US2080731A - Heating of fluids - Google Patents

Description

May 18, 1937. L. A. MEKLER 2,080,731

' HEATING 0F FLUIDS Fiied Oct. 24, 1933 mm v2 2 2 2-32 2 INVENTOR m, 2 LEV A. EKLER Patented May 18, 1937 UNiTE STATES HEATING F FLUIDS Lev A. Mekler, Chicago, Ill., assignor to Universal Oil Products Company, Chicago, 111., a corporation of Delaware Application October 24, 1923, Serial No.- 694,961

GClaims. (o1.19s 47') C This invention particularly refers to an improved furnace and an improved method of heating fluids passing therethrough, especially adapt ed to heating hydrocarbon oils to the high temperatures required for their conversion. More specifically, the invention is of special advantage in the conversion of relatively low-boiling hydrocarbon oils which'require prolonged conversion time at a carefully regulated relatively high temperature in order to secure the production of high yields of motor fuel of high anti-knock value.

It is now well recognized that the most advantageous method of converting low-boiling hydrocarbon oils, such as gasoline or gasoline fractions of low anti-knock value, naphtha, kerosene or kerosene distillate, pressure distillate bottoms and the like, or mixtures of such materials, is to bring the oil to the desired relatively high tem- 2 perature at substantial superatmospheric pressure and to maintain the oil at or near the maximum conversion temperature attained and under substantial superatmospheric pressure for a predetermined time. This method has been found to produce high yields of motor fuel of high antiknock value and obviates the use of a high-pressure reaction chamber following the heating coil for appreciable continued conversion of the vaporous products therefrom. I have previously disclosed a furnace particularly designed to permit the methodof heating above described by employing two independently fired heating zones, in one of which the oil is quickly heated to or near the maximum conversion temperature desired, while in the other heating zone only sufficient heat is added to the stream of oil passing therethrough to maintain it'at or near the temperature attained in the preceding heating zone for a predetermined time. In this furnace the combustion gases from both heating zones are commingled and pass through a centrally located heating zone, through which the oil supplied to the furnace is first passed to receive fluid heat from the commingled combustion gases.

In the present invention changes in the firing conditions in either independently fired heating zone may be made without greatly, affecting the conditions prevailing in the other independently fired heating zone. This is accomplished by passing the stream of oil, after it has attained a relatively high temperature, through that portion of the fluid conduit in the centrally located heating zone which is subjected to heating substantially by both radiation and convection fromrelatively high temperature combustion gases entering this zone and from the adjacent high refractory furnace walls. Preferably, the oil passes through this section of the fluid conduit just prior pendently fired heating zon'e Withoutany appreciable effect upon the operating conditions in the other independently fired heating zone.

One specific embodiment of the present invention comprises a furnace structure, having two independently fired combustion and heating zones, a separate convection heating zone supplied with combustion gases from both of said independently fired combustion and heating zones, a fluid conduit located within each heating zone and means for passing fluid to be heated, in a continuous stream, first through that portion of the fluid conduit in said separate convection heating zone subjected to heating from the combustion gases at a relatively low temperature, then through. thefluid conduit in one independently fired combustion and heating zone, then through that portion of the fluid conduit in said separate convection heating zone subjected to heating from the relatively high-temperature combustion gases entering this zone and finally through the ,fluid conduit in the other independently fired combustion and heating zone.

The accompanying diagrammatic drawing illustrates one specific form of furnace embodying the features of the present invention.

Fig. 1 of the drawing is a sectional side elevation of the furnace and Fig. 2 is a sectional plan View of the same furnace structure taken alonga horizontal plane indicated by the line 2-2 in Fig. 1.

Referring to the drawing, the main furnace structure comprisesside walls I, 2, 3, and 4, a roof 5 and a floor 6. Bridge walls 1 and 8 divide the main furnace structure into three sepa rate heating zones 9, l0 and- H, heating zones 9 and l ll being located on either side of the bridge walls and heating zone ll between the bridge Walls.

