Flue gas waste heat gradient utilization system based on heat pipe type heat exchanger

Abstract

The utility model discloses a flue gas waste heat gradient utilization system based on a heat pipe type heat exchanger, which comprises the heat pipe type heat exchanger, the heat pipe type heat exchanger comprises a condensed water-flue gas heat exchanger and a heating medium water-flue gas heat exchanger, and the condensed water-flue gas heat exchanger is connected with an air preheater; the condensed water-flue gas heat exchanger is connected with the electric dust remover through the heating medium water-flue gas heat exchanger; and a condensed water pipeline of the low-pressure heater is connected with a heating medium channel of the condensed water-flue gas heat exchanger. According to the flue gas waste heat gradient utilization system based on the heat pipe type heat exchanger, the heat pipe wall temperature controllability is utilized, the problem of dew point corrosion of the heat exchanger is solved, the equipment safety and the system operation stability are improved, and the cost is reduced; the two-stage arrangement of the heat pipe heat exchanger is adopted, flue gas waste heat is utilized in a gradient mode, the wide-load operation efficiency of the unit is improved, coal consumption is reduced, and the effects of saving energy and reducing consumption are achieved.

Description

Technical Field

[0001] The utility model relates to the technical field of flue gas waste heat utilization, in particular to a flue gas waste heat cascade utilization system based on a heat pipe type heat exchanger. Background Art

[0002] In my country's thermal power plants, the heat loss of boiler flue gas accounts for 60% to 70% of the total heat loss of the boiler. For every 10°C increase in flue gas temperature, the boiler efficiency decreases by 0.6% to 1.0%, and the corresponding increase in coal consumption is 1.2% to 2.4%, resulting in a large amount of energy waste. With the increasingly stringent requirements for energy conservation and emission reduction, improving the utilization rate of flue gas waste heat and reducing the flue gas temperature have become important ways to improve the efficiency of the unit.

[0003] At present, the exhaust gas temperature of the air preheater of large coal-fired power station boilers is generally between 115℃ and 150℃, while the electrostatic precipitator after the air preheater generally requires the inlet flue gas temperature to be between 80℃ and 90℃. Many power plants adopt flue gas waste heat utilization technology. The most widely used is to set a low-temperature economizer between the air preheater and the electrostatic precipitator to heat the condensate and reduce the flue gas temperature. However, due to the low temperature flue gas waste heat utilization area, the conventional low-temperature economizer is limited to heating the condensate at a lower temperature and displacing the low-grade steam turbine extraction steam, but does not change the air preheater and the flue duct layout before it, and cannot achieve full cascade utilization of flue gas heat, and the energy-saving effect is very limited. At the same time, the low-temperature economizer is set in the high dust area before the electrostatic precipitator, and the pipe wall is severely worn. After the flue gas temperature is reduced, the air preheater will suffer from low-temperature corrosion. The traditional low-temperature economizer also has problems such as wear and leakage, local corrosion and dust accumulation on the heated surface, which cannot meet the requirements of stable and efficient operation of the system. Utility Model Content

[0004] The utility model aims to provide a flue gas waste heat cascade utilization system based on a heat pipe heat exchanger to achieve long-term stable operation of a boiler unit.

[0005] In order to achieve the above purpose, the utility model provides the following technical solutions:

[0006] A flue gas waste heat cascade utilization system based on a heat pipe heat exchanger includes a heat pipe heat exchanger, which includes a condensate-flue gas heat exchanger and a heat medium water-flue gas heat exchanger, wherein:

[0007] The condensate-flue gas heat exchanger is connected to the air preheater;

[0008] The condensate-flue gas heat exchanger is connected to the electrostatic precipitator via a heat medium water-flue gas heat exchanger;

[0009] A boiler having a condensate pipeline of a low-pressure heater connected to a heat medium channel of the condensate-flue gas heat exchanger;

[0010] The heat medium water heater for heating cold air is connected to the heat medium channel of the heat medium water-flue gas heat exchanger as an air preheater.

