US2875156A - Inhibition of foaming in steam generation - Google Patents

Description

United States Patent INHIBITION OF FOAMING IN STEAM GENERATION Carl E. Johnson, Westchester, llL, assignor to National Aluminate Corporation, Chicago, Ill., a corporation of Delaware N 0 Drawing. Application March 7, 1956 Serial No. 569,958

The present invention relates to the inhibition of foaming in steam generation and more particularly to the prevention or reduction of foaming in steam generators operating under superatmospheric pressure and temperature conditions.

It is well known that in the operation of steam boilers, such as in railroad locomotives, in electric power plants and the like, or in other boiling operations where steam is formed, as for example, in evaporators, that the water therein, even though initially it shows little tendency to foam, will, when the amount of total dissolved'solids approaches a relatively high concentration due to the production of steam, develop a very decided tendency to foam. This foaming of the water in a boiler producing steam is characterized not only by an accumulation of relatively stable froth or foam on. the surface of the boiler water but also by the formation at the heat transfer surfaces in the boiler of extremely small steam bubbles. These minute bubbles show almost no tendency to coalesce and the result is that the entire volume of water in the steam generator is lifted in the form of so-called light water, which is actually an intimate mixture of boiler water and tiny steam bubbles. When this occurs, considerable quantities of boiler water are physically carried out of the boilers or evaporators with the steam, thereby introducing solid matter into the steam lines and into the eventual condensate. disadvantages because it tends to contaminate and restrict the steam lines, to plug or corrode the valves, to deposit on turbine blades, to plug and cause burning out of superheater tubes, andunder serious conditions may.

even impair the cylinders and piston rods of steam engines or otherwise render the steam unfit for use. The j carryover is frequently due in part, at least, to priming,

or what may be described as surging or boilinggover of the water.

One of the objects of this invention is to provide a new and improved process for preventing the foaming and priming of steam generators, thus improving the,

quality of the steam produced thereby.

' Another object is to provide new and improved compositions for adding to the water in a steam generator to prevent or reduce its'tendency to foam. 7

Another object isto provide antifoaming compositions which are effective to prevent foaming when used 1n very low dosages.

Such carryover has many A further object is to provide highly effective .anti- I foam compositions which are readily and easily dispersible when added to the feedwater entering a steam generator. t p

Another object of this invention is to provideantifoam compositions in which the active effective ingredicuts are readily soluble in water at relatively low tem-' W peratures (e. g., 75 F.), but decrease in solubility when An additional object is to provide new and useful antifoaming compositions of an extremely high order of resistance to decomposition under the conditions prevailing in steam generation. Other objects will appear hereinafter.

In accordance with this invention it has now been found that there is a series of compounds which may be broadly designated as high molecular weight trihydroxypolyoxyalkylene ethers of alkylene triols containing 3 to 6 carbon atoms which are very effective in inhibiting foaming in the generation of steam from water under superatmospheric pressure and temperature conditions."

oxide and ethylene oxide or mixtures of propylene oxide and ethylene oxide, the relative proportions of propylene oxide to ethylene oxide being within the range from 9:1 to 1:9 and the condensation being carried to a stage such that the molecular weight is at least 1500. The

oxyalkylene groups apparently add on to the free hydroxy groups of the triol to produce chains. It is possible that the reaction occurs to a greater extent at the primary hydroxyl groups than at the secondary hydroxyl group of the triol. Since ethylene oxide has a molecular weight of 44 and 1,2-propylene oxide has a molecular weight of '58, the quantity of alkylene oxide required to produce a compound of a given molecular weight can readily be calculated. This quantity will depend to some extent, of course, upon the relative proportions of the ethylene oxide and propylene oxide. The products may be cogeneric mixtures of addition products and the present invention contemplates the employment of such mixtures provided the average molecular weight is at 'least 1500 as measured by the acetyl value and reckoning three free hydroxyl groups per molecule.

In general, the mol ratio of alkylene oxide per mol of triol such as glycerine or 1,2,6-hexanetriol should be within the range from about 30:1 to 3002-1 and especially good results have been obtained by the employment of such addition products having an average molecular weight within the range from about 1500 to about 6000.

When the addition products employed for the purpose of the invention are prepared by adding a mixture of ethylene oxide and propylene oxide to the initial triol such as glycerine or 1,2,6-hexanetriol, they are referred to herein as trihydroxy mixed poly(oxythylene-oxypropylene) ethers of the triol. Excellent results are obtained in the practice of the invention when these compositions are prepared as described in U. S. Patent 2,733,272, have the oxyethylene groups from about 20 to about 80 mol percent of the total oxyalkylene groups and have a minimum average molecular weight of at least 1500.

