A method for optimizing full load operation of a double-reheat ultra-supercritical tower boiler

Abstract

The application provides a kind of double-reheat ultra-supercritical tower type boiler full load operation optimization method, the method comprises: step S1, real-time acquisition unit load, steam temperature, desuperheating water flow, heating surface wall temperature and exhaust smoke temperature;Step S2, determine the steam temperature condition and execute the two-way dynamic reconstruction of flame center, raise the flame center under the condition of insufficient temperature, lower the flame center under the condition of over-temperature and large desuperheating water;Step S3, execute one-sided flue gas damper directional correction to double-reheat double-side steam temperature deviation;Step S4, perform segmented quantitative power saving control on the air mill system according to the load section;Step S5, linkage air preheater bypass damper, coal saving device water flow and soot blower realize exhaust smoke temperature closed loop control;Step S6, reduce the desuperheating water consumption according to the wall temperature margin self-adaptive reduction.The application solves the problems of existing technology, such as double-reheat tower type boiler full load section steam temperature not meeting the standard, large reheating desuperheating water quantity, high air mill power consumption and difficult control of exhaust smoke temperature.

Description

Technical Field

[0001] This invention relates to the field of power plant boiler combustion optimization and thermal system energy saving technology, specifically to a method for optimizing the full-load operation of a double reheat ultra-supercritical tower boiler. Background Technology

[0002] Double reheat ultra-supercritical power generation technology adds a reheat process to the conventional single reheat process, further improving the unit's cycle thermal efficiency. It represents a crucial route for the development of coal-fired power generation technology towards higher efficiency and cleaner operation. Tower boilers suspend all heating surfaces, including superheaters and reheaters, above the furnace, allowing for vertical flue gas flow without horizontal flues. This design offers advantages such as compact heating surface arrangement, relatively small flue gas lateral deviation, and smaller footprint, and has already been applied to 1000MW-class double reheat ultra-supercritical units. However, due to the tower boiler's long and narrow furnace, all-high heating surface arrangement, and vertical flue gas flow characteristics, conventional operation has unique technical limitations: the flame center height significantly affects the heat absorption of the high-level heating surfaces. When using a fixed air distribution and fixed burner angle operation mode, the furnace flame tends to sink under low load conditions, resulting in insufficient heat absorption by the high-level heating surfaces. Consequently, the main steam temperature and reheat steam temperature struggle to reach the rated ultra-supercritical parameters, limiting the unit's cycle efficiency.

[0003] Meanwhile, the multiple heating surfaces and strong heat absorption coupling of primary and secondary reheat units make it easy for flue gas deviations to cause uneven steam temperatures on both sides. To control overheating of the heating surfaces, large amounts of reheat desuperheating water must be continuously added during operation, resulting in severe heat loss and becoming the core reason for the high energy consumption of secondary reheat units. In addition, the flue gas system of tower boilers has high resistance and a small tolerance range for the ratio of primary to secondary air. During normal operation, there is redundancy in air pressure and air volume, and the fans and coal mills operate at high power consumption rates for a long time, resulting in high plant power consumption. The flue gas heat exchange coupling characteristics of the air preheater and the high and low pressure economizers in tower boilers are special, lacking load-adaptive bypass regulation and soot blowing logic. At low loads, the flue gas temperature is too low, which can easily induce low-temperature corrosion, while at high loads, the flue gas temperature is too high, which increases the heat loss of flue gas.

[0004] To address the aforementioned issues, the industry has employed various methods for steam temperature regulation, including flue gas recirculation, burner angle adjustment, and flue gas damper temperature control. However, these methods are all single-mode adjustments and are not compatible with the structural characteristics of tower boilers, such as vertical combustion, high-level heat absorption, and dual reheat heating surface arrangement. This results in poor parameter control and an inability to simultaneously achieve target steam temperature, reduced desuperheating water consumption, energy savings in the air mill system, and control of exhaust gas temperature under full-load conditions. Therefore, how to combine the structure and heat exchange characteristics of tower boilers to achieve synergistic optimization of precise and stable main reheat steam temperature across the entire load range, deep energy reduction of dual reheat desuperheating water, energy savings in the air mill system, and closed-loop control of exhaust gas temperature has become a critical issue urgently needing to be addressed by the industry. Summary of the Invention

[0005] The main objective of this invention is to provide an optimization method for the full-load operation of a double reheat ultra-supercritical tower boiler, in order to solve the problem in the prior art that double reheat tower boilers are unable to simultaneously achieve the target main reheat steam temperature, reduce reheat desuperheating water consumption, save electricity in the air mill system, and control the flue gas temperature during the full-load period.

