US2209974A

US2209974A - Fluid heat exchange apparatus

Info

Publication number: US2209974A
Application number: US169440A
Authority: US
Inventors: David S Jacobus
Original assignee: Babcock and Wilcox Co
Current assignee: Babcock and Wilcox Co
Priority date: 1934-11-20
Filing date: 1937-10-16
Publication date: 1940-08-06
Anticipated expiration: 1957-08-06

Description

Aug. 6, 1940. D. s. JAcoBus FLUID HEAT EXCHANGE APPARATUS Original Filed Nov. 20, 1934 INVENTOR.

Patented ug. 6, 1.94()y PATENT OFFICE 2,209,974A A FLUID HEAT EXCHANGE APPARATUS David S. Jacobus, Montclair, N. J., assignor to The Babcock & Wilcox Company,

Newark,

N. J., a corporation of New Jersey Original application November 20, 1934, Serial No. 753,828. Divided and this application October 16, 1937, Serial No. 169,440

5 Claims.

This invention is predicated upon improvements in metallic `tubular structures, and-.it is exemplified herein by tubular connections employed in fluid heat exchange apparatus.

When, in such apparatus, a fiuid at one temperature passes through tubes to a, metallic vessel at a higher temperature, experience has shown that the consequent differential metal expansions soon cause defects in the connections between the tubes and the metal of the vessel. This is especially true of economizer tubes connected to the drums of steam boilers operating at high fluid pressures.

It is an object of the invention to overcome this disadvantage.

A further object is to provide a Stirling boiler with an integral economizer the tubes of which are joined to a feed-water drum in accordance with the teachings of this invention.

Other objects will appear from consideration of the followingY description ofthe Stirling water tube steam boiler shown in the accompanying drawing, in which:

Figs. 1-5 inclusive are detail sections indicating different steps of a method which may be employed in practicing the invention.

Fig. 6 is a vertical section through a boiler drum having tubes connected thereto.

Fig. 7 is a section showing a tubular drum connection.

Fig. 8 is a view in the nature of a vertical section, showing a Stirling boiler having an integral economizer.

Figure 9 is a sectional view.

The drawing discloses a Stirling boiler including the mud drum IIJ and the upper steam and water drums l2, I4 and I6, the first of which is provided with a steam off-take I'I. The latter drums are connected to the mud drum by separate banks of steam generating tubes I8, 20 and 22, exposed 1n separate gas passes to furnace gases from the combustion chamber 24.

Feed water is supplied from any suitable source to the economizer drum' 26 which is connected to the rear drum I6 bythe economizer tubes 28 located in the last gas pass of the boiler. Although the temperature of the feed water is raised during its movement through these tubes it may be at a. temperature much less than the temperature of the drum I6 when it enters the latter. The tubes 28 therefore tend to contract relative to the metal of that drum, causing a loosening of the tubes when they are directly expanded into the drum. Furthermore, this undesirable condition is aggravated by the continued supply of low temperature fresh feed water to the drum 26 and the continued circulation through the drum I6 of water which has been heated to a higher temperature by the tubes 22 in the hottest gas pass. Such circulation takes place through the druml I0 which directly connects thebanks of tubes I8 5 and 22.

When it is considered that many boilers of the type shown operate at fluid pressures in excess of 1000 lb. per sq. inch it will be readily appreciated that any loosening of the tubes 28 in their seats in 10 the drum I6 isapt to be a matter of no small moment. As a matter of fact, experience has shown that such results are grave disadvantages in boilers operating at much lower pressures. This is particularly true when the boilers are operated l5 at 300 to 500% ratings. The water level in the drum I6 is apt to be below the upper ends of some of the tubes 28. The connections of these tubes with the drum are then apt to become loosened so that steam leaks develop. It finally becomes 20 necessary to take the boiler oi the line for repairs, and if the tubes are merely re-expanded into the drum, the same cycle is repeated. To avoid this excessive outage the economizer tubes are connected to the drum I6 in the `manner described 25 given thickness of drum shell. In constructions other than the Stirling boiler shown it is sometimes preferable to refrain from swaging down the ends of the economizer tubes where they are connected to the steam and water drum. 40 As the next step in the illustrative procedure a sleeve 36 is telescoped upon the swaged end of the tube. When this sleeve is of the internal diameter shown it ts tightly upon the

ribsl

32 and 34 and is heldv in position thereby, spaced from the exterior surface of the tube. It is preferably formed of some self-supporting material, and, under different embodiments of the invention the material may be paper, or a metal having a low 50 fusing temperature. Low fusing point alloys may be used in some instances, and in others, a cellular heat insulating material. Tin and leadare examples of metals which maybe used.

In the illustrative method, a tubular metallic 5 ferrule 40, preferably of the same material as the tube, is tightly telescoped over the sleeve 36. This may be done in some cases before the sleeve is placed in the position shown in Fig. 3, but the particular sequence of these acts depends upon the sequence of the remaining method steps, as well as upon the materials used.

The sleeve 36 and the ferrule d0 both terminate coincidentally with the tube to facilitate the completion of the circumferential weld 42 which forms a fluid tight connection between the tube and the ferrule but the invention also contemplates the extension of the tube beyond the ferrule in some cases. The tube is now ready to be held within a. tube seat in the drum I6 while an expander is operated within the tube to form a rigid and uid tight drum connection. When the

circumferential grooves

43 and 44 are formed as parts of the tube seat, the expanding operation will cause some of the metal of the ferrule to occupy the grooves to lock the ferrule more securely to the drum. Fig. 7 shows the grooves to be entirely lled with such metal. The expanding operation may also result in such a belling of the end of the tubes as indicated at 46 in Fig. '7. This further locks the ferrule to the drum and tends to prevent any endwise movement of the ferrule.

