US1946329A - Process of cracking mineral oil - Google Patents

Description

Feb, 6, 1934. A. E. PEw, JR

PROCESS OF CRACKING- MINERAL OIL Filed No'v.

Patented Feb.. 6, 1934 UNITED STATES PROCESS F CRACKING MINERAL OIL Arthur E. Pew, Jr., Bryn Mawr, Pa., assigner to Sun Oil Company, of

poration of New Jersey Philadelphia, Pa., a corpplication November 9,1929. Serial No. 405,870

8 Claims.

In order to crack,'in the vapor phase, crude oil or any product, such as gas oil, resulting from the distillation of crude oil, in order to produce comparatively low boiling products such as gasoline, such oil as is passed through the vapor phase cracking zone should not only be completely vaporized, but it is important that the vapor should be perfectly dry. An oil may be so completely vaporized that no entrained liquid may be separated therefrom by any mechanical device for throwing out any entrained liquid, but it may still contain sufcient very finely divided particles or very moist vapors that are practically at the dew point, in consequence of which, when the vapors are exposed to moderately high temperatures, there is a decided formation of carbon on the metal surface through which the heat is conducted to the vapors.' The amount of carbon so formed is relatively very small, but it builds up on the metal walls and in time so reduces or obstructs the ow that it is necessary to shut down the equipment for cleaning.

It is, ofl course, obvious that one method of overcoming this difculty is to superheat or raise the temperature of the vapors so that they are completely dried and free of any moisture or nely divided entrainment. 'Ihis method has been used for this purpose with proper distribution of heating surface. In a very mild form of heating this can be done with a reasonable degree of success. When, however, the drying of the vapors is eiected in this way, the lack of uniform conditions, which it is almost impossible to maintain, militates against success.` Any excessive temperature in the drying zone causes accumulation of carbon in a relatively short period, while any drop in temperature in the drying zone which does not fully dry' the vapors, even for relatively 'short periods, allows the moist vapors to go into the cracking zone and thus form carbon very rapidly in the cracking tubes. Another cause of trouble with such an arrangement is that the carrying over of any actual liquid into the drying zone causes the formation of vapors in the drying zone, which then are saturated or even carry entrained liquid, thus introducing such saturated vapor or entrained liquid into the cracking tubes.

The process involving the present invention is intended and adapted to overcome these dilculties and to provide more positive means of cracking.

The entire .process will rst be described and completely drying the vapors before they are n- 'troduced into the vapor phase cracking zone. ItA

the invention will then be particularly pointed outin the claims.

The charging stock (preferably gas oil) is taken from the tank through line 1 and pump 2 through heat exchangers 3 and 150 into the pipe still 4, where it isheated up to practically completely vaporize the oil as it enters the vaporizer 5. The preferred pressure set up by pump 2 is such that the outlet pressure on the pipe still 4 is maintained at from 50 to 100 pounds, which is` simply the lback pressure of the vapor phase cracking and fractionating equipment. The vapors leave the top of vaporizer 5 and pass through a separator 6, which takes out any mechanical entrainment of liquid and prevents any liquid passing beyond this part of the line. From separator 6 the vapors go to a gas and vapor mixer 8, where a dry gas is introduced which has been heated, preferably, to about the same temperature as the vapor. Here the dry gas and oil vapors are thoroughly mixed. The mixture then passes into the vapor phase crackingA coil 9, is raised therein to the required or desired temperature (say about 950 F. or above) andpasses out at 10 into the spray cooler tower l1, where it is cooled and partially separated. In tower 11 the heavier portion is drawn off at the bottom through outlet 12 and the remainder goes out as vapor through line 13 and into fractionating tower 16, where the lighter portions are separated. Gasoline and gas go out through line'17, through a clay tower 23 and through a condenser 24 into a gas separator 30, from which gasoline is taken out through line 3 1. 'Ihe gas escapes through line 32 into an absorption tower 33 and thestripped gas is passed out through lines 34 and line 40 to a gas holder, or tothe atmosphere; or the gas, -or a portion thereof, may pass to line 36.

From tower 16 an intermediate product is taken out through line 19 and, after passingthe heat exchanger 3 and/or other coolers, goes to loo by being conducted through by-pass line 190 to the feed or changing stock line; the product being very similar to the original gas oil which is .used as charging stock.

All of the gasoline vapors and gas are not taken out of tower 16 through line 17, but a regulable proportion is taken out through line 18 and passed through condenser 26 into tank 27;'the condensate being taken through pump 28 and line 22 back 4into the top of the fractionating tower. This condensate is used for controlling the temperatures at the top of the tower in order to fix the maximum boiling point of the product taken through line 17. Line 29 is the vent which vents the gas from tank 27 soas to maintain the proper level of liquid in this tank.