[0006] To achieve the above objectives, according to a first aspect of the present invention, a method for optimizing the full-load operation of a double reheat ultra-supercritical tower boiler is provided, the method comprising: Step S1: Collect unit load, main steam temperature, primary reheat steam temperature, secondary reheat steam temperature, primary reheat desuperheating water flow rate, secondary reheat desuperheating water flow rate, heated surface wall temperature, and exhaust gas temperature at the inlet of the induced draft fan. Step S2: When the double reheat steam temperature is lower than the preset steam temperature value: If no desuperheating water is introduced, it is determined to be an under-temperature condition and the flame center is raised, including increasing the flue gas recirculation output, swinging the burner angle upward, reducing the air distribution in the bottom area of ​​the burner, and increasing the upper burnout air volume; If the desuperheating water supply exceeds the preset flow rate value, it is determined to be an over-temperature large desuperheating water condition and the flame center is lowered, including reducing the flue gas recirculation output, swinging the burner angle downward, increasing the air distribution in the bottom area of ​​the burner, and reducing the upper burnout air volume. Step S3: When the temperature difference between the two sides of the primary reheat steam temperature or the secondary reheat steam temperature exceeds the preset deviation value, the opening of the flue gas damper on the side with the lower steam temperature is increased. Step S4: Based on the load segment of the unit load, perform segmented quantitative energy-saving control on the air mill system, including primary air pressure control, oxygen offset control, and coal mill start-up and shutdown control. Step S5: Adjust the air preheater bypass damper, economizer water flow and soot blower in conjunction with the unit load to control the exhaust gas temperature at the induced draft fan inlet below the preset exhaust gas temperature. Step S6: When the wall temperature margin of the heated surface is greater than the preset margin value, reduce the amount of reheat desuperheating water used. The wall temperature margin is the difference between the alarm limit of the heated surface wall temperature and the actual wall temperature.

[0007] Furthermore, in step S2, within the load range of 30% to 100% of the boiler's maximum continuous evaporation capacity, the main steam temperature is controlled to be no lower than 600℃, and the superheat of the superheated steam is controlled to be no greater than 70℃; when performing the operation of raising the flame center, the air distribution in the bottom area of ​​the burner is reduced and the air distribution in the upper burnout air area is strengthened, while maintaining the opening of the auxiliary air damper at no less than 25%, the opening of the oil auxiliary air damper at no less than 15%, and the opening of the fuel air damper at no less than 20%, and maintaining the differential pressure between the secondary air box and the furnace at no less than 0.3 kPa.

[0008] Further, in step S2, when the unit load is under ultra-low load conditions of 280MW to 300MW, the flue gas damper opening is fixed so that the opening of the flue gas damper on the low-temperature reheater side is greater than that on the low-temperature superheater side; at least two layers of burnout air are maintained with an opening of 50%; the auxiliary air dampers of layers AB are closed to 70%, the auxiliary air dampers of the remaining operating layers are closed to 20%, the oil auxiliary air damper is closed to 20%, the fuel air dampers of layers A1 and A2 are not less than 30%, and the fuel air dampers of the remaining layers are closed to 20%; the differential pressure between the secondary air box and the furnace is maintained to be not less than 0.2kPa, and the superheat of the working fluid at the economizer outlet is controlled to be not greater than -10℃; when the main steam temperature is lower than 590℃, at least two of the upper layers of burnout air are maintained with an opening of 50%, and the burnout air operation level is gradually lowered as needed.

[0009] Further, in step S3, when the unit load is greater than 700MW or the feedwater flow rate is greater than 1870t / h, and the deviation of the steam temperature at the outlet of the third-stage superheater is greater than 10℃ and the main steam temperature does not reach 600℃, one to two sets of soot blowing are added to the superheater; and / or, when the unit load is greater than 700MW, and at least one of the following occurs: a deviation of 10℃ to 15℃ between the two sides of the reheater, a deviation of 50℃ between the flue gas temperature at the furnace outlet, a reheat desuperheating water input exceeding 15t / h, or a flue gas temperature at the outlet of the high-temperature reheater greater than 800℃, one to two sets of soot blowing are added to the abnormal side reheater.

[0010] Furthermore, in step S2, within the load range of 50% to 100% of the boiler's maximum continuous evaporation capacity, the temperature of both the primary reheat steam and the secondary reheat steam is controlled to be no lower than 620℃, and under the operating condition of 30% of the boiler's maximum continuous evaporation capacity, the temperature of both is no lower than 598℃, and the average total amount of primary reheat desuperheating water and secondary reheat desuperheating water is no greater than 15t / h; and / or, when the unit load is greater than 500MW, the burner tilt angle is adjusted to a horizontal position to weaken the tangential combustion bias.

[0011] Furthermore, in step S4, the boiler is equipped with six coal mills, which are put into operation in the order of B, C, D, E, F, and A during normal operation. When the amount of reheat desuperheating water exceeds the preset limit and the steam temperature rise is limited, coal mill A and the upper coal mill are put into operation first. When there is internal leakage in the reheater desuperheating water valve, the main desuperheating water valve is closed, and the coal flow rate of coal mill B is controlled at 35t / h, the coal flow rate of coal mill C is controlled at 45t / h, and the output of coal mill D is increased. At the same time, the superheat of the working fluid at the economizer outlet is controlled to be no more than -10℃.

[0012] Further, in step S4, the primary air pressure control includes: stabilizing the coal mill outlet temperature at 95℃, controlling the coal mill air volume offset to be no greater than 0, maintaining the average opening of the coal mill hot air regulating damper to be no less than 60%, and maintaining the coal mill outlet air velocity at 20m / s~27m / s; under the stable operating condition of 300MW, controlling the pressure of the hot primary air main pipe to be no greater than 7.5kPa.

