SEAWATER REVERSE OSMOSIS COUPLED WITH POWER GENERATION USING PRESSURE RETARDED OSMOSIS
Publication Date: 2013-Mar-19
The IP.com Prior Art Database
The invention concerns reverse osmosis of seawater and reducing power consumption thereof. The invention is a hybrid seawater reverse osmosis (SWRO) - pressure retarded osmosis (PRO) system that will simultaneously generate potable water at reduced energy requirement while consuming the SWRO concentrate as well as effluent wastewater streams. A PRO unit is installed in tandem with the SWRO unit, and operates on the concentrate stream from SWRO, being roughly twice as concentrated in salts as seawater, as the high salinity stream, while secondary effluent from a wastewater treatment plant is the low salinity stream. The output from the PRO device is a mixed stream of moderate salinity that has a high hydraulic pressure, which is mixed with the pressurized seawater at the SWRO inlet. The invention achieves seawater desalination at much lower energy use than current systems. Further, using an ERD to transfer energy from PRO to SWRO feed should be more efficient than using a hydroturbine to generate electricity and will enable using a smaller high pressure pump for the RO plant.
The invention concerns reverse osmosis of seawater and reducing power consumption thereof. Because of the high pressures involved in seawater desalination, it will usually be more expensive to generate potable water from seawater than from a low salinity water source. Today many urban communities meet some of their potable water requirements through reverse osmosis of seawater, yet at the same time, disposing at sea low salinity brackish water in the form of treated secondary effluent ("toilet water"). Secondary effluent water is recycled, almost entirely for non-potable use by industry. The fundamental problem faced by water recyclers is that reclaimed wastewater will not or cannot be used as potable water, while desalinated water can. Although expensive reclamation technology will be increasingly employed to create more water for "indirect potable" reuse, desalination will be preferred for potable water, and large volumes of low salinity wastewater will continue to go into the sea. The invention intends to use the low salinity wastewater stream to reduce the energy requirement of desalination rather than to use it to create potable or indirectly potable water.
Seawater reverse osmosis (SWRO) is a very well-known process and there are many suppliers of this technology, as disclosed in US patent no. 3,906,250. Using seawater + river water to generate electricity through pressure retarded osmosis (PRO) has been considered (see WO 02/13955A1), which is however, not very successful because of the relatively low osmotic pressure difference between the two streams, with consequent low driving force for transport and large membrane area requirement. In US 2008/0230376A1, which proposes to use SWRO followed by a salinity gradient power unit, the salinity gradient power unit (either PRO or reverse electrodialysis) generates electricity and the electricity is used as an energy source for the desalination plant. There is no special synergy between the SWRO and salinity gradient power units. The invention proposes an integrated energy recovery scheme by directly coupling the pressure retarded osmosis with the sea water reverse osmosis in a more efficient configuration.
Seawater reverse osmosis coupled with power generation using pressure retarded osmosis is disclosed further with reference to the following drawing:
Figure 1 shows the power generation scheme using pressure retarded osmosis, coupling seawater reverse osmosis with effluent wastewater.
The invention is a hybrid seawater reverse osmosis (SWRO) - pressure retarded osmosis (PRO) system that will simultaneously generate potable water at reduced energy requirement while consuming the SWRO concentrate as well as effluent wastewater streams, as shown in Fig. 1. A PRO unit follows the SWRO unit, and operates on the concentrate stream from SWRO, being roughly twice as concen...