US2822787A - Method of and apparatus for removing the internal tube deposits in a oncethrough forced circulation vapor generator - Google Patents

Description

M. GAUGER 7 Feb. 11, 1958 2,822,787 NAL.

ETHOD OF AND APPARATUS FOR REMOVING THE INTER TUBE DEPOSITS IN A ONCE-THROUGH FORCED CIRCULATION VAPOR GENERATOR 2 Sheefcs-Sheet 1 Filed April 7, 1954 FiG.l'

INVENTOR .Marzfz'z? Gauyer I BY ATTORNEY Feb. 11, 1958 M. GAUGER 2,822,787

METHOD OF AND APPARATUS FOR REMOVING THE INTERNAL TUBE DEPOSITS IN A ONCE-THROUGH FORCED CIRCULATION VAPOR GENERATOR Filed April 7, 1954 2 Sheets-Sheet 2 FIGZ F l G. 3

lNVENTOR I {WZIZLZZZ Gauge? W ATTORNEY United States Patent METHOD OF AND APPARATUS FOR REMOVING THE INTERNAL TUBE DEPOSITS IN A ONCE- THROUGH FORCED CIRCULATION VAPOR GENERATOR Martin Gauger, Oberhausen, Germany, assignor to The Babcock & Wilcox Company, New York, N. Y., a corporation of New Jersey Application April 7, 1954, Serial No. 421,640 2 Claims. (Cl. 122-379) This invention relates in general to apparatus for, and a method of, removing internal tube deposits from the vapor generating tubes of a once-through forced circulation vapor generator having a plurality of vapor generating tubes arranged in parallel flow relation. More specifically, the invention involves the removing of internal tube deposits by supplying redissolving or flushing liquid to less than the total number of vapor generating tubes at a position ahead of the zone in which the final evaporation of the liquid to one hundred percent (100%) vapor occurs, a plurality of vapor-liquid separators each arranged to receive vapor and the flushing liquid from less then the total number of vapor generating tubes at a position beyond (i. e. downstream of) said zone, a flushing liquid receiver which receives the separated liquid by gravity flow from a plurality of separators, and a flushing liquid level controller which controls the rate of discharge of the flushing liquid from the receiver.

The invention is characterized by the fact that the common receiver for the separated flushing liquid from a plurality of such separators is placed at a level substantially below the level of the associated separators. This arrangement of cleaning and separating equipment when operatedaccording to the invention has the advantage that the tubes may be cleaned while the vapor generator is delivering its vapor output while requiring only a minimum amount of flushing liquid; the cleaning being carried out in successive tubes or groups of tubes until the entire unit is cleaned.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which I have illustrated and described several embodiments of my invention.

In the drawings:

Fig. 1 is a schematic diagram of a once-through vapor generator showing a prefrred arrangement of the components of the apparatus and flow directions of the various fluids of the invention.

. is separated in the separators 6' Fig. 2 is a side elevation of a similar vapor generator showing a modified draining arrangement; and

Fig. 3 is a rear elevation of the vaporgenerating unit shown in Fig. 2.

The invention is shown as incorporated in a once through type vapor generator wherein a vaporizable fluid, such as water, is pumped into one end of a plurality of continuous flow circuits, the fluid being heated more or less continuously throughout its flow path and emerging from the discharge end of each circuit as superheated vapor. The fluid is pumped into a distributing header 2 by a feed pump 1, as shown in Fig. 1. The fluid is then distributed to a pluralityof parallel flow circuits 3 in which it is heated. At the position in each circuit indicated at 4, the vaporizable fluid has reached a condi- 2,822,787 Patented Feb. 11, 1958 tion wherein it is normally on the verge of becoming one hundred percent vapor. In the zone beyond or downstream of the position 4, the remaining liquid is normally evaporated to dry vapor and the vapor partly superheated. The liquid which enters this zone usually contains a high percentage of impurities in suspension or solution and as the liquid is evaporated from the walls of the tubes 3, these impurities are left on the internal tube surfaces as scale. This zone is generally referred to as the transition zone. In accordance with the present invention the deposited scale is removed from the tubes 3 by injecting a flushing liquid, such as pure water, at the position 4 into the tubes 3 for redissolving the impurities in the flowing stream. The flushing operation is preferably carried out through corresponding flushing liquid injecting lines 5 having control valves 5 and connected to the vapor generating tubes 3 at position 4. The addition of the flushing liquid by operating the control valves 5' causes the transition zone in those tubes to be moved downstream and thus the scale to be removed by or become redissolved'in the contacting liquid.

