Anti-corrosion device and method for low-temperature economizer

Abstract

The invention provides an anti-corrosion device and method for a low-temperature economizer, and belongs to the technical field of thermal power generation. The device comprises a low-temperature economizer, a flue gas temperature sensor and a flue gas component analyzer which are sequentially arranged from the upstream to the downstream of a flue; the low-temperature economizer comprises a high-temperature section heat exchanger and a low-temperature section heat exchanger, the high-temperature section waste heat water mother pipe is communicated with a condensation water connection branch pipeline and a heat exchanger bypass pipeline which are connected in parallel, the condensation water connection branch pipeline is connected with a plurality of low-pressure heaters respectively, and a high-temperature section electric control valve is arranged on the heat exchanger bypass pipeline; the low-temperature section waste heat water main pipe is communicated with a plurality of air heaters which are connected in parallel; and a low-temperature section electric control valve is arranged on the low-temperature section waste heat water mother pipe. The high-temperature section is provided with a plurality of branch pipelines, the connecting position of the high-temperature section waste heat water main pipe and the condensation water pipeline is flexibly adjusted, and it is ensured that the condensation water heating process has high waste heat recovery efficiency. A circulation network is independently established in the low-temperature section, and the influence of the low-temperature section of the low-temperature economizer on a steam turbine regenerative system is reduced.

Description

Technical Field

[0001] This invention belongs to the field of thermal power generation technology, specifically relating to a low-temperature economizer corrosion prevention device and method. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] In thermal power generation, waste heat loss from the flue gas of coal-fired boilers is the main energy loss, accounting for about 4% of the fuel's heat release. Recovering and utilizing this waste heat can effectively reduce coal consumption. Installing a low-temperature economizer in the area between the air preheater and desulfurization tower in the flue gas system to recover waste heat and use it to heat the condensate in the regenerator system is an effective method for waste heat recovery. However, in actual operation, it has been found that low-temperature economizers are prone to corrosion, especially in the later stages. This is because when the coal type changes or the unit load is low, the actual operating conditions deviate from the economizer's design conditions, causing temperatures in some areas of the economizer to fall below the flue gas acid dew point. This leads to acid condensation on the tube walls in these areas, causing corrosion of the heat transfer tubes. Furthermore, current low-temperature economizers use waste water temperature as the control target, making it difficult to effectively regulate the flue gas temperature.

[0004] Low-temperature economizers that are idle due to corrosion problems not only fail to recover waste heat from flue gas, but also increase the resistance of the flue gas system. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a corrosion prevention device and method for low-temperature economizers. By adjusting system operating parameters, the flue gas temperature in the low-temperature section of the low-temperature economizer is controlled to be no lower than the acid dew point temperature, thereby preventing corrosion of the low-temperature economizer and extending its service life.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: In a first aspect, a low-temperature economizer corrosion protection device includes: a low-temperature economizer, a flue gas temperature sensor, and a flue gas composition analyzer arranged sequentially from upstream to downstream of the flue; the low-temperature economizer includes a high-temperature section heat exchanger and a low-temperature section heat exchanger; the high-temperature section heat exchanger is connected to a high-temperature section waste hot water main pipe, the high-temperature section waste hot water main pipe is connected to a parallel condensate connecting branch pipe and a heat exchanger bypass pipe, the condensate connecting branch pipe is connected to multiple low-pressure heaters respectively, a high-temperature circulating water pump is installed on the high-temperature section waste hot water main pipe, and a high-temperature section electric regulating valve is installed on the heat exchanger bypass pipe; The low-temperature section heat exchanger is connected to the low-temperature section waste hot water main pipe, which is connected to multiple parallel air heater pipes, and the air heater pipes are connected to the air heaters; a low-temperature section electric regulating valve is installed on the low-temperature section waste hot water main pipe.

[0007] Secondly, the low-temperature economizer corrosion prevention method based on the aforementioned low-temperature economizer corrosion prevention device includes the following steps: S1. Compare the outlet condensate temperature of multiple low-pressure heaters with the inlet and outlet temperatures of the high-temperature section heat exchanger. Supply water to the high-temperature section waste water header through the low-pressure heater whose condensate outlet temperature is lower than the inlet temperature of the high-temperature section heat exchanger and has the smallest temperature difference. After being heated by the high-temperature section heat exchanger, return water to the downstream of the low-pressure heater whose outlet temperature is lower than the outlet temperature of the high-temperature section heat exchanger and has the smallest temperature difference. S2. Supply water to the air heater through the low-temperature section waste hot water main pipe, and adjust the low-temperature section electric regulating valve to make the temperature of the low-temperature section waste hot water higher than the set value. S3. Calculate the flue gas dew point temperature based on the flue gas composition detected by the flue gas composition analyzer; S4. Adjust the electric regulating valve in the high-temperature section so that the temperature measured by the flue gas temperature sensor is within the set temperature range above the flue gas dew point temperature.

[0008] The beneficial effects of this invention are as follows: 1. This invention, by incorporating an electrically controlled regulating valve in the high-temperature section, allows for flexible adjustment of waste heat recovery between the high-temperature and low-temperature sections of the low-temperature economizer. This ensures sufficient waste heat from the flue gas is retained in the low-temperature section for heating primary and secondary air, and also prevents corrosion caused by the flue gas temperature in the low-temperature section falling below the dew point. The high-temperature section, through multiple branch pipes, allows for flexible adjustment of the connection position between the high-temperature waste hot water header and the condensate pipe, ensuring that the waste hot water is connected to the regenerative system at the most suitable location. This maximizes the replacement of high-parameter extraction steam, ensuring high waste heat recovery efficiency and economic benefits in the condensate heating process. The low-temperature section is separately connected to a circulating network, with all recovered waste heat used for heating primary and secondary air, thus separating it from the condensate system and reducing the impact of the low-temperature economizer section on the turbine regenerative system.

