Full load denitrification control method for circulating fluidized bed boiler units

Abstract

The present invention relates to the technical field of flue gas denitrification and generators, and in particular, to a full-load denitrification control method for a circulating fluidized bed boiler unit. The circulating fluidized bed boiler unit has a split-flow ash return heat exchanger, and the control method includes a first startup stage, a second startup stage, a third startup stage, a fourth startup stage, a first shutdown stage, a second shutdown stage, a third shutdown stage, and a fourth shutdown stage. The full-load denitrification control method for a circulating fluidized bed boiler unit can utilize a split-flow ash return heat exchanger, and through changes in the combustion adjustment method, adjust the boiler bed temperature, the cyclone separator smoke temperature, and the oxygen content to an ideal operating condition, and basically achieve full-load denitrification of a 330MW circulating fluidized bed boiler unit.

Description

Technical Field

[0001] The invention relates to the technical field of flue gas denitration and generators, and in particular to a full-load denitration control method for a circulating fluidized bed boiler unit. Background Art

[0002] At present, the thermal power generating unit is in the start-up and shutdown stage, NO X Emission control is a difficult point. Due to the special combustion mode of circulating fluidized bed boilers, during the regular start-up and shutdown stages of the unit, the separator flue gas temperature, operating oxygen content, and bed temperature do not meet the ideal operating boundary conditions of the SNCR denitrification system, resulting in NO X Emissions exceed current ultra-low emission standards. Summary of the invention

[0003] The objects of the present invention include, for example, providing a full-load denitrification control method for a circulating fluidized bed boiler unit, which can utilize a split-flow ash return heat exchanger and adjust the boiler bed temperature, cyclone separator flue gas temperature, and oxygen content to achieve ideal operating conditions through changes in the combustion adjustment method, thereby basically achieving full-load denitrification of a 330MW circulating fluidized bed boiler unit.

[0004] The embodiments of the present invention can be implemented as follows:

[0005] In a first aspect, the present invention provides a full-load denitration control method for a circulating fluidized bed boiler unit, wherein the circulating fluidized bed boiler unit has a split-flow ash return heat exchanger, comprising:

[0006] In the first startup stage, the amount of circulating ash added to the bed feeder is adjusted to maintain the pressure of the water-cooled air chamber above 15Kpa, and circulating ash is added to each of the split-flow ash return heat exchangers according to the heating time;

[0007] In the second startup phase, the coal is added and the oil is withdrawn for stable combustion until the units are connected in parallel, and a stable combustion time of 4-5 hours is reserved to ensure that the circulating ash in the furnace is collected and stored to increase the flue gas temperature in the separator to meet the ideal reaction temperature range for denitrification.

[0008] In the third startup phase, multiple split-flow ash return heat exchangers are put into use one by one, and the adjustment range is prevented from being too large, which may cause excessive drop in bed pressure and lead to drastic fluctuations in the combustion conditions in the furnace;

[0009] In the fourth startup phase, the adjustment of flue gas recirculation is strengthened. In the startup phase, when the boiler bed temperature reaches above 900°C after the coal is added and the oil is stopped, the flue gas recirculation system is put into use to reduce the bed temperature and suppress the increase of oxygen content.

[0010] In the first shutdown phase, the combustion is stabilized and the drum pressure is maintained at a low value, creating conditions for subsequently increasing the boiler temperature;

[0011] In the second shutdown phase, flue gas recirculation is adjusted to maintain low oxygen content, and the split-flow ash return heat exchanger is used to maintain a stable bed temperature until the split-flow ash return heat exchanger is shut down;

[0012] In the third shutdown stage, adjust the load stage stabilization time and turbine high-pressure bypass intervention time, and adjust the split-flow ash return heat exchanger to exit operation in the preset manner;

[0013] In the fourth shutdown stage, adjust the unit load to below 30-40MW and allow the boiler to burn stably for 10-15 minutes, and control the oxygen content not to exceed 8%. When the steam turbine quickly reduces the load to below 10%, the generator is disconnected from the system.

[0014] During the normal start-up and shutdown phases of the unit, the separator flue gas temperature, operating oxygen content, and bed temperature do not meet the ideal operating boundary conditions of the SNCR denitrification system, resulting in NO X The technical problem of emissions exceeding the current ultra-low emission standards, this control method can improve the special combustion mode of circulating fluidized bed boilers by adjusting the startup and shutdown stages of circulating fluidized bed boiler units. Further, by adjusting the process of circulating fluidized bed boilers, especially giving full play to the characteristics of split-flow ash return heat exchangers, without modifying the boiler structure, by changing the combustion adjustment mode, the boiler bed temperature, cyclone separator flue gas temperature, and oxygen content can reach the ideal operating conditions, and the full-load denitrification of 330MW circulating fluidized bed boiler units can be basically achieved.

[0015] In an optional embodiment, the control method is NO at any time period X The hourly average emission value is controlled at 45mg / Nm 3 Within, and ensure NO X The hourly average value of the indicator is 50mg / Nm 3 and leave a margin to cope with the index fluctuations caused by abnormal working conditions.

