US2094911A - Method of heating fluids - Google Patents

Description

M. wBARNE's METHOD OF HEATING FLUIDS Filled July 15, 1955 Oct. 5, 1937.

Patented Oct. 5, 1937 UNiTsD STATES Q METHOD or HEATING FLUIDs Marion W. Barnes, Chicago, Ill., assignor to Universal Oil Products Company, Chicago, Ill., a corporation of Delaware Application July 15, 1933, Serial No. 680,571

7 Claims.

This invention relates to a method of operating a furnace of improved design particularly adapted to the heating of hydrocarbon oils to the high temperatures required for their conversion, and more particularly refers to an improved method of simultaneously subjecting different oils to independently controlled heating conditions in a single furnace structure.

I have previously disclosed an improved type of furnace wherein independent control is obtainedA over the rate of heat input in different portions of the iluid'conduit through which oil is passed and wherein it is subjected to pyrolysis.

The present invention embodies another furnace of the same general type but particularly designed for simultaneously heating oils of different characteristics whereby each of the different oils is subjected to independently controlled heating conditions regulated to suit the requirements of substantial superatmospheric pressures are ein-- ployed, and to maintain it at or near the maximum conversion temperature vattained for an appreciable predetermined length of time. With higher boiling oils such as heavy crudes or topped crudes, fuel oil, heavy gas. oil and the like, it is essential for the best results to quickly bring the oil to the desired conversion temperature, for example, from 850 to 950 F., at substantial superatmospheric pressure, and then to either quickly cool the total conversion products to reduce their temperature to below that at which appreciable further conversion will occur or to quickly separate the heavy residual conversion products from the lower boiling vaporous products and prevent extensive further conversion of the former by direct `coolingpressure reduction or both, in order to prevent extensivercoke and gas formation. In the present invention quick heating of heavy oils to the desired temperature is accomplished by passing the same in a single continuous stream through a fluid conduit within the furnace in such a mannerrthat it is subjected to progressively'increasing rates of heat input in its-path of travel therethrough. Subsequent cooling of, the total products and/or rapid separation of the light and heavy products may be accomplished in subsequent portions of the cracking process not pertinent to the present invention. Heating of the light oils to the desired conversion temperature and maintaining them at the desired conversion temperature for a predetermined time is accomplished Yin the present invention by passing the lsame through another lluid conduit within the same furnace4 structure in such a manner that it is subjected to a progressively decreasing rate of heat input as it passes through the fluid conduit.

In a iluid conduit employing a soaking section wherein a single stream of low boiling oils, heated in the preceding portions of the fluid conduit to Y a suitable conversion temperature, is maintained under conversion conditions for an appreciable predetermined length of time, an unusually large amount of friction is encountered between the oil and the uid conduit through which it passes, due to the length of the fluid conduit required to obtain the desired time factor. This necessitates the use of exceptionally high pressure upon the stream of oil entering the fluid conduit in order to insure the desired superatmospheric pressure in the soaking section and at the outlet from the heating coil and not' only results in excessive pumping costs and the installation of expensive pumping equipment for operation at the unusually high pressures necessary but also involves additionalrre hazard, due to the unnecessarily high pressures employed in that portion of the fluid conduit wherein the oil is brought to the desired conversion temperature. Also, in such cases, that portion of the heating coil employing the highestV pressures is also the portion wherein it is desirable to -employ the highest ratesL of heat input since a large amount of sensible heat and nearly all of the latent heat` of vaporization as well as a substantial portion of. the latent heat of cracking must be imparted to the oil in this portion of the fluid conduit while in the soaking section a relatively small amount of sensible heat, only suflicient, in most cases, to overcome radiation losses, and little, if any, latent heat of vaporization, is required so thatV much lower rates of heat input may be employed in this portion of the fluid conduit.

In the present invention I not only take advantage of the diierent heating conditions in different portions of the furnace by passing the light oil rst through that portion of the fluid conduit located in a highly heated zone of the furnace and subsequently passing it through a soaking section comprising that portion of the fluid conduit located in a more mildly heated zone of the furnace, but I also provide for decreasing the friction and pressure drop throughout the Y entire heating coil by employing parallel iiow in the soaking section, since the decreased velocity and consequent decreased rate of heating is not objectionable in this portion of the fluid conduit;

The accompanying diagrammatic drawing illustrates one specific form-.of furnace embodying the various Vfeatures of the present invention. Fig. l Y

is a sectional side elevation of the furnace, and

Fig. 2 is a sectional end elevation of the same means of burners of any suitable form (not shown) through ring- `compartments 9 Vof the tunnels, together with an atomizing medium such as steam rand/or a portion of the air required for combustion. Additional air. is supplied to vthe combustion zones through compartments IB of the ring tunnels, regulated by suitable dampers I I. Combustion of the fuel occurs in zones 5 and 6 of the furnace, each zone being` maintained under independently controlled temperature conditions by control of the ring in each zone. The materials undergoing combustion give up heat to the refractory walls of the furnace and to the oil passing through the fluid conduits located within the combustion zones, as will be later more fully described, and the heated refractory walls in turn re-radiate heat to the fluid conduits. The

' h'ot 'combustion gases pass from combustion zones through ue I2 to astack (not shown).

