System for controlling corrosion prevention and blockage prevention of air preheater by using separated heat pipe

Abstract

The invention discloses a system for controlling corrosion prevention and blockage prevention of an air preheater by using a separated heat pipe, which is characterized in that a heat pipe evaporation section is arranged in a flue gas channel connected with the air preheater, a heat pipe condensation section is arranged in an air channel connected with the air preheater, and the heat pipe evaporation section is communicated with the heat pipe condensation section through a steam ascending pipe and a condensate descending pipe. Smoke coming out of the air preheater enters the evaporation section of the heat pipe through the smoke channel and exchanges heat with a working medium in the pipe, the working medium is vaporized into steam, the steam exchanges heat with cold air in the condensation section and is condensed into liquid after releasing heat, and therefore circulation heat exchange of the working medium is achieved. The invention provides a set of novel heat pipe heat exchanger which is matched with an air preheater to work, so that the effect of preposed air preheating is achieved, the defects of a'air heater 'are avoided, the phenomena of low-temperature corrosion and ash deposition blockage of the air preheater are reduced, and passive active heat exchange and additional energy consumption are reduced, so that multiple effects are achieved.

Description

Technical Field

[0001] The invention belongs to the field of power station boiler and waste heat recovery, and in particular relates to a system that utilizes a separate heat pipe to control low-temperature corrosion and ash accumulation and blockage of an air preheater. Background Art

[0002] In the tail heating surface of a large boiler, the air preheater is an important waste heat recovery equipment. During the combustion of fuel, SO2 and a small amount of SO3 are generated. When SO3 is below 200°C, it will combine with water vapor to generate sulfuric acid vapor. Other acids (hydrochloric acid, nitric acid, etc.) also exist in the flue gas in gaseous form. When the temperature of the heating surface is lower than the dew point temperature of the acid, the acid vapor will condense on the heating surface and cause corrosion, that is, low-temperature corrosion. During the operation of the SCR denitrification system, NH3 gas will inevitably be generated. The escaped NH3 will react with SO3 and water vapor in the flue gas to form ammonium bisulfate condensate. After condensation, ammonium bisulfate adheres to the heating surface and captures fly ash in the flue gas, causing the air preheater to be blocked. The survey results of the operation of coal-fired boiler air preheaters show that more than 95% of the boiler air preheaters have different degrees of ash accumulation and blockage, resulting in reduced heat exchange efficiency of the air preheater, increased energy consumption of the unit, and increased emission of smoke pollutants, affecting the economic operation and pollutant emission indicators of the unit.

[0003] At present, the measures to control low-temperature corrosion and ash accumulation and blockage of air preheaters are: 1) Increase the temperature of the metal wall. The reason for low-temperature corrosion is that the wall temperature of the cold end of the air preheater is lower than the acid dew point of the flue gas. The sulfuric acid vapor condenses when it encounters cold, causing metal corrosion. If the wall temperature of the cold end of the air preheater is increased, the corrosion will inevitably weaken. At present, the ambient air is generally preheated by investing in a heater and opening a large hot air recirculation to increase the wall temperature of the cold end of the air preheater. However, the investment in the installation of a heater system is large, and the inlet air volume increases, the system resistance increases, and thus the power consumption increases. 2) Reduce the SO3 concentration, use low-sulfur coal, use an appropriate amount of CaO and coal for mixed combustion, and reasonably adjust the combustion air intake. Install an oxygen concentration monitoring point in the flue at the rear of the boiler to monitor in real time to ensure that the boiler is properly oxygenated. 3) The low-temperature heating surface is made of corrosion-resistant materials. The heating surface at the rear of the boiler is generally made of 20 steel. The sulfuric acid vapor is deposited when it encounters cold, causing serious low-temperature corrosion. In China, some power plants use enamel plating on low-temperature heating surfaces to reduce corrosion and wear of tube bundles, but enamel tubes are prone to glaze shedding and insufficient heat exchange capacity. 4) Improve the automatic injection rate of ammonia spray adjustment. During the ammonia spraying process, the water vapor content in the flue gas increases, which increases the partial pressure of water vapor. After combining with SO3, more sulfuric acid vapor is generated, which will cause a sharp increase in the dew point temperature of the flue gas. In addition, the adsorption capacity of high ash for SO3 further increases the probability of corrosion and ash blockage. According to the test of the ammonia nitrogen molar ratio distribution in the SCR reactor, necessary improvements are made to the ammonia spray grid system to increase the range and flexibility of adjustment. 5) Urea is used as a denitrification catalyst. Since ammonia water and liquid ammonia, the raw materials for ammonia production, are both major hazardous sources and pose major safety hazards, urea is a green fertilizer that does not pollute the environment. It is essentially the same as liquid ammonia in denitrification efficiency and performance, and is not subject to regulatory restrictions, making it easy to transport, store and use. Summary of the invention

