Organic Matter in Boiler Feed-Water Treatment D. K. FREKCH, 503 Hawthorn Lane, Winnetka, Ill. In the field of water treatment N THESE days of general T h e influence of tannins in water treatment, and special interest in methcombined’ with inorganic compounds, is greater there are three ty~’es Of to be considered if a boiler is to ods for obtaining maximum 1hu.n is generally realized. Examples are cited operate smoothly, economically, efficiency f r o m t h e m o d e r n in the Jields ?f scale formation, corrosion, and and safelv: scale formation (the steam-generating plant, the subfoaming, and a n efforl i s made to explain the deposition of impurities from ject of water and its treatment is of special importance, as i t is results. As gas absorbents and embrittlement water), corrosion (the destrucone of the three essential factors ~ y action of the water or its byinhibitors, the tannins hate been s u c c e s s j ~ a ~tive products on the boiler or a n y in steam production; the other used. part of the boiler system), and two are the fuel, and the boiler foaming (the uneven steaming itself. A search of the literature shows a marked absence of work relative t o the effect of the in the boiler or the removal, mechanically or otherwise, of addition of organic matter to the boiler water. The use of boiler water through the medium of steam). organic matter is not, as a rule, taken seriously by the scientist; SCALE FORM-4TIOK and although this use is quite general, it is almost entirely Much scientific research has been done in the field of scale through the niediuni of boiler compounds (preparations of unknown or disguised chemical content) used under such condi- formation, but in almost every case it has been from the viewtions that data on results obtained are unreliable. Consider- points of the scale-forming impurity, its solubility, and its able success has been achieved through the use of properly ad- separation, and of the mechanics and chemistry of scale justed compounded material, but absence of reliable knowledge formation. With this knowledge has come the certainty of its compoFition has robbed the data obtained of scientific that the scale-forming agent can and should be completely value. Furthermore, a$ the most valuable results are brought removed, and that once removed all danger from it will be about in the boiler and under greatly increased boiler pressures gone. As a result, scale-preventing technic has concentrated and temperatures, it is difficult to carry out constructive work on the removal of the scale former. The assumption is not without special and elaborate equipment with which fern re- entirely true. There are natural solubilities characteristic search laboratories are fully supplied. of the various water impurities which limit the degree to This is unfortunate as there is a n important place in boiler which they can be purified; in the absence of heat and withwater control for certain of the organic or vegetable mate- out the exchange silicates, this degree is far from complete. rials. It is the purpose of this article to call attention to ex- I n the field of organic chemical compounds there are available periences, observations, and investigations from which it is additional materials which can supplement, increase, or comhoped that greater interest will be aroused in the latent pletely replace some of these familiar inorganic reagents; possibilities in this field. as their efficiency is greatest in the boiler itself and under Organic or vegetable matter has been referred to in water conditions entirely different from those involving softening treatment since the days of the Old Testament (4). I n the reactions, more should be known about them. early days of the steam boiler, the use of kerosene, potato With much work being published on the mechanics of scale peelings, logwood, molasses, etc., was mentioned, but the fact formation (Is),the fact is fairly well accepted that scale was usually overlooked that an organic constituent had been formed in the presence of certain of the tannins is not as responsible in some measure for the observed results. When compact or as certain in its crystalline structure as scale the water softener was in its infancy, organic and inorganic formed in the absence of organic-matter influences. In the chemicals were used internally to such an extent as to neces- open discussion following the initial presentation of this sitate the warning that “the boiler should not be used as a paper, it was brought out that, in the presence of organic reaction kettle.” I n 1900 Edgar (7‘) tried to explain how matter of the tannin type, calcium sulfate crystals were much small amounts of tannins and similar organic materials could smaller, less regular, and in appearance more like fuzz from bring about as satisfactory results as much greater quantities upholstery, than in its absence. The fact can undoubtedly of inorganic chemicals, and in 1913 Wherry (16) suggested be established that crystallization occurring in the presence t h a t colloidal chemistry might offer some explanation At of certain organic materials (especially where the formation t h a t time, and