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1 The fuel injection quantity of the oil gun must be suitable. In the initial stage of operation of a 300MW boiler unit in a certain factory, an accident occurs due to poor quality of coal and unstable combustion under a 230MW load, and the deflagration of the upper part of the cold ash hopper after 10 min of oil injection causes partial back wall water cooling. Wall damage.
After analysis, because the individual oil gun output is too large, part of the fuel without fogging falls on the upper part of the cold ash bucket after separation. The vaporized gas fume is mixed with some unfired coal powder and encountered after increasing the concentration. A deflagration is caused when falling hot ash. Although the high furnace pressure of the FSSS triggered the FMT action and cut off the fuel and coal fuel, it played a role in limiting the accident expansion. However, this example shows that the excessive oil gun output is a potential threat to the safe operation of the boiler. The high furnace pressure protection of the FSSS can only be actuated when the impact force of the detonation reaches its set value, and thus cannot completely prevent the occurrence of a deflagration accident. From this, it can be seen that the fuel injection quantity of the oil gun must be controlled within the specified range, and it is necessary to insist on the trial shooting of the oil gun on a regular basis. It is found that the oil quantity exceeding the limit should be discontinued in a timely manner. In the case of uneven powder and poor combustion, it is advisable to invest fuel oil in the combustion center as soon as possible. After the oil gun is put into use, check the actual atomization and ignition of the fuel.
2 Check fuel cut immediately after main fuel trip (MFT) After boiler fire extinguishes MFT, as long as the cause is clear, it should normally resume normal operation after being purged. In the extinguishing treatment process, in order to avoid a significant drop in steam temperature and steam pressure, delay recovery time, and even increase the accident, the operator is required to perform a quick inspection and perform multiple operations. However, in the treatment after the boiler fire extinguishing, the operator often pays more attention to the recovery operation and it is easy to neglect the inspection of whether the fuel entering the furnace has been completely removed (eg, check the oil gun system, powder feeder, primary fan, coal mill, and If the dumper trips, this could cause a deflagration accident.
A boiler in a factory accidentally discovered that there was a flash of fire on the flame monitor screen twice in a hurry after the “full flame lost the flame†MFT. The inspection found that one powder remover with exhaust gas was not jumped, causing the powder in the primary air duct to enter the furnace, causing deflagration, but fortunately it did not cause equipment damage. Although this phenomenon is accidental, due to its extremely dangerous nature, it is required to check whether the fuel entering the furnace immediately after the boiler has been extinguished has been completely removed as the primary task of extinguishing the fire.
3 The boiler starts to check the atomization and ignition of the oil gun. In the initial stage of the boiler ignition, due to the low temperature of the furnace, the fuel discharged from the oil gun often cannot fully ignite, especially if the oil is not met during the start of the cold furnace ignition in winter. Good, igniter performance is poor, the atomization of steam vapor is not net and other issues, there are often frequent advances and retreat of the oil gun, repeated repeated ignition. In this case, it was found that a large amount of oil accumulates on the surface of the cold ash bucket, creating a safety hazard. Therefore, before the ignition of the boiler, the leakage test of the oil gun should be qualified. After the ignition, it is necessary to pay attention to maintaining the stable oil pressure and the flow of the oil gun is appropriate. Check the atomization and ignition of the oil gun on the spot, and quit the treatment when there is oil drop separation. When the oil gun cannot be ignited or the fire is unstable, frequent throw-in and throw-back should be avoided. Problems such as clogging of the oil gun head, wax precipitation, and poor igniter performance should be checked. Local test shotguns should be switched as far as possible. In the initial stage of boiler ignition, pay attention to keep the water level of the cold slag bucket in overflow condition. If you find that the overflow water is obviously oily, you should find out the reason as soon as possible.
4 After the accident is stopped, the oil system should be immediately unloaded for furnace purging. At the initial stage of commissioning of a plant, after the unit trips the ganged boiler MFT, the cause of the trip was checked. During the period of waiting for recovery, the boiler flame monitoring screen was found to have a flash of fire. Hear the sound of the furnace. Local inspection revealed that the boiler wall at the B side of the boiler was deformed and leaked from several heated surfaces.