The invention also contemplates the use of polyoxyethylated-polyoxypropylated triols containing 2 to 6 carthe water is heated to relatively high temperatures such as are employed in the generation of steam under superatmospheric pressures and the corresponding tempera tures.

bon atoms in the initial triol which are prepared by first adding propylene oxide, e. g., 1,2 -propylene oxide, to the initial triol followed by the addition of ethylene oxide.

As in the case of the mixed polyethers, the weight ratio of propylene oxide to ethylene oxide should be within the range of from 9:1 to 1:9.

The addition products employed for the practice of the invention for the most part are liquids, although it is possible to employ compositions which are solids provided Patented Feb. 24, 1959 v in inhibiting the foaming of water in a steamgenerator' will depend upon several factorsarnong them the percent of solids in the foaming liquid, the nature of the solids,

the alkalinity, temperature and pressure, the type and degree: of circulation in the steam generator, the rate of steam production and the amount of foam suppression desired. It is therefore impossible to state any rigid rules for estimating the amount of the antifoam composition to be employed. The amounts of the antifoam compositions employed in the present invention, however, are ex tremely small and for most purposes satisfactory results are obtained at dosages within the range of 0.001 grain per gallon (g. p. g.) to 0.02 g. p. g, Within this range it will often be found that an optimum foam suppressing effect occursat a particular dosage. For example, in one series of tests as hereinafter described, the optimum suppression of'foam on a water containing 5 0 g. p. g. of dissolved solids was obtained at a'dosage of 0.005 g. p. g. Since one grain per gallon corresponds to -17.1 parts per million it will be recognized that the quantities of antifoam composition required for the purpose of the invention are very small indeed and in general it can be said thatquantities greater than 0.1 g, p. g. in the feedwater would seldom be required and depending upon the conditions of operation might produce a less desirable result,

than a smaller dosage.

The tests to evaluate the invention were carried out in a Industrial and Engineering Chemistry, vol. 27, pages It was also equipped with an automatic tion at the rate of 5 to 6 gallons per hour at 250 pounds per square inch (p. s. i.) gauge pressure. A continual recording was made of the relative co nductivity of the condensate from the'boiler, and continual observations were made of the character of the'boili ng andthe amount of foaming as seen through the sight glasses. When the antifoam thus introduced continuously/with the feedwater was no "longer able to overcome the foaming tendencies brought about by the concentration of dissolved solids in the boiler water, the foam height became great enough to cause boiler water to be carried out of the boilerwith the steam, and this end point of the test was determined both by observation through the sight glasses, and, particularly, by the abrupt increase in the conductivity of the 4 EXAMPLE I e The test water employed in this example was prepared from a zeolite-softened Chicago tap water which, after '-the addition of various salts contained 30 g, p. g. of iNa SO 5 g. p. g. of NaCl, 1 g. p. g. of Ca (as CaCO 1 g. p. g. of Mg (as CaCO and enough sodium bicarbonate to giveanM alkalinity (as NaHCO of 17 g. p. g. This water was then treated with 2. g. p. g. of chestnut organic tannin and. various dosages of. the compositions to be tested' and evaporated in a test, boiler of the type previously described at 250 p. s, i. at the rate o f 5,gallonis per hour until gross carryover occurred.

A blankrun on this testwater under these test=conditions where no antifoam c omposititon was added to the 'water gave a carryover at a total dissolved solids value of approximately 134 g. p. g.

The results obtained with various antifoam compositions in accordance with the invention at various dosages were as follows:

Dissolved Solids at Carryover (a p. a)

Material Amount In the foregoing tests Composition A was a test-composition known as Dow Polyglycol 90-1 having a molecular weight in excess of 1500, and made by the addition of ethylene oxide and propylene oxide to glycerol in a weight ratio of 90% ethylene oxide and 10% 1,2-propylene oxide. This composition had a viscosity of 1225 centistokes at 100 F.

Composition B was a composition known as Dow Polyglycol 19-350 made by the addition of a mixture of ethylene oxide and propylene oxide to glycerol in the manner describedin U. S. Patent 2,733,272, the weight ratioof propylene oxide to ethylene oxide being approximately 2:1 and the reaction being carried out until the viscosity, was 350 centistokes at 100 F.

