US2076856A - Furnace for and method of heating fluids - Google Patents

Description

April 1937!- w. H. MINKEMA 2,076,856

FURNACE FOR AND METHOD OF HEATING FLUIDS Original Filed June 8, 1953,

I l I k o gfioooo-oo-oo-o- 4 ooo o-oo-oo-oo-o u' ll" Q Q Q -a INVENTOR WILLIAM H. MINKEMA ATTORNEY Patented Apr. 13, 1937 PATENT OFFICE FURNACE FOR, AND

METHOD OF HEATING FLUIDS William H. Minkema,

Chicago, Ill., assignor to Universal Oil Products Company, Chicago, 111., a corporation of Delaware Application June 8, 1933, Serial No. 674,801

Renewed September 11, 1936 7 Claims.

This invention is particularly directed to the heating of fluids, such as hydrocarbon oils, to the high temperatures required for their pyrolytic conversion and is especially concerned with improvements to, a type of furnace designed for simultaneously subjecting equal streams of the same oil to equal heating conditions and with the method of operating such improved furnace.

The high charging capacities of modern cracking units has necessitated the design of furnaces to heat the large quantities of oil processed to the high temperatures now commonly employed with a minimum pressure drop, due to friction, through the heated fluid conduit without sacrificing their heating efliciency. The most successful method of accomplishing this, without excessively increasing the cross sectional area of the fluid conduit and thereby too greatly reducing the ratio of heating surface to volume in the fluid conduit and thereby sacrificing heating efiiciency, has been to split the oil flowing through the heating coil into two or more equal streams, each of which are simultaneously subjected to equal heating conditions in similar fluid conduits of the proper size, the separate streams being commingled at some point within or subsequent to their passage through the fluid conduit and the comminglecl streams supplied to succeeding portions of the cracking system. The major difficulty encountered with such split flow through theheating coil has been in obtaining equal heating of the different streams and, more particularly, in arranging the heating coil or fluid conduit and so directing the flow of the separate streams therethrough that equal heating conditions are obtained in the separate streams. This is somewhat complicated by the fact that equal pressure drop, due to friction, in the different streams is ordinarily depended upon to maintain anequal volume of oil in the different streams. The friction encountered by the oil passing through the fluid conduit varies in direct relation to the volume of the oil at a given velocity or the velocity of a given volume of oil and is, of course, directly affected by the degree of vaporizationof the oil which in turn is dependent upon the heating conditions to which it is subjected. It is thus apparent that the heating conditions and the volume of oil flowing through the heating coil are inter-dependent and that the bad effects of unequal heating, in different parallel streams in fluid conduits connected at their inlet and discharge ends, are accumulative.

- The present invention is concerned primarily ,55 with modern furnaces utilizing heating by both radiation and convection and employing high rates of heating, particularly in the radiant section of the furnace, and, for the purpose of illustration, we may consider a furnace having a bank of tubes comprising a horizontal exposed row of horizontal tubes and a parallel shielded row of tubes located adjacent the roof of the furnace and heated primarily by radiation from the combustion Zone and a fluid heating bank W comprising horizontally parallel rows of horizontal tubes running at right angles to the direction of the radiant roof tubes and separated from the combustion zoneof the furnace by a bridge wall. In a furnace of this character equal heating of two separate streams of oil may be obtained to a satisfactory degree in the fluid heating bank by, for example, dividing the bank vertically, in effect, into two banks containing an equal number of tubes and passing each stream successively through half of the tubes in each successive horizontal row, the two streams flowing in parallel and in the same direction through the two halves of the entire bank. 'This same method of flow, however, as applied to the radiant bank of roof tubes is satisfactory only when substantially identical heating conditions are maintained on opposite sides of the furnace. This is a diflicult condition to maintain since it is ordinarily necessary to employ a plurality of burners in large furnaces of this character and slight variations in the adjustment of different burners as well as changes in the draft will materially change the heating conditions in different portions of the furnace. Also eddy currents set up by the combustion gases in the combustion zone, due tothe cooling effect of the tubes of the fluid conduit on the gases, are particularly subject to change with slight changes in the firing conditions and draft and exert a marked influence upon the heating conditions in different portions of the furnace.

In the present invention such changes in the firing conditions are prevented from upsetting equal heating conditions in the two streams by causing the streams to cross fromthe exposed row of roof tubes to the shielded row of roof tubes at the middle of the radiant bank so that each stream flows through the tubes in half of the exposed row and through the tubes in the opposite half of the shielded row. In this manner different streams flow through the adjacent exposed row and shielded row on each side of the furnace and both streams are affected by any change in the heating conditions on either side of the furnace.