[0004] The purpose of the present invention is to provide a system for controlling the corrosion and blockage prevention of an air preheater by using a separate heat pipe, using the flue gas at the air preheater outlet to heat the ambient air, and controlling the wall temperature by adjusting the areas of the hot end and the cold end, thereby avoiding high corrosion areas and alleviating low-temperature corrosion and dust accumulation, thereby achieving the effect of preheating the air and avoiding the shortcomings of a "warm air machine", thereby realizing the recovery and utilization of waste heat from low-temperature flue gas. The present invention can be widely used in power station boilers.

[0005] The present invention can be implemented by relying on the following technical solution: a system for controlling the corrosion and blocking prevention of an air preheater using a separate heat pipe, characterized in that a heat pipe heat exchanger is respectively arranged at the hot end and the cold end of the air preheater, and the two heat pipe heat exchangers are connected.

[0006] Furthermore, the present invention utilizes a system for controlling low-temperature corrosion of an air preheater using a separate heat pipe, wherein a heat pipe evaporation section is provided in a flue gas channel connected to the air preheater, and a heat pipe condensation section is provided in an air channel connected to the air preheater, and the heat pipe evaporation section and the heat pipe condensation section are connected via a steam riser and a condensate descender.

[0007] Furthermore, the heat exchange tube bundle inside the evaporation section of the heat pipe is a vertically placed elliptical heat tube bundle, which is perpendicular to the flue gas scouring direction, thereby reducing the gas flow resistance and enhancing the heat exchange capacity between the working medium and the flue gas in the tube.

[0008] Furthermore, the elliptical heat pipe bundles are arranged in a staggered arrangement.

[0009] Furthermore, the heat exchange tube bundle inside the heat pipe condensation section is a vertically placed spiral fin circular heat pipe bundle, which is perpendicular to the air sweeping direction. Fins are installed on the outside of the heat pipe to increase the contact area with the air and enhance the heat exchange capacity between the superheated steam in the tube and the air outside the tube.

[0010] Furthermore, the elliptical heat pipe bundle, the spiral fin circular heat pipe bundle, the steam riser and the condensate descender form a closed heat cycle loop.

[0011] Furthermore, the closed loop is vacuum treated and filled with circulating water to exchange heat with the flue gas.

[0012] Furthermore, the heat pipe condensation section is equipped with an air intake valve and an exhaust valve. By controlling the air intake valve, a part of the cold air enters the heat pipe condensation section, and enters the air preheater through the air channel after heat exchange with the heat pipe condensation section, and the other part of the cold air enters the cold air bypass duct and mixes with the air at the outlet of the air preheater. When the temperature of the tail pipe wall of the air preheater is lower than the dew point of sulfuric acid, the air inlet flow rate is adjusted by controlling the air intake valve to increase the air temperature at the inlet of the air preheater and slow down low-temperature corrosion.

[0013] Furthermore, the heat pipe evaporation section and the heat pipe condensation section are both provided with a thermometer and a pressure gauge for measuring the inlet and outlet temperatures and pressures of the flue gas and the air.

[0014] Furthermore, a steam collecting pipe is provided at the upper end of the heat pipe evaporation section and the heat pipe condensation section, and a liquid collecting pipe is provided at the lower end of the heat pipe evaporation section and the heat pipe condensation section.

