Clean fuel coupling thermal load control method under low-load working condition of coal-fired boiler

Abstract

The invention discloses a clean fuel coupling thermal load control method under a low-load working condition of a coal-fired boiler, and belongs to the technical field of flexible peak regulation of the coal-fired boiler. According to the control method, based on multi-point temperature monitoring data in a hearth, areas with unstable combustion and uneven thermal load distribution under low load are dynamically identified; by cooperatively regulating and controlling the blending combustion proportion, the injection momentum and the injection time of hydrogen, ammonia gas, methane or methanol clean fuel at different heights and circumferential positions of the hearth and linkage with graded air distribution, accurate optimization and reconstruction of hearth heat load distribution are achieved. According to the control method, flame pulsation, local overtemperature of the water cooling wall and thermal deviation during low-load operation can be effectively restrained, the flow field structure of four-corner tangential combustion is strengthened and maintained, and the requirements for deep peak regulation and clean operation of the unit are met on the premise that combustion stability and heating surface safety are guaranteed.

Description

Technical Field

[0001] This invention relates to the field of flexible peak-shaving technology for coal-fired boilers, and in particular to a method for controlling clean fuel coupled heat load under low-load conditions of coal-fired boilers. Background Technology

[0002] To meet the power grid's demand for flexible and safe operation, coal-fired power generating units often need to operate stably under low loads to undertake deep peak shaving tasks. However, under low load conditions, the concentration of pulverized coal and the wind speed in the furnace decrease, leading to poor combustion stability and uneven distribution of heat load in the furnace, which in turn causes safety problems such as local overheating of the water-cooled walls and excessive thermal deviation on both sides of the furnace.

[0003] Taking a tangential pulverized coal boiler as an example, its combustion zone along the height direction is mainly divided into the main combustion zone and the burnout zone. Under normal load, a stable rotating flame can be formed through reasonable air distribution, and the heat load distribution is relatively uniform. However, under low load, the number of burner layers in operation decreases, the flame center shifts downward, the heat intensity in the lower part of the furnace increases, and the rotating airflow weakens, which easily leads to flame deflection and increased thermal deviation.

[0004] Hydrogen, ammonia, methane, and methanol exhibit diverse combustion characteristics and adjustable reactivity. For multi-fuel coupled utilization scenarios, the spatial redistribution of furnace heat load can be achieved by rationally incorporating clean fuels at different heights and in different sidewall regions. This mitigates thermal shock in the lower water-cooled wall region, reducing the risk of overheating, and dynamically adjusts the heat load differences between the left and right sidewalls, improving the overall thermal deviation level. Optimizing heat load distribution under low load conditions through precise control strategies becomes the key to solving this problem. Summary of the Invention

[0005] This invention aims to provide a clean fuel coupled heat load control method for coal-fired boilers under low load conditions, which can solve problems such as water-cooled wall overheating, large thermal deviation and damage to swirl structure caused by unstable combustion and uneven heat load distribution under low load conditions.

[0006] This invention provides a method for controlling clean fuel coupled heat load under low-load conditions in a coal-fired boiler. The method is applied to a clean fuel coupled combustion system in a coal-fired boiler under low-load conditions. The system includes a pulverized coal boiler with a tangential combustion configuration, multiple pulverized coal burners arranged at the four corners of the boiler's furnace, multiple clean fuel burners arranged in layers along the circumference of the furnace, multiple storage tanks connected to the clean fuel burners, multiple air zone nozzles arranged alternately with the nozzles of the clean fuel burners in a horizontal cross-section, and multiple temperature measuring points set along the height of the furnace in multiple representative cross-sections or key combustion areas. The combustion area of ​​the furnace includes a main combustion zone and a burnout zone from bottom to top along the height direction. The air distribution system has primary air and secondary air nozzles, as well as a burnout air nozzle, supplying air to the main combustion zone and the burnout zone, respectively. The control method includes the following steps: Based on multiple temperature measurement points, the temperature distribution in multiple local areas within the furnace is monitored; When the unit is detected to be operating at a low load of no more than 40% of its rated power, the clean fuel blending will be automatically started. Based on the preset strategy, real-time operating conditions, and the temperature distribution data, the co-firing position, area, and proportion of clean fuel injected into different combustion zones and / or air zones in the furnace are coordinated and controlled to optimize and homogenize the heat load distribution in the furnace, ensuring combustion stability and the safety of the heating surface.

