controlling fisheyes in pulp drying

We operate an old pulp flash drying plant. In the past the mill
had problems with fisheyes in the pulp and added SO2 to deal with
problem. The mill continues to use SO2, however the reason for this
solution is unknown and the SO2 is causing severe corrosion damage
to the surrounding buildings. Does anyone know what the SO2 does to
stop fisheyes and is there an alternative?