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INDUSTRIAL A N D ENGINEERING CHEMISTRY
Vol. 21. No. 3
Intensive Production of 60 Be. Sulfuric Acid' O
George A. Perley
,
UNIVERSITY OF N E W HAMPSHIRE, DURHAM, N. H.
HE conversion of sulfur Simple chemical reactions are t h e basis of a tower place the Gay-Lussac towers. dioxide into 60" BB. system for t h e production of 60" Bk. sulfuric acid. Miller2 has suggested the use s u l f u r i c acid by the A high reaction rate is secured by utilizing a n oxidation of silica gel as an adsorber for in t h e liquid phase. A recovery of nitric oxide as nitric chamber process is characterthe exit gases from the last ized by the fact that the r e x acid rather t h a n as nitrous vitriol makes possible a chamber, Our l a b o r a t o r y tions within the chambers are high niter recovery. The complete oxidation of sulfur has been studying the preferfor the most part in the gas dioxide is quickly obtained. ential adsorptive v a l u e s of phase. Such r e a c t i o n s a r e On t h e laboratory scale t h e process requires less various hydrous oxides, such slow and involve large volt h a n 0.01 cubic foot of sulfurous oxidation tower space as those of iron, cobalt, nickel, and manganese, a l o n e a n d umes. Theliterature of the per pound of sulfur oxidized per 24 hours. This is chamber process is very voluabout one fifteen-hundredth t h a t of t h e lead chamber prepared in the presence of minous and all sorts of patplant for similar capacity. sodium silicate, for such gases ents exist upon various imThe high speed of reaction and small equipment as nitric oxide, nitrogen diprovements. The great size space mean low installation and maintenance charges. oxide, air, etc, The data of the chambers, the mass of The ability to govern the reaction temperature by show that there is consideralead used, the repairs, and control of t h e rate of acid circulation gives a positive ble variation in the adsorp operation expense have caused control of the process. tive powers of these oxides manufacturers to study the More acid circulation and cooling and a 15 to 20 according to the method of process critically. per cent larger nitric oxide recovery system t h a n used preparation. Some of the adThere arevaried claims relain the normal chamber Plants are t h e only extra consorbers are characterized by a tive to the performance of a siderations involved when comparing this process with lower and lower capacity upon modern plant in respect to the t h e chamber method. re-adsorption. T h e s e d a t a cubic feet of chamber space -dlbe the subject of another required per pound of sulfur made into acid per day. H o w paper; yet it is evident that in the future an adsorption ever, such a statement alone does not represent the true system will be operated in place of the Gay-Lussac unit. economy of operation, since with a low ratio of surface to CHAMBERPRocEssEs-some chamber plants have been volume one gets poor mixing and cooling in return for low operated on the principle that an increased proportion of construction cost per cubic foot. Wells and Foggl.* estimate nitrogen oxides to the sulfur dioxide in circulation should the efficiency of a lead chamber plant from three viewpointsincrease the speed of reaction. The maintenance of such a the amount of chamber space required for each unit of sulfur system is costly. Thede3 suggests that 1000 per cent of the burned per unit of time, the amount of acid made per unit of acid produced should be circulated over the Glover and 500 sulfur burned, and the consumption of nitrate of soda or its per cent over the Gay-Lussac tower and thereby intensify equivalent. the operation. Since nearly 70 per cent of the acid made in a chamber A more rapid rate of mixing of the gases and the condenplant may be produced in the Glover tower and first chamber, sation of the mists has been secured by Lunge plate towers,4 and since the active work of a chamber is probably within the Gilchrist pipe column^,^ Pratt converters,6 The Chemical first 30 per cent of its space, it is logical that many suggestions Construction Company intermediate towers,' and the like. The Falding high chambers utilized a different type of as to intensifiers, cooling towers, etc., should be made. Whether the mechanical improvements essential to an in- chamber whereby' the convection currents set up by the tensified process, or the construction of a pipe system, packed chamber reactions maintained a zone of great chemical actower set, or what not, is the best, depends a good deal upon tivity in the upper part of the chamber and the inert cooler whether or not the combined increased installation and gases settled to the bottom. Operations upon small comoperation costs are lower than those of the ordinary simple mercial units showed that only 6.85 cubic feet of chamber chamber plant. The chief aim in improving any process for space were needed per pound of sulfur and nearly the same the production of 60" B6. sulfuric acid is to obtain the largest niter per