INDUSTRIAL A N D ENGINEERING CHEMISTRY
248
be produced. To yield this amount, the quantity X of rectified brine required is determined by the ratio 120.6 : 54.68 =
X : 1000; or X = 2205.5
The manipulation of this volume in accordance with Case I11 is illustrated by Table VIII. I n practice, then, 2205.5 liters of rectified brine A are reduced in Evaporator 1 to a volume of 1000 liters, with the loss of 1060.3liters of water and the precipitation of 288.3 kg. potassium chloride. The brine is then cooled to 50" C., when 89.1 liters of water are evaporated and 130.7 kg. potassium chloride precipitated. It is then transferred from the crystallizer via the preheater to Evaporator 2, and the volume reduced to 554.3 liters with the separation of 81.0 kg. of sodium chloride and 253.5 liters of water (the composition following the curve G P J ) , and then back to Evaporator 1, its volume increased t o 1458.8liters (point E ) by the addition of 750 liters of rectified brine; and after evaporation, from R to F , with the separation of 407.1 liters water plus 102.4 kg. potassium chloride, the cycle is repeated.
Case I V-Solar
Vol. 16, No. 3
ration undergoes changes described by E1lKIJ, indicating the precipitation of sodium chloride over a wider range. This and the precipitation of potassium chloride over a wider range and of a higher degree of purity, yielding both in larger quantity per cycle, are the advantages of this modification. As the solution on each cycle is brought back to the composition of point F , the changes effected are only in that part of the field bounded by FIEIIII1lJ.
Evaporation
It has been pointed out that a further yield of potassium chloride can be obtained from a saturated kelp brine with a less marked contamination with sodium chloride and yielding a mother liquor of a higher vapor pressure, if the brine is cooled still further than the limiting point afforded by the vacuum crystallizer. Cooling below 50" C. cannot be accomplished by boiling in vacuum. Cooling by conduction is suggested, but serious difficulties are encountered here in the invariable caking of the cooling surfaces with masses of crystalline potassium chloride, immediateIy retarding and soon entirely stopping the transfer of heat. Cooling coils or refrigerating-brine-jacketing should be adopted only after careful consideration. For further cooling, the spray pond suggests itself as a possibly advantageous instrument, inasmuch as it makes possible the effectual prevention of insulating deposits of crystals forming over the cooling surfaces. The cooling surface, being the aggregate of the surfaces of all the innumerable droplets constituting the spray, is relatively enormous. Cooling by conduction and without evaporation is desirable, since the purpose is to secure potassium chloride in as pure a state as possible. Without evaporation no sodium chloride precipitates, and the proportion that does crystallize is determined by the amount of evaporation. However, it has been shown in Case I1 that a brine saturated a t 100' C. with potassium chloride, but so far removed from saturation with sodium chloride that considerable further evaporation of water is possible, permits a further cooling of the solution by evaporation and the consequent precipitation of potassium chloride, without the crystallization of sodium chloride. Such a solution may quite properly be cooled in a spray pond. The effect of spray cooling depends on the temperature and degree of humidity of the air. Under normal conditions there is always some evaporation, the maximum being that theoretically required to effect the cooling ahserved, assuming that no heat is absorbed from outside sources. &cordingly, the curve representing the further cooling of the brine of the composition of that at D (50" C.) (Diagram VIP) is properly the approximate projection of the curve BD. The application of this modification to the system of operating as described under Case I introduces the change that the cooling curve BD is,prolonged to E', which is on the 26' C. solubility curve of potassium chloride. The application of the spray pond to Case I1 introduces the modification that the solution represented by Ell1 on evapo-
* Rased on a priori and not experimental data.
Likewise, in its application t o Case 111, inasmuch as the solution in each cycle is brought to a definite composition F1 before being cooled, the changes induced are in the field FIE1llI1,J and exhibit themselves as a larger precipitation of both salts, a somewhat purer grade of potassium chloride, solutions of higher vapor pressures, and an increased degree of evaporation per cycle. The use of a spray pond offers certain advantages. Its cost of operation is represented mainly by that of running a pump to maintain the sprays and to return the cooled brine to the preheater. It acts as a storage reservoir for a large volume of brine of high concentration and purity, thus reducing fluctuation in composition and the effects of faulty operation. On the other hand, its use leads to the production of potassium chloride at a point considerably removed from that at which the bulk of the potash is being produced, thus introducing a certain complication in the manipulation of the salts. Air cooling connotes air circulation; unless this is carefully regulated there will be heavy losses through the blowing away of the finest spray. On the other extreme there is the possibility of cooling entirely by the spray pond method with the elimination of the vacuum crystallizer.
ACKNOWLEDGMENT For a review of the manuscript and valuable criticism the authors are indebted to W. C. Blasdale, of the University of California, W. E. Burke and Harold de Ropp, of the American Trona Corporation, Trona, Calif., and L. B. Olmstead, of the Bureau of Soils, Washington, D. C. Conquering the E a r t h "Conquering the Earth" is the title of a brochure recently issued by the Hercules Powder Company in which is assembled a unique collection of information on a variety of subjects. While calling special attention to historical facts upon which certain advertisements have been based, the text, which is well illustrated, offers in convenient form a number of facts not easily accessible to the average reader. These facts have t o do principally with certain industrial operations throughout the world's history, including the mining of copper in the Stone Age, building the pyramids, the Chinese wall, the Roman tunnels, ancient coal operations, and the like. This book may be obtained without charge by addressing the advertising department of the Hercules Powder Company, Wilmington, Del.
