Article Open Access MOISTURE-HOLDIN CAPACITY OF COAL Yanya Balaeva, Denis Miroshnichenko *, Yury Kaftan Ukrainian State Research Institute for Carbochemistry (UKHIN), 0, Kharkiv, 7 Vesnina Str., Ukraine Received March, 07; Accepted May, 07 Abstract The moisture-holding capacity of metamorphically distinct coals does not depend on their ash content (in the range.7. %) nor on the chemical composition of the ash, expressed by the basicity index B b (in the range. 7.8) and the base/acid ratio I b (in the range 0.98.8). Although the oxidation of coal also increases the moisture-holding capacity, this change is less than the error in its determination (0. %). The oxidation of practically 0 % of the coal s organic mass increases the moisture-holding capacity by no more than 0. %. Analysis of samples of coal concentrates (from Ukraine, Russia, the United States, Canada, Australia and Poland) currently employed at Ukrainian coke plants indicates that the prediction of the moisture-holding capacity of coal may expediently be based on R 0 and Q s af deterd, respectively, in plant laboratories and in power station laboratories. Keywords: coal; moisture-holding capacity; oxidation; basicity index; mathematical equations; statistical estimates.. Introduction The moisture-holding capacity indicates the rank of hard coals and is used in coal classification (ASTM D 88 Standard Classification of coals by Rank) for collecting the calorific value of the sample to the moist ral matter-free basis. The full moisture-holding capacity is that of the coal in equilibrium with atmosphere saturated with water vapor. Since there are insuperable experimental difficulties in working with such an atmosphere, the determination is carried out at 9 % relative humidity.. Experimental Accordingly ISO 08:7 (en) Hard Coal Determination of moisture-holding capacity, a representative sample of crushed coal is mixed with distilled water for h. The excess water is removed and a subsample is placed in a vacuum desiccator with the pressure set at kpa (0 mm Hg), the humidity set at 9 97 %, and the temperature set at 00 o C for up to 7 h (or until equilibrium is attained). For some low-rank coals, equilibrium may take up to 7 days to attain. The coal is weighed and then dried to constant mass at 0 o C. The mass loss is consiered the Moisture-holding capacity, Equilibrium moisture or Bed moisture. The result for moisture-holding capacity is given as the mean of duplicate determination, reported to the nearest 0. %. It is expedient to investigate the influence of the content and chemical composition of the ash on the moisture-holding capacity in coal at different metamorphic stages, since there is no indication of the sample s ash content in ISO 08:7. Table presents the results of proximate analysis of the coal samples, together with the moisture-holding capacity. Table presents the chemical composition of the ash, basicity index (eq. ) and base/acid ratio (eq. ) of enriched (to a density of 00 kg/m ) and enriched coal samples at different metamorphic stages. 0 Pet Coal (07); 9(): 0-0 ISSN 7-707 an open access journal
B b = 00Ad (Fe O +CaO+MgO+Na O+K O), () (00 V daf )(SiO +Al O ) I b = Fe O +CaO+MgO+Na O+K O, () SiO +Al O According to point Preparation of sample of ISO 08:7 it is essential that the coal be in fresh, unchanged state. If the sample cannot be exad immediately, it shall be protected from oxidation by storing under water. Table. Properties of coal samples Supplier Rank Sample Proximate analysis, % Moisture-holdingcapacity,% Ernakovskaya Uskovskaya Esaul skaya Osinnikovskaya CCI Lubelia, bed n9 CCI Lubelia, bed n7 Zh Zh A d S d t V d V daf Wmax Unenriched.7 0.8 9.9 0.. Enriched. 0.. 7.7.8 Unenriched 7.8 0...8. Enriched.8 0. 7. 9.. Unenriched. 0.7 8..7. Enriched.8 0..9 9.. Unenriched. 0.9.0 7.. Enriched.9 0.8 0.9.. Unenriched 0.0. 9... Enriched..9 0.0.. Unenriched 7. 0.9.7 7..9 Enriched.7 0.7.9.9.9 Table. Chemical composition and basicity of coal samples Supplier Rank Sample Chemical composition of ash, % Basicity Ernakovskaya Uskovskaya Esaul skaya Osinnikovskaya CCI Lubelia, bed n9 CCI Lubelia, bed n7 Zh Zh SiO AlO FeO MgO CaO NaO KO SO Bb Ib Unenriched.78.7.98.. 0.89.79.9 8.0 0.98 Enriched 7.9 9.0.7..8.8.0.78.97 0.98 Unenriched 0.7 8. 7.8.9. 0.9.0.9. 0.0 Enriched.0.0 8.98.77 9.8..0 7.7.99 0.79 Unenriched. 