[0015] Furthermore, a heat transfer unit steam collecting pipe is provided at the upper end of the elliptical heat pipe bundle of the heat pipe evaporation section, and a heat transfer unit liquid collecting pipe is provided at the lower end of the elliptical heat pipe bundle, and both the steam collecting pipe and the liquid collecting pipe are circular pipes.

[0016] Furthermore, the steam riser and the condensate descender can both be made of carbon steel.

[0017] Furthermore, the elliptical heat pipe bundle in the evaporation section of the heat pipe can be made of carbon steel, stainless steel, copper, fluoroplastics, etc.

[0018] Furthermore, the spiral fin circular heat pipe bundle in the heat pipe condensation section can be made of carbon steel, stainless steel, copper, fluoroplastics, etc.

[0019] Compared with the prior art, the present invention has at least the following beneficial technical effects: (1) Monitor the temperature of the air preheater tail pipe wall, adjust the air inlet flow rate by controlling the air intake valve, increase the temperature of the air preheater tail pipe wall, and effectively prevent low-temperature corrosion; (2) The cold air diverted from the heat pipe condensing section by the air inlet valve is directly mixed with the hot air at the outlet of the air preheater through the cold air bypass duct and then enters the furnace; (3) The heat exchange tube bundle inside the heat pipe condensation section is a spiral fin circular heat pipe bundle, and fins are installed on the outside of the heat pipe to increase the contact area with the air and enhance heat transfer; (4) The heat exchange tube bundle inside the evaporation section of the heat pipe is an elliptical heat tube bundle, which makes the internal structure more compact, reduces the gas flow resistance, and enhances heat transfer; (5) Compared with ordinary heat exchangers, the elliptical heat pipe technology has the advantages of heat transfer efficiency more than 15% higher than other types of heat exchangers, reduced flue gas pressure, resistance to low-temperature corrosion, resistance to fly ash wear, not easy to accumulate ash, high overall safety factor, the working fluid and air in the tube will not leak into the flue gas, and a wide operating temperature range; (6) By adjusting the area of ​​the hot end and the cold end, the wall temperature is controlled, the wall temperature of the cold end of the air preheater is increased, thereby avoiding the high corrosion area, slowing down low-temperature corrosion and ash accumulation, achieving the function of preheating the air, avoiding the shortcomings of the "air heater", and realizing the recovery and utilization of low-temperature flue gas waste heat; (7) A new type of corrosion-resistant and wear-resistant waste heat exchanger that combines separate heat pipe heat exchange technology and elliptical heat pipe technology has been developed to develop a heat pipe heat exchanger for utilizing waste heat from air preheater flue gas with high heat exchange performance, low flue gas pressure drop, low ash deposition performance, low corrosion characteristics and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the overall structure of the system according to the embodiment of the present invention.

[0021] Figure 2 Schematic diagram of the structure of the air preheater in the embodiment.

[0022] Figure 3 Schematic diagram of the separate heat pipe structure in the embodiment.

[0023] In the figure, 1. flue gas channel, 2. thermometer, 3. pressure gauge, 4. heat pipe evaporation section, 5. elliptical heat pipe bundle of heat pipe evaporation section, 6. air intake valve, 7. steam riser, 8. condensate downcomer, 9. spiral fin circular heat pipe bundle of heat pipe condensation section, 10. exhaust valve, 11. heat pipe condensation section, 12. air channel, 13. cold air bypass pipe, 14. gas collecting pipe, 15. liquid collecting pipe. Implementation

[0024] To make the present invention more clearly understood, a system of the present invention using a separate heat pipe to control low-temperature corrosion and dust accumulation and blockage of an air preheater is further described below. The specific examples described here are only used to explain the present invention and are not used to limit the present invention. Example

[0025] refer to Figure 1-3 A system for controlling the corrosion and blockage prevention of an air preheater by using a separated heat pipe is mainly used for flue gas waste heat recovery and air preheater corrosion and blockage prevention, and is composed of a flue gas channel (1), a thermometer (2), a pressure gauge (3), a heat pipe evaporation section (4), an elliptical heat pipe bundle (5), an air inlet valve (6), a steam riser (7), a condensate downcomer (8), a spiral fin circular heat pipe bundle (9), an exhaust valve (10), a heat pipe condensation section (11), an air channel (12), a cold air bypass pipe (13), a gas collecting pipe (14), a liquid collecting pipe (15) and other main components.

