US2094913A - Heating of fluids - Google Patents

Description

Oct. 5, 1937. 9 M. w. BARNES 2,094,913

HEATING OF FLUIDS Filed My 21, 1934 2 Sheets-Sheet l INVEN OR MARION W. RNES ORNEY I Oct. 5, 1937. M. w. BARNES 2,094,913

HEATING QF FLUIDS Filed May 21, 1934 2 Sheets-Sheet 2 INVEN OR 4 MARION W. NES

AT ORNEY Y Patented Oct. 5, 1937 PATENT OFFICE HEATING 0F FLUIDS Marion W. Barnes, Chicago, Ill., assignor to Universal Oil Products Company, Chicago, 11]., a corporation of Delaware Application May 21, 1934, Serial No. 726,690

7 Claims.

This invention refers to an improved process and apparatus for the heating of continuous streams of fluids, and more particularly to the heating of hydrocarbon oils to the high temperatures required for their pyrolytic conversion. The invention will be found especially advantageous in the conversion or reforming of hydrocarbon oils of relatively low-boiling characteristics such as, for example, straight-run gasoline or other motor fuel of inferior antiknock value, naphtha, kerosene or kerosene distillate, pressure distillate, pressure distillate bottoms and the like.

It has been proven by present practice that the most advantageous method of converting relatively lowboiling hydrocarbon oils, of the type which are practically entirely vaporized under the conversion conditions of temperature and pressure to which they mustbe subjected for the production of motor fuel of high antiknock value, is to preheat the oil to near a cracking temperature, then rapidly heat it to or near the maximum conversion temperature desired and finally to maintain it at or near the maximum temperature attained for a predetermined time. Following this treatment the stream of heated oil ordinarily is quickly cooled to a temperature at which no appreciable further conversion will occur. By this method of treatment a definite control is exerted not only over the temperature and pressure conditions to which the oil is subjected but also over the time during which the oil is subjected to appreciable conversion.

When this type or" treatment is employed in the type of furnace structures ordinarily utilized in the conversion of hydrocarbon oils it necessitates transferring the. stream of oil undergoing heating from fluid conduits in one portion of the furnace to fluid 'conduits in another rela means of connecting lines located entirely outside the iurnace or at least outside of the heating zone. In such cases difliculties are often encountered in arranging the inlet and outlet connections to the furnace and the outside crossovers between difierent portions of the fluid conduit so that they do not interfere and, to avoid such interference, it is sometimes necessary to eliminate one or more available tubes from the fluid conduit. The use of outside crossovers also necessitates the use of extra terminal fittings as well as additional pipe sleeves in the furnace brick work. Connections between various portions of the fluid conduit located outside the furnace or outside the heating zone also materially increase radiation losses and the fire hazard is also increased on account of the additional stresses in the fluid conduit, due to cooling in the outside crossovers.

The present invention offers an improved meth 0d and means for obtaining the heating conditions most desirable for the conversion of lowboiling hydrocarbon oils in conventional furnace structures by passing the oil first through that portion of the fluid conduit located in the mildest heating zone of the furnace, wherein it is preheated to or near the conversion temperature, then passing the oil through that portion of the fluid conduit subjected to the most severe heating conditions, whereby it is quickly heated to or near the maximum conversion temperature desired, and finally passing the stream of highly heated oil through a portion of the fluid conduit subjected to heating conditions intermediate to those in the mildest and most severe heating zones of the furnace, whereby the oil is maintained at or near the maximum conversion temperature previously attained for a predetermined time. In the present invention this is accomplished without passing the oil through crossovers connecting the various portions of the fluid conduit located outside the furnace. Instead the lines'connecting the various portions of the fluid conduit themselves comprise a portion of the fluid conduit and are located within the heating zone. This elimination of connecting lines or crossovers between various portions of the fluid conduit obviates all the disadvantages attendant with their use and the features of the present invention provide other advantages not otherwise obtainable which will be later more fully described.

The accompanying diagrammatic drawings illustrate two specific forms of conventional furnace structures to which the features of the present invention are readily adaptable and demonstrates two specific methods and means of adapting the ieatures'of the invention to each of the structures illustrated.

Figs. 1 and 2 are cross-sectional elevations of what is ordinarily termed a convection type furnace While Figs. 3 and 4 are sectional elevations of a combination radiant and convection type furnace. A somewhat different flow through the fluid conduit is indicated in each of the four figures.

Referring particularly to Fig. 1, the main furnace structure comprises side walls I and 2, a roof 3, a floor 4 and end walls which are not shown in the particular view here illustrated. The interior of the furnace is divided by means of a partition or bridge wall 20 into combustion zone 5 and'heating zone 6.

