Harrison, - University Of Illinois Urbana-Champaign
J. A. Harrison, H. W. Jackman, and J. A. SimonABSTRACTPreviously published c u r v e s based on c o a l petrographyand coking d a t a t h a t h a v e been used s u c c e s s f u l l y in predictingt h e ASTM s t a b i l i t y factor of c o k e were found t o be not generallya p p l i c a b l e t o Illinois c o a l s . Using Illinois c o a l s or blendscontaining Illinois and other c o a l s , petrographic a n a l y s e s andcoking d a t a , derived from pilot coke oven t e s t s , provided b a s i cinformation for modifying t h e s e c u r v e s . The information i s presented in t h i s report. The application of petrographic d a t at o the c u r v e s for predicting coke s t a b i l i t y i s demonstrated.INTRODUCTIONC o a l petrography, or t h e s y s t e m a t i c and descriptive study of t h e physicalcomponents of c o a l , i s a relatively new s c i e n c e t h a t h a s developed rapidly s i n c et h e e a r l y part of the 20th century. In t h e l a s t 10 years, there h a s been increasingi n t e r e s t in t h e application of c o a l petrography for evaluating individual c o a l s andblends of different c o a l s u s e d in t h e production of metallurgical coke. The i n c r e a s e di n t e r e s t h a s resulted largely from t h e development of procedures in which numericalv a l u e s , determined from petrographic a n a l y s e s of c o a l s , permit prediction of t h eASTM tumbler stability factor, which i s t h e major b a s i s of coke evaluation in t h ecoking industry.Systems of c o a l petrographic nomenclature, u s e d by various laboratories,h a v e not a l w a y s been c o n s i s t e n t . Some confusion h a s resulted from t h e i n c o n s i s t e n tu s e of term-s, both for t h e c o a l petrographer and t h e n o n s p e c i a l i s t interested in t h eapplication of c o a l petrographic d a t a . It i s felt, however, t h a t t h e importance of t h evarying nomenclature in c o a l petrography may have been exaggerated by some nons p e c i a l i s t s Actually t h e similarities between t h e various s y s t e m s far outweigh t h edifferences between them.Problems a s s o c i a t e d with improvements in petrographic nomenclature andmethods of a n a l y s i s a r e of importance t o c o a l petrographers. However, efforts ofc o a l petrographers t o make t h e s e improvements should not be confused with t h e a p p l ication of petrographic methods t h a t have been developed. The most recent and.
I L L I N O I S STATE G E O L O G I C A L S U R V E Y C I R C U L A R 3 6 6probably t h e b e s t known development i s t h e u s e of petrographic a n a l y s i s of c o a lt o provide d a t a for predicting t h e s t a b i l i t y factor of coke produced from t h a t c o a l .National and international bodies of c o a l petrographers a r e currently consideringproblems of definitions, a n a l y t i c a l methods, and c l a s s i f i c a t i o n s y s t e m s . The r e s u l t s of t h e s e cooperative efforts undoubtedly w i l l produce more uniformity in petrographic nomenclature and methods of a n a l y s i s . It i s emphasized, however, t h a tt h e nomenclature of petrographic a n a l y s i s should not a d v e r s e l y concern t h e coket e c h n o l o g i s t s in t h e application of c o a l petrography b e c a u s e in t h e prediction ofc o k e s t a b i l i t y , t h e e s t a b l i s h e d terms of coke technology a r e u s e d .The primary objective of t h i s report i s t o present petrographic d a t a t h a t w a su s e d t o predict t h e s t a b i l i t y factor of c o k e s which were derived from Illinois c o a l sor blends containing Illinois and other c o a l s . The secondary objective is t o reviewin d e t a i l t h e method of evaluating t h e coke s t a b i l i t y factor by t h e petrographicmethod.Since 1935, t h e Illinois State Geological Survey h a s made e x t e n s i v e s t u d i e sof t h e u s e of Illinois c o a l s in blends for t h e production of metallurgical c o k e . Ther e s u l t s of t h e s e s t u d i e s h a v e been reported in a number of publications (Thiessen,1937; Reed and a s s o c i a t e s , 1947; Jackman and Helfinstine, 1961; and Risser, 1962).Although limited pilot coke oven r e s u l t s were related t o petrographic investigationsby Marshall and a s s o c i a t e s (1958), t h e present report p r e s e n t s for t h e f i r s t time,correlations of petrographic