Low-pressure water-medium heat exchanger for recovering waste heat from flue gas, anti-blocking and anti-corrosion method and system

Abstract

The present invention discloses a low-pressure water-medium heat exchanger for recovering waste heat of flue gas, a method and a system for preventing blockage and corrosion. The method for preventing blockage and corrosion of the low-pressure water-medium heat exchanger for recovering waste heat of flue gas: The low-pressure water-medium heat exchanger is composed of more than three independent heat exchange units connected in parallel; the low-pressure water-medium heat exchanger is installed in the flue to absorb the waste heat of the flue gas; each heat exchange unit is in the shape of a tube bundle composed of heat exchange tubes. Boiler flue gas flows outside the heat exchange tubes of each heat exchange unit, and liquid water and dry steam flow alternately inside the heat exchange tubes of each heat exchange unit, and the temperature of the dry steam is not lower than 200 °C. By alternately flowing liquid water and gaseous steam in each heat exchange unit of the low-pressure water-medium heat exchanger and periodically displacing the medium water in each heat exchange unit with dry steam, the present invention can significantly increase the temperature of each heat exchange unit periodically with less steam consumption, completely solve the problems of corrosion and ash blockage of the low-pressure water-medium heat exchanger, have low operating costs, and have remarkable engineering economic value.

Description

Technical Field

[0001] The present invention relates to a low-pressure water-medium heat exchanger for recovering flue gas waste heat, a method and a system for preventing blockage and corrosion, and belongs to the technical field of flue gas waste heat utilization. Background Art

[0002] Low-pressure water-based heat exchangers are widely used in industrial fields, such as coal-fired power generation. With the advancement of low-carbon and environmental protection policies in my country's power generation industry, the technology for utilizing waste heat from coal-fired boilers has made great progress. Installing a low-pressure water-based heat exchanger after the air preheater is a specific form of this waste heat utilization. A low-pressure water-based heat exchanger consists of several tube bundles, with water (cold medium) inside the tubes and flue gas (hot medium) outside the tubes. The water inlet temperature of the low-pressure water-based heat exchanger is generally 30-80°C, while the flue gas temperature outside the tubes is generally 120-180°C, thereby transferring the heat of the flue gas outside the tubes to the medium water inside the tubes.

[0003] However, in the field of coal-fired power generation, traditional low-pressure water-based heat exchangers are prone to corrosion, leakage, ash accumulation and blockage. The reasons for this are at least the following two: 1) After combustion, the sulfur in the coal is partially converted into sulfur trioxide (SO3), which reacts with water vapor (H2O) in the flue gas to form sulfuric acid vapor (H2SO4). When the flue gas temperature is lower than the acid dew point (generally 95-160°C, which is closely related to the SO3 concentration in the flue gas), the sulfuric acid vapor will condense and adhere to the wall of the heat exchange tube of the low-pressure water-based heat exchanger together with the fly ash; 2) In order to reduce NOx emissions, coal-fired boilers are generally equipped with denitrification equipment, which is generally used. The technical routes include selective catalytic reduction (SCR), selective non-catalytic reduction (SNCR) or SCR+SNCR combination. No matter which technical route is adopted, it is necessary to spray a reducing agent (liquid ammonia, urea or ammonia water) into the flue gas upstream of the air preheater. The reducing agent will not react completely with NOx, which will cause ammonia (NH3) to escape from the denitrification system. The escaped NH3 reacts with SO3 in the flue gas to form ammonium bisulfate (NH4HSO4). This by-product is molten at a temperature of 146-207°C and is very easy to adhere to the air preheater heat storage element and the wall of the heat exchange tube of the downstream low-pressure water medium heat exchanger together with the fly ash.

[0004] Similar to the air preheater blockage problem in coal-fired power generation, the flue gas reheater in the denitrification emission system of sintering machines in the steel industry also faces this problem. To achieve ultra-low NOx emissions in flue gas, the steel industry also widely adopts SCR denitrification technology. The inlet and outlet of the SCR denitrification device are connected to the raw flue gas side and the clean flue gas side of the flue gas reheater, respectively. This low-temperature section of the flue gas reheater is also susceptible to blockage due to similar reasons as air preheaters in coal-fired power generation. Summary of the Invention

[0005] In order to solve the problems of low-temperature condensation, corrosion, and ash fouling of the low-pressure water-medium heat exchanger for recovering waste heat from flue gas in the prior art, the present invention provides a low-pressure water-medium heat exchanger for recovering waste heat from flue gas, an anti-blocking and anti-corrosion method, and a system.

