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Vol. 17, No. 2
INDUSTRIAL A N D ENGI MEERING CHEMISTRY
I n this connection the ostimate of Parr and Kressmad as t o the m o u n t of heat evoked in the oxidation of pyriticsulfuris of interest, in view of the bearing small increments of heat may have as a booster for further oxidation activities, both of the hydrocarbons and of the sulfur constituents. According to those calculations, 0.1 per cent of sulfur in the pyritic form upon oxidation will raise the mass through a temperature of 14.5" C.; hence the oxidation of so small an amount as 0.5 @am of sulfur would result in a heat rise of 71.5" C.-a really dangerous boost. The purpose of this paper is merely to point out that sulfur may he the initial source of heat after all, and that we need to suspend judgment in the matter until further evidence is in hand. The workof Yancey3shows the distribution of pyritic sulfur in microscopic form to be quite as common as in the massive fonn. Some work along this line in the writers' laboratory shorvs that mother of coal frequently hss a very high sulfur content. If it is also in the finely divided form, it is in an especially advantageous condition for starting oxidation. But
Carbon Dioxide as an Index of the Critical Oxidation Temperature for Coal in Storage' By S. W. Parr and C. C. Coons UNIYBRSlrY 01 ILLINOII. U R B I N A .
ILL
ROM the accompanying studies it is evident that coal is continuously reactive with oxygen to a greater or less degree, depending upon various factors, hut chiefly upon temperature. The two products most in evidence are, first, water and then carbon dioxide. An a p paratus that would give the initial appearance of these products of oxidation would be of both practical and scientific interest. The difficulties attending the indication for the appearance of water are far greater than those for carbon dioxide; hence it is the latter that will be considered a t this time. Apparatus and Procedure The apparatus devised for this purpose uses a solution of barium hydroxide as the indicating medium, while temperature control is obtained by an electric resistance coil so placed that the rise in temperature can he maintained evenly and a t any desired point. The mechanism for indicating the appearance of carbon dioxide is shown in Figure 1. Figure 2 is a photograph of the apparatus. In this apparatus, which embodies a number of features suggested by the investigations of FrancisZand also of Whceler,a there is a resistance furnace with a rheostat controlling the rise in temperature to about Lena of Pyrite from C u d Showing Sulfate Oxidation. VermUlon 10" C. per minute. Immediately below the furnace is the C w n f y Coal carbon dioxide detection assembly, as shown in Figure 1. The of especial interest is the fact that a study of the forms of other accessories are crystallization in the Illmois coal measures shows marcasite to for washing the gases he almost always present, if indeed it does not predominate used in the tests. Oxyover the usually assigned pyritic form of crystallization. gen thus purilied is led Even so, it is not clear from experiments in this laboratory into the upper part of that marcasitic sulfur is necessarily more susceptible to ox- the furnace and after idation than the pyritic form, when both arc in a fine state of passing through the coal is delivered below division. This point offers a field for investigation. A few illustrations are of interest in showing the presence of into the dioxide detectmarcasitic sulfur in pyritic masses in certain of the Illinois ing tube, through a 1-mm. capillary. This coal deposits. capillary is so placed Univcrsityof Illinois, Ens. Expt.Sta.. Bull. I6 (IOIO). that the gas from the 1 Tars Joumar,IS,501 (1924). coal impinges upon a drop of bafium hydroxNew Canadian Publication ide suspended from a The Canadian Department of Mines has issued a 310-page solid rod having a publication on "The Development of Chemical, Metallurgical, flat, ground tip. The and Allied Industries in Canada in Relation to the Mineral barium hydroxide soluIndustry," which sets a high standard in government publications tion is contained in a and presents in concise form much information of value to the chemical industry. The publication is provided with a number of separatory funnel hav- o r _ useful tables, such BS one upon the principal chemicals used in ing a tube filled with 1 industry, trade statistics of chemicals and allied products, and lime fitted into F i ~ u r el-Carbon Diorfde Detectloo Tubs charts which give in concise form information pertaining to "da the top of it in order electro products and some of their uses, the alkali industry, the to remove the carbon dioxide and moisture from the air as the industrial applicationsof lime, some of the many uses of alcohol, and products derived from coal. The discussion of primary solution is removed from the fnnnel. The barium hydroxide inorganic products contains information worthy to class this solution can he conducted to the lower end of the drip rod by publication as a source of reference reading, while primary or- a rubber and a glass tube, the latter being drawn out to a ganic products are treated in the same thoroughgoing manner. The parts devoted to manufacturing treat explosive mannfac- narrow tip which is placed so that it just touches the drip ture, the fertilizer, ceramic, and glass industries, besides a num- rod. In this way a h e r adjustment of the harinm hydroxber of those classed as miscetlaneaus and minor, so far as Canada ide can be obtained. The acid tube is placed directly.above is concerned. The metallurgical industries are treated in another part, as are food products and general manufacturing. The publication is recommended to those who find interest in such general as well as specific information which finds a proper place in a well-indexed government publication of this character.