a n a l y s e s of many Illinois c o a l s and blends with t h e a c t u a lASTM tumbler s t a b i l i t i e s of c o k e s produced in t h e Survey's pilot c o k e oven.Previous InvestigationsPrior t o 1913, many i d e a s were advanced t o explain t h e nature and formationof c o a l , but in 1913 White and T h i e s s e n published what i s probably t h e f i r s t systema t i c study baked on examination of t h e bright and dull bands of c o a l . They e s t a b l i s h e d a relation between t h e s e bands a n d t h e individual plant components fromwhich t h e c o a l w a s derived, and t h e y developed a s y s t e m a t i c nomenclature t od e s c r i b e t h e s e materials.Subsequently, a relatively small group of s c i e n t i s t s in s e v e r a l c o a l producingcountries of t h e world, h a s advanced t h e knowledge of c o a l by petrographic methods.T h e s e s t u d i e s were, for t h e most part, independent and had markedly differingo b j e c t i v e s , ranging from t h e most fundamental t y p e of study t o t h e most directlyapplied obj e c t i v e The differing techniques of study and t h e varying o b j e c t i v e sr e s u l t e d i n t h e u s e of different terms or different meanings for t h e same terms.Most of t h e e a r l y s t u d i e s of c o a l by i c r o s c o p emethods utilized thins e c t i o n s of c o a l t h a t were mounted on g l a s s s l i d e s and ground t o t h e t h i c k n e s s ofapproximately .0 00 3 inch (about 8 microns) T h i s rendered t h e principal c o n s t i t u e n t sof bituminous c o a l t r a n s l u c e n t . This methbd of examination, u s e d by Thies s e n ,permitted r e a d y recognition of most of t h e plant c o n s t i t u e n t s and r e s u l t e d i n a nomenclature and c l a s s i f i c a t i o n t h a t considered c o a l s a s c o l l e c t i o n s of recognizableplant materials. T h i e s s e n ' s c l a s s i f i c a t i o n , which developed during h i s mic'roscopicinvestigation of c o a l s , w a s included in numerous papers but w a s never presentedsystematically. Parks and OIDonnell (19 56) reviewed and summarized T h i e s s e n ' sc l a s s i f i c a t i o n b a s e d upon h i s microscope criteria.During t h e e a r l y 1 9 2 0 1 s , particularly in England and Germany, workers beganpetrographic examination of c o a l by reflected light from polished c o a l s u r f a c e s ,measuring t h e amount of r e f l e c t a n c e by means of t h e Berek photometer. T h e s e.
COKE STABILITY F R O M P E T R O G R A P H I C ANALYSIS3methods a r e similar t o t h o s e used i n metallurgy. The physically differing c o a lmaterials, considered by t h i s type of investigation, a r e c a l l e d macerals (Stopes,1935) and a r e analagous t o mineral constituents of rocks.Marshall (1955) presented a rather comprehensive review of work in t h efield of c o a l petrography up t o t h e year 1950, listing over 300 references. The workof Stach and Hoffmann (193 l ) , Hoffmann and Jenkner ( l 9 3 2 ) , and Seyler (1943) particularly contributed t o t h e evolution of methods used for t h e practical applicationof c o a l petrography, which is t h e subject of t h e present paper.In 1958, Marshall e t a l . , reported a comprehensive laboratory coking studyt h a t related petrographic composition t o coking quality. Although t h i s study g a v einsight into petrographic relations favorable t o improved coking character of Illinoisc o a l s and evaluated many other factors t h a t influence coking character, it did nots e t forth t h e foundation for predicting coke quality in terms of s p e c i f i c numericalv a l u e s for coke stability or h a r d n e s s .In a 1957 report, Arnmosov and a s s o c i a t e s presented, i n broad outline, amethod of using petrography t o predict coke stability from c o a l and blends of c o a l s .Schapiro and Gray (1960), following t h e b a s i c methods of Ammosov, refined t h eprocedure and developed b a s i c data for many c o a l s and related t h e s e data t o standard methods of coke t e s t i n g used in t h e United S t a t e s .Although t h e petrographic nomenclature employed differs from laboratory t olaboratory in t h e United States, the b a s i c method of predicting coke stability ofc o a l s i s t h e one used a t t h e United S t a t e s S t e e l Corporation Applied ResearchLaboratory (Schapiro, Gray, and Eusner, 19 6 1).PETROGRAPHIC NOMENCLATURESome adherence t o t h