US2801824A - Self-cleaning heat exchanger - Google Patents

Description

Aug. 6, 1957 I J. TAPROGGE 2,801,824 SELF-CLEANING HEAT EXCHANGER Filed Feb. 2, 195:5 V 5 Sheeis-Shegt 1 Inventor."

JOSEF TAPRQG'GE BY K, K ATTORN 'Aug. 6, 1957 I J. TAPROGGE 2, 1,

SELF-CLEANING HEAT EXCHANcER JOSEF mm'oaaf J. TAPROGGE SELF-CLEANING HEAT EXCHANGER Aug. 6, 957

5 sheeti eet 5 Filed Feb. 2 1953 Inv or w JOSE TA OGGE AT ORNH Aug. 6, 1957 J. TAPROGGE 2,801,324

SELF-CLEANING HEAT EXCHANGER Filed Feb. 2,1953 I 5 Sheets-Sheet 4 Inventor JOSEF. TAPROGGE l(. A.

ATTORNEY Filed Feb. 2, 1953 Aug. 6,11957 JITAPROGGE I I 2,801,824 v SELF-CLEANING HEAT EXCHANGER I 5 Sheet's-Sheet 5 lure/710R aosEr mmosa:

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ATTORNEK United States Patent SELF-CLEANING HEAT EXCHANGER Josef Taprogge, Essen-Kupferdreh, Germany Application February 2, 1953, Serial No. 334,687

9 Claims. (Cl. 257-1) This invention relates to a method and an apparatus for self-cleaning heat exchangers of the tube-type, i. e. at which a heat transition is effected between two media, one of these media being conveyed through sets of tubes connected in parallel and the other medium passing through the space between these tubes. Since this invention afiords great advantages especially in the use for vacuum condensers, mainly this kind of heat exchangers is in the following referred to. Naturally, the invention is not restricted to this kind but may be used advantageously with all other kinds of heat exchangers of the tube-type.

As known by all skilled in the art, the efiiciency of a heat exchanger of the tube-type is unavoidably lessened after some time of operating the exchanger. This is due to deposits along the tube walls, especially to deposits at the inner tube walls. Such deposits are caused by mechanical impurities carried with the medium such as cooling water passing through the tubes and/or by substances contained in this medium in a state of solution but precipitated therefrom by thermal and/or chemical influences. These deposits impede the heat transition or transfer through the tube walls and deteriorate the efiiciency of the heat exchanger. When this elficiency is lowered to a certain fraction of the original one, the tubes have to be cleaned mechanically and/or chemically.

Many methods and apparatus are in use for removing impurities and other noxious substances from the medium passing through the tubes and for periodically cleaning these tubes. Forinstance, chlorine is added to the fresh cooling water for precipitating the above named organic substance entering into the tubes. Or, mechanical impurities are removed by filtering the fresh water. Furthermore, in circulation cooling systems the increased hardness of the circulating cooling water due to evaporation is counteracted by chemically softening the water. All 7 these methods are rather expensive and are, therefore, not in common use. As a rule, the tubes of the tube-type heat exchangers are only periodically cleaned by mechanically and/or chemically removing the above named deposits from the tube walls.

Loose sludge may be removed by increasing the velocity of the cooling water, by condenser rinsers and the like, solid sludge is removed by ordinary wire brushes, while very hard sludge deposits are drilled out, and solid stone, such as lime deposits are dissolved chemically. In all the possibilities referred to it is not always easy to remove the deposits entirely without damaging the tubes. Furthermore, the cleaning of the tubes can only be effected when the condenser is wholly or partly out of operation or while working at a reduced load and with a correspondingly impaired vacuum.

Due to the fact that each subsequent cleaning of the condenser can only be effected after acertain period of time, the level of the average heat transition of the cooling tubes, or of the condenser efficiency is, in many cases considerably lower than the maximum values obtained 2,801,824 l 'atented Aug. 6, 1957 immediately after the cleaning. For reasons connected with the operation of the plant sometimes the operating period of the condenser ascertained as being economical has to be exceeded, the average vacuum of the condenser being further impaired as a necessary consequence of this. With the methods of cleaning hitherto customary, the average vacuum of a condenser cannot be further improved appreciably in view of the high costs of a preliminary treatment or conditioning of the cooling water.

