Steam Driven Crystallizer Systems
The crystallization process has long been used in the manufacture of commodity chemicals such as sodium chloride and sodium sulphate. However, unlike commodity production where only one salt precipitates, typical reduction of industrial waste to dryness involves crystallizing multiple salts. This type of mixed salt crystallizer requires significantly different design parameters to avoid problems such as severe foaming and rapid scaling. Furthermore, mixed salt solutions have significantly high boiling point rises requiring detailed attention to design parameters when sizing vapour compressors. Innovative filtering techniques have been developed to reduce the cost of smaller crystallizer systems.
Crystallizers typically have an external heater in which the solution is heated by steam in the shell. The heated solution then flashes into a large vessel called a vapor body. The heater tubes are flooded, with boiling water in the tubes suppressed by the liquid elevation in the vapor body (submergence). A slipstream is drawn off into a solids separation device (a centrifuge) and crystals are removed. Different energy sources are used.
Steam Driven Crystallizer with Thermo-compressor
Steam enters the thermo-compressor and a portion of the vapor that is evaporated in the vapor body is recycled to the suction of the thermo-compressor. Then the steam enters the heater shell. This configuration typically results in 20 – 30% reduction in steam usage. A condenser is required to condense the remainder of the vapor that is not recycled to the thermo-compressor.
Use of renewable energy for the stated process scheme
Concentrated Solar Panel (CSP) technology can be used for steam production for the Steam Driven Crystallizer as well as molten salt storage to operate the plant during night time. For the realization of a large scale plant, the use of CSP can be evaluated in case there is no waste heat available to operate the Steam Driven Crystallizer.
The electricity needed can be generated by photovoltaic (PV) solar panels.
Application of Zero Liquid Discharge (ZLD)
ZLD can be used pretty much anywhere in industrial environments where disposal into rivers, ground or sea is not permitted for environmental / ecological reasons.
Some common ZLD workflows include:
- Treatment of Produced Water from Oilfields
- Treatment of Industrial Effluents
- Treatment of Effluent from Power Plants