June, 1932
I N D U S T R I A L A N D E N G I N E E R I N G CHE,MISTRY
14" F. (and hence refrigeration) to prevent the escape of sulfur dioxide. HIDESTORAGE.Both the meat-packing and the leather industries use refrigeration for the storage of raw hides as a take-up between supply and demand. CANDY MANUFACTURE. I n processing and finishing candies (particularly those made with chocolate coatings) it is necessary that the temperature be kept low in the processing rooms and that humidity be carefully controlled. This requires considerable refrigeration in addition to that used for the storage of the finished materials. BIOLOGICAL MEDICIKES.An increasing number and volume of vaccines, glandular extracts, and other similar medicinals are being made and used each year. Diphtheria toxin-antitoxin, smallpox vaccine, adrenalin, insulin, and liver extracts are typical of the products of this growing branch of the pharmaceutical industry. The annual value of these products reached a total of more than $18,000,000 in 1927. QUEKCHING OILS. I n handling many of the newer structural alloys (especially duralumin and others containing aluminum), low-temperature quenching (below 0 O F.) is
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required to make them workable. Duralumin rivets, for instance, must be quenched at very low temperatures and held there until used to prevent hardening. Some of the new alloy steels require similar low temperatures for hardening. I n finishing molded rubber articles RUBBERINDUSTRY. (particularly golf balls), extreme cold (solid carbon dioxide) is used to render the rubber mold fins brittle and allow them to be wiped off by hand instead of requiring a lathing operation. I n the manufacture of "cut sheet," blocks of rubber are molded under pressure, refrigerated to a low temperature, and cut into sheets on a lathe. Cut sheet is used in making many rubber products. COKCLUSION Obviously the applications of refrigeration here noted point to a growing use of refrigeration technic in chemical processing. The diversity of the fields of its use and the possibilities of further development into others of like importance necessarily lead to placing refrigeration definitely within the scope of chemical engineering as an essential workaday tool. RECEIVED February 29, 1932.
EEcient Production of Manufactured Ice DANABURKS,JR.,University of Illinois, Urbana, Ill.
T
H E object of the present investigation has been, first, to render all industrial water supplies available for the production of marketable ice in completely electrified plants, and second, to d e t e r m i n e the possibility of reducing production costs by using low brine temperatures and to develop methods to utilize low-temperature operation, should it prove to be economically profitable.
which are invariably characterized by the p r e s e n c e of dissolved salts. I n the steamoperated plants, the distilled w a t e r was a l l o w e d to freeze quietly in metal cans submerged in a brine maintained a t a temperature c o n s i d e r a b 1y below the freezing point of the water. When t h i s procedure was followed in the case of solutions c o n t a i n i n g even small amounts of dissolved salts, the ice f o r m e d was i n v a r i a b l y opaque, as indicated in Figure 1. Owing to its a p p e a r a n c e alone, the opaque ice was highly unmarketable. The a p p e a r a n c e of opacity has been shown in the oresent investigation (3) to result primarily from marked alteration in the size and orientation of the ice crystals themselves because of concentration of the salts a t the freezing surface. Within the ice industry it developed that this difficulty could be overcome, when the initial salt concentration of the water was not excessive, by air agitation of the solution throughout the entire freezing process. In this manner localized concentration of the dissolved salts in the surface film was effectively prevented. The salt solution concentrating between the walls of transparent ice was then removed when further concentration resulted in the formation of an opaque core and was replaced by a fresh supply of the water originally used. When the present investigation was started, however, the efficiency of the agitation resulting from standardized procedure was such that marketable ice cou!d not be produced from solutions in which the salt concentration exceeded 600 parts per million. To use even solutions of this concen-
Formerly marketable ice could be produced f r o m solutions containing high salt concenlrations only after the salts had been removed by distillation. Such procedure rendered eflcient operation in electrified plants impossible. Methods have been developed whereby a n y industrial water supply may be used in electrified operation at average commercial brine temperatures. Lowering the brine temperature f r o m 16' to 6'" F. has been shown to result in marked reduction in production cost. Therefore, a process has been developed in which it is possible to produce marketable ice without distillation at 6" F. f r o m solutions previously considered too coccentrated to be used in electrified production at 16' F.
