Exhaust gas contains minimal amounts of SO2, unreacted SO3, and some parts of organic acid. The ESP consists of a bundle of round tubes containing perfectly centred axial electrodes.
The difference potential (D.D.P.) created between the pipe walls and the electrodes charges the impurities in the gas stream, and as a consequence they migrate onto the internal surface of the tubes, where gravity will cause them to drain down.
The residual parts of SO2 are treated in a scrubbing column where a solution of water and caustic soda is continuously added and recycled. The correct pH level is maintained by a control loop which checks the NaOH valve.