The present invention has for its main object to provide a method which, due to its character and the simplicity of means, only involves low initial and operating costs but enables a continuous automatic or self-cleaning of the tubes and the average condenser vacuum to be considerably increased thereby.

According to the invention, the heat exchanging elements, such as cooling tubes, are automatically cleaned by rubbing bodies in turns at short intervals during the operation of the heat exchanger such as a vacuum condenser, these rubbing bodies being carried along the tube walls by a liquid medium, such as cooling water, on its way through the condenser, the cooling water serving as the carrier liquid and within the cooling tubes as pressure medium for the rubbing bodies. Advantageously, the rubbing bodies are moved through the heat exchanger in a continuous circulation intercepted at the outlet of the spent medium by a suitable device and returned again into the fresh liquid medium supplied to the heat exchanger. The spent cooling water, i. e., the heated cooling water leaving the condenser may be conducted through a device permitting the water to flow on unimpeded into the outlet conduit, while the rubbing bodies are intercepted and may be conducted in a branch stream of the heated cooling water into a return conduit through which, for example, by mean-s of a pump, such as a return pump, they are re-introduced into the fresh cooling water flowing into the condenser, thus once more commencing their circulation.

The invention also provides a method and apparatus for cleaning and reconditioning the rubbing bodies after use. According to this feature of the invention the rubbing bodies, after leaving the cooling tubes of the condenser or the like, are conducted in continual succession over a cataract which permits the flow of water to pass substantially without hindrance but which, like a sieve, holds back the rubbing bodies, subjecting the same to repeated dropping impacts producing elastic deformation, whereby the bodies get rid of retained foreign particles and are regenerated.

According to a modification of this method a portion of the rubbing bodies leaving the cataract may be withdrawn, preferably by means of a lock device, from the shunt circuit and then re-introduced after thorough regeneration or replaced by other bodies. The method may be further modified by providing the rubbing bodies with a coating of abrasive material.

The invention is illustrated by way of example in the accompanying drawings in which:

Fig. 1 is a diagram showing a condenser plant incorporating one embodiment of the present invention,

Figs. 2 and 3 show modifications thereof,

Figs. 4 and 5 are an axial section and plan view respectively of one form of cleaning device for the rubbing bodies,

Figs. 6 and 7 are details thereof shown at a larger scale,

Figs. 8 and 9 illustrate the manner in which the device may be cleaned,

Figs. 10 and 11 are sectional views illustrating two modifications,

Fig. 12 is an axial section of another modification,

Fig. 13 is a cross-section on line A-B of Fig. 12, and

these bodies.

3 Fig. 14 is a diagrammatic view showing an axial acceleration pump for use in conjunction with the method of the present invention.

Referring first to Figs. 1 to 3 the condenser elements, such as cooling tubes 19, are arranged to be cleaned by rubbing bodies 27 in turn at short intervals during the operation of the condenser, the condenser liquid such as cooling water serving, on its way through the condenser, for carrying the rubbing bodies along and also acting, within the cooling tubes, as pressure medium for During the cleaning of the condenser tubes the rubbing bodies move in a continuous circulation by being conveyed through the condenser by the cooling water, intercepted at the condenser outlet 21 by a suitable device 23 and returned again into the cooling water supplied to the condenser by a cooling water pump 16; The heated cooling water leaving the condenser passes the device 23, the latter permitting the cooling'water to flow on unimpeded into an outlet conduit 22, while causing the rubbing bodies to be intercepted and conducted in a branch stream of the heated cooling water into a return or shunt conduit 24 through which they are re-introduce-d (Figs. 1 and 2) by means of a pump 25 into the fresh cooling water flowing into the condenser at the condenser inlet side, thus once more commencing their circulation.

The intercepting and conducting device for the rubbing bodies may consist of a funnel-shaped strainer 23 or of a screen or grating arranged within the condenser outlet pipe 22 and connected to a return device for the rubbing bodies. This device may comprise a return pipe 24 equipped with a return pump 25, which may be constructed as a centrifugal pump, water injector pump, or the like. a

It is generally possible to convey the rubbing bodies without damage through the condenser cooling water pump 16. In this case (Figs. 2 and 3) the return conduit 24 for the rubbing bodies may open into the suction pipe of the condenser cooling water pump 16. Since, on the other hand, in most practical cases, a substantial pressure difference exists between the condenser outlet conduit 22 and the suction pipe 15 of the cooling water pump 16, a separate return pump for recirculating the rubbing bodies is unnecessary. Such an arrangement ofiers a particularly advantageous and simple form of apparatus for carrying out the method of the invention, since in addition to the particular rubbing bodies only the intercepting and conducting device 23 at the con-denser outlet and the return conduit 24 to the suction pipe 15 of the condenser cooling water pump 16 are necessary for completing the installation.

