The cost of delivering deep-sea-cold-water using pipes has always been notoriously high, and commercial development has failed.
Deep sea cold water is valuable; just a few litres per second is sufficient to help generate enough power for one household.
What about hoses?
Hoses are an attractive prospect because they have numerous physical advantages that mean that they are less costly than pipes.
Material, transport, and installation costs are all lower than pipes.
How can hoses be used?
The turbo-pump comprises a hydro-turbine joined to a pump through a common shaft. Seawater drives the turbine generating shaft power, and that power is transferred to the pump through the shaft.
A turbo-pump must use two hoses, one to deliver water to the turbine and one to deliver water from the pump.
An electric pump is required to drive seawater to the turbine.
The turbo-pump can operate in deep water without any sophisticated technology, hence the attraction.
Why use a turbo-pump and two large bore hoses and not a hydraulic motor and pump?
The wastewater can balance the head on the system on or offshore because it is the driving fluid.
The energy used to drive up the fluid created potential energy in the water, and this energy is recovered and used for the most part to drive the turbine side of the turbo-pump.
This means improved efficiency.
- Low-pressure, low-cost hoses are possible.
- PVC. can have a very long operating life in seawater, PVC. is low cost and punctures are very easy to fix.
- Remote-site friendly as the system is easy to transport, assemble and install.
- Low risk implementation and a low risk of petty but costly failures due to the low operating pressure and ease of assembly.
- Large bore hoses can run at a very low pressure on both sides of the turbo-pump and that can result in long operating lifetimes with little maintenance.
- Hydraulic motors are more sensitive and complex than the turbo-pump, and thus they may more readily fail or may more likely require more regular maintenance.
- High pressure hoses are more likely to leak or burst at the coupling points.
- The turbo-pump uses larger bore bearings at relatively low rpm for the shaft, thus they are less susceptible to fatigue and can be expected to have relatively long bearing lifetimes.
- Larger turbo-pump parts mean less fatigue and corrosion risk, and therefore, a longer service life is predicted.
- Two large bore hoses offer greater pumping efficiency due to the wastewater head, and its potential energy; the energy used to bring the water up is mostly recovered.
- Option to release deep sea-cold-water into the photic zone to create plankton blooms, offsetting Co2, and boosting marine life.
- Option to release wastewater well below the photic zone, lowering both the thermal impact, and the marine life impact, ideal for genuinely sensitive areas like the Great barrier reef.
- Option to release waste warm water below the photic zone where it can then rise due to its temperature difference, thereby causing an additional plankton bloom.
Lower costs and higher system efficiencies.
What with the low cost, and ease of installation, larger diameter hoses are much less costly than smaller diameter pipes. Larger diameters mean lower pressure drops, and higher flow rates, for a lower cost, and this is an exceedingly desirable outcome for power applications where efficiency is so important.
The future of turbo-pumps.
We expect to move from centrifugal pumps to propeller pumps as the water delivery requirement increases. OTEC water delivery is a high volume, low head exercise. Centrifugal pumps can work into the MW category and then we expect to see propeller pumps take over.
The largest propeller pump in the World can pump 60 m3 per second and that is enough for 30 MW of traditional OTEC and 180MW (or more) of Hybrid OTEC.
‘Geared’ sea-water turbo-pumps are certainly possible. A ‘geared’ turbo-pump has a smaller turbine / motor side of the turbo-pump and can therefore use lower bore hose including hydraulic hose.
It is possible that the system can be rearranged to at least partially include a more traditional hydraulic system, and this is covered in principle by some of our granted patents.
Any of these methods can provide a cost effective solution with pros and cons to each. Time will tell which method proves to be the most popular.