US2048548A - Oil cracking system - Google Patents

Description

W. Tv HANCOCK OIL CRACKING SYSTEM July 21, 1936.

2 Sheets-Sheet 2 Filed Oct. 9, 1934 KNE m -0 00r00 0000. 00000000 W %00 0 00 OH 000 00000000 000000 00 00000000 000000 M 00 00000000 Q RUN 000000M 00 00000000 0 R 5 R\ @000000 OAWQWQQOQOOOOO $5 00 0G0 @QQQ fiwmm E. 0 O OO OOOOOOM xwoooooow C OOOOOO O 0 0 %0 O O O O Patented July 21, 1936 UNITED STATES PATENT OFFICE OIL CRACKING SYSTEM William '1. Hancock, IlongBeach, Calif. 7 Application October 9, 1934, Serial No. 747,552

6 Claims.

This invention has to do with improvements in liquid phase oil cracking systems, and has for its primary object to increase the yield and quality of gasoline obtainable by single passage of the charging stock through a tube still.

In the more common oil cracking tube stills, the oil is pumped under high pressure through tubes Within which the oil velocity is substantially constant throughout, except as it may be increased by partial vaporization of the oil.

Ordinarily the oil is heated to cracking temperatures and then immediately passed into a fractionating system, or sometimes by way of a conversion pressure chamber extraneous to the still.

I have found that by departing from the usual practice in tube still construction and operation in accordance with this invention, the yield of cracked distillate obtainable from the pressure distillate produced at the end of a single passage of the charging stock through the still, can be increased in very substantial amounts, and the character of the product, particularly as regards its octane rating, greatly improved.

In carrying out the invention, I subject the charging stock to cracking within the heating chamber of the still, and thereafter pass the oil through a soaking zone within that same chamber, in an extended path of flow-and at a velocity substantially lower than the oil velocity in the cracking stage. Preferably the cracking tubes will be located in the hottest portion of the heating chamber, since it is in these tubes that the oil will ordinarily be heated to its highest temperature, and the soaking tubes in a somewhat cooler section, although the oil flowing through them will remain at or near the conversion and reformation of the oil molecules may progress to the fullest'possible extent. before the oil leaves the still. Provision is also made 50 for maintaining the oil in the cracking and soaking tubes at any desired superatmospheric pressure, and if desired, for maintaining differential pressures in the two sets of tubes. 7

All these, as well as further objects and fea- 55 tures of the invention will be more fully understood from the following detailed description of certain typical forms of the invention. Throughout the, description, reference is madeto the accompanying drawings, in which: 7

Fig. 1 is a sectional view showing a preferred 5 form of tube still; a

Fig. 2 is an enlarged fragmentary view taken on broken line 2'2 of Fig. 1, showing the connection between the cracking and soaking tubes of the still; 10

Fig. 3 is an enlarged section taken on line 33 of Fig.1 through the orifice valve;

Fig. 4 is a view similar to Fig. 1, showing a variational form of the invention; 7

Fig. 5 is a fragmentary enlarged View in the 15 aspect of line 5-5 of Fig. 4, showing the expansion fitting connecting the soaking and cracking tube'sections; and

Fig. 6 is a View similar to Fig. 5 showing avariational placement of the orifice valve. 29

Referring first to Fig. 1, the still H] comprises Walls H enclosing a heating zone l2 which includes .a radiant heating chamber l3, and a convection preheating chamber l4 separated from the first mentioned chamber by baffle wall 25' I5. Hot combustion gases from burners [6 flow upwardly within chamber I3, then through space a H above the baffle wall and downwardly through chamber M to the outlet flue I8. The temperatures are of course highest within chamber I3, 30 and the hereinafter described cracking and soak-' ing tubes within that chamber are-heated both by radiation and convection. Also, as willbe readily apparent, the highest temperatures exist within the lower portion of chamber I3, and the 35 temperature of the combustion gasesprogressive- 1y, decreases as the gases rise in passing toward the convection heating chamber I 4.