[0026] The system of the embodiment is provided with a heat pipe evaporation section (4) in a flue gas channel (1) connected to an air preheater, and a heat pipe condensation section (11) in an air channel (12) connected to the air preheater; the heat pipe evaporation section (4) and the heat pipe condensation section (11) are connected via a steam riser (7) and a condensate descender (8).

[0027] The air preheater is connected to the flue gas channel (1), which is connected to the heat pipe evaporation section (4). The heat pipe evaporation section is equipped with a thermometer (2) and a pressure gauge (3). The internal heat exchange tube bundle is an elliptical heat pipe bundle (5) placed vertically, with a steam riser (7) and a condensate down pipe (8) connected to the top. The upper ends of the steam riser (7) and the condensate down pipe (8) are connected to the heat pipe condensation section (11). The heat pipe condensation section is equipped with a thermometer (2) and a pressure gauge (3). The internal heat exchange tube bundle is a spiral fin circular heat pipe bundle (9) placed vertically, with spiral fins on the outside of the tube bundle, arranged in a staggered arrangement. The condensation section is equipped with an air intake valve (6) and an exhaust valve (10). By controlling the air intake valve (6), a part of the cold air enters the heat pipe condensation section (9), exchanges heat with the condensation section, and enters the air preheater through the air channel (12). The other part of the cold air enters the cold air bypass pipe (13), mixes with the air from the air preheater, and enters the furnace.

[0028] In the embodiment, the elliptical heat pipe bundle (5), the spiral fin circular heat pipe bundle (9), the steam riser (7), and the condensate descender (8) tube form a heat cycle closed loop, and the closed loop is vacuum treated and filled with circulating water to exchange heat with the flue gas.

[0029] In the embodiment, a heat transfer unit steam collecting pipe (14) is provided at the upper end of the elliptical heat pipe bundle of the heat pipe evaporation section and the heat pipe condensation section, and a heat transfer unit liquid collecting pipe (15) is provided at the lower end of the elliptical heat pipe bundle of the heat pipe evaporation section and the heat pipe condensation section, and both the steam collecting pipe and the liquid collecting pipe are circular pipes.

[0030] In the embodiment, the steam riser (7) and the condensate descender (8) can be made of carbon steel; the elliptical heat pipe bundle (5) in the evaporation section of the heat pipe can be made of carbon steel, stainless steel, copper, fluoroplastics, etc.; the spiral fin circular heat pipe bundle (9) in the condensation section of the heat pipe can be made of carbon steel, stainless steel, copper, fluoroplastics, etc.

[0031] Working principle of this embodiment 1. Working principle of flue gas waste heat recovery using separate heat pipe heat exchanger: The separated heat pipe heat exchanger uses the flue gas at the air preheater outlet to heat the ambient air. Based on the separation of the heat pipe evaporation section and the heat pipe condensation section, the heat can be transported over a long distance, thereby realizing the recovery and utilization of flue gas waste heat. The flue gas from the air preheater enters the heat pipe evaporation section (4) through the flue gas channel (1), flushes the elliptical heat pipe bundle (5) in the evaporation section, and the temperature of the working medium in the tube increases, vaporizing into working medium steam. The working medium steam enters the heat pipe condensation section (11) through the steam riser, and exchanges heat with cold air in the spiral fin circular heat pipe bundle (9) in the condensation section, heating the cold air to preheat the air. The working medium steam releases heat and condenses into liquid, and flows into the heat pipe evaporation section through the condensate downcomer (8), completing a cycle, thereby realizing the cyclic heat exchange of the working medium. The separate heat pipe heat exchanger controls the wall temperature by adjusting the area of ​​the hot end and the cold end, thereby increasing the wall temperature of the cold end of the air preheater, thereby avoiding the high corrosion area and slowing down low-temperature corrosion and ash accumulation. It not only achieves the purpose of preheating the air, but also avoids the shortcomings of the "air heater" and realizes the recovery and utilization of low-temperature flue gas waste heat.

