INDUSTRIAL AND EKGINEERING CHEMISTRY
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implies that, a t the close of the fermentation period, the fermentation shall be vigorous and that there shall be an adequate residue of sugar to result in a brown crust and a suitable sweetness of flavor in the baked loaf.
Literature Cited (1) Bailey, C. H., “ C h e m i s t r y of W h e a t Flour,” p. 135 (1925). (2) Bailey, C. H., a n d Greme, Emily, Cereal Chem., 4, 244 (1927). (3) Blish, M. J., Sandstedt, R. M.. and Astleford, G. R., Ibid., 9, 378 (1932). (4) B u c h a n a n , J. H., a n d N a u d a i n , G. G., ISD.ENG.C H E Y . ,15, 1050 (1923). (5) Clayson, D. H. F., a n d Schryx-er, S. B., Biochem. J . , 17, 493 (1923).
Solid Matter in Boiler Water r ‘oaming
VOL. 27, NO. 12
(6) Gruss, J., Vochschr. Brau., 49, 389 (1932). (7) hlalloch, J. G., Can. J . Research, 1, 111 (1929). (8) Mangels, C. E., and Bailey, C. H . , IND.ENG.CHEX, 25, 456 (1933). (9) Markley, M., a n d Bailey, C. H.. Cereal Chem., 11, 515 (1933). (10) Rask, 0. S., and dlsberg, C . L., Ibid., 1, 7 (1924). (11) Rumsey, L. .I., A m . Inst. Baking Bull. 8 (1922). (12) Skovholt, Oscar, Cereal Chem., 11, 321 (1935). (13) T i l l m a m . %J.,Holl, H . , and Jariwaler, L., 2.untersuch. Lebensm., 56, 26 (1928).
RECEIVED May 23, 1935. Presented as part of the Symposium on Starch before the Division of Agricultural and Food Chemistry a t the 89th Meeting of the American Chemical Society, New York, N.Y.. April 22 t o 26. 1935. Published a2 Paper No. 1373, Journal Series, Minnesota .igricultural Experiment Station.
111. Effect of Calcium Carbonate and Magnesium Hydroxide Precipitated
inside the Boiler‘
n
C. W. FO ;LK A K D H. C. BRILL
Ohio State University, Columbus, Ohio
The experiments were conducted at 17.6 kg. per sq. cm. (250 pounds per square inch) pressure and at an evaporation rate of 450 to 500 QC. per minute. Calcium carbonate precipitated inside the boiler by the decomposition of calcium bicarbonate reduced the priming. Calcium carbonate precipitated by pumping sodium carbonate solution into calcium chloride in the boiler gave inconclusive results. Calcium carbonate precipitated by pumping calcium chloride solution into sodium carbonate
T
solution in the boiler increased the priming. Calcium carbonate that increased priming when first formed lost that property after several hours of contact with the hot boiler water. Magnesium hydroxide produced by pumping magnesium chloride into sodium hydroxide in the boiler reduced priming and, when precipitated along with calcium carbonate in an excess of sodium carbonate in the boiler, counteracted the tendency of the carbonate to increase the priming.
HIS paper deals with the effect of solid matter precipitated inside a n experimental boiler a t a pressure of 17.6 kg. per sq. em. (250 pounds per square inch). The temperature of liquid water a t this pressure is 205” C. (401” F.). The precipitated solids studied were calcium carbonate, magnesium hydroxide, and various mixtures of the two. Joseph and Hancock ( 7 ) carried out the first quantitative study of solids precipitated in a boiler. They pumped calcium chloride solution into a boiler containing sodium car-
bonate and noted that the percentage of priming did not increase. (The word “priming” as used in their paper, and also in the present one, means any carry-over of liquid water into the steam line.) Holmes ( 6 ) also studied the effect of precipitates formed inside a boiler, but he used natural waters from iyhich a mixture of precipitates formed so that the results are difficult to interpret. Holmes also observed that the precipitated solids lost their foam-stabilizing effects on long boiling and called this phenomenon “aging of the sludge.”