Zones 9 and I!) are independently fired by means of a plurality of firing tunnels l2, communicating therewith as illustrated. Each firing tunnel comprises, in the case illustrated, a combustion tunnel I3 and air ducts |4 located above and below each combustion tunnel through which air is admitted in regulated quantities controlled by dampers I5. Any desired form of fuel such as oil, gas or pulverized solid fuel is supplied by means of valved burners I6 of any suitable form to each combustion tunnel and a regulated portion of the air required for combustion is also supplied through tunnels l3, the remainder as well as any desired excess air being supplied in regulated amounts through air ducts M to combustion and heating zones 9 and ID.

The combustion gases from the combustion and heating zones 9 and Ill pass over the respective bridge walls I and 8 and thecommingled combustion gases from both combustion zones pass downward through heating zone H and out of furnace through a flue I'l to a suitable stack, not shown.

A fluid conduit l8 comprising, in the case illustrated, a plurality of superimposed horizontal rows of horizontally disposed tubes |9 is located within the lower portion of heating zone H. In the case here illustrated, adjacent tubes in each row and the end tubes in adjacent rows are connected at their ends in series by means of suitable return bends or headers located outside the heating zone and indicated in Fig. 2 at 20.

Another fluid conduit 2|, preferably comprising only two or three horizontal rows (three are illustrated in the drawing) of horizontally disposed tubes I9, is located in the upper portion of heating zone above tube bank I8. Adjacent tubes and adjacent rows of tubes in bank l9 are also preferably connected at their ends in series by'means of suitable return bends or headers, not illustrated, but similar, for example, to those indicated at 20.

Another fluid conduit 22 comprising, in the case illustrated, a single horizontal row of horizontally disposed tubes i9 is located adjacent thefloor of combustion zone 9, and a fluid conduit 23 comprising, in the case illustrated, a single horizontal row of horizontally disposed tubes i9 is located adjacent the roof of the furnace above combustion zone 9 and convection heating zone Another fluid conduit 24 comprising, in the case illustrated, a single horizontal row of horizontally disposed tubes I9 is located adjacent the roof of the furnace above combustion zone l9 and a fluid conduit 25 comprising, in the case illustrated, a single horizontal row. of horizontally disposed tubes I9 is located adjacent the floor of combustion zone In.

Preferably, adjacent tubes in each of the fluid conduits 22, 23, 24 and 25 are connected in series by means of suitable headers or return bends, not illustrated, at the ends of the tubes outside the heated zone and similar, for example, to those indicated at 2 0, in Fig. 2. The lines connecting alternate tubes in Fig. 1 indicate the connections between the tubes in the various fluid conduits at the near end of the furnace. The connections between alternate tubes at their far ends are not indicated.

The fluid conduits adjacent the roof and floor of combustion zones 9 and Ill are supplied with radiant heat from the fuel-air mixture undergoing combustion in these zones and from the hot refractory walls of the furnace as well as with convection heat from the hot combustion gases.

The rate of heating as well as the proportion of radiant and convection heat supplied to the floor and roof banks of tubes in each of the heating zones 9 and iii are controlled to suit requirements by means of the firing tunnels I2. Ordinarily a much higher temperature and rate of heating is employed in combustion and heating zone 9 relative to that employed in combustion and heating zone ID; the latter being used as a soaking zone wherein the oil from the fluid conduits in the preceding sections of the furnace is maintained at a fairly constant relatively high conversion temperature for a predetermined time and wherein the final outlet temperature of the stream of heated oil is controlled. Considerable heating by radiation is also obtained in that portion of fluid conduit 23 indicated in the drawing at 23', which is located above heating zone I l, as well as in fluid conduit 2| and a relatively high rate of heat input is ordinarily imparted to the tubes in fluid conduits 2| and 23'. Substantially only convection heat from the combustion gases is imparted to the tubes in fluid conduit l8 and a much lower rate of heat input is ordinarily obtained therein.

