INDUSTRIAL AND ENGINEERING CHEMISTRY
February, 1930
137
A Study of Certain American Coals at Temperatures near Their Softening Points';' Alpheus Prl. Ball and Harry A. Curtis DEPARTMEXT OF CHGMXC 4~ ENGIKEERING, YALEUNIVERSITY, YEWHAVEN,CONX.
HEN the ti,imp erature of a mass of
A study has been made of various American bituminous coals to determine their behavior in the neighborhood of their softening temperatures. The softening temperatures were determined by the gas-flow method and also under reduced pressure and upon single pieces of coal. I t is shown that the coals differ widely in their softening points, in their sensitivity to oxidation and to preheating, in degree of fluidity reached above their initial softening points, and in degree of plasticity below their softening points.
b i t u m i n o u s coal particles is raised a t a rate of a few degrees per minute, the coal presently undergoes a sort of fusion, varying for different coals all the way from only a slight sintering t o g e t h e r of t h e individual particles to R fusion so complete that all trace of the individual particles of coal iq lost. The temperature a t which a coal softens, as a result of this more or less complete fusion, is not very sharply defined, but is nevertheless fairly characteristic of the given coal. Generally speaking, a bituminous coal begins to evolve easily condensable vapors a t a temperature considerably below its softening point, but a3 the softening point is passed therezis a large increase in the rate of evolution of volatile products.
passed through it. The thermocouple intended to measure the coal temperature in the Layng apparatus was located outside the tube containing the coal, between this tube and the hot wall of the furnace, where it certainly didn't read the temperature existing in the coal mass. Lay-ng evidently attached great importance to the slopes of the temperature-pressure curves obtained. Without doubt the slopes of such curves are significant. but in the Layng apparatus one of the factors determining the slope of the temperature-pressure curve was the amount of water Jvhich happened to be in the gas container a t the time; for obviously the addition of unit volume of water when the gas container was nearly full of water caused a much larger pressure increase than %-henthe container had but little water in it. Finally, in this apparatus the temperature of the nitrogen flowing through the coal mass was not known. I n the present investigation the softening temperatures of a number of American coals were first determined by the gasflow method used by Foxwell and later by Layng, with such modifications as were deemed desirable. The thermocouple measuring the coal temperature was placed in the coal. The nitrogen was drawn from a commercial cylinder of the compressed gas and passed a t a controlled and constant rate through several wash bottles containing alkaline pyrogallol
Figure 1-Coal S o f t e n i n g P o i n t Apparatus (Vertical Section)
Likewise, the plasticity of a coal increases slowly as the softening point i s approached, with a fairly sudden increase at the softening point,. The present paper records observations of the differences exhibited by certain American coals. Gas-Flow Method for Determining Softening Point of a Coal
Foxwell studied what he called "the plastic state of coal" by heating a plug of coal in a horizontal tube by means of an electric furnace and measuring the resistance which the coal offered to a stream of inert gas flowing through it. From the sketch of the apparatus used by Foxwell (3) it is difficult to believe that the temperature a t the thermocouple junction was that existing in the coal. Layng and his students ( 2 , 4 , 5 )used a similar method, the coal being heated in a vertical tube and a current of inert gas Received December 9, 1929. The experimental data of this paper were taken from a dissertation presented to the faculty of Yale University by Alpheus M . Ball in candidacy for the Ph.D. degree. 2
Figure 2-Change
of S o f t e n i n g P a i n t by Air Oxidation at 1O5-11O0C.
solution, then dried, and finally passed through the apparatus shown in Figure 1, the initial rate of gas flow in every case being such as to give a pressure of 1 to 2 cm. of water on the manometer. I n using this apparatus the thermocouple was put in place and the crushed coal packed around it so as to give a column of coal 6/8 inch (1.6 cm.) in diameter and 2 inches (5.1 cm.)
