I N D IJ S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
732
12. The experiments here described are not of sufficient scope to justify definite and final conclusions but they may serve as a guide and stimulus for further study of the corrosion problem. LITERATURE CITED (1) Am.Petroleum Inst., Producfion Bull. 208 (1931). (2) Burns and Salley, IND.ENG.CHEM.,22, 293 (1930). (3) Evans, U. R., "Corrosion of Metals," Edward Arnold, London, and Longmans, Green & Co., N. Y . , 1925.
Vol. 26, No. 7
(4) Evans, U.R.,J.Inst. Metals, 30,239 (1923). (5) Handy, J. o., Am. SOC. Heatinu Ventilating Engm., 23, 125 (1917). ( 6 ) Logan, Bur. Standards, Research Paper 95; J. Research, 3, 275302 (1929). (7) . . Loaan and Grodskv. Bur. Standards. Research PaDer 329: J . Research, 7,l-35 (1931). (8) Logan and Taylor, Bur. Standards, Research Paper 638; J. Research, 12, 119 (1934). RXCEIVED
April
,
1934
Hygroscopicity of High- and LowTemperature Cokes D. A. REYNOLDS, Experiment Station, U. S. B u r e a u of Mines, Pittsburgh, Pa.
T
HE hygroscopicity of high-temperature coke has been studied and may be regarded as well known, whereas that of cokes made at intermediate and low temperatures has received little attention. Heretofore such cokes have not been sufficiently important industrially to merit investigation of this property, affecting, as it does, the amount of inert matter in coke offered on the market. However, cokes made a t low and intermediate temperatures are now being sold in increasing quantities in European markets (&6) and several processes are being operated experimentally in
FIGURE1.
MOISTURE ABSORPTION BY COKES RELATION TO TIME
IN
this country. It is therefore of importance to know, as this paper proves, that cokes made a t lower temperatures are considerably more hygroscopic than those made a t the ordinary by-product oven temperatures. Previous investigations of the U. S. Bureau of Mines (6) and Moore (3) have shown that high-temperature coke is comparatively nonhygroscopic, since the total moisture absorbed a t 75 per cent humidity is usually well under 2 per cent. Lowtemperature coke, however, is much more reactive than hightemperature coke and may be expected to absorb much moisture from humid atmospheres. The experiments described in this paper were undertaken to determine the influence of carbonization temperature and rank of coal on the hygroscopic properties of the resulting coke. The Bureau of Mines-American Gas Association cooperative investigation (1) of the gas- and coke-making properties of American coals provided excellent material for the research. Twenty-seven series of cokes made from different coals or blends at temperatures ranging from 500" to 1100" C. were available for study. COKESTESTED The proximate analyses of seven coals selected for this study are given in Table I, together with the analyses of the
cokes produced a t 600" C. The coals range from 15.5 to 40.6 per cent volatile matter, and from 51.7 to 79.6 per cent fixed carbon on the moisture-free basis. The analyses of the 600" C. cokes are given because generally they were most hygroscopic. Since the chemical composition was not found to be of particular significance in this study, analyses of other cokes are not included in Table I.
EXPERIMENTAL PROCEDURE A relative humidity of 75 per cent, maintained by use of a saturated aqueous solution of sodium chlorate a t 20" C. (Q), was used in all tests because such humidity is common in the eastern United States. The saturated solution of sodium chlorate was placed in the bottom of a large glass desiccator, and the cokes were distributed on two racks over the solution. The temperature inside the desiccator was measured with a mercury thermometer. The humidors were not maintained a t constant temperature, although it is recognized that such procedure affords greater accuracy in the results obtainable. All the determinations were made within the temperature range 20" to 23" C. Actually, the small temperature changes had no effect on the ind i v i d u a l curves (Figure 2) because each r e p r e s e n t s moisture absorptions determined simultaneously and therefore a t one temperature only. Preliminary experiments on 600" C. coke from P i t t s b u r g h coal FIGURE2. ABSORPTIONOF MOISTURE s h o w e d a slight BY 4- TO ~O-MESH COKES decrease in hygroscopicity as the size of coke was decreased from 0.5 inch (1.27 cm.) to fines passing a 100-mesh screen (Table 11). Moore (5') has shown that with very fine sizes of gas coke the absorption of moisture increases with fineness. Moore (5') found that equilibrium was attained in 24 hours. In the present study the moisture absorbed by the 600" C. cokes made from Pittsburgh and Green River coals was determined at intervals for 40 hours. The cumulative amounts of absorbed moisture, calculated as percentage of dry coke, a t various time intervals are shown in Figure 1. Obviously,, the absorption is complete a t the end of 24 hours.
July, 1934
TABLEI.
INDUSTRIAL AND ENGINEERING CHEMISTRY PROXIMATE
ANALYSESO F
(MOISTURE-FREE BASIS), AND CONTENTS OF COALSAS CARBONIZED"
COALS AND 600' COKES
733
MOISTURE .4ND SULFUR
( I n per cent) COALAS CARBONIZED Moisture S 7.9 0.8
COALBED STATE COUNTY Franklin Ill. Illinois No. 6 10.1 Muhlenberg Green River Ky. Carbon 4.6 Utah Lower Sunnvside Marion W. Va. 1.9 Pittsburgh Jefferson 4.2 Ala. Mary Lee (washed) Garrett 1.4 Md. Davis 0.8 3lcDowell W. Va. Pocahontas No. 4 By H. M.Cooper, supervising chemist, coal analysis section.
