HE Bureau of Mines is conducting an in-
T
Oxidation
which carbon monoxide is liberated may have a direct or indirect relation to the tendency of carbonaceous materials to heat spontaneously. This conclusion is partly borne out by the results given here. The materials used in this preliminary study consisted of a set of sixteen coal and rock samples, representing:a vertical section of the Top Split of the Mammoth Vein near a fire zone area in a mine near Locust Gap, Pa.; the samples were taken on January 10,1936. Included for comparison are two subbituminous coals, one from the State of Washington, suspected of heating spontaneously, a n d o n e f r o m Colorado, definitely known to heat s p o n t a n e o u s 1y . Details of the anthracite samples are given in Table I.
vestigation d e a 1i n g ’with the causes, behavior, and control of anthracite mine fires. The question of spontaneous heating of a n t h r a c i t e has received s o m e consideration as a p o s s i b l e c a u s e . It is generally agreed that a high-grade screened anthracite does not heat spontaneously, e v e n d u r i n g long periods of storage. The c a r b o n a c e o u s materials (roof rock, coal, bone, slate, a n d timber) o c c u r r i n g underground in anthracite mines, however, vary in chemical composition; they also vary widely at times with respect to the accomp a n y i n g mineral matter, both as to amount and composition and as to the degree of dispersion of this matter throughout the carApparatus and bonaceous substance. Procedure 0. S. SCOTT AND G. W. JONES Keene, Turner, and Scott U. 6. Bureau of Mines Experiment Station, The apparatus used for (2) showed that the “initial Pittsburgh, Pa. the determination of ignireaction temperature” of tion temperatures was patanthracites towards carbon terned after that described d i o x i d e varies inversely by Holmes and Davis ( 1 ) with the volatile content of A method and apparatus are described with the exception that a the carbonaceous m a t t e r m e c h a n i c a1 arrangement and i n v e r s e l y with the for obtaining the relative rates of liberawas used to decrease conamount of accompanying tion of carbon monoxide from carbonatinuously the outside resistmineral matter. A good ceous substances during heating and for ance in such a manner as c o r r e l a t i o n is shown bedetermining the ignition temperatures to produce a uniform heattween volatile content and ing rate, giving a rate of at the same time. The tests were deinitial r e a c t i o n temperatemperature rise of approxiture, b u t n o t b e t w e e n signed primarily to identify quickly the 6 ” C. per minute. mately initial reaction temperature most readily ignitible coals or other mateFigure 1 i l l u s t r a t e s the and ash c o n t e n t . The rials found in an anthracite mine, and apparatus. chemical composition of the form a part of the Bureau of Mines’ inash appears to have a conTemperatures were measvestigation into the causes, behavior, siderable influence; those ured by means of a 22-gage, bare iron-constantan thermoashes high in oxides or carand control of anthracite mine fires. cou le and recorded on the bonates of the more basic Special emphasis is placed on the rate at o d 8 p o i n t s of an 8-point metals exert the greatest Leeds & Northrup Micromax which carbon monoxide was liberated catalytic effect in lowering recorder. The electromotive when the carbonaceous materials were force developed by the comthe initial reaction temperabustion of the carbon monheated at a constant rate in the presence ture, oxide in the Hopcalite cell To identify quickly for of air. The initial temperature and rate of a carbon monoxide indicaf u r t h e r study the most tor (Mine Safety Appliances at which carbon monoxide is liberated C o m p a n y ) was recorded readily ignitible coals or may have a direct or indirect relation to directly on the even points other materials found in an of the same recorder. the tendency of carbonaceous materials anthracite mine, the appaThe mechanical arrangeto heat spontaneously. ratus shown in Figure 1 was ment for producing a straightline h e a t i n g curve was as buiIt. It was designed for follows: A slidinn contact a study of the ignition temrheostat, with 46 cm. of adjustment travel, was fasteGed to an peratuie and t& liberation of carbon monoxide during heatassembly frame and actuated by a 0.25-h. p. motor and two ing in a current of air a t temperatures UP to the ignition speed-reducing gears in series with a total speed reduction of 20,000 to 1. The bra9s cone on the end of the slow shaft of the temperature of the coal or other substance. second reducing gear wound up a heavy linen cord which pulled Special emphasis is placed on the rate a t which carbon the sliding contact of the rheostat and thereby cut out resistmonoxide was liberated when the parbonaceous ance at a decreasing rate. were heated a t a constant rate in the presence of air. The The large stopper, containing the three bell-shaped funnels, was placed in the top of the combustion tube. The thermocouple writers believe that the ignition temperature and .rate a t 106
of Anthracite
Liberation of Carbon Monoxide and Its Relation to Ignition Temperature
~
JANUARY, 1937
INDUSTRIAL AND ENGINEERING CHEMISTRY
TABLE I. DESCRIPTION OF SAMPLES FROM TOPSPLITOF MAMMOTH VEIN Sample No.