ISDCSTRIAL A S D ENGINEERIXG CHEMISTRY
138
Table I-Composition
S T0
16 1 2 18 12 15 23 7 9 10 21 22 11 5
TRADENAME Island Creek Brilliant Black Band Benham Pond Creek Hazard Big Moshannon Davis White Oak Beckley Stineman Manor Rockhill Georges Creek h'on-fusing coal.
a n d Softening Points of Coals Studied
SEAM Island Creek Black Creek Winifrede Keokee Pond Creek Hazard No. 6 Moshannon Pool 71 Sewell Beckley Moshannon or Lower Freeport Kittanning Fulton Big Vein (Pittsburgh)
VOLATILE COMBCSTIBL~ FIXED MATTER CARBON
LOCALITY Logan Co , W. \'a. Marion Co , .41a. Kanawha Co , W. Va. Harlan Co., Ky. Mingo Co., W. Va. Perry Co., K y Clearfield Co., Pa. Tucker Co., W. Va. W. Va. Raleigh Co., W Va. Cambria Co., Pa. Garrett Co., Md. Broadtop field in Eastern Pa Allegany Co , Md.
long. The nitrogen stream was started and the temperature of the bath then brought up as rapidly as possible t o within about 50" C. of the softening point of the coal. The rate of heating was reduced to 2" C. per minute and continued so until the coal softened. The temperature of the thermocouple and the pressure on the manometer were read a t short intervals and the temperature-pressure curve was plotted. It should be remarked that the apparatus used by Foxwell, by Layng, and in the present investigation does not truly measure the temperature at which some of the components of coal fuse, but actually indicates the temperature a t which closing of the interstices between coal particles becomes appreciably rapid.
Figure 3-Change
Val. 22, No. 2
70
70
39.4 38.3 38.1 37.2 35.9 35.8 23.8 23.1 21.3 17.3 17.1 16.3 15.9 15.0
55.3 59.0 57.8 60.4 62.2 59.0 67.7 70.0 68.6 81.0 76.1 75.1 77.6 74 0
ASH
70 5 2 4 2 1 5 8 6 10 1 6 8 6 11
3 7 1 4 9 2 5 9 1 8 7 6 5 0
VOLATILE COMBUSTIBLE SOFMATTER ASH-FREE TENING BASIS TEMP.
70 41.6 39.4 39.8 38.1 36.6 37.8 26.0 24.8 23.7 17.6 18.4 17.9 17.0 16.8
c. 39: 340 390 38: 410 395 395 430 425 435 440 440
the coals listed in Table I were examined with regard to their sensitivity toward air oxidation a t 105-110" C. Fresh portions of the samples prepared for determining softening point. were used. Each sample was heated a t 105-110" C. in air for a predetermined period, the coal being spread out in a thin layer during heating. The softening points were then determined, with the results shown graphically in Figure 2. There are irregularities in behavior of the coals, the significance of which is not yet known fully, but the graphs show the general nature of the oxidation effect and the great differences of coals in sensitivity toward air-oxidation. As a check on the effect of oxidation by air, three runs were made with No. 2 (Black Band) coal, using various amounts of sodium nitrate as the oxidizing agent. The samples were moistenedwith such amounts of a 2 per cent sodiumnitratesolution as would represent 5, 10, and 20 pounds of the salt per ton of coal, and were then air-dried at room temperature and the softening points determined. The results are shown graphically in Figure 3.
