US2856902A - Tubular furnace - Google Patents

Description

TUBULAR FURNACE Oct. 21, 1958 s Sheets-Sheet 1 Filed Jan. 8, 1953 TTUIP/VEY Oct.'21, 1958 J. w. THROCKMORTON ETAL 2,856,902

. TUBULAR FURNACE Filed Jan. s, 1955 s Sheets-Sheet '2 "MIMI m H HIII IN V EN TORJ V ATTORNEY Oct. 21,1958 J. w. THROCKMORTON ETAL 2,

TUBULAR FURNACE Filed Jan. 8, 1953 3 Sheets-Sheet s IN VEN TORS Q 'fakn lif'firmfmariam BY .fdlfit J. 41113 HTTORNEY United States 2.856302 TUBULAR FURNACE John W. Throckmortonnand John 'S. Wallis, New York,

N. Y., assignors to Petra-Chem Process Company, Incorporated, New York, N. Y., a corporation of Delaware Application January 8, 1953, Serial No; 330,191

1 Claim. ((11.122-356) Vertical 1 tube. furnaces. having a single circular; bank of. tubes symmetrically arranged and; having upshot burners. producinga central axial flame within the:,ho1-- low cylinder formed by the circular. tube bank such as for example those shown in U. S. Patents-2,33,3.,077, Wallis and Throckmorton, issued October 26., .1943, and 2,340,287, Throckmorton et al., issued February 1, 1944,

are particularly well adaptedfor use in vacuum stills fordesirable tocarefull'y avoidcracking in the productionof lubricating oils, great care and skill are exercised to avoid any tendency to crack.

The vacuum, which is maintained in the bubble tower into which the oil discharges, extends back into the tubes at thedischarge end of the heater and tends,

in accordance with the physical laws, to reduce the-boiling point temperature of the oil and thus avoid the tendency to crack.

However, in applying to vacuum stills, vertical tube heaters ofwthe types referred to it is found desirable to connect the bulk of the tubes in series and" to connect the tubes at the outlet in multiple because of the enormous increase in the volume of theoilfrom the introductory end where it is introduced in.liquid formto. the discharge end where a large percentage is vaporized,

The vaporization takes place near: the outlet ofthe tube bank and in order to obtain the maximum eihciency ofthis type of heater, which relies almost entirely on heat transfer by radiation, it is highly desirable to keep the single row of tubes in a symmetrical circular bank and to have the tubes spaced from one-another by spaces which are; proportioned, to the, tube diameters; the. tubes of each size being equally spaced.

If normal return bends are employed to connect the bulk of the tubes in series and then the last tube of the series is connected to two or more tubes in parallel as has hitherto been done, the distribution of vapors under the subatmospheric pressure conditions is found to be unequal to such an extent that one of the tubes of the parallel connection is heated to as much as 30 above the temperature of the other.

Such temperature increase at this point is a serious matter and may mean a certain amount of cracking which is not only detrimental to the oil product desired but also tends to carbonize the tube.

In accordance with our invention We provide a novel arrangement whereby the final tube of the series group, which for convenience is referred to as the feeder tube for the outlet tubes, is double spaced from the next preceding tubewftthc.seriessand afinalpair of outlet tubes are set one .oneither: side of the end tube of the seriesor feeder tube, but said outlet tubes are connected in parallel bynovel,end-connectors. Thus the symmetry of allthe tubes in the; bankismaintainedand at the same timethe. vapors-flowing fromthe series-are equally distributed as they pass through the outlet tubes which are connected in -multiple A. stillfurther improvement. -in;resul ts is obtained by a.- certain amount of:- grading of; the: tubes insize from the introductory. end where liquid oil enters to the exit or. discharge end Ofjthfl bank where theoil is discharged inrvapor form. Thetarrangementzwhich wexhave found to bepreferableiis .to,-makeja-large proportion-of the total number of tubesof ,arrelativel-y smallsize, such-as for example of 1 4': diameter: (I. 13.), then: to-providea few tubes, ofimediumisize say of- 6(-' diameter (I..D.), and, thenitmadequateIy-"take care; of the enormous increase, in volume at thedischarge end ofthe coil, to employ a fewrelativelylarge tubes of say- 8," diameter (I. D.), thelastttwo being connectedin multiple as'described:

Eventhough the -'tubes;are made of-unequal-size it is still highly desirable to=maiutain the symmetry or the circular bankandto spacewthe ztubes-in thebank in proportion 1 to their sizes.

A.further'objectiof=ourinyention is to provide a special jumper for connecting the-feederrtube hear the discharge endof the coilso as zto prov-ide the-uniform distribution of vapors ;in-the;- final .pair'; of parallel'tubes Without interfering withthezsymmetrical arrangement of the tubes in the bank:

Other advantages of our invention will appear from the detailedidescription of a preferred embodiment hereinafter described" andi'shown in' the accompanying drawings, which Fig. 1 is an elevation largely in cross-section of-a vertical tube .heaterembodiedin our invention;

Fig. 2 is' a sectional plan view takenon the line 2-2 of'Fig. 1'; k I

Fig. 3 is a section taken on the-lin'e'3'3 ofFig. 1;

Fig. 4 is a diagrammatic view showing the arrangement of the tubes, and

Fig. 5 is a detailed view 0113. larger scale of the return bendjumper shown in Fig. 4. l

Referring tothe-drawfings, the-heater of Figs. 1, 2 and 3 has a steel shell lwith a lining 2 of insulation in which refractory 3 is mountedi Thefurnace is supported above the foundation by legs 4 and the bottom plateS hasappropriately'mounted therein burners 6. Vertical tubes 7 arearrangedin a singlecircular bank and are spaced from one another in proportion to their diameters, as shownin Figs. 2-- and; 3. The circular bank is somewhat smaller-in diameter so thatthe tubes are spaced inwardly from the lining 2 and the refractory 3. Mounted in the upper part of the heater is a baffle having a cylindrical body 8 with an inverted conical extension 9 which projects downwardly into the main body of the furnace which constitutes the radiant zone 30 of the heater.