Lab. No.
Material
1 2 3 4 5 0 7 8 9 10 11 12 13 14 15 16
B-14325 B-14326 B-14327 B-14328 B-14329 B-14330 B-14331 B-14332 B-14333 B-14334 B-14335 B-14336 B-14337 B-14338 B-14339 B-12473
Top slate Coal (2.5-inoh slate bands) Slate Coal Slate Coal Slate (bone) Coal Coal (dirty) Coal Slate Coal Slate Coal Slate Coal
&;ir A”,6”
cThiokness-
HzO 2.0 1.2
0.4 4.6
56.5 88.3
4 9 1 3
1
3 1.5 67 3 24 1 0
6 7 7 54
2.0 3.1 0.3 1.6
86.7 17.2 72.5 17.7
0.4 1.1 0.5 0.6 0.9 1.1 1.0 4.3 0.3 0.6
55.0 14.4 35.4 8.7 63.0 14.1 76.1 14 3 55.6 6.0
::: :
H 2.3 2.8
leads passed through the outside funnels SO that the position of the hot junction could be placed exactly on the rate. Rubber stoppers were then inserted and ressed into t f e tops of the funnels until practically air-tight. geventy-five cubic centimeters of sample (14to 28 mesh) were then poured through the larger center funnel, and the opening was closed with a rubber stopper. The temperature recorder motor was then started, the pump motor of the carbon monoxide indicator unit started, and the pump valve adjusted until the flowmeter indicated a rate of air flow equal to 3.3 liters per minute (7 cubic feet per hour). The carbon monoxide indicator contained an ammeter for showing the percentage of carbon monoxide directly. The needle was
Heating Value Cal. 4972 7767
34 5 5.9
Ultimate, %
7
Sample 9 Sample 16 a As reoeived basis.
5%
In.
Analyses= of Samples 9 and 16 Proximate, 7 Volatile Fixe3 matter C Ash
r
Sample 9 Sample 16
Cm. 10 23 2.5 7.5 2.5 7.5 4 170 7.5 61 2.5 15 12.6 18 18 137
107
C
N
55.8 86.5
1.0 1 0
0 5.9 3.2
-0.1
S
0 5 0 6
I
TABLE 11. IGNITION TEMPERATURES AND CARBON MONOXIDE INFLECTION POINTSOF SAMPLES” FROM TOPSPLIT,MAMMOTH VEIN Ignition Ternp.,b Sample No.
A
..
1
,
2 3
450 498 432
4
5
6
7 8
9
10 11 12 13 14 15 10
O C. DifferE ence .Did not ignite..
4ii
438 . . . .Did not ignite..
435 456 468 346 471 450 450
.. ... 7
4471 47 471 348 483 453 456 .Did not ignite.. 429 420 432 438 408 471
...
.6,
12 15 3 3 12 3 0
.. 9
6
3
GO Inflection Point,b A 453 375 447 387 323 375 384 375 333 374 369 357 393 361 345 381
B 480
dii
384 341 381 396 369 330 369 378 366 366 364 348 363
C. Differenoe 27
..
-0
21 3 18 6 12 6 3 6 9 9 27 3 3 18
Time, minutes
FIGURE 2. RECORDER CHART FOR SAMPLE 15 (14 T0428-MESH)
actuated by the current from a series of thermocouples, whose hot junctions were embedded in the active compartment and whose cold junctions were embedded in the inactive compartment of the Hopcalite cell. The terminals of the thermocouple series were connected directly to the even points of the recorder and the ercentage of carbon monoxide was obtained directly from the &art without the necessity of taking readings on the indicator. When the carbon monoxide line became constant, heater switch a was turned on; and motor b driving the reducing gears, c and d, and cone e controlling the outside resistance, f, was started. When the upper limit of the carbon monoxide indicator was reached (i. e., 0.1 per cent carbon monoxide), this instrument was disconnected from the circuit as follows: The pump motor was stopped, and air line g was turned on and adjusted, if necessary, to the rate of 3.3 liters per minute. A test was concluded when the temperature reached 600’ C .
