US3365386A - Process and apparatus for producing variable boiling point distillates - Google Patents

Description

Jan. 23, 1968 J. VAN POOL PROCESS AND APPARATUS FOR PRODUCING VARIAB BOILING POINT DISTILLATES Filed April 4, 1966 2 III'. 8 O f 7 1 I 1 l 1 s I I 1 I O 8 O 3. E Dn w r O ..l|||v| 4 f w l I u r- 6 8 3 3 H f O I||||||L S MW 4 6 8 4 2 23 r u -m -fl F 2238 zoF jFm5 76 HEAVY GAS OIL ASPHALT PROD ZONE INVENTOR JOE VAN POOL A TTORNEVS United States 3,365,386 PROCESS AND APPARATUS FOR PRODUCING VARIABLE BOILING POINT DISTILLATES Joe Van Pool, Bartiesville, Okia., assignor to Phillips Petroleum Company, a corporation of Delaware Fited Apr. 4, 1966, Ser. No. 539,817 Claims. (Cl. 2084l) ABSTRACT OF THE DISCLOSURE Crude oil is distilled to produce a naphtha stream having a boiling range of about 220 to 400 F. suitable for blending with an asphalt cement to produce a road oil, using a distillation column from which the usual gasoline and gas oil cuts are withdrawn and, in addition, a light naphtha cut having a boiling range of about 200 to 300 F. and a heavier naphtha out having a boiling range of about 300 to 400 F. are withdrawn at selected tray levels of the column, the naphtha cuts are passed into a stripping and blending tower where they are treated to produce the required naphtha stream for blending. The lighter naphtha cut requires a substantial amount of stripping while the heavier naphtha cut requires little or no stripping and is introduced to the tower at a lower level than the lighter cut. The minimum boiling temperature of 220 F. of the bottoms stream from the tower is maintained by a boiling point analyzer-controller on this stream in operative control of a motor valve in the line carrying the lighter naphtha cut.

This invention relates to a process and arrangement of apparatus for producing variable boiling point distillates from crude oil. One aspect of the invention relates to the production of variable boiling point distillates from crude oil, one of these distillates being adapted for blending with an asphalt cement or asphaltic residuum to produce a suitable road oil.

Crude oil is conventionally fractionally distilled to produce any number of distillate streams, such as an overhead vaporous hydrocarbon material suitable for blending or further conversion to gasoline, various intermediate distillate streams such as naphtha, kerosene, stove oils, diesel fuel, and gas oil, and a bottoms stream of topped crude oil. This bottoms stream is conventionally further treated to recover a heavy gas oil and an asphalt cement or asphaltic residuum which may be used as such or which may be blended with a suitable naphtha stream to produce road oils.

In one area a refinery is faced with the problem of producing a second naphtha stream of rather definite boiling range from a crude oil being processed. This second naphtha stream must have a boiling range of about 220 to 400 F. in order to be suitable for blending with asphalt to produce certain cut-backs or road oils. This cut is not adaptable to small volumes as needed and cannot be withdrawn from one t-ray location.

This invention is concerned with a process and arrangement of apparatus which produces such a naphtha stream when there is demand for it, and producing the usual streams at other times.

Accordingly, it is an object of the invention to provide a process and arrangement of apparatus for distilling a crude oil so as to produce a distillate naphtha fraction of selected boiling range while producing the usual distillate streams. A further object is to provide a process and arrangement of apparatus which combines and blends separate distillate streams from a fractional distillation column while carefully controlling the boiling range of the blended stream. Another object is to provide a process and arrangement of apparatus for distilling a crude 3,3655% Patented Jan. 23, 1%68 ice oil to produce gasoline blending stock, a naphtha sidestream of carefully controlled boiling range for use in blending with asphalt, along with the conventional cuts obtained in fractional distillation of a crude oil and blending the naphtha fraction with an asphalt product recovered from the distillation column bottoms stream or kettle product. Other objects of the invention will become apparent to one skilled in the art upon consideration of the accompanying disclosure.

In accordance with the invention, two different streams removed from diiferent trays of a crude oil fractional distillation column are passed to a combination stripping and blending tower, the flow rate of the higher-boiling stream being on tower bottoms liquid level control and the flow rate of the lower-boiling stream being on initial boiling point control of the stripped and blended product. The vapor overhead from the tower is passed to a level of the column intermediate the distillate withdrawal levels. The take-off levels for the two distillate streams are selected to obtain a desired boiling range for each stream and the stripping in the tower is controlled so as to produce a blended stream of the desired character or boiling range.

