Heat exchange system of secondary reheating coal-fired straight condensing unit

Abstract

The utility model provides a heat exchange system of a secondary reheating coal-fired straight condensing unit, and belongs to the technical field of thermal power generation. The secondary reheating coal-fired straight condensing unit comprises an air preheater, a primary reheater and a secondary reheater; the heat exchange system comprises a hot secondary air heater and a steam bypass. The hot secondary air heater is arranged on a hot secondary air mother pipe of the air preheater; the steam bypass penetrates through the hot secondary air heater, the input end of the steam bypass is connected with the output end of the primary low-temperature reheater, and the output end of the steam bypass is connected with the input end of the secondary low-temperature reheater; the steam bypass is used for receiving primary low-temperature reheat steam from the primary low-temperature reheater, and heat exchange is conducted between the primary low-temperature reheat steam and hot secondary air in the hot secondary air heater in the hot secondary air heater so as to heat the hot secondary air in the hot secondary air heater. And the steam bypass outputs the primary low-temperature reheated steam subjected to heat exchange to the secondary low-temperature reheater.

Description

Technical Field

[0001] The utility model relates to the technical field of thermal power generation, and particularly to a heat exchange system for a secondary reheat coal-fired condensing unit. Background Art

[0002] With the increasing proportion of clean energy such as photovoltaic and wind power, in the power system dominated by new energy, the role of coal power has gradually changed from the dominant power generation to the backup power supply. In 2020, the proportion of coal-fired installed capacity has dropped below 50%. To improve the consumption capacity of new energy, coal-fired units need to maintain a deep flexible operation state for a long time, and low-load operation has gradually become the norm. This operation state has a significant impact on the operation of the unit. Particularly prominent problems are low steam temperature and low temperature of the hot secondary air.

[0003] When the boiler is operating at low load, the steam temperatures of the superheater and reheater often decrease with the decrease of the load. Especially when the reheater steam temperature is too low, it will lead to a decrease in the relative internal efficiency of the steam turbine, a reduction in the overall efficiency of the unit, an increase in the exhaust steam humidity, and further deteriorate the working conditions of the last few stages of blades, affecting the safe operation of the steam turbine.

[0004] On the other hand, the hot secondary air plays a key role in maintaining the furnace temperature distribution and combustion stability. However, under low-load conditions, the temperature of the hot secondary air decreases, which will further affect the combustion efficiency of the boiler, reduce the furnace temperature, and lead to unstable combustion. Especially for boilers burning pulverized coal with a low volatile content, if no fuel-assisted combustion measures are taken, there is even a risk of furnace flameout, and at the same time, the loss of mechanical incomplete combustion will also increase.

[0005] Therefore, it is crucial to take effective solutions to the problems of low steam temperature and low temperature of the hot secondary air under low-load operation. Studying how to increase the steam temperature and the temperature of the hot secondary air under low-load conditions is of great significance for the stable operation of coal-fired power plant units. Content of the Utility Model

[0006] To solve the above technical defects, the utility model provides a heat exchange system for a secondary reheat coal-fired condensing unit. The heat exchange system extracts a part of the primary low-temperature reheated steam output from the primary low-temperature reheater through a steam bypass, and uses the heat of the primary low-temperature reheated steam to heat the hot secondary air through a secondary hot air heater to increase the temperature of the hot secondary air; and after extracting a part of the primary low-temperature reheated steam through the steam bypass, the primary low-temperature reheated steam input into the primary high-temperature reheater has a mismatch in the flue gas flow rate of the primary high-temperature reheater, which can effectively increase the temperature of the primary reheated steam at the outlet of the primary high-temperature reheater. At the same time, the once-cooled primary reheated steam after heat exchange is input into the secondary low-temperature reheater, which can increase the steam temperature at the inlet of the secondary low-temperature reheater to increase the temperature of the secondary reheated steam.

