91.Explain the principle of EP and their components? What may the reason for low current and High voltage and High current and Low voltage? How to set the operating condition manually?

Two Electrodes at high potential difference of DC supply will be build in the flue gas path after air heater before ID fan. The emitting electrode is a thin wire. The potential strength around wire will ionize the gas. This is known as Corona. The ionized gas will be with Electrons and positive ions. The collecting electrode are plates and provide large area.

The electrons are traveling from discharge electrode towards the collecting electrode at a high velocity. ( Normally the gap is 250 mm).The flue gas consists of dust is passing through the electrode at a low velocity of 1 m/sec or less. The dust particles are bombarded by  the electrons and attached to the dust. The dust will be now charge –vely. They are attracted by collecting electrode plates. The velocity at which the dust is moving towards collectors is known as migration velocity.

Migrations velocity will be more than the gas velocity.  This bring the dust to the collectors. There they are attached to the plates. The efficiency of a zone of ESP will be around 90%.

Discharge electrodes, collecting electrodes, Insulators, high voltage transformer/rectifiers, hammering systems for the electrodes and  controllers are some of the main components of an ESP.

Low current and High voltage is caused by the deposit of fine dust on discharge electrode.

High current and low voltage is caused by deposit of coarse dust on the collecting plates. High resistive dust will make the condition worst in this case. There will be corona near collecting plated when high potential strength is established by the dust deposit. This phenomenon is called Back Carona. The electrons from this corona will combine with the positive ion from the main corona and similarly the positive ion from back corona will combine easily with electrons from main corona. The dust will escape from ESP to chimney.

When control is on Manual, increase the current until there is spark. Leave at a level where 2 to 5 sparks/min is occurring.