US2439784A - Process of boiling out steam boilers prior to placing them in operation and composition therefor - Google Patents

Description

rials, WIP'QII ere i seht in i e' f l wh h Patented Apr. 13, 1948 iJN'l TED. STATES QF Fg gg 2,439,784 PBoQhs's QF 13.0mm our sum BOILERS PRIOR; To" PLAGING THEM; INFOPEMHGN AND GOMBOSITION THERE-151231 v Cgna ld-s d signs Sepial No. 57053 57.-

7. C aims.- (C -fi rlik This inven ion el tes .9 ihe bqilihs 9! 9f steam boile s p ior to. pla in them h e erd hh er the enerat n i s eam- 1; no ommon w. .s hdiiers with el se ihe seiusiehs e hiaih s .ehe ieel su h as sedihi s i at ed Q'IQX QQ sediiim eifbe hte s dium phqd e. 9. i iies ee Th shied; e t is ieq ihs out or sleeh he r ces s he remove eii dirt, he e euiiih s, m l scale an Qiher wide rabi s meteconstructed. Solid foreign niatter should, mov d f om e W heiler before s p eeersiieh in rder 9 P FB Q i ens fih erierehee t he flee 319W of Weber thrbush rgst ipt ions in the boiler such as tube ptramies eh s iiee I is ad isab e he mo h 'qi ehehhss b eu o erw se he e iid e i w th pr r h e s h ier, thereby esul ing n eizheeiihe ith eon eh dama e to e boiler h e or a e st te' ee z d erees- E mhehm f Ql m 1l 2 oi a e ho 1 1 191 6 he pre th boi er s pissed in o t o sehenifieef iqhef sheh oi y m ter re u ts irehi c bin iieh i h soluble e heiis n the a er-used fer nredhsihs ste m and eh s n ee eh esult intihe iqrmation pf soap which induces eitreii e ihihess of the whe This ehd ieh deseleretes har -o er f l u d r m he i r whis in hse n iderab e d mage is aux iar I equ pment such a supe hehiers ih ile s ne sfenere hg or ower-d i e equ pment iie e sieemh eh b n s shd Pu p and i er ain reee se w er t m s u e in d m e t9 th prpdiiet- Q As n evio is y me tioned the s e hi el w ieh have been used in the p s ior s ehihe new i rs have always been the sqd hm e e hieh s- Sod um si e o exam le sodium me t9. pgqqucg sigeam the high pressures and temfiqn of sodium'silicate I d in spite cases the silica, i'sfigie darned ever with the steam d1 te deposits 01113116, blades The dehe of ilic des reqpgesf the capacity a a W re t e ee lar e in .e s P QB! 0111? he turb an 1984 it such as. yvgsmng withstrqng dseis de sehh ehsi h heh e l e l f the scalas by sand'blasigin $1. deegydenee w the Rreseht inven io I e e? T is lt he" m h d? see h e i i s h hpii n Whe ea is e'seele forms i b iie s e d h s he e her i e en hil ih ldih i s ih s a em era res an shim ch m cals Q by isfeeh e h s e s i s e i m 8 s ,Jgierein geg'r xiom particularly s he l hs ou ste m it, th m tio Q 9r iiihihe. w en h .ehi- To red hi st .eisisi whe e h h sil ca M25103, h e b used r d a ine-ou L .7

new heiie he si ca e b n pa t c la y deine le beca of the r emuls yin hhd nep' izih e iesi o il a d re se he te ent W99 ties and hei abil t t9 di perse sol d fi e 12 times. be n use along ith the sodium ii eie d 1 pd othe des ed p ep s o the bqi ihi selui en- A u h sod um s ica e s i ve f stive deter ent, i is alm t mpp s bl 0 i iis out the boiler so as to rempve all of this cleaning e e l ethe sed h C emi al ha e i ch mical a er h in o nrdeess he .be h

Qmme e As e r su t undesi b eh hi hig of so ium silicate may 3 119 131 inthehe dirte she o di ar boi n eute s iiiis he ener- 3 5191.15 Wh n th he ier s pi sed h epeheiihh fpig 15 p913 slum is i mere esne- 91 y dhe preis e s hei hyihe t m- .h QSfiY? 2f 5 9b ibees is mo e regdll attained. It as be j 'b .Qed e eatedly v es ha 5811 2 th hdilers e 'f d '91:" d a l erhqilirg out w th mixe his ding he e iim ehehi ee s m s:-

grease are more completely emulsified than when sodium salts only are employed. 7

There is a wide variety of compositions and solutions which may be employed according to my invention. The solution must be sufiiciently alkaline to efiectively remove oil and grease. It should contain a silicate because'of the detergent properties which silicates possess. There should be a certain maximum ratio of silica to.