[0009] 2. The present invention includes an emergency heater as an emergency heating device, which can provide thermal compensation to the low-temperature waste hot water system based on the ambient temperature and the waste heat of the flue gas, preventing corrosion of the low-temperature economizer caused by excessively low temperature of the low-temperature waste hot water, as well as freezing of the primary and secondary air heaters. Attached Figure Description

[0010] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0011] Figure 1 This is a schematic diagram of the anti-corrosion device for the low-temperature economizer in Example 1.

[0012] Among them, 1. M1 electric gate valve; 2. T1 temperature sensor; 3. M2 electric gate valve; 4. T2 temperature sensor; 5. M3 electric gate valve; 6. T3 temperature sensor; 7. M4 electric gate valve; 8. T4 temperature sensor; 9. E1 High-Temperature Section Electric Regulating Valve; 10. T5 Temperature Sensor; 11. T6 Temperature Sensor; 12. Low-Temperature Section Heat Exchanger; 13. High-Temperature Section Heat Exchanger; 14. Emergency Heater; 15. M5 Electric Gate Valve; 16. E2 Low-Temperature Section Electric Regulating Valve; 17. High-Temperature Circulating Water Pump; 18. T7 Temperature Sensor; 19. F Flue Gas Composition Analyzer; 20. T8 Temperature Sensor; 21. Check Valve; 22. Pressure Regulating Valve; 23. High-Temperature Section Waste Hot Water Main Pipe; 24. Low-Temperature Section Waste Hot Water Main Pipe; 25. Low-Temperature Circulating Water Pump; 26. Primary Air Heater; 27. Secondary Air Heater; 28. T9 Temperature Sensor; 29. ​​T10 Temperature Sensor; 30. Pressure Transmitter. Detailed Implementation

[0013] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0014] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0015] One or more embodiments of the present invention provide a low-temperature economizer corrosion protection device, comprising: a high-temperature section heat exchanger, a low-temperature section heat exchanger, a flue gas temperature sensor, and a flue gas composition analyzer arranged sequentially from upstream to downstream of the flue. A low-temperature economizer corrosion protection device includes: a low-temperature economizer, a flue gas temperature sensor, and a flue gas composition analyzer arranged sequentially from upstream to downstream of the flue; the low-temperature economizer includes a high-temperature section heat exchanger and a low-temperature section heat exchanger; the high-temperature section heat exchanger is connected to a high-temperature section waste hot water main pipe, the high-temperature section waste hot water main pipe is connected to a parallel condensate connecting branch pipe and a heat exchanger bypass pipe, the condensate connecting branch pipe is connected to multiple low-pressure heaters respectively, a high-temperature circulating water pump is installed on the high-temperature section waste hot water main pipe, and a high-temperature section electric regulating valve is installed on the heat exchanger bypass pipe; The low-temperature section heat exchanger is connected to the low-temperature section waste hot water main pipe, which is connected to multiple parallel air heater pipes, and the air heater pipes are connected to the air heaters; a low-temperature section electric regulating valve is installed on the low-temperature section waste hot water main pipe.

[0016] In the above devices, the high-temperature section waste water header can utilize the waste heat of flue gas to heat the condensate in the power plant turbine regenerative system, while the low-temperature section waste water header can utilize the waste heat of flue gas to heat the primary and secondary air in the power plant turbine, thus realizing the recovery and utilization of waste heat from the flue gas. At the same time, the output of waste heat from the flue gas is limited by the electric regulating valve in the high-temperature section to prevent acid condensation on the pipe wall and corrosion of the heat transfer tubes due to excessively low flue gas temperature. Furthermore, while ensuring that the flue gas temperature is within the set range, the waste heat recovery amount of the high-temperature and low-temperature sections can be adjusted according to the operating conditions to achieve the best waste heat recovery effect.

[0017] Optionally, a temperature sensor is installed at the outlet of the low-pressure heater; electric gate valves are installed on multiple branch pipes; check valves are installed between adjacent branch pipes on the condensate connecting branch pipes; condensate heated to a set temperature by the set low-pressure heater enters the high-temperature section waste water header through the branch pipes, and after being heated by the high-temperature section heat exchanger, it is returned to the condensate pipe; by controlling the electric gate valves, the flow path of the condensate can be regulated so that the condensate gradually increases in temperature during the process of entering the high-temperature section heat exchanger from the condensate pipe and returning to the condensate pipe from the high-temperature section heat exchanger.

[0018] Optionally, a pressure regulating valve is installed downstream of the branch pipe on the condensate connecting branch pipe; the pressure regulating valve is used to adjust the residual hot water pressure before the high-temperature section electric regulating valve to be greater than the pressure after the valve, so that the condensate in the high-temperature section heat exchanger flows in a specific direction.

[0019] Optionally, a circulating water pump is installed on the high-temperature section waste water header, and temperature sensors are installed at the inlet and outlet ends of the high-temperature section heat exchanger. The circulating water pump is used to provide power for the condensate in the high-temperature section heat exchanger and pipeline. The temperature measured by the temperature sensor is compared with the outlet temperature of each low-pressure heater to determine the opening and closing status of the electric gate valve on each branch pipeline.

