Optimal water cost from solar-powered multieffect distillation

This paper presents a short review of solar distillation followed by a description of conventional distillation methods and associated energy consumption. The paper then presents a system where solar energy is used to generate steam to drive a multieffect distillation plant. The system is optimized on the basis of minimum water cost . The analysis shows that enhancement of heat-transfer coefficients in the distillation section and increasing steam temperature from solar boiler result in lower water cost as well as increase the output per unit area of solar collectors. This study shows that a solar boiler producing saturated steam at 60 C in combination with an evaporator-condenser, developed and tested at this Laboratory, resulted in minimum water costs ranging from $1.40 to $3.70 per m3 for brackish water feed and $2.15 to $4.70 per m3 for seawater feed. At these conditions, the daily productivity per unit area of solar collectors ranged from 45 to 130 liters per m2. This study also shows that when the steam temperature was increased from 60 C to 88 C . the minimum water cost decreased from $2.15/m3 to $1.37/m3 for brackish water feed and from $3.60/m3 to $2.05/m3 for seawater feed. Also, at these conditions, the daily productivity per unit area of solar collector increased to 288 l/m2 for brackish water feed and to 151 l/m2 for seawater feed. These predicted values for the daily productivity are as much as seventy times the average productivity of simple solar stills at the assumed value of solar insolation.