[0007] The first aspect of the present utility model provides a heat exchange system for a secondary reheat coal-fired condensing unit. The secondary reheat coal-fired condensing unit includes an air preheater, a primary reheater, and a secondary reheater. Among them, the primary reheater includes a primary low-temperature reheater, and the secondary reheater includes a secondary low-temperature reheater. The system includes: a hot secondary air heater and a steam bypass.

[0008] The hot secondary air heater is arranged on the hot secondary air main pipe of the air preheater.

[0009] The steam bypass penetrates through the hot secondary air heater. The input end of the steam bypass is connected to the output end of the primary low-temperature reheater, and the output end of the steam bypass is connected to the input end of the secondary low-temperature reheater.

[0010] The steam bypass is used to receive the primary low-temperature reheated steam from the primary low-temperature reheater, exchange heat between the primary low-temperature reheated steam and the hot secondary air in the hot secondary air heater in the hot secondary air heater to heat the hot secondary air in the hot secondary air heater, and the steam bypass outputs the primary low-temperature reheated steam after heat exchange to the secondary low-temperature reheater.

[0011] In an embodiment of the present utility model, the primary reheater further includes: a primary high-temperature reheater.

[0012] The output end of the primary low-temperature reheater is connected to the input end of the primary high-temperature reheater through a primary steam pipeline. The primary low-temperature reheater is used to convey the primary low-temperature reheated steam to the primary high-temperature reheater.

[0013] The input end of the steam bypass is connected to the primary steam pipeline, and the steam bypass is used to extract a part of the primary low-temperature reheated steam in the primary steam pipeline.

[0014] In an embodiment of the present utility model, a stop valve is provided in the steam bypass, and the stop valve is used to close or open the steam bypass.

[0015] In an embodiment of the present utility model, a regulating valve is further provided in the steam bypass, and the regulating valve is used to regulate the flow rate of the primary low-temperature reheated steam in the steam bypass.

[0016] In an embodiment of the present utility model, a flow meter is further provided in the steam bypass.

[0017] The flow meter is used to measure the flow rate value of the primary low-temperature reheated steam in the steam bypass.

[0018] In an embodiment of the present utility model, a first temperature measuring device and a second temperature measuring device are further provided in the steam bypass.

[0019] The first temperature measuring device is arranged at the input end of the steam bypass and is used to measure the temperature value of the primary low-temperature reheated steam input in the steam bypass;

[0020] The second temperature measuring device is arranged at the output end of the steam bypass and is used to measure the temperature value of the primary low-temperature reheated steam after heat exchange in the steam bypass.

[0021] In the embodiment of the present utility model, a third temperature measuring device and a fourth temperature measuring device are further arranged in the steam bypass;

[0022] The third temperature measuring device is arranged at the input end of the hot secondary air main pipe of the air preheater and is used to measure the temperature value of the hot secondary air before being heated by the hot secondary air heater;

[0023] The fourth temperature measuring device is arranged at the output end of the hot secondary air main pipe of the air preheater and is used to measure the temperature value of the hot secondary air after being heated by the hot secondary air heater.

[0024] In the embodiment of the present utility model, a pressure measuring device is further arranged in the steam bypass;

[0025] The pressure measuring device is used to measure the pressure value of the primary low-temperature reheated steam in the steam bypass.

[0026] In the embodiment of the present utility model, the regulating valve adjusts the flow rate of the primary low-temperature reheated steam in the steam bypass according to the temperature value of the primary low-temperature reheated steam after heat exchange, the flow rate value of the primary low-temperature reheated steam in the steam bypass, the pressure value of the primary low-temperature reheated steam in the steam bypass, the temperature value of the hot secondary air before being heated by the hot secondary air heater, and the temperature value of the hot secondary air after being heated by the hot secondary air heater.

[0027] In the embodiment of the present utility model, the materials of the hot secondary air heater and the steam bypass are the same as those of the primary low-temperature reheater.

