Dissolution rate of sodium salt scales in falling film evaporators
Paper in proceedings, 2013
In pulp mills, fouling can be a significant problem in
the black liquor evaporation plant. Part of the black liquor
evaporation plant works as a crystallizer where large
amounts of sodium carbonate and sodium sulphate will
saturate and precipitate.
In this work, the dissolution rate of sodium scales was
experimentally investigated and modelled. Experiments
were conducted in a pilot falling film evaporator where a
sodium carbonate and sodium sulphate solution was
evaporated on the outside of a vertical stainless steel tube to
form the scales. The aim was to relate the dissolution rate to
wetting degree (i.e. the mass flow rate per unit
circumference) and temperature of the wash liquid.
An effective experimental method to measure the
removal of sodium scales in falling film evaporators was
developed and a 1st order model with respect to the
difference in mass fraction between the scaling layer surface
and the bulk of the wash liquid was shown to fit the
experimental data well.