for many years after, these “compounds” of an organic compound is possible) is not as certain, as (about the only name internal or organic treatment materials rapid, or as complete as where such contamination is absent. had a t that time) mere supposed to act in a purely mechanical It is even possible, when a tannin concentration of 8 to 10 way, and methods of tests x-ere based on that idea ( I , 3 ) . grains per gallon is carried consistently in a boiler for a long Articles appearing on the subject of such treatment were by time, to trace a gradual change in the character of crystalline representatives of companies selling the materials and were boiler scale, already deposited, into a soft, dark colored, easily of necessity vague and stressed results rather than reasons removed, noncrystalline deposit. and theories. This was but natural for the entire knowledge I n following what seems to happen, imagine a hypothetical of this a r t of chemical treatment was locked u p in the files water carrying 6.5 grains per gallon of calcium carbonate, 3.5 and records of a few companies. The consultant looked with grains of magnesium carbonate, 3 grains of calcium sulfate, distrust on boiler compounds, discouraged their use, and a t and 5 grains of combined sodium chloride and sodium sulfate. any reference to organic chemicals, naturally thought of them Now imagine a powdered mixture composed of 50 per cent soin the same category as compounds. dium hydroxide and 50 per cent sodium phosphate (n’a2HP04
I
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preferred). This is not what mould be used for external softening, but, as the comparison is to be made on internal results, the presence of so much phosphate is desirable because of the physical characteristics of the phosphate precipitate. Should this preparation be added externally, a pound (or slightly more) per 1000 gallons of water would be necessary for satisfactory softening. I n a hot-process softener, less would be requircd. But assume that the plant has no softener and is so arranged as to necessitate treatment directly introduced into the boiler. Almost the moment this compound is added precipitation d l start. Even without this mixture, increasing temperatures in the feed line will start precipitation because of the liberation of the loosely bound carbon dioxide which is holding the calcium carbonate and magnesium carbonate in solution. The result will be deposition in the feed lines and scaling of the pumps. The powdered mixture will only exaggerate and accelerate this trouble from the point of addition. If, however, this mixture is changed by the addition of a liquid tannin extract, in the rough proportion of one-third tannin extract, one-third sodium hydroxide, and one-third disodium phosphate plus the necessary water to maintain the mixture in the form of a thick paste, and this preparation is substituted for the powdered mixture in even so small a dosage as 0.5 pound per 1000 gallons of water, an entirely different set of conditions will be created. I n the first place, precipitation will not start immediately, but a flocculent, nonsettling sludge will form. I n the case of the inorganic compounds the reactions will be rapid, the phosphate probably acting first and being exhausted before the caustic reactions are well under way. With the addition of tannin the precipitation is retarded to such a degree that very little separation occurs outside of the boiler. This tendency of tannin, in combination with such precipitating agents as have been mentioned, to retard precipitation and inhibit feed-line deposition, while known and used by many for years, has had recent indirect confirmation in the form of a patent (11) taken out on this very feature. I n one case not only was feed-line precipitation stopped, but old deposits, existing a t the time, were slowly softened and removed. The plant, in the neighborhood of Pittsburgh, was one of the largest and oldest of the steel mills. It had a complete softening plant, which, because of unexpected variations in the river supply, frequently delivered incompletely treated water to its several boiler plants. For economy the softening tanks stood together in the center of the plant. Treated water was distributed by underground pipes to the various boiler units, some of which were over 1500 feet away. When the case was brought to the writer’s attention, these pipe lines were nearly plugged up with deposited sludge and the boilers were badly scaled. The treatment prescribed was almost the same as that just mentioned; a mixture of about 60 per cent sodium hydroxide and 40 per cent disodium phosphate was concentrated in tannin extract until the final preparation contained 30 to 35 per cent extract. This was added to the softening tanks, following the addition of the regular softening chemicals. In this way regular softening was not retarded nor were the added chemicals reactive in the tanks. Results did not come a t once, and impurities from the boilers tried the patience of the operators who continued the test. I n the end the supply lines n-ere considered virtually clean, and the boilers in much better shape than ever before. As the alkaline salts employed to produce an insoluble state would naturally discourage a return to the soluble state, i t must be evident that in some way the small tannin content of the treated feed water was the disintegrating factor. Let us return to the hypothetical mater and follow, in theory, the action of this paste on the boiler. From the standpoint of sodium oxide value this mixture will carry
