Experimental Dryer for Pre-Pilot 'ID' A. COLKER', Eadem
,
Rogiona I Research Laborata~ry,Philadelphia 18, Pa.
1qr-iipment with which to study
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air is regulated. The air next passes through an orifice noazle, 2. Centrally located in the nomle is Pitot tube, which is connected to the upper inolined manometer on the cabinet and gives a reading of velocity head in inches of water; from this and from the temperature the volume-flow of the air is oalculated. The air now enters the drying cabinet and passes down through the material in the pan. The pan rests o n a shelf which forms an orifice in the drying cabinet. Static pressure openings above and below the shelf and connected to the lower inclined manometer indicate the loss in pressure BS the air passes throuxh the material and the pan. This information is vital t o tho design of a blower for larger equipment. Mounted just above and behind the drying pan are the dry and wet bulbs of the air-operated temperature recorder-controller (Figure 2), by which the temperature and humidity .of the air blowing on the wet material are controlled. A slight error in the wet-hulh temperature of the drying air is introduced here, since the evaporation from the wick is included in tho air passing through the pan. Also entering the drying cabinet just above the pan is an iron-constantan thermocouple, connected to a potentjometer.. . The thermocouple lead w+ FrePoiled, so tpat wheq the point IS Injected into tne wec matenal, cne pan can oe raisea and lowered for weighing and the additional tare due to the thermocouple will he practically constant. As the air leaves the bottom of the pan, i t passes over the sensitive portion of ~n industrial thermometer and then enters the return duet. Here the amount of spent air vented a t 4 is automatically controlled by damper, 3, operated by a diaphragm motor which functions from the wet bulb of the controller. An equal amount of fresh air e n t e s et 5. The recirculated air plus the fresh sir then enters the conditioning cabinet. I n the conditioning cabinet the air first passes through the steam heater. The supply of steam is automatioally controlled bv a dianhraem valve which functions from the drv bulb of the i&trum&t. 'If necessary. the heated air is then humidified by
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developed in the laboratory, expcrimental drying apparatus is frequently needed capable of determining the drying characteristies of diflerent materials under widely varying conditions and of yielding data translattahle to larger soale operations. Such a machine should require a small quantity of material. In recent years, drying techniques have been aimed a t achieving the most rapid rate of drying possible without introducing deleterious effects on the product and consistent with the most economical methods for handling the msterid This has been accomplished in many cases by employing a through-air eircule tion method of drying, by which heated air is farced at high velocity through a porous bed of the material supported on a perforated-metal or screen surface. An experimental unit which meets these requirements is here described. EQUIPMENT
Figure 1 shows a general layout of the unit. It consists essentially of a centrifugal hlawer, A , 7.5 inches in diameter with a Vbelt drive from a 0.5-horsepower motor; a drying cabinet, B; a torsion balance C , reading t o 0.2 gram; a n automatic wet and dry-bulb recorder-oontroller, D, having throttling control and automatic reset and equipped with a chart reading to 300' F.; an air-conditioning cabinet having a 2 m w finned-tube steam coil with 39 square feet of heating surface; plus ductwork, eontml valves, and accessories. The entire unit is constNcted of sheet metal covered with 2 inches of 85% magnesia insulation. For supporting the material several stainless steel pans are orovided. each 1 sauare foot in area. The hottoms are constructed of perforated metal or wire screen havina amrtures of
wet"bu1b i f the i&trumeh. Either water or steam can be s u p plied to the humidifying control valve,, the choice being determined hy the,wet-bulb temperature required.
and clamped t o the drying pan a i its four corners pass through the roof of the drying cabinet (Figure 2). The holes in the roof
Thus when the air enters the d+nK
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cabinet. its velocitv is re~~"
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&thout shutting oh the air supp5 add upsetting thk control conditions. A further advantage of this plenum chamber above the
the drying cabinet. At location 1, Figure lyis a ma'nually uper-
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Present sddresa. National Drying Maohinery Co., Philadelphia. Pa.
Figure
1. Dryer
Figure
71
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INDUSTRIAL A N D E N G INEERING CHEMISTRY
12
Vol. 18, No. 1
EXAMPLE OF USE
The utility of such an experimental dryer was demonstrated during the development of a pilot-plant pmeess for extracting rubber from the Russian dandelion. The purified rubber as extracted from the root was in the form of small discrete particles which floated in water. This material
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from eneh test were dhheeked
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175 c.f.in. per square foot of pan a&; the tray was loaded with 0.75 pound (dry woight) of rubher per square foot.
MOISTURE. DRY 8ASlS-LBS.1100 LBS RUBBER
It was demonstrated that such a heat-sensitive material could be dried verv raoidlv at. an olcvat,ed temuerature with better results and more economioally than by a conventional method for drying such vacuum drying. The data Obtained made possible the operation of a pilot-plant dryer under conditions which yielded the best quality of dried rubber. I
The conditioned air finally p a w s through a copper diffusing screen, 6, which eliminates any droplets of water. If the humidifying nozzles were located in the duct lesding to the heater, the diffusing screen would be unnecessary. The air now returns to the blower for mother cycle.
Pycnometer
.
.
Holder
ROBERT E . LEDLEY, JR., Sun Oil Company, Norwood, Pa
SINCE
the publication by Lipkin, Davison, Harvey, and Kurtz (1) of a new design of pycnometer especially suited t o
the meeise determination of the densities of volatile liauids. mutine use of this instrument has indicated the need for a multiple holder assembly with which to support two or more pycnometers at one time in a glass jar thermostat. A simple and satisfactory type of holder which has heon in use in this laboratory for several years is illustrated and described herewith. Figure 1 shows the structural details of the holder proper. 1
SECTIONA A SOLDER
TO ROD
SHEET
,
It may be made of brass or any other available metal which can be hard- or soft-soldered and will not oorrodc in the thermostat linnid.
Figure 2 illustrates a convenient mounting for suspending the holders in the thermostat. It consist8 of a brass bar 0.125 inch thick, 1 inoh wide, and 12 inohes long with seven inch holes drilled 1.5 inches apart to acoommodate the threaded ends of the holders. Two nuts support each holder and permit regulation of the depth of immersion of the pycnometers. A total of six holders with pycnometers may be conveniently suspended in a 12-inch diameter jar with this mounting. The ends of the mounting as illustrated are drilled to fit over posts clamped to the sides of the thermostat. However, the pasts need not be used, the bar simply being allowod to rest on the edges of the jar. Individual mountings for each holder which can be hooked or clzrnpeil to the edee of the jar may he used if desired.
METAL
WING NUT I
SUPPORT
out removing the' assembly from the bath or disturbing other pycnometers mounted in it.
HEX. NUT
LITERATURE CITED (1)
Lipkin, M. R., Dsvison. J. A.. Harvey, W. T..and Kurt.. S. 8.. Jr.. IND.END. CHEM., ANAL.ED.,16. 55 (1944).
SECTION Figure
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1. Pycnometer Holder Detail
Figure 2.
Multiple Holder Assemblq
