Mechanical vapour recompression

The evaporation with mechanical vapour recompression corresponds to the ideal evaporation the vapour energy is completely used since no pressure graduation is required as it is the case for the multi-stage evaporation. Apart from the starting steam only electric energy is required to drive the compressor. 

4 Evaporation body, 1st, 2nd, 3rd, 4th stage, 5 Condenser, 6 Feedtank, 7 Condensate tank A Fresh product, B Concentrate, C Condensate, D Fresh steam, E Cooling water, F Ventilation 

At a working pressure of approximately 200 mbar, for example, theoretically a work of 2.0 kWh degree ton will be required. With a compression efficiency of 80% an electrical work of 2.5 kWh degree ton would have to be supplied. 

When working with a temperature increase of 6 degrees, with a corresponding design of the evaporator an electrical energy requirement of 15 kWh ton of water evaporation is required. 

(1962) Thermodynamik, Springer-Verlag, Berlin, Gottingen, Heidelberg. 

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King, R.J. (1984) Mechanical vapour recompression crystallizers. Chemical Engineering Progress, 80, (7), 63-69. 

Reverse osmosis and NF processes are, however, not suitable for treating high salinity produced waters, i.e., TDS > 40,000 mg/1, because of very high osmotic pressures. Thermal processes such as mechanical vapour recompression (MVR) are the most robust, require minimum pre-treatment, and can treat feed waters with TDS >100,000 mg/1. 

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