[0007] In one embodiment, the clean fuel includes at least one of hydrogen, ammonia, methane, and methanol.

[0008] In one embodiment, the coordinated regulation of clean fuel based on preset strategies, real-time operating conditions, and temperature distribution data includes: Feedback adjustments are made based on temperature monitoring data of the water-cooled walls inside the furnace. When the monitored value of the water-cooled wall temperature corresponding to the main combustion zone is higher than the safety threshold, or the temperature distribution in the water-cooled wall area is uneven and exceeds the preset limit, the heat flow distribution in the area is optimized by adjusting the injection position and blending ratio of clean fuel, so as to control the water-cooled wall temperature and temperature difference within the safe range.

[0009] In one embodiment, the coordinated regulation of clean fuel injected into different combustion zones and / or air zones within the furnace includes: Under low-load conditions, the clean fuel injected into different locations in the furnace is adjusted independently and differentiatedly. By independently controlling at least one of the injection quantity, flow rate, and injection angle of each clean fuel burner, differentiated jet momentum input is formed to compensate for the insufficient combustion momentum of the main pulverized coal, thereby restoring the swirling intensity in the center of the furnace and optimizing the overall heat load distribution of the furnace.

[0010] In one embodiment, the control method further includes: Real-time coordinated adjustment of the flow rate and temperature of clean fuel, as well as the air distribution at the corresponding air zone nozzles; By changing the air distribution intensity above the main combustion zone and differentially adjusting the injection parameters of clean fuel at the four corners of the furnace, the flame path above the main combustion zone is extended, and the rotating flow field formed by the tangential combustion method at the four corners is strengthened and maintained.

[0011] In one embodiment, the control method further includes: Identify temperature anomaly areas based on temperature distribution data measured from multiple temperature measurement points; When the water-cooled wall temperature in the abnormal temperature zone exceeds the safety threshold, or when the temperature distribution in the zone indicates a risk of instability in the tangential flow field at the four corners, the clean fuel burner at the corresponding position is automatically activated or adjusted to implement directional cooling or flow field correction in the zone, thereby controlling the water-cooled wall temperature within a safe range and maintaining a stable tangential combustion flow field.

[0012] In one embodiment, when the clean fuel being blended includes ammonia, the control method further includes: Real-time monitoring of flue gas composition at the furnace outlet or a specific flue section; Based on the monitored ammonia concentration or ammonia escape concentration, dynamically adjust the ammonia injection parameters and / or the air distribution parameters of the relevant air zones to control the ammonia escape concentration within the preset safety limit.

[0013] In one embodiment, to compensate for combustion deviations under low loads and accelerate the transition to the target operating condition, the control method further includes performing at least one of the following compensation adjustment operations: Adjust the fuel injection rate of the clean fuel burner; Adjust the jet direction of the nozzle in a specific wind zone; Adjust the air volume distribution ratio between nozzles in different air zones.

[0014] In one embodiment, the target operating condition or steady-state operating condition of the boiler furnace includes the following comprehensive indicators: The temperature field distribution inside the furnace meets the preset uniformity standard; The ammonia escape concentration in the flue gas is lower than the preset environmental safety limit; The wall temperature in each area of ​​the water-cooled wall is within the preset safe operating temperature range.

[0015] In one embodiment, the triggering condition for automatically starting clean fuel blending is: receiving a low-load dispatching instruction from the power grid dispatching system, and / or locally detecting that the real-time operating power of the unit is not higher than 40% of the rated power.

