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What is the dust pre-coating works for bag filter housing? How to pre-coat the dust?

The dust filter bags pre-coating or dust seeding means pre-coat the filter aid dust on the surface of the dust filter bags before the systems running normally when installed the new filter bags.
The advantages as following:
1. When the dust collector start, especially the earlier period, dust air may include high moisture content, also include some incomplete combustion ignition oil, sticky oil coke as well as the hydrocarbon materials and so on, if the filter bags with pre-coated, these wet or sticky materials won’t touch with the filter bags directly, so not easy to bring the block problems or corrode the filter bags, so can prolong the service life of the filter bags.
2. When the dust air have some acid materials, such as SOx and so on which may need to insert some alkali powders, such as CaO, but at the beginning hard to get the suitable content of the material to insert, if without pre-coating layer, may corrode the filter bags at earlier period.
3. Also the protective layer over the surface of the filter bags, can help to increase the filter efficiency of the new filter bags.

But how to pre-coat the dust filter bags with the filter aid dust?
According to the long time operate experiences, Zonel Filtech was offered following suggestions to our client’s for reference:
a. The pre-coating works need to arrange before the boiler ignition or production, and stop the purging systems, open the dust air inlet valve.
b. Turn on the fan and increase the air flow gradually until it meet the 70% of the design, and record the resistance for different chambers.
c. Insert the filter aid dust from the access hole of the main pipe.
As usual the filter aid dust particle size is less than 200 micron, moisture content less than 1%, without oil, the quantity of the dust need to insert is 350~450g/m2 according to filter area.
d. Before insert the filter aid dust, make sure the air flow volume is more than 70% of the design, and make sure the bypass valve is closed, lift valve is on line. The fan need to working about 20 minutes when finished the filter aid dust adding, make sure the dust pre-coated on the filter bags equally.
e. When the pre-coating works finished, the resistance as usual will increase about 250~300Pa, if the resistance not increased as requested, that’s mean the operating failed, may need to repeat the procedures again.
f. When the pre-coating works finished, stop the fan, the inspector go to the clean air housing to check whether have any leakage, if yes, may need some repairing.
g. If without leakage and all data shown normal, then can operating according to the designed data, open the purging system and operating normally.


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