[0006] To solve the above technical problems, the technical solutions adopted by the present invention are as follows:

[0007] An anti-blocking and anti-corrosion method for a low-pressure water-medium heat exchanger for recovering waste heat from flue gas. The low-pressure water-medium heat exchanger is composed of three or more independent heat exchange units connected in parallel; the low-pressure water-medium heat exchanger is installed in the flue to absorb waste heat from the flue gas; each heat exchange unit is in the form of a tube bundle composed of heat exchange tubes. Hot flue gas flows outside the heat exchange tubes of each heat exchange unit, and liquid water and dry steam flow alternately inside the heat exchange tubes of each heat exchange unit, and the temperature of the dry steam is not lower than 200 °C.

[0008] By alternately introducing dry steam into the heat exchange tubes in the above method, the heat exchange tubes are heated, so that the condensed water on the wall surface of the heat exchange unit in contact with the boiler flue gas is vaporized, and the adhered fly ash becomes loose at high temperature and is carried out by the flue gas. It is simple and efficient, with low operating costs and significant engineering economic value.

[0009] For the convenience of operation, a water inlet valve and an air inlet valve are respectively provided on each heat exchange unit, and the water inlet valves of each group of heat exchange units are closed in turn; the air inlet valve on the heat exchange unit with the water inlet valve closed is opened (that is, when the water inlet valve on the heat exchange unit is closed, the air inlet valve on this heat exchange unit is opened), and dry steam not lower than 200 °C is introduced until the liquid water in the heat exchange tubes of this heat exchange unit is completely discharged and filled with dry steam, and the wall temperature of the heat exchange tubes of this heat exchange unit rises, so that the condensed water on the wall surface of the heat exchange tubes of this heat exchange unit in contact with the flue gas is vaporized, and the adhered fly ash becomes loose at high temperature and is carried out by the flue gas.

[0010] The applicant has found through research that liquid water and gaseous steam flow alternately in each heat exchange unit of the above low-pressure water-medium heat exchanger, and the medium water in each heat exchange unit is displaced by dry steam in turn. It is possible to significantly increase the temperature of each group of heat exchange units by alternately using less steam consumption, with low operating costs and significant engineering economic value. When a certain heat exchange unit of the low-pressure water-medium heat exchanger is dry-fired, the wall temperature of this heat exchange unit can be greatly increased, from 80-120 °C during normal heat exchange to above 160 °C during dry firing. By alternately dry-firing multiple groups of heat exchange units, the corrosion and ash fouling problems of the low-pressure water-medium heat exchanger are completely solved.

[0011] In order to improve the energy utilization rate, reduce energy consumption, and realize the near-use of energy, the liquid water flowing out of the heat exchange tubes of the heat exchange unit is used to heat the air preheater in the inlet air duct of the air heater.

[0012] To achieve the recycling of liquid water, the liquid water heated by the air heater circulates into the heat exchange tubes of the heat exchange unit. Of course, new liquid water can also be replenished into the heat exchange unit as needed.

[0013] A low-pressure water medium heat exchanger for recovering waste heat from flue gas includes a heat exchange unit, a water supply pipe, and a gas supply pipe; the number of heat exchange units is more than three groups, and the structures of each heat exchange unit are the same and are connected in parallel with each other; each heat exchange unit is in the shape of a tube bundle composed of heat exchange tubes, one end of the heat exchange unit is an inlet and the other end is an outlet, one end of the water supply pipe is connected to a water source and the other end branches into more than three water supply branch pipes, the water supply branch pipes are connected to the inlets of the heat exchange units, each group of heat exchange units corresponds to at least one water supply branch pipe, and an inlet valve is provided on each water supply branch pipe; one end of the gas supply pipe is connected to a gas source and the other end branches into more than three gas supply branch pipes, the gas supply branch pipes are connected to the inlets of the heat exchange units, each group of heat exchange units corresponds to at least one gas supply branch pipe, and an inlet valve is provided on each gas supply branch pipe.

[0014] The above-mentioned low-pressure water medium heat exchanger for recovering waste heat from flue gas can effectively achieve the alternate flow of liquid water and dry steam in the heat exchange tubes of the heat exchange unit, fundamentally solving the problems of corrosion and ash blockage of the low-pressure water medium heat exchanger.