[0016] Compared with the prior art, the advantages of the present invention are that, through the coordinated regulation of multi-point temperature monitoring and clean fuel space injection, it can accurately identify and compensate for uneven heat load distribution under low load, effectively prevent local overheating of water-cooled walls while maintaining stable swirl combustion, and significantly improve the operational safety and flexibility of coal-fired boilers under deep peak shaving conditions. Attached Figure Description

[0017] The invention will now be described in more detail with reference to embodiments and the accompanying drawings.

[0018] Figure 1 This is a flowchart of the control method of the present invention; Figure 2 This is a schematic diagram of the combustion system of the present invention; Figure 3 This is a cross-sectional schematic diagram of the furnace chamber of the present invention; Figure 4 This is a flowchart of the closed-loop control of water-cooled wall overheating according to the present invention; Figure 5 This is a flowchart of the closed-loop control for the recovery of the rotating structure according to the present invention; Figure label: 1. Pulverized coal boiler; 2. Clean fuel burner; 3. Storage tank; 4. Main combustion zone; 5. Burnout zone; 501. OFA zone; 502. SOFA zone; 6. Side wall; 7. Front wall; 8. Rear wall; 9. Above the burnout zone. Detailed Implementation

[0019] The invention will now be further described with reference to the accompanying drawings.

[0020] Existing technologies have significant shortcomings in low-load operation, failing to effectively balance combustion stability and heat load balance. Although co-firing hydrogen and ammonia can reduce the minimum load of pulverized coal boiler 1 and suppress emissions, the design of co-firing location, zone division, and proportional control is relatively simple, lacking a systematic control strategy, and does not fully consider the multi-fuel co-firing characteristics of hydrogen and ammonia. As a result, under deep peak-shaving conditions, pulverized coal boiler 1 is prone to problems such as flame instability, local overheating, and thermal deviation.

[0021] This invention provides a clean fuel coupled heat load control method for coal-fired boilers under low load conditions. Through real-time monitoring and coordinated regulation, it solves the problem that traditional co-firing technology cannot effectively guarantee combustion stability and heat load balance.

[0022] Reference Figure 2 and Figure 3This invention provides a method for controlling clean fuel coupled heat load under low-load conditions in a coal-fired boiler, applied to a clean fuel coupled combustion system for a coal-fired boiler under low-load conditions. The system includes a pulverized coal boiler 1 with a tangential combustion configuration, multiple pulverized coal burners arranged at the four corners of the furnace of the boiler 1, multiple clean fuel burners 2 arranged circumferentially along the furnace, multiple storage tanks 3 for storing clean fuel, multiple air zone nozzles arranged alternately with the nozzles of the clean fuel burners 2 on a horizontal cross-section, and multiple temperature measuring points set along the height of the furnace at multiple representative cross-sections or key areas. The combustion zone of the furnace includes a main combustion zone 4 and a burnout zone 5 from bottom to top along the height direction. The air distribution system has primary air and secondary air nozzles and burnout air nozzles arranged in layers along the height, supplying air to the main combustion zone 4 and the burnout zone 5 respectively. The burnout air nozzles include burnout air nozzles in OFA zone 501 (staged air zone) and separate burnout air nozzles in SOFA zone 502 (deep staged air zone), located at a higher position. The clean fuel burner 2 is connected to the storage tank 3 via a pipe.

[0023] By adding clean fuel burners 2 to the windward and leeward sides of the furnace, the temperature and flow rate of the gas on each side are controlled to ensure the uniformity and stability of the combustion process. Figure 3 As shown, the main airflow rotates in the opposite direction to the main airflow near the front wall 7, and in the opposite direction to the main airflow near the rear wall 8, causing the main airflow in the furnace to be... Figure 3 As shown, the windward side faces the direction from which the main airflow originates, while the leeward side faces the opposite direction. Specifically, a closed-loop control strategy based on real-time temperature monitoring is adopted to dynamically adjust the supply of hydrogen and ammonia gases to achieve temperature balance, avoid thermal deviations, and improve the overall stability and thermal efficiency of the system.

[0024] Regarding clean fuels and monitoring arrangements, clean fuels include at least one of hydrogen, ammonia, methane, and methanol. The system can be configured with independent storage tanks and supply pipelines for different fuels.

