356
Energy & Fuels 1990,4, 356-360
Supercritical Fluid Extraction of Mild Pyrolysis Products from Western Canadian Coals Masahiro Shishidot and Nosa 0. Egiebor* Department of Mining, Metallurgical and Petroleum Engineering, University of Alberta, Edmonton, Alberta, Canada T6G 2G6 Received February 2, 1990. Revised Manuscript Received April 10, 1990
Three Western Canadian subbituminous and one medium-volatile bituminous coals were subjected to mild pyrolysis under nitrogen at 653 K, 0.1 MPa, followed by supercritical toluene extraction of the pyrolysis products at the same temperature and 20 MPa. The results show that the total conversion and tar yield are linearly correlated with the H/C ratios of the feed coal. The amounts of pyrolysis tars produced with supercritical toluene extraction were found to be significantly higher than the previously reported values for Western Canadian coals under conventional and flash pyrolysis reactions at 773-873 K. Furthermore, it was observed that an increase in pyrolysis hold time, before supercritical toluene extraction, led to a decrease in the total conversion and tar yield. This observation suggests that diffusion limitations leading to secondary polymerization and dealkylation reactions are important factors mitigating against the production of higher amounts of liquid products during conventional coal pyrolysis. Analysis of the extracts, using the Brown-Ladner structural parameters, also show that the degree of aromatic ring substitution decreases with increasing pyrolysis hold time.
Introduction In an attempt to attain a more efficient use of coals, pyrolytic preprocessing to generate liquid hydrocarbons and the subsequent combustion of the residual chars have been subjects of research and industrial interests for several years.'V2 It has been reported3 that as much as 0.2 m3 of crude oils per metric ton of coal could be obtained by pyrolytic preprocessing and that the residual chars, which can possess higher heating values than their precursors, could be burned with existing coal-fired burners without major modifications. Despite intensive laboratory studies of conventional and flash pyrolysis of several technically important questions and controversies remain unresolved. Many of these controversies arise from disparate views on the phenomenological sequence of coal devolatilizationand the important physico-chemicalparameters that determine the response of various ranks of coal to pyrolysis in terms of tar yields. Some investigators have reported that, within the limits of experimental error, the chemical kinetic parameters that describe tar evolution from a wide range of coals do not vary with coal type.8 Others have noted that the underlying mechanism of tar formation, evolution, and secondary reaction vary with coal rank*" and that the primary tars are similar to those present in the parent coal.12 Recently, Freihaut et al.13 reported that, for any given extent of tar evolution, the lower the rank of coal, the more dissimilar the evolved tars are to the parent coal. They also concluded that heat- and mass-transport factors play a significant role in the heavy hydrocarbon evolution process during pyrolysis. Others have also reported the significant role of transport phenomena and diffusion limitations on the tar-generating efficiency of coal during pyr~lysis.'~J~ The formation of a glasslike "melt" as an intermediate phase during pyrolysis of a bituminous coal and the observed changes in tar yield with pressure have led to the conclusion that mass-transport phenomena are very important factors in the pyrolysis preprocessing of ~0a1.~~-~~ 'Present address: Department of Chemical Engineering, Yamagata University, 4-3-16, Jyonan, Yonezawa, Yamagata 992, Japan.
