US3181508A - Industrial furnaces - Google Patents

Description

y 1965 c. HENNIPMAN 3,181,508

INDUSTRIAL FURNACES Filed June 12, 1962 2 Sheets-Sheet 1 FIG. I

KNVENTOR:

CORNELIS HENN'PMAN HIS ATTORNEY May 4, 1965 Filed June 12 1962 C. HENN l PMAN INDUSTRIAL FURNACES 2 Sheets-Sheet 2 FIG. 4

INVENTOR:

CORNEUS HENNIPMAN A/ D @miz HIS ATTORNEY United States Patent 3,181,508 INDUSTRIAL FURNACES Cornelia Hennipman, The Hague, Netherlands, assignor to Shell Oil Company, New York, N.Y., a corporation of Delaware Filed June 12, 1962, Ser. No. 261,925 Claims priority, application Netherlands, June 26, 1961, 266,352 9 Claims. (Cl. 122-356} The invention relates to an industrial furnace for heating liquid or gaseous media in heating tubes, which tubes are arranged in rows in the heating space and issue in headers or similar structures present outside the heating space. The invention relates in particular to industrial furnaces of the type used in the processing of petroleum products, for example, for keeping intermediate or final products at the required temperature or heating or reheating intermediate products to the conversion temperature.

It appears that in industrial furnaces, and in particular in furnaces of the vertical type, special attention should be paid to securing and supporting the heating tubes. These tubes are either supported underneath and attached at the upper end to a guide element, or suspended from the top in the heating space. Since it is customary to arrange that the ends of the tubes, which are generally joined together to form one or more series of tubes or coils of tubes, issue in headers or similar structures present outside the actual heating space, the passage of the tube ends through the wall of the heating space or of a fastening element raises a problem for which, as far as is known, no completely satisfactory solution has yet been found. In the first place, sealing dii'nculties are particularly liable to arise in running the tube ends through the wall of the heating space since provisions should simultaneously be made to protect the material from thermal stresses and deformations, e.g. expansion of the tube material and the associated sealing plates. Secondly, it was hitherto difficult, if not impossible, to provide a supporting structure of sufiicient strength in the case of tubes or pipe series suspended from the upper end without recourse to heavy sectional steel forming part of the supporting structure of the whole furnace to which the central section of the roof was also attached.

The object of the invention is to provide a construction in which the above-described disadvantages can be completely avoided and which is moreover inexpensive.

This is attained according to the invention in an industrial furnace of the type referred to in the preamble which is characterized in that the tubes are secured in hollow, closed elements entirely separated from the Wall of the hearth space and in consequence externally cooled, which elements communicate with the hearth space by means of a plurality of gas-tight ducts for running through the tube ends or elements securing the tubes.

In furnaces of the vertical type, the tubes may equally wellbe suspended from an upper element in the upper part of the furnace, either directly or indirectly by means of some securing element, or supported in a lower element, viz. under the heating space. The supporting element or suspension element fulfills the function of bearing element. With horizontal tubes the construction according to the invention is also very effective in sealing ofl the heating space from the atmosphere.

The present construction has the following advantages: in the first place a space is formed around the element by its total separation from the wall of the heating space, which space may be used as a cooling channel suitable for air-cooling.

In this case the temperature of the elements is equal or nearly equal to that of the wall of the heating space, and this entirely avoids difiiculties arising from expan- 3,1815% latented May 4, 1965 sion. Secondly, leakage of evaporating gases, air leakage and the like are completely avoided owing to the fact that the elements and the ducts which establish communication with the hearth space are completely sealed. Thirdly, with vertical furnaces a separate bearing construction is unnecessary since the elements can be connected in a simple manner to the furnace structure. Moreover, the draining away of rainwater is hereby more easily eifected.

This last advantage is especially desirable, since it results in a considerable economy in construction costs.

The ducts preferably consist of pipe lengths which are rigidly connected to the hearth wall and the (bearing) elements, which lengths are of such a diameter that the tube ends can be passed through them with clearance.

According to the invention, the tubes issuing in a (bearing) element may communicate with headers, returnheaders or bends, which are entirely accommodated within the hollow space of the (bearing) element.