[0025] To monitor the furnace thermal state in real time, multiple temperature measuring points are distributed along the height and circumference of the furnace. In one embodiment, 20 to 25 temperature measuring points can be set in the front, back, left, and right directions at key sections in the lower part (main combustion zone 4), middle part (burnout zone 5), and upper part (above the burnout zone 9 and side wall 6). Redundancy can be used in key areas to ensure reliability.

[0026] The control method includes the following steps: Based on multiple temperature measurement points, the temperature distribution in multiple local areas inside the furnace is monitored.

[0027] When the generator is detected to be operating at a low load of no more than 40% of its rated power, it will automatically start the co-firing of clean fuel.

[0028] Based on the preset strategy, real-time operating conditions, and the temperature distribution data, the co-firing position, area, and proportion of clean fuel injected into different combustion zones and / or air zones in the furnace are coordinated and controlled to optimize and homogenize the heat load distribution in the furnace, ensuring combustion stability and the safety of the heating surface.

[0029] Among them, the coordinated regulation of clean fuel by preset strategy, real-time operating conditions and temperature distribution data includes: feedback adjustment based on temperature monitoring data of water-cooled walls in the furnace; when the monitored value of the water-cooled wall temperature corresponding to the main combustion zone 4 is higher than the safety threshold, or the temperature distribution of the water-cooled wall area is uneven and exceeds the preset limit, the heat flow distribution in the area is optimized by adjusting the injection position and blending ratio of clean fuel, so as to control the water-cooled wall temperature and temperature difference within the safe range.

[0030] The coordinated regulation of clean fuels injected into different combustion zones and / or air zones within the furnace includes: Under low-load conditions, the clean fuel injected into different locations in the furnace is adjusted independently and differentiatedly.

[0031] By independently controlling at least one of the injection quantity, flow rate and injection angle of each clean fuel burner 2, differentiated jet momentum input is formed to compensate for the insufficient combustion momentum of the main pulverized coal, thereby restoring the swirling intensity in the center of the furnace and optimizing the overall heat load distribution of the furnace.

[0032] Specifically, the control methods also include: real-time coordinated adjustment of the flow rate and temperature of clean fuel, as well as the air distribution of the corresponding air zone nozzles; by changing the air distribution intensity above the main combustion zone 4 and differentially adjusting the injection parameters of clean fuel at the four corners of the furnace, the combined effects are used to extend the flame path above the main combustion zone 4 and strengthen and maintain the rotating flow field formed by the tangential combustion mode at the four corners.

[0033] like Figure 1 , Figure 4 and Figure 5 As shown, in this embodiment, taking the co-firing of hydrogen and ammonia as an example, the following steps are included: Step 1: System initialization and parameter setting.

[0034] Initial control parameters are set, and functional checks are performed on all temperature measurement points, sensors, and safety interlocks. Baseline operating data is recorded over a period of time. In this embodiment, the initial parameters include: The initial hydrogen co-firing calorific value percentage (e.g., 0.5%); the initial ammonia co-firing calorific value percentage (e.g., 0%); the maximum allowable calorific value percentage injected (i.e., the upper limit of single-point / overall co-firing); and the co-firing rate limit. The maximum allowable calorific value percentage injected includes hydrogen ≤ 10% calorific value percentage, ammonia ≤ a set calorific value percentage (the set calorific value percentage is 5%–10%, which can be selected according to actual conditions), and hydrogen + ammonia ≤ 10% calorific value percentage. The co-firing rate limit can be, for example, 0.5%–1.0% / min to prevent thermal shock.

[0035] Step 2: Load monitoring and mode determination.

[0036] Real-time monitoring of unit load. When the real-time operating power of the unit is detected to be no higher than 40% of the rated power and / or a low-load dispatch instruction is received from the power grid dispatch system, clean fuel blending is automatically started, entering deep peak shaving mode, and step 3 is executed; otherwise, the conventional combustion mode is maintained.