While it is likely that a variety of factors contribute to the response of coal to tar generation during pyrolysis, it is conceivable that one or two of the contributing factors such as diffusion, coal structure, and chemical composition may predominate with specific coals depending on the rank and geological history. For example, although flash pyrolysis have been reported to furnish more volatile matter than is obtainable from the classical Fischer and Gray-King assays,17a recent study of Western Canadian subbituminous coals by Takeuchi and Berkowitzla clearly indicated the contrary. It was concluded from their study that the minimal tar yields from flash pyrolysis of Western Canadian coals, which are characterized by high oxygen content, are a consequence of pyrolytic reactions between oxygen and labile hydrogen in these coals. However, the effects of other parameters such as diffusion limitations, secondary reactions, and H/C ratios were not investigated on these Western Canadian coals. Since the flash pyrolysis studies were conducted at relatively high temperatures, i.e., 773-873 K, the primary carbon-carbon bond cleavage reactions are quickly followed by secondary repolymerization, coking, and thermal decomposition. These (1) Rau, E.; Robertson, J. A. Fuel 1966, 45, 73. (2)Mentser, M.;O'Donnell, H. J.; Ergun, S. Prepr. Pap.-Am. Chem. Soc., Diu. Fuel Chem. 1970, 14 (5), 94. (3)McMath, H.G.;Lumpkin, R. E.; Sas, A. Proceedings of the 66th Annual Meeting, AIChE, Philadelphia, USA, November 1973. ( 4 ) Edwards, J. H.; Smith, I. W. Fuel 1980, 59, 674. (5) Stangeby, P. C.; Sears, P. L. Fuel 1981,60, 131. (6)Desypris, J.; Murdoch, P.; Williams, A. Fuel 1982, 61, 807. (7)Arendt, P.; van Heek, K. H. Fuel 1981, 60, 779. (8)Solomon, P. R.; Hamblen, D. G . h o g . Energy Combust. Sci. 1983, 9. 323. (9) Doolan, K. R.; Mackie, J. C.; Tyler, R. J. Fuel 1987, 66,572. (10)Tyler, R. J. Fuel 1980, 59,218. (11)Calkins, W.H.; Tyler, R. J. Fuel 1986,63, 1119. (12)Orning, A. A.; Grieter, B. Fuel 1956, 35, 381. (13)Freihaut, J. D.;Proscia, W. M.; Seery, D. J. Energy Fuels 1989, 3, 693. (14)Klose, W.;Lent, M. Fuel 1984,64, 198. (15)Fong, W.S.;Peters, W. A.; Howard, J. B. Fuel 1986, 65,251. (16)Unger, P.E.; Suuberg, E. M. Fuel 1984, 63, 606. (17)Selvig, W.A.;Ode, W. H. US.Bur. Mines Bull. 1957, No. 571. (18)Takeuchi, M.;Berkowitz, N. Fuel 1989, 68,1311.
0~~~-0624/90/2504-0356$02.50/0 0 1990 American Chemical Society
Pyrolysis of Western Canadian Coals
coal Highvale (HV) Drumheller (DH) South Tofield (ST) Cardinal River (CR)
Energy & Fuels, Vol. 4, No. 4, 1990 357
Table I. Proximate and Ultimate Analvsis Data for Coals proximate analysis, wt % db ultimate analysis, wt % daf VM FC ash C H N S
Odm -.
36.8 38.5 41.3 19.5
23.2 23.0 22.3 7.1
52.8 52.6 42.5 62.3
10.4 8.9 16.2 18.2
secondary reactions are enhanced in the presence of intraphase and interphase diffusion limitations leading to a reduction in tar yields and an increase in the production of gases. The work reported here was aimed at studying the responses of some Western Canadian coals to tar generation during mild pyrolysis, followed by supercritical toluene extraction. The supercritical extraction aspect of the work was incorporated in order to aid the removal of the pyrolyzed product from the reacting coal mass, thereby reducing the effect of diffusion limitations and secondary reactions. In addition, the effect of pyrolysis hold time, before supercritical fluid extraction, on total conversion and tar yields was also studied. Other objectives of the study included an investigation of the effect of the H/C ratios of the feed coal on the extraction yield and the influence of the pyrolysis hold time on the Brown-Ladner19’20structural parameters of the liquid extracts. The study was based on the premise that if the liquid products formed at mild pyrolytic conditions can be recovered more effectively, the quantity and properties of these products can be more easily controlled and enhanced.
