XXDI;;STRIdL A S D EXGINEERING CHEMISTRY
October, 1930
behind. Inasmuch as its sodium chloride has been almost entirely washed out, but not its lime content, it offers promise as a n ingredient in mixed poultry food. Undoubtedly i t may also serve the fiber-board industry. Other Seaweeds
Common brown kelp, or seaweed, does not yield agar-at least not in appreciable quantity. It does yield, however, colloidal material of quite different character, such as the elginic products. The quantity of common weed is so enormous that a much greater industry could be developed if the market should require it. Tlre initial development of this industry is already started in the San Diego district. During the World War a considerable amount of aliphatic acid products, including acetic anhydride, acetone, propionic acid, and the like, were made near San Diego. The process involved fermentation of the weed. The processes
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are not economical with peacetime prices, however, and this industry is indefinitely suspended. It is quite possible, on the other hand, to produce the more unusual acids such as butyric, valeric, and higher members of the fatty series, in quantity from kelp. Bibliography
Further details of the manufacture and purification of agar may be seen in publications by Fellers ( 2 )and the Department of Commerce (4). Literature Cited (1) Fairbrother nnd Mastin, J . Chcm. Soc., 123, 1412 (1923).
(2) Pellers, J. IND. ENQ.CHBM.,8,1128 (1916). (3) Mackionon, Food I n d . , March, 1930. (4) “Methods of Manufacturing Agar-Agar in Japan,” in Commerce Rcpls., October 10, 1927.
Dust Control in Phosphate Rock Grinding’ W. H. Gabeler DAVISON CEQMICAL
COMPANY,
T THE Baltimore plant of the Davison Chemical Company on Curtis Bay phosphate rock from the company’s Florida sources is treated to produce superphosphate. The first operation after the raw material is unloaded to bins is the pulverizing of the rock for the acidulating process. The equipment for this purpose consists of twelve Raymond mills with air separators discharging to an intermediate storage bin. M7hen placed in operation, there were two features which required adjustment. The first mas the irregular load curve on the mill motor, which was corrected by providing mill feed control from a pick-up actuated by a solenoid in the
A
Figure 1-Dust
Received June 26, 1930.
which were not precipitated in the cyclone. The dust discharge from these twelve vents, shown partially in Figure 1, was a serious nuisance to the plant and neighborhood, as well as constituting an appreciable loss of material. Preliminary Experiments
T o remedy the dust discharge a number of experiments were tried, beginning with the simplest and least complicated methods. The first plan was to close off the vents and run the air-separation systems without excess air. Table I shows a
Nuisance Created by Cyclone V e n t Air before Installation of Air Filters
mill motor line. The load curve on this motor is now uniform, to give maximum grinding capacity, which averages about 4 tons per hour. The second feature of the system which required remedy was the dust discharge in the vent air from the cyclones. This vent airt amounted to about 1000 c. f . m. per mill, and carried with it the extreme fines from the grinding operation 1
BALTIMORE. MD
few comparative operating data for one system operating venting and closed. A number of objections to this system were revealed under operating conditions, of which the most serious was the increase in the moisture content of the circuit air, as the moisture in the material was liberated during pulverization. I n a comparatively short time saturation was approached, and consequent condensation occurred in the exposed piping and cyclone.
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Vol. 22, No. 10
efficiency filtration was necessary to produce required results, and a recommendation was requested from engineers and manufacturers of such equipment. Two plans were submitted, both using standard Dracco high-efficiency bag filters equipped with cotton-napped filter bags. The first was to group in one unit the collecting equipment for all cyclone vents, and the second, to erect a two-compartment filter for each set of two vents. This second plan was adopted, because it approached more closely unit operation of each mill, because it eliminated redistribution by screw conveyor of the collected material, and finally because it made possible the operation of a small test plant before the purchase of the complete equipment. Filter Arrangement Adopted
Figure 2-Special A r r a n g e m e n t of Dracco Air Filters H a n dling Excess Air f r o m T w o C y c l o n e Separator S y s t e m s
This caused the material to clog and build up sufficiently to make the operation very unsatisfactory. Since this test showed the necessity of drawing off from the system a certain amount of excess air, the problem was to find the simplest and best method of recovering the dust burden in this air. A simple water spray in a horizontal pipe was first tried, but the material was not precipitated in any appreciable amount.