[0028] The heat exchange system of the secondary reheat coal-fired condensing unit extracts a part of the primary low-temperature reheated steam output from the primary low-temperature reheater through the steam bypass, and uses the heat of the primary low-temperature reheated steam to heat the hot secondary air through the secondary hot air heater to increase the temperature of the hot secondary air; and after the steam bypass extracts a part of the primary low-temperature reheated steam, the primary low-temperature reheated steam input into the primary high-temperature reheater has a mismatch with the flue gas flow rate of the primary high-temperature reheater, which can effectively increase the temperature of the primary reheated steam at the outlet of the primary high-temperature reheater. At the same time, the primary lowest-temperature reheated steam after heat exchange is input into the secondary low-temperature reheater, which can increase the steam temperature at the inlet of the secondary low-temperature reheater to increase the temperature of the secondary reheat steam.

[0029] Other features and advantages of the technical solution of the present utility model will be described in detail in the following specific implementation section. Description of the Drawings

[0030] The drawings described herein are used to provide a further understanding of the present utility model and form a part of the present utility model. The schematic embodiments of the present utility model and their descriptions are used to explain the present utility model and do not constitute an improper limitation to the present utility model. In the drawings:

[0031] Figure 1 It is a schematic structural diagram of the heat exchange system of a secondary reheat coal-fired condensing unit provided by an embodiment of the present utility model.

[0032] Description of the Reference Numerals in the Drawings

[0033] 1 - Superheater, 2 - Ultra-high pressure cylinder, 3 - Primary low-temperature reheater, 4 - Primary high-temperature reheater, 5 - High-pressure cylinder, 6 - Secondary low-temperature reheater, 7 - Secondary reheat high-temperature superheater, 8 - Intermediate-pressure cylinder, 9 - Hot secondary air heater, 10 - Air preheater, 11 - Stop valve, 12 - Control valve, 13 - First temperature measuring device, 14 - Second temperature measuring device, 15 - Pressure measuring device, 16 - Fourth temperature measuring device, 17 - Third temperature measuring device, 18 - Hot secondary air main pipe, 19 - Cold secondary air main pipe, 20 - Cold primary air main pipe, 21 - Air preheater outlet flue main pipe, 22 - Flowmeter, 23 - Steam bypass. Specific Embodiments

[0034] In order to make the technical solutions and advantages in the embodiments of the present utility model clearer and more understandable, the following further describes the exemplary embodiments of the present utility model in conjunction with the drawings. Obviously, the described embodiments are only a part of the embodiments of the present utility model and not an exhaustive list of all embodiments. It should be noted that, without conflict, the embodiments in the present utility model and the features in the embodiments can be combined with each other.

[0035] In the description of the present utility model, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. They are only for the convenience of describing the present utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present utility model.

[0036] In addition, the terms "first" and "second" are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present utility model, the meaning of "a plurality" is at least two, such as two, three, etc., unless otherwise specifically defined.

[0037] In the present utility model, unless otherwise clearly specified and defined, terms such as "installed", "connected", "joined", "fixed", etc. shall be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or integrated; it may be a mechanical connection, an electrical connection, or a connection that allows mutual communication; it may be directly connected, or indirectly connected through an intermediate medium, and may be the internal communication of two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present utility model can be understood according to specific circumstances.

[0038] In the process of implementing the present utility model, the inventor found that as the proportion of clean energy such as photovoltaic and wind power has been increasing day by day, in the power system dominated by new energy, the role of coal-fired power has gradually changed from the dominant power generation to the backup power supply. In 2020, the proportion of coal-fired power installed capacity has dropped below 50%. To improve the consumption capacity of new energy, coal-fired units need to maintain a deep flexible operation state for a long time, and low-load operation has gradually become the norm. This operation state has had a significant impact on the unit operation, and the particularly prominent problems are low steam temperature and low temperature of the hot secondary air.