4 of the operation by the conversion of the trime taphosphate to sodium tripolyphosphate.

The water-insoluble crystalline alkali-metal metaphosphates also become effective under the conditions of use. Water-insoluble crystalline sodium metaphosphate is solubilized by potassium salts, and water-insoluble crystalline potassium metaphosphate is solubilized by sodium salts. The insoluble crystalline alkali-metal metaphosphates will even cause each other to go mutually into solution in water, the dissolving action being accelerated by increase in temperature. Since both potassium and sodium salts will i usually be present in the water during the boilalkali-metal oxide, and a certain minimum ratio of potassium to sodium in order to insure that the silicate formed will be predominantly potassium silicate rather than sodium silicate, thereby producing a soluble silicate rather than an insoluble silicate. The composition used in making the cleaning solution may be made up entirely of potassium chemicals, or of potassium and sodium chemicals, provided it has the required minimum ratio of potassium to sodium.

In order to form soluble silicates rather than insoluble silicates, the ratio of silica to alkalimetal oxide, when expressed in equivalents, should be not more than 1:1, and the ratio of potassium to sodium, when expressed inequivalents, should be at least 0.5:1. I

The composition always contains one 'or more alkali-metal silicates, the preferred range being about 10% to 40% by weight. Although the alkali-metal metas'ilicatesjarefpreferred, I may use alkali-metal silicates having a lower 'or a higher ratio of alkali-metaloxide'to SiOz than the metasilicates', provided that the composition as a whole has'the properalkalinity, ratio'of silica to alkalinity, and ratio of'potassium to sodium. I may use alkali-metal silicates having a mol ratio of alkali-metal oxide to Si02 from 2:1 to 1:4. I may use "the alkali metal ortho silicates, sesquisilicates, metasilicates, disilicates, or tetrasilicates. The orthosilicates and tetrasilicates have, respectively, mol ratios of alkalimetal oxide to Si02 of 2:1 and 1:4. The other silicates have intermediate ratios. The silicates may be either potassium silicates or sodium silicates, or mixtures of potassium and sodium silicates.

In addition to the'silicates the composition preferably contains one or. more 'molecularly dehydrated phosphates which have the property of sequestering calcium. Among the molecularly dehydrated phosphates are the crystalline alkalimetal metaphosphates, pyrophosphates, tripolyphosphates and the alkali-metal phosphate glasses. Either glassy or crystalline'molecularly dehydrated phosphates may be'employed; provided that they have the property of sequestering calcium under the conditions of" use.

The water-soluble crystalline sodium metaphosphate commonly known as sodium trimetaphosphate does not exhibit this property in neutral solution at ordinary temperatures. However, in an alkaline solution it'is converted into the calicum-sequestering sodium tripolyphosphate, this conversion being accelerated by in crease in temperature. Thus, when sodium trimetaphosphate is used with the alkaline materials required to produce the desired detergent action during boiling out a boiler, sequestration of calcium is developed during the early stages ing out of a boiler according to my invention, the water-insoluble alkali-metal metaphosphates may be employed eifectively.

When an alkaline solution is used in boiling out a boiler containing oil or grease, and if the water used in making up the boiling out solution contains calcium,or if calcium is present in the dirt contained in the boiler, the calcium will form insoluble soaps; By the use of a molecularly dehydrated phosphate, the formation of insoluble soaps is prevented until the alkalis present have had an opportunity to react with the oil or grease. Upon continued heating the sodium metaphosphate or other molecularly dehydrated phosphate reverts to the orthophosphate, forming calcium orthophosphate'sludge which adsorbs the oil or grease and other foreign material. r V

The molecularly dehydrated phosphates may be made from potassium salts, sodium salts, or

mixtures of potassium and sodium salts, provided the cleaning composition as a whole has the proper ratio of alkali-metal oxide to silica and the proper ratio of potassium to sodium. The molecularly dehydrated phosphate or mixtures of such cium for a time sufficient to enable the alkaline solution to efiectiveiy emulsiiy any oil or grease that may be present in the boiler which is being cleaned. Where the boiler to be cleaned contains a large amount of oil or grease, it may be found desirable in some cases to acid calcium or magnesium salts which are ultimately precipitated in the boiling out process, thereby increasing the amount of precipitate available for adsorbing the oil or grease. Instead of, or in conjunction with, the addition of calcium or magnesium salts, the effect of producing precipitate for oil or grease adsorption may be obtained by using raw water or sea water which naturally contain these calcium and magnesium salts.