[0020] Optionally, an emergency heater is installed upstream of the heater pipe; the heat source for the emergency heater is auxiliary steam; the inlet pipe of the emergency heater is connected upstream of the low-temperature section electric regulating valve, and the outlet pipe of the emergency heater is connected downstream of the low-temperature section electric regulating valve. The temperature of the residual hot water in the low-temperature section is adjusted by adjusting the opening of the low-temperature section electric regulating valve to prevent the heater from freezing.

[0021] Optionally, the heater includes a primary air heater installed on the primary air duct and a secondary air heater installed on the secondary air duct. Temperature sensors are installed upstream of the heaters on both the primary and secondary air ducts to detect the inlet air temperature. The primary air heater is used to heat the primary air using the waste heat of the flue gas in the low-temperature section, and the secondary air heater is used to heat the secondary air using the waste heat of the flue gas in the low-temperature section.

[0022] Optionally, a circulating water pump is installed on the low-temperature section waste hot water header, and a temperature sensor is installed at the circulating water inlet of the low-temperature section heat exchanger; the circulating water pump is used to provide power to the low-temperature section heat exchanger and pipeline, and the temperature sensor is used to detect the temperature of the low-temperature section waste hot water.

[0023] One or more embodiments of the present invention provide a method for preventing corrosion of a low-temperature economizer based on a low-temperature economizer corrosion prevention device, comprising the following steps: S1. By comparing the outlet condensate temperature of the low-pressure heater with the inlet temperature of the high-temperature section heat exchanger, start the low-pressure heater with the condensate outlet temperature lower than the inlet temperature of the high-temperature section heat exchanger and the smallest temperature difference between the two to supply water to the high-temperature section waste water header, and return water to the downstream of the low-pressure heater with the condensate outlet temperature lower than the outlet temperature of the high-temperature section heat exchanger and the smallest temperature difference between the two. S2. Water is supplied to the air heater through the low-temperature section waste hot water main pipe. The low-temperature section electric regulating valve is adjusted to make the temperature of the low-temperature section waste hot water higher than the set value to prevent the air heater from freezing. S3. Calculate the flue gas dew point temperature based on the flue gas composition detected by the flue gas composition analyzer; S4. Adjust the electric regulating valve in the high-temperature section so that the temperature measured by the flue gas temperature sensor is within the set temperature range above the flue gas dew point temperature.

[0024] In the above process, the flue gas temperature is the control target. By controlling the degree of utilization of flue gas waste heat, the flue gas temperature is prevented from dropping below the flue gas dew point temperature, thus avoiding the risk of corrosion in the low-temperature section of the economizer and extending the service life of the economizer.

[0025] Optionally, in S1, condensate from the condensate pipe is used to replenish and pressurize the high-temperature section waste hot water main pipe, establishing a high-temperature section waste hot water circulation system. Then, the inlet and outlet temperatures of the high-temperature section heat exchanger are monitored, and the opening and closing status of the electric gate valves on the branch pipes is adjusted to allow condensate with a temperature lower than and closest to the inlet water temperature of the high-temperature section heat exchanger to enter the heat exchanger. The outlet water of the high-temperature section heat exchanger then enters a low-pressure heater with an inlet temperature lower than and closest to the outlet water temperature of the heat exchanger. This ensures the condensate is gradually heated, guaranteeing the waste heat recovery rate.

[0026] Optionally, in S2, the circulating water in the low-temperature section waste hot water header is heated by an emergency heater; the opening of the low-temperature section electric regulating valve is adjusted based on the data of the inlet air temperature of the primary air duct and the secondary air duct and the low-temperature section waste hot water temperature to prevent the heater from freezing due to excessively low temperature of the circulating water in the low-temperature section waste hot water header or excessively low inlet air temperature.

[0027] Optionally, in S4, when the temperature measured by the flue gas temperature sensor is lower than the set temperature range, the opening degree of the high-temperature section electric regulating valve and the low-temperature section electric regulating valve is increased; when the temperature measured by the flue gas temperature sensor is higher than the set temperature range, the opening degree of the high-temperature section electric regulating valve and the low-temperature section electric regulating valve is decreased; so as to effectively regulate the flue gas temperature, and also to regulate the recovery ratio of flue gas waste heat between the high-temperature section heat exchanger and the low-temperature section heat exchanger.

[0028] The present invention will be further described below with reference to specific embodiments.

[0029] Example 1 The flue gas waste heat recovery process consists of two stages. The first stage is the condensate heating stage, such as... Figure 1 As shown, the turbine regenerative system of the thermal power unit includes condensate pipes. The condensate pipes are sequentially equipped with low-pressure heaters #8, #7, #6, and #5, arranged according to the condensate flow direction. The condensate gradually heats up as it passes through these heaters. Temperature sensor 8 (T4) is installed at the outlet of low-pressure heater #8, temperature sensor 6 (T3) at the outlet of low-pressure heater #7, temperature sensor 4 (T2) at the outlet of low-pressure heater #6, and temperature sensor 2 (T1) at the outlet of low-pressure heater #5. The second stage is the boiler intake air heating stage, where air heaters using low-temperature waste water are installed in both the primary and secondary air ducts.

[0030] This embodiment provides a low-temperature economizer corrosion protection device, such as... Figure 1 As shown, it includes: a low-temperature economizer arranged sequentially from upstream to downstream of the flue, a T7 temperature sensor 18 for detecting flue gas temperature, an F flue gas composition analyzer 19, and a pressure transmitter 30; the low-temperature economizer includes a high-temperature section heat exchanger 13 and a low-temperature section heat exchanger 12 arranged along the flue gas flow direction.

