US2193362A - Radiant tube furnace - Google Patents

Description

' loi Patented Mar. 12, 1940 PATENT LOFFICE 2,193,362 RADIANT TUBE' FURNACE James C.'Woodson, Cleveland, Ohio, assignor to Lee Wilson Sales Corporation, Cleveland, Ohio,

a corporation of Ohio Application January 16, 1939, Serial No. 251,131

7 Claims.

This invention relates to a furnace and, in particular, to a furnace adapted to be heated by radiation from heat-exchange tubes mounted interiorly thereof for conducting hot combustion gases or other fluid heating medium.

Numerous types of radiant tube furnaces have been proposed heretofore and it is the general object of this invention to improve upon such fur-v naces as previously constructed.

The invention is concerned particularlywith a novel form of heat-exchange tube of such construction as to provide better fuel economy than has been obtainable with the heat-exchange tubes now in use. A further object of the invention is to provide a tube having a longer useful life than the tubes now in use and, furthermore, to provide a tube which may be readily fabricated at relatively low cost. y,

In a preferred form of the invention, I provide a heat-exchange tube having substantially parallel branches or passages and preferably mount it adjacent a wall of the furnace. To thedischarge end of the tube, I connect an exhaust flue embedded in the furnace wall. I also provide a connection from the discharge end of the tube to the entrance thereof to permit a small portion of the combustion gases to be induced into the stream of freshly -burning gases for rev-circulation` therewith.

Further details of the embodiment outlined above will be explained herebelow with reference to the accompanying drawing in which Fig. 1 is a transverse sectional view through a furnace having the invention incorporated there- 1D;

Fig. 2 is a partial sectional view taken substantially along the plane of line II-lI of Fig. 1; and Fig. 3 is a sectional view through the heat-exchange tube alone along the plane of line III-III of Fig. 1. V

Referring now in detail to the drawing, I have l illustrated therein a furnace I of the cover type merely as a convenient example since the invention may be applied to various types of furnace structures. The furnace I0 includes a cover II removably disposed on a -base or hearth, aportion `of which is shown at I2. The cover II is open at the bottom and comprises side walls, end walls and a. roof of refractory material assembled within a structural frame I3 and sheathing plates Il. The base' j| 2 is built up from rey fractory material assembled on any suitable supporting foundation. The base is adapted to support a charge of material I5 such as a stack of vsheets or coil of strip to be subjected to process- .disposed at any convenient angle. A central lonshortly.

ing, e. g. annealing. The base also provided with a, sealingchannel I6 adapte to receive the lowerv edge of an open-bottomed protective cover Il fabricated from light plate. The base I2 also has a shoulder or margin I8 adapted to receive the bottom edge of the side and end walls of the cover. v

Heat-exchange tubes I9 are mounted interiorly of the furnace and may conveniently be disposed in spaced relation along the side walls. of the cover. The tubes I9 may be of any convenient construction but I prefer a tubeof substantially oval section, the lower end of which is disposed substantially at right angles to themain body of the tube, as indicated at 20. This portion of `the tube traverses the furnace wall and is embedded therein.

-As shown, the tubes I9 are disposed with their longer portions 2| vertical although they may be gitudinal partition 22 disposed in each tube divides it into a pair of substantially parallel passages or branches 23 and 24. A cross wall 25 substantially in line with the partition 22 divides the lower portion 20 of the tube andwith the partition, constitutes a baie extending from the bottom of the tube to a point spaced below the top thereof, thereby establishing communication between the passages 23 and 24 at their upper ends. A 'port or opening 26 is formed in the cross wall 25 for a purpose which will appear A burner 21 extends into the side of the bottom portion 20 of the tube which is in communication with the passage 23. The other side of the portion 20 terminates in the side wall of the furnace and does not extend outwardly therethrough, the outervend of this portion being indicated at 28. A spark gap igniter 29 is disposed adjacent each burner and is connected to an energizing transformer 30. A manifold 3l extends along each side of the furnace for supplying to the burners a combustible mixture of air and gas.

The side of the lower portion 20 of each tube opposite that into which the burner 21 exten-ds, indicated at 32, has an opening 33 at the top thereof. Anrexhaust ue 34 embedded in the furnace wall fits down over the opening 33. The exhaust ue serves to carry waste gases upwardly through the furnace wall and to the exterior atmosphere for discharge. This construction has a particular advantage in that the waste gases contain a substantial amount of heat even after traversing the passages 23 and 24. A portion of this remaining heat content ofthe exhaust gases is absorbed by the brlckwork composing the furnace wall, thereby making up at least in part, the heat lost from the exterior of the walls. i

The operation of the furnace of my invention will now be explained briey. It will be understood that the covers H and I1 are raised to pei".- mit the charge I5 to be initially placed on the base I2. The covers are then replaced as illustrated. A combustible mixture such asfuel ses and air in proper proportions is supplied to the manifolds 3| under the control of suitable valves in a' supply main and the mixture issuing from the burners 2l is ignited by spark gaps created understood, of course, that where the furnace is employed in continuous processing, the burners remain ignited and it is necessary to energize the igniter points only when starting up.

