US2203930A - Petroleum distillation - Google Patents

Description

June 11, 1940. J n- 2,203,930

PETROLEUM DI STILLATION Filed Oct. 15, 1937 42 1' V X72 fl] Feed 77 INVENTOR 4 FrankJSmi/h 2 M17@ F 2 Aspha/f M ATTORN EY and kerosene.

Patented June 11, 1940 I PATENT OFFICE lETROLEUM DISTILLATION Frank J. Smith, Louisville, Ky; assignor to Standard Oil Company, Chicago, 111., a corporation of Indiana Application October 15, 1937, SerialNo. 169,129

7 Claims. (01. 19 -73 This invention relates to a process and apparatus for distilling petroleum oils and more particularly heavy residual petroleum oils. An object of the invention is to provide a method for controlling pipe still distillation and more particularly for controlling the operation ofa two coil pipe still wherein two or more streams are separately heated in a single pipe still furnace. An-

other object of the invention is to regulate the 1 operation of a two coil pipe heater with maximum heat economy. Another object of the invention is to provide a method of controlling the temperatures obtained in a two coil heater by trans ferring heat from one coil to the stockcharged to the other coil in variable amount as desired to balance the respective coil outlet temperatures. Still another object of the invention is to obtain close control of the temperatures of two oil streams from a single pipe heating furnace with- :20 out the necessity of interfering with the combustion balance in the furnace. Another object of the invention is to provide a method of producing especially high quality asphalt from crude petroleum and other heavy petroleum products by 25 rapid evaporation of heavy oils therefrom without permitting decomposition of the asphalt which results in its being contaminated by relatively low boiling hydrocarbons. Other objects of the invention will be apparent from the fol- 3 lowing description.

My invention is illustrated by the accompany ing drawing in which Figure 1 shows a schematic arrangement of one modification in which heat may be transferred from the oil entering the second coil to the charge of the first coil in a two coil heater. Figure 2 is a diagram showing another modification of my process in which heat from the products of the second coil is transferred to the charge of the first coil in a two coil pipe heater.

Referring to Figure l, topped crude petroleum which has been distilled substantially free of gasoline and which may be at a temperature of 375 F. for example, is introduced by line II] to heating 45 coil I I in pipe heating furnace I2 where the temper-ature of the oil may suitably be raised to 700 F. in the transfer line I3. The heated oil is transferred to fractionatlng tower, where light fractions are removed, including naphtha The unevaporated oil is withdrawn from the base of tower M by line l5 and pump I6 through exchanger l1 and thence by line I8 to the. second coil I9 in pipe furnace I2.

The oil may be charged to coil l9 at a temperature 55 of about 550 to 650 F. and discharged by transfer line 2n at a temperature of about 750 F. The. hot oil and vapors are introduced into fractionating tower 2!. This tower is preferably operated under vacuum, for example 50 mm; mercury absolute pressure and gasoil and lubricating oil 5 fractions may be withdrawn as desired. For example; gas oil vaporsmay be withdrawn by vapor line 22 and a lubricating oil fraction may be trapped out as a side stream by line 23. The unevaporated residue may be withdrawn by line 24 and employed in the manufacture of asphalt or as a heavy residual fuel oil. I

A portion of the stock flowing through line II] may be diverted through heat exchanger I! by partially closing valve 25 and opening valve 26 16 in line 21. By regulating valves 25 and 26 any desired amount of the stream flowing in line I0 may be thus diverted through the heat exchanger H where it absorbs part of the heat of the oil flowing through line I8. The temperature of the oil in line It may thus be raised or 50 for example, thereby reducing the heat duty on coil II and increasing the heat duty on coil l9. As a result of the changein the heat duty of coils II and I9 theoutlet temperature of coil I9 will be 25 reduced and that of coil II will be increased a proportionate amount without altering the firing of the heater I2. Of course if the temperatures of both coils are too low or too high these may be corrected by regulating the firing in the conven- 3o tional manner. This device therefore provides a very convenient method of controlling the outlet temperatures of the respective coils II and I9 and thereby regulating the operation of fractionating towers I4 and 2| within narrow limits. If

desired, I may employ automatic means for regulating valves 25 and 26 to maintain a constant temperature in either line l3 or line 20, the firing of the heater I2 being controlled by the temperature of the other line.

Referring to Figure 2, crude oil may be heated by passing through reflux exchangers 4|] and 4| and topped in the customary topping still to remove gasoline. The topped crude is introduced by line 42 leading to exchanger 43 and is then 4 conducted by line 44 to pipe heater 45 where it flows through economizer 46 and thence through radiant heating coils 4T, discharging by transfer line 48 into flash drum 49. If desired,

a portion of the heated stock in line 44, leaving 5 exchanger 43 may be vaporized by flashing in a I flash drum (not shown) and the vapors conducted directly to fractionator 5| later described.