e nomenclature of Thiessen remains particularly in t h eUnited S t a t e s . However, in the p a s t 15 t o 20 y e a r s , most of t h e world's petrologistsh a v e adopted the petrographic c l a s s i f i c a t i o n and nomenclature e s t a b l i s h e d by Stopes(1935) a t t h e Heerlen Congress of Carboniferous Stratigraphy and Geology. This i snow known a s the Stopes-Heerlen System.Recognizing t h e need for a better comprehension of a l l terms u s e d i n c o a lpetrology nomenclature and for a n international g l o s s a r y of t h e s e terms, t h e ThirdInternational Conference on Carboniferous Stratigraphy and Geology appointed acommittee in 195 1 t o review and r e l a t e t h e two principal systems of nomenclature,t h e Thiessen- Bureau of Mines and Stopes-Heerlen Systems. Efforts of t h e Committeefor Coal Petrology Nomenclature resulted in t h e publication of two editions (1957;19 63) of a g l o s s a r y The international standard nomenclature of c o a l petrography,a s published in t h e g l o s s a r y of 19 63, and t h e modified reflectance categoriesof Schapiro and Gray (1960) a r e employed in t h i s report (table 1 ) .One of t h e recent a c c e s s i o n s t o the International G l o s s a r y is a c l a s s i f i c a t i o nproposed by Spackman, who first presented in 1958 a framework in which new termswere introduced. This c l a s s i f i c a t i o n , presented i n t h e 1963 edition of t h e G l o s s a r ya s t h e "Coal Constituent Classification " (Spackman) , w a s initially developed int h e C o a l Laboratories of The Pennsylvania State University. However, t h e termsnow employed a r e b a s e d mainly upon t h e reflectance measurements of maceralse s t a b l i s h e d by Schapiro and Gray (1960) a t t h e laboratories of t h e United S t a t e sSteel Corporation in MonroevilLe, Pennsylvania. The terms a r e t h e principal o n e semployed i n t h e petrographic laboratories t h a t h a v e developed in t h i s country int h e p a s t five y e a r s .
I L L I N O I S S T A T E G E O L O G I C A L SURVEY C I R C U L A R 3 6 6Definition of TermsAn explanation of some of t h e common terms u s e d i n t h i s report, based onwork of Arnmosov (1957), Schapiro and Gray and Eusner ( 1 9 6 1 ) and Harrison (1961)may be helpful in applying petrographic d a t a t o carbonization evaluations.Reactive sThis term i s applied t o c o a l constituents t h a t soften during carbonizationand l o s e their physical and chemical c h a r a c t e r i s t i c s . Examples of t h e s e r e a c t i v e sa r e vitrinite, exinite, and r e s i n i t e (table 1).Inert sThis term a p p l i e s t o t h o s e c o a l constituents t h a t maintain their characteris tics throughout t h e carbonization p r o c e s s or t h a t a r e relatively l i t t l e altered.Usually, t h e y c a n b e identified in t h e resulting coke with a microscope. Examplesof i n e r t s a r e inertinite, fusinite, and micrinite (table 1).Stability FactorThis i s a measure of coke strength and refers specifically t o t h e percentageof a coke sample t h a t is retained on a one-inch sieve after testing by t h e standardASTM Tumbler T e s t procedure (American Society for Testing and Materials: Designation D 294-50). It is a n indication of t h e r e s i s t a n c e of coke p i e c e s t o breakage a st h e y d e s c e n d through t h e shaft of t h e b l a s t furnace. Of t h e various physical evalua t i o n s for a s s e s s i n g quality of b l a s t furnace coke, t h e stability factor is perhapst h e most widely u s e d i n t h e United S t a t e s . For t h i s reason, c o a l petrographywork related t o c o a l carbonization i s now correlated largely with t h i s factor.OptimumIn t h i s paper, optimum refers t o t h e b e s t coking r e s u l t s t h a t c a n be obtainedwith a standard s e t of operating conditions corresponding t o good commercialoperating practices. By varying t h e s e standard conditions, such a s c o a l pulverization, coking rate, bulk density, e t c . , the optimum r e s u l t s a l s o vary.Reflectance C l a s sThis term a p p l i e s t o grouping of reflectance v a l u e s and i s obtained bymeasuring the percentage of light reflected from t h e polished c o a l s u r f a c e s .Standard g l a s s e s with known reflectance percentage values were u s e d t o standardizet h e photometer. The percentage of light reflected from t h e vitrinite varied over arelatively large range depending