[0011] As a preference, it further comprises a first air heater connected to the cold end of the heat medium water-smoke heat exchanger and a second air heater connected to the hot end to form a heat medium water closed circulation loop;

[0012] Wherein, the cold end inlet of the heat medium water-flue gas heat exchanger is provided with a first inlet valve, and the cold end outlet is provided with a second outlet valve;

[0013] The cold end inlet of the first air heater is connected to the cold air outlet of the first fan and the cold end inlet of the first air duct of the air preheater;

[0014] The cold end inlet of the second air heater is connected to the cold air outlet of the air supply fan and the cold end inlet of the second air duct of the air preheater.

[0015] Preferably, a constant pressure expansion water tank, a condensate inlet valve, a heat medium water booster circulation variable frequency pump and a bypass heat medium water vapor heater are sequentially arranged along the water flow direction on the water inlet pipeline of the heat medium water-flue gas heat exchanger, the inlet of the constant pressure expansion water tank is connected to the outlet of the variable frequency feed water pump, and the water inlet and outlet pipelines of the heat medium water vapor heater are respectively provided with a first inlet valve and a second outlet valve;

[0016] The constant pressure expansion water tank is arranged beside the flue frame of the dust collector and is connected to the inlet pipe of the heat medium water pressurized circulation variable frequency pump through a water supply pipeline.

[0017] The heat medium water circuit is provided with a heat medium water bypass pipe, one end of the heat medium water bypass pipe is connected to the water inlet pipe of the heat medium water-flue gas heat exchanger, and the other end is connected to the water outlet pipe of the heat medium water-flue gas heat exchanger. A heat medium water bypass regulating valve is provided on the heat medium water bypass pipe.

[0018] As a preferred embodiment, it also includes a boiler induced draft fan, a desulfurization tower and a chimney;

[0019] Among them, arranged in sequence along the flue gas flow direction are:

[0020] The water inlet and outlet of the condensate-flue gas heat exchanger are both connected to the condensate pipeline of the boiler low-pressure heater;

[0021] The condensate-flue gas heat exchanger:

[0022] The cold end outlet pipeline is equipped with a condensate outlet valve and a condensate booster variable frequency pump;

[0023] The cold end inlet pipeline is equipped with a condensate inlet valve;

[0024] It also includes that its water inlet pipeline includes a two-point water intake circuit, one water intake point of the two-point water intake circuit is connected to the condensate water pipeline in front of the No. 9 low-pressure heater, and the other water intake point is connected to the condensate water pipeline between the No. 9 low-pressure heater and the No. 8 low-pressure heater.

[0025] Preferably, a plurality of gravity heat pipes are arranged in the condensate-flue gas heat exchanger and the heat medium water-flue gas heat exchanger, and the gravity heat pipes are vacuum tubes;

[0026] A double-layered tube sheet is arranged between the heat pipe evaporation section and the heat pipe condensation section on the condensate water-flue gas heat exchanger and the heat medium water-flue gas heat exchanger. A jacketed tube is arranged outside the heat pipe condensation section. The heat pipe evaporation section is a finned tube.

[0027] As a preferred embodiment, a heat pipe heat exchanger is also included, which can be divided into a condensed water-smoke heat exchanger in a high-temperature section and a heat medium water-smoke heat exchanger in a low-temperature section along the direction of flue gas flow;

[0028] A 5m-8m straight section is left between the smoke outlet of the heat pipe heat exchanger and the inlet of the dust collector.

[0029] Preferably, the first air heater, the second air heater and the heat medium water steam heater are all shell and tube heat exchangers, the tube side medium is heat medium water, and the shell side medium is cold air and auxiliary steam respectively;

[0030] The heat medium water heater is a steel-aluminum composite spiral tube;

[0031] The heat medium water vapor heater is controlled by a return water drain valve, the heating steam source is the auxiliary steam of the power plant, the steam pressure is between 1.0 and 1.2 MPa, and the temperature is between 300 and 350°C.

