'S 14.QS* G>tA SulOO^ OR dAX> ^L_* J STATE OF ILLINOIS WILLIAM G. STRATTON, Governor DEPARTMENT OF REGISTRATION AND EDUCATION VERA M. BINKS, Director • Comparison of Methods for Determination of Volatile Matter and Ash in Coal O. W. Rees F. A. Coolican E. D. Pierron DIVISION OF THE ILLINOIS STATE GEOLOGICAL SURVEY JOHN C. FRYE, Chief URBANA CIRCULAR 240 ILLINOIS GEOLOGICAL 1957 SURVEY LIBRARY NOV 1 >» D 7 ILLINOIS STATE GEOLOGICAL SURVEY 3 3051 00004 4655 COMPARISON OF METHODS FOR DETERMINATION OF VOLATILE MATTER AND ASH IN COAL O. W. Rees, F. A. Coolican, and E. D. Pierron ABSTRACT This study was undertaken as part of the effort to standardize national and international methods of testing coal. Methods for the determination of volatile matter and ash in coal are empirical in na- ture, and details of the methods used vary considerably indifferent countries. This report presents (1) determinations for volatile matter ob- tained by four methods, two American and two European, and (2) de- terminations for ash at two different final temperatures as well as at certain different rates of heating. For volatile matter the results indicate that the slower the rate of heating, the lower will be the results obtained. Ash values ob- tained at the two final temperatures tried compare favorably, but too rapid a rate of heating for coals containing appreciable amounts of calcite and pyrite gives ash values which are too high. INTRODUCTION For many years the Illinois State Geological Survey has cooperated actively in the work of Committee D-5 , Coal and Coke, of the American Society for test- ing Materials, whose goal is establishment of national standard methods for the analysis of coal and coke. More recently, we have also shared in the participa- tion of Committee D-5 with the International Organization for Standardization, Technical Committee 27 (Solid Mineral Fuels) , which is attempting to establish international standard methods for analyzing coal and coke. This latter activity has brought to our attention a large amount of information regarding methods used in other countries and proposals which are being advanced for International Stand- ards. As might be expected, methods and proposals from other countries often dif- fer considerably from those accepted as standard in the United States. The dif- ferences frequently are not so much in fundamental design as in details of proce- dure. However, coal analysis methods are largely empirical in nature so that de- tails are of prime importance. In this connection, therefore, it becomes neces- sary to compare methods which differ in detail in order to learn how much the dif- ferences influence results and whether or not the methods are applicable to a wide range of coals. Methods have been found to differ considerably for the determinations of volatile matter and ash of coal. Methods in use in various countries for the deter- mination of volatile matter vary in specified temperature of heating from 875 ° to 1040°C. and in time of heating from seven minutes to 20 minutes. Methods for determining ash specify temperatures from 700° to more than 850°C. A temper- ature of 815°C. is under consideration as an international standard. This is higher than the American standard specification of 700-750°C. Furthermore, there is difference of opinion as to the proper rate of heating for the determina- tion of ash in coals high in calcite and pyrite. [1] 2 ILLINOIS STATE GEOLOGICAL SURVEY For the volatile matter determination, we have compared four methods; for the ash, we have compared two final temperatures of determination. Furthermore, we have studied the effect of rate of heating on the ash determination. This re- port covers results of these studies. VOLATILE MATTER Volatile matter in coal and coke is defined by the American Society for Testing Materials (ASTM D 120-30, 1954) as "those products, exclusive of mois- ture, given off by a material as gas or vapor, determined by definite prescribed methods which may vary according to the nature of the material. " It is one of the important determinations in the proximate analysis for use in certain classi- fication systems and for evaluating coals as to combustion and coking character- istics. The determination of volatile matter in coal is empirical, requiring rigidly specified conditions. Differences in temperature and in time or rate of heating are known to influence results beyond permissible tolerances. To meet the need for definite specifications, the American Society for Testing Materials in the United States sponsors two standard methods (ASTM D 271-48, 1954). The first, commonly referred to as the standard method, consists of heating the coal at a rapid rate in a vertical tube furnace maintained at 950°C.