Experimental Section The four coals studied were obtained from the Alberta Research Council’s Sample Bank and are representative of Western Canadian subbituminous and bituminous coals. Three of the coals, Drumheller (DH), and South Tofield (ST), were Highvale (HV), of subbituminous B/C rank and are generally similar in petrographic composition. The fourth sample, Cardinal River (CR), was a medium-volatile bituminous coal. The proximate and ultimate analysis data for the four coals are presented in Table 1. Bulk samples of these coals (2-4 kg) were coarsely crushed, riffled to provide a set of 250-300-g aliquots, saturated with moisture, and stored in sealed polythene bags a t 269 K until required. Approximate amounts of all samples were further comminuted to -14 28 Tyler mesh sizes and dried a t 383 K in nitrogen immediately before use. The reactor system consisted of a semibatch type of a supercritical fluid extraction apparatus as schematically illustrated in Figure 1. The various components of the reactor setup are numbered and identified in the figure legend, and the symbol TC refers to the furnace temperature controller. The reactor consisted of a 10.5-cm-long stainless-steel tube, 10-mm id., 2-mm wall thickness, and a total volume of about 8 cm3. The reaction temperature was measured by means of a k-type thermocouple attached to the external surface of the tubing bomb. Preliminary experiments had shown that the external wall temperature of the reactor tubing was within f 2 K of the internal reaction temperature. A heating rate of 6 K/min was employed throughout. Pyrolysis runs were carried out under flowing nitrogen gas a t a reaction temperature of 653 K and 0.1 MPa pressure, before supercritical toluene was fed into the reactor a t the same temperature and 20 MPa pressure. The critical temperature and pressure for toluene are 592 K and 4.2 MPa, respectively. Approximately 4 g of coal was charged into the reactor for each run, and the solvent flow rate during supercritical extraction was about 3-4 mL/min in the liquid state. The pyrolysis products are supercritical toluene extracts were recovered together in a con-
+
(19) Brown, J. K.; Ladner, W. R. Fuel 1960, 39, 87. (20) Brown, J. K.; Ladner, W. R.; Sheppard, N. Fuel 1960, 39, 79.
70.8 69.9 70.6 84.7
4.8 4.9 4.8 6.7
1.0 1.6 1.4 1.5
0.2 0.6 0.9
~~
ASTMRank subbitum B subbitum B subbitum C mv bitum
6 Preheater 7 Reactor 3 Back pressure regulator 8 Metering valve 4 Pressure gauge 9 Cooler 5 Furnace 10 Sampler 1 Solvent reservoir
2 Pump
Figure 1. Schematic diagram of experimental assembly.
-
40
-
I
I
1
*
/
rl( 73
30-
?i
L-I
20
, 10 -
0‘
0.6
I
0.7
I
0. E
0.9 I
10 1
HIC of coal Figure 2. Plot of conversion and yield against H / C ratios of parent coal (symbols: circles, this work; squares, Japanese study).
