US2240206A - Means for eliminating corrosion in economizers - Google Patents

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` a 0 l V fo coman/zik l v l /7- April 29, 1941. w. E. CALDWELL 2,240,206

MEANS FOR ELIlIINATING CORROSION IN ECOHOMIZERS Filed June 21, 192x59-v LL I A 27.06 TR INVENToR Wn, f. 'zwfu Patented Apr. 29, 1941 UNiTI-:D sf-rares aeree Afri-ENT i MEANS 'FR'ELIll/IINA'IINGA CORROSIN IN ECONQDHZERS William E. Caldwell, New RochelleNY.

Application June 21, 1939,`ScrialvNo. 280,271

"3 Claims.

This invention relates to steam generating plants of the type that are equippedwitheconomizers and particularly to means for eliminating corrosion in the economizers.

In a modern high 'capacity steamgenerating;

plant an economizer is justified by economic considerations in most installations. However, the economizer has certain'disadvantages from the standpoint of maintenance which. at'times are serious in their effectfon the availabilityof the.

economizer and the boiler. The-major cause of economizer maintenance is internal corrosionwith consequent increase in' ovr resistance resulting from corrosion products vand entailing reduced life for the economizer. flcient de-aerating apparatus provided in modern steam generating plants; somec'orrosion orfoxidation takes place in the 'economizen Many modern high pressure economizers are of completely welded construction which renders the internal..

cleaning of the tubes bythe ordinary turbine cleaner impracticable. Therefore, -it becomes necessary to provide such favorable Watercon'ditions for the economizer that internal corrosion may be eliminated in order to avoid such increase in flow resistance.

'Alkaline feed water suppresses the usual corrosion tendencies due tooxygen or otherY causes. It is impractical to add sullicient-alkalinity to the 4boiler feed water forfproducing appropriate alkalinity in the economizer since this would'result in an excessive concentration inthe boiler vdue to the evaporative process. Inasmuch as the normal feed water treatment for prevention of scale within the boiler results in fairly high ali ,kalinity therein, a methodheretofore. employed inlet of the economizer to recirculate part of the D The disadvantages Vof this blow-down water. system are that such a pump is rather expensive and complex for high pressures,.it introduces added losses due to leakage past the high. pressure packingand also requires additional powerl y 'to operate the pump.

In spiteV of highly ef- In accordance with the present invention the disadvantages of such lprior arrangements are -obviatedby vproviding an -eductor connected to the boilerv at the blow-downor other suitable .point and sc arrangedas -to employ the ordinarily wasted energy in' the 'feed waterto `draw alkaline water-fromthe'boiler vand force it vthrough -theeconomizer and thence. back intothe boiler.

-When cer-tain chemicals such asphosphate are usedfor 'conditioning-the feed -water the boiler waterA must havea minimum alkalinity in .order that the phosphate f sludge resulting from the chemicalrreaction .within the' boiler withv calcium .and magnesium vwillnot adhere toi the boiler heating surface. Under such circumstances, it: may not be practical to reintroduce a part-of 'the boiler water to the econornizer since the precipitated sludge lor solids in suspension'which are thereby carried into the economizer may adhere to the econornizerr' surface. -It is further not practical I underthe circumstancesV to` maintain the i lWater within the economizer atY a suiciently high alkalinityin order to prevent such anadherence, because maintaining such Ya high.. alkalinity withinthe economizer would in turn result in a too .highy concentration of r alkali Within the boiler proper. The use of organic compounds, such as tannin, to prevent the sludge formed within the boiler'from.. adhering to the boilerheating surface, isopen to the same objections.' If alkali, tannin or lsimilarly acting compounds are used in an economizer in the amounts necessary to prevent the adherence of sludge to its tube surface,

Vanexcessive amount of blow down from the boiler `would -be necessary to keep the boiler water con'- -centration therein Within suitable limits.

