US3364990A

US3364990A - Impingement protection for heat exchanger

Info

Publication number: US3364990A
Application number: US501696A
Authority: US
Inventors: Frank L Rubin
Original assignee: Frank L. Rubin
Current assignee: FRANK L RUBIN
Priority date: 1965-10-22
Filing date: 1965-10-22
Publication date: 1968-01-23
Anticipated expiration: 1985-01-23

Description

F. L. RUBIN Filed Oct. 22, 1965 IMPINGEMENT PROTECTION FOR HEAT EXCHANGER Jan. 23, 1968 2 1, f ag:

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United States Patent Ofifice 3,34,9% Patented Jan. 23, 1%68 Filed Oct. 22, 1965, Ser. No. 501,696 2 Claims. (Cl. 165-134) ABSTRACT OF THE DISCLGSURE This disclosure is directed to providing impingement protection for the tubes of a heat exchanger by positioning a body of closely interwoven impervious elements in the throat of the nozzle directing flow into the exchanger. The arrangement of the nozzle and body is such that all flow into the exchanger is directed through the body of the interwoven impervious elements in entering the heat exchanger. The gaseous medium and liquid droplets, or other non-gaseous elements, entrained in the flow all pass through the body with the interstices formed by the interwoven impervious elements permitting gaseous medium to flow freely into the heat exchanger whereas the imperious elements interrupt flow of the liquid droplets reducing their velocity so that, although the liquid droplets eventually pass through the body, they are discharged onto the tube bundle at a velocity which is not suificient to cause erosion due to direct impingement on the tubes.

This invention relates to heat exchangers and, more particularly, to protection of the tube bundle of the exchanger from erosion by fluid impingement, or the like.

In certain applications, it is necessary to protect the tube bundle against undesirable direct impingement by fluids entering the exchanger, particularly where such fluids are condensable vapors. If condensation occurs before the vapors enter the exchanger, liquid droplets are formed in the vapor and travel along at approximately the vapor velocity. Vapor velocity is generally quite high and droplets traveling at such high velocities can have an erosive effect on the tubes. Common practice is to place a generally imprevious plate at the nozzle to intercept the droplets and prevent their impinging directly on the tubes. In order to meet standard requirements for bundle entrance area, i.e. sufiicient open area at the point of entry of fluid from the nozzle into the tube bundle area to insure proper flow of fluid, it has been common practice, Where impingement protection is provided, either to place the impingement plate in the tube bundle area which necessitates eliminating a number of tubes to accommodate the plate, or to place the impingement plate in the throat of the nozzle and provide an enlarged external enclosure in the nozzle to accommodate the plate. Another proposed solution places the impingement plate within the exchanger shell and increases the shell diameter to accommodate the impingement plate so that there is no need to eliminate any tubes. The former has the disadvantage of decreasing the exchanger capacity and the latter two add to the basic cost of the exchanger. It should be noted at this point that, in some designs, even without provision for fluid impingement protection it may be necessary to eliminate some tubes at the nozzle to insure adequate bundle entrance area and desired fluid flow, placing the impingement plate in the bundle area increases the number of tubes which must be removed to provide the proper bundle entrance area thereby reducing the capacity of the heat exchanger.

This invention is directed to the solution of this problem of impingement protection and has as a general object the provision of improved impingement protection for the tube bundle of a heat exchanger.

A more specific object is to provide an improved, eifective and economical arrangement for achieving such fluid impingement protection while maintaining a compact and simple exchanger construction of desired capacity.

For the achievement of these and other objects, this invention proposes to place an impingement protective device at the inlet nozzle of the exchanger and preferably confined to an area within the nozzle throat. The impingement protective device preferably has a mesh-type construction being made up of interwoven fibers, or similary meshed elements, cooperating to form a network of interstices and impervious elements. The interwoven or meshed elements efiectively intercept and markedly reduce the velocity of any entrained droplets 0t liquid while the interstices provide suflicient open area to permit free passage of vapor into the interior of the exchanger shell, and the impingement protection arrangement of this invention requires the removal of no more tubes than might be required if impingement protection were not provided.