[0032] Preferably, the heat pipe heat exchanger, the first air heater, the second air heater, and the heat medium water vapor heater all adopt countercurrent heat exchange, and an inlet header and an outlet header are arranged on the water side, a drain valve is arranged at the water outlet below, and an exhaust valve is arranged at the air outlet above.

[0033] As a preferred embodiment, it also includes:

[0034] A heat medium water booster circulation variable frequency pump for regulating the heat medium water flow rate of the heat medium water-flue gas heat exchanger;

[0035] The dust collector of the heat medium water-flue gas heat exchanger is controlled to control the inlet flue gas temperature, and the inlet flue gas temperature is maintained at 90±1°C;

[0036] The condensation-water flue gas heat exchanger is connected to the heat network circuit of the heating boiler.

[0037] In the above technical scheme, the utility model provides a flue gas waste heat cascade utilization system based on a heat pipe heat exchanger, which has the following beneficial effects: by arranging a condensate flue gas heat exchanger and a heat medium water flue gas heat exchanger on the horizontal flue between the air preheater and the electrostatic precipitator, the flue gas waste heat can be efficiently recovered and utilized. The cold end water inlet of the condensate heat exchanger is connected to the main water intake circuit of the two-point water intake circuit of the boiler condensate pipeline. The condensate mixing temperature is regulated by feedback of the flue gas temperature measurement point signal to ensure that the condensate heat exchanger does not suffer from dew point corrosion. The cold end outlet of the condensate heat exchanger is connected to the condensate return pipeline, and the condensate booster variable frequency pump is used to provide kinetic energy for the condensate pipeline, and the flue gas temperature at the outlet of the condensate heat exchanger is controlled to be around 115°C.

[0038] Secondly, the heat medium water flue gas heat exchanger and the heat medium water air heater are connected through a heat medium water closed circulation pipeline. The heat medium water is heated by the waste heat of the flue gas and used as the heat source of the air heater to heat the cold air. The heat medium water control system controls the air preheater inlet air temperature to be no less than 50°C, ensuring that the air preheater does not suffer from dew point corrosion and at the same time improving the unit's coal combustion efficiency.

[0039] Furthermore, the heat medium water volume is adjusted by the heat medium water circuit bypass regulating valve and the cold end inlet valve of the heat medium water heat exchanger to control the inlet flue gas temperature of the dust collector at 90±1℃. When the flue gas temperature is reduced, the dust resistivity is reduced, which can improve the dust removal efficiency and solve the corrosion problem of downstream equipment; the flue gas volume is reduced, reducing the power consumption of the induced draft fan and the dust collector; the flue gas temperature is reduced, reducing the desulfurization water consumption, and the energy-saving function is significant.

[0040] Furthermore, a bypass heat medium water steam heater is provided in the heat medium water circuit to assist steam heating of the heat medium water in winter or under low load conditions to offset the influence of factors such as ambient temperature on the outlet air temperature of the heater.

[0041] Among them, the condensate heat exchanger is used as a redundant adjustment means when the flue gas heat meets the outlet air temperature of the heat medium water heater. At the same time, it heats the condensate and discharges the steam from the steam turbine to achieve energy saving and consumption reduction effects.

[0042] Furthermore, the system introduces heat pipe technology, utilizing the superconducting properties, isothermal properties and heat flux density variability of the heat pipe to control the heat pipe wall temperature to be higher than the flue gas dew point temperature, thereby solving the dew point corrosion problem of the heat exchanger. The flue gas side and water side of the heat exchanger are completely isolated and wear only occurs on the flue gas side, ensuring equipment safety.

