Coal-fired boiler flue gas circulation system and control method

Abstract

This invention provides a flue gas recirculation system and control method for a coal-fired boiler, relating to the field of flue gas treatment technology. Specifically, it includes a furnace, economizer, denitrification assembly, air preheater, dust collector, induced draft fan, and desulfurization tower connected in sequence. It also includes a first circulation pipeline, a second circulation pipeline, a first valve body, a second valve body, and a control unit. The control unit is connected to the first and second valve bodies to adjust the flow rates of high-temperature and low-temperature recirculated flue gas leading to the furnace. The first and second circulation pipelines respectively deliver high-temperature and low-temperature recirculated flue gas, and the control unit precisely adjusts the opening of the two valve bodies, achieving flexible control of the furnace combustion temperature, thereby effectively reducing the risk of fouling of the heating surfaces and the initial NO₂ levels. x The generation rate was increased, and the rate of load increase and decrease during peak shaving was improved by adjusting the flue gas recirculation ratio, thereby enhancing the system's flexibility and operating efficiency.

Description

Technical Field

[0001] This invention relates to the field of flue gas treatment technology, and more specifically, to a flue gas recirculation system and control method for a coal-fired boiler. Background Technology

[0002] Flue gas recirculation (FGR) is a low-NOx combustion technology that mainly extracts low-temperature flue gas (mainly composed of nitrogen, oxygen and carbon dioxide) from the tail end of the boiler and returns it to the furnace to participate in auxiliary combustion.

[0003] In the field of flexible peak shaving for coal-fired boilers, flue gas recirculation technology is widely used to regulate combustion temperature and oxygen content in the furnace to cope with load changes and reduce pollutant emissions. Existing technologies typically achieve flue gas recirculation by installing multi-point injection devices (including multiple injection guns at the furnace bottom, main combustion zone, and reduction zone) and flue gas recirculation pipelines.

[0004] While such systems can adjust oxygen content and temperature to some extent, their technical solutions mainly focus on the layout of flue gas injection points and macroscopic adjustment methods, lacking specific means of oxygen and temperature control. In actual operation, this makes it difficult to precisely control combustion temperature and easily leads to issues such as fouling of heated surfaces and NO2. x High generation rates and slow peak-shaving response speed limit the efficient application of the system in flexible peak-shaving. Summary of the Invention

[0005] The purpose of this invention is to provide a flue gas recirculation system for coal-fired boilers to alleviate the difficulties in accurately controlling combustion temperature and the resulting fouling of heating surfaces and NO emissions in existing technologies. x High generation rates and slow peak-shaving response speed are technical problems that limit the efficient application of the system in flexible peak-shaving.

[0006] This invention provides a flue gas recirculation system for a coal-fired boiler, comprising a furnace, economizer, denitrification assembly, air preheater, dust collector, induced draft fan, and desulfurization tower connected in sequence, and further comprising: The first circulation pipeline has one end connected to the gas outlet of the furnace and located before the gas inlet of the economizer, and the other end connected to the furnace.

[0007] The second circulation pipeline is connected at one end to the air outlet of the induced draft fan and is located before the air inlet of the desulfurization tower, and at the other end to the furnace.

[0008] The first valve body is located in the first circulation pipeline.

[0009] The second valve body is located in the second circulation pipeline.

[0010] The control unit is connected to the first valve body and the second valve body.

[0011] The control unit is used to adjust the opening of the first valve body to regulate the flow rate of high-temperature flue gas into the furnace. The control unit is also used to adjust the opening of the second valve body to regulate the flow rate of low-temperature flue gas into the furnace.

[0012] Furthermore, the flue gas recirculation system of a coal-fired boiler also includes premixing equipment and a circulating fan.

[0013] The premixing equipment has a mixing space, and both the first circulation pipeline and the second circulation pipeline are connected to the mixing space. The mixing space is connected to the furnace to discharge flue gas into the furnace.

[0014] A circulating fan is located at the connection between the premixing equipment and the furnace to discharge the flue gas in the mixing space into the furnace.