[0016] In an optional embodiment, the control method is such that the boiler oxygen content should be controlled at 4%, and the boiler is operated at a reduced oxygen content to reduce NO when the temperature at each point of the furnace / separator does not exceed 960 / 985°C. X The conversion value should be increased or decreased slowly and steadily to prevent the combustion adjustment fluctuation and oxygen content change from causing NO X Unusual changes in emissions.

[0017] In an optional embodiment, the control method detects a coal shortage signal and promptly starts the transfer bin and scraper to eliminate the coal shortage phenomenon, so as to prevent abnormal fluctuations in boiler combustion caused by untimely coal feeding adjustment or untimely load reduction, resulting in NO X In case of abnormal emission changes, return to the planned load in time after combustion stabilizes.

[0018] In an optional embodiment, the coal blending and combustion principle of the control method is:

[0019] The calorific value of coal for zero-shift load 200MW shall not be less than 3800 kcal, and the volatile matter shall not be less than 12%;

[0020] The calorific value of coal for zero-shift load 220MW shall not be less than 4100 kcal, and the volatile matter shall not be less than 14%;

[0021] When the morning peak load is above 260MW, the coal calorific value shall not be less than 4,300 kcal and the volatile matter shall not be less than 16%;

[0022] When the evening peak load of the evening shift is above 260MW, the calorific value of coal shall not be less than 4300 kcal, and the volatile matter shall not be less than 16%;

[0023] When the morning peak load is above 280MW, the coal calorific value shall not be less than 4500 kcal and the volatile matter shall not be less than 16%;

[0024] When the evening peak load of the night shift is above 280MW, the calorific value of the coal shall not be less than 4500 kcal and the volatile matter shall not be less than 16%.

[0025] In an optional embodiment, the flue gas recirculation damper of the control method is used in the following principles:

[0026] When the exhaust gas temperature at the air preheater outlet exceeds 170℃, stop adjusting the flue gas recirculation damper and close the flue gas recirculation damper to reduce the exhaust gas temperature. After that, the flue gas recirculation damper should be adjusted slowly, 2% at a time, to prevent the increase in the adjustment range from causing the bed pressure, bed temperature, and NO X Emissions fluctuate widely.

[0027] In an optional embodiment, the control method controls the boiler unit parallel time to within 10 minutes after the hour, and the unit de-connection time to within 10 minutes before the hour. By reserving sufficient adjustment time, the hourly average environmental emission is lowered to ensure that the hourly average is within a preset range.

[0028] In an optional embodiment, the control method controls the unit parallel time to within 10 minutes after the hour, and the unit de-parallel time to within 10 minutes before the hour, leaving enough adjustment time to lower the hourly average and ensure that it is within a preset range.

[0029] In an optional embodiment, the control method controls the hourly average NOx target to be less than 40 mg / Nm during the start-up and shutdown phases of the unit. 3 , ensure SNCR high output operation within 30 minutes before shutdown and decoupling, and reduce the hourly average NOx emissions.

[0030] In an optional embodiment, the control method ensures that the atomizing air pressure of the spray gun is not less than 0.5 MPa, the pressure difference between the atomizing air pressure and the ammonia main pipe pressure is not greater than 0.1 MPa, and the ammonia main pipe pressure is higher than the atomizing air pressure.

[0031] The beneficial effects of the embodiments of the present invention include, for example:

[0032] This control method adjusts the process of circulating fluidized bed boiler, especially gives full play to the characteristics of the split-flow ash return heat exchanger. Without modifying the boiler structure, the boiler bed temperature, cyclone separator flue gas temperature and oxygen content are adjusted to the ideal operating conditions through the change of the combustion adjustment method, basically achieving full-load denitrification of the 330MW circulating fluidized bed boiler unit. This improves the existing technology that the separator flue gas temperature, operating oxygen content and bed temperature of the circulating fluidized bed boiler do not meet the ideal operating boundary conditions of the SNCR denitrification system during the regular start-up and shutdown stages of the unit, resulting in NO X Technical issues with emissions exceeding the current ultra-low emission standards. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0034] Figure 1 It is a schematic flow chart of a full-load denitration control method for a circulating fluidized bed boiler unit according to an embodiment of the present invention. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0036] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0038] In the description of the present invention, it should be noted that if the terms "upper", "lower", "inside", "outside", etc. appear to indicate an orientation or position relationship, they are based on the orientation or position relationship shown in the accompanying drawings, or are the orientation or position relationship in which the product of the invention is usually placed when used. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0039] In addition, the terms “first”, “second”, etc., if used, are merely used to distinguish between the descriptions and should not be understood as indicating or implying relative importance.

[0040] It should be noted that, in the absence of conflict, the features in the embodiments of the present invention may be combined with each other.