[0039] When the boiler is operating at low load, the steam temperatures of the superheater 1 and the reheater often decrease as the load decreases. Especially when the reheater steam temperature is too low, it will cause a decrease in the relative internal efficiency of the steam turbine, a reduction in the overall efficiency of the unit, an increase in the exhaust steam humidity, and further deteriorate the working conditions of the last few stages of blades, affecting the safe operation of the steam turbine.

[0040] On the other hand, the hot secondary air plays a key role in maintaining the furnace temperature distribution and combustion stability. However, under low-load conditions, the decrease in the temperature of the hot secondary air will further affect the combustion efficiency of the boiler, reduce the furnace temperature, and lead to unstable combustion. Especially for boilers burning pulverized coal with a low volatile content, if no fuel-assisted combustion measures are taken, there is even a risk of furnace flameout, and at the same time, the loss of mechanical incomplete combustion will also increase.

[0041] Therefore, it is crucial to take effective solutions to address the problems of low steam temperature and low temperature of the hot secondary air under low-load operation. Studying how to increase the steam temperature and the temperature of the hot secondary air under low-load conditions is of great significance for the stable operation of coal-fired power station units.

[0042] In view of the above problems, in the embodiments of the present utility model, a heat exchange system for a double reheat coal-fired condensing unit is provided. The double reheat coal-fired condensing unit includes an air preheater 10, a primary low-temperature reheater 3, and a secondary low-temperature reheater 6. The system includes: a hot secondary air heater 9 and a steam bypass 23; the hot secondary air heater 9 is arranged on the hot secondary air main pipe 18 of the air preheater 10; the steam bypass 23 penetrates through the hot secondary air heater 9. The input end of the steam bypass 23 is connected to the output end of the primary low-temperature reheater 3, and the output end of the steam bypass 23 is connected to the input end of the secondary low-temperature reheater 6; the steam bypass 23 is used to receive the primary low-temperature reheated steam from the primary low-temperature reheater 3, exchange heat with the hot secondary air in the hot secondary air heater 9 by using the heat of the primary low-temperature reheated steam in the hot secondary air heater 9 to heat the hot secondary air in the hot secondary air heater 9, and the steam bypass 23 outputs the primary low-temperature reheated steam after heat exchange to the secondary low-temperature reheater 6. The system extracts a part of the primary low-temperature reheated steam output from the primary low-temperature reheater 3 through the steam bypass 23, and uses the heat of the primary low-temperature reheated steam to heat the hot secondary air through the secondary hot air heater, which is used to increase the temperature of the hot secondary air; and after the steam bypass 23 extracts a part of the primary low-temperature reheated steam, the primary low-temperature reheated steam input into the primary high-temperature reheater 4 has a non-matching flue gas flow rate in the primary high-temperature reheater 4, which can effectively increase the temperature of the primary reheated steam at the outlet of the primary high-temperature reheater 4. At the same time, the primary lowest-temperature reheated steam after heat exchange is input into the secondary low-temperature reheater 6, which can increase the steam temperature at the inlet of the secondary low-temperature reheater 6 to increase the temperature of the secondary reheated steam.

[0043] Figure 1 is a schematic structural diagram of the heat exchange system of the double reheat coal-fired condensing unit provided by the embodiment of the present utility model. As Figure 1 shown, the double reheat coal-fired condensing unit includes: a superheater 1, an ultra-high pressure cylinder 2, a primary low-temperature reheater 3, a primary high-temperature reheater 4, a high-pressure cylinder 5, a secondary low-temperature reheater 6, a secondary reheat high-temperature superheater 7, an intermediate-pressure cylinder 8, and an air preheater 10. Among them, the air preheater 10 further includes: a hot secondary air main pipe 18, a cold secondary air main pipe 19, a cold primary air main pipe 20, and an air preheater outlet flue main pipe 21.