[0043] Furthermore, the heat pipe adopts an exhaust valve structure to prevent non-condensable gases from deteriorating heat transfer, and a fin structure is used on the flue gas side to expand the heat transfer surface and improve the heat transfer efficiency while effectively reducing the wear of flue gas fly ash particles on the base pipe. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present utility model. For ordinary technicians in this field, other drawings can also be obtained based on these drawings.

[0045] Figure 1 A schematic diagram of the system structure provided for an embodiment of the utility model;

[0046] Figure 2 A schematic diagram of the pipe group module structure of the condensate-flue gas heat exchanger and the heat medium water-flue gas heat exchanger provided in the embodiment of the utility model;

[0047] Figure 3 A schematic diagram of a single module structure of a heat pipe heat exchanger, a heat medium water heater, and a heat medium water steam heater provided in an embodiment of the utility model.

[0048] Description of reference numerals:

[0049] 1. Boiler; 2. Flue; 3. Air preheater; 4. Condensate-flue gas heat exchanger; 5. Heat medium water-flue gas heat exchanger; 6. Dust collector; 7. Draft fan; 8. Desulfurization tower; 9. Chimney; 10. First air heater; 11. Second air heater; 12. First fan; 13. Supply fan; 14. Condensate booster variable frequency pump; 15. Condensate outlet valve; 16. Condensate inlet valve; 17. First regulating valve; 18. Second regulating valve; 19. No. 9 low-pressure heater; 20. No. 8 low-pressure heater; 21. No. 7 low-pressure heater; 22. Heat 1. Heat medium water steam heater; 23. Heat medium water boost circulation variable frequency pump; 24. Constant pressure expansion water tank; 25. Variable frequency make-up water pump; 26. First inlet valve; 27. Second outlet valve; 28. Heat medium water bypass regulating valve; 29. ​​First outlet valve; 30. Second inlet valve; 31. Fin tube; 32. Double sandwich tube sheet; 33. Jacketed tube; 34. Water inlet end; 35. Water outlet end; 36. Exhaust valve; 37. Shell; 38. Inlet isolation valve; 39. Outlet isolation valve; 40. Inlet header; 41. Outlet header; 42. Exhaust valve; 43. Drain valve. DETAILED DESCRIPTION

[0050] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below in conjunction with the accompanying drawings.

[0051] like Figure 1-3As shown, a flue gas waste heat cascade utilization system based on a heat pipe heat exchanger includes a heat pipe heat exchanger composed of a condensate-flue gas heat exchanger 4 and a heat medium water-flue gas heat exchanger 5. The cold end inlet of the condensate-flue gas heat exchanger 4 is connected to the main circuit of the two-point water intake circuit of the condensate pipeline. One of the water intake points of the two-point water intake circuit is connected to the condensate pipeline in front of the No. 9 low-pressure heater 19, and the other water intake point is connected to the condensate pipeline between the No. 9 low-pressure heater 19 and the No. 8 low-pressure heater 20. The two-point water intake circuit is connected to the main water intake circuit. The two-point water intake circuit and the main water intake circuit are respectively provided with a condensate inlet valve 16, a first regulating valve 17, and a second regulating valve 18.

[0052] The condensate pipeline between the cold end outlet of the condensate-flue gas heat exchanger 4 and the No. 7 low-pressure heater 21 and the No. 8 low-pressure heater 20, and the cold end outlet pipeline is provided with a condensate booster variable frequency pump 14 and a condensate outlet valve 15.

[0053] The cold end of the heat medium water-smoke heat exchanger 5 is connected to the hot end of the heat medium water heater of the first air heater 10 and the first fan 12 to form a heat medium water closed circulation loop, and the water side of the heat medium water heat exchanger 5 is provided with a first inlet valve 26 and a second outlet valve 27. The first air heater 10 is provided in the cold air duct of the first fan 12, and the second air heater 11 is provided in the cold air duct of the blower 13.

