REFINING Crude oil, as it comes from the wells, can rarely be used directly except for fuel purposes. The heavy California and Gulf Coast oils can be burned directly under boilers to generate steam, and are so used to a large extent. The lighter Eastern oils are rarely so used.
The value of crude oil depends upon the products that can be obtained from it by refining. Crude oil is a mixture of a large number of hydrocarbon compounds. When the crude oil is heated vapors are given off which when condensed give products such as gasoline, kerosene, fuel distillates, and wax, all having different physical properties.
Kinds of Crude in a refining sense are said to have paraffin, asphalt, or mixed bases. A paraffin base oil is one that has a waxy paraffin residue in the still. An asphalt base leaves an asphaltic residue in the still. A mixed crude is one that has both paraffin and asphaltic residues.
Examples of oil of paraffin base are the light oils of Pennsyl vania and West Virginia; oils of asphaltic base are the heavy oils of California and the Gulf Coast area of Texas and Louisiana. Mixed base oils comprise the light oils of Upper Louisiana, of Oklahoma, Kansas and Wyoming. There is, of course, not only a physical but a chemical difference in such oils. The paraffin base oils belong to the chemical series C„ H2. + 2; the asphaltic oils belong to the series C,, H2„, and the mixed bases have ele ments of both series. Refining methods vary for each kind of oil.
The light Eastern and the Nlid-Continent oils carry larger quantities of gasoline, and the lighter naphthas, than do the heav ier oils of California and the Gulf Coast fields. Some idea of the products obtained and their per cents from 100 gal. of crude oil are given below in Tables 12, 13, and 14.
Principles of Oil principles of oil refining are simple, but actual practice is quite complicated. It was early found that by heating petroleum it gave off hydrocarbon vapors which, when condensed or cooled, formed products having properties different from crude petroleum. If the temperature
were raised to a very high point, all but a small per cent of the crude oil evaporated; the residue was a coke. It was found too that within certain ranges of temperature for the same oil a uniform product was formed. By using higher temperatures, other products were obtained.
. The next move was merely the application of these simple facts to the making of various products in commercial quantities.
Instead of laboratory apparatus, steel stills similar to boilers were used. They are heated by fire from below or by steam coils inside, or by a combination of fire below and steam inside. Cool ing and collecting tanks are necessary. The early apparatus was simple, but as the demands for various grades of products have developed many and various types of stills and coolers have resulted.
In present practice a refinery consists essentially of stills, con densers (coolers), agitators, for treatment of the condensed prod uct, to take out bad odors and to give good color. Filters are also used to take out impurities and to give good color to the oil. Tanks to store the refined products are also necessary.
Boiler houses, laboratories and offices are all a part of the general plan'of operation.
Refining Operations.—In refining, the scheme of operation centers upon the end-products and the by-products desired. If gasoline is the main object, the scheme will be to turn all prod ucts as far as possible into gasoline. If kerosene is the main object, gasoline must be secondary. Gasoline is, however, in such demand that at present it is the chief product of the refineries.
Before a comprehensive refining scheme for an oil is determined the quality of the crude oil must be known, and its pe culiarities studied. A careful physical analysis is made and a laboratory refining test carried out. Actual commercial runs should be made where a large amount of oil is to be refined. The evaluation of crude oil will not, however, be treated here.