Contact Process - DCDA

DCDA

The next step to the Contact Process is DCDA or Double Contact Double Absorption. In this process the product gases (SO₂) and (SO₃) are passed through absorption towers twice to achieve further absorption and conversion of SO₂ to SO₃ and production of higher grade sulphuric acid.

SO₂-rich gases enter the catalytic converter, usually a tower with multiple catalyst beds, and are converted to SO₃, achieving the first stage of conversion. The exit gases from this stage contain both SO₂ and SO₃ which are passed through intermediate absorption towers where sulphuric acid is trickled down packed columns and SO₃ reacts with water increasing the sulphuric acid concentration. Though SO₂ too passes through the tower it is unreactive and comes out of the absorption tower.

This stream of gas containing SO₂, after necessary cooling is passed through the catalytic converter bed column again achieving up to 99.8% conversion of SO₂ to SO₃ and the gases are again passed through the final absorption column thus resulting not only achieving high conversion efficiency for SO₂ but also enabling production of higher concentration of sulphuric acid.

The industrial production of sulphuric acid involves proper control of temperatures and flow rates of the gases as both the conversion efficiency and absorption are dependent on these.