The cultivation of date palms was almost the only industry on the island of Abadan, in the Persian Gulf, at the beginning of the twentieth century. To-day the island has the largest and most modern oil refinery in the Eastern Hemisphere
A VAST OILFIELD is situated at Masjid-i-Sulaiman, among the foothills of the Iranian plateau, about 130 miles inland from the Persian Gulf. An enormous pipe line links Masjid-i-Sulaiman and another oilfield at Haft Kel with the great refinery at Abadan.
OIL may be extracted in vast quantities from the earth, but in the crude form in which it then exists it is of little use. After the discovery and production of oil, by far the most important part of the great oil industry is the refining of the raw product and its separation, on the most profitable basis, into its many useful components. An excellent example of modern practice in oil refining is the great plant owned by the Anglo-Iranian Oil Company at Abadan, situated at the head of the Persian Gulf.
Not many years ago the island of Abadan was merely a stretch of flat, alluvial desert fringed with date palms. To-day Abadan is the largest oil port in Asia, with a great refinery employing a personnel of nearly 11,000. Among the foothills of the Iranian plateau, about 130 miles inland, lie two vast oilfields, in districts known as Masjid-i-Sulaiman and Haft Kel. A Y-shaped pipe line links these fields with Abadan and delivers more than 7,000,000 gallons of crude oil every day. Nearly 80 per cent of this is refined at Abadan, the remainder being shipped to the company’s other refineries in Europe and in Australia. During the past few years the plant at Abadan has been almost entirely rebuilt and greatly enlarged, and it is now the largest oil refinery in the Eastern Hemisphere. The two latest distillation units to be installed are the largest of their type in the world. Each of them has a capacity of 2,250,000 gallons of crude oil a day, and is capable of producing the full range of petroleum products, from petrol to bitumen.
Crude oil, when it issues from the depths of the earth, is in the same condition as soda water in a siphon: it contains large quantities of dissolved gas, which is held in solution by the heavy overhead pressure. As soon as this pressure is released - when the wellhead valve is opened - the gas escapes from solution and the oil issues as a froth. This oil-gas froth must be handled in such a way that the oil and the gas are effectively separated and the gas used on the spot in the most profitable way.
OILFIELDS OF IRAN, formerly Persia, are situated at Masjid-i-Sulaiman and Haft Kel, about 130 miles from Abadan, at the head of the Persian Gulf. A Y-shaped pipe line delivers the oil under pressure to the refinery. Steam turbines drive centrifugal pumps in the pumping stations.
The oil issuing from the well-head is therefore led to high-pressure separators - long, horizontal cylinders some two and a half feet in diameter - in which the pressure is allowed to fall to 30 lb. or 40 lb. per square inch, but not lower. At this pressure a portion of the gas content of the oil is separated out, and this is used to supply the local fuel requirements of the oilfields.
This gas is used for steam boilers at the electric generating stations, for steam-raising plant in the workshops and for heating or cooking purposes in the bungalows, houses and offices. There is a superabundant supply of natural gas for the entire requirements of the industrial community at or near the oilfields. The quantity of gas so used, however, is but an infinitesimal fraction of the total amount available, and steps are being taken to recover more and more of it for domestic and industrial purposes.
The crude oil now has the high-pressure gas removed and proceeds to great tanks, where the pressure drops almost to atmospheric level. All these operations take place at the oil-fields, before the oil enters the pipe line. In the flow tanks much of the gas still dissolved in the oil evaporates and is separated. This gas is far heavier than the high-pressure gas already dealt with, and is laden with petrol vapour.
BENCH 55 AT ABADAN, which is still in use, is part of the earlier plant used in the refinery. Bench 65, which is illustrated below, is a further development which incorporates the most modern improvements in refinery technique.
It is therefore led through pipes to absorption and compression plants for the recovery of light spirit or petrol. The gas is compressed, cooled and driven up an absorption tower, down which heavy oil is flowing. This “lean oil” absorbs from the gas its light fractions and becomes, in the terminology of the works, “fat oil”. The fat oil is distilled to yield the petrol which it has absorbed. Thus the process is a continuous cycle - lean oil absorbs petrol and becomes fat oil; fat oil is distilled, gives up the petrol and becomes lean oil, which is used again for the same process. The petrol goes by pipe line to be added to the crude oil which is destined for the refinery.
