Recovering oil from sunken vessels

	“Prestige” oil on the Galician coastline.

In the aftermath of the “Prestige” disaster, recovering oil cargoes from sunken vessels has come into focus. Recently, the first trials using shuttle bags from the wreck on the seabed 3,700 metres below surface was successful and 250 tonnes of oil were removed. The question now is whether ship design could be improved to prevent pollution from wrecks on the seabed.

Stricter rules, enforced inspections, improved technology and more quality aware shipowners and charterers will prevent many accidents, but not all. Ships will still collide, run aground and catch fire. In most cases, accidents occur in congested coastal areas, where the environmental consequences often are significant.
Till now, development and improvement of environmental protection resources have been focused on the recovering of oil and pollutants from the sea surface and from beaches. Recovering oil from wrecks are still time-consuming, expensive and in some cases risky.
The Spanish oil company Repsol has been given the responsibility to remove the remaining 14,000 tons of oil in the “Prestige” wreck. Together with an international group of companies, Repsol is using a gravity extraction process that never has been used at such depths. A 70-centimetre hole is drilled into the tank and a valve is inserted. A shuttle bag is connected to the valve. When full, the bag is released and flows to the surface, guided by ROV’s. The work to remove the remaining oil cargo will commence in the spring 2004.
Following the “Erika” and the “Prestige” disasters, new methods to improve ship design to facilitate the recovery of oil from cargo and bunker tanks have been presented.

The JLMD System
One is the JLMD System, developed by the French inventor Jean-Luc Dabi. Based on the Archimedes principle and a pre-installed system in the vessel, oil remaining in the wreck can be removed effectively and safe. Removing the oil from the “Erika” cargo tanks took eight months.
According to JLMD, the operation would have taken a week if their system had been installed on the vessel.
The JLMD system is installed in all four corners of the lateral compartments. Port and starboard tanks are connected by bulkhead valves. The design provides high and low point irrespective of the wreck’s position on the seabed.
An underwater robot is used to connect hoses to cubic boxes of 50 centimetre dimensions at low and high points of the sunken ship. The boxes contain two valves attached to two 20 centimetre diameter pipes. One extends to the bottom of the tank and one opens below the tank top. Seawater under hydrostatic pressure then propels the oil through extraction hoses to a surface vessel.
The JLMD system can be installed on all tankers. According to the company, the cost is less than one per cent of a tanker’s operating costs.

Another patented system
An aggressive marketing campaign has triggered interest. Recently Qatar Navigation confirmed orders for installation of the JLMD system on two tankers and Qatar Shipping has shown interest in fitting the system to six new vessels.
A similar system has been developed and patented by the Swedish inventor Sune Dahlström. Although based on the same principle, this system doesn't require any equipment installation on the tanker. Two holes are drilled in the tank, one placed high and one low. To reduce the viscosity of the oil, steam is pressed through a hose connected to the lower hole. If needed, a vacuum pump could be connected to the evacuation hose.
Efficient methods for recovery of oil from sunken vessels will clearly reduce pollution and costs for the clean-up operations after an accident. The always present question “who should pay for the investment?” however still remains to be solved.

//Rolf P. Nilsson

Back to SSG 20, 31 October