[0015] Furthermore, the flue gas recirculation system of a coal-fired boiler also includes a high-temperature dust collector.

[0016] The high-temperature dust collector is located at the connection between the first circulation pipeline and the premixing equipment.

[0017] Furthermore, the flue gas recirculation system for coal-fired boilers also includes: First test piece, second test piece, and third test piece; The first detection element is located at the air outlet of the furnace to detect the total amount of flue gas discharged from the furnace; The second detection element is installed inside the first circulation pipeline to detect the amount of flue gas inside the first circulation pipeline; The third detection element is installed inside the second circulation pipeline to detect the amount of flue gas inside the second circulation pipeline.

[0018] Another objective of this invention is to provide a control method for a flue gas recirculation system of a coal-fired boiler, which is applied to the control unit in the provided system.

[0019] The methods include: Obtain operational data during the operation of a coal-fired boiler: Calculate the current combustion temperature based on the operating data.

[0020] Calculate the difference between the current combustion temperature and the preset temperature threshold.

[0021] The target operating condition is determined based on the comparison between the difference and the preset difference threshold.

[0022] Control the flue gas recirculation system of the coal-fired boiler to operate under target conditions.

[0023] Furthermore, the step of calculating the current combustion temperature based on operational data includes:

[0024]

[0025]

[0026]

[0027] in, The combustion temperature after mixing, K represents the initial combustion temperature, and K represents the flue gas recirculation ratio. The total flue gas volume is [missing information]. For the volume of circulating flue gas, It is the lower calorific value of coal. The average specific heat capacity of the combustion products, The amount of flue gas generated per unit of combustion products. This is the first flue gas recirculation ratio. This is the second flue gas recirculation ratio. This refers to the oxygen content of the flue gas in the first cycle. For the second cycle of flue gas to contain oxygen, This represents the initial oxygen content in the furnace.

[0028] Furthermore, the target operating condition includes the first operating condition.

[0029] The steps for controlling the flue gas recirculation system of a coal-fired boiler to operate under target conditions include: Reduce the opening of the first valve body and open the second valve body to adjust the mixing ratio of high-temperature flue gas and low-temperature flue gas leading to the furnace.

[0030] Furthermore, the target operating condition includes the second operating condition.

[0031] The steps for controlling the flue gas recirculation system of a coal-fired boiler to operate under target conditions include: Increase the opening of the first valve body and close the second valve body to introduce high-temperature flue gas into the furnace.

[0032] Furthermore, the method also includes: In response to the load increase command, the opening of the first valve body is reduced to reduce the flow rate of high-temperature flue gas into the furnace.

[0033] Furthermore, the method also includes: In response to the load reduction command, the opening of the first valve body is increased to increase the flow rate of high-temperature flue gas into the furnace.

[0034] Beneficial effects: In this application, the first and second circulation pipelines respectively transport high-temperature and low-temperature recirculated flue gas, and the control unit precisely adjusts the opening of the two valves to achieve flexible control of the furnace combustion temperature. When a significant cooling is required, the first valve can be opened wider to inject a large amount of low-oxygen, high-temperature flue gas, diluting the oxygen concentration in the furnace and reducing the flame center temperature, thus precisely controlling the combustion temperature below the ash fouling temperature, thereby effectively reducing the risk of fouling on the heated surfaces and the initial NO. x The system generates steam and simultaneously improves the boiler's load increase and decrease rates during peak shaving by adjusting the flue gas recirculation ratio. When a load increase is needed, the control unit closes the first valve, directing more of the high-temperature flue gas that was originally circulating and storing heat within the system to heat exchange equipment such as the economizer, accelerating steam generation and thus significantly increasing the load increase rate. When a load decrease is needed, the first valve opens, redirecting more high-temperature flue gas back into the furnace for recirculation, reducing its heat release to subsequent heating surfaces, slowing the increase in steam production, and achieving rapid load decrease, thereby enhancing the system's flexibility and operating efficiency. Attached Figure Description

[0035] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0036] Figure 1 This is a schematic diagram of the structure of the delayed circulation system for a coal-fired boiler provided in Embodiment 1 of the present invention; Figure 2 This is a flowchart illustrating the control method for a delayed circulation system of a coal-fired boiler provided in Embodiment 1 of the present invention.

