US2076855A - Heating of fluids - Google Patents

Description

April 13, 1937. MEKLER 2,076,855

' HEATING OF FLUIDS- Filed July 2, 1934 2 Sheets-Sheet 1 FURNACE 26 FURNACE 5 FIG. I

INVENTOR LEV' EKLgR ATTORNEY April 13, 1937. L ME'KLER I 2,076,855

HEATING OF FLUIDS Filed July 2, 1934 2 Sheets-Sheet 2 INVENTOR LEV EKLER TTORNEY so f Patented Apr. 13,. 1937 UNITED STATES ,HEATING .OF FLUIDS Lev A. Mekler, Chicago, 111., assignorto Universal Oil Products Company, Chicago, Ill., a corporation of Delaware Application July 2, 1934, Serial Nohzsasir "2 Claims.

, The present invention provides an improved method and means for heating fluids. The invention is particularly adapted to the heating of hydrocarbon oils to the high temperatures re- 5 quired for their pyrolytic conversion and is particularly directed to the simultaneous conversion of separate streams of relatively low-boiling and relatively high-boiling oils under independently controlled conversion conditions of temperature 1:) and pressure, the present invention providing also for independent control of the heating conditions to which each stream of oil is subjected.

The trend of modern practice in the pyrolytic conversion of hydrocarbon oils is toward selec- 13 tive cracking. This is the term ordinary applied to the separation of charging stock from the cracking operation and/or intermediate conversion products of the cracking process into selected relatively low-boiling and high-boiling fractions and the simultaneous conversion of the selected fractions each under independently controlled conversion conditions regulated to suit the particular characteristics of each fraction. The best practice in such processes calls for independent control of the heating conditions to which each of the different selected streams 'of oil is subjected. Higher furnace temperatures and higher rates of heat input are ordinarily employed for relatively low-boiling oils, such as, example, gasoline, naphtha, kerosene, kerosene distillate, pressure distillate, pressure distillate bottoms, light gas oil and the like, than those to'which higher boiling oils, such as, for

example, heavy gas oil, heavy crude petroleum, topped crude, fuel oil and residual oils, generally may be safely subjected without the danger of excessive formation of coke and gas'and the deposition of coke in the heating coil. Independent control of the heating conditions about 41), each conduit through which a separate stream of hydrocarbon oil is passed may be accomplished by disposing each separate conduit in a separate furnace structure or maybe accomplished by some of the more modern types of heaters where- 43 in independent control of the heating conditions to which two or more separate fluid conduits located within the same furnace structure isobtained. In either case, if the furnaces are efficient from the standpoint of utilizing-the maximum available heat, there is ordinarily at least one portion of the fluid conduit located within a zone of the furnace wherein it is exposed to high furnace temperatures and a relatively high rate of heat input ordinarily too severe for the most advantageous treatment of relatively high-boil ing o'ils. This is due, in some cases, to exposure of the same surface of a portion of the fluid conduit both to radiant heat from the materials undergoing combustion and/or from the 'hot refractory walls of the furnace and to considerable additional heating by contact with hot combustion gases and, in other cases, may be due to contact of the surface of a'portion of the fluid conduit with hot combustion gases from more than one combustion zone. The latter condition is found particularly in cases wherein two ,or more combustion zones are employed within the same furnace structure for the separate treatment of two or more streams of different hydrocarbon oils. i

It is the purpose of the present invention to utilize the above mentioned zones of high heat input to better advantage and this is accomplished by so arranging the path of flow of relatively low-boiling and relatively high-boiling streams of hydrocarbon oil through various portions of different fluid conduits so as to eliminate from the stream of relatively high-boiling oil that portion of'the fluid conduit exposed to. excessively highrates of heating but to include such zones of high heat input in the path of flow of the stream of relatively low-boiling hydrocarbon oils.