[0032] 2. Working principle of preventing low temperature corrosion and ash accumulation and blockage of air preheater: During the operation of the boiler air preheater, a large amount of ammonia escape and a low cold end temperature will cause ammonium bisulfate to condense and adhere to the heating surface, and capture fly ash in the flue gas, causing the air preheater to be blocked. Before entering the air preheater, the cold air exchanges heat with the working medium steam in the heat pipe condensation section (11), absorbs heat to increase the temperature, and plays a role in preheating the air. If the preheated air is still lower than the sulfuric acid dew point temperature after heat exchange, the air intake valve (6) is controlled to increase the cold air flow from the cold air bypass channel (13) to the air outlet of the air preheater. Correspondingly, the cold air flow entering the heat pipe condensation section is reduced, while the working medium flow remains unchanged, thereby increasing the air temperature entering the air preheater, increasing the cold end wall temperature, and slowing down corrosion and ash accumulation.

[0033] The above is a detailed description of the implementation methods of the present invention in conjunction with the accompanying drawings, but the present invention is not limited to the described implementation methods. For ordinary technicians in this field, within the scope of the principles and technical ideas of the present invention, various changes, modifications, substitutions and deformations of these implementation methods still fall within the protection scope of the present invention.

Claims

1. A system for controlling the corrosion and blocking of air preheaters using separate heat pipes, characterized in that A heat pipe heat exchanger is respectively arranged at the hot end and the cold end of the air preheater, and the two heat pipe heat exchangers are connected.

2. A system for controlling low temperature corrosion of an air preheater using a separate heat pipe according to claim 1, characterized in that A heat pipe evaporation section is arranged in the flue gas channel connected to the air preheater, and a heat pipe condensation section is arranged in the air channel connected to the air preheater. The heat pipe evaporation section and the heat pipe condensation section are connected through a steam riser and a condensate descender.

3. A system for controlling low temperature corrosion of an air preheater using a separate heat pipe according to claim 2, characterized in that The heat exchange tube bundle inside the evaporation section of the heat pipe is a vertically placed elliptical heat tube bundle.

4. A system for controlling low temperature corrosion of an air preheater using a separate heat pipe according to claim 3, characterized in that The arrangement of the elliptical heat tube bundles is a staggered arrangement.

5. A system for controlling low temperature corrosion of an air preheater using a separate heat pipe according to claim 2, characterized in that The heat exchange tube bundle inside the heat pipe condensation section is a vertically placed spiral fin circular heat pipe bundle.

6. A system for controlling low temperature corrosion of an air preheater using a separate heat pipe according to claim 2, 3, 4 or 5, characterized in that The elliptical heat pipe bundle, the spiral fin circular heat pipe bundle, the steam riser and the condensate descender form a closed heat cycle loop.

7. A system for controlling low temperature corrosion of an air preheater using a separate heat pipe according to claim 6, characterized in that The closed circuit is vacuum treated and filled with circulating water.

8. A system for controlling low temperature corrosion of an air preheater using a separate heat pipe according to claim 2, characterized in that The heat pipe condensation section is equipped with an air inlet valve and an exhaust valve. By controlling the air inlet valve, a part of the cold air enters the heat pipe condensation section, exchanges heat with the heat pipe condensation section and enters the air preheater through the air channel, while the other part of the cold air enters the cold air bypass duct and mixes with the air at the air preheater outlet.

9. A system for controlling low temperature corrosion of an air preheater using a separate heat pipe according to claim 2, characterized in that The evaporation section and the condensation section of the heat pipe are both provided with a thermometer and a pressure gauge.

10. A system for controlling low temperature corrosion of an air preheater using a separate heat pipe according to claim 2, characterized in that The upper ends of the elliptical heat pipe bundles of the heat pipe evaporation section and the heat pipe condensation section are provided with heat transfer unit steam collecting pipes, and the lower ends of the elliptical heat pipe bundles of the heat pipe evaporation section and the heat pipe condensation section are provided with heat transfer unit liquid collecting pipes.

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