[0015] To facilitate installation and at the same time meet the engineering requirements, the number of water supply branch pipes is equal to the number of heat exchange units and corresponds one by one, and the water supply branch pipes are connected to the inlets of their corresponding heat exchange units; the number of gas supply branch pipes is equal to the number of heat exchange units and corresponds one by one, and the gas supply branch pipes are connected to the inlets of their corresponding heat exchange units.

[0016] A low-pressure water medium heat exchanger anti-blocking and anti-corrosion system for recovering waste heat from flue gas includes the above-mentioned low-pressure water medium heat exchanger for recovering waste heat from flue gas, an air preheater, a buffer water tank, an air heater, and a hot water circulation pump;

[0017] An inlet air duct, an outlet air duct, an inlet flue duct, and an outlet flue duct are provided on the air preheater, which is common knowledge in the art and will not be elaborated in this application;

[0018] The low-pressure water medium heat exchanger is installed in the outlet flue duct of the air preheater;

[0019] The air heater is installed in the inlet air duct of the air preheater;

[0020] The outlet of the heat exchange unit, the inlet of the buffer water tank, the outlet of the buffer water tank, the inlet of the air heater, the outlet of the air heater, the inlet of the hot water circulation pump, the outlet of the hot water circulation pump, the water supply pipe, and the inlet of the heat exchange unit are connected in sequence and form a cycle. <www.

[0021] The above-mentioned system not only realizes the full utilization of energy and the recycling of resources, but also completely solves the problems of corrosion and ash blockage of the low-pressure water medium heat exchanger.

[0022] The above-mentioned air preheater is used to heat the inlet air of the air preheater.

[0023] For the safety and cleanliness of the system, an overflow pipe is provided at the top of the side wall of the buffer water tank, and an overflow valve is provided on the overflow pipe; a blowdown pipe is provided at the bottom of the buffer water tank, and a blowdown valve is provided on the blowdown pipe. An outlet check valve is provided on the pipeline at the outlet of the heat exchange unit.

[0024] To improve efficiency, the heat exchange units of the low-pressure water medium heat exchanger are arranged vertically, with the upper end as the inlet and the lower end as the outlet. That is, the heat exchange units are arranged vertically to facilitate the rapid expulsion of liquid water by gaseous steam and the rapid drying of the inner wall of the heat exchange tubes when a certain group of heat exchange units is dry-fired, so that the heat exchange tubes are filled with dry steam.

[0025] Preferably, the heat exchange units of each group of the low-pressure water medium heat exchanger are arranged in sequence along the width direction of the cross-section of the outlet flue of the air preheater, and the width of the cross-section of the outlet flue of the air preheater is perpendicular to the flue gas flow direction.

[0026] The above-mentioned heat exchange unit includes both a shell-and-tube heat exchange structure and a heat pipe heat exchanger structure, without limiting the specific type.

[0027] Technologies not mentioned in the present invention shall refer to the prior art.

[0028] The method and system for preventing blockage and corrosion of the low-pressure water medium heat exchanger for recovering flue gas waste heat according to the present invention can alternately flow liquid water and gaseous steam in the heat exchange units of each group of the low-pressure water medium heat exchanger, and alternately expel the medium water in each heat exchange unit as dry steam. It can significantly increase the temperature of each group of heat exchange units by alternately using less steam consumption, completely solve the problems of condensation, corrosion, and ash fouling of the low-pressure water medium heat exchanger, with low operating costs and significant engineering economic value. Brief Description of the Drawings

[0029] Figure 1 It is a schematic diagram of the low-pressure water medium heat exchanger for recovering flue gas waste heat according to the present invention.

[0030] Figure 2 It is a schematic diagram of the system for preventing blockage and corrosion of the low-pressure water medium heat exchanger for recovering flue gas waste heat according to the present invention.

[0031] In the figure, 1 is liquid water, 2 is gaseous steam, 3 is the cross-section of the flue, 4 is the heat exchange unit, 5 is the inlet valve, 6 is the inlet gas valve, 7 is the outlet check valve, 8 is the buffer water tank, 9 is the overflow valve, 10 is the blowdown valve, 11 is the inlet air duct of the air preheater or the flue gas reheater, 12 is the air preheater, 13 is the hot water circulation pump; 20 is the air preheater or the flue gas reheater. Detailed Embodiments

[0032] To better understand the present invention, the content of the present invention will be further clarified below in conjunction with embodiments, but the content of the present invention is not limited to the following embodiments.

