ZLD evaporation-crystallization plant in the power industry

Environmental considerations as well as the economical benefits of water re-use have raised the interest of the power industry to improve zero-liquid-discharge technologies for the treatment of effluents from power plants, Typical streams to be treated are the effluents from the water demineralization system, first rain water and various blow-down. Such streams are diluted saline waters containing chlorides, sulphates, nitrates and carbonates, usually saturated in CaSO4. Due to their nature, evaporative crystallization of such brines leads to heavy encrustation problems. Scope of such ZLD units is to recover high quality process condensate and separated solids of disposable quality satisfying at the same lime the stringent requirements of a power plant in terms of system reliability and availability. GEA has developed a concept for modular systems with a special approach in order to obtain very long operating cycles between consequent washouts, acting both on the process design (seen as a real crystallization system) and on the mechanical design of the equipment itself. This paper describes the main design criteria, comparing the expectations with the operating behaviour of a plant designed accordingly, that is on stream successfully since two years.