EXAMPLE II The test procedure was carried out as in Examplel v except that the test waterwas a well water re-enforced with NaCl, NaHCO Na SO and Na CO togive a;con-,, centratable dissolved solids content of 210 g.;p. g. with; an M alkalinity equal to 10% of the dissolved sol ids This waterwas then treated with 3.0 g. p. g. of chestnutsteam, as shown in the continuous-recorder. Atthis end 7 point, a sample of the boiler water was withdrawn from j the boiler and analyzed, and ltheelfectiveness of the antifoam, expressed in terms of the totaldissolved-solids con-. centration which it permitted the.b0iler; to .carry, was

noted.

By comparing the totaldissolved solidsvalue of a water... I

containing no added antifoam. composition iththe total i x i i iier hs .i l at a sq b ti qt i it dby te ely ns aa r.

dissolved solids; value of thewat er containing the antifoam.

organic tanninandthe antifoam tests were carriedout;

according to the test procedure previously described by; boiling the water in a boiler at 250 p. s. i.vand at--a rate 1;: of 6 gallons perhour until gross carryover was obtained.

In this series of tests a composition known as Dow.-

Polyglycol 15200-at a dosage of 0.005 ;grain per gallon gave a total dissolved solids value at carryover of 1106 g. p.g.

Another composition within the scope of the invention,; namely, Dow Polyglycol 15-500, under the same test con-.. ditions at a dosageof 0.005 g. p. g. gave atotaldissolved 1, solids value at carryover of 2791 g. p. g.

The Polyglycol 15-200 is a trihydroxy mixed poly.-.. .(oxyethylene-oxy-1,2-propy1ene) ether of glycerol made by adding a mixture of ethylene oxide and 1,2-propylene oxide in an equal molarratio as described-in Example II of U. S.:Patent 2,733,272,-the mol ratio of said oxides to.

said glycerolbeing 72:1 and the viscosity of the resultant-.-.-'

product .being approximately 200 centistokesat=-100. F;

'TheBolyglycol 15 500 is similarly preparedexcept-thata the mol ratio of alkylene oxides to glycerol is 264:1 and l l 1 l product is around 489 centi Parts per million Calcium hardness (as CaCO 178.0. Magnesium hardness (as CaCO 185.0 Alkalinity (methyl orange) (as CaCO 1370.0 Sodium chloride (as NaCl) 334.0 Sodium sulfate (as Na SO 1950.0 Tannin extract, dry"-. 51.0

EXAMPLE III This example illustrates the preparation of polyoxyethylated-polyoxypropylated glycerol suitable for the practice of the invention.

One pound of glycerine and 60 grams of an alkaline catalyst such as NaOH or KOH was charged to a pressure kettle, with good agitation and proper temperature controlling facilities. This mixture was heated to 120 C. to 150 C. and then 1,2-propylene oxide was added maintaining a temperature of 120 C. to 150 C. and pressure of 25 to 100 pounds per square inch gauge until 70 pounds of 1,2-propylene oxide per pound of glycerine was added. Samples were taken when 40, 50, 52 /2, 55 and 57 /2, 60, 62 /2, 65 and 70 pounds of 1,2-propylene oxide per pound of glycerine had been added. To each of the above samples 0.35, 0.44, 0.51, 0.57, 0.62 and 0.65 pound of ethylene oxide per pound of oxypropylated glycerine base material were added. In this way a series of 54 compositions. suitable for the practice of the invention are prepared. These compositions are preferably neutralized with glacial acetic acid to neutralize the catalyst and stop the reaction.

As previously pointed out the oxyethylene groups in the oxyalkylated trihydroxy polyethers preferably represent from about 20 to about 80 mol percent of the total oxyalkylene groups. The optimum results appear to be obtained with compositions in which the oxyethylene groups represent from 33 to 60 mol percent of the total oxyalkylene groups. Especially good results have been obtained where the oxyethylene groups represent about 50 mol percent of the total oxyalkylene groups and there is an average of at least 50 oxyalkylene groups 'per glycerol nucleus.