The baffle forms a comparatively narrow annular space 10 through which the tubes extend and which forms the convection zone 31 of the heater. The tubes are preferably provided with fins or extended surface elements 11 but only in the convection zone of the heater. The furnace has the usual structural elements and the stack 12 is mounted at the top.

Our invention pertains more specifically to the arrangement of tubes and the method of interconnecting them which is better illustrated in Figs. 4 and 5.

While in Figs. 1, 2 and 3 we have shown our preferred vertical tube heater having a single circular bank of tubes, our invention may be applied to heaters in which the tubes are arranged in one plane but in either case the arrangement of tubes which we now consider preferable is shown in Figs. 4 and 5, in which for convenience the tube bank is developed into one plane.

The tubes may be all of equal size but we prefer to employ tubes of varying sizes, particularly when the heater is to be employed in a vacuum distillation unit for hydrocarbon oils.

In Fig. 4 tube 13 is an inlet tube and has an inlet connection 14 at the bottom. This tube and the eight adjacent tubes are shown of equal and relatively small size. Of course this portion of the heater may be made up with more or less tubes and particularly for very large size furnaces would usually have many tubes and all of them are connected in series by return bend structures 15. From this series of tubes the fluid to be heated passes through a return bend structure 16 into a medium size tube 17 of which three additionaltubes of the same size are shown, all connected in series by return bend structures 18. The last tube of medium size is marked 19 and is connected by return bend structure 20 to the first tube 21 of the large tubes, The next large tube 22, which is designated a feeder tube for the outlet tubes, is spaced from the first large tube 21 sufiiciently to permit the introduction of a large size tube 23. Another large tube 24 is located at the outer end of the bank so that the large tubes 23 and 24 are located one on either side of the feeder tube 22, whi e the symmetry of arrangement 'of the tubes in the bank is maintained.

The large size tube 21 is connected to the feeder tube 22 by a specially constructed return bend or jumper 25, which is shown in detail in Fig. 5. At the top the outer ends of the last three large tubes are connected by a manifold 26.

The two large tubes 23 and 24 are provided with outlets 27 and 28, which are coupledto' and discharge into u by radiation and the oil is heated and-becomes close to I the boiling point as the oil approachesthe medium size tubes. It is partially vaporized in the medium size tubes and its volume is enormously increased since the last few tubes of the heater, which are connected to the vacuum chamber or fractionator, are maintained under subatmospheric pressure, which may be in the order of 6 or 7 lbs. absolute.

It is for this reason that large tubes are provided near the end and the final pair of large tubes are connected in multiple.

It is highly advantageous to insure that the oil which is largely in the form of vapor, is uniformly divided between the two large tubes 23 and 24 and the arrangement of tubes above described has proven to bring about this highly desirable result.

If the invention is applied to a heater such as shown in Figs. 1, 2 and 3, and the tubes are of varying sizes, as shown, the fins or extended surface elements 32 on the large tubes are confined to the circumferential sides of the tubes and are omitted from the radial sides of such tubes.

This is important because the best results are obtained by keeping the convection annulus 10 narrow and thereby forcing the hot furnace gases from the radiant zone of the furnace into close surface contact with the tubes and fins in the convection zone.

Variations may be made without departing from the spirit of our invention and it is not essential to make the tubes of unequal size but particularly when the-heater is used for vacuum distillation units, we regard it as preferable to do so.

We claim:

A vertical tube heater comprising an upright cylindrical furnace shell, a stack at the top, a single circular bank of vertical tubes within the furnace shell, said tubes being spaced from each other and from the furnace shell to form a hollow cylindrical heating coil, upshot burners at the bottom of the furnace adapted to discharge flame and hot gases upwardly and axially within the heating coil, said circular tube bank having an inlet connection to one tube and outlet connections to two tubes, a feeder tube between the outlet tubes, a manifold for interconnecting the outlet tubes and the feeder tube at their ends opposite the outlet connections, return bend connections for interconnecting all of the tubes in series, except the feeder tube and the two outlet tubes, and a jumper connection for connecting the inlet of the feeder tube to the outlet end of the series connected tubes, whereby the fluid in the feeder tube which is received from the series tubes is uniformly divided between the outlet tubes, said series connected tubes comprising a group of small tubes at the inlet end, a group of medium size tubes in sequence and a plurality of large size tubes at the outlet end.

References Cited in the file of this patent UNITED STATES PATENTS.

701,422 Thompson June 3, 1902 2,029,293 Alther a Feb. 4, 1936 2,132,965 Nash Oct. 11, 1938 2,170,342 Bailey Aug. 22, 1939 2,232,935 Bailey Feb. 25, 1941 2,340,287 Thockmorton et al Feb. 1, 1944 2,641,234 Mekler et a1. June 9, 1953 FOREIGN PATENTS 463,549 Italy May 12, 195 l

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