In order to increase the alkalinity of the composition strong alkalis such as sodiiun or potassium hydroxide, orthophosphate or carbonate, may be included. Thus, where the silicate used is the metasilicate, or when any silicate which is less alkaline than the metasilicate is employed, it may be found desirable to include one or more of sodium or potassium hydroxide or carbonate in the composition. Where the orthosilicate is used it may be found that no additional alkali is required. If sodium or potassium hydroxide or carbonate is used it may be used in amount up to' about 50% by weight of the composition, for example, in amounts from about 10% to 50%.

Although tripotassium orthophosphate or trisodium orthophosphate are not essential constituents of the composition,'-they-are desirable ingredients. They form calcium :orthophosphate precipitate uponultimate-reaction with the cal.- ciumpfshard water, this precipitate aidingw in adsorbing oil.

if desired, the boiling outcomposition may contain an inhibitorof embrittlement such, for examples/s tannins, lignins, the waste sulphite liquors :produced in paper making, or nitrates such assodium or potassium nitrates, all of which provide additional protection against embrittlee ment of the boiler metal. Wetting agents'which are stable in alkaline solutions may also be included in the chemical-mixture for cleaning boilers in order to efieot better wetting of surfaces and thus prcduceabetter cleaning action by the other chemicals used.

The iollowing are examples of suitablecompcsitions'ior use according to my invention.

Example No. 1 g

f Parts llripotassium phosphate. 14 S dium or po as iummolecularly d hydrated phosphate s. 36 Sodium or potassium metasi1icatc 23 Potassium hydroxide v r 27 Erample N0. 2

Parts Trisodium -phos,phate. 12 Potassium pyrophosphate- 38 Sodium metasilicate l- 21 Potassium hydroxide.-. 27 Sodium nitrate,.- 2

Example No. 3

Parts Sodium or potassium molecularly dehydrated phosphates 24 d um or potassium metasilicate 30 Sodium or potassium sesquisilicates 6 Potassium hydroxide c 40 Example No. 4

Parts Sodium or potassium molecularly dehydrated phosphate 24 Sodium or potassium metasilioates 29 Sodium o l-potassium sesquisilicates '6 Potassium hydroxide 39 Tannin i l 2 Erample No. 5

Parts Tripotassium phosphate 16 Potassium molecularly dehydrated phosphate 38 Sodium metasilicate 21 Sodium hydroxide 25 Example No. 6

Parts Potassium pyrophosphate Sodium or potassium molecularly dehydrated phosphate 40 Sodium or potassium metasilicate 21 Potassium hydroxide 27 Sodium or potassium nitrates 2 Example 7 Parts Sodium or potassium molecularly dehydrated phosphate 24 Sodium or potassium metasilicates 28 Sodium or potassium sesquisilicates 6 Potassium hydroxide 38 Calcium hydroxide 4 In cleaning a new boiler it is only necessary to heat the cleaning solution to a temperature 16 suflicient inset. circulation, I a pressure of about 10'toz150 pounds per square inch generally being sufiicient. The compositions are used in an amount ofat least3 pounds per thousand pounds ofcwater in the boiler, which is aconcentration of 3,000 P. P. M. Preferably the amount of the composition used is such as to produce a concentration of solids in-solution of at least 5,000 P. P. M. up to 10,0001P'. P. M., or 20,000 P. P. M. The'proportion of alkali in the composition and the. amount of the composition used in making thecleaning outsolution preferably are such as to produce a cleaning out solution having a caustic alkalinity of from aboutloo to about 2500 P. P. M., the caustic alkalinity desirably being not lessthan 500 P. P. M. The boiler preferably is boiled out for 24 hours or more, although this will vary according to the'particular conditions encountered. After the cleaning of the boiler has been completed, the cleaning solution is withdrawn from the boiler and the boiler is flushed out with clean water, after which it is ready to be put into operation for the generation of steam.

The invention is not limited to the examples which have-beengiven merely by way of illustration, but may be otherwise-embodied or practiced within the scope of the following claims.

I claim:

1. r The process of boilingout steam boilers'prior to placing-them in operation for the generation of steam, which comprises circulating through the boiler a heated aqueous alkaline cleaning solution having a concentration of solids in solution of at least 3,000 parts per million by weight, saidsolution containing about 10% to 40% by weight of at least one alkali metalsilicate selected from the group consisting of sodium silicate and. potassium silicate based on the solids in solution,

said solution having a caustic alkalinity of about to about 2500 parts per million by Weight, maintaining in said solution a ratio in equiva-- lents of silica to'total sodium oxide plus potassium oxide of not more than 1:1 and'a' ratio in. equivalents of potassium to sodium of at least. v 0.5:1, said circulation being continued until the:

boiler is effectively cleaned, withdrawing the: cleaning solution from the boiler and flushing it out with'clean water.