The charging stock is fed to a bank IQ of oil preheating tubes 29' within chamber M,through 40 line 2| and fitting 22 into the two lowermost horizontal tube rows 23 and 24, the oil in each of these lower rows of tubes flowing upwardly through alternate rowsyas indicated by the arrows,.into the outlet line 25; Tubebank l9 serves tov preheat the oil to a suitable temperature prior to its passage into the cracking tubes, and if desired, to vaporize any predetermined range of the more volatile fractions of the charging stock prior to cracking. In cases where the tube bank [9 is used to top as well as preheat the charging stock, line 25 is connected with a sep-t arator 26 of suitable design, from which the vapors pass through line 21 to be condensed, fractionated, or treated as may be desired. Any

suitable back pressure may be maintained within the preheating tubes by adjustment of valve 28in the vapor line. 7 7

V sumin g both the cracking and the soaking tubes V The unvaporized portion of the charging stock leaves the base of separator 26 through line 29 and is forced under high pressure by pump 30 through line 3| into the cracking and soaking tube'banks within chamber I3. ence of description, the entire tube bank 32 may be regarded as comprising two sections 32a, 32b, the general direction of oil flow through which is asillustrated to be of the same length, although the drawings will serve to illustrate the general.

arrangement and principles involved.

Thetubes in the horizontal rows of each section are connected in series, as are also vertically adjacent rows, with some modification in the cracking tube bank as will later appear, so

that, for example in tube bank section 32b, the 'oil entering thetop row of tubes from line 3| flows down through the section in the path indie V cated by the arrows. The tubes in the lowermost rows of both sections are connected in'series so t'ain.. Generally speaking, ithas been round that that upon reaching the lower end of tube bank 321), the oil then passes into the bottom tubes of section 32a and then flows upwardly throughthat section in the path indicated by the arrows; It

will be noticed that tube bank section 32b is substantially narrower tha'n'section 32a, and that all the tubes in the entire bank'32 have the same diameter. The relative number of tubes in the two s ect ions'32a and 32b, may be varied in specific designs and in accordance with particular operating conditions which it is desired to 'mainbestresults in furthering the maximum produc- *tion of cracked distillate are obtained by heat- "ing the oil 'comparatively'rapidly to the maxiing theoil at high temperature over an extended period of time, thereby enabling the cracking'remum cracking temperature, and then maintainaictionto continue to the fullest extent under the tio'n 32b, the oil follows a path generally counterexisting temperature and pressure conditions.

In flowing downwardly through tube bank seccurrent to the stream of hot combustion gases rising within chamber l3, and during this course or, its flow, is heated comparatively rapidly to a cracking temperature in the'neighborhood of perature over an extended period of time during the course of its upward flow through section 32a of the tube bank. While the oil preferably will be heated to cracking'temperatures by the time it reaches the lower end of section 32b, it ordinarily will be heated to still higher temperatures in passing through the lowermost tubes of bank 32a. Due to the fact'that the combustion gases will have become somewhat cooled before reachingthe upper tubes in chamber [3, the .oil temperature may drop somewhat as the oil flows upwardly through tube bank section 32a. However, the temperature drop will'be comparatively For convenie 'taining the oil stream in. an elongated path' of V tube banks, but reduce the oil velocity-within the 7 Then after being heated to, cracking temperature, the oil is held at high temsmall, and the oil at the point of discharge into outlet line 34 will remain at a cracking temperature.

The particular features of the typical formbf. still described thus far are more specifically and extensively dealt with in my copending application Ser. No. 724,135, filed May 5,1934, now U. S. Patent No. 2,034,094 on Oil'cracking still. ,The present invention is more particularly concerned with the soaking. tube bank. and its structural I and functional association with the cracking tubes.

