US2315226A - Method of and apparatus for washing steam - Google Patents

Description

March 30, 1943. v. A. ROHLIN I 2315,226

METHQD OF AND APPARATUS FOR WASHING STEAM Filed Dec. 6, 1939 4. 4 V JIIVENTOR v 1 BY 1W 21W ATTORNEY Patented Mar. 30, 1943 METHOD OF AND APPARATUS FOR WASHING STEAM Victor A. Rohlin, Philadelphia, Pa., assignor to Cochrane Corporation, Philadelphia, Pa., a corporation of Pennsylvania Application December 6, 1939, Serial No. 307,750

3 Claims.

The general object of the present invention is to provide an improved method of and apparatus for washing wet steam to reduce the amount of solids carried by the steam. While not restricted to such use, the invention was primarily devised and is especially adapted for use in treating the steam generated in power plant boilers operating at relatively high ratings and supplied with boiler feed water containing impurities.

In the operation of such a power plant boiler, the bulk of the impurities carried into the boiler with the feed water, does not pass out of the boiler with the steam discharged, and, in consequence, the water within the boiler normally contains a much higher percentage of impurities than does the boiler feed Water. For example, the impurities in water fed to power plant boilers seldom amount to more than about 200 parts of solids per million parts of water, while it is customary to permit an impurities concentration in the boiler as high as 2000 parts of solids per million parts of water. The concentration of impurities in the boiler water is regulated by the blow down discharge of or so of the Water supplied to the boiler. The steam liberated in a power plant boiler operated at high rating invariably carries entrained Water which has the same impurities content as the boiler water not entrained.

Solids carried out of the boiler by the steam have an injurious effect on apparatus in which the steam is subsequently treated or used, and

particularly on superheaters and turbines. It is generally recognized, for example, that if the solids content of the steam amounts to as much as one part of solids per million parts of the condensate formed by condensing the steam, the solids may deposit in a superheater and cause superheater tubes to burn out, and may erode or cut the blades, and deposit on the blades and thereby lower the efficienoy and disturb the balance of a steam turbine in which the steam may be used.

The injurious efiects of a considerable solids content in water entrained by the steam have long been generally recognized and have led to a considerable use of one or another of various arrangements for washing impurities out of the steam by mixing boiler feed water with the boiler water entrained in the steam. Such dilution of the impurities in the water entrained in the steam is effected in some cases within the boiler drum from which the steam generated is withdrawn from the boiler, and in other cases is eftact with the boiler feed water which is in a finely subdivided form, and particularly by causing the steam to move at a relatively slow velocity through a spray or curtain, of finely divided boiler feed water.

In washing steam in accordance with the present invention, the solids content of the water entrained in the steam is reduced in successive stages, in each of which diluting water in fineli divided form is first added to the steam, and thereafter water is separated from the steam to reduce the moisture content of the latter. In the preferred form of the invention, the diluent water is sprayed into admixture with the steam in each treatment stage while the steam is moving at a relatively high velocity through a restricted flow path portion of the washing apparatus into a less restricted portion of the flow path where water is separated from the steam.

The multistage treatment of the water has the fundamental advantage of requiring substantially less diluent, or waste, water than is required for a similar elimination of impurities in a single stage treatment. Thus, for example, it is theoretically possible in washing steam entraining one half per cent of water having an impurities content containing 2,000 parts of solids per million parts of water, with wash water having an impurity content of 200 parts of solids per million parts of Water to eliminate as large a portion of the impurities in a two stage treatment in which the steam is washed with about 7% of the boiler feed water in each stage, as can be eliminated by using all the boiler feed water as wash water in a single stage steam washing operation.

The reduction in the amount of wash water required, which is characteristic of the invention, permits of a reduction in the bulk and cost of the washing apparatus, and makes it practically possible to maintain operating conditions which of themselves contribute to a further reduction in the bulk and cost of the apparatus described.

A reduction in the amount of wash water required makes it practically possible and desirable to use condensate or other wash water purer than the boiler feed water, in some cases in which it would not be feasible to use the purer water for passing the drainage, mainly wash water, to

the boiler from the Washer which may then be located below the boiler water level. An increase in the pressure at which the wash water is supplied to the spraying nozzles of the washer the boiler is provided with a steam superheater A A steam washer B constructed and arranged in accordance with the present invention, has its steam inlet B connected to the outlet end of the boiler steam pipe A, and has its steam outlet B connected by a pipe B to the inlet of the superheater A In the preferred form shown, the steam washer B comprises a horizontal tank having its interior divided by partitions into an inlet chamber C at one end of the tank, to which the steam inlet B opens, an outlet chamber E at the other end of the tank, from which the steam outlet B opens, and two intermediate permits of a finer subdivision and dispersion of the water sprayed into the steam, and thereby increases the efficiency of mixture of the wash water with the water previously entrained in the steam, and such an increase in mixing efficiency directly increases the amount of impurities which can be eliminated from the steam by a given amount of wash water. i

A further advantage of the reduction in the amount of wash Water needed, is that the correspondingly small amount of water draining from the washing apparatus may be wasted, or used less efficiently than when it is returned directly to the boiler, without significant detriment to the overall efliciency of the power plant, and with the advantage of making it unnecessary to elevate the washing apparatus so that it may drain directly into the boiler.