In the case here illustrated, the fluid to be heated enters the bottom row of tubes in fluid conduit 8, passing through successive tubes in each row and upward through the successive rows of tubes in this bank, in a general direction counter-current to the flow of combustion gases through this zone, then passes in series through the tubes of fluid conduit 22, in a general direction counter-current to the general direction of firing, then in series through the tubes of fluid conduit 23, in a general direction concurrent to the general direction of firing and direction of flow of the combustion gases, then passes in series through adjacent tubes and successive rows of tubes in fluid conduit 2|, in a general direction countercurrent to the general direction of flow of combustion gases, then enters fluid conduit 24, flowing in series through the tubes of this bank in a general direction countercurrent to the general direction of firing and general direction of flow ofthe combustion gases, and finally passes in series through the tubes of fluid conduit 25 in a general direction concurrent to the direction of firing, from which it is discharged from the furnace. The flow described, is indicated in Fig. 1 of the drawing by the lines and arrows, the solid lines'indicating the cross-overs between the various tube banks on the near side of the furnace.

As a modification of the specific form of furnace and flow of oil therethrough, above described, which is specifically within the scope of the present invention, that portion of fluid con-' duit 23 indicated in the drawing at 23', which is adjacent the roof of the furnace directly above heating zone may be eliminated, in which case the path of flow of the fluid undergoing treatment, between tube banks 23 and 2|, is indicated in the drawing by line 26. With this alternative flow a somewhat higher rate of heating is obtained in the fluid conduits in heating zone H and particularly in fluid conduit 2| comprising, in the case illustrated, the three upper rows of tubes in this zone.

It will be understood that the invention is not limited to the specific form of furnace illustrated and above described nor to the specific arrangement of the various fluid conduits and path of flow therethrough above described. The invention is, rather limited only to the improved methods and means defined in the appended claims. For example, the sequence of fluid conduits 22 and 23 may be reversed to that above described as may also the sequence of tube banks 24 and 25. Also the general direction of flow through any or all of the various fluid conduits may be reversed. However, as applied to the conversion of low-boiling hydrocarbon oils, the oil to be heated, in all cases, passes first through that portion of the fluid conduit in the convection heating zone supplied with the commingled combustion gases from both independently fired combustion zones of the furnace, (i. e. zone H), which is subjected to heating by relatively low temperature gases substantially by convection heat, then through the fluid conduit in an independently fired combustion and heating zone (i. e. zone 9) wherein a major portion of the sensible heat, the latent heat of vaporization, and a portion of the latent heat of cracking is imparted to the oil, then through a fluid conduit in said heating zone supplied with the commingled combustion gases from both independently fired combustion zones of the furnace, (i. e. zone ll) which is subjected to heating by relatively high temperature gases with a substantial radiant heat component supplied from the gases and the adjacent refractories and finally through the fluid conduit in independently fired combustion and heating zone (1. e. zone I) wherein a minor portion of sensible heat and a major portion of the latent heat is imparted to the oil, from which the oil is discharged to subsequent cracking equipment not pertinent to the present invention.

As an example of specific operating conditions obtainable by the present invention in an apparatus such as illustrated and above described, a charging stock such as naphtha, for example, is supplied to fluid conduit l8 in a continuous stream at a superatmospheric pressure of approximately 1200 pounds per square inch and a temperature of about 385 F., it is subjected in this zone to heating substantially by convection heat from relatively low temperature gases and leaves fluid conduit 18 at a temperature of approximately 625 F. The stream of oil then passes through fluid conduits l9 and 23 wherein it is subjected to a relatively high rate of heating and brought to a conversion temperature of approximately 930 F. The oil then passes through fluid conduit 2| wherein substantially the same rate of heating is obtained as that in the preceding portion of the fluid conduit and wherein the temperature of the oil is increased to approximately 950 F. The stream of heated oil then passes through fluid conduits 24 and 25 wherein the oil is gradually increased to an outlet temperature of approximately 980 F., and from which it is discharged at a superatmospheric pressure of approximately 800 pounds per square inch. In the present invention the outlet temperature may be increased, for example, to 1080 ER, or thereabouts, by regulation of the firing conditions in combustion zone ill without the necessity of changing the firing conditions in combustion zone 9 and without appreciably altering the temperature of the oil emerging from fluid conduit 23, or by changing the firing conditions in zone 9 to raise the temperature of the oil entering fluid conduit 24 without appreciably changing the temperature difference between the oil entering fluid conduit 24 and the oil leaving the furnace.

