INDUSTRIAL AND ENGINEERING CHEMISTRY
824
VOl. 21,
3.0, 9
Some Examples and Precepts of Water Conditioning' R. E. Hall HALLLABORATORIES, INC.,304 Ross Sr., PITTSBKRGH. PA.
Operating data are given to show the results obtained in boiler plants where the author's system of water conditioning has been used. Experiments with antifoaming material indicate that other means should be taken to avoid wet steam in modern stationary boiler plants.
C
ONCERTED attacks during the past several years on the problems of water for steam generation have borne fruit in exact and systematic procedure for the solution thereof. The arrival of this state of affairs is timely and a vital factor to success in the modern scheme of substituting for many small boilers a limited number of large, high-pressure units that must operate continuously and a t high rating. To obtain a kilowatt of power a t minimum cost, the maximum nicety of synchronism must be a certainty in all operating details, and haphazard outages and maintenance or replacement costs originating from incorrect or inadequate water conditioning cannot be tolerated. Several years ago the author ( 2 ) showed that prevention of scale formation in the boiler may be obtained by rightly controlling the chemical equilibria in the boiler water a t the evaporating surfaces. Analysis of conditions yielded definite relations between naturally present and added conditioning radicals that must be maintained in the boiler water a t different operating pressures in order to control the equilibria. Bccause of the increasing instability of carbonates a t higher operating pressures, and absence in the gaseous phase of any appreciable carbon dioxide content, it pointed a t once to the infeasibility of using soda ash or other carbonate as added reagent beyond fairly well-defined pressures, and the necessity of substituting therefor a radical, such as phosphate, whose stability is unquestioned for any operating pressures possible with water. The problems of water for steam generation were becoming increasingly difficult because of the rapid trend to higher pressures, and the extremely hard service to which tubes were being subjected in water-cooled walls and screens used in place of refractories in the boiler setting. The changed operating conditions demanded, not limitation, but absence of scale, since uncertain outages of large units could not be tolerated. Lime-soda and zeolite processes of softening water would remove a large proportion of the scale-forming constituents in the natural water, but the softened water was subject to unavoidable fluctuations in calcium or magnesium content, and concentration in the boiler relentlersly integrated any entering hardness. Use of evaporated water and condensate greatly ameliorated, but in most cases did not entirely solve, the problem of clean surfaces, since carry-over from evaporators and leakage of condensers could not be readily eliminated completely and continuously. Troub!es from embrittlement were coming into more prominence, and the necessity for maintaining relatively high sulfate concentration in the boiler water as a preventive measure augmented the scale problem. Maintenance of desired definite chemical equilibria at the evaporating surfaces formed a new base from which to attack the problcms. It immediately brought the focus of attention to the negative radicals in the boiler water, since through them control of equilibria could be accomplished. Once the necessary constants had been established, conditioning of the boiler water became systematized to maintaining therein 1
Received April 2, 1929.
those ratior of key radicals essential to controlling the type of solid phase that might separate under various operating conditions. From the standpoint of preventing scale formation, the source of calcium coming to the boiler mater-whether from softener, condenser leakage, or foaming of the evaporator-was a matter of indifference; so long as the essential ratios were maintained, separation of solid phase could occur only in non-adherent form. Through the dual control of softener and maintenance of well-defined relations in the boiler water, extremely low residual hardness in softened water was no longer a necessity, and more leeway could be given in establishing conditions therein that would prevent corrosion of economizers, development of unbridled caustic alkalinity in the boiler water, and uncalled-for quantities of carbon dioxide in the steam. Installation of evaporator or softener for 2 or 3 per cent of make-up water was no longer essential to scale-free conditions, but a matter for judgment based on other considerations. The urge to maintain specific relations between sulfate and total alkalinity in the boiler water has increased tremendously in this five-year period owing to better recognition of the dangers of embrittlement (6, 8). Maintenance of these ratios is difficult with carbonate as conditioning radical, owing to its ready decomposition. The use of a stable radical presents no such difficulty, but permits control by maintenance of a definite minimum of alkalinity, thus minimizing the requisite sulfate concentration. The author and his associates have applied these principles to the problems of modern boilers for a number of years now. In choice of material for this paper, it seemed that some examples of their application and discussion of some of the problems met in application would be of value and interest. Feed Water Problems
INTERPRETATION OF AivaLYsEs-Doubtless for some time to come different laboratories will present analytical results on waters with all the variations possible in the use of grains per gallon, hypothetical combinations, radicals, and pal ts per million. The report in hypothetical combinations is least satisfactory of all because it injects into the correct and impartial report of balance and buret the personal preferences of the analyst. 9 s these personal preferences differ, so differ the combinations concocted from identical data. The personal equation should be lacking in the presentation of analytical data. Its elimination necessitates uniform and exact manipulation of the data minus hypothetical interpretation. This may be accomplished readily by expression of results as parts per million and equivalents per million, the latter being simpler to use than Stabler's coefficients (?), and more in keeping with parts per million than the expression milli-equivalents per liter. A few examples of calculating the lime and soda ash requirements of different waters, taken from Table I, will suffice for illustrating the simplification obtained by use of equivalents per million.