[0037] icon: 100-Furnace; 101-Circulating fan; 102-Premixing equipment; 200-Economizer; 300-Denitrification assembly; 400-Air preheater; 500-Dust collector; 600-Induced draft fan; 700-Desulfurization tower; 800-First circulation pipeline; 810-First valve body; 900-Second circulation pipeline; 910-Second valve body. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0039] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0040] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0041] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention. In addition, the terms "first," "second," "third," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0042] Furthermore, terms such as "horizontal" and "vertical" do not imply that components must be absolutely horizontal or suspended, but rather that they can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal than "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0043] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0044] The present invention will now be described in further detail with reference to specific embodiments and accompanying drawings.

[0045] See Figure 1The flue gas circulation system for a coal-fired boiler provided in this embodiment includes a furnace 100, an economizer 200, a denitrification assembly 300, an air preheater 400, a dust collector 500, an induced draft fan 600, and a desulfurization tower 700 connected in sequence. It also includes a first circulation pipeline 800, a second circulation pipeline 900, a first valve body 810, a second valve body 910, and a control unit.

[0046] One end of the first circulation pipeline 800 is connected to the gas outlet of the furnace 100 and is located before the gas inlet of the economizer 200, while the other end is connected to the furnace 100.

[0047] One end of the second circulation pipeline 900 is connected to the air outlet of the induced draft fan 600 and is located before the air inlet of the desulfurization tower 700, while the other end is connected to the furnace 100.

[0048] The first valve body 810 is located in the first circulation pipeline 800. The second valve body 910 is located in the second circulation pipeline 900.

[0049] The control unit is connected to the first valve body 810 and the second valve body 910.

[0050] The control unit is used to adjust the opening degree of the first valve body 810 to adjust the flow rate of high-temperature flue gas to the furnace 100. The control unit is also used to adjust the opening degree of the second valve body 910 to adjust the flow rate of low-temperature flue gas to the furnace 100.

[0051] Specifically, in this embodiment, the first circulation pipeline 800 and the second circulation pipeline 900 respectively transport high-temperature and low-temperature recirculated flue gas. The control unit can adjust the opening degree of the first valve body 810 and the second valve body 910 in the two pipelines, thereby realizing flexible control of the combustion temperature of the furnace 100.

[0052] When a significant reduction in the furnace combustion temperature of 100°C is required, the first valve body 810 can be opened to inject a large amount of low-oxygen, high-temperature flue gas, diluting the oxygen concentration in the furnace and reducing the temperature at the center of the flame. This allows the combustion temperature to be precisely controlled below the ash fouling temperature, thereby effectively reducing the risk of fouling on the heating surface and the amount of original NOx generated. At the same time, by adjusting the flue gas circulation ratio, the rate of load increase and decrease of the boiler during peak shaving can be improved.

[0053] When a load increase is required, the control unit closes the first valve 810, directing more of the high-temperature flue gas that was originally circulating and storing heat in the system to heat exchange equipment such as the economizer 200, accelerating steam generation, and thus significantly improving the load increase rate.

[0054] When a load reduction is required, the first valve body 810 is opened to allow more high-temperature flue gas to be recirculated back into the furnace 100, reducing its heat release to subsequent heating surfaces, slowing down the increase in steam production, and achieving rapid load reduction, thereby enhancing the system's flexibility and operating efficiency.

[0055] In this embodiment, the flue gas recirculation system of the coal-fired boiler also includes a premixing device 102 and a circulating fan 101.

[0056] The premixing device 102 has a mixing space, and the first circulation pipe 800 and the second circulation pipe 900 are both connected to the mixing space. The mixing space is connected to the furnace 100 to discharge flue gas into the furnace 100. The circulating fan 101 is located at the connection between the premixing device 102 and the furnace 100 to discharge the flue gas in the mixing space into the furnace 100.

