US2274256A - Fluid heater - Google Patents

Description

Feb.

` FLUID HEATER Filed Aug. 24, 1959 H. PRAEGER 2,274,256

3 Sheets-Sheet 2 ATTORNEY.

Feb. 24, 1942. F. H. PRAEER 2,274,256

FLUID HEATER Filed Aug. 24, '1959 s sheetsfsnee't s Ffa. /0 g BY uw 2" U ATTORNEY.

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In carrying out my invention in one form.

along the Peteeted Feb. 24, 1942l Frank H. Praeger, Cynwyd, Pa., assignor to'Alcorn t Combustion Company, Philadelphia., Pa., a corporation ot Delaware Application August 24, 1939, Serial No. 292,313.

` 8 Claims.. My'mventien relates te fluid heaters of the 'tubular type, more particularly to methods of and apparatus for elevating the temperature of a fluid, and has for an object the provision of a heater of exceptionally low cost and which isentirely satisfactory for its intended, purposes.

Fig. 4 is a vertical section taken on the section line 4 of Fig. lor Fig. 2;

Fig. 5 is a vertical section of a modified form of a heater embodying my invention, the position at which the section is' taken corresponding with Fig. 3;

In thepetroleum industry there is frequently' need for a heater capable of transferring one to ten'million B. t. u."s per hour to a uid and in cost so low that the economies effected by the use of the heater are not'diminished or lost as a.

example, within this classification are the heatresult of high ill-st cost and maintenance. For i ers used in pumping lines to vlower the pumping 'l cost by reduction -in the viscosity of the oil or petroleum.

Another type of application is where steam is to be heated to a .temperature ofbetween 800 F. and 1000 F., the quantity of steam needed being much less than would warrant the installation of expensive boiler and superheater equipment.

It is an object of my invention to provide a fluid heater meeting the requirements of low cost, but in which the distribution of heat over the transfer rates thereinwell within permissible thereof, I provide aplurality of muilles, or elon'- gated tubular combustion chambers which extend centrally of adjacent circular or regular geometrical arrays of tubes. Within the muflles the combustion of fuel. is initiated and to large extent completed, the muilles themselves being heated to incandescence or to a temperature for radiation at high rate from the walls thereof of heat to the tubes. The still burning gases issuing from the muilles, which are not at an excessively high temperature, pass generally axially of, but in increasingly 'greater convective the heating surface is relatively uniform, and

Fig. 6 is a vertical section of the modified form of my invention, the position at which' the section is takencorresponding with Fig. 4;

Fig. 7 illustrates a modified tube arrangement for adifferent iiow of fluid through a heater;

Fig-s.` 8 to 10 show heat-density curves illustrative of the operation of my invention; and

Fig. 11 illustrates a further modified arrange# ment of heat absorbing tubes within a heater embodying my invention.

Referring to the drawings, I have shown my invention in on`e form as applied to a petroleum heater comprising walls III formed of rebrick or equivalent refractory and encased in and supported by a structural steel frame comprising a base member II, side wall members I2 and.) I3, and a roof member I I, the upper and lower members II and Il overlying the members I2 and I3, Figs. 3 and 4, for the reception of anglesupports I5 at each of the four corners thereof'. 'I'he angle supports I5 may be riveted, welded or bolted to the frame members.'

The fluid-conducting heat-absorbing structure comprises a plurality of tubes I6 disposed within the heater and supported by tube. sheets II, I8 and I9. The tubes may be connected 'for any desired sequence oi' ow therethrough, or in as many parallel groups asmay be required from consideration -of pressure dropvtherethrough'. Referring particularly to Fig. 3. it will be observed lthat the tubes I6 are connected for the flow of four streams of fluid, which enter respectively at the ring end of the heater by 'way of inlet lines 2|, 22, 23, and 2l. As viewed in .y Fig. 3, the stream 2I passes through the leftcontact` with, the heat-asborbing tubes, and

thence to a stack. l

My invention, together with other objects and advantages thereof, will be more fully understood upon reference to the following description and the accompanying drawings forming a part of the specification and of'which:

Fig. (il is a vertical section taken through the center of a heater embodyingfmy invention, and

section line I of Fig. 3 or Fig. 4;

Fig. 2 is a horizontal section taken on the sectiorl1ine2ofFig.3or1lg.4;

l'ig. 3 is a. vertical section taken on the section hand row of tubes; the stream 24 through the right-hand row; and the streams 22 and 23 re,

- spectively through the intermediate vertieelrew of tubes I8; each of the streams, Fig. 4, leaving the heater at the stack end thereof by way of exit lines 25. 20.21 and 28.

