Load adjusting method for power station boiler

Abstract

The invention relates to a load adjusting method for a power station boiler, which comprises the following steps: in the dry and wet state conversion process of the boiler, keeping a boiler load set value unchanged or keeping a change value within 2% of the load set value, controlling the coal feeding amount through main steam pressure deviation, reducing the adjusting speed of boiler main control PID (Proportion Integration Differentiation), enabling the coal feeding amount to fluctuate within a preset range, and controlling the coal feeding amount to fluctuate within the preset range; the boiler load is kept stable; and the boiler feed water flow is adjusted at the preset speed, and conversion of the dry-state operation mode and the wet-state operation mode of the boiler is achieved.

Description

Technical Field

[0001] The embodiments of the present disclosure relate to the field of research on power plant boiler operation modes, and in particular to a load adjustment method for a power plant boiler. Background Art

[0002] my country's energy consumption has grown rapidly, and energy development has entered a new stage. As of 2021, my country's installed capacity of new energy power generation has reached 1.12 billion kilowatts, accounting for 47.10% of the total installed power generation capacity. Both the installed capacity in operation and under construction ranks first in the world.

[0003] On the one hand, new energy sources such as wind power and photovoltaics provide us with a large amount of clean electricity. On the other hand, the randomness and instability of their power generation output also bring huge challenges to the safe operation of the power system and the security of power supply.

[0004] Thermal power is mature in technology and has flexible power generation. It can comprehensively improve the system's peak load regulation and new energy consumption capabilities. At present, my country's coal-fired thermal power units can adjust the peak by 60-70% under pure condensing conditions. The deep peak load regulation of coal-fired units will inevitably affect the safety and environmental protection of the units, mainly manifested in the problem of unstable low-load combustion and low flue gas temperature at the inlet of the low-load SCR reactor affecting the normal operation of the equipment. Summary of the invention

[0005] The present disclosure is proposed to solve or alleviate at least one aspect of the problems in the prior art.

[0006] The embodiment of the present disclosure relates to a load adjustment method for a power station boiler, comprising the steps of:

[0007] During the dry-wet state conversion of the boiler, the boiler load setting value is maintained unchanged or the change value is within 2% of the load setting value, wherein: the coal feed rate is controlled by the main steam pressure deviation, the adjustment speed of the boiler main control PID is reduced, and the coal feed rate fluctuates within the preset range to keep the boiler load stable; and

[0008] Adjust the boiler feed water flow at a preset rate to achieve the conversion of the boiler's dry and wet operation modes. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 is a schematic structural diagram of a supercritical once-through boiler as an example for illustrating the technical solution of the present disclosure;

[0010] Figure 2 is a schematic structural diagram of a boiler burner according to an embodiment of the present disclosure;

[0011] Figure 3 is a furnace flue gas temperature comparison analysis diagram according to an exemplary embodiment of the present disclosure;

[0012] Figure 4 yes Figure 1 The shown boiler has a flue gas temperature curve at the SCR inlet before modification;

[0013] Figure 5 This is the SCR inlet flue gas temperature curve after utilizing the technical solution of the present disclosure. DETAILED DESCRIPTION

[0014] In order to make the purpose, technical solutions and advantages of the embodiments of the present disclosure clearer, the technical solutions in the embodiments will be clearly and completely described below in conjunction with the drawings in the embodiments of the present disclosure. The following embodiments are used to illustrate the present disclosure but are not used to limit the scope of the present disclosure.

[0015] The present disclosure is further described in detail below in conjunction with the accompanying drawings, attached tables and specific embodiments.

[0016] The boiler in this disclosure is the #2 boiler of the 2×600MW unit of Chaoyang Yanshan Lake Power Generation Co., Ltd. The boiler is a HG-1930 / 25.4-HMⅡ boiler, a once-through boiler with a single intermediate reheat and supercritical pressure transformer operation and a built-in recirculation pump starting system. The boiler is designed with the maximum continuous output condition (BMCR) as the design parameter. The main design parameters of the boiler are shown in Table 1.

[0017] Table 1 Boiler design performance calculation data table

[0018]

[0019]

[0020] Figure 1 This is a schematic diagram of the supercritical unit system.