In some embodiments of the invention the ferrule 4I] may be separately expanded against the tube seats, and the tubes thereafter co-axially placed within and spaced from the ferrules so that the circumferential welds may then be completed. In these cases the ferrules may be additionally welded directly to the drum metal, and this welding as well as the expanding of the ferrules may be clone in the shop where the drum is manufactured. This promotes economy of manufacture by reducing erection costs.

When the boiler is put into operation after a heat convertible material such as paper is used between the ferrule and the tube, the paper or the compound formed on heating the paper acts to insulate the main body of the ferrule from the tube. When tin, lead, or some low fusing point alloy is used as the sleeve, the latter melts when the boiler is placed in operation, leaving an annular space between the ferrule and the sleeve.

In some embodiments of the invention the

ribs

32 and 34 may not be employed. The sleeve may fit the tube tightly throughout its length. Such an arrangement of elements is indicated in Fig. 9 of the drawing, wherein the ferrule 48 may be expanded into the drum in the shop and the tube thereafter inserted and Welded to the inner end of the ferrule in the field. With this construction there is an annular space between the tube and the ferrule.

The construction may be used to advantage for connecting alloy steel superheater tubes to the outlet header of a superheater when the header is made of plain carbon steel. In such a case expanding the alloy steel tubes directly into the outlet header may result in leakage in a hydrostatic test of the superheater such as is usually made during a shutdown period after the superheater has been in service. The coefficient of expansion and contraction of the alloy steel on changing the temperature is greater than in plain carbon steel and, on cooling down the superheater after it has been in operation, the alloy steel tubes may leak where they are expanded into the carbon steel headers. By employing ferrules of plain carbon steel around the ends of the alloy steel superheater tubes arranged in the Way shown and described and extending the ferrules and tubes a suflcient distance into the header the difference in the expansion of the tubes and the ferrules will not cause the ends of the plain steel ferrules to become loose where they are expanded into the header as these ferrules will have the same coefficient of expansion as the header. This will overcome the tendency to leak on account of a difference in the coefficients of expansion. If desired, the ferrules may be welded to the header in which case it is advantageous to have the same coefficient of expansion in the ferrules as in the header. By Welding the ferrules to the header on the outside of the header the stresses due to the expansion of the tubes and the ferrules would be distributed along the lengths of the ferrules thereby avoiding a concentration of stress due to the reinforcing action of the welding. The ferrules may be made of comparatively thin wall section because the tube ends would prevent them from collapsing.

What is claimed is:

1. In uid heat exchange apparatus, a thick walled pressure vessel in the nature of a drum or header, tubes of much less Wall thickness communicating with the interior of the vessel and adapted in practice to conduct a liquid at lower temperature to the liquid supply in the vessel, metallic ferrules externally telescoped upon the ends of the tubes and spaced therefrom, a ller interposed between each ferrule and its tube, and circumferential welds joining the inner ends of the tubes and the inner ends of the ferrules; each filler cooperating with a ferrule and a tube to maintain them in predetermined spaced relationship while the assembly is being expanded to form a pressure tight joint between the ferrule and the metal of the drum.

2. In fluid heat exchange apparatus, a thick walled pressure vessel in the nature of a drum or header, tubes of such less wall thickness communicating with the interior of the vessel and adapted in practice to conduct a liquid at lower temperature to the liquid supply in the vessel, metallic ferrules externally telescoped upon the ends of the tubes and spaced therefrom, a ller interposed between each ferrule and its tube, the filler being formed of combustible material, and circumferential welds joining the inner ends of the tubes and the inner ends of the ferrules; each ller cooperating with a ferrule and a tube to maintain them in predetermined spaced relatlon` ship while the assembly is being expanded to form a pressure tight joint between the ferrule and the pressure vessel.

3. In tubular connections between a steam and water drum and tubes .through which water is adapted to enter the drum at a temperature lower than that of the body of fluid within the drum, the drum being formed with openings providing tube seats, the tubes having reduced ends extending a substantial distance into the interior of the drum, sleeves or ferrules externally telescoping the tubes and circumfcrentially insulated therefrom, the ferrules extending similar distances into the interior of the drum, and circumferential welds formed at the inner ends of the tubes and ferrules while the latter are maintained in circumferentially spaced relationship to the tubes, the ferrules and the tubes being simultaneously expanded into the tube seats.

4. In fluid heat exchange apparatus, a thick walled pressure vessel in the nature of a drum or,

header, tubes of much less wall thickness communicating with the interior of the vessel and 75 adapted inpractice to conduct a liquid at lower temperature to the liquid supply in the vessel, metallic ferrules externally telescoped upon the ends of the tubes and spaced therefrom, a 1111er of a low fusing point metal interposed between each ferrule an dits tube, and circumferential welds joining the inner ndsof the tubes and the v inner ends of the ferrules; each ller cooperating with a ferrule and a tube to maintain them in predetermined spaced relationship while the assembly is being expanded to form a pressure-tight joint between the ferrule and the pressure vessel.

5. In fluid heat exchange apparatus, a thick walled pressure vessel in the nature of a drum or header, tubes of much less wall thickness communicating with the interior of the vessel and adapted in practice to conduct a liquid at lower temperature to the liquid supply' in the vessel,.

the pressure vessel ends of the tubes having preformed circumferential ribs, metallic ferrules externally telescoped upon the ribbed ends of the tubes and spaces therefrom, a ller interposed between each ferrule and its tube, and circumferential welds joining the inner ends of the tubes and the inner ends of the ferrules; each illler cooperating with a ferrule and a. tube to maintain them in predetermined spaced relationship while the assembly is being expanded to form a pressure tight joint between the ferrule and the pressure vessel.

, DAVID S. JACOBUS.