[0033] Example 1

[0034] As Figure 1 shown, a low-pressure water-medium heat exchanger for recovering waste heat from flue gas includes a heat exchange unit, a water supply pipe and a gas supply pipe; the number of heat exchange units is more than three, and the structures of each heat exchange unit are the same and are connected in parallel with each other; each heat exchange unit is in the shape of a tube bundle composed of heat exchange tubes, one end of the heat exchange unit is an inlet and the other end is an outlet, one end of the water supply pipe is connected to a water source and the other end branches into more than three water supply branches, the number of water supply branches is equal to the number of heat exchange units and corresponds one by one, the water supply branches are connected to the inlets of the corresponding heat exchange units, and an inlet valve is provided on each water supply branch; one end of the gas supply pipe is connected to a gas source and the other end branches into more than three gas supply branches, the number of gas supply branches is equal to the number of heat exchange units and corresponds one by one, the gas supply branches are connected to the inlets of the corresponding heat exchange units, and an inlet valve is provided on each gas supply branch.

[0035] The above-mentioned low-pressure water-medium heat exchanger for recovering waste heat from flue gas can effectively realize the alternate flow of liquid water and dry steam in the heat exchange tubes of the heat exchange unit, and fundamentally solve the problems of corrosion and ash blockage of the low-pressure water-medium heat exchanger.

[0036] Example 2

[0037] As Figure 2 shown, an anti-blocking and anti-corrosion system for a low-pressure water-medium heat exchanger for recovering waste heat from flue gas includes the low-pressure water-medium heat exchanger for recovering waste heat from flue gas in Example 1, an air preheater, a buffer water tank, a warm air heater and a hot water circulation pump;

[0038] An air preheater is provided with an inlet air duct, an outlet air duct, an inlet flue duct and an outlet flue duct;

[0039] The low-pressure water-medium heat exchanger is installed in the outlet flue duct of the air preheater;

[0040] The warm air heater is installed in the inlet air duct of the air preheater;

[0041] The outlet of the heat exchange unit, the inlet of the buffer water tank, the outlet of the buffer water tank, the inlet of the warm air heater, the outlet of the warm air heater, the inlet of the hot water circulation pump, the outlet of the hot water circulation pump, the water supply pipe and the inlet of the heat exchange unit are connected in sequence and form a cycle.

[0042] The above system not only realizes the full utilization of energy and the recycling of resources, but also completely solves the problems of corrosion and ash blockage of the low-pressure water-medium heat exchanger.

[0043] Example 3

[0044] Based on Embodiment 2, the following further improvements are made: For the safety and cleanliness of the system, an overflow pipe is provided at the top of the side wall of the buffer water tank, and an overflow valve is provided on the overflow pipe; a sewage pipe is provided at the bottom of the buffer water tank, and a sewage valve is provided on the sewage pipe. An outlet check valve is provided on the pipeline at the outlet of the heat exchange unit.

[0045] Embodiment 4

[0046] Based on Embodiment 3, the following further improvements are made: To improve efficiency, the heat exchange units of the low-pressure water medium heat exchanger are arranged vertically, with the upper end as the inlet and the lower end as the outlet. That is, the heat exchange units are arranged vertically, which is beneficial for the gaseous steam to quickly displace the liquid water and quickly dry the inner wall of the heat exchange tubes when a certain group of heat exchange units is dry-burned, so that the heat exchange tubes are filled with dry steam. Each group of heat exchange units of the low-pressure water medium heat exchanger is arranged in sequence along the width direction of the cross-section of the outlet flue of the air preheater, and the width of the cross-section of the outlet flue of the air preheater is perpendicular to the flue gas flow direction.

[0047] For a 600MW unit, a low-pressure water medium heat exchanger is installed in the downstream flue (outlet flue) of the air preheater, and a warm air heater is installed in the inlet air duct of the air preheater. Through engineering practice, the low-pressure water medium heat exchanger before the transformation had problems such as ash accumulation, corrosion, and blockage.