1 This is the third paper from the Ohio State Laboratory on solid matter in boiler water foaming. The first ( 3 ) dealt with the effect of solids on the foaming of salt solutions boiling a t atmospheric pressures, and the second ( 4 ) had t o do with the effects of solids added t o salt solutions boiling a t pressures from 3.5 t o 10 kg. per sq. om. (50 t o 150 pounds per square inch). The present paper is the firet dealing with the effect of solids precipitated inside the boiler. It is to be followed by others along the 8ame line.
Apparatus EXPERIMEXTAL BOILER. The boiler was of cabt bteel, identical in design with one used by the h-ational Aluminate Corporation and described by Christman, Holmes, and Thompson (Id). d few details are different-for example,
INDUSTRIAL A S D ENGINEERING CHEMISTRY
DECEMBER, 1935
11
i
lt31
5/ e a .
condenser
I
I Took
the location of the -team line and the sampling valve. Figures 1 and 2 give the diiiien-ions and appearance of this boiler. Its capacity when filled to t h e middle of the n-aterlevel mark on the gage glass is 3.75 liters. This particular boiler design i. of special interest becauqe it is the outcome of several year-' development by a commercial company, the Sational Aluminate Corporation, whose technical staff say that it duplicates field results in a way which makes It easy to recommend treatment for any particular job. ELECTRICAL INDICATIXG DEVICE. This device (Figure 1) showed the beginning of priming. It consisted of a glass apparatus m-ith a dropping mercury electrode after the manner of a Heyrorsky polarograph cell ( 5 ) . This dropping electrode and the pool of mercury in the bottom of the cell were connected in a circuit with a dry cell, a galvanometer, and a variable resistance. The total ejectate from the boiler (condensed \team and any boiler water thrown crier) pas-ed through the cell. With proper adjustment of the resiitance, even a few drops of boiler mater in the steam were a t once shown. REPUNPIXG RE5ERVOIR. This reservoir (Figure 1) n as used when ejectate was being pumped back into tl-e boiler, or n h e n a small volume of salt solution was to be pumped into it. The piping was so arranged that the pump m-ould draw solution from this reservoir or from the tank by operating appropriate valves.
Experimental Procedure Since foaniiag and priming are so strongly affected by the design and operation of the boiler, these factors require special attention. The most important operational items are water level, pressure, rate of evaporation, and cleanlines.. Unless othernise gtated the following conditions were maintained : WATERLEVEL* The surface of the liquid water was kept as closely as possible at a point halfway between the top and bottom
of the gage glass. This was 2 1 cni. (9.5 inches) below the steam outlet. 1-ariations of 2 cm. sometimes occurred but as a rule they were much less. A uniform pressure of 17.6 kg. per sq. cm. (250 PRESSURE. pounds per square inch) was maintained. The masimum variation during a run m-as 0.7 kg. (10 pounds) but as a rule the variations were half that amount. KATEOF E v a p o R a T I o N . This rate was kept between 450 and 500 cc. per minute. CLEANISG THE BOILER. The boiler was frequently cleaned by draining out the contents and boiling distilled water in it with the sampling valve slightly open (continuous blow-down) ; thr water level was kept up by pumping in distilled water. This procedure was continued until the boiler water hecamc clear and gave no chemical test for the salt previously used. When the electrical device showed S.ihiPLING THE EJECTATE. that, priming had begun, the feed-water valve was closed and t,he valve connecting the pump with the repumping reservoir opened. With the hose from the steam condenser (Figure 1) in this reservoir, this disposition of the valves results in repumping the ejectate, thus maintaining the water in the boiler at constant level and constant composition. During this repumping period, a 100-cc. sample was taken from the ejectate hose through a T-tube over a period of 5 minutes, which gave a composite sample. SAMPLING THE BOILERWATER. The procedure consisted in opening the sampling valve (No. 4,Figure 1) and allowing about 500 cc. of the contents of the boiler to discharge through the sampling condenser.
