US2081973A - Method of heating fluids - Google Patents

Description

June 1,-1937.

J. G. ALTH ER METHOD OF HEATING FLUIDS 3 Sheets-Sheet l Original Filed June 4, 1952 .1. G. ALTHl-:R 2,081,9 73

METHOD oF HEATING FLUIDS Original Filed June 4, 1932 3 Sheets-Shet 2 June l,V 1937.

U0 um@ bln@ June 1 1937 J. G. ALTH ER METHOD OF HEATING FLUIDS 5 sheets-sheet :s

Original Filed June 4, 1932 FIG. 7

end ...o mmsrmmmzm PROGRESS OF FLUID THROUGH HEATING COIL Flc. 8

INVENTOR JOSEPH G. ALTHER, 6M/5% ATTOR Y Patented June' 1, 1937 METHOD OF HEATING FLUIQSV Joseph G. Alther, Chicago, Ill., assignor, by mesne assignments, to Universal Oil Products Company, Chicago, Ill., a corporation of Delaware IApplication June 4, 1932, Serial No. 615,361 `Renewed August 11, 1936 7 Claims.

This invention particularly refers to an improved method and means of heatingI fluids during their passage through a fluid conduit, which comprises subjecting the maximum surface of a fluid conduit to high rates of heating in order to obtain a high average rate of heat input over the entire sin-face of the conduit.

More particularly the invention relates to a method and means of heating fluids by subject- 10 ing the surfaces of the fluid conduit to radiant and convection heat so as to obtain-the maximum average rate of heat'input oyer the entire surface of thesaid fluid conduit.

While the invention may be applied to the heating of uids generally, its preferred use is in the heating of hydrocarbon oils, and it is especially applicable to the cracking 'of hydrocarbon oils.

Among the advantages of the present invention may be mentioned: (a) The control of velocity, pressure drop and turbulence in the fluid conduit irrespective of the total quantity of oil undergoing treatment at one time; (b) high average heat input over the entire surface of the 2r uid conduit and uniform application of heat to opposite sides of the'conduit; (c) flexibility of control of heat application to obtain any desired rate of heat input by direct control o-f the firing conditions and direct control of heat diso tribution around each section of the coil to obin the heatingA coil; (d) high tube efliciency. Maximum capacity for a fluid conduit of given size or, vice. versa, minimum tub'e surface for a 35 given capacity;1 (e) quick heating of the oil and vapors to-relatively high temperatures with mini mum time which, as applied Yto the conversion of hydrocarbonoils, reduces over-cracking with a consequent reduction in coke formation and deposition in the fluid conduit and in'g'as production and with an increase in gasoline yield and octane number or knock rating of the same. The use of the invention also reduces installa# tion, 45 proves the safety factor. By the application of the invention a large quantity of oil 'may receive the same heat treatment as a small quantity of oil with all of thefresulting advantages.

Modern heaters employing both'radiantand convection heat provide for the application of direct o r nascent radiant heat energy from a source of` heat to the fluid conduit or heating tubes fromeone direction only, the opposite sides of the tubes ordinarily receiving indirect radiant 55 heat from adjacent reflecting surfaces, Whilethe tain any desired heating curve for the material operation and maintenance cost and imdistribution of convection heat around the tubes is uncontrolled and varies with different furnace structures and tube arrangements as well as with variations in the draft and other iiring conditions in the furnace. Obviously this method gives unequal heating around the tube or fluid conduit, the side exposed to direct radiation from the source of heat usually receiving heat at an average rate approximately twice as great as the averagerate of heating' on the opposite surface of the tube, which is exposed to reflected radiant heat, thus greatly decreasing the average rate of heat input over the entire surface of the tube, below thevmaximum rate. Due to unequal heat intensity, at different points around the circumference of the tubethe walls of the tube are subjected to unequal expansion stresses and, in the heating of hydrocarbon oils to the high temperatures required for their conversion, often causes local overheating of a portion of the oil and the resulting formation of excessive quantities of coke and gas. Also as the capacity of the furnace is increased, usually involving anincrease in the length of the fluid conduit, the velocity and pressure drop are correspondingly increased, also, turbulence, heat transfer and other conditions are changed, all of which factors may result in overcracking, coke deposition and reduced yield of gasoline and a poorer quality of the same. 'I'hese disadvantages areovercome in the present invention.