+
Mg > HCOB; HCOI = 0 Water 8: Lime requirement, Mg eq. p. m. Soda ash requirement, Ca = 2.58 eq. p. m. Case 2: Ca Mg > HCOs; HCOB> 0 Water 3: Lime requirement, Mg eq. p. m.
C u s e l : Ca
+
+ H2SOa = 1.33 + Mg + HsSOd
+ HCOs
= 2.37
I N D U S T R I A L A Y D EXGINEERIYG C H E * I S T R Y
September, 1929
Soda ash requirement, Ca f Mg =
+
0.30 eq. p. rn.
- HC03
M g < HCOI Water la: Lime requirement, MgHe03 = 5.17 eq. p. m. Soda ash requirement, Ca Mg - He03 = -1 0 eq. p. m.
Case 3: Ca
+ +
The negative value for soda ash requirement necessitates substances buch as calcium sulfate or sulfuric acid for satisfying it; hence one equivalent per million of either one may be used for the purpose. Refinements on these calculations may he made by allowing for Fe, and for dissolved Con. All desired data on alkalinity or hardness expressed as CaC03 in p. p. m. may be obtained by multiplying the appropriate equivalent per million by 50. Equivalents of lime and soda ash are likewise changed to p. p. m . through multiplying by their respective equivalent weights. EXAhlPLES OF CONDITIONNG W A T E R S - T ~ examples ~ that follow are actual cases chosen t o illustrate various problems that must be met in conditioning waters. -4nalyses of these waters are given in Table I.
825
for operation, since the records are indisputable evidence t h a t they had followed the best recommendations known for avoidance of embrittlement. Heavy though the feed ivaters are in calcium and magnesium, careful control of softener and boiler water has resulted in no outages whatever for a year and a quarter because of tube losses or necesqity for turhining. Those two wolds "careful control'' signify not only good but immediate routine testing of samples, and as immediate action according to the results thereof. Wuter ?. Inasmuch as the Operating pressure is 150 pounds, final Conditioning by carbonate is feasible. Because of the considerable bicarbonate hardness, a lime-soda bof tener would be the preferred equipment, but until funds are available for its purchase, direct conditioning by soda ash is being used. Naturally, sludge collects in quantity in the heater, but the evaporating surfaces are clean. TVater 3. I n this case the operating pressure is 185 pounds, and high rating and water-cooled side walls make thoroughly clean surfaces obligatory. The raw water make-up is 40 per cent. Final conditioning by phosphate is best suited for
of Various Feed Waters WATER7 WATER8 WATGR6 WATER4 WATER5 P . p , m . E?. P . P . m . El. P . P . m . E l . P . 9 . m . E l . P . p . m . E?. P . p . m . E q . p . m. P . m. p . m. p . m. p . m. p . m. 104 1.71 9 O,l5 25 0.41 417 7.32 74 1.21 0 0 10 0.21 9 0.19 0.15 17 0.35 13 0.27 138 2 . 8 8 7 0.20 1 0.03 ? 0.14 21 0.59 15 0 . 4 2 10 0.28 8 0.27 4 0.13 o 0.17 15 0 . 5 0 . 18 0.60 1 0 . 0 5 0 . 1 0.01 8 0.43 ... 7 0:37 11 0 . 5 9 4:95 20 1 . 0 3 25 1.25 27 1.35 4 0.20 16 0.80 99 2.55 5 0.41 8 0.66 8 0.66 1 0.09 2 0.16 31 0 . 7 4 11 0 . 4 3 7 0 .32 17 4 0.17 2 0.09 . 0 33 0.67 0 0 0 U
Table I-Analyses WATERl a
P.p,m. HCOa
so4
CI Si02
+ A1 Ca Fe
H2S04 Temporary hardness Permanent hardness
260 44 369 10 2 47 11 288
0
Eq.