[0044] As Figure 1 shown, a heat exchange system of a double reheat coal-fired condensing unit provided by the present embodiment, the system is applied to a double reheat coal-fired condensing unit. The double reheat coal-fired condensing unit includes an air preheater 10, a primary low-temperature reheater 3, and a secondary low-temperature reheater 6. The system includes: a hot secondary air heater 9 and a steam bypass 23;

[0045] The hot secondary air heater 9 is arranged on the hot secondary air main pipe 18 of the air preheater 10;

[0046] The steam bypass 23 penetrates through the hot secondary air heater 9. The input end of the steam bypass 23 is connected to the output end of the primary low-temperature reheater 3, and the output end of the steam bypass 23 is connected to the input end of the secondary low-temperature reheater 6;

[0047] The steam bypass 23 is used to receive the primary low-temperature reheated steam from the primary low-temperature reheater 3, and exchange heat between the primary low-temperature reheated steam and the hot secondary air in the hot secondary air heater 9 to heat the hot secondary air in the hot secondary air heater 9. The steam bypass 23 outputs the primary low-temperature reheated steam after heat exchange to the secondary low-temperature reheater 6.

[0048] The steam bypass 23 is used to receive the primary low-temperature reheated steam output from the primary low-temperature reheater 3. The steam bypass 23 exchanges heat between the heat of the primary low-temperature reheated steam and the hot secondary air in the hot secondary air heater 9 to heat the hot secondary air. The primary low-temperature reheated steam after heat exchange is input to the secondary low-temperature reheater 6 through the output end of the steam bypass 23.

[0049] In this embodiment, the secondary reheat coal-fired condensing unit further includes a primary high-temperature reheater 4;

[0050] The output end of the primary low-temperature reheater 3 is connected to the input end of the primary high-temperature reheater 4 through a primary steam pipeline. The primary low-temperature reheater 3 is used to convey the primary low-temperature reheated steam to the primary high-temperature reheater 4;

[0051] The input end of the steam bypass 23 is connected to the primary steam pipeline. The steam bypass 23 is used to extract a part of the primary low-temperature reheated steam in the primary steam pipeline.

[0052] In this embodiment, a stop valve 11 is provided in the steam bypass 23. The stop valve 11 is used to close or open the steam bypass 23.

[0053] In this embodiment, a regulating valve 12 is further provided in the steam bypass 23. The regulating valve 12 is used to regulate the flow rate of the primary low-temperature reheated steam in the steam bypass 23.

[0054] In this embodiment, a flowmeter 22 is further provided in the steam bypass 23;

[0055] The flowmeter 22 is used to measure the flow rate value of the primary low-temperature reheated steam in the steam bypass 23.

[0056] In this embodiment, a first temperature measuring device 13 and a second temperature measuring device 14 are further provided in the steam bypass 23;

[0057] The first temperature measuring device 13 is arranged at the input end of the steam bypass 23 and is used for measuring the temperature value of the primary low-temperature reheated steam input in the steam bypass 23;

[0058] The second temperature measuring device 14 is arranged at the output end of the steam bypass 23 and is used for measuring the temperature value of the primary low-temperature reheated steam after heat exchange in the steam bypass 23.

[0059] In this embodiment, a third temperature measuring device 17 and a fourth temperature measuring device 16 are further provided in the steam bypass 23;

[0060] The third temperature measuring device 17 is arranged at the input end of the hot secondary air main pipe 18 of the air preheater 10 and is used for measuring the temperature value of the hot secondary air before being heated by the hot secondary air heater 9;

[0061] The fourth temperature measuring device 16 is arranged at the output end of the hot secondary air main pipe 18 of the air preheater 10 and is used for measuring the temperature value of the hot secondary air after being heated by the hot secondary air heater 9.

[0062] In this embodiment, a pressure measuring device 15 is further provided in the steam bypass 23;

[0063] The pressure measuring device 15 is used for measuring the pressure value of the primary low-temperature reheated steam in the steam bypass 23.