[0048] As Figure 2 4]shown, after the transformation according to the structure in Embodiment 4, the inlet valves of each group of heat exchange units are closed in turn, the intake valves on the heat exchange units with the inlet valves closed are opened, and dry steam not lower than 200°C is introduced until the liquid water in the heat exchange tubes of this heat exchange unit is completely discharged and filled with dry steam. The wall temperature of the heat exchange tubes of this heat exchange unit rises, so that the condensation on the wall surface of the heat exchange tubes of this heat exchange unit in contact with the boiler flue gas vaporizes, and the adhered fly ash becomes loose at high temperature and is carried out by the flue gas. That is, liquid water and gaseous steam flow alternately in each group of heat exchange units of the low-pressure water medium heat exchanger, and the medium water in each heat exchange unit is displaced by dry steam in turn. It is possible to significantly increase the temperature of each group of heat exchange units by turning on and off in turn with less steam consumption, with low operating costs and significant engineering economic value. When a certain heat exchange unit of the low-pressure water medium heat exchanger is dry-burned, the wall temperature of this heat exchange unit can be greatly increased, from 80 - 120°C during normal heat exchange to more than 160°C during dry-burning. By dry-burning multiple groups of heat exchange units in turn, the corrosion and ash blockage problems of the low-pressure water medium heat exchanger can be completely solved. After continuous operation for 18 months, there are no problems of condensation, corrosion, and ash blockage in the low-pressure water medium heat exchanger. The liquid water flowing out of the heat exchange tubes of the heat exchange units is used to heat the warm air heater in the inlet air duct of the air preheater, and then heat the inlet air of the air preheater. The liquid water after heating the warm air heater circulates into the heat exchange tubes of the heat exchange units for heating, and then circulates into the warm air heater to heat the inlet air after passing through the buffer water tank.

[0049] Embodiment 5[[ID=]8]

[0050] The technical route for treating sintering machine flue gas is to denitrate first and then desulfurize. The sintering flue gas first passes through a dust removal device. After dust removal, the original flue gas enters the denitration flue gas reheater. After the original flue gas is heated, it passes through a supplementary combustion device to raise the temperature of the sintering flue gas to the denitration required temperature and then enters the SCR denitration device. After denitration, the clean flue gas enters the flue gas reheater. The high-temperature clean flue gas exchanges heat through the flue gas reheater, and after cooling, the clean flue gas enters the subsequent equipment of the desulfurization device. In the original design, the inlet temperature of the original flue gas of the flue gas reheater is 150°C, the outlet temperature is 300°C, and the flue gas temperature reaches 330°C after passing through the supplementary combustion device, thus meeting the SCR denitration temperature requirement. The outlet temperature of the clean flue gas of the flue gas reheater is about 180°C. Using the above process, the ammonia escape from the SCR denitration device enters the flue gas reheater and reacts with acidic substances such as sulfur trioxide in the sintering flue gas to generate sticky substances, resulting in the blockage of the flue gas reheater.

[0051] To solve the above problems, a low-pressure water medium heat exchanger in Embodiment 1 is installed at the clean flue gas outlet of the flue gas reheater, and at the same time, a warm air heater is installed at the original flue gas inlet of the flue gas reheater, and a closed water cycle is used to achieve heat exchange between the clean flue gas and the original flue gas. By setting heat exchangers on the clean flue gas side and the original flue gas side respectively, the cold end temperature of the flue gas reheater is greatly increased, thus avoiding the formation of sticky substances in the flue gas adhering to the surface of the heat storage elements of the flue gas reheater.

[0052] In this case, the inlet temperature of the original flue gas of the warm air heater is 150°C, and the outlet temperature of the original flue gas reaches 180°C, that is, the inlet temperature of the original flue gas of the flue gas reheater is 180°C, and the outlet temperature of the clean flue gas of the corresponding flue gas reheater reaches about 210°C, and then drops to about 180°C after passing through the low-pressure water medium heat exchanger. Thereby effectively preventing the blockage of the flue gas reheater.

Claims

1. A method for preventing blockage and corrosion of a low-pressure water-based heat exchanger for recovering waste heat from flue gas, characterized by: The low-pressure water-based heat exchanger consists of three or more independent heat exchange units connected in parallel. The low-pressure water-based heat exchanger is installed in the flue to absorb the waste heat of the flue gas. The heat exchange units are all bundled with heat exchange tubes. Hot flue gas flows outside the heat exchange tubes of the heat exchange units, and liquid water and dry steam flow alternately inside the heat exchange tubes of the heat exchange units. The temperature of the dry steam is not less than 200℃. Each heat exchange unit is provided with a water inlet valve and an air inlet valve. The water inlet valves of each heat exchange unit are closed in turn. The air inlet valves on the heat exchange units with closed water inlet valves are opened, and dry steam with a temperature not lower than 200°C is introduced until the liquid water in the heat exchange tubes of this heat exchange unit is completely discharged and filled with dry steam. The wall temperature of the heat exchange tubes of this heat exchange unit rises, thereby vaporizing the condensation on the wall surface of the heat exchange tubes of this heat exchange unit that is in contact with the flue gas, and the adhered fly ash becomes loose under the high temperature and is carried out by the flue gas.