[0021] Figure 1 The steam-water process of a supercritical boiler is illustrated as follows:

[0022] The feed water from the high-pressure heater flows into the economizer 18 for heating and then enters the water-cooled wall 23 for further heating. After the steam-water mixture enters the steam-water separator 1, the water flows into the water storage tank 2, passes through the boiler water circulation pump 3, and flows into the economizer 18 together with the high-pressure heater feed water for heating; the steam passes through the low-temperature superheater 17, the screen superheater 13, and the high-temperature superheater 14 respectively, and then goes to the high-pressure cylinder of the steam turbine to perform work. After performing work, the steam flows through the low-temperature reheater 16 and the final superheater 15 and then goes to the medium-pressure cylinder to perform work.

[0023] Figure 1 The following is an example of the air and smoke flow process of a supercritical boiler:

[0024] The primary air 21 and the secondary air 22 pass through the air preheater 19 and then enter the furnace through the pulverizing systems 4, 5, 6, 7, 8, 9, and 10 for ignition and combustion, and the combustion efficiency is improved by the burnout air 11 and 12. The flue gas flows into the air preheater 19 in the tail flue, and after denitrification in the SCR reactor 20, it is discharged into the atmosphere through the chimney after desulfurization and dust removal.

[0025] It should be pointed out that Figure 1 The arrangement, the steam-water flow and the wind-smoke flow are exemplary, and the technical solution disclosed in the present invention is not limited to application in Figure 1 The arrangement, steam-water process and wind-smoke process are shown.

[0026] The coal sample used in the supercritical boiler disclosed in the present invention is lignite from the No. 2 open-pit mine of Baiyinhua Coalfield in Inner Mongolia. The received basic industrial analysis and elemental analysis data of coal 1 are shown in Table 2.

[0027] Table 2 Coal quality and ash analysis

[0028]

[0029] The recommended ranges of furnace characteristic parameters of a 600MW boiler burning high-moisture lignite (M>30%) and bituminous coal and adopting multi-angle tangential combustion are compared with the Yanshan Lake #2 boiler.

[0030] Table 3 Comparison of recommended ranges of furnace characteristic parameter limits for opposed combustion of high-moisture lignite and bituminous coal

[0031]

[0032] It can be seen that the furnace characteristic parameter limit of the boiler burning high-moisture lignite is lower than that of the boiler burning bituminous coal. From the perspective of stable combustion, it is more difficult to stabilize the combustion of lignite boilers than bituminous coal boilers. The design parameters of the boiler of Yanshan Lake Power Generation Company are also lower than those of the boiler burning lignite. The furnace design is larger than that of the lignite boiler, and the stable combustion ability is worse. Therefore, the technical solution in this disclosure is universal for general supercritical units.

[0033] The dry-wet state conversion strategy of the boiler disclosed in the present invention is exemplified below.

[0034] (1) In the present disclosure, during the dry-wet state transition process, the load setting value is maintained unchanged or the change value is within 2% of the load setting value, the coal feed rate is controlled by the main steam pressure deviation, and the adjustment speed of the boiler main control PID is appropriately reduced to make the coal feed rate fluctuate within a preset range (for example, not more than

[100] t / h), basically keeping the boiler load stable; at the same time, the boiler feed water flow rate is adjusted to realize the conversion of the boiler dry and wet operation modes.

[0035] During the conversion from dry state to wet state, the water supply flow rate can be gradually increased, and during the conversion from wet state to dry state, the water supply flow rate can be gradually reduced until dry state operation.

[0036] (2) Optionally, in the present disclosure, in order to maintain system stability, during the dry-wet state conversion of the boiler, the primary frequency modulation function on the CCS side and the DEH side is cut off, and the end of the state conversion is delayed for a period of time, for example, 120s, and the primary frequency modulation function is put into operation again after the system stabilizes.

[0037] (3) In an optional embodiment, the increase and decrease rates of the feed water flow rate during the dry-wet state transition process are adjusted online, and the adaptive function of the feed water flow rate change rate is achieved by comprehensively judging the water level of the water storage tank 2, the opening of the adjustment door of the outlet of the boiler water circulation pump 3 and other parameters. Further, the upper and lower limits of the feed water flow rate can be set to prevent the feed water flow rate from exceeding the limit and endangering the safety of boiler operation. Furthermore, when the water level of the water storage tank 2 is higher than a certain water level threshold, such as 6000mm, or the opening of the adjustment door of the outlet of the boiler water circulation pump 3 is less than 5%, the change rate of the feed water flow rate can be appropriately increased to shorten the time of the dry-wet state transition process.