of Softening Point by Sodium Nitrate Oxidation
Coals Used and Softening Temperatures Observed
The coals used in the present investigation are indicated in Table I. Each sample was crushed t o pass 10 mesh and the material finer than 80 mesh discarded. With fine material present it is more difficult to get checking data, but it is realized that in discarding the small fraction of finest material the softening temperatures observed are not as certainly characteristic of the coals as they might otherwise be. A better procedure would have been t o briquet the fine coal and recrush it. The writers were a t the time less concerned with the true softening points than with changes in softening points caused by pre-oxidizing, preheating, etc. I n any event the softening points determined in such an apparatus as here used vary so much with the manner of operating the apparatus that the softening temperatures recorded niust be regarded as approximate. Sensitivity to Oxidation
It has long been known that oxidizing a coal destroys its coking quality (6). Layng and Coffman (4),Audibert ( I ) , Porter and Ralston ( 7 ) , and others have shown that coals differ greatly in their sensitivity toward oxidation. Four of
Figure 4-Change
of Softening Point by Preheating
Sensitivity to Preheating at Temperatures near Their Softening Points
It is known that long heating of a coal at someyhat elevated temperature reduces its tendency to swell during the temperature range in which it is in a plastic condition. The effect of thus preheating a coal is apparently to reduce the degree of fluidity reached when the temperature is raised above the softening point. If this effect results from some sort of an internal rearrangement of the coal substance, it would be reasonable to expect that such change would be the more rapid the higher the temperature a t which the preheating
February, 1930
ISDUSTRIALi AXD ENGIh'EERISG CHE-VISTRY
was carried out, In order to test this idea, a sample of coal KO.2 (Black Band) was heated to 372' C. in the apparatus of Figure 1 a t the same rate used in determining softening point. At this temperature the inner tube, containing the coal, was removed from the lead bath and the coal cooled in the nitrogen stream, the cooling requiring approximately 30 minutes. 2 coal was similarly treated except that Another sample of KO. the heatingwas carried to 380" C. before cooling. The softening points of the two samples mere then determinild with the results shown in the lower part of Figure 4.
Figure 5-Apparatus
for Visually Observing Coal S o f t e n i n g
The same procedure applied to No. 16 (Island Creek) coal showed that this coal is less sensitive to heat treatment, the swelling property being but little changed by heating to 390 'C., the softening point of the coal. Accordingly the procedure mas modified in that when the upper temperature of preheating had been reached the coal was held for an hour a t this temperature before cooling. In this manner the results shown in the upper part of Figure 4 were obtained. It was observed in these operations that even a t 376' C., considerably below the softening temperature previously determined for this coal, the prolonged heating had caused a small but quite visible sintering together of the coal particles. Softening Temperatures under Reduced Pressure
The apparatus shonn in Figure 1 was rearranged so as t o permit determination of softening temperatures when the pressure of the nitrogm flowing through the appxatus was reduced to about 2 min. mercury gage. It was found that, within the limits of error of measurement, the coals softened a t the same temperature under reduced pressure and under atmospheric pressure.
139
apparatus shown in Figure 5 was constructed. The coal particle, mounted a t the center of the inner tube, was bathed in a slow stream of nitrogen of known temperature, and the particle observed in silhouette by placing a light a t one of the glass-covered ends of the inner tube and a telescope a t the other end. I n this apparatus changes in the sharp edges and corners of a particle, due to distortion, could be observed readily, and the temperature a t which this occurred in a given coal could be checked fairly well. As in the case of the microfusion apparatuq, no real fusion of lone coal particles could be observed a t such rates of heating as could be obtained. When a particle of a very fusible coal, such as No. 16 (Island Creek), was heated, the particle became somewhat rounded and swollen, with many wide cracks over the surface. In all cases it was necessary to use a relatively slow rate of heating, not more than about 1" C. per minute, if checking results were to be obtained. If rapid heating was used, higher temperatures of distortion were observed, indicating too great lag of coal temperature behind that of the heating gas. Table I1 shows the temperatures a t which coal particles were seen to distort in this apparatus as compared with the softening temperatures determined by the gas-flow method. Table 11-Comparison of Softening Temperatures by Gas-Flow Method a n d of Individual Particles SOFTENIKG POINT DISTORTIOS TEMP.OBSD. COALS o . B Y GAS-FLOW METHODFOR SINGLEPARTICLES 1 3
5
7 10 11 21 22 23
c.
c.
400 380 440 395 430 440 430 435 410
385 380 430 395 425 440 425 430 395
I n the apparatus of Figure 5 small briquets of coal (without binder) distorted a t temperatures 15 to 20 degrees higher than observed for single particleq of the same coal.
