INDUSTRIAL AND ENGINEERING CHEMISTRY
548
Vol. 20, No. 5
Total Carbon in Coal’ A. R. C a m a n d A. M. Rente THECOLLEGE
OF THE CITY OF
HE efficiency of a furnace is determined from its heat balance. If the heat energy is supplied to the furnace
T
by the combustion of fuel, the heat balance depends upon the nature, amount, and disposition of the fuel burned. These may be obtained from the material input and output, or the material balance of the furnace. The determination of a material balance requires two things: the products of combustion must be analyzed; and either the air or the fuel used for combustion must be analyzed and measured. An analysis of the products of combustion is readily made. Since the air used for combustion enters the furnace at more than one point, its direct measurement is impossible. Therefore, the method employed is to measure and analyze the fuel input. The total carbon, ash, moisture, and heating value of the fuel are determinations necessary for computing a material and heat balance. The last three determinations are comparatively simple and rapid; the determination of total carbon, however, is more difficult. The standard method, that of Liebig, is slow and tedious, demanding expensive apparatus and skilful operation. Because of these difficulties, numerous attempts2 have been made to simplify and shorten t h e Liebig method.
DETROIT, DETROIT, MICH.
Apparatus The apparatus is shown in the accompanying diagram. A is the monel-metal bomb, which is placed on the shelf of a table used for gas analysis. It is attached to the apparatus by means of the steel nipple, C, which is screwed into the oxygen intake in the head of the bomb. The needle valve, B , which closes the bomb is carefully packed so that the gases cannot escape around the stem of the valve when it is open. This is accomplished by winding asbestos cord around the valve stem and by tightening the packing nut upon the asbestos packing. The detailed drawing of the bomb3 is shown in the lower left-hand comer of the figure. The nipple C is connected with the leads of Pyrex glass tubing by a short rubber tube, as shown in the figure. The few rubber connections necessary are securely wired to prevent leakage. A short distance from the bomb a small bulb, D,is inserted in the line. This bulb is a small calcium chloride tube, which is packed with moist cotton lamp wicking in such a manner that the free space in the tube is completely filled. A few cubic centimeters of water in the enlarged part of the tube keep the wicking wet and saturate the gases with water vapor as they e s c a p e from the bomb. This step is necessary, as the gases must be analyzed either completely dry or completely saturated if accurate results are to be obtained. In the course of experimentation a t t e m p t s w er e E
l
TO GAS.BURETTE
I1
Ill
I
A
The method proposed in this paper is similar to that described by Watkins, except that a special type of mercury gasometer is not needed. The coal sample is exploded and its heating value is determined in a Mahler type of bomb. The products of combustion are expanded into a rubber balloon inside a large bottle filled with water and the displaced water is weighed. The pressure and temperature of the gas in the balloon are recorded. The carbon dioxide content is estimated by means of a caustic pipet and the total carbon in the sample is computed. This method requires no special apparatus other than that in general use for coal calorimetry and gas analysis. 1 Received
January 26, 1028. 2 Parr, “Fuel, Gas, Water, and Lubricants,” p. 179, McGraw-Hill Book Co., Inc., 1022; Goutal, Fuel Science Practice, 2, 344 (1023); Watkins, IND. ENO.-CHBX.,19, 1052 (1027).
vapor absorbed by the gases from the solution in the caustic pipet. These results were found to be less accurate than those obtained by saturation of the gases with water before measurement and analysis. From D the gases are led to E, a glass tee, which is connected on one side with the mercury manometer, F, and on the other with the tube leading to the rubber balloon, H. G is a tee:leading to the gas buret, through which the samples for gas analysis are drawn. Stopcocks are placed in the lines leading to the manometer, gas buret, and rubber balloon. The balloon, H , is wired to a short, curved brass nipple, I, which is inserted into a one-hole rubber stopper, J. In order to prevent the wire from cutting the balloon, both the neck of the balloon and the nipple are taped before the connection is wired. The nipple I is also connected to the lead from the bomb. The stopper J is securely wired into the bottle, K , which is tall and narrow and has a capacity of about 12 liters. As the balloon expands, the water in the bottle overflows through the glass pipe, L,inserted into a rubber stopper securely fastened into the neck of the bottle K. The overflow is caught in the beaker, M. The bottle must be sufficiently tall t o enable the balloon to expand freely and not fill the neck of the bottle, thus stopping the overflow. The carbon dioxide in the gas is analyzed by means of a gas buret filled with mercury and a bubbling pipet containing caustic solution.
Fuels Studied
The accuracy of the apparatus was checked by means of standard benzoic acid and five coals obtained from A. C. 1 Taken from White’s “Fuel and Gas Analysis,” p. 260, McGraw-Hill Book Co., Inc., 1920.