I claim as my invention: 1. A process for heating hydrocarbon oils to the high temperatures required for theircon heating by radiation and convection in a hotter portion of the first-named zone supplied with combustion gases from both independently fired combustion and heating zones and finally to a relatively low rate of heating predominantly by radiation in the other independently fired combustion and heating zone.

In a process for heating hydrocarbon oils to conversion temperatures in a furnace comprising independently fired combustion and heating zones, a separate heating zone supplied with commingled combustion gases from the combustion and heating zones and a fluid conduit located within each heating zone, the improvement which comprises passing the oil to be heated, in a continuous stream, first through that portion of the .fluid conduit in said separate heating zone subjected to heating from relatively low-temperature combustion gases, then through the fluid conduit in one independently fired combustion and heating zone, then through that portion of the fluid .conduit in said separate heating zone subjected to heating from relatively high-temperature combustion gases and adjacent radiating surfaces of the furnace and finally through the fluid conduit in another independently fired combustion and heating zone.

3. In a process for heating hydrocarbon oils to conversion temperatures in a furnace comprising independently fired combustion and heating zones, a separate heating zone supplied with heat of the commingled gases from the combustion zones and a fluid conduit located within each heating zone, the improvement which comprises passing the oil first through that portion of the fluid conduit in said separate heating zone, heated primarily by convection from the commingled combustion gases, then through the fluid conduit in one of said independently fired combustion and heating zones, then through that portion of the fluid conduit in said separate heating zone subjected to substantial components of both radiant and convection heat and finally through the fluid conduit in another independently fired combustion and heating zone.

4. A furnace for heating fluids comprising, in combination, independently fired combustion and heating chambers, a separate, centrally located, heating chamber supplied with combustion gases from said independently fired combustion cham- I bers, a fluid conduit comprising a plurality of superimposed horizontal rows of horizontally dis-' the fluid conduit in one independently fired combustion and heating chamber, then through the upper-rows of tubes in said centrally located heating chamber, which are adapted to be subj ected to heating substantially by both radiation and convection, and finally through the fluid conduit in another independently fired combustion and heating chamber.

, 5. A furnace for heating hydrocarbon oils to conversion temperatures comprising, in combination, twoindependently fired combustion and heating chambers, a separate, centrally located, heating zone supplied with combustion gases from-both independenty fired combustion chambers, a fiuid conduit comprising a plurality of superimposed horizontal rows of horizontally disposed tubes in said separate heating zone, a fluid conduit-comprising horizontal rows of horizontally disposed tubes adjacent the floor and adjacent the roof of each independently fired combustion and heating zone, means for passing the oil in a continuous stream first through the lower rows of tubes in said centrally located heating zone, which are adapted to be subjected to heating primarily by convection from the commingled combustion gases, then through the fluid conduit in oneindependently fired combustion and heating zone, then through the upper rows of tubes in said centrally located heating zone, which are adapted to be subjected to heating substantially by both radiation and convection, and finally through the fluid conduit in the other independently fired combustion and heating zone.

6. In the heating of hydrocarbon oils to conversion temperatures in furnaces of the character comprising a pair of independently fired radiant heat zones and a separate heating zone receiving commingled combustion gases from the radiant heat zones, the method which comprises passing the oil in a restricted stream first through a relatively cool portion of said separate heating zone and therein heating the same predominantly by convection from said gases, then through one of said radiant heat zones and therein heating the oil predominantly by radiation, then through a relatively hot portion of the separate heating zone and therein heating it by radiation and convection, and finally through the other of said radiant heat zones wherein the oil is again subjected to predominantly radiant heat.

LEV A. NLEKLER.

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