upon t h e rank of c o a l from which the vitrinite w a sderived or t h e degree of coalification of t h e vitrinite particle. Arbitrary reflectancec l a s s e s from 0 t o 70 were a s s i g n e d t o cover t h e entire reflectance range (Schapiroand Gray, 19 60). Readings of reflectance from 0.30 t o 0.39 were e x p r e s s e d a svitrinite r e f l e c t a n c e c l a s s 3, and readings of reflectance from 0.40 t o 0.49 wereexpressed a s vitrinite reflectance c l a s s 4, e t c . The upper limit h a s been raisedsubsequently, from 70 t o 80 a s a r e s u l t of s t u d i e s of anthracite.It appears, from e x p e r i p e n t a l data, t h a t exinite and r e s i n i t e contributet o the quality of c o k e s t o a degree comparable to, or perhaps even greater than,a s s o c i a t e d vitrinites The percentage of reflectance from exinite and r e s i n i t e i s.
COKE STABILITY F R O M PETROGRAPHIC ANALYSIS5-TABLE 1 MACERAL REFLECTANCE CLASSES ANDRJIACTIVITY DURING rotiniteExiniteGroupMineralsMinera 1sAlginiteSulphidesPyrite, etc.ResiniteCarbonatesCalcite, etc.SilicatesIllite, etc.SporiniteCutiniteFusibleInertinite SemifusinitetMicrinite* Nomenclature as defined in Glossary of International Committee for Coal Petrology and based primarily on Stopes-Heerlen System of Classification. Range of reflectance values of macerals based on values of Schapiro, N. and Gray, R. J . ,1960, Petrographic Classification Applicable to Coals of A11 Ranks: Proceedingsof the Illinois Mining Institute, 68th year, p. 83-97.Estimated values, reactive group is about 1/3fusinite total, Ammosov, I. L., Eremin, I. V.,L. S o , 1957, Calculation of Coking Charges onacteristics of Coke: Koks i Khimiya, No. 12,and inert group about 213 of semiSukhenko, S. I.,and Oshurkova,the Basis of Petrographic Charp. 9-12.
6I L L I N O I S S T A T E G E O L O G I C A L SURVEY C I R C U L A R 3 6 6generally lower t h a n from a s s o c i a t e d vitrinite, e s p e c i a l l y in t h e high and mediumvolatile c o a l s , therefore, in calculations, t h e t o t a l percentage of exinite and r e s i n i t eh a s been prorated, or distributed proportionately, t o vitrinite of reflectance c l a s s e s11 through 15 (Gray, personal communication 1961). In t h e present study, exiniteand r e s i n i t e have been distributed in t h e vitrinite c l a s s e s according t o t h i s pract i c e . However, in the 4 t e s t s i n which vitrinite 1 1 through 15 were a b s e n t , t h e s ecomponents were allocated t o t h e vitrinite 1 1 reflectance c l a s s .Inert IndexAn optimum coke c a n be produced from e a c h vitrinite reflectance c l a s s(including other r e a c t i v e s allocated and equated t o e a c h c l a s s ) provided t h a t t h eproper ratio e x i s t s between t h e inerts and t h e vitrinite. The percentage of inertsrequired and t h e strength of t h e optimum coke will vary depending upon the degreeof coalification (apparent rank) of t h e vitrinite, a s measured by reflectance.The relation, between t h e percentage of inerts present i n a n y given coal andt h e percentage of i n e r t s needed in t h e c o a l t o produce a n optimum coke, i s basedon t h e apparent rank and t h e quantity of e a c h vitrinite present and i s known a s theinert index. The inert index c a n be calculated from Equation No. 1, which is givenl a t e r in t h i s paper.Strength IndexThe strength of t h e coke (calculated and expressed in arbitrary relativeunits) t h a t is produced b y blending various percentages of inerts with each vitrinitereflectance c l a s s is designated a s t h e strength index for e a c h particular mixtureof r e a c t i v e s and inerts. The strength index of a c o a l or a blend t h a t contains morethan one vitrinite reflectance c l a s s , and generally most c o a l s do, c a n be calculatedby using Equation No. 2.The arbitrary v a l u e s for strength index, a s developed by Schapiro and a s s o c i a t e s (1961), were b a s e d on about 400 m i c r o - o v e n t e s t s . These t e s t s provideb a s i c d a t a for the strength index curves d i s c u s s e d below. These d a t a were modified by d a t a from 500 pound coke oven t e s t s and the Russian tumbler d a t a .CURVES DEVELOPED FOR PREDICTING THE STABILITY FACTORAmmosov and a s s o c i a t e s (1957) developed a s e r i e s of curves for predictingt h e c o k e s t a b i l i t y factor. T h e s e curves were based on c o a l petrography d a t a relatedt o industrial