In vertical furnaces, the lowest elements are preferably arranged below the fuel and combustion air supply lines of the combustion device(s) fitted in the bottom of the heating space.

in a construction wherein vertically arranged tubes are suspended at the top from a bearing element, for instance, in a tube arrangement in which the tubes communicate in pairs by means of a return-header, the suspension may be effected by means of annular collar pieces externally welded near the ends of the tube ends, which collars rest on the upper edge of the pipe lengths constituting the ducts and at the same time prevent communication with the hearth space.

if the heating tubes are connected in series to coils of tubes by means of bends within the heating space the ducts for the passage of the tube ends or securing elements are oblong, so that a coil of tubes can be removed in its entirety from the heating space via the relative ducts when the (bearing) element is open. In this case the tube ends constituting the ends of a vertically arranged coil of tubes may be passed through the duct, they may be provided near the end with a Welded-on annular collar by which they rest on the upper edge of the duct wall and are thereby supported, and securing elements may be welded to one or more bends, in the hearth space, which elements are also passed through the duct, and provided at the upper end with openings such that the coil of tubes is additionally supported by bearing elements passed through each of these openings, which elements at the same time rest on the edges of the duct wall. A suitable insulation may provide the seal.

The invention will now be further illustrated with reference to the drawing.

FIG. 1 is a diagram of a partial vertical cross-section of a furnace to which the invention is applied; FIGS. 2 and 3 show details, likewise in vertical cross-section but on a larger scale, of another part of the design of FIG. 1, and FIG. 4 also shows a detail but in this case of a different fastening of the tubes according to the invention.

Referring to FIG. 1, the bottom part of a vertical-type industrial furnace, such as is used in refineries in the processing of petroleum product, is shown, partly in vertical cross-section and partly in elevation.

Referring to the FIG. 1 the foundation is designated by l, and supports the various structural elements constituting the furnace wall. These structural elements are designated by 2, 3, 4 and 5 and are of substantially the same construction. These are separately prefabricated structural elements consisting of a closed profiled metal peripheral wall of rectangular cross-section lined on the inside with refractory cement, which elements are stacked on each other and inter-connected by means of flanges. The bottom or end wall '6 of the heating spaces inside e3 these structural elements is secured in the lowest element and the bottom is provided with arches 7 containing the is no need to remove any air passage when the tubes 12v and 13 are repaired or cleaned. The same advantage applies to the fuel lines and, if desired, the steam lines connected to the combustion devices.

In the present example the furnace is constructedthat four heating spaces are formed inside the side walls of the furnace. One of these is designated by 14 in the FIG. 1. These heating spaces are laterallybounded by rows of vertical tubes. The tube designated in the drawing by 12 is one of a row of tubes juxtaposed along the wall; in the drawing these tubes are thus in front of or behind the tube 12 at'a certain distance from each other and from the wall. The rear wall of the space 14 is also provided with such a row of tubes disposed against the wall, but for the sake of clearness this row is not shown. The tube 13 is one of a row disposed in the center of the furnace chamber, and this is next toanother row of tubes, the individual tubes being arranged back-to-back. This other row is located inside the right-hand part of the furnace shown in the drawing in elevation. Such an arrangement of rows of tubes centrally in the furnace chamber erects a kind of imaginary wall, since the tubes shield each other from excessive heating originating from another adjacent heating space or section differing from the one to which these tubes themselves belong. Finally, the heating space is bounded by a fourth row of tubes, located in front of the plane of the drawing, which row is likewise disposed centrally in the furnace space and forms the fourth side of the rectangle which, in horizontal section, constitutes the heating space 14. Thislast row is also. disposed in a back-to-back arrangement with an adjacent row of tubes in the furnace space.

Thus four heating spaces or sections of equal dimensions are formed within the funrace space. The ends of the tubes'disposed against the side wall of the furnace space including the tube 13 are accommodated in the element 10. 'At the other end of the tube 12 and the other tubes in this row is the bearing element which is shown on a larger scale in FIG. 2.

The ends of the tube 13 and the other tubes in this row, together with the ends of the tubes in the adjacent back-to-back arrangement, are accommodated in the element 11 only half of which is shown in cross-section. The other end of thetubes in both these rows is accommodated in a bearing element shown on a larger scale in FIG. 3.

Referring to FIG. 2, the numeral designates the wall of the furnace space. This is the uppermost prefabricated element which completes the side wall of the furnace by a stacked arrangement of similar structural.

elements, shown in FIG. 1. This top element 26 supports a roof or end wall 21 which is centrally provided above each heating space 14 with a combustion gas exit conduit. The numeral 22 designates the side wall of such a conduit. A bearing element 23, in which the end of the tube 12 and the ends of the other tubes in that row are accommodated, is completely separated from the furnace. The heating space 14 communicates with a'closed space 29 by means 'of the channels present inside a pipe length 24, through each of which channels is passed with clearance a tube, including the tube 12. The tube issues in a return-header 25 in which a second tube also issues so that the medium to be heated enters the header from the one tube and is returned through the other tube. The tube 12 is provided near the end with a support element in the form of a flange-shaped collar 26, welded on the tube, with which collar the tube rests on the end of the pipe length 24. This provision also ensures a proper sealing of the furnace space from the atmosphere, even when a cover plate 28 of the bearing element23 is removed, for example, for inspection of the return-headers in the space 29.

