INDUSTRIAL A N D ENGINEERING CHEMISTRY
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Vol. 16, No. 11
Use of Koehler Safety Lamp in Testing Tanks for Combustible Gases or Vapors' By Robert E. Wilson and Robert E. Wilkin STANDARD OILCo. (INDIANA), WHITING,IND.
height, and was sensitive to HEN gasoline or As a result of thorough trial at Whiting, the Koehler safety lamp the presence of gas. It other light disis recommended as a means of testing tanks and other inclosed therefore seemed desirable tillate tanks are spaces for freedom from explosive concentrations of combustible to learn just what concenpumped out and cleaned, gases. I t is simple, safe. and gioes reliable indications if directions trations of gasoline and air it is frequently necessary to are followed. I t is especially useful in detecting gas pockets in corcould be detected by its use, make certain that no high ners, or around outlets, sumps, etc. and what flame height, etc., concentration of combustiA series of tests was made to determine the e$ect of flame height could best be used in makble gas or vapor is present, on various concentrations of gasoline in air. If a flame with a n ing a semiquantitative test. prior to making r e p a i r s initial height of 20 to 25 mm. is used, concentrations of gasoline which might produce sparks vapor as low as 0.5 per cent by volume can be detected with certainty. EFFECTOF GASOLINE CONand set fire to any comThis is from one-third to one-fourth the concentration of the lower exCENTRATION I N AIR O N bustible mixture. In the plosive limit, but somewhat more than the safe limit f o r breathing FLAME HEIGHT past the nose has very often for more than a f e w minutes. Because of the difficulty been the judge on this point, The method recommended for testing tanks with the KoehIer lamp in obtaining gasoline-air but experience has shown for gas is given in detail. mixtures at ordinary temthat it is by no means altoperatures without partial gether reliable, especially around a refinery where odors frequently pervade the entire condensation of the high boiling ends, a refinery cut-called surroundings. In some cases, particularly on oil tankers, the "hexane," boiling from 38" to 82" C., was used to make up the underwriters' rules demand actual gas analyses before permit- mixtures. This probably is comparable to the gas found in ting repairs to be made. This is a difficult and time-consuming gasoline tanks, since it is the lighter ends of gasoline which operation, and even this may be unsafe if, as frequently hap- evaporate most readily. KOEHLERSAFETYLAitw-The Koehler safety lamp was pens in large tanks, there are gas pockets in some parts of used as received from the dealers except that a graduated the tank. To care for this situation it was thought that a Davy safety paper scale was pasted on each side of the lamp glass in order lamp (a wick flame surrounded by a single gauze) might be to measure the height and variation of the flame (Fig. 1). used for such tests since its flame is known to flare up when This lamp has an aluminium frame. The flame is inclosed by placed in a combustible mixture. This lamp was tested in a glass and double, truncated. concentric gauzes. The gauzes are shielded from air gasoline-air mixtures under difcurrents by a perforated aluferent conditions and appeared minium bonnet or shield. The to be safe under all conditions burner takes a No. 1 wick and which it would be likely to the fuel used was aviation gasomeet, provided the flame was line of a p p r o x i m a t e l y 6.5' not turned very high. It was A. P. I. gravity. The lamp is accordingly used in testing lighted by an internal mechantanks, being carried into all ical relighter and the flame parts of the tank. height is regulated from the It was found, however, that bottom of the lamp. It has the Davy lamp had several been approved by the U. 8. Budrawbacks for the purpose. reau of Mines for use in mines. It extinguished readily when METHODOF MAKINGTHE carried o u t d o o r s , a n d w a s D E T E R MI N A T I 0 xs-Known rather difficult to relight in a mixtures of air and gasoline wind. Moreover, it gave a vapor were obtained by passing flame of rather irregular height, a measured amount of air and gave no clear evidence of through a 200-cc. flask into the presence of the gas until which hexane was dropped the concentration approached from a buret. This flask was the lower explosive limit. h e a t e d t o insure complete To overcome these objecvaporization of the hexane. tions recourse was had to a The mixed gases were then Koehler safety lamp, which difpassed into a 2-liter flask to fered from the ordinary Davy get uniform mixing before they in being larger, better conwent into the chamber containstructed, and provided with a ing the lamp. The lamp chammechanical lighter and a glass ber was 23 X 23 X 38 cm., shield for the flame. This lamp with a glass window in one side. gave a very steady flame The top was covered only with a sheet of cardboard. FIG. ~-KOI$H&BR SAFIVY L A M P 1 Received June 18, 1924.
