gas F pipe. The flue gas outlet of the induced draft fan 104 is connected to the flue gas deep waste heat recovery tower 5. The top of the deep waste heat recovery tower 5... The section is a smoke outlet section 26, which has a smoke outlet for low-temperature ultra-clean flue gas Q; the waste water outlet of the flue gas deep waste heat recovery tower 5 is connected to the inlet of the medium-temperature waste water pump 9 through the waste heat outlet pipe 17, and the outlet of the medium-temperature waste water pump 9 is connected to the heating water inlet of the low-temperature sensible heat heater 4; the outlet of the pre-energy saver 1 is connected to the heating water inlet of the high-temperature sensible heat heater 3 through the energy saver circulation pump 2, and the heating water outlet of the high-temperature sensible heat heater 3 is connected to the inlet of the pre-energy saver 1.

[0022] The deep waste heat recovery heating and process heating subsystem also includes a humidifying air heater 6, a process water heater 7, and a low-temperature waste heat pump 10. The bottom of the humidifying air heater 6 is a fresh air tower bottom water tank 11. Above the liquid surface of the fresh air tower bottom water tank 11 is an air inlet section 12. An air inlet for ambient air A is opened on the side of the air inlet section 12. The upper part of the air inlet section 12 consists of a spray humidification section 13, a humidification spray device 14, a fresh air humidity regulating device 15, and an air outlet section 16. The air outlet section 16 has an air outlet for saturated humid air B, which is connected to the air inlet of the low-temperature sensible heat air heater 4. The waste heat circulating water outlet of the fresh air tower bottom water tank 11 is connected to the inlet of the low-temperature spray device 24 of the deep waste heat recovery tower 5 via the low-temperature waste heat pump 10. The inlet of the humidifying spray device 14 of the deep waste heat recovery tower 5 is connected to... The high-temperature outlet of the process water heater 7, the heating water outlet of the low-temperature sensible heat heater 4, and the inlet of the medium-temperature spray device 22 of the flue gas deep waste heat recovery tower 5 are connected. The high-temperature inlet of the process water heater 7 is connected to the outlet of the medium-temperature waste water pump 9. The low-temperature inlet of the process water heater 7 is connected to the main pipe of the process water inlet G. The low-temperature outlet of the process water heater 7 is connected to the main pipe of the process water outlet H. A flue gas tower bottom water pool 19 is provided at the bottom of the flue gas deep waste heat recovery tower 5. The flue gas tower bottom water pool 19 has a waste heat circulating water outlet connected to the waste heat outlet water pipe 17. Above the liquid surface of the flue gas tower bottom water pool 19 is the flue gas inlet section 20. The upper part of the flue gas inlet section 20 consists of a medium-temperature heat exchange section 21, a medium-temperature spray device 22, a low-temperature heat exchange section 23, a low-temperature spray device 24, a flue gas humidity regulating device 25, and a flue gas outlet section 26.

[0023] The humidifying air heater 6 and the flue gas deep waste heat recovery tower 5 are either set up separately or as an integrated unit. If they are set up as an integrated unit, a tower partition plate 18 is set between the humidifying air heater 6 and the flue gas deep waste heat recovery tower 5, and the waste heat outlet water pipe 17 is set inside or outside the humidifying air heater 6.

[0024] The inlet of the medium-temperature waste water pump 9 is also connected to the outlet of the water quality conditioning device 8, which is also equipped with an inlet for the water quality conditioning agent K.

[0025] The main pipe of the process water inlet G is connected to the main pipe of the heating network water return, or to the main pipe of the demineralized water makeup water or the main pipe of the steam condensate water.

[0026] The material heating module 102 is located inside the shell of the gas heating furnace 101 and has an inlet for feeding I and an outlet for discharging O.

[0027] The spray humidification section 13, the medium-temperature heat exchange section 21, and the low-temperature heat exchange section 23 are vertically arranged counter-current heat exchange structures composed of fresh air or flue gas and spray water, with the interior using hollow sections or packing structures.

[0028] The spray humidification section 13, the medium-temperature heat exchange section 21 and the low-temperature heat exchange section 23 adopt a single-layer trough-type water distribution structure, a trough-type structure or a water distribution structure composed of N layers of nozzles, where N is greater than or equal to 1.