[0013] Further, in step S4, the oxygen offset control includes: the baseline oxygen offset is not greater than 0; when the sulfur dioxide concentration in the raw flue gas is greater than 2800 mg / m³, the oxygen offset is set to 0.5 to 0.7; when the sulfur dioxide concentration in the raw flue gas is greater than 3200 mg / m³, the oxygen offset is set to 0.7; before the unit load increases, the oxygen offset is increased by 0.5 to 1 in advance; when the load increment is greater than the preset increment value, the oxygen offset is not less than 1; after the load stabilizes, the oxygen offset is gradually reduced to zero.

[0014] Furthermore, in step S4, the start-up and shutdown control of the coal mill unit includes: shutting down one coal mill when the average output of six coal mills is less than 52t / h, the average output of five coal mills is less than 50t / h, or the average output of four coal mills is less than 48t / h; controlling the speed of the coal mill separator to not exceed 75rpm when the unit load is greater than 400MW; maintaining the differential pressure at the inlet and outlet of the coal mill to not exceed 5kPa, and cleaning the coal mill when the differential pressure exceeds this; and adjusting the coal quality and the operating conditions of the coal mill unit when the frequency of stone coal discharge is greater than 20min per tank.

[0015] Further, in step S5, the inlet flue gas temperature of the induced draft fan is controlled to be less than 112℃; when the unit load is less than 500MW, the air preheater bypass damper is fully closed; when the flue gas temperature is low, the water flow of the high-pressure economizer and the low-pressure economizer is reduced to maintain the outlet water temperature of the high-pressure economizer not lower than the feedwater temperature; when the unit load is greater than 500MW, the air preheater bypass damper is gradually opened to control the average sum of the outlet flue gas temperature and the outlet air temperature of the air preheater to be not less than 150℃; when the unit load is greater than 850MW, the air preheater bypass damper is fully opened; and / or, when the unit load is greater than 700MW or the feedwater flow is greater than 1870t / h, at least two sets of long soot blowing are completed by selecting the unoperated soot blowers in each shift; and / or, when the unit operates at low load for 5 to 7 consecutive days, systematic furnace body soot blowing is performed.

[0016] Compared with existing technologies, the beneficial effects of this invention are as follows: By applying the technical solution of this invention, the vertical combustion and heat absorption characteristics of the tower boiler's high and low bidirectional dynamic reconstruction of the flame center are adapted to the high-level heating surface, ensuring that the main steam temperature and double reheat steam temperature reach the rated parameters stably throughout the entire load range; by directional correction of the flue gas damper on one side and targeted soot blowing, the temperature deviation between the two sides of the double reheat is eliminated, significantly reducing the total amount of reheat desuperheating water; by segmented and quantified primary air pressure, oxygen offset, and pulverizer start-up and shutdown control, redundant output of the air mill system is eliminated, reducing plant power consumption; by load-adaptive air preheater bypass, economizer water flow, and soot blowing linkage, the flue gas temperature is stably controlled within a reasonable range, avoiding low-temperature corrosion and flue gas heat loss. Therefore, the technical effect of synergistic optimization of steam temperature, desuperheating water, power consumption, and flue gas temperature throughout the entire load range can be achieved. Attached Figure Description

[0017] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0018] In the attached diagram: Figure 1 A flowchart of the optimization method for full-load operation of a double reheat ultra-supercritical tower boiler provided in an embodiment of the present invention; Figure 2 A logical schematic diagram of bidirectional dynamic reconstruction of the flame center provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of the adaptive closed-loop control of flue gas temperature load provided in an embodiment of the present invention. Detailed Implementation

[0019] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0020] This embodiment takes a 1000MW-class ultra-supercritical tower boiler with double reheat as an example. The boiler has a tower layout, with all heating surfaces such as the superheater, primary reheater, and secondary reheater suspended above the furnace. After flowing vertically in the furnace, the flue gas flows sequentially through the high-level heating surfaces and enters the tail flue. The tail flue is equipped with a high-temperature superheater, a high-temperature reheater, a low-temperature reheater, a low-temperature superheater, a high-pressure economizer, a low-pressure economizer, and a rotary air preheater arranged along the flue gas flow direction. The lower part of the furnace is equipped with multi-layer pulverized coal burners, each layer of burners is equipped with fuel dampers, auxiliary dampers, and oil auxiliary dampers, and multi-layer burnout air nozzles are arranged above the burners. The boiler is equipped with a flue gas recirculation fan, six medium-speed coal mills, a double flue temperature regulating baffle, and a steam soot blowing system covering the water-cooled walls, superheaters, and reheaters. The air preheater is equipped with a flue gas bypass baffle, and the water flow of the high-pressure economizer and the low-pressure economizer is adjustable. The six coal mills are numbered A to F and arranged in layers along the height of the furnace, with mill A corresponding to the upper burner. The distributed control system of the unit can collect all the operating parameters required by this method in real time. The various optimization strategies of this invention can be executed by operators according to operating procedures, or they can be solidified into control logic and automatically executed by the distributed control system.