According -to this invention under the above 'or similar conditions, I Yprovide-within 'the connection for reintroducing. the t boiler water of relatively high alkalinity into the reconornizer,

`means for removingsubstantially all ofthe precipitated sludge or solids in suspension from said vboiler "Water thereby preventing `its entering the -economizer and either depositing'in the economizer `tubes or being carried over into the boiler A.andcausing an accumulationy of too high a concentration therein.

IAv have further .found vthat by the usual method of blowing down boilers now iniuse, the suspended solids do not `blow oif .in

`proportion tothe solids in solution. By the .use

kof -rny means for removingthe-sludge the suspendedsolids are removed to a relatively greater extent. than they wouldobe by the usual blow down. Alsaifthe normal blow down is 11/2 to 2% andif I recirculate'4 ofthe Water fed to the boiler thru the economizer, I will removeby my means a greater amount of sludge or solids in suspension and will remove them in a concentrated form with a substantially smaller blow down.

How the foregoing, together with other objects and advantages as may hereinafter appear or are incident to my invention are realized, is illustrated in preferred form in the accompanying drawing, wherein- Fig. 1 is a schematic View showing a steam generating plant having an eductor associated with the feed water system and arranged to draw Water from the boiler through a sludge remover and cause it to be circulated through the economizer; and

Fig. 2 is a similar view showing part of the feed water system and illustrates a somewhat different manner of connecting the eductor.

In the drawing the numeral Il) designates a steam generating boiler equipped with an economizer II in which the feed water is heated before being discharged into the steam and water drum I2 of the boiler. Feed water treated to render it alkaline is withdrawn from a source of supply I3 by the feed water pump I4 and delivered through the feed water line I5 to the economizer. Interposed in the feed water line I5 between the pump I4 and economizer l I are a shut-off valve I B and a feed water regulating valve I '1. The feed water regulating valve I'I is automatically controlled in any suitable manner, as in response to water level in the drum I2, so as to vary the amount of feed water delivered to the boiler through the economizer as the load upon the boiler, and hence the evaperating rate, rises and falls. e

In the usual economizer the pressure drop at maximum iiow is about 40 pounds and diminishes according to well-recognized laws as the flow decreases. In the conventional plant there is a substantial pressure difference across the feed water regulating valve I1 and in Fig. 1 there is shown a means of utilizing this pressure difference for drawing water out of the boiler and discharging it into the economizer at a higher pressure. An eductor 2B connected by piping 2|, 22 to the boiler I0 is so arranged in a by-pass 23 formed by piping connected to the feed water lines at points beyond the inlet and outlet sides of valve I1 that part of the feed water flows through the by-pass around the valve and its energy is utilized to draw part of the water from the boiler and introduce it inlto the feed water line at a point beyond the valve I1. A Suitable amount of boiler water recirculated through the economizer may be about four per cent, for example, of the feed water. In the connection between lthe boiler and the economizer there may be provid-ed means for removing substantially all of the suspended solids or sludge from the boiler water before it is reintroduced into the economizer. Such means are shown diagrammatically at 21 in the pipe 22 and may be a filter, a deconcentrator or the like, and may be blown down through vaived connection 2B. The pipe connection 22 may be made to the boiler at any point considered suitable for removing concentrates and nced not be connected directly to the boiler blow-down piping. The discharge pipe 28 from filter 27 may, however, be utilized as the only means for regularly blowing down the boiler. A discharge pipe 24 may also be provided and connected either to pipe 22 or directly to the boiler to dispose of blow-down water which it is desired to remove from the boiler to reduce concentration therein.

Piping 25 between the feed Water line I5 and pipe 2l connecting the eductor with the boiler forms a cooling connection for mixing relatively cooler feed water with the hotter boiler water so that cavitation and reduced eductor capacity may be avoided because the water from the boiler water approximates saturation temperature while the feed water is at times substantially below this.

