CO2 Emissions in kgs per kilolitre
| Tankering from the Ord* 1.77 |  |
| Desalination 4.46 |  |
Due to the abundance of natural gas in the Kimberley region we intend to power the ships with LNG in the event that the combined Tidal Power/Hydrogen innovation does not prove to be viable. Preliminary discussions with LNG developers indicate LNG to be an economic and technically feasible fuel for the ships proposed.
As with all motorised forms of transport, shipping has in recent years become extremely more efficient in the amount of energy it needs to do its job. Some of the efficiency is by better design:
- more fuel efficient engines
- more fuel efficient hull shapes
- more fuel efficient hull coatings
- etc., etc., etc.
Other efficiencies can be achieved by using larger ships. For example the 516,000 DWT "Esso Atlantic" at 211 tons per day HFO (Clarkson's, 'The Tanker Register', 1986) uses only 20% more fuel than the 254,000 DWT "Apollo Sun' at 175 tons per day (op cit). Both ships were built within a year of each other and both cruise at 15.65 knots. The largest ship built to date is the 564,650 DWT "Knock Nevis", however a number of dry docks have been purpose built to build 1,000,000 DWT ships. The advantage of using such large ships is that an increase in dimensions of approximately 20% results in a doubling of carrying capacity and a reduction in fuel required per tonne of cargo of approximately 40%. From the 1960's there was a four fold increase in the largest size ships constructed and the only limiting factor known for increasing ship size even further remains as demand, subject to the fact that such ships contemplated need only travel in deep water and do not need to enter a port.
"Knock Nevis"
Other efficiencies can be gained by going slower. Water unlike oil, iron ore or other cargoes is not valuable for its bulk, so the optimum economic speed to transport water is much lower. An example is the newbuild design by Tsuneishi Shipbuilding (R, Scott ,Standard Ship Designs, Fairplay 1985) for a 54,000 DWT bulker that goes from 41 tons per day at 15.5 knots to 24.5 tons per day at 13.5 knots. This is a 40% reduction in fuel consumption per day or a 31% reduction in total fuel used by slowing down 13%.
Another example is the 300,000 DWT "Iran Delvar" which goes from 87 tpd at 15.5 knots to 59 tpd at 13.5 knots. This is a 32% reduction in fuel consumption per day or a 22% reduction in fuel used by slowing down 13%. Consequently by allowing the ship to go slow, we can save significant amounts of fuel.
The SEDO (Sustainable Energy Development Office) in the KEP report (appendix 11) calculated (based on the information supplied by Clough**) that 511,000 kl of bunker fuel is required to power ships to deliver 200 million m3 of water in 1 year.
Our calculations are as follows:
- The 310,000 DWT "Tijuca" O/O uses 74 tpd at 13.5 knots
- (refer Clarkson's 1986 'Bulk Carrier Register')
- Double size ie 1.2 times gives 620,000 DWT at 89 tpd at 13.5 knots
- Double size ie 1.2 times gives 1,240,000 DWT at 107 tpd at 13.5 knots
- 3,400 nautical miles divided by 324 (ie 13.5 knots) = 10.5 days steaming
- 10.5 times 107 = 1,123 tons for delivery of 1 million m3
- 200 times 1,123 = 224,600 tons
Accordingly the SEDO has over allowed for energy usage by more than double.
Based on the conversion rates of bunker fuel to CO2 emissions used by SEDO the CO2 emissions for the ocean journey from the Ord to Perth calculate to be 3.36 kgs per kilolitre. Blending with slightly too salty water from say the Wellington dam would reduce the CO2 emissions to (50/95) 0.526 times 3.36 ie 1.77 kg's CO2 per kilolitre although some additional energy would be required for land based pumping of water.
If we are serious about saving the planet from the environmental harm caused by fossil fuels then we could investigate doubling of ship size again (40% energy saving) and slowing them down (approximately 22% reduction in total fuel used for every 13% of speed reduced). Transporting water from the Kimberley's to Perth using a tiny fraction of the energy required by desalination is easily possible.
Tankering is without doubt the most energy efficient water supply option for Perth.
* Ocean transport of water from the Ord that can then be blended with water from the Wellington Dam. This excludes an amount of energy required for land based pumping at either end which needs to be further investigated.
** SEDO in Appendix 11 indicated that the data provided by Clough on energy inputs was different to other estimates they had and this could 'be due to a transcribing error'.