p. m. 4.26 0.92
10.4 0.33 0.17 2.35 0.91 12.50
WATERl b
P . p . m . Eg. p. m. 97 1.59 232 5.46 58 16 6
106 31 28 0
1.63 0.53 0.32 5,30 2.55 1.22
WATER2 P , p . m . Eq.
p . m. 244 4.00 24 0.50 9 0.25 19 0.63 1 0 . 0 5 39 1.95 30 2.47 20 0.87 0
WATER3
"
3.26
1.59
4.0')
1.71
0.15
0.81
7.32
1.21
0.0
0.0
6.26
0.42
0.30
0.13
0.55
0.18
0.20
1.91
Waters I n and fb. These well waters are used in varying proportions as feed water for a cross drum boiler of 425 pounds operating pressure and all raw water make-up. The feedwater heater is of the open type, well vented, and operates at or above normal boiling temperature. Primary removal of calcium and magnesium is made by a hot-process lime-soda softener, and final protection of the evaporating surfaces, because of the operating pressure involved, is obtained by careful maintenance in the boiler water of the necessary concentrations of stable scale-preventing radical, phosphate. With or without continuous blow-down, the concentration of dissolved substances in the boiler water is high, and hence every precaution has had to be taken to protect the superheater froin carry-over of boiler water with the steam. Saponifiable contamiixxtion in the boiler water is almost nil. The feed-water regulator is quickly responsive, and maintains uniformity of water level. The steam nozzle is guarded by a vertical baffle against which steam from the crowover tubes impinges, and by a purifier discharging to a well-rented trap. It is essential that this trap be in excellent condition a t all times, else loss of superheater tubes cjuickly occu -9. There are phases of interest in every case. When this boiler hac1 been in actual operation for about 6 months, leakage occurred a t a seam, and the question of embrittlement was raised. The'value of definite records on the boiler mater was then fully illustrated, for during the period in question over 375 determinations of alkalinity, sulfate, and phosphate had been made as routine tests, the large number arising from variability of feed water and the consequent close control deemed necessary. According t o these analyses, if embrittlement had occurred, ratios recommended for its prevention must be unavailing (1). Needless to say, caulking of the seam was the requisite remedy. The point to be emphasized is that no blame in any event could attach to those responsible
certainty of clean evaporat'ing surfaces, and for simultaneous maintenance of low enough alkalinities so that einbrittlement ratios may be maintained. These conditions are representative of the dividing line on one side of which economy would require a primary treatment by softener followed by st,able radical to control the equilibria a t the evaporating surfaces, on the other side of which economy lies in direct use of stable radical without primary treatment. I n this case, direct conditioning by phosphate is used, but with a greater degree of hardness in the water; or if raw water make-up were 60 per cent, for instance, in place of 40 per cent, t'he outlay necessary for installation of softener might well be justifiable. TVuter .$. The conditions are 100 per cent raw water makeup, 400 pounds operating pressure. Use of zeolite or limesoda softener offers little advantage, and direct conditioning by phosphate is used. The dominant feature of this water is its content of organic contamination. I n spit'e of its purification for city use, concentration thereof ten or twenty times results in marked coloration, and t!ie boiler waters are distinctly brown. Only part of the organic matter is saponifiable, but is sufficient to cause bad boiling conditions if hydroxide alkalinity in the boiler water is not carefully limited. From the standpoint of embrittlement ratios, and of boiling conditions, therefore, an exact upper limit to concentration of hydroxide alkalinity is essential; on the other hand, its concentration must not fall much below 25 p. p. m., else increasing solubility of calcium phosphate, in step with decreasing p H value, may allow calcium sulfate t o become solid phase in equilibrium with the boiler water, and t,herefore t o be deposited as adherent scale. (See KO.8, Table IV.) Of especial general value is the possibility noted in this case of maintaining simultaneously pleasingly low concent,rations of hydroxide in the boiler water and cleanliness of surfaces in
