Heat Exchanger With Double Wall Tubes and Three Tube Sheets

This invention relates to heat exchangers and more particularly to heat exchangers having double wall tubes and three tube sheets.

It is desirable to ensure the separation of heating and heated fluids in heat exchangers and depending on the compatibility of the fluids involved, the effort and expense expended to ensure the separation of these fluids varies. Double wall tubes with grooves in one of the walls at the interface have been proposed as a highly reliable method of maintaining the separation between the fluids. However, two tube sheet junctures are susceptible to leaks. Double tube sheets on each end of the tubes may be utilized to detect leaks at the tube-to-tube sheet juncture further decreasing the possibility of undetected leaks and admixing of the two fluids.

In general, a heat exchanger, made in accordance with this invention, comprises a shell, a plurality of double wall tubes having an inner wall portion and an outer wall portion, a single tube sheet adjacent one end of the tubes, and a pair of tube sheets adjacent the other end of the tubes. The pair of tube sheets are disposed in a spaced relationship with the inner wall of one end of the tubes terminating adjacent one of the tube sheets forming the pair and the outer wall of the one end of the tube terminating adjacent the other tube sheet of the pair.

The objects and advantages of this invention will become more apparent from reading the following detailed description in connection with the accompanying drawings, in which:

FIG. 1 is an elevational view, partially in section; of a heat exchanger made in accordance with this invention;

FIG. 2 is an enlarged partial sectional view showing the tube-to-tube sheet juncture with the single tube sheet; and,

FIG. 3 is an enlarged partial sectional view showing the tube-to-tube sheet juncture with the pair of tube sheets.

Referring now to the drawings in detail and in particular to FIG. 1, there is shown a heat exchanger 1 having an outer shell 3 and a plurality of double wall tubes 5. A single tube sheet 7 is disposed on one end of the shell 3, the lower end as shown in the drawings, and a pair of tube sheets 9 and 11 are disposed on the other end of the shell 3, the upper end as shown in the drawings. The tube sheets 9 and 11 are disposed in a spaced relationship and cooperate with the shell 3 to form an enclosed space 13 therebetween.

Hemispherical heads 15 and 17 are attached to the tube sheets 7 and 11, respectively, and cooperate therewith to form headers for directing the flow of fluid through the tubes 5. The shell 3 is expanded outwardly adjacent each end thereof to provide controlled flow paths for the influent and effluent shell side fluid.

The tubes 5 are double wall tubes which have a gap or one or more grooves 6 at the interface of the two walls.

One end of the tube terminates adjacent the single tube sheet 7 as shown in detail in FIG. 2. The end of the double wall tube 5 is sealed by forming a circumferential weld 19 at the interface of the inner and outer wall 21 and 23, respectively. The tube sheet 7 has a plurality of holes 25 for receiving the tubes 5 (only one is shown). Each hole has a boss 27 disposed at each end thereof to facilitate forming a seal weld 28 between the outer wall 23 and the boss 27 on both sides of the tube sheet 7. The portion or segment of the outer wall 23 between the welds 28 disposed within the holes 25 in the tube sheet 7 have one or more openings 29 disposed therein in communication with the grooves 6 to allow any fluid leaking past either of the seal welds 28 to enter the groove 6 so that it may be detected.

As shown in FIG. 3, the pair of tube sheets 9 and 11 are spaced apart and the inner tube sheet 9 has holes 31 for receiving the double wall tubes 5 and a boss 27 surrounding each hole to facilitate forming a seal weld 28 between the boss 27 and the outer wall 23 of the tube passing therethrough. The outer wall 23 terminates adjacent the inner tube sheet 9 and the inner wall 21 extends through the space 13 between the tube sheets 9 and 11 and through holes 35 in the outer tube sheet 11. Bosses 27 surround the holes 35 in the outer tube sheet 11 and facilitates forming a seal weld 28 with the ends of the inner wall 21 as it extends through the tube sheet 11. the grooves 6 at the interface of the inner and outer wall 21 and 23, respectively, is in communication with the space 13 between the tube sheets 9 and 11 and the space 13 serves as a header for collecting any leakage of either the heating or the heated fluid through either wall 21 or 23 of the tubes or through any of the sealed welds 28 between the tubes and the tube sheet giving an indication of a leak before there is contamination of one of the fluids by the other. The heat exchanger hereinbefore described advantageously utilizes only three tube sheets, yet provides an indication of leakage from any tube-to-tube sheet weld and any wall of the double wall tubes to assure separation of the heating and heated fluids.