[0057] According to the principles of combustion, the stability of combustion and the amount of pollutants generated within the furnace 100 depend heavily on the uniformity of the incoming medium. If flue gas with significant differences in temperature, oxygen concentration, and density (high temperature, low oxygen; low temperature, high oxygen) from the first circulation pipe 800 and the second circulation pipe 900 is directly and independently injected into the furnace 100, strong local concentration and temperature gradients will form near the injection point. In this embodiment, the premixing device 102 and the circulating fan 101 can fully mix the high-temperature and low-temperature recirculated flue gas in the mixing space before it enters the furnace 100, thereby ensuring the uniformity of composition and temperature of the flue gas entering the furnace 100. This effectively avoids problems such as uneven distribution of temperature and concentration fields and unstable local combustion that may result from the independent injection of the two flue gas streams. The circulating fan 101 provides stable and controllable transport power for the flue gas, overcomes the system's own flow resistance, ensures precise control of the total amount of recirculated flue gas, and thus enhances the uniformity, stability, and precision of the entire combustion process.

[0058] In this embodiment, the flue gas recirculation system of the coal-fired boiler also includes a high-temperature dust collector 500.

[0059] The high-temperature dust collector 500 is located at the connection between the first circulation pipeline 800 and the premixing equipment 102.

[0060] Specifically, the first circulating flue gas drawn from the economizer 200 has a high temperature (approximately 500°C) and has not been treated by the dust collector 500, thus containing a high concentration of fly ash particles. These fly ash particles may soften at high temperatures, exhibiting stronger adhesion and abrasiveness. The high-temperature dust collector 500 can remove the high concentration and high hardness dust carried in the high-temperature recirculated flue gas, thereby avoiding wear, blockage, and ash accumulation problems caused by this dust in the subsequent premixing equipment 102, circulating fan 101, and connecting pipes. This not only reduces the frequency and cost of system maintenance but also ensures the long-term operational reliability and control accuracy of the premixing equipment 102 and circulating fan 101, which are core regulating components of the system. This ensures the durability and stability of the entire flue gas recirculation system under harsh high-temperature environments, and is an important guarantee for achieving its long-term, efficient peak-shaving function.

[0061] In this embodiment, the flue gas recirculation system of the coal-fired boiler further includes a first detection element, a second detection element, and a third detection element.

[0062] The first detection device is installed at the air outlet of the furnace 100 to detect the total amount of flue gas discharged from the furnace 100. The second detection device is installed in the first circulation pipe 800 to detect the amount of flue gas in the first circulation pipe 800. The third detection device is installed in the second circulation pipe 900 to detect the amount of flue gas in the second circulation pipe 900.

[0063] The first, second, and third detection devices construct a real-time data acquisition and feedback network for key parameters of the flue gas recirculation system. This upgrades the decision-making of the control unit from relying on theoretical estimation or lagging manual judgment to closed-loop automatic control based on real-time, accurate flow data. This directly supports and realizes the accurate calculation and dynamic optimization of the flue gas recirculation ratio, ensuring that combustion temperature control, load regulation, and pollutant suppression strategies can be executed accurately, quickly, and adaptively according to the actual operating status of the boiler. This significantly improves the accuracy, response speed, and automation level of the entire system control.

[0064] Combination Figure 2 The control method for the flue gas recirculation system of a coal-fired boiler provided in this embodiment is applied to the control unit in the provided system.

[0065] The methods specifically include: S100, acquires operational data during the operation of the coal-fired boiler: S200 calculates the current combustion temperature based on operating data.

[0066] S300 calculates the difference between the current combustion temperature and the preset temperature threshold.

[0067] S400 determines the target operating condition based on the comparison between the difference and a preset difference threshold.

[0068] S500 controls the flue gas recirculation system of a coal-fired boiler to operate under target conditions.

[0069] In this embodiment, the operating data includes at least the circulating flue gas volume of the first circulation pipeline 800 and the circulating flue gas volume of the second circulation pipeline 900.

