Heat exchanger

June 22, 1937,

2,084,743

J. P. RATHBUN

HEAT EXCHANGER

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June 22, 1937.

J. P. RATHBUN ; HEAT EXCHANGER Filed May 17, 1935

2,084,743

Sheets-Sheet 2

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Patented June 22, 1937

2,084,743

UNITED STATES PATENT OFFICE

2,084,743

HEAT EXCHANGER

John P. Rathbun, prospect Park, Pa., assignor to Westinghouse Electric &amp; Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania

Application May 17, 1935, Serial No. 22,085

Claims. (CL 257—236)

My Invention relates to heat exchange apparatus, more particularly to heat exchange apparatus In which one fluid is at least partially vaporized, and it has for an object to provide 5 improved apparatus.

A further object is to improve the heat transfer rate of such apparatus.

In accordance with my invention, I provide a shell or other vessel in which there are disposed 10 heating elements, such as tubes containing heating fluid. Baffles are arranged to provide a plurality of passages through which liquid flows upwardly in contact with the heating elements to be heated thereby,, Other passages convey the 15 fluid, out of contact with the heating elements, from the upper ends of heating passages to the lower ends of the heating passages. The vapor formed in each heating passage is removed through the upper portion of the shell. Thus, ₂₀ natural convection currents are utilized to provide maximum flow and heat transfer.

The above and other objects are effected by my invention as will be apparent from the following description and claims taken in con₂₅ nectlon with the accompanying drawings, forming a part of this application, in which:

Fig. 1 is a plan view, partly in section, of one embodiment of the apparatus;

Fig. 2 is a vertical longitudinal section thereof; 3Φ Figs. 3, 4, and 5 are transverse sectional views taken on the lines HI—HI, IV—IV, and V—V, respectively of Fig. 2;

Mg. 6 is an enlarged broken perspective view showing the baffles;

₃₅ Mg. 7 is a vertical longitudinal section of a modified form of heat exchanger;

Mgs, 8 and 9 are transverse sectional views taken on the lines VIH—VUI and IX—IX of Mg. 7; and

Mg. 10 is a fragmentary section of a modified baffle construction.

* Referring to the drawings in detail, the heat exchange apparatus comprises a cylindrical shell 16 which may have an integral closure li at 45 one end. The shell 10 contains tubes 12 and 13 for circulating heating fluid, the tubes being arranged in a nest or bundle in the lower portion of the shell, that is, somewhat below the top of the shell, as shown on the drawings. The tubes are 50 secured at one end to a tube sheet 14, which is clamped between a flange 15 of the shell 10 and a flange 16 of a removable head 17. The latter comprises an inlet chamber 18 having an inlet connection 19 and an outlet chamber 21 havM ^lng outlet connection 22. At the opposite end, the tubes are secured to a floating tube sheet 23, to which a floating head 24 is secured. The floating head 24 provides a reversing chamber for directing the heating fluid from the tubes 12 to the tubes 13. It is to be understood that any ₅suitable heating fluid may be used. For example, steam may be used as contemplated by the illustrated embodiment, in which case the tubes i 2 may be greater in number than the tubes 13. The steam gives up its latent heat in the ₁₀tubes 12 and the tubes 13 serve primarily for returning the condensate to the head 17. It is to be understood that any desired number of tube passes and any other desired arrangement of tube nest may be used. 15

As shown in Figs. 4 and 5, the tube nest is spaced from the cylindrical wall of the shell 11, and curved baffles 25 partially enclose the tube nest, extending about the sides and partly about the bottom of the tube nest and providing ₂θ downwardly extending passages 26 between the tubes and the cylindrical wall of the shell. The upper edges of the baffles 25 extend approximately to the top of the tube nest, and the lower edges extend to the bottom of the tube nest but are in spaced relation to each other so as to provide communication between the lower ends of the passages 26 and the tube space which is partially enclosed by the baffles 25. The baffles 25 may be continuous, as in the illustrated embodiment, extending from the tube sheet 14 to the tube sheet 23.