While it is theoretically possible to obtain an advantage by further increasing the number of steam washing stages, in ordinary practice the advantage obtained by using more than two stages, will not be suflicient to justify the small increase in apparatus cost required for the use of more than two'stages.

The various features of. novelty which characterize my 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, however, its advantages, and specific objects attained with its use, reference should be had to the accompanying drawing and descriptive matter in which I have illustrated and described preferred embodiments of the invention.

Of the drawing:

Fig. 1 is a diagrammatic representation of one embodiment of the invention;

Fig. 2 is a vertical section through the steam washer shown in Fig. 2"; V

Fig. 3 is a section on the line 3-3 of Fig. 2; and

Fig. 4 is a diagrammatic showing of the second embodiment of the, invention.

In the drawing and referring first to the form of the invention shown in Figs. 1, 2 and 3, A represents a steam generating boiler discharging saturated steam through a steam pipe A, and receiving feed water through the feed water supply connected to "the rear drum A As shown, also,

chambers F and G. A transverse partition C separates the chambers C and F, except for a communicating passage formed by the bore of a mixing nozzle H which extends axially through the partition C The chambers F and G are separated by a transverse partition 0, except for a communicating passage formed by the bore of a mixing nozzle I extending through the partition C The chambers G and Eare separated by a transverse partition 0 except for a communicating passage formed by the central opening C in the partition and by the bore of an axially extending pipe C supported by the partition C at its chamber G side. As shown, the adjacent ends of the pipe C and nozzle I are separated by a distance substantially greater than their internal diameter. As shown, the partition C C and C are sheet metal discs welded at their peripheral edges to the tank body of the washer.

The steam passing from the boiler A to the washer inlet B, is discharged into the chamber C in an axial jet which impinges against a liquid separating baflle C interposed between the inlet B and outlet nozzle H. In the advantageous forms shown, the baifie C comprises a plate slightly inclined to the vertical, and welded at its upper and lower ends to the wall of the washer tank, and of a width somewhat less than the internal diameter of the tank, so as to provide a steam port between each side edge of the baflie and the adjacent portion of the tank wall. At its side adjacent the inlet B, the bafile C is provided with a plurality of longitudinal ribs C In the chamber E, another liquid separating plate D is interposed between the outlet end of the nozzle C and the washer steam outlet B The baflie has ribs D at its inlet side and may be of the same width as and otherwise like the baffle C, but'as shown is vertical. Steam passing through the nozzles H and I is subjected to the action of wash water sprays discharged into the inlet ends of the nozzles H and I, by axially disposed Water discharge nozzles K and K. Advantageously, and as shown, each of the nozzles H and I is adapted to act as a centrifugal separator of the water and steam passing through it. To this end, a spiral vane h is mounted in the nozzle H and aspiral vane i is mounted in the nozzle 1: As shown each of said vanes is in the form of a metal strip twisted to form about one helical turn, and extends along about the final two thirds or three quarters of the length of the nozzle. Each of the nozzles H and I with its spiral vane, is thus adapted to give the water entrained and added to the steam entering the nozzle, a, tangential movement as it leaves the nozzle, whereby much of the water is separated from the steam in the chamber-into which the nozzle discharges.

Water separating from the steam in the compartments C, F and G, passes out of those chambers through their respective downwardly extending drain pipes L, L and L and water separating from the steam in the final washer chamber E, passes away from the latter through one or the other of two downwardly extending drains L and L which communicate at their upper ends with the portions of the chamber at opposite sides of the baffle D. The various drains L, L L L and L are connected at their lower ends by a horizontal pipe L, so as to maintain water sealed communication between the lower ends of the different drain pipes. Water draining out of the washer B through its different drain pipes is returned to the boiler by a return pipe M shown as having one end connected to the lower boiler drum A and its upper end connected to the drain L, somewhat above the pipe L.

With their lower ends in water sealed communication, the water levels in the pipes L, L L L and L will be at progressively increasing heights, since, as a result of friction losses, the steam pressures in the different compartments of the washer will progressively decrease from the inlet compartment C to the outlet compartment E. With the arrangement shown, the water levels in the drain pipes are prevented from becoming unduly low by connecting the upper end of the return pipe M to the drain pipe L' at a level suitably above the level of the bottom connection pipe L.