Val. 26, No. 12
about 25 per cent sodium oxide (15 per cent due to sodium hydroxide and 10 per cent to the phosphate). One pound will contain sufficient sodium oxide to react with about 2 grains per gallon of calcium sulfate and on the way will remove perhaps 4 or 5 grains of calcium carbonate and magnesium carbonate. This occurs when one considers only the reactive values of the sodium constituents and ignores the tannin. I n practice, however, entirely different results were obtained in which there seemed to be little relationship between theoretical requirements and actual results. This water approximates the supply of a large utilities plant in Kansas City; using Missouri River water, sometimes the calcium sulfate content ran as high as 5 grains per gallon, and in no case were the theoretical sodium oxide requirements added in the recommended dosage of treatment. This dosage was in the neighborhood of 0.25 pound per 1000 gallons of feed water. Boiler samples were collected for over a year and complete analyses made. I n no case during that period while the treatment was in use was calcium sulfate present; the excess alkalinity represented 75 per cent or better of that added originally as treatment. In addition, the boiler conditions a t the plant were considered most satisfactory. I n the absence of tannins similar results could not be expected. In the presence of tannins, however, some retarding of reactions evidently took place. It is possible that calcium sulfate was precipitated in the presence of the tannin as a noncrystalline sulfate before the alkali of the treatment became reactive. There was calcium sulfate in the boiler sludge although no scale formed, but this may have been as much from disintegrating old scale as from direct precipitation. I n practice, where the use of tannins is understood, treatment of a “starvation” type is being used continuously which is far under the theoretical alkaline requirement. It is true that sludge-removal facilities must be efficient and well used. Mud drums, blow-off (intermittent or continuous), or deconcentrators can solve the sludge problem, and the boiler will benefit through slower concentration of soluble byproducts. Another example is found in a small power plant in Lexington, Mo. The supply at that point shows the following principal impurities : CaCOs
Cas04
MgCOa
4.802 3.079 3.008
NazSO4
NaCl
Total solids
4.419 3.060
-
19.038
The treatment recommended contains 200 pounds of chestnut oak extract and 250 pounds of caustic soda and soda ash to a barrel of approximately 600 pounds. By calculation the estimated sodium oxide content is 29.2 per cent, and in terms for comparison 1 pound per 1000 gallons will add 2 grains per gallon of sodium oxide. The recommended dosage is 0.5 pound per 1000 gallons, which means the addition of 1 grain of sodium oxide per gallon, for a water that actually is softened would require six or seven times as much; a rough calculation calls for approximately l pound of lime and 0.4 pound of soda ash, representing nearly 10 grains per gallon total chemicals. The average run was rarely in excess of 30 days. The first run of about 60 days, with the tannin type of treatment, ended with “scale light and easily removed, mud, no pitting . . . much better than heretofore.” In May a run of 4992 hours (208) days was ended. The boiler water was watched throughout the entire run, and the alkalinities to phenolphthalein were held between 4.5 and 8.0 grains per gallon and always exceeded half the methyl orange alkalinity. The superintendent’s comments were: We have just opened the boiler that \vas taken off duty a few days ago after a continuous run of some 4992 hours. We find the inside condition of the boiler very satisfactory, having no new
December, 1934
ISDUSTRIAL
AND ENGINEERI%G
scale, which means that all residue can be removed by the use of water hose without the need of mechanical turbining. The water line (feed) was found t o be unusually clean and our investigation failed t o disclose any evidence of pitting. There was Some loose scale in the bottom of the boiler that, we are inclined to believe was old scale, perhaps from inaccessible points, that had come loose and fallen out. Sodium tannate itself is an alkaline earth precipitant, and boiler water containing tannins will frequently show a lower residual calcium and magnesium content than where that organic reagent is absent. When the treatment is so constructed, apportioned, and fed into the water as to produce a slight excess of caustic alkalinity, an excess of tannin as re11 is created. The latter tends to increase in concentration while the alkalinity remains within a controlled range. When this caustic excess does not exist, the tannin seems to act