A reverse osmosis desalination unit

A reverse osmosis desalination unit is proposed to desalinate seawater. The pressure required to overcome the osmotic pressure and initiate the reverse osmotic process is provided by utilizing the mechanical potential energy results from the difference in heads between a high level column of seawater and a low level column of purified water. A mathematical model is proposed to simulate the proposed unit behavior under steady and transient conditions. The effect of different operating and design conditions on the purified water production rate is investigated.

A reverse osmosis desalination unit is proposed to desalinate seawater. The pressure required to overcome the osmotic pressure and initiate the reverse osmotic process is provided by utilizing the mechanical potential energy results from the difference in heads between a high level column H of seawater and a low level column h of purified water. It is found that the unit production rate Nw is linearly proportional to the saline water head H and as the height of the purified water head h increases, the unit production rate decreases. The minimum depth H required to initiate the desalination process increases as h increases. Also, it is found that the specific gravity ratio r has insignificant effect on the unit production rate Nw especially at small saline water head H. The unit produces about 0.1 kg/m2s of purified water for H = 2000 m using membranes of permeability Aw = 5×10–4 .kg/m2s.atm. The unit production rate is linearly proportional to Aw and may be increased by using membranes of larger permeability. The ratio of the power consumption of the . modified RO unit Wm to the power consumption . of the classical RO unit Wc is derived. From the derived ratio, it is found that the modified unit consumes less power as compared to the consumption of the classical unit as the ratios r and h/H increase. For fixed h, here is an optimum insertion depth H at which the net financial gain is maximum. The location of this optimum H depends on h, r and k. It is clear that the optimum H increases as h increases. Also, the maximum . gain G/F increases as h increases due to the reduction in pumping cost. The optimum insertion depth H is independent on the membrane property Aw independent on k if k is not so small.