US2897838A - Heat exchanger - Google Patents

Description

Augi4, 1959 w. o. WEBBER ET AL 2,897,338 HEAT EXCHANGER Filed July 29, 1957 FIG. I.

ALKLATION I Asmsmofl OLEFINS 2 1 AND ISOPARAFFINS '51 v I AEMULSION PUMP l3 1% I4 27 was MAKE UP ACID 22 37 u 11 1W i 5 37a -38 FIG. 2.

FIG. 3.

t INVENTORS. W|H|am O. Webber, J Delmos A. Smith,

United States Patent Chi ice HEAT EXCHANGER William 0. Webber and Delmas A. Smith, Baytown,

Tex., assignors, by mesne assignments, to Esso Research and Engineering Company, Elizabeth, N.J., a corporation of Delaware Application July 29, 1957, Serial No. 674,807

3 Claims. (Cl. 138-38) The present invention is directed to a heat exchanger. More particularly, the invention is concerned with a heat exchanger having improved heat transfer characteristics. In its more specific aspects, the invention is directed to a heat exchanger of the shell and tube type provided with means in the heat exchanger tubes for improving heat transfer characteristics.

The present invention may be briefly described as a heat exchanger of the shell and tube type having improved heat transfer characteristics which comprises an elongated supporting member longitudinally arranged in each of the tubes of the heat exchanger and a plurality of horizontally spaced apart means carried on and supported by the supporting member for creating turbulent flow in the tubes, the supporting member being arranged against the walls of the tubes and the turbulent flow creating means being preferably substantially co-axial with the tubes.

The turbulent flow creating means employed in the present invention suitably comprises a plurality of discs arranged on and supported by an elongated supporting member arranged in the tubes of the heat exchanger, the supporting member being arranged along the Walls of the tubes while the discs are arranged to project into the path of flow through the tubes to cause mixing or turbulence. The supporting member is preferably 'a crimped metal wire having metallic discs welded to the wire on the inner side of the crimps. The wire may carry discs hon'zontally spaced apart a distance in the range from about 0.25 to about feet. Discs spaced apart about 1 foot give very desirable results.

The discs are preferably concentric with the tubes but may be arranged eccentric with respect to the axis of the tubes.

The turbulent flow creating means or discs may be suitably sized to provide an area of flow through the tubes no greater than about 75% of the diameter of the tubes to create the turbulence. Desirable results are ob tained with an area of flow of about 64% of the tube diameter.

The invention is directed also to heat exchangers Which employ finned tubes which serve to increase the efficiency of the heat exchanger.

The present invention is particularly adaptable for use in reactions involving mixing of dissimilar fluids. For example, it is suitable in alkylation reactions where an emulsion of acid and hydrocarbon reactants is contacted.

In using the present invention in alkylation reactions, the emulsion is circulated through a heat exchanger employing the present invention which serves to improve the heat transfer rate and improve efficiency of the operation.

The invention will be further illustrated by reference to the drawing in which:

Fig. l is a schematic flow diagram showing the present invention used in an alkylation reaction;

Fig. 2 is a cross-sectional view of a heat exchanger 2,897,838 Patented Aug. 4, 1959 tube provided with a supporting member and discs in accordance with the present invention; 7

Fig. 3 is a partial view of the supporting member of the present invention;

Fig. 4 is a view showing a disc attached to the supporting member; and

Fig. 5 is a view taken along the lines 5-5 of Fig. 4;

Referring now to the drawing, and particularly to Fig; l, numeral 11 designates an alkylation reactor into which a mixture of olefins and isoparafl'ins is introduced by way of line 12. The olefins may suitably comprise butylenes or pentylenes, while the isoparaffins may suitably comprise isobutane, isopentane, and the like. While these particular olefins and isoparafiins in an alkylation reaction are given by way of illustration and not by way of limitation, the invention is applicable to many types of reactions involving heat transfer. The mixture of olefins and isoparafiins, with the olefins and isoparalfins employed in a ratio in the range from about 1:2 to about 1:10, is contacted in the alkylation reactor 11 with an emulsion of the hydrocarbon reactants and a sulfuric acid catalyst introduced into the system by way of line 13, controlled by valve 14. The sulfuric acid may have a strength in the range from about to about percent H 80 The emulsion is circulated through the alkylation reactor 11 by way of line 13 to which the emulsion is supplied by way of line 15 from a source which Will be described further, and the admixture is suitably contacted in reaction zone 11 to cause the reaction to proceed to form an alkylated product. The product is withdrawn from reaction zone 11 by way of line 16 and dis charged into a product accumulator 17 which is of sufficient capacity to allow a separation to be made between the acid and hydrocarbon components of the emulsion, The separated hydrocarbon product is withdrawn by way of line 18 for separation of high octane number constituents therefrom, while the acid phase of the emulsion is withdrawn by way of line 19 and may suitably be reintroduced into the system as may be desired.