The concentration of the boiler water sample is always higher than the water in the boiler a t the time when the electrical device first indicates priming. This is due to the fact t h a t the pipes between the pump and boiler are full of feed water when the pump is connected to the repumping reservoir. If, as was sometimes the case, the feed wat,er was a strong salt solution, there was an appreciable increase in the concentration of the boiler water, which accounts for the high percentage of priming sometimes observed. 2 Weeks of practice were required to develop the technic for maintaining reasonable constancy in water level, pressure, and rate of evaporation in this little boiler. The details have all been recorded and will gladly be furnished t o those interested.
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VOL. 27, NO. 12
The calculation of the effects of various salts in a boiler to a common basis is absolutely necessary in interpreting experimental priming data. This generalization was first seen when a member of the Sational Aluminate Corporation (1) called attention to the fact that in the reaction between sodium carbonate and calcium chloride, both of which prime at low concentrations, sodium chloride is formed which does not cause priming until a relatively high concentration is reached. Consequently when this reaction occurs in a boiler, a change in the priming might be ascribed to the wrong cause if the difference in the priming values of the salts were not considered.
Priming Concentrations of Salt Solutions in Absence of Solid Matter
FIGURE 2. BOILERWITH STEELFRAMEWORK FOR FIRE-BRICK INSULATIOS
General Method of lMeasuring Priming A threshold method of measuring priming was used; that is, with the boiler operating under nonpriming conditions, the concentration of the boiler water was increased until priming began. Samples of the ejectate and boiler water were then taken. This general method was also used by Holmes (6) and by Eberle ( 2 ) . The concentration of a salt in the boiler water a t which priming begins is called the “priming concentration.” For example, the priming concentration of sodium chloride is 4235 p. p. m. This value applies only to the experimental conditions employed in this investigation. Two general methods were used for increasing the salt concentration in the boiler: I. If the feed water were a dilute salt solution, it was pumped in from the large tank (Figure 1). 11. If concentrated salt solutions were to be added, the repumping reservoir was used instead of the tank: and the procedure was as follows: h measured volume of the strong salt solution was put into the reservoir while ejectate was being repumped. h 5-minute interval was then allowed for clearing the pipes so that no reaction would take place in them if the next addition were a precipitant. In this way solutions such as calcium chloride and sodium carbonate could be added to the boiler alternately, and good control of the relative concentrations could be maintained. Experiments were made to see whether this portion-wise addition gave results that differed from those by a continuous addition. No difference was found. The measurement of the amount of priming was based on a n analytical determination of some constituent (usually chloride) in both the ejectate and boiler water samples. SODIUM CHLORIDEVALUE. This means the concentration of sodium chloride which would have the same effect on priming as the salt under consideration. The method of calculating this value is as follows: Concentration a t which sodium chloride begins to prime is 4235 p. p. m . Concentration a t which sodium carbonate begins to prime is 3945 p. .p. m. I n other words, 3945 p. p. m . of sodium carbonate primes as much as 4235 p. p. m . of sodium chloride. Therefore parts per million of sodium carbonate multiplied by (4235/3942 = ) 1.07, gives the parts per million of sodium chloride that would have the same effect on priming; that is, it gives the sodium chloride value of the carbonate.
Although this investigation is on the effect of precipitated solids, it is necessary to have accurate knowledge of the effect of the dissolved salts resulting from the precipitating reaction; otherwise the final results cannot be interpreted. Therefore the concentrations at which priming begins in the case of sodium chloride, sodium carbonate, and sodium hydroxide were determined. Kine duplicate runs were usually made in order to obtain a reliable average value. It was found that the average of one set of nine runs agreed within 7 or 8 per cent of the average of another set of nine runs made in the same way. This reproducibility of results applies throughout the paper. The final averages of the concentrations a t which various pure salt solutions begin to prime are as follows: Subatance in Soln.
