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Volume 15, Number 4July/August 1964

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Cool, Condense and Ship

A surplus of gas was available in Saudi Arabia, but a feasible method of transportation was not…

Written by Homer Dixon

In a small home on the Japanese island of Shikoku not long ago, Noriko Ieda, a housewife, turned on a gas jet, touched a match to it and began to prepare the evening meal for her family.

It was, on the surface, a most unremarkable scene, one common to households around the world. Yet to Noriko Ieda and to a group of engineers thousands of miles away, the scene had a particular significance. To Noriko Ieda it meant the end of a bothersome chore—cooking meals over a slow, charcoal-fueled habachi burner. To the engineers it meant the successful completion of more than ten years of expensive, complicated research on a process that today links the rich deposits of gas in Saudi Arabia's oil fields with the kitchens and factories of Japan: refrigeration of liquefied petroleum gas (LP Gas). In most advanced regions of the world today gas is nearly as common as fresh air. It reaches industry and homes even in the most remote areas' and where readily available challenges and has even supplanted coal and wood as basic fuels. Until recently, however, gas was not readily available in many countries. The gap between source and consumer was too large to bridge, or the expense of bridging it too great. Great stretches of land and sea, for example, separate crowded Japan, where a soaring economy has created an urgent demand for industrial and domestic fuels, from Saudi Arabia, where vast supplies of gas are much greater than presently needed there.

The most logical method of transportation was, of course, ships. But ten years ago, when such firms as the Arabian American Oil Company (Aramco) began to concentrate on the problem, there were serious obstacles to such shipment. In the first place, any container strong enough to hold LP Gas under sufficient pressure to keep it liquid at normal temperatures would be prohibitively expensive. Moreover, the walls of such containers would have to be so thick that ships of enormous size would be required to carry them. Since transporting LP Gas in liquid form at normal temperatures simply did not make economic sense, engineers began to seek another solution. Why not, they asked themselves, cool and condense the gas into liquid form, keep it refrigerated until it reaches its destination, and then vaporize it there into its original gaseous state?

The advantages of this approach were obvious. A ship carrying 100,000 barrels of gas in its condensed form would actually be carrying 150,000,000 cubic feet of vapor, enough to supply 350,000,000,000 BTU's (British Thermal Units) of heat, roughly the equivalent of 12,000 tons of coal. In short, shipment of a refrigerated liquid would involve only a fraction of the expenditure required for shipment of LP Gas under high pressure at normal temperatures.

Between the idea and its realization, however, stood formidable barriers. Aramco customers—other oil companies—had to first determine the world market potential. A price structure and tentative product specifications had to be set. Enormous amounts of data on production, processing and transportation had to be compiled and evaluated to determine if ocean shipment of refrigerated gas were economically feasible. Engineers had to develop the various processing methods—and determine their costs—that could be used to produce, according to required standards of purity, finished gas from the raw gas available in Saudi Arabia, and also to evaluate the problems involved in cooling and liquefying the processed gas and in storing and handling it. Owner companies simultaneously had to study the problems of transporting it by ocean-going tankers and of storing it and handling it again in marketing areas.

As the project got under way, engineers decided to concentrate their studies on the butane and propane portions of the available gas because of the problems foreseen if other portions—ethane or methane, for example—were used too. To liquefy petroleum gases for ocean shipment at atmospheric pressure it is necessary to lower their temperatures, and the lighter the gas the colder the temperature must be. Butane, for example, has to be cooled to 31°F., propane to -44°F., ethane to -128°F., and methane down to -259°F. But it happens that the lower the temperatures required to liquefy a given gas, the greater the number of technical problems that must be faced in the cooling and subsequent transportation of that gas by refrigerated ship. Thus, the handling of butane and propane liquefied petroleum gases is relatively easier than, say, that of ethane or methane.

Even with butane and propane, however, the technical problems were still great, problems such as the development of special metals strong enough to stand the stresses of temperatures as low as -50°F.

Engineers responsible for selecting the steel that would go into the tanks and pipes in which LP Gas would be processed, moved, stored and transported had in mind constantly two events that underlined the importance of their search:

  —  On January 16, 1943, the brand-new tanker Schenectady, sitting empty in calm water at a Boston dock, suddenly and violently broke in two. Investigators found that the vessel had been constructed of steel of approved quality, had been constructed according to an accepted design and had been competently built. They found too that there were no external factors that could have caused the fracture.

  —  On Oct. 20, 1944, in Cleveland, a cylindrical pressure vessel designed to store liquid methane at-260°F. ruptured. According to the American Society for Testing Material there was a rumble followed by fire and an explosion. Twenty minutes later an adjacent tank failed. Liquid gas flowed into neighborhood sewers, spreading the holocaust which killed 128 people and caused nearly $7,000,000 damage. Investigators found that there had been no initial explosion in the methane tank itself.

Both events highlight what metallurgists call "brittle fracture," the tendency of metal to fail at extremely low temperatures. Studies showed that nearly 300 ships in World War II experienced brittle fracture and that there were numerous instances of metal in ships, storage tanks, pipelines, bridges, stacks and even power shovel booms failing without warning and often without explanation.