definitely as a reagent and is almost completely removed by precipitation. While the tannates of lime and magnesium unquestionably make up part of a precipitated sludge, they are not stable compounds and apparently decompose. Carbonates of these alkaline earths are finally formed, while the tannin radical to a large extent remains in solution. This explains the selective concentration. Xot all organic materials of a tannin origin are effective, however, in controlling scale formation. I n one case where several plants were involved, the supply was from the Wisconsin River which rarely carries a t this point over 3 grains per gallon (50 p. p. m.) total solids. This particular section supplied feed water to and carried wastes away from a dozen paper mills, most of them using sulfur in their manufacturing processes. The water a t this point was always a pale straw color, but the nature of the organic matter producing that color had not bothered anyone seriously. Analyses of the river water made in the usual way showed only traces of sulfate. The scale, which seemed impossible to prevent, glowed like punk when touched with a flame because of the organic matter it carried. and showed high percentages of calcium sulfate on analysis. The boiler carried large excesses (30 grains or more) of sodium carbonate and hydroxide but nevertheless calcium sulfate scale continued to form. There was evidently a n interference of some kind or some sulfur compound which had not been recognized. Finally the analytical methods were modified and the organic matter was destroyed by ignition before each determination was made. The result was an increase of sulfates of virtually 2 grains per gallon (30 to 35 p. p. m.). Further examination of the water showed that it contained much organically combined sulfur with liquid, other woody and resinous impurities, and sulfite cellulose. This organic! matter existed in the water in concentrations varying from 2 to 10 grains per gallon. Chemical treatment in the boiler had no effect whatever. At the same time, as operation continued, this organic matter burned or charred on the heating surfaces. Then through increased insulation sufficient overheating occurred to completely carbonize and decompore it, permitting the released sulfur compounds to combine vith the calcium of the ash produced. Thus a calcium sulfate film was created, regardless of the chemical balance of the water itself. Only a complete removal of the organic contamination could overcome the trouble. A new mater supply (a Tyell), proved a cheaper way out of the difficulty. There are two types of scale deposita -those readily soluble in acid (as the carbonates) and those not readily dissolved (as the siilfates and silicates). Both types can be broken down and removed through the aid of tannin compounds ( s l o ~ ~ lity ,is true) with the boiler operating. Chemical excesses must be properly gaged, and sludge-removing facilities must exist which are capable of removing the disintegrated scale. As to a possible theory behind this, i t seems natural to assume that the character and density of
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slowly deposited scale will bear some relationship to its molecular weight. Then a calcium sulfate scale having a molecular density equivalent of 136, if changed to either calcium carbonate (100) or calcium hydroxide (74), while occupying the same space should lose its compactness to just the degree that its molecular weight is lowered. Becoming less compact it should also be more easily subject t o removal through penetration by decomposing agents. In bringing this change about, it seems that the combination of tannins with any one of the sodium compounds, because of the organic, colloidal, or noncrystalline nature of the tannins, produces the proper conditions to change some of the crystalline constituents in the scale. The scale is then more easily penetrated, is altered physically as well as chemically, gives the appearance of a rotting porous formation, and is so weakened in physical structure that erosion, due to rapid circulation of the boiler water, results finally in its disintegration and removal. Where silicates predominate also, the presence of tannins with caustic soda seems to stimulate the solvent action of the alkali. The sludge produced in the case of either sulfates or silicates will be made up of a mixture of changed and unchanged scale particles, showing that the action is due to physical as well as chemical changes. Where the scale is mainly carbonate, acids are used successfully. The combination or admixture of tannin extract with hydrochloric acid changes materially the nature and extent of its solvent action. Where ,the hydrochloric acid alone would bring about a solution of calcium and magnesium carbonates until exhausted or neutralized, the presence of the organic acids seems to effect an extensive change of much of the crystalline carbonate into a sludgy noncrystalline condition n7ith no binding or adherent properties which, while not dissolved, is just as easily removed by washing, so that the action of a given amount of mineral acid seems greatly increased.