At no stage since its recovery from the depths of the earth has the pressure on the crude oil been entirely released. All the way from the well-head to the refinery it is under pressure. Thus the crude oil is made to carry with it along the pipe line not only a quantity of petrol, but also large quantities of gas, still in solution. This gas is a valuable source of fuel and is far more useful at the refinery at Abadan than it would be at the oilfields. It could not otherwise be conveyed to Abadan without great expenditure.
THREE FRACTIONATING COLUMNS are incorporated in Bench 65, the most recent installation at the Abadan refinery. The fractionating columns are used to separate the crude oil into different groups of “fractions” for the distillation of the numerous by-products. The largest column, which operates at atmospheric pressure, is 122 feet high and has a diameter of 22 feet.
Delivered Under Pressure
In the great pumping stations along the pipe line are steam turbines driving powerful centrifugal pumps, and the crude oil - though not so crude as it was at the well-head - is thus delivered under pressure to Abadan. The first step is the recovery of the gas which is to be used as fuel. This is precious, and petrol is even more so. If the oil were allowed to stand in tanks at atmospheric pressure, the gas and the petrol would evaporate and be lost. The crude oil is therefore led directly from the pipe line to heaters, and it passes at about 120° centigrade into large towers which are kept under vacuum. The oil flows down these towers and off to the refinery, but much of the gas and some of the petrol are sucked out of the oil and led to a recovery plant.
The entire story of an oil refinery is that of separating and putting to the best possible use all the various constituents of that highly complex fluid, crude oil. It is a mixture of many compounds, including tar, pitch, paraffin wax, lubricating oil, fuel oil, kerosene (lamp oil) and petrol, but there is no hard and fast division between these constituent parts. The various “fractions” must be separated by distillation, and each distillate must be purified by the removal of certain undesirable ingredients.
The separation of the crude oil into different groups of fractions is carried out in a fractionating column, and such units as the new “Bench 65” at Abadan are divided into three sections, each provided with its own fractionating column.
These columns are of the “bubble tower” type - the only important type in use to-day. The first operates at high pressure, the second at atmospheric pressure and the third in a vacuum. These bubble towers vary in size. Their dimensions are given on below. The towers are fitted throughout their height with perforated plates through which the oil vapours pass, and the holes have a diameter of some 5 in. or 6 in.
GAS ABSORPTION TOWERS at the oilfields. After high-pressure gas has been separated from the crude oil, more dissolved gas evaporates and is separated. This gas is laden with petrol vapour, and is driven up an absorption tower, down which heavy oil is flowing. This oil absorbs the petrol and is then distilled.
Above every hole but one in each plate is a metal dome called a bubble cap. The hole not provided with a cap is at the side of the plate, and is fitted with a tube leading down to the next plate. This tube, called a “downcomer”, enables surplus liquid on the plate to overflow on to the plate below. The edge of each hole is raised by a metal ridge about 2 in. High. Thus liquid can collect on the plate until there is a depth of more than 2 in. before it runs down to the plate below. Also - a more important point - vapour rising through the tower can escape through the holes only by bubbling through the liquid which surrounds them.
The division of crude oil into petrol and fuel oil in a fractionating column depends upon three physical facts. First, petrol vaporizes at quite a low temperature, fuel oil at a higher temperature. Secondly, when a mixture of petrol and oil is heated until part of it vaporizes, the vapour will contain more petrol than fuel oil. Thirdly, any vapour contains two kinds of heat - sensible heat, which can be felt, and latent heat, which does the work of turning a liquid into a vapour and is absorbed by the vapour without raising its temperature. As soon as the vapour condenses into liquid again, it gives out its latent heat. One pound of fuel-oil vapour condensing into liquid gives out enough heat to vaporize a pound of petrol.