[0037] Step 3: Spatial Differentiation Injection Regulation of Clean Fuels.

[0038] Based on a preset strategy or real-time temperature field, the injection layout of clean fuel at different heights and circumferential positions in the furnace is determined and adjusted, specifically including: On the one hand, by extending the injection area of ​​clean fuel, and to optimize the heat load distribution, the clean fuel injection point can be gradually extended from the main combustion zone 4 to the upper burnout zone 5. Specifically, the clean fuel injection point gradually extends into the OFA zone 501 (staged air zone) and SOFA zone 502 (deep staged air zone) within the burnout zone 5. In this embodiment, this is achieved by sequentially activating clean fuel burners 2 corresponding to different height air zones.

[0039] On the other hand, by coordinating the air distribution at the nozzles in the air zone, the air distribution intensity at the corresponding nozzles can be moderately increased simultaneously when the injection of clean fuel from the upper part is increased. In this embodiment, the air volume in the relevant area can be increased by 5% to 15% on the baseline to promote mixing and burnout.

[0040] Step 4: Dynamically adjust the blending ratio.

[0041] Based on the spatial layout in step 3, the proportion of clean fuel at each injection point is dynamically adjusted. In this embodiment, the blending ratio of hydrogen and ammonia is adjusted to optimize the heat load distribution.

[0042] When adjusting the hydrogen content, start with a low proportion and gradually increase it to the target range at a limited rate. In this embodiment, based on the need for stable combustion, the target range for the calorific value of hydrogen is set between 3% and 6%.

[0043] When regulating ammonia, the ammonia blending ratio must balance calorific value compensation and ammonia slip control. Start with a low ratio (e.g., 0.1%–2.0%) and gradually increase it according to demand, while monitoring the ammonia slip concentration in real time.

[0044] After each adjustment, the system must be allowed to stabilize (e.g., 3-10 minutes) to determine if a steady state has been reached, and to monitor whether key parameters have reached preset targets. The target operating conditions of the boiler furnace are defined by multiple comprehensive indicators, which can be reflected in the following examples: To ensure the uniformity of the temperature field distribution within the furnace, in this embodiment, the maximum temperature difference between temperature measurement points on the same cross-section is ≤120℃, and the average temperature difference is ≤80℃. The ammonia escape concentration in the flue gas is lower than the preset environmental safety limit; that is, in this embodiment, the preferred ammonia escape concentration is less than or equal to the preset safety limit (10 ppm(v)). The wall temperature of each area of ​​the water-cooled wall is within the preset safe operating temperature range; in this embodiment, the wall temperature at each point of the water-cooled wall is within its preset safe operating temperature range, i.e., lower than the allowable temperature of the material by a certain margin.

[0045] When the clean fuel being blended includes ammonia, the control method also includes: real-time monitoring of the flue gas composition at the furnace outlet or a specific flue section; and dynamic adjustment of the ammonia injection parameters and / or the air distribution parameters of the relevant air zone based on the monitored ammonia concentration or parameters related to ammonia escape, so as to control the ammonia escape concentration within the preset safety limit.

[0046] Step 5: Real-time monitoring and diagnosis.

[0047] Continuously monitor the furnace temperature field, water-cooled wall temperature, and key operating parameters. Diagnose any abnormal operating conditions such as "local overheating of the water-cooled wall" or "instability of the tangential flow field at the four corners".

[0048] During the adjustment process, abnormal temperature areas are identified based on temperature distribution data measured at multiple temperature measurement points. When the water-cooled wall temperature in an abnormal temperature area exceeds the safety threshold, or when the temperature distribution in that area indicates a risk of instability in the tangential flow field at the four corners, the clean fuel burner 2 at the corresponding position is automatically started or adjusted to implement directional cooling or flow field correction in that area, thereby controlling the water-cooled wall temperature within a safe range and maintaining a stable tangential combustion flow field.