2.5 1.0 0.6 0.8 1.5 0.5
Volatile matter 34.9 40.2 40.6 38.0 28.8 22.4 15.5
COALFixed C 51.7 52.4 53.1 55.9 62.5 67.6 79.6
Ash
Ash
13.4 7.4 6.3 6.1 8.7 10.0 4.9
17.5 9.9 9.5 8.7 11.3 10.6 5.8
TABLE11. COKESIZEAND AMOUNTOF MOISTUREABSORBED Through 2 on 4 Through 4 on 8 Through 8 on 14 Through 14 on 20 Through 20 on 40 Through 40 on 100 Through 100 4.9 4.8 4.8 4.7 4.6 4.5 4.7
Screen size Moisture absorbed, %
After the foregoing preliminary tests were made, all coke samples were tested as follows:
change in going to this next higher temperature of carbonization. I n every case the 700" cokes are more hygroscopic than those made at 500". The 800" cokes, except From a 1-pound (0.45-kg.) Sam le, representative of the coke from a single test (about 65 pounfs or 29.5 kg.), a 4- to 10-mesh that made from Illinois coal, absorb less moisture than those sample was prepared, and approximately 6 grams were taken for made at lower temperatures. Increasing the carbonizing testing. The samples were weighed on watch glasses and dried temperature beyond this point reduces the hygroscopicity at 120" C. for 1 hour, cooled in a desiccator, and weighed again. of the coke to a low value and minimizes the effect of the rank These latter weighings were made uickly to the closest milligram to avoid absorption of moisture. St was not difficult to estimate of coal carbonized. The 900" cokes absorb only 0.4 to 1.1 these weights closely, as well as those of the saturated cokes, per cent moisture, and the 1000" cokes 0.1 to 0.3 per cent. from the wei ht of the original sample and to have approximately The cokes made at 1100" from six coals absorb only 0.1 per the correct talance weights on the pan before exposin the cent moisture. samples. The dry cokes were then placed in the humidors for 24 The hygroscopicity of cokes from a given coal depends upon t o 30 hours. The increase in weight (moisture absorbed durin the carbonizing temperature and is greatest for those made this period) was calculated as percentage of dry coke. AI! determinations were made in duplicate, and the average value was at 600" or 700" C. The hygroscopicity of low-temperature reported. cokes made from coals of different rank varies considerably The results of these tests are given in Figure 2. Cokes with the rank of coal and is greatest for low-rank coals. The curve for the cokes from Illinois coal differs noticeably made at 500" C. absorb from 2.2 to 5.3 per cent moisture. The 600" cokes are more hygroscopic, absorbing 3.4 to 5.6 from the others. Cokes made from this coal a t temperatures per cent moisture. For both carbonizing temperatures it is above 600" C. absorb much more moisture than those made important to note (a) that the hygroscopicity of the cokes from the other coals at the same temperatures. Selvig and increases as the fixed carbon of the original coals (Table 111) Kaplan (6) obtained a similar result in their study of a decreases, and (b) the difference in the hygroscopicity of the commercial coke made from this coal. 500" and 600' C. cokes increases with increase in rank of CONCLUSIONS coal. I n Table I11 two values are given for each of the 600" cokes. 1. The hygroscopicity of cokes made from the same coal Those in the first column were determined independently of depends upon the carbonizing temperature and usually is one another, but simultaneously with the 500" C. andxigher- greatest for cokes made at 600" and 700" C. temperature cokes from the same coal. They are the values 2. The hygroscopicity of low-temperature cokes from shown by the curves of Figure 2. The values in the second different coals depends upon the rank of the coal and is higher column were obtained simultaneously, hence a t one tempera- for those from coals of lower rank. ture. A new sample of coke was used for each of these re3. The hygroscopicity of high-temperature cokes from determinations. These latter determinations, therefore, different coals is practically independent of the coal rank and are strictly comparable with one another and free from criti- is of a very low order. cism as to temperature variation. The temperature within ACKNOWLEDGMENT the humidor at equilibrium was 21" C. The satisfactory agreement of the two values for each of the 600" cokes proves The writer wishes to acknowledge the assistance received that the test conditions, especially temperature, did not during this investigation from J. D. Davis of the U. S. Bureau vary enough to detract from the value of the results obtained. of Mines. TABLE111. FIXED-CARBON CONTENT OF COALSAND MOISTUREABSORBEDBY THEIRCOKES COALB E D Illinois No. 6 Green River Lower Sunnyside Pittsburgh Mary Lee Davis Pocahontas No. 4
LITERATURE CITED (1) Fieldner, Davis, e t al., Bur. Mines, Bull. 344,33-5 (1931). (2) Koppers, J. Znst. Fuel, 7 , 13 (1933). (3) Moore, J. SOC.Chem. Znd., 44,200T (1925). (4) Obermiller, 2. physik. Chem., 109, 145 (1924). ( 5 ) P o r t e r , IND. ENQ.CHEM., 26,150 (1934). (6) Selvig and Kaplan, Zbid., 12,783 (1920).
(In per cent) FIXEDC MOISTURE ABSORBED 500' C. coke 600' C. coke COAL
IN
51.7 52.4 53.1 55.9 62.5 67.6 79.6
5.3 4.8 3.8 3.6 3.0 2.3 2.2
5.6 5.4 5.1 4.6 4.2 3.7 3.4
5.5 5.2 5.2 4.6 4.1 3.4 3.2
The hygroscopicity of the 700" C. cokes is of the same magnitude as that of the 600" cokes, there being no uniform
-
..
RECEIVEDApril 21, 1934. Presented before the joint meeting of the Divisions of Gas and Fuel Chemistry and of Industrial and Engineering Chemistry a t the 87th Meeting of the American Chemical Society, St. Petersburg. Fla., March 25 to 30, 1934. Published by permission of the Director, U. S Bureau of Mines. (Not subject to copyright.)
