AN AUTOMATIC PROCESS IN
POWDERED MILK MANUFACTURE G.P. LONERGAN The Bristol Company, Waterbury, Conn. X THE processing of foods, as well as in innumerable chemical manufacturing operations, control of critical process factors can be safely entrusted t o automatic instruments with substantial savings through increased output of continuous processes and reduction of spoiled material. Few materials processed are as delicate as milk, and the operation of powdering liquid milk emphasizes this delicacy more than any other treatment which it undergoes. Overheating not only damages t h e essential vitamin constituents but a t the same time is likely to cause deposition of casein on
Kumerous methods of concentrating and completely dehydrating milk have been devised, and many of them are in satisfactory operation. Of these the so-called Douthitt process' has been one of the most successful, yet it, like other concentrating processes, requires the most accurate control of temperature t o prevent scorching on the one hand and reduced output on the other. Essentially the process consists in partially concentrating the liquid milk by passing it countercurrent to a stream of warm air and finally completing the dehydration by spraying the thickened milk into a
(Upper) FIRST-FLOOR EQUIPMENT
Heater 7 is t o the right with storage tanks 1 behind. Spray drier 6 is to theleft. The instrument controlling the operation is i n the background. The hydraulic pump delivers milk to the spray headsin the drier.
(Extreme left) THE TEMPERATURE-CONTROL INSTRUMENT W I T H ITS COMPRESSED AIR SUPPLYIs C O N V E N I E N T L Y LOCATED ON TEE FIRST FLOOR (Left) EQUIPMEKT ON
THE
SECOND FLOOR
Heater 4 is in the foreground. Above to the right is conical concentrator 3. In the baqkground is the b!ower supplying air t o the spray dner.
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NOVE.MBER, 1936
INDUSTRIAL AND ENGINEERING CHEMISTRY
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w a r m a i r s t r e a m . I n operation, several points require close attention, closer in fact than a n o p e r a t o r i s likely to give them, to ensure t h a t the t e m p e r a t u r e s are kept within prescribed limits and that other variables are under control.
THE operation of this process in a €D midwestern milk plant is shown in the flow sheet (Figure 1) and photographs. Raw milk, as received, is warmed t o 130' F. in a Jensen heater and passed through a cream separator. From the separator, the milk is conducted t o two storage tanks maintained a t 170" F. b y c i r c u l a t i o n t h r o u g h a s e c o n d heater. From storage tanks 1 (Figure l ) , the warm milk is pumped through line 2 to concentrator 3. The level of the concentrated milk in concentrator 3 is controlled a t a definite point by a floato p e r a t e d valve in the supply line. The milk in t h e c o n c e n t r a t o r is FIGURE 1. APPLICATIONOF BRISTOL'SFREE VANE APPARATUSFOR CONTROLLING pumped through a heater, which mainTEMPERITURE AT OUTLET O F FINAL HEATERIN DOUTHITTMILK DRYINGPROCESS tains its temperature a t 1 6 l o F . , to the toD of the concentrator itself. Here the milk drops over a distributor system into a stream of warm, consist chiefly in supervising a continuously operating unit partially saturated air from the spray drier, and thus part of and in packing the finished product into barrels. On this its moisture content is removed. In this partially concenaccount the presence of the operator is required a t the outlet trated condition the milk is likely to cake on the warm surof the drier, but the delicacy of control necessary to prevent faces of the heater if its temperature is allowed to rise even clogging of heater 4 has needed his frequent attention on the slightly, and consequently the most accurate control must be upper floor. Despite visits of the operator at 15-minute inexercised t o prevent the equipment from clogging. From the tervals t o the control point, experience showed that frequent shutdowns of several hours were necessary t o keep the heater bottom of the concentrator the partially concentrated milk is drawn by a hydraulic pump and fed under a pressure of 3000 clean and functioning properly. The installation of a n acpounds per square inch to spray nozzles located in the top of curate instrument t o operate this control continuously has funnel-shaped spray drier 6. Here it is met by a current of successfully solved this problem and materially increased the heated dry air t h a t has been carefully filtered to free i t from output of the plant over a period. The instrument is located near the operator's accustomed post on the ground floor, but i t dust. The volume and temperature of the incoming air stream are such as to evaporate all the water in the tiny dropcontrols a valve admitting steam to heater 4 on the floor lets of milk spray i t encounters, and the shape of the drier is above according to the temperature of the milk in concentracyclonic so t h a t t h e solid particles of milk are thrown out and tor 3. Control is accurate within a single degree and obdrop t o t h e bottom. The air from the spray drier, still warm viates the necessity for interrupting the continuous operation and not yet saturated with moisture, contains some milk of the unit. particles and is passed t o concentrator 3 for the dual purpose I n this case the saving of spoiled milk and the increased of preconcentrating the milk fed t o t h e spray and washing output of the unit have repaid the cost of the instruments out any solid particles that have escaped the cyclone. The many times during each year of operation. Similar savings dried milk powder is drawn from t h e bottom of the conical can be shown in many other processes where exact control is drier and packed into barrels for shipment. necessary to the efficient operation of continuous or frequently Because of the size of the spray drier, part of this plant must repeated batch processes. be located on the ground floor and part on a higher level. Only a single operator per shift is necessary, since his duties RECEIVED August 4, 1936
0 ONE HUNDRED ~ ~ I L L I O DOLLARS S WORTHOF
CHEMICALS ExTHISYEAR. Export,s of chemicals and related products from the United States continued at record post-depression levels in August with substantial gains being recorded in shipments of high-grade specialties, printing and lithographing inks, potash, sulfur and industrial explosives, according t o the Department of Commerce. The total value of such foreign shipments during the month mere valued at S12,661,300,compared with $12,204,000 in August, 1935; 910,612,000 for the corresponding month of 1934; and 89,434,000 in August, 1933. Since the beginning of the current year foreign countries have purchased more than 8100,000,000 worth of American chemical products-a value increase of approximately 55 per cent over the first eight months of 1933. PORTED
Foreign demand for chemical specialties was especially active in August, the total value of such shipments reaching $1,800,800, compared with $1,162,000 in August, 1935. Metal, leather, shoe, floor, and automobile polishes; textile specialty compounds; wat,er softeners and purifiers; synthetic resins; pyroxylin products; and household and agricultural insecticides were prominent. Foreign demand for industrial chemicals also continues active. Exports of such products, not including sulfur, aggregated $1,766,000in August, compared with $1,675,000 in August, 1935. Export trade in American sulfur has recovered remarkably during the current year. August shipments aggregated 53,611, tons valued at S1,006,300, bringing the total for the first eight months of 1936 to 402,132 tons, compared with 247,800 tons during the corresponding months of 1935.