The invention is applicable to the distillation of various crude oils having a specific gravity in the range of about 0.80 to 0.93. Rangely, Colo., crude having a specific gravity of the order of about 0.85, is a preferred feed and this crude oil may be blended with minor proportions of other crudes such as Red Wash crude.

A more complete understanding of the invention may be had by reference to the accompanying schematic drawing which is a process flow or arrangement of apparatus in accordance with the invention.

Referring to the drawing, a conventional fractional distillation column 10 is provided with trays 12, a steam stripping section 14 including a steam inlet line 16, a crude oil feed line 18, a bottoms product outlet line 20, an overhead vapor line 22, a reflux line 24, and a gas oil withdrawl line 26. A first distillate withdrawal line 28 connects with a tray in an upper level of the column below reflux inlet line 24 and with an upper section of a stripping and blending tower 30. This line is provided with a motor valve 32 and flow rate sensing means 34. Line 35 connects with line 28 for withdrawing the stream therefrom as a desired product or blending stock. A second distillate withdrawal line 36 connects with a lowerlevel tray in the upper section of the column and with an intermediate section of column 30. Line 36 is provided with a motor valve 38. Dotted line 39 alternatively connects line 28 with line 36 to feed both streams into tower 30 at the same level. However, this is a less desirable arrangement and procedure because of the necessity for more stripping of the distillate from line 28 than that from line 36. Overhead vapor line 40 connects the vapor outlet of tower 30 with column 10 at a level intermediate the level of take-01f of lines 28 and 36.

A liquid level controller 42 is sensitive to the level of liquid in the lower section of tower 30 and is in operative control of motor valve 38 to maintain a selected liquid level in the tower. Heat for the stripping in tower 30 is provided by an indirect heat exchanger 44 in the form of a steam coil which is adapted to supply a constant flow of heat to the tower. Efiiuent line 46 leading from the bottom of tower 30 conveys the blended product to storage or to conventional blending equipment (not shown) for blending with an asphaltic residuum or an asphalt cement. A motor valve 48 in line 46 is operated by a flow rate controller 50 to maintain a constant preselected flow of product thru this line.

Overhead vapor line 22 passes thru condenser 52 and into accumulator 54 which eifects phase separation of the condensate. Any uncondensed light gases may be withdrawn thru line 56. The bottom layer of water is withdrawn thru line 58. Condensed hydrocarbons are withdrawn from accumulator 54 via line 60 under the impetus of pump 62, a portion passing thru product line 64 to storage or use and another portion passing thru line 24 as reflux to column 10. The reflux is regulated at a constant rate by a conventional flow rate controller 66. Takeoff thru line 64 is regulated to maintain a suitable level in accumulator 54 by means of level controller 68 which is in operative control of motor valve 70.

Line 20 carrying topped crude passes into asphalt production zone 72 which represents conventional equipment utilized for producing an asphalt of any specification characteristics desired which is recovered thru line 74 and a heavy gas oil which is recovered thru line 76. The asphalt cement or residuum may be recovered as such or passed thru line 78 to conventional blending equipment for blending with the 220 to 400 F. boiling range product from line 46 to produce such as RC (rapid cure) road oils.

An initial boiling point analyzer-controller 80 is connected thru a sample line 82 with product line 46 and is in operative control of motor valve 32 in line 28 thru flow rate controller 84. Instrument 80 is a commercially available instrument.

The invention is best illustrated by reference to the arrangement of apparatus shown in the drawing. A woods Cross crude oil charge (principally Rangely crude) is heated to about 745 F. and injected thru line 18 at the rate of 21,000 B./D. (barrels per day) and at a pressure of about 14 p..s.i.g. Stripping steam is injected thru line 16 to effect final stripping of the topped crude as it passes thru section 14. The steam stripping is not a heating operation since the crude oil is heated to a sufliciently elevated temperature to effect the distillation in column 10. An overhead vapor stream of gasoline boiling range hydrocarbons (naphtha) is withdrawn from the top of the column at a temperature of about 200 F. and a pressure at about 8 p.s.i.g. This stream is cooled and condensed in condenser 52 before passing to accumulator 54 which is maintained at a temperature of about 115 F. and at about 3 p.s.i.g. Product withdrawn thru line 64 amounts to 2,600 B./D. and approximately 9,600 B./D. of condensed hydrocarbons are passed as reflux to the column thru line 24 at a relatively uniform flow rate controlled by the set point of instrument 66. There is substantially no light gas removed thru line 56.

