US2973944A - Heat transfer apparatus - Google Patents

Description

Filed Feb. 10, 1955 March 7, 1961 J. A. ETTER HEAT TRANSFER APPARATUS 5 Sheets-Sheet 1 FIG. 1

INVENTOR. JOSEPH A. ETTER ATTORNEY March 7, 196E Filed Feb. 10, 1955 FIG- 2 FIG- 3 J. A. ETTER HEAT TRANSFER APPARATUS 3 Sheets-Sheet 2 INVENTOR. JOSEPH A. ETTER ATTORNEY March 7, 1961 J. AJETTER 2,973,9 4

HEAT TRANSFER APPARATUS Filed Feb. 10, 1955 3 Sheets-Sheet 3 INVENTOR. JOSEPH A. ETTER States '7 6 Claims. (Cl. 257-448) This invention relates to heat transfer apparatus and arm processes and has especial application to the control of chemical processes in which there is a necessity for acculrately controlling the temperature of a batch of chemica s.

This is a continuation-in-part of my application Serial No. 280,441, filed April 3, 1952, now Patent No. 2,- 764,476.

As stated in the parent application the heat transfer problem for whose solution the present invention is particularly applicable, is found in the manufacture of synthetic rubber. This manufacture involves mixing various ingredients in a tank, the nature of the ingredients being such that a tremendous quantity of heat is liberated. Heretofore, in order to prevent the attainment of injurious temperatures and pressures the rate of reaction of the batches has been limited, because of limited refrigeration, thus restricting the production rate. Various methods of applying refrigeration to the batches have been attempted but their success has beenvery limited.

Using the heat transfer equipment of the present invention and its refrigerant control, the rate of production has been increased so that a process which formerly re quired twelve to fourteen hours now can be accomplished in three hours or less. Furthermore, the efliciency has been improved.

Accordingly, it is an object of the invention to provide heattransfer equipment which affords maximum fluid contact with the heat transfer surface of the equipment and whch offers minimum resistance to flow between the equipment and the fluids between which heat is transferred.

A further object is the provision of heat transfer apparatus especially adapted for use in chemical reaction equipment and in which the operation of the apparatus is not adversely affected by sudden changes in temperature and also'in which the apparatus operates with very high efliciency under extremely wide load variations.

A further object of the invention is the provision of cooling coils especially adapted for chemical reaction apparatus and in which the maximum height of the apparatus is maintained at a minimum while still providing for substantial flooding of the cooling coils with refrigerant under all conditions of temperature and variable load normally encountered in the use of such apparatus.

A further object is the provision of heat transfer apparatus including cooling coils which may be completely prefabricated with a minimum number of joints and in which the individual coil units may be introduced into a reactor through a conventional size manhole and the units assembled and suspended within the reactor out of contact with the lining therein and when thus suspended will be rigidly supported in position against sifting movement or vibration resulting from agitation of the contents of the reactor but without impeding expansion and contraction caused by temperature changes. 7

Further objects and advantages of the inventionwill be apparent from the following description considered in conjunction with the accompanying drawings wherein:

Fig. 1- is a perspective of a heat exchanger constructed in accordance with the present invention;

Fig. 2, a top plan view of the structure of Fig. 1 illus-I Fig. 3, a horizontal sectional view ofthe apparatus of Fig. l illustrated in a reactor as in Fig. 2, and taken approximately midway 'of the unit of Fig. 1;

Fig. 4, a side elevation of one of the individual coil units of Fig. 1; a

. Fig. 5, an end view of one of the coil units;

Fig. 6, a top plan view of a coil unit;

Fig. 7, a bottom plan view of a coil unit; and

Fig. 8, a fragmentary elevation partly in section of the upper end portion of a modified form of coil unit.

Briefly stated, the invention is directed to heat exchange apparatus comprising a plurality of individual coil units arranged in a partial circle or horseshoe. Each coil unit has a downcomer connected to a horseshoe inlet header positioned at the upper ends of the coil units and a plurality of vertical riser pipes which are connected at their upper ends to a horseshoe outlet header. The individual coils are composed of individual groups of parallel tubes, as for example, three in number, located so that a plane therethrough is normal to the radius of the circular arrangement of coil units. This arrangement is particularly suitable because when used with an agitator operating from the center of the circle the fluid is driven over a staggered arrangement of tubes, thus providing maximum contact between the tubes and the agitated material. Furthermore, the disposition of the vertical tubes does not interfere with the normal rolling contact of the batch with the outer shell of the reactor and the power required for agitation is, therefore, not substantially increased. The result is that high heat transfer may take place but with? out requiring an excessive agitation speed.