Three separate banks of fluid conduits I3, It,V

5 and 6 over the respective bridge walls 4and 4' and the commingled gases pass downward through fluid heating zone 'Iand out of the Vfurnace and I5 each comprising horizontally parallel rows of horizontal tubes I6 are located Vwithin fluid heating zone YTbetween .bridge walls 4 and 4 ofthe furnace. The .tubes in the upper rows comprising'bank I5 receive a considerable proportion of radiant heat from the combustion gases and f from that portion of the roof V2 immediately above these tubes while vthe tubes in banks lf3 and I 4-1'eceive primarily convection heat, although aminor portion of radiant heat may .also be imparted'to the tubes in banks I 3 and I4 and considerable heating is also accomplished in bank I5 by convection. The flowrof oil through the rows of tubes in banks I3 and I5 is` in a counter-current, tozthe flow of the combustion gases through zone 'I while the flow ofroil Vthrough the rows of tubes in bank I4 is in a general directionconcurrent to the flow ofcombustion gases through zone I. Y

. A bank I 'I comprising a single horizontal row k of horizontal tubes I6 is located adjacent floor 3 of combustion zone 5 and in the case here illustrated this tube bank is depressed somewhat below theoutlet from firing tunnels 8 in orderthat the tubes will not be in the direct path of firingY and will not be swept by the gases undergoing combustion, thereby minimizing convection heating in this bank, radiant heating from the combusrroof 2 of combustion zone 5 and in general directionv tubes I6 is located adjacent roof 2 of Vcombustion z zone 6, the tubes of this bank, in the oase illustrated, being parallel to the tubes in floor bankv I 8. A `bank 20 comprising two horizontal parallel rows of horizontal tubes I6 is located adjacent the case illustrated the tubes of this bank are disposed at right angles to the tubes of bank I'I and parallel to the direction'of ring in combustion zone 5. That portion of roof 2 adjacent tube bank 2! is ele- Y vated somewhat above the rest of the furnace in order toV permit easy access to the headers or return bends 2l. This also minimizes the extent to which the furnace gases will sweep the tubes of this bank so that convection heating is minimized andY radiant heating is predominant.

Suitable headers or return bends similar to those illustrated at 2| in connection with bank 20 are attached to the ends of tubes I6 in each bank Y and connect adjacent tubes in each row of the respective banks in series.k The solid lines between the tubes indicate the return bends on the near side of the furnace. Those on the far side are not indicatedrin the drawing.

' v'Tube bank I4 is divided into two similar banks each Vcontaining an equal number of tubes andY n each having the same number of tubes in each horizontal row so that two streams of oil may be passed in parallel through the two similar banks, each stream being subjected to equal heating conditions therein.

Tube bank 20 is also arranged, in the case illustrated, for parallel flow therethrough of two substantially equal streams of oil. One streamv of oil flows through half of the exposed row 20Y of this bankwhile the other stream flows through the opposite half of the same row. The two streams thenV cross at the middle of the furnace,Y

each stream flowing through that portion of the shielded row 2G" adjacent the portion o f row 20 through which the other stream is flowing. In

this manner both streams are subjected to the vheating conditions prevailing on the opposite sidesV Vof the furnace, thereby tending toward minimizing unequal heating in the two streams, due to any difference in the firing conditions on opposite sides ofthe furnace. In this mannerthe two streams of oil flowing through tube bank 20, as well'as the two parallel streams, flowing through tube bank I4 are subjected to substantially equal heating conditions.

In the case here illustrated, the heavy or highboiling oil is treated in that portion of thev fluid conduit comprising tube banks I3, I5, I9 and' I8 and the ow of oil through the Various tube banks is in nthe order named, as. indicated in the drawing by the dotted 'line 22; the oil entering the the radiant floor bank I8 and being Vsubjected during its passage through the uid conduit to a progressively increasing rate of heating.

The light'orloW-boiling oil passes, in the case;y

.bottom row of tube bank I3 and emerging from the drawing but in rits broader aspects embraces Y any method of simultaneously heating separate streams of relativelyV low boiling, and relatively high boilinggoils in the same .furnace structure wherebyeach stream is subjected to independently controlled heating conditions and whereby the high boiling oil is subjected to a progressively increasing rate of heating during its passage through the furnace while the low boiling oil is subjectedl to a progressively decreasing rate of heating and is maintained for a predetermined time in the latter stages of the fluid conduit through which it passes at a temperature near the maximum attained in the preceding portions of the heating coil. Y

I claim as my invention:

1. In a process for heating hydrocarbon oils in a furnace comprising two independently fired combustion and heating Zones and a substantially convectively heated zone located between said combustion zones-and supplied with combustion gases from both, a plurality of vertically spaced horizontally parallel rows of tubes in said convectively heated Zone and rows of tubes adjacent the roof and adjacent the floor of each combustion Zone, the improvement which comprises passing a stream of hydrocarbon oil through the lower rows of tubes in said convectively heated zone, then through the tubes adjacent the roof of one combustion zone and nally through the tubes adjacent the floor of the same combustion zone while simultaneously passing a separate stream of lower boiling hydrocarbon oil first through the tubes adjacent the floor of the other combustion zone, then through the tubes adjacent the roof of the last mentioned combustion Zone and finally through the central rows of tubes in the said convectively heated Zone.