CORROSIOK I n the field of corrosion and its control, the value of organic reagents is more obvious. One of the disadvantages of external softening or treatment with inorganic materials lies in the lack of any action on free and dissolved oxygen and the evident tendency to increase the soluble salt content of the treated water, as well as to effect the removal of materials which might have served as protective agents in the untreated supply. This point was discussed in 1911 by Clark and Gage (5) who found corrosion increased, especially in hot water pipes, after softening. Corrosion is so well established as an electrolytic action, with oxygen as the accelerator, that any treatment which increases the concentration of the soluble salts and does nothing to reduce the oxygen content must be used with reservations or ivith some additional cooperative help. The action of organic matter in reducing the danger through electrolytic action is somewhat uncertain, though in theory dilution or adulteration of an electrolyte with a nonelectrolyte should retard or interfere with that type of corrosion. The author has seen cases where tannin compounds have deposited a black protective film of iron tannate that has seemed very resistant. Also, it can be easily proved by control tests on boiler m-aters that under certain conditions apparent addition products of sodium salts, particularly sodium chloride, can form lyith the nontannin-reducing bodies from a tannin extract to such a degree that complete titration of sodium chloride with 0.1 N silver nitrate is impossible until the organic compound is destroyed by ignition. It should be reasonable to assume that such sodium chloride n o longer ionizes and is no longer a factor in electrolytic action. Observation or results seem t o indicate that the presence of
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alkaline tannates or tannins in alkaline waters have a tendency to reduce corrosion to a marked degree. The alkaline tannates play another role, however, in corrosion control, and oxygen absorption rather than electrolytic interference may be responsible for the above observations. The ability of alkaline tannates t o absorb oxygen has been known for years, though the application of such knowledge in boiler feed-water control has been hesitating. One of the early references is by Cushman and Gardner (6): “ . . . or, the oxygen in the water may be absorbed by feeding into the boiler with water a very small quantity of an alkaline soIution of a tannin material, etc.” Even before, however, engineers in flue gas analysis were absorbing oxygen rapidly and quantitatively in the Orsat apparatus with potassium pyrogallate. This affinity for oxygen is not altered if sodium replaces potassium (12). If other tannins replace pyrogallic acid and alkali exists, while the absorption is slowed slightly the affinity still exists (8). This absorption by a commercial tannate is chemical, and a stable higher tannin, still retaining oxygen-absorbing powers, is the result. Since the writer’s reference to this fact in 1923 ( I O ) , considerable research has been attempted under his supervision. Preliminary results were published in 1929 ( 8 ) . The commercially available tannin extracts, both in dry and liquid form, were examined, and the results showed oxygen-absorbing powers in all cases. Using pyrogallic acid as the standard, these absorptions varied from a minimum of 17 per cent for liquid spruce (sulfite cellulose) to 80 per cent for chestnut oak extract. This work was done a t ordinary pressures and temperatures, and Some additional but unpublished investigations indicated that increases in alkalinity, temperature, and pressure served greatly to increase and hasten the action of these oxygenabsorbing powers. As this absorption is chemical and not mechanical, and as destruction or decomposition of this tannin in the boiler produces carbonates and not the absorbed oxygen, what happens after the absorption process has been completed has no bearing on the problem. [In addition to work done in the writer’s laboratory on the role of tannins in oxygen absorption, attention should be called to that of Merry (13). This work was done from a different point of view, but offers interesting confirmations of many of the ideas advanced here.] This oxygen-absorbing property of tannin compounds works perfectly in practice. One of the author’s earliest records concerns an eastern railroad using an oxygen-carrying corrosive water. Following the addition of tannin extract to the tender water, which was highly alkaline (on the basis of about 0.5 pound of extract to 1000 gallons of water), careful analysis failed t o detect the presence of any oxygen whatever. Whether the plant is a low-pressure heating plant or a superpressure power plant, the results are equally certain. Several S the first to examples may be cited. One plant T ~ among operate a t 1200 pounds per square inch pressure. Evaporator water was used, but, as the condensers were cooled with sea water, the resultant corrosion produced leaks and undesirable impurities. The plant was equipped with the best of deaerators, but oxygen control and elimination seemed impossible. Inspection showed everything (boiler drums, economizers, etc.) through which the steam and water passed t o be of a red color. The color was as uniform as though painted with an old-rose water paint. Analyses made beforehand showed an original supply of about 50 p. p. m. total solids, an evaporator supply somewhat better, but boiler waters acid in character and containing excesses of chlorides of all kinds. Two things were necessary: The boiler water had to be carried consistently in an alkaline condition, and chemicals t o absorb or combine in a fair degree of stability with the oxygen had to be part of the treatment. Advantage was taken of the tendency of the alkaline tannates t o combine
