Recovery of sulphate from spinning baths
During the viscose fibre manufacturing process, sodium sulphate produced as a by-product can be crystallised as Glauber salt. The spinning bath solution containing sodium sulphate is led to multiple-stage thickeners to raise the concentration of sodium sulphate. There, water is vaporised to saturation point and crystallisation of sodium sulphate takes place. By recrystallising in melting pots and evaporation of the crystal water in crystallisers, a pulp of sodium sulphate is obtained.
This pulp is centrifuged and dried at 450 °C in a drying tower by direct heating with a natural gas burner. Another technique for drying is the usage of a tumble dryer and a subsequent separation in a cyclone.
Calculation of sodium sulphate recovery
Sodium sulphate recovery (%) =[ (quantity of sodium sulphate produced as by-product (tonne)/ viscose or modal fibres produced (tonne)]*100