[0021] During step S1, the distributed control system of the unit collects real-time data on unit load, main steam temperature, primary reheat steam temperature, secondary reheat steam temperature, primary reheat desuperheating water flow rate, secondary reheat desuperheating water flow rate, superheater and reheater heating surface wall temperature, and induced draft fan inlet flue gas temperature. Simultaneously, it collects auxiliary parameters such as feedwater flow rate, furnace outlet flue gas temperature, raw flue gas sulfur dioxide concentration, output of each coal mill, differential pressure at the coal mill inlet and outlet, primary air header pressure, and differential pressure between the secondary air box and the furnace. Specifically, the dual reheat steam temperature is the average of the primary and secondary reheat steam temperatures; the temperature deviation between the two sides is the difference between the outlet steam temperatures on the left and right sides of the same reheater; and the reheat desuperheating water input is the sum of the primary and secondary reheat desuperheating water flow rates.

[0022] Step S2's bidirectional dynamic reconfiguration of the flame center utilizes the unique vertical heat exchange characteristics of tower boilers. In tower boilers, the superheaters and reheaters are all located in the high-level region above the furnace. Changes in the flame center height directly alter the radiative and convective heat absorption ratios of the high-level heating surfaces: when the flame center rises, the flue gas temperature at the furnace outlet increases, heat absorption by the high-level heating surfaces increases, and the main steam temperature and reheat steam temperature rise accordingly; the opposite occurs when the flame center sinks. Traditional fixed air distribution and fixed swing angle operation modes cannot actively adjust the flame center position according to load and steam temperature deviations. At low loads, flame sinking leads to insufficient heat absorption by the high-level heating surfaces. This embodiment uses the flame center position as the core adjustment variable, performing bidirectional reconfiguration based on steam temperature conditions, replacing the passive adjustment method that solely relies on desuperheating water and fixed air distribution.

[0023] When the average temperature of the double reheat steam is below 610℃ and no desuperheating water is added on-site, the boiler is determined to be in an under-temperature condition. An operation to raise the flame center is then implemented, specifically by increasing the output of the flue gas recirculation fan, tilting the burner angle upwards, reducing the air distribution in the bottom area of ​​the burner, and increasing the upper burnout airflow. Flue gas recirculation returns some low-temperature flue gas to the furnace, altering the distribution of the temperature and airflow fields within the furnace; tilting the burner angle upwards shifts the ignition and burnout zones of the pulverized coal flow upwards; reducing the air distribution in the bottom area of ​​the burner weakens the combustion intensity at the bottom; and increasing the upper burnout airflow extends the burnout process to the upper part of the furnace. These four methods work synergistically to raise the flame center overall, increasing the heat absorption of the high-level double reheat heating surfaces, thus achieving a temperature increase without the addition of desuperheating water.

[0024] When the average reheat steam temperature is below 610℃ and the desuperheating water input exceeds 15t / h, it indicates that the boiler is in a contradictory operating condition of local overheating of the heating surface and insufficient overall steam temperature. This is identified as an overheating and large desuperheating water condition, and the boiler reverses the operation to lower the flame center. Specifically, this involves reducing the output of the flue gas recirculation fan, swinging the burner angle downwards, increasing the air distribution in the bottom area of ​​the burner, and reducing the upper burnout air volume, thereby shifting the flame center downwards and suppressing local overheating of the high-level reheater heating surface. At the same time, this is combined with water-cooled wall and superheater soot blowing to remove ash from the heating surface, reducing the frequency of reheater overheating from the root cause and significantly reducing the amount of desuperheating water used. This bidirectional reconfiguration mechanism ensures that the direction of flame center adjustment precisely corresponds to the nature of the steam temperature deviation, avoiding the problem of one-sided adjustment in contradictory operating conditions.

[0025] Regarding rated parameter control, within the boiler's maximum continuous evaporation load range of 30% to 100%, the main steam temperature is stably controlled above 600℃, the superheater wall temperature does not exceed the limit, and the superheat of the superheated steam does not exceed 70℃, ensuring the stability of ultra-supercritical operating conditions. When implementing air distribution for temperature increase, a fixed lower limit for safe air distribution is established: the opening of the auxiliary air damper is not less than 25%, the opening of the oil auxiliary air damper is not less than 15%, and the opening of the fuel air damper is not less than 20%. The differential pressure between the secondary air box and the furnace is maintained at not less than 0.3 kPa to prevent combustion deterioration or uneven air distribution caused by excessive air distribution contraction, ensuring that the temperature increase operation is always within the safe boundary of stable combustion. The control threshold for double reheat steam temperature is as follows: within the range of 50% to 100% of the boiler's maximum continuous evaporation load, both the primary reheat steam temperature and the secondary reheat steam temperature shall not be lower than 620℃; under the condition of 30% of the boiler's maximum continuous evaporation load, both shall not be lower than 598℃; and the average total amount of primary reheat desuperheating water and secondary reheat desuperheating water shall not exceed 15t / h.

[0026] For ultra-low load conditions of 280MW to 300MW, where the furnace heat load is low and the flame tends to sink, a customized control strategy is implemented. The flue gas damper opening is fixed, with the low-temperature superheater side flue gas damper opening at 50% and the low-temperature reheater side flue gas damper opening at 80%, tilting the flue gas flow towards the reheater side to enhance reheat absorption under low load. At least two layers of burnout air are maintained at 50% opening. The auxiliary air dampers for layers A and B are closed to 70%, the remaining operating auxiliary air dampers are closed to 20%, the oil auxiliary air damper is closed to 20%, the fuel air dampers for layers A1 and A2 are opened to at least 30%, and the remaining fuel air dampers are closed to 20%. The differential pressure between the secondary air box and the furnace is maintained to be at least 0.2 kPa. The superheat of the working fluid at the economizer outlet is controlled to be no greater than -10℃, meaning the economizer outlet water temperature is more than 10℃ lower than the saturation temperature at the corresponding pressure, preventing vaporization of the working fluid inside the economizer. When the main steam temperature is below 590℃, maintain the opening of at least two of the upper three layers of burnout air at 50%, and gradually lower the burnout air operation level as needed to match the furnace heat load distribution under low load and stabilize the main steam temperature.