During operation, when the bearing element 23 is normally closed, a complete sealing can obviously be guaranteed in all circumstances. It is even possible to connect a source of compressed air to the space 29 whereby the said space may be subjected to a certain degree of excess pressure relative to the furnace space. This may be important when the combustion gases, which generally still contain a fairly large amount of heat energy,

are used for further heat transfer after leaving the heating space 14 and the other corresponding heating zones.

It is, for example, possible to arrange behind the heating spaces, in which the heat is chiefly transferred by radiation, one or more spaces in which heat is transferred by convection, thus allowing a completely free choice of a medium to be heated therein in tubes or pipe bundles. I

The chief object, however, is to keep flue gas out of the space 29 and to prevent corrosion if, for one reason or another, there is still some leakage through the upper cover, bringing the temperature of the section of the wall below the dew-point of the flue gases.

A passage 27 is provided between the bearing element 23 and the furnace roof 21, 22 which acts as a cooling passage through which atmospheric air flows and ensures that the temperature of the bearing element is approximately the same as that of the furnace wall, thereby eliminating the problem of expansion. is is true that a small section of the pipe length 24 is also cooled, wh ch is actually undesirable in theory, but in practice the influence of this is quite negligible. In

fact only a very short section is cooled, and moreover V the heating tube is passed with clearance through the pipe length so that there is an insulating layer of hot gas around the tube which counteracts cooling of the heated medium inside the tube. It is, however, more important to avoid excessive cooling of fiue gases which would give use to the above-mentioned corrosion.

In the embodiment according to FIG. 3, a construc tion similar to that of FIG. 2 is shown, but in this case the construction relates to the accommodation of the rows of tubes which are centrally placed in the furnace space. A central part 30 of the roof, which may be integral with the roof structure 21 of FIG. 2, has an upright side wall 31 on the left which may also be integral with. the wall section 22. These parts may together form the cylindrical wall of an exit conduit for the combustion' gases from the heating space'14. An upright wall 32 forms a corresponding part of a passage for discharging the combustion gases from the adjacent heating space 1411. All the ends of the rows of tubes, which are centrally placed in the furnace space in a back-toback arrangement, are accommodated in the bearing element. The drawing shows the tube 13 with the adjacent tube 13a.

The construction also comprises pipe lengths 34 and 34a, return- headers 35 and 35a and collars 36 and 36a. welded on the tubes. A cooling passage 3'7 separates a bearing element 33 from a furnace wall 31), 31, 32.

The ends of the bearing element 33, like those of the bearing element 23 in FIG. 2, are supported in such a way that the elements are carried by the furnace Wall 20, thereby eliminating a separate framework.

Finally, FIG. 4 shows a construction in which the tubes are joined together to form coils of tubes inside a heating space.

Referring to the figure, the numeral 49 designates the uppermost structural element of the furnace wall. This supports a roof or end wall 4-1 with an upright part 42, which is the side wall of an exit conduit for the combustion gases from the heating space 43.

A row of tubes joined together to form a coil of pipes is disposed near the wall. The individual tubes are interconnected in pairs by bends. A closed bearing element 45 is, like the above-mentioned constructions, completely separated from the furnace wall 41 and communicates with a space 43 by means of a pipe length 46. A cover plate or support element 47 rests on the u per edge of a pipe length 46, which in this case is not given in cylindrical cross-section but is in fact oblong. The length is such that a complete pipe length may be removed from the space 2 3 through the slot thus formed.

A securing element 48 is welded to the top of the bend in between each pair of tubes, which element is pro vided with an opening or slot 5-9 through which may be passed a wedge or peg supported at both ends on the cover plate 47 and thus carrying the pipe. A space 59 between the pipe length 46 and the securing elements 48 is packed with insulation material surrounded by a metal jacket to facilitate its removal when the pipe series must be repaired or inspected.

The end of a coil of tubes is constituted by tube ends issuing in the bearing element, the further assembly and connection thereof corresponding to that of the construction described in FIG. 2.

The invention is particularly advantageous with regard to inspection and replacement possibilities of the tubes or pipe series, while the simple assembly of the tubes permits an inexpensive construction. This results in very considerable economy as regards both the investment required for building such furnaces and their maintenance during operation.

