An energy saving atmospheric evaporator utilizing low grade thermal or waste energy

A specially designed compact thermal unit has been developed and tested for reducing the quantity of thermal energy required in evaporation and thickening processes. In this unit, a relatively large fraction of the heat of condensation and the sensible heat of the warm distillate is recycled and utilized for preheating the feedstock and evaporating the liquid phase within the evporation chamber. The yields obtained in such a thermal recycle unit can be increased by a factor of three relative to a simple single-effect (i.e. without recycling) evaporation unit operating under the same thermal energy input conditions. The proposed unit operates under atmospheric conditions and below the liquid boiling point. It resembles a multi-tubular film absorber. Since the evaporation chamber casing is heated (as opposed to being cooled), it performs as an air-blown film evaporator. A laboratory scale unit was built and tested to produce distilled water from city mains water. Its thermal efficiency corresponded to a three-stage vacuum evaporator. The main advantages of the proposed design are: simple construction, low fixed capital investment costs, low operation/maintenance costs and its amenability to utilize low grade thermal or waste (e.g. wet steam, exhaust gas, hot fluid) energy resources.