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2.4.2. Electrostatic precipitators 
This technique uses electrostatic forces to separate particles from gases. The gas passes 
through a passage formed by the discharge and collecting electrodes. Particles receive a 
negative charge and are then attracted to a positively charged electrode. Collected particles 
are then removed by rapping or vibrating electrodes continuously or intermittently. 
2.4.3. Fabric filtration 
Fabric filters use filtration to separate particles from gas. The gas stream enters the baghouse 
and passes through fabric bags that act as filters. The fabric used can be cotton, synthetic or 
glass-fibre materials. This technique is very efficient and cost effective.

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Figure A-2-4: Baghouse 
Fabric filters are classified according to their cleaning methods (mechanical shaking, reverse 
air injection). 
2.4.4. Scrubbing systems 
 
This technique uses a scrubbing liquid (generally water) that comes into contact with the gas 
stream. The three basic operations of wet scrubbers are gas humidification, gas-liquid contact 
and gas-liquid separation. The outlet liquid is either cleaned and discharged or recycled into 
the scrubber. 
Figure A-2-5: Wet scrubber 
2.4.5. Selection of the control technique for PM emissions 
Design, effectiveness, space requirements, investment, operating, and maintenance costs 
differ widely according to the technique. A compromise must be done in function of 
advantages and drawbacks of each technique and SOx level emitted. Moreover, general 
factors influent the selection of the PM-control technique. These factors are: 
- PM concentration and particle size. 
- Degree of particle removal required. 
- Characteristics of gas stream. 
- Characteristics of particles. 
- Methods of disposal. 
The table below (Table 2-2) indicates some advantages and drawbacks concerning each 
technique. 

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Advantages 
Drawbacks 
Inertial collectors 
- Low-cost equipment 
- Continuous or batch unloading 
- Primary technique 
- Abrasion problems for high