The crude oil is heated in a still, similar to a water tube boiler, but without any drums, and the hot oil from this still enters the fractionating column about half-way up. Its temperature is such that nearly all the petrol and some of the fuel oil vaporizes, but the bulk of the fuel oil remains liquid.
The liquid flows down the tower by way of the downcomers. The vapour rises through the holes, bubbles through the liquid and rises to the next plate. In this way the vapour is forced to bubble through the liquid on each plate until it finally comes out at the top of the tower.
Each time the hot vapour bubbles through liquid on one of the plates, some of it condenses. The part that condenses will contain more fuel oil than petrol, so that the uncondensed vapour is richer and richer in petrol after each operation.
Thus, if the fractionating column is correctly designed, the vapour at the top will consist entirely of petrol and will be free from fuel oil. The oil which, in liquid form, finally reaches the bottom of the column will still contain a small quantity of petrol; this, however, is freed by injecting steam at the bottom of the column and the petrol vapour will therefore rise to the top.
This brief description, for the sake of simplicity, has dealt only with the separation of fuel oil and petrol. The whole process of refining, however, is conducted on similar principles - but there are many more fractions which have to be separated from one another.
Washing Petrol
Bench 65 at Abadan, with its three fractionating columns, works in the following way. The high-pressure column (known as a primary flash tower) extracts petrol. The atmospheric column separates out benzine, naphtha, kerosene, gas oil and fuel oil. These various constituents are extracted at different heights up the tower. Benzine comes from the top. The third, or vacuum column, produces gas oil at the top, its other products being a waxy distillate and asphalt.
The primary flash tower, which is 36 feet high and has a diameter of 18 ft. 6 in., operates at a pressure of 50 lb. per square inch. The atmospheric tower, which is the largest, is 122 feet high and 22 feet in diameter, and the vacuum tower is 87 feet high and 32 feet in diameter. The vacuum is maintained in this tower by a system of steam ejectors.
Many special features have been incorporated in Bench 65. Automatic controls and automatically operated valves have reduced the reliance that must be placed on manual labour, on which this large plant would otherwise make unreasonably heavy demands. Some of the statistical details referring to Abadan give an excellent idea of the Bench 65 plant. Each of the furnaces for heating the crude oil before it is passed to the towers covers an area equal to about one-half that of the standard tennis court and is 26 feet high.
THE PIPE LINE from the oilfields to Abadan crosses the most barren and difficult country, such as the Imam Reza Ridge, in the south of Iran. More than 7,000,000 gallons of crude oil are delivered through the pipe line every day.
There are approximately eleven miles of piping, varying in diameter from one-eighth of an inch to 28 in., and more than 1,400 valves. To condense and cool the products, fifteen million gallons of water are required every twenty-four hours, and the fuel consumed amounts to 250 tons a day. This vast single unit is taking the place of at least four of the older units at Abadan, which became obsolete because of their inability to yield the products for which the market was calling. Gas oil and fuel oil, as distilled, are finished products ready for marketing, and they are pumped directly into storage tanks. A considerable portion of the fuel oil is reserved for the British Navy. Such products as petrol and kerosene, however, require chemical purification before they are ready for the market. This treatment is largely one of deodorization, as petrol and kerosene contain small quantities of evil-smelling compounds of sulphur.
Petrol is “washed” in a special plant operating on what is known as the continuous counter-current principle. The petrol flows continuously through the plant in one direction, and is brought into contact with the purifying chemicals, which flow in the opposite direction.
Purified petrol leaves the plant at one end and exhausted chemicals at the other. The plant has been so designed that its operation is almost entirely automatic, and a washery capable of purifying 500,000 gallons of petrol in a day may be completely controlled by one man. Kerosene is desulphurized and purified by liquid sulphur dioxide, which is used over and over again with negligible loss. Refined kerosene is further purified by filtering through bauxite (a clay forming the main source of aluminium).
Another important section of the refinery deals with “cracking”, or retreating the pressure distillate, breaking up complex hydrocarbons into simpler ones (see the chapter “The Story of Oil”). Heavy oil residues may be converted into petrol by cracking, which is a science of immense importance to the modern refinery. Motoring has led to a constantly increasing consumption of petrol, and it is doubtful whether the world’s needs could be met by the old straightforward methods.