I claim as m invention:

1. An industrial furnace for heating fluids, comprismg:

(a) a hearth chamber defined by side walls and end walls;

(b) at least one source of heat arranged within said chamber and supported by one of said end walls;

(0) a plurality of fluid conveying heating tubes disposed within said chamber and extending through at least one end wall thereof;

(d) ducts disposed externally of said chamber and scalingly secured to the end walls thereof having the tubes extending therethrough, said ducts being aligned with the tubes and defining passages through which the tubes may pass without obstruction;

(e) closed hollow bearing elements spaced laterally from said chamber and secured in communication with said ducts, said elements having access means therein to permit the tubes to pass therethroug'n without obstruction; and,

(f) support elements secured to the tubes within the bearing elements to support tubes therein.

2. An industrial furnace according to claim 1 wherein 6 the ducts comprise pipes which are rigidly connected to both the end walls of the hearth chamber and said bearing elements, said pipes being of a diameter sufficient to permit the tubes to pass therethrough with clearance.

3. An industrial furnace according to claim 2 including headers entirely situated within the bearing elements and communicating with the interior of the tubes extending into said elements.

4. An industrial furnace according to claim 2 wherein the tubes are vertically arranged and suspended at the top through said support elements and said elements comprise annular collar pieces externally welded to the tubes, which collar pieces sealingly rest on the upper edges of the pipes.

5. An industrial furnace according to claim 4 wherein the ends of the bearing elements are supported from the walls of the hearth chamber by means of short tubular members that surround the heating tubes and are fastened to both the bearing elements and the Walls.

6. An industrial furnace according to claim 4 wherein the bearing elements are spaced from the exterior walls of the chamber sufliciently to allow fuel and combustion air supply lines to be located between said elements and walls.

7. An industrial furnace according to claim 1 wherein the heating tubes are interconnected in series inside of the hearth chamber to form coils of tubes and the ducts are of oblong shape to permit said coils to pass therethrough without obstruction.

8. An industrial furnace according to claim 7 wherein the support elements comprise:

(a) annular collars externally welded to the tubes, which collars are supported on the upper edges of the duct walls when the tubes extend therethrough; and,

(b) securing elements welded to one or more bends of the coils of tubes within the hearth chamber, which elements extend through the ducts when the tubes are disposed in the chamber and are provided with means adapted to rest on the duct walls when the tubes are disposed in the chamber.

9. An industrial furnace according to claim 8 wherein the securing elements extend loosely through the ducts when the tubes are disposed in the hearth chamber and including insulating materials to seal the securing elements within said ducts.

References Cited by the Examiner UNITED STATES PATENTS 2,385,749 9/45 Wallis ct al. 122-356 2,45 4,943 11/48 Reed 122-356 X 2,856,903 10/58 Leech et al l22356 3,062,197 11/62 Fleischer 122-510 PERCY L. PATRICK, Primary Examiner.

KENNETH W. SPRAGUE, ROBERT A. OLEARY,

Examiners.

Claims (1)

1. AN INDUSTRIAL FURNACE FOR HEATING FLUIDS, COMPRISING: (A) A HEARTH CHAMBER DEFINED BY SAID WALLS AND END WALLS; (B) AT LEAST ONE SOURCE OF HEAT ARRANGED WITHIN SAID CHAMBER AND SUPPORTED BY ONE OF SAID END WALLS; (C) A PLURALITY OF FLUID CONVEYING HEATING TUBES DISPOSED WITHIN SAID CHAMBER AND EXTENDING THROUGH AT LEAST ONE END WALL THEREOF; (D) DUCTS DISPOSED EXTERNALLY OF SAID CHAMBER AND SEALINGLY SECURED TO THE END WALLS THEREOF HAVING THE TUBES EXTENDING THERETHROUGH, SAID DUCTS BEING ALIGNED WITH THE TUBES AND DEFINING PASSAGES THROUGH WHICH THE TUBES MAY PASS WITHOUT OBSTRUCTION; (E) CLOSED HOLLOW BEARING ELEMENTS SPACED LATERALLY FROM SAID CHAMBER AND SECURED IN COMMUNICATION WITH SAID DUCTS, SAID ELEMENTS HAVING ACCESS MEANS THEREIN TO PERMIT THE TUBES TO PASS THERETHROUGH WITHOUT OBSTRUCTION; AND, (F) SUPPORT ELEMENTS SECURED TO THE TUBES WITHIN THE BEARING ELEMENTS TO SUPPORT TUBES THEREIN.

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