The tubes of the several vertical rows are disposed symmetrically about ii'n'gmuilles or elongated tubular combustionjchambers 30-39, the tubes about each combustion chamber" being shown as located at the apices ofa hexagon. and the plurality of hexagone being '-contiguous. While the hexagonal arrangement may be preferred, in accord with myf'iiiventionl the tubes may be disposed in other geometrical relations as, for example, an octagon, or there may be some departure from a purely symmetricaly -or regular geometrical arrangement and a polygonal arrangement used.

Each of muflles 30-39 is constructed of a material which may be heated to incandescence, or to a temperature at which radiant heat may be effectively transmitted to the heat-absorbing surfaces. For example, the muflies may be constructed of silicon carbide, though I prefer a refractory metal having a high heat conductivity, such, for example, as one of the high heatresistant alloys now known to the art and of which may be mentioned as exemplary an alloy comprising nickel 12%, chromium 30%, carbon .35%, and iron. With an alloy of this character the wall of each mufile may be extremely thin, as fcr example, five-sixteenths of an inch, or less, with the result that a very substantial proportion of the total heat generated may be transferred by direct radiation to the fluid-conducting, heat-absorbing tubes.

In operation fuel. oil, or gas, or both, is by a burner introduced into .the inlet end of each muille in mixture with an adequate vamount of air to insure rapid combustion thereof within each muiiie. All burners may be of the same construction, and as diagrammatically illustrated in Fig. 1, the burners 4I-44 respectively under the control of valves 45-48 project fuel into the mutiles 30, 32, 36, and 39. For the introduction of air each muiile may be provided with an insert forming one or more constrictions. For the muftles 30, 32, 36 and 39 th'e inserts 5I-54 have been illustrated. In lieu of the Venturi sections providedl by the inserts .6L-54, air for combustion may be mixed with the fuel in other ways known to the art.

WhileV the combustion of fuel may be substantially complete within the muiiles, nevertheless the gases, which may still be burning, are in any event highly radiant, in terms of the amount of radiant heat which may be transmitted to the tubes. From the ends of the muiiles, the gases are projected horizontally, and with substantial velocity, so that impingement upon the tubes I6 is minimized. To prevent escape of radiant heat from the fluid-conducting, heat-absorbing zones, and to insure flow of the gases in intimate heatexchange with a part of the tubes, heat insulating or refractory material which may be in the form of targets, may be secured to the tube sheet I1 to form targets for the gases from the muiiies. The targets also protect those portions of the tube sheet directly opposite the mutlies. As shown in Fig. 1 refractory cones 55, 56, 51 and 59 are opposite the muies 30, 32, 36, and 39, while in Fig.

4 there is shown in cross section a cone opposite N each of muiiles 30-39.

While the tube sheets I8 and I9 may be relatively imperforate except for the openings for the reception of the heat-absorbing tubes, and the mufiles, the tube sheet I1 is provided with openings IIa, Fig. 4, for the exit of the combustion gases to a fluo or duct 60, leading to a stack not shown. The openings I'Ia extend on opposite sides of each tube and upwardly thereabove, the

net cross-sectional area of each opening available for the passage of gases therethrough, being large enough so that themaximum quantity of gases which may be generated as a result of the combustion of fuel in the muiiies may readily pass to 1 the flue 60. As an example and not by way of limitation. for a one million B. t. u. per hour heater, Figs. 5 and 6, with 31/2 inch outside diameter tubes, a net area for each opening of about eleven square inches would be adequate for a heater having some 18 horizontally disposed tubes.

In the operation of my invention, the fluid to be heated, oil in liquid or vapor phase, water or steam, or other fluid, may be circulatedV through the tubes I6, and fuel supplied to the burnerses, also radiate heat in large quantity and at high rate to the tubes directly exposed thereto.