[0054] A heat medium water bypass pipe is provided in the heat medium water circuit, one end of the heat medium water bypass pipe is connected to the water inlet pipe of the heat medium water heat exchanger 5, and the other end is connected to the water outlet pipe of the heat medium water heat exchanger 5, and a heat medium water bypass regulating valve 28 is provided on the heat medium water bypass pipe. A constant pressure expansion water tank 24, a first inlet valve 26, a heat medium water boost circulation variable frequency pump 23 and a bypass heat medium water vapor heater 22 are provided in sequence along the water flow direction on the water inlet pipe of the heat medium water heat exchanger 5, the constant pressure expansion water tank 24 is connected to the variable frequency water supply pump 25, and the water inlet and outlet pipes of the heat medium water vapor heater 22 are provided with a second inlet valve 30 and a first outlet valve 29 respectively.

[0055] Combination Figure 1 It can be known that the air preheater 3, the condensate-flue gas heat exchanger 4, the heat medium water-flue gas heat exchanger 5, the dust collector 6, the induced draft fan 7, the desulfurization tower 8, and the chimney 9 are arranged in sequence in the flue 2 along the flue gas flow direction.

[0056] Working principle:

[0057] Before starting the system, open the condensate inlet valve 16 and condensate outlet valve 15 at the cold end of the condensate-flue gas heat exchanger 4, shut down the condensate booster variable frequency pump 14, and open the first inlet valve 26, the second outlet valve 27, and the heat medium water bypass regulating valve 28 at the cold end of the heat medium water heat exchanger. Shut down the heat medium water booster circulation variable frequency pump 23, close the second inlet valve 30 and the first outlet valve 29, open the inlet isolation valve 38, the outlet isolation valve 39, and the exhaust valve 42 of all modules of the heat exchanger, and close the module exhaust valve after the variable frequency water supply pump 25 injects desalted water into the heat medium water pipeline.

[0058] When the system is running, the flue gas at the tail of boiler 1 carries a large amount of waste heat and passes through air preheater 3, condensate-flue gas heat exchanger 4, heat medium water-flue gas heat exchanger 5, dust collector 6, induced draft fan 7, desulfurization tower 8, and finally discharged to the atmosphere through chimney 9. The condensate inlet valve 16 and condensate outlet valve 15 at the cold end of condensate-flue gas heat exchanger 4 are opened to mix the condensate from the condensate pipeline between No. 9 low-pressure heater 19 and No. 8 low-pressure heater 20. After the combination, the condensate is introduced into the flue gas heat exchanger 4. After heating, the condensate booster frequency conversion pump 14 provides kinetic energy and adjusts the condensate flow in the condensate pipeline between the No. 7 low-pressure heater 21 and the No. 8 low-pressure heater 20. Two condensate booster frequency conversion pumps 14 are set, and one is in operation and one is in standby mode to ensure that the inlet flue gas temperature of the heat medium water heat exchanger 5 is around 115°C under partial load conditions. By heating the condensate and displacing the steam extracted by the steam turbine, energy saving and consumption reduction are achieved. The heat medium water is powered by the heat medium water boost circulation variable frequency pump 23 and sent to the heat medium water heat exchanger 5 to absorb heat, then flows to the hot end of the first air heater 10 and the second air heater 11, heats the cold air sent to the air preheater 3, and then returns to the inlet of the heat medium water boost circulation variable frequency pump 23 to form a closed circulation loop. The loop is equipped with three heat medium water boost circulation variable frequency pumps 23, which adopt a two-in-one mode to jointly adjust the heat medium water flow at the inlet of the heat medium water heat exchanger 5 with the heat medium water bypass regulating valve 28 and the first inlet valve 26 to ensure that the inlet smoke temperature of the dust collector 6 is 90±1℃, and the outlet wind temperature of the first air heater 10 and the second air heater 11 is about 50℃. If there is residual heat, the condensate-flue gas heat exchanger 4 can absorb the excess flue gas waste heat to heat the condensate sent to the No. 7 low-pressure heater 21, so as to realize the cascade utilization of flue gas waste heat. During operation, when the temperature drops and the volume of the heat medium water decreases, the constant pressure expansion water tank 24 is used for replenishment. Nitrogen is filled in the water tank for protection to prevent the heat medium water from being vaporized due to too low pressure after being heated, and to prevent cavitation of the heat medium water booster circulation variable frequency pump 23. During normal operation, the heat medium water does not need to be replenished or drained. The liquid level of the water tank 24 must be controlled. When the liquid level is lower than 0.5m, the water replenishment gate automatically opens to replenish water, and when it is higher than 2m, the water replenishment gate automatically closes.

