US1939274A - Cracking process - Google Patents

Description

Dec. 12, 1933. wv .1. PERELIS CRACKING PROCESS Filed Feb. 14, 1929 Patented Dec. 7,12, 1933 1,939,274 CRACKING PROCESS Walter James "Perelis, Martinez, Calif., assignor, by mesne assignments, to Universal Oil Products Company, Chicago, Ill., a corporation of South Dakota Application February 14, 1929. Serial No. 339,796

.f 1 claim.

1 invention relates generally to the conversion of heavier hydrocarbon oils into lighter hydrocarbons by means of heat and superatmospheric pressure, for the production of gasoline like motor fuels. Y K y It is the object of this invention to provide a novel arrangement of a continuous process for Acracking heavy oils, in whicha larger percentage of the lighter hydrocarbons ,is obtained than was heretofore considered possible, with a minimum production of coke or carbon and fixed gases, and which results in greater eiiiciencyY and economy of operation.

g More particularly my invention consists in the combination of a short time and a long time cracking treatment in suchway that lthe oil, while containing heavy asphaltic matterwhich easily cokes, and would coke during a long time cracking treatment, is only subjectedto a primary shorttime cracking treatment, yand that only after removal of Vsuch asphaltic matter a secondary long time. cracking treatment is applied.

Further objects, features and advantages ,of this invention will appear from .the-following description in which I have set forth the preferred application of my invention. It will be understood that different modifications are possible without departing from the principles of my invention and Ido not limit myself to the particular construction shown and operation described. It will be further understood thatthe appended claims are to be accorded thescope and range of equivalents consistent with the state of the prior art.

It has long been known that in the cracking of hydrocarbon oils the rate of lconversion increases very rapidly with the temperature,A especially above 850 F., and it has been found that around 900 F. an increase of 10 degrees F. will nearly double the rate of cracking. To obtain a maximum yield of gasoline it is therefore .desirable to use high temperatures. However,

these temperatures can cause overcracking of those components of the oil which crack easily,r

possible to maintain a heavy asphaltic residualv oil at a temperature of about 900 F. for more than a few seconds without causing a most excessive coke formation. For this reason most cracking processes which crack the oilfor longer time, either by the use of digesting drums or expansion chambers or tanks, are in actual practice often operated at moderate temperatures, as 840-870" F., in these vessels. A higher temperature of around 900 F., wouldmomentarily result in an increased yield of gasoline, but cokes the plant up in a comparatively short time.

In these cracking processes the oil is kept in the drum at cracking temperature from a few minutes to several hours; these long time processes may be contrasted with short time processes in which the oil reaches cracking temperature only at or near the outlet of the heating coil, and cracks only a few seconds before it is cooled or vaporized; only about 10% of the material passed through the heater is converted during each passage, whereas in the long time cracking process 15% or more is converted each passage. I have found that in short time cracking, even a heavy asphaltic residual oil may be heated to a high temperature of 900 F. provided enough turbulence is maintained in the heating coil.

It is the object of my invention to provide a cracking process for heavy oils, which will make it possible to maintain most of the oil to be cracked, for a long time at a high temperature of around 900 F. and over, and so make use of the most efficient conversion temperature with a maximum yield of gasoline while avoiding coke formation.

I propose to do this and it is the principle of my invention to combine a short time and a long' time cracking process in such way that both at the end of the short time and all through the long time cracking process temperatures of around 900 F. can be used; the heavy asphaltic matter which cannot stand this high temperature for more than a few seconds without forming coke, I subject only to the short time cracking treatment, and after removal thereof I apply a secondary long time cracking treatment. This heavy matter is the black viscous substance of asphaltic nature which forms the heaviest fraction of most crude oils, and which may contain more or less paraffin wax.

Other features of the invention will bev mentioned hereunder after the explanation of the attached drawing which by way of example illustrates more or less diagrammatically an apparatus designed to carry a preferred application of my process into effect.

The cracking apparatus shown consists of:

heater 1, heaters 2a, b and c, evaporator 3', residuum cooler 4, dephlegmator 5, cooler 6, condenser 'I and pressure distillate receiver 8.

In the operation of this apparatus, the charging stock or feed, either crude oil or residual oil, which may be preheated to some extent, is passed through line 11, and forced by pump 12 through .primary tubular heater 1 where it is heated to a cracking temperature around 900 F., producing gasoline. From heater 1 the oil passes through pressure valve 13 and line 14 into evaporator 3, where evaporation is assisted by open steam from coil 15. The residue passes from the evaporator through valve 16 line 17 and cooler 4 to storage.

The vapors from the evaporator pass through line 18 into dephlegmator 5, where the heavy fractions are condensed as reflux and collect in surge tank 19, from which they are removed through line 20; the largest part of the reflux passes through valve 21 and line 22 and, by the action of pump 23 is forced through the secondary tubular heaters 2a, b and c. Leaving the last heater 2c, this part of the reflux joins in line 14 through pressure valve 24 and line 25, the

incoming feed, which is heated to around 900 v1". in heater 1. A small part of the reflux is used to cool the vapors in dephlegmator 5 by direct contact, and passes through valve 26 and line 27 into cooler 6, in which it is cooled, and then pumped over the top of the dephlegmator through line 28 by pump 29. The pressure distillate vapors pass from dephlegmator 5 through line 30 to condenser 7; the condensate together .with uncondensable gases passes to pressure distillate receiver 8, in which they are separated, the gases being removed through line 32 and pressure valve 33, theI pressure distillate through line 34 and valve 35.

