Sulfur trioxide (S03)

The combustion transforms fuel bound sulfur to sulfur dioxide (S02) and SCR catalysts may convert parts of this S02 into S03. In the presence of ammonia (NH3) the formation of ammonium hydrogen sulfate (NH4HSO4) becomes possible at lower temperatures. This has to be considered when heat exchangers are installed downstream of the converter.

Possible accumulations of ammonium hydrogen sulfate are water soluble and can be washed out easily. In order to minimize maintenance of the heat exchanger appropriate coolant temperature, low sulphur in the fuel and minimal NH3 slip are desirable. In any case, the operator is responsible for adequate design, layout and operation of such heat exchangers.

Special types of catalysts with minimal S02-S03 conversion rate will be adequate when fuel with high sulfur content is used.