The present invention includes within its scope practically all types of furnace structures and firing arrangements wherein two or more separate streams of different hydrocarbon oils are heated simultaneously to the high temperatures required for their conversion. The specific flow arrangement employed in each case to accomplish the objects of the present invention may vary considerably, depending upon the particular type of furnace structure or structures employed as well as the firing conditions employed in each furnace or in each combustion zone of the same furnace. The accompanying diagrammatic drawings will serve to illustrate several typical cases. Fig. 1 of the drawings illustrates how the features of the present invention may be applied in two similar furnace structures of the type generally known as a combination radiant and convection 1 furnace. Fig. 2 illustrates the features of the present invention as adapted to a single furnace structure with two separately fired combustion zones and a centrally located convection heating zone and Fig; 3 illustrates another type of furnace structure, which, in reality, without the features of the present invention, is two independently'fired furnaces in juxtaposition, and

a method of adapting the features of the present invention to this particular type of furnace installation.

Referring particularly to Fig. 1 which illus- 5 trates, in cross-sectional elevation, two similar furnaces designated as A and B, each of the combination radiant and convection type. The main furnace structure of furnace A, which, in the case here illustrated, contains'the total heating l coil. or fluid conduit through which the relatively high-boiling hydrocarbon oil is passed, comprises side walls I and 2, a roof 3, a floor 4 and endwalls which are not shown in the particular view of the furnace here illustrated.

15 The interior of furnace A, is divided into a combustion and heating zone and a convection heating zone 8 which are separated by means of bridge wall I.

Combustible fuel of any desired form, such as 20 oil, gas or pulverized solid fuel, is supplied to combustion zone 5 through the central duct 8 of suitable firing tunnels such as indicated at 9 by means of burners of any suitable form, such as indicated, for example, at Ill, and a regulated 5 portion or all of the air required for combustion may be supplied to the combustion zone together with the fuel through firing compartment 8, any desired quantity of additional air being supplied in regulated amounts to the combustion zone by means of ducts II located above and beneath firing compartment 8 in tunnels 9.

A tube bank I2 comprising, in the case illustrated, a. single horizontal row of horizontally parallel tubes I3 connected at their ends in series is located adjacent the floor 4 of furnace A. Another tube bank I4 comprising, in the case illustrated, a single horizontal row of horizontally parallel tubes I3 is located adjacent the roof of 'furnace A. Another tube bank I5 comprising, 40 in the case illustrated, a plurality of superimposed horizontally parallel rows of horizontally disposed tubes I3 is located within convection heating zone 6 of furnace A.

The materials undergoing combustion in com- 45 bustion zone 5 and the hot refractory walls of the furnace give up heat, primarily by radiation, to tube banks I2 and I4. The hot combustion gases pass over bridge wall I into convection heating zone 6, passing downward in this zone 50 over the tubes of bank I5, to which they give up convection heat, to flue I6 from which they may pass to a suitable stack, not shown in the drawings.

Furnace B, which in the case here illustrated 55 contains a major portion of the heating coil or fluid conduit through which the relatively lowboiling hydrocarbon oil is passed, is similar with respect to the structure of furnace A and the location of the different tube banksto furnace A and the reference numbers I to I6 inclusive in furnace B indicate parts of this furnace similar to the corresponding numbers I to I6 inclusive in furnace A.

According to the conventional method of opcrating furnaces A and B for the treatment of separate streams of relatively low-boiling and high-boiling oils, the entire tube banks I2, I4 and I5 of furnace A, for example, might comprise the heavy oil heating coil with the corresponding 70 tube banks I2, I4 and I5 of furnace B utilized for the treatment of the relatively low-boiling oil, thereby obtaining independent control of the conversion conditions to which each stream of different oil is subjected by virtue of the different 75 firing conditions which it is possible to obtain .in the two furnaces. However, that portion of heating coil when employed for the treatment of relatively high-boiling oils.

In the present invention, therefore, section II comprising'the two uppermost rows of tube bank I5 in furnace A will be by-passed by the stream of relatively high-boiling oil undergoing treatment in this furnace and included in the fluid conduit through which the relatively low-boiling oils are passed. The solid lines and the arrows in Fig. 1 illustrate the direction and course of travel of the two streams of oils through furnaces A and B which may be employed within the scope of the present invention.