[0038] (4) In an optional embodiment, during the dry-to-wet conversion process, the water level in the water tank can be controlled by controlling the opening of the overflow valve of the water tank 2 to achieve the change from water appearing, to water level dropping, and then to water level rising (more specifically, when evaporation begins, the steam-water mixture in the water-cooled wall is separated in the separator, saturated steam enters the superheater, and saturated water returns to the water tank. Due to the generation of steam, the water level in the water tank drops, the circulation flow rate decreases, and the feed water flow rate is increased to maintain the native flow entering the water-cooled wall). Finally, the overflow valve is automatically used to control the water level to maintain it at a certain water level threshold, such as 7500 mm, until the boiler water circulation pump 3 is started, completing the process of conversion from dry state to wet state.

[0039] In one embodiment of the present disclosure, after the boiler is switched from the dry state to the wet state, the load of the boiler is reduced to 20% of the rated load of the boiler.

[0040] In one embodiment of the present disclosure, during the dry-wet state conversion of the boiler, the boiler load value is maintained, and the boiler load setting value may be 30% of the rated load of the boiler.

[0041] In the present disclosure, the primary frequency regulation of the boiler generator set can be optimized.

[0042] The frequency difference load value of primary frequency modulation is obtained by multiplying the primary frequency modulation theoretical curve by the correction coefficient.

[0043] The theoretical curve of the unit design primary frequency regulation is as follows:

[0044] Table 4 Theoretical curve of primary frequency regulation of unit design

[0045]

[0046] Where X is the speed difference and Y is the load value of the primary frequency modulation action.

[0047] The correction factor is introduced below. Exemplarily, the correction factor can be composed of three parts.

[0048] Part 1: Main steam pressure function output. As the main steam pressure increases, the function output decreases.

[0049] Table 5 Main steam pressure function

[0050]

[0051] X is the main steam pressure, Y is the function output

[0052] Part 2: Actual power function output, divided into three sections

[0053] The first stage: one frequency modulation action - lasting for 15 seconds

[0054] Table 6 Actual power function

[0055]

[0056] X is the actual power and Y is the function output

[0057] Second segment: 15s-18s, output is 0

[0058] The third stage: 18s-one frequency modulation action ends

[0059] Table 7 Actual power function

[0060]

[0061] Part 3: Comprehensive valve position corresponding function, the output is 1.

[0062] In the present disclosure, the sum of the main steam pressure function output and the actual power function output is used as the overall correction coefficient. From the existing logic, the maximum frequency difference load value output by a frequency modulation action can reach 138.6. However, the frequency difference has an upper and lower limit of ±36.

[0063] In the existing scheme, there are two main logics for primary frequency regulation under deep peak load conditions:

[0064] First, the load command is lower than the first threshold, for example, 195MW, and then the theoretical load value of the primary frequency regulation follows a new function.

[0065] Table 8 New function of primary frequency regulation theoretical load value

[0066]

[0067] Second, if the load is lower than the second threshold, for example, 185MW, the frequency regulation is switched once.

[0068] In the solution disclosed herein, the specific optimization is as follows:

[0069] First, the frequency regulation under deep peak load conditions must be fully implemented, and the original logic of switching on the frequency regulation when the load is lower than, for example, 185MW is cancelled.

[0070] Secondly, when the load is lower than 195MW, although the theoretical curve is lowered when the primary frequency regulation needs to reduce the load, the correction coefficient is still large, and the final output is not limited after multiplication. Therefore, it is necessary to adjust the correction coefficient of the primary frequency regulation under the deep peak regulation condition to ensure that the overall action amplitude of the primary frequency regulation is reduced under the deep peak regulation condition. At the same time, when the primary frequency regulation action load moves downward, the lower limit can be performed to prevent the load overshoot from causing the boiler to extinguish.