[0031] The high-temperature section heat exchanger 13 is connected to the high-temperature section waste hot water header 23. The high-temperature section waste hot water header 23 is connected to parallel condensate connecting branch pipes and the heat exchanger bypass pipe. The condensate connecting branch pipes are connected to the outlet condensate pipes of the #8, #7, #6, and #5 low-temperature heaters via multiple branch pipes. An M4 electric gate valve 7 is installed on the branch pipe connecting to the #8 low-temperature heater outlet condensate pipe; an M3 electric gate valve 5 is installed on the branch pipe connecting to the #7 low-temperature heater outlet condensate pipe; an M2 electric gate valve 3 is installed on the branch pipe connecting to the #6 low-temperature heater outlet condensate pipe; and an M1 electric gate valve 1 is installed on the branch pipe connecting to the #5 low-temperature heater outlet condensate pipe. A pressure regulating valve 22 is installed downstream of the branch pipe on the network branch pipe; an E1 high-temperature section electric regulating valve 9 is installed on the heat exchanger bypass pipe. When the water in the high-temperature section waste hot water header 23 flows through the heat exchanger bypass pipe, it will not flow through the condensate connecting branch pipe; a high-temperature circulating water pump 17 is installed on the high-temperature section waste hot water header 23 on the inlet side of the high-temperature section heat exchanger 13. A T6 temperature sensor 11 is installed at the inlet end of the high-temperature section heat exchanger 13, and a T5 temperature sensor 10 is installed at the outlet end; check valves 21 are installed between adjacent branch pipes on the condensate connecting branch pipe to prevent condensate from flowing from the branch pipe where the M4 electric gate valve 7 is located to the branch pipe where the M1 electric gate valve 1 is located. The low-temperature section heat exchanger 12 is connected to the low-temperature section waste hot water header 24, which in turn connects to the parallel primary air heater pipes and secondary air heater pipes. The primary air heater pipes are connected to the primary air heater 26, and the secondary air heater pipes are connected to the secondary air heater 27. An E2 low-temperature section electric regulating valve 16 is installed on the low-temperature section waste hot water header 24 connected to the outlet end of the low-temperature section heat exchanger 12. An E2 low-temperature section electric regulating valve 16 is installed upstream of the heater pipes, and it is connected in parallel with the emergency heater 14. The emergency heater 14 is used for heating auxiliary steam for the plant. The heat source for the heater is auxiliary steam from the plant. An M5 electric gate valve 15 is installed on the auxiliary steam pipeline. The inlet pipe of the emergency heater 14 is connected upstream to the E2 low-temperature section electric regulating valve 16, and the outlet pipe of the emergency heater 14 is connected downstream to the E2 low-temperature section electric regulating valve 16. The E2 low-temperature section electric regulating valve 16 is used to regulate the amount of residual hot water entering the emergency heater 14 and to regulate the amount of heating of the low-temperature section residual hot water by the emergency heater 14, so as to ensure that the temperature of the low-temperature section residual hot water is maintained within the set range, thereby ensuring that the primary and secondary air heaters will not freeze due to the low temperature of the residual hot water in winter.

[0032] A T9 temperature sensor 28 is installed upstream of the primary air heater 26 in the primary air duct, and a T10 temperature sensor 29 is installed upstream of the secondary air heater 27 in the secondary air duct; a low-temperature circulating water pump 25 is installed on the low-temperature section waste hot water header 24, and a T8 temperature sensor 20 is installed at the circulating water inlet of the low-temperature section heat exchanger 12; the low-temperature circulating water pump 25 is used to provide power to the low-temperature section heat exchanger 12 and the pipeline, and the T8 temperature sensor 20 is used to detect the temperature of the low-temperature section waste hot water.

[0033] The corrosion prevention method for low-temperature economizers based on low-temperature economizer corrosion prevention devices includes the following steps: S1. Open the M4 electric gate valve 7 to replenish water and set the pressure in the high-temperature section waste hot water header 23 using the condensate in the condensate pipe. After starting the high-temperature circulating water pump 17 to establish the circulation of the high-temperature section waste hot water, use the T6 temperature sensor 11 to detect the inlet temperature of the high-temperature section heat exchanger 13 and the T5 temperature sensor 10 to detect the outlet temperature. Compare the inlet temperature with the values ​​of the T1 temperature sensor 2, T2 temperature sensor 4, T3 temperature sensor 6, and T4 temperature sensor 8 respectively. Adjust the M1 electric gate valve 1 and the M2 electric gate valve 7 accordingly. The opening and closing states of electric gate valves 3, 5, and 7 allow condensate with a temperature lower than and closest to the inlet temperature of the high-temperature heat exchanger 13 to enter the high-temperature waste water header 23. After being heated by the high-temperature heat exchanger 13, the condensate is transported to the low-temperature heater in the condensate pipeline with a temperature lower than and closest to the outlet temperature of the high-temperature heat exchanger 13. The condensate continues to be heated by multiple low-temperature heaters. Multiple check valves 21 can prevent condensate from being discharged back into the condensate pipeline directly through other branch pipes without passing through the high-temperature heat exchanger 13.