' The presentinventlon embodies a furnace in 'which the fluid conduit is heated from opposite sides by both radiant and convection heat in such a manner that the maximum surface of each tube of the fluid conduit is subjected to the maximum rate of heat input under the existing conditions and uniform heating conditions are obtained on opposite sides of the tube. In this manner the average rate of heating over the entire tube surface may be greatlyincreased over that obtain able by other vmethods without increasing the maximum rate of heating. Thus a much higher tube eiliciency is obtainable and the fluid undergoing heating may be heated to the desired teminates local overheating of the uid passing through the tube and results in the production of less gas and coke and in a motor fuel product of increased antiknock value, as applied to the conversion of hydrocarbon oil.

As a further feature ofthe invention, the fluid conduit may be divided into a plurality of tube banks each of which is independently heated from opposite sides. The various tube banks may be connected either in series or in parallel. When Y connected in series, the arrangement provides a method and means of obtaining a close control over the intensity of heating in each section of the entire iiuid conduit independent of that in any other section so that the rate of heat input -may be varied in different sections of the uid invention permit increasing the capacity of the furnace by the simple addition of unit sections without changing any of the heating characteristics. Forexample: given a furnace with a fluid conduit comprising two banks of heating tubes, the tubes of each bank being connected in series and the two banks being connected in parallel, the rcapacity of the furnace may be doubled by the addition of two similar unit sections having two similar banks of tubes, without increasing the pressure drop through the total fluid conduit,

'which now comprises thevfourl tube banks con- C nected in parallel, without changingthe velocity of the fluid flowing lthrough the heating coil and without otherwise changing the heating conditions such as the intensity of heating in each unit section and each portion of the various unit sections\of the furnaceand without changing the type of heating curve. .y

A multiple-unit furnace of the type provided by the features of the present invention may also be utilized to specialadvantage as applied to the conversion of hydrocarbon oils when it is desirable to subject two or more different types of oil to independently controlled heating conditions in the same cracking system. lIn this connection,

any number of unit sections of the same furnace may be employed for any number of different oils,

4one or` more sections being utilized for each type of oil with independently controlled heating conditions in each unit section.

Figures 1 and 2 of the attached diagrammaticv drawings illustrate al simple furnace structure comprising one specific form of apparatus embodying the features of the present invention.

Referring to the drawings, Figure 1 is a sectional end View of the furnace and Figure 2 is a sectional elevation of the same structure. The

main furnace structure comprises side walls I and I', end walls 2 and 2, a roof 3 and a floor 4. The uid conduit comprises a multiplicity of verk tical tube banks 5, 6, 1, l8 and 9, each consisting of a number of horizontally disposed tubes I0 extending between the end walls 2 and 2 of the furnace.l The tubes of each vertical row or bank are connected in series by means of suitable headers or return bends II. Inlet and outlet ports I2 are provided at opposite ends of each bank of tubes,

each of which may be utilized as either the inlet or outlet port so that the flow of oil or other iluid to be heated may be either upward or downward through any individual bank of tubes, as desired.

In the particular form of furnace here illustrated, ring and combustion tunnels I4, I5, I6, I.1, I8, I9, 20, 2|, 22 and 23 are provided beneath the roof 3 and above the sub-roof 24 of the furnace, one tunnel being provided on each side of each vertical bank or row of tubes. Firing ports 25 are provided for each firing tunnel through which fuel of any desired form is supplied by means of suitable burners, not shown in the drawings.