cent was obtained as with the regular chamber plant. The Hartmann and Benkers system operates on a someconversion per unit cost of investment and operation. All things being equal, the smaller and more compact the plant what similar basis with dimensions about 20 feet wide by 33 and the more durable the materials of construction, the more feet high. The reactions are in the gas phase. The Meyer tangential chamber 10 and the multiple tangenfavorable is the economic aspect. tial system" also utilize a new chamber design of cylindrical form in which the spiral motion of the gases produces more Modern Developments in Sulfuric Acid Manufacture thorough mixing. From 4 to 5 cubic feet of chamber space The majority of the modern improvements utilize the same per pound of sulfur were claimed of this process. Here again old types of chemical reactions and depend upon the principle we are dealing with gaseous reactions. of the Gay-Lussac tower to recover the nitrogen oxides. The Kaltenbach processW4 consists of a series of packed Since the efficiency of an acid plant depends in part upon the pipes instead of chambers where the most favorable reaction loss of oxides of nitrogen, it is strange that more attempts have temperature is maintained a t the point of gas oxidation. not been made to improve this part of the chamber process. The Mills-Packard system13 of water-cooled chambers, Unquestionably, a better form of adsorption unit could re- with the water applied to the outer walls, makes it possible to intensify the normal chamber reaction to such a degree 1 Received September 5, 1928. that only 3.66 cubic feet of chamber space are required per * Numbers in text refer t o bibliography at end of article.
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March, 1929
INDUSTRIAL AND ENGINEERIiYG CHEMISTRY
pound of sulfur. The chambers are in the shape of a frustrum of a cone and utilize 350 gallons of cooling water per hour with the intermediate size. A normal niter consumption is obtained. Yet again the same old types of gas oxidation are used. I n the above four modified chamber types we find that all use very much the old order of gas reactions. Many attempts to secure more intimate mixtures of the gases with nitrous vitriol have also been made by the use of tower systems. The Gaillard p r o ~ e s s attempts ~ ~ , ~ ~ to improve the normal chamber process by using unpacked Glover and GayLussac towers into which the acid is atomized and thus secure more intensive operation. TOWER SYsrms-The Larison packed ce111B16f17J8 changes from lead construction to brick cells or towers. Large surfaces are afforded upon which the gases may impinge and have vigorous mixing and a t the same time he cooled by a circulation of cold sulfuric acid of such gravity as not to dissolve the oxides of nitrogen. The installation cost is but 50 per cent of the normal chamber plant and only 30 per cent of the ground area is utilized. Only 1 foot of tower space is required per pound of sulfur burned, but a somewhat high (around 4.8 per cent) niter consumption results. The Opl systern,l9~20~21 as originated a t Hruschau, Austria, utilizes a mixed gas-liquid phase reaction in a series of three Glover towers and three Gay-Lussac towers as one unit. I n reality the system employs the normal Glover tower reactions for the complete acid production. This system utilizes between 1.5 and 2 cubic feet of chamber space per pound of sulfur burned. MeyerZ2claims that the cost of the Opl is less than the chamber, but that it costs more to produce 60" BB. acid by the Opl process. The Schmiedel-Klencke ~ y s t e r n ~mixes ~ J ~ the gases thoroughly with nitrous vitriol in an acid-proof boxlike reaction chamber equipped with a revolving drum. Excellent contact with the acid results, but maintenance costs are large. The Parrish bubbler tankz5also brings the gas mechanically in contact with the nitrous vitriol. The power and maintenance charges are high. Parrish makes the following interesting notation on the time of the gas in various systems: ordinary chamber, 144 minutes; Mills-Packard, 40 minutes; Opl, 24 minutes; Schmiedel, 2 minutes; Parrish, 2 minutes. Peterson,26,27 in discussing the chamber process without chambers, points out that about 200 tons of lead are required to produce 35 tons of 50" BC. sulfuric acid per 24 hours, and this constitutes 40 per .cent of the total plant costs exclusive of the roasters. He suggests a system of seven denitrifying towers with twelve Gay-Lussac towers in place of the usual type of plant. TungayZ8advocates as an intensive system the use of a tower set consisting of a Glover tower, a finishing tower, two reaction towers, and two Gay-Lussac towers. The Quinan plantZgJ0uses a Glover, a converter tower, and two Gay-Lussac towers to secure intensive operations, but here again the Gay-Lussac acid is fed over the converter tower at 80" C. The converter tower is equipped with diaphragms and a large volume of circulating acid is used to remove the heat of reaction. Not all the references to tower systems have been discussed, yet the last seven cases include the more important develop ments along these lines. The system of the Chemische Fabrik Greisheim Elektrons' embodies another principle, which is quite a contrast to those previously mentioned. I n this system the sulfur dioxide is oxidized with nitric acid. A similar type of plant is suggested in "The Manufacture of Sulfuric Acid by Means of Towers."32 All the sulfur dioxide from 10 tons of pyrites per day was actually converted to sulfuric acid by 30 cubic meters in a