Where the addition product employed in the practice of the invention is made from glycerol, ethylene oxide and 1,2-propylene oxide, it has the following structural n o onormxocntom).

in which as and y are integers such that the total average molecular weight is at least 1500, the weight ratio of 1,2-oxypropylene groups to oxyethylene groups is within the range of 9:1 to 1:9 and the oxyalkylene groups can square inch and the corresponding temperatures. Excel lent results have been obtained with the practice of the invention at pressures within the range of 100 to 300 pounds per square inch and the corresponding tempera tures. The invention can also be used, however, in con nection with the generation of steam at much higher pressures and the corresponding temperatures, as, for example, in stationary boilers operating at pressures as high as 1000 to 1500 pounds per square inch. The compositions employed in accordance with the invention are elfective not only in inhibiting foaming but also in conditioning and improving the quality of the steam. For this purpose, they may be used in even smaller amounts than the amounts required for the complete inhibition of foaming and priming.

The compositions employed in .the practice of the invention are desirable when used in conjunction with other organic water treating chemicals of the tannin and lignin types. On waters high in mangesium salts in which the magnesium in the boiler will generally be in the form of magnesium hydroxide, it is desirable that a suflicient amount of a powdered tannin, sodium lignin sulfonate or desulfonated lignin be employed along with the antifoaming composition of the present invention to nullify the effect of the magnesium hydroxide in selectively adsorbing the antifoam material. If this effect is not nullified the magnesium hydroxide may take the antifoam material out of the boiler water so that the full antifoam action is not exerted by the antifoam composition. However, when an organic material such as a tannin is added, magnesium hydroxide appears to lose its ability to interfere with the action of the antifoam agent. Inasmuch as most boiler feedwaters encountered will have varying amounts of magnesium salts present, it is desirable that the compositions used in the practice of the present invention be mixed with the hydroxylated organic compound such as tannin, sodium lignin sulfonate or desulfonated lignin, prior to addition to the boiler feedwater. In general, when the polyoxyalkylated triol is incorporated with tannins, sodium lignin sulfonate and desulfonated lignins prior to adding it to the boiler feedwater, the quantity of the polyoxyalkylated triol is within the range of 0.5% .to 12% by weight of the total composition and the total quantity of tannins, sodium lignin sulfonate and/or desulfonated lignins is within the range of about 50 to about 97% by weight of the composition.

A few examples will serve to illustrate the preparation of suitable dry-appearing, dispersible compositions adapted to be added to boiler feedwater in the practice of the invention.

Example A: Parts by Weight Polyoxyalkylene triol of Examples I, II and III 3 Desulfonated li nin 97 The resultant composition is prepared by adding the polyoxyalkylated triol to the dry pulverized lignin derivative in a putty chaser type mixer. It is a dry, freeflowing composition readily dispersible in water.

, Example B: Parts by weight Polyoxyalkylated triol of Examples I, II and III 3 Refined tall oil 2 Desulfonated lignin 95 This composition is readily and completely dispersible in water, the residual alkalinity of the lignin derivative serving so convert the refined tall oil to soap when the composition is added to water and the strong foam inhibiting action of the polyoxylalkylated triol serving not only to abate the foam produced during steam generation but also overcoming any foaming action that might ordinarily be caused by the tall oil soap.

It will be understood that the tennis, sodium lignin sulfonate and/ or desulfonated lignins are not necessarily addition of the latter to the feedwater. Where it is 'de'-' sirable to use tannins, sodium lignin sulfonate and/o1 Table Tannins, Sodium, Lignin Sulfonate and/r Desulfonated Lignins, Grains per Gallon in Boiler Water Magnesium-Grains per Gallon in Boiler Water (expressed as OaC Os) As will be apparent from the foregoing description, the compositions employed in accordance with the invention do not all give the same results and from that standpoint are not necessarily equivalents.

ing and condition steam on a very economical basis.

In the specification and claims the expression boihng under superatmo-spheric pressure and temperature cond1- tions is intended to include and cover those conditions where steam is generated at temperatures above 100 C.

and at superatmo-spheric pressures. The expression addition products substantially insoluble in said boiler waterat the temperature of steam generation refers to thecharacteristic of the addition product which causes it to separate into two phases when a solution thereof-is heated 1 from ordinary temperatures around C. to the temperature at which steam is generated. The quantity of the addition product actually employed for the purpose Some of these compositions are exceptional in their foam inhibitingproperties and their use makes it possible to inhibit fo'am-- of the invention may be so small that this insolubility is diflicult to observe but any-of the polyoxyalkylene triols of the type herein described whendissolved in a 1% -solu tion in water at ordinary temperatures and heated to 100 C. at atmospheric pressure with the separationv of an in soluble phase is satisfactory for the purpose of the invention.

