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INDUSTBIAL A N D ENGINEERING CHEMISTRY
Operating Data As a check on the calibration, analysis of vapor-air mixtures when naphtha and benzol vapor were used ha.s been carried out by the Haldanc combustion method and by the gns interferometer; fluctuations in vapor content are more easily observed by the int.erfcrometer. The determinations in Table I are typical; they have been extracted from a larger list compiled from determinations inado a t random on five of the described apparatus units in operation. The samples were taken from the tuhe t. Although not significant nor markedly greater than the error of the methods of analysis employed (approximately 0.02 per cent), the variations in the results may be due in part to slight fluctuations in the gasoline feed or evaporation, and would be less if the samples had been obtained from the heli jar rather than from the place designated. This is somewhat substantiated by a series of determinabions made during a single run of the apparatus, the samples being taken from
VOI.
17, KO. 7
the boll jar, where small fluctuations woiild be smoothed out on account of its large volume (Table 11). Tabie II-Resulr~ of Annlysia Showing Uniformity of C o n c e n ~ s t i ~ ~ in Chamber
A-Perceiiiage
B-Pemeniase
concentration expected lrom calibration dam. coneentratian found by interferunietcr analysis
A s stated before, each of the seven unit.s was operated at three different concentrations each day. The change in concentration necessitated merely changing the hydrostatic head in the water orifice, or, specifically, raising vater reservoir r to a predetermined mark on its support.
The Combustion of Carbon-I' By H. F. Smith and W. C. Ebaugh Gas RBSBARC"Co., DIYION,0x10
T
EXTBOOKS and technical articles dealing with the formation of producer gas, the combustion of fuels on a grate or in a furnace, the action of carbon in a metallurgical charge, etc., give the impression that the carbon must first undergo an oxidation to carbon dioxide and that later this carbon dioxide is reduced to carbon monoxide when it comes in contact with hot carbon in a more or less distant reducing zone. The illustrations accompanying such articles emphasize this concept by showing relatively large oxidizing zones near the point of air ingress and equally well-defined reducing zones farther along in the path of the hot gases.* The studies of Bone, Rhead, Wheeler, and their associates in England;3 of Boudonard' and Wendt6 on the continent; of Haslam, Lewis, and their eo-workers at the Massachusetts Institute of Technolo& of Langmuir;~and especially of Fieldner, Kreisinger, Sherman, Perrott, Kinney, and others connected with the U. S. Bureau of Mines,8 have done much to give definiteness to otherwise hazy statements concerning the mechanism of the reactions involved when carbon unites with oxygen. Perhaps the most striking fact brought to light or emphasized by the more recent work is that the oxygen introdneed as primary air is convorted so quickly, and after traveling through such a thin bed of fuel, into carbon dioxide 2 Presented before the Secilon of Gas and I ' d Chemistiy at tbe 87111 Meeting of the American Chemirsl Society, Wnrhington, D. C., April 21 lo 28, 1924. 2 Sexton. "Producer Gas." p. 3, Scientific Pubiisliing Co..Manchester. England; Dowson and Lartei, "Producer Gar." p. 2 , Lonp-mans, Green 81 Co.; Holmer, "General Chemistry,(' p. 309, The Maccinillair C o . ; Smith, Keodall. and Slosson, "Intermediate Che'mistry,'' p. 337, The Century Co.: Uradbury, "A First Book In Chemistry," p. 327,D. Applrlon & Co. 8 Bone and Wheeler, Enginming, 86, 837 (1894); Rhead and Wheeler, J , C h o n . SOC.(London), 91, 2178 (1910); 99, 1140 (1911); 101, 831 (1912): 4 Ann. chirn. fihys., Series VII. %I, 3. SIoil u. Eisen, P6, 1184 (1906). 0 Haslam, 1Iitchcock. and Rudow, Term JOUBNAL, 16, 115 (1023); Lewis, Ibirl., 16, 502 (1923). I 3 . Am. Chem. SOL.,81. 1154 (1915). I Fieidner, A m . Inst. Chem. E n g , preprints, December 5 to 6 , 1923; Krrisinger, Ovitz, and Augustine, Bur. Mines. Tech. Paper 181; Sherman and Blizzard, Troai. Am. inif. Mi% iMel. Ens., 1117-8; Sherman and Kinney, Iron Agc, 111, 1838 (1823); Peirott and Kinoey, Trans. A m . I l s l . .win. lilci. E ~ ~la=-8. . ,
and carbon monoxide; and quite as important is the rapid disappearance of carbon dioxide and corresponding increase in carbon monoxide. The influence of high temperature and of increased pressure in favoring a large CO: COSratio is also important. I n view of the statements so generally accepted to the effect that carbon burns first to carbon dioxide and that this is later reduced to carbon monoxide, it seemed of interest to try to separate the oxidizing and reducing zones of a producer, and to study the composition of the gases formed. The results should be important in discussing not only producers, but any case involving the combustion of fuel within a confined space. Apparatus Iii Figure 1. a represents a "home gas producer" employing charcoal as a fuel and watm vapor in regulated amounts; h is a purifier to remove tar, dust, and other impurities from the
Figure 1
producer gas; c is a fao drawing either gas only i r o n the purifier,
INDUSTRIAL A N D EXGINEERING CHEMISTRY
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into the bottom of the experimental producer 1-h; j and k are sampling tubes. The experimental producer, 2-h, was built up from five fireclay rings, 13 cm. ( 5 inches) i. d. and 23 cm. (9 inches) 0. d., dipped in cement slurry, placed in a section of 25cm. (10-inch) i. d. iron pipe, i, and then backed up with cement. A 30 X 38 X 5 cm. (12 X l5.X 2 inches) firebrick formed the base, h. The lower section of the producer was filled with broken firebrick to a depth.of 15 cm. (6 inches), and above that was 5 fuel space 69 cm. (27 inches) deep. Over the top of the experimental producer was laid loosely a cover made from 6-mm. (l/r-inch) iron plate. The sampling tube, k , could be inserted to any depth desired, and a current of gas drawn off through one of the ends by means of an aspirator; and then a sample of gas would be obtained through the other end by means of a Williams gas analysis apparatus, which was used for all analytical work.
Method
Gas generated in the producer, a, was burned in the lower 15 em. (6 inches) (combustion chamber) of the experimental producer, I-h, and the valves, d, were so adjusted as to give a maximum carbon dioxide value in the products of combustion. The firebrick-filled chamber soon became heated intensely, and when it had been proved by preliminary experiments that a certain setting of the valves could be depended upon to bring about a maximum combustion of the air-gas mixture blown into the combustion chamber, charcoal was placed in the upper part of the experimental producer and allowed to become hot>. This gave virtually the effect of the conventional oxidizing zone in the bottom of the experimental producer, with its hot, completely burned gas rich in carbon dioxide and very low in carbon monoxide passing through a space containing broken firebrick heated to incandescence. Immediately above this part of the cylinder was a layer of incandescent charcoal representing the conventional reducing zone. There could be no doubt as to an actual separation of the two zones. Table I Distance of point of sampling above firebrick Cm.
Depth of fuel below point of sampling Cm. FEED Preliminary runs
coz
io2
%.A%
19.6 0 . 4
7 ( 3 in.) 7 38 (15 in.) 38 3s 38
