US2037952A - Conversion of hydrocarbon oils - Google Patents

Description

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QVERSION 9F HYDHOCARBON OILS Filed May 1,9,L :931

ma ZM INVENTOR @www ATTORNEY UNITED STATES PATENT OFFICE 2,037,952 CONVERSION OF HYDROCARBON OILS Richard F. Trow,

The Texas Company, poration of Delaware Port Arthur, Tex., assignor to New York, N. Y., a cor- Application May 19, 1931, Serial No. 538,591

1 Claim.

This invention relates to the conversion of higher boiling hydrocarbon oils into lower boiling ones and relates of treating a charge yield of motor fuel distillate havi knock value and densable gas and heavy residue particularly to a method oil to produce a maximum ng a high antia minimum yield of non-conwhiclr contains little or no convertible constituents.

The invention broadly contemplates a method of cracking Ipetroleum oils to ultimate yield, so-

called because uncracked portions of the charge oil or such fractions produced in recycled and further cracked, and

the process are ultimately only a desirable distillate, a small quantity of gas and a relatively heavy pitch-like residue is delivered from the system.

According to my invention a relatively dirty higher boiling oil, such as unclean gas oil or topped crude, may be heated by heat interchange with hot vaporous products from the reaction zone and/or in a heating coil to cosity and distill off a fraction,

break the Visrelatively clean gas oil while clean recycle oils may be removed by reflux condensation from the hot vaporous products and by flash distillation from residual portions developed in the cracking step and the clean oils combined to form a stock.

clean cracking In the past a preference has been shown for the the gas oil treating separately from crude oil and fresh gas oil fractions fractions from residues developed in cracking operations, which are of a more refractory nature, in such manner as would be most effective to each. For example,

a fresh gas oil may have been cracked in the liquid phase and satisfactory yields of motor fuel obtained with a minimum production of gas,

while a gas oil from cracked residues, which would probably not be susceptible to conversion under the mild conditions of liquid phase cracking, may

phase and satisfactory yields nimum producliquid phase process usually produces a considerable quantity of coke and the .anti-knock value of the motor fuel is low while a vapor phase process usually produces a Aconsiderable quantity of non-condensable gas.

Recently there has come into use in the refining industry a cracking procedure generally known as low liquid level cracking. This method is generally characterized by the use of lower temperatures but longer time of digest under heat ofthe vapors, as compared with vapor phase cracking, While at the same are higher and the time of diges time the temperatures t under heat of the liquid oil is shorter than in liquid phase cracking. As will become apparent hereinafter, my invention comprises certain improvements in this general type of operation.

As previously stated I prefer to combine the 5 clean gas oil fractions from the cracking step in the system and that from the charge oil and subject them together to suitable cracking conditions to produce an ultimate yield of motor fuel from the charge oil. As such a, cracking stock 10 will contain both relatively highly refractory and less refractory constituents it is particularly advantageous to process it under conditions of 10W liquid level cracking Where the more refractory constituents become vaporized and are subjected 15 to slightly longer time of digest than the less refractory constituents, most of which remain liquid, with the result that minimum percentages of non-condensable gas and pitch or coke are produced.

Where charging topped crude or an oil of greater viscosity than the usual gas oil it is preferable to subject it to a sufciently high temperature in the initial stages of heating to break or reduce the viscosity somewhat and thus 25 make available an additional amount of the charge as a cracking stock.

These and other objects and advantages of my invention will be better understood by referring to the following description taken in connection 30 with the accompanying drawing, the single figure of which illustrates in diagrammatical elevation a preferred embodiment of apparatus adapted to practice the invention.

Element I is a furnace, 2 and 3 are reaction 35 vessels, 4 is a dephlegmator, 5 is a reflux condenser, 6 is a final condenser, 1 is a trap and 8 is an accumulator drum, which constitutes the main items of the cracking portion of the apparatus.

Element I0 is a combination still and dephlegmator, II is a condenser, i2 is a trap, and I3 is an accumulator, which constitutes the main items of the sensible heat or autogenous distillation Zone in which the clean cracking stock is de- 45 veloped and from which an uncrackable residue is released from the system and a small quantity of desirable distillate is fractionated out.

A charge line I5 may lead through a preheater coil I6 situated in reflux condenser 5 into a vapor 50 line 51 which connects the upper portion of the vessel 3 with the lower portion of the dephlegmator 4 or by manipulation of valves 20, ZI, 22 and 23 may lead through I6 to a heater coil 26 or bypass I6 or a combination `of the three.

A line 25 connects the lower portion of the dephlegmator 4 with the heater coil 26 which is preferably situated in the upper portion of the furnace I. By manipulation of the valves 21 and 28 the coil 26 may be by-passed and a direct connection effected with the lower portion of the combination vessel I0.