[0059] When the boiler load is low or the ambient temperature is low in winter, in order to ensure that the outlet air temperature of the first air heater 10 and the second air heater 11 is around 50°C and the inlet smoke temperature of the dust collector 6 is 90±1°C, open the second inlet valve 30 and the first outlet valve 29, and use auxiliary steam to heat the heat medium water to ensure that dew point corrosion does not occur in the air preheater 3 and ensure the optimal working efficiency of the dust collector 6.

[0060] In the above-mentioned specific embodiment of the present utility, the condensate-flue gas heat exchanger 4 and the heat medium water-flue gas heat exchanger 5 are reasonably designed to ensure that the tube wall temperature is higher than the flue gas dew point corrosion temperature. The flue gas side adopts an enhanced heat transfer fin tube 31 structure, the tube and fin material is ND steel, the fin form is a pin tube or a similar extended heat transfer surface type, the water side adopts a jacket tube 33 structure, and the jacket tubes of multiple heat pipes are connected by a connecting pipe to form a heat pipe group. The upper and lower parts of the heat pipe group are respectively provided with a water inlet end 34 and a water outlet end 35. The heat pipe adopts a method of extending the header pipe and adopts an exhaust valve type 36 structure, which can timely discharge the non-condensable gas in the pipe to prevent the deterioration of heat transfer. The bottom end of the heat pipe is blocked, and the flue gas side and the water side are completely isolated by a double sandwich tube sheet 32 ​​structure. Due to the high smoke dust content, two rows of Q345 anti-wear false pipes are arranged on the windward side of the flue gas side, and a sonic soot blower is arranged on the flue gas side to regularly blow away the accumulated dust.

[0061] The pressure of the main pipe of the low-temperature section of the heat pipe heat exchanger shall not be less than 1.6MPa, and the high-temperature section shall be controlled at about 5.2MPa. The flue gas resistance of the high-temperature and low-temperature section heat exchangers shall not exceed 650Pa. The wall thickness of the heat exchange tube shall not be less than 4mm, the thickness of the fin shall not be less than 2mm, and the thickness of the heat exchanger shell 37 shall not be less than 6mm.

[0062] Furthermore, the first air heater 10, the second air heater 11 and the heat medium water vapor heater 22 are tubular heat exchangers, the tube side is heat medium water, and the shell side is cold air and steam respectively. The first air heater 10 and the second air heater 11 use steel-aluminum composite spiral tubes, the pressure components and tubes are made of 20G steel, the fins are made of tensile cold-rolled aluminum strips, and are hot-dip galvanized or nickel-plated to improve heat exchange and corrosion resistance. The base tube and the fin are made of embedded manufacturing technology to prevent falling off and ensure the heat transfer coefficient. The outlet air temperature of the first air heater 10 and the second air heater 11 is controlled at about 50°C, the air resistance does not exceed 400Pa, the heat exchange tube pressure is not less than 1.6MPa, and the temperature is not less than 150°C. The heat medium water vapor heater 22 controls the heating effect through the second inlet valve 30 and the first outlet valve 29. Safety valves are arranged on the water side and the steam side of the heat medium water vapor heater 22 to protect the heat medium water vapor heater 22 from overpressure due to thermal expansion when the second inlet valve 30 and the first outlet valve 29 are closed and there is steam on the steam side. Drain ports are arranged on the steam side and the water side of the heat medium water vapor heater 22 to relieve pressure and drain accumulated water during shutdown and maintenance. An exhaust valve should be arranged at the highest point on the water side of the heat medium water vapor heater 22 to discharge air in the pipe system during water injection. The heating steam source is auxiliary steam from the power plant, with a steam pressure between 1.0 and 1.2 MPa, a temperature between 300 and 350°C, and a shell pressure of not less than 2.5 MPa.

