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In a sulphuric acid plant absorbing tower the gas stream contains SO3, H2SO4 vapour and H2O vapour. As the gas is cooled, H2SO4 vapour condenses and submicron particles are formed by the "shock cooling". In addition, the SO3 vapour and the H2O vapour react to form submicron H2SO4 mist. |
In Sulphuric Acid Plants
Larger acid mist particles are created in sulphuric acid drying and absorbing towers as a result of the splash and shear of liquid acid in the distributor and over the packing. These particles are entrained in the upward gas flow. More difficult to collect small acid particles are formed by the reaction of sulphur trioxide with any water vapour present and by the condensation of acid from the gaseous or vapour phase. These acid particles can corrode blowers, ductwork and heat exchangers, damage catalyst and cause atmospheric pollution.
As an example, in a sulphuric acid plant, much of the mist is mechanically
generated. The frothing action in the distributor along with bubbling in the
downcomers generate spray particles. Also acid drops are stripped off the acid
flowing over and through the tower packing 
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