[0041] At present, the thermal power generating unit is in the start-up and shutdown stage, NO X Emission control is a difficult point. Due to the special combustion mode of circulating fluidized bed boilers, during the regular start-up and shutdown stages of the unit, the separator flue gas temperature, operating oxygen content, and bed temperature do not meet the ideal operating boundary conditions of the SNCR denitrification system, resulting in NO X Emissions exceed current ultra-low emission standards.

[0042] Through the operation exploration of the 330MW circulating fluidized bed boiler unit, especially giving full play to the technical advantages of the split-flow ash return heat exchanger, without any special technical transformation, through the change of the combustion adjustment method, the boiler bed temperature, cyclone separator flue gas temperature and oxygen content reached the ideal operating conditions, basically realizing the full load denitrification of the 330MW circulating fluidized bed boiler unit.

[0043] In order to improve the above technical problems, a full-load denitrification control method for a circulating fluidized bed boiler unit is provided in the following embodiment.

[0044] Figure 1 Schematic diagram of the flow chart of the full load denitration control method of the circulating fluidized bed boiler unit according to the embodiment of the present invention. Figure 1 , a full-load denitration control method for a circulating fluidized bed boiler unit, wherein the circulating fluidized bed boiler unit has a split-flow ash return heat exchanger, which includes:

[0045] In the first startup stage, the amount of circulating ash added to the bed feeder is adjusted to maintain the air chamber pressure above 15Kpa, and circulating ash is added to each of the split-flow ash return heat exchangers according to the heating time;

[0046] In the second startup phase, the coal is added and the oil is withdrawn for stable combustion until the units are connected in parallel, and a stable combustion time of 4-5 hours is reserved to ensure that the circulating ash in the furnace is collected to raise the flue gas temperature in the separator to make it close to or meet the ideal reaction temperature range for denitrification;

[0047] In the third startup phase, multiple split-flow ash return heat exchangers are put into use one by one, and the adjustment range is prevented from being too large, causing the bed pressure to drop too much and causing drastic fluctuations in the combustion conditions in the furnace;

[0048] In the fourth startup phase, the adjustment of flue gas recirculation is strengthened. In the startup phase, when the boiler bed temperature reaches above 900°C after the coal is added and the oil is stopped, the flue gas recirculation system is put into use to reduce the bed temperature and suppress the increase of oxygen content.

[0049] In the first shutdown phase, stable combustion and low drum pressure are maintained to create conditions for subsequent increase in boiler temperature;

[0050] In the second shutdown phase, flue gas recirculation is adjusted to maintain low oxygen content, and the split-flow ash return heat exchanger is used to maintain a stable bed temperature until the split-flow ash return heat exchanger is shut down;

[0051] In the third shutdown stage, adjust the load stage stabilization time and turbine high-pressure bypass intervention time, and adjust the split-flow ash return heat exchanger to exit operation in the preset manner;

[0052] In the fourth shutdown stage, adjust the unit load to below 30-40MW and allow the boiler to burn stably for 10-15 minutes, and control the oxygen content not to exceed 8%. When the steam turbine quickly reduces the load to below 10%, the generator is disconnected from the system.

[0053] Optionally, the 330MW circulating fluidized bed boiler unit in this embodiment is taken as an example. The 330MW circulating fluidized bed unit has passed the ultra-low emission acceptance and is now NO X The emission value has officially implemented the ultra-low emission standard (< 50mg / Nm 3 ), to ensure that NO X , the emission values ​​are stable and meet the emission standards, and the following regulations are hereby made:

[0054] 1. General Provisions

[0055] 1. NO at any time X The hourly average emission value is controlled at 45mg / Nm 3 Within, and ensure NO X The hourly average value of the indicator is 50mg / Nm 3 A certain margin is left to cope with the index fluctuations caused by abnormal working conditions.

[0056] 2. To prevent NO from being caused by high oxygen levels XThe conversion is high. In principle, the oxygen content of the boiler should be controlled at about 4%. When the temperature of each point in the furnace / separator does not exceed 960 / 985℃, the oxygen content should be reduced as much as possible to reduce NO X The conversion value should be increased or decreased slowly and steadily to prevent the combustion adjustment fluctuation and oxygen content change from causing NO X Unusual changes in emissions.

[0057] 3. Attach great importance to the alarm of coal-out signal of weighing coal feeder (notify maintenance personnel to check the operation every Monday morning). If coal-out signal is found, the transfer bin and scraper should be started in time to eliminate the coal-out phenomenon. If the coal feeder is out of coal for a long time or the coal feeder fails suddenly, the duty officer should be informed immediately to contact the steam turbine to reduce the load appropriately. At the same time, the operation adjustment on the boiler side should be strengthened to prevent abnormal fluctuation of boiler combustion due to untimely coal feeding adjustment or untimely load reduction, resulting in NO X In case of abnormal emission changes, return to the planned load in time after combustion stabilizes.