coke t e s t s using t h e Sundgren tumbler. A similar s e t of c u r v e s relatedt o ASTM procedures h a s been developed by Schapiro and a s s o c i a t e s (1961). Theseinvestigators prepared a curve, similar t o t h e one in figure 1, by plotting t h e different vitrinite reflectance c l a s s e s a s t h e a b s c i s s a and t h e ratio of r e a c t i v e s t oi n e r t s (R/I) a s the ordinate, for t h e production of a n optimum c o k e . The percentageof i n e r t s n e c e s s a r y for production of a n optimum coke for e a c h vitrinite reflectancec l a s s is u s e d a s t h e M value in t h e calculation of t h e inert index (Equation No. 1).Equations 1 and 2, u s e d i n calculations n e c e s s a r y for predicting t h e stabilityfactor, a r e d i s c u s s e d in l a t e r paragraphs.A second s e t of d a t a w a s plotted (Schapiro and a s s o c i a t e s , 1961) a s afamily of curves, similar t o t h o s e shown in figure 2 . Concentrates of vitrinite ofe a c h reflectance c l a s s t h a t had varying percentages of inerts were coked i n laboratory coke t e s t s and arbitrarily t e s t e d for their r e l a t i v e coke strength. This provided
C O K E S T A B I L I T Y F R O M P E T R O G R A P H I C FLECTANCE CLASSESFigure 1 - Optimum ratio of reactives t o inerts (R/I) for e a c h vitrinite reflectancec l a s s (modification of curve by Schapiro, Gray, and Eusner, 1961).d a t a for the "strength index, " t h e ordinate in B e figure. The percentage of inertsw a s systematically varied for vitrinites of each reflectance c l a s s t e s t e d and w a splotted along the a b c i s s a . Some of t h e original curves have been altered on t h eb a s i s of pilot s c a l e coke t e s t d a t a in the present study. The figure (or the tablefrom which the figure is derived) provides t h e b a s i s for determining the strengthindex for each reflectance c l a s s in Equation 2.A third e s s e n t i a l procedure in the correlation of petrographic compositionand coke properties w a s provided by t h e various t e s t s of Schapiro and a s s o c i a t e s(1961) and involved t h e development of a graph similar t o the one in figure 3 . Thisgraph made u s e of a grid in which the strength index of a blend (composed of different reflectance c l a s s e s and determined by the u s e af Equation 2) is plotted a sthe ordinate and t h e inert index (determined by the u s e of Equation 1) is plottedas t h e a b s c i s s a on a logarithmic s c a l e . By testing c o a l blends which represented awide variety of possible combinations of strength and inert indices, i t w a s possiblet o construct a s e r i e s of curves. These curves indicated the approximate positionsof the coke stability factors t h a t vary between values of 10 t o 65 (fig. 3 ) .The original curves t h a t were compiled by Schapiro and a s s o c i a t e s (1961)were used successfully for predicting the stability factor of c o a l blends containingIllinois c o a l s when t h e inert index (called "composition balance index" by Schapiroand a s s o c i a t e s ) w a s between 1.3 and 0.60. However, when t h e inert index dropped
I L L I N O I S STATE G E O L O G I C A L SURVEY C I R C U L A R 3 6 65045Figure 240-353025INERTS, VOLUME20151050PERCENTStrength index for vitrinite reflectance c l a s s e s depending upon t h eamount of i n e r t s present (modification of curve by Schapiro, Gray, a n dEusner, 1961).below 0.6, t h e s t a b i l i t y factors predicted from petrographic a n a l y s i s were generallylower than the a c t u a l v a l u e s obtained from pilot coke oven t e s t s . A s e r i e s of t e s t swith Illinois c o a l s i n t h e Survey's pilot coke oven provided d a t a t h a t permittedc h a n g e s in t h e curves of Schapiro and a s s o c i a t e s . These changes, which wereincorporated into t h e curves shown in figure 3, make t h e curves applicable t o mostIllinois c o a l samples t e s t e d .ProceduresForty coke runs were made in t h e Survey's pilot coke oven, and coket e s t r e s u l t s were correlated with c o a l petrographic d a t a . Various blends of Illinoishigh volatile bituminous c o a l s and different percentages of medium and low volatilebituminous c o a l s from t h e Appalachian f i e l d s were coked. In three s e r i e s , Illinoisand medium volatile c o a l s were coked independently and then in blends consistingof 20 percent variations of t h e proportion of t h e two c o a l s .