The 220 to 400 F. naphtha stream for blending with asphalt is produced in tower 30 by withdrawing about 800 B./D. of liquid from about the third tray in the top of the column thru line 28 and passing this light naphtha stream into the upper portion of the tower 30, and by withdrawing about 2,000 B./D. of a second heavier naphtha stream from about the eleventh tray and passing this stream thru line 36 into a lower tray in tower 30 in the upper section thereof. The withdrawal point for the lighter naphtha stream is selected so as to obtain a cut having a boiling range of about 200 to 300 F. and the heavier naphtha cut is selected with a boiling range of about 300 to 400 F.

The heavier naphtha stream from line 36 requires substantially no stripping while the lighter stream from line 28 does require substantial stripping. Heat for the stripping step is supplied at a uniform rate thru steam coil 44 to maintain a temperature of about 300 to 310 F., specifically 305 F. at p.s.i.g., in the bottom or reboiler section of tower 30. The flow rate of the stream in line 36 is regulated to maintain a selected liquid level in the reboiler section of the tower via level controller 42 and valve 38. The flow rate in line 23 is regulated so as to maintain a selected initial boiling point of about 220 F. in the product in line 46 by means of initial boiling point analyzer-controller 80 whch varies the flow rate by controlling valve 32. When the initial boiling point tends to rise above 220 F., cont-roller 80, operating thru instrument 84, opens valve 32 so as to feed more of the lighter naphtha stream into the column, and vice versa; thus it can be seen that tower 30 functions principally as a stripper for the lighter naphtha fraction introduced thru line 28 and also as a blender for blending the stripped lighter naphtha fraction and the heavier naphtha fraction introduced thru line 36. Flow rate controller 50 regulates the flow rate in line 46 at about 2,450 B./D. of 220 to 400 F. boiling range naphtha.

The topped crude passing into asphalt production zone 72 from line 20 is treated in conventional manner to recover a heavy gas oil thru line 76 and asphalt cement thru line 74, any portion of which may be passed thru line 78 along with any portion of stream 46 in proper proportions for blending to road oil. The production of gas oil thru line 26 runs about 5,700 B./D.; heavy gas oil recovered thru line 76 runs about 5,000 B./D.; and the asphalt passing thru line 74 amounts to about 5,250 B./D. These production rates will vary as the character of the crude oil in line 18 varies, and the gas oil 26 quantity may be less when additional side draws (not shown), e.g. diesel base, are made from column 10.

The alternative procedure to that illustrated as the invention is to take all naphtha overhead with the gasoline and then cut a 220 to 400 F. naphtha as a tower bottoms. The increased cost of utilities in this procedure amounts to at least 7,000 dollars per year in addition to the added investment and additional labor costs involved.

When a suflicient stock of road oil is built up and the demand for 220 to 400 F. naphtha is lacking, the naphtha stream from line 28, if not taken overhead with gasoline, can be recovered thru line 35, and the heavier naphtha in line 36 is passed into tower 30 to produce a naphtha cut in line 46 of any preselected higher boiling range suitable for use as Stoddard solvent, or as a blend component for gasoline, diesel fuel, or kerosene.

Certain modifications of the invention will become apparent to those skilled in the art and the illustrative details disclosed are not to be construed as imposing unnecessary limitations on the invention.

