US2037953A - Method of converting hydrocarbon oils - Google Patents

Description

C. E. WATSON EIT AL METHOD OF' CONVERTING HYDROCARBON OILS Filed Aug. 1930 @#03 OJOS n. aoo@ ok cowl CII Patented Apr. 2l, 1936 UNITED STATES PATENT OFFICE METHOD OF CONTVERTING HYDROCARBON OILS Application August 8,

4 Claims.

This invention relates to an improved method of cracking hydrocarbon oils to produce oils of low boiling range from the original oils having a higher boiling range. It is a primary object of the present invention to provide an improved process by which the cracking of oils may be carried on economically and continuously and wherein a high yield of a desired low boiling end product is obtained with minimized yields of certain undesired products such as fixed gases, high boiling oils and carbon.

For a further understanding of the invention reference is to be had to the following description and to the accompanying drawing, wherein:

Figure 1 is a diagrammatic view illustrating apiparatus employed in the cracking and heat treatment of hydrocarbons in accordance with the method steps of the present invention, and

Figure 2 is a similar View disclosing the practicing of the present invention with apparatus differing structurally from that disclosed in Figure 1.

Referring more particularly to Figure 1 of the drawing, the numeral l designates an oil heater or converter. This converter consists of a wall structure divided internally by a bridge wall 2 into combustion and tube chambers 3 and 4. Burners 5 are disposed in the combustion chamber and produce the necessary heated furnace gases used in the heating of converter tubes 6 disposed in the converter. Vaporized oil is passed through the tube 6 and during the travel of such vapors through the tubes, the internal temperature of the converter is such as to heat said vapors to converting temperatures varying between 1000 F. and 1250 F.

Following the securing of the desired conversion reactions and the production of low boiling point hydrocarbon compounds, the vapors travel by way of an outlet pipe 1, while at a temperature in excess of 1000 F., into a conversion arrester or cooler 8. The heated vapors in the cooier 8 are brought into intimate contact with a continuously supplied spray of low temperature cooling oil comprising the charging stock, the latter being led into the cooler by way of a pipe line 0 from a make-up tank l0, the line 9 being provided with a pump Il. 'I'he contact of the hot vapors from the converter with the cool oil forced from the tank l0 results, first, in dropping the temperature of the converted vapors from .an active converting temperature in excess of 1000 F. to a nonreactive fractionating temperature not substantially in excess of 600 F., this drop in temperature being effected abruptly and substantially in- 1930, Serial N0. 473,897

(Cl. ISG-60) stantaneously by the heat exchange contained through the hot and cool iiuids. Second, in the cooler t the low boiling compounds present in the make-up or charging stock are vaporized and combined with the vapors which remain following the cooling of the converted products led into the cooler il.

The liquid oils and vapors from the cooler 8 enter a vaporizer l2 wherein there takes place a separation of the high boiling oils from the low boiling vaporized oils. These vaporized oils, at a temperature of approximately 600 F., are led from the top of the vaporizer into a fractionating tower lit through which the vapors pass upwardly and are deprived of the high undesired boiling compounds therein contained. The vapors leaving the top of the fractionating tower are composed of oils having an end boiling point of approximately 400 F., and these vaporized oils are condensed in the condensing coil i4 and collected as a motor fuel condensate in the receiving tank l5.

The high boiling liquid fraction, mainly fuel oil, which accumulates in the bottom of the vaporizer l2 is removed from the bottom of said vaporizer by way of a pipe line I6. This liquid fraction may possess a gravity of 20 Baum and a viscosity equivalent to 300 to 400 sec. Saybolt furol at 122o F. This high viscosity oil is forced through a pipe line I6 by means of a hot oil pump il and is delivered under pressure varying between 500 and 600 pounds per square inch to` the heating coil h3 of a tubular viscosity still I9. In the tube still this high boiling liquid fraction is subjected to temperature varying between 800 and 950 F., wherein some considerable cracking of the oil takes place in the liquid phase, resulting in a considerable reduction in viscosity of the fuel oil fractions. The cracked, or partially cracked oils are continuously discharged from the pipe still under reduced pressure into an evaporator 20. The heavy oils which remain in liquid form in the bottom of the evaporator are withdrawn by way of a pipe line 2| and delivered to a tank 22 as low viscosity fuel oil, while the lower boiling products, under the reduced pressures present in the still 20, are passed as vapors through the line 23, which leads to the bottom of the fractionating tower i3, wherein such vaporized oils are combined with the vaporized oils entering the fractionating tower from the vaporizer l2 and subjected to fractionation to further effect the removal of oils having boiling points higher than those which are desired to be collected in the receiving tank l5.