0.0.7. 7.0.0.99.9. 0. Enriched.8..97.0.9...9.89 0.0 Unenriched.0 7.0.99.9.08..8.. 0.98 Enriched 7. 0.0.7.9.8.0...70 0.8 Unenriched 8.8. 8.. 8. 0. 0. 8. 7.8.8 Enriched.8. 9.88.. 0.8 0. 8..9.8 Unenriched.. 8..89 8.9 0..0 7.0.8 0.89 Enriched. 7..98.9 7. 0. 0.87 9.. 0. The influence of oxidation on the moisture-holding capacity of coal was studied in []. Zasyad ko bituminous coal (Donetsk Basin), crushed until it consists entirely of the < mm class, was oxidized in a drying chamber at 0 C, with free access of atmospheric oxygen. The 0 C temperature was chosen on the basis of the results in [ ]. In the course of the experiment, the coal was constantly mixed so as to ensure uniform oxidation. At fixed inter-vals, coal samples were taken for measurement of the oxidation index Δt. With C variation in Δt, samples were taken for proximate analysis (A d, V daf ) and determination of the moisture-holding capacity Wmax and the degree of oxidation d0. Table presents the variation in Wmax on oxidation. 0 Pet Coal (07); 9(): 0-0 ISSN 7-707 an open access journal
Table. Variation in coal properties during its oxidation Oxidation time, h Proximate analysis, % Moistureholdingcapacity, % Coal oxidation (Ukrainian State Standard DSTU 7:0 A d S d t V daf W max Δt, С d 0, % 0 7..8.. 9. 7 7..87 0..7. 08 7..87..9 7.9 80..88..0 0 9.. Results and discussion The error in determining the moisture-holding capacity is 0. %, according to ISO 08:7. Therefore, in the range.7. %, the ash content of the sample has no significant influence on the moisture-holding capacity. Likewise, the chemical composition of the ash has no influence, within the ranges Bb =. 7.8 and Ib = 0.98.8. On the basis of Table, we may conclude that increase in oxidation of the coal is associated with increase in its moisture-holding capacity. In Figs. and, we plot the moisture-holding capacity against Δt and d0. Analysis of Table and Figs. and indicates that, although oxidation of the coal increases the moisture-holding capacity, the increase is smaller than the error in determining the oxidation (0. %). The oxidation of practically 0 % of the coal s organic mass increases the moisture-holding capacity by no more than 0. %. However, despite the results, we believe it is necessary to uphold the requirement in ISO 08:7 the moisture-holding capacity must be deterd for a freshly prepared coal sample. In the present work, we have developed formulas for predicting the moisture-holding capacity Wmax of coal from Ukraine, Russia, the United States, Canada, Australia and Poland based on data for the sample in []. We have calculated pair correlation coefficients between the coal properties and the moistureholding capacity of the coal. The significance of the correlations is verified by comparing the absolute magnitude of the product r n with its critical value H for specified reliability P of the conclusion []. With P = 0.999, the critical value H for samples is.8. Table. present the correlation coefficients for each pair of variables. Comparison of the actual values with the tabular values indicates that, with P = 0.999, Wmax is correlated with W a, V daf, R0, C daf, ca, fa, Car, and δ. In Figs., we plot the moisture-holding capacity as a function of the other properties of the coal. Analysis indicates that these relationships are primarily quadratic. Table. Pair correlation coefficients r and r n for the moisture-holding capacity and other variables Coefficients W a V daf R o Vt FC C daf O daf d Q daf s са r 0,90 0,9-0,79 0,00-0,0-0,7 0,770-0,8-0,7 r n 7,,0,70 0,7 0,,7,0,08,09 Coefficients f a С аr δ r -0,7-0,8-0, r n,,0,079 Table presents Eqs. () () and statistical estimates of their validity. Analysis shows that satisfactory prediction of the moisture-holding capacity (with the permissible discrepancy σ 0. %) is possible by means of W a, R0, Od daf and Qs daf : specifically, σ = 0., 0.9, 0., and 0. %, respectively. It is expedient to predict Wmax on the basis of Eq. (), since the analytical moisture content in the fuel depends on the temperature and the relative air humidity within the laboratory [7], while the oxygen content in the coal s organic mass is not deterd at coke plants. For power-plant laboratories where the heat of combustion is deterd, the moisture-holding capacity may be deterd with high precision from on the basis of Eq. (8). 0 Pet Coal (07); 9(): 0-0 ISSN 7-707 an open access journal
