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BAG FILTER

The most commonly bag filter used techniques to remove dust are :

• Shaking Systems
• Reverse Air Cleaning
• Pulse/Jet Cleaning

A short description on each technique can be found below.



SHAKING SYSTEMS

The filter bags or envelopes are shaked by means of an eccentric rod assembly & can only take place if the filtration through the fabric is stopped. This cleaning technique is mostly used in smaller sized filter systems while the fabric load has to stay low. This system is normally used in combination with weaved fabric filters.

The cleaning function is not optimum & over the last decades this technique is more & more taken over by the next techniques.



REVERSE AIR CLEANING

In this type of system the air or gas stream will be forced by a ventilator in the reverse direction to clean the filter bags. During this filtration action the filter system or a relevant section has to be shut off .This type of system can be used for low up till medium fabric loads. Also, the filter medium for this system is normally a weaved fabric.



PULSE/JET CLEANING

In pulse/jet dust collector systems the air or a short shot of air will be given, opposite to the normal air stream, in a bag or a row of bags.This air shot will create a shock wave that breaks the dust cake from the fabric which will fall down in a hopper & can be removed. Depending on the type of installation a typical pulse time is around 400 msec. While the interval between the pulses on each bag or row of bags is around 3 to 6 minutes. More & more the pulse sequence will depend on DP measurements over the filter bags.

Sequential controllers or PLC’s are used to set the times & giving commands to the pulse valves. There are systems using medium pressure (2-3 bar) & systems for high pressure (6-8 bar). Venturies are used to increase the air speed. The cleaning normally takes place while the filter system is in operation. The fabric materials used in these systems have to be adapted to:

• The particle size
• Degree of filtration
• Filter resistance