denser kept at about 278 K. The extracts were recovered by distilling off the solvent a t temperatures slightly above the boiling point of toluene. The hydrocarbon gases and moisture produced were not analyzed. The extraction conversion and yield were defined and determined by the following equations: extraction conversion (wt %) = sample wt (daf) - residue wt (daf) x 100 sample w t (daf) extraction yield (wt %) =
tar extract wt (daf) x 100 sample wt (daf)
The difference between the extraction conversion and extraction yield was estimated as the total gases, and moisture produced, and referred to as “gases”. In order to establish the reproducibility of the extraction results, duplicate runs were carried out with the four coal samples studied. The results were within *2% of the reported values. As an illustration, the extraction yield and conversions obtained for the duplicate runs with Highvale (HV) and Drumheller (DH) coals are reported in Figure 2. The variation in the results of the duplicate runs with the other two coals was insignificant. The extracts and tars were characterized by ‘HNMR spectroscopy on a 200-MHz Bruker (WH-200) spectrometer using
Shishido and Egiebor
358 Energy & Fuels, Vol. 4, No. 4, 1990 CDC13 as solvent and tetramethylsilane (TMS) as an internal standard. The bond assignments, which were used to estimate the fraction of protons in the various bonding environments, have been reported previously.21*n The data from the proton NMR analysis were used to estimate some structural parameters, viz., the aromaticity cf.), the degree of aromatic ring substitution (u), and the aromatic hydrogen to carbon ratios (H,/C,) according to the method of Brown and Ladner.lgsm In addition to the above-mentioned experiments, two blank runs were carried out to investigate the possible conversion of toluene into biphenyls and other aromatic products under supercritical conditions. One of the blank experiments was done by continuously pumping toluene through the empty reactor at 653 K and 20 MPa for 1 h. The second blank run was performed with the reactor charged with 5 g of -28 60 mesh size coal-ash particles. In both cases, the toluene leaving the reactor was condensed and analyzed by use of a H P 5830A gas chromatograph (GC) equipped with a bonded phase, fused-silica DB-1 capillary column (0.25 mm X 30 m) and a flame ionization detector. All GC analyses were done with hydrogen as carrier gas and nitrogen as makeup gas. The results of the GC analyses showed that, in both blank runs, less than 0.5 wt % of the total toluene feed was converted to benzene and p-xylene. No biphenyls were found in the products. On the basis of these results, it was assumed that no significant toluene conversion to biphenyls and other aromatic compounds occurred under the experimental conditions used in this study. For comparison, the results of a previous Japanese study with Westem Canadian coals,= using similar pyrolysis and supercritical extraction conditions are reported. The coals studied in Japan were Highvale, HV (subbituminous B); Coal Valley, CV (hvB bituminous); Vesta, VS (subbituminous B); and Obed Marsh, OM (hvC bituminous).
+
Results and Discussion
Conversion and Product Yield. The extraction yields and conversions obtained for the four coals studied here are plotted against the H/C ratios of the parent coals in Figure 2. The circles represent the results of this study while the square characters represent the results of a previous Japanese study with Western Canadian using similar pyrolysis and supercritical extraction conditions. The extraction and pyrolysis pattern employed in both studies involved heating the coal samples under a stream of nitrogen gas until the reaction temperature of 653 K was reached and immediately feeding toluene continuously at 20 MPa for an additional 1.5 h before the run was terminated. The data of Figure 2 indicate a good correlation between the extraction yield and conversion and the H/C ratios of the coal. This observation suggests that, in the pyrolysis and supercritical extraction with toluene, the yield of extracts depends on the average chemical composition of coal. It is noteworthy that two samples of the same coal, Highvale, with different values of H/C ratios gave different extraction conversions that were well correlated with the H/C ratios. The two Highvale coal samples were obtained from different locations in the mine although from the same seam. Furthermore, the duplicate extraction yield and conversion results for Highvale (HV) and Drumheller (DH) coal samples, obtained in this study, are also indicated in Figure 2. The total conversions for all the Western Canadian coals studied here ranged from 23 to 35 wt %, while the tar yield ranged from 10 to 25 wt %. When compared to the (21) Egiebor, N. 0.;Jacobson, J. M.; Gray, M. R. Fuel Sci. Technol. Int. 1989, 7 (3), 251. ( 2 2 ) Chamberlain, N. F. The Practice of NMR Spectroscopy; Plenum Press: New York, 1974. (23) Shishido, M. Unpublished work.