IXDUXTRIAL A.VD EiVG7NEERING CHEMISTRY
826
contact therewith. Under these conditions, concentration of sulfate need not be extremely high for maintenance of the sulfate-alkalinity ratios requisite to meet the recommendations of the boiler code on prevention of embrittlement. This is beneficial in that artificial addition of sulfate is less frequently necessary, and because of lower concentration of dissolved solids in the boiler water, boiling conditions are better. Then, too, if incidental lapse in maintenance of the embrittlement ratios occur, the low hydroxide concentration can a t worst exercise but slow deteriorating influence on the boiler metal. Water 5. The operating pressure is 275 pounds, the makeu p is practically 100 per cent raw water. The calcium content and percentage of make-up of this filtered water are high enough perhaps to justify installation of a softener. However, space therefor is not available, since the softener would have to be of very large capacity. Hence, direct conditioning by phosphate has been used. I
k
€hminofibn o f Ammonio ond Albuminoid Ni'troyen br Ch/orne Featment
P f a / Ammonia ond A/bumino!d Nitroyen Remaininp. P a r t s PerM//kon
One of the questions that had to be answered by observation in this case was whether sludge accumulation a t the 90degree bend of the side-wall tubes close to their point of juncture with their header might present a serious problem by restricting circulation. The service on side-wall tubes, especially of the bare and fin types, is severe. I n case of treatment of water 5 by a limited amount of caustic soda, the alternate formation and disruption of scale resulted in rapid accumulation of piles of chips thereof a t the bends in question. I n an instance which has recently come to the author's attention, and in which the hardness of the water was similar to number 5 in quality but less in quantity, 5 days of operation with no treatment were sufficient t o cause complete clogging in the bend of a corner side-wall tube. But if equilibria are maintained in the boiler water at these surfaces such that the solid phase is of impalpable fineness of division, formation of any chips should be impossible and circulation through the tubes be sufficient to prevent any accumulation a t bends. The results have fully justified all expectations. So long as the essential equilibria are maintained, the bends remain free of all obstruction. Water 6. A primary treatment by softener is essential. Lime-soda seems the desirable type, in order to remove bicarbonate as sludge. With operating pressure of 225 pounds, practically 100 per cent make-up of raw water, and relatively high rating, assurance of complete protection of side walls from scale and simultaneous maintenance of eulfate-alkalinity ratios in accordance with the boiler code necessitate secondary control on the boiler water with stable radical. The conditions pertaining to water 7 are quite similar to those of water 3, except that the operating pressure of the boilers is 400 pounds. Here, again, direct conditioning by phosphate has presented no difficulties. Water 8. For one boiler house, operating pressure 280
Vol. 21, No. 9
pounds, this water taken direct from a river receives primary preparation in an intermittent lime-soda softener; final conditioning with stable radical is accomplished by addition of phosphate a t the heater. I n these boilers of cross-drum type, very marked differences in Concentration of dissolved solids characterized samples drawn from opposite ends of the drum, until they were minimized by approximately uniform distribution of the feed water throughout its length. Conditions of this character seem common in cross-drum boilers, and should be corrected, else quality of steam from the two ends may not be uniform. , In another boiler house, operating pressure 135 pounds, this water, neutralized and purified for city use, is treated in a zeolite softener. I n this case addition a t the heater of soda ash provides alkalinity in the boiler water requisite t o inhibit corrosion. COXTIXUITY OF EFFIcIEXcY-Deterioration of B batteries in radio sets and accumulation of scale in boilers are alike in causing gradual decrease in efficiency. Elimination of the former has occurred with rapidity; but it is difficult to eradicate the deeply ingrained idea of many operators that