±20°C. The other method, commonly referred to as the modified method, consists of heating the coal in the same furnace at a considerably slower rate. Two methods are neces- sary because certain solid fuels (such as subbituminous coal, lignite, peat, cer- tain cokes, chars, anthracites, and semianthracites) spark appreciably when heated at the rapid rate, causing high values through mechanical loss. By the slower rate of heating used in the modified method, sparking is reduced to a minimum. Unfortunately, the two ASTM standard methods may not give the same re- sults. The modified method frequently gives results as much as three percentage units lower than the rapid heating procedure. Because of this, it is not satis- factory to compare coals, some of which are analyzed by the standard method and some by the modified method. At the present time, Technical Committee 27, Solid Mineral Fuels, of the International Organization for Standardization is attempting to establish inter- national standard methods for the determination of volatile matter. The Illinois State Geological Survey is interested in the problem from the standpoint of es- tablishing national and international standards, in addition to its own research program. Hence, we have compared the American, British, and Franco-Belgian methods, the last two of which have been proposed as international standards. Equipment The equipment used in this comparison was that specified by the American Society for Testing Materials for the American methods (ASTM D 271-48, 1954); by the British Standards Institution for the British method (BSI 1016-1942, 1942); and by the Association Francaise de Normalization for the Franco-Belgian method (AFN NF-M-03-004, 1950). Briefly, equipment used for the three methods is described as follows- (1) For the American methods- Platinum crucibles of 15 ml. capacity with tightly fitting capsule lids were used for both the standard and modified methods. Heating was done in a vertical tube or volatile -matter furnace, commonly known as the Fieldner furnace. VOLATILE MATTER AND ASH IN COAL 3 (2) For the British single-crucible method: Fused-silica cylindrical cruci- bles with capsule-type lids were obtained from England for this method. Heating was done in an electric muffle furnace. A refractory stand or "gas mantle" was used to hold the crucible in the furnace. Two discs of asbestos, each one mm. thick were placed between the bottom of the crucible and the inside projections of the three legs of the stand. Mounting the crucible in this way removes it about 6 mm. from the floor of the furnace. (3) For the Franco-Belgian double-crucible method: A double -crucible (one inside the other) arrangement is specified and was used for this method. The smaller, or inner, crucible with lid was of glazed porcelain, and the larger, or outer crucible with cover was quartz. The two crucibles were separated by a layer of crushed wood charcoal. All crucibles and covers were obtained from France. Heating was done in an electric muffle furnace. In all methods, temperatures were measured by means of thermocouples and pyrometers. Samples Five samples of Illinois coals representing the three ranks, high-volatile bituminous A, B, and C were used in this comparison. Because of the Survey's interest in char and because the determination of volatile matter in char is trouble- some , four char samples were included in this study. Procedure Details of procedure as specified in the various standards were followed in this work. The more important details of the four methods are shown in Table 1. Table 1. - Details of Methods British French ASTM ASTM Single Double Standard Modified crucible crucible Top temp, of heating 9 50°+20°C. 950°+20°C. 925°C. 960°+10°C, Total time of heating - min. 7 15 7 20 Time subjected to top temp. - min. 7 6 7 20 Comparative rate of Inter- sample heating Rapid Slow mediate Slow Crucibles Platinum Platinum Fused silica Porcelain and quartz In all methods, 