[0027] Under high-load conditions, heat absorption deviation caused by ash accumulation on the heating surface is the main cause of uneven steam temperature. When the unit load exceeds 700MW or the feedwater flow rate exceeds 1870t / h, and the steam temperature deviation at the outlet of the third-stage superheater exceeds 10℃ and the main steam temperature does not reach the rated value of 600℃, one to two sets of soot blowing should be added to the superheater to remove ash from the high-level heating surface, restore the heat absorption uniformity of the heating surface, and balance the steam temperature on both sides. When the unit load exceeds 700MW and at least one of the following occurs: reheater steam temperature deviation of 10℃ to 15℃, furnace outlet flue gas temperature deviation of 50℃, reheat desuperheating water input exceeding 15t / h, or high-temperature reheater outlet flue gas temperature exceeding 800℃, one to two sets of special soot blowing should be added to the abnormal side of the reheater to eliminate the heat absorption deviation caused by ash accumulation. The above-mentioned soot blowing trigger criteria couple multiple parameters such as steam temperature deviation, flue gas temperature deviation, desuperheating water volume and flue gas temperature level, so that the timing and target of soot blowing operation have clear quantitative basis, avoiding steam loss and heat exchange surface wear caused by blind soot blowing.

[0028] When the unit load exceeds 500MW, localized overheating is likely to occur on the heating surfaces. Adjusting the burner tilt angle to a horizontal position weakens the tangential combustion bias, ensuring a more uniform distribution of heat load in the furnace and reducing the local wall temperature of the reheater. This approach avoids the need for passively injected desuperheating water from a combustion organization perspective. This measure, combined with flame center reconfiguration and directional soot blowing, constitutes a complete chain of measures for controlling high-load wall temperature.

[0029] Step S3 performs directional correction for uneven double reheat steam temperature caused by flue gas side skew in tower boilers. The primary and secondary reheat heating surfaces have multiple layers and strong heat absorption coupling. Deviations in flue gas velocity and temperature on the left and right sides cause differences in heat exchange between the heating surfaces, resulting in bilateral steam temperature deviation. When the bilateral steam temperature deviation exceeds 5°C, the opening of the flue gas damper on the side with the lower temperature is increased, increasing the flue gas flow and heat exchange on that side, thus accurately balancing the flue gas distribution on both sides. Single-sided adjustment only changes the flue gas share on the skewed side, avoiding overall flue gas temperature fluctuations caused by coordinated bilateral adjustments. This eliminates steam temperature deviation without affecting the overall heat exchange level of the boiler, reducing the need for superimposed desuperheating water losses to control the overheated side.

[0030] Step S4, the segmented quantitative energy-saving control of the air mill system, uses the quantitative indicators of power consumption rate for each load segment as the control target: fan power consumption rate is less than 1.8 in the 75%–100% boiler maximum continuous evaporation load range, less than 1.9 in the 50% boiler maximum continuous evaporation load condition, and less than 2.3 in the 30% boiler maximum continuous evaporation load condition; coal mill power consumption is less than 0.35 in the 75%–100% boiler maximum continuous evaporation load range, less than 0.4 in the 50% boiler maximum continuous evaporation load condition, and less than 0.42 in the 30% boiler maximum continuous evaporation load condition. These indicators match the high resistance characteristics of the tower boiler flue gas system and serve as quantitative constraints for primary air pressure control, oxygen bias control, and coal mill start-up and shutdown control.

[0031] In primary air pressure control, the pulverizer outlet temperature is stabilized at 95℃, and the amount of cold primary air mixed in is strictly controlled to reduce energy loss caused by the mixing of hot and cold air. The pulverizer airflow offset is set to no greater than 0, and the primary air pressure redundancy is appropriately reduced. The average opening of the pulverizer hot air regulating damper is maintained at no less than 60% to avoid throttling losses caused by the hot air regulating damper being at a small throttling opening for a long time. The pulverizer outlet air velocity is maintained at 20m / s to 27m / s. Too low an air velocity can easily cause coal dust to accumulate and block the pipe, while too high an air velocity will aggravate pipe wear and increase friction resistance. Under stable operating conditions of 300MW, the pressure of the hot primary air main pipe is controlled to no greater than 7.5kPa to eliminate the power consumption of the fans caused by high-pressure redundant air supply.

