US2374797A - Heating of fluids - Google Patents

Description

Patented May-1. A194s l uNrrrzD fsTATEs PATE-NT OFFICE HEATING oF mums e y Marlon W. Barnes, Chicago, Ill., assigninto niversal Oil Products Co mpany, Chicago, lll., a corporation of Delaware Application october' z3, r1942, serai No. '46a-ose z claims. (ci.' 12a-ase) Numerous industrial processes, including, for

example, operations conducted for effecting the catalytic or thermal conversion ofhydrocarbons,

ploying fuels of relatively lowA caloriiic value.

- Therefore, in the heater herein provided I employ flue gas recirculation and also lemploy direct.L

radiation from the flames and nascent hot combustion gases, but limit flue gasrecirculation to that section of the heater in which combustion 'gases which have given up a large portion 'of their radiant energy are directly contacted with the fluid conduits through which the material undergoing treatment is passed. In another section of the heater, through which no flue gases are reinvolve heating relatively large quantities ofgas or vapor to lnghtemperatures, such as, for example, of the order of 800 to 1200 F. In some instances it is necessary to re heaters employed for this class of service with fuels,'such as blastfurnace gas. producer gas, etc., which have a lo'w caloriilc value and give a relativelyA low flame-` burst temperature as. compared with the more preferable. fuels, such as natural gas, fuel oil, re-

Afinery gases and the like. y

It isA well known that the use of radiant heat energy from iiames and hot combustion 'gasesis practically mandatory to obtain quick heating of hydrocarbon oils, gases and vapors to high reac` tion temperatures due to' the ,high heat transferv ratesrequired. However, the high heat `transfer rates'obtainable by radiant heating with fuels of high caloric value cannot be-achieved with low value and lowl flame-burst'temperatura Conse- 'l quently, the best types of heaters heretofore commonly employed by the renning industry in thermal and catalytic processes, which were designed to operate oni'uels of high caloric value to give -high radiant heat liberation and empldy arelatively high ratio of radiant heating surface to conthe'present problems above outlined.

It is the primary object of the present invenvection surface, are not so successful as applied to cycled, I provide fluid conduits dispOsed outside the direct path ofA travel of the flames and freshly generated hot combustion gases and transmit radiant, heat directly to these conduits from said flames andv hot combustion`gases and from refractory surfaces over which the flames andhot combustion gasesare 'passedbefore being commingled with the recycled flue gas. Thuspthe radiant and convection heating sections are main tained separate and rates of heat transmission closely approaching the highest obtainable with the parti':ular` type of fuel and*l type lof heating employed, are obtained in each of these sections. The features and advantages of the invention will be more apparent with reference to the accompanying diagrammatic drawing which is .an

'elevational view,vshown principally in section, of

Y one specic form of the improved heater provide@ i v by the invention. grade lor diluted fuels due to. their low caloriilc general typ now widely used in the oil refining tion to provide an improved form o'f heater and method of heating which pbvia the dimculties above mentioned,l permitting the use'of relatively low grade fuels'and providing high rates of heat .transfer from the llames and .freshly generated combustion gases which' closely approach the maximum rates obtainable with theparticular fuelempioyed. l, J

It is well known that fairly'v high heat transfer with nue gas recirculation. 'Howeverfthe rates thus obtainable are not as high as those which canbe achieved by direct radiation from flames lndustry and known as an equinux heater. This typeof heater, without the improvements herein provided, is disclosed in U. S.'Patent 2,029,293 of J. G; Alther, Patent 2,212,526 of L. A. Mekler and my c'o-pending application Serial No. 364,832 and numerous other patents and pending applications.

'I'he figure of the drawing shows a vertical section of the heater.

. Referring to the drawing, the structure here illustrated isa single cell equinux heater comprising substantially vertical refractory side walls l and 2.

refractoryend walls, one of which lis designated at #,andarefractory roof l.

The upper section of the heater comprises combustion and radiant heating zones 5 and between which is disposed equinux' tube bank 1 comprising, in the particular case illustrated,` two so." rates can be accomplished by convective heating substantially parallel vrows of horizontally disposed tubes 8, although a bank containing a single row oftubes or more .than two rows may be substituted, when desired. l

g 'Ine lower section of the heater comprises a and -nascent hot combustion gases even when emuuid heating zone 9 containing a tube bank Il' which comprises, in this particular instance, a plurality of superimposed horizontal rows of horizontally disposed tubes I I.