The features of the present invention and the specific manner in which equal heating of two equal streams of the same fluid is accomplished in a furnace of the type above described will be more apparent with reference to the accompanying diagrammatic drawing of such a furnace and the following description thereof. It will be understood, however, that the features of the invention are not limited to use in the specific form of furnace illustrated and described but may be utilized to advantage in many different types of furnaces and in its broad sense the I invention embraces any method and means of obtaining equal heating in different streams of the same fluid wherein the streams are caused to cross from one row to another of the fluid conduit in a manner substantially as herein disclosed.

Referring to the drawing, Fig. 1 is a cross sectional elevation of a furnace in which the features of the present invention are incorporated and Fig. 2 is a longitudinal elevation shown in cross section of the same furnace structure, the section being taken along a vertical plane indicated by the line 22 in Fig. 1.

The main furnace structure comprises side walls I and I, end walls 2 and 2', a roof 3 and a floor 4. The interior of the furnace is divided 1 by means of a bridge wall 5 into a combustion and radiant heating zone 6 and a fluid heating zone I. A bank 8 of horizontal tubes 9 which,

in the case illustrated, is divided into two similar banks 8' and 8" is located in the fluid heating zone I of the furnace. The tubes of bank 8 are arranged in a series of superimposed horizontal rows and each of the banks 8' and 8" contain an equal number of tubes in the same row and the same total number of tubes.

A radiant bank ll of horizontal tubes 9, comprising a shielded row I2 and an exposed row l3 are located within the roof 3 of the furnace and parallel thereto. In accordance with the features of the present invention, the radiant bank ll of shielded and exposed roof tubes is divided into two similar banks II and H"; bank II containing the tubes in the left hand half of exposed row 13 and the right hand half of shielded row l2 while bank ll" contains the tubes in the right hand half of exposed row I3 .and .the left hand half of shielded row l2. The two banks II and H" contain an equal total number of tubes, each bank containing the same number of exposed tubes as the other bank and each bank containing the same number of shielded tubes as the other bank. Also, there are an equal number of tubes in each of the banks H and II" on opposite sides of the furnace.

Combustibles of any desired form are supplied to the combustion zones 6 of the furnace by means of suitable burners of any desired form (not shown) through firing ports such as indicated, for example, at H5 in Fig. 2 located in wall 2 of the furnace. When desired, one or a plurality of checker walls such as indicated at [5 in Fig. 2, located at any desired point along the floor 4 of the furnace, may be utilized to break up the flame and assist combustion in the combustion zone. The tubes 9 in roof bank H of the furnace are heated, primarily by direct radiation from the flames and hot combustion gases in the combustion zone as well as reflected radiant heat from the hot refractory walls of the furnace. A minor amount of convection heat will ordinarily be imparted to the tubes in bank II from the hot combustion gases which come in contact therewith. The combustion gases from combustion zone 6 of the furnace pass over the bridge wall 5 and downward through the fluid heating zone I to flue l6 and thence to a suitable stack (not shown). The tubes of bank 8, located within convection zone I, are thereby heated primarily by fluid heat from the hot combustion gases passing from combustion zone 6 to flue l6, although some radiant heat may be imparted to the tubes of this bank, particularly those in the upper rows.

The tubes 9 of both banks are connected in series at their ends by means of suitable headers or return bends, located outside the heating zone, for example, such as indicated at ll in Fig. 2.

In accordance with the features of the present invention the fluid flowing through the heating coil is divided into two substantially equal streams. The path of flow of the two streams through the fluid conduit, in the particular case here illustrated, is indicated in the drawing by the single lines l8 and I8. The dotted portions of these lines between tubes 9 indicates return bends I! on the far side of the furnace and the solid portions of the lines between the tubes indicates return bends I"! on the near side of the furnace. The direction of flow of the fluid in the two streams is indicated by the arrows. It will be noted, with reference to Fig. 1, that the two streams cross from the shielded row l2 to the exposed row l3 at the middle of the radiant bank I I. By means of this arrangement both streams have an equal number of tubes on opposite sides of the furnace in radiant bank I l and both streams contain an equal number of exposed tubes and an equal number of shielded tubes. Also, the total number of tubes in one stream is equal to the total number of tubes in the other stream. In this manner each stream is equally affected by any variation in the firing conditions on opposite sides of the furnace so that equal heating conditions are obtained in both streams and thus with fluid of the same character supplied under uniform pressure to the inlet to the two parallel fluid conduits comprising the two streams equal volumes of fluid will be discharged from each coil at the same temperature.

