electrodes. Between the collecting electrodes there are discharge electrodes
which are supplied with high voltage to create a corona discharge from their
sur face as shown in below Fig. Due to the corona effect, dust particles are
elec trically charged by the adhesion of gas ions and are subsequently deposited
on the collecting electrodes. Then the dust particles are then collected with suit
able rapping system. With this system, dust emission rates <50mg/Am3 can be achieved
and in certain cases it is even possible to observe limits of 20–30mg/Am3.
However, in comparison to bag filters, it is not possible to adhere continuous
guarantee dust emission values with electrostatic precipitators. For example,
during cement plant starting-up and shutting-down phases and “upset conditions”.
The specific electrical resistance of the dust particles and the gas temperatures,
moisture contents and CO concentration levels are important factors for the dust
collection efficiency. As a result of high field intensities in the deposited layer of
dust, a back corona effect can occur, removing the charge of the negatively
charged particles. In such cases the precipitator voltage has to be reduced, which
results in deterioration of the collection efficiency. High CO concentrations caused
by process conditions may even lead to an emergency shutdown of the precipitator.
Set against these system disadvantages are the advantages of low pressure drop
and lower capex and operating costs in comparison to bag filters. For this reason,
electrostatic precipitators are mainly used in countries which have less stringent
environmental regulations.
5.5 Technical Comparison
The table-1 shows the technical comparison between Reverse Air Bag House and
Pulse Jet Bag House.