[0064] In this embodiment, the regulating valve 12 adjusts the flow rate of the primary low-temperature reheated steam in the steam bypass 23 according to the temperature value of the primary low-temperature reheated steam after heat exchange, the flow rate value of the primary low-temperature reheated steam in the steam bypass 23, the pressure value of the primary low-temperature reheated steam in the steam bypass 23, the temperature value of the hot secondary air before being heated by the hot secondary air heater 9, and the temperature value of the hot secondary air after being heated by the hot secondary air heater 9.

[0065] Specifically, a hot secondary air heater 9 is installed on the hot secondary air main pipe 18 at the outlet of the air preheater 10; under the low load condition of the unit, a part of the primary low-temperature reheated steam is extracted from the outlet of the primary low-temperature reheater 3 and passes through the hot secondary air heater 9 to transfer part of the heat of the primary low-temperature reheated steam to the hot secondary air to increase the temperature of the hot secondary air; the steam after heating the hot secondary air is sent back to the inlet of the secondary low-temperature reheater 6 by relying on the pressure difference between the primary reheated steam and the secondary reheated steam to increase the inlet steam temperature of the secondary low-temperature reheated steam.

[0066] The steam flow rate Q steam at the outlet of the above-mentioned extracted primary low-temperature reheater 3 is monitored by the flowmeter 22. After the steam is extracted, the steam flow rate entering the high-pressure cylinder 5 and the subsequent intermediate-pressure cylinder 8 shall not be lower than the minimum flow rate Q of the high-pressure cylinder 5 and the subsequent intermediate-pressure cylinder 8. min The minimum flow rate is provided by the steam turbine manufacturer.

[0067] Under the high-load condition of the unit, since the temperature of the hot secondary air and the steam temperature can both reach the rated value, no steam extraction is required. At this time, the stop valve 11 is closed; under the low-load condition of the unit, when the hot secondary air, the primary reheated steam, and the secondary reheated steam are under-temperature, the stop valve 11 is opened, and the extraction steam flow rate is adjusted through the regulating valve 12, which can ensure effective adjustment under different under-temperature conditions in the low-load condition. As the load increases, the opening degree of the regulating valve 12 decreases.

[0068] The above-mentioned first temperature measuring device 13 monitors the inlet steam temperature T1 of the hot secondary air heater 9, the second temperature measuring device 14 monitors the outlet steam temperature T2 of the hot secondary air heater 9, and the pressure measuring device 15 monitors the inlet steam pressure P of the hot secondary air heater 9. Since the pressure loss on the steam side is small, it can be considered that the steam side pressure at the inlet and outlet of the hot secondary air heat exchanger remains unchanged.

[0069] The above-mentioned fourth temperature measuring device 16 monitors the outlet hot secondary air temperature t2 of the hot secondary air heater 9, and the third temperature measuring device 17 monitors the inlet hot secondary air temperature t1 of the hot secondary air heater 9.

[0070] The steam temperature T2 monitored by the above-mentioned second temperature measuring device 14 needs to be greater than the exhaust steam temperature T of the high-pressure cylinder 5.

[0071] Therefore, the following three requirements need to be met simultaneously for each parameter:

[0072] T2>T;

[0073] Q 汽 <Q - Q min ;

[0074] Q 汽 (H1 - H2) = Q 风 (C2·t2 - C1·t1); Energy conservation.

[0075] Among them:

[0076] Q is the total steam flow rate entering the high-pressure cylinder 5;

[0077] Q 风 is the hot secondary air flow rate;

[0078] H1 and H2 are the enthalpy values of the steam at the inlet and outlet of the hot secondary air heat exchanger respectively, which can be obtained by querying T2, T1, and P;

[0079] C2 and C1 are the specific heat capacities of the hot secondary air at the outlet and inlet of the hot secondary air heat exchanger, respectively, which can be obtained based on the hot air temperature.

[0080] The above conditions can be input into the control system to ensure the safety and reliability of system operation.

[0081] In this embodiment, in order to ensure the safety of the system, the material of the hot secondary air heater 9 and the steam bypass 23 , the stop valve 11 and the regulating valve 12 is consistent with the material of the primary low-temperature reheater 3 .