[0058] 4. Principles of coal blending and combustion:

[0059] The calorific value of coal for load of about 200MW shall not be less than 3800 kcal, and the volatile matter shall not be less than 12%;

[0060] The calorific value of coal for load of about 220MW shall not be less than 4100 kcal, and the volatile matter shall not be less than 14%;

[0061] When the peak load of the morning (evening) shift is above 260MW, the coal calorific value shall not be less than 4300 kcal, and the volatile matter shall not be less than 16%;

[0062] When the morning (evening) shift peak load is above 280MW, the coal calorific value shall not be less than 4500 kcal and the volatile matter shall not be less than 16%.

[0063] 5. Principles for using flue gas recirculation dampers (usually flue gas recirculation dampers will raise the exhaust temperature by about 6°C):

[0064] At any time, the exhaust gas temperature at the air preheater outlet exceeds 170℃, and the flue gas recirculation damper is not allowed to be adjusted. The flue gas recirculation damper should be closed to reduce the exhaust gas temperature. The flue gas recirculation damper should be adjusted slowly, 2% at a time, to prevent excessive adjustment from causing bed pressure, bed temperature, NO X Emissions fluctuate widely.

[0065] 6. The unit paralleling time is controlled within 10 minutes after the hour, and the unit de-coupling time is controlled within 10 minutes before the hour. By reserving sufficient adjustment time, the hourly average environmental emission can be lowered to ensure that the hourly average does not exceed the standard.

[0066] (II) Preparation before starting up the 330MW circulating fluidized bed unit

[0067] 1. Ensure that the liquid level of the ammonia storage tank is not less than 3000mm, and take samples of the ammonia storage tank solution for testing to ensure that the ammonia concentration is around 20%.

[0068] 2. Prepare 320 tons of dry bed material with a required particle size of D50 = 1.2 mm. Before the boiler is started, the bed material in the furnace must reach a water-cooled air chamber pressure of more than 15Kpa (about 300 tons). Sufficient circulating ash must be added to the four split-flow return ash heat exchangers. Each split-flow return ash heat exchanger must add 6 to 7 tons of circulating ash, including 2 to 2.5 tons for the return valve and 4 to 4.5 tons for the external bed.

[0069] 3. Prepare 20 tons of primer coal in the corresponding coal bunkers in front of and behind the furnace, with a calorific value of 5,000 kcal and a volatile content of 25%. The subsequent coal entering the furnace has a calorific value of 3,800 kcal and a volatile content of 15%.

[0070] 4. The pressure of the compressed air main pipe for the denitrification system spray gun atomization shall not be less than 0.5Mpa to ensure the atomization effect.

[0071] (III) Boiler combustion adjustment steps from start-up to low load (165MW) of 330MW circulating fluidized bed unit:

[0072] 1. Establish the boiler air and smoke channel loop: open the secondary fan inlet and outlet dampers and the upper secondary air damper.

[0073] Open the flue gas inlet damper and start the main motor of the rotary air preheater.

[0074] 2. Start an induced draft fan to control the negative pressure in the furnace within -100pa.

[0075] 3. Start a high-pressure blower to maintain the high-pressure air pressure>35Kpa, adjust the air volume of each air chamber, and the high-temperature return chamber 1862Nm 3 / h, distribution chamber 733Nm 3 / h.

[0076] 4. Start a secondary fan, with the liquid couple within 5%, and the upper and lower secondary air main doors open by 5%.

[0077] 5. Start a primary fan, and adjust the air volume control damper to make the single-side air volume reach the minimum given value of 165000Nm 3 / h, furnace purge, MFT reset after 120 seconds of purge.

[0078] 6. Ignite #1 and #4 air duct burners, check the oil gun ignition condition on site, and control the flue gas temperature at the burner outlet not to exceed 1300℃ to prevent burning of the burner outlet expansion joint.

[0079] 7. Ignite #2 duct burner and #3 duct burner in turn every 60 minutes.

[0080] 8. During the ignition process of the boiler, the temperature change rate of all temperature measuring points on the flue gas side, including the duct burner, must be controlled to be less than 100℃ / h, the upper and lower wall temperatures of the steam drum ≤50℃, and the saturation temperature change rate ≤56℃ / h.

[0081] 9. When the bed temperature at the bottom of the dense phase zone is greater than 450°C, try to add the ignition coal and start the coal feeder on the rear wall corresponding to the coal bunker. Feed coal into the furnace in a pulsed manner. Pay attention to check the changes in bed temperature and oxygen content. When the bed temperature increases by 5°C and the oxygen content decreases, it is confirmed that the coal has been burned. Maintain the minimum speed to feed coal continuously, reduce the output of the oil gun, and add the ignition coal to the front wall corresponding to maintain the minimum speed to feed coal continuously.

[0082] 10. When the bed temperature reaches 860°C, if the bed temperature continues to rise and the oxygen content decreases, the duct burner can be gradually shut down (after 30 minutes of the duct burner, fully open the mainstream damper, and then close the ignition damper and mixing damper).