The tube space is divided transversely of the tubes, by two groups of baffles, 28 and 29, arranged alternately, into a plurality of compart- ₃₅ments 46 and a plurality of compartments 47, arranged alternately. As shown in Fig. 4, the baffle 28 comprises a member 30 which is disposed between the baffles 25 and which is slightly more than semi-circular in form. It further ₄₀comprises an approximately semi-annular member 31 extending between the baffles 25 and the shell up to the height of the baffles 25. Thus, the baffle part 30 extends upwardly above the part 31, to form slots 32 as shown in Figs. 4 and 6 ₄₅for flow of liquid, as hereinafter described. The baffle parts 30 and 3i are secured to each other and to the baffles 25 in any suitable manner, as by welding. They together form tube supports adapted to slide on the bottom of the shell. ₅₀

The transverse baffles 29 comprise a central baffle part 33, similar in form to the baffle part 30, also extending upwardly above the tube nest. It further comprises arcuate parts 34 between the baffles 25 and the shell. The parts 34 ex2,084,743 tend upwardly to the upper edge of the part 33 and extend downwardly only to the lower edges of the baffles 25, thereby forming a port 35 in the bottom of the baffle 29, through which liquid ₅ may flow from one compartment 47 to the next compartment 46.

The entire tube bundle, including the baffles, may be removed as a unit through the left hand end of the shell upon disengaging the flanges 16 ₁₀ and 15.

The shell is provided with a liquid inlet 36 in the bottom thereof in the end adjacent the head structure 11 and with a liquid outlet 37 at the other end. It is formed with a vapor outlet 38 15 in the upper portion thereof adjacent the end wall II. A weir 39 may be provided adjacent the floating head 24 to insure complete submergence of the tubes in the liquid, and the shell may be extended beyond the weir 39 to provide a stor20 age chamber 41 for liquid leaving the shell. A baffle 42 may be provided at the top of the shell between the weir 39 and the vapor outlet 38 and provided with a trough 43 adapted to collect and drain to the cylindrical wall of the shell any 25 liquid particles collected by the baffle 42. A liquid separator 44 may be provided at the vapor outlet 38 to separate out any liquid particles carried in suspension by the vapor leaving the shell. The liquid may be drained through a conduit 45 30 into the storage chamber 41.

The. operation of the above-described apparatus is as follows: while the above-described apparatus is useful generally for vaporizing liquid, it is particularly adapted to be used as a reboiler 35 in oil refinery apparatus, to separate a component or components of lower boiling point from a component or components of higher boiling point. Natural convection or thermosyphonic circulation of liquid in each compartment 46, 40 41 is effected by the heating action of the tubes 12, 13, the liquid flowing upwardly through the space between the baffles, over the upper edges of the baffles 25, downwardly through the passages 26 around the lower edges of the baffles 25 45 back into the space between the baffles 25. In each of the compartments 46, 47, a portion of the circulating liquid is continually passed on to the next compartment and added to the liquid circulating therein, as will now be described. The 50 liquid containing a mixture of components of both higher and lower boiling points is admitted to the shell 10 through the inlet 36 into the first compartment 46. It joins the liquid coming down through the passage 26, and the mixture 55 flows upwardly through the passage provided between the lower edges of the baffles 25 into the tube space enclosed by said baffles. As it flows upwardly it comes in contact with the heating tubes 12 and 13 and is heated thereby. As it 60 reaches the top of the tube nest, the components of lowest boiling points, or lighter fractions, vaporize and flow off into the vapor space formed in the upper portion of the shell above the tube nest. One portion of the liquid rising to the top 65 of the tube nest spills over the upper edges of the baffles 25 and flows downwardly through the passages 26. From the latter, it is again admitted through the passage between the lower edges of the baffles 25 to the tube space enclosed by said 70 baffles and is recirculated as described. Another portion of the liquid rising to the top of the tube nest spills over the upper edges of the baffle parts 31, through the notches 32, into the next compartment 47 between the baffles 28 and 29.

In the compartment 47, the liquid flows downwardly through the passages 26 to the bottom of the shell. One portion of the liquid then flows upwardly through the tube space of the compartment 47, and. another portion flows through the port 35 into the next compartment 46 between 5 baffles 29 and 28. The portion of the liquid flowing upwardly through the tube space in the compartment 47 spills over the upper edges of the baffles 25, giving off to the vapor space the vapor formed as it is passed over the tubes, and 10 again passes downwardly through the passages 26. The portion of the liquid passing through the port 35 joins the liquid in the next compartment 46 which is flowing upwardly through the tube space. 15

The liquid then flows successively through the remaining compartments 46 and 47 in the same manner as just described, the components of successively higher boiling points being gradually vaporized. From the last port 35, the liquid flows 20 upwardly over the ends of the tubes 12 and 13 and the floating head 24, and spills over the upper edge of the weir 39 into the storage chamber 41, from which it is withdrawn through the outlet 37. 25

In the above arrangement, the liquid flows upwardly in contact with the heating tubes and downwardly out of contact with the tubes, thereby setting up natural convection currents within each compartment, resulting in increased rate of 30 flow and increased rate of heat transfer. The flow from one compartment to the next is effected by gravity, the liquid being admitted under pressure and rising to a sufficiently high level in the first compartment to effect, such flow, the 35 liquid levels in the successive compartments being successively lower.