Other objects and advantages will be pointed out in, or be apparent from, the specification and claims, as will obvious modifications of the single embodiment shown in the drawings, in which:

FIG. 1 is a side elevation partially in section of a portion of a heat exchanger incorporating this invention;

FIG. 2 is a section through the nozzle area of the heat exchanger and taken generally along line 22 of FIG. 1;

FIG. 3 is a plan view looking into the inlet nozzle gen erally in the direction of the flow indicating arrow in FIG. 2; and

FIG. 4 is an enlarged perspective view of a portion of the interwoven body of the impingement protective device.

Throughout this description reference Will be made to a heat exchanger and it is intended that this term he used in its broader meaning to relate generally to heat exchanger units such as feed water heaters, condensers, reboilers, steam heating units, etc. Since a complete illustration and description of the heat exchanger is not necessary to an understanding of this invention, only a portion of a heat exchanger is illustrated in FIG. 1. The heat exchanger includes an outer shell 10 and tube bundle 12 of conventional construction supported in the shell in a well-known manner. Inlet nozzle 14 communicates with the interior of the shell through opening 16 in the shell and extends outwardly of the shell leaving the shell interior open for receipt of the tubes. A suitable flange 18 is provided adjacent the outermost end of the nozzle to cooperate in connecting the exchanger to an appropriate system conduit (not shown) through which a particular process medium is delivered to the exchanger. In accordance with common practice this medium may be in the form of a vapor, or a liquid or a mixture of liquid and vapor, and is directed into the interior of the shell where it passes from the inlet nozzle through a series of internal bafiies 20 over and around the tube bundle and is expelled from the exchanger through a suitable outlet passage 23. It will be appreciated that headers (not shown) of suit able construction are generally provided at the opposed ends of the exchanger shell. Also, for convenience the tube bundle has not been shown in FIG. 1.

In various system applications the vapor directed into the shell interior through nozzle 14 is condensable and is directed into the tube bundle area at a relatively high velocity. Being condensable, the possibility exists of portions of the vapor condensing in the form of droplets which become entrained with the vapor and enter the shell at a relatively high velocity. The droplets traveling at a high velocity strike the tube bundle and can have an erosive effect on the tubes. This invention proposes an effective solution to the problem of erosion due to fluid impingement on the tube bundle and one which maintains the capacity, simplicity of construction and compactness of the basic heat exchanger construction. More particularly. a fluid impingement protective assembly 22 is positioned in the throat of nozzle 14. The impingement protective device includes a body 24 comprising a plurality of interwoven impervious fiber-like elements 26 which are closely woven and form a network of interstices 28 therebetween. Fiber elements 26 of body 24 maintain a somewhat assembled form by virtue of their being interwoven with each other. To insure maintaining the interwoven nature of the fiber elements, body 24 is supported between grid supports 30 and 32 which extend over the oppositely facing, outer surfaces of body 24. Grid supports 30 and 32 are each made up of interconnected

strips

31 and 33 arranged with a relatively wide spacing therebetween to provide adequate support for fiber elements 26 of body 24 while offering negligible interference to the passage of the vapors through the body and the nozzle. Grid supports 30 and 32 are preferably suitably attached to body 24, for example by wires 34 extending between the grid supports and tying the grid supports and body in a unitary assembly.

In assembly impingement protective device 22 is placed in nozzle 14 and rests on a plurality of supports legs 36 spaced around the inner Wall of the nozzle. Support lugs 36 are positioned at the outlet end of nozzle 14 and preferably position impingement protective device 22 within the nozzle so that it does not project into the tube bundle area. The protective device can be attached to the support plates as by wires 39, however, other means of attachment can be used.

The vapor medium flowing through the nozzle passes through interstices 28, as illustrated by the arrows in FIG. 1 and FIG. 4, and the impervious fiber elements 26 have virtually little effect on the velocity of the vapors. However, any droplets (or foreign particles in general) entrained with the vapors will be interrupted in their flow through body 24 by the impervious elements and their velocity issubstantially retarded. These droplets will eventually pass through body 24 and be discharged from the impingement protective device 22 but at the time they leave the protective device their initial velocity is substantially zero and because of the closeness of the tube bundle to the nozzle inlet they cannot attain a sufiiciently high velocity in that short distance to erode the tubes (see FIG. 2).