[0049] Specifically, two types of problems will occur inside the boiler furnace: First, localized overheating of the water-cooled wall will occur. In this case, closed-loop control of the water-cooled wall overheating will be implemented, such as... Figure 4As shown. Specifically, when the water-cooled wall temperature corresponding to the main combustion zone 4 is detected to be higher than the safety threshold, in this embodiment, the safety threshold can be set to the absolute value of the wall temperature of 480°C, or the wall temperature rises by more than 50°C relative to the reference operating condition, or the local temperature distribution unevenness exceeds the limit as in step 4 (such as the maximum temperature difference > 120°C), the system automatically performs regulation.

[0050] Second, the flow field at the four corners becomes unstable. In this case, closed-loop control to restore the swirling structure will be implemented, such as... Figure 5 As shown in the figure. Specifically, when the temperature distribution indicates that the symmetry of the tangential flow field at the four corners is disrupted, the system compensates for the momentum imbalance by differentially adjusting the momentum of the clean fuel injection at the four corners of the furnace, such as adjusting the flow rate and velocity of the fuel at each corner and coordinating the secondary air distribution, in order to restore and maintain a stable central rotating flow field.

[0051] If no abnormal state of "local overheating of water-cooled wall" or "instability of tangential flow field at four corners" occurs, proceed to step 6; if "local overheating of water-cooled wall" occurs, perform closed-loop control of water-cooled wall overheating (step 7), and return to step 5 after completion; if "instability of tangential flow field at four corners" occurs, perform closed-loop control of vortex structure recovery (step 8), and return to step 5 after completion.

[0052] If, after adjustments in step 5, the system still has not fully reached the steady-state target (e.g., there are still localized low temperatures or large temperature differences), at least one of the following operations can be performed for more refined compensation fine-tuning: fine-tuning the injection speed of a specific clean fuel burner 2; adjusting the jet direction of the nozzle in a specific airflow zone; adjusting the airflow distribution ratio between nozzles in different airflow zones. These fine-tuning steps should be performed in a small, gradual manner, and the system response should be observed until all indicators meet the definition requirements of steady-state operating conditions. Subsequently, the system records all adjustment parameters and the final state.

[0053] Step 6: Confirm steady state and record it.

[0054] When all monitored parameters meet the definition of steady-state operating conditions, the system is confirmed to have entered a steady state. Record the entire control sequence and data. After completion, return to continue monitoring the entire system.

[0055] In this embodiment, when "local overheating of the water-cooled wall" occurs, closed-loop control of the water-cooled wall overheating is performed. This includes the following steps: Step 7.1: Implement comprehensive cooling and control strategies.

[0056] Step 7.2: Wait and observe the system's stability for 3 to 10 minutes.

[0057] Step 7.3: Relocate the temperature measurement points and obtain the latest temperature field data.

[0058] Step 7.4: Determine whether the water-cooled wall temperature has fully recovered to the safe operating temperature range and whether the temperature distribution uniformity meets the requirements.

[0059] If so, exit the water-cooled wall over-temperature closed-loop control and return to step 5.

[0060] If not, determine whether the safety control limit has been reached. If not, return to step 7.1, adjust the strategy, and control again. If the limit has been reached, trigger the emergency protection logic.

[0061] The comprehensive cooling control strategy implemented in step 7.1 includes one or more of the following: switching the injection strategy, which can immediately reduce or cut off the injection of clean fuel in the corresponding high-temperature zone; increasing the cooling air volume, which can be achieved by increasing the primary and / or secondary air volume corresponding to the high-temperature zone; and transferring the combustion load, transferring part of the combustion load to the burnout zone 5 above the furnace. In this embodiment, the upper clean fuel burner 2 is activated, and the corresponding burnout air volume (burnout air volume of OFA zone 501 and / or SOFA zone 502) is increased by 5% to 15%.

[0062] In this embodiment, when "quadrilateral flow field instability" occurs, closed-loop control for swirl structure restoration is performed. This includes the following steps: Step 8.1: Implement a comprehensive flow field restoration and control strategy.

[0063] Step 8.2: Continuously monitor the flame images inside the furnace and the distribution of key temperature measurement points.

