US2004694A - Treating water - Google Patents

Description

June 11, 1935. J. M. GlLLET 2,004,694

TREATING WATER Filed Sept. 2, 1951 Patented June 11, 1935 TREATING WATER James M. Gillet, Evanston, 111., assignor to Victor Chemical Works, a corporation of Illinois Application September 2, 1931, Serial No. 560,819

2 Claims.

The present invention relates to improvements in treating Water, more particularly for use in steam boilers, and will be fully understood from the following description illustrated by the accompanying drawing in which the figure illustrates diagrammatically and partly in section, apparatus suitable for carrying the invention into effect.

In carrying out the present invention, I apply the treatment hereinafter described more particularly to feed water for steam boilers or steam generating plants in general, the water treated being usually previously subjected to a softening treatment, such as treatment with a base exchange silicate, by the cold lime-so'da process, or by various other softening processes, such as the hot process softener. As will be apparent, in ordinary steam generators, Where a considerable proportion of the steam generated is condensed and returned to the boiler, it is necessary to treat only the additional or make-up water. However, the process of this invention is particularly effective when applied in those cases in which comparatively little or none of the steam generated is condensed and returned to the boiler and the greater part, or all, of the'water fed to the boiler is fresh feed or make-up water, since by the use of the present invention, the precipitation of solids and formation of caustic in the boiler and resulting embrittlement are markedly reduced.

The invention will be fully understood from the following description of a specific embodiment thereof, it being understood that the specific details given in connection therewith are not to be regarded as limitations upon the scope of the invention, except insofar as embodied in the following claims.

Referring more particularly to the drawing, the numeral 5 indicates a suitable enlarged container for the feed water to be subjected to treatment in accordance with the present invention, the container being of sufficient size to hold the quantity of water required for completion of the treatment in accordance with this invention, which may vary, say, from one-half to one hour. It will be readily understood that if economic and practical considerations so require, the single container 5 may be replaced by a plurality of containers in parallel or in series. The treating container 5 is provided at its top with a suitable cover 6, preferably pressure tight, provided with a pressure gauge I, and with a vent 8, so that the container may be maintained under any desired pressure, or, by opening vent 8, may be maintained under atmospheric pressure.

The feed or make-up water to be treated is supplied to the container through the line 9. The feed water thus supplied, may, if desired, be previously subjected to treatment, for example, with a base exchange silicate, by the lime-soda process, or in a hot process softener. If not heated in its previous treatment, it is preferably heated to a temperature of at least C. and in general to C. or higher, before it is supplied into the tank 5, which latter may be thermally insulated to maintain the temperature of the water while under treatment. The water to be treated is supplied continuously through line 9, which extends to and discharges near the bottom of the container 5, suitably through an elbow It.

A phosphate solution of a predetermined composition is likewise supplied in the enlarged container 5, being forced in continuously through the line H, which extends to the lower portion of the container and discharges into or near the open-ing of the feed water line 9, as indicated at l2. The opening I2 of the line for supplying the phosphate solution is so placed with respect to the opening Iil of the line supplying the feed water as to secure a thorough mixture of the phosphate solution and the feed water. The relative proportions of the phosphate solution and the feed water are so adjusted as to secure in the mixture the desired proportion of phosphate ions. For example, if it is found that 205.6 parts of sodium phosphate are desired per million parts of water, the phosphate solution may be made up to a concentration of 20.56 parts per thousand, and the resulting phosphate solution supplied into the container in the proportion of one part thereof to one hundred parts of the feed water.

The feed water and phosphate solution entering the container 5, are mixed thoroughly and travel upwardly through the container, passing out of the latter near its top through the outlet pipe l3, which leads, for example, to the filter M of any usual type, for example, a sand filter. From the latter, the treated water goes through the pipe l5 to the boiler, being forced into the boiler either under the pressure of the treating system or by a pump (not shown).

In traveling upwardly through the container, as a result of the reaction between the phosphates supplied through the line H and calcium and magnesium salts present in the feed water, there is a, formation and flocculation of insoluble phosphate compounds. enlarged diameter of the container 5, the upward flow of the water under treatment therethrough is relatively slow and the flocculated insoluble phosphates tend to settle and do not rise, except in the case of isolated particles or masses, to the outlet I3, the water discharged from the container through the outlet being substantially clear. Any phosphate particles or masses remaining therein are retained in the filter l4.

