US2100922A - Process of cracking hydrocarbons - Google Patents

Description

Noviso, 1937, P, ACHS 2,100,922

PROC ESS OR CRACKING HYDROCARBONS Filed Aug. 31,' 1935 COMM/V850? COMPRESSOR Actual/Aron assa /v3 NOAgDVJJ VAPOR/25R INVENTOR Ala-er f? skews ATTORNEY Patented Nov. 30, 1937 UNITED STATES PATENT OFFICE PROCESS OF CRACKING HYDROCARBONS Albert P. Sachs, New

York, N. Y., assignor to Petroleum Conversion Corporation, New York, N. Y., a. corporation of Delaware Application August 31, 1935, Serial No. 38,688

1 Claim.

-My present invention relates to improvements in processes of cracking hydrocarbons in the vapor phase wherein the cracking is brought about by the aid of a heat carrier gas physically 5 mingled with the vapor to be cracked. After cracking occurs in such processes, the mixture of gas and cracked products is subjected to progressive dephlegmation to separate out various products involved in the cracking reaction including those useful as motor fuels. This leaves the gas saturated with light hydrocarbon fractions. A major problem in connection with processes of this type is to recover such light fractions and according to the process as heretofore practiced this recovery of the light vapors has been eiiected simply by the use of an absorber, after which a portion of the stripped gas is recirculated to constitute in part at least the heat carrier gas.

According to my present invention I recover the light ends by compression of the residual gas to a point where at least a major portion of the light vapors will become liquid at moderately low temperatures, after which the compressed gas after having passed through an absorber, or not, as the situation may require, is then led to a prime mover of some sort, as for example a turbine or other machine for converting the pressure and/or velocity of the gas into mechanical energy. Where an absorber is used, the stripping of the gas will be greatly facilitated because of its increased pressure. Such prime mover, however, will discharge the gases at the system pressure or somewhat above in order that the gases may be available for ,re-use in the system. By means of the process set forth, recovery of the light ends is greatly facilitated while the energy required for the compression is largely recovered in the prime mover.

My invention will be best understood by reference to the following detailed description taken with the annexed drawing showing diagrammatically an illustrative embodiment thereof.

In this drawing, l0 denotes a heater by means of which gas admitted thereto through pipe I l is heated. to above the cracking temperature for the oil vapor, as for example in the neighborhood of 1200 degrees F. -Such gas leaves, the heater through pipe l2 and passes therethrough to re action chamber l4. At the same time, oil vapor is fed to said reaction chamber by first vaporizing oil in a heating coil l6 and flash drum I! and the produced vapor conveyed through pipe l9 to superheater 2i whence the vapor, now superheated to a temperature say up to 950 degrees F., is conducted by pipe 22 to pipe I 2 and hence to reaction chamber H. The relative temperatures and quantities of the vapor and gas are so chosen as to heat the vapor in reaction chamber l4 to a cracking temperature desirably between 950 and 1050 degrees F., whereupon the mixture of cracked products and gas is withdrawn from said chamber through pipe 24 and passed to a fractionator 26. In the'fractionator 26 the reaction products are progressively dephlegmated so as to yield first of all a residue withdrawn through pipe 28 which after having been cooled by various heat exchange steps, as for example as set forth in the patent to Beardsley No. 1,883,744, is in part returned to the fractionator by pipe 23. Further up the column from the pipe 28 a distillate on the order of gasoil may be withdrawn through pipe 30 and if desired may be. passed back to vaporizer l6 through pipe 3|. At the top of the column a mixture of gasoline vapor and residual gas may be withdrawn through pipe 33 and led to condenser 33a from which the. condensate is collected in accumulator 34. A portion of the gasoline so condensed may be refluxed back into the column through pipe 35 and a pump 35'.

The residual gas now saturated with vapors of varying boiling point whose recovery is now desired, passes on through pipe 36 to compressor 31 by means of which the pressure may be greatly increased, as for example from a system pressure of around fifty pounds gauge to a pressure of as high as two hundred fifty pounds. The compressed gas is then led through pipe 38 to condenser 39 wherein the light ends because of the favorable pressure are easily condensed and pass to an accumulator 40. Since liquid may condense in the compressor, the latter is desirably located above the condenser so as to permit any such condensate to drain into the condenser. The lean gas may now, if desired, be passed to an absorber 4| to take out still further small quantities of vapors although if a suflicient pressure and a sufilciently low temperature are available in the condenser 39, such absorbermay not be necessary, in which case the gas may be bypassed around the absorber through pipe 4 la. In any event, the compressed gas passes through pipe 42 to a prime mover 43, as for example a gas turbine which may be used to supply energy wherever the same may be needed either about the plant or elsewhere. In this prime mover the gas is discharged under suflicient pressure to enable it to enter the system. Usually, this pressure will be fifty pounds gauge or higher. The

being recirculated through pipe 46 communicating with pipe H already described.

It will be understood that the temperature prevailing in the condenser 39 will be as low as the source of cooling water will permit, and that the lower such temperature, the more effective will be the recovery of the desired light ends.

In the example given, the pressure is boosted from fifty to two hundred fifty pounds; This ratio, however, is not to be considered critical, it being understood that the increased pressure employed will be sufiicient to greatly facilitate the stripping of the gas and to yield recoverable energy by means of a suitable prime mover.

I claim: 1

The process of converting hydrocarbon oils which consists in heating up a heat carrier gas to a temperature at least equal to that of the cracking temperature, simultaneously vaporizing the oil to be cracked, admitting the vapor to be cracked into contact with said heated heat carrier gas in said reaction chamber, while maingas leaves prime mover through pipe 44, part leaving the system through pipe 45 and the rest taining a system pressure not greatly in excess of 50 pounds per square inch, said gassupplying the necessary heat for the cracking ofsaid vapor, and withdrawing the mixture of gas and vapor products from the reaction chamber when the reaction .has proceeded to a desired degree, sub-- jecting such products to progressive dephlegmation to yield hydrocarbons of the gasoline range as the final product and a residual gas rich in light vapors, compressing said residual gas to a pressure not substantially lessthan250 pounds 'per square inch, whereby substantially all of the ALBERT P. SACHS.

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