US2019070A - Vapor phase cracking - Google Patents

Description

Oct. 29, 1935. c. B. BUERGER VAPOR PHASE CRACKING Filed June 4, 1926 nwmtoi (2me/55. affaf/P, 55% y/14 79m Patented Oct. 29, 1935 UNITED STATES VAPOR PHASE CRACKING Charles B. Buerger, Pittsburgh, Pa., assignor to Gulf Refining Company, Pittsburgh, Pa., a corporation of Texas Application June 4, 1926, Serial No. 113,778

Claims.

This invention relates to vapor phase cracking; and it comprises a method of cracking petroleum oils as vapor wherein oil to be cracked is contacted with hot cracked oil vapors to distil it and free it 5 of non-volatilizable matters, the mixed oil vapors thus produced are subjected to partial refluxing condensation and thev condensate so formed is utilized to produce said cracked oil vapors; all as more fully hereinafter setjorth and as claimed.

The advantages of cracking in the vapor phase are well recognized but there is diiiculty in providing efficient method and means for accomplishing this in any continuous way. In the art, the expressions low boiling oils and light oils are equivalent and the expressions high boiling oils and heavy oils are equivalent. Most petroleum oils used for cracking carry heavy ends; on vaporization there is not a complete vaporization and there is a production of carbon-rich oils, tars and coke. By direct introduction of any such oil into a heating zone at a cracking temperature not all of it vaporizes; there is formed a residue of coke. By the expedient of distilling the oil in a still and superheating the vapor, true Vapor phase cracking can be performed; but this is an additional complication and expense.

It is the purpose of the present invention to provide a simple and direct method of effecting cracking in the vapor phase with the use of simple organizations of apparatus. To this end I take the oil to be treated and bring it into effective large area contact with hot cracked oil vapors coming from a suitable cracking apparatus. This lowers the temperature of the cracked oil vapors and vaporizes the volatilizable portions of the charge oil, producing a residuum which is discarded from the system. In a good embodiment of the present invention the mixture of oil vapors, those coming from the charge oilv and from the cracking device, are passed into a device of the general nature of a refluxing column wherein the heavier portions of the cracked oil vapors and of the charge oil vapors are condensed. The residual uncondensed vapors of lighter oils, coming both from the charge oil and from the cracking device, go forward through a water-cooled condenser to be condensed and treated in the usual manner. The mixture of liquid oils produced in the refluxing column as described is sent to the cracking device wherein it is vaporized and cracked. The operation may be under as much pressure at any point as may be desired; but ordinarily I provide merely as much pressure as is necessary to force the oil and vapor through the cracking device. This being commonly tubular in construction and of relatively great length and small diameter, .sometimes rather high pressures are necessary at its inlet to overcome friction, etc. In performing the vaporizing and condensing operations speci- 5 iied I commonly provide a tower like apparatus of the general nature of a column or reflux tower but divided into two sections, an upper and a lower which are in vapor communication, with means at the bottom of the upper section for intercept- 10 ing condensed liquid at that point. Into the lower section I discharge hot vapors coming from the cracking apparatus and also introduce the charge oil to be treated. From the base of this lower section I remove unvolatilized residuum 15 which is sent out of the system. The cracked oil vapors, now somewhat cooled, and the vapors derived from the charge oil go together into the base of the upper section wherein they are subjected to a reflux condensing action in an or- 20 dinary way with production of a condensate and of uncondensed vapors which go forward to a nal water-cooled condenser for appropriate treatment. The condensate from the base of the upper section is taken by pumping means and 25 delivered to the inlet of a cracking coil in a suitable furnace. Ordinarily I pass the oils through a vaporizing preheater en route; this preheater being supplied with heat from the waste gases from the cracking furnace.

Since the condensate formed in the tower is at a lower temperature than is desirable for oil fed to the cracking coils, I provide a reboiler through which the oil is circulated, thereby not only heating the oil but freeing it of any gasoline it may 3,5 retain at refluxing temperatures.

In one particular case in dealing with a dirty gas oil or alight fuel oil, the oil was charged into the lower section of such a tower as that described, this being maintained at a temperature 40' of approximately 1,000 F. Into this section, hot cracked oil vapors were supplied. About per cent of the liquid oil charged into this section was vaporized and carried out of the lower section into the upper section. At the top of the 45 upper section a vapor temperature of about 300 F. was obtained. Oil from the base of the upper section was circulated cyclically to, through and from a heater so as to maintain a temperature of about 600 F. in the recirculated oil delivered 50 to the tower. The condensed oils from this upper section were placed under pump pressure of Iabout 350 pounds and forced forward at a tem- -perature of about 400 F. through a preheater and into a tubular cracking device wherein there was 55 maintained a temperature of about 1100 F. The

initial pressure inthe particular tubular cracking system used Was, as stated, about 350 pounds while at the discharge end of the pressure was about 15 pounds.