[0071] In the present disclosure, during the boiler load reduction process, after the boiler load is lower than a first threshold, a frequency regulation is fully put into operation. The first threshold is higher than a second threshold. Optionally, the second threshold is higher than the rated minimum design load for stable operation of the boiler and the difference does not exceed 5% of the rated minimum design load for stable operation of the boiler.

[0072] In the present disclosure, optionally, the rated minimum design load for stable operation of the boiler is 30% of the rated load of the boiler; and / or the first threshold is 8MW-15MW higher than the second threshold, or the first threshold is 5%-10% higher than the second threshold by the minimum design load.

[0073] In the present disclosure, optionally, during the load reduction process, after the boiler load is lower than the first threshold value, the boiler load value is changed based on the modified primary frequency regulation theoretical curve; and during the load reduction process, there is a situation where the absolute value of the load value reduced based on the modified primary frequency regulation theoretical curve (for example, see the Y value in Table 8, such as -12, -12, -12) is smaller than the absolute value of the load value changed based on the primary frequency regulation theoretical curve designed based on the generator set (for example, see the Y value in Table 4, such as -36, -36, -13.5).

[0074] In the technical solution disclosed in the present invention, the powder making system can also be adjusted.

[0075] Through the adjustment of 4-10 and operation parameter control of the pulverizing system, when the boiler load is reduced to 240MW, four pulverizing systems are operated, with a total coal volume of about 170t / h, and an average coal volume of about 42.5t / h for each pulverizing system; when the load is reduced to 180MW, the air volume of a single pulverizing system is about 120t / h, the total coal volume is reduced to about 130t / h, and the average coal volume of each pulverizing system is about 35t / h; when the unit load is reduced to 150MW, the boiler operates three pulverizing systems, turns off one burner, and keeps four burners in each pulverizing system in operation. When the unit load continues to drop to 120MW, the air volume of a single pulverizing system is about 110t / h, the coal volume is reduced to 115t / h, the coal volume of each powder tube is about 9.6t / h, and the burner can maintain normal ignition; when the unit load continues to drop to 120MW, the air volume of a single pulverizing system is about 105t / h, the coal volume is reduced to about 100t / h, and the coal volume of each powder tube is about 8.5t / h. At this time, taking into account the possible deviation of the powder tube wind speed in the hot condition and the minimum ventilation volume requirement of the pulverizer, the ventilation volume of the pulverizer is guaranteed to be not less than 90t / h during the load reduction process.

[0076] In the present disclosure, illustratively, for the boiler water circulation pump 3, its operation is described as follows:

[0077] The boiler water circulation pump 3 can be gradually put into operation. For example, when the unit load drops to 180MW, the boiler circulation pump 3 is operated and the unit switches to wet operation, which increases the water circulation flow of the water-cooled wall 23 and the inlet feed water temperature of the economizer 18, thereby reducing the heat absorption of the economizer 18 and increasing the flue gas temperature at the outlet of the economizer 18. In addition, as the load decreases and the amount of recirculating water increases, the flue gas temperature at the outlet of the economizer 18 shows an upward trend, which increases the inlet temperature of the SCR reactor 20, meets the operating requirements of the denitration catalyst, and improves the denitration efficiency.

[0078] In the present disclosure, in order to facilitate stable combustion under low load, the structure of the boiler burner is also adjusted.

[0079] like Figure 2 As shown, by reducing the inner wall size of the throttle ring 23 (specific value is, for example, 581-570 mm), it is beneficial to make the coal powder airflow closer to the center of the primary air, thereby increasing the coal powder concentration at the burner outlet, and the air-powder mixture ignites quickly and earlier than the original structure. Figure 2 As shown, the throttling ring 23 is arranged in an annular shape on the inner wall of the secondary air tube of the burner.

[0080] According to the above technical measures, the 600MW supercritical unit in the example can reach 20% of the rated load and operate stably. The safety and environmental protection at this time are introduced below.

[0081] (1) Security

[0082] After adopting the above load adjustment scheme, the combustion stability was evaluated and the flue gas temperature in the furnace of Yanshan Lake Power Plant was measured. The results are as follows: Figure 3 As shown, the minimum flue gas temperature in the burner area is 995°C, which is higher than the ignition point of lignite. At the same time, the test results under different loads are not much different, which also shows that the boiler combustion is stable, the furnace temperature has not dropped significantly, and it can operate stably for a long time.