The temperature of the oil flowing through line 48 may be about 690 F. Vapors of gasoline, r

oil, kerosene and naphtha are withdrawn from the flash drum by line 55 and fractionated in tower 5!, light gas oil being withdrawn at the bottom by line 52 and naphtha or kerosene vapors being withdrawn by line 53 leading to a condenser not shown.

Unevaporated oil is drawn from the base of flash drum 59 by line 54 to accumulator 55, the pressure of which is balanced against the flash drum pressure by line 56. Oil from the base of accumulator 55 flows by line 5? and pump 53 to heating coil 55 within the heater 35. Steam may be admitted by line til to the stream entering heating coil 59 to increase the velocity, reduce coking and corrosion and otherwise facilitate the distillation of the heavy stock flowing through this coil. The temperature of the oil introduced to the coil may be about 550 to 675 F., depending principally on the temperature of the oil in line it and the extent of distillation in flash drum 49.

Hot oil is conducted from coil 59 by line 5!, suitably at a temperature of about 750 F. to fractionating tower 62 wherein light constituents are evaporated from the asphalt and vapors reiiuxed in the upper section of the tower by the reflux coils 40 and il. Uncondensed vapors are withdrawn by line 53 leading to a condenser not shown.

In the tower B2 reflux is largely prevented from passing to the bottom by trap-out plate 64 from which heavy gas oil and/or lubricating oil are withdrawn by line 85. If desired additional trapout plates may be provided in the upper section of tower 52 to remove other fractions, such as light lubricating oils. When not employed for the manufacture of lubricating oils the stream withdrawn by line 65 may be subjected to cracking for the production of gasoline.

A portion of the heavy residual oil in the base of tower 52 may be collected by trapout plates 55 and conducted by pump El and line 68 to heating coil 59, preferably by passing first through heating coil 59, which discharges into the inlet of coil 59. The purpose of returning part of the asphalt to the heater is to increase the amount of heat introduced into tower 52 by the stock in line 5!, thus facilitating the operation of the tower by permitting higher reflux ratios resulting in better fractionation and separation of heavy distillates from the asphalt. Recycling of residues in this manner has been previously practiced in the vacuum distillation of lubricating oils as described in Bahlke and Stockdale Patent 1,997,675 and is not a part of my invention. The amount of residual oil which may be recycled in this manner may be about 20 to 60% of the unevaporated. residue in tower 52.

Asphalt which overflows trapout plate 56 passes to the base of tower at where it may be subjected to the stripping action of steam introduced by line iii, the purpose of the steam being to strip from the asphalt as completely as possible all lower boiling oils which adversely affect the properties of the asphalt if allowed to remain therein. I prefer also to operate tower 52 at a reduced pressure, for example 50 mm. mercury absolute to facilitate the removal of oils from the asphalt and avoid the necessity of operating the fractionating tower at a higher temperature which would increase the decomposition of the asphalt with the formation of lighter oils in situ.

When operating tower 52 under vacuum the asphalt may be withdrawn from the bottom thereof by pump H and line '12 at a temperature of about 600 F. The asphalt is immediately cooled by passing through exchanger 43 and discharged from the process by line 13. The purpose of the immediate cooling of the asphalt stream as indicated above is to reduce the temperature below the decomposition point, for example about 450-500 F., and thus prevent the formation of light oils therein by thermal decomposition since light oils present in asphalt have been found to cause objectionable staining when the asphalt is used for certain purposes, such as in the manufacture of roofing materials. Their presence in amounts of only fractions of 1% can be readily detected by the .socalled stain test which asphalt must pass before they are acceptable for the purposes indicated. Various methods may be employed for testing the staining characteristics of the asphalt as placing a sample of the asphalt in contact with paper, talc, etc. Applicant prefers to employ the following test: A sample of asphalt is placed in a shallow fiat dish and melted to form a layer. A thin layer of talc powder is then placed on the asphalt and the dish placed in an oven at a temperature of F. for 48 hours. The sample is then removed from the oven, excess talc discarded and the color of the talc layer adhering to the asphalt is examined. The discoloration of the white talc layer is a direct indication of the staining characteristics. Two or more specimens of asphalt may be compared in this way.