[0083] 11. After the duct burner is shut down, the boiler continues to heat up and increase pressure. The furnace bed temperature is generally high, and the oxygen content is high, which is not conducive to NO X Emission control, at this time, the adjustment of the flue gas recirculation damper should be strengthened. Usually, during the startup phase, when the boiler bed temperature reaches above 900℃ after the coal is added and the oil is stopped, the flue gas recirculation system is put into use to reduce the bed temperature and inhibit the increase of oxygen content. The flue gas recirculation damper is controlled to open at 50-70% (flow rate is about 10-12m / s), and the operating oxygen content should be controlled below 8%. At this time, NO X The conversion value should be controlled at 200mg / Nm 3 Within.

[0084] 12. When the pressure of the water-cooled air chamber is above 12.5Kpa, a heat exchange fan is started and the split-flow ash return heat exchanger is put into operation. Since the furnace bed is too low, it takes 40 to 60 minutes to establish normal circulation inside the split-flow ash return heat exchanger. Therefore, the split-flow ash return heat exchangers can only be put into operation one by one. First, put into operation the #1 and #2 split-flow ash return heat exchangers on the reheater side, and the air door opening of the flow equalization chamber should be slowly adjusted to 30% (the air door opening is limited to 10% each time, and the interval time is 15 minutes) to prevent the adjustment range from being too large, causing the bed temperature and bed pressure to drop too much, resulting in drastic fluctuations in the combustion conditions in the furnace, thereby affecting NO X Emissions, control the bed temperature at the bottom of the boiler dense phase zone not to exceed 920℃, the flue gas temperature of the cyclone separator not to be lower than 750℃, and the operating oxygen content should be controlled below 7%. At this time, NO X The conversion value should be controlled at 130mg / Nm 3 Within.

[0085] 13. The boiler continues to strengthen combustion, making the main steam parameters close to the turbine run-up parameters (main steam pressure 4.0Mpa, main steam temperature 380℃, reheat steam pressure 1.5MPa, reheat steam temperature 360℃). At this time, the bed temperature at the bottom of the boiler dense phase zone should be within 950℃, the flue gas temperature of the cyclone separator should be around 800℃, and the operating oxygen content should be controlled below 6%. At this time, NO X The conversion value should be controlled at 110mg / Nm 3 Within.

[0086] 14. Put the denitrification system into operation, control the flow rate of desalted water at 4T / H, the flow rate of ammonia water at 2.5~4T / H, and the pressure of atomizing compressed air not less than 0.5Mpa. X The conversion value should be controlled at 50 mg / Nm 3 Within.

[0087] 15. Observe whether the differential pressure of the furnace suspension section reaches 300pa or above, and judge whether the circulating ash in the furnace meets the grid connection and rapid load increase requirements of the unit. X Emissions are stably controlled at 50mg / Nm 3 Within the startup plan, the boiler still needs to ensure stable combustion time of about 4 to 5 hours from the time coal is added and oil is withdrawn until the units are connected in parallel, so as to ensure further accumulation of circulating ash in the furnace to increase the separator flue gas temperature, so that the cyclone separator flue gas temperature approaches or meets the ideal denitrification reaction temperature of 820 to 950°C.

[0088] 16. Unit grid connection, NO X The converted emission value is stably controlled at 50mg / Nm 3 Within.

[0089] 17. When the unit load is 120MW, the flue gas recirculation damper is gradually closed. Considering the impact of the flue gas recirculation damper adjustment on the boiler fuel side, the air door opening is limited to 5% each time, with an interval of 10 minutes. When the unit load is 150MW, the flue gas recirculation damper should be completely closed.

[0090] 18. When the flue gas recirculation is put into operation, the bed temperature will rise by 15-25℃. When the bed temperature is higher than 960℃, NO XEmissions will increase significantly. When the unit load is 130MW, start the second heat exchange fan, and then gradually increase the output of the #1 and 2 split-flow ash return heat exchangers on the reheater side, and slowly adjust the damper opening of the equalizing chamber to 60% (the damper opening is limited to 10% each time, with an interval of 10 minutes). Control the bed temperature at the bottom of the dense phase zone of the boiler not to exceed 920℃, the flue gas temperature of the cyclone separator is above 850℃, and the operating oxygen content should be controlled at 4-5%. When adjusting the damper in the equalizing chamber, it is necessary to prevent the adjustment range from being too large, causing the bed temperature and bed pressure to drop too much, resulting in drastic fluctuations in the combustion conditions in the furnace. Because the bed temperature is too low, the flue gas temperature of the separator will be lower than the denitrification reaction temperature, which will cause a large amount of ammonia escape and other hazards (ammonia bisulfate will block the air preheater), so the bed temperature at the bottom of the dense phase zone is required to be controlled at 900-940℃.