1 claim:

1. A process for fractionally distilling a crude oil to produce a naphtha fraction suitable for blending with an asphalt cement to produce a road oil which comprises the steps of:

(1) feeding said oil at a distilling temperature into a lower section of a fractional distillation column so as to distill said oil;

(2) withdrawing an overhead vaporous gasoline fraction containing any light ends in said crude oil, condensing same, returning a substantial portion thereof to an upper section of said column as reflux, and recovering another substantial portion as gasoline product;

(3) withdrawing a first liquid naphtha fraction having a boiling range of about 300 to 400 F. from an intermediate section of said column;

(4) withdrawing a second liquid naphtha fraction having a boiling range of about 200 to 300 F. from a level intermediate the levels of withdrawals of said first liquid fraction of step (3) and the level of reflux return;

(5) passing the fractions of steps (3) and (4) into a stripping and blending tower and heating the liquid in the bottom of said tower by indirect heat exchange so as to drive off light ends in the mixed fractions and produce a bottoms fraction having a boiling range of about 220 to 400 F.;

(6) passing the stripped light ends into said column intermediate the levels of withdrawal of said first and second fractions; and

(7) withdrawing the resulting bottoms fraction of step (5) as a product of the process.

2. The process of claim 1 wherein a gas oil fraction is withdrawn from said column at a level below the level of withdrawal of said first liquid fraction; the resulting topped crude is withdrawn from a bottom section of said column and treated to recover therefrom a heavy gas oil and an asphalt cement; and at least a portion of said asphalt cement is blended with at least a portion of the bottoms fraction of step (7) to produce a suitable road oil.

3. The process of claim 1 wherein said crude oil is introduced to said column at a temperature in the range of about 740 to 750 F. and at a pressure of about 14 p.s.i.g.; and said overhead fraction has a dew point of about 200 F. at the pressure in the top of said column.

4. The process of claim 3 wherein the flow rate of said first fraction into said tower is controlled to maintain a selected liquid level in the lower section of said tower; the flow rate of said second fraction into said tower is controlled to maintain a selected initial boiling point in the bottoms fraction of step (5); said bottoms fraction is withdrawn at a constant rate; and the liquid in the bottom of said tower is heated to a constant temperature.

5. The process of claim 3 including the steps of:

(8) heating the liquid in the bottom of said tower to maintain a temperature therein of about 305 F. at about 5 p.s.i.g.;

(9) regulating the flow rate of said first liquid fraction into said tower so as to maintain a selected liquid level in the bottom section thereof;

(10) withdrawing said bottoms fraction from said tower in step (5) at a substantially constant rate; and

(11) sensing the initial boiling point of the bottoms stream of step (10) and regulating the rate of flow of said second fraction in response to the sensed value so as to maintain an initial boiling point of about 220 F. in said bottoms stream, thereby producing said bottoms stream boiling in the range of about 220 to 400 F.

6. The process of claim 5 wherein at least a portion of a liquid stream in an upper section below said reflux inlet, a second outlet for a liquid stream in an upper section below said first outlet, a third outlet in an intermediate section for gas oil, and an inlet intermediate said first and second outlets for vapor;

(b) a stripping and blending tower having indirect heat exchange means in its bottom section for supplying stripping heat a vapor outlet in its top section connected by first conduit means with said vapor inlet, inlet means for liquid in its upper section, a bottom outlet for liquid product, and a liquid level controller in its lower section;

(c) a second conduit connecting said first outlet of (a) with said inlet means of (b) having a first motor valve therein;

(d) a third conduit connecting said second outlet of (a) with said inlet means of (b) having a second motor valve therein, said liquid level controller being operatively connected with said second motor valve;

(e) a product line connected with the bottom outlet of (b) having uniform flow rate control means therein;

(f) an initial boiling point analyzer connected with the product line of (e) by a sample line and in operative control of said first motor valve of (c);

(g) an efiluent vapor line connected with the vapor outlet of (a) provided with a condenser and an accumulator downstream of said condenser with product take-off means; and

(h) a reflux line connecting the bottom section of said accumulator with said reflux inlet of (a) having flow control means therein.

9. The apparatus of claim 8 wherein said inlet means for liquid of (b) comprises an upper inlet and a lower inlet, said second conduit of (c) connecting with said upper inlet and said third conduit of (d) connecting with said lower inlet.

10. The apparatus of claim 8 including a steam stripping section on the lower end of said column of (a) below said feed inlet.

References Cited UNITED STATES PATENTS 2,032,666 3/1936 Roberts 208355 2,963,415 12/1960 MacDonald 20839 3,296,121 1/1967 Potts 208-350 3,301,778 1/1967 Cabbage 208-355 3,310,487 3/1967 Johnson et al. 208355 HERBERT LEVINE, Primary Examiner,

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