[0064] Step 8.3: Relocate the temperature measurement points and obtain the latest temperature field and symmetry data.

[0065] Step 8.4: Determine whether the temperature difference between the flue gas and air on both sides of the furnace is stable, and whether the temperature field distribution indicates that the tangential flow field at the four corners has returned to stability.

[0066] If so, exit the swirl structure and restore closed-loop control, then return to step 5.

[0067] If not, determine whether the adjustment limit has been reached. If the limit has not been reached, return to step 8.1, adjust the strategy, and then adjust again. If the limit has been reached, perform protective operations.

[0068] The integrated flow field recovery and control strategy implemented in step 8.1 includes one or more of the following: Momentum compensation regulation employs differentiated adjustment of the injection parameters of the clean fuel burners 2 at the four corners of the furnace, including flow rate, velocity, and angle, to compensate for the side with weakened momentum. Air-coal synergistic regulation corrects the gas flow distribution by adjusting the secondary air volume in corresponding areas or making minor adjustments to the coal feed rate at the four corners. Enhanced upper rotation is achieved by temporarily increasing the overall hydrogen blending ratio and simultaneously increasing the upper burnout air volume to enhance the rotational momentum at the furnace center.

[0069] The control method also includes safety interlocking and exit mechanisms. When abnormalities such as severely excessive water-cooled wall temperature, excessive ammonia escape concentration, or hydrogen leakage occur, an emergency plan will be triggered, such as quickly cutting off fuel injection.

[0070] When the power grid requires the unit to increase its load, the control system can gradually exit the clean fuel blending process and return to the normal operating mode in the reverse order and at a controllable rate (e.g., ≤1% / min).

[0071] This invention, through a specific implementation method of "monitoring-diagnosis-spatial differential dynamic control", uses clean fuel as an active control medium to achieve precise optimization of furnace heat load distribution and active maintenance of combustion flow field under low load. It effectively solves the problems of water-cooled wall overheating and thermal deviation, and significantly improves the safety and flexibility of deep peak shaving operation of the unit.

[0072] Although the invention has been described with reference to preferred embodiments, various modifications can be made and components can be replaced with equivalents without departing from the scope of the invention. In particular, the technical features mentioned in the various embodiments can be combined in any manner as long as there is no structural conflict. The invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for controlling clean fuel coupled heat load under low-load conditions of a coal-fired boiler, characterized in that, A clean fuel coupled combustion system for low-load coal-fired boilers is provided. The system includes a pulverized coal boiler with tangential combustion, multiple pulverized coal burners arranged at the four corners of the boiler's furnace, multiple clean fuel burners arranged in layers along the circumference of the furnace, multiple storage tanks connected to the clean fuel burners, multiple air zone nozzles arranged alternately with the nozzles of the clean fuel burners in a horizontal cross-section, and multiple temperature measuring points set along the height of the furnace in multiple representative cross-sections or key combustion areas. The combustion area of ​​the furnace includes a main combustion zone and a burnout zone from bottom to top along the height direction. The air distribution system has primary air and secondary air nozzles, as well as burnout air nozzles, supplying air to the main combustion zone and the burnout zone respectively. The control method includes the following steps: Based on multiple temperature measurement points, the temperature distribution in multiple local areas within the furnace is monitored; When the unit is detected to be operating at a low load of no more than 40% of its rated power, the clean fuel blending will be automatically started. Based on the preset strategy, real-time operating conditions, and the temperature distribution data, the co-firing position, area, and proportion of clean fuel injected into different combustion zones and / or air zones in the furnace are coordinated and controlled to optimize and homogenize the heat load distribution in the furnace, ensuring combustion stability and the safety of the heating surface.

2. The method for controlling clean fuel coupled heat load under low-load conditions of a coal-fired boiler according to claim 1, characterized in that, The clean fuel includes at least one of hydrogen, ammonia, methane, and methanol.

