The spent gas
from the sulph(on)ation reactor cannot be directly discharged
to the atmosphere as it contains traces of organic aerosols,
unconverted SO2
and unreacted SO3
gases.
The first step
of the spent gas treatment takes place in an electrostatic precipitator
(ESP), where organic particles and SO3
are separated.
As the SO2
cannot be removed by electrostatic precipitation it remains in
the gas wich must be treated in an absorption column by a diluted
solution of caustic soda, forming a sodium sulphite/sulphate
solution.
The spent gas
leaving this unit can be released into the atmosphere and it
meets the most stringent environmental regulations.
