US1868418A - Process of cracking petroleum hydrocarbons - Google Patents

Description

July 19, 1932. A. M. HoUGHToN 1,868,418

PROCESS` OF CRACKING PETROLEUM HYDROCARBONS Filed May s, 1927 CHA/M6672 Patented July 19, 17932 PATENT OFFICE ALFRED M. HOUGHTON, OF WASHINGTON, DISTRICT F COLUMBIA, ASSIGNOR T0 GULF REFINING COMPANY, 0F PITTSBURGH, PENNSYLVANIA, A CORPORATION 0F TEXAS PROCESS OF CRACKING PETROLEUM HYDROCARBONS Application lcd May 3, 1927.

This invention relates to improvements in processes of cracking petroleum hydrocarbons; and comprises cleaning the draw-off line of a cracking still by admitting to the still 5 through the draw-off line a portion of the oil either on its way to the cracking Zone or immediately after it has passed the cracking zone; all as more fully hereinafter set forth and as claimed.

Oil cracking processes now in use to a large extent involve heating the heavier hydrocarbon to be cracked in one Zone, delivering the heated products to another Zone, removing and condensing vapors from the second zone l5 and removing heavy uncracked oil and tarry residual petroleum hydrocarbons from the second zone. Sometimes the oil is heated in the first zone under conditions whereby there is substantially no conversion and is then delivered to the second Zone and maintained there as a body of oil While conversion takes place. In such a process there results a large amount of heavy tarry and asphaltic hyd-ocarbons which gradually accumulate and which tend to clog the draw-off pipe. In one process now in use to a large eX- tent the oil is heated in the first Zone to a cracking and vaporization temperature and there substantially vaporized and converted and the products o-f such heating are delivered to a separating chamber from which the vapors are removed and from which residual oil is removed substantially as fast as it accumulates. In this process there is a tendency for the drawoff line to become clogged by heavy hydrocarbons and asphaltic matter which acts as a binder. Attempts have been made to keep the draw-off line clear of accumulation of the residue by mes chanical scraping devices and the like but these are not eminently successful due to inherent disadvantages in the operation of a mechanical device inside a pipe where high pressures prevail.

In accordance with my invention the oil from the heating zone is delivered to the second zone in one of the known ways and the draw-off pipe from the second zone is kept open for continuous withdrawal of residue` After a time when there is a tendency for Serial N0. 188,490.

ing Zone is caused to travel to the second zone through the draw-off pipe. This oil being hot i and under high pressure and traveling at a considerable rate of speed forces out accumulation of solid and tarry matters in the drawolf pipe and causes them to mingle with any oil in the second zone. A minute or so of such purging the draw-off pipe is usually sufficient, whereupon the normal process is resumed. Should the clogging of the draw-olf pipe be occasioned by an undue accumulation of asphalt binder this may be dissolved more readily by a distillate which has not undergone any substantial conversion and therefore I may force through the draw-off line and into the second Zone some of the charge oil before it has reached and passed through the first heating` Zone, this charge oil containing a quantity of reflux condensate.

The accompanying illustration shows one form partly in section and partly in elevation of a cracking unit in which my process may be performed.

' In the drawing l indicates the furnace heated by means of oil burners located at 2 and having mounted therein a coil 3 to which the Oil to be cracked is supplied. This oil may comprise charge oil which has been used to scrub outgoing vapors from the second zone, as will be hereinafter described. The heated oil passes from the coils 3 by means of line 4L to the chamber 5 which is provided with the dephlegmator 6, baffle plates 7, and inlet for charge oil 8. At a low point the chamber is provided with continuous drawoff line l0 having continuation 10A. Vapors from the dephlegmatO-r are delivered by line 13 to the final condenser. The charge oil after scrubbing the vapors arising in the separating chamber is delivered together with condensate by means of trap l1 and line l2 to the inlet of the cracking coils by means of pump 12-A. Pressure may be maintained past the reflux condenser or past the final condenser 9 by means of the valves 14 and 15 respectively and, if desired, the pressure may be released before the oil is delivered from the first zone to the separating chamber.

In addition to the connections described I r provide a valved line 17 leading` from the dis 3f charge or cracking coils to the draW-oi line. Also in addition to the charge line leading to the zone of heating I vprovide a line 18 communicating the charge line With the tar drawoii. These lines are properly valved so that 10 some or Vall of the highly heated oil from the heating zone may be sent through the dravvoff line into the chamber or some or all of the charge oil may be sent through the draw-off line into the chamber. 19 indicates a sample 15 line Which may be used from time to time for the purpose of observing the character of the ,draw-off andrQO indicates the charge line which may be used at the beginning of an operation for filling the system.

kClogging of the draw-ofi" line is due to a largey extent to a thickening or solidification of asphaltic or tarry hydrocarbons acting as a binder for the carbon; the thickening or solidification being incident to a drop in temperature between the cracking Zone proper and the separation chamber. By adding het oil ofthe same character, this thickening or solidication is obviated and the Whole mass is made mobile enough for removal.

What I claim is: l. In an oil cracking process in Which the oil is heated in one zone and delivered to a Second zone from Which heavy residue is Withdrawn through a draW-of line, the step which comprises cleaning the draw olif line by'intermittently forcing therethrough into the second zone some or' the cracked oil directly from the first zone.

2. In an oil cracking` process in which the oil isheated in one Zone and delivered to a second zone from which heavy residue is Withdrawn through a draweoif line, the improvement Which comprises, during the cracking process, intermittently forcing 4Q through the draw-off line in a direction opposed to the normal draw-ofi', a quantityot the oil immediately as it leaves the rst zone.

8. In an oil cracking process in which the oil is heated in one zone and delivered to a 59 secondv zone from which heavy residue is Withdrawn through a dravv-oi line, the improvement Which comprises intermittently, during the cracking process, forcing through the draw-ofi1 line in a direction opposed to the i?? normal draw-off, a quantity of oil directly from the first zone.

f In testimony whereof, I have hereunto affixed my signature. 6o ALFRED M. HOUGHTON.

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