The soaking tubes receive the oil directly from the cracking tubes, and have a substantially greater oil passing capacity than the latter so that the oil flows through the soaking tubes at substantially less velocity. In the'broad aspects of the invention, the soaking tubes may beof any suitable sizeand arrangement capable, of mainfiow and ,for angextended "period of time at substantially reduced velocity. In the form of the invention shown in Fig. l, I provide the same diameter tubes in both the cracking and. soaking latter bypassing the oil through two, instead of one series of tubes. I Thus as'shown in Fig. 2, the oil leaving the final tube 35 of the cracking tube bank 'flows through fitting 36 into two tubes 31 and '38 in the lowermost rows 39 and 40 of the soaking tube bank. The oil then passes through the soaking V tubes at reduced velocity, alternate horizontalrows of the tubes being interconnected so that the oil takes the path indicatedby the arrows.

The outlet tubes 4| and 42 of the two uppermost rows are connected bya fitting 43, similar to 36,- with outlet line 34. e I Outlet line 34 leads 'to a separator 45, which may consist simply of a hollow shell, and from which the unvapor'ized residuum is continuously withdrawn through line 46. The vaporsare dis-D charged through line '41- and are subsequently condensed; fractionated or otherwise treated in suitable apparatus, notshown; Preferably a rating chamber, may be maintained withinthe cracking and soaking tubes;

As shown in detail in Fig. 3, va1v 49.13 g gfi type comprising a body 49a and a gate in the form of aplate 50 having acentral orifice 5| of such restricted area as to maintain the desired back pressure. V

when it becomes necessary to blowout thegtubes to remove accumulated, carbon, plate50 maybe raised by turning screw 52 to permit unrestricted flow through the outlet line. V V V V Theflvariati'onal form of the invention shown. in Fig. 4 is generally similar to that of Fig. 1, and correspondingv parts are indicated by the same numbers with primes added. Whilein the variational 7 form, similar conditions exist high back pressure is maintained within both- During operation, the orifice plate is in itslowerclosed position as illustrated, but

throughout, the soaking tube section difiers in that instead of having increased flow capacity and retarded oil velocity by virtue of two sets of tubes connected in parallel and individually having the same cross sectional area as. the cracking tubes, one set of soaking tubes of enlarged diameter is provided to produce the same retardation in the rate of oil flow. Thus as particularly illustrated in Fig. 5, the final cracking tubeiiis connected by an enlarged return bend 54 with the initial soaking tube 55 of increased diameter. As before, the oil velocity through the soaking tube bank is at reduced velocity and under substantially the same pressure as that existing in the cracking tubes. It will be understood that the relative numbers of cracking and soaking tubes may be varied to give best results,

as may also the relative diameters of the tubes in the two sections.

In Fig. 6, I show a further variant provision whereby convection and reformation of the oil within the convection zone may occur at a pressure below the pressure in the cracking tubes. By placing a suitable valve 55, for example of the type shown in Fig. 3, at the return bend 51 connecting the soaking and cracking tubes 55 and 53', any suitable pressure drop may be maintained on the oil at the point of entry to the soaking tube bank. Where valve 56 is used, valve 49' in the outlet line may be dispensed with and the back pressure in the soaking tubes controlled by valve 48 in the vapor outlet line.

Under typical operating conditions, fuel oil fed to preheating tubes I9 from line 2|, will be heated and discharged into separator 26 at a temperature around 500 F. and under any suitable pressure; for example, a pressure ranging from substantially atmospheric, up to 100 lbs. per sq. in. Then in flowing through the cracking and soaking tubes, the oil is heated to a higher temperature which may range from 800 to 1000 F., and under a pressure within the range of from 300 to 850 lbs. per sq. in. In cases where valve 49 is used, the pressure in separator 45 may be reduced to in the neighborhood of from 200 to 300 lbs. per sq. in., under control of valve 48 in the vapor line.