In the case illustrated the relatively highboiling oil enters the lowermost row of tube bank I5, passing in series through adjacent tubes and successive adjacent rows of tubes in this bank in a general direction counter-current to the direction of flow of the combustion gases but, instead .of passing through the two uppermost rows of this bank, the stream of high-boiling oil is diverted from the third row from the top of bank I5 into the end tube of bank I4 adjacent wall 2 of the furnace, passes in series through adjacent tubes in this bank toward wall I of the furnace, transferring from the end-tube of bank I4 adjacent wall I to the end-tube of bank I2 adjacent the same wall and passes in series through adjacent tubes of bank I2 toward bridge wall I, to be discharged from the end-tube of bank I2 adjacent the bridge wall to subsequent portions of the cracking system, not illustrated. The stream of relatively low-boiling oil may enter the bottom row of tubes of bank I5 in furnace B passing in series through adjacent tubes and adjacent successive rows of tubes of this entire bank in a general direction counter-current to the direction of flow of the combustion gases, passing then through the upper two rows of tubes of bank I5 in furnace A, then back to furnace B and through tube bank I4 and finally through tube bank I2 of furnace B and out of the furnace to subsequent cracking equipment, not illustrated.

It will be understood, of course, that the features of the invention as'applied to furnaces such as illustrated in Fig. 1 are not limited to the exact sequence of the different tube banks illustrated nor to the direction and general course of flow shown but may be varied with differentco charging stocks and different firing conditions to suit requirements, the only limitation being that a portion of the fluid conduit located within the furnace which is devoted primarily to the treatment of relatively high-boiling oils, which portion is exposed to relatively high and uncontrolled rates of heating, is utilized, together with fluid conduits located within a separate furnace, for the treatment of relatively low-boiling oils.

As an example of one modification of the flow through furnace A illustrated and above described, which is also within the scope of the present invention, that portion of tube bank I3 designated in the drawings as I8, which is above bridge wall I may also be subjected to relatively aovaasc is indicated in the drawings by the broken lines I9, 28 and 21.

Referring now to Fig. 2, which is a sectional elevation of a single furnace structure having two heating coils or fluid conduits, one of which is devoted to the treatment of relatively high boiling oils while the other is devoted to the treatment of relatively low-boiling oils, each under independently controlled conversion conditions, the main furnace structure comprises side walls 25 and 26, a roof 21,- fioors 28 and end walls which are not shown in the-particular view of the furnace here illustrated. The interior of the furnace is divided by means of bridge walls 29 and 29' into two separate combustion and heating zones 38 and 30' and a centraily located convection heating zone 3|.

Combustible fuel of any suitable form is separately supplied to combustion zones and 30 by means of burners 32 and 32', respectively, through the respective firing compartments .33 0 and 33' of firing tunnels 34 and 34', respectively. A regulated portion or all of the air required for combustion in combustion zones 30 and 38' may be supplied thereto through the respective ducts and, 35' of firing tunnels 34 and 34, 35 located above and beneath firing compartments 33 and 33', respectively. A tube'bank 36 comprising, in the case illustrated, a single horizontal row of horizontally parallel tubes 4|, connected at their ends in 40 series, is located adjacent the floor of combustion and heating zone 3|]. A similar tube bank 36 is located adjacent the fioor of combustion zone 38'. Another tube bank 31 comprising, in the case illustrated, a single horizontal row of horizontally parallel tubes 4|, connected at their ends in series, is located adjacent the roof of combustion andheating zone 38 and asimilar bank 31 is located adjacent the roof of combustion and heating zone 38. Another tube bank 38 comprising, in the case illustrated, a

plurality of superimposed .horizontally parallel .rows of horizontal tubes 4| is located Within convection heating zone 3| of the furnace.

The materials undergoing combustion in combustion zones 30 and 30 give up heat primarily by radiation to the tube banks located adjacent the roof and fioor of the respective combustion zones andthe hot combustion gases from both combustion zones commingle, after passing over the respective bridge walls 29.and 29' and pass downward through convection heating zone 3|,

giving up convection heat to tube bank 38in this zone. The combustion gases having passed over the tubes of bank 38 may be directed through flue 42 to a suitable stack, 'not shown.

