Norwegian?s groundbreaking vapour gas venture

Tanker owner Frontline has joined with fellow Norwegian company Venturie to develop a low-tech oil vapour recovery system. The system has recently undergone trials on Frontline?s suezmax tanker Front Granite. The companies say the trials have confirmed the system?s promise to offer a practical and cost effective solution to crude oil cargo loss through vapour emissions. Originally conceived by Venturie, the volatile organic compounds (VOC) vapour recovery system combines membrane and filter technology and is based on oil-gas absorption methodology. It uses existing pipework, thereby utilising a ship?s available structures. The VOC vapour recovery system reduces gas pressure by mimicking a phenomenon experienced in a bottle of champagne when it is opened. With champagne, the gas under pressure turns into bubbles when released. These are then slowly reabsorbed into the liquid. With the new VOC vapour recovery system, a membrane and filter unit installed in the oil-recycling pipe act as a bubble generator. These bubbles are mixed with oil pumped from the cargo tanks and the mixture is returned to the tanks via a recycling pipeline. Since oil and gas substances are the same, the cargo is inclined to reabsorb and merge the gas. This solves an environmental problem. But the principle benefit is that the cargo owner receives more oil after a tanker completes a voyage, particularly the lighter, more valuable components in the crude. The shipowner?s fleet therefore becomes more attractive to the charterer. Further trials are currently underway with another vapour recovery unit on a second Frontline vessel. More tests are also needed to solve emissions problems during loading. The VOC vapour recovery unit will then need to process larger quantities of gas. The likely solution will involve using the VOC vapour recovery unit in combination with changes in the loading procedures. Approval from a classification society is also needed. Commercial and environmental issues coincide Vapour emissions are very difficult to estimate accurately. This is due to the many variables such as volatility of the oil, temperature, movement, volume ratio of vapour to liquid and operating procedures. These factors together create the total vapour pressure. When this exceeds the pressure-vacuum valve setting, vapour is released into the atmosphere. The body for independent tanker owners, Intertanko, has recently joined with a consortium of oil majors and government bodies to compile a database in which the behaviour of crude oil during its transportation is recorded. The preliminary findings of this research programme, called the Crucogsa project, recognise that operational and accidental liquid oil pollution make up less than 0.5% of the quantities released as vapours in transit (excluding loading and discharging). A 98% laden VLCC carrying a crude oil cargo of average volatility (14 pounds per square inch absolute total vapour pressure), between West Africa and the US Gulf typically loses about 0.28% of the cargo in transit. This corresponds to a pint for every barrel of oil or a total of 700-800t on each voyage. Estimates on this basis put the total volatile gas vapour escaping from oil cargoes during sea transport at about 3.75 million tonnes per year. This represents an economic loss of over $700 million. By preventing this loss, crude oil tanker operators could provide cargo owners with an average extra cargo valued at over $450,000 per vessel per year (the larger the vessel, the larger this figure). They will also contribute to a cleaner environment. The Crucogsa study points to the insulating effect of double hull tankers. This helps preserve often high loading temperatures. This increases the risk of vapour emissions compared to single skin ships where the cargo is cooled by surrounding water. Consequently, when comparing total oil pollution from different types of tankers, the pre-MARPOL single skin tanker operating in hydrostatic balanced loading generates significantly less oil pollution than double hull newbuildings. Recovery alternatives Intertanko is examining alternative vapour recovery solutions to the Frontline-Venturie system. These include recovery and storage onboard or ashore. It has also suggested ways of reducing vapour emissions. These include changing the design of tanks, increasing ullage space and even painting decks white (to reflect heat). The Frontline-Venturie system will compete with a number of existing systems. Cool Sorption, for example, has a cold liquid absorption system based on absorption and condensation processes. Vapours are compressed to 3-6 bars and then washed with crude oil in a pre-absorber. This recovers hydrocarbons in the crude oil. Vapour from the pre-absorber is then washed with cold kerosene in an absorber and the resultant inert gases are vented. The kerosene itself is regenerated by distillation in a splitter. The concentrated vapours from the splitter are returned and mixed with the inlet vapour to the pre-absorber. The system is said to recover 90% of escaping crude oil vapours and have a projected payback time of seven to eight years. Hamworthy KSE is currently running a full-scale pilot test plant of its Moss VOC recovery system on the shuttle tanker Navion Viking. This prototype is designed to use the VOC recovered to feed the main engines. But it can also be re-injected into the crude oil cargo while discharging the ship. The Moss unit recovers hydrocarbon emissions from the tanks during loading via a dedicated condensation and separation process plant. It stores the liquefied VOCs in a separate tank on deck. The complete system, including a 400m3 storage tank, electric motors and heaters, weighs about 270t. It has exceeded its operational specifications. The basic weakness of these alternatives is that they can cost up to $10 million per unit, which compares with about $300,000 with the Frontline-Venturie system. The technology is also relatively complex, which can result in high maintenance costs. Future prospects Frontline and Venturie expect to complete trials and finalise their design by the end of this year. They anticipate starting production and marketing in the second quarter of 2002. The companies claim the system will reduce VOC emissions by a minimum of 80%. In light of this, Frontline?s technical director, Oscar Spieler, told The Motor Ship that several of the major players in the oil industry have expressed a keen interest in the system. Frontline?s confidence is such that it plans to fit a VOC vapour recovery unit to every ship in its 60-strong fleet as and when each vessel enters dry dock to undergo routine maintenance. Frontline has options on 20% of the stock of Venturie. Therefore if there is a widespread take-up of the system by other shipowners, thus eroding Frontline?s relative advantage in terms of attractiveness of its fleet to charterers, it can declare its option on the stock and share in the financial success of Venturie. Long-term objectives and action Every vessel carrying oil, petroleum products, solvents or any of dozens of other volatile flammable liquids to or from the USA is obliged to have a vapour recovery system. Similar obligations will soon apply in Europe. Legal requirements aside, most shipowners and harbour authorities worldwide recognise the importance of vapour recovery and of monitoring the correct operation of the system to ensure safety. Vapour recovery systems must meet the US Coast Guard approval requirements for marine vapour control systems. On top of that, the Clean Air Act amendments of November 15, 1990 require stringent control of the emission of VOCs to the atmosphere. This requirement has the effect of applying marine monitoring standards to shore-based installations. The purpose of these rules is to ensure that flammable vapours are handled safely and to prevent the discharge of detrimental gases to the environment. The result is that US law requires monitoring of the oxygen and hydrocarbon content of gas streams at various take-off points: on the ship itself; on the shore-based storage unit and on the transfer lines. The EU Directive will require broadly the same standards, although with differences of detail. Norway has already followed US standards and other countries are following suit. The term vapour recovery is somewhat misleading, since the vapour is not necessarily collected, contained and re-used. Frequently, recovered vapour is disposed of by flaring or by incineration. Recycling the VOC vapour is obviously a more cost-effective solution.