[0083] (2) Environmental protection

[0084] Before adopting the technical solution disclosed in this invention, the inlet flue gas temperature of the SCR reactor 20 of the boiler is as follows: Figure 4 When the boiler load rate is lower than 35%, the inlet flue gas temperature of the SCR reactor 20 reaches above 310° C., reaching the minimum operating temperature requirement of the catalyst.

[0085] After adopting the technical solution of the present disclosure, the inlet flue gas temperature of the SCR reactor 20 is significantly increased. Figure 5 shown.

[0086] From the above, it can be seen that when Yanshan Lake Power Plant is operating at a load of 120MW, the flue gas temperatures at the A and B sides of the denitrification inlet of Unit 2 are both above 310°C, reaching the temperature range required for the operation of the denitrification catalyst. The denitrification efficiency of Unit 2 is 89.89%, the average outlet NOx concentration is 29.93mg / m3, and the average ammonia slip is 6.82ppm, which meets the technical requirements of the denitrification equipment. This technology ensures the environmental protection of the unit operation.

[0087] Based on the above, the present invention aims at the problems existing in the above-mentioned prior art and proposes an adjustment method for the safe and stable operation of a supercritical boiler burning high-moisture lignite at 20% of the rated load, which can solve the safety and stability problems of supercritical boilers burning high-moisture lignite at low load in the prior art.

[0088] By applying the technical solution disclosed in this disclosure, the load regulation lower limit of the unit can be reduced to 20%. Specifically, the lower limit of the 600MW unit is reduced from the original regulation lower limit of 180MW to 120MW, so that the deep peak regulation service compensation for one year is not less than 2 million yuan; at the same time, it can effectively improve the peak regulation and frequency regulation capabilities of the unit, which is not only conducive to the safe and stable operation of the power grid, but also has the significance of promoting similar work for various power generation companies, and has broad application prospects.

[0089] In addition, in the present disclosure, unless explicitly stated otherwise, a numerical range includes endpoint values, and the numerical range also includes a midpoint value, a one-third value, and a two-thirds value, etc.

[0090] Based on the above, the present disclosure proposes the following technical solutions:

[0091] 1. A method for adjusting the load of a power station boiler, comprising the steps of:

[0092] During the dry-wet state conversion of the boiler, the boiler load setting value is maintained unchanged or the change value is within 2% of the load setting value, wherein: the coal feed rate is controlled by the main steam pressure deviation, the adjustment speed of the boiler main control PID is reduced, and the coal feed rate fluctuates within the preset range to keep the boiler load stable; and

[0093] Adjust the boiler feed water flow at a preset rate to achieve the conversion of the boiler's dry and wet operation modes.

[0094] 2. The method according to item 1, wherein:

[0095] During the dry-wet state conversion of the boiler, the primary frequency modulation function on the CCS side and the DEH side is cut off, and the primary frequency modulation function is put back into operation after a preset time period after the dry-wet state conversion is completed.

[0096] 3. The method according to 2, wherein:

[0097] During the dry-wet state conversion process of the boiler, the frequency regulation function will be put into operation again after a delay of 120s after the dry-wet state conversion is completed.

[0098] 4. The method according to item 1, wherein:

[0099] During the dry-wet state conversion of the boiler, the increase and decrease rates of the feed water flow are adjusted online, and the feed water flow rate change rate is adaptively adjusted by at least comprehensively judging the water level of the water storage tank and the opening of the boiler water circulation pump outlet adjustment door.

[0100] 5. The method according to 4, wherein:

[0101] Set the upper and lower limits of the feed water flow rate to prevent the feed water flow rate from exceeding the limit and endangering the safe operation of the boiler.

[0102] 6. The method according to claim 4, wherein:

[0103] When the water level in the water storage tank is higher than the first preset water level or the opening of the boiler water circulation pump outlet adjustment door is less than 5%, the change rate of the feed water flow rate is increased to shorten the time of the boiler dry-wet state conversion process.