Softening Temperature of Single Pieces of Coal
h microfusion apparatus which could be mounted on the stage of a microscope was constructed, and an effort made to observe the softening of single pieces of coal. This apparatus consisted of a block of copper containing an electrical heating element. A small cylindrical well was drilled in the top of the block in which the coal particle could be placed, and provision mas made for a thermocouple in the block just undc,r the well. With this apparatus a temperature of 500" C. could easily be reached in tlie well. The accuracy of the apparatus was checked against salts of known melting points. 13y placing a glass cover over the well and passing a gas stream slowly through it, or by enclo3ing the coal particle in a g1:tss ampule with a capillary outlet and filling tlie well with a fusible salt, the coal particle could be kept in a non-oxidizing atmosphere. I n this apparatus it waj found impossible t o fuse a lone particle of coal. At various temperatures within 30 or 40 degrees of their known softening points, the coal particles would crack on the surfaces and swell a little, but nothing approaching fusion wai: observed, and the temperature a t which cracking occurred could not be checked for a given coal. It was thought that if a coal particle were heated evenly over the whole surface the temperature a t which the surface cracked and the particle distorted due to internal swelling might be found to be the same as the softening temperature as determined by the gas-flow method. Accordingly the
Figure 6-Coal
Plasticity Apparatus
Plasticity of Coal below Softening Temperature
The slight sintering of coal X o . 16 when heated for an hour a t a temperature 15 degrees below its apparent softening point as determined by the gas-flow method led to the surmise that a coal might exhibit plasticity a t temperatures below that a t which it becomes sufficiently fluid to give an indication in the gas-flow apparatus. To study this possibility, the apparatus shown in Figure 6 was built.
INDUSTRIAL AND ENGINEERING CHEMISTRY
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The heating chamber of this apparatus was essentially the same as that in Figure 1 4 . e., a vertical inner tube to receive the sample, this tube immersed in a lead bath, and the bath heated in an electric furnace. As in determining the softening point, nitrogen was passed down through the steel coil and up through the inner tube containing the coal sample. At the bottom of the inner tube was placed a short solid cylinder of steel, somewhat smaller in diameter than the inner tube, with a flat-bottom well a t its upper end. The coal to be tested was made into a briquet and placed in the well. On the briquet rested a steel rod which passed up through guides and carried a platform for weights a t its upper end. I n order not to place too much weight on the electric furnace, the inner tube was supported independently of the furnace as indicated in Figure 6. Table 111-Plasticity
of Coal at Temperatures below t h e S o f t e n i n g Point
COAL
TIME ROD NO. TEMP.ELAPSED SETTLED a C. Min. Mm.
