Steam transformer as an inexpensive production system for desalinating water Original Research Article

An untypical seawater distillation project is now being engineered according to the special requirements of a power plant in Venezuela. The project consists of 5×20 t/h steam transformers, totalling 100 t/h production capacity. Each unit is fed with the second last steam bleeding from the steam turbine at 0.64 bar, and generates vapour at 0.25 bar equal to the turbine end pressure. The new vapour generated by the evaporation of seawater after control of the conductivity, is returned into the main steam flow to the turbine condenser. The quality of the vapour is guaranteed carrying less than 0.1 ppm residual salinity according to the (patented) SED technology. The seawater evaporates at 65°C as appropriate for the prevention of scaling, with the condensation of the steam extracted from the turbine at 88°C. The condensate is available as distillate suitable for make-up service to the cycle. The steam transformer is arranged with horizontal tubes identical to a typical MED effect, and the seawater is uniformly sprayed through nozzles, outside the tube bundle. No steam consumption is actually accounted for, being the energy consumption only consisting in the difference of the enthalpy of vapour feed at 0.65 bar(a) and returned at 0.24 bar(a), for the condensation. This technology is applicable with remarkable benefits whenever two steam flows are available at very low pressure, as appropriate for seawater evaporation. This possibility is often present in the steam cycles of the power generation plants.