The rubbing bodies impinging upon the intercepting device 23 provided in the condenser outlet tubes 22 are there cleaned by the heated cooling water passing therethrough and return into the circulation in a regenerated, i. e., clean condition.

The elasticity and size of the rubbing bodies is so chosen that as great as possible a rubbing surface can be formed in the cooling tube. This is obtained by giving to the rubbing bodies a free diameter which is at least as great as the internal diameter of the tubes through which the rubbing bodies move, although in practice it is preferable to use a greater diameter. The rubbing bodies are subjected in the cooling tubes to a maximum drive corresponding to the pressure drop which in operation of the condenser develops between the inlet and outlet ends of the cooling tubes 19 or of the water passages 20 in' the condenser. This pressure drop corresponds mainly to the resistance to flow which the cooling water normally undergoes while passing through the cool ing tubes. In order to avoid the risk of the tubes becoming blocked, this drop must be so great as to enable the cooling water to convey,if necessary, a plurality of rubbing bodies simultaneously through a coolingtube. This safety factor must be also taken into consideration in choosing the elasticity and size of the rubbing bodies. If the contamination of the cooling water is low, it is not generally necessary to choose the cross-section of the rubbing bodies greater than that of the cooling tubes, the irregular movement of the rubbing bodies in the cooling tubes being sufficient for effecting the cleaning.

As material for the rubbing bodies sponge rubber is particularly suitable. The cleaning effect of this porous substance is so great that the deposits, which in view of the frequent cleaning of each individual tube are only minute, are entirely removed during each cleaning operation. While the rubbing bodies are forced through the cooling tubes by the cooling Water, the water conveys the deposits and other impurities detached from the walls of the tube in front of the rubbing bodies, thereby preventing the rubbing bodies from becoming excessively soiled.

With regard to the shape of the rubbing bodies, a spherical shape is particularly advantageous. The fact that the surface of a sphere is small in relation to its volume permits a long use of the bodies. Furthermore, the resistance of a spherical body is approximately equal in all positions, which is of particular importance at the entry of the rubbing bodies into a cooling tube. Moreover, the interception and return of spherical rubbing bodies after passage through the condenser is relatively easy owing to the rolling movement of the bodies.

Since the specific weight of the rubbing bodies may be chosen equal or almost equal to that of water, they float in the cooling water. This floating and the stirring of the bodies by the pump 16 or by a special stirring apparatus 28 in the supply passage 17 and in the water chambers 18 of the condenser ensures a uniform distribution of the rubbing bodies through all the cooling tubes and therewith a uniform and satisfactory cleaning of all cooling tubes. In each case with a suitable number of the rubbing bodies held in circulation a perfect cleaning of all cooling tubes is effected. The impurities are removed from the cooling tubes in the shortest possible time according to the number of the rubbing bodies without the danger that any soiling of the cooling device of any practical significance may first take place. By choosing the number of rubbing bodies in accordance with the cooling water qualities and the cooling surface of the condenser, and by the possibility of using at the same time rubbing bodies having different friction qualities, the maximum possible heat transition may be maintained in the cooling tubes.

In this method of self-cleaning, the cooling water capacity of the condenser is almost not influenced by the presence of the rubbing bodies. The fact that a small amount of heated cooling water enters into the fresh cooling water with the returned rubbing bodies has likewise little practioal effect upon the vacuum obtained in the condenser, more particularly in view of the gain which is permanently obtained by the relatively clean condenser cooling surface. i

The device 23 for cleaning the used rubbing bodies may, with advantage, be constructed as a funnel-shaped cataract, and one suitable form will now be described with reference to Figures 4 to 8. A funnel-shaped cataract or intercepting device 2 is mounted in the cooling water outlet pipe indicated by reference numeral 1 whereby the rubbing bodies are intercepted at the lowest point 3 of the funnel-shaped cataract and thereupon are returned to the shunt or return tube 4 of the water circulation circuit. The cataract 2 is formed of individual rings 6 disposed coaxially in a step-like manner and held together by supporting bars 5. As will be seen more clearly inFigs. 6 and 7, the rings 6 are stream-lined in cross-section, that is to say, their cross-section may be drop-shaped or shaped similarly to steam-turbine blades. The spacing a of th e'rings 6 must be smaller than the diameter of the rubbing bodies 7. It is, however, advisable to reduce this spacing further to a value smaller agar-e24 than the radius r of the bodies 7 in order to avoid the risk of any rubbing bodies becoming wedged and stuck between the rings. In this manner it is ensured that the rubbing bodies 7 will roll downwardly over the rings 6.