Those portions of the tubes to the right of the discharge ends of the muilies, as viewed in the drawings, also receive heat by convection, and in the region approaching the tube sheet I1 a substantial quantity of heat is transmitted by convection. Danger of overheating the tubes beyond the discharge ends ofthe muiiles is minimized by providing munies of such length that the temperature of the gases issuing from the muiiles, and the completeness of the combustion within the muilles is sufcient to prevent overheating, or excessive rate of transfer thereto. For many designs of heaters, the muiiies should be about one-,fourth the length of the tubes as between tube sheets I1 and I9, though they may be longer, and possibly somewhat shorter.

With respect to the modification of my invention shown in Figs. 1 to 4, I provide especially efficient heat-absorbing surface, since each of the muiiles 30-39 is surrounded by tubular heat-absorbing surface, which receives radiant heat. Moreover, all tubes in all modifications other than the outermost tubes of the assembly, receive heat directly by radiation from two or more muilies; 4and a large proportion of the tubes of a group or assembly receive radiant heat directly from three muiiies. The` result of transmitting heat by radiation from inutiles circumferentially spaced with respect to a particular tube is to supply heat uniformly and at high rate throughout the circumferential area of that tube. This eliminates uneven heating of tubes, and the effective heatabsorption area of the tube is greatly increased; also, mechanical and thermal strains are minimized by the uniform application of heat throughout the entire circumferential surface of eachA tube, and there is a correspondingly greater absorption of heat. quantitatively considered. As a result of the foregoing, for a heater of given capacity, the size and cost is greatly-reduced, and the heating conditions obtaining are satisfactory.

Itis to be understood that the number of mufes and the number of tubes are to be selected with reference to the capacity of the heater, which may be of any desired size, depending upon the number of muffle and tube assemblies utilized, and for any size of heater, the heat-load is carried by a plurality of burners, muilles, and tube-assemblies, the burning of fuel from a plurality of burners contributing to uniformity of heat application.

Since the tubes o f each group or assembly, for example the hexagonal group about :nume 33 are equidistant from'a center line through the unobstructed space extending longitudinally of the tubes, the heat application is equalized as between adjacent tubes. For the outermost tubes within 2,274,256 3 the fire chamber, the heat-density curves are.

represented by curve 82 of Fig. 8 plotted from the circumference of a typical tube, 81, and represents the heat application throughout the radiant section, as between the stube sheets I8 and I9. As shown the' 'application of heat is greatest over that portionof tube 8I which sees the muflie 33.

For the next adjacent row of tubes, those receiving heat from two radiant sources of munies, the heat-density curves are represented in Fig. 9 by the curve 83 plotted from the circumference vof typical tube 84 of, and common to, the

hexagonal groups around muilles 34 and 31. The heat application is relatively uniform over more than half the circumferential surface of tube 84, and is distributed over the surface in view of muffles 34 and 31.

For the remaining tubes still nearer the center of the re -chamber than the first and second outer rows, such for example as typical tube 85, radiant heat is received from sources (the mufiies and gases) displaced from each other by'approximately 120, so that throughout the entire circumferential area radiant heat is applied at uniformly high rate. The heat density curve 86 of Fig. 10 represents the heat application to these inner tubes, and is plotted from the circumference of typical tube 85. Stated in another way, when all the tubes of a group valso comprise tubes of other groups maximum uniformity of heatjapplication issecured. Illustrative of this fact are the groups about muilies 32 and 36 of Fig. 3, all tubes of -which form one or more tubes of othergroups such as the groups about muies 38, 3|, 33, 34, 35, 31, 38, and 39. In all casesthe maximum rate o'f application of heat per unit area remains'the same as shown by equality of the greatest ordinates in Figs. 8-10. The heat input, however, is greater for the tubes heated from more than one muie.

Referring to Figs. and 6, for a relatively small heater, for example, of about one million B. t. u.s heat input per hour, only a single row of muiiles 1I, 12, 13, and 14 need be provided.

Each muffle is provided with its own burner, valve, and Venturi section; as described above.

In this modification of my invention I have also illustrated the tubes 16 ,disposed in hexagonal grouping around the respective muilles., 1I-14. with inlets 11 and 18 and with outlets 19 and 80.