[0029] The pre-energy saver 1 and the low-temperature sensible heat heater 4 adopt the structure of a fluoroplastic coil heat exchanger, a carbon-based material coil heat exchanger, a fluoroplastic steel coil heat exchanger, a stainless steel heat exchanger, or an ND steel heat exchanger with corrosion resistance on the smoke and flue side.

[0030] It should be noted that this utility model proposes to realize deep condensation heat recovery of flue gas from a gas-fired heating furnace and use it for heating the furnace intake air, or heating other process intake air, water, or heat network return water. However, this overall solution can have different specific implementation measures and different structural implementation devices. The above-mentioned specific implementation method is only one of them. Any other similar simple modifications, such as adding or removing one or two stages in a multi-stage heat exchange process, simple adjustments to the series or parallel relationship between stages on the heated water side; using different heat exchange element structures and their simple modifications; or simply adjusting the source of waste hot water or process air and the number of stages for heating; or modifications that can be conceived by ordinary professionals, or applying the same or similar structure to different flue gas or exhaust types, and other similar applications, all fall within the protection scope of this utility model.

Claims

1. A deep waste heat recovery system for flue gas from a gas-fired heating furnace with a humidifying air heater, comprising two parts: a gas-fired heating furnace and its auxiliary subsystem, and a deep waste heat recovery heating and process heating subsystem. The gas-fired heating furnace and its auxiliary subsystem include a gas-fired heating furnace (101), a material heating module (102), a flue gas treatment device (103), an induced draft fan (104), and a forced draft fan (105). Its features are: The aforementioned deep waste heat recovery heating and process heating subsystem includes a pre-energy saver (1), an energy saver circulation pump (2), a high-temperature sensible heat heater (3), a low-temperature sensible heat heater (4), a deep waste heat recovery tower (5), a medium-temperature waste water pump (9), and their connecting pipes and components. The air inlet pipe of the low-temperature sensible heat heater (4) is connected to ambient air (A) via a bypass air inlet. The air outlet of the low-temperature sensible heat heater (4) is connected to the air inlet of a blower (105) via a low-temperature superheated air (C) pipe. The air outlet of the blower (105) is connected to the air inlet of a gas-fired furnace (101) via a high-temperature superheated air (D) pipe. The flue gas outlet of the gas-fired furnace (101) is connected to the flue gas inlet of a downstream flue gas treatment device (103) via a high-temperature flue gas (E) pipe. The flue gas outlet of the downstream flue gas treatment device (103) is connected to... The inlet of the pre-energy saver (1) is connected, and the outlet of the pre-energy saver (1) is connected to the inlet of the induced draft fan (104) through a pipe for medium-temperature flue gas (F). The outlet of the induced draft fan (104) is connected to the inlet of the deep waste heat recovery tower (5). The top of the deep waste heat recovery tower (5) is the outlet section (26), and the outlet section (26) has an outlet for low-temperature ultra-clean flue gas (Q). The waste hot water outlet of (5) is connected to the inlet of the medium-temperature waste hot water pump (9) through the waste hot water outlet pipe (17), and the outlet of the medium-temperature waste hot water pump (9) is connected to the heating water inlet of the low-temperature sensible heat heater (4); the outlet of the pre-energy saver (1) is connected to the heating water inlet of the high-temperature sensible heat heater (3) through the energy saver circulation pump (2), and the heating water outlet of the high-temperature sensible heat heater (3) is connected to the inlet of the pre-energy saver (1).