May, 1928
INDUSTRIAL A S D ENGINEERIJYG CHE-VIXTRY
Fieldner of the Bureau of Mines, Pittsburgh, Pa., through the courtesy of G. B. Watkins. The ultimate analyses of the coals were made a t the Bureau of Mines. The samples include semianthracite, semibituminous, bituminous, and lignite coals. Experimental Work
549
the buret to compensate for any dehydration of the gas due to the caustic. A number of gas analyses are made on each run and the average of the results is used to compute the percentage of carbon dioxide. The total carbon is then calculated from the results of the carbon dioxide analysis and the total volume of the gas. The stopcock in the line from the balloon is opened, the bomb is disconnected, and the water in the overflow beaker is returned to the bottle. This flushes the sample out of the apparatus and makes it ready for another run. The leads are left filled with the old sample but, since their volume is only 39 cc., and the percentage of carbon dioxide varies only slightly in the samples of coal, the error introduced ic negligible. The balloon is of good-quality rubber and mill last for a large number of runs. Since the total time for the carbon determination is only 25 to 30 minutes, the amount of difTusion”_f the gaseous product into the mater is so slight that it does not cause serious error.
d 0.3- to 0.6-gram sample of coal is exploded in the bomb calorimeter containing about 15 atmospheres of oxygen. This size sample is found to be more suitable in the apparatus described than the 1-gram sample ordinarily used for coal analysis, as it requires less volume of oxygen for complete combustion. This makes the volume of the gaseous product correspondingly smaller and the balloon expands freely in the bottle without choking the overflow. If 1-gram samples are exploded, a somewhat larger bottle should be used. The initial temperature of the water in the calorimeter is slightly below room temperature and the final temperature is approximately equal to that of the room. The timeResults temperature readings ordinarily taken for coal calorimetry are recorded. As the primary object of the experiment is Table I gives the results of the determinations on benzoic to check the accuracy of the total carbon determination, the acid and Table I1 the data obtained from the coals studied. heating values are not given in the table. ‘However, the A sample computation for total carbon from the experimental bomb is always exploded and allowed to come to thermal data is given. The experiments show that the method deequilibrium in the calorimeter as if a heating value were scribed is accurate and rapid and does not require special actually determined. The bomb is then removed from the or expensive apparatus. calorimeter and connected to the rubber balloon by screm-ing T a b l e I-Total C a r b o n of Benzoic Acid the nipple C into the head of the bomb. The bottle K is THEORETICAL EXPERIMENTAL filled with water a t room temperature. Placing a rubber Per tent Per cent stopper in the bottle fills the overflow pipe L through the 68.6, 69.0, 68.9 Average 68.8 68.8 displacement of water from the neck of the bottle. The beaker M is placed in position. The manometer is read Table 11-Total C a r b o n of C o a l COALN o under atmospheric pressure. The stopcocks in the lines (B. OF &I.) KINDOF COAL B. O F >I. EXPERIMENT~L leading to the manometer and buret are then closed and the Per cent Per cent cock in the line leading to the balloon is opened. The gas A26839 Semianthracite 62 6, 62.5, 62 7, 63 0 Average 6 2 . 7 62 7 is allowed to pass slowly from the bomb by opening the A26566 Semibituminous 83.3, 82.9, 83 1, 8’’ 5 needle valve slightly. The d a t i o n of the balloon causes Average 83.1 83.2 the water to overflow into the beaker, M . When the flow A26840 Bituminous 73.5, 7 3 . 2 , 7 3 . 1 , 73.4 of water slackens, the needle valve is opened further and the Average 73.5 73.3 process is continued until the valve in the bomb is fully open. A26847 Bituminous 76.7, 7 6 . 1 . 7 5 . 9 , 7 5 . 9 Khen the flow of water stops, the system is allowed to come Average 76.1 76.15 to equilibrium. If there are no leaks in the line, the water A27336 Lignite 52.3, 5 2 . 0 , 5 2 . 5 , 5 2 . 1 will stop flowing from the overflow pipe, leaving the pipe Average 52.4 52.2 full of water as it was a t the beginning of the run. The Calculation of Total C a r b o n f r o m Experimental D a t a usual time taken by the gas in expanding from the bomb is 7 to 8 minutes. As an example of the use of the experimental data in comWhen the pressure in the system is equalized, the stopputing total carbon, the calculation for the first run listed, cock in the manometer line is opened and the pressure on the manometer is read. This is above atmospheric pressure that of semianthracite coal (Sample A 26839), follows: 0.4770 gram Weight of coal sample as the balloon is always under a slight head of water. The 1651 cc. Volume of overflow water barometer is read and the manometer reading is added 296 cc. Volume of bomb and leads 1947 cc. Total volume of gaseous product to the barometric pressure to determine the absolute presBarometric pressure 737.6 mm. Hg Manometer reading 2 0 . 0 mm. H g sure. The amount of overflow water is weighed and its Absolute pressure 757.6 mm. H g temperature is recorded. To the volume of the overflow Temperature of overflow water 2 5 . 5 C. 3 1 . 4 per cent Average COz content of gaseous product is added the volume of the bomb and leads (296 cc.), which represents the total volume of the gaseous product under 273 12.005 757.6 0.314 1947 X F~ X 22400 X - X - X 100 = 62.6 per cent 298.5 0.477 the conditions of the experiment. The volume of the bomb Factor which occurs in all computations is and leads is determined by weighing the water and the merX 12.005 0.0001925 cury, respectively, required to fill them. 22400
is
G a s Analysis
The valve in the line leading to the 100-cc. gas buret is opened and gas is allowed to escape into the air through the three-way stopcock in the buret. After this has flushed out the line, a sample is drawn into the buret and measured over mercury. The carbon dioxide content is estimated by bubbling the sample into a caustic pipet. -4few drops of acidified water are always kept on top of the niercury in
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Allegheny Forest Experiment Station Philadelphia has been chosen as headquarters for the Allegheny Forest Experiment Station of the Forest Service, U. S. Department of Agriculture. Headquarters are being established in cooperation with the University of Pennsylvania. Field work will be conducted a t various centers in Pennsylvania, Maryland, New Jersey, and Delaware, in cosperation with a number of organizations and educational institutions, including state agricultural colleges.