[0034] S2. Water is supplied to the primary air heater 26 and the secondary air heater 27 through the low-temperature section waste hot water header 24. The low-temperature section electric regulating valve is adjusted to make the temperature of the low-temperature section waste hot water higher than the set value, so as to meet the heating requirements of the primary and secondary air and heat the primary and secondary air to the set temperature. Since the temperature of the primary and secondary air participating in the boiler combustion process is high, the temperature of the flue gas entering the high-temperature section heat exchanger 13 will also increase, thereby increasing the temperature difference between the flue gas temperature and the flue gas dew point and preventing the heaters from freezing. On the other hand, when the ambient air temperature is too low as measured by the T9 temperature sensor 28 or the T10 temperature sensor 29, and the primary air heater 26 and the secondary air heater 27 are at risk of freezing, the emergency heater 14 is activated in time and the opening of the E2 low-temperature section electric regulating valve 16 is adjusted to heat the circulating water in the low-temperature section waste hot water header 24 and increase the temperature of the primary air heater 26 and the secondary air heater 27.

[0035] S3. Calculate the flue gas dew point temperature T using the flue gas composition detected by the F flue gas composition analyzer 19. L ; Specifically, TL =255+26.7*LOG((F1)*0.02)+18.7*LOG((F2*(p / 101.3)))+A; Wherein, F1: sulfur dioxide volume content (volume content, a decimal between 0 and 1). F2: Water vapor volume content (volume content, a decimal between 0 and 1); p: Flue gas pressure (absolute pressure, kPa) measured by pressure transmitter 30; A: Correction parameters, take values ​​between -5 and +5 depending on the volatile matter content of different coal types, take positive values ​​for lignite and negative values ​​for anthracite, unit: ℃; The values ​​255, 26.7, 0.02, 18.7, and 101.3 represent the standard atmospheric pressure.

[0036] S4. Adjust the opening of the E1 high-temperature section electric regulating valve 9 so that the temperature measured by the T7 temperature sensor 18 is within the set temperature range above the flue gas dew point temperature; when the temperature measured by the T7 temperature sensor 18 is lower than the set temperature range, increase the opening of the E1 high-temperature section electric regulating valve 9 and the E2 low-temperature section electric regulating valve 16; when the temperature measured by the T7 temperature sensor 18 is higher than the set temperature range, decrease the opening of the E1 high-temperature section electric regulating valve 9 and the E2 low-temperature section electric regulating valve 16; this effectively controls the flue gas temperature and also regulates the proportion of flue gas waste heat recovery between the high-temperature section heat exchanger 13 and the low-temperature section heat exchanger 12.

[0037] Specifically, in S1, the temperature measured by temperature sensor 2 (T1) is T1, the temperature measured by temperature sensor 4 (T2) is T2, the temperature measured by temperature sensor 6 (T3) is T3, the temperature measured by temperature sensor 8 (T4) is T4, the temperature measured by temperature sensor 10 (T5) is T5, and the temperature measured by temperature sensor 11 (T6) is T6. The condensate temperature at the outlet of the #8 low-pressure heater is set to T0 under the specified operating conditions. The opening and closing methods of electric gate valves M1 to M4 are as follows: M4 electric gate valve 7 opens and closes according to temperature T4: it opens when T4≥T0 and closes when T4<T0-δt. When T0-δt<T4<T0, M4 electric gate valve 7 does not need to operate and remains unchanged. M3 electric gate valve 5 opens and closes according to temperature T3: it opens when T5≥T3≥(T6-δt) and closes when T3<(T6-δt) or T3>(T5+δt); M2 electric gate valve 3 opens and closes according to temperature T2: it opens when T5≥T2≥(T6-δt) and closes when T2<(T6-δt) or T2>T5; M1 electric gate valve 1 opens and closes according to temperature T1: it opens when T5≥T1≥(T6-δt) and closes when T1<(T6-δt) or T1>T5; Furthermore, at least two of the M1 to M4 electric gate valves are open, and the condensate flow direction is as follows: Taking the opening of electric gate valve 1 (M1) and electric gate valve 3 (M2) as an example, at this time, because the pressure at the #5 low inlet is greater than the outlet pressure, the condensate enters the high-temperature section waste hot water header 23 from electric gate valve 3 (M2), then enters the high-temperature circulating water pump 17 through check valve 21 and pressure regulating valve 22, and then returns to the condensate at the outlet of the #5 low inlet from electric gate valve 1 (M1). Taking the opening of electric gate valve 1 (M1), electric gate valve 3 (M2), and electric gate valve 5 (M3) as an example, at this time, because the pressure at the #6 low-pressure inlet is greater than the pressure at the #5 low-pressure outlet, the condensate enters the high-temperature section waste hot water header 23 from electric gate valve 5 (M3), and then enters the high-temperature circulating water pump 17 through check valve 21 and pressure regulating valve 22, and then returns to the condensate at the #5 low-pressure outlet from electric gate valve 1 (M1). If only one of the electric gate valves M1 to M4 meets the opening condition, then the upstream valve should be opened accordingly: Only when the conditions for opening M1 electric gate valve 1 are met can the corresponding electric gate valve 3 be opened; Only when the conditions for opening the M2 electric gate valve 3 are met will the corresponding M3 electric gate valve 5 be opened; Only when the M3 electric gate valve 5 meets the opening conditions should the M4 electric gate valve 7 be opened. Only when the M4 electric gate valve 7 meets the opening conditions will the corresponding M3 electric gate valve 5 be opened.

[0038] Where δt∈(0~20℃), the value is taken and adjusted according to the system operation needs or design requirements.