Gases 1 4,6
Extracts
301
0
4OwtY.daf
20
Heat up (6Klmin)
I 20MPa
-
--
OlMPa lhr
15hr
b-4 Heal up(6Klmin)
I1
116.81
276
0 lMPa
k+ Heat up
I11 20MPa
-----1.5hr
15hr
N : Nitrogen T : Toluene
-
113511351 0
0 lMPa Heal Hup
20
270
40 wt'ledaf
IV
wl 0
Heal up
20
250
40 wt'lodaf
v
Figure 3. Pyrolysis, extraction patterns, and conversion data for Drumheller
(DH)coal.
maximum conversion and yield values of 22 and 7 w t 3'% respectively, reported in a recent study on a suit of similar Western Canadian coals under flash pyrolysis,18it is clear that the extraction of the pyrolysis products with supercritical fluid result in a significant enhancement of the conversion and tar yield. The amounts of gases and moisture produced in this study ranged from 10 to 13 wt %, which are smaller than the 15-18 wt % reported by Takeuchi and Berkowitz18 under flash pyrolysis a t 823-873 K. The lower amounts of gases observed in this study are due to the mild pyrolytic temperatures used. However, the higher total conversions are attributable to the improved removal efficiency of the pyrolysis tars by supercritical toluene and the consequent reduction in diffusion limitations and secondary polymerization reactions. We believe that the low conversion values reported earlier from Western Canadian coals are due to the poor recovery efficiency of the pyrolysis products, resulting from diffusion limitations and secondary reactions.
Energy & Fuels, Vol. 4, No. 4, 1990 359
Pyrolysis of Western Canadian Coals
coal DH DH DH
DH CR HV
ST
Table 11. Elemental Analysis and Hydrogen Content Distribution for Tar Extracts extraction pattern' Cb Hb Nb odiffb H*, I1 79.2 6.8 1.3 12.7 0.56 1.3 11.7 0.49 7.1 111 79.9 0.45 7.0 1.2 11.5 IV 80.3 0.42 6.9 1.4 12.0 79.7 v 0.28 1.1 5.6 87.6 5.7 I1 0.39 6.5 0.8 11.5 I1 81.2 0.47 1.1 12.7 79.1 7.1 I1
H*, 0.23 0.30 0.33 0.33 0.33 0.34 0.29
~
H*, 0.21 0.20 0.22 0.25 0.39 0.27 0.24
OExtraction patterns correspond to those shown in Figure 3. * w t % daf.
In order to investigate the effects of increased hold time and possible secondary reactions on the product yield, a series of experiments was conducted with one of the coal samples, Drumheller (DH), using different pyrolysis and extraction patterns. Figure 3 shows the various extraction patterns employed and the conversion results. In pattern I, the extracting fluid was fed at 20 MPa throughout the heating sequence until the extraction temperature was reached and continued for an additional 1.5 h before the reaction was terminated. In pattern 11, nitrogen was passed through the reactor during the heat-up period at 0.1 MPa and immediatelyreplaced by supercritical toluene when the reaction temperature of 653 K was achieved. This run represented a hold time of 0 min. The pyrolysis hold time is defined here as the time difference between the achievement of the reaction temperature, under nitrogen gas at 0.1 MPa, and the commencement of supercritical toluene extraction. Patterns 11-V were carried out with increasing pyrolysis hold time from 10 to 90 min. The data presented in Figure 3 show that pattern I gave the highest total conversion of 30.1 wt %. This pattern represents a reaction regime where the pyrolysis products from the coal are immediately extracted from the reacting mass once they are formed. The results from patterns 11-V indicate a gradual decrease in the total conversion and tar yield and a significant increase in the production of gases with increasing pyrolysis hold time. It is clear from these results that diffusion limitations and secondary polymerization and gas-forming reactions play a major role during coal pyrolysis. The observed significant increases in gases produced with increasing hold time suggest that secondary dealkylation reactions occur to a great extent even under mild pyrolysis conditions. These reactions will be accelerated under conventional and flash pyrolysis conditions which are normally carried out at 773-873 K. These phenomena may explain the low conversion yields previously reported for Western Canadian coals during pyrolysis.18 