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stallation may be of interest. A large refiner was rebuilding a pressure distillate stabilizer, a reformed gas stabilizer, a depropanizer, and a prefractionator. The total heat input for the four direct-fired heating reboilers was to be 36,000,000 B. t. u. per hour divided into two 10,000,000 B. t. u. per hour units and two 8,000,000 B. t. u. per hour units. Finally, four identical heaters were required for this duty a t a n installed cost of $80,000. Since it was necessary to pump the reboiler feed through the heaters, charge pumps were necessary. These pumps had a daily electric power consumption of 1350 kilowatt-hours. The furnaces were designed with a n average efficiency of 70 per cent, based on a net heating value of the gas fuel. A complete Dowtherm installation for these duties, including two complete boilers, controls, condensate pumps, receiver tank, storage tank, four reboilers, and Dowtherm A to fill the system, would have cost about $66,000, or an initial saving of $14,000. For this, two boilers of 18,000,000 B. t. u. per hour load each would be used, each boiler serving two shell-and-tube reboilers. By using this method of heating, the four oil charge pumps would be eliminated since the Dowtherm reboilers would be of the thermosiphon type. If sufficient head were not available for the gravity return of the Dowtherm condensate, two pumps would be required for this service. These pumps would have a daily power consumption of only 150 kilowatt-hours, and would thus save a t least 1200 kilowatt-hours daily or $6.00 when power is worth $0.005 per kilowatt-hour. The efficiency of the Dowtherm boilers would be a t least as high as the direct'
VOL. 31, NO. 7
fired heaters, and the operating results due to accurate temperature control would be much better. There are no construction difficulties experienced in Dowtherm heating systems beyond those involved because of the high temperature handled and the low surface tension of Dowtherm. Piping designed for superheated steam and joints made up to hold kerosene will be tight and satisfactory with Dowtherm. Because of the temperature involved, pressure tanks, shells, heaters, and receivers should be fabricated in accordance with A. S. M. E. specifications for Class I welding. Piping may be of standard weight steel, but screwed fittings should not be used above 1 1/4 inches. For fittings of 1 '/z inches and larger, welded flanges of 300-pound standard should be used with soft corrugated iron gaskets between smooth flange faces. Globe valves are necessary to ensure tight seats, and angle valves should be used to reduce pressure drop. Valve stuffing-box packing should be of the hightemperature type, consisting of asbestos and antifriction metal lubricated with graphite and nonliquid lubricant that will withstand the temperature. Experience derived from the appreciable number of Dowtherm vapor heating systems has already shown that the assembly is remarkably free from cleaning expense and maintenance trouble. The availability and flexibility are both high, the speed with which changes in load and temperature can be made is greater than can ordinarily be used, and the closed system operating under low pressure requires minimum supervision.
Effect of Various Insulating Materials on Cellulose H. C. P. WEBER Westinghouse Research Laboratories, East Pittsburgh, Penna.
A
NUMBER of years ago several insulating varnishes were
investigated in this laboratory. The point in view a t that time was to determine the effect of acidity, especially volatile acids, formed during the drying process of the varnish. I n connection with this investigation, a varnish manufacturer supplied about thirty samples of varnish specially made for the tests. I n these varnishes the variations, carefully controlled, consisted of the kind of oil, method of boiling the oil, resin used, and driers used. The difference found in the amount of volatile and watersoluble acids (largely acetic, formic, etc.) was striking and, calculated as acetic acid, ranged from 5 to 0.5 per cent of the varnish film. These same tests gave the opportunity for obtaining a rather unusual life test on cellulose a t ordinary temperature. It is customary for the varnish manufactuer to make socalled slip tests on his varnish batches. This consists in taking strips of a standard grade of bond paper, 4 X 20 inches (10.2 X 50.8 em.), and dipping, draining, and baking these strips (at 100" C.) according to definite procedure. These test strips yield important data concerning the varnish. The test strips were made as usual for the special varnishes described. After examination they were rolled up, enclosed
in a screw-capped jar, and stored in the laboratory a t ordinary temperatures without particular precautions. The samples were inspected from time to time. I n 1935 (14 years after preparation) the samples were mounted and photographed. Upon comparison, the samples could be arranged in three groups with rather rough but quite obvious differences. I n the worst group the original cellulose strip had become so brittle that it could be crumpled to flakes in the hand. The second group could not be powdered in this way, but the paper broke if it was bent over and creased with the thumbnail. The third and best group could be creased without breaking the paper, which was still pliable and strong.