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I N D U S T R I A L A N D ENGINEERING CHEMISTRY
November, 1924
The air and hexane were passed through the apparatus a t a constant rate for 5 minutes and then the lamp with a previously measured height of flame was placed in the chamber. The height of the flame was observed immediately and again after 5 minutes. The lamp was then removed and the height of the flame was observed outside to detect any creeping up due to heating of the lamp. If any creeping of the flame was detected the original height of the flame was corrected by this amount. A large number of tests were made, varying both the gas-air ratio and the original height of flame. The measured riFe in the flame and the calculated per cent of hexane gas by volume were recorded as in Table I and plotted in Fig. 2 .
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combustion but enriched by combustible vapors from the wick. The indications of 1.5 to 1.8 per cent are, however, in general agreement with the literature. It is therefore possible by the recommended method to detect concentrations of one-fourth to one-third of this explosive limit by flame measurements with an original height of 20 to 25 mm.
TABLE I (The number of decimals used here a n d on the figure are greater t h a n warranted by t h e accuracy of t h e d a t a , b u t they are used because the results a r e corrected from the oriainal measurements in tenths of Inches ) Gas Gas Per cent Flame height Rise Rise Per cent Flame height bvvolume Mm. Mm. Mm. by volume Mm. 5.0 1.42 8.8 1.2 0.57 12.5 5.0 0.88 16.3 1.2 0.76 7.5 5.0 0.82 16.3 1.2 0.36 11.3 0.69 3 3 . 8 5.0 1 . 2 0.32 11.3 0.66 23.8 5.0 1.2 0.95 10.0 6 .2 0 . 7 5 2 7 . 5 1 . 2 0.73 10.0 6.2 0.67 27,5 1.2 0.60 15.0 1 , 1 9 2 0 . 0 7 . 5 1.2 0.51 6.3 7.5 1.08 20.0 1.2 0.66 6.3 0.87 28.8 8.7 1.2 1.09 6.3 0.94 23.8 8.7 2.5 0.08 21.3 0.88 23.8 8.7 2.5 1.03 13.8 1.46 13.8 10.0 2.5 1,29 6.3 1.61 6.3 10.0 2.5 1.03 6.3 10.0 2.5 1.24 16.3 1.06 3.8 1.47 17.5 11.2 2.5 0.67 16.3 12.5 2.5 1.82 12.5 0.64 16.3 12.5 2.5 1.10 27.5 0.36 33.8 1.84 7.5 EX.^ 2.5 0.3.5 35.0 2.00 12.5 2.5 0.36 28.8 Ex. 2.5 2.12 6.3 0.91 * 10.0 Ex. 2.5 2.12 13.8 0.69 15.0 Ex. 2.5 2.12 28.8 0.39 25.0 Ex. 2.5 1,57 23.8 0.36 31.3 Ex. 2.5 2.05 22.5 0.38 32.5 Ex. 2.05 33.8 3.7 0.50 36.3 Ex. 1.80 31.3 3.7 0.71 21.3 Ex. 1.94 10.0 5.0 0.45 28.8 Ex. 0.. 6 0 28.8 1.59 31.3 5.0 Ex. E l . itldic2tt.a that the flamt did not burn steadily, hut flared irreyular:y within tbc gauze, indicatind t h a t rht :ewer explosive : i n i t was approximated. ~~
In these tests there were two independent variables, the concentration of gas and the required height of the flame. I t was almost impossible to predetermine accurately the exact concentration of the gas, or the height of the flame, so that one variable could be held constant while determining the effect of the other. The results, therefore, had to be obtained by varying both the flame height and the gas concentration over a wide range. I n order to show these results to the best advantage they are plotted theoretically in three dimensions, but practically by locating the points on a plane surface, in this case with the per cent of hexane and initial height of the flame as coordinates, designating the rise in the flame by numerical figures corresponding to each point, and drawing contour lines to represent the horizontal sections of equal rise in the flame height on the hypothetical three-dimensional diagram. By passing sections through the contours parallel to the two axes the effect of holding one variable constant is shown. For convenience three diagrams are given in which the three coordinates are combined in different ways. cONCLUSIONS--E’ig. 2 shows that, while the results are slightly variable, on the whole the agreement is quite good. It is evident that the lamp is most sensitive when the flame height is 25 mm. or more. However, owing to the difficulty of being sure of a rise of 1.25 mm. and the fact that the higher flames tend to vary somewhat, an original height of approximately 20 to 25 mm. is recommended. The “explosions” or flaring up of the flame within the gauze is not a reliable method of determining the lower explosive limit, as the composition of the gas within the gauze is not identical with that entering the chamber, being impoverished by the products of
