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Chapter 44.4.4 Application of a Cs-promoted catalystDescriptionThe conversion of SO 2 into SO 3 is thermodynamically favoured by a lower temperature leveldue to the exothermic reaction. Conventional catalysts are usually operated at temperature levelsof about 420 – 660 °C. Cs-promoted catalysts are sufficiently active at lower temperatures (380– 400 °C) and can therefore be operated at lower temperatures (380 – 620 °C), which increasesthe SO 2 conversion rate. Cs-promoted catalysts can be used in the first bed to reduce the bedinlet temperature or in the final catalyst bed (at a low inlet temperature).Achieved environmental benefits• increased conversion rate by 0.1 % [17, 2nd TWG meeting, 2004]• a plant in the Czech Republic reports conversion rates of 99.8 – 99.9 % (double contact, 4beds, Cs-promoted, 150000 tonnes/year), after 4 years the catalyst is due for exchange andthe conversion rate has dropped to 99.7 % [17, 2nd TWG meeting, 2004]• at double contact plants with sulphur burning SO 2 conversion rates of 99.9 % and anemission reduction of 30 – 70 % (compared to conventional catalysts) are achievable. Atsingle contact plants, conversion rates of 99.5 % and emission reduction rates of about 50 –70 % are achievable.Cross-media effectsAdditional pressure drop of 15 mbar and higher catalyst volume required [58, TAK-S, 2003].Operational dataNo specific information provided.ApplicabilityGenerally applicable.At Voest Alpine Stahl Linz GmbH, a single contact plant (processing H 2 S gases from a cokeoven plant) has been modified by enlargement of the catalyst layers and by application of a Cspromotedcatalyst in the 4 th layer. SO 2 emissions could be reduced from about 1500 mgSO 2 /Nm 3 to