I M P R O V E D FERMENTATION EQUIPMENT & DESIGN file was actually measured by taking the bed apart in the manner previously outlined. In this experiment the filter was operated under the following conditions: Air rate, standard cu. feet/hour 345 Total air volume, standard cu. feet
33,200
Air velocity, feet/sec. 3.7 Downstream pressure, lb./sq. inch Pressure, drop, lb./sq. inch gage Total air contamination, spores
10 3.5 lo9
Artificially contaminated airwas passed through the filter for about 2 hours at a time, at three separate times during the 96-hour operating period. The observed penetration pattern is shown in Figure 3. The fact that penetration was logarithmic (after the first section) shows that the spores did not migrate. They were irreversibly absorbed on the filter bed material. The first section of the filter removes proportionately more spores than succeeding sections. This is undoubtedly due to the high entrance velocity, with resultant higher filtering efficiency, caused by the dispersion plate. In instances where the filter was not dried before use, penetration was much deeper and was not logarithmic. The filters must be dry for effective operation. I n actual operation, contamination may occur during drying. There are, however, only a few minutes before the first layers are dry and even a filter of poor efficiency is adequate for this short period. As a precaution, the air used for drying should not be passed into the fermentor. The pressure drop is higher than predicted from laboratory data: 3.5 against 2.4 pounds per square inch gage. The difference is caused in part by entrance and exit effects but mostly by the tighter compaction of filter disks required for stability of the bed. Effect of Steam Sterilization. In the
previous work ( 2 ) I M F filter beds were sterilized with ethylene oxide. Autoclave tests had shown that this filter material was stable under general steam sterilization conditions, but these are not typical of the rigorous treatment encountered in a commercial filter installation. T o check this point a number of runs were made with different periods of steam sterilization prior to operation (Table 11). Steam sterilization had little effect on filter efficiency, k, as measured by this method. I t did, however, cause loss of the resin (phenol-furfural) binder. After 12 hours of steaming most of the binder remained; after 48 hours it was removed. There are, however, other manifestations of filter deterioration with sterilization. There appears to be a breakdown of the filter bed starting with the end at which steam enters. This results in a loss in filter material from this end but does not affect the packing of the remainder of the bed. This type of deterioration will, of course, decrease the efficiency in proportion to the amount of material lost or disrupted. The amount of material lost can be measured either by weighing before and after sterilization or by determining the pressure drop across the filter under constant conditions of air flow and back pressure. The latter technique gives variable results but was used because it does not involve unpacking the filter. Sixty hours of continuous sterilization with steam a t 40 pounds per square inch gage caused a 20% decrease in pressure drop, while GO hours of intermittent sterilization with 15 operating cycles caused ,a 45y0 decrease. Evidently the loss of packing material is not alone a function of the total length of sterilizing time or of the number of sterilizing cycles but a combination of the two.
Acknowledgment The authors wish to acknowledge the assistance of R. G. Pearson in collecting the experimental data and of T. H. Elferdink and C. W. Means in the design and construction of the filter and test apparatus. They wish to thank H. A. Nelson and D. R. Colingsworth for helpful suggestions and support. literature Cited (1) Gaden, E. L., Jr., Humphre A. E., IND.ENC.CHEM.48. 2172 2 9 5 6 ) . (2) Humphrey, A. E., Gaden, E. L., ’Jr., Ibid., 47, 924 (1955). ( 3 ) Rosebury, T., “Experimental AirBorne Infection,” Williams & Wilkins, Baltimore, -1947.
RECEIVED for review August 9, 1956 ACCEPTED October 2 3 , 1956
Correct ions In the article on “Difunctional Acids by Petroleum Hydrocarbon Oxidation” [IND.ENG.CHEM.48, 1938 (1956)] on page 1938 footnote 2 should read: “Present address, Food Machinery & Chemical Corp., Princeton, N. J.” In Table V I the structure of dimer g (right center of table below “Flash distn. a t 350’ C.”) should be: (CHz)s-CH-O-CH=CH-(
On page 1946, third column, the structural formulas should be : CHz-CHz-CH2-CHO.
4
booH CH2-CH 2-CH 2-CHOH
I
I co
0
On page 1947, top of first column, the structural formulas should be : R-CH-CH
b-0 .
2-CH 2-CH 2-R
Table II.
LO-OH I
Effect of Air Velocity on Efficiency of IMF Packed Air Filters
(Back pressure, Velocity, feet/second Test filter bed, No. of layers No. of spores entering section No. of spores leaving section - iog (fractional penetration) k = bed depth - inches (nominal) Expected k, from laboratory data (8)
10 lb./sq. inch gage) 1.22 2.75 600 470 1.7 X lo’ 8.6 X lo7 21 140 0.50
-1
0.31
3.70 375 9.0 x 108 12
0.65
1.05
0.56
1.0
Effect of Sterilization Time on Efficiency of IMF Packed Air Filters
Sterilizing steam pressure, 40 lb./sq. inch gage. Time of sterilization, hours Test section, No. of layers No. of spores entering section No. of spores leaving section k
12 375 9.0 x 10s 12 1.05
Air velocity, 3.7 feet/sec. 30 48 360 385 2.5 X lo8 2.3 X 25 12 0.97 0.94
lo8
I
COOH
COOH OH
R-CH-CH Table 1.
CHz)z
I
’
+
2-CH z-CH-R
’
CARLN. ZELLNER FREDLISTER Th‘e senior author “Heterogeneous Acid tive Cellulose Fibers” 48, 1183 (1956)l is E.
of the article on Hydrolysis of Na[IND.ENG.CHEM. H. Immergut.
Frederick S. Mallette, coauthor of the Workbook Feature on “StandardizaGon Aspects of Air Pollution Control” [IND. ENG.CHEM. 48, 69 A (September 1956)] is no longer with Resources Research, Inc., but is a consultant with headquarters a t 56 Winthrop Drive, Riverside, Conn. VOL. 48, NO. 12
DECEMBER 1956
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