A combustible fuel-air mixture is supplied to combustion zone 5 of the furnace through firing ports I by means of suitable burners, the tips of which are indicated at 8 in the drawings. Combustion is entirely or substantially completed in combustion zone 5 and the hot combustion gases pass through openings 9 provided in the upper portion of wall 20 into heating zone 6, passing downward therethrough over the fluid conduit provided in this zone to flue in from which they are directed to a suitable stack, not shown.

A fluid conduit ll comprising a plurality of superimposed, horizontally parallel rows of horizontally disposed tubes I2 is located within the heating zone 6 and, in the case here illustrated, is divided into a lower section I 3, an upper sec tion l4 anda central section l5. Section l3 comprises, in the case here illustrated, the lower three horizontal rows of tubes and the tube on the left hand of each of the succeeding (higher) six rows, while section it comprises the upper three horizontal rows of tubes and section I 5 comprises the remaining tubes in the 6 centrally located rows of tubes. In the particular embodiment of the invention here illustrated the oil to be treated enters the end tube of the lower row of section l3 adjacent side wall 2 of the furnace, flowing in series through adjacent tubes and adjacent rows of tubes in this section by means of suitable return bends or headers disposed alternately on the far end and near end of the furnace, as indicated in the drawings by the. dotted lines l6 and the full lines l1, rapectively. The oil then flows from bank l3 upward in series through adjacent tubes at the end of each horizontal row adjacent wall 20 to the uppermost row of tubes in the huid conduit comprising the top row of section ll, passing in series through adjacent tubes of thisrowand in seriesthrough the adjacent rows of this section of the fluid conduit, in a general downward direction, and then continuing from section It in series through adjacent tubes of the uppermost and-subsequent rows of tubes in section l5, being discharged-from the last tube of the. lowermost row of this section adjacent wall 2 of -the furnace to subsequent portions of the cracking system 'not pertinent to the present invention.

It will be apparent that section II of the fluid conduit, comprising that portion with which the hot products of combustion are first contacted, is subjected to the most severe heating conditions and, in accordance with the features of the present invention, this is the zone wherein the stream of hydrocarbon oil undergoing treatment is quickly brought to or near the maximum conversion temperature attained. Section l3 of the fluid conduit, with which the combustion gases are last contacted, prior to their removal from the furnace, is exposed to the mildest heating conditions employed in the furnace and, in accordance with the features of the present invention, comprises that section of the fluid conduit wherein the stream of hydrocarbon oil supplied to the-furnace is heated, at a relatively slow rate, to or near a mild conversion temperature. Section l5 of the fluid conduit is subjected to heating conditions intermediate to those employed in sections II and parts of this furnace similar to the respective parts I to 20 inclusive of Fig. 1.

In Fig. 2 the flow of oil through section H of the furnace is reversed to that in section II of Fig. 1 so that the flow of oil in both the preheating section of the furnace and in the section wherein the oil is brought to or near the maximum conversion temperature is in a general direction counter-current to the flow of combustion gases through heating zone 6' while the flow of oil through the soaking section 15', wherein it is maintained at or near the maximum conversion temperature previously attained for a predetermined time, is in a general direction concurrent to the flow of combustion gases through heating zone 6'.

It is, of course, within the scope of the invention to utilize any desired number of tubes and any desired number of rows of tubes in each section of the furnace and it is evident that the flow arrangement illustrated in Figs. 1 and 2 may be altered, when desired, to give more or fewer tubes or rows of tubes in any of the sections I3, I4 and I5 or 13', I4 and i5' without changing the total number of tubes in the fluid conduit. These details may be altered to suit the requirements of the particular oil undergoing treatment to obtain the desired results and should not be considered as limitations to the invention.

Referring now to Fig. 3, the main furnace structure here illustrated. comprises side walls 2| and 22, 'a roof 23, a floor 24 and end walls which are not illustrated in this particular view of the furnace. The interior. of the furnaceis divided by means of bridge wall 35' into a combustion and heating zone 25 and a convection heating zone 26.

Combustible fuel and air are supplied to the combustion zone, in the case here illustrated, through fli'ing tunnels such as indicated, for example, at 21; fuel of any suitable form, together with a regulated portion or all of the air required for combustion, being supplied by means of a suitable burner 28 through combustion compartment 29 of the firing tunnels, while regulated quantities of additional air may be supplied to the conbustion zone through ducts 30 located above and beneath combustion compartment 29 of the flring tunnels.