The arrangement and configuration of the heat transfer member is also especially desirable insofar as the internal flow therethrough is concerned. For example, the the inherently low flow resistance permits complete flooding of the coils by rapid supply through the down pipes and vertical gas removal from the risers. This arrangement also affords gravity circulation by reason of the difierence in heads of the downcomers and the risers. A further re sult is that rapid flow through the coils effects efficient heat transfer by keeping liquid in contact with the walls substantially continuously by rapidly removing vapor there from.

In view of the large surface area of the coils Wide load variations may be accommodated and still maintain the coils in a fully flooded condition. i

The structure of the coils permits them to be prefabricated with a minimum number of joints and the coils may be conveniently lowered through a manholea'nd, assembled together with a minimum number of joints. As

the joints are above the production line the probability of detecting leaks by inspection before the leaking 'ma-,

terials mixes with the product is increased. The horseshoe arrangement permits the unit to be placed within a reactor in such a way that it does not block access therewithin.

Referring to the drawings, the heat transfer member has an inlet conduit 1d and an outlet 11. Conduit 10 is connected to a header 12 and outlet conduit 11 is connected to outlet 13. Headers 12 and 13 are of arcuate configuration and extend through approximately 270 and are disposed in a substantially horizontal plane, the inletihead er being shown as disposed within the outlet header.

Connected to the lower side of inlet header 1 2 are a series of downwardly extending relatively short pipes provided with one flange 15 of a flanged joint, the purposeof which will be presently described. Connected to the' 2,973,944 Patented Mar; 7, a

lower side of outlet header 13 are a series of spaced downwardly extending relatively short lengths of pipe 16 which are attached to flanges 17 forming one part of a flanged joint.

The heat transfer coils comprise a plurality of individual coil units 18 and are best shown in Figs. 4-7. Each of these coil units 18 includes a liquid refrigerant supply conduit 19 provided with a flange 20 for mating with the flange on inlet pipe 14 to provide a supply of liquid refrigerant from inlet header 12. Similarly, each individual refrigerating coil unit 18 has a refrigerant outlet pipe 21 having a flange 22 for mating with flange 17 on outlet pipe 16 to provide a path for flow of a gaseous refrigerant to the outlet header 13 and the outlet pipe 11.

With particular reference to Figs. 2 and 3, the liquid refrigerant supply conduit 19 for the first cooling coil unit 18 is connected to the inlet header 12 adjacent to the inlet connection thereto and the outlet 21 of this same coil unit 18 is connected to the outlet header 13 at the end of such outlet header furthest removed from the outlet pipe 11. Similarly, the liquid refrigerant supply conduit 19 of the last individual cooling coil unit 18 in the series is connected to the inlet conduit 12 at the end thereof remote from the inlet connection 18; the outlet 21 of this last individual coil unit 18 is connected to the outlet header 13 at a point adjacent to the outlet pipe connection 11. This arrangement of connections of the individual coil units 18 with the inlet and outlet headers 12 and 13 results in a progressive or continuous flow of refrigerant from inlet to outlet thereby eliminating any traps or inactive areas in the circuit. This represents a further feature of the invention which materially contributes to the ability of this system to adequately compensate for rapid changes in temperature and to operate efiiciently under extremely wide load variations.

Each of the individual coil units 18 comprises an upper header 23 to which an outlet pipe 21 is attached, and a lower header 24 to which liquid refrigerant conduit 19 is attached. The refrigerating coils comprise a series of heat transfer tubes which may be attached by welding or the like to upper header 23 and lower header 24. As shown in the drawing these tubes may comprise an outer pair of tubes 26 curved at their ends to properly enter the upper and lower headers 23 and 2 respectively, and a centrally disposed straight tube 27 which communicates with the upper and lower headers 23 and 24. Four groups of these tubes 26 and 27 are illustrated in each coil but this number is merely illustrative and any desired number may be used in accordance with the dimensions or heat transfer requirements of the particular application.