a boiler cannot be operated over protracted periods a t high rating without accumulation of scale. Keverthcless, maintenance of well-defined conditions in the boiler water assures to the evaporating surfaces absence of scale formation, and hence uniformity and continuity of heat transfer. Regardless of pretreatment of the water, scale-forming substances may gain entry to the boiler water by various paths. Detection of such entry is automatic, however, in maintenance of specified conditions therein, and the replacements of desirable conditioning radical essential to recoup its losses are deiignated by the periodic routine tests. A Problem in Quality of Steam
I n general, more attention is paid to limitation of oxygen and carbon dioxide in the steam than to other gaseous impurities. When the steam is used for heating purposes, however, and source of feed water is limited unavoidably t o a stream that is in effect a common sewer, another problem arises in elimination of ammonia. The data herewith reported were obtained in the study of such a case. I n Table I1 are presented the results of analysis for animonia nitrogen and albuminoid nitrogen in different water samples. I n the raw water the nitrogen is largely in albuminoid form; by the time the water has passed the hotprocess lime-soda softener, considerable decomposition of albuminoid nitrogen has occurred and the ratio of ammonia nitrogen thereto has largely increased (twenty fold). The ammonia, however, is still retained in the water. In the boiler-water ammonia nitrogen is relatively slight in amount, owing to the caustic alkalinity therein (211 p. p. m. of OH) and the consequent removal of ammonia by the steam. Continued decomposition of albuminoid nitrogen is evidenced by the presence in the boiler water of only 2.8 p. p. in. thereof, representing a 14.7 fold concentration of that in the softened water, whereas comparison of the sulfate concentration in boiler water and softened water shows a concentration of 33.6 to 55.5 fold (in softened water 56 p. p. ni., in boiler nater 1886 to 3100 p. p. m.) Table 11-Ammonia
Nitrogen and Albuminoid Nitrogen in Different Water Samples RarIo OF
S O U R C E O F WATER
Raw water Water from hot-process lime-soda softener Boiler water Condensed steam
AMMONIA ro AMMONIA ALBUMIXOIDALBUXINOID NITROGEN SITROCEN XITROGEN P.b.m. P.9.m 0.04 0.28 0.14
0.55 0.28 0.96
0.19 2.80 0.03
2 89 0.10 31' 0
ISDCSTRIAL i l S D E,VGISEERISG CHEMISTRY
September, 1929
I n the water sample composed of condensed steam, albuminoid nitrogen has practically disappeared (1 per cent carryover of boiler water in the steam would account for that found) while ammonia nitrogen has increased to its highest value. Elimination of ammonia from the steam must, be encompassed by decomposition of both ammonia and albuminoid nitrogenous substances before the water is fed to the boiler. The decomposition may be effected by chlorine. The data of Table 111, comprising results obtained by use of varying quantities of chlorine, were obtained as follows A varying amount of chlorine was added to samples of the raw mater which had been made alkaline to the extent of approximately 50 p. p. in. of OH. The samples were then brought to boiling temperature and held thus for an hour without actually boiling, to siniulate conditions in the softener. On each sample a determination was then made for combined ammonia and albuminoid nitrogen. The results are sho1v-n graphically in Figure 1.
827
water, it may be the result also of hydrolysis of calcium carbonate:
++COz Cas04
++
CaC03 H20+Ca(OH), Ca(OH)Z MgS04 +Mg(0H)Z
since with long enough boiling and absence of partial pressure of carbon dioxide in the gaseous phase all carbonates must wffer decomposition. S o . 2 is a sulfate scale, and indicates both a more concentrated condition of the boiler water in contact with the fin furnace tubes, and more severe conditions of temperature and evaporation at these surfaces. S o . 3 is a sulfate xale derived from use of feed water containing but little hardness of either type. This water had been used with little or no treatment for many years on lowpressure boilers without development of serious conditions; but with 400 pounds operating pressure and water-cooled surfaces for the combustion chamber, prevention of scale formation became a primary essential to operation of the boiler. T a b l e 111-Results of T r e a t m e n t w i t h C h l o r i n e S o . 