[0104] 7. The method according to claim 4, wherein:

[0105] During the dry-wet state conversion process of the boiler, the water level in the water tank is controlled by controlling the opening of the overflow valve of the water tank to change from water seeping, to the water level dropping, and then to the water level rising. The overflow valve is then engaged to automatically control the water level to maintain it near the second water level preset value until the boiler water circulation pump is started, completing the process of the boiler converting from dry state to wet state.

[0106] 8. The method according to item 1 further comprises the steps of:

[0107] After the boiler is switched from dry state to wet state, the boiler load is reduced to 20% of the boiler rated load.

[0108] 9. The method according to any one of 1 to 8, further comprising the steps of:

[0109] The primary frequency regulation of the generator set including the boiler is optimized.

[0110] 10. The method according to 9, wherein:

[0111] The frequency difference load value of primary frequency regulation is obtained by multiplying the primary frequency regulation theoretical curve by the correction coefficient, and the sum of the main steam pressure function output and the actual power function output is taken as the overall correction coefficient.

[0112] 11. The method according to 10, wherein:

[0113] During the boiler load reduction process, after the boiler load is lower than the first threshold, the primary frequency regulation is fully put into operation to change the boiler load value based on the modified primary frequency regulation theoretical curve;

[0114] During the load reduction process, there is a situation where the absolute value of the load value reduced based on the modified primary frequency regulation theoretical curve is smaller than the absolute value of the load value changed based on the primary frequency regulation theoretical curve designed for the generator set;

[0115] The first threshold is higher than the second threshold, the second threshold is higher than the rated minimum design load of the boiler for stable operation, and the difference does not exceed 5% of the rated minimum design load of the boiler for stable operation.

[0116] 12. The method according to 11, wherein:

[0117] The rated minimum design load for stable operation of the boiler is 30% of the rated load of the boiler; and / or

[0118] The first threshold is 8MW-15MW higher than the second threshold, or the first threshold is 5%-10% higher than the second threshold by the minimum design load.

[0119] 13. The method according to 11, wherein:

[0120] During the load reduction process, when the primary frequency modulation action based on the modified primary frequency modulation theoretical curve moves downward, the correction coefficient corresponding to the modified primary frequency modulation theoretical curve is adjusted.

[0121] 14. The method according to 13, wherein:

[0122] During the load reduction process, when the primary frequency regulation action based on the modified primary frequency regulation theoretical curve moves downward, the downward adjustment limit is limited.

[0123] 15. The method according to any one of 1 to 14, further comprising the steps of:

[0124] The coal feed rate is controlled by adjusting the boiler's pulverizing system and controlling the pulverizing system operating parameters.

[0125] 16. The method according to 15, wherein:

[0126] When the boiler load is reduced to 40% of the rated load, four pulverizing systems are operated with a total coal capacity of about 170 t / h, and an average coal capacity of about 42.5 t / h per pulverizing system;

[0127] When the boiler load is reduced to 30% of the rated load, the air volume of a single pulverizing system is about 120t / h, the total coal volume is reduced to about 130t / h, and the average coal volume of each pulverizing system is about 35t / h;

[0128] When the boiler load is reduced to 25% of the rated load, the boiler operates three pulverizing systems, one burner is turned off, and four burners of each pulverizing system are kept running. The air volume of a single pulverizing system is about 110t / h, the coal volume is reduced to about 115t / h, and the coal volume of each pulverizing tube is about 9.6t / h. The burner can maintain normal ignition;

[0129] When the boiler load is reduced to 20% of the rated load, the air volume of a single pulverizing system is about 105t / h, the coal volume is reduced to about 100t / h, and the coal volume of each pulverizing tube is about 8.5t / h.

[0130] 17. The method according to 16, wherein:

[0131] When the boiler load is reduced to 20% of the rated load, taking into account the deviation of the powder tube wind speed in the hot condition and the minimum ventilation volume requirement of the coal mill, the ventilation volume of the coal mill is guaranteed to be no less than 90t / h during the load reduction process.

[0132] 18. The method according to any one of 1 to 17, further comprising the steps of:

[0133] When the boiler load is reduced to the rated load of the boiler, the boiler water circulation pump starts to operate, so that the boiler switches from dry state to wet state operation, the water circulation flow of the boiler water-cooled wall is increased, and the feed water temperature at the economizer inlet is increased, thereby increasing the flue gas temperature at the economizer outlet.

