US1812658A - Apparatus for cracking hydrocarbons - Google Patents

Description

June 30, 1931. N. s. Looms 1,812,658

APPARATUS FOR CRACKING HYDROCARBONS Filed July 22, 1925 2 Sheets-Shet 1 Nmumm. R.Looms awuentoz June 30, 1931. LQQMIS I 1,812,658

APPARATUS FOR CRACKING HYDROCARBONS Filed July 22, 1925 2 Sheets-Sheet 2 N M 2% s 5 & gfi 0 z \1 Q g 3 U Q E @51 k lbiiozmeg Patented dune 30, 1931 MED s'ras amass NATHANIEL ELLOOMIS, F ELIZABETH, NEW EEBSEY, ASSIGNOB T0 STANDARD OIL DEVELOPMENT COMPANY, -A CORPORATION 0E DWARF! APPARATUS FOR GRACKING- ROCARLBONS Application filed July .22,

This invention relates to improvements in processes and apparatus for the cracking of hydrocarbons into lower boiling products; The invention will be fully understood from the following description, taken in connection with the accompanying drawings, in which t Fig. 1 is a diagrammatic elevation of one suitable form of apparatus, and

Fig. 2 is a plan view of the same.

Referring to the drawings, reference numeral 1 denotes a shell still or equivalent distillation or vapor-separating means, arranged in a furnace setting 2. The still 1 is preferably provided with internal horizontal lines 3, through which hot combustion gases from the furnace pass to astack, not shown. The still is connected through line 4: with condensing and fractionating equipment, such as a bubble tower 5. This tower has the usual plates 6, receiving pan 7, vapor heat exchanger 8, vapor line 9, and condenser 10.

A condensate draw-oil line 11, having a valve 12, conveys a fraction of the type of gas oil from the pan 7 to an accumulator tank 13. A line 14 serves to supply cooling fluid (ordinarily feed stock for the system) to the vapor heat exchanger 8. A. by-pass 15 in line 14 and valves 14', 15', are provided for the regulation of the supply of feed stock.

A line 16 carries the preheated feed stock to a tar heat exchanger 17 which is supplied with hot residuum or tar from the still 1 through line 18, having a valve 19. The feed stock passes through the tar heat exchanger and thence through lines 20 and 21, the latter preferably extending below the surface of the liquid in still 1. Tar is withdrawn from the tar heat exchanger through valved line 22 to storage or other suitable disposition.

The gas oil or similar fraction in the ac cumulator tank 13 is forwarded through line 23 by the pump 24: to a cracking coil 25 arranged in a furnace setting 26. The cracking coil discharges through line 27 into either or both oftwo digesting chambers or soaking drums 28 and 29,-in accordance with the regulation of valves 30 and 31 inbranch lines 32 and 33. While two or more drums may be operated in series, the parallel arrangement 1925. Serial No. @5395.

illustrated is preferred. Draw-off lines 34 and 35 connect drums28 and 29 respectively to a line 36 which discharges into the still 1, preferably through the same line, 21, which serves for introducing the preheated feed oil.

A pressure relief valve 37 is provided in the line 36. The coil and drums are designed to be operated. at relatively high pressure, as is well understood in the art, and the drums should be thermally insulated as b means of a lagging 38, or in some other suita le way.

The following example of the use of the process is given as illustrative: Assuming the system to be in operation, a stream of oil to be cracked, for example a crude petroleum, is preheated in the vapor heat exchanger 8 and tar heat exchanger 17 and is then passed continuously into the still 1 at a temperature around 500 .F. The preheated oil becomes mixed with the cracked stock entering the still from the digesting chambers or soaking drums 28 and/or 29 through lines 36 and 21.

The temperature at which the oil enters the drum or drums may beabout 850 F. The temperature of the product withdrawn may be 775 F. Vapors and liquids together are passed from the drum or drums into the still.

through the lines 36 and 21.

The pressure inthe coil and drums may be about 300 to 350 lbs. per sq. in. This pressure may be reduced through the release valve 37 to substantially atmospheric pressure. The vcoolingincident to expansion of vapors may reduce the temperature of the oil entering the still to about 725 F.

The heat content of this oil isnot usually suflicient to distill the crude oil. The proper amount of additional heat is therefore supplied to the still, preferably by passing hot combustion gases through its internal lines 3. This method of heating is preferred, asv it in large measure avoids the coking difficulties in the still which might be encountered if'it were attempted to apply external heat. However, some external heat may be applied to the still in the installation shown. All the heat may be supplied externally, if adequate precautions are taken to prevent overheating, for example by using mufile furnaces.

The supplying of additional heat to the still is an important feature of the invention, as it enables me to interpose a digestion zone between the cracking coil and the still. The yield of light fractions is materially increased by the digesting operation. Direct injection of the stock from the coil into the still might supply sutficient heat for disti1la tion purposes, but the improved results characteristic of my invention would not be obtained. The temperature of the oil in the still may be about 650 F. The still may be operated under pressure, for example 60 lbs. per sq. in. in such case some cracking may take place in the still. Ordinarily, however, the primary purpose of the still is to strip the feed stock, and the distillation is conducted under atmospheric or lower pressure so that the heat requirements may be kept low.

In starting the operation, the still 1 is charged with the feed oil and fired to a distillation temperature. Meanwhile, gas oil or the like is supplied from an external source to the cracking coil, which is suitably fired. lhe efliuent from the coil is discharged into the drum or drums, and the cracked product is delivered into the still, in the manner described. As soon as the system produces an adequate amount of gas oil, this alone is used as the stock to be cracked.

The cracking oil and soaking drums may be operated under any suitable conditions. Generally, the oil will be passed through the coil at such a velocity that most of any carbon forming therein is swept out into the drums. Conversion takes place in the coil and drums, in a manner well understood in the art; that is, incipient or partial conversion occurs in thecoil and further conversion is efiected in the drum, by virtue of the contained heat of the oil.

The system described is particularly advantageous in the cracking of heavy crudes, such as Smackover crude, which ordinarily give difiiculty because of excessive scale formation in the coil. lit will be noted that according to this invention the crude itself does not enter the cracking apparatus; only the distillate from the crude is cracked. ln this way scaling troubles are substantially avoided. The invention is equally applicable to the treatment of the higher grade crudes and other feed stocks. The still and tower operate as a dehydrating means, so that crudes containing water may be treated without the necessity for additional equipment to remove the water. The heat exchange is very efiicient and the fuel consumption of the process is therefore correspondingly 10W.

lhese and other advantages of the invention are not necessarily dependent upon specific details of the construction and operation described, and various changes and alternative arrangements may he made withestates exchanger, whereby the oil is preheated, a M

tar heat exchanger connected to the still and adapted to receive hot tar therefrom, means for passing the preheated feed stock through the tar heat exchanger and thence into the still, means for conveying heavy condensate formed in the tower to an accumulator tank and thence through the cracking coil and digesting drum, a pipe for withdrawing the oil from said drum and passing it directly to the still, and a pressure release valve in such withdrawal ipe.

NATHANIEL E. LOOMIS.

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