The rings of the cataract are preferably staggered in such a manner that the flow of cooling water can only cause the rubbing bodies to impinge upon, and thus be pressed against, the edge of one ring at a time ensuring particularly high deforming pressure on the rubbing bodies. Owing to this, the rubbing bodies are relatively heavily compressed and in repeated alternation subsequently expanded whereby the rubbing bodies get rid as completely as possible of any particles of deposits and other impurities carried along. The flow resistance of the cataract funnel may be reduced to a very small amount by smoothing the ring surfaces, for example, by enamelling them or coating them with foil. The direction of flow prescribed for the interception and conduction of the rubbing bodies is produced by the blade rings of the funnel-shaped cataract 2 or, if necessary, by deflector sheets placed in front of it. The cooling water thus conducts the rubbing bodies to the middle of the funnel and into the return conduit 4 provided thereat. The height of the funnel-shaped cataract device is advantageously approximately equal to the radius of the cooling water conduit.

The cataract funnel 2 is adapted to be tilted, during the operation of the condenser, about two trunnions 8 or a shaft secured on a holder ring 9 (Figs. 8 and 9). In this manner impurities which have settled between the blade rings may be rinsed off.

The smoothening of the blade surfaces, for example the enamelling, is simpler in the case of the insertible blade rings than in the case of the straight bars of a rake or grate, because the latter are usually rigidly connected to cross bars and 'are therefore liable to become warped at the high temperatures of the enamelling process.

Referring now to a modified form of the funnel cataract illustrated in Figs. 10 and 11, the funnel is divided in two halves, which halves are adapted to be tilted apart as shown in Fig. 11.

In a further modified construction illustrated in Figs. 12 and 13, a rotatable scraper 10 is arranged inside the cataract funnel 2, this scraper being adapted to be put into rotation by means of a shaft 11, for example under the action of a turbine blade 12 actuated by the flow of water, the rotation taking place continuously or at intervals as desired.

In addition to these described possibilities of the automatic cleaning of the funnel-shaped cataract, taking place from time to time or continuously, there are also other possibilities which cannot all be here described in detail.

For the acceleration of the water circulation through the shunt or return conduit 4 use may be made of an acceleration pump according to the invention of special construction as schematically illustrated in Fig. 14. In Figure 14, reference numeral 13 indicates a substantially cylindrical rotor the peripheral surface of which takes the water along in a spin-like manner and by boundary layer adhesion. By means of a stationary flow lock 14., which allows the rotor 13 to pass with a small distance between the lock and the peripheral surface of the rotor, a predetermined flow in the pump chamber is ensured.

Further it appears advantageous, in order to ensure a uniform distribution of the rubbing bodies to the tube bundles of the condenser and in order to increase the velocity and thereby the cleansing eflect of the rubbing bodies in the condenser tubes, to supply the rubbing bodies from the shunt circuit to a trough which by slow rotation places itself in turn in front of all the tube inlets, thus ensuring a flow of the rubbing bodies in turn through all the tubes.

Cooling tubes of old condensers are in many cases covered with stony depositsformed after years of operation. Such deposits cannot be removed by elastic rubbing bodies, for example rubbing bodies of sponge rubber such as are provided in the case of new condensers originally equipped for use with the method according to the invention. For the initial cleansing and the removal of hard fur or the like in cooling tubes, other kinds of rubbing bodies are more suitable. Such bodies may consist of elastic material their surface being covered with a lining containing granular abrasive substances. In order to reduce damage to the tubes it is advisable to employ for this purpose a coating of the rubbing bodies which is permeated by filing or metal dust of the same material as that of the cooling tubes. Since such rubbing bodies of more rigorous action would attack the cooling tubes after removing the fur they have to be removed from the circulation after a certain time of operation. For this purpose it is advisable to provide a lock or other suitable device in the circulation conduit 4 which enables the rubbing bodies to be led off.