[0070] Step S100 is the sensing and data input stage of the entire control method. The control unit realizes real-time data acquisition by detecting various parts of the boiler and flue gas circulation system through manual detection or sensors (such as detection devices, oxygen meters, thermometers, coal quality analysis data, etc.).

[0071] In this embodiment, key data include total flue gas volume, flue gas volume in the first circulation pipeline 800, oxygen content in the flue gas in the first circulation pipeline 800, flue gas volume in the second circulation pipeline 900, oxygen content in the flue gas in the second circulation pipeline 900, low calorific value of coal, coal type information, and current boiler load command.

[0072] Step S200 is the calculation step of the method provided in this embodiment. The control unit uses the data collected in S100 to perform a series of formula calculations to calculate the furnace combustion temperature, which is difficult to measure directly, in real time and accurately through measurable parameters, making the invisible combustion process "visible" and "controllable".

[0073] Subsequently, step S300 calculates the difference between the current combustion temperature and the preset temperature threshold. Then, in step S400, the system's operating condition is determined based on the comparison between the difference obtained in step S300 and the preset difference threshold.

[0074] Specifically, if the difference ΔT obtained in step S300 is greater than A (A is a positive number, indicating that the temperature is too high and dangerous), the target operating condition is determined to be "emergency cooling mode". The decision logic is: open the first valve body 810 to inject a large amount of low-oxygen, high-temperature flue gas, forcibly and significantly reducing the combustion temperature after mixing.

[0075] If B < ΔT ≤ A (B is another small positive number, indicating that the temperature is too high and caution is needed), then the target operating condition may be determined as "fine-tuning cooling mode". The decision logic is: appropriately open the second valve body 910 or fine-tune the first valve body 810.

[0076] If ΔT ≤ B (indicating that the temperature is within a safe range with sufficient margin), then the target operating condition can be determined as "priority peak-shaving mode". In this case, the control system can prioritize responding to load change commands, such as closing the first valve 810 when a load increase is required, in order to improve the load increase rate.

[0077] Step S500 is the execution phase of the control method. The control unit translates the "target operating condition" determined in S400 into specific, executable instructions to send specific opening adjustment signals to the first valve body 810 and the second valve body 910, thereby precisely controlling the flow rates of the first and second circulating flue gas, and finally adjusting the calculated mixed combustion temperature T2 to the target range, so that the boiler can operate safely, cleanly, efficiently, and flexibly under complex operating conditions of flexible peak shaving.

[0078] In this embodiment, step S200, calculating the current combustion temperature based on the operating data, includes:

[0079]

[0080]

[0081]

[0082] in, The combustion temperature after mixing, The initial combustion temperature, The flue gas recirculation ratio for the first circulation pipeline is 800. The flue gas recirculation ratio for the second circulation pipeline is 900. The total flue gas volume emitted from furnace 100 (unit: kg / h). The circulating flue gas volume (in kg / h) of the first circulation pipeline 800. The circulating flue gas volume (in kg / h) of the second circulation pipeline 900. The lower heating value of coal (unit: kJ / kg). The average specific heat capacity of combustion products [unit: kJ / (Nm³)] 3 ·℃)], The amount of flue gas generated per unit of combustion products (in Nm³) 3 / kg), The flue gas recirculation ratio for the first circulation pipeline is 800. The flue gas recirculation ratio for the second circulation pipeline is 900. The oxygen content of the flue gas in the first circulation pipeline is 800. The flue gas in the second circulation pipeline 900 contains oxygen. This represents the initial oxygen content in furnace 100.

[0083] The above formula allows for adjustment... , Achieve and Adjustments are made to determine the target temperature. The system can predict how different regulation strategies will affect temperature, thus taking the right action before contamination occurs, achieving a shift from "post-event remediation" to "pre-event prevention".

[0084] In this embodiment, the target operating condition includes a first operating condition. Step S500, controlling the flue gas recirculation system of the coal-fired boiler to operate under the target operating condition, includes: S510, reduce the opening of the first valve body and open the second valve body to adjust the mixing ratio of high-temperature flue gas and low-temperature flue gas leading to the furnace.

