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Refining facilities. Integration of the separate processing plants in a modern refinery has resulted in economies of services, intermediate tankage, and manpower. The simplest refinery contains a distillation unit, catalytic reformer, and various treatment units. Small refineries of this type supply local markets in many parts of the world. With such units, it is possible to produce motor gasolines of different octane numbers, lamp kerosene, jet fuel, gas and diesel oil, and residual fuels. There may also be a plant for recovery of propane and butane.

In deciding which process to use, refinery managers analyze the market for residual fuel oil, which may amount to 40 or 50 percent of the crude oil processed. In some countries of the Eastern Hemisphere this fuel oil is easily marketed. But in the U.S. and Canada, where large quantities of gasoline are required, less fuel oil is used because natural gas is available within reach of consuming areas. Cracking plants, usually catalytic, together with vacuum-distillation units to produce fractions for use as feedstock, solve this problem. The production of gasolines can then be further augmented by polymerization or alkylation, superfractionation, and possibly hydrocracking.

With further additions of plant facilities, it is possible to build a fully integrated, comprehensive refinery by stages, including solvent extraction (of kerosene), hydrodesulfurization, a lubricating-oil plant (propane de-asphalting, solvent extraction, dewaxing, and clay treatment or hydrofining), and a plant for the production of asphalt, wax; sulfur, and special products.

Tankage. The manufacturing units form only part of a refinery, though the most important one. A large proportion of the cost, and the area covered is taken up by tankage, handling facilities, etc.

The storage capacity allocated to crude oil may be minimal if the refinery is connected to the oil fields by pipeline. When crude oil has to be imported, however, sufficient tankage is provided to enable continuous refinery operation while still allowing for the irregular arrival of tankers. Scheduling of tanker movements is important in integrated oil operations, particularly with very large tankers (up to 250,000 tons and more) in service.

Finished products require much more tankage in terms of storage capacity than crude oil. Provision is made for short-term variations in the sales of refinery products to avoid frequent alterations in the refinery process units. Nonvolatile products such as diesel oils and fuel oils are stored in large-diameter cylindrical tanks with low-pitched conical roofs. Tanks with floating roofs are used to reduce evaporation losses in gasolines and other volatile products, including crude oils. The roof, which resembles a pontoon, moves up and down inside the tank, thus eliminating the air space that could contain a considerable proportion of petroleum vapour. Fire hazards are also reduced by the use of floating-roof tanks.

For liquefied petroleum gases, pressure vessels (usually spherical) are used. Alternatively, these materials may be stored in suitable geological formations underground, such as cavities in salt domes. Large refrigerated tanks are a recent development. In these, the liquefied gas is stored at normal pressure but at reduced temperatures.

Bulk transportation. The supertankers have sharply cut the cost of transporting crude oil, making it practical to locate refineries near areas of consumption rather than adjacent to oil fields. Deepwater ports have been built to receive these large tankers, particularly in Europe, which obtains most of its supplies from the Middle East and Africa. Examples are Rotterdam, Gothenburg, Le Havre, Foss near Marseille, and Milford Haven in the United Kingdom. Groups of refineries have been constructed near these ports or connected to them by pipeline.

If pipelines are not practical or economic, water transport is the first choice for petroleum products. Full-size tankers or smaller coastal vessels, with capacities of 15,000 barrels or less, distribute the different grades of oil to depots situated on the coastline.

Countries having networks of canals and navigable rivers afford many opportunities for using barges, a very cheap method of transportation. On the Mississippi, barges of over 5,000-tons (37,000-barrels) capacity are in use; the Rhine and the Seine are also suitable for large barges. Many canals, however, can only accommodate 200-ton barges (1,500 barrels). Each barge is divided into separate calibrated compartments so that more than one type of product can be carried on a voyage; pumps are fitted for the discharge of the cargo.

Transport by rail tank car is still widely used. The cars normally have capacities of up to 50 tons (390 barrels), but there is a trend to larger sizes.

The final stage of delivery to the majority of customers is by the familiar road tank trucks, whose earning capacity is about 150 to 200 barrels.

Pipelines and pumping stations. Pipelines. Development of crude-oil trunk lines began in the United States in the early years of the 20th century when refineries in the populous eastern area had insufficient supplies from convenient oil fields. Pipelines were used for the transportation of crude oil in the United States in the late 19th century, supplying refineries in the general areas of to the known oil fields. After 1900 there was a rapid development of crude-oil trunk lines following the discoveries of oil in Texas, Kansas, and Oklahoma. These fields were used to supplement the declining production of the eastern oil fields. By 1940 more than 85 percent of the crude oil supplied to eastern refineries came from west of the Mississippi River. By the last quarter of the 20th century, there were about 400,000 kilometres (170,000 miles) of oil pipeline in operation in the United States; about one-third of the total mileage consisted of crude-oil trunk lines and a similar amount smaller feeder lines in the oil field areas. A pipeline to bring crude oil from the fields on the North Slope of Alaska to the southern port of Valdez was completed in 1977. Europe also has several crude-oil pipelines supplying inland refineries. In the Middle East large pipelines have been built for transporting crude oil from the oil fields of Iraq, Saudi Arabia, and other oil-exporting countries to deepwater terminals in the eastern Mediterranean.

More and more large pipelines are coming into operation to pump batches of different products successively down the line, since it is possible to do this without intermingling them. The «Big Inch» line, completed in 1943 to transport crude oil from Texas and Louisiana to refineries in the eastern United States, was converted for carrying gas from Texas to New Jersey, a distance of 2,375 kilometres (1,475 miles). In 1964 it was replaced by the world's largest products line, which can transport 1,000,000 barrels of products per day from Houston, Texas, to New Jersey. In Europe the first product line was the TRAPIL line from the lower Seine region to Paris, completed in 1953. This and other such lines on the Continent and in the United Kingdom enable inland refineries to dispose of products economically when the local market pattern does not match the proportions manufactured.

Centrifugal pumps are almost invariably used for mainline pumping, and with long lines the capacity can be increased by installing booster stations at intermediate points along the line. In recent years, many of these have been designed for unattended operation, the starting of pumps and the opening or closing of valves being carried out by automatic sequence control initiated by signals sent over telephone lines or by radio or by instruments responding to line pressure at the unattended pump station.

Service plant and facilities. Present-day refineries contain much equipment for servicing refinery operations. This includes the plant for steam generation and in some cases electric power, water treatment, effluent systems, and antipollution facilities. This equipment is essential for the operation of the industry within the community. One of the advantages of the self-contained refinery is its flexibility regarding surplus products; usually gas and heavy residue can be used for the generation of steam and power and for combustion in the oil-plant furnaces.