Multiple effect stills produce hot (~95⁰C) WFI from RO feedwater. In each column feedwater is evaporated in a thin falling film heat exchanger. The steam is separated from water vapour and entrained impurities in a separation chamber, leaving the steam dry and pure, still at a high temperature and pressure. The residual feedwater passes to the next stage where the evaporation / separation process is repeated.
 In the first column, the feedwater is evaporated using plant steam at 6-8 barg or (occasionally) electrical heating. In subsequent stages it is heated using the pure steam from the previous stage. This condenses the pure steam to hot WFI, while simultaneously recovering much of its latent heat.
The whole process is repeated through further columns, each being an energy recovery step - the more stages, the more thermally efficient is the process.  Sensible heat left in the condensed WFI is recovered by using it to pre-heat the incoming feedwater. The last stage produces dry steam close to ambient; it is condensed to WFI by incoming feedwater, or by supplementary cooling.  A conductivity sensor controls sanitary output/divert valves

1. output ranges are typically 60 l/h-22m3/hr WFI;
2.  each model is offered with different numbers of effects, allowing optimal trade-off between capital costs and running efficiency.
3.  electrical (rather than plant steam) heating of the first stage is an option on smaller models.
4.  output may optionally be modulated with automatic adjustment of feedwater, plant steam and coolant.
5.  The pure steam from the first stage can be diverted  instead to other applications including self-sterilisation of the still
6.  Standard build is to cGMP, AISI316L with DTS heat exchangers for all WFI contact.
7.  Heat exchangers use a high number of fine-bore tubes to achieve an exceptionally large surface area
8.  Skids are complete with electrical cabinet, all instrumentation and Siemens PLC (or others as required)