Feed Water is supplied to the boiler as required through a feed pipe P and boiler feed regulator P. The latter has one outlet branch pipe P connected to the boiler water inlet A and a second outlet branch pipe P connected through outlet branches P and P to the previously mentioned wash water supply nozzles K and K in the steam-washer. To ensure that a suitable portion of the boiler feed washer is delivered to the steam washer nozzles K and K, the branch P of the boiler feed line leading to the boiler feed water inlet A includes a loaded check or preference valve N which will open only when the pressure at its inlet side P exceeds the pressure at its outlet side by a predetermined amount.

To guard against an objectionable accumulation of water in the chamber D, such as may result from an overload condition, or a failure of the regular drainage system of the washer, I provided a supplementary, or emergency, drain pipe connection 0 for the chamber E. As shown, the pipe 0 is connected at its upper end to the drain pipe L at a level somewhat above the level of the water in the pipe L under normal operating conditions. The lower end of the drain pipe 0 is connected to a trap or discharger O, which discharges to waste, or to some suitable receiving space for boiler feed water, or water to be used for some other purpose.

In the normal operation of the apparatus collectively shown by Figs. 1, 2 and 3, a consider able portion of the moisture content of the steam entering the washer B through the inlet B is eliminated in the chamber C by the bafiie C. The steam passing through the mixing and separating nozzle H from the chamber C into the chamber F has itsv moisture content substantially increased by the wash water spray jet discharged by the spray nozzle K. As the steam and water mixture passes from the nozzle H into the chamber F, water is separated from the steam in an amount which is comparable with, and may be equal to the amount of water discharged by the nozzle K. In passing through the mixing and separating nozzle I, the moisture content of the steam is again increased, and thereafter water is separated from the steam in the chamber G in the same manner, and substantially to the same extent, as in the chamber F. The steam passes from the chamber G through the pipe C in a high velocity stream which impinges against the ribbed baffle D, with the result of a further reduction in the moisture content of the steam.

The operating results obtainable with the apparatus shown in Figs. 1, 2 and 3, are dependent on the size and relative proportions of the washing apparatus, and upon the conditions of operation. With all normal operating conditions, however, it will be possible to obtain as good steam cleaning results by passing a fraction only of the boiler feed water through the nozzles K and K of the apparatus, as are obtainable with all of the boiler feed water used as wash water and all of the entrained water are uniformlymixed in the passage of the steam through each of the mixing chambers H and I, and that the steam leaving the washer entrains one fifth of one percent of water, and that seven percent of the boiler feed Water is discharged by each of the spray nozzles K and K, then, as can be shown by simple arithmetic, the steam leaving the washer will carry less than one half, approximately .416, of a part of solids per million parts of steam. That solids content is a triflle less than will be carried by steam subjected to a single stage washing operation in which all of the boiler feed water is used as wash water, if it be assumed that the steam washed entrains one half percent of water containing two thousand parts of solids per million parts of water, and that the feed water carries two hundred parts of solids per million parts of water, and that all of the wash water is uniformly mixed with allof the Water entrained by the steam, and that after the single stage washing operation, water is eliminated from the steam to reduce its entrained water content to one fifth of one percent. As can be shown by simple arithmetic, the steam so treated will then carryapproximately .418 of a part of solids per million parts of steam.

In practice, the mixing efficiency of the apparatus shown in Figs. 1-3 will not be as good as assumed in the preceding paragraph, so that some of the minute entrained droplets of impure water will not have added to them their proper proportion of the wash Water. lowever, if the assumptions made in the previous paragraph are modified by the assumption that only eighty percent of the entrained water entering each of the mixing nozzles H and G, is therein mixed with its proper proportion of the wash water sprayed into that mixing nozzle, and that twenty percent of the entrained water which the steam carries into each mixing chamber, passes out of the latter without any dilution by the wash Water, the spraying of seven percent of the boiler feed water, into each of mixing nozzles H and I, will reduce thesolids content of the steam leaving the washer with a moisture content of one fifth of one percent, to about sixty-three hundredths of a part of solids per million parts of steam,

' may be as much as them more pounds, under heavy load conditions. With the arrangement shown in Fig. -1, the steam washer B mustthe'refore be located at a level definitely above the boiler water level, to enable the steam washer to drain freely to the boiler. The location of the steam Washer B at alevel below the boiler water level may be made possible by the provision of a pump for returning drainage from the washer to the boiler, or by the provision of means for delivering the water drained from the washer to some receiver or Water-using apparatus to which the drainage water may be delivered at a pressure lower than the boiler pressure. It is possible also, to use the general principles of the steam washing apparatus shown in Figs. 1, 2 and 3, in washing steam with pure water and thereby'obtaining a washed and dried steam with a smaller solids content than is possible, other things being equal, when impure boiler feed water is used as the wash water.