[0063] The condensate-flue gas heat exchanger 4, the heat medium water-flue gas heat exchanger 5, the first air heater 10, the second air heater 11, and the heat medium water vapor heater 22 all adopt countercurrent heat exchange to increase the temperature difference and improve the heat transfer efficiency. The heat pipe heat exchanger is preferably in a modular and detachable form. If a local leak occurs in the heat pipe heat exchanger, the module can be removed independently without affecting the overall operation of the equipment. Each module is provided with an inlet header 40 and an outlet header 41, wherein: the inlet is provided with a shutoff valve 38, the outlet is provided with a shutoff valve 39, the drain outlet is provided with a drain valve 43, and the exhaust hole is provided with an exhaust valve 42.

[0064] The above only describes some exemplary embodiments of the present invention by way of illustration. It is undoubted that those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the above drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A flue gas waste heat cascade utilization system based on a heat pipe heat exchanger, It is characterized in that It comprises a heat pipe heat exchanger, which comprises a condensate water-smoke heat exchanger (4) and a heat medium water-smoke heat exchanger (5), wherein: The condensate-flue gas heat exchanger (4) is connected to the air preheater (3); The condensate-flue gas heat exchanger (4) is connected to the electrostatic precipitator (6) via a heat medium water-flue gas heat exchanger (5); A boiler (1) having a condensate pipeline of a low-pressure heater connected to a heat medium channel of the condensate-flue gas heat exchanger (4); The heat medium water heater for heating cold air is connected to the air preheater (3) of the heat medium channel of the heat medium water-smoke heat exchanger (5).

2. According to claim 1, a flue gas waste heat cascade utilization system based on a heat pipe heat exchanger, It is characterized in that It also includes a first air heater (10) connected to the cold end of the heat medium water-smoke heat exchanger (5) and a second air heater (11) connected to the hot end to form a heat medium water closed circulation loop; Wherein, the cold end inlet of the heat medium water-flue gas heat exchanger (5) is provided with a first inlet valve (26), and the cold end outlet is provided with a second outlet valve (27); The cold end inlet of the first air heater (10) is connected to the cold air outlet of the first fan (12) and the cold end inlet of the first air duct of the air preheater (3); The cold end inlet of the second air heater (11) is connected to the cold air outlet of the air supply fan (13) and the cold end inlet of the second air duct of the air preheater (3).

3. According to claim 1, a flue gas waste heat cascade utilization system based on a heat pipe heat exchanger, It is characterized in that A constant pressure expansion water tank (24), a condensate inlet valve (16), a heat medium water boost circulation variable frequency pump (23) and a bypass heat medium water vapor heater (22) are sequentially arranged on the water inlet pipeline of the heat medium water-flue gas heat exchanger (5) in the water flow direction; the inlet of the constant pressure expansion water tank (24) is connected to the outlet of the variable frequency water supply pump (25); the water inlet and outlet pipelines of the heat medium water vapor heater (22) are respectively provided with a first inlet valve (26) and a second outlet valve (27); The constant pressure expansion water tank (24) is arranged beside the flue (2) frame of the dust collector (6) and is connected to the inlet pipe of the heat medium water boost circulation variable frequency pump (23) through a water supply pipeline; The heat medium water circuit is provided with a heat medium water bypass pipe, one end of the heat medium water bypass pipe is connected to the water inlet pipe of the heat medium water-smoke heat exchanger (5), and the other end is connected to the water outlet pipe of the heat medium water-smoke heat exchanger (5), and a heat medium water bypass regulating valve (28) is provided on the heat medium water bypass pipe.