In accordance with the present invention, the mixture of vapor and flushing liquid is then discharged into a plurality of vapor-liquid separators 6, which are connected to corresponding flow circuits or groups of flow circuits. The liquid retaining the impurities discharges from the individual separators through flushing liquid drain lines 7, while the separated vapor is discharged into a common mixing header 8. The separated liquid drains through the lines 7, and is discharged into a common flushing liquid receiver 10.

Also in Fig. 1 there is shown in dotted lines a plurality of separators 6' which are connected to another generating tube bank such as 3 in Fig. 2. When tubes of the tube bank 3' are being cleaned the vapor-liquid with the vapor being discharged to the mixingheader 8 and the liquid being drained into the common receiver 10 by the drain lines 7' which enter below the liquid level. The separated vapor would go on to the superheating zone via the connecting lines 15' and the vapor distributing header 14.

The receiver 10 is arranged at a level substantially below that of the connected separators 6, such level being low enough to facilitate the drainage of the separated liquid to it and to provide a hydraulic head in any nonused drain pipe greater than the velocity head in any used drain pipe. Internally of the receiver 10 there is arranged a liquid level controller 11 which operates a blow-down valve 12 in response to any increase in the liquid level within the receiver 10 above a predetermined value. A blowdown line 13 connects the receiver 10 to the valve 12. If the receiver 10 should be located subjacent to the associated separators, and less than all of the tube are being cleaned, there arises the problem of the flushing liquid backing up from the receiver into the separators of the circuits not being cleaned. This would scale the superheater in a zone which could not be cleaned without shutting down the vapor generator and perhaps worse, may cause the prime mover to become scaled. This problem is solved in the present invention by placing the common receiver 10 a distance below the level of the separators 6. This distance is great enough so that of parallel vapor superheating circuits 16 wherein it is heated to its final temperature. The heated vapor then enters a collecting header 17 and passes through a line 18 to its point of use.

The injection of a flushing liquid into the vapor generating tubes 3 that are to be cleaned at the position 4 ahead of the transition zone causes a vapor-liquid mixture to enter the vapor-liquid separators 6 of those tube circuits. During the passage of the flushing medium through the transition zone portion of the vapor generating tubes, the internal scale in the tubes is picked up by the liquid and the separators 6, 6' then discharge the impurities-carrying liquid via individual drain lines 7, 7' to the common receiver 10. The lower level location of the receiver is particularly conducive to cause high flow rates fromrthe separators to the receiver. The individual separator discharge lines 7, 7. serve the particular. useful purpose of conducting the fluid directly. to the receiver 10 and thus there is a large flow resistance which normally prevents overflow from a separator in use to a separator not in use. Additionally, the maintenance of a liquid level in the common receiver 10 keeps vapor in the separator drain lines which are not in use, which is a further deterent to the spilling over of the flushing liquid to the separators not in use.

Figs. 2 and 3 show a modified arrangement of the invention apparatus which would be used on a large capacity vapor generator whereby the individualvseparators 6 and 6' are connected to tube groups with the separated liquid conducted to the common receiver 10 by the lines 9, 9. The lines 9 and 9 can be considered extensions of the receiver 10 as the line size is considerably larger than either of the drain lines 7, 7. The connection of the separators and drain lines may be varied according to the size and particular arrangement of the vapor generating tubes with the understanding that there is at least one common receiver from which the flushing liquid is blown down.