In order to balance the operation of coils 41 and 59 and maintain the desired control of flash drum' i9 and fractionating towers 5! and 62 I continuously withdraw a portion of the asphalt from the cooled stream passing through line 73 by means of valved line it leading to accumulator 55. This may be conveniently accomplished by regulating valves l5 and it. The temperature of the oil withdrawn may, for example, be about 425 F. The amount of asphalt recycled in this manner is usually relatively small and will ordinarily be about 5 to 20% of the total asphalt in tower 52. By increasing or decreasing the amount of asphalt by-passed in this manner the temperature in transfer line 6! may be respective- 'ly reduced or raised as desired. When maximum reduction ofthe transfer line temperature in 6| is required it may be desirable to slow down pump 61 with the result that the asphalt recycled to coil 59 is returned at a lower temperature,.for example 425 R, instead of GOO-650 F. which is the approximate temperature of the oil in line 68. Thus my process provides a very sensitive means of heat control which responds to the mere turning of a valve. At the same time no heat is wastefully discarded from the system since the heat removed from the oil recycled in line 14 is all absorbed by the oil charged through line 44 to heating coil 41. By increasing the amount of asphalt recycled through line l4 and reducing that recycled through line 68 I am thus enabled to increase the heating duty of coil 59 and reduce that of coil 4'? with the result that the transfer line temperatures in lines 65 and 48 are lowered and raised respectively without changing the firflux to lower the temperature therein and pre- I vent decomposition and coke formation.

temperature of the oil from each stream. by exstream.

Having thus described my invention, what I claim is:

1. In the process of distilling petroleum oils wherein the .oil is heated in arestricted stream in a heating zone, a portion of the oil is evaporated and the unvaporized oil is further heated in another restricted stream in the said heating zone and then another portion of the oil is evaporated, the improvement comprising controlling the changing heat between the oil to be heatedin one of said restrictedstreams with the oil introduced into said other restricted stream.

2. In the distillation of petroleum oils wherein oil is supplied to two separate fractionating zones from two separate restricted streams located in a single heating zone, the first of which restricted streams is supplied with hot feedstock and the second with a cooler stock, theimprovement comprising reducing the temperature of the oil discharged from said first restricted stream charged with hot feed stock by exchanging heat between the hot feed charged thereto and the cooler stock charged to saidsecond restricted stream.

I 3. The process of claim 2 in which said heat exchange is accomplished by by-passing a regulated' portion of the cooler feed stock of said second restricted stream into heat exchange retransferring regulated amounts, of heat to the oil entering said first heating zone from the charged to said second heating zone.

5. In the process of distilling residual petroleum oils wherein a stream. of said oil is heated.

oil

in a firstheating zone, partially distilled, the 1111- I distilled residue is heated in a second heating zone to a higher temperature and then further distilled said heating zones being both supplied with heat from the same source, the improve ment comprising lowering the temperature of the oil leaving said second heating zone by transferring heat from the oil entering said second heating zone to the oil entering said first heating zone.

6., The process of producing from crude petroleum, asphalt having. a satisfactory stain test which comprises removing frornsaid crude petroleum lighter fractions and light gas oil by heating in a continuous restricted stream and flashing oif said light fractions, returning the unevaporated residue xirom said flashing operation to a second heated stream supplied by heat from the same combustion gases employed in heating said first mentioned restricted stream, conducting the heated oil from said second heated stream to a fractionating zone wherein heavy oils are evaporated from asphaltic constituents, withdrawing and immediately cooling said asphaltic constituents to prevent thermal decomposition thereof, employing a variableamount of the heat removed from said asphaltic constituents to regu-.

late the temperature of ,the crude petroleum charged to said restricted stream first mentioned, and returning a regulated portion of said cooled asphalt to the stock charged to said second heated stream for controlling the outlet temperature thereof.

. 7. In the process of producing asphalt of desirably low stain characteristics whereina stream.

of crude petroleum is heated in a first heating zone, light fractions, including light gas oil, are removed by evaporation and the stream of unevaporated oil is heated to a higher temperature in a second heating zone located in the same furnace with said first heating zone, the hot products from said secondheating zone are distilled under vacuum in a fractionating zone where heavy oil constituents are evaporated from the asphaltand the asphalt is withdrawn from the fractionating zone and immediately cooled by heat exchange with said stream of crude petroleum charged to said first heating zone to prevent thermal decomposition thereof, the improvement comprising recycling a portion of the hot asphaltfrom said fractionating zone to the inlet of said second heating zone, recycling a portion of the cooled asphalt withdrawn from said fractionating zone to the inlet of said second heat-.

ing zone and controlling the temperature of the oil discharged from said second heating zone by regulating the relative amounts of hot asphalt and cooled asphalt recycled thereto.

FRANK J. SMITH.

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