Electro Static Precipitator
● Electrostatic Precipitator is introduce by Dr. F. G. Cottel in 1906. It is a type of air filter that utilizes electric energy for removing the impurities fly-ash, dust particles from the flue gases in steam power plant. This is a commonly used device for controlling air pollution.
● When these fuels burn, then the smoke will generate which includes the small soot particles that are balanced the air. The carbon particles which are not burned can pull out from the smoke with the help of electrical energy in the precipitator. It is essential for removing carbon particles from the burn because it can harm human health.
Construction:
The components of electrostatic precipitator include Electrodes, 3 phase supply 50 Hz 440V, control cabinet, High voltage transformer, Rectifier, Hooper and Insulators. This device includes two sets of electrodes namely positive as well as negative. The shape of the two electrodes mainly depends on the type of precipitator employed like bars, plates, metal wires, etc. The appearance of the positive electrodes is like plates whereas the negative electrodes are in the shape of a wire mesh or rod. These two electrodes are arranged vertically one after another in the precipitator. The connection of the two electrodes can be done by connecting the positive and negative electrodes to the two terminals of the DC source. The DC source positive terminal may be connected to GND for getting strong negativity to the negative terminals. The distance between the two electrodes and applied DC voltage are corrected.
Working :
The working principle of Electrostatic Precipitator. The unclean flue gas flowing through the s supplied by two electrodes, i.e, is passed between a pair of oppositely charged conductors and it becomes ionised as the voltage applied between the conductors is sufficiently large. As air is passed through this ionised chamber, both negative and positive ions are formed. The air carrying the ions and coming out of the ionizing chamber is further passed through the collecting unit. This unit consists of a set of vertical metal plate spaced 15 to 20 centimeter apart. The plates are positively and negatively charge. The voltage applied to the plates is approximately half the potential of the ionizing wires.
The high intensity electrostatic field exerts a force on charged particles. The negative ions moves toward positive plate and positive ions moves toward negative plate. The dust accumulation on plates are cleaned periodically by giving shaking motion to plate with the help of cam driven by external source. The dust remove from plate is collected in hopper.
Advantages:
1. It require small installation space.
2. This is very effective for high dust loaded gas and small particles like smoke or mist and flyash.
3. It has low initial cost, working cost and low maintenance cost.
4. It is easy in operation
Disadvantages :
1. It forms small percentage of ozone when the air is passed through this. The formation of ozone is objectionable due to irriating effect to nose and throat.
2. A pre-filter is necessary before electrostatic filter to reduce the load on this filter.
3. The efficiency of the filter decrease when quantity of air flow increases.
4. Due to closeness of the charged plates and high potentials used, it is necessary to protect the whole apparatus by placing fire mesh in the air stream before the ionization chamber because small particle of paper cause sparking when it is carried across adjacent plates.
5. The direct current is not available with modern power plant, so electrical equipment is require to convert low A.C. voltage to high D.C voltage.
