High-Efficiency Osmotic Power Process

An improved process design is shown in Figure 3. It uses a PX energy recovery device. The high-pressure pump is eliminated and only a portion of the dilute water from the membranes passes through the turbine. The rest of the high-pressure dilute water flows to the PX device where it is replaced with salt water. This exchange occurs at up to 98% efficiency with no energy consumption and without significant reduction of the pressure of the stream. A circulation pump moves the pressurized salt water and dilute water in a loop through the membranes and the PX device. Because the circulation pump does not pressurize the stream, it consumes very little energy.

Figure 3 – High-efficiency Osmotic Power Process with PX Energy Recovery Device

After exchanging the dilute water with salt water at high-pressure, the spent dilute water is discharged from the PX device at low-pressure. In addition to performing this exchange with very high efficiency – up to 96% – the PX device serves as a seal. High-pressure in the loop is separated from the low-pressure seawater entering the process and low-pressure dilute water leaving the process by seals within the PX device. As a result, nearly all of the water that enters the high-pressure loop through the membranes leaves through the turbine. Therefore, incorporation of PX devices solves both the problems identified in the discussion of Figure 2. Specifically, PX devices allow replacement of the high-pressure pump with a low-energy circulation pump and limit the flow through the turbine to just that necessary to produce net power, making the process more efficient. They also effectively keep the salinity in the high-pressure loop high, increasing the driving force for osmotic power production.

Copyright 2009 Osmotic Power Inc.