PROCEDURE RECOMMEKDED FOR TESTING TAKKS The lamp should be lighted outside about 5 minutes before entering the tank in order to insure a constant flame height. The flame is adjusted to between 20 and 25 mm. high and its height is accurately measured. If there is any appreciable odor of gasoline vapors near the outlet, the test should preferably be postponed to allow further ventilation. If the test is made under these conditions, a charcoal-filled gas mask should be worn. The tank is then entered and any rise in the flame can be interpreted roughly in terms of per cent of gas from the curve. As a precaution, the flame height should be checked outside the tank after the test to eliminate any error caused by the flame creeping up. In general, a tank should not be considered safe if the flame shows .a definite rise of 2.5 mm. or more. As an auxiliary to the lamp, it is desirable to fasten a mirror to the side a t an angle of 45 degrees which makes it possible to observe the flame height more easily and yet keep the lamp near the tank bottom where the concentrations of gas are likely to be a maximum. The lamp is carried around inside the tank making observations with the lamp near the floor and also in the down pipes. Any likely place for gas pockets should be especially tested. One precaution must be emphasized-namely, that a tank may be substantially gas-free at the time of a test and then later become dangerous owing to a marked increase in temperature or decrease in air circulation. This, of course, can only happen if some liquid gasoline or oil is present a t some point, and the danger can be eliminated by inspecting thor-
IhTDUXTRIAL A N D ENGINEERING CHEMISTRY
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oughly for liquid as well as gas at all points. This can be done simultaneously if desired, utilizing the light of the safety lamp. It must also be emphasized that the lower limit of 0.5 per cent detectable by this method is somewhat above the safe
Vol. 16, No. 11
limit for breathing for more than a few minutes. Ordinarily the tank repairs do not require men to remain inside the tank for any considerable period, but if this is necessary, gas mask protection might still be required for complete safety.
How Coal-Handling Costs Were Cut $5000 a Year‘ By J. J. Hartley LINK-BELT Co , CHICAGO, ILL
NE of the most interesting examples of the reduction of overhead through the employment of mechanical means is that accomplished by a prominent Chicago concern. For a number of years all the coal for their power plant was handled by hand. Under this method it was necessary to employ six firemen, in addition to drafting three or four men from other work, when there were cars of coal to unload. About six years ago it was decided that this method was too costly and the boiler room and power plant were completely automatized through the installation of a coal-handling system. This system consists of a track hopper, apron conveyor, gravity discharge elevator, overhead bunker, and weigh larry. Of course, net savings cannot be calculated without first considering operation and maintenance costs. For this
0
this investment a t 6 per cent and depreciation at the rate of 5 per cent a year totals $2200. The items of repair, oil, attention, and so forth can be figured a t 1per cent of the total cost, which $200, when added to the annual operation charge, totals $2400. This last item is a very conservative figure, for, truth to tell, they have had only $51 worth of repairs in the entire time of this machinery’s operation-about six years. Only about 50 gallons of oil are used annually, and a half hour of one man’s time once each week is all that is necessary to keep the entire equipment in first-class working condition. Now for the brighter side of the calculations. The equipment has reduced the number of firemen necessary from six to one, and the elimination of five firemen a t $1500 a year means lopping off the pay roll a total of $7500 annually. Furthermore, the coal can be dumped into the track hopper (from bottom dump cars) without the necessity of extra men from the plant, and this eliminates considerable labor and cost. Not alone this, but the men in the plant did not relish leaving their regular work to shovel coal for a half day, and the installation of the track hopper and apron conveyor has completely done away with the old grumbling and complaint on the part of these men. But considering only the major item of $7500 a year through the elimination of the five firemen, the net annual saving would be in excess of $5000--after having subtracted from the gross saving the operating and maintenance costs.
APRONCONVEYOR CARRYING COALFROM TRACK HOPPER TO ELEVATOR GSNERALV I E W
OF
BOILERROOMSHOWING OVERHEAD BUNKER AND TRAVELING WEIGHLARRY
reason, the “dark” side of the installation will first be considered. The entire installation cost about $20,000. Interest on 1
Received August 13, 1924.
Thus the equipment pays for itself every four years. This may seem a long period in comparison with the performance of some other machines, but it is an excellent example of what mechanical means can do to overcome labor difficulties and reduce overhead. The installation would probably be considered profitable if it saved only half the annual amount.