Extract Characterization. To obtain some information about the alterations in the chemical structure of the tars, the Brown-Ladner structural parameters of the extracts were determined from their proton NMR spectra and the ultimate analysis data. This method, published e l s e ~ h e r e , ' ~involves ,~ the conversion of the hydrogen distribution data to the analysis of carbon structure. The data in Table I1 show the fractions of protons in a-carbons (H*,), other aliphatic carbons (H*,), and aromatic carbons (H*,) for extracts obtained from the four coals studied. For DH coal, the content of hydrogen bonded to a-carbons shows a decrease from 0.56 to 0.42 while the content of hydrogen in other aliphatic groups show an increase from 0.23 to 0.33, with an increase in pyrolysis hold time from 0 to 90 min. This trend suggests that dealkylation of substituted aromatic structures occurs with increasing hold time. The content of hydrogen attached to aromatic carbons does not show any definitive trend. In a comparison of the extracts from the four coals recovered using similar extraction patterns, Cardinal River (CR) coal shows
0.9
HaR / c a ~
0.5
I
I
I
I
I
I
I
0.5 I 0-0-0
0.4 t11 In
0.3L)
' 20'
I
0 V
fa .-
IV
I 40 I I 60 I Hold time [ m i n l
'
80 I
I
100 I
Figure 4. Composite plot of aromatic H,/C, ratios, aromatic ring substitution ( a ) ,and apparent aromaticity (fa) against hold time for extracts from DH coal.
the lowest content of hydrogen attached to a-carbons and the highest aromatic hydrogen content. Figure 4 presents a composite plot of aromatic H/C ratios, degree of aromatic substitution (a), and the apparent aromaticity (fa)vs the pyrolysis hold time for extracts obtained from Drumheller (DH) coal. The Greek symbols correspond to the extraction patterns shown in Figure 3. The data in Figure 4 indicate a significant drop in aromatic H,/C, ratios with hold time from 0 to 10 min but remain relatively constant thereafter. The degree of aromatic ring substitution shows a continuous decrease with hold time throughout, suggesting increasing levels of dealkylation reactions. Since the apparent aromaticity cf,) remains relatively constant, the observed decrease in aromatic hydrogen to carbon ratios is attributable to aromatic nuclei condensation and polymerization during pyrolysis. These reactions will be enhanced under more severe pyrolysis conditions, leading to a significant reduction in the amount of tars produced.
Conclusions From the results presented here, the following conclusions can be drawn: 1. A significant amount of coal decomposes at 653 K, which is relatively mild in comparison to the conventional and flash pyrolysis conditions. 2. Supercritical fluid extraction is an effective means for the recovery of liquid pyrolytic products from coal. 3. The conversion of coal during pyrolysis depends to a great extent on the average chemical composition, particularly the H/C ratios. 4. Mass transfer and diffusion limitations are important factors that can influence the amounts of products recovered during pyrolysis. Even under mild pyrolysis conditions, secondary reactions involving dealkylation and aromatic nuclei condensation and polymerization occur and could mitigate against the production of valuable liquids. 5. The presence of diffusion limitations and the occurrence of deleterious secondary reactions, during conventional and flash pyrolysis, are mainly responsible for the low conversions and tar yield previously reported for Western Canadian coals. Under mild pyrolysis and su-
360
Energy & Fuels 1990,4, 360-364
percritical fluid extraction, Western Canadian coals are promising candidates for pyrolytic preprocessing of coal destined for combustion and electrical energy generation.
Acknowledgment. Financial support for this work was provided by the Natural Sciences and Engineering Re-
search Council (NSERC) of Canada and is gratefully acknowledged. We are also grateful to the Canada-Japan Joint Academic Research Program on the Efficient Use of Coal for sponsoring M.S. Registry No. Toluene, 108-88-3.
