A comparison of some existing feasibility studies for large dual-purpose plants reveals marked differences in the relationship between the electricity produced and the water desalination output. For example, in the study by Kaiser Engineering for Israel, an output of 200 MW is proposed with 100 mgpd desalination, whereas General Electric submitted a paper on the occasion of the Nuclex in Basle (September 1966) in which a power output of 300 MW with a desalination output of only u) mgpd was mentioned. In both cases there are provided light water-nuclear power plants with same data of living steam. However, in the case of General Electric the back pressure is particularly low, with 3 corres~ndingly hi&er turbine operating gradient. The outstanding differen= is that the specific heat consumption of the desalination plant in the GE case is twice as high as in the case of the study for Israel. In both cases, the results have been based on careful optimisation calculations and the question arises as to which factor determines the amount of kWh produced!'m' of desalted water and whether limiting conditions can be stated which will facilitate design calculations. The following considerations refer to back pressure plants where the steam throughput of the turbines is defined by the heat consumption of the water plant. The elect& power is thus a function of the specific heat consumption of the desalination process, on the one hand, and the specific heat consumption of electric power generation, on the other hand. The latter is hardly variable in the case of nuclear power stations of the light water moderated type, but in fossil fuel power sta:ions it depends very much on the initial condition of the steam. The following model analysis refers to 200,000 m3/d (approximately 50 mgpd), and with plants of such large size relatively high steam conditions are justified in every case.
A reduction of these conditions results only in very minor savings in plant costs and emphasis is always laid on keeping the back pressure power as high as possible by means of a great heat gradient for reasons of economy. This is because the heat consumption is in the region of only 950 kcal/kWh as compared with 2,250 kcal/kWh in a condensing power station.