[0134] 19. The method according to 18, wherein:

[0135] As the boiler load decreases and the amount of recirculating water increases, the flue gas temperature at the economizer outlet shows an upward trend, thereby increasing the SCR reactor inlet temperature to meet the operating requirements of the denitrification catalyst.

[0136] 20. The method according to any one of 1 to 19, further comprising the steps of:

[0137] The boiler burner is structurally adjusted by reducing the inner wall size of the throttling ring so that the pulverized coal airflow entering the boiler furnace is closer to the center of the primary air, thereby increasing the pulverized coal concentration at the burner outlet and facilitating the ignition of the air-pulverized coal mixture, wherein the throttling ring is annularly arranged on the inner wall of the secondary air tube of the burner.

[0138] 21. The method according to 20, wherein:

[0139] The inner diameter of the throttle ring is between 581mm and 570mm.

[0140] 22. The method according to any one of 1 to 21, wherein:

[0141] The boiler load setting is 30% of the boiler rated load; and / or

[0142] The boiler is a supercritical boiler.

[0143] 23. The method according to any one of 1 to 22, wherein:

[0144] The pulverized coal introduced into the boiler is lignite pulverized coal.

[0145] Although embodiments of the present disclosure have been shown and described, it will be appreciated by those skilled in the art that changes may be made to the embodiments and combinations of elements may be made without departing from the principles and spirit of the present disclosure, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for adjusting the load of a power station boiler, comprising the steps of: During the dry-wet state conversion of the boiler, the boiler load setting value is maintained unchanged or the change value is within 2% of the load setting value, where: The coal feed rate is controlled by the main steam pressure deviation, which reduces the adjustment speed of the boiler main control PID and makes the coal feed rate fluctuate within the preset range to keep the boiler load stable. as well as Adjust the boiler feed water flow at a preset rate to achieve the conversion of the boiler's dry and wet operation modes.

2. The method according to claim 1, wherein: During the dry-wet state conversion of the boiler, the primary frequency modulation function on the CCS side and the DEH side is cut off, and the primary frequency modulation function is put back into operation after a preset time period after the dry-wet state conversion is completed.

3. The method according to claim 2, wherein: During the dry-wet state conversion process of the boiler, the frequency regulation function will be put into operation again after a delay of 120s after the dry-wet state conversion is completed.

4. The method according to claim 1, wherein: During the dry-wet state conversion of the boiler, the increase and decrease rates of the feed water flow are adjusted online, and the feed water flow rate change rate is adaptively adjusted by at least comprehensively judging the water level of the water storage tank and the opening of the boiler water circulation pump outlet adjustment door.

5. The method according to claim 4, wherein: Set the upper and lower limits of the feed water flow rate to prevent the feed water flow rate from exceeding the limit and endangering the safe operation of the boiler.

6. The method according to claim 4, wherein: When the water level in the water storage tank is higher than the first preset water level or the opening of the boiler water circulation pump outlet adjustment door is less than 5%, the change rate of the feed water flow rate is increased to shorten the time of the boiler dry-wet state conversion process.

7. The method according to claim 4, wherein: During the dry-wet state conversion process of the boiler, the water level in the water tank is controlled by controlling the opening of the overflow valve of the water tank to change from water seeping, to the water level dropping, and then to the water level rising. The overflow valve is then engaged to automatically control the water level to maintain it near the second water level preset value until the boiler water circulation pump is started, completing the process of the boiler converting from dry state to wet state.

8. The method according to claim 1, further comprising the steps of: After the boiler is switched from dry state to wet state, the boiler load is reduced to 20% of the boiler rated load.

9. The method according to any one of claims 1 to 8, further comprising the steps of: During the dry-wet state conversion process of the boiler and the subsequent boiler load reduction process, the primary frequency regulation of the generator set of the boiler is fully put into use.

10. The method according to claim 9, wherein: The frequency difference load value of primary frequency regulation is obtained by multiplying the primary frequency regulation theoretical curve by the correction coefficient, and the sum of the main steam pressure function output and the actual power function output is taken as the overall correction coefficient.