[0032] In oxygen offset control, the baseline oxygen offset is not greater than 0, so that the boiler operates with a lower excess air coefficient under normal conditions, reducing the output of the forced and induced draft fans. When the sulfur dioxide concentration in the raw flue gas is greater than 2800 mg / m³, the oxygen offset is set to 0.5-0.7. When the sulfur dioxide concentration in the raw flue gas is greater than 3200 mg / m³, the oxygen offset is set to 0.7 to ensure the combustion completeness of high-sulfur coal and the inlet conditions of the desulfurization system. Before the unit rapidly increases the load, the oxygen offset is increased by 0.5-1 in advance. When the load increases continuously and significantly, the oxygen offset is not less than 1 to match the rapid increase in fuel quantity and prevent oxygen-deficient combustion. After the load stabilizes, the oxygen offset is gradually reduced to zero to balance combustion stability and optimal fan power consumption.

[0033] In the start-up and shutdown control of coal mill units, when the average output of six coal mills is less than 52t / h, the average output of five coal mills is less than 50t / h, or the average output of four coal mills is less than 48t / h, one coal mill should be shut down in a timely manner to keep the operating coal mills within the economic output range of a single mill and avoid multiple coal mills operating at low output and inefficiently at the same time; when the unit load is greater than 400MW, the speed of the coal mill separator should be controlled to be no more than 75rpm to reduce the ineffective energy consumption of the separator; the differential pressure at the inlet and outlet of the coal mill should be maintained to be no more than 5kPa, and if the differential pressure exceeds this, it should be cleared in time to prevent the increase in power consumption caused by the accumulation of powder and blockage inside the coal mill; when the frequency of stone coal discharge is greater than 20 minutes per tank, the coal quality and the operating conditions of the coal mill unit should be optimized in a timely manner to reduce grinding losses.

[0034] The commissioning sequence of the coal mill units is adapted to the high-level heat absorption characteristics of the tower boiler. During normal operation, coal mills are commissioned in the order of B, C, D, E, F, and A. When the reheat desuperheating water input exceeds the preset limit and the steam temperature increase is limited, coal mill A and the upper coal mill are commissioned first to increase the heat load of the upper part of the furnace and match the heat absorption demand of the high-level reheater. When there is internal leakage in the reheater desuperheating water valve, the main desuperheating water valve is closed to cut off the leakage, and the coal ratio of the coal mill units is optimized. The coal input of coal mill B is controlled at 35t / h, the coal input of coal mill C is controlled at 45t / h, and the output of coal mill D is increased. At the same time, the superheat of the working fluid at the economizer outlet is controlled to be no greater than -10℃ and the reheater wall temperature is not exceeded. The low-load reheat steam temperature is stabilized under the condition of desuperheating water cut-off.

[0035] The closed-loop control of flue gas temperature in step S5 is based on a flue gas temperature at the induced draft fan inlet of less than 112℃. The flue gas heat exchange coupling characteristics between the air preheater and the high and low pressure economizers in tower boilers are unique, and a single fixed operating mode cannot simultaneously meet the flue gas temperature requirements under both high and low loads. When the unit load is less than 500MW, the air preheater bypass damper is fully closed, allowing all flue gas to flow through the air preheater for heat exchange. When the exhaust gas temperature is low, the water flow rate of the high-pressure economizer and the low-pressure economizer is appropriately reduced to decrease the heat absorption on the economizer side, maintain the outlet water temperature of the high-pressure economizer not lower than the feedwater temperature, and ensure that the outlet water temperatures of the high and low-pressure economizers are matched to raise the temperature level of the flue gas entering the air preheater and avoid low-temperature corrosion. When the unit load is greater than 500MW, the air preheater bypass damper is gradually opened, and some flue gas is diverted through the bypass to control the average sum of the air preheater outlet flue gas temperature and the outlet air temperature to be not less than 150℃, balancing heat exchange efficiency and equipment safety. When the unit load is greater than 850MW, the air preheater bypass damper is fully opened, and the exhaust gas temperature is locked at the limit throughout the process.

[0036] Regarding the prevention and control of ash accumulation under high load, when the unit load exceeds 700MW or the feedwater flow rate exceeds 1870t / h, at least two sets of long sootblowing should be carried out by selecting the non-operational sootblowers each shift to remove ash from the high-level heating surface and prevent the increase in flue gas temperature and heat loss caused by ash accumulation. During long-term low-load operation, the flue gas velocity is low and fly ash is easy to accumulate. When the unit operates at low load continuously for 5 to 7 days, systematic boiler body sootblowing should be performed to avoid ash accumulation leading to a decrease in steam temperature, an increase in flue gas temperature, and an increase in power consumption.

[0037] Step S6, adaptive wall temperature margin control, constitutes a safety net for reducing desuperheating water consumption. The wall temperature margin is the difference between the alarm limit for the heated surface wall temperature and the actual wall temperature. When the wall temperature margin is greater than 15°C, it indicates that the heated surface still has heat absorption margin, and the amount of desuperheating water is actively reduced, utilizing the heat absorption margin of the high-level heated surface of the tower boiler to achieve temperature increase and consumption reduction. When the wall temperature margin is insufficient, priority is given to ensuring the safety of the heated surface. The control objects in the above steps are intercoupled, with steam temperature, wall temperature, desuperheating water, flue gas temperature, oxygen content, air distribution, and coal mill unit operating conditions being linked for coordinated adjustment, forming a closed-loop optimization system covering the entire load range.