In the accompanying illustration I havel shown, more or less diagrammatically, an embodiment of apparatus elements within the purview of the present invention and susceptible of use in the performance of the described process. The showing is mainly in vertical section with certain partsA in elevation.

In the structure shown, charge oil istaken from storage tank I by pump 2 and forced through line 3 into the lower section 4 of a two-part tower. As shown, this section is provided with the lusual surface-giving devices. The charge oil is introduced near the top of the section. From this section vapors are taken by by-pass 4a into an upper section 5 of much the same construction. This upper section serves however as a reflux condensing device while the lower section described is a vaporizing device. Condensate produced in this upper section is taken by line 6 to charge tank 'I whence it goes via pump 8 to a surge tank 9. From the surge tank oil passes forward past valve I0 and meter AII into a preheating and vaporizing coil I2 located in the ciftake of a furnace chamber. From the preheater the oil passes through diagrammatically shown cracking tubes I3. In practice many of these tubes may be arranged in series and in parallel but for convenience in illustration I have shown merely one tube. From the cracking tubes the cracked oil vapors pass into an expansion chamber or tube I4 and thence back tothe bottom of the described lower section of the tower (4). Returning to the reflux condenser (5), uncondensed vapors pass from its top through the usual condenser I5. The condensate `goes into trap tank I6, whence gas is vented through Il to any suitable place of use. Condensed naphtha from the trap tank goes to storage tank I8. In order to take oil'out of this part of the system at a relatively high temperature, positively freed of gasoline and light oils, I circulate oilfrom the base of .the section through a reboiler. `As will be seen, liquid oil is taken from the base of the upper secv tion through I9 by pump 2U and forced through heatingcoil 2l, thence returning to the base of .the upper section through return pipe 22. Heat for the whole system is furnished by furnace chamber 23 which may conveniently be fired by gas from I1. As this furnace is shown the cracking coil assemblage is in front oi.' a bridge wall 24, back of which are located the, stated preheating coils and the heater coilfor the circulating system, thus exposing the cracking coil to radiant heat from the furnace and shielding from radiant heat the preheating and vaporizing coils I2 and heater coil 2l of the reflux circulatory system. Furnace gases finally go away through oiTtake 25. Unvolatilized residuum from the base of the lower Asection is continuously taken through cooler 26 by pump 21 and sent to residuum tank 428. Imperforate partition 29 separates the upper and lower sections of the two-part tower.

What I claim is:-

1. In the cracking of petroleum oils, the process which comprises cracking an oil in the vapor phase, intimately contacting the hot cracked vapors with charge oil thereby vaporizing the vayporizable constituents thereof, removing and discarding all liquid residuum of the charge oil, subjecting the mixed vapors :to reiiux condensation in a reuxing zone, removing and condensing uncondensed vapors, withdrawing condensate from said refluxing zone, heating the same to a temperature of about 600 F. and returning it to the refluxing zone, and subjecting condensate from said reiiuxing zone to vapor phase cracking for the production of additional hot cracked vapors for intimate contact with further quantities of charge oil.`

2. In the `cracking of petroleum oils, the process 10 which comprises intimately contacting hot vcracked oil vapors at a temperature of about l000 F. with charge oil thereby vaporizing vaporizable Vconstituents of the charge oil, removing Vand discarding all liquid residuum of the 15 Acharge oil, 'subjecting the mixed vapors to rectificontact with the charging oil.

4. In the cracking of petroleum oils, the proc- 30 ess which comprises continuously passing the oil in a conned stream through a heating zone and there vaporizing the oil; passing the vaporized oil through a second heating zone. and there heating the oil vapors to a temperature of the order 35 of 1100 F.; maintaining the oil and vapors, throughout their heating, under pressure not sub stantially greater than suiiicient to eiect their passage through the heater tubes; intimately contacting the stream of heated vapors with a 40 stream of Vfresh oil, thereby effecting heat interchange between the two streams and vaporizing a portion of the fresh oil, said contacting being effected under a pressure not greatly in excess of atmospheric pressure; discharging vfrom the 4-5 process the liquid residue from said contacting of heated vapors and fresh oil; subjecting the remaining vapors to partial condensation; heating the higher boiling condensate from said partial condensation to a temperature of the order of 50 600 F. to free it of any constituents which may not require further cracking; and utilizing the stripped heavy condensate as the oil feed to the first mentioned heating zone.

5. In the cracking of petroleum oils, .the process 55 which comprises continuously passing the oil in a coniined stream through a heating zone and .there vaporizing the oil; passing the vaporized oil through a second heating zone and thererheatg ing the oil vapors to a temperature of the order 6o of 1100" F.; intimately 'contacting the stream oi.' heated vapors with a stream of fresh oil, thereby .eiecting heat interchange between the two streams and vaporizing aV portion of the fresh oil; ldischarging from the process the liquid 05 Vresidue from said contacting of heated vapors

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