[0082] The object of this embodiment is a 1000MW ultra-supercritical secondary reheat wet cooling unit. The steam turbine is an ultra-supercritical, secondary intermediate reheat, single-shaft, five-cylinder, four-exhaust, eleven-stage heat recovery, condensing steam turbine, and its model is N1000-31 / 605 / 623 / 623. The boiler adopts a single furnace, secondary reheat, balanced ventilation, open-air layout, solid slag discharge, all-steel frame, full suspension structure, tangential combustion mode, and tower boiler. At 20% load, the boiler main steam temperature is 560℃, the primary reheat steam temperature is 575℃, and the secondary reheat steam temperature is 580℃. At 20% load, the primary low-temperature reheater 3 outlet parameters are 520℃, 2.19MPa, and the enthalpy value found is 3510.35 kJ / kg; the secondary low-temperature reheater 6 inlet parameters are 411℃, 0.73MPa, and the enthalpy value found is 3291.9kJ / kg. The hot secondary air temperature at the outlet of the air preheater 10 is 275°C.

[0083] After adopting the technical solution of this patent, after calculation by the main engine factory of the steam turbine, the maximum steam extraction volume at 20% load cannot exceed 70t / h. Therefore, under this load, steam extraction is carried out at a steam extraction volume of 60t / h. After steam extraction, the temperature of the hot secondary air is increased from 275℃ to 294.5℃, an increase of 19.5℃. After the temperature of the hot secondary air is increased, the stable combustion effect of the boiler is greatly improved. The previous individual fire detection flickering problem is immediately improved, and the fire detection no longer flickers. At this time, the steam at the outlet of the primary low-temperature reheater 3 transfers about 3.1MW of heat to the hot secondary air. After heating the hot secondary air, the steam temperature is 436℃. After mixing at the inlet of the secondary low-temperature reheater 6, the steam temperature is increased from 411℃ to 413.2℃. Finally, due to the mismatch between the working fluid flow rate in the primary high-temperature reheater 4 and the corresponding flue gas flow rate, the working fluid temperature in the primary high-temperature reheater 4 increases significantly, causing the primary reheat steam temperature to increase from 575℃ to 597℃, an increase of 22℃. Due to the increase in inlet steam temperature, the secondary reheat steam temperature increases from 580 degrees Celsius to 582.6 degrees Celsius.

[0084] Although the preferred embodiments of the present utility model have been described, those skilled in the art can make additional changes and modifications to these embodiments once they learn the basic creative concept. Therefore, the appended claims are intended to be construed as including the preferred embodiments as well as all changes and modifications that fall within the scope of the present utility model.

[0085] Obviously, those skilled in the art can make various changes and modifications to the present utility model without departing from the spirit and scope of the present utility model. Thus, if these modifications and variations of the present utility model fall within the scope of the claims of the present utility model and their equivalent technologies, the present utility model is also intended to include these modifications and variations.

[0086] The optional embodiments of the present utility model have been described in detail above in conjunction with the accompanying drawings. However, the embodiments of the present utility model are not limited to the specific details in the above embodiments. Within the scope of the technical concept of the embodiments of the present utility model, various simple modifications can be made to the technical solutions of the embodiments of the present utility model, and these simple modifications all fall within the protection scope of the embodiments of the present utility model. Additionally, it should be noted that in the above specific embodiments, the various specific technical features described can be combined in any suitable manner without contradiction, as long as the combination does not violate the idea of the embodiments of the present utility model, and it should also be regarded as the content disclosed by the embodiments of the present utility model.