[0091] 19. Boiler combustion adjustment should be strengthened during the low load stage of the unit, because air staged combustion can reduce NO X The emission has a significant effect. The upper and lower secondary air staged combustion can make the dense phase area of ​​the furnace in a reducing atmosphere (oxygen-deficient combustion state). A large amount of test data shows that increasing the upper secondary air volume and reducing the lower secondary air volume can effectively reduce NO X Therefore, it is required that the opening of the lower secondary air damper should not exceed 10% before 50% load, and the upper secondary air damper (more than 40%) should be used as much as possible to participate in the oxygen adjustment. In order to ensure the influence of secondary air on the oxygen-poor zone in the center of the furnace, the penetration of secondary air (i.e. high secondary air pressure) should be guaranteed at all times, and the unit load should be gradually increased to 165MW. The oxygen content of the boiler operation should be controlled from 5-6% to 4-5%, and the secondary air main pipe pressure should be controlled from 2Kpa to 5Kpa.

[0092] 20. Excess air coefficient is too large (total air volume), which will cause NO X Emissions increase, so the total air volume control of primary and secondary air should be comprehensively adjusted according to the furnace bed temperature, oxygen content and exhaust gas temperature. When it is within 165MW, the operating inverter current of the two primary fans shall not exceed 190A (it can be appropriately increased if the bed pressure is too high), and the primary fan / secondary fan inlet damper should be closed to 50 / 40~50% to participate in the air volume adjustment to control the total air volume.

[0093] (IV) 330MW circulating fluidized bed boiler unit medium and high load section NO X Recommended parameters for boilers that meet emission standards:

[0094] 1. 165-220MW medium and low load operation

[0095] 1.1 Control oxygen content to 4.5%;

[0096] 1.2 One ammonia water pump is running, and the frequency conversion opening is above 42%;

[0097] 1.3 The ammonia valve opening is more than 60% (ammonia flow rate 1.5~2.5m 3 );

[0098] 150-220MW medium and low load NO X The recommended parameter ranges for boilers that meet emission standards are as follows:

[0099]

[0100]

[0101] 2. 220-250MW load operation

[0102] 2.1 Control oxygen content to 4.5%;

[0103] 2.2 One ammonia water pump is running, and the frequency conversion opening is above 45%;

[0104] 2.3 The ammonia valve opening is more than 70% (ammonia flow rate 1.5~3m 3 );

[0105] 220MW--250MW load NO X Recommended parameter range for boilers meeting emission standards

[0106]

[0107]

[0108] 3. 250-270MW load operation

[0109] 3.1 Control the oxygen content to 3.5-4.5%;

[0110] 3.2 One ammonia water pump is running, and the frequency conversion opening is above 48%;

[0111] 3.3 Ammonia valve opening is more than 95% (ammonia flow rate 4m 3 );

[0112] 250MW--270MW load NO X Recommended parameter range for boilers meeting emission standards

[0113]

[0114]

[0115] 4. 270MW--300MW load operation

[0116] 4.1 Recirculation opening 30-50%; control oxygen content 3.5~4.5%;

[0117] 4.2 The frequency conversion opening of the ammonia delivery pump is 50%. If necessary, two ammonia pumps can be started; 4.3 The ammonia valve is automatically released and the opening is above 95% (ammonia flow rate 4m 3 ); 270MW--300MW load NO X Recommended parameter range for boilers meeting emission standards

[0118]

[0119]

[0120] (V) Boiler combustion adjustment steps during the shutdown phase of a 330MW circulating fluidized bed unit.

[0121] 1. Ensure that the ammonia level is not lower than 3000mm, and take samples of the ammonia storage tank solution for testing to ensure that the ammonia concentration is around 20%.

[0122] 2. When the unit load drops to 165MW, gradually exit the operation of #3 and 4 split-flow ash return heat exchangers on the superheater side, slowly close the damper opening of the equalizing chamber (limit the damper opening to 10% each time, with an interval of 10 minutes), shut down one heat exchange fan, control the bed temperature at the bottom of the boiler dense phase zone not to exceed 920°C, and the flue gas temperature of the cyclone separator to be above 850°C. The operating oxygen content should be controlled at 4-5%. When adjusting the damper in the equalizing chamber, avoid excessive adjustment that may cause excessive drop in bed temperature and bed pressure, resulting in drastic fluctuations in the combustion conditions in the furnace.

[0123] 3. Load reduction process of unit load 150MW↘100MW: gradually put into use 70% of the flue gas recirculation damper (flow rate of about 12m / s) to suppress the increase of oxygen content, gradually reduce the output of #1 and 2 split-flow return ash heat exchangers on the reheater side, and slowly adjust the air door opening of the flow equalization chamber to 30% (the air door opening is limited to 10% each time, with an interval of 15 minutes). Control the bed temperature at the bottom of the boiler dense phase zone to not less than 920℃, the flue gas temperature of the cyclone separator to above 820℃, and the operating oxygen content to be controlled at 4-5%.