The total fluid conduit, in the case here illustrated, comprises a plurality of horizontally parallel rows of horizontally disposed tubes 32 located within fluid heating zone 26 of the furnace, two vertically parallel rows of horizontally disposed tubes 32 located adjacent the upper portion of the side wall 22 of the furnace and two horizontally parallel rows of horizontally disposed tubes 32 located adjacent the roof 23 of the furnace. wall 22 as well as the upper row or upper two rows of tubes in the convection heating zone receive an appreciable quantity of radiant heat f romthe materials undergoing combustion in the furnace and the hot refractory walls of the furnace, while the remaining tubes in the convection The tubes adjacent roof 23 and side.

heating zone receive primarily convection heat by contact with the hot combustion gases which pass from combustion zone 25 over bridge wall 36 and downward through convection heating zone 26 to flue 3|, from whichthey pass to a suitable stack, not illustrated.

Section 33 of the fluid conduit, comprising,

in the case illustrated, the lowermost rbws of tubes in the convection heating zone, is located in the mildest heating zone of the furnace and comprises the preheating section to which the oil to be subjected to conversion is supplied and passed in series through adjacent tubes in each row and through adjacent rows of tubes in a general upward direction, counter-current to the flow of combustion gases, whereby it is preheated to or near a. mild conversion temperature. The oil then passes in series through the end tubes adjacent bridge wall 36 of each of the remaining rows of tubes in the convection heating zone to the uppermost row of tubes in the convection heating zone. Section 34 of the fluid conduit, comprising the uppermost row of tubes in the convection heating zone, the two rows of vertical tubes adjacent the upper portion of wall 22 and the two rows of tubes adjacent the roof of the furnace; is subjected to the most severe heating conditions employed in the furnace and comprises that portion of the fluid conduit wherein the preheated oil is brought rapidly to or near 'the desired maximum conversion temperature.

The oil flows through this section of the furnace, in the case here illustrated, first in series through adjacent tubes of the upper horizontal row in the convection heating zone, then in series through adjacent tubes of the exposed vertical row along the upper portion of wall 22, then in series through adjacent tubes of the exposed row adjacent roof 23, then in series through adjacent tubes of the shielded row adjacent roof 23 and finally through the shielded row of tubes adjacent wall 22 to the second horizontal row of tubes from the top of-convection heating zone 26. Section 35 of the fluid conduit, comprising the remaining tubes in the 8 horizontal rows of tubes immediately beneath the uppermost row of tubes in convection heating zone 26, is exposed to heating conditions intermedate to those employed in sections 33 and 34 of the fluid conduit and section 35 comprises the soaking section wherein the treatment of highly heated hydrocarbon oil from section 34 is maintained at or near the maximum conversion temperature previously attained for a predetermined time. The oil flows in series through adjacent tubes in each row and through adjacent rows of tubes of section 35, in a general direction concurrent to the flow of combustion gases through convection heating zone 26 and is discharged from the furnace from the last tube of this section adjacent wall 22.

' Referring now to Fig. 4, the furnace structure except for the specific flow arrangement shown, is the same as that illustrated in Fig. 3. The reference numbers 2| and 36 inclusive in Fig. 4 designate the same parts of the furnace as the respective reference numbers 2| to 36 inclusive in Fig. 3. I

.In Fig. 4 the direction of flow through-section 34' of the fluid conduit is reversed to that through section 34 in Fig. 3. This is accomplished, in the case illustrated, by eliminating one row of tubes in preheating section 33 and adding a row of. tubes to soaking section 35' The preheated oil from section 33' passes upward in series through adjacent end tubes next to side wall 22' of each horizontal row above the fifth row of tubes from the bottom in the convection heating zone, entering'the shielded row of vertical side wall tubes adjacent the upper portion of wall 22' flowing in series through adjacent tubes of this row and the shielded row of roof tubes, then through the exposed row of roof tubes and the exposed row of wall tubes and through the top row of tubes in convection heating zone 26, passing therefrom to the soaking section 35' wherein the stream of highly heated oil flows in series through adjacent tubes of each row and through successive lower rows of tubes to and through the fifth row from the bottom from which it is discharged from the furnace.

With the flow arrangement illustrated in Fig. 4 a progressive rate of heating may be obtained throughout substantially the entire length of section 34 of the fluid conduit, wherein the oil is brought quickly to or near the maximum desired conversion temperature, the general direction of flow of the oil through preheating section 33' being counter-current to the direction of flow of the combustion gases through convection heating zone 26 while the direction of flow of the oil through the soaking section 35 is concurrent to the flow of combustion gases through the convection heating zone.