F
I I
Rmived AvgUst 8. 1924. Parr and Frsnds, Univvsiiy of Illinois, Eng. Expt. Sta., Bull. %I
(1808). s J . Chcnr. Soc (Landon),11% 945 (1918).
INDUSTRIAL A N D ENGINEERING CHEMISTRY
February, 1925
it, so that when necessary any barium carbonate precipitate adhering to the drip rod can be conveniently removed. The atmosphere in the carbon dioxide detection tube is continually changed by forcing air through it that has been passed through, first, 50 per cent potassium hydroxide and then w a t e r . The potassium hydroxide removes the carbon dioxide and the water s a t u r a t e s t h e air. The latter precaution is taken because it has been found that dry a i r evaporates t h e water from the barium hydroxide drop, causing a precipitate of barium hydroxide. The air is directed upward against the rnbher stopper through two openings a n d thus ureveuts an aeitatioi of the harigm hydroxide drop which would result if the air were forced directly down t h r o u g h t h e tube. During the e a r l y part of the investigation a straight carhon dioxide d e t e c t i o n tube was used, but it WRP. fniind .. _ . . .-..- dhat ...-.the .... Figure z-~ppaaracus for Determink? gases from the coal Ininal Appearance of Carbon Dioxide in could not he kent CMl thGnghly swept out of the tube, owing to eddy currents. By making use of the principle of the Venturi meter, the tube was constricted. This caused the air to attain a greater velocity through the constricted portion and successfully kept the excess carbon dioxide removed from around the harium hydroxide drop. The gas passed through the coal is either oxygen or nitrogen, obtained from cylinders in which the gases are stored under pressure. The oxygen is first passed through a wash bottle containing 50 per cent potassium hydroxide and then through
I19
can he passed through a liter flask containing distilled water kept a t 50' C . which has previously been boiled to remove carbon dioxide. The nitrogen is passed through alkaline pyrogallate to remove oxygen, 50 per cent potassium hydroxide to remove
carbon dioxide, and lastly, through concentrated sulfuric acid to dry it. Any of these various gas-purifying procedures can he carried out by correct connection of the wash bottles. At the end of a run the gas pressure between the coal and high-pressure gas cylinder can he released by means of a 2-way stopcock, situated directly behind the wash bottle containing the alkaline m,rozallate. The stomcock cannot he seen in the photograph. The furnace tube containing the coal is of Pyrex glass, 10 inches long, with an inside diameter of 0.5 inch. Within this small retort a thermometer is suspended extending into the center of the column of coal, which is about 4 inches in
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Figure 5
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Figure 3
concentrated sulfuric acid to remove carbon dioxide and moisture. The oxygen can then be passed directly through the coal or, if it is desired to saturate it with water vapor, it
height. A second thermometer is suspended outside of the retort in the space between the heating element and the Pyrex glass tube. The resistance wire is wound about a 1.75 inch Pyrex tube, and to equalize the transmission of heat from thewirea3-ply coil sheet of aluminium is placed around the inner wall of the furnace tube. It will he seen that by this arrangement, notation can be made of the temperature at which carbon dioxide 6 r t nukes its appearance in the detector tube, and also that p i n t where the heat oxidation within the coal sample attains an impetus whereby it becomes self-propelling or autogenous. This point will, of course, show itself by the temperature reading on the
INDULYTRIAL A N D ENGINEERING CHEMI8TRY
120
inner thermometer. On plotting the readings for the two thermometers it will be indicated at the crossing of the two lines. This point is of such great significance from the standpoint of spontaneous combustion of coal that it is here designated as the critical oxidation temperature for the particular
Vol. 17,No. 2
Deterioration and Spontaneous Combustion of Coal in Storage’ By S. W. Parr U N I V s R S I T Y OF ILLINOIS, URBANA,
ILL.