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tower set with a total of 200 cubic meters space using nitric acid. The nitric oxide was absorbed in the last tower by water as 30" to 35" BB. nitric acid. By the use of 59" BB. sulfuric acid in place of water to absorb the oxides of nitrogen it is claimed it would have been possible to use a total of only 120 cubic meters for the whole set. F a i ~ d i ein , ~connection ~ with the recovery of nitrogen oxides in the manufacture of sulfuric acid, suggests the use of nitrogen oxides for the oxidation of sulfur dioxide and the subsequent recovery of the nitrogen oxides by water absorption. Principle of New Process
During 1920 to 1923 this laboratory conducted studies relative to the use of a system employing the oxidation in the liquid phase. It was the plan to continue the laboratory work on a semi-commercial installation before publication of the results, but five years have elapsed since the laboratory data were secured and it seems wise to publish the summarized data obtained on the small-scale apparatus. Valuable experimental assistance in this work was rendered by E. W. Coughlin in connection with his senior research. Very old and simple chemical reactions were the basis of this work. The various steps include: ( A ) Burner reactions: The same as in the normal chamber process. ( B ) Glover tower reactions: ( a ) Gases are cooled. ( b ) The 60 odd per cent acid is concentrated. ( c ) Gases are cleaned of impurities. (d) The nitric acid from the sulfurous chamber exit is converted to nitrous acid. ( e ) There is but little nitrous vitriol to denitrate. (C) Sulfurous oxidation tower reactions: 3Soz 3HzOe3HzSOs (1) 3HzSOs 2HN03+3H2SOd Hz0 2 N 0 (2) (D)Absorption tower reactions: 6N0 302e6N02 (3) 2N0 6N02 2 H z O a H N O a (4)
++ ++
+
+
+
Reaction 1is easily reversed as the temperature rises, while reaction 2 is accompanied by considerable heat evolution. Adequate acid circulation with proper provision for cooling is all that is essential for the completion of the first two reactions. The last three reactions are the familiar ones of the arc fixation, ammonia oxidation, and niter recovery systems. A 90 to 95 per cent recovery of the nitrogen oxides has been industrially obtained by means of suitable absorption towers in ammonia oxidation plants where a 10 per cent nitrogen dioxide is absorbed. The loss of nitrogen or nitric acid vapor in these commercial systems has been found to be small if the towers are properly designed. The recovery and resultant concentration of nitric acid depends upon the partial pressure of nitric oxide and nitrogen dioxide, the temperature of absorbing liquid, and the circulation and method of contact of absorbing liquid. As a matter of fact, the water absorption system for the last stage of the process is by far the most costly unit of the system under discussion. An ultimate unit for the selective adsorption of the oxides of nitrogen and their resultant concentration w ill apply in this case as well as in the normal Gay-Lussac substitution. The outstanding feature of this method of producing sulfuric acid lies in the fact that the oxidation of the sulfur is carried out wholly in the liquid phase, where a high concentration of oxidizer and oxidizable sulfur compounds may be obtained in the most intimate contact. It certainly presents a great contrast to the type of reactions that take place in the chambers of a normal acid plant. The greatest intensity of reaction must occur from this liquid contact. The chief
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I-1-D C-STRIAL S X D EiVGINEERING CHE*VISTRY
problem is not one of chemistry, hut that of tower and circulating system design by which the great heat of reaction from the highly concentrated reactants may be controlled. Description of Process The chief units of this process are: a burner set, a dust collector, a Glover tower, fans, two or more sulfurous oxidation towers, a small nitric oxide cooler oxidation tower, one set of nitrogen dioxide absorption towers or an adsorption unit and exhaust fans. Each of the towers must be provided with the necessary liquid circulation pumps, meters, lines, etc. The design of the sulfurous oxidation towers is quite like that of the normal Glover tower, while the nitrogen dioxide absorption towers are similar to those now on the market for such purposes. The intake sulfur dioxide-air mixture enters the Glover unit where in general the usual Glover concentrating and