Walls 26, 21, 28 and 29, within the main furnace structure, divide the entire furnace here illustrated into five unit sections comprising heating zones 30, 3I, 32, 33 and 34 containing the respective tube banks 5,- 6, 1, 8 and 9. Firing tunnels I4 and I5 are located on opposite sides of the vertical center line through tube bank 5 and discharge' their products on opposite sides of the tubes. In a similar manner pairs of firing tunnels IIi and I1, I8 and I9, 20 and 2|, 22 and 23 discharge their products on opposite sides of the tubes in the respective banks 6, 1, 8 and 9. Dividing walls 35 may separate the members of each pair of firing tunnels or this dividing wall may be eliminated, as desired. Also that portion of walls 26, 21, 28 and 29, between the sub-roof 24 and roof 3 of the furnace which separates adjacent ring tunnels of different pairsmay, when desired, be eliminated. Combustion gases are removed from each of the heating compartments 3i, 32, 33 and 34 through openings 36 and the floor 4 of the 'furnace' into the respective gas passageways 31, 33, 39, 40 and 4I from which they are discharged through a iiue 42 to a suitable stack or air preheater section, not shown in the drawings. s Y

Uniform firing conditions are employed in the pair of firing tunnels contained in each unit section of the furnace in order that equalized heating ,conditions are obtained on opposite sides of each tube bank. In this manner radiant heat from incandescent gases, directed on opposite sides of each tube bank, and convection heat obtained by contact of the hot combustion products, which are directed equally on opposite sides of each bank of tubes, serve to equally heat the opposite sides of each individual tube.

`By controlling firing conditions in any pair of firing .tunnels and in the heating zone on opposite sides of the corresponding bank of tubes, substantially the same or different heating conditions may be obtained for the various tubes from top to bottom of any bank so that the rate of heating in any unit section ofthe furnace may be substantially uniform, increasing or decreasing from top to bottom. In a similar manner by controlling the intensity of ring in each unit section of'the furnace, substantially equalized or diierent rates of heating may be obtained in the various unit sections of the furnace so that a uniform, decreas- 65 and 66 through openings 16.in the floor of theconditions are to be employed' in'each unit section of the furnace. Also, when desired, the firing tunnels I 4 to 23 inclusivemay be eliminated, in which case combustion may be accomplished entirely in heating zones 30, 3|, 32, 33 and 34, equalized heating conditions, however, being employed on opposite sides of each tube bank so that the opposite sides of each individual tube are heated equally.

Another specific form of furnace structure embodying the features of the presentl invention is illustrated in Figures 3 and 4 of the attached diagrammatic drawings.` Figure 3 is an end view of the furnace shown in cross-section and Figure 4 is a sectional side elevation of the same furnace 'and 52 of the furnace, are located one bank within 'each unit section of the furnace. The tubes of each vertical row or bank are connected in series by means of suitabl headers or return bends 16. Inlet and` outlet ports.11 are provided at opposite ends of each tube bank, each of which may be utilized as either the inlet or outlet port so that the flow of oil or other uid to be heated may be either upward or downward through any individual bank of tubes, as desired.

Perforated walls 6| and 6| separate `heating zone 62 containing tube bank 51 from combustion zones 63 and 63' respectively. In a similar manner, perforated walls 64 and 64', respectively, separate heating zone 65 containing tube bank 58 from combustion zones 66 and 66 and perforated walls 68 and 61', respectively, separate heating zones 69 and 69.

It is evident from the drawings and the above description that the furnace structure is symmetrical on opposite sides of the vertical center line through each tube bank, as viewed from the end of the furnace, as in Figure 3. Due to this symmetry of structure on opposite sides Jof each bank of tubes and by employing equalized ring conditions between the ring compartments in each unit section of the furnace, equal heating is obtained on opposite -sides of each individual vtube in the entire fluid conduit. i

Each firing compartment .is supplied withany suitable form of fuel through burner ports 10, located in the roof of the furnace, by means of any suitable type of burner, not illustrated. Combustion products pass through openings 1| in each of the walls 6|, 6|', 64, 64'61fand 61 into contact with opposite sides of the tubes 60 in the heating compartments 62, 65 and 66, imparting heat thereto by convection. Radiant heat is supare constructed of a refractory material of high thermal conductivity such as fused or molded alumina or silica, artificial or natural mullite, etc.,

capable of assuming incandescence upon heating furnace into the respective gas passageways 12,

13 and 14 and thence through flue 15 to a suitable stack, not shown.