2. The deep waste heat recovery system for flue gas from a gas-fired heating furnace with a humidifying air heater as described in claim 1, characterized in that... The aforementioned flue gas deep waste heat recovery heating and process heating subsystem also includes a humidifying air heater (6), a process water heater (7), and a low-temperature waste water pump (10). The bottom of the humidifying air heater (6) is a fresh air tower bottom water tank (11), and above the liquid surface of the fresh air tower bottom water tank (11) is an air inlet section (12). An air inlet for ambient air (A) is opened on the side of the air inlet section (12). The upper part of the air inlet section (12) consists of a spray humidification section (13) and a humidification spray device (14). 4) Fresh air humidity control device (15) and air outlet section (16), wherein the air outlet section (16) is provided with an air outlet for saturated humid air (B), which is connected to the air inlet of the low-temperature sensible heat heater (4); the waste heat circulating water outlet of the bottom water tank (11) of the fresh air tower is connected to the water inlet of the low-temperature spray device (24) of the flue gas deep waste heat recovery tower (5) via the low-temperature waste water pump (10), and the water inlet of the humidification spray device (14) of the flue gas deep waste heat recovery tower (5) is respectively The process water heater (7) is connected to the high-temperature side outlet, the heating water outlet of the low-temperature sensible heat heater (4), and the inlet of the medium-temperature spray device (22) of the flue gas deep waste heat recovery tower (5). The high-temperature side inlet of the process water heater (7) is connected to the outlet of the medium-temperature waste water pump (9). The low-temperature side inlet of the process water heater (7) is connected to the main pipe of the process water inlet (G). The low-temperature side outlet of the process water heater (7) is connected to the main pipe of the process water outlet (H). The bottom of the waste heat recovery tower (5) is provided with a flue gas tower bottom water pool (19). The flue gas tower bottom water pool (19) has a waste heat circulating water outlet connected to the waste heat outlet water pipe (17). Above the liquid surface of the flue gas tower bottom water pool (19) is the flue gas inlet section (20). The upper part of the flue gas inlet section (20) consists of a medium temperature heat exchange section (21), a medium temperature spray device (22), a low temperature heat exchange section (23), a low temperature spray device (24), a flue gas humidity regulating device (25), and a flue gas outlet section (26).

3. The deep waste heat recovery system for flue gas from a gas-fired heating furnace with a humidifying air heater as described in claim 2, characterized in that... The humidifying air heater (6) and the flue gas deep waste heat recovery tower (5) are set separately or as an integrated unit. If they are set as an integrated unit, a tower partition plate (18) is set between the humidifying air heater (6) and the flue gas deep waste heat recovery tower (5), and the waste heat outlet pipe (17) is set inside or outside the humidifying air heater (6).

4. The deep waste heat recovery system for flue gas from a gas-fired heating furnace with a humidifying air heater as described in claim 1, characterized in that... The inlet of the medium-temperature waste water pump (9) is also connected to the outlet of the water quality regulating device (8), and the water quality regulating device (8) is also provided with an inlet for water quality regulator (K).

5. A deep waste heat recovery system for flue gas from a gas-fired heating furnace with a humidifying air heater as described in claim 2, characterized in that... The main pipe of the process water (G) is connected to the main pipe of the heating network water return, or to the main pipe of the demineralized water makeup water and the main pipe of the steam condensate water.

6. The deep waste heat recovery system for flue gas from a gas-fired heating furnace with a humidifying air heater as described in claim 1, characterized in that... The material heating module (102) is located inside the shell of the gas heating furnace (101) and has an inlet for feeding (I) and an outlet for discharging (O).

7. A deep waste heat recovery system for flue gas from a gas-fired heating furnace with a humidifying air heater as described in claim 2, characterized in that... The spray humidification section (13), the medium-temperature heat exchange section (21) and the low-temperature heat exchange section (23) are vertically arranged counter-current heat exchange structures composed of fresh air or flue gas and spray water, wherein the interior adopts a hollow section or a packing structure.

8. A deep waste heat recovery system for flue gas from a gas-fired heating furnace with a humidifying air heater as described in claim 2, characterized in that... The spray humidification section (13), the medium-temperature heat exchange section (21) and the low-temperature heat exchange section (23) adopt a single-layer trough-type water distribution structure, a trough-type structure or a water distribution structure composed of N layers of nozzles, wherein N is greater than or equal to 1.

9. A deep waste heat recovery system for flue gas from a gas-fired heating furnace with a humidifying air heater as described in claim 1, characterized in that... The aforementioned pre-energy saver (1) and low-temperature sensible heat heater (4) adopt the structure of a fluoroplastic coil heat exchanger, a carbon-based material coil heat exchanger, a fluoroplastic steel coil heat exchanger, a stainless steel heat exchanger, or an ND steel heat exchanger with anti-corrosion properties on the smoke and flue side.

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