3. The method for controlling clean fuel coupled heat load under low-load conditions of a coal-fired boiler according to claim 1, characterized in that, The preset strategy, real-time operating conditions, and temperature distribution data collaboratively regulate clean fuel, including: Feedback adjustments are made based on temperature monitoring data of the water-cooled walls inside the furnace. When the monitored value of the water-cooled wall temperature corresponding to the main combustion zone is higher than the safety threshold, or the temperature distribution in the water-cooled wall area is uneven and exceeds the preset limit, the heat flow distribution in the area is optimized by adjusting the injection position and blending ratio of clean fuel, so as to control the water-cooled wall temperature and temperature difference within the safe range.

4. The method for controlling clean fuel coupled heat load under low-load conditions of a coal-fired boiler according to claim 1, characterized in that, The clean fuels injected into different combustion zones and / or air zones within the furnace in a coordinated manner include: Under low-load conditions, the clean fuel injected into different locations in the furnace is adjusted independently and differentiatedly. By independently controlling at least one of the injection quantity, flow rate, and injection angle of each clean fuel burner, differentiated jet momentum input is formed to compensate for the insufficient combustion momentum of the main pulverized coal, thereby restoring the swirling intensity in the center of the furnace and optimizing the overall heat load distribution of the furnace.

5. The method for controlling clean fuel coupled heat load under low-load conditions of a coal-fired boiler according to claim 4, characterized in that, The control method further includes: Real-time coordinated adjustment of the flow rate and temperature of clean fuel, as well as the air distribution at the corresponding air zone nozzles; By changing the air distribution intensity above the main combustion zone and differentially adjusting the injection parameters of clean fuel at the four corners of the furnace, the flame path above the main combustion zone is extended, and the rotating flow field formed by the tangential combustion method at the four corners is strengthened and maintained.

6. The method for controlling clean fuel coupled heat load under low-load conditions of a coal-fired boiler according to claim 1, characterized in that, The control method further includes: Identify temperature anomaly areas based on temperature distribution data measured from multiple temperature measurement points; When the water-cooled wall temperature in the abnormal temperature zone exceeds the safety threshold, or when the temperature distribution in the zone indicates a risk of instability in the tangential flow field at the four corners, the clean fuel burner at the corresponding position is automatically activated or adjusted to implement directional cooling or flow field correction in the zone, thereby controlling the water-cooled wall temperature within a safe range and maintaining a stable tangential combustion flow field.

7. The method for controlling clean fuel coupled heat load under low-load conditions of a coal-fired boiler according to claim 1, characterized in that, When the clean fuel being blended includes ammonia, the control method further includes: Real-time monitoring of flue gas composition at the furnace outlet or a specific flue section; Based on the monitored ammonia concentration or ammonia escape concentration, dynamically adjust the ammonia injection parameters and / or the air distribution parameters of the relevant air zones to control the ammonia escape concentration within the preset safety limit.

8. The method for controlling clean fuel coupled heat load under low-load conditions of a coal-fired boiler according to claim 3 or 5, characterized in that, To compensate for combustion deviations under low loads and accelerate the transition to the target operating condition, the control method further includes performing at least one of the following compensation and adjustment operations: Adjust the fuel injection rate of the clean fuel burner; Adjust the jet direction of the nozzle in a specific wind zone; Adjust the air volume distribution ratio between nozzles in different air zones.

9. The method for controlling clean fuel coupled heat load under low-load conditions of a coal-fired boiler according to claim 1 or 7, characterized in that, The target operating condition or steady-state operating condition of the boiler furnace includes the following comprehensive indicators: The temperature field distribution inside the furnace meets the preset uniformity standard; The ammonia escape concentration in the flue gas is lower than the preset environmental safety limit; The wall temperature in each area of ​​the water-cooled wall is within the preset safe operating temperature range.

10. The method for controlling clean fuel coupled heat load under low-load conditions of a coal-fired boiler according to claim 1, characterized in that, The triggering conditions for automatically starting clean fuel blending are: receiving a low-load dispatch instruction from the power grid dispatch system, and / or locally detecting that the real-time operating power of the unit is not higher than 40% of the rated power.

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