Drying system is generally the last, but a very important section of the Zero Liquid Discharge setup. In most cases, it succeeds the Multiple Effect Evaporator (MEE), where it is employed for converting the liquid effluents/concentrates into dry powder or thick paste. In other cases, dryers are used for drying wet solids in crystalline/amorphous forms to dry powder/flakes/ lumps with desired moisture content.
Selection of the dryer depends on the specific application and the duty conditions. Energy consumption per unit production is an important consideration. A dust collection system on the exhaust air from the dryer is a must for the protection of the environment.
Liquids and slurries are dried using SST Dryer (Scraped Surface Dryer) or Spray Dryer. Solids from the Crystallizers/Filters after the MEE are dried using a Paddle Dryer or Continuous Fluid bed Dryer (Static or Vibratory type). In cases, where the condensate from effluent evaporation is to be totally avoided, a Spray Dryer is used.