4 typifies a severe silicate condition. The operating (Caustic alkalinity of water was approximately 50 p p m of OH) pressure is low (150 pounds), yet silicate dominated the TOTAL. 4 M M O N I 4 A N D RETEXTION AT . 4 L B U M I N O l D XITROGEN boiler mater t o such extent that it forced division of calcium CHLORINE USED BOILING TEMPERATLRE REUAININO between itself and phosphate, resulting in the adherent scale P.p . m. P. p . m. Hours 1 0.32 0 whose analysis is presented, and in which the adsorptive prop0.22 1 10 erties of silicate formations is demonstrated by the large 1 0.08 20 0.05 1 40 quantity of calcium phosphate retained therein. 0,016 1 80 S o . 5 is interesting in that approximately 51 per cent of The question must now be answered as to how far elimina- CaO is in the form of Ca(0H)Z. The operating pressure of tion must be carried to obviate troubles from corrosion or odor the boiler is 90 pounds; treatment of feed water is by hot conin radiators of the heating system. It is essential that the tinuous lime-soda system. Inexact proportioning of lime has chlorine treatment be kept as low as possible, both from resulted in excessive concentration thereof in the boiler water; standpoint of cost and from other difficulties, mainly corro- and since for calcium hydroxide the slope dS/dT of the solubilsion, incidental to its use. Pittsburgh city water, which gives ity-temperature curve is negative, whenever its solubility has no trouble of this kind, was sampled a t the laboratory faucet, been exceeded solid phase has separated as adherent scale. No. 6 is similar in type to No. 5, but higher in content of and found to contain 0.052 p. p. m. of combined nitrogen. Thus treatment of the water in question with 40 p. p. m. of Ca(OH)2. I n this case lime had been used for direct internal chlorine could be depended on to eliminate ammonia in the treatment. steam. The outstanding feature of S o . 7 is the presence of approxiOther careful adjustments made necessary in the water by mately 28.5 per cent of sodium sulfate. With so little caluse of chlorine, while not impossible, make advisable another cium sulfate present there is no possibility that the sodium source of feed water. sulfate separated more than in part as glauberite [Na?Ca(SO&], and therefore the solubility of sodium sulfate must Some Deposits of Interest have been exceeded at the time of deposition. As the boiler BOILERDEPosITs-Deposits of scale on the boiler surfaces water in general contained from 3000 to 4000 p. p. m. of SO4, bear infallible witness to equilibria existent in the boiler water and as the solubility of sodium sulfate a t this temperature is at their genesis. Discussion concerning more common 297,000 p. p. m., extreme concentration must hare occurred to types of scales has been given in previous papers ( 2 , 6). I n produce saturation. I t is the author's belief that the tube Table 11-are presented a few analyses of special interest. became so filled vith small bubbles characteristic of steam T a b l e IV-Various
S c a l e s from Boilers NET
No. 1
2
3 4 5
6 7 8 9 10
LOCATIOS IN BOILER Water drum Fin furnace tubes Side-wall tuhes Tubes Tubes Tubes Tubes bottom row Water screen tube Tubes Side-wall fin tubes
LOSS AT
SO3 c ;o
2.6 46.4 41.8 1.2 3.6 1.2 16.5 44.5 5.7 29.2
CO?
70 35.4 4.2 1.7 1.1 9.3 5.8 1.j 1.1 Trace Trace
P?Os c7 ,O
... ...
Si02
c
1 8 6 9
...,.
3 5 11 0
,....
9.9
44 3 0 34 4 6 4
1.0 8.1 6 5
CaO
S
c-
1;
...
A1?03
3 9
...
... ...
Fe?Ol
:
, 6 2 9 7 5
.....
OS 3 0
6.1 5 0 39 0 5 5
Xos. 1 and 2 represent deposits from the same boiler, and illustrate widely different equilibria that may exist in the boiler water when concentration of feed water occurs therein without interference from any conditioning of the water. KO.1 is decidedly a true carbonate scale, and arises doubtless from decomposition of bicarbonates in the feed water as the temperature of the latter increases. Magnesium oxide is higher in KO.1 than in KO.2. While this may be due in part t o soiiie incidental mixing of feed water with alkaline boiler
'I
c.C-
..... ..... ... ..... ..... I
11 2
.
Present Present
47.3 37.6 38.2 24.4
Me0
XalO
NaCl
105'C.
i7
C /c'
5.1 2.2 1.0 2.1 2 0
0.4 0.2 0.2 0.6 0.1 0.04 1.4 0.1
66.; 68.f
0.2
4.4 41 0 21 4 34.1
Trace Trace
0 .t 1 6
.. ..