Vol. 2 6 , No. 12
~vitli oxygen, and a preparation in paste forni waq constructed carrying 200 pounds of chestnut oak extract to a 600pound barrel. The alkali salts were caustic soda and disodium phosphate, between 250 and 300 pounds to the barrel being prescribed in the proportion of 40 per cent sodium hydroxide and 60 per cent disodium phosphate. Soda ash was purposely excluded as nothing should be added which might later decompose and produce an acid or corrosive gas. This preparation was added directly to the boiler to create a definite caustic alkalinity into which the impurities due to condenser leakage would be neutralized and controlled, and daily tests were made to see that this alkaline excess always existed. The boiler water showed sufficient color to overcome the fear that the tannins might break down at the unusually high operating temperatures. This treatment -was continued for some time, and the writer was informed from reliable sources that the corrosion, as shown by visible indication, had been completely stopped, A similar treatment was worked out for a large paper plant using a zeolite system. However, as the alkali in this case already existed in the treated supply, only the acids of the tannin extract were neutralized with sodium phosphate t o avoid liberation of carbon dioxide gas. Later when the tannin treatment was added to the high sodium carbonate supply, analysis showed in the treated water an almost complete absence of oxygen, a distinct action on the mucilaginous magnesium silicate coating previously formed, and a marked reduction in total solids in the steam due to improvement in steaming conditions. A third case is probably of greater interest because it is being carried on a t the present time and involves ti utilities plant near New York. The boilers develop about 1200 h. p. and operate a t about 400 pounds per square inch pressure; the steam temperature ranges from 600’ to 700” F. Corrosion and pitting preceded by tuberculation has always been a problem, and various treatments have been tried. About a year ago alkaline tannates were used for the first time. T h e original feed supply is of low mineral content. Khile most of the supply comes from evaporators, this low mineralized feed is sometimes necessary to furnish sufficient water. T h e make-up is relatively smaI1, most of the steam being recovered. Ocean water is used as a cooling supply and leaks occur frequently. Oxygen has always been present in both the boiler and condensate. Two treatments were worked out: One for direct addition into the boiler, to control incrustants as well as oxygen, contained 200 pounds of tannin extract, 150 pounds of sodium hydroxide, and 150 pounds of disodium phosphate to the 600-pound barrel. Another to be used especially when condenser leakage was detected, contained 300 pounds of tannin extract and 200 pounds of sodium hydroxide. The boiler water and condensate are tested regularly. All old tubercles were removed mechanically. Nom the iron of the tubes is blackening and oxygen seems to be completely absent, both in the boiler and in the condensate. Snother phase of corrosion in which the organic tannins are of use is known as “embrittlement.” Work done a t the University of Illinois under Parr’s supervision and a t the miter’s solicitation indicated inhibitive properties on the part of tannic acid (14) fifty or more times as effective as the original and more primitive sulfate. The mechanism of this inhibition seems to invol7-e the fact that the organic material must be capable of breaking down when it is finally decomposed to produce carbon dioxide and carbonates. Under such conditions the theory behind its action is reasonably simple, In preparing pure caustic soda every device must be employed to exclude the agents in the atmosphere and solution that tend to produce sodium carbonate. Just as certainly in a boiler, when the solid phase of this same causticis approaching, any carbonate-producing impurity %-ill tend
Dwember, 1934
E Ei R IN G CHEMISTRY I N D USTR IA L AN D E N G I ?
to prevent the deposition or formation of the pure caustic. To juit the extent that this caustic is changed tci carbonate, its embrittling properties will be reduced. That rarbonates are considered embrittleinent inhibitors has been frequently stated by those doing reqearch and investigation on the subject. There is no reason Jyhy the reaction which creates caustic soda in the boiler cannot, under proper conditions and a t the proper time, be subject to reversal. I n the author‘s wried experience of the past 12 t o 15 years he has never known of a case where embrittlement occurred when proper tannin treatment existed in the boiler, even though all the conditions favorable to embrittlement existed. The remoyal of scale, as effected by the addition of tannin to inorganic chemicals, has already been discussed. In the case, h o x e w r , of the acid treatment of carbonate scale, the combination of tannin with hydrochloric acid does more than increase the effectiveness of the acid. I t acts as a buffer, cutting down materially the solvent action of the hydrochloric acid on the metal with which it is in contact as long as the carbonate release (’an continue. Smaller quantities of other inhibitors, such as furfural or formaldehyde, are equally successful in retarding metal solution but do not compare with tannin when efficiency and speed in scale disintegration and removal are considered.
