Green Liquor Cooling Crystallisation, 1998 International Chemical Recovery Conference Proceedings

Cooling crystallization of green liquor is a means of separating out substantially pure sodium carbonate for use in split-sulphidity pulping. Previous studies have measured equilibrium behaviour in synthetic mixtures. This paper investigates crystallization from mill green liquor for short residence times - comparable with those practiced in a commercial plant.

It was found that the abnormal solubility of sodium carbonate above 35° the tendency to form metal-stable solutions above 15°C and the exothermic nature of the crystallization process all prevent significant crystallization until the temperature of the green liquor is below ca 15°C. This is useful in reducing the tendency of fouling of heat exchange surfaces.

At temperatures below 15°C crystallization proceeds rapidly to a residual sodium carbonate concentration similar to the level at equilibrium in synthetic solutions. This shows that short processing times need not significantly affect the yield from the green liquor.