T
TNne /n Mhufes Figure 6
coals studied. Determinations of this point were made upon a number of freshly prepared samples and also upon parallel samples of the same coals which had been subjected to oxidation or what might be called complete “weathering” or saturation with oxygen at a temperature below the critical point. Discussion of Results
A few typical charts giving the results on freshly prepared samples are first presented as Figures 3,4, and 5. The critical oxidation temperatures for the samples of Illinois coal are within a range of 138’ to 143’ C., and the corresponding temperature for the Pocahontas coal is 202’ C. It seems fair to conclude that, in the case of these coals in storage, assuming free accessibility of oxygen, a temperature within the mass approximating the range indicated by the charts would denote a speedy progression to the stage of ac-
HE first organized attempt along scientific lines to bring about improved conditions in the operation of the coal industry in the United States reached a definite status when the administrative board of the American Engineering Council, in 1923, officially authorized the appointment of a committee on storage of coal. This committee has made a comprehensive study of the various problems pertaining t o the topic,2 such as production, distribution, transportation, handling, and storage, but it is evident that the factor of fundamental importance, and the one that is directly associated with every phase of the problem, is the matter of storage, with the attending questions of deterioration and spontaneous combustion. It is entirely appropriate, therefore, that in this symposium we call attention t o this report, not only because of the related information it contains, but because of the profound importance of the subject, not only to the coal business, but in some form or other t o almost every phase of our industrial, economic, and social life. Let it be emphasized, also, that the problems connected with the storage of coal depend upon chemical phenomena to a far greater extent than any other, and their solution must be worked out by the chemist. It is the purpose of this paper, therefore, to review briefly those chemical activities which are recognized as peculiarly characteristic of coal and to indicate the results of recent studies along this line. Indeed, it is believed that the accompanying papers will convey more conclusive evidence as to the underlying factors connected with the storage of coal than has heretofore been available. Coal and Free Oxygen
The ability of coal to absorb oxygen from the air is well recognized. A summarized statement of the conclusions growing out of avidity of coal for oxygen is as follows: 1-Coal,
by reason of its peculiar composition and structure,
is capable of absorbing very considerable quantities of oxygen.
Figure 7
tual ignition. Although these charts are based on the use of pure oxygen the conditions under contact with the oxygen of the air would show a lag as to time, but substantially in agreement as to effect, provided other things, such as radiation, are the same. Figure 6 repeats the conditions on the Montgomery County coal, but after it had been saturated with oxygen-that is, “weathered”-at an oven temperature of 100” C. A consistent increase in the critical range of oxidation is evident. Figure 7 represents the temperature required to produce autogenous oxidation for the several stages of “weathering” with coal from Saline County.
2-In general, the coals with higher free or textural moisture have the greatest avidity and the largest capacity for oxygen. 3-The avidity of a coal for oxygen is augmented by a rise in temperature. &By the process of adsorbing or condensing oxygen upon the surfaces, including the interior or textural structure of the coal, the oxygen is in the best possible form for promoting the oxidation of the material with which it is associated. This readiness to pass over from the form of surface combination is enhanced by ( a ) heat, ( b ) the catalytic properties inherent in the material, and (c) the unsaturated character of many of the constituents of the coal, which thereby accentuate the readiness with which chemical combinations are entered into. 5-Under suitable conditions the sulfur of iron pyrites reacts chemically with oxygen, resulting in the generation of heat. Deterioration
OXYGENhsomTIoN-The first result of oxygen absorption on the part of coal at ordinary atmospheric temperatures is physical rather than chemical. It would be expected, therefore, that at normal temperatures and for a reasonable length of time the actual deterioration of coal as indicated by loss of heat units is apparent rather than real. The increase of weight due to the absorption of oxygen is therefore in the Received August 5, 1824. “Industrial Coal: Purchase, Delivery, and Storage.” American Engineering Council, The Ronald Press Co., 1914. 1
3
Report of the