The condensate in tower 16 is conducted back to the upper part of tower 11, where it promotes or eiects the cooling and fractionation of the cracked vapors from the cracking coil 9 and controls the outlet temperature through line 13. This condensate is conveyed to tower 11 through lines 20 and 15, being, co'oled by heat exchange, at'l50, with incomingcharging stock.v The line 50, which leads from the outlet at the bottom of vaporizer 5, is for conveying away any heavy ends' which may not be completely vaporized when the oil leaves the pipe still. This high boiling product may becarried back into line 15, as shown, or may be withdrawn from the system. If a relatively heavy charging stock, such as a topped crude, is used, then a considerable portion is drawn ofi at the bottomiof vaporizer 5 and this should then be passed through line 14 into tower 1l. Such heavy portions are exposed to the highest temperature in tower l1 and in this way cracked to some extent and the heavy portions are drawn oi through line l2 along with the heavy products from the vapor phase cracking coil.

As hereinbefore stated, the gas which is cornbined with the vapor atv 8 may be taken from the dry gas line 34 of the plant or, through line 41,

' from any other source. It may go through line 36 and be heated partially by heat exchange at 360 with the oil from tower' 16 and partially by tubes 3 7 which are provided in the pipe still or cracking furnace. This gas is thereby raised, preferably, to the same temperature as the vapor, or approximately 750. This gas, when heated to the same temperature as the oil vapor, con' vious to their combination. This mixture of saturated vapor with the superheated gas has the effect of reducing the dew point ofthe mixture so that no form of moisture can exist at this temperature. The greater the amount of the superheated gas which is used, the lower will become the dew point of the mixture. The ratio of such gas, by weight, to the oil vapor, is preferably .from 5 to 15%. This percentage of gas effectively maintains the vapors in a perfectly dry state, so that when the mixture is introduced into the cracking coil at 9 itwithstands the high temperature heating surface without any substantial carbon formation. The percentage of gas, by weight, may, under exceptional conditions. be as low as 1% or higher than 15%. An excessive volume of gas may not affect operativeness, but would be open to serious objections.

The drying of the oil vapors may also be effected by combining the process herein described of mixing dry gas therewith with a reduction of pressure between the vaporizer and the cracking coil,v as set fortlr in an application, Serial No. 405,11, filed of even date herewith.

Having now fully described my invention, what I claim and desire to protect by Letters Patent is:

l. 'I'he process of cracking mineral oil charging stock which comprises vaporizing the voil in one locus, removing from the vapors mechanically entrained liquid particles, then drying the oil vapors in another locus by mixing therewith a relatively small proportion of a dry hydrocarbon gas, then at still another locus heating the mixture to a cracking temperature and cracking the oil vapors, and cooling and fractionating the vapors.

2. The process of cracking mineral oil charging stock which comprises vaporizing the oil in one locus, removing from the vapors mechanically entrained liquid particles, then drying the oil vapors in another locus by mixing therewith a relatively small proportion of a dry hydrocarbon gas at a temperature close to but not substantially exceeding that of the oil vapors, then at still another locus heating the mixture to a cracking temperature and cracking the oil vapors, and cooling and fractionating the vapors.

3. The process of cracking a mineral oil charging stock which comprises vaporizing the oil in one locus, removing from the vapors mechanically entrained liquid particles, then drying the oil vapors in another locus by mixing therewith a relatively small proportion of a dry gas, then at still another locus heating the mixture to a cracking temperature and cracking the oil vapors, and cooling and fractionating the vapors.

4. The process of cracking a mineral oil charging stock which comprises vaporizing the oil, allowing the vapors to expand and removing heavy fractions and mechanically entrained liquid particles, then drying the oil vapors by mixing therewith a. relatively small proportion of a dry gas, then heating the mixture to a cracking temperature and cracking the oil vapors, .and then cooling and fractionating the vapors.

5. The process of cracking a mineral oil charging stock which comprises vaporizing the oil in one locus, removing from the vapors mechanically entrained liquid particles, then drying the oil vapors in another locus by mixing therewith a substantial proportion of dry gas less than about 15%, vby weight, of the vapors, then at still another locus heating the mixture to a cracking temperature and cracking the oil vapors, and cooling and fractionating the vapors.

6. The process of cracking a mineral oil charging stock which comprises vaporizing the oil'in one locus, removing' from the vapors mechanically entrained liquid particles, then drying the oil vapors in another locus by mixing therewith a relatively small proportion of a dry gas at a temperature close to but not substantially exceeding that of the vapors, then at still another locus heating the mixture toa cracking temperature and cracking the oil vapors, and

vapors, and cooling and fractionating the val pors,

8. The process of cracking a. mineral oil charging stock which comprises vaporizing the oil in one locus, removing from the vapors mechanically entrained liquid particles, then dry- 2 ing the oil vapors in another locus by mixing therewith a substantial percentage of a dry gas less than about 15%, by weight, of the vapors and a temperatureclose to and not substantially exceeding the temperature of the vapors, then'at still another locus heating the mixture to a cracking temperature and cracking the oil vapors, and cooling'and fractionating the vapors. y n

, ARTHUR E. PEW. Jn.

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