The heater is red through. rows of burner ports I2 disposed in the roof 4 adjacent the refractory side walls I and 2. by means of burners I3 to which fuel is supplied through lines I4 and valves I5. 'Ihe burners project flames and nascent hot combustion gases downwardly over the surface of the refractory walls'l and 2v facing the tubes of bank 1. The surfaces of walls I and 2 are heated to a highly radiant condition by the flames and nascent hot combustion gases passing thereover and heat is transmitted from the walls and from said names and hot combustion gases .directly to opposite sides of the tubes of bank 1 through which the fluid undergoing heating is passed in any desired manner. vIt will be noted from the arrows in combustion zones 5 and `6, which indicate the general path of travel of the flames and hot combustion gases therethrough, that tube bank 1lis disposed outside the direct path of flow of the flames and nascent hot combustion gases and is heated predominantly by radiation. A

The combustion gases which have given up all or a major portion of their radiant heat to the .tubes of ,bank 1 pass from combustion zones 5 and 6 -through fluid heating zone 9 wherein they wash the tubes of bank I0 and supply uid heat thereto and to the fluid undergoing treatment which is passed through these tubes.' 'Ihe combustion gases are directed from zone 9 through the combustion gas tunnel or flue I6 leading to a suitable stack, not shown.

In accordance with the provisions of the i'nvention, regulated quantities ofthe gases discharged fromiluid heating zone 9 are directed from flue I6 through; duct I1 to a suitable flue 'gas reclrculating fan or blower I8, wherefrom they are supplied through duct I9 and branch ducts I9' and I9" to the respective chambers 2II and 2I. Chambers 20 and 2l are disposed adjacent the lower portions of the respective walls I and 2 and communicate through suitable conduits 22 with a zone 33 provided within the heater between the lower extremity of tube bank 1 and the upper extremity of tube bank I0. Recirculated vflue gases are directedfrom chambers 'and 2l through conduits 22 into zone 33 wherein they commngle with the combustion gases passing from combustion zones 5 and 6 to fluid heating zone 9, thus setting up a cycle of combustion gasesfthe cycle excluding combustion and radiant heating zones 5 and 6. Thus, dilution ofA the freshly generated hot combustion gases in zones 5 and 6 is avoided, whereby the rate of radiant heat transmission to the tubes of bank 1 is kept at a value closely approaching the maximum' obtainable with the particular type of fuel employed, While a highly increased rate of heating by convection is obtained in bank IIJ by ue.

gas recirculation through zone 9. f

'The invention also contemplates, .when desired, 4preheating the air utilized to support combustion of the 'fuel in zones 6 and 6. -.Although this is not a limitingfeature of the `invention'it is pref- .erably employed when fuel yof' relatively low' calorificvalue is utilized, in order to increase the ame temperature in zones 6 and 6 and increase the radiant heat transmission to the tubes of bank 1. Preheating of the air is accomplished.

in the case illustrated, by'admitting itto zones; y. 23 and 24 through the respectiveconduitsl 25 and v 26 controlled, respectively, by dampers 21 and 28. Zones 23 and 24 are formed', in the case illustrated, as are chambers 20 and 2 I, between the side walls I and 2 and an outer jacket 29 formed of sheet metal or other suitable sheet material.

and preferably lined with suitable insulating material 30. The Jacket 29 extends over the burner ports I2 to enclose burners I3 in zones 3I and 32 and air admitted to zones 23 and 24, as previously Any other convenientmethod and means ofl preheating the air employed for combustion of the fuel in zones 5 and 6 may'be employed within the -scope of the invention in Vconjunction with or in place of the method and means illustrated. For

example, I may employ the method and means ili lustrated in the aforementioned Alther Patent 2,029,293, utilizing any suitable form of air preheater in the combustion gas passageway leading to the stack for recovering heat from the stack gases by indirect contact between the latter and air, the resulting preheated air being supplied through ducts 25 and 26, as previously described, to the combustion zones ordirectly to the chambers 3| and 32 within which the burners I3 are disposed. Air may be drawn through the preheater and/or through zones 23 and 24 by the inspirator action of the burners or it may be supplied by means .of a suitable fan or blower, not illustrated. I claim as my invention 1. A heater for fluids comprising a furnace having a l radiant heating section and a convection heating section in vertical alignment, said sections being spaced from each other to provide a mixing zone therebetween, a vertical bank of heating tubes disposed within said radiant section and dividing the latter into a pair of combustion zones, means for passing combustion products. vertically through each of the combustion zones and from both of the last-named zones into said mixing zone and thence through said convection section, heating-tubes in the convection section disposed in the path `of travel of the combustion products therethrough, a combustion gas discharge flue communicating with the convection section, and means for introducing to said mixing zone a regulated portion of the combustion gases discharging through said flue. f

2. A heater for uids comprisingfav furnace having a radiant heating section and a convection heating section in' vertical alignment, said sections being spaced from each other to provide mixing zone therebetween, aA` vertical bank of heating tubes disposed within' said radiant section and dividing. the latter into a pair of combustion' zones, means for passing combustion products vertically through eachof the combus- 'tion zones and from both-,of the last-named'zones into said mixing zone and thence through said convection section",` heating tubes in the convection section disposed in the path'of travel of the combustion, products therethrough, -a combustion gas. discharge flue communicating with the convection section, and' means for supplying combustion gases from said flue to said mixing zone on each side of fthe vertical plane of said tube MARION BARNES.

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