One plant arrangement or form, in which the relative washer and boiler levels is important, and in which pure wash water is used is diagrammatically illustrated in Fig. 4. The boiler A, washer B, and. super-heater A of the plant shown in Fig. 4, may be exactly like the corresponding parts of the plant shown in Fig. 1, and the wash- .er B may be connected'to the boiler steam outlet and to the superheater exactly as in Fig. 1. In Fig, 4, however, the main and emergency drain pipes M and 0, respectively, are connected to the inlets of steam traps Q and QA, respectively, which have their discharge outlets connected to the inlet of a flash tank R, in which'the pressure is below boiler pressure, and may well be but little above atmospheric pressure.

The water discharged by the traps Q and QA,

at a temperature but little below the boiler steam temperature, is subjected to a flashing action in the flash tank R, by which a portion, dependent in amount on the boiler and flash tank pressures, is evaporated. The steam thus formed in the flash tank R passes away from the latter through a steam pipe R. The water not evaporated in the flash tank R is discharged from the latter through a pipe R In the arrangement shown in Fig. 4, the pipe R leads to the inlet of a trap QB employed to pass water intoan open feed water heater S which may be a deaera ting heater, to which boiler makeup water is passed by the water supply pipe P, through a regulating valve S. A float S in theheater 6, opens and closes the valve S as required'to maintain an approximately constant water level in the heater.

In the plant'arrang'ement shown in Fig. 4, the boiler feed water is passed to the boiler by the boiler feed pump V, through a feed line including pipe sections P 9, P and P and th water heating space of aclosed water heater W. As much of the condensate formed in the steam space of the heater Wand collecting in its hot well or receiver W, as is required for steam washing is passed by a separate pump Y through a pipe P and throttling valve W to the Wash water supply branches P and P of the washer B. The pump Y maybehand controlled and the valve W may be a handadjusted gate valve. As diagrammatically shown, the boiler feed line section P includes a boiler feed regulator P and a nonreturn valve N Condensate normally accumulates in the hot well or receiver W in excess of the wash water requirements and overflows through th pipe W'- to the trap QB by which it is discharged into the heater S. The steam used in heating the boiler-feed water in the heaters S and W may be taken from any available source or sources. Advantageously, it includes the flash steam discharged from the flash tank R through th pipe R, and as shown in Fig. 4, the pipe R delivers the flash steam to the steam inlet of the heater W. The additional steam utilized in the heater W, is bled through a pipe T from an intermediate stage of a steam turbine T, and steam bled from a lower pressure stage of that turbine through a pipe T, is employed to heat the water passing through the heater S.

While the arrangement shown in Fig. 4 is somewhat lesssimple than that shown in Fig. 1, the Fig. 4 arrangement possesses the advantages that it provides, and makes use of, pure wash water, and it permits the washer to be located below the boiler water level, and attains those advantages, moreover, without significant im-' palrment of the high operating efficiency of the arrangement shown in Fig. 1.

While the invention in its broader aspects permits the use of other forms of washing apparatus, the particular form illustrated is compact and efficient, and makes use of water separating and drainage 'expedients of well tested merit which have been successfully employed in the extensively used receiver separator for eliminating water and oil from steam, disclosed in the Fowler Patent 1,869,371, filed Aug. 1, 1932.

While in accordanc with the provisions of the statutes, I have illustrated and described the best forms of embodiment of my invention now known to me, it will be made in the form of the apparatus disclosed without departing from the spirit of my invention as set forth in the appended claims and that in some cases certain features of my invention may be used to advantage without a corresponding use'of other features.

Having now described my invention, what I claim as new and desire to secure by Letters P'atent,is:

1. In the oper'ationof a steam generating boiler with impure feed. water, the method which consists in preheatingthe boiler feed water with steam thereby condensed and producing condensate'separate from th boiler feed Water, increasing thepressure of the condensate and spraying it into the steamge'nerated by the boiler, separating water from the steam, and flashing the water separated and thereby providing steam used in preheating the boiler feed water.

2; The combination with a steam generating boiler, of means including a closed water heater for supplying preheated boiler feed water to the boiler, a steam Washer through which steam generated inthe boiler ispas'sed, means for supplying water preheating steam to said heater and in which water separates from said steam, means 10 to the boiler feed water.

separates from said steam, means for supplying water preheating steam to said heater, means for spraying condensate formed in said heater into the steam passing through the washer, flashing means for flashing water separating from the steam in the washer, means for passing flash steam from said flashing means to said water preheating steam supply means and means for adding the unflashed residue of the drainage water VICTOR A. ROHLIN.

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