[0124] 4. Load reduction process of unit load 100MW↘30MW: When the unit load is about 100MW, the main steam pressure needs to be reduced to below 9Mpa, and the high and low pressure paths of the turbine are gradually opened for operation. The high bypass is slowly opened to 75%, and the low bypass is slowly opened to 50%. The boiler side pressure is further reduced through the bypass system to reduce the load. Usually, when the unit load drops below 50MW, the main steam pressure should be less than 6Mpa; because the flue gas recirculation damper will reduce the boiler bed temperature, when the unit load is 30MW, exit the reheat The #1 and #2 split-flow return ash heat exchangers on the reactor side are running, the damper opening of the equalizing chamber should be slowly closed (the damper opening is limited to 10% each time, and the interval time is 15 minutes), the heat exchange fan is stopped, the bed temperature at the bottom of the boiler dense phase zone is controlled to be no less than 900℃, the flue gas temperature of the cyclone separator is above 800℃, and the operating oxygen content should be controlled at 5-6%. At this time, the denitrification system desalted water flow rate is controlled at 4T / H, the ammonia water flow rate is controlled at 2.5-4T / H, and the atomizing compressed air pressure is not less than 0.5Mpa. At this time, NO X The conversion value should be controlled at 40mg / Nm 3 Within.

[0125] 5. Load reduction process of unit load 30MW↘10MW: Continue to reduce boiler combustion, control the bed temperature at the bottom of the boiler dense phase zone to not less than 900℃, the flue gas temperature of the cyclone separator to above 780℃, the operating oxygen content should be controlled at about 8%, the boiler burns stably for 10-15 minutes, contact the steam turbine to quickly reduce the load to 10MW and decouple. At this time, the denitrification system operates at maximum output, the desalted water flow is controlled at 4T / H, the ammonia water flow is controlled at 4T / H, the atomizing compressed air pressure is not less than 0.5Mpa, and NO X The conversion value should be controlled at 50mg / Nm 3 Within.

[0126] 6. According to the planned shutdown time, the load reduction rate (2-3MW) and short-term stable load node time (5-15 minutes) must be planned to prevent the abnormal fluctuation of bed temperature and oxygen content caused by rapid load reduction, which will affect NO X Emissions: In principle, the unit load needs to be reduced to about 100MW 90 minutes before decoupling, and the load reduction rate should be controlled within 2MW 60 minutes before decoupling. The boiler combustion adjustment pressure is relatively small, which is conducive to low-load combustion adjustment before decoupling.

[0127] (VI) Precautions

[0128] 1. The parallel connection time of the units should be controlled within 10 minutes after the hour, and the disconnection time should be controlled within 10 minutes before the hour. Sufficient adjustment time should be reserved to lower the hourly average and ensure that it does not exceed the standard;

[0129] 2. The hourly average target of NOx during the start-up and shutdown phase of the unit is controlled to be less than 40 mg / Nm 3, especially within 30 minutes before shutdown and decoupling, ensure that SNCR operates at high output to lower the hourly average NOx emissions.

[0130] 3. To ensure the atomization effect of the spray gun, the atomization air pressure of the spray gun should not be lower than 0.5Mpa, the pressure difference between the atomization air pressure and the ammonia main pipe pressure should not be greater than 0.1Mpa, and the ammonia main pipe pressure should be slightly higher than the atomization air pressure.

[0131] 5. Self-calibration maintenance time period of environmental protection facility instruments:

[0132] 02:19-02:26; 05:19-05:26; 08:19-08:26; 11:19-11:26; 14:19-14:26; 17:19-17:26; 20:19-20:26; 23:19-23:26.

[0133] During the above period, the environmental protection parameters will remain unchanged when the SO2, NOX and smoke measurement points are self-calibrated. The shutdown time should be avoided during the self-calibration retention time of the environmental protection facility instrument to prevent the self-calibration when the emission value is high, which will affect the hourly average. During normal operation, it is required that each value should be controlled before this period. X The parameters are in a lower range, and a large amount of ammonia water input should be maintained in this interval to prevent the environmental protection parameters from being too low during the self-calibration stage and reducing the amount of ammonia water input, causing the environmental protection parameters to rise rapidly after being released after the self-calibration is completed.

[0134] Through the operation exploration of the 330MW circulating fluidized bed boiler unit, especially giving full play to the technical advantages of the boiler's unique split-flow return ash heat exchanger (equipment not available in conventional circulating fluidized bed boilers), without undergoing special technical transformation, through changes in the combustion adjustment method, the boiler bed temperature, cyclone separator flue gas temperature, and oxygen content reached the ideal operating conditions, basically achieving full-load denitrification of the 330MW circulating fluidized bed boiler unit.