Acid Formation I n analyzing the conditions responsible for the greater or smaller destruction of the cellulose fiber in these samples, a n almost exact parallel is to be noted between the deterioration and the amount, or rate, of acid formation by the varnish. When air-dried, varnishes A to F in Figure 1 developed a n acidity of 5.0, 4.3, 3.3, 4.5, 4.3, 4.1 per cent, respectively (average, 4.25). For varnishes G to L, the first three averaged
INDUSTRIAL AND ENGINEERING CHEMISTRY
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805
2.3 per cent and the second three, 2.6 per cent. These are somewhat better than varnishes A to F , particularly G, If, and Z. They are not nearly so good as varnishes M to Q. The lat.ter developed an acidity of 0.5, 2.4, 1.3, 1.1, 1.4 per cent, respectively (average, 1.3 per cent). Since these photographs were prepared in 1935, the samples in the first two groups have perished completely. I n the last group, P and Q have in the meantime become brittle, but M , N , and 0 have retained their original pliability. In these results the relation between deterioration and acidity of the impregnating material is striking. Of course, it is not news that acids hydrolyze cellulose. However, organic acids (say the lower fatty acids) are not usrially thought of in this connection. It may he argued that the effect is simply due to oxidation. In a way tliis is true as far as these results are concerned, but all samples were subjected to the same degree and length of air exposure. The amount of deterioration was dominated by the products formed in the material accompanying the cellulose, SNAP ON CREASE SNAP ON CREASF and the effect is the result of oxidation "once mwmi F removed", not of direct nxidation of the GlC3Ol cellulose. In order to obtain an idea concerning the relative importance of atmospheric oxygen in the destruction of the cellulosic material as compared with the impregnating or filling cornpound itself, the following tests were nia& : Sticks of straight-grained ash (dowel material), 0.75X 4.25 inches (1.91 X 10.8 ern.), were impregnated in duplicate u%h a number of materials. Impregnation was carried on at * 100" C., and vacuum was applied during the process. Most of the air and a large part of the nroisture of the wood were removed during this operation. The surplus u'as wiped off while the sticks were hot, and they were tlien weighed. The ~ e i g l r of t the sticks was FIGURE 1 ACIDITYOF VAKYIsIlEs DEvELOPED WHEN AIH-DRIED uniformlv 20 * 0.5 rram before treatment. Average actdity. A to F,4 25 per cent; G to L, 2 45; M to Q, 130 After impregnation, one speciineii of each treatment was baked in t.lie open and one in Both sets were hakcd side by side at, 150" C. for 50 hours. a sealed glass tuhc which had been evacuatcd to 10 min. The open speeimens \\-ere weighed from time to time, the sealed ones a t the end of the treatment. The weights for the sticks in the sealed tubes were obtained after being washed with alcohol-toluene TABLE I. CHAXGES IN WEXGHT OF IMPREGNATED SAMPLES (IN GRAMS) to remove soluble dec.oniposition products. The Not Gain after Heating Gain 0% It 150' C. pressure excess was perhaps 0.5 to 1 atmosphere; Tmetrnent No. Irnpiegnstxon 7 hr. 31 hr. 50 lir. Coinmenta odor. molasseslike and tarrv: " . acids aresent.. verv" Blank n U -1 -1 ... -3.5 SliZhL pressure, little volatile (formic, acetic). Blank b U Seeled ... tST The first column of Table I shows the material 1 mhyl s/l/c~te 4.7 +6 +6 . .. used for inrpreguatiun, the second the gain in 2 Ethyl a i , c a t e Sealed .. . +3 No pressore, "0 t a i 3 Tung oil 5 +6 +4.5 +4.5 ... weight as found previous to heating. The third 4 Tung oil 5 Sesled -2.5 Piersure, tsr, sc/d CohITirn shorvs the net gain (or loss) after heating 5 Linseed oil 13 +0.6 fh.5 +B Pressure, tar, acid to 150" C. for 7 hours. The difference hetween 6 Linseed oil 1s Senieci ... -1.0 Presuie. tar, acid 7 Clrlorobenzene 14.5 +I +0 +0 5 .. this and t,he second eolumn gives the loss by 8 Clilorubeniene 14.5 Sded ... -4.0 Pressure. hi, noid, C h S i i d volatilization at this bemperaturc, plus any de9 Crude phenanthrene 20 1-12 +6 +3.5 ... composition of the wood. In tlic case nf un10 Crude phessntlireue 2U Sealed ... +3.U Pressure, tar. soid impregnated wooil it represents losses of tlic 11 Crudeplienanthrene 16 17 +4 +3.5 ... 12 Crude phenanthrene 16 Snaied ... +3.5 Piessuie. tar. w i d wood alone. 13 Purified phenanthrene 13 17 +6 +5 The sticks heated in the men were weighed 14 Purified phenanthrene 11 Sealed . .. +2 S o piesniie, tar a t intervals. In t,hese samples, after the first
+;:
I
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VOL. 31,NO. 7
Crushing Strength
6000
As another measure of the amount of destruction, the crushing strength of the samples was determined. A oneinch piece was cut from each sample and compressed in the direction of the fiber. The values are given in Table 11. The wide difference in effects is apparent (1 and 2, 3 and 4, etc., are alike in impregnating treatment).