11. The method according to claim 10, wherein: During the boiler load reduction process, after the boiler load is lower than the first threshold, the primary frequency regulation is fully put into operation to change the boiler load value based on the modified primary frequency regulation theoretical curve; During the load reduction process, there is a situation where the absolute value of the load value reduced based on the modified primary frequency regulation theoretical curve is smaller than the absolute value of the load value changed based on the primary frequency regulation theoretical curve designed for the generator set; The first threshold is higher than the second threshold, the second threshold is higher than the rated minimum design load of the boiler for stable operation, and the difference does not exceed 5% of the rated minimum design load of the boiler for stable operation.

12. The method according to claim 11, wherein: The rated minimum design load for stable operation of the boiler is 30% of the rated load of the boiler; and / or The first threshold is 8MW-15MW higher than the second threshold, or the first threshold is 5%-10% higher than the second threshold by the minimum design load.

13. The method according to claim 11, wherein: During the load reduction process, when the primary frequency modulation action based on the modified primary frequency modulation theoretical curve moves downward, the correction coefficient corresponding to the modified primary frequency modulation theoretical curve is adjusted.

14. The method according to claim 13, wherein: During the load reduction process, when the primary frequency regulation action based on the modified primary frequency regulation theoretical curve moves downward, the downward adjustment limit is limited.

15. The method according to any one of claims 1 to 14, further comprising the steps of: The coal feed rate is controlled by adjusting the boiler's pulverizing system and controlling the pulverizing system operating parameters.

16. The method of claim 15, wherein: When the boiler load is reduced to 40% of the rated load, four pulverizing systems are operated with a total coal capacity of about 170 t / h, and an average coal capacity of about 42.5 t / h per pulverizing system; When the boiler load is reduced to 30% of the rated load, the air volume of a single pulverizing system is about 120t / h, the total coal volume is reduced to about 130t / h, and the average coal volume of each pulverizing system is about 35t / h; When the boiler load is reduced to 25% of the rated load, the boiler operates three pulverizing systems, one burner is turned off, and four burners of each pulverizing system are kept running. The air volume of a single pulverizing system is about 110t / h, the coal volume is reduced to about 115t / h, and the coal volume of each pulverizing tube is about 9.6t / h. The burner can maintain normal ignition; When the boiler load is reduced to 20% of the rated load, the air volume of a single pulverizing system is about 105t / h, the coal volume is reduced to about 100t / h, and the coal volume of each pulverizing tube is about 8.5t / h.

17. The method of claim 16, wherein: When the boiler load is reduced to 20% of the rated load, taking into account the deviation of the powder tube wind speed in the hot condition and the minimum ventilation volume requirement of the coal mill, the ventilation volume of the coal mill is guaranteed to be no less than 90t / h during the load reduction process.

18. The method according to any one of claims 1 to 17, further comprising the steps of: When the boiler load is reduced to the rated load of the boiler, the boiler water circulation pump starts to operate, so that the boiler switches from dry state to wet state operation, the water circulation flow of the boiler water-cooled wall is increased, and the feed water temperature at the economizer inlet is increased, thereby increasing the flue gas temperature at the economizer outlet.

19. The method of claim 18, wherein: As the boiler load decreases and the amount of recirculating water increases, the flue gas temperature at the economizer outlet shows an upward trend, thereby increasing the SCR reactor inlet temperature to meet the operating requirements of the denitrification catalyst.

20. The method according to any one of claims 1 to 19, further comprising the steps of: The boiler burner is structurally adjusted to reduce the size of the inner wall of the throttle ring so that the pulverized coal airflow entering the boiler furnace is closer to the center of the primary air, thereby increasing the pulverized coal concentration at the burner outlet and facilitating the ignition of the air-pulverized coal mixture. The throttle ring is arranged in an annular shape on the inner wall of the secondary air pipe of the burner.

21. The method of claim 20, wherein: The inner diameter of the throttle ring is between 581mm and 570mm.

22. The method according to any one of claims 1 to 21, wherein: The boiler load setting is 30% of the boiler rated load; and / or The boiler is a supercritical boiler.

23. The method according to any one of claims 1 to 22, wherein: The pulverized coal introduced into the boiler is lignite pulverized coal.

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