2. The processofboilingout steam boilers prior to placing themin operation for the generation of steam, which comprises circulating through the boiler a heated aqueous alkaline cleaning solution having a concentration of solids in solution of at least 3,000 parts per million by weight, said solution containing about 10% to 40% by weight of at least one alkali metal silicate selected from the group consisting of sodium silicate and potassium silicate based on the solids in solution and from about 5% to 50% by weight of at least one molecularly dehydrated phosphate selected from the group consisting of molecularly dehydrated sodium phosphate and molecularly dehydrated potassium phosphate based on the solids in solution, said solution having a caustic alkalinity of about 100 to about 2500 parts per million by weight, maintaining in said solution a ratio in equivalents of silica to total sodium oxide plus potassium oxide of not more than 1:1 and a ratio in equivalents of potassium to sodium of at least 0.5:1, said circulation being continued until the boiler is effectively cleaned, withdrawing the cleaning solution from the boiler and flushing it out with clean water.

3. The process of boiling out steam boilers prior to placing them in operation for the gen 7 v eration of steam, whichzfcomprises, circulating through the. boiler a heated aqueous alkaline cleaning solution having a concentration of solids in solution of at least 3,000 parts per million by weight, said solution containing about 10% to 40% by weight of at least one alkali metal silicate selected from the group consisting of sodium silicate and potassium silicate based .on the solids in solution and from about to 50% by weight of at least one molecularly dehydrated phosphate selected from the group consisting of molecularly dehydrated sodium phosphate and molecularly dehydrated potassium phosphate based on the solids in solution and an eflective amount up to about 50% by weight based on the solids in solution of at least one strong alkali selected from the group consisting of the shydroxides and carbonates of sodium and potassium, said solution having a caustic alkalinity of about 100 to about 2500 parts per million by weight, maintaining in said solution a ratio in equivalents of silica to total sodium oxide plus potassium oxide of not more than 1:1 and a ratio in equivalents of potassium to sodium of at least 0.5:1, said circulation being continued until the boiler is effectively cleaned, withdrawing the cleaning solution from'the boiler and flushing it out with clean water. p

4. A composition for boiling out steam boilers, comprising by weight about to about 40% of alkali metal silicate selected from the group consisting of sodium silicate and potassium silicate, having a molar ratio of alkali metal oxide to silica between 2:1 and 1:4, and about 5% to 50% of at least one molecularly dehydrated alkali metal phosphate selected from the group consisting of molecularly dehydrated sodium phosphate and molecularly dehydrated potassium phosphate, the ratio in equivalents of silica to total sodium oxide plus potassium oxide in the composition being not more than 1:1, the ratio in equivalents of potassium to sodium in the composition being at least 0.5:1.

5. A composition for boiling out steam boilers, comprising by weight about 10% to about 40% of at least one alkali metal silicate selected from the group consisting of sodiumsilicate and potassium silicate, having a molar ratio of alkali metal oxide to silica between 2:1 and 1:4, and about 5% to 50% of at least one molecularly dehydrated alkali metal phosphate selected from thegioup consisting "of molecularly dehydrated sodium phosphate and molecularly dehydrated potassium phosphate and about 10% to of at least one strong alkali selected from the group consisting of the hydroxides and carbonates of sodium and potassium, the ratio in equivalents of silica to total sodium oxide plus potassium oxide in the composition being not more than 1:1, the ratio in equivalents of potassium to sodium in the composition being at least 0.521.; 1 v

6. A composition for boiling out steam boilers, comprisingby weight about 10% to about 40% of at least one alkali metal silicate selected from the group consisting of sodium silicate and potassium silicate, having a molar ratio of alkali metaloxide to silica between 2:1 and 1:4, and about 5% to 50% of at least one molecularly dehydrated alkali metal phosphate selected from the group consisting of molecularly dehydrated sodium phosphate and molecularly dehydrated potassium phosphate and about 10% to 50 of potassium hydroxide, the ratio in equivalents of silica to total sodium oxide plus potassium oxide in the composition being not more than 1:1, the ratio in equivalents of potassium to sodium in the composition being at least 0.511.

7. A composition for boiling out steam boilers, comprising by Weight about 10% to 40% of potassium silicate having a molar ratio of K20 to SiOz between 2:1 and 1:4, about 5% to 50% of at least one molecularly dehydrated sodium phosphate and about 10 %-t0 50% of potassium'hydroxide, the ratio in equivalents of silica to total sodium oxide plus potassium oxide in the composition being not more than 1:1, the ratio in equivalents of potassium to sodium in the composition being at least 0.5:1.

' WENDELL W. CERNA.

REFERENCES CITED The following references are of record in the file of this patent:

V ,UNITED V STATES PATENTS Date Number Name 2,035,652 Hall Mar. 31, 1936 2,248,656 'Bird July 8, 1941 2,333,443

Robinson Nov. 2, 1943