In this modification of my invention all but the' outer rows of tubes receive heat from at least two muflies-spaced' circumferentially of each particular tube. Inaccord with this modification of my invention, no diiculty was encountered in superheating steam to upwardly of 1000 F.

For heaters of capacity intermediate the previously described embodiments, two heaters of the type shown in Figs. 5 and 6 may be assembled so. that the adjacent tubes of the two heaters form hexagonal groups within which may be disposed muilles 88, 89 and 90. The hexagonal groups about muiiies 1I14 b ear the same ref-v erence numerals as in Figs. 5 and 6, and the duplicate assemblies or groups around mufes 1 I and 14 the saine numbers primed to indicate a construction similar to Figs. 5 and 6. In accord with-the embodiment of my invention as shown in Fig. '11, the heat input is disproportionately.

' higher thantwice the unit heater of Figs. 5 and 6. Without increasing' either the maximum tube result is possible by the ldouble duty imposed on the tubes forming the hexagonal groups around munies 88-90 andthe gases issuing therefrom. The maximum tube-wall temperature is not increased since the heat developed by muilles 88-90 is not applied to the heat absorption areas exposed to the -heat generated from mutlles 1I-14 and 1I14, but to heat absorption surfaces shielded therefrom. In consequence the average a tube of a hexagonal. group95 comprising the radiant section. A lring muiiie omitted for sake of clarity is concentric with a central axis of the hexagonal groups and extends three to'six feet within the radiant section 95, or about onefourth or more of the length of radiant and convection sections 83 and 95. Radiant heat is applied to the tubes of section 95 substantially solely by radiation and to the tubes of section 93 by convection'and radiation. The fluid outlet is shown at 96.

If desired, the arrangement of Fig. 7 may be applied to the preceding modifications with slightly modified sequence of flow as required by cross overs between radiant and convection sections, only one of the hexagonal groupings beingY shown in Fig. 7. y In all modification, I have shown simple return bends, which may be welded to the ends of the tubes, but any suitable type of returnnbend may be utilized. v

While I have shown particular embodiments of my invention, it will be understood that I do .not limit myself thereto, since many modifications may be made and I thereforel contemplate by the appended claims to cover any such modi'- cations as fall withinthe spirit and scope of my invention. y

each of said muilies, certain of the tubes being disposed in said circumferential relation with respect to at least two of said muilles for receivwall temperature, or the number .of tubes, the

two units constructed as shown, with muiiies 88-90,'wil1 develop at least 2.75-times the heating capacity of one of the heating umts. This ing concurrently therefrom radiant heat on different heat-absorption areas thereof, means located within the region occupied by saidmutiies for supporting said tubes and' saidmuiiies, a tube-sheet for supporting said tubes in spaced relation from the discharge ends of said munies, said last-named tube-sheet having openings around theN sides and above each of said tubes for the passage therethrough of combustion gases in convection heating relation with said tubes,

and means for circulating through said tubes fluid to be heated.

2. A fluid heater comprising a plurality of groups of fluid-conducting, heat-absorbing tubes, each group having a plurality of tubes symmetrically disposed around a center line for that group which is parallel to the axes of the tubes, and a spaced circumferential areas of a plurality of said tubes to equalize and maintain a high heat input throughout the circumferential area thereof, tube supports spaced lengthwise of said muffies for the support of the muilies and of the tubes, and at least another tube support disposed adjacent the ends of the tubes remote from s aid muflies, said last-named tube support having a' plurality of openings for the .exit of gases therethrough inintimate convection heat exchange with said tubes, and means for burning fuel within each of said muiiles for the transfer by radiation from each of said muiiies of a substantial portion of the generated heat.

3. A iiuid heater comprising an outer and an inner row .of tubes, said tubes of both rows being disposed in groups with thetubes of each group generally symmetrical about and equidistant from a central line for that group, a muiiie disposed co-axially of each `of said central lines for radiating heat to said tubes, said tubes of said inner row receiving heat by direct radiation from at least two of said muflies, a convection bank comprising tubes disposed in groups of the same general configuration as said first-mentioned groups of tubes and disposed individually to receive combustion gases from one of said mufiles for convective heating of iiuid therein, and

means connecting all of said tubes for passage of fluid therethrough.