FOA~VISG The third type of feed water trouble is kncinn as foaming and includes priming which is the even and uneven removal of water from the boiler in conjunction with the steam. Foaming has occupied the attention of many engaged in feed-water research, and its mechanism is pretty well understood. Foulk (R) has been the source of the most recent information. Foaming is a physical manifestation, brought about by concentration of soluble salts and of insolitble suspended solids. The c a u m are frequently beyond the operator’s control. After every precaution has been taken t o eliminate sludge and solid matter and to slow down the rate a t which soluble salts concentrate, the only resort the operator has is the use of organic materials, because the cure of foaming is pliy.ica1, induced by chemical means. Castur oil has been known as the most generally successful cure. Castor oil is an unusual material aniong oils and a study of the yarious alcoliols, acids, and sterols in its make-up will he illuminating. A\ an oil it is no more valuable than any of the other vegetable or animal oilGj. Saponify castor oil, throw out the fatty acid., use the waste liquid containing these other constituents in foaming tests, and i t will be evident where the control lies. Caprylic alcohol is an example of one of theqe constituents. References in the biological field have been made to its antifoaming properties in specimen handling. It is insoluble and lighter than r a t e r , and so floats on its surface. Its boiling point is slightly above 212’ F. so that it mill not evaporate as rapidly. Its presence evidently affects the strength of the surface film, prevents stabilizing of solid matter, and thus reduces the film interference to the passage of steam, thereby permitting the steam to escape uncontaminated. Castor oil must be employed with care. There are casesfor instance, with zeolite-softened water-where foaming has been increased owing to the alkaline soda excess which forms sodium soaps There are other types of foaming than those attracting attention as being the Fesult of sodium salts and suspended matter. I n one case the term “foaming” was never used. Water was being treated for scale formation. The plant, a huge one in the neighborhood of Cleveland, had a softening system similar to that a t the Pittsburgh plant described earlier. In this case, however, a paste preparation similar to the one used st tlie Pittsburgh plant but in a larger dosage
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(0.5 pound per 1000 gallons of water) m-ac used in place of any softening. I n calculating the cost lor coinpariaon xvith other plants using the cheaper lime and soda ash, it was discovered one 200,000-gallon tank less was being treated in a 24hour period. As there had been no reduction or change in operating load and conditions, the natural inference was that that muchwater under the other method had been carried away as steam contamination. As lubrication costs dropped and lubrication efficiency improved to a marked degree, this property of producing a clean steam seems t o be supported. In this case no castor oil figured, and it seems reasonable to credit the tannin in the boiler with the improvement in steam quality. The writer has found many cases where treatment depending almost exclusively on sodium tannate and sodium phosphate has been equally effective in controlling foaming. The efficiency in such cases is no doubt due to the clarifying properties of the precipitates formed and the qualities of the surface film. Sterols have been credited with antifoaming properties, and the writer’s experience has been that under certain conditions (with acetic acid and some of the acetates) foaming can be reduced. However, to the best of his knon-ledge foaming cannot be surely stopped. It can be controlled to such a degree that foaming conditions or causes can become several times more acute than is usual before foaming actually occurs. But sooner or later the danger line will be passed. The best technic involves effective antifoaming agents and then the most careful use of every mechanical agent t o postpone the arrival of the danger point.
COXCLL-SIOS Of what has been presented here, nothing except tlie theories that endeavor to explain what has happened is based on guess work or imagination. I n the literature of widely separated fields confirmation of a possibility has frequently been found. Experience has offered an opportunity not only to create a cure but to supervise and observe its workings. More than we realize is known about the tannins but that knowledge has not been properly coordinated for successful use in the boiler feed-water field. Their use should h more general as there are few phases of boiler feed-water treatment \There the addition of a tannate cannot change and frequently improre the results for which inorganic chemicali alone are being used. Few industrial laboratories are equipped to do high-pressure research, and still fewer mill be disposed to share their results Ivith tlie mater-treating world. It remains for the university laboratory to start the fundamental work which will make it possible for the water engineer to use these organic reagents with the same confidence that backs his use of the inorganic reagents so generally used a t present. LITERATURE CITED Bartow, E., and hlarti, W.J., Unir. Ill., State Water Survey, Bull. 8 , 5 9 (1911). Beilstein, Handbuch der organischen Chemie, 5’01. 11, G. E. Stechert & Co., Kew York, 1925. Benson, H. K., and Hougen, G. A , J. ISD. E m . Cmbf., 8, 435-6 (1916). Bible, Exodus, Chap. XV, verses 23-5. Clark and Gage, Mass. State Board Health, 42nd Ann. Rept., 1911. Cushman and Gardner, “Corrosion and Preservation of Iron and Steel,” 1st ed., p. 101, Iron Age Book Dept., New York, 1918. Edgar, W.H., Proc. Western Railway Club (Jan., 1900). Fager, E. P., and Reynolds, A. H., IND. ENQ.CBEM.,21, 357 (1929). Foulk, C. W., Ibid., 16, 1121 (1924), 23, 1283-8 (1931), 24, 277-81 (1932); Trans. SOC.M e c h . Eng., pp. 54-5 (1931). French, D. K., IND. ENQ.CHEV.,15, 1239 (1923). Hall, R. E. (to J. M. Hotwood), Canadian Patent 315,770 (Sept. 29, 1931).