5000.
4000. I
3000,
TABLE11. COMPRESSION STRENGTHS AFTER HEATING 2000 CRUSHING
STRENGTHT
'\
I
500 -I
.+5 -1 1
I
*S
I
I
*I1 *I3
I
*3
I
I
I
BL *2 *6
-
I
d:
'\\,
1000.
,,'
1~
' 8 'IO
-Heated OpenTreatment Strength, No. Ib. 1 5500 a 3500 5 4350 7 5400 9 5600 11 4400 13 5650 Blank 5600 Av. 5000
I
t
l
I
I
*I2 "14 #4
OPEN c- 50 HOURS 150°C. d S E A L E D
J
-Heated SealedTreatment Strength, No. Ib. 2 2400 4 2850 6 1800 8 550 950 12 lo 2000 14 2100 Blank 3900 Av. 2070
40
30.
20 5
*I
*!
14 4 '
BL
OF HEATON TREATED WOOD FIGURE2. EFFECT
adjustment during 7 hours a t 160" C., there is relatively little change during the succeeding 43 hours a t 150" C. Note, for instance, the blank run. The wood (and the cellulose present in it) is quite stable a t 150" C. under these conditions. I n the cases where the wood was sealed in the glass tubes, the samples were steeped and washed in a mixture of toluene and alcohol to remove readily soluble decomposition products (and part of the impregnating material). I n the case of the blank sample this loss was 3.5 grams or 17.5 per cent. When the sealed tubes were opened, pressure, estimated a t about 1 or 2 atmospheres, was found in all but two cases. Possibly there was carbon dioxide. The blank gave very little pressure or tar. The vapors were highly acid in every case, (HCOOH, CHaCOOH, etc.) and had a molasseslike, tarry odor. Acid, tar, and moisture were formed in varying degrees; in the case of the oil treatment there was an accumulation of several cubic centimeters of liquid. The wood was more or less charred in some cases, only slightly darkened in the case of the blank, and practically unaffected in one or two cases (in which no pressure had developed, as it happened).
The most plausible explanation for the difference in effect is that the destruction of the fiber has been hastened by the products initially formed, particularly if they are acid. I n the case of the open samples, these products escaped and little further harm was done. Samples 9, 10, 13, and 14 were phenanthrene; but with 9 and 10, an impure, slightly acid product was used, whereas in 13 and 14, a much purer material was taken. The extremely destructive effect of trichlorobenzene, when confined, is striking. I n this 'case the wood actually appears carbonized. This result might be ascribed to formation of hydrochloric acid-actually or potentially-during the prolonged heating.
Summary of Results These results may be taken to show that: 1. Up to 150" C. no rapid deterioration of the cellulose occurred in air due t o oxidation alone. The practical realization of this inherent stability of cellulose is an important problem in electrical applications. 2. Slight amounts of acids, even organic acids, have a marked effect on the deterioration of the cellulose. These may readily overshadow the effects of direct oxidation. The acids may or may not be the result of oxidation. 3. There is evidence of s ecific effects of direct reaction between cellulose and some of &e varnishing and impregnatingmaterials. These results were not obtained with pure or ideal cellulose, and it is hoped that further evidence will be available for it. As a matter of fact, most of the problems of practical use have to do with the natural, more or less complex, compositions of cellulose. Although the results shown may not apply to pure cellulose in degree, it seems probable that they do apply in kind. PR~PSBNTBD before the Division of Cellulose Chemistry at the 97th Meeting of the American Chemical Society, Baltimore, Md.