The liquid oils which accumulate in the bottom of the fractionating tower constitute clean overhead distillates having the boiling range of a light gas-oil fraction, and these oils are withdrawn from the bottom of the fractionating tower and forced by means of a pump 24 through a pipe line 25, which leads to a bank of vaporizing coils 26 arranged in the flue outlet duct 21 of the converter I. Sufcient furnace temperatures exist in the duct 2I to vaporize the greater portion of the oil led from the bottom of the fractionating tower and these vaporized oils are delivered to an evaporator 28 which functions to remove undesirable high boiling liquid oils which may be returned to the inlet side of the hot oil pump I'I. The liquid-free vaporized oils then pass from the top of the evaporator 28 to a bank of drying tubes 29 arranged in the converter I between the tubes 6 and 2e, and from the tubes 29 the vapors are conducted in a diy state, suitable for conversion to the converting tubes 6.

By the arrangement described, we combine both Vapor and liquid phase cracking in such manner as to secure a high yield of end point gasoline from the total high boiling oil stock charged to the system with a greatly reduced quantity of low viscosity fuel oil. Only clean overhead charging stock, free from high boiling fractions, is charged to the system. The process has the advantage of continuous operation and is capable of being maintained on sustained runs of prolonged duration.

In the form of the invention disclosed in Figure 2, a slightly diiferent type of converter has been illustrated from that set forth in Figure 1. In the form of the converter disclosed in Figure 2 the wall structure, as indicated at 3D, is provided forwardly with a Dutch oven 3l equipped with burners 32. The vaporizing tubes 2601f are arranged in the upper portion of the converter, the drying tubes 29a in the lower portion of the converter and the converting tubes 4a being disposed in the wall structure above the drying tubes and above the outlet bank of vaporizing tubes. With the exception of the structural arrangement of the tubes in the converter, the system as set forth in Figure 2 operates in exactly the same manner as that described in reference to the mechanism illustrated in Figure 1.

The present invention provides, therefore, a system of cracking hydrocarbon oils to produce a high yield of a motor fuel condensate which is characterized by its high anti-knock Value and its ability to be readily treated for commercial use as motor fuel spirit. rIlhe system provides for marked fuel economies and also the elimination of obstructive carbon deposit in such a manner as not to interfere with the sustained operation of the system. Fixed gas production is low, and, likewise, the heavy residual oils discharged from the system are maintained at an extremely low percentage of the total charging stock supplied thereto. The residual oils are subjected to a cracking action which serves to produce a low viscosity product that will fall under normal fuel oil specifications.

The apparatus above described is controlled by means of rate of flow controllers in both the vapor phase cracking and the viscosity stills, and by liquid level controllers on the vaporizer I2. The amount of fresh crude or charging stock delivered to the system is controlled by a liquid level regulator on the fractionating tower, which permits additional charging oil to be introduced as the oil level in the bottom of this tower falls.

Should the oil level in the vaporizer I2 tend to fall, the liquid level controller on this part of the equipment will permit additional oil to be introduced into the charging line from the conversion zone, the oil being taken from the bottom of the fractionating tower. It has been determined that the temperature of the materials entering the vaporizer I2 will always be low enough (not in excess of 600 F.) to prevent coke formation. The system described, therefore, combines both vapor phase and, to a limited degree, liquid phase cracking of hydrocarbon oils in a single, economically operated unitary system, minimizes fuel oil production and increases the yield of gasoline distillate.