1-gram samples of minus 60-mesh coal or char were used, and all determinations were made in duplicate. In the American standard method, the sample, in a platinum crucible, was introduced directly into the hottest zone of the furnace (950°C.) for exactly 7 minutes, thus obtaining a rapid rate of heat- ing. In the American modified procedure, the sample, in a platinum crucible, was suspended in the Fieldner furnace (95 0°C.) such that the top of the crucible lid was even with the top of the furnace. After 5 minutes, it was lowered one- ILLINOIS STATE GEOLOGICAL SURVEY o c o •H CO (D O c x: ■ H +J E fH 2 0) +-> C Q en (H OJ 0) CD -t-> I ' • H d) ro c (h .-{ CO U-, o I > - Q X! ^H O -H +J 4-> 0) C -H -H O M o mms M - to c Q. ro E o O -H U M d> CM ON cd h < o X c-i u % cc o < a- 5 £ re o < CO O o CQ to if> c < a> co -h p> in u £ H o to » CM C O CD I -H > CO tflHl QH % 10 On -H E CO O CQ (0 CM C O 0) I -H > CO M —( 5C CO CO C0 CO CO CO ON CO vO CM O ox o o CM CO CO CO CM CM CM CN CM O in co o 00 r- CO CO CM CO CM CM CM CM CM CM CM CM if) O ON • • • NO •O if) nO ^r ON O r~ cH NO vO If) NO lT) nD CO If) 00 • • • o a- ON CM .-H ,_ ( CM CO IT) If) r- 00 O o ON ON On ON CM CM rH 1-1 1-1 r-4 CM CO v£> • • • ON 00 •—* CM CM 00 00 NO if) ON ON 00 00 co 00 CM CO CM CO r- co r- co CO ON CO on in CM CO ^r ^ CM CM CO CO co CO 00 CO 00 CO o <* r- in CM CO in -3- CM CO CM CO co r- CO r- co On CO O t- CM ON CO ON CO o o St o ON CO CM CD x: a> +> x> >- 03 0Q w 00 -h E O O CQ to CO C CQ (JJ CO -H > CO I .-H X °3 £ CO N0 ** CO CO CO O 00 in CO I $ NO CO NO co NO CO CO co co CO 1} CO in co vO ON in CO in m CO oo r- o >- M O -P ro (H O XI to Q. CD Q ON CD cc H CO < 00 < X XI 00 CD tH M .-4 O f-i ON 3 H C h CC -H O CQ 00 2 < i— i -— ^ O 0) l-J ^H uu xi cq a> -h I r-l o O X D U D h ZOO 3 Q VOLATILE MATTER AND ASH IN COAL quarter inch for 2 minutes, then one- half inch further for 2 minutes, after which it was lowered to the hottest zone of the furnace and heated 6 min- utes. By this means, a slower rate of heating was obtained. A mechanical device (fig. 1) was employed for low- ering the samples into the furnace in order to duplicate the position for all samples. Heating rates for both Amer- ican methods are shown in figure 2. For the British single-crucible method, the sample was introduced into the hottest zone of the muffle fur- nace (925°C.) and heated for exactly 7 minutes. A rather rapid rate of heat- ing was obtained, but not as rapid as in the American standard procedure. For the Franco-Belgian double- crucible method, the smaller porcelain crucible, containing the coal sample, was placed inside the larger quartz crucible with a layer of wood charcoal surrounding it and separating it from the inside of the larger crucible. It was then inserted into the hot zone of the muffle furnace (9 60°C.) and heated for exactly 20 minutes. By this procedure, a slow rate of heating was obtained. Results and Discussion Volatile matter values obtained by the four methods under study for all samples are shown in table 2. In only one case did duplicates fail to check within ASTM tolerance (0.5 percent); duplicate values by the ASTM regular method for sample DPS-2164 were slightly outside tolerance. A third value was obtained and the three averaged. For the coals, results obtained by the British method lie between those obtained by the American standard and modified methods. Results obtained by the Franco- Belgian method check closely those obtained by the American modified method. However, they are definitely lower than those obtained by the American standard method. For the chars the American modified method gave highest results. With all three methods' applied to chars no objectionable sparking was evident. The magnitude of determined value's decreases with slower heating rates. In addition, experience indicates that slower heating rates are necessary for the determination of volatile matter in sparking coals. If we assume that the higher results obtained by the American standard method are more nearly correct, it would appear that, of the three methods involving slower heating rates, the British method would approach most closely the requirements for a single method equally applicable to all samples. Fig. 1. - Mechanical device for positioning crucibles in furnace. ILLINOIS STATE GEOLOGICAL SURVEY 1000 900 800 700 600 500 400 a 300 E