Since the reaction proceeds best at a temperature in the range from about 35 to about 55 F., it is desirable to maintain a temperature within this range at about 40 F. To this end, a portion of the emulsion is withdrawn from the alkylation reactor 11 by line 20 and introduced into a heat exchanger 21 of the shell and tubetype, wherein the emulsion is circulated through the bank of tubes 22 and, with heat transfer from a body 23 of evaporating light hydrocarbon, is suitably .cooled on passage through the bank of tubes 22. The

cooled emulsion is then discharged from the bank of tubes 22 by way of line 24 into an emulsion accumulator 25 for recirculation by way of line 26 and line 15 back into the alkylation reactor 11. It is to be noted that line 15 is provided with an emulsion pump 27, and line 26 is provided With a valve 28 for discharge of acid to maintain the strength of the acid in the system by introducing a like amount of fresh acid by way of line 13, controlled by valve 14.

The temperature control in heat exchanger 23 is maintained by evaporating the light hydrocarbon, such as butane, forming the body 23. To this end, vapors of the light hydrocarbon are withdrawn fromthe vapor space 29 by way of line 30, compressed in compressor 31, then introduced by line 32 into cooler 33, from whence the cooled and compressed vapors are introduced by line 34 into a condensate drum 35, wherein the condensate accumulates for return by line 36 to the body 23.

The tubes 22 of heat exchanger 21 have arranged in each of the tubes 22 an elongated supporting member 37, which is shown more clearly in Fig. 2. The elongated supporting member 37 is formed to provide crimps 37a to which the discs 38 are attached by spot Welding,

It is to be noted that the elongated supporting member 37, which suitably may be a wire of suflicient strength, is arranged along the wall of tubes 22 while the crimps and the discs attached thereto project across the tubes such that the discs are preferably co-axial with the axis of the tubes 22.

Referring to Figs. 3, 4, and 5, the supporting member 37 and the discs 38 are shown more clearly. Referring to Fig. 3, the supporting member 37 is provided with crimps 37a throughout its length, with the crimps having an overall height of about 0.77. The supporting member 37 may suitably be constructed of 12 gauge type 304 wire.

Referring to Figs. 4 and 5, it will be seen that the discs 38 are welded by spot Weld 39 to the inner surface of the crimps 37a.

As an example of a heat exchanger having tubes of about 16.5 in length, a wire supporting member will be provided with about 15 crimps about 12" apart, to which the discs will be welded. These discs may have an outside diameter of about 0.4" and be about A thick.

The discs may suitably be constnucted of metal, but

may be constructed of other material which is resistant to the fluids with which it comes into contact. For example, the discs may be constructed of a plastic, such as Teflon, which is polytetrafluoroethylene. Other suitable construction materials for the discs may include Hastelloy B and other alloys of a similar nature.

The present invention is quite advantageous and useful in that it improves heat transfer, and in an alkylation operation such as described, the improved heat transfer allows the use of a lower over-all temperature difference. For example, when butane is evaporating outside the tubes of the heat exchanger 21, inside of which flows an emulsion of acid and hydrocarbon reactants, the butane on the outside of the tubes may evaporate at a higher temperature than heretofore. temperature means that evaporation may be conducted at a higher pressure and thus the refrigerant vapors are sent to the compressor at a higher suction pressure, which allows the compressor to work through a lower compression ratio, defined as discharge pressure divided by the suction pressure, which requires less horsepower. For example, a horsepower savings of about 500 may be achieved employing the present invention in a heat exchanger system in an alkylation reaction.

The present invention has been used successfully over a long period of time in a commercial alkylation plant in which olefins are alkylated with isoparaflins using sulfuric acid as a catalyst. By employing the present invention, heat transfer rate was increased approximately to 50 percent over that obtainable prior to installation of the present invention.

Operation at an increased The placement of a supporting member adjacent the wall of the heat exchanger tubes does not increase the pressure drop substantially. In other words, the effect of the supporting member on pressure drop is negligible, and the pressure drop experienced by employing turbulent fiow creating means is accounted for substantially by the installation of the metal discs on the metallic sup porting member.

The size of the metallic discs employed on the supporting member is selected such that they are substantially equal in diameter to provide an area of flow through the tubes no greater than about percent of the diameter of the tubes. In other words, the passage around the metallic discs should be below about 75 percent of the pipe diameter. In a commercial installation very satisfactory results were obtained with about 64 percent area open for flow.

The nature and object of the present invention having been completely described and illustrated, what we wish to claim as new and useful and secure by Letters Patent 1. A heat exchanger tube adapted for use in a heat exchanger of the shell and tube type, said tube having improved heat transfer characteristics and having an elongated crimped wire longitudinally arranged therein, and a plurality of horizontally spaced apart discs secured to the wire on the inner side of the crimps, said wire being arranged against the wall of the tube and said disc being substantially coaxial with the tube.

2. A heat exchanger tube in accordance with claim 1 in which the discs are sized to provide an area of flow no greater than about 75% of the diameter of the tubes.

3. A heat exchanger tube adapted for use in a heat exchanger of the shell and tube type, said tube having improved heat transfer characteristics and having an elongated crimped wire longitudinally arranged therein,

and a plurality of horizontally spaced apart discs secured to the wire on the inner side of the crimps, said discs being substantially equal in diameter, said wire being arranged against the wall of the tube, and said discs being substantially coaxial with the tube.

References Cited in the file of this patent UNITED STATES PATENTS

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