It will be noted in connection with the foregoing description and the accompanying drawings that the method and means employed in thepresent invention for connecting the various portions of the fluid conduit eliminates sudden changes in the heating condition to which the oil is subjected. For example, in all of the cases illustrated, the stream of oil transferred from a relatively cool to a relatively hot zone of the furnace is passed through successive zones of progressively increasing temperatures from the relatively cool to the relatively hot zone and, vice versa, the oil transferred from a relatively cool to a relatively hot zone of the furnace flows through successive zones of progressively decreasing temperatures from the relatively hot to the relatively cool zone. The advantages of this feature of the invention will be readily apparent to those skilled in the art related but additional to the advantages obtained by the elimination of connecting lines between various portions of the fluid conduit located outside the heating zone.

I claim as my invention:

1. A means of heating a continuous stream of fluid which comprises,. in combination, a tube bank comprising a plurality of superimposed, horizontally parallel rows of horizontally disposed tubes,'means for passing hot combustion gases downwardly over said tube bank, another tube bank comprising a row of tubes exposed to direct radiant heat and a row of tubes exposed to shielded radiant heat, means for passing the stream of fiuid to be heated first through several rows of tubes in the lowermost portion of the first mentioned tube bank, then through adjacent end tubes in successively higher rows of the first mentioned tube bank to the second mentioned tube bank, then through the second mentioned tube bank and finally through the remaining rows of tubes in the first mentioned tube bank.

2. In combination with a furnace, fluid heating means in the furnace comprising a plurality of serially connected horizontal tubes in the upper rows of horizontal tubes positioned in the furnace intermediate said plurality of tubes and the first-mentioned set of rows of tubes, and means connecting the first-mentioned set of rows of tubes in the lower portion of the furnace with said plurality of tubes in the upper portion of the furnace, said means comprising adjacent end tubes of the rows of said additional set, the remaining tubes of said additional set being connected with said plurality of tubes in the upper portion of the furnace.

3. In combination with a furnace, fluid heating means in the furnace comprising a first and a second set of vertically. spaced, horizontal rows of serially connected horizontal tubes disposed respectively in the upper and lower portions of the furnace, an additional set of vertically spaced,

horizontal rows of tubes disposed in the furnace intermediate said first and second sets, and means connecting said first and second sets comprising adjacent end tubes of said additional set, the remaining tubes of said additional set being connected with the tubes of said first set.

4. In combination with a furnace, fluid heating means in the furnace comprising a first and a second set of vertically spaced, horizontal rows of serially connected horizontal tubes disposed respectively in the upper and lower portions of the furnace, an additional set of vertically spaced, horizontal rows of tubes disposed in the furnace intermediate said first and second sets, means for passingcombustion gasm downwardly through the furnace over said fiuid heating means, and means connecting said first and second sets comprising adjacent end tubes of said additional set, the remaining tubes of said additional set being connected with the tubes of said first set.

5. In a furnace having a combustion zone and a convection heating zone through which combustion gases from the combustion zone are passed, the combination of a plurality of serially connected tubes in the combustion zone, a set of vertically spaced, horizontal rows of serially connected horizontal tubes in the upper portion of the convection zone and connected to the tubes in the combustion zone, another set of vertically spaced, horizontal rows of serially connected horizontal tubes in the lower portion of the convection zone, and means for connecting the lastnamed set of rows of tubes with the tubes in the combustion zone comprising a plurality of serially connected, vertically spaced, horizontal tubes disposed in the convection zone, each of the last named tubes being in horizontal alignment with 'a row of said set in the upper portion of the convection zone.

6. In a furnace having a combustion zone and a convection heating zone through which combustion gases from the combustion zone are passedfthe combination of a. plurality of serially connected, radiantly heated tubes in the upper portion of the combustion zone at a higher level in the furnace than the upper portion of the convection zone and out of the main path of combustion gases from the combustion zone to the convection zone, a set of vertically spaced,

' horizontal rows of serially connected horizontal tubes in the upper portion of the convection zone, connecting means between said set of rows of tubes, and the tubes in the combustion zone and comprising a plurality of serially connected, vertically spaced, horizontal tubes disposed in the furnace, another set of vertically spaced, horizontal rows of serially connected horizontal tubes in the lower portion of the convection zone, and

means for connecting the last-named set of rows of tubes with the tubes in the combustion zone comprising a plurality of serially connected, vertically spaced, horizontal tubes disposed in the convection zone, each of the last named tubes being in horizontal alignment with a row of said forming a connection between said sets of serially connected tubes and the remaining tubes of said rows being serially connected to provide continuous fluid flow through said remaining tubes.

MARION W. BARNES.

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