US2068856A - Combined still and coil cracking - Google Patents

Description

Jan. 26, 1937. F. A. HOWARD 2,068,856

, COMBINED STILL AND COIL CRACKING Filed July 25, 1929 ATTORNEY Patented Jan. 26, 1937 UNITED STATES PATENT OFFICE Frank A. Howard, Elizabeth, N. J., assignor to Standard Oil Development Company, a corporation of Delaware Application July 25, 1929, Serial No. 380,783

2 Claims.

This invention relates to improvements in combined still and coil cracking of hydrocarbon oil, particularly that type in which a hot product from the coil is used to heat the oil in the still.

A principal object of the present invention is to provide an improved cyclic circulation including coil, still and fractionation means. A clean circulation is secured by removing tar in an expansion zone. Heat from the cracked product is imparted to the oil in the still by indirect heat exchange.

The invention will be fully understood from the following description read in connection with the accompanying drawing in which the figure is a diagrammatic side elevation of preferred equipment.

Referring to the drawing, the equipment comprises a cracking coil I located in a furnace setting 2 and discharging through line 3 having a pressure control valve 3a into the lower portion of a vapor separator 4. Oil is passed into the system through a line 21, subsequently described. A line 5, controlled by a valve 6, permits the discharge of tar from the separator.

Vapors from the separator 4 are conducted through line 1 and valve 8 into the lower portion of a bubble tower III, which is provided with the usual bell caps II, down-flow pipes I2 and top cooling coil I3. Vapors issuing from the bubble tower pass through a line I4 to a condensing coil I5 and receiving drum I6. A distillate outlet I! and a gas outlet I8 communicate with the 'drum. Valves I9 and 20 are provided in these outlets respectively. A pressure control valve 2I is provided in line I4 between condenser I5 and tower Ill.

A still 25 is provided intermediate cracking coil I and separator 4 with the line 3 passing therethrough whereby the contents of the still can be heated by the hot oil passing through the line 3. This line can be manifolded or coiled so as to secure more extensive contact surface.

The still is preferably heavily lagged and is set over a furnace 25a. Vapors from the still are passed into the bubble tower through the line 26 in which there is a pressure control valve 260.. Feed oil, together with the heavier constituents condensed from the vaporous product in the bubble tower are introduced into the still through a line 30. A spreader plate 30a is preferably provided to distribute the oil. A valve 3| is provided in line 30. A line 32 connects line 30 thru valve 32a and pump 33 with cracking coil I, for the introduction of feed oil and condensate into the cracking coil. A line 34 communicates with the bottom of still 25 and the line 32. A valve 35 is provided in line 34. The still bottoms can be conducted from still 25 through lines 34 and 32 into the cracking coil I. A line 36 connects line 21 with cracking coil I and permits of the 5 introduction of fresh feed oil directly into the cracking coil. A valve 3'! is provided in the line 36.

In operating the equipment, feed oil such as gas oil or the like is introduced through line 21, bubble tower I0 and lines 30 and 32 into cracking coil I and thence into separator 4. The oil is subjected to a temperature of approximately 850-900 F. inthe cracking coil. Tar accumulating in the separator 4 is withdrawn through the line 5. The vapors are withdrawn from the separator through line 1 into the bubble tower I0 Where they are rectified and in part condensed by the feed oil, the lighter ends thereof being simultaneously vaporized. The rectified vapors are withdrawn and condensed toform end products of fixed gas and cracked distillate.

The feed oil, together with the heavier constituents obtained from the vapors in the bubble tower, are subjected in the still to temperatures approximating 775 to 800 F., whereby additional cracking of the oil is obtained. Some or all of the heat used for distillation is obtained from the indirect heat exchange effected by the highly heated oil passing through line 3.

The oil is preferably maintained under a pressure of approximately 450# per sq. in. while passing through the cracking coil and separator and a pressure of approximately 200 to 400# per sq. in. is preferably maintained in the still and tower. A lower pressure than 450 pounds per square inch can be maintained in the separator and some of the advantages of the invention will be retained. Bottoms are continuously withdrawn from the still through pipes 34 and 32 by means of pump 40 33 or otherwise and pass through the cracking coil I where they are raised in temperature approximately to 125 F. thereby vaporizing approximately 60 to of the bottoms when the pressure is reduced as in the separator 4. The 45 highly heated oil and vapors passing through the line 3 supply the heat for cracking and vaporizing the oil in the still, and also offset the heat lost by radiation from the still, and drop in temperature approximately 75 to as a consequence thereof. Heat from other sources may be also supplied to the still, if required.

Numerous changes and alternative arrangements may be made within the scope of the ap- 55 pended claims in which it is the intention to claim all novelty inherent in the invention as broadly as the prior art permits.

I claim:

1. The method of cracking petroleum which comprises introducing said petroleum into a fractionating zone, passing it counter-currently in said zone to vaporous cracking products whereby said petroleum is partially stripped, introducing the residual petroleum into a cracking and distillation zone where it is subjected to conditions suitable for limited cracking and distillation, removing vaporous products from this zone, passing the residual petroleum from this zone to an elongated narrow heating zone in which it is subjected to more severe cracking conditions, conducting the total cracked eflluent directly through the said cracking and distillation zone in indirect heat exchange relation thereto without permitting any of said cracked effluent to come in contact with products undergoing cracking in said cracking and distilling zone, passing said cracked effluent to a separator, withdrawing tar from said separator and rejecting it from the system and passing vaporous products to said fractionating zone.

2. The method of cracking petroleum, which comprises the cracking distillation of the petroleum at temperature and pressure of the order of 775 to 800 F. and 200 to 400 pounds per square inch, taking ofi vapors, Withdrawing unvaporized residues and heating them to cracking temperature and pressure of the order of 850 to 900 F. and above 400 pounds per square inch, passing the heated residues while at cracking temperature in indirect heat exchange relationship with the oil undergoing cracking distillation to heat said oil, separating the residues into vapors and tar in a separation zone maintained under a pressure between 200 and 450 pounds per square inch, withdrawing the tar, stripping light fractions from the petroleum passing to the cracking distillation, by contact with vapors from the cracking distillation and the separation Zone and supplying additional heat to the oil undergoing cracking distillation from a source independent of the products of cracking.

FRANK A. HOWARD.

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