[0085] Specifically, compared to adjusting a single flue gas path, the coordinated control of the first valve body 810 and the second valve body 910 enables more precise "fine-tuning" of the combustion temperature, resulting in a smoother response and avoiding large temperature fluctuations. This is particularly suitable for scenarios involving slight changes in coal quality or minor load fluctuations. While performing a slight cooling, the relatively high oxygen content of the low-temperature flue gas injected into the second valve body 910 minimizes the negative impact on combustion stability compared to simply injecting a large amount of low-oxygen flue gas. This allows the system to safely control the temperature within the target range while ensuring combustion efficiency and flame stability, even when participating in grid peak shaving or requiring minor adjustments to operating parameters.

[0086] Furthermore, stable temperature regulation reduces thermal stress impact on the boiler's heating surface. At the same time, reducing the flow rate of high-temperature flue gas in the first circulation pipeline also indirectly reduces the load on the high-temperature dust collector 500, which is beneficial to the long-term reliable operation of the entire system.

[0087] In this embodiment, the target operating condition also includes a second operating condition. Step S500, controlling the flue gas recirculation system of the coal-fired boiler to operate under the target operating condition, further includes: Increase the opening of the first valve body and close the second valve body to introduce high-temperature flue gas into the furnace.

[0088] When the combustion temperature approaches or exceeds the fouling temperature threshold, posing a risk of slagging, or when the temperature rises sharply under conditions such as sudden changes in coal type, the second operating mode provides the strongest and fastest cooling effect, quickly pulling the temperature back to a safe range. It serves as the last automated line of defense against severe boiler fouling, slagging, and even shutdown. The second operating mode significantly reduces the combustion temperature, thereby suppressing the formation of thermal NOx. This mode minimizes the flame center temperature, reducing the amount of primary NOx generated and meeting environmental emission requirements.

[0089] Furthermore, the second mode complements and gradients the first mode, allowing for intelligent switching or combination between the two modes based on the magnitude of the temperature deviation. This enables precise, flexible, and powerful intelligent control of the boiler combustion conditions around the clock and across the entire range.

[0090] Example 2 In this embodiment, the control method for the flue gas recirculation system of a coal-fired boiler includes: S600, in response to a load increase command, reduces the opening of the first valve body to reduce the flow rate of high-temperature flue gas into the furnace.

[0091] During active regulation, the control unit receives a load increase command from the power grid dispatcher or operators and immediately reduces the opening of the first valve body 810. This reduces the flow rate of the high-temperature recirculated flue gas (first circulation pipeline 800) drawn from the economizer 200, i.e., reduces the circulation ratio of the first circulation pipeline 800.

[0092] During steady-state operation, a large amount of high-temperature flue gas (first circulation pipe 800) circulates between the boiler tail flue and the furnace 100. This high-temperature flue gas carries a large amount of heat energy and continuously circulates within the system, forming a huge "heat storage pool." Reducing the flow rate of the first circulation pipe 800 is equivalent to closing the circulation valve of this "heat storage pool," forcing the high-temperature flue gas, which was originally circulating within the system, to change its path and flow more towards the economizer 200, superheater, and other tail-end heating surfaces. This high-temperature flue gas rapidly releases the heat it carries to the boiler's working fluid (water and steam), thereby accelerating feedwater heating and promoting steam generation and superheating, thus increasing the flow rate and parameters of the main steam. By actively managing the boiler's thermal inertia using the recirculation system, the peak-shaving response capability of the boiler unit is improved.

[0093] In this embodiment, the control method for the flue gas recirculation system of a coal-fired boiler further includes: S700, in response to a load reduction command, increases the opening of the first valve body to increase the flow rate of high-temperature flue gas into the furnace.

