Fire cause and countermeasures of air preheater.
The analysis on firing
A large amount of unburned combustible material is deposited on the heat transfer element as a necessary condition for the fire of an air preheater and also is the key.
The heat transfer element of the air preheater is composed of thin sheet, which is very dense and the unit volume is very high. In the lower part, the metal temperature is low, and the low load is the lowest, and it is easy to accumulate dust.
In boiler initial debugging stage, in ignition ignition (oil) and under the condition of long-term low load operation (cast), due to the incomplete combustion, brought from furnace of condensate oil mist and not burning fuel accumulation at the bottom of the air preheater in the middle and the cold end heat transfer components, this is the source of fire.
The main reasons for a lot of accumulation oil mist and unburnable fuel in the air preset are:
1.There are many failures in the equipment.Run the debugger lacks experience.It leads to too long debugging cycle, too much oil burning and bad combustion.
2.Oil pressure or atomized vapor pressure is not appropriate, gas hole, oil hole blockage, atomization is not good.
3.Improper air distribution
5.Long - term low - load operation, the boiler starts to stop more times.
6.The air blower failed to invest effectively.In the boiler start-up and low load operation, because the cold end metal temperature is low, so that the air preheater is easy to accumulate ash, then the blowing dust should be strengthened.However, due to some reasons, the vapor pressure and steam temperature of the blowing medium in the initial stage are insufficient, and the effect of blowing ash is not ideal.
Prevention measures of firm
Minimize the deposition of combustible material on the air preheater.
The key is to make the fuel burn completely. Oil temperature, oil pressure and vapor pressure should be suitable for oil ignition and low load. Oil gun is not blocked, oil leakage; Combustion is stable and sufficient to minimize unburnable combustible.
Strengthen the monitor of air preheater
Conduct a comprehensive examination of the air preheater before starting the unit,If there are more unburned combustible materials in the air preset, it must be cleaned and dried.
It is necessary to ensure that the blower can input properly and the parameters of the blowing medium are qualified.
In the process of operation, in particular, after start-up, hot standby restarting, and the sudden stop and stop of the air preheater, the endpoint temperature of the air preheater should be closely monitored (inlet and outlet air temperature of air preheater). If one or more of the temperature is not normal, the study should be analyzed immediately so that the fire can be found immediately.
For example, if the exhaust temperature exceeded normal value 30℃， it indicates it will fire when running, if the temp continues to raise that's firing. If the temperature continues to rise, it must be on fire.
After the stop, the air preset has stopped rotating, the inlet smoke temperature is unchanged or changed for an hour, and the exit smoke temperature slowly increases at first, and then rises sharply, indicating that the air preheater is on fire. The operator should monitor the furnace flame and observe the chimney regularly. After the rotor is stopped, the current of the drive motor should be observed.
Experience shows that fire is most likely to occur in boiler stop after a few hours, while most of the operating personnel have been evacuated from the scene, people often do not pay attention to the endpoint temperature of the air preheater, when suddenly discovered fire, generally has burned more than 1 h, increase the loss. Therefore, familiarity with preheater performance and operating procedures is a prerequisite for monitoring an empty preserver.
Installing a fire detection system.
Infrared detection system: fire in air preheater air side entry or exit to install a number of infrared probe, probe to do rectilinear motion, the preheater turns, one scan of all heat transfer components on about 10 min. If the air preset is on fire, the infra-red radiation exceeds the normal level, and the alarm signal is sent out. The system has the advantage of high sensitivity and early detection of fire. Immediately put in a lot of water to put out the fire, usually quickly put out the fire.
Effective blowing dust
A large amount of dust can reduce the heat transfer efficiency and increase the resistance of the air preheater. Because the cold end of the air preheater is the easiest to accumulate dust, the soot blower is usually installed in the flue gas side of the air preheater.
In order to prevent the fire from blowing ash effectively, the normal operation time is 8h. Once every 4h during start-up; Dust should also be blown before stopping the furnace; During ignition, long - term low - load operation or heavy dust should increase the number of blowing.
In the initial stage, the compressed air can be purged if the parameters of the blowing steam cannot meet the requirements.
Proper water cleaning
The effect of the air blower is limited, for example, the heat transfer element in the lower part of the air preheater is easy to be blocked, and the soot blower can not be removed.In addition, certain combustible materials can only be cleaned with water.
General water cleaning period is 1~2 times/year. After the water is cleaned, must dry the air preset, otherwise the air preheater will soon corrode,accumulate dust.
Add fire water system.
The flue gas side, primary wind and secondary air side of the air preheater are equipped with a ring fire water pipe, and dozens of nozzle are installed on the pipe.
Fire treatment of air preheater.
The fire of an air preheater is usually derived from the lower part of the middle layer and the heat transfer element of the cold end.It takes a long time to burn from a small area to a large area, usually 1-2h, sometimes longer. In order to reduce the loss, determine if the fire is on fire.
Usually begin from air preheater endpoint temperature and sometimes by air preheater air outlet into the observation hole is on fire, and fire shall be immediately closed observation hole is found, there is gas leakage or fire serious and obvious radiation, the chimney will smoke
When it is found that the air preset is on fire, it should immediately manually operate the MFT, stop the fan running, isolate the air preset, and close the air preheater and exit the damper.The air preheater is kept rotating, the fire hydrant and the multi-nozzle cleaning water line immediately put out the fire and open the drain on the chimney.
Experience shows that it is not good to use foams, chemicals or vapors to extinguish the flame. No holes can be opened after the air preheater is on fire to prevent air from entering combustion.
As a last resort, such as fire water and cleaning water pipe failure without water input, can open the hole, use the power plant fire water to extinguish fire. Pay attention to the fire fighting must be thorough, and careful examination will not leave behind.