The proportions and the nature of the phos- By reason of the.

phate supplied in solution through the line ll,

' are determined in accordance with the hydrogen ion concentration or the alkalinity desired in the treated water and the constituents of the water subjected to treatment, in order to effect as complete as possible a removal of solid matter, thereby avoiding formation of solids, either as scale or sludge in a boiler. The use of phosphates for this purpose is particularly desirable in that it efiects a maximum removal of solids and secures complete freedom from scale-forming impurities without involving the retention in the water fedto the water of harmful proportions of soluble carbonates, such as sodium carbonate. Their retention is particularly disadvantageous in the operation of high pressure boilers by reason of the decomposition of sodium carbonate in the solution at the temperatures at which such boilers are operated, with formation of caustic soda, which does not pre-f vent scale formation and does tend to increase embrittlement. A further advantage of the use of phosphates in accordance with the present invention is that the nature of the phosphate employed may be selected with respect to its acidity or alkalinity to secure a desired hydrogen ion concentration. Thus,- if greater alkalinity is desired trisodium phosphate may be employed; and for less alkalinity or for a reduction 'in alkalinity, disodium phosphate, mixtures thereof with monosodium phosphate of monosodium phosphate alone may be employed.

By'carrying out the invention as hereinbefore described, a serious difficulty hithereto encounteredin the use ofphosphates in the final treatment of boiler feed water is avoided in-that the slow formation and accretion of deposits of insoluble phosphate in the feed lines leading to the boiler are completely prevented. In order to prevent such deposits, it has hitherto been the practice, particularly inhigh pressure boiler operation,- to supply the required amounts of phosphate directly in the boiler; but this practice has serious disadvantages in that it increases the total proportion of solids within the boiler itself, and in a battery, each boiler requires individual regulation of the supply of phosphate.

The following example illustrates the operation of the present invention in connection with certain feed waters as supplied to boilers.

In one case, the raw water total solids comprised 416 ppm..CaCz, 267 ppm. MgCOs and 768 ppm. Na2SO4. After treatment with a limesoda softening process, the water had a total solid content of 765 ppm., comprising 21 ppm.

'* CaCOa, 21 ppm., MgC0 a,- and 674 ppm, NazSOa It was treated in accordance with the present process with sufficient trisodium phosphate solutated material reached a level considerably below the outlet l3, through which substantially clear water was drawn off. This treated water was found'to have a temporary hardness of La permanent hardness of 18, and the proportions of case, trisodium phosphate was employed as the phosphate treating material, in order to secure a desired alkalinity of about 60 or somewhat lower. (expressed as ppm. CaC03) on titration with methyl orange.

' In another case, the feed water after softening by an ordinary softening process had a content of 52 ppm. CaCOa and 9.1 ppm. MgCOs. In this case, by reason of the higher alkalinity of the water, the phosphates employed for treatment in accordance with, the present invention were a mixture of disodium phosphate and monosodium phosphate, the proportion employed being such' as to supply 51.3 ppm. of the phosphate ion in the water being treated. After treatment in accordance with the present invention at a temperature of 90 to 95 F., the treated water had a temporary hardness of 6 ppm. and permanent hardness of 11 ppm. and a content of 16 ppm. CaCO: and 4.2 ppni. and MgCOs with 16.7 ppm. of P04 ions.

In carrying out the invention, the precipitation and flocculation of the insoluble phosphates may be materially accelerated by increasing the temperature at which the treatment is eflected, at the Sametime correspondingly increasing the pressure so asto secure the desired temperature without substantial vapor formation. .Thus, in a case in which flocculation began in about sixteen minutes at 90 C. and was complete in less than fortyfive minutes, by increasing the temperature to between 110 and 115 C. while maintaining a pressure sufiiciently high'to prevent va-' por formation, say pounds gauge or higher, precipitation and flocculation were apparent in between five and six minutes, and a substantially complete precipitation and flocculation were effected' within twelve to fifteen minutes. It will thus be "readily apparent that in operations in connection with high pressure boilers, by supplying the feed water to the treating systemfor treatment in accordance with the present invention at a substantial pressure or even at boiler pressure and at a higher temperaturasay 110 to 125 C(or higher, thetotal time of retention .of..the body of water in which precipitation and flocculation is taking place in accordance with the present system, may be decreased-and the rate of flow of the water through the apparatus and its capacity correspondingly increased.

I claim:

'1. The process of softening boiler feed water consisting in adding to .thefeed water soluble phosphates to flocculate and precipitate impurities as insoluble phosphates, maintaining the wa- .ter in a relatively quiescent state under pressure at a temperature above 110 C. to accelerate the flocculation and to permit the insoluble phosphates to settle, decanting the water largely freed from suspended phosphates, and supplying sof-- tened water to a boiler. f

2. The process of claim 1 in which the temperature is 110 to 125 C.

JAMES M. GILLET.

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