Each individual coil unit 18 is prefabricated prior to introduction into a vessel or reactor and in this operation the upper and lower headers 23 and 24, respectively, are provided with the proper openings and the curved tubes 26 are preshaped and the straight tubes 27 are cut to the proper length. Prior to attaching the tubes 26 and 27 to the headers 23 and 24, upper and lower bracing members 28 and 29 having apertures therein to receive the tubes 26 and 27 are installed thereon and tack welded in their proper location. These bracing members 28 and 29 properly locate and space the tubes 26 and 27 and after installation of the bracing members on the tubes, the latter are attached to the upper and lower headers by welding or the like. Similarly, liquid refrigerant supply conduit 19 is attached to the lower header 24 by welding or the like. After assembly the units are preferably tested to be certain that they are leakproof, both at the welded and the flanged joints.

Since it is sometimes desirable to drain each individual coil unit 18, a removable drain plug 30 is threadedly received in the lower side of lower header 24.

In one application the heat transfer apparatus is mounted within a vessel or reactor 31 having an outer shell 32 and a lining 33 of glass, vitreous enamel, or other suitable substance. In order to circulate materialswithin the reactor an agitator is provided having a rotatable vertical shaft 34 to which a plurality of blades or paddles 35 are connected by radially extending arms 36 affixed to hubs 37 on the shaft. The shaft may extend outside the reactor and be rotated by a suitable power source (not shown).

In accordance with the foregoing description and with particular reference to Fig. 3, it is apparent that the liquid supply conduit 19 for each individual coil unit 18 is relatively large in diameter when compared to the tubes 26 and 2 7; this feature materially contributes to the efficiency of the device in that the liquid refrigerant may flow down wardly through the supply conduit 19 with little resistance to such flow and as the volume of the liquid refrigerant expands during the vaporization the gas flows upwardly through the relatively larger crosssectional area provided for the tubes 25 and 27.

As illustrative of one example of theinvention, a ratio of 8.8 to 1 has been found efiicient for the ratio between the riser area and the downcomer area. This feature represents one of the basic reasons making it possible to pro vide an apparatus of minimum height since the aocumulator may be placed immediately over the reactor and not at a great distance thereabove since the head required to provide gravity flow of refrigerant through the individual cooling units 18 is relatively small. This results from the relationship between the cross-sectional area of the cooling supply conduit 19 and the riser tubes 26 and 27 through which the vaporized refrigerant passes. This relationship is likewise very important in contributing to the ability of the apparatus to accommodate sudden changes in temperature and to handle an extremely wide variation in refrigeration load requirements.

The coil assembly described may be suspended from the upper wall of the shell by suitable means such as bolts 38 from which hang support members 39 attached to the inlet and outlet headers by welding or the like, as is more fully described in the parent application.

As a result of the coil assembly being suspended from the upper wall of the reactor its expansion and contraction may easily take place without producing strains in the reactor, thus eliminating the possibility which would otherwise be present of fracturing the vitreous enamel or glass lining 33 of the reactor shell. This is important since the materials used in the reactor may be corrosive in nature and a fracture of the vitreous lining would be likely to cause damage to the reactor shell 32.

In the use of the coil assembly with a reactor, such as that described which has a manhole access opening, both the individual coil units and the inlet and outlet headers 12 and 13 may be introduced into the reactor through such access opening. The inlet and outlet headers 12 and 13 are provided with flanged joints 40 and 41, respectively, which divide these headers into two arcuate sections so that they may be easily introduced into the reactor through the access opening. After the headers 12 and 13 are assembled and attached to the upper wall of the reactor shell the individual coil units 18 are each attached to the headers by connecting the flanges 15 and 20 of the downwardly extending liquid refrigerant supply conduit 19 and the flanges 17 and 22 of the gaseous refrigerant outlet pipe 21. It will thus be seen that each individual coil unit 18 is suspended from the headers 12 and 13 by the associated flanged joints.

Where the coil assembly is mounted in a reactor in which the material is undergoing chemical reaction and is violently agitated in a generally circular path by movement of the paddles or blades 35, it is necessary that the individual coil units 18 be adequately braced against lateral or swinging movement. This is accomplished by means of the bracing members 28 and 29 which are attached by angle irons or the like 42 and 43, respectively, to annular rings 44 and 45 which in turn are connected to bracket members 46 and 47 secured to the shell 32 of the reactor, as more fully described in the parent application. Since the upper and lower bracing members 28 and 29 embrace the tubes 26 and 27 of the individual coil units and, further, since these bracing members are attached to the shell 32 of the reactor the tube units are retained against lateral or swinging movement under the action of the material within the reactor which impinges against these tubes due to the action of the agitating blades or paddles 35. The bracing members 28 and 29, however, will not prevent expansion or contraction of the tubes or the conduits 19 in a vertical direction.