14 to 28 mesh Tyler. b A and B are duplicate determinations.
c
Air
B
regulator
FIGURE 1. APPARATUS FOR STUDY OF CARBON MONOXIDE LIBERATION
Results of Tests Figure 2 illustrates a typical test, redrawn from the recorder chart so as to make time the abscissa and temperature the ordinate. The carbon monoxide percentages are shown on the same chart. The ignition temperature is considered to be that point at which the time-temperature curve begins to depart from the straight-line heating curve, and is so indicated on Figure 2. The carbon monoxide inflection is that point at which the carbon monoxide content of the gases from the fuel b e d c h a n g e s f r o m a slowly increasing to a rapidly i n c r e a s i n g
INDUSTRIAL AND ENGINEERING CHEMISTRY
108
VOL. 29, NO. 1
Table IV shows the effect of coal size and of moist and dry air on the ignition temperature and carbon monoxide inflection point. TABLEIV. EFFECTOF SCREENSIZBOF COALAND OF DRIED AIR ON IGNITION TEMPERATURE AND CARBON MONOXIDE INFLECTION POINT OF SAMPLE 16 -Atmospheric Air--Dried
Air-
co
Size 4 to 8 meah: A
B 8 to 14 mesh: A B 14 to 28 mesh: A B
Ignition inflecton Ignition temp., ' C. point, C . temp., O C.
co
inflection point, C.
495 501
432 414
... ...
... ...
462 486
387 393
495 480
402 402
468 471
381 363
...
... ...
...
Figure 4 shows the content of carbon monoxide in the gases given off during heating in air by two anthracites, and by the three subbituminous coals previously mentioned. FIGURE 3.
TEMPERATURE AND CARBON MONOXIDEINFLECTION
IGNITION
O .07
s
a4
percentage, or the point a t which the tangent to the timecarbon monoxide per cent curve is 45". A summary of these ignition temperatures and carbon monoxide inflection points is given in Table I1 for the sixteen samples describgd in Table I. With one exception, the ignition temperatures fall between 420" and 498" C. Carbon monoxide inflection points were obtained from samples from which an ignition temperature could not be obtained in the apparatus shown in Figure 1. Ignition temperatures under the conditions of the test were not obtained for samples containing more than about 73 per cent ash. Carbon monoxide inflection points were obtained, however, for samples containing 86.7 per cent ash (the highest ash in the group). Of the sixteen samples, No. 9 shows the lowest ignition temperature and the lowest carbon monoxide inflection point, and therefore may be the most susceptible of this group to heating spontaneously. Figure 3 gives the data of Tables I and I1 in graphic form. TABLE111. IGNITION TEMPERATURES AND CARBON MONOXIDE INFLECTION POINTS OF SELECTED SAMPLES'
Sample Av for anthracite samples M i s t readily ignitible anthracite Washineton coals 6UaDeCted of heating spGntaneously: A
Ignition Temp., O C.
co
Inflection Point,
451 346
O C. 376 331
291 234 186
228 204 141
~
B
Colo. coal known to heat spontaneously 14 to 28 mesh, Tyler.
1
I I
.05
a
Table I11 shows a comparison between the data on the anthracite samples, two subbituminous coals suspected of heating spontaneously, and a subbituminous coal known to heat spontaneously.
,03
Colondo svbblNmlnovs I/
=
I I
I
,I
I
/
l
I I
..dl
I
I 1 I
I
I/
I
,
*A ',"
dI
I/ , ,
I
.01
.cQl
I FIQURE
AT OF CARBON MONOXIDE 4. CONCENTRATION
IN
GASESFROM DIFFERENT COALS
Acknowledgment The writers acknowledge the cooperation of J. D. Davis and C. R. Holmes who kindly loaned them their ignition temperature equipment until such time as the one described could be built. The samples of materials used in this work were analyzed by the Coal Analysis Laboratory under the direction of H. M. Cooper, and the carbon monoxide indicator was calibrated by L. B. Berger of the Gas Section.
Bibliography (1) Holmes, C.R., and Davis, J. D., IND.ENG.CHEM., 28,484(1936).
(2) Keene, W. L., Turner, H. G., and Scott, G. S., Tranu. Am. Inst. Mining Met. Engrs., 108,303-23(1934). (3) Lists of references on the ignition temperaturea and apontaneous heating of coal are given in the following: Brown, C . R . , Fuel, 14, 14-18. 56-9,80-5,112-16, 149-52, 173-9
(1936). Davis,J . D., and Reynolds, D. A., Bur. Minen, Tech. Paper 409 (1928). RECEIVED August 20, 1936. Presented before the Diviaion of (3- snd Fuel Chemistry at the 92nd Meeting of the American Chemical Soaicty. Pittsburgh, Pa., September 7 to 11, 1936. Published by permiasion of the Director, U. S. Bureau of Mines. (Not subject t o copyright.)
