The Exxon Valdez oil spill and subsequent legislative pressure for tankers with double hulls and double sides has overshadowed another legislative measure to reduce pollution from tankers that has not been received well in parts of the shipping industry.
Latest proposals being put together by the U.S. Coast Guard are designed to tackle the problem of inert and hydrocarbon gases vented to the atmosphere when a tanker loads a cargo of crude oil. Some are "greenhouse" gases.
TODAY'S PRACTICE
For many years tankers have been obliged to fill empty crude oil tanks with inert gases to prevent a buildup of dangerous accumulations of hydrocarbon gases from the residue of previous cargoes.
Scrubbed C02 from the tanker's boilers is the most cost effective way of providing substantial volumes of inert gas required for a large tanker.
When the tanker arrives at the loading terminal inert gases are vented to the atmosphere as the tanks fill with crude oil. At the same time hydrocarbon gases are given off from the crude oil being loaded. This too is vented to the atmosphere throughout the loading operation.
John Dunn, managing director of Papachristidis Ship Management Services, London, is a staunch opponent of proposals to control such emissions. He claims that reducing atmospheric pollution from ships may mean trading a minor environmental gain for a major increase in tanker accident risks.
The proposed U.S. Coast Guard regulations would require construction of onshore vapor emission control systems (VECS) that would move inert gases by pipeline to a processing plant. Each onshore plant would cost about $7 million, while tanker conversions would cost about $1 million/ship.
Dunn says the pipeline would have to draw off gas from a very large crude carrier at a rate of 25,000 cu m/hr. If problems developed ashore, an instantaneous pressure pulse running back to the vessel could tear the ship apart.
"An incident of this type would certainly mean severe structural damage," Dunn said. "The deck may be lifted or tanks ruptured, causing serious pollution.
"While a multiline VECS arrangement would reduce the pressure pulse risk, we are still left with the inherent safety hazards posed by static sparks and fire."
The U.S. and a number of other countries have persuaded the International Maritime Organization to develop VECS requirements for its members from more than 130 nations.
SHIPOWNERS' COMPLIANCE
Dunn says if these plans proceed there could be more accidents at tanker terminals in exchange for a negligible reduction in air pollution and huge bills for shipowners and port authorities.
However, he takes a skeptical view of the likelihood of governments and port authorities around the world building the gas reception plants because many of them have failed to honor their international obligations to build shore facilities to receive oil and chemical wastes.
"Once again compliance may be left to the shipowners," Dunn said. "All they will get for their money is the greater risk of an accident at the terminal."
Copyright 1990 Oil & Gas Journal. All Rights Reserved.