cooling take place; but little nitrous vitriol is present. However, any nitric acid entering from the subsequent sulfurous tower is converted to nitric oxide. A somewhat lower concentration of sulfur dioxide gas admixed with nitric oxide and air then passes on into the sulfurous oxidation tower, where all the sulfur dioxide is converted to sulfuric acid by the nitric acid made farther on in the last unit. Nitric oxide and air pass out through the exit of this tower. Water is added to the last tower of the nitrogen dioxide absorption set. An ever increasing concentration of nitric acid is passed forward towards the sulfurous tower unit. The equilibrium concentration of nitric acid is thus built up according to the partial pressure of the nitrogen oxides and oxygen. Laboratory Studies of Process I n our laboratory experiments we were first concerned with the concentration of nitrogen oxides evolved from the sulfurous tower. This controls the strength of nitric acid which can be made economically in the absorptive set, which in turn governs t,he concentration of sulfuric acid that can be made in the sulfurous unit. The first qualitative experiments were performed on a nitrogen-oxygen-sulfur dioxide mixture similar to that secured from a brimstone burner. When using a 10 per cent sulfur dioxide the nitrogen oxides evolved from the exit of the sulfurous tower averaged practically 7 per cent calculated to nitric oxide. Since a reference to reactions 1 and 2 clearly shows that the atmospheric oxygen is not involved in the reactions within the sulfurous tower, it seemed clear that the partial pressure of the oxygen was not involved in the basic study. The oxidizing agent is nitric acid and not air. The object of the study was not to work out the details of the nitrogen oxide recovery, since this information had been investigated by the Nitrate Division of the War Department, the Fixed Nitrogen Laboratory, and individual investigatorss'#86 of ammonia-oxidation absorption systems. It was also realized that a 10 per cent sulfur dioxide mixture produced from brimstone carries an excess of practically 3 per cent oxygen, while a 10 per cent sulfur dioxide and 90 per cent air mixture produced by simple admixture carries approximately 18 per cent oxygen. This excess oxygen has no bearing on the sulfurous oxidation tower reactions. The consumption of oxygen in this Glover unit must be less than in the normal plants, since there is but little denitration of materials such as the nitrous vitriol of the normal plant. A variable amount of nitric acid is handled in the Glover tower of the process under discussion. Air may be added at will in the nitric oxide adsorption system, if a higher partial pressure of oxygen is desired in the last unit. This,of course, affects in a small way the size of the nitric oxide absorption system; yet the variation between the size of the system for the 10 per cent
Vol. 21, Yo. 3
nitric oxide-gas mixture of the ammonia oxidation recovery systems from that of approximately 1 per cent nitric oxidegas mixture of the arc fixation plants is not extremely large. With all these considerations in mind, it seemed as if we were justified in the use of sulfur dioxide-air mixtures as mechanically prepared in the majority of the tests. A very general summary is given of a large number of tests on a laboratory tower set constructed of glass and utilizing glass tubes as packing. The packed space of the towers was 3 inches in diameter by 13.3 inches high. The towers were equipped with half-inch inlets and outlets. A continuous acid circulation was employed a t the rate of 0.15 gallon per minute per square foot of crowsectional area. The sulfur dioxide-air mixture was obtained by carefully metering the sulfur dioxide from cylinders and the air from a high-pressure line. A gas flow of 0.63 cubic foot per minute was used in the majority of the tests, since the available air lines would not deliver a larger quantity. The packed volume of each tower was 94 cubic inches with a cross-sectional area of 7.4 square inches. Tests as to the variable factors were carried out, but since the data were on a small laboratory scale the details will not be given here. Variations in gas and liquid composition were fairly large during a 4- or 5-hour test; yet the final acid concentrations were closely checked. The purpose of this paper can best be served by pointing out the chief features that may deserve study on a semi-commercial unit. All compositions of nitrogen oxides were calculated as nitric oxide. Table I-Composition Glover unit: SO1 intake SO1 exit Sulfurous tower: Front tower intake: SOa NO End tower exit:
of Gases Variable, as low as Variable to
so2 NO
P n cent 10.50 5.80 5,80 Variable 0.00 7.2
Absorption unit: NO intake NO exit
7.2 0.02
Table 11-Composition of Liquids HNOa NITROUS VITRIOL H&Oi Per cent Per cent Per cent Glover unit: Sulfurous tower: Front tower exit
0.00
2.80
End tower intake
40.0
Absorption unit: Front tower exit End tower intake
40.0
Trace
0.07 but variable
....