[0039] Specifically, in S2, the inlet temperatures of the primary and secondary air are detected separately: the temperature measured by temperature sensor 28 (T9) is T9, and the temperature measured by temperature sensor 29 (T10) is T... 10 T a The antifreeze warning temperature for a primary air heater is 26°C, T. b This is the temperature at which the antifreeze warning for the secondary air heater 27 is lifted; if T9 < T a or T 10 <T a This indicates that either the primary air heater 26 or the secondary air heater 27 is at risk of freezing. In this case, the electric gate valve 15 of the auxiliary steam inlet pipe M5, located at the heat source of the emergency heater 14, should also be activated. If T9 > T b And T 10 >Tb This indicates that the risk of freezing in primary air heater 26 or secondary air heater 27 has been eliminated, and electric gate valve 15 (M5) is closed; among which T a ∈ (0~5℃), T b ∈ (2~10℃), T b >T a The value is selected and adjusted according to the system's operational needs or design requirements.

[0040] On the other hand, the overall residual hot water temperature of the detection temperature range is: T d The emergency heater 14 is set to the switching temperature; the temperature measured by temperature sensor 20 is T8. Determine the relationship between T8 and T... d Size, when T8 < T d This indicates that the overall temperature of the waste hot water in the low-temperature section is too low, and the heat provided by the low-temperature section heat exchanger 12 is insufficient to heat the waste hot water in the low-temperature section to the set temperature. To prevent the primary air heater 26 and the secondary air heater 27 from freezing, the emergency heater 14 also needs to be put into the system. In order to minimize the auxiliary steam consumption of the emergency heater 14, T8=T d To achieve the control objective, the PID controller adjusts the opening of the E2 low-temperature section electric regulating valve 16. When T8 > T d If the emergency heater 14 is heating too much, open the electric regulating valve 16 in the low-temperature section of E2 to reduce the amount of residual hot water entering the emergency heater 14; similarly, if T8 < T d At that time, the opening of the E2 low-temperature section electric regulating valve 16 is reduced; among which T d ∈ (50~90℃), the value is selected and adjusted according to the system operation needs or design requirements.

[0041] Specifically, in S4, the temperature measured by temperature sensor 18 is T7, compared to T... L The temperature sensor reading T7 on the flue gas outlet duct of the low-temperature economizer is: when T7 ≤ (T L When T7 > (T1 + δT), open the electric regulating valve 9 in the E1 high-temperature section to reduce the amount of condensate participating in the turbine regenerative system; when T7 > (T1 + δT), open the electric regulating valve 9 in the E1 high-temperature section to reduce the amount of condensate participating in the turbine regenerative system. L +δT), close the electric regulating valve 9 in the E1 high-temperature section to increase the amount of condensate participating in the turbine regenerative system, so that T7 = (T L +δT) is the control target, and the PID controls the opening of the electric regulating valve 9 in the high-temperature section of E1.

[0042] Where δT∈(-5~30℃), the value is taken and adjusted according to the system operation needs or design requirements.

[0043] Example 2 The corrosion prevention method of the low-temperature economizer corrosion prevention device in Example 1 under high load of pure condensing operation.

[0044] According to the unit manual, the outlet temperature of the condensate from the #8 low-pressure heater under pure condensate THA conditions is T0=80℃.

[0045] S1. After opening the M4 electric gate valve 7 and establishing the high-temperature section waste water circulation, the temperatures measured by each temperature sensor are: T1=140℃, T2=125℃, T3=100℃, T4=78℃, T5=120℃, T6=95℃; taking δt=5℃, then the M3 electric gate valve 5 and the M4 electric gate valve 7 are opened, and the M1 electric gate valve 1 and the M2 electric gate valve 3 are closed; since the pressure in the condensate pipeline is greater upstream than downstream, the condensate enters the system through the branch pipeline where the M4 electric gate valve 7 is located, enters the high-temperature section heat exchanger 13 for heating via the high-temperature circulating water pump 17, and then returns to the condensate pipeline of the turbine thermal system through the branch pipeline where the M3 electric gate valve 5 is located, completing the condensate heating process.

[0046] S2. Start the low-temperature circulating water pump 25. After establishing circulation, the temperature measured by each temperature sensor is: T8 = 75℃; take T... d =60℃ (the same applies below); T8>60℃, so open the E2 low-temperature section electric regulating valve 16 to increase the opening until T8=60℃ or the E2 opening reaches 100%; control the auxiliary steam heating participation rate in the boiler air intake heating process through the E2 low-temperature section electric regulating valve 16; T9=15℃, T 10 =11℃, take T a =2℃ (the same applies below), T b =5℃ (the same applies below), satisfying T9>5℃ and T 10 The condition >5℃ indicates that the ambient temperature is high, and there is no possibility of freezing for the primary air heater 26 and the secondary air heater 27. Therefore, the electric gate valve 15 of the auxiliary steam inlet pipe of the emergency heater is closed.

[0047] The flue gas composition analyzer S3 and F19 obtained the following values ​​for sulfur dioxide volume content F1 (0.00054) and water vapor volume content F2 (0.12573) in the flue gas. T7 = 110℃, and the flue gas pressure p is 97 kPa. Based on the characteristics of the coal purchased by the power plant, a correction parameter A = -1.5℃ is used. The flue gas dew point temperature T is then calculated using the following formula. L : T L =255+26.7*LOG((F1)*0.02)+18.7*LOG((F2*(p / 101.3kPa)))+A=103.66℃.