Engineers assigned to the LP Gas project knew that brittle fracture at such installations as Aramco's Ras Tanura Refinery or Marine Terminal, where major elements of the new LP Gas plants would be built, could be catastrophic. But they knew too that there were also economic factors to be considered. If, for example, refrigerated tanks and pipelines were built of nickel alloy steel, there would be no question that they would be safe, but the cost would be double. Thus their challenge was to find a metal that would be safe, yet economical.

In beginning their quest the engineers and metallurgists, much like lawyers examining case precedents, studied the histories of such failures as those in Boston and Cleveland. More than 300 such cases were carefully investigated and on the basis of those findings tests were begun on samples of specially-made carbon steel. Studies had disclosed that 15 foot-pounds of energy absorption at the intended service temperature was a reasonable level of safety, but Aramco set 20 foot-pounds as the minimum requirement and began to test the samples against this standard.

One test—called the Charpy V-Notch test—subjected a sample of steel, which had been chilled by dry ice in alcohol to the specified temperature, to a blow from a pendulum at a point where a notch had been made in the metal. This test determines the amount of energy metal will absorb before breaking and discloses the tendency toward behaving in a brittle fashion. Another test was conducted to evaluate the metal's reaction, again at the specified temperature, to the explosive effects of a charge of TNT.

Out of the testing came, eventually, the metal that was needed—a low-carbon, high-manganese steel sufficiently ductile to resist brittle fracture yet economically acceptable for use in the huge quantities needed for the complex of tanks, pipelines, vessels, and heat exchangers envisioned for the Ras Tanura Refinery.

Such pioneering work, along with development of insulation materials, loading methods and designs for the vital special tankers, required hundreds of thousands of hours of study and experiment before construction could even begin. But in 1959, some six years after concentrated work on the project got under way, the decision was made to construct an LP Gas plant in Aramco's Ras Tanura Refinery.

Initial plans called for the installation of facilities at Ras Tanura which could produce about 2,000 barrels a day of butane and 1,500 barrels a day of propane. Those gases, extracted from crude oil, were to be then "dried," to prevent the formation of ice when cooled later, and then pumped some seven miles to the Aramco Marine Terminal area at Ras Tanura where refrigeration equipment and other low temperature facilities were to be located.

Even as construction got under way problems continued to crop up but for each, regardless of its magnitude, specialists found an answer and the project moved toward completion.

It was realized on December 6, 1961, with the shipment to Japan of 50,000 barrels of butane and propane as refrigerated liquefied petroleum gas, the first large commercial shipment of such gases in this form. On that day the oil industry also chalked up two other "firsts." The new Aramco plant at Ras Tanura's Marine Terminal was the first facility ever designed and constructed specifically to refrigerate propane and butane for shipment by ocean tanker. The Japanese tanker, Gohshu Maru, which carried the chilled liquid to Japan, was the first ship ever designed and built for the express purpose of carrying refrigerated LP Gas.

When the new 46,000 deadweight-ton tanker cleared Berth 6 at the terminal's North Pier, she was carrying, in five insulated tanks not unlike giant Thermos bottles, 30,000 barrels of refrigerated propane and 20,000 barrels of refrigerated butane to be consumed in Japan as domestic and industrial fuel, and as a raw material in petrochemical processes.

Meanwhile, some two months prior to the first successful shipment, Aramco management had approved a significant expansion of the company's refrigerated LP Gas facilities—from an existing capacity of 3,500 barrels a day of propane and butane to 12,000 barrels.

Because the enlargement would require larger supplies of gas, the company had to go approximately 70 miles inland to the oil-producing center of Abqaiq and there tap the large quantities of raw gas produced in association with crude oil. The raw gas is separated from crude oil and is available for other uses. At Abqaiq, installations were designed which would remove the so-called "heart-cut" (the middle range of a product being distilled) of propane and butane from some of the raw gas and send it via pipeline to Ras Tanura. The installations included two fractionating columns (in which the gases are separated)—one of which is a seven-story-high deethanizer tower (in which ethane and lighter gases are removed) over 11 feet in diameter, with walls about 2⅓ inches thick and weighing 150 tons.

The lighter and heavier gases, left over after the propane and butane had been extracted, are injected into nearby reservoirs to help maintain underground pressure.

Another expansion project within the Ras Tanura Refinery itself involved the addition of new LP Gas processing plant units. These included treating facilities to remove hydrogen sulfide and mercaptan sulfur, a depropanizer, a 12-story-high deisobutanizer, a debutanizer and new driers.

Three new insulated 80,000-barrel tanks were added to three already-existing tanks of the same size at the Ras Tanura Marine Terminal, bringing to six the total number of storage tanks for refrigerated propane and butane there. New refrigeration compressors, heat exchangers, vessels and pumps also were installed.

The cost of such projects, like the cost of development, was, of course, large. By September, 1963, when the expansion at Abqaiq and Ras Tanura was finished, Aramco alone had spent approximately 125,000,000 for its LP Gas facilities in Saudi Arabia.

So the basic problem was solved. Special tankers now cross the seas, transporting LP Gas on regular schedules, and in Saudi Arabia planners have already begun estimating the future expansion of the installations that are prepared to supply essential fuel—to Noriko Ieda, Japan, or to peoples elsewhere around the globe.

Homer Dixon, a chemical engineer, studied at Yale and at the University of Washington. For the past five years he has lived in The Hague working as a project manager for the Aramco Overseas Company.

This article appeared on pages 9-13 of the July/August 1964 print edition of Saudi Aramco World.


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