75.0 62.5
....
0.00
Although a large number of experimental tests have been conducted on the glass laboratory tower set, the exact concentrations can only have true significance when obtained on commercial units. However, the figures are certainly very indicative as the experimental tower set was operated for hours a t a time on a packed sulfurous oxidation tower space of less than 0.01 cubic foot per pound of sulfur burned per 24 hours, and a 50" B8. sulfuric acid was produced at the front outlet of a two-tower oxidation unit. The upper capacity of this set was never reached, so the figures of Tables I and I1 are not for maximum capacity. The upper limit to the capacity in actual practice will be governed by the cost of circulating and cooling the acid made in the oxidation towers. The gas remains in an ordinary chamber plant from 1 to 2 hours, while in the tower set described above the reactions are instantaneous. The greater the concentration of sulfur dioxide in the gas the more favorable will conditions become. This process would be ideal for high concentrations. Although the sulfurous oxidation tower utilizes but one fifteen-hundredth of the space of the normal lead chamber,
March, 1929
INDUSTRIAL AlYD ENGINEERING CHEIMISTRY
this great decrease in volume must in part be compensated by the use of extra pumping equipment and external cooling apparatus whereby a high circulation of cool acid may be maintained. Furthermore, the present nitric oxide-water absorption tower systems require a larger installation to obtain a 90 per cent absorption efficiency than those GayLussac tower sets which operate on about 85 per cent efficiency. Our estimates indicate that this process is worthy of study on a larger scale. Bibliography 1-Wells and Fogg, Bur. Mines, Bull. 184. 2-Miller, Chcm. M c f . Eng., 23, 1155 (1920); U. S. Patent 1,335,348. 3--Thede, Z . angew. Chem., 31, 1 (1918). 4-Lunge, “Sulfuric Acid and Alkali,” Vol. I, Pt. 2, p. 656 (1913). 5-Gilchrist, J . SOC.Chem. I n d . , 13, 1142 (1894). 6--Pratt, Am. Fertilizer, 13, 33 (1900); U. S. Patents 546,596 and 652,687. 7-Chemical Construction Company. Bulletins. 8-Falding and Cathcart, J. ISD. ENG. CHEM., 6, 223 (1913); U. S. Patent 932,771. 9-I,unge, 09. c i f . , 3rd ed., p. 459. 10-Meyer, C h e m . - Z f g . , 24, 601 (1900).
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11-Thiele, Trans. Am. Inst. Chem. En&, 11, 171 (1918). 12-Kaltenbach, Chimic et industrie, 3, 407 (1920). 13-Fairlie, Chem. Met. En&, 24, 786 (1921). 14-Gaillard, British Patent 202,629 (1923). 15-LeBreton, Ckimie cf industrie, 11, 662 (1924). 16-Fairlie, Chem. Met. Eng., 25, 1005 (1921). 17-Larison, Ibid., 22, 1127, 1174 (1920); 26, 830 (1922). 18--Larison, U. S. Patents 1,342,024 and 1,334,384 (1920). 19--Wilke, Chem. Trade J., 61, 294 (1912). 20-Opl, U. S. Patent 1,012,421 (1911). 21-Hartmann, Z . angew. Chem., 24, 2302 (1911). 22--Meyer, Z . angew. Chem., 26, 203 (1912). 23-Schmiedel, British Patents 149,647, 149,648, and 184,966 (1921). 24-Schmiedel and Klencke, British Patent 187,016 (1921). 25-Parrish, Chem. Age, 10, 316 (1924); 12, 128 (1925). 26-Peterson, Chem.-Zfg., 36, 493 (1911)d 2i-Peterson, I b i d . , 47, 227 (1923). 28--Tungay, Ibid., 6, 831 (1922). 29-Quinan, Chem. Met. Eng., 23, 847 (1920); U. S. Patent 1,355,357. aO-MacNab, Chem. Age, 6, 872 (1922). 31-Chem. Fabrik Griesheim Elektron, French Patent 406,641 (1909). 32-Anon, I n d . Chim., 11, 137 (1911); cf. Chem. Abs., 6, 3501 (1911). 33-Fairlie, U. S. Patent 1,420,477 (1922). 34-Partington and Parker, J . SOL.Chem. I n d . , 38, 75 (1919). 35-Burdick and Freed, J . A m . Chem. SOL.,43, 518 (1921).