COKE S T A B I L I T Y F R O M P E T R O G R A P H I C ANALYSISSTRENGTH-INDEX--OF-BLEND9COKE STABILITYFACTORFigure 3 - Curves showing relation between strength index, inert index, andstability factor (modification of curves by Schapiro, Gray, and Eusner, 19 6 1).Coking ProceduresThe pilot coke oven used for t h e s e t e s t s h a s been operated for t h e p a s tten years for the Survey's metallurgical coke project (Jackman and a s s o c i a t e s 1955;a l s o Illinois State Geological Survey Reprint Series, 1955 E). The coking chamberis approximately 36 inches deep, 3 6 inches high, and 17 inches wide (a commercialoven width), and it holds about 700 pounds of coal. Oven walls are heated electric a l l y by nonmetallic heating elements. Flue temperatures may be regulated t oduplicate any rate of heating normally used in commercial practice. With standardoperating conditions, t h e cokes produced in t h e pilot oven duplicate c l o s e l y t h ecommercial cokes made from the same c o a l blends under equivalent heating conditions.Petrographic ProceduresRepresentative samples of the c o a l or c o a l blend tested were taken forpetrographic analysis, using sampling techniques similar t o those used forobtaining samples for chemical analysis. To prevent e x c e s s i v e breakage of themore friable coal components, t h e coal sample w a s alternately crushed and screeneduntil t h e entire sample p a s s e d through a 20-mesh Tyler sieve. Fifteen grams of t h i sc o a l were added t o a mixture of 5 grams of a n epoxy resin (Biggs Bonding Agent 823)and 20 drops of hardener, placed in a cylindrical mold, and compressed for 10 t o 15minutes a t 2000 pounds per square inch. Pressure w a s released, and t h e s t e e l
10I L L I N O I S STATE G E O L O G I C A L SURVEY C I R C U L A R 3 6 6cylinder w a s s e t a s i d e until the coal briquette cured. After 10 t o 1 3 hours a t roomtemperature t h e briquette w a s ejected from the mold. It was ground on a BuehlerAutomet using 240 and 400 grit water-resistant emery paper, and w a s polishedusing Buehler alumina Nos. 1 and 3 in a water suspension on a nap free cloth. Anessentially flat, scratch free surface w a s produced by t h i s method of grinding andpolishing. The sample w a s then ready for examination with the microscope.Quantitative petrographic analysis, using the point count method (Chayes,1956) for t h e percentage of reactive and of inert macerals and group macerals ineach sample, w a s performed with the aid of a Leitz BMe microscope a t a magnification of 320 X using a n 8mm (25 X) oil immersion objective. The percentages of reactive macerals and inert macerals obtained by t h e s e analyses provided t h e b a s i c datanecessary t o calculate t h e inert and strength indices, according t o procedures outlined later.The maximum percentage of incident light reflected from the polished surfacesof vitrinite fragments w a s measured, and the values were assigned t o vitrinitereflectance c l a s s e s . Vitrinite that h a s a reflectance value that exceeds 2.1 (reflectance c l a s s 22 and higher) h a s the apparent rank of anthracite and i s classified a sa s an inert (table 1). Reflectance measuring equipment used in t h i s investigationi s similar t o that described by Schapiro and Gray (1960). The Leitz UAM microscope,used for reflectance measurement of coal, is equipped with a photoelectric c e l l onthe monocular tube which i s , in turn, connected t o a Photovolt photometer (Model520 M). A pin hole diaphragm t o restrict the area of measurable light on t h e samplet o a 7 micron circle and a combination of two Eastman Wratten Filters, numbers 58and 77, which provided a monochromatic light were placed in the monocular tube oft h e microscope through which a l l reflectance measurements were made. Reflectancevalues for