The disposition of the tubes 26 and 27 forming the individual coil units 18 with relation to the flow of material caused by rotation of the agitating paddles 35 is important in providing for maximum contact between the reacting materials and the surfaces of the tubes 26 and 27 as well as with the inner surface of the shell 32. This produces maximum cooling effect for a given heat transfer area and requires less horsepower input forthe operation of the agitating means, in view of the fact that with the more efficient heat transfer a slower speed may be used.

In carrying out the foregoing, the tubes 26 and 27 which comprise the groups in each individual tube unit are arranged in such a manner that the plane of each group is substantially perpendicular to the radius of the shell 32. Referring particularly to Figs. 2 and 3, it is apparent that rotation of the paddles 35 causes the material within the shell to move in a substantially circular path, the path of movement being in a direction tangential to the circular path through which the paddles move; thus, the material is moved at an angle to the plane of each group of tubes 26 and 27, resulting in improved contact between such materials and the tubes. Furthermore, in View of the fact that the materials being agitated by, the paddles are directed outwardly toward the shell of the reactor, the resulting movement is a rolling motion around the inner surface of the reactor shell. This results in bringing a larger volume of the material into contact with the shell and the tubes than would be the case if the cooling units 18 were not disposed within the reactor shell and the material therewithin merely rotated as a single mass.

Under certain circumstances it may be desirable to pass a relatively non-volatile fluid through the coil units, such as brine, for the purpose of eifecting heat transfer between it and other material in contact with the exterior of the tubes. In such a case, inasmuch as the fluid does not volatilize materially, it would be ineflicient to use an 8 to 1 ratio between the riser area and the downcomer area. In order to provide for this situation, the apparatus described may be simply modified as illustrated in Fig. 8 in order to more nearly equalize the riser and downcomer areas.

In Fig. 8 the upper header 23 has been modified by placing a transverse sheet member or plate 48 thereacross with the lower portion of the plate being positioned intermediate the upper ends of the middle pair of tubes 26 and the upper portion being positioned just to the left of outlet pipe 21, as viewed in Figs. 4 and 8. A further modification is that an elbow 49 is connected between the upper end of the supply conduit 19 and the left end portion of the upper header 23 as viewed in Figs. 4 and 8. With this modified construction fluid entering the supply conduit 19 at the flange 20 will divide and pass downwardly through supply conduit 19 and also through the two tube units to the left of the transverse plate 48. After reaching the lower header 24 the fluid will pass upwardly through the two coil units to the right of the transverse plate 48 and outwardly through the outer pipe 21.

Other modifications for varying the flow path may be simply provided.

Accordingly, it will be seen that the invention includes a relatively simple heat exchange structure including cooling coil units which maybe installed within are actor chamber if desired; the units are prefabricated arid may be introduced into a reactor chamber through the usual manhole opening without requiring anywelded joints after introduction into'the reactor. Furthermore,

the cooling coils are supported within thechamber in such a manner that expansion and contraction thereof is facilitates the transfer of heat and'the agitation of the material within the reactor without producing an un-' desirable increase in the load on the agitator.

Another important feature is that the design of the coils provides for minimum flow resistance internally thereof which permits the achievement of an extremely compact unit with particular regard to its height in that it is only necessary to provide a relatively low head for the liquid refrigerant flowing into the cooling coils. The minimum flow resistance referred to contributes materially to the efficiency of the apparatus and results in obtaining extremely accurate control of the reaction temperatures even though such temperatures may rapidly change and the refrigerant load requirements may cover a very wide range.

It has been found that by utilizing the heat exchange structure described that the reaction time required in a reactor of this nature is very substantially reduced and that reaction temperatures may be maintained within reasonable limits.

It will be obvious to those skilled in the art that various changes may be made in the invention without departing fromthe spirit and scope thereof and, therefore, the invention is not limited by that which is illustrated in the drawing and described in the specification, but only as indicated in the accompanying claims.