Experience indicates that local corrosion is less prevalent where high water velocities prevail, as at high boiler ratings, and corrosion becomes more active as the velocities diminish. The eductor 20 provides for this condition since at low ratings on the boiler the feed water regulating valve Il' approaches its closed position thereby increasing the pressure difference across the valve and resulting in increasing the amount of water recirculated from the boiler through the economizer by the eductor 2i). A valved by-pass 30 may be provided around filter 2l'. In shutting down a boiler arranged as in Fig. 1, the valve 26 controlling the by-pass in which the eductor is located would be the last to be closed and this would result in increasing the pH value or alkalinity of the water in the economizer as the flow diminishes. At all ratings there will be substantial recirculation of boiler water with consequent corrosion protection and a simultaneous removal of suspended solids from the recirculated water when the lter 21 is used.

The eductor shown in Fig. 2 functions in a manner quite similar to that of Fig. 1, but is located directly in the feed line rather than in a by-pass around the feed water regulating valve. It may be seen that in this arrangement also the eductor utilizes the energy of the feed water to draw Water from the boiler and cause it to be delivered to the economizer.

Although an arrangement is shown in which alkaline feed water is admitted at 'the suction side of pump I 4, this is merely illustrative and not a prerequisite for successfully protecting an economizer by circulating through it alkaline water derived from the boiler. It is possible to introduce alkalinity to the drums of the boiler or other part thereof by a separate pump and thus build up a concentration independent of alkalinity in the feed water itself.

Applicants recirculation of boiler water to the economizer through a filter within the recirculation line then performs the simultaneous func tions of minimizing accumulation of sludge in the economizer while producing a proper alkalinity of the feed water to the economizer to prevent corrosion therein and in serving as a boiler blow down obviates the necessity for an otherwise excessive blow down from the boiler.

Applicants filter 21 may be located in the line I5 beyond by-pass 23 and there serve to filter out the suspended solids carried over from the boiler and those formed in the feed water by a possible reaction between the recirculated boiler water and feed water. With this arrangement the boiler may be blown down separately. Or a second filter may be installed in line I5, ahead at by-pass 23.

The present application is a continuation-inpart of my earlier application Serial No. 189,937, filed February 11, 1938.

What I claim is:

1. In a steam generating boiler arranged to receive feed water from an economizer supplied by a pump through a feed line having a flow regulating valve therein; a blow-down for said.

boiler; an eductor so connected to said blowdown and so associated with said feed water line as to utilize the energy of feed water to draw water from said boiler and introduce it into said feed line to flow through said economizer; and piping connecting said feed line at a point ahead of said eductor to the connection between the boiler blow down and said eductor for mixing feed water with water drawn from the boiler before it enters said eductor.

2. In a steam generating boiler arranged to receive feed water from an economizer supplied by a pump through a feed line having a ow regulating valve therein; a blow-down for said boiler; piping connected to :said feed line beyond the inlet and outlet sides of said valve and forming a by-pass for feed water around said valve; and an eductor so connected to said blow-down and so located in said by-pass piping as to utilize the energy in the feed water flowing through said by-pass to draw water from the boiler and introduce it into said feed line at the outlet side of said valve to ow through said economizer; and piping connecting said feed line at a point ahead of said eductor to the connection between the boiler blow down and said eductor for mixing feed water drawn from the boiler before it enters said eductor.

3. In a steam generating boiler arranged to receive feed water from an economizer supplied by a pump through a feed line having a iow regulating valve therein; a connection for the withdrawal of alkaline feed water from the boiler; piping connected to feed said line beyond the inlet and outlet sides of said valve and forming a lay-pass for feed water around said valve; and an eductor -so connected to said withdrawal connection and so located in said bypass piping as to utilize the energy in the feed water flowing through said bypass to draw water from the boiler and introduce it into said feed line at the outlet side of Valve to flow through said economizer.

WILLIAM El. CALDWELL.

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