In Figs. 7, 8, and 9, I show a modified baffle arrangement, the remainder of the structure being the same as in Figs. 1 to 5. A curved baffle 40 member 51 extends about the sides and bottom of the tube nest in spaced relation to the wall of the shell, providing passages 52 and 53, shown in Figs. 8 and 9, respectively. The baffle member 51 may be continuous between the tube sheets. 45 The tube space is divided by transverse baffles 54 into compartments 55. The baffle 54, as shown in Fig. 9, comprises an intermediate member 56 having openings through which the tubes extend and arcuate members 57 between the circular 50 member 51 and the shell 10. The lower edges of the latter are in spaced relation to form a port 58, while the upper edges of the parts 56 and 57 are spaced a short distance above the top of the baffle member 51 and the tube nest. As shown 55 in Fig. 8, an arcuate baffle member 59 between the curved baffle member 51 and the shell provides a division wall between the passages 52 and 53, and extends continuously from one side to the other to a height even with the top edge of 60 the baffle member 51. The curved baffle member 51 is formed with a slot 61 in the bottom thereof in the part of each compartment 55 adjacent the passage 52, that is, from the tube sheet 14 or the baffle 54 to the baffle 59, while it is continu- 65 ous adjacent the passage 53, that is, from the baffle 59 to the baffle 54.

In the operation of this embodiment, the liquid to be partially vaporized is admitted under pressure through the inlet 36, as in the first embodi- 70 ment, and rises through the slot 61 and the tube space to the top of the group of tubes. From there, it spills oww the upper edges of the baffle member 51 into the passages 52 and 53. The portion entering the passage 52 flows down- 75

9,084,743 wardly, joins the liquid entering through the inlet 38, and reenters the tube space through the slot 61. The flow of this portion is effected by the natural convection or thenno-syphonic circu₅ latlon induced by the heating action of the tubes.

The portion of the liquid entering the passage 53 flows downwardly to the bottom thereof and/then through the port 58 in the baffle 54 into the next compartment. In the latter, it flows upwardly jo through the slot 61 into the tube space. The cycle of operation just described is then repeated in each compartment. From the last port 58, the liquid flows upwardly over the ends of the tubes and. the floating head 24 and spills over 15 the weir 39.

In this embodiment, the liquid flows upwardly in contact with heating tubes and downwardly out of contact therewith as in the first embodiment. The passages 52 provide recirculation of 20 liquid within the several compartments, while the passages 53 provide for flow from one compartment to the next. In this case, the convection currents through the passages 53 assist the gravity flow of the liquid from the inlet to the 25 outlet end of the tube space, since the head of the heavier unheated liquid in the passages 53 exceeds the head of the lighter boiling liquid flowing upwardly into the tubes in the next compartment.

As shown in Fig. 10, the curved baffles 25α may be made in sections so as to be removable. Each of the transverse baffles 28α and 29α is integral, instead of comprising separate parts as in Figs. 4 and 5. Each baffle section 25ά extends between 35 adjacent transverse baffles and is detachably secured thereto by angle members and bolts shown at 62. Upon removing the curved baffle sections 25α, access to the tubes is provided for periodically cleaning the same. In all other respects, 40 the baffle structure of Fig. 10 may be the same as that shown in Figs. 1 to 6.

A further advantage of the present invention is that all of the liquid is caused to rise repeatedly to the surface, at least once in each compartment, 45 where the vapor separates from the liquid to a much greater extent because of the low hydrostatic head.

While I have shown my invention in several forms, it will be obvious to those skilled in the 50 art that it is not so limited, but is susceptible of various other changes and modifications without departing from the spirit thereof and I desire, therefore, that only such limitations shall be placed thereon as are imposed in the prior art or 55 as are set forth in the appended claims.