Figure 2 s h o w the arrangement of the two-compartment Dracco filter to handle the excess air from two mill separation systems. The air volume through the two-compartment collector is 1800 c. f . m., or 900 c. f . m. excess air from eachmill system. This has been determined to be the minimum quantity to provide proper static conditions, to prevent dust leakage in the piping, and to maintain a constant air balance. The static pressure at the intake to the filter is 1 inch positive, and at the filter exhaust fan 2 inches negative, giving a 3inch drop through the equipment. A 5-horsepower motor is connected to the exhaust fan, but the average load is less than 2 horsepower. Figure 1 shows the first filter unit erected and in operation a t the extreme left, on mills number 1 and 2. The discharge from the exhaust faxi is free from any visihle solids, and the lack of dust at these points presents an interesting comparison with the discharge from the other vents. (Mills number 7 and 8 were not in operation when this photograph was taken.) The collected material is discharged to the pulverized-rock hopper through a gravity discharge box. Tests show a recovery of 32 pounds per hour for two mills, which is 0.2 per
T a b l e I-Comparative Operating D a t a for R a y m o n d Mill a n d Air S e u a r a t i o n S y s t e m w i t h a n d w i t h o u t V e n t i n g of Excess Air
I
RELIEFVENT ON RETURN LINEF R O M CYCLONE CLOSED
Static pressure Temp.
Inlet to mill Mill Fan discharge Inlet to cyclone Outlet from cyclone Return air, cubic feet per minute Rock ground, tons per hour Load on fan motor. amperes
Inches H 2 0 F. 112 2.6 -3.5 116 8.6 126 126 8.4 116 4.2 6000 3 13 30 0
OPEN
Static pressure
Temp.
Inches Ha0 F . -0.1 100 -7.2 105 4.7 114 106 4.4 102 0.5 4330 4.07 32.4
It was then considered possible that a small-diameter cyclone might accomplish the result, and the connection was made to one vent. The exceeding fineness of the dust, however, made the cyclone efficiency too low to justify the installation. To test the possibility of wetting the particles in conjunction with centrifugal separation, water sprays were introduced in an effort to improve the dust precipitation. This effected but little improvement in the volume of dust dist harge. A wet washer was tried out as a final effort to collect the vent dust by mechanical means, but the results fell far short of satisfactory collection. It then became evident that high-
Figure 3-Photograph d u r i n g I n s t a l l a t i o n of Air Filters The piping from the Raymond mills to the cyclonb separators, as originally installed, has been modified only by the connection of excess air lines to the air filters as evident at the extreme upper le!t.
October, 1930
INDUSTRI.4 I, A N D En'GIYEERI.VG CHEMISTRY
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Flgurc I--I)ust-Free Operafine Uondiflons Obtained w i t h Air Filfers HandlinO Excess Air from Cyclone Separators Compare with r l i ~ ~ r1.c which shows ogri~tirreconditions before inslrilrliun of the liiters.
cent of tlie averagc mill capacity of 1 tons pcr hour. The perfortiiance of this first equipmeiit proved coiripletely satisSactnry, and after a suitaide test run was cornplctcd five additional itnits were ordered to equip all twelve mills. Figiire 3 sho4;9 t,hc equiptneiit during erection, arid Figure 4 sliows t,he complete absenre of dust in the filt.cred air. Dust Recovery and General Efficiency
7'1~0 IBCOVFIY friiin blie cirinulebe collceiirm installation wiouiits to a. little less than a tori i i day (PI.lioiirs) of cxtreinely fine plioslihat,e rock. Table I1 givcs comparative scree:, tests of the iiiaterial rerov