[0048] S4. Taking δT = 5℃ (the same applies below), then at this time T7 > (T L+δT), the opening of the electric regulating valve 9 in the high-temperature section of E1 should be reduced to decrease the bypass flow of residual hot water in the high-temperature section, thereby increasing the amount of condensate participating in the turbine regenerative system, so that T7 = (T L +δT) is the control objective. The PID controller adjusts the opening of the electric regulating valve 9 in the high-temperature section of E1 until T7 = (T L +δT) or E1 high-temperature section electric regulating valve 9 can be fully closed.

[0049] Example 3 The corrosion prevention method of the low-temperature economizer corrosion prevention device in Example 1 under low load in pure condensing conditions.

[0050] S1. After opening the M4 electric gate valve 7 and establishing the high-temperature section waste water circulation, the temperatures measured by each temperature sensor are: T1=110℃, T2=92℃, T3=72℃, T4=55℃, T5=110℃, T6=85℃; taking δt=5℃, then the M1 electric gate valve 1 and the M2 electric gate valve 3 are opened, and the M3 electric gate valve 5 and the M4 electric gate valve 7 are closed; since the pressure in the condensate pipeline is greater upstream than downstream, the condensate enters the system through the branch pipeline where the M2 electric valve 3 is located, enters the high-temperature section heat exchanger 13 for heating via the high-temperature circulating water pump 17, and then returns to the condensate pipeline of the turbine thermal system through the branch pipeline where the M1 electric valve 1 is located, completing the condensate heating process.

[0051] S2. Start the low-temperature circulating water pump 25. After establishing circulation, the temperature measured by each temperature sensor is: T8 = 65℃; take T... d =60℃; T8>60℃, so open the E2 low-temperature section electric regulating valve 16 to a larger extent until T8=60℃ or the E2 opening reaches 100%; control the auxiliary steam heating participation rate in the boiler air intake heating process through the E2 low-temperature section electric regulating valve 16; T9=5.2℃, T 10 =0.6℃, take T a =2℃ (the same applies below), T b =5℃ (the same applies below), satisfying T9 < 2℃ or T 10 The condition <2℃ indicates that the ambient temperature is low, and there is a possibility of freezing in the primary air heater 26 and the secondary air heater 27. Therefore, the electric gate valve 15 of the auxiliary steam inlet pipe of the emergency heater is opened. Once the temperature of the residual hot water in the low-temperature section T8 is <60℃, the auxiliary steam heating is switched on to prevent the primary air heater 26 and the secondary air heater 27 from freezing.

[0052] The flue gas composition analyzer S3 and F obtained the following values ​​for the volume content of sulfur dioxide (F1) in the flue gas: 0.00054; the volume content of water vapor (F2): 0.12573; T7 = 100℃; and the flue gas pressure p = 97 kPa. Based on the characteristics of the coal purchased by the power plant, a correction parameter A = -1.5℃ is taken. The flue gas dew point temperature T is then calculated using the following formula. L : T L =255+26.7*LOG((F1)*0.02)+18.7*LOG((F2*(p / 101.3kPa)))+A=103.66℃.

[0053] S4. Taking δT = 5℃, then T7 < (T L +δT), the opening of the electric regulating valve 9 in the high-temperature section of E1 should be increased to increase the bypass flow of waste water in the high-temperature section, thereby reducing the amount of condensate involved in the turbine regenerative system, so that T7 = (T L +δT) is the control objective. The PID controller adjusts the opening of the electric regulating valve 9 in the high-temperature section of E1 until T7 = (T L +δT) or E1 high-temperature section electric regulating valve 9 can be fully opened.

[0054] Example 4 The corrosion prevention method of the low-temperature economizer in Example 1 under rated steam extraction heating conditions.

[0055] According to the unit manual, the condensate outlet temperature of #8 under rated extraction steam conditions is T0=60℃.

[0056] S1. After opening the M4 electric gate valve 7 and establishing the high-temperature section waste water circulation, the temperatures measured by each temperature sensor are: T1=138℃, T2=95℃, T3=75℃, T4=53℃, T5=120℃, T6=95℃; take δt=5℃; then, based on the temperature judgment, the M4 electric gate valve 7, M3 electric gate valve 5, and M1 electric gate valve 1 are closed, while the M2 electric gate valve 3 is open. Since only the M2 electric gate valve 3 is open at this time, the M3 electric gate valve 5 is opened again to establish a complete condensate heating circulation; at this time, the condensate enters the system through the M3 electric gate valve 5, passes through the high-temperature circulating water pump 17, enters the high-temperature section heat exchanger 13 for heating, and then returns to the condensate pipeline of the turbine thermal system through the M2 electric gate valve 3, completing the condensate heating process.

[0057] S2. Start the low-temperature circulating water pump 25. After establishing circulation, check T8 = 55℃. Since T8 < 60℃, reduce the opening of the low-temperature section electric regulating valve 16 (E2) until T8 = 60℃ or E2 is completely closed; T9 = -2.5℃, T 10 = -8.0℃, satisfying T9 < 2℃ or T 10<2℃ indicates that the ambient temperature is low, and there is a possibility that the primary air heater 26 and the secondary air heater 27 may freeze. Therefore, open the M5 electric gate valve 15 to switch on the auxiliary steam heating to prevent the primary air heater 26 and the secondary air heater 27 from freezing.