Drain lines 30 and 3| lead from the bottoms of vessels 2 and 3 to a main line 32 connecting with the lower portion of the still section of the vessel I0. A vapor line 35 connects the lower or still section with the upper or dephlegmating section of the vessel I and a release line 36 leads from the bottom of the lower section of this vessel.

A vapor line 40 connects the dephlegmating section with the condenser II and a line 4I connects the condenser I I with the trap I2. A pump 43 takes suction from the trap I2 through a line 42 and discharges into the upper portion of the dephlegmating section through a line 44. A line 45 connects the condenser II with the accumul-ator I3 which has a liquid outlet 46 and a gas outlet 41.

A pump 50 takes suction from the lower portion of the dephlegmating section of vessel I0 through a line 49 and discharges through a, line 52 into a heater coil 53 situated in the lower portion of the furnace I. A branch line I leads from the discharge line 52 into the upper portion of the still section of I0 onto the uppermost of a series of baiiles situated therein.

A line 55 connects the heater coil 53 with the first reaction vessel 2 and a line 56 connects the lower portion of the vessel 2 with the lower portion of the Vessel 3. The vapor line 51 leads from the upper portion of the vessel 3 to the lower portion of the ldephlegmator 4 as previously mentioned.

A vapor line 60 connects the upper portion of the dephlegmator 4 with the lower portion of the reux condenser 5 as does also a run back line 6I. A nal vapor line 62 leads from the reflux condenser 5 to the nal condenser 6. A line 63 connects the final condenser 6 with the trap 1 from which a pump 65 takes suction through a line 64 and discharges thru a line 66 into the upper portion of the dephlegmator 4. A line 61 connects the trap 1 with the accumulator 8, which has a liquid outlet 68 and a g-as outlet 69.

When beginning to operate, a suiicient amount of clean oil may be drawn in thru a pipe 48 from a source not shown and pumped into the heater 53. After operating conditions are established a switch may be made and fresh charge oil supplied to the system thru the line I5.

In a preferred mode of operation a fresh charge oil which may be a topped crude oil is charged thru the preheater I6 and emerging therefrom at a temperature of approximately 450 F. is delivered into the vapor line 51 near its connection to the lower portion of the dephlegmator 4. 'I'he thus commingled cooler charge oil and hot vaporous products from the reaction zone undergo heat interchange by which a portion of the fresh charge may be vaporized while the remainder, with reflux condensate resulting from the dephlegmation of the vaporous products is deposited in the bottom of the dephlegmator. The liquid being deposited in the dephlegmator is regularly discharged therefrom at approximately ri50 F. and may be passed thru a heater coil 26 in the upper portion of the furnace I or may be passed direct to the lower portion of the still section of the vessel I0.

In some instances it may be found preferable to heat the fresh charge oil alone and to deliver the reilux condensate in dephlegmator 4 direct to the flash distillation zone. Thus the fresh charge may be passed through the heaters I6 and 26 and merging with the reflux condensate near the entrance be delivered into the lower section of the vessel I0.

While the heater coil 26 is shown Iand described as being situated in the upper portion o-f the furnace I it is pointed out that it may be preferable to situate it in a separate furnace where the heating could be regulated independently. Such an arrangement as this is of advantage where the fresh charge is of relatively high viscosity and it is desirable to raise the temperature high enough to break or reduce the viscosity by effecting a small amount of cracking. For example, a topped crude which may have a viscosity of approximately 400 universal at 100 F. when treated in this manner will be reduced to approximately 100 at 100 F.

The purpose of breaking the viscosity is to develop and extract the maximum percent of gas oil from the fresh charge. Frequently enough heat to accomplish the desired result can be imparted to the charge oil in the coil I6 and in the line 51. This is not true, however, of all stocks nor all operating conditions consequently the heater coil 26 is provided in which the charge oil may be heated to the desirable temperature.

Residue collecting in the bottoms of the vessels 2 and 3 may be released therefrom at a temperature of the order of 850 F., and is conducted into the lower portion of the still section of the vessel I0.

The combined charge and recycle oil from the dephlegmator 4 and the residue from the vessels 2 and 3 are subjected to autogenous distillation in the vessel I0 under a slightly or greatly reduced pressure and the resulting vapors moving upwardly are scrubbed by the downwardly moving liquid reiluxed to the top of the series of bailles. The resulting clean vapors are conducted thru the line 35 into the dephlegmating section of the vessel I0, while a heavy residue collecting in the bottom of the still section is released as desired.

The liquid delivered to the upper of the series of baiiles is a portion of that liquid accumulating in the dephlegmating section and is accordingly itself a clean scrubbed fraction. The amount of this liquid is just suiiicient to effect a desirable scrubbing of the new vapors and is in turn revaporized by the heat of these vapors and with them is returned to the dephlegmating section thru the line 35.

