US2006188A - Method of cracking - Google Patents

Description

June 25, 1935. H. SYDNOR METHOD OF CRACKING Filed Dec. 6, 1929 zJNVENTOR BY i Patented June 25, 1935 PATENT OFFICE METHOD or CRACKING Harold Sydnor, Elizabeth, N. J.. assignor to Standard Oil Development Company, a corporation of Delaware Application December 6, 1929, Serial No. 412,193

1 Claim.

This invention relates to an improved method of cracking petroleum products and will be fully understood from the following description in conjunction with the accompanying drawing.

The main object of the invention is to produce, from poor stocks. gasoline having good knock rating without the deposition of large amounts of coke in the reaction chamber, usually called soaking drum.

In the drawing Figure 1 represents a diagrammatic elevational view of the apparatus with two soaking drums connected in parallel and Figure 2 represents a similar view of the apparatus with two soaking drums in series.

When the operation is carried out in the apparatus shown in Figure 1, the mixed feed, consisting of the fresh feed to be cracked and the cycle stock, is pumped through heating coil 1 arranged in furnace and heated to cracking temperature. The hot oil is discharged through line 3 and branch lines 4 and 5 into the top of the soaking drum 6 and l in which most of the cracking takes place. The cracked efliuents leave through valved lines 8 and 9 at the bottom of the soaking drums, are united in line l0 and discharged into the bubble tower I l in which separation at reduced pressure takes place according to the boiling range. The gas and the light distillate leave the bubble tower through line l2 are condensed in a condenser (not shown) separated and stored.- The tar is pumped off through the bot-. tom line [3 and cooler (not shown) into a storage tank (not shown) The middle fraction or cycle stock is removed by line H part of it or the whole being returned by line IE to coil I for further cracking.

In Figure 2 the same numerals, primed, designate identical parts. The operation is similar to that described with Figure 1 with the only difference that the two soaking drums are now connected in series-the hot oil from coil I' is introduced through line 3' at the top of the soaking drum 6' in which it undergoes cracking. The cracked effluent leaving drum 6 at the bottom is discharged through line l6 into drum 1' at the top thereof, undergoes further cracking and leaves through valved bottom line I 0' to be discharged at reduced pressure into bubble tower I l'.

The novelty of the process consists in the combination of two steps: (1) introduction of the hot oil at the top of the soaking drums and removal of the cracked efiluent at the bottom thereof, (2) the use of several soaking drums connected in parallel or in series. In the drawing only two soaking drums have been shown but more of them may be used if necessary in one unit. In the latter .case they may be connected partly in series partly parallel. Thus, for instance, when 3 soaking drums are used I may pass the entire heated 011 through the first drum in downward direction, and pass the cracked effluent through the other two drums connected in parallel, the direction of flow being again downward.

The intensity of cracking may be measured by the amount of gasoline produced per hour, calculated as percentage of the mixed feed pumped to the coil per hour. This percentage of gasoline, which is usually called conversion per pass, depends, besides the intensity of cracking, also on the percentage of the cycle stock in the mixed feed, but when this last mentioned percentage is kept approximately constant, the conversion per pass indicates the intensity of cracking. Now, there are certain stocks which, when produced by mild or not intensive cracking yield a poor quality gasoline which causes knocking in the internal combustion engine. same stock is cracked in a usual tube and tank unit provided with one soaking drum, under intensive cracking conditions, too much coke is formed and deposited in .the soaking drum, necessitating frequent shutdowns of the unit.

By my invention intensive cracking can be maintained and a good grade of gasoline obtained from poor stocks without excessive coke formation. The following table serves for comparison of two operations: (1) run No. 1 carried out in a usual tube and tank unit in which the hot oil from-the heating coil was introduced at the bottom of the single soaking drum used and the cracked effluent removed through a single line at the top of the drum, and (2) run No. 2 carried out according to'the present invention with two soaking drums in parallel as shown in Figure 1 of the drawing. The oil submitted to cracking was a Talang Akar (Sumatra) paraffin distillate from which paraffin has been removed by pressing without much refrigeration.

Table Run No. l Run No. 2

Coil'outlet temperature F 870 875 Pressure on soaking drum, lbs/sq. in 750 750 Feed rate, gallons per hour l5, 000 12, 300 Yields Gasoline, percent by volume on fresh eed ...5-. ..l.'. 39. 0 41. 2 Cycle gas oil, percen y vo ume on fresh feed 24. 2 16.2 Tar, percent by volume on fresh feed- '19. 2 27. 4 Gas, percent by weight on fresh feed 17. 8 19. 3 Coke, percent by weight on fresh feed. 2. 8 l. l Tar gravity, "A. P. I 10.9 11. 1 Percent fresh feed in mixed feed 61. l 53. 6 Conversion per pass l9. 9 22. 1

Engine tests showed that the gasoline produced in run No. 2 was of a much better quality and less inclined to induce knocking than the gasoline of No. 1. It will be noticed that the conversion perpass was higher in run N0. '2; As a further advantage, thecoke production in run No.

ing conditions, liquid may accumulate in the soaking drumeither by incomplete vaporization or in consequence of polymerization, and such accumulated liquid may produce excessive amount of coke under the desired intensity of cracking.

Although I have described my process with special reference to the cracking of petroleum oils, it will be understood that the same process can be applied to the cracking of other oils, such as for instance shale oils for the production of lower boiling oils from higher boiling ones.

sired cracked product.

I claim:

The method of cracking hydrocarbon oil which comprises heating the oil to cracking temperature in a zone of restricted cross-section, then passing all the oil directly from said zone downward through a plurality of substantially vertically arranged cracking zones of large cross-section, in which a substantial amount of cracking takes place, without additional application of heat, the cracking zones of large cross-section being substantially maintained free of oil in the liquid phase by discharging liquid and vapor from the lower part of one zone of large cross-section into the upper part of another such zone, passing the resulting liquid and vapor from the lower part of the last-mentioned zone at reduced pressure into a rectifying zone, and segregating the de- H AROLD SYDNOR.

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