[0094] Upon receiving a load reduction command, the control unit immediately increases the opening of the first valve body 810. This increases the flow rate of the high-temperature recirculated flue gas drawn from the economizer 200 (first circulation pipeline 800), effectively increasing the circulation ratio of the first circulation pipeline 800. This actively increases the system's thermal inertia by "drawing" more high-temperature flue gas back from the tail flue to the furnace 100 for circulation. The heat carried by this portion of the high-temperature flue gas no longer flows through the economizer 200, superheater, and other tail heating surfaces. The effective flue gas heat used to heat the boiler working fluid (water, steam) decreases. The steam generation rate and superheat decrease accordingly, leading to a reduction in the boiler's output load (power generation), thus achieving a rapid load reduction.

[0095] Unlike simply reducing fuel to reduce load, this embodiment first rapidly absorbs energy through flue gas recirculation to steadily reduce steam parameters, while coordinating the reduction of fuel quantity. This avoids the risk of combustion instability or fire extinguishing that may result from rapidly reducing fuel, making the load reduction process more stable and controllable.

[0096] Example 3 In this embodiment, the coal-fired boiler is specifically a 1000M coal-fired boiler, and the coal used is high-sodium, high-potassium, and high-sulfur coal. The lower heating value of this coal is 18924 kJ / kg, and its combustion product fouling temperature is above 1200°C. Therefore, the combustion temperature needs to be controlled below 1200°C. The combustion product volume fraction is 7.91 Nm³. 3 / kg, the average specific heat capacity of the combustion products was calculated to be 1.6 kJ / (Nm³). 3 ·℃).

[0097] The initial combustion temperature was calculated using Example 1. It is 1495℃.

[0098] The flue gas volume at full load is 2724238 Nm³. 3 / h, the oxygen content of the flue gas drawn from the first circulation pipeline 800 and the second circulation pipeline 900 is 3.5% and 8.2%, respectively. At this time, the flue gas circulation ratio in the first circulation pipeline is adjusted to 23.9. It can be calculated that the combustion temperature after mixing is... It is 1198℃.

[0099] When the unit is operating at 20% full load for peak shaving, the flue gas volume is 953285 Nm³. 3 / h, the oxygen content of the flue gas drawn from the first circulation pipeline 800 and the second circulation pipeline 900 is 5.7% and 10.5%, respectively. At this time, the flue gas circulation ratio of the first circulation pipeline 800 is adjusted to 27.2. The combustion temperature after mixing can be calculated. The temperature is 1199℃, which is lower than the contamination temperature, thus preventing contamination.

[0100] Example 4 In this embodiment, the coal-fired boiler is specifically a 1000M coal-fired boiler, and the coal used is high-silicon, high-alumina coal. The lower heating value of this coal is 19822 kJ / kg, and its combustion product fouling temperature is above 1400°C. Therefore, the combustion temperature needs to be controlled below 1400°C. The combustion product volume fraction is 8.31 Nm³. 3 / kg, the average specific heat capacity of the combustion products was calculated to be 1.62 kJ / (Nm³). 3 ·℃).

[0101] The initial combustion temperature was calculated using Example 1. It is 1472℃.

[0102] The flue gas volume at full load is 2,829,723 Nm³. 3At a rate of / h, the oxygen content of the flue gas drawn from the first circulation pipe 800 and the second circulation pipe 900 is 3.3% and 8.4%, respectively. At this time, the flue gas circulation ratio in the first circulation pipe 800 is controlled at 2.2, and the flue gas circulation ratio in the second circulation pipe 900 is controlled at 7.9. Calculations show that the combustion temperature after mixing is... It is 1375℃.

[0103] When the unit is operating at 20% full load for peak shaving, the flue gas volume is 1121331 Nm³. 3 At a rate of / h, the oxygen content of the flue gas drawn from the first circulation pipe 800 and the second circulation pipe 900 is 6.1% and 9.8%, respectively. At this time, the flue gas circulation ratio in the first circulation pipe 800 is controlled at 3.1, and the flue gas circulation ratio in the second circulation pipe 900 is controlled at 7.5. Calculations show that the combustion temperature after mixing is... The temperature is 1381℃, which is lower than the contamination temperature, thus preventing contamination.