In condensers which from the beginning are operated by the self-cleaning methods herein-above described, these devices maybe utilised for removing rubbing bodies which have become ineffective by wear or bodies excessively loaded with impurities from the circulation and replacing them by other bodies.

In order to reduce wear of the walls of the acceleration pump shown in Fig. 14, cage-like structures. may be arranged in the pump chamber which prevent contact of the rubbing bodies with the walls of the pump. This feature is particularly advantageous when rubbing bodies having abrasive coatings are employed.

An apparatus has already been proposed for internally cleaning the tube coils of water-tube boilers or the like by friction bodies. This apparatus comprises a tube connecting the ends of the tube coil. Into this tube opens a separate pressure conduit. By simultaneous and alternate opening and closing of stop members in the pressure conduit and in the connecting tube the friction bodies are forced through the tube coil. The operation of the stop members is effected manually. The important differences, as compared with the self-cleaning method of the invention, consist in the presence of a connecting tube between the ends of the tubes to be cleaned, in the stop members which must be manually controlled, in the separate pressure means for the circulation of the rubbing bodies, and in the fact that the cleaning can only be carried out when the boiler is out of operation.

What I claim is:

1. An apparatus for self-cleaning the tubes of a heat exchanger having a plurality of tubes connected in parallel, an inlet conduit connected with said tubes for conducting a heat exchange fluid to said tulbes, an outlet conduit connected with said tubes, a plurality of rubbing elements in said heat exchange fluid for circulation therewith through said inlet conduit, all of said tubes and said outlet conduit, said rubbing elements being made of elastic material having an average specific gravity about equal to that of said heat exchange fluid and of a free diameter at least as great as the internal diameter of said tubes to assure as great as possible a rubbing surface thereof in the cooling tubes while at the same time propelling said rubbing elements through said tubes by the pressure drop existing between said inlet conduit and said outlet conduit to thereby assure uniform distribution of said rubbing elements throughout all of said tubes by the normal flow of said heat exchange fluid, an intercepting device for said rubbing elements disposed in said outlet conduit to intercept said elements while affording free passage therethrough for said heat exchange fluid, and a conduit connected with said intercepting device to conduct said rubbing elements from said intercepting device in said outlet conduit to said inlet 7 conduit so as to assure continued circulation of said rubbing elements.

2. An apparatus according to claim 1, wherein said intercepting device is of funnel shape, and wherein said last-mentioned conduit isv connected with said funnelshaped intercepting device inside of said outlet conduit.

3. An apparatus according to claim 1,, wherein said intercepting device includes a plurality of annular members of different diameters positioned coaxially and spaced from one another to form a funnel for catching said elements, and bars disposed in radial planes with respect to said annular members and connected with the latter forholding the same in the desired position.

4. An apparatus according to claim 3, wherein said annular members have a tear-shaped cross-sectional configuration.

5. An apparatus according to claim 1, wherein said intercepting device is ofrfunnel shape, and further comprising a scraper rotatably connected in said outlet conduit for scraping the inside of said funnel-shaped intercepting device, and an impeller disposed in said outlet conduit and connected with said scraper and adapted to be rotated by the fluid flowing through said outlet conduit for rotating said scraper.

6. An apparatus according to claim 1, wherein said intercepting device is of funnel shape and is split into halves, said. halves being tiltably connected with said outlet conduit.

7. An apparatus according to claim 1, further comprising a circulating pump interposed in said last-mentioned conduit, said circulating pump having a housing provided with an annular inside surface, a rotor insaid housing having an annular surface concentric with and spaced from said inside surface for taking along fluid adhering to the surface of said rotor while simultaneously affording passage through the space formed between said inside'surface and the circumferential surface of said rotor to said rub bing elements, and a stationary flow block disposed in said last-mentioned space for dividing the same into an inlet and outlet chamber.

8. An apparatus according to claim 1, further comprising a cooling Water pump in said inlet conduit, the conduit connected with said intercepting device being connected with the input of said pump.

9. An apparatus according to claim 1, further comprising stirring means in the form of propellers rotated by the fluid and located in said inlet conduit.

References Cited in the file of this patent UNITED STATES PATENTS Clarkson Mar. 2,. 1954

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