What is claimed is:

1. The continuous process of converting highboiling hydrocarbon oils into low-boiling oils, which comprises: subjecting such high-boiling oils to low pressure vapor phase cracking at temperatures of the order of 1000 to 1250 Fah., cooling the cracked oil vapors substantially immediately upon their discharge from the vapor phase cracking stage to non-converting temperatures by bringing into intimate contact therewith fresh charging oils, regulating the mixture of the charging oils with the cracked vapors issuing from the vapor phase cracking stage so that the final temperature of the mixture is sufciently high to vaporize and retain in a vaporous state for subsequent fractionation all but the heavier fuel oil fractions found in said mixture, fractionating the Vaporized oils to separately obtain a low-boiling motor fuel distillate and a recycle distillate composed of hydrocarbons having an intermediate boiling range falling between the motor fuel distillate and the fuel oil fraction, delivering the oils of intermediate boiling range to the vapor phase cracking stage, withdrawing the heavy fuel oil fraction from the vapor phase cracking stage, and subjecting said fuel oil fraction without cooling while maintained in the liquid phase to cracking temperatures lower than those which prevail in the vapor phase cracking stage, whereby to reduce the viscosity of the fuel oil fraction and to eiect the formation of additional quantities of low boiling gasoline-like hydrocarbons and commingling the vapors from the liquid phase cracking step with vapors from the vapor phase cracking step for unitary fractionation.

2. The process of cracking hydrocarbon oils, which consists in subjecting said oils to cracking conditions While in the Vapor phase under low pressure conditions, rapidly cooling the cracked vapors upon their emergence from the vapor phase cracking stage to fractionating temperatures at which further cracking ceases by directly contacting said vapors with a charging oil, fractionating the mixture of cracked vapors and charging oil to obtain therefrom in separate stages a low boiling gasoline-like fraction, a completely vaporizable recycle fraction of intermediate boiling range and a high boiling fraction composed mainly of fuel oil, revaporizing said recycle fraction and recycling the vapors to the Vapor phase cracking stage, subjecting the high boiling fuel oil fraction to viscosity breaking conditions by passing the same through an high pressure liquid phase conversion stage, and delivering the liquid phase cracked products to an enlarged zone under reduced pressures whereby to remove from said zone a fuel oil fraction having a viscosity lower than that removed from the vapor phase cracking stage and to also reinove from said enlarged zone as vapors low boiling oils formed incidentally to the viscosity breaking operation, and fractionating the latter vapors commingled with the vapors from the Vapor phase cracking stage.

3. The continuous process of converting high boiling oil into low boiling oil which comprises vaporizing oil, subjecting the vapors to cracking conditions at low pressure and under temperatures of the order of from 1000 F. to 1250 F., separating the cracked products into a residue, a condensate of intermediate boiling point, and a fraction boiling within the gasoline range, recycling the intermediate condensate through the vapor phase cracking process, withdrawing the residue while in a heated condition and subjecting the residue to liquid phase cracking under high super-atmospheric pressure, separating vapors from the cracked residue and commingling the vapors from the two cracking stages and fractionating the combined vapors.

4. The continuous process of converting high boiling oil into low boiling oil which comprises vaporizing oil boiling substantially above the gasoline range, subjecting the resulting vapors only, to vapor phase cracking conditions of temperature and pressure, separating the cracked products into a residue, an intermediate condensate boiling above the gasoline range, and an overhead product containing the gasoline fraction, withdrawing and passing the hot residue through a liquid phase cracking stage under high super-atmospheric pressure, separating vapors from the cracked products issuing from said stage, uniting said vapors with the vapors resulting from the vapor phase cracking step, and fractionating the combined vapors to produce a gasoline fraction and a condensate heavier than gasoline, and recycling said condensate free from unvaporized residue to the vapor phase cracking step.

CORNELIUS B. WATSON. CLYDE L. SMITH.

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