The process of cracking leads on, in turn, to other processes. In the operation of cracking petroleum to produce motor spirit, large quantities of uncondensable gas are also produced. Until comparatively recent years this gas has been regarded as a useless by-product. The world’s daily production of such gas is well over a thousand million cubic feet a day.
CONTINUOUS COUNTER-CURRENT WASHERS purify the petrol that is distilled in the refinery at Abadan. Petrol flows continuously through the plant in one direction and comes in contact with the purifying chemicals that flow through the plant in the opposite direction. Operation of the plant is almost entirely automatic, and 500,000 gallons may be “ washed ” in a day under the direction of one man,
By a process that is known as polymerization, some of the constituents of this gas may be induced to combine with one another, forming “polymergasolene”, which can be blended with petrol to improve its antiknock value. Another product is iso-octane, which makes possible a 20 per cent increase in the efficiency of an aircraft engine. Other fractions of the “useless” gas, submitted to a pressure of 800 lb. per square inch and a temperature of 500° C., will combine to form an alternative type of synthetic gasolene, which is an excellent motor spirit.
Even this only touches the fringe of the subject, for the remaining hydrocarbons in the gas can be cracked again, producing more of the useful constituents which can, in turn, be converted into motor spirit. Truly the end of the petrol era, which has been so often predicted by scientists, appears extremely remote when all these potential sources are considered. A refinery of the type of the one at Abadan is capable of turning out various residues from which innumerable by-products, all with important commercial applications and possibilities, can be recovered by the chemical industry. Synthetic rubber, colourless substitutes for resin and shellac, plastics of all kinds and lacquers are among these by-products.
By a continuous scepticism of the perfection of existing methods the chemist and the engineer are gradually eliminating all sources of waste, and it seems doubtful if there will, eventually; be any useless by-products after the splitting up and refining of crude oil as received directly from the earth.
The refining process at Abadan is essentially flexible. The proportions in which the various products are obtained can be varied within wide limits to meet the current demands. There are a large staff of chemists and a wonderful set of laboratories in which the various products are daily tested at every stage.
Much modern machinery, too, is in constant use. The oil and the intermediate products travel to and from the various units of the plant through a maze of hundreds of miles of pipe, and the entire circulatory system has to be maintained by the use of electrically driven centrifugal pumps.
2,500,000-Tons Storage Areas
Light products are led away to storage tanks, there to await shipment in tankers. The storage of these highly inflammable products is located well away from the refinery to minimize the danger of fire during loading. The tanks are interesting as an application of scientific principles. If they were normal dome-shaped tanks of fixed capacity, much waste would be involved in Iran’s temperatures of 120° F. in the shade. The heat would cause expansion and vaporization, with an inevitable escape of valuable petrol vapour into the atmosphere. During the cool of the night, contraction would take place, and air would be drawn into the tanks, which would thus behave in the manner of enormous lungs expiring petrol during the day and inspiring air during the night. To guard against this eventuality the tanks used are provided with floating roofs which rise and fall as the level of spirit within the tanks varies.
At Abadan a huge electric power station and a pumping station for the industrial water supply are powered by steam, which is generated by oil and gas from the fields or from the distillation process. The pumping equipment circulates 200 million gallons of water every day, and the power house has a capacity of 24,000 kilowatts.
The great storage tank areas provide capacity for 2,500,000 tons of crude oil and finished products, and there is a long line of loading jetties where the 10,000-tons tankers of the British Tanker Company come and go, often at the rate of ten a week, their journeys amounting to some six million miles a year.
There are also great residential areas where the staff (some 600 Europeans and 10,000 Iranians) are housed. These areas have been laid out to make living conditions tolerable in a trying climate.
The rapid and successful growth of the great centre of Abadan may be regarded as one of the triumphs of a modern industry.
ACROSS A DEEP RAVINE near Masjid-i-Sulaiman the pipe line is carried on a suspension bridge. In this illustration men are seen assembling the lengths of pipe line after the completion of the bridge.
[From part 22 & part 23, published 27 July & 3 August 1937]