At that time, the boiler was out of flame for more than 1 hour. The pneumatic equipment was stopped. The oil system shutoff valve and the fuel gun solenoid valve were closed. After analysis, the furnace oil system only has a quick-closing valve on the incoming oil pipeline. The oil return is connected to the return oil mother pipeline via a manual isolation gate. Because the return flow volume of the adjacent furnace is too large, the oil return gate on the oil depot side There is throttling, causing pressure in the oil return system. After the furnace is shut down, the No. 2 solenoid valve of the oil gun is not strict, causing the fuel to leak into the air duct of the B side of the boiler, causing a deflagration. Therefore, after the boiler is extinguished, the recovery operation will not be performed for the time being. Immediately, the oil return isolation door should be closed and the system oil pressure should be confirmed as zero. The return amount of each boiler shall be determined according to the maximum startup method of the whole plant and the diameter of the return header, and the isolation door on the return converence mother shall not be throttled to ensure that the return header is free of pressure.
Another problem that should be noticed after the boiler is turned off is that it is necessary to purge the furnace, especially after the accident is stopped. This operation cannot be ignored due to a lot of operational matters. If the furnace purging is affected due to the temporary loss of power for the plant, the suction baffle should be manually opened to conduct natural ventilation for a period of time. At the same time, attention should be paid to avoid the sudden cooling of the boiler. After the plant is restored to electrical power, furnace purging is carried out according to regulations regardless of ignition.
5 It is strictly forbidden to withdraw and interfere with the FSSS fire extinguishing protection function. The FSSS system uses coal and oil flame detection devices to judge the presence of fire and fire by measuring the frequency and intensity of the fire light. When the detected number of no-fire reaches the set conditions, A "full hearth loses flame" signal is issued and the MFT command is activated to remove all fuel and prevent the boiler from firing.
In the boiler operation, especially in the initial stage of the new unit being put into operation, due to the problems in the changes of coal quality, combustion adjustment, flame detector debugging, or contamination, boiler fires frequently occur and it is difficult to maintain stable combustion of the boiler. In this case, some plants are forced to use a signal to stably drag one or two frequently flickering, very unstable flame detectors or to short-circuit one of the most unstable flame detectors. There is a fire condition. In this way, even if the whole fire is extinguished in the boiler, it can send a signal that the whole furnace loses flame, but it has reduced the FSSS-set criteria for giving out the whole furnace without fire, and therefore, the boiler flame detection signal is unstable. A solution to the problem should be found, and the FSSS protection function cannot be compromised.
Before starting the boiler, the FSSS system should be carefully inspected to ensure its reliability after the investment, because once the FSSS system fails during operation, it is very passive. Therefore, it is necessary to strengthen the management of the FSSS system as an important measure to ensure the safe operation of the boiler.
6 Strengthen Fuel Management The quality of fuel oil has a great influence on the ignition and ignition effects of oil guns. Impurities in the oil will not only block the nozzles of the oil guns, but deposits in the valves may also cause the valves to close tightly and leak oil. Therefore, we must strictly control the inspection of good oil, and at the same time ensure that the filter system of the oil system is put into operation normally, and periodically clean the filter screen to prevent impurities from entering the front oil system. The oil depot should also periodically check the discharge of water to prevent water in the oil.
The fluctuation of the system oil pressure has a great influence on the fuel injection quantity of the oil gun, especially when the adjacent boiler throws the oil gun back and forth. The frequency control of the fuel pump plays a very good role in stabilizing the pressure of the oil source, and at the same time it can also receive a significant energy saving effect.
The problems encountered in the actual operation of the boiler are various, and the cause of the deflagration of the boiler hearth is complicated and changeable, but the fuel problem is often one of the main causes of the deflagration. Pay attention to the links and status of the oil gun investment, removal and oil quantity control, and ensure the reliability of the boiler interlock and FSSS protection investment. Under various abnormal conditions, we must first pay attention to the problems jeopardizing boiler safety in order to prevent more effectively. The occurrence of a boiler deflagration accident.
Boiler deflagration is a vicious accident that causes serious damage to boiler equipment. It is also one of the countermeasures of State Power Corporation's 25 key requirements for preventing major accidents. The causes and phenomena of the deflagration of the furnace are diversified, and operators must pay great attention to it. In order to prevent boiler deflagration accidents, several issues need to be noted.