PRESSURE RETARDED OSMOSIS

By: Matthew FenechSubject: Alternative Power GenerationLecturer: Ing.T. Darmanin

Ocean Technology

• Tidal Energy; Abundant but Untameable!

– Unpredictable

– Requires large control effort

• Calmer Waters are also abundant in energy

– Osmosis is the key!

– Dealing with forward osmosis (not reverse)

Theory of Operation• Osmotic Power, “A pressure that must be applied

to the solution (sea water) to just prevent osmotic flow”

• Harnessing energy where river freshwater and seawater meet

• Seawater is pumped into a pressure exchanger where the osmotic pressure is less than that of the freshwater pressure

Theory of Operation

• Freshwater(solvent) flows through the semi-permeable membrane towards the seawater (solute) chamber and increases the mass and volume (Δh)

– But Why? Water flows from a lower concentration to a higher concentration to equalize the concentration levels

– Semi-permeable inhibiting salts to pass through the fresh water side

• The head that is generated where generally heads of 120 - 270m (26Bar) are reached

• Compared to a waterfall head, for hydro-power generation (Fernanda Helfer, N/D)

History of Pressure Retarded Osmosis

• 1954, Pattle published free-energy acquisition via freshwater and saltwater mixing

• 1973, interest in technology reemerged due to oil crisis

• 1975, PRO was first invented by Prof. Sidney Loeb & Osmotic Heat Engine

• 2006, Starkraft (Norway) developed the first PRO powerplant generating 10KW

(Andrea Achilli, 2010)

Pressure Retarded Osmosis

Technology

• “The Energy Released from the mixing of freshwater with saltwater”

• Salinity gradient power is the energy created from the difference in salt concentration between two fluids, fresh & salt water.

• Applications:

– Standalone power plants

– Hybrid power plants

Pressure Retarded Osmosis

Technology

• Main Components

– Pumps

– Stacks of Semi-permeable membrane, Hollow Fibre Membranes, generating 4.4W/

– Pressure Exchanger, energy recovery system

– Piping Network

– Hydro-Turbine

– Generator

Geographical Power

Generation

(Irena, 2014)

Economics

• Membranes account up to 80% of capital costs

– EUR10/ -> EUR30/

– To be competitive (with other renewables) must be dropped down to EUR2/ -> EUR5

• For a 2MW plant, 2million of membranes are required

• Cost projections for 2020 EUR0.08/KWh to EUR0.15/KWhr

(Irena, 2014)

Drivers and

Barriers

+ Emission Free power generation

+ It is alternative and sustainable

‒ Biological Fouling due to microorganisms

‒ Excessive capital costs‒ Membrane lifetime, 5 years

‒ Ecological Aspects; River deviations

‒ Environmentalists unrest

Conclusion

• Infant technology

• Other Salinity Gradient Technology

– Reversed Electro Dialysis (RED)

– Osmotic Heat Engine

• Future trends…

Questions?

References

• Andrea Achilli, A. E. (2010). Pressure retarded osmosis: From the vision of Sidney Loeb to the first prototype. Nevada: Elsevier.

• Fernanda Helfer, C. L. (N/D). Osmotic Power with Pressure Retarded Osmosis: Theory, Performance and Trends – a Review. Southport.

• Irena. (2014). Salinity Gradient Energy, Technology Brief. IRENA (International Renewable Energy Agency).