Corona Power

As stated previously, a strong electric field is needed for achieving high collection efficiency
of dust particles. The strength of the field is based on the rating of the T-R set. The
corona power is the power that energizes the discharge electrodes and thus creates the
strong electric field. The corona power used for precipitation is calculated by multiplying
the secondary current by the secondary voltage and is expressed in units of watts. In ESP
design specifications, the corona power is usually given in units of watts per 1000 m3/h
(watts per 1000 acfm). Corona power expressed in units of watts/1000 acfm is also called
the specific corona power. Corona power for any bus section of an ESP can be calculated
by the following approximate relation:

As you can see, corona power increases as the voltage and/or current increases. The total
corona power of the ESP is the sum of the corona power for all of the individual T-R sets.
In an ESP, the collection efficiency is proportional to the amount of corona power supplied
to the unit, assuming the corona power is applied effectively (maintains a good sparking
rate).

From above equation, you can see that for a given exhaust flow rate, the collection efficiency
will increase as the corona power is increased. This efficiency will depend on the operating
conditions of the ESP and on whether the amount of power has been applied effectively.
For high collection efficiency, corona power is usually between 59 and 295 watts
per 1000 m3/h (100 and 500 watts per 1000 acfm). Recent ESP installations have been
designed to use as much as 470 to 530 watts per 1000 m3/h (800 to 900 watts per 1000
acfm).
The terms current density and power density are also used to characterize the design of the
ESP. Current density is the secondary current supplied by the T-R set for the given plate
area and expressed in units of mA/ft2 of plate area. Power density is the corona power
supplied to the plate area and is expressed in units of watts per ft2 of plate area.
The size of the individual power sets (T-R sets) in the ESP will vary depending on their
specific location and the conditions of the flue gas such as particle size, dust concentration,
dust resistivity, and flue gas temperature. In an ESP, the T-R sets are selected to provide
lower current density at the inlet sections, where the dust concentration will tend to
suppress the corona current, and to provide higher current density at the outlet sections,
where there is a greater percentage of fine particles.