2. The method for preventing blockage and corrosion of a low-pressure water-based heat exchanger for recovering waste heat from flue gas according to claim 1, characterized in that: The liquid water flowing out of the heat exchange tube of the heat exchange unit is used to heat the heater in the inlet air duct of the air preheater.

3. The method for preventing blockage and corrosion of a low-pressure water-based heat exchanger for recovering waste heat from flue gas according to claim 2, characterized in that: The liquid water heated by the heater circulates into the heat exchange tubes of the heat exchange unit.

4. A low-pressure water-based heat exchanger for recovering waste heat from flue gas that implements the anti-blocking and anti-corrosion method for a low-pressure water-based heat exchanger for recovering waste heat from flue gas as described in any one of claims 1 to 3, characterized in that: It includes heat exchange units, water supply pipes and air supply pipes; the number of heat exchange units is more than three groups, the structure of each heat exchange unit is the same and they are connected in parallel; the heat exchange units are all in the shape of a bundle of heat exchange tubes, one end of the heat exchange unit is the inlet and the other end is the outlet, one end of the water supply pipe is connected to the water source, and the other end branches into three or more water supply branches, the water supply branches are connected to the inlet of the heat exchange unit, each group of heat exchange units corresponds to at least one water supply branch, and each water supply branch is provided with a water inlet valve; one end of the air supply pipe is connected to the air source, and the other end branches into three or more air supply branches, the air supply branches are connected to the inlet of the heat exchange unit, each group of heat exchange units corresponds to at least one air supply branch, and each air supply branch is provided with an air inlet valve.

5. The low-pressure water-based heat exchanger for recovering waste heat from flue gas according to claim 4, characterized in that: The number of water supply branches is equal to the number of heat exchange units and corresponds one to one, and the water supply branches are connected to the inlets of the corresponding heat exchange units; the number of gas supply branches is equal to the number of heat exchange units and corresponds one to one, and the gas supply branches are connected to the inlets of the corresponding heat exchange units.

6. A low-pressure water-based heat exchanger anti-blocking and anti-corrosion system for recovering waste heat from flue gas, characterized by: It includes the low-pressure water-medium heat exchanger for recovering waste heat from flue gas as claimed in claim 4 or 5, an air preheater, a buffer water tank, an air heater and a hot water circulation pump; The air preheater is provided with an inlet air duct, an outlet air duct, an inlet flue and an outlet flue; The low-pressure water-medium heat exchanger is installed in the outlet flue of the air preheater; The heater is installed in the inlet air duct of the air preheater; The outlet of the heat exchange unit, the inlet of the buffer water tank, the outlet of the buffer water tank, the inlet of the heater, the outlet of the heater, the inlet of the hot water circulation pump, the outlet of the hot water circulation pump, the water supply pipe and the inlet of the heat exchange unit are connected in sequence to form a cycle.

7. The low-pressure water-based heat exchanger anti-blocking and anti-corrosion system for recovering waste heat from flue gas according to claim 6, characterized in that: An overflow pipe is provided at the top of the side wall of the buffer water tank, and an overflow valve is provided on the overflow pipe; a drain pipe is provided at the bottom of the buffer water tank, and a drain valve is provided on the drain pipe; an outlet check valve is provided on the outlet pipe of the heat exchange unit.

8. The low-pressure water-based heat exchanger anti-blocking and anti-corrosion system for recovering waste heat from flue gas according to claim 6 or 7, characterized in that: The heat exchange unit of the low-pressure water medium heat exchanger is arranged vertically, with the upper end being the inlet and the lower end being the outlet.

9. The low-pressure water-based heat exchanger anti-blocking and anti-corrosion system for recovering waste heat from flue gas according to claim 6 or 7, characterized in that: The heat exchange units of the low-pressure water medium heat exchanger are arranged in sequence along the width direction of the cross section of the air preheater outlet flue, and the width of the cross section of the air preheater outlet flue is perpendicular to the flue gas flow direction.

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