Claims

1. A heat exchange system for a secondary reheat coal-fired condensing unit, characterized in that, The secondary reheat coal-fired condensing unit includes an air preheater, a primary reheater, and a secondary reheater; among them, the primary reheater includes a primary low-temperature reheater, and the secondary reheater includes a secondary low-temperature reheater; The system includes: a hot secondary air heater and a steam bypass; The hot secondary air heater is arranged on the hot secondary air main pipe of the air preheater; The steam bypass penetrates through the hot secondary air heater. The input end of the steam bypass is connected to the output end of the primary low-temperature reheater, and the output end of the steam bypass is connected to the input end of the secondary low-temperature reheater; The steam bypass is used to receive the primary low-temperature reheated steam from the primary low-temperature reheater, exchange heat between the primary low-temperature reheated steam and the hot secondary air in the hot secondary air heater in the hot secondary air heater to heat the hot secondary air in the hot secondary air heater, and the steam bypass outputs the primary low-temperature reheated steam after heat exchange to the secondary low-temperature reheater.

2. The heat exchange system of the secondary reheat coal-fired condensing unit according to claim 1, wherein The primary reheater further includes: a primary high-temperature reheater; The output end of the primary low-temperature reheater is connected to the input end of the primary high-temperature reheater through a primary steam pipeline, and the primary low-temperature reheater is used to transport the primary low-temperature reheated steam to the primary high-temperature reheater; The input end of the steam bypass is connected to the primary steam pipeline, and the steam bypass is used to extract a part of the primary low-temperature reheated steam in the primary steam pipeline.

3. The heat exchange system of the secondary reheat coal-fired condensing unit according to claim 1, characterized in that A stop valve is provided in the steam bypass, and the stop valve is used to close or open the steam bypass.

4. The heat exchange system of the secondary reheat coal-fired condensing unit according to claim 1, characterized in that, A regulating valve is further provided in the steam bypass, and the regulating valve is used to adjust the flow rate of the primary low-temperature reheated steam in the steam bypass.

5. The heat exchange system of the secondary reheat coal-fired condensing unit according to claim 4, characterized in that A flowmeter is further provided in the steam bypass; The flowmeter is used to measure the flow rate value of the primary low-temperature reheated steam in the steam bypass.

6. The heat exchange system of the double reheat coal-fired condensing unit according to claim 5, characterized in that, A first temperature measuring device and a second temperature measuring device are further provided in the steam bypass; The first temperature measuring device is arranged at the input end of the steam bypass and is used to measure the temperature value of the primary low-temperature reheated steam input into the steam bypass; The second temperature measuring device is arranged at the output end of the steam bypass and is used to measure the temperature value of the primary low-temperature reheated steam after heat exchange in the steam bypass.

7. The heat exchange system of the secondary reheat coal-fired condensing unit according to claim 6, characterized in that, A third temperature measuring device and a fourth temperature measuring device are further provided in the steam bypass; The third temperature measuring device is arranged at the input end of the hot secondary air main pipe of the air preheater and is used to measure the temperature value of the hot secondary air before being heated by the hot secondary air heater; The fourth temperature measuring device is arranged at the output end of the hot secondary air main pipe of the air preheater and is used to measure the temperature value of the hot secondary air after being heated by the hot secondary air heater.

8. The heat exchange system of the secondary reheat coal-fired condensing unit according to claim 7, characterized in that, A pressure measuring device is further provided in the steam bypass; The pressure measuring device is used to measure the pressure value of the primary low-temperature reheated steam in the steam bypass.

9. The heat exchange system of the double reheat coal-fired condensing unit according to claim 8, characterized in that, The regulating valve adjusts the flow rate of the primary low-temperature reheated steam in the steam bypass according to the temperature value of the primary low-temperature reheated steam after heat exchange, the flow rate value of the primary low-temperature reheated steam in the steam bypass, the pressure value of the primary low-temperature reheated steam in the steam bypass, the temperature value of the hot secondary air before being heated by the hot secondary air heater, and the temperature value of the hot secondary air after being heated by the hot secondary air heater.

10. The heat exchange system of the double reheat coal-fired condensing unit according to claim 1, characterized in that, The materials of the hot secondary air heater and the steam bypass are the same as those of the primary low-temperature reheater.

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