Table. Formulae and corresponding statistical characteristics Eq. Formulae Statistical characteristics r D,% σ, % W max = 0. (W a ) +0.9 W a +.9 0.9 88. 0. W max = 0.0 (V daf ) 0.779 V daf + 9.70 0.80. 0.0 W max = 7. (R 0 ) -8. R 0 +.987 0.8 7. 0.9 W max = 0.08 (C daf ).00 C daf + 8.97 0.8 7. 0. 7 W max = 0. (O d daf ) -0.7 O d daf +. 0.87 7. 0. 8 W max = 0. (Q s daf ) -9.7 Q s daf + 8.7 0.90 80. 0. 9 W max = 9. (ca). ca. 0.70 8. 0.8 0 W max =.9 (f a ).9 f a +. 0.7. 0.8 W max = 0.0 (C ar ) 0.797 C ar +.9 0.77 9. 0.7 W max = 0. (δ) 7.9 δ + 8.8 0.7. 0.0,,9,8,7, 7 8 9 0 Δt, 0 C,,9,8,7, Fig.. Relation between W max and Δt 0 0 0 d 0, % Fig.. Relation between W max and d 0 0 Pet Coal (07); 9(): 0-0 ISSN 7-707 an open access journal
0 0,,, W a, % Fig.. Relation between W max and W a 0 0 0 V daf, % Fig.. Relation between W max and V daf 7 0, 0,8,,, R 0, % Fig.. Relation between W max and R 0 0 Pet Coal (07); 9(): 0-0 ISSN 7-707 an open access journal
7 8 8 8 88 90 C daf, % Fig.. Relation between W max and C daf 7 7 8 9 0 O d daf, % Fig.7. Relation between W max and O d daf 7 7 Q s daf Fig.8. Relation between W max and Q s daf 07 Pet Coal (07); 9(): 0-0 ISSN 7-707 an open access journal
0,80 0,700 0,70 0,70 0,70 0,780 0,800 0,80 са Fig.9. Relation between W max and ca 0,00 0,0 f a 0,700 0,70 Fig.0. Relation between W max and f a Wmax, % 0,00,00 0,00,00 0,00,00 Car % Fig.. Relation between W max and C аr 08 Pet Coal (07); 9(): 0-0 ISSN 7-707 an open access journal
. Conclusions Fig.. Relation between W max and δ The moisture-holding capacity of metamorphically distinct coals does not depend on their ash content (in the range.7. %) nor on the chemical composition of the ash, expressed by the basicity index Bb (in the range. 7.8) and the base/acid ratio Ib (in the range 0.98.8). Although the oxidation of coal increases the moisture-holding capacity, this change is less than the error in its determination (0. %). The oxidation of practically 0 % of the coal s organic mass increases the moisture-holding capacity by no more than 0. %. Analysis of samples of coal concentrates from Ukraine, Russia, the United States, Canada, Australia and Poland) currently employed at Ukrainian coke plants indicates that the prediction of the moisture-holding capacity of coal may expediently be based on R0 and the gross calorific value Qs daf deterd, respectively, in plant laboratories and in power-station laboratories. Symbols W max moisture-holding capacity, %; Q daf s gross calorific value in the dry, ash-free state, MJ/kg; R 0 mean vitrinite reflection coefficient, %; A d ash content of coal, %; V daf volatile matter, %; W a moisture in the analysis sample, %; FC sum of fusinized components, %; B b basicity index; I b base/acid ratio; Δt oxidation index, C; d 0 degree of oxidation, %; D determination coefficient, %; r correlation coefficient; σ mean square deviation, MJ/kg. Fe O, CaO, MgO, Na O, K O, Al O, and SiO are the mass contents of the corresponding oxides in the ash, %. References,000 8,000 0,000 [] Miroshnichenko DV, Kaftan YuS, Desna NA and Sytnik AV. Oxidation of bituminous coal.. Expansion pressure, Coke Chem., 0; vol. 8(0): 7 8. [] Miroshnichenko DV, Drozdnik ID, Kaftan YuS and Desna NA. Oxidation of Pokrovskoe coal in laboratory and natural conditions.. Kinetics of oxidation and technological properties, Coke Chem., 0; 8(): 79 87. [] Miroshnichenko DV, Desna NA and Kaftan YuS. Oxidation of coal in industrial conditions.. Coal temperature in heap storage, Coke Chem., 0; 8(): 8. [] Desna NA, Miroshnichenko DV. Oxidized coal in coking: a review, Coke Chem., 0; (): 9. δ 09 Pet Coal (07); 9(): 0-0 ISSN 7-707 an open access journal
[] Balaeva YaS, Miroshnichenko DV and Kaftan YuS. Predicting the classification characteristics of coal. Part. The gross calorific value in the wet ash-free state, Coke Chem., 0; 8(9): 8. [] Rumshinskii AZ. Mathematical Analysis of Experimental Results: A. Handbook, Moscow: Nauka, 97. [7] Avgushevich IV, Bronovets TM, olovin S. Standard Methods for Testing Coals. Coal Classification, Moscow: NTK Trek, 008. To whom correspondence should be addressed: Tel.: + 8 0 7 700--8, +8 0 0 8-8-8 E-mail address: dvmir79@gmail.com 0 Pet Coal (07); 9(): 0-0 ISSN 7-707 an open access journal