The bag filter industry in China has developed in the past decade, and there are already a large number of bag filter manufacturers in the country. Significant progress has been made in the mechanism research, structural form, dust cleaning technology, control, as well as filter media and filter bags of bag filters. However, there is still a gap between China's bag filter technology, especially its design technology, and developed levels such as Germany and Japan.
The current design theory of large-scale bag filters in China is basically in the empirical stage. Ability is not yet. Compared to some developed computer simulation technologies, China's design capabilities are still relatively backward. Many bag filters currently in operation suffer from uneven airflow distribution and short lifespan of filter bags. The design of bag filter is a complex system engineering. In engineering practice, there will be various difficulties, so when designing a bag filter, various factors should be considered as much as possible, such as installation site, processing air volume, smoke concentration, temperature, quality, and other factors that affect the overall performance of the equipment.
In the context of variable coal types and non-standard operation in China, the reasonable service life of bag filters is over 20000 hours, but there have been instances of operation for more than 30000 hours. The service life of the filter bag is guaranteed to be 30000 hours, which was selected for a common 4a overhaul. Therefore, it has been used until now. If the above design requirements are strictly followed and the following operation methods are followed, it can still be achieved. If the filter bag is changed online, restrict the airflow until the filter bag is fully conditioned! The new bag should be pre coated with a dust layer to make its resistance comparable to other filter bags, so as not to cause damage to the filter bag due to excessive filtering wind speed.
2. Low temperature operation can cause acid condensation on the ash layer, which can corrode the filter bag and bag cage. Leakage of the boiler pipeline can cause smoke and water to form a hardened ash layer! Improper fuel operation can lead to smoke and oil carryover, resulting in local filter bag failure. This is a common problem during operation, and attention should be paid during operation.
3. Reduce smoke temperature, avoid air leakage, and adjust the dispersion of cold and hot air flow. a. Repair the air preheater and economizer, improve their heat exchange efficiency, and reduce the flue gas temperature below 150 ℃. b. Avoid air leakage in the furnace, air preheater, flue, and bag filter, and reduce the oxygen content in the flue gas of the dust collector (less than 8%). c. The insulation of the bag filter should be good to avoid condensation and acid erosion. d. Adjust the dispersion of cold and hot airflow.
4. Control the blowing pressure and extend the blowing distance. The low resistance of newly put into operation equipment can appropriately reduce the injection pressure, pulse width, and extended injection distance, which is beneficial to the service life of the extended bag filter bag. Around the time of operation, the resistance of the filter bag will gradually become constant. Depending on the needs, the injection pressure can be appropriately increased and the injection distance can be shortened.
5. Pre spray the filter bag before starting. Reflection: The ash storage tank should have sufficient ash volume. Start the induced draft fan and pre spray the bag filter bag of the bag filter until a 2-3mm thick dust layer accumulates on the surface of the bag filter (which takes about 3 hours or more). Then, the boiler can be burned with oil. To maintain the filter bag, it should be pre sprayed before each boiler burn and the results of the pre spraying should be reflected upon. The atomization and combustion of the burning oil gun should be good to avoid many unburned oil droplets from being carried to the furnace and forming a paste bag.
When the boiler is running normally, the oxygen content in the furnace should be maintained at 2% to 3%, and the oxygen content in the bag filter should be less than 8%.
7. During normal operation, if the differential pressure of the filter bag is greater than 1500Pa (1200Pa for electric+bag), start spraying and stop cleaning at 800-900Pa. The typical pressure difference for a new bag is 1.0kPa, and it is 2.5kPa when approaching its lifespan!
When the exhaust temperature reaches 150 ℃, the maintenance alarm will be triggered. The stoker can accept methods such as reducing load, reducing air supply, and induced draft. When the exhaust temperature reaches 160 ℃, the second alarm will be triggered. Continuous load reduction and other methods will be used to achieve the goal of reducing exhaust temperature. If the alarm reaches 170 ℃, maintenance measures such as spraying water will be taken. Monitor the decreasing trend of smoke temperature, stop spraying water when it drops below 160 ℃, and continue monitoring until the exhaust temperature returns to normal. The furnace should be shut down urgently at 180 ℃.
9. During operation, it was found that a decrease in room differential pressure in a certain unit led to an increase in emission concentration, resulting in bag breakage. The small hole on the filter bag with smooth air flow would cause rapid damage to the filter bag and nearby filter bags, leading to catastrophic damage. Therefore, detect the bag filter and replace or seal the broken bag in real time. Fluorescent powder can be sprayed and a UV lamp can be used to make the fluorescent powder glow to detect and locate broken bags.
10. When judging from parameters such as water level, flow rate, furnace negative pressure, and the sound of explosion and leakage, it is not allowed to delay the work and the furnace should be shut down urgently to avoid bag sticking. Install a hygrometer at the outlet of the air preheater to detect the moisture content of the flue gas, in order to detect pipe leaks in advance and adopt emergency measures in advance.
11. Avoid the accumulation of unburned coal powder from bituminous coal with high volatile matter in the dead corners of the flue and dust collector, or the sudden extinguishing of the boiler and the extraction of coal powder into the furnace to form secondary combustion. When the temperature of the bag filter suddenly rises significantly, immediately shut down the furnace and adopt methods such as stopping the induced draft fan, jumping the supply fan, and feeding powder.