The clean cracking stock thus developed is withdrawn from the lower portion of the dephlegmating section of vessel I 0 and is passed thru the heating coil 53. Emerging therefrom at a temperature of approximately 950 F. it is conducted into the upper portion of the reaction vessel 2, which is preferably maintained at a pressure of approximately 400 pounds per square inch, as is the remainder of the system except the autogenous distillation portion.

There is a certain amount of cracking effected in the coil and a portion of the oil becomes vaporized therein. The heated products transferred from the coil into the upper portion of the vessel 2 at relatively high velocity are further vaporized therein and the vapors are passed thru the vessel 2 and into the vessel 3 by the connecting line 56.

Remaining vapors emerge'from the upper portion of the vessel 3 while liquid portions depositing in the bottoms of the vessels 2 and 3 are preferably kept drawn down lo-w so as to prevent collection of substantial bodies of liquid therein.

The liquid portion of the heated oil is subjected to just such time of digest in the vessel 2 as is required for the liquid to move from the entrance pipe 55 to the outlet pipe 30. A certain amount of the liquid particles are carried into the vessel 3 and this portion has an additional time of reaction which lasts until it is deposited and withdrawn thru the pipe 3l. The vapors are subjected to a time of digest in the system running from the instant they are formed until they are quenched by the entering charge in the vapor line 51.

The oil which condenses and remains condensed in the vessels 2 and 3 is deposited in the bottoms thereof and released thru the lines and 3| to the main line 32 to be eventually discharged into the lower portion of the still section of vessel Iii. It is preferable to reduce the pressure on the residue as soon as it leaves the reaction vessels to a suicient extent to effect a desirable temperature reduction of the o-il by the resultant expansion or distillation. In other words a sufficient time of reaction is provided for the liquid in the vessels and it is not desirable to allow a prolongation of the cracking conditions after the residue leaves the vessels.

The vapors emerging from the vessel 3 are conveyed thru the line 51, wherein the fresh charge is delivered from the line l5, and by heat interchange serve to warm up the fresh charge and to cool the hot vapors.

The vapors, and combined fresh charge, are conducted to the dephlegmator 4, and are therein subjected to any conventional method of fractionation. A portion condensed from the vapors and a portion remaining condensed from the fresh charge in the dephlegmator 4 is discharged therefrom thru the line 25 and, according to the nature of the charge stock, is passed thru the heater coil 26 or is delivered direct into the lower portion of the still section of vessel l under reduced pressure as previously described.

The vapors dephlegmated in 4 are passed thru the reflux condenser 5 where remaining heavier portions are condensed and a portion of their heat is imparted to the fresh charge which is being passed to the coil I6. The nal vapor is conducted thru the line 62 to condenser 6 and nally to storage. 'Ihe portion condensed in the condenser 5 is returned to the upper portion of the dephlegmator 4 thru the line 6I as is also a portion condensed in the condenser 6 and trapped out in the trap 'I as a reflux cooling medium.

A suitable clean cracking stock for passing heating coil 53 may be a gas oil having a straw or light straw color or an oil of I5-20 on the 1/2 cell, Lovibond scale; however, the use in this stage of other relatively clean cracking stocks is not precluded.

While a preferred mode of operation has been described herein in detail it is to be understood that neither this form nor the approximate temperatures given are intended to serve as a limitation to the spirit and scope of my invention which is believed to be adequately defined and limited by the appended claims.

I claim:

The method of converting relatively viscous petroleum oil to a mo-tor fuel and to pitch-like residue in a combined distilling and cracking operation, which comprises heating the fresh oil to a mild cracking temperature to materially reduce the viscosity thereof while maintaining such pressure on the oil as to prevent vaporization of the more viscous constituents, flashing the viscosity-broken stream in a zone of lower pressure wherein separation of vapors and pitch-like residue occurs, passing the separated vapors to a fractionating zone and fractionating the vapors therein to recover a clean gas oil condensate therefrom, subjecting the gas-oil condensate to a relatively high cracking temperature while in transit through a confined heating zone, discharging the cracked products into an enlarged reaction zone maintained at cracking temperature under superatmospheric pressure wherein separation of liquid and vapors occurs, withdrawing liquid from said enlarged cracking Zone at a rate adequate to prevent accumulation of liquid therein and flashing the withdrawn liquid into said low-pressure flashing Zone, withdrawing vapors from said enlarged reaction Zone, dephlegmating and fractionating them to produce a final light motor-fuel distillate and a heavier condensate and delivering said heavier condensate to said low-pressure flashing zone.

RICHARD F. I'ROW.

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