Density differential desalination
View Patent ↗A system for desalinating water is disclosed. The system comprises a subsea reverse osmosis unit located beneath the surface of a body of water, a first liquid column comprising seawater, a second liquid column comprising desalinated water with a salinity less than seawater, and a brine discharge outlet. Due to the difference in density between the seawater and the desalinated water, the gravitational hydrostatic pressure of the first liquid column may be greater than the gravitational hydrostatic pressure of the second liquid column. At least a portion of the pressure difference for reverse osmosis desalination may be provided by the difference in gravitational hydrostatic pressure between the first liquid column and the second liquid column. A significant reduction in desalination energy consumption may be enabled by discharging the brine at an elevation lower than the maximum elevation of the first liquid column or the second liquid column.
1. A system for desalinating water comprising:
a pump located at or near a surface of a body of seawater;
a reverse osmosis membrane located in the body of seawater at an elevation below the pump;
a first pipe operably connected to transfer a seawater feed from the pump to the reverse osmosis membrane;
a second pipe in fluid communication with the reverse osmosis membrane to transfer water desalinated by the reverse osmosis membrane to an application located at or above the pump; wherein at least a portion of the first pipe and at least a portion of the second pipe are in the body of seawater;
wherein the system further comprises a lower pressure tank operably connected to the second pipe;
a discharging fluid displacement energy storage system; and
a pressure exchanger operably connected to the lower pressure tank and the discharging fluid displacement energy storage system such that desalinated water is transferred from the lower pressure tank to the application located at or above the pump and wherein the pressure exchanger is powered by the discharging fluid displacement energy storage system wherein the system disperses brine into the body of seawater.
2. The system of claim 1 wherein said water desalinated by the reverse osmosis membrane comprises freshwater.
3. The system of claim 1 wherein the body of seawater comprises an ocean, or a sea.
4. The system of claim 1 wherein said second pipe comprises a riser.
5. The system of claim 1 wherein the reverse osmosis membrane is greater than 1,000 meters below the pump.
6. The system of claim 1 wherein a desalination concentrate is discharged at an elevation within 50 meters of the elevation of the reverse osmosis membrane.
7. The system of claim 1 wherein a desalination concentrate is discharged at an elevation which at least one point is equal to or lower than the elevation of the reverse osmosis membrane.
8. The system of claim 1 wherein the seawater feed is pre-treated.
9. The system of claim 1 wherein the seawater feed comprises a feed wherein at least a portion of dissolved gases are removed.
10. The system of claim 1 wherein the system further comprises a discharging fluid displacement energy storage system to apply pressure to the seawater feed in the first pipe.
11. The system of claim 1 wherein the difference in gravitational hydrostatic pressure is greater than 5 Bar.
12. The system of claim 1 wherein the system is configured to supplement the difference in gravitational hydrostatic pressure by a reduction of the pressure of the second pipe.
13. An offshore desalination system for desalinating water comprising:
a pump located at or near a surface of a body of seawater;
a reverse osmosis membrane located in the body of seawater at an elevation below the pump;
a first pipe operably connected to transfer a seawater feed from the pump to the reverse osmosis membrane;
a second pipe in fluid communication with the reverse osmosis membrane to transfer water desalinated by the reverse osmosis membrane to an application located at or above the pump; wherein at least a portion of the first pipe and at least a portion of the second pipe are in the body of seawater; and
wherein all components of the system are offshore;
wherein the system further comprises a lower pressure tank operably connected to the second pipe;
a discharging fluid displacement energy storage system; and
a pressure exchanger operably connected to the lower pressure tank and the discharging fluid displacement energy storage system such that desalinated water is transferred from the lower pressure tank to the application located at or above the pump and wherein the pressure exchanger is powered by the discharging fluid displacement energy storage system wherein the system disperses brine into the body of seawater.