Disposal of Industrial Wastes’ Wastes from Corn Products and Paint and Dye Works F. W. Mohlman and A. J. Beck SANITARY DISTRICT O F CHICAGO, 1014 SOUTH MICHIGAN AVE., CHICAGO, ILL.
HE industrial waste problem is of particular importance in Chicago from several standpoints. There are various classes of wastes, some of which augment the sewage load, others interfere with sewage treatment processes, and others from nearby cities cause tastes in the water supply. Detailed investigations have been made of three types of wastes in the first classification-namely, $hose from stockyards and packingtown, from tanneries, and from a corn products refining company. Extensive studies have been made of the second type-namely, wastes from a paint and dye factory, which have seriously interfered with the operation of a sewage treatment plant. Studies are now being made of the third type, wastes from by-product coke plants, particularly with the object of determining whether it is feasible to handle such wastes, mixed with sewage, in a sewage treatment plant. This paper will deal exclusively with the results of investigations of corn products wastes and paint and dye wastes. It is intended to show that the problem of disposal of wastes frequently becomes simplified if a thorough study is made of the various types of wastes contributing to the problem, followed by intensive study in the factory of methods for eliminating or minimizing wastes from certain processes in order of their importance. In the case of the Corn Products Refining Company, the outcome was far more gratifying than had been anticipated when the studies were commenced, and what a t one time appeared to be a costly process of sewage treatment was changed to a scheme of recovery of valuable corn solids worth possibly half a million dollars per year. Our studies of the industrial waste problem in general have indicated that industrial chemists do not always appreciate the problem from the same angle as chemists and engineers who are interested in sewage treatment and prevention of stream pollution. The sanitary chemists and engineers deal with sewages which contain only 0.01 or 0.02 per
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1 Presented before the Division of Water, Sewage, and Sanitation at the 78th Meeting of the American Chemical Society, Swampscott, Mass., Septem%er 10 t o 14, 1928.
cent of suspended solids and rarely more than 0.1 per cent of total solids. They are interested primarily in oxygen demand of wastes, whether they are inhibitive to bacterial action, or whether they may interfere in one way or another with biological processes of sewage treatment. The industrial chemist is usually concerned with concentrations far greater than the parts per million of the sanitary chemist; he rarely has studied the biochemical oxygen demand, pH, bacterial content, or toxic effect of waste discharged from his factory. When cooperative investigations are made, such as have been conducted in two instances described in this paper, a better understanding is gained of the viewpoint from both sides. CORN PRODUCTS WASTES
The wastes from the Corn Products plant a t Argo have been studied since 1920. A testing station was operated for six years,*and after it had been discontinued daily analyses were made of all wastes of importance discharged from the plant. Source and Nature of Wastes The corn received at the plant is first steeped in a weak solution of sulfur dioxide.s This process softens and swells the kernels so that the separation into various products may be accomplished. The steeping is on the countercurrent principle and the sulfur dioxide water is kept in circulation until the total solids build up to a concentration of about 7 per cent. The “light steepwater” is then drawn off and concentrated to 45 per cent solids in vacuum evaporators. The sirupy ‘‘heavy steepwater” is added to other parts of the corn to produce a valuable stock food which sells for $30 or $40 per ton. This process of recovery is important, since i t was the main factor in solving the problem of disposal of wastes from this factory. 2
Mohlman, IND.END. CABM..18, 1076 (1926).
a Sjostrom, Ibid., 3, 100 (1911).
