We propose a design of seawater desalination plant (SDP) consisting of two vertical shafts at underground. One shaft is designed for producing fresh water, in which the reverse osmosis modules (ROMs) are installed several hundred meters deep. The other shaft is used to reserve the brine rejected from the ROMs. The pressure required to force the seawater penetrate through the ROMs is provided by the hydrostatic pressure of seawater of 550m deep or more. Consequently, the main energy consumption of the SDP is the power required to pump the fresh water up to the ground. Therefore, if coupled with other sporadic energy consumptions, the power consumption per cubic meter of fresh water produced is approximately 2KWh/m3, which can be generated by, for instances, wind turbines or photovoltaic panels on the ground. In the case where the generated brine can be fully recovered, the entire SDP is a non-polluted freshwater production facility, which is quite in line with today’s energy and environmental requirements. （應力所陳發林教授提供）
Figure 1. The schematic illustration for the vertical shaft desalination plant (or VSDP). In the figure, A is the horizontal channel to introduce seawater into the vertical shaft, B is the seawater inlet filter, C is the freshwater pump, D is the brine pump. Moreover, the depth of the fresh water is h=550m, the seawater inlet depth is H which shall be 600m plus the height of ROMs, the brine level is d2=10m underground, the pipe length on the ground is d1=10m.