I claim:

1. A tube still comprising opposed vertical walls forming a heating chamber, a bank of horizontally extending tubes in said chamber, and means for feeding oil to said tube bank, the tubes in said bank being connected in series so that the oil flows downwardly through horizontal rows of a relatively narrow vertically extending cracking section of the tubes, and subsequently passes upwardly through horizontal rows of a relatively wide adjacent vertically extending soaking section of the tubes located directly between the first mentioned section and one of said vertical walls, the cross sectional passage area of the tubes in said soaking section being substantially greater than the cross sectional passage area of the tubes in said cracking section, so that the oil flows through the soaking tubes at substantially reduced velocity.

2. A tube still comprising opposed vertical walls forming a heating chamber, a bank of horizontally extending tubes in said chamber, and means for feeding oil to said tube bank, the tubes in said bank being connected in series so that the oil flows downwardly through horizontal rows of a relatively narrow vertically extending cracking section of the tubes, and subsequently passes upwardly through horizontal rows of a relatively wide adjacent vertically extending soaking section of the tubes located directly between the first mentioned section and one of said vertical Walls, the cross sectional passage area of the tubes in said soaking'section being substantially greater than the cross sectional passage area of the tubes in said cracking section, so that the oil flows through the soaking tubes at substantially reduced velocityythe aggregate length of the tubes in said soaking section being substantially greater than the aggregate length of the tubes in r the cracking section.

3. A tube still comprising spaced vertical walls forming a preheating chamber and a heating chamber, oil heating tubes in said preheating chamber, a bank of horizontally extending tubes in said heating chamber, and means for passing oil from said preheating tubes to said tube bank, the tubes in said bank being connected in series so that the oil flows downwardly through horizontal rows of a relatively narrow vertically extending cracking section of the tubes, and subsequently passes upwardly through horizontal rows of a relatively wide adjacent vertically extending soaking section of the tubes located directly between the first mentioned section and one of said vertical walls, the cross sectional passage area of the tubes in said soaking section being substantially greater than thecross sectional passage area of the tubes in said cracking section, so that the oil flows through the soaking tubes at substantially reduced velocity.

4. A tube still comprising spaced vertical walls forming a preheating chamber and a heating chamber, oil heating tubes in said preheating chamber, a bank of horizontally extending tubes in said heating chamber, means for separating vapors from the oil leaving the preheating tubes and before entry of the oil to said tube bank, and means for passing oil from said preheating tubes to said tube bank, the tubes in said bank being connected in series so that the oil flows downwardly through horizontal rows of a relatively narrow vertically extending cracking section of the tubes, and subsequently passes upwardly through horizontal rows of a relatively wide ad- Jacent vertically extending soaking section of the tubes located directly between the first mentioned section and one of said vertical walls, the cross sectional passage area of the tubes in said soaking section being substantially greater than the cross sectional passage area of the tubes in said cracking section, so that the oil flows through the soaking tubes at substantially reduced velocity.

5. A tube still comprising opposed vertical walls forming a heating chamber, a bank of horizontally extending tubes in said chamber, and means for feeding oil to said tube bank, the tubes in said bank being connected in series so that the oil flows downwardly through horizonpositioned in the lower portion of said chamber so that the combustion gases fiow upwardly and counter-current to the oil flowing downwardly through said cracking section.

GQA' tube f still comprising opposed vertical wallsfforming a. heating chamber, a bank of horizontally extending tubes in said chamber, and means for feeding oil ,to said tube bank, the

' tubes in said bank being connected in series so that the oilflows downwardly through horizontal rows of a relatively narrow vertically extending section of the tubes, and subsequently passes upwardly through horizontal rows of a relative- 1y wide adjacent vertically extending section of the" tubes located directly between theflrst mentioned section and one of said verticalwalls, a the cross sectional passage area of '7 the tubes ina plurality of upper'tube rows in said relatively 7 wide section being substantially greater than the cross; sectional passage area of .the remaining tubes in said tube bank, so that the oil flows through said enlarged cross sectional passage area tubes at substantially reduced velocity.

WILLIAM T. HANCOCK.

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