Concn. at Which Priming Begins
P. p . m.
P. p . m.
Sodium chloride 4235 42745 Sodium carbonate 3946 ... Sodium hydroxide 3151 2988G a These results were obtained by R. C. Ulmer who is continuing with the investigation. Each one is the average of nine determinations. The value 3946 for sodium carbonate is the average of twenty-four determinations.
Priming Concentrations of Salt Solutions in Presence of Solid Matter The effect of calcium carbonate precipitated by the decomposition of calcium bicarbonate was as follows: 8 . Solutions of calcium bicarbonate from 545 to 930 p. p. m. were pumped into the boiler until the precipitated calcium carbonate became so large in amount that the boiler tubes were clogged. At no time was any priming indicated. It should be noted that in this experiment no salts were present in the boiler water, since the only products of the decomposition of the bicarbonate are solid calcium carbonate and carbon dioxide which escaped with the steam. B. In a second series of experiments a small concentration of sodium hydroxide was maintained by adding 50 p. p. m. to the first boilerful. The feed water consisted of 400 p. p. m. calcium bicarbonate and 400 p. p. m. sodium chloride. It contained no hydroxide. On pumping this solution into the boiler, priming did not begin until the sodium chloride concentration reached 7723 p. p. m. (average of nine runs). In other words, in the presence of the calcium carbonate precipitated in the boiler under the conditions of the experiment, 82 per cent more sodium chloride could be carried in the boiler water without priming than if sodium chloride alone were present. In these experiments only a small part, 5 to 6 per cent, of the precipitated carbonate was in suspension circulating in the boiler water. The average of the amount in suspension was 192 p. p. m. The reduction in the priming concentration of the salt was the more remarkable because the appearance of the water as viewed through the gage glass would have suggested the opposite. The layer of foam on the surface appeared firmer than in the case of pure sodium chloride solutions, and there was also more surging up and down of the water level. The average time of a run in this group of experiments was 72 minutes.
I n determining the effect of calcium carbonate precipitated by pumping sodium carbonate solution into calcium chloride
A t "recip;tati""
After B hour. oI boi!ing
1I. This exi,enment WLLS the ranw BS 1 except t , h t ttic pre(:ipit;itimof the calcium carbonrte WRY made more slowly to see vviriit effect t h i s would have. A smdler percentage of the precipit,atc iviis in suspcnsion than in experiment I, and a highcr conrrmt,r:itionUS salt wm in the boiler w&r before orirnine beesn. The precipitated cslci"m carbon&! increased thk rimTng'ht not as iniicli as in t:xperimcnt,I whcrc 1,Ire pwcipitate l%rned more rapidly. 111. I n tliia cxgeriinent. r:aleiom carbonate a i d magnesium hydroxide were pmcipitatcd tog&er in thc ratio of 6 parts calcium cxrbanate t o 1 part, magnesium hydroxide. The f e d
of t h e smo&t, required for precipitation. The hydroxyl iuii resulting from t,be hydrolysis of, the sodium carbonat? W&H SUEcimt t , preeipiiate ~ the mspnrsium. A hrge percentage of t h e p x c i p i t r b t c was in sus ension and the boiler uatcr eoncent,rrtt,ion wm 4109 (sodium clkride vz~ulue) before priming began. In utliiir words tliis precipitate had little if any effecton the priming.