It will be appreciated that impervious elements 26 can be of any suitable material, for example, they can be wire mesh or screen, steel, copper or stainless wool, or Raschig rings or any equivalent type of packing which will pass the vapors but interrupt the flow of liquid droplets. Also, it is possible that screening could be used, i.e. one or more screens could be placed at the nozzle to pass the vapor and interrupt liquid droplets or the like.

Grid supports 30 and 32 do not extend completely over the oppositely facing surfaces of body 24 but terminate in spaced relationship from the outer periphery of the body and the body extends beyond the supports. Preferably body 24 has a relaxed or free dimension which is greater than the inner diameter of nozzle walls 37. In this manner a transverse sectional area of the nozzle is completely filled with the network of impervious fibers and interstices and body 24 is slightly compressed in the area of the nozzle walls so that all vapor flowing into the exchanger must pass through the impingement protective device and, moreover, a denser obstruction to fluid flow is provided at the nozzle walls.

With this arrangement adequate fluid impingement protection is provided and the network of fibers and interstices inherently provides sufiicient entrance area to acof any tubes, or at least no more tubes than would be required with no impingement protection being provided,

' nor any modification ofthe exchanger.

Although but one embodiment of the present invention has been illustrated and described, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit'of the invention or from the scope of the appended claims.

I claim:

1. In a heat exchanger having a shell, a tube bundle in said shell and an inlet nozzle opening through said shell to said tube bundle, the improvement of impingement protection means in the path of flow of a medium through said nozzle into said shell and characterized by a body 7 of a plurality of impervious elements interwoven with each other and defining a network of interstices, said interstices passing a gaseous medium freely into said shell and providing, within said impingement protection means, a prescribed amount of entrance area into said shell to accommodate a given amount of gaseous medium flow into said shell, said impervious elements interrupting the passage of non-gaseous elements through said nozzle and retarding the speed thereof so that said non-gaseous elements leave said impingement protection means at a ve- I locity substantially below the velocity of said gaseous medium and insufiicient to erode the tubes of said tube bundle as a result of impingement of said non-gaseous elements upon said tubes, said body of impervious elements extending to and engaging the inner walls of said nozzle so that said body substantially fills a transverse sectional area of said nozzle and all medium passing through said nozzle passes through said combination of interstices and impervious elements, and the relaxed peripheral dimension of said body being greater than the inner dimension of the walls of said nozzle and said body is compressed in the area of said walls so that said impingement protection device is relatively denser adjacent said walls.

2. In a heat exchanger the combination of a shell, a

plurality of tubes supported within said shell, means de-- fining an inlet nozzle opening into said shell, an impingement protection device disposed in the path of flow through said nozzle for protecting said tubes from erosion by high velocity impact thereon of liquid droplets or the like entrained with a gaseous medium flowing into the exchanger through said nozzle, said impingement protection device comprising a body of interwoven members and having oppositely facing surfaces spaced apart in the direction of flow through said nozzle, said body disposed wholly within said nozzle, support means in engagement with and extending over each of said surfaces, said support means being of generally open construction to support said body without interfering with flow through said impingement protection device, said support means extending transversely of said flow path and said body extending beyond the termination ofsaid support means and engaging the interior walls of said nozzle, said body 'below that of the gaseous media and insufficient to erode said tubes as a result of impingement of said droplets upon 7 5 6 said tubes, the spacing between said impervious elements References Cited providing, within said impingement protection device, a UNITED STATES PATENTS prescribed amount of entrance area into said shell to accommodate a given amount of gaseous media flow into 1,534,671 5/1926 SIePPY 165 119 X said heat exchanger, and the relaxed peripheral dimension 5 2366339 12/1960 Morgan 165 134 X of said body being greater than the inner dimension of 3,087,474 4/1963 Catha 165 119 X the walls of said nozzle and said body being compressed in the area of said Walls so that said impingement pr0tec- ROBERT 0 LEARY Pnmary Exammer tion device is relatively denser adjacent said walls. M. A. ANTONAKAS, Assistant Examiner.