4. According to claim 1, a flue gas waste heat cascade utilization system based on a heat pipe heat exchanger, It is characterized in that It also includes a boiler (1) induced draft fan (7), a desulfurization tower (8) and a chimney (9); Among them, arranged in sequence along the flue gas flow direction are: The water inlet (34) and the water outlet (35) on the condensate-flue gas heat exchanger (4) are both connected to the condensate pipeline of the low-pressure heater of the boiler (1); On the condensate-flue gas heat exchanger (4): The cold end outlet pipeline is provided with a condensate outlet valve (15) and a condensate booster frequency conversion pump (14); The cold end inlet pipeline is provided with a condensate inlet valve (16); It also includes that its water inlet pipeline includes a two-point water intake circuit, one water intake point of the two-point water intake circuit is connected to the condensate water pipeline in front of the No. 9 low-pressure heater (19), and the other water intake point is connected to the condensate water pipeline between the No. 9 low-pressure heater (19) and the No. 8 low-pressure heater (20).

5. According to claim 1, a flue gas waste heat cascade utilization system based on a heat pipe heat exchanger, It is characterized in that A plurality of gravity heat pipes are arranged in the condensate water-flue gas heat exchanger (4) and the heat medium water-flue gas heat exchanger (5), and the gravity heat pipes are vacuum tubes; A double-layered tube sheet (32) is provided between the heat pipe evaporation section and the heat pipe condensation section on the condensate water-flue gas heat exchanger (4) and the heat medium water-flue gas heat exchanger (5); a jacketed tube (33) is provided outside the heat pipe condensation section; and the heat pipe evaporation section is a finned tube (31).

6. A flue gas waste heat cascade utilization system based on a heat pipe heat exchanger according to claim 1, It is characterized in that It also includes a heat pipe heat exchanger, which can be divided into a condensed water-smoke heat exchanger (4) in a high-temperature section and a heat medium water-smoke heat exchanger (5) in a low-temperature section along the direction of flue gas flow; A 5m-8m straight section is left between the flue gas outlet of the heat pipe heat exchanger and the inlet of the dust collector (6).

7. A flue gas waste heat cascade utilization system based on a heat pipe heat exchanger according to claim 2, It is characterized in that The first air heater (10), the second air heater (11) and the heat medium water steam heater (22) are all shell and tube heat exchangers, the tube side medium is heat medium water, and the shell side medium is cold air and auxiliary steam respectively; The heat medium water heater is a steel-aluminum composite spiral tube; The heat medium steam heater (22) is controlled by a return water drain valve, the heating steam source is the auxiliary steam of the power plant, the steam pressure is between 1.0 and 1.2 MPa, and the temperature is between 300 and 350°C.

8. The flue gas waste heat cascade utilization system based on a heat pipe heat exchanger according to claim 1, It is characterized in that The heat pipe heat exchanger, the first air heater (10), the second air heater (11), and the heat medium water vapor heater (22) all adopt a countercurrent heat exchange form, and an inlet header (40) and an outlet header (41) are arranged on the water side, a drain valve (43) is arranged at the water outlet below, and an exhaust valve (42) is arranged at the air outlet above.

9. The flue gas waste heat cascade utilization system based on a heat pipe heat exchanger according to claim 1, It is characterized in that Also includes: Regulating the heat medium water-flue gas heat exchanger (5); A heat medium water boost circulation variable frequency pump (23) for regulating the flow rate of heat medium water in a heat medium water-flue gas heat exchanger (5); A dust collector (6) for controlling the inlet flue gas temperature of the heat medium water-flue gas heat exchanger (5), and the inlet flue gas temperature is maintained at 90±1°C; The condensate-flue gas heat exchanger (4) is connected to the heat network circuit of the heating boiler (1).

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