INDUSTRIAL AND ENGINEERING CHEMISTRY
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(12) Jones, G. W., and Meighan, M. H., J. IND.E m . CHEM.,11, 311-16 (1919). (13) Merry, E. W., J.Intern. SOC.Leather Trades' Chem., 16, 239-53, 358-77,489-504 (1932). (14) Parr, S. W., and Straub, F. G., Univ. 111. Eng. Expt. Sta., Bull. 177,45-6 (1928); Straub, F. G., Ibid., 216, 79-81 (1930).
Vol. 26, No. 12
(15) Partridge, E. P., Univ. Mich., Eng. ResearchBuZZ. 15 (1930). (16) Wherry, E. T., and Chiles, G. S., Eng Mag., 45, 518-23 (1913).
RECEIVED June 29, 1934. Presented before the Division of Water, Sewage, and Sanitation Chemistry at the 88th Meeting of the American Chemical Society, Cleveland, Ohio, September 10 t o 14, 1934.
Rate of Solution of Methane in Quiescent Liquid Hydrocarbons. I1 E. S. HILLAND W. N. LACEY,California Institute of Technology, Pasadena, Calif. INCE its first commercial success in 1912, repressuring of oil formations with natural gas has been considered
S
and used. Repressuring has been done both for the purpose of recovering more oil and for the storage of gas. There has been a need for information on the rate at which the gas dissolves in the oil in the formation and on the quantity of the gas that will dissolve. Before the rate of solution of a natural gas can be predicted from its analysis, it is necessary to study the rate of solution of the pure constituents. The principal constituent of most natural gases is methane, which has therefore been investigated first. It has been shown by Pomeroy and co-workers in the first paper of this series ( I ) that the Fick proposition integrated for the case of a cylinder of infinite length gives a satisfactory means of calculating the diffusion constant from the data on the rate of solution of methane obtained with the apparatus described in the same article. The integrated equation is:
Q where Q A
=
2C,A
any deviation from the original assumption beyond the experimental error. Two determinations of a preliminary character were made a t 2000 pounds per square inch (136 atmospheres), with the apparatus which has been described ( 2 ) for phase-equilibrium studies, showing a small but hardly significant increase in the diffusion constant for the rate of solution of methane in kerosene as compared to determinations made a t lower pressures. Hence it is concluded that these assumptions are valid for somewhat higher pressures than those used in the determination.
MATERIALS CSED The methane used in the determinations made at 113' and 140" F. (45' and 60" C.) was prepared from natural gas in the same way as that which had been used formerly (1) The
4;
~-
I -
quant,ity of gas which has passed a given point area at right angles t o the direction of flow C, final equilibrium concn. of gas in s o h . t = time D = diffusion constant = = =
VISCOSITV
O F ORIGINAL O I L IN CENTIPOISES
OF SOLUBILITY OF METHANE FIGURE 2. RELATION TO VISCOSITY OF OIL
FIGURE1. RELATIONOF SOLUBILITYOF METHANE TO SPECIFICGRAVITY OF OIL
Certain assumptions were made in obtaining this solution of the Fick proposition which limited its application. It was verified ( I ) that these assumptions were valid for the rate of solution of methane for partial pressures up to 300 pounds per square inch (20.4 atmospheres). Nothing in the additional data obtained for methane and here reported indicates
purity was not as good as desired, and a better method of preparation was devised. The treatment of the natural gas with activated charcoal was improved so that the ethane content of the gas was reduced to 0.36 per cent. After treatment with charcoal, the methane was passed through a steel bomb surrounded by liquid air. The pressure inside this bomb was maintained at 40 mm. of mercury. At this temperature and pressure most of the methane dropped out of the gas stream as a solid, The remaining nitrogen and similar gases were constantly removed by a vacuum pump connected to the bomb. The vapor pressure of solid methane is about 20 mm. a t liquid air temperatures, depending somewhat on the composition of the cooling medium. By this method, in which the methane is condensed as a solid from a gas space