The invention is herebyclaim'e'd as follows:

1. A method of generating steam from a boilerwater having a tendency to foam on boiling which comprises.

dispersing in said watera quantity of an addition product of an alkylene triol containing 3 to 6 carbon atoms, propylene oxide and ethylene oxide. in which theweight ratio of propylene oxide to ethylene oxide is within the range of 9:1 to 1:9, the average molecular weight of said addition product is at least- 1500 and said addition product is substantially insoluble insaid boiler water at the temperature of steam generation,- thequantity of said dispersing in said water a quantity of an addition product of analkylene triol containing 3 to 6 carbon atoms, propylene oxide and ethylene oxide in which the weight ratio of propylene oxide to ethylene oxide is within the range of 9:1 to 1:9, the average molecular weight of said addition product is at least 1500 and said addition product is substantially insoluble in said boiler water at the temperature of steam generation, the quantity of said addition product being effective to inhibit the tendency of said water to foam on'boiling, and boilin'gthe'resultant aqueous dispersion under superatmospheric pressure and temperature conditions.

3. A method'of generating steam from a boiler water having a tendency to foam" on boiling which'co'mprises dispersing'in said water a quantity of anaddition product of an alkylene triol containing 3'to 6 carbon atoms, propylene oxide and ethylene oxide in which the weight ratio of propylene oxide to ethylene oxide is within the range of '9:1 to 1:9, the average molecular weight of said addition product is at least 1500 and said addition product is substantially insoluble in said boiler water at the tem perature of steam generation, the quantity of said addi tion product being effective to inhibit the tendency of said water to foam on boiling, and heating the resultant aqueous dispersion-at pressures within the range of 100' to 1500 pounds per squareinch and the corresponding temperatures.

4. A method as claimed in claim l in whichthe oxy-. ethylene groups represent from about 20 to about 80' mol percent of the. total oxyalkylene groups in said addi tion product.

5. A'method as claimed in claim 1 in which the oxyethylene groups represent from 33% to of the total oxyalkylene groups in said addition product.

6. A method as claimed in claim 1 in 'whichsaid addition product has a molecular weight within the range from 1500 to 6000.

7.. A method as claimed in claim 1 in which said addition product contains a mol ratio of alkylene oxide per mol of triol within the range from about 30:1 to 300:1.

8. A method of generating steam from a boiler water having 'a tendency to foam on boiling which comprises" dispersing in said water a quantity of a trihydroxy mixed poly (oxyethylene-oxy-1,2-propylene) ether of glycerol in' which the oxyethylene groups represent from about 20' to about mol percent of the total oxyalkylene groups, there'is an average from 30 to 300 oxyalkylene groups per'glycerol nucleus, and the average molecular weight is atleast 1500,. the quantity of said addition product beingeffective to inhibit the tendency of said water'to foam on boiling, and boiling the resultant aqueousdis per'sion under superatmospheric pressure'andtemperature" conditions.

a 9. A method as claimed in claim 8 in which the oxy- "ethylene groups represent. about 50 mol percent of the total oxyalkylene groups in said polyether.

References Cited in the file of this patent UNITED STATES PATENTS 2,575,276 Jacoby Nov. 13, 1951 2,727,009 Jursich Dec. 13, 1955 2,733,272 Horsley an; Jan."31,1956

Claims (1)

1. A METHOD OF GENERATING STEAM FROM A BOILER WATER HAVING A TENDENCY TO FORM ON BOILING WHICH COMPRISES DISPERSING IN SAID WATER A QUANTITY OF AN ADDITION PRODUCT OF A ALKYLENE TRIOL CONTAINING 3 TO 6 CARBON ATOMS, PROPYLENE OXIDE AND ETHYLENE OXIDE IN WHICH THE WEIGHT RATIO OF PROPYLENE OXIDE TO ETHYLENE OXIDE IS WITHIN THE RANGE OF 9:1 TO 1:9, THE ETHYLENE OXIDE IN WHICH THE WEIGHT SAID ADDITION PRODUCT IS AT LEAST 1500 AND SAID ADDITION PRODUCT IS SUBSTANTIALY INSOLUBLE IN SAID BOILER WATER AT THE TEMPERATURE OF STEAM GENERATION, THE QUANTITY OF SAID ADDITION PRODUCT BEING EFFECTIVE TO INHIBIT THE TENDENCY OF SAID WATER TO FOAM ON BOILING, AND HEATING THE RESULTANT AQUEOUS DISPERSION TO THE BOILING POINT.