[0038] Taking a 1000MW-class double reheat ultra-supercritical tower boiler as an example, when the unit is operating at 750MW, the coal mill outlet temperature is stabilized at 95℃, the average opening of the hot air regulating damper is maintained above 60%, the oxygen offset is 0, the burner swing angle is placed in a horizontal position, and the air preheater bypass damper is gradually opened to control the average sum of the air preheater outlet flue gas temperature and outlet air temperature to be no less than 150℃. When the average double reheat steam temperature is 605℃ and the desuperheating water input reaches 18t / h, it is judged as an overheating and large desuperheating water condition. The output of the flue gas recirculation fan is reduced, the burner swing angle is lowered, the air distribution at the bottom of the burner is increased, the upper burnout air volume is reduced, and soot blowing is added to the abnormal side reheater. The desuperheating water input drops back to below 15t / h, and the double reheat steam temperature rises and stabilizes above 620℃. When the unit is operating under 280MW ultra-low load conditions, the opening of the flue gas damper on the low-temperature superheater side is fixed at 50%, the opening of the flue gas damper on the low-temperature reheater side is fixed at 80%, the auxiliary air dampers of the AB layer are closed to 70%, the opening of the fuel air dampers of the A1 and A2 layers is not less than 30%, the differential pressure between the secondary air box and the furnace is maintained at not less than 0.2kPa, and when the main steam temperature is lower than 590℃, the upper burnout air is maintained at no less than 50% opening for two layers and the operating level is moved down layer by layer, and the main steam temperature steadily rises. After operating according to this method, the main steam temperature is stable at no less than 600℃ within the maximum continuous evaporation load range of the boiler from 30% to 100%, the double reheat steam temperature reaches the rated parameters, the average total amount of primary reheat desuperheating water and secondary reheat desuperheating water is no more than 15t / h, the power consumption rate of the blower and the power consumption of the coal mill are both controlled within the aforementioned load segment indicators, and the exhaust gas temperature at the inlet of the induced draft fan is stable at less than 112℃. This achieves synergistic optimization of steam temperature balance across the entire load segment, desuperheating water consumption reduction, power saving of the blower and mill, and exhaust gas temperature control.

Claims

1. A method for optimizing the full-load operation of a double reheat ultra-supercritical tower boiler, characterized in that, include: Step S1: Collect unit load, main steam temperature, primary reheat steam temperature, secondary reheat steam temperature, primary reheat desuperheating water flow rate, secondary reheat desuperheating water flow rate, heated surface wall temperature, and exhaust gas temperature at the inlet of the induced draft fan. Step S2: When the double reheat steam temperature is lower than the preset steam temperature value: If no desuperheating water is introduced, it is determined to be an under-temperature condition and the flame center is raised, including increasing the flue gas recirculation output, swinging the burner angle upward, reducing the air distribution in the bottom area of ​​the burner, and increasing the upper burnout air volume; If the desuperheating water supply exceeds the preset flow rate value, it is determined to be an over-temperature large desuperheating water condition and the flame center is lowered, including reducing the flue gas recirculation output, swinging the burner angle downward, increasing the air distribution in the bottom area of ​​the burner, and reducing the upper burnout air volume. Step S3: When the temperature deviation between the two sides of the primary reheat steam temperature or the secondary reheat steam temperature exceeds the preset deviation value, the opening of the flue gas damper on the side with the lower steam temperature is increased. Step S4: Based on the load segment of the unit load, perform segmented quantitative energy-saving control on the air mill system, including primary air pressure control, oxygen offset control, and coal mill start-up and shutdown control. Step S5: Adjust the air preheater bypass damper, economizer water flow and soot blower in conjunction with the unit load to control the exhaust gas temperature at the induced draft fan inlet below the preset exhaust gas temperature. Step S6: When the temperature margin of the heated surface wall is greater than the preset margin value, reduce the amount of reheating and de-heating water used.

2. The method for optimizing the full-load operation of a double reheat ultra-supercritical tower boiler according to claim 1, characterized in that, In step S2, within the load range of 30% to 100% of the boiler's maximum continuous evaporation capacity, the main steam temperature is controlled to be no lower than 600℃, and the superheat of the superheated steam is controlled to be no greater than 70℃. When performing the operation of raising the flame center, the air distribution in the bottom area of ​​the burner is reduced and the air distribution in the upper burnout air area is strengthened. At the same time, the opening of the auxiliary air damper is maintained to be no less than 25%, the opening of the oil auxiliary air damper is no less than 15%, and the opening of the fuel air damper is no less than 20%. The differential pressure between the secondary air box and the furnace is maintained to be no less than 0.3 kPa.

3. The method for optimizing the full-load operation of a double reheat ultra-supercritical tower boiler according to claim 1 or 2, characterized in that, In step S2, when the unit load is at an ultra-low load of 280MW to 300MW, the flue gas damper opening is fixed so that the opening of the flue gas damper on the low-temperature reheater side is greater than that on the low-temperature superheater side; at least two layers of burnout air are maintained at an opening of 50%; the auxiliary air dampers of layers AB are closed to 70%, the auxiliary air dampers of the remaining operating layers are closed to 20%, the oil auxiliary air damper is closed to 20%, the fuel air dampers of layers A1 and A2 are not less than 30%, and the fuel air dampers of the remaining layers are closed to 20%; the differential pressure between the secondary air box and the furnace is maintained to be not less than 0.2kPa, and the superheat of the working fluid at the economizer outlet is controlled to be not greater than -10℃; when the main steam temperature is lower than 590℃, at least two of the upper layers of burnout air are maintained at an opening of 50%, and the burnout air operation level is gradually lowered as needed.