2. In a process for heating hydrocarbon oils in a furnace comprising two independently fired combustion and heating zones and a substantially convectively heated zone located between said combustion zones: and supplied with combustion gases from both, a plurality of vertically spaced horizontally parallel rows of `tubes in said convectively heated zone and rows of tubes adjacent the roof and adjacent the floor of each combustion zone, the improvement which comprises passing a stream of hydrocarbon oil through the tubes in the said convectively heated zone which are subjected to the mildest heating conditions therein, then through the tubes in the said convectively heated zone subjected to the most severe heating conditions therein, then through the tubes in one combustion zone subjected to the mildest heating conditions therein and finally through the tubes in the same combustion zone subjected to the most severe heating conditions therein and simultaneously passing a separate stream of lower boiling hydrocarbon oil first through the tubes in the other combustion zone subjected to the most severe heating conditions therein then through the tubes in the last mentioned combustion'zone subjected to the mildest heating conditions.4 therein and finally through tubes in the said convectively heated Zone subjected to heating conditions intermediate to the most severe and the least .severeY heating conditions therein. 'Y Y 3. In a process for heating hydrocarbon oils in a furnace comprising two independently red combustion and heating zones and a substantially convectively heated Zone located between said combustion zones` and through which combustion gases from both flow in a downward direction, a plurality of vertically spaced horizontally parallel rows of tubes in said convectively heated Zone and rowsv of tubes 'adjacentthe roof and adjacent the iioor ofeach combustion zone, the improvement which comprises passinga stream of hydrocarbon oil ;rstthrough at least the two ,lowermost rows-of tubes in the sai-dconyectivelyheated Zone, in a general direction counter-currentto the iiow of combustion gases therethrough, then through not more than the two uppermost rows of tubes in the convectively heated zone, in the same general direction, then through the tubes adjacent the roof of one combustion zone, in a general direction counter-current to the direction of firing and the direction of flow of the combustion gases, and finally through the tubes adjacent the iioor of the same combustion zone, in a general direction concurrent to the direction of iiring and the direction of fiow of the combustion gases, and simultaneously passing a separate stream of lower boiling hydrocarbon oil through the tubes adjacent the floor of the other combustion zone, in a general direction countercurrent to the direction of firing and the direction of flow of the combustion gases, then through the tubes adjacent the roof of the last mentioned combustion zone, and finally through the central rows of tubes in the said convectively heated zone in a general direction concurrent to the flow of combustion gases therethrough.

4. In the heating of hydrocarbon oils to conversion temperatures, the method which comprises passing a relatively heavy oil rst through a section of a furnace wherein it is heated pre-` dominantly by convection and then through aV section of the furnace wherein it is heated pre-- dominantly by radiation and subjecting the same during such flow to a progressively increasing rate r of heating, simultaneously passing a lighter oil through a section ofV saidfurnace wherein it is heated predominantly by radiation and in a path such that it is subjected therein to a progressively decreasing rate of heating, and then passing the lighter oil through the rst mentioned section of the furnace and therein maintaining the Y same' at conversion temperature for a predetermined time.

5. In the heating of hydrocarbon oils to conversion temperatures, the method which comprises passing a relatively heavy oil first through a convection section and thence through a radiant heat section of a furnace and subjecting the same during such flow to a progressively increasing rate of heating, simultaneously passing a lighter oil through a second radiant heat section in said furnace in a path, such that it is subjected therein to a progressively decreasing rate of heating, then passing the lighter oil through said convection section of the furnace, and passing combustion gases from both said radiant heat sections in indirect heat exchange relation with the oils in the convection section. Y

6. In the heating of hydrocarbon oils to'conportions and a substantially convectively heated version temperatures in furnaces of the type having a pair of combustion and radiant heating zones which are independently 'red near their lower zone receiving combustion gases from-both said combustion zones, the method which comprises passing Ya relatively heavy oil first through" said convectively heated zone and then adjacent the roofV and finally adjacent the floor of one Vof said ioV combustion zones and'subjectingthe same during such flow to a progressively increasing rate of heating, simultaneously passing a lighter oil rst adjacent the 'oor and then adjacent the'y roof of the other of said combustion zones and subjecting Y the same toV a progressively decreasing rate vof heating during its ow through this zone.

Y 7. In the heating of hydrocarbon oils to conversion temperaturesin furnaces of the type having a pair ofl combustion and radiant heating Zones which are independently fired near their lower portions and a substantially convectively heated zone receiving combustion gases from both said combustion zones, the method which cornprises passing a relatively heavy oil first through said convectivelyVV heated zone and then adjacent the roof `and finally adjacent the oor of one of Vsaid combustion zones and Vsubjecting the same

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