[0104] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A coal-fired boiler flue gas circulation system comprising, in sequence, a furnace, an economizer, a denitration assembly, an air preheater, a dust collector, an induced draft fan, and a desulfurization tower, characterized in that, Also includes: The first circulation pipeline has one end connected to the gas outlet of the furnace and located before the gas inlet of the economizer, and the other end connected to the furnace. The second circulation pipeline has one end connected to the air outlet of the induced draft fan and located before the air inlet of the desulfurization tower, and the other end connected to the furnace. The first valve body is located in the first circulation pipeline; The second valve body is located in the second circulation pipeline; The control unit is connected to the first valve body and the second valve body; The control unit is used to adjust the opening of the first valve body to adjust the flow rate of high-temperature flue gas to the furnace; the control unit is also used to adjust the opening of the second valve body to adjust the flow rate of low-temperature flue gas to the furnace.

2. The flue gas recirculation system for a coal-fired boiler according to claim 1, characterized in that, The flue gas recirculation system of the coal-fired boiler also includes a premixing device and a circulating fan; The premixing equipment has a mixing space, and the first circulation pipeline and the second circulation pipeline are both connected to the mixing space. The mixing space is connected to the furnace to discharge flue gas into the furnace. The circulating fan is located at the connection between the premixing equipment and the furnace to discharge the flue gas in the mixing space into the furnace.

3. The flue gas recirculation system for a coal-fired boiler according to claim 2, characterized in that, The flue gas recirculation system of the coal-fired boiler also includes a high-temperature dust collector; The high-temperature dust collector is located at the connection between the first circulation pipeline and the premixing equipment.

4. The flue gas recirculation system for a coal-fired boiler according to claim 2, characterized in that, The coal-fired boiler flue gas recirculation system also includes a first detection element, a second detection element, and a third detection element; The first detection element is located at the air outlet of the furnace to detect the total amount of flue gas discharged from the furnace; The second detection element is installed inside the first circulation pipeline to detect the amount of flue gas inside the first circulation pipeline; The third detection element is installed inside the second circulation pipeline to detect the amount of flue gas inside the second circulation pipeline.

5. A control method for a flue gas recirculation system of a coal-fired boiler, characterized in that, A control unit applied to the system as described in claim 1; The method includes: Obtain operational data during the operation of a coal-fired boiler: Based on the aforementioned operational data, calculate the current combustion temperature; Calculate the difference between the current combustion temperature and the preset temperature threshold; Based on the comparison between the difference and the preset difference threshold, the target working condition is determined; Control the flue gas recirculation system of the coal-fired boiler to operate under the target conditions.

6. The method according to claim 5, characterized in that, The step of calculating the current combustion temperature based on the operational data includes: Among them, among them, The combustion temperature after mixing. K represents the initial combustion temperature, and K represents the flue gas recirculation ratio. The total flue gas volume is [missing information]. For the volume of circulating flue gas, It is the lower calorific value of coal. The average specific heat capacity of the combustion products, The amount of flue gas generated per unit of combustion products. This is the first flue gas recirculation ratio. This is the second flue gas recirculation ratio. This refers to the oxygen content of the flue gas in the first cycle. For the second cycle of flue gas to contain oxygen, This represents the initial oxygen content in the furnace.

7. The method according to claim 5, characterized in that, The target operating condition includes the first operating condition; The steps for controlling the flue gas recirculation system of the coal-fired boiler to operate under the target conditions include: Reduce the opening of the first valve body and open the second valve body to adjust the mixing ratio of high-temperature flue gas and low-temperature flue gas leading to the furnace.

8. The method according to claim 5, characterized in that, The target operating condition includes the second operating condition; The steps for controlling the flue gas recirculation system of the coal-fired boiler to operate under the target conditions include: Increase the opening of the first valve body and close the second valve body to introduce high-temperature flue gas into the furnace.

9. The method according to claim 5, characterized in that, The method further includes: In response to a load increase command, the opening of the first valve body is reduced to reduce the flow rate of high-temperature flue gas into the furnace.

10. The method according to claim 5, characterized in that, The method further includes: In response to a load reduction command, the opening of the first valve body is increased to increase the flow rate of high-temperature flue gas into the furnace.

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