PRODUCTION BY ELECTRIC POWER The production of artificial ice d e v e l o p e d at a time when the only economical source of uower for r e f r i g e r a t i o n was Steam. In planG operated under these conditions the exhaust steam was condensed and the distilled water recovered was frozen. Distilled water, being free from dissolved salts, produced ice which was extremely clear and transparent. Because ice possessing these qualities was originally offered to the consuming public, the demand for a product of similar quality persisted. With the rise of the electric power industry, however, the manufacture of ice entered an era of increased operating efficiency. It was demonstrated that, \Thereas a ton of coal burned in a steam-driven ice plant produced 4 to 6 tons of ice, the same amount of fuel utilized in a central generating station produced sufficient electric power t o manufacture from 15 to 18 tons of ice when the plant was electrified. General application of electrified operation was limited by the fact that distilled water was no longer available. In this operation ice must be frozen from natural water supplies
tratiori t.he terriperilturc US the briiie could it I w ~ I X I I Z W To~owrcsjine this difficulty, an iw ctui modified design below 16’ F., and \ms generally liiglicr. Iii I w d i wits developed, the details of w h i c h arc shown in Figure 3. the water contained salt conrcntration.: i n excws of G(K) pnrtr Ihiring the initial frec%ingpcriod, tlie volume of air used is per million; marketable ice coiild lie prodiircrl oiily a h the iii excess of that conimonlg employed in standard procedure, water had lmii distilled, a prmediire wvliieli rciidcred tlic USE increasing wit,li the salt, concentration of the water being of electric power impossible. frozrn. For es:irnple, iii t,hc case of water coutaining 900 Therefore, the first phase uf tlie iii~~stigatioii i \ ~ si y ~ l - to 1000 parts per m i l h i of dissolved saks frozen at 16” F., cerned with the dwelopinent of nirilioilc wliidi \vvould allow 1.5 cu. ft. of air are required during the first 2 hours. The marketalk ica t u lie prodiird w l m i xoliit,iuns ioiitiiininp air cnbcring the diatriljulion header at C , Figure 3, is forced into tlie soliitioii at the extreme sidcs of the caii tlirougli a hrge number of small orifices, I). T i l e solution is thus agitated at thc freezing surface while the rate of ice forma.tioii is high, and concentration of the salt at this point is thus effectively prevented. As soon as ice for~nsa t t,lie sides of the can, the rate OS , Sitlee !,Vat l1lllst SUbEequently be .en vater tlirinigli a .ivall of ice which iii thickness and possesses only a fraction of the heat conductivity of the steci can vrall. The tendency for dissolved salts to coilcentrate at the freezing surface therefore steadily decreases, and a point is filially reached at which the standard volume oE air applied through a single point located in t,lic center of tlir bottom of the can is sufficient to prevent the formation of opaque ice. Tlrerefor?, when the volume of air is reduced to 0.3 cu. ft. per inin., tlie orifices located iii i k i e outer header, A , become cfrectirely closed by ice forming in Sroiii t,he sides of t!ie can, and the final air enters the solution mainly at C. Even with the decreased freezing rate iriiposed by the ice u-alls, the salts dissolved i n the unfrozen core water will r\mtually coilcentrate to the point xlierc opaque ice will 1,o formed, iiccessitating t,lie removal of the core and its high conoent,r;it,iont;of & s o l d salts \vim, f n r a e o at :s l n i i i e rtydaccmcnt by a fresh supply of the water originally used. temperature representing average op tiirg corrditi(,iis iri In the case of the wat,er containing 950 parts per niilliori of tlie industry-namely, 16” F. As a result, a new t,ype OS dissolved salts, two corings wore required, one of 10 gallons ice can was developed (2) in which tho efhtiveness of air Eollowed by a second of 1 gallon. agitation was so improvcd 1li:it ice oE niarhetable i1iialit.p has been produced from solutions coiitaiiiirig as high as 1300 parts per million. A ease typical of tlie applicatioii of tlicse results is foiiiid in a plant controlled by un elcctric power company i n a district where tlie only local water supply coiitains ?,iop:vts per million of dissolrcd sa1t.s. Wlicn this solution is frozen according to the procedure u;liii.lihad lrreviousig berr)mc standardized, the result, is that sliown in figure 2. lee of this quality cannot lie sold locally. Although electric power is available, coal must be liauled 1.31 rniles ta rlistil the water in order that transparent ice caii be produi:nl. It lias been estimated tlint. electrifimtioir of this pliirit \vorild result i n a yearly siiririg in opemtiiig r o s t alone of l,ctwixw $15,000 and W,OO0. 3 l o U l F l E D I I’nIlc,.:”r:nr: F R O M WATEN C ~ N T A ~ N I9.50 N C P. IS. 3,. OF DIE soI.vI:I’ SALTS
Fiuuwe 2.
To illiiatmt,e tbe cffeet,iveness of this procedure, the ice frozen at 16” P. froin tlir: water previously referred to as eontaining 050 parts per million of dissolved sails is shown i11 Figure 4. Anot,lier esnniple of tho t4feet~iwness of the procedure ilcveloged is found i n tliir caw of a p l a n t situated in n locality wherein tlic only availal,le water siipj>lycontains 1300 parts per nill lion of d i s w h d salts even following efficient lime softening. Tlic ice frozcn from t,Siii solution according to
tlie saving resulting from elec,t,rificd operatioo is iiiiire tlian sufficient to \varrant the procedure described. Since salt comcntrat,ioiis of 1300 parts per rriillioii may be considered to represent the upper limit for industrial supplies, tlie results obtained indicated tirat the first phase of the investigation had been completed.
l'lrouncrio~AT LOWERBRINETEUPEKITDKO~ TIE invest.igation was then centered upon determining the gossiliilit,y of producing ice at brine temperatures helow 16" F., and tho development of methods which would allow ice of marketable quality to be produced a t these lower temperatures. It has been stated that if t~hebrine temperatures in the plants controlled by a large operating conrpany could he reduced from 16" t.o even 12", production would be inFmutir: 3 . DI.:T.