As an example of one conventional method of operating the furnace of Fig. 2 which, how- ,-ever,lis not illustrated in the drawings, the furnace may, for the sake of convenience, be considered as divided into two furnaces, one on the right-hand side of .a vertical center line through Fig. 2 and the other on the left-hand side. The stream of relatively high-boiling oil may, for

example, pass through half of the tubes in each 1 75 row of bank 38 comprising those on the lefthand side of the center line and through tube banks 31 and 36 in the order mentioned, while the stream of relatively low-boiling oil passes through the remaining tubes of bank 38, comprising rows on the right-hand side of the center line, and through tube banks 38' and 31 in the order mentioned. In such cases independent control of the firing conditions in combustion zones 30 and 38' permits independent regulation of the heating conditions to which each stream of oil is subjected during its passage through the roof and floor banks of the respective conibustion'and heating zones. However, the heating conditions in tube bank 38, over which the commingled combustion gases from both combustion zones pass, are the result of the firing conditions in both combustion zones and. the first tubes of bank 38 to come in contact with the commingled hot combustion gases, for example, the two uppermost rows of tubes, are subjected touncontrolled relatively high rates of heating.

Therefore, in accordance with the provisions of the present invention in order to avoid exposing the stream of relatively high-boiling hydrocarbon oil to the uncontrolled relatively high rates of heating which ordinarily prevail in the upper two rows of tubes of bank 38, the tubes in the upper two rows of this bank;on the lefthand side. of the center line are, in the case illustrated, by-passed by the stream of relatively high-boiling oil and the stream of relatively low-boiling oil is passed through all of the tubes in the upper two rows-of bank 38, thus dividing tube bank' 38' into two sections desi nated inthe drawings as 39 and 48, the stream of relatively low-boiling oil being passed through section 39 and the stream of relatively highboiling oil through section 48.

portion of the fluid conduits and between different portions of the fluid conduits and the arrows indicate the general direction of flow of each stream through the different portions of the various conduits. It will be understood, of course, that the invention is not limited to the specific direction of fiow nor the specific sequence of flow through the various portions of the light oil and heavy oil conduits since these may be varied, at will, to suit the requirements of the particular oils undergoingtreatment and different firing conditions in each combustion zone in order to obtain the desired results, the only' limitation to the present invention being that a portion of the, fluid conduit located within the section of the furnace devoted primarily to the treatment of relatively high-boiling oils, which portion is exposed to relatively high and uncontrolled rates of heating, is utilized, together with the fluid conduit located in the other section of the furnace, for the treatment of. relatively low-boiling oils. 3

As an example of one of the many possible modifications of the specific fio'w illustrated in modification, however, is not illustrated in the 40 connections between the various tubes in each drawings; when the firing conditions are such that portions of tube banks 31 and 31' located above convection heating zone 3| of the furnace are subjected to uncontrolled relatively high .rates of heating the stream of relatively lowboiling hydrocarbon oil may be passed through this portion of tube bank 31 as well as'the entire bank of tubes 31' and the same portion of tube bank'31 may be by-passed by the stream of relatively high-boiling hydrocarbon oil. This flow may be utilized, as desired, either instead of or in conjunction with passing the stream of rela- CTl entire upper two rows of tubes in bank 38.

Referring now to Fig. 3 which, as already mentioned, illustrates, in cross-sectional elevation,

another specific type of furnace to which the features of the present invention are readily adaptable; the main furnace structure comprises side walls 45 and 46, a roof 41, a sub-roof 48, a floor 49 and a partition 50 extending throughout the length of the heating and combustion zones of the furnace between end walls which are not shown in the particular view of the furnace here illustrated. Partition 50 divides that portion of the furnace beneath sub-roofs 48 into two separate combustion and heating zones 5| and 5| and extensions 50 of partition 50, above subroof 48, divide the upper portion of the furnace into two separate convection heating zones 52 and 52.