I claim as my invention:

1. In heating hydrocarbon oils to conversion temperatures in a furnace having a fluid conduit comprising an exposed row and an adjacent shielded row of parallel tubes adjacent the roof of the furnace and above a combustion zone therein and having means for supplying combustible fuel to the combustion zone through a plurality of burners and in a general direction parallel to the tubes whereby to heat the tubes primarily by radiation, the improved method of securing uniform heating of two streams comprising equal quantities of the same oil which comprises passing the two streams, respectively, through the tubes in opposite halves of one row and then through the'tubes in the opposite half of the adjacent row whereby each stream is subjected to the heating conditions prevailing on opposite sides of the combustion zone.

2. In a furnace for heating hydrocarbon oils to conversion temperatures having a fluid conduit comprising an exposed row and an adjacent shielded row of parallel tubes adjacent the roof of the furnace and above a combustion zone therein, and means for supplying combustible fuel to the combustion zone through a plurality of burners and in a general direction parallel to the tubes whereby to heat the tubes primarily by radiation, so that two streams comprising equal quantities of the same hydrocarbon oil are uniformly heated, the combination of means for conmeeting the tubes in opposite halves of each row in series and means for connecting the tubes in half of one row in series with the tubes in the opposite half of the adjacent row whereby each stream is subjected to the heating conditions prevailing on opposite sides of the combustion zone.

3. In heating hydrocarbon oils to conversion temperature in a furnace having a fluid conduit comprising an exposed row and an adjacent shielded row of parallel tubes adjacent the roof of the furnace and above a combustion zone therein and having means for supplying combustible fuel to the combustion zone through a plurality of burners whereby to heat the tubes primarily by radiation, the method of uniformly heating two substantially equal streams of the oil which comprises passing each of the streams 530 in opposite directions simultaneously through approximately half of the exposed row of tubes and through approximately half of the shielded row of tubes.

4. In heating hydrocarbon oils to conversion temperature in a furnace having a fluid conduit comprising an exposed row and an adjacent shielded row of parallel tubes adjacent the roof of the furnace and above a combustion zone therein and having means for supplying com- 30 bustible fuel to the combustion zone through a plurality of burners whereby to heat the tubes primarily by radiation, the method of uniformly heating two substantially equal streams of the oil which comprises passing one of the streams 35 through approximately half of the shielded row of tubes and then through approximately half of the exposed row of tubes, and simultaneously passing the other stream in an opposite direction through the remaining portion of the shield- 40 ed row and then through the remaining portion of the exposed row of tubes.

5. In the heating of hydrocarbon oils to conversion temperatures in an exposed row and an adjacent shielded row of parallel heating tubes 45 disposed in a combustion zone of a furnace having means for supplying combustible fuel to the combustion zone through a plurality of burners and in a general direction parallel to the tubes whereby to heat the tubes primarily by radiation, the improved method of securing uniform heating of two streams comprising equal quantities of the same oil which comprises passing the two streams, respectively, through the tubes in opposite halves of one row and then through the tubes in the opposite half of the adjacent row whereby each stream is subjected to the heating conditions prevailing on opposite sides of the combustion zone.

6. In the heating of hydrocarbon oils to conversion temperatures in an exposed row and an adjacent shielded row of parallel heating tubes disposed in a combustion zone of a furnace having means for supplying combustible fuel to the combustion zone througha plurality of burners whereby to heat the tubes primarily by radiation, the method of uniformly heating two substantially equal streams of the oil which comprises passing each of the streams 'in opposite directions simultaneously through approximately half of the exposed row of tubes and through approximately half of the shielded row of tubes.

7. In the heating of hydrocarbon oils to conversion. temperatures in an exposed row and an adjacent shielded row of parallel heating tubes disposed in a combustion zone of a furnace having means for supplying combustible fuel to the combustion zone through a plurality of burners whereby to heat the tubes primarily by radiation, the method of uniformly heating two substantially equal streams of the oil which comprises passing one of the streams through approximately half of the shielded row of tubes and then through approximately half of the exposed row of tubes, and simultaneously passing the other stream in an opposite direction through the remaining portion of the shielded row and then through the remaining portion of the exposed row of tubes.

WILLIAM H. MINKEMA.

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