4. The optimization method for full-load operation of a double reheat ultra-supercritical tower boiler according to claim 1, characterized in that, In step S3, when the unit load is greater than 700MW or the feedwater flow rate is greater than 1870t / h, and the deviation of the steam temperature at the outlet of the third-stage superheater is greater than 10℃ and the main steam temperature has not reached 600℃, one to two sets of soot blowing are added to the superheater; and / or, when the unit load is greater than 700MW, and at least one of the following occurs: a deviation of 10℃ to 15℃ between the two sides of the reheater, a deviation of 50℃ between the flue gas temperature at the furnace outlet, a reheat desuperheating water input exceeding 15t / h, or a flue gas temperature at the outlet of the high-temperature reheater greater than 800℃, one to two sets of soot blowing are added to the abnormal side reheater.

5. The optimization method for full-load operation of a double reheat ultra-supercritical tower boiler according to claim 4, characterized in that, In step S2, within the 50% to 100% boiler maximum continuous evaporation load range, the temperature of both primary and secondary reheat steam is controlled to be no lower than 620℃, and no lower than 598℃ under the 30% boiler maximum continuous evaporation load condition, and the average total amount of primary and secondary reheat desuperheating water is no greater than 15t / h; and / or, when the unit load is greater than 500MW, the burner tilt angle is adjusted to a horizontal position to weaken the tangential combustion bias.

6. The method for optimizing the full-load operation of a double reheat ultra-supercritical tower boiler according to claim 1 or 5, characterized in that, In step S4, the boiler is equipped with six coal mills. During normal operation, the coal mills are put into operation in the order of B, C, D, E, F, and A. When the amount of reheat desuperheating water input exceeds the preset limit and the steam temperature rise is limited, coal mill A and the upper coal mill are put into operation first. When there is internal leakage in the reheater desuperheating water valve, the main desuperheating water valve is closed, and the coal flow rate of coal mill B is controlled at 35t / h, the coal flow rate of coal mill C is controlled at 45t / h, the output of coal mill D is increased, and the superheat of the working fluid at the economizer outlet is controlled to be no greater than -10℃.

7. The method for optimizing the full-load operation of a double reheat ultra-supercritical tower boiler according to claim 6, characterized in that, In step S4, the primary air pressure control includes: stabilizing the coal mill outlet temperature at 95°C, controlling the coal mill air volume offset to be no greater than 0, maintaining the average opening of the coal mill hot air regulating damper to be no less than 60%, and maintaining the coal mill outlet air velocity at 20m / s to 27m / s; and under stable operating conditions of 300MW, controlling the pressure of the hot primary air main pipe to be no greater than 7.5kPa.

8. The optimization method for full-load operation of a double reheat ultra-supercritical tower boiler according to claim 1 or 7, characterized in that, In step S4, the oxygen offset control includes: a baseline oxygen offset of no more than 0; when the sulfur dioxide concentration in the original flue gas is greater than 2800 mg / m³, the oxygen offset is set to 0.5 to 0.7; when the sulfur dioxide concentration in the original flue gas is greater than 3200 mg / m³, the oxygen offset is set to 0.7; the oxygen offset is increased by 0.5 to 1 before the unit load is increased; when the load increment is greater than the preset increment value, the oxygen offset is no less than 1; and after the load stabilizes, the oxygen offset is gradually reduced to zero.

9. The optimization method for full-load operation of a double reheat ultra-supercritical tower boiler according to claim 8, characterized in that, In step S4, the start-up and shutdown control of the coal mill unit includes: shutting down one coal mill when the average output of six coal mills is less than 52t / h, the average output of five coal mills is less than 50t / h, or the average output of four coal mills is less than 48t / h; controlling the speed of the coal mill separator to not exceed 75rpm when the unit load is greater than 400MW; maintaining the differential pressure between the coal mill inlet and outlet to not exceed 5kPa, and cleaning the coal mill when the differential pressure exceeds the specified value; and adjusting the coal quality and the operating conditions of the coal mill unit when the frequency of stone coal discharge is greater than 20min per tank.

10. The method for optimizing the full-load operation of a double reheat ultra-supercritical tower boiler according to claim 1 or 4, characterized in that, In step S5, the inlet flue gas temperature of the induced draft fan is controlled to be less than 112℃; when the unit load is less than 500MW, the air preheater bypass damper is fully closed; when the flue gas temperature is low, the water flow of the high-pressure economizer and the low-pressure economizer is reduced to maintain the outlet water temperature of the high-pressure economizer not lower than the feedwater temperature; when the unit load is greater than 500MW, the air preheater bypass damper is gradually opened to control the average sum of the outlet flue gas temperature and the outlet air temperature of the air preheater to be not less than 150℃; when the unit load is greater than 850MW, the air preheater bypass damper is fully opened; and / or, when the unit load is greater than 700MW or the feedwater flow is greater than 1870t / h, at least two sets of long soot blowing are completed by selecting the unoperated soot blowers in each shift; and / or, when the unit operates at low load for 5 to 7 consecutive days, systematic furnace body soot blowing is performed.

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