10
412
60
18
10 10 2
405 395 385
110 251 25
3 4 23
2
348
95
0
REMARKS
N o further settling after 1 hour, briquet deformed Briquet barrel-shaped at end of run
Briquet had flowed up around rod, the coal quite plastic Briquet distorted
I n making a run the lead bath was brought up to the desired temperature and the nitrogen stream started through the apparatus. The briquet was then lowered into place, the rod brought down upon it, and weights amounting to 25 pounds (11.35 kg.) placed on the platform. The rod and platform weighed 1 pound (0.45 kg.), so that the load on the briquet was 26 pounds (11.80 kg.) or nearly 340 pounds per square inch (24 kg. per sq. cm.). As soon as steady conditions were established a t the predetermined constant temperature, the position of a mark on the vertical rod was observed
Vol. 22, KO.2
with a cathetometer. Plasticity in the briquet w&s indicated by a slow settling of the vertical rod and the briquet was examined for deformation a t the end of the run. The results obtained with this apparatus are summarized in Table 111. It will be noted that both these coals exhibited plasticity at temperatures as much as 35 degrees below their softening points as determined by the gas-flow method, and that S o . 2 coal is more plastic near its softening point than is No. 10 coal. There is probably a relationship between the degree of plasticity exhibited below the softening point and the degree of fluidity reached after the coal passes the softening point; and the difference in plasticity exhibited a t temperatures below the softening points may be one of the factors which cause wide variation in the ease with which different coals can be briquetted. Plasticity of the sort exhibited by bituminous coals is characteristic of amorphous substances such as glass. Some investigators claim that coal and coke give x-ray diffraction patterns. This argument has been considerably weakened by a recent observation that the ash of a particular anthracite coal gave the same pattern as the coal itself. During the course of the present investigation x-ray photographs were made of No. 10 coal and of its semi-coke, using powdered samples. No diffraction patterns were discernible in either case. Coal No. 10 is so low in ash that interference from this source disappears. Literature Cited (1) Audibert, Fuels Science Praclice, 6, 229 (1926). (2) Coffman and Layng, IND.ENG CHEM.,20, 165 (192s). (1924). (3) Foxwell, Fuels Science Practice, 3, 122,174,206,227,276,316,371 (4) Layng and Coffman, IND.ENG.CHEM.,19,924 (1927). ( 5 ) Layng and Hathorne, I b i d . , 17, 165 (1925). (6) Parr and Olin, University of Illinois Eng. Expt. Sta., Bull. 60 (1912). (7) Porter and Ralston, Bur. Mines, Tech. Paper 66 (1914).
Carbon Dioxide Preservation of Meat and Fish' D. H. Killeffer DRYICE CORPORATION
OF
AMERICA, 52 VANDERBILT AVE., NEW YORK,N. Y.
Carbon dioxide atmospheres have long been known preserved meat and fish better to exercise a preservative action on certain food prodt h a n o t h e r perishable prodpreliminary character ucts. This paper describes the results of a preliminary ucts. M a n y s t a t e m e n t s , and do not by any study of the effect of carbon dioxide on meat and fish b a s e d f r e q u e n t l y on very means exhaust the subject. and on certain common bacteria. It is shown that s c a n t evidence, have been C o n s i d e r a b l e temerity in meat and fish can be kept fresh longer when refrigerated made regarding the efficiency d r a w i n g conclusions from in a carbon dioxide atmosphere than in air, that carof c a r b o n dioxide atmossuch scanty observations is bon dioxide is absorbed by meat and fish as indicated pheres in preventing spoilage freely admitted, particularly by pH changes, and that the growth of common bacof foods. Long ago patents since the bacterial studies do teria studied is greatly impeded, if not actually stopped, were issued on preservation of not include many of the types by the presence of dissolved carbon dioxide in the foodstuffs by carbon dioxide of bacteria common to meat culture medium. Further work on the subject is atmospheres. Many of them a n d f i s h . Xevertheless, in desirable on account of the increasing importance have proved disappointing on view of the obvious imporof solid carbon dioxide (Dry-Ice) as a commercial recareful i n v e s t i g a t i o n , but tance to the meat industry of frigerant. nevertheless in the particular t h e f i n d i n g s , it has been case of flesh foods really rethought wise to publish this preliminary discussion a t this time for criticism and suggestion. markable results have been obtained. It is the purpose of I n attempting to explain some of the facts of Dry-Ice refrig- this paper to describe some investigations of this preservaeration, it early became obvious that mere refrigerating effect tive effect of carbon dioxide atmospheres and to point out alone could not cover the entire situation as it was observed, a hitherto neglected field for further research and applicaespecially with respect to meat and fish. Strangely enough, tion to the meat industries. identical refrigerating systems using Dry-Ice as the refrigerant Effect of Carbon Dioxide Gas on Meat
T
HESE studies are of a
1 Received December 5, 1929. Presented before the Scientific Section of the Convention of the Institute of American Meat Packers, Chicago, Ill., October 18, 1929.
I
Questions arose early in the commercial application of solid carbon dioxide refrigeration, as to whether the gas itself had