[0058] The flue gas composition analyzer S3 and F obtained the following values ​​for flue gas: sulfur dioxide volume content F1 = 0.00043, water vapor volume content F2 = 0.12192, T7 = 105℃, flue gas pressure p = 95kPa. Based on the characteristics of the coal currently purchased by the power plant, a correction parameter A = 0.5℃ is taken, and the flue gas dew point temperature T is calculated using the following formula. L : T L =255+26.7*LOG((F1)*0.02)+18.7*LOG((F2*(p / 101.3kPa)))+A=102.9℃.

[0059] S4. At this time, T7 > (TL + δT), the opening of the electric regulating valve 9 in the high-temperature section of E1 should be reduced to decrease the bypass flow of the waste hot water in the high-temperature section, so as to increase the participation of condensate in the turbine regenerative system. With T7 = (TL + δT) as the control target, the opening of the electric regulating valve 9 in the high-temperature section of E1 should be adjusted by PID until T7 = (TL + δT) or the electric regulating valve 9 in the high-temperature section of E1 is completely closed.

[0060] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A corrosion prevention device for a low-temperature economizer, characterized in that, include: The following components are arranged sequentially from upstream to downstream of the flue: a low-temperature economizer, a flue gas temperature sensor, and a flue gas composition analyzer; the low-temperature economizer includes a high-temperature heat exchanger and a low-temperature heat exchanger. The high-temperature section heat exchanger is connected to the high-temperature section waste hot water main pipe. The high-temperature section waste hot water main pipe is connected to the parallel condensate connecting branch pipe and the heat exchanger bypass pipe. The condensate connecting branch pipe is connected to multiple low-pressure heaters respectively. The high-temperature section waste hot water main pipe is equipped with a high-temperature circulating water pump. The heat exchanger bypass pipe is equipped with a high-temperature section electric regulating valve. The low-temperature section heat exchanger is connected to the low-temperature section waste hot water main pipe, which is connected to multiple parallel air heater pipes, and the air heater pipes are connected to the air heaters; a low-temperature section electric regulating valve is installed on the low-temperature section waste hot water main pipe.

2. The low-temperature economizer corrosion protection device as described in claim 1, characterized in that, The outlet of the low-pressure heater is equipped with a temperature sensor; each of the multiple branch pipes is equipped with an electric gate valve; and a check valve is installed between adjacent branch pipes on the condensate connecting branch pipe.

3. The low-temperature economizer corrosion protection device as described in claim 1, characterized in that, A pressure regulating valve is installed downstream of the branch pipe on the condensate connecting branch pipe.

4. The low-temperature economizer corrosion protection device as described in claim 1, characterized in that, A circulating water pump is installed on the waste hot water header of the high-temperature section, and temperature sensors are installed at the inlet and outlet ends of the heat exchanger of the high-temperature section.

5. The low-temperature economizer corrosion protection device as described in claim 1, characterized in that, An emergency heater is installed upstream of the heater pipe; the heat source for the emergency heater is auxiliary steam for the plant.

6. The low-temperature economizer corrosion protection device as described in claim 1, characterized in that, The heater includes a primary air heater installed on a primary air duct and a secondary air heater installed on a secondary air duct. Temperature sensors are respectively installed upstream of the heater on the primary air duct and the secondary air duct.

7. The low-temperature economizer corrosion protection device as described in claim 1, characterized in that, A circulating water pump is installed on the waste hot water header of the low-temperature section, and a temperature sensor is installed at the circulating water inlet of the low-temperature section heat exchanger.

8. A method for preventing corrosion of a low-temperature economizer based on the low-temperature economizer corrosion prevention device as described in any one of claims 1-7, characterized in that, Includes the following processes: S1. Compare the outlet condensate temperature of multiple low-pressure heaters with the inlet and outlet temperatures of the high-temperature section heat exchanger. Supply water to the high-temperature section waste water header through the low-pressure heater whose condensate outlet temperature is lower than the inlet temperature of the high-temperature section heat exchanger and has the smallest temperature difference. After being heated by the high-temperature section heat exchanger, return water to the downstream of the low-pressure heater whose outlet temperature is lower than the outlet temperature of the high-temperature section heat exchanger and has the smallest temperature difference. S2. Supply water to the air heater through the low-temperature section waste hot water main pipe, and adjust the low-temperature section electric regulating valve to make the temperature of the low-temperature section waste hot water higher than the set value. S3. Calculate the flue gas dew point temperature based on the flue gas composition detected by the flue gas composition analyzer; S4. Adjust the electric regulating valve in the high-temperature section so that the temperature measured by the flue gas temperature sensor is within the set temperature range above the flue gas dew point temperature.

9. The method for preventing corrosion of a low-temperature economizer as described in claim 8, characterized in that, Through branch pipes, condensate from the condensate pipes is used to replenish water to the high-temperature section waste hot water main pipe and maintain pressure, thus establishing a high-temperature section waste hot water circulation system. Then, the inlet and outlet temperatures of the high-temperature section heat exchanger are monitored, and the opening and closing status of the electric gate valves in the branch pipes is adjusted.

10. The method for preventing corrosion of a low-temperature economizer as described in claim 8, characterized in that, In S2, the circulating water in the low-temperature section waste hot water main pipe is heated by the emergency heater, and the opening of the low-temperature section electric regulating valve is adjusted based on the inlet air temperature of the primary air duct and the secondary air duct and the low-temperature section waste hot water temperature. Alternatively, in S4, if the temperature measured by the flue gas temperature sensor is lower than the set temperature range, the opening of the high-temperature section electric regulating valve is increased; if the temperature measured by the flue gas temperature sensor is higher than the set temperature range, the opening of the high-temperature section electric regulating valve is decreased.

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