most substances will vary if t h e wave length of light i s altered; therefore,a restricted and constant wave length must be used t o obtain accurate and reproducablereflectance readings. Six polished g l a s s standards of known reflectance value wereused t o standardize the photometer a t the beginning of the run and after each 25reflectance readings. Reflectance values of t h e s e standards ranged from 0.30 6 t o1.832.CalculationsEquations needed for calculating the two parameters, inert index and stabilityindex, that are used for predicting coke stability factors from petrographic analysisare given below.Inert IndexOne of the values needed for predicting the stability factor of coke frompetrographic a n a l y s i s of coal i s the inert index. This index expresses the relationbetween the inerts in a c o a l or blend and the reactives of each reflectance c l a s s .This i s expressed in Equation 1.
C O K E S T A B I L I T Y F R O M P E T R O G R A P H I C ANALYSISwhenNQP1s P 2 - e P 2 1 inert index total percentage of inerts in t h e blend percentage of reactives in reflectance c l a s s e s 1, 2,.2 1that may be present in t h e c o a l sampleM1, M2. M21 ratio of reactives t o inerts (R/I) for t h e production ofoptimum coke for each reflectance c l a s s 1, 2,.2 1,.Values in Equation 1 are derived a s follows:Q, the total percentage of inerts in t h e blend (fusinite, micrinite, 2/3 semifusinite,P2, e t c . , the percentage of reactives (vitrinite, exinite,and a s h by volume), and P1Iresinite, and 1/3 semifusinite), can be taken from t h e petrographic a n a l y s e s .Petrographic a n a l y s e s for c o a l s used in t h i s study a r e shown in table 2. The valuesof M1, M2, e t c . , can be read from t h e curves in figure 1. For each vitrinite reflectance c l a s s represented in t h e reflectance a n a l y s i s and shown on t h e a b s c i s s aof figure 1, project a vertical line t o the curve. Then project a horizontal line t ot h e ordinate a t t h e left where t h e optimum ratio, or M value, can be read directly.These values can be placed in Equation 1 and t h e value of N, or inert index, c a l culated.Strength IndexThe strength index of t h e blend (KT,) is calculated by multiplying t h e strengthindex of each vitrinite reflectance c l a s s , by the.percentage of reactives (vitrinite,exinite, resinite, and 1/3 semifusinite) in that reflectance c l a s s . The sum of t h e s eproducts i s then divided by the total percentage of reactives in t h e blend.This i s expressed in Equation 2.when5p K1,5,- m e K 2 1pl, p2, -PZ1 strength index of the blend total percentage of reactives in t h e blend strength index of reactives in reflectancesclasses1, 2,2 1 t h a t may be present in t h e coal sample percentage of reactives in reflectance c l a s s e s 1, 2,that may be present in t h e coal sample.21Values in Equation 2 are derived a s follows:K1, K2, e t c . , are obtained from the family of curves in figure 2. Locate t h e pointalong the a b s c i s s a that corresponds t o t h e percentage of inerts determined from t h equantitative petrographic a n a l y s i s of-the coal sample. Project a vertical line fromt h i s point until i t intersects t h e line for each vitrinite reflectance c l a s s presentin t h e sample. Then project horizontal lines t o the left until they intersect t h e ordinate. Read t h e strength index for each reflectance c l a s s from t h e numbers pl
Arbitrary reflectance classes from 0 to 70 were assigned to cover the entire reflectance range (Schapiro and Gray, 19 60). Readings of reflectance from 0.30 to 0.39 were expressed as vitrinite reflectance class 3, and readings of reflectance from 0.40 to 0.49 were expressed as vitrinite reflectance class 4, etc. The upper limit has been raised
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