While the foregoing is a general description of the main pieces of equipment necessary to carry out the operation of the system in its simplest formit will be understood that in actual practice more parts are required which for the clearness of the description have been omitted here; these can readily be supplied by those skilled in the art. Such equipment may comprise heat exchanging apparatus, automatic controls of liquid levels, of temperatures and pressures, different recording instruments etc.

As secondary long time' cracking process I prefer to use for my invention a three step cracking process similar to the processes described in my co-pending applications Serial Nos.

' 16,952, 39,280 and 137,344; however. other arrangements may be made by those skilled in the art to carry out the principle of my invention.

'I'he long time cracking process described in my previous applications consists mainly of three steps. each carried out in a separate heater. In the first step the oil is heated to the point where cracking begins to become more pronounced: in the second step the temperature is decreased or kept constant so as to give the material at this temperature of incipient cracking time to form enough gasoline vapor to create turbulence; in the third step the4 temperature of the turbulent stream is increased again to obtain the maximum rate of conversion. I found in the operation of this process, that if I used a temperature of 900 F. in the third heater 2c, it was desirable to maintain a pressure of around 200 lbs. at-the outlet thereof, to have sufficient turbulence in the oil stream in that heater to prevent coke formation; to obtain a pressure of 200 lbs. in the third heater it was necessary to operover to overcome the friction caused by the turbulent stream in the long coils. I further found when handling oil containing much asphalt that at that pressure of 400 lbs. I could not raise the temperature in the first heater to 900 F. without causing the formation of coke in the tubes of that heater, as the pressure prevented suiiicient turbulence to overcome the in creased cracking caused by the raise in temperature, and I was obliged to limit myself to moderate temperatures of the order of S40-870 F. in heaters 1 and 2. The most advantageous temperature of around 900 F., giving maximum conversion I found I could only use in heater 3 without causing coke formation, after suflicient turbulence of the stream of heavy oil has been developed in heater 2, while keeping the temperature of the oilI approximately at the same moderateheight or allowing it to drop slightly.

It will be seen from the description and the drawing of this invention, that in the present arrangement I have succeeded in overcoming this diiiiculty of having to use comparatively low temperatures in heaters 1 and 2. By eliminating from the long time cracking process carried out in the three heaters 2a, 2b and 2c those substances which because of easy coking prevent the use of high temperatures in the first heater 2a, I am able to raise the temperature of the oil already in the first heater to 900 F. or over, and keep it at approximately that range all through heaters 2b and 2c, with a slight decrease in heater 2b if necessary, and a slight increase in heater 2c if preferred. By maintaining the oil in this way for a long time at a higher average temperature I obtain a considerable increase in gasoline recovery in the long time cracking process, as the cracking rate of oils is a function of time and temperature. i

In addition to this increase in gasoline recovery. in the secondary cracking, I also obtain gasoline by the primary short time cracking in heater 1 at 900 F.. without coke formation. The asphaltic material in the heavy oil cracks easily with a substantial rate of conversion, but'as mentioned before, also forms coke very easily. if the right conditions are not observed. I have found that there is no difficulty in cracking this material at a temperature of 900' F., provided the pressure does not exceed 200 lbs. as otherwise there is not enough turbulence to prevent coking, and provided the material is kept only for a few seconds at this high temperature, to avoid overcracking and consequent coke formation.

The material passed through the long time cracking process consists of the heavy asphaltic charging stock from which the asphalt has been removed. in the evaporator, and the pressure distillate in the dephlegmator. During the long time cracking treatment some new asphalt is formed, which is also removed in the evaporator. Preferably, I employ open steam in the evaporator, and maintain a temperature between 650 and '120 F. but higher temperatures may be used according to the nature of the charge, and the products it is desired to obtain. The pressure in the evaporator is only an operating pressure, preferably not over 50 lbs.; the pressure in the cracking coils is released at the valves 13 and 24. Higher pressures than 200 lbs. may be desirable in the last heater 2c of the long time cracking process; a correspondingly higher pressure has then to be usedvin the iirst heater 2a. Where I mention a high temperature of 900 F., the actual temperature used in operation may vary say, between 880 and 930 F., according to circumstances.

The many advantages of my process will be clear from the above. By this combination of a short and a long time cracking process I have made possible the carrying of temperatures of the order of 900 F. in each heater of the combination, whereby a large part of the heavy oil is getting a more advantageous long time cracking treatment, and yielding a maximum quantity of gasoline, without producing large amounts of coke. With long time cracking less refluxing is required and therefore it requires less heating equipment and less fuel, which is an additional advantage of a long time cracking process, as the operating costs are lower.

I claim as my invention:

In a process for the cracking of heavy petroleum oils the combination ofv different cracking treatments for the feed oil and the reflux condensate produced in the process comprising heating the feed oil in a tubular heater to an eective cracking temperature under a pressure not over 200 lbs., terminating the heating in this primary cracking treatment as soon as the effective cracking temperature is reached, heating the reflux condensate in a tubular heater to an effective cracking'temperature and prolonging this secondary cracking treatment while rst lowering and then raising the temperature again, both within the cracking range of temperatures, the pressure at the termination of the secondary cracking treatment being at least 200 lbs., uniting the efflux of both cracking treatments, removing easily coking heavy material from the joint stream by vaporization of the lighter material,

thereafter condensing the material heavier than pressure distillate and passing this reflux condensate to the secondary cracking treatment.

JAMES PERELIS.

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