IGXITIOX
Loss c;
0.4 1.6 2.2 4.9 15.8 18.7 5.3 2.9 22.6 17.5
generation in contaminated boiler waters that circulation was retarded, and that conditions were more nearly akin t o those in superheater tubes than in boiler tubes. (See, for instance, KO. 6, Table V.) The high content of alumina in this scale deserves notice. KO.8 presents the interesting case of a sulfate scale deposited with maintenance of conditioning by phosphate. With hydroxide concentration in the boiler water, if phosphate is maintained in sufficient quantity, a few parts per million
INDUSTRIAL AND ENGINEERING CHEMISTRY
828
Table V-Various
Vol. 21, No. 9
Superheater Deposits NET
SO.
a
SO3
COz
P10s
Si02
S
%
5%
5%
%
R
LOSS A T
Fez03 A1303
CaO
70
%
NazO
%
MgO
%
105'C.
XaC1
7%
%
IGNITION
Loss
70
Reported as FezOs, but considerable FeaOa present.
Table VI-Comparison
of Boiling Conditions with and without the Use of Antifoaming Material
S o . 5 boiler was so treated, No. 6 was not; both were equipped with steam purifiers discharging t o traps. All concentration data refer to the boiler water, and represent approximate means for consecutive 6-hour periods. (Trap dumps were recorded automatically.) SO. CARBONATE HYDROXIDE SULFATE SUSPENDED SOLIDS CONTAMINATION TRAPDUMPS No. 5 No. 6 No. 5 No. 6 No. 5 h-0. 6 No. 5 No. 6 No. 5 So. 6 No 5 No. 6.
p.g.m. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
260 330 450 5iO 450 500
570 570 450
260 200 230 350 250 300
...
P.g.m. 110 125 150 200 150 175 160 130 200 90 110 100 125 125 2M)
..
P.9.m.
P.g.m.
400 450 675 925 925
195 125 150 250 225 250 200 150 110 85 80 110 200 160 175
800
825 775 450 275 225 250 300 350 400
..
P.g.m.
P.g.m.
Experiments with Antifoaming Material Some general principles that govern boiling conditions have been set forth in a recent paper by the author and his associates (3). I n the development work leading thereto certain results in the laboratory seemed to justify demonstration of their value under ordinary operating conditions. For these experiments water-insoluble antifoaming material, of the
P.g.m.
..
lib0
. .
concentration of calcium therein cannot become enough to overstep the solubility product value of calcium sulfate. But if the hydroxide concentration falls to a point a t which PO1 is in large part replaced by HP04, then, even though analyses of the boiler water show the presence of considerable phosphate, enough calcium may be simultaneously present to allow deposition of calcium sulfate as solid phase. It is preferable that caustic alkalinity in the boiler water be low; but the results just noted are conclusive in their dictum that definite limitation of the lower limit is essential. Nos. 9 and 10 are examples of deposits from tremendously contaminated water, and are distinguished primarily by high organic content and by the presence of considerable sulfide. The deposits are due primarily to lack of hydroxide in the boiler water, as in the preceding case (KO.8). The ram water is contaminated by waste waters from paper mills. Thus, the sulfide may represent reduction of contamination in the raw water a t boiler water temperature; or it may represent reduction of sulfates as in the case of superheater deposits. (See Table V, Nos. 3 and 4.) In the latter event conditions akin to the superheater probably prevailed, as noted in the case of No. 7 analysis. SUPERHEATER Dmosms-Table JT presents analyses of a few superheater deposits. I n general, they represent evnporation to drynws of portions of the boiler water and subsequent ignition of the solid deposits, as retardation of heat transfer results in overheating of the superheater tubes. To the author, the presence of sulfide in many of the*e deposits is their most interesting characteristic. In both ?;os. 3 and 4 the boiler waters are quite free from contamination, and it seems necessary to predicate reduction of sulfates to account for the presence of sulfides. Yo. 5 represents the tightly adherent, pure oxide coating that may develop in the superheater under correct operating conditions.
P.g.m.
..
2000 2500 3500 3500 3300 2600 1800 1300 700 6 00 600 500
..
P.3.m. 40 40 35 40 35 35 60
__
a .