Conditions may be so controlled in thecombustion zones in any unit section of the furnace that the several tubes in each bank will be heated equally or different intensities of heating may be employed in different sections ofthe same tube bank. The drawings illustrate how the openings 1| andthe distributing walls may be graduated in size so that a greater'quantity of combustion gases will pass into the lower section of each heating zone than into the upper section.

This is one means of supplying additional heating by convection in the lower section of the tube bank to compensate for the normally lgreater' amount of radiantheat received by the upper section of the same tube bank. However, by varying the size and spacing of openings 1| and/or by properly regulating the firing condillions in the combustion zones, such as changing the length of flame by increasing ,or decreasing the quantity of excess air admitted to the combustion zone, any desired heating condition may be obtained in the tube bank of each unit section of the furnace. Also by regulating the intensity of firing in each unit section of thefurnace, 'the rate of heating in each tube bank may be regulated so that oil or other fluid to be heated may be subjected to an increasing. decreasing or a substantially uniform rate of heating during its illustrate diagrammatically the two general types of now through the heating coil which may be employed in either form of furnace structure aboveillustrated and described. Figure 5 illustrates parallel ow and Figure 6 .illustrates series flow through the heating coil.- Figure 'I illustrates a somewhat modified form of series flow arrangement. It will be understood that many modifications of the two general forms may be employed without departing from the scope of the invention.

The numerical designation given to the tube -ve general types of heating curves obtainable with the improved furnace of the present invention. Curve A illustrates a constantly increasing rate of temperature rise through the entire heating coil; curve B illustrates a constantlyA decreasing rate of temperature rise; curve C illustrates a uniform rate of vtemperature rise; curve D illustrates a heating curve with a maximum rate of temperature rise in the first stages of the heating coil. and curve E illustrates a heating curve with the maximum rate of temperature rise in the latter stagesof .the coil. l

Any of the type of heating curves illustrated in Figure 8-may be obtained with either of the furnace structures illustrated and above de- -scribed and with either parallel or series flow of uid through the heating coil. For example, when a constantly increasing rate of temperature rise.

such as indicated by curve A in Figure 8, is deequalized in the several sections of the furnace so that equal heating is obtained in every bank of tubes and the rate of heating is progressively increased from top to bottom of every vertical tube row. When this same type of heating curve is desiredwith series ilow, as illustrated in Figure 6, progressively more severe heating conditions are employed from top to botto-moi each tube bank and progressively more severe heating conditions are employed in the unit sections of the furnace from left to right. With a flow, such as illustrated by Figure 7, the` same type of heating curve may be obtained by employing progressively more severe firing conditions inthe'unit sections of the furnace from left to right and by alternating the firing conditions around adjacent tube banks, progressively increasing heat intensities being employed from top to bottom of the first tube bank, progressively increasing heat intensities being employed from bottom to top of the second tube bank and so on through any` number of tube banks in the fluid conduit.` In a s'milar manner, by suitable regulation of the ilring conditions, curves of the type illustrated by curves B, C, D and E in Figure 8 may be obtained with flows through the fluid conduit such as illustrated in any of the Figures 5, 6 and 7 or in any modification of4 the flows illustrated.