What is claimed is:

1. In a heat exchanger, an inlet header comprising a conduit arranged in a partial circle and having an inlet end and a closed end, a discharge header comprising a conduit arranged in a partial circle of substantially the same extent as the inlet header, the two being substantially co-planar and having the same axis, the discharge header having a greater radius than the inlet header and having a closed end adjacent to said inlet end and a discharge end adjacent to the closed end of said inlet header, whereby the inlet header is spaced inwardly of the discharge header, and a plurality of coil units depending from the headers and substantially parallel to the axis thereof, each coil unit comprising a supply pipe having its upper end connected to the inlet header and having its lower end connected to a transverse supply header extending in a direction substantially radially from the axis about which the inlet and discharge headers are formed, a transverse discharge header extending parallel to and above said transverse supply header and spaced just below the inlet and discharge headers, means connecting the transverse discharge header to the discharge header, and a plurality of spaced substantially straight conduits extending from the transverse supply header to the transverse discharge header, the sum of the crosssectional areas of said straight conduits being greater than that of said supply pipe.

2. In a heat exchanger, a horseshoe inlet header having an inlet end and a closed end, a horseshoe discharge header of substantially the same extent as the inlet header, the two being co-planar and having the same axis, the discharge header having a greater radius than the inlet header and having a closed end adjacent tov said inlet end and a discharge end adjacent to the closed end of said inlet header, whereby the inlet header is spaced inwardly of the discharge header, and a plurality of coil units depending from the headers and substantially parallel to the axis thereof, each coil unit comprising a supply pipe having its upper end connected to the inlet header and having its lower end connected to a transverse supply header extending in a direction substantially radially from the axis about which the inlet and discharge header are formed, and a plurality of spaced substantially straight conduits extending from said transverse supply header to said discharge header, the sum of the cross-sectional areas of said straight conduits being greater than that of said supply pipe.

3. In a heat exchanger, a horseshoe inlet header having an inlet end and a closed end, a horseshoe discharge header of substantially the same extent as the inlet header, the discharge having a closed end adjacent to said inlet end and a discharge end adjacent to the closed end of said inlet header, and a plurality of coil units depending from the headers and substantially parallel to the axis thereof, each coil unit comprising a down pipe having its upper end connected to the inlet header and having its lower end connected to a plurality of spaced substantially straight conduits extending to the discharge header.

4. In a heat exchanger, an inlet header comprising a conduit arranged in a substantial circle and having an inlet end and a closed end, a discharge header adjacent to the inlet header and comprising a conduit arranged in a substantial circle of substantially the same extent as the inlet header, the two conduits being substantially coaxial, the discharge header having a closed end adjacent to said inlet end and a discharge end adjacent to the closed end of said inlet header, heat exchange means depending from the headers substantially parallel to the axis thereof, said heat exchange means comprising a plurality of coil units, each coil unit having upper and lower transverse headers, a plurality of substantially straight spaced pipes extending directly between said upper and lower headers, means connecting the upper transverse header to the outlet header, and a downcomer from the inlet header and connected to the lower transverse header.

5. A coil unit of relatively small cross-sectional area and of relatively great heat exchange area, comprising upper and lower parallel headers, heat exchange means connecting the headers, the heat exchange means comprising a plurality of substantially straight equidistantly spaced pipes extending directly between the lower and the upper headers, a down pipe connected to the lower header and extending in parallel spaced relation to the pipes of said heat exchange means, conduit means extending from the upper portion of said down pipe to said upper header, said upper header having an outlet substantially centrally of the connections of said spaced pipes thereto, and a transverse barrier across said upper header and immediately to one side of said outlet, said barrier preventing short circuiting from the upper portion of said down pipe to the outlet and the upper ends of the spaced pipes in direct proximate communication with said outlet.

6. In a heat exchanger and arcuate inlet header and a similar outlet header, a series of individual coil units spaced along each of said headers and comprising a depending liquid refrigerant supply pipe and a group of substantially parallel heat exchange tubes, said liquid re frigerant supply pipe having its upper end connected to said inlet header, a connection between the lower end of said depending refrigerant supply pipe and the lower ends of said substantially parallel heat exchange tubes, and a connection across the upper ends of said heat exchange tubes and to said outlet header.

References Cited in the file of this patent UNITED STATES PATENTS 1,116,646 Thomson Nov. 10, 1914 1,919,029 Lucke July 18, 1933 2,149,954 Brock Mar. 7, 1939

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