Estimation of Ash Softening Temperatures Using Cross Terms and Partial Factor Analysis William G. Lloyd,* John T. Riley, Mark A. Risen, Scott R. Gilleland, and Rick L. Tibbitts Department of Chemistry and Center for Coal Science, Western Kentucky University, Bowling Green, Kentucky 42101 Received February 5, 1990. Revised Manuscript Received April 20, 1990
The relationship between elemental composition of coal ash and ash softening temperature has been studied, using a set of 70 ashes prepared from blends of seven source coals. Simple multiple linear regression analysis is of limited value. The inclusion of second-order cross terms, representing acid-base and other metathetic reactions, markedly improves the precision of predictive regressions. Excessive collinearity, notably among five major components of these coal ashes, limits the combinations of regressor terms usable in a predictive equation. A strategy for avoiding collinearity problems by means of partial factor analysis is illustrated. Best estimates of ash softening temperature show root mean square errors of 45 O F (25 K) or less.
Introduction Most coal-fired boilers are designed for the continuous removal of bottom ash as a dry solid. Others are engineered to burn at higher temperatures, with the removal of slagged ash as a viscous fluid. None, however, can operate in both modes. Since ash softening temperatures are commonly found over a range of 900 O F (500 K), it is of great importance to the power plant operator to know something about the ash softening temperature of his boiler feed before the coal is fed to the boiler. The experimental determination of ash fusion temperatures, for example, by ASTM Procedure D 1857 (IS0 540), provides a useful laboratory measurement closely related to fireside slagging potential.' This determination requires both skill and time. The ASTM procedure requires that the coal, after sampling, be prepared in accordance with Method D 20132and that it be ashed to two stages (in air and again under pure oxygen). The resulting ash is then compounded with a dextrin solution, the paste thus formed is pressed into cone molds, and the resulting ash cones are dried and then fired to remove the dextrin binder. All of these steps must be carried out before starting the actual determination of ash fusion temperat u r e ~ .In ~ the hands of experienced and careful workers (1)Gluskoter, H.J.; Shimp, N. F.; Ruch, R. R. Coal Analysis, Trace Elements, and Mineral Matter. In Chemistry of Coal Utilization;Elliott, M. A., Ed.; W h y : New York, 1981;2nd suppl. vol., pp 394-395. (2) Method of Preparing Coal Samples for Analysis; Method D 2013; Annual Book of ASTM Standards, Vol. 5.05; American Society for Testing and Materials: Philadelphia, PA (published annually). (3) Test Method for Fusibility of Coal and Coke Ash; Method D 1857; in ref 2.
this procedure provides fusion temperatures which are repeatable and which correlate well with boiler'performance. From the viewpoint of the power plant operator, however, there are two big problems with reliance upon the determination of ash fusion temperatures: 1. If the above laboratory steps are followed faithfully, an ash fusion temperature determination will require a t least 3 days. The plant operator often needs to know the answer within hours, or even within tens of minutes. 2. Most power plants burn blended coals. The ash fusion temperatures of ashes from blended coals are not even roughly approximated by interpolations from the ash fusion temperatures of the unblended source coals.4* When a desired property, such as ash softening temperature, can be correlated with a more easily measured property, such as a specific ash component, regression analysis can provide a predictive equation that may be useful. For example, for the 70-ash database of this study Tso, is significantly correlated with the TiOpcontent of the ash:
?'son
(OF)
= 1652
+ 520.6[% Ti02]
(1)
For this regression the correlation coefficient R = 0.67. R2 (0.45) is the fraction of the variation in values of T S O ~ explained by the regression, the balance of variation being attributed to random error. (4)Riley, J. T.; Gilleland, S. R.; Forsythe, R. F.; Graham, H. D., Jr.; Hayes, F. J. Proc. Conj.-Znt. Coal Test. Conj. 1989, 7, 32-38. (5)Gray, V. R.Fuel 1987, 66, 1230. (6) Huffman, G. P.; Huggins, F. E.; Dunmyre, G. R. Fuel 1981,60,585.
0887-0624/90/2504-0360$02.5O/O 0 1990 American Chemical Society