4. A fluid heater comprising an outer and an inner row of ltubes, -said tubes ,of both rows being disposed in groups .generally symmetrical about and equidistant from a line central of each group, a muiiie disposed co-axially of each central line for radiating heat to saidtubes, said tubes of said inner row receiving heat by direct radiation from at least two of said muiiies, a convection bank with the tubes disposed in groups of the same general conguration as said first mentioned groups and each group of convection tubes receiving convection gases directly from one of said muifies for convection heating of iiuid therein, and means connecting al1 of said tubes for passage of fluid first through said convectively heated tubes and then through said radiantly heated tubes.

5. vA fluid heater comprising a re chamber,

an outer and a plurality of linner rows/ of tubes within said chamber, said tubes of said rows being disposed in -groups with the axes of the tubes :of each group parallel and generally symmetrical about and equidistant from a central line for that group, and a tubular muiiie disposed co-axially of each of said central lines for radiating heat to the tubes of each group, some of the tubes of one group comprising tubes of another group whereby tubes 'of said outer row receive overlapping each other, a convection bank with the tubes thereof disposed in groups of the same configuration as said mst-mentioned groups and y each group of convection tubes disposed individually-to receive combustion gases from one of said muies for convection heating of the fluid, and means connecting all of said tubesy for passageof fluid therethrough. o

6. A fluid heater comprising a fire chamber, an outer and a plurality of inner rows of tubes within said`chamber, said tubes of said rows being disposed in groups with the axes of the tubes of each group parallelI and generally symmetrical about and equidistant from a. central line for .that group, and a tubular mufile disposed co-axially of each of said central lines for radiatingl heat to the tubes of each group, some of the tubes of one group comprising tubes of another group whereby tubes of said outer row receive heat largely from mufiles individual thereto, and tubes of the next adjacent row receive heat from two mufes individual thereto, and the remaining tubes receive radiant heat from'at least three 'of said muftles. each of the tubes 'receiving radiant heat from more than one munie receiving it on heat absorption areas circumferentially spaced one from the other and not to substantial degree overlapping each other, a convection bank with the tubes `disposed in groups of the same general configuration as said first-mentioned groups and each group of convection tubes'disposed to receive gases from one ofy said muffles for convection heating of fluid therein, and means connecting all of said tubes for passage of iiuid rst through said convectively heated tubes'and then through said radiantly heated tubes.

7. A uid heater comprising a pluralityv of elongated tubular muies formed'of a heat radiating material, a plurality of tubes disposed in spaced relation with, and circumferentially of. each of said muiiies, certain of the tubes being disposed in said circumferential relation with-respect to at least two of said muilles for receiving concurrently therefrom radiant heat on dif- `ferent heat-absorption areas thereof, means 1ovcated Within the region occupied by said muiiies for supporting said tubes and said muiiles, a tubesheet for supporting said tubes in spaced relation from the discharge ends of said muiiles, said lastheat largely from muiiies individual thereto, and' tubes of the next adjacent row receive heat from two muilles individual thereto, and the remaining tubes receive radiant heat from at least three of said muilles, each of the tubes receiving radiant heat from more than one muiiie receiving it on heat absorption areas circumferentially spaced one from the other and not to substantial degree named tube-'sheet having openings around the sides and above each of said tubes for the passage therethrough of 'combustion gases in convection heating relation with said tubes, means for circulating through said tubes fluid to be heated, and means for* withdrawing gases from the heater on the side of said tube-sheet remote fromsaid muiiies. A

8. A iiuid heater comprising a plurality of tubes disposed parallel. to each other and with their centers forming apices of adjoining hexagons, .mules for burning fuel in streams concentrically of, and individual to, each hexagonal group of tubes, spaced tube sheets for supporting said tubes in said hexagonal relationship. the tube sheet remotely located from said muflies having openings around the sides and top of the tubes extending therethrough for the passage of combustion gases in convective-heating relation with said tubes, and means for withdrawing the gases from the heater without return thereof to the region in which said munies are located.

-- ERANK H. PRAEGER.

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