Page:Popular Science Monthly Volume 89.djvu/401

 Popvlar Science Monthly

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���Fi2. 2. How Pennsylvania Crude Oil Is Refined B — Steam Still D— Agitator F — Chilling Tank H — Wax Sweater

C — Steam and Fire Still E— Fuller's Earth Filter G— Wax Filter Press K— Air Drying Tank

��pass up through alternate boxes and air-cooled tubes, where products of different boiling points are simultaneous- ly condensed and thus automatically separated into groups. The lightest l^roducts pass completely through the tower and flow in vapor form to a water cooled condensing coil, where all light hydro-carbons condensable without the application of pressure, are liquefied and separated from the remaining \apors, which arc further treated at a compressor plant, for the separation of very light hydro-carbons from the "fixed" gases. Of the remaining vapors, the heaviest condense upon striking the first air- cooled tubes, and the lightest upon striking the last tubes. Intermediate jiroducts, lying between the light and lieav>' ends, condense in ihe intermediate tubes, depending upon their respective boiling point. The vapors liquefying in different sections of the aerial condenser fall back into corresponding collector pans, whence each is led by wav' of a separate water-cooled coil to the storage tanks, called "running tanks." The liquids reco\'ercd in the collector pans are still at a temperature above their fire points, and it is necessary to cool them down to prevent spontaneous ignition.

��when they come into contact with air in the running tanks.

Distillation continues until a residue (crude cylinder stock), of about 15 per cent, remains, when the fires are drawn and the remaining oil is pumped from the still through a cooler into a running tank.

The quantit>' and quality of products obtained from this first separa.lion de- pend upon the method of distillation employed and from the base or "family" to which the crude petroleum belongs. This description, however, only concerns Pennsylvania crude oil of paraffin base. High quality oils are obtained when the sep;xration is made by distilling under vacuum or by the use of fire in combina- tion with steam injection. Due to the mixture of (jil and water vapors in fire and steam distillation, oil vapors pass over at lower temperatures than were fire used alone. This prevents the occur- rence of any serious "cracking" of the heavier products.

Second Stage — Separation and Finishing of First Groups

The prime object of subjecting the group-distillates from the running tanks to different processes is to further

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