Combustible fuel of any desired form is supplied by means of suitable burners, such as indicated, for example, at 53, through firing compartments 54 and 54 of firing tunnels 55 and 55, respectively, to the respective combustion and heating zones 5| and 5| and a regulated portion of the air required for combustion may also be supplied to the respective combustion and heating zones together with the fuel through firing compartments 54 and 54. Any desired quantity of additional air may be supplied in regulated amounts to combustion zones 5| and 5|, respectively, through ducts 56 and 56' located on opposite sides of each of the combustion compartments 54 and 54'.

- A tube bank 51 comprising, in the case illustrated, a single vertical row of horizontally disposed tubes 58 is located adjacent side wall of the furnace within combustion and heating zone 5|. A similar tube bank 5'! is located within combustion and heating zone 5| adjacent par- 45 tition 5!]. Another similar tube bank 51? is located within combustion and heating zone 5| adjacentpartition 5D and another similar tube bank 51" is located adjacent side wall 46 of the furnace within combustion and heating zone 5|. 50 A tube bank 59 comprising, in the case illustrated, a plurality of superimposed horizontal rows of horizontally disposed tubes 58 is located within convection heating zone 52 of the furnace and a similar tube bank 59' is located within con- 55 vection heating zone 52'.

Primarily radiant heat is imparted to the tubes of banks 51, 51, 51'. and 57 by the materials undergoing combustion in the respective combustion zones and the hot refractory walls of the 60 furnace. The combustion gases from combustion zones 5| and 5| pass over the tubes of banks 59 and 59', respectively, imparting convection heat thereto, and the combustion gases passtively low-boiling hydrocarbon oil through the tubes, look directly uponthe flames in combustion zones 5| and 5| and the hot refractory walls of the furnace, so that they are subjected to appreciable heating by direct radiation as well as by contact with the hot combustion gases; the rate of heating being relatively high and uncontrolled in these tubes. Therefore, in accordance with the features of the present invention, the relatively low-boiling hydrocarbon oil to be treatedis passed, in the case here illustrated, through all of the tubes in the two lowermost rows of tube bank 59' as well as all of tube bank 59 and all of tube banks 51 and 51' while the remaining portion of tube bank 59 and all of tube ,banks 51" and 51" comprise the fluid conduit through which the relatively high-boiling hydrocarbon oil is passed.

The single lines and arrows in Fig. 3 illustrate the'general direction and path of flow of the relatively low-boiling and relatively highboiling oils through the different tube banks, line 62 representing the stream of relatively low-boiling oil and line 63 representing the stream of relatively high-boiling oil entering the furnace. Each stream is divided, in the case here illustrated, into two substantially equal streams which flow in parallel through the fluid conduits devoted, respectively, to the treatment of the relatively low-boiling and high-boiling oils. The two substantially equal streams of each.separate oil may be again commingled, following their discharge from the furnace, and supplied to subsequent cracking equipment, not shown in the drawings. It will be understood, of course, that the invention is not limited to the specific direction and course of flow illustrated in the drawmgs.

I claim as my invention:

1. In the heating of hydrocarbon oils to conversion temperatures in furnaces having a pair of independently fired combustion and radiant heat zones provided with fluid conduits and a convection heat zone receiving combustion gases from both said combustion zones and having a tube bank in the path of flow of the combustion gases, the method which comprises passing a relatively light oil, and a heavier oil in parallel streams through the cooler tubes of said bank, then passing the light oil through the hottest tubes of the bank and through one of said combustion zones, and passing the heavier oil directly from said cooler tubes through the other of said combustion zones.

2. In a. furnace having a combustion section and a communicating convection heat section through which combustion gases from the combustion section are passed thereby forming in the. convection section a zone of high rate of heating anda zone of lower rate of heating, the combination of a fluid conduit in the combustion section, a tube bank in the convection section and having tubes in both said zones, means for passing two parallel streams of fluid through the tubes in said zone of lower rate of heating and for then passing one of said streams of fiuid through said conduit and the other through the tubes in said zone of high rate ofheating.

' LEV A. MEKLER.

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