contained 80 ma& of maknesium ohioride nnd 20 mams of cat-
DECEMBER, 1935
INDUSTRIAL AND ENGINEERING CHE-MISTRY
Results of the Investigation The results offer evidence both for and against the theory that suspended solids increaPe priming. Calcium carbonate formed in the boiler by the decomposition of the bicarbonate decreased priming. Magnesium hydroxide decreased priming. Calcium carbonate precipitated b y pumping sodium carbonate into calcium chloride solution in the boiler had no effect on priming. Calcium carbonate precipitated by pumping calcium chloride into sodium carbonate solution in the boiler increased priming, but the precipitate lost this property after several hours in the hot boiler. Magnesiurn hydroxide in sufficient amount counteracted the priming tendencies of the calcium carbonate. If this testimony is counted, more will be found against the theory than for it. Evidence, however, should be weighed as well as counted; the experiment in which calcium carbonate was precipitated in a n excess of sodium carbonate in the 1)oiler takes on extra significance because it i s common practice to maintain a cert>ainconcentration of sodium carbonate in a modern boiler. The sludge formed in such a case is therefore likely to contain a greater or less amount of the priming-promoting variety of calcium carbonate. 1-arious conditions, however, niay obtain. There is first the ratio of the rate of formation of this type of carbonate to the rate a t which i t loses its priming tendency by contact with the hot boiler water, and there is also the possibility that the feed water may be high in carbonate hardness which would result in the formation in the boiler of a quantity of the priming-reducing variety of carbonate. This carbonate, if sufficient in amount, would counteract the effect of the other form. Also if much magnesium hydroxide precipitated, the priming would be cut down. The cauqe of the different effects of the calciurn carbonate in these experiments appeared to be in its different physical stateq. When thrown down in a n excess of sodium carbonate, the particles were fine and remained in suspension to a mucli greater extent than when precipitated under other conditions. This difference was also shown by photomicrographs. The particles were large and granular if the precipitate was thrown down by the decomposition of bicarbonate, and small and fluffy if precipitated in an excess of sodium carbonate. Photomicrographs of the precipitate before and after long
1435
contact with the hot boiler water showed the same difference (Figure 3). The light feathery particles became granular. It also appears from the experiments that’ magnesium hydroxide not only does not increase priming but actually reduces it. The presence of magnesium hydroxide even counteracts the effect of the priming-promoting calcium carbonate (experiments I11 and IV, Table I). Photomicrographs of the mixed precipitates showed that the calcium carbonate particles -were enveloped by the gelatinous hydroxide (Figure 4). It will be interesting in later work to study the effect of other gelatinous precipitates, especially aluminum hydroxide and magnesium aluminate.
Conclusions The results of this paper offer evidence for both sides of the quest’ion: Do suspended solids promote priming? Some precipitates which formed inside the boiler not only did not increase priming but actually reduced it. One common boiler precipitate promoted priming but lost that property after several hours of contact with the hot boiler water. The priming-reducing precipitates counteracted the effect of one that’ increased priming. These facts are new and, the aut’hors believe, important, but out of them no broad generalization can yet be made until further work is done.
Acknowledgment Grateful acknowledgment is made to the Ohio State University Engineering Experiment Station for valuable assistance, and especially to the Sational Aluminate Corporation of Chicago for its generous financial aid in carrying on this research.
Literature Cited (1) Bird, p r i r a t e communication. (1.1) Christman, Holmes, and Thompson, ISD. E m . CHEY.,23, 637 (1931).
Eberle, Arch. Turmwirt., 10, 329 (1929). Foulk a n d Hansley, ISD. ESQ. CHEM.,24, 277 (1932). Foulk a n d Whirl, Ibid., 26, 263 (1934). Heyrovsky, Phil. Mag., 45, 303 (1923). Holmes, Trans. A m . SOC.Mech. Eng., R-P-54-5 (1932). (7) Joseph a n d Hancock, J . SOC.Chem. Ind., 46, 315T (1927). (2) (3) (4) (5) (6)
RECEIVED August 27, 1955~
Correction Through inadvertence, the accompanying cut, which appeared on page 1135 of October issue of ISDUSTRIAL AND ESGINEERING CHEW ISTRT t o illustrate an article by William Spraragen on ‘Welding in the Building Industry,” was erroneously credited to t,he Lincoln Electric Company. The cut shows an arc-welded building of the General Electric Company completed in 1928 by the General Electric Company, using G-E welders and electrodes. It is equivalent t o a building 13s feet wide and 552 feet long; it contains 745 tons of welded steel, and the total weight, of steel in the building is 989 tons. Courtesy, General Electric Company
ARC-WELDEDBUILDING OF
THE GENERAL ELECTRIC COMPANYAT W E S T PHILADELPHIA