As a specific example of the increased eillciency of a furnace such as illustrated and above described, as compared with the usual type of radiant and convection heaters, we will assume two cases. In the ilrst case wherein the features of the present invention are not utilized, a single row of radiant roof and wall tubes is employed in the radiant heating section of the furnace and additional heat is recovered by convection from the hot combustion gases before they pass from the furnace by means of a separate bank of con- ,vection` tubes. In the second case wherein the features of the present invention are utilized, the furnace structure is of the type above illustrated and both radiant and convection heating is accomplished in the same tube bank. 'I'he size and spacing of the tubes in the second case is the same as the size and spacing of the tubes in the radiant bank of the rst case and the firing conditions are equivalent heat absorbing surface is available,

theoretically, for absorption by the tubes. In the first case approximately 66 percent of this total is absorbed by that half of the surface of the tubes exposed to direct radiation and about 22 percent is absorbed by the other half of the tube surface, making a total of approximately 26,400 B. t. u. absorbed in the radiant bank, per projected square foot of tubing or about 8,300 B. t. u. per circumferential square foot of tubing. In addition about 6,000 B. t. u. per circumferential square foot of tubing .are absorbed by convection in the radiant bank and the convection bank receives an average of about 5,000 B. t. u. per circumferential square foot of tubing. With about 70 'percent of the total tube surface located in the radiant section ofthe furnace and about 30 percent in the con-l vection section, the average rate of heat input for the total fluid conduit is about 11,500 B. t. u. per hour, percircumferential square foot. f

In the second case, due to the application of direct radiant heat to opposite sides of each tube of the fluid conduit, about 66 percent of the 30,000 B. t. u.available, per square foot of projected tube surface, is absorbed on each half of the tube, giving a total of approximately 39,600 B. t. u.,

per. projected square foot of tube surface, as compared with 26,400 Bl t. u. in 'the first case or 12,600 B. t. u. per circumferential square foot in the second case as compared with 8,300, in the first. Assuming that about 30 percent of the total heat input in the second ca se is by convection, in order to make it comparable to the ilrst case, an additional 5,400 B. t. u., or thereabouts, per square foot of circumferential `tube surface is absorbed by convection. This gives a total average heat input of approximately 18,000 B. t. u.

per hour, per circumferential square foot of tub,

ing in the second case as compared with about 11,500, asv above shown in the first case, which is an increase of approximately 52 percent in favor of the improved method of heating of the present invention.

With firing conditions such that a greater proportion of radiant to convection heating is employed, a still greater percentage increase in the rate of heat input may be accomplished by use of the features .of the present invention.

I claim as my invention:

1. In a process for heating fluid in a plurality of banks of fluid conduits comprising connected elongated passageways vertically super-imposed in a heating zcne and equi-spacedfrom the adjacent side walls of the heating zone, the improvement which comprises subjecting the exterior portions of said side walls to heat of sulcient intensity whereby the opposite surfaces thereof radiate heat simultaneously to opposite sides of each passageway, causing hot products of combustion to pass through openings in said walls and bringing same' into contact with opposite sides of each passageway.

2. A process such as is claimed in claim 1, wherein the radiant heat is generated by direct impingement of the flame on the outside of said walls and the gases 'of combustion generated by said flame constitute the products of combustion passing through said openings.

i 3. A method for heating fluid which comprises passing the fluid in a restricted stream througha plurality of parallel heating tubes disposed in a common plane` between a pair of heat radiant Walls parallel to the plane of the tubes, maintaining said walls at heat radiating temperature by combustion of fuel as free flame on the sidesy -sid the plane of the tubes and adjacent each of the walls, the ame being directed angularly away from the tubes, thereby generating combustion gases, and heating the opposite sides of the tubes by radiation from the walls, by 'radiation from the flames and by convection from the'combustion gases.

5. A method for heating fluid which comprises passing the fluid ina restricted stream through a plurality of superimposed horizontal `heating tubes disposed between a pair of vertical heat radiant walls spaced from the tubes, maintaining said walls at heat radiating temperature byindependent combustion of fuel as free flame outside the plane of the tubes and adjacent each of the 6. The method as dened in claim 5 further walls, the ame being directed angularly away characterized in that the fuel is burned adjacent from the tubes, thereby generating combustion the sides of said walls Afacing the tubes.

gases, and heating the opposite sides of the tubes 7. The method as defined in claim 5 further by radiation from the wa11s,by radiation from the characterized in that the flames are impinged 5 flames and by convection from the combustion against said walls.

gases. JOSEPH G/ALTHER.

Images