A new type of seawater desalination plants using solar energy

This paper presents a new water desalination process. The basic unit operation in this process is to use solar energy for heating of an air stream and in the second step to add seawater into the hot air in order to humidify it. It follows a cooling step of the humid air providing potable water as a condensate. On the base of this solar desalination process, a desalination plant is predicted and designed to provide 10 m(3) of potable water daily. The main feature of the new process is the stepwise loading of air by vapour. The process consists of several steps for air heating, each followed by a humidification stage. This manner of operating makes it possible to obtain high vapour concentration in the air flow, thus reducing the air flow rate through the plant. The power necessary for air blower and the size of pipes and other equipment decrease. Experimental and computational work has been conducted to realise the application of that new desalination idea. New collectors for solar heating of air and humidifying equipment to moisten that heated air are developed. Heat exchanger for recovery of water by dehumidifying of the humid air could be designed and tested. Using this new equipment, a small pilot plant could be constructed and run to test the new process under different operating conditions. The results of these tests will be presented. A dynamic simulation program to predict, to optimise and to design solar desalination plants according to the new process has been developed. The program includes also an economic part, which enables the optimisation of the process under consideration of thermodynamic aspects as well as from the economic point of view. Applying the dynamic simulation program and the developed economic optimisation procedure, it is possible to design and to optimise any desired plant using, the new process. As a demonstration, a plant with a capacity of 10 m(3) of potable water per day is designed and optimised-according the developed planning and optimisation procedure. For this plant the size and the optimum operating conditions of each kind of equipment are determined. The process flow sheet of this desalination plant is provided. The required investment costs are determined under variation of some plant design parameter.