After ignition, the combustible gases burn as they traverse the passages 23 and 24. After passing around the upper end of the partition 22 and descending through the passage 24, the combustion gases having given out most of their heat to the walls of the' tubes I9, enter the portions 32 of the lower ends of the tubes and thence pass upwardly through the openings 33 and through the exhaust hues 34. A small portion of the combustion gases which have traversed the passages 23 and 24 is induced through the opening 26 in the cross Wall 25 into the stream of freshly burning gases ascending from the burner through the passage 23. This re-circulation of a portion of the combustion products tends to eliminate substantial differences between the temperatures of different parts of the tube by cooling the gases slightly in the initial stages of combustion. This reduces erosion of the tube in the area on which the flame jet impinges and thereby lengthens the useful life of the tubes. As previously pointed out, as the combustion gases ascend through the exhaust flue 34 they give up a certain portion of their heat to the furnace walls, thereby making up at least in part, the heat lost from the exterior of the walls, and increasing the overall thermal efficiency of the furnace. It will be noted that while the shape of the iiues 34 in sectionis different from that of the passages 23 and 24, the dimensions are such that the sectional areas are approximately the same at all points along the path of the gases.

After the charge I5 has been heated to the proper temperature, the cover Il is removed and disposed on another previously loaded base, the cover l1 being left in place to protect the charge during the slow cooling thereof.

It will be apparent from the foregoing description and explanation that the invention provides a radiant tube furnace having numerous advantages over furnaces of this type previously available. In the rst place, a relatively long path is afforded for the combustion gases which increases the amount of heat given out by them to the surrounding heat-conducting walls of the tube. Re-circulation of a portion of the combustion gases tends to make the temperature of all portions of the tube substantially uniform.

The economy obtained by leading the exhaust pre-mixed'airand gas which also contributes to a high thermal efiiciency.

Although I have illustrated and described but a single preferred embodiment of the invention,

:incassa it will be understood that Anumerous changes and modifications therein may be made without departing from the spirit of the invention or the scope of the appended claims.

I claim: e

1. In a furnace having a side wall and a roof, a heat-exchange tube disposed substantially vertically adjacent said wall, said tube being substantially oval-shaped in section and having a baie extending longitudinally therethrough providing a pair of substantially parallel gas passages and having a portion at its lower end disposed substantially at right angles to the remainder of the tube, said portion extending into said wall, and an exhaust ii`ue extending upwardly within said wall from the lower end of said tube and communicating with one of said having a portion at its lower end disposed sub` stantially at right angles to the remainder of the tube, said portion extending into said wall, and an exhaust fiue embedded in said wall and extending upwardly therein, said flue communieating with one of said passages at the lower end of the tube.'l

3. In a furnace having a side wall and aroof, a heat-exchange tube disposed substantially vertically adjacent said wall, said tube providing a pair of substantially parallel gas passages and having a portion at its lower end disposed substantiallyvat right angles tothe remainder of the tube, said portion extending into said wall, one of said passages terminating within the wall and being open at the top whereby it communi` prising a plurality of heat-exchange tubes mounted interiorly of said cover, each tube comprising a .burner portion extending through the cover below the top of said base when the cover is positioned thereon and adapted to receive a burner therein, a vertical heat-exchange portion extending upwardly from said burner portion, a second heat-exchange-portion substantially parallel to the first and communicating therewith at the upper end thereof, an outlet portion communicating with the lower end of said second heat-exchange portion and extending outwardly therefrom below the top of said base when the cover is positioned thereon, and a stack communicating with each outlet portion and extending upwardly therefrom.

5. In a furnace including a cover having side walls and a roof and a base, a heat-exchange tube disposed substantially vertically adjacent said wall, said tube providing a pair of substantially parallel gas passages and having a portion at its lower end disposed substantially at right angles to the remainder of the tube, said portion extending into said wall below the top of said `base when the cover is deposited thereon,k

and an exhaust ue extending upwardly along said wall from the lower end of said tube and communicating with one of said passages.

' 6. In a furnace having aside 'wall and a roof, a heat-exchange tube disposed substantially vertically adjacent said wall, said tube being subfio stantially oval-shaped in seotion and having a baille extending longitudinally therethrough, providing a pair of substantially parallel gas pas? sagesV and having a portion at its lower end disposed substantially at right. angles to the remainder of the tube, said portion extending into said Wall, an exhaust ue 'extending upwardly along said Wall from the lower end of said tube and communicating with one of said passages, and a burner extending into the other passage, said baille having a bleeder port adjacent said burner. y

7. In a furnace having a sidewall and a roof, a heat-exchange tube disposed substantially vertically adjacent said wall, said ltube providing a pair of substantially parallel gas passages, a burner supplying combustion gases to one of said passages, and an exhaust vue connected to the other passage at. the lower end of said tube and embedded in said wall.

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