[0135] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A full-load denitration control method for a circulating fluidized bed boiler unit, wherein the circulating fluidized bed boiler unit has a split-flow ash return heat exchanger, characterized in that: The control method comprises the following steps: In the first startup stage, the amount of bed material and circulating ash added is adjusted to maintain the air chamber pressure above 15Kpa, and circulating ash is added to each of the split-flow ash return heat exchangers according to the heating time; In the second startup phase, the coal is added and the oil is withdrawn for stable combustion until the units are connected in parallel, and a stable combustion time of 4-5 hours is reserved to ensure that the circulating ash in the furnace is collected and stored to increase the flue gas temperature in the separator to meet the ideal reaction temperature range for denitrification. In the third startup phase, multiple split-flow ash return heat exchangers are put into use one by one, and the increase in adjustment range is prevented to prevent the bed pressure from dropping and causing drastic fluctuations in the combustion conditions in the furnace; In the fourth startup phase, the adjustment of flue gas recirculation is strengthened. In the startup phase, when the boiler bed temperature reaches above 900°C after the coal is added and the oil is stopped, the flue gas recirculation system is put into use to reduce the bed temperature and suppress the increase of oxygen content. In the first shutdown phase, the combustion is stabilized and the drum pressure is maintained at a low value, creating conditions for subsequently increasing the boiler temperature; In the second shutdown phase, flue gas recirculation is adjusted to maintain low oxygen content, and the split-flow ash return heat exchanger is used to maintain a stable bed temperature until the split-flow ash return heat exchanger is shut down; In the third shutdown stage, adjust the load stage stabilization time and turbine high-pressure bypass intervention time, and adjust the split-flow ash return heat exchanger to exit operation in the preset manner; In the fourth shutdown stage, adjust the unit load to below 30-40MW and allow the boiler to burn stably for 10-15 minutes, and control the oxygen content not to exceed 8%. When the steam turbine quickly reduces the load to below 10%, the generator is disconnected from the system.

2. The full-load denitration control method for a circulating fluidized bed boiler unit according to claim 1, characterized in that: The control method is NO at any time X The hourly average emission value is controlled at 45mg / Nm 3 Within, and ensure NO X The hourly average value of the indicator is 50mg / Nm 3 and leave a margin to cope with the index fluctuations caused by abnormal working conditions.

3. The full-load denitration control method for a circulating fluidized bed boiler unit according to claim 1, characterized in that: The control method is to control the oxygen content of the boiler to 4%, and operate with reduced oxygen content to reduce NO when the temperature of each point of the furnace / separator does not exceed 960 / 985°C. X The conversion value should be increased or decreased slowly and steadily to prevent the combustion adjustment fluctuation and oxygen content change from causing NO X Unusual changes in emissions.

4. The full-load denitration control method for a circulating fluidized bed boiler unit according to claim 1, characterized in that: The control method detects a coal shortage signal and promptly starts the transfer bin and scraper to eliminate the coal shortage phenomenon, so as to prevent abnormal fluctuations in boiler combustion caused by untimely coal feeding adjustment or untimely load reduction, resulting in NO X In case of abnormal emission changes, return to the planned load in time after combustion stabilizes.

5. The full-load denitration control method for a circulating fluidized bed boiler unit according to claim 1, characterized in that: The coal blending principle of the control method is: The calorific value of coal for zero-shift load 200MW shall not be less than 3800 kcal, and the volatile matter shall not be less than 12%; The calorific value of coal for zero-shift load 220MW shall not be less than 4100 kcal, and the volatile matter shall not be less than 14%; When the morning peak load is above 260MW, the coal calorific value shall not be less than 4,300 kcal and the volatile matter shall not be less than 16%; When the evening peak load of the evening shift is above 260MW, the calorific value of coal shall not be less than 4300 kcal, and the volatile matter shall not be less than 16%; When the morning peak load is above 280MW, the coal calorific value shall not be less than 4500 kcal and the volatile matter shall not be less than 16%; When the evening peak load of the night shift is above 280MW, the calorific value of the coal shall not be less than 4500 kcal and the volatile matter shall not be less than 16%.

6. The full-load denitration control method for a circulating fluidized bed boiler unit according to claim 1, characterized in that: The principles for using the flue gas recirculation damper in the control method are: When the exhaust gas temperature at the air preheater outlet exceeds 170℃, stop adjusting the flue gas recirculation damper and close the flue gas recirculation damper to reduce the exhaust gas temperature. After that, the flue gas recirculation damper should be adjusted slowly, 2% at a time, to prevent the increase in the adjustment range from causing the bed pressure, bed temperature, and NO X Emissions fluctuate widely.

7. The full-load denitration control method for a circulating fluidized bed boiler unit according to claim 1, characterized in that: The control method enables the boiler unit paralleling time to be controlled within 10 minutes after the hour, and the unit de-coupling time to be controlled within 10 minutes before the hour. By reserving sufficient adjustment time, the hourly emission average of environmental protection emissions is lowered to ensure that the hourly average is within a preset range.

8. The full-load denitration control method for a circulating fluidized bed boiler unit according to claim 1, characterized in that: The control method enables the NOx hourly average target to be controlled to be less than 40 mg / Nm during the start-up and shutdown phases of the unit. 3 , ensure SNCR high output operation within 30 minutes before shutdown and decoupling, and reduce the hourly average NOx emissions.

9. The full-load denitration control method for a circulating fluidized bed boiler unit according to claim 1, characterized in that: The control method ensures that the spray gun atomizing air pressure is not less than 0.5 MPa, the pressure difference between the atomizing air pressure and the ammonia main pipe pressure is not greater than 0.1 MPa, and the ammonia main pipe pressure is higher than the atomizing air pressure.

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