The operation of a vapor generatorin accordance with this invention would be essentially as follows:

Flushing liquid is injected, for example, into one of the vapor generating tubes 3 of Fig. l ahead of the transition zone at position 4. The vapor delivery rate of the vapor generating unit would be maintained at some predetermined value. The mixture of vapor and'liquid, after having removed the scale from the scale forming zone, is then subjected to the action of one ofthe separators 6, passing the vapor to the superheater and draining the separated liquid flushing medium through the individual parallel drains to a common flushing liquid receiver 10 and maintaining liquid level in the receiver 10 by the control valve 12 which is responsive to the liquid level in the receiver. While the one circuit is being cleaned the other circuit of the tube bank 3 and the circuits of tube bank 3' would be delivering one hundred percent vapor through the separators 6' and the other separator 6. Thus there would be quiescent vapor in the unused drain lines 7 and 7 which would prohibit overflow of the flushing liquid to the unused separators. This process is repeated until all of the tube circuits have been flushed.

The apparatus and method disclosed allows a oncethrough vapor generator to be cleaned of internal scale which occurs in the transition zone while the generating unit continues to deliver substantial quantities of vapor. This is accomplished by an apparatus and method which allows individual circuits to be individually washed independently of other generating circuits. This invention is specifically directed to the cleaning of less than the total of all of the circuits simultaneously. If all circuits were to be cleaned at one time the vapor generator output would be reduced to an undesirable value because the vapor generator heat absorption would be largely taken up by the flushing liquid which is dischargedout of the vapor generator. The present inventionprovides a solution to that problem by cleaning less than the total num 4 her of circuits at any one time, thus allowing the generator to continue to deliver substantial amounts of vapor to the prime mover.

It is considered that this invention can be applied to a once-through vapor generator in which there may be a multiplicity of tube circuits discharging to a separator instead of the arrangement described herein of one separator per circuit.

The flushing liquid for cleaning the scale may be pure water as in the example above or may be a weak acid or basic solution depending on the composition of scale encountered.

While in accordance with the. provisions of the statutes, 1 have illustrated and described herein a specific form of the invention now known to me, those skilledin'the art will understand that changes may be made in the form of the apparatus disclosed without departing from the spirit of the invention covered by my claims, and that certain features of the invention may sometimes be used to advantage without a corresponding use of the other features.

What is claimed is:

1. In a vapor generator of the once-through type hav ing tubes arranged in parallel flow paths in the transition zone of which internal scale deposits tend to occur, the combination of means for injecting flushing liquid into each tube path of said vapor generator at a position priorto the entry of vaporizable fluid into said transition zone, a plurality of vapor separators each arranged to receive the vapor-flushing liquid mixture from one of said paths insaid transition zones and to separate the higher density liquid from the lower density vapor, vapor superheating means arranged to receive the separated vapor from said separators, a flushing liquid receiver arranged below said separators at a pressure substantially equal to the operating pressure of said tubes, a drain pipe from each of said separators continuously in open communication with the corresponding separator and said receiver for the gravitational draining of separated liquid from said separators to said receiver, and means for controlling the liquid level in said receiver and for discharging liquid from said receiver in proportion to the amount of separatedliquid drain thereto.

2. In a vapor generator of the once-throughtype'having tubes arranged in parallel flow paths in the transition zone of which internal scale deposits tend to occur, the

combination of means for injecting flushing liquid into:

each tube path of said vapor generator at a position prior to the entry of vaporizable fluid into said transition zone,

a plurality of vapor separators each arrangedto receive:

the vapor-flushing liquid mixture from one ofisaidtpaths in said transition zones and to separate the higher density.

liquid from the lower density vapor, vapor:superheating means arranged to receivethe separated vapor from said separators, a flushing liquid receiver arranged below said separators at a pressure substantially equal to the :operating pressure of said tubes, a drain pipe from each of said separators continuously in open communication with the corresponding separator and said receiver for the gravitational draining of separated liquid from. said separators to said receiver, and means for controlling the liquid level in said receiver and for discharging liquid from said re ceiver in proportion to the amount of separated liquid drained thereto, a few of said drain pipes arranged to drain to the vapor space and the rest of the pipes to drain to the liquid space of said receiver.

References Cited in the file of this patent UNITED STATES PATENTS 1,925,222 Abendoth Sept. 5, 1933 1,942,861 Huster Jan. 9, 1934 2,032,924 Eule Mar. 3, 1936 FOREIGN i PATENTS 431,241 Great Britain July 3; 1935 441,278 Great Britain Jan. 16, 1936

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