- Email: [email protected]
Flash hydrogenation of coal. 3. A sample of US coals
Flash hydrogenation of coal. 3. A sample of US coals Wei-Yin
Chen,
Albert0
I. LaCava and Robert
A. Graff
The Clean Fuels Institute, The City College, of The City University York, NY 10031, USA (Received 6 February 1981; revised 9 August 1982)
of New
York, New
The susceptibility of a group of US coals to the production of light gaseous and liquid hydrocarbons during flash hydrogenation is examined. Eight coals ranging from lignite to high-volatile A bituminous and representing five provinces, have been flash heated in 101.3 MPa of flowing hydrogen using a bench scale reactor. A 0.6 s gas phase residence time was provided to hydrocrack the vapour products. Temperatures ranged from 750 to 85o”C, where maximum yields of ethane and BTX (benzene+toluene +xylene) are found. The carbon conversion decreased with increasing rank at fixed reaction conditions. Methane yields are highest for lignite. Peak ethane yields range from 6.4 to SE&carbon conversion. BTX yields have a shallow maximum at intermediate ranks, decreasing towards high and low rank coals. Total liquid yields range from 14 to 43%. Although a definite variation of yield with rank is evident, the trends, especially total liquid yields, are attended by considerable scatter. Rank is not the only, and indeed may not be the most significant variable in determining the yield of individual species in flash hydrogenation. To establish the significant variables a stepwise regression procedure was applied to the experimental data using information from the elemental, proximate and petrographic compositions of the coals as independent variables. Two variables are adequate in all cases to correlate species yield and coal properties. Exinite appears to be capable of increasing the amount of liquid obtained from other macerals. (Keywords:
coal; flash hydrogenation;
US)
Flash hydrogenation of coal has potential as a process for the production of synthetic fuels, namely, substitute natural gas, light aromatic liquids (to be used as a fuel or as petrochemical feedstock) and low sulphur char. The process is based on the thermal reactions of coal and the volatiles generated by rapid heating under hydrogen at high pressure. Rapid heating of coal enhances the yield of light species.’ Early work on rapid-heating coal devolatilization in inert or hydrogen atmospheres and the effect of operating conditions on the total coal weight loss has been reviewed.2 The effect of the operating variables, including gas phase residence time for the upgrading of volatiles, on the total coal weight loss and the yield of individual products (methane, ethane, carbon oxides and single ring aromatics) has been reported for the flash hydrogenation of Illinois No. 6 coal in small scale, captive sample equipment. 3*4 Dilute phase entrained bed reactors have been built and operated by Brookhaven National Laboratories,’ Cities Service,6 Rockwell International’ and the Institute of Gas Technology.* However, because of plugging problems, studies in these reactors have been largely restricted to lignites and subbituminous coals. Only three bituminous coals have been tested by Rockwell,’ at temperatures above 700°C. Cities Service’ has operated with low-temperature air preoxidized bituminous coal, Brookhaven’ and the Institute of Gas Technology’ with CaO pretreated bituminous coals, as well as with mixtures of bituminous coals with sand and with char. 0016~2361/83/01005~06$3.00 01983 Butterworth & Co. (Publishers) Ltd
56
FUEL,
1983,
Vol 62, January
Gray,’ in a study comparing the available hydropyrolysis data, concluded that the variability in reported yields was largely the result of differences in equipment used by various investigators. Mass transfer limitations were cited as a likely cause. This conclusion, however, was without foundation since little or no data were available on different coals run under identical conditions in the same equipment. The study reported in this Paper attempts to remedy this situation. Indeed, the extreme variability of coals, even those close in rank (as discussed below), suggests that the use of different coals is the most important reason for the inconsistent yields reported by different investigators. In view of the limited number of coals which have been studied under flash hydrogenation, in particular those using the same equipment, yield data for a sampling of US coals under identical conditions in a single apparatus were obtained. Eight coals, broadly representative of the US spectrum, were selected for study. The results described below show the range in performance to be expected from US coals under flash hydrogenation. Empirical correlations are presented and some inferences are drawn regarding the basic reasons for the observed variations. Practical considerations limited the number of different coals which could be tested in this study. A far larger group would be required to provide an adequate statistical sample of US coals. This must be noted, therefore, when viewing the results presented here.
Flash hydrogenation
EXPERIMENTAL Reactor
of coal: W.-Y.
Chen
et al.
between two quartz wool plugs, as shown in Figure 1, give identical results. In addition, the sample size can be increased to 20 mg without affecting the observed yields. In a second modification of the system the gas chromatograph has been replaced by a mass spectrometer for on-line analysis of products up to xylene. For those species determined by direct analysis the standard deviation has been calculated from the experimental data: methane 1.6 %, ethane 0.8 %, BTX 1.2 %, total carbon oxides 2.6x, char 4.1%. In the work reported here, heavy liquids are determined by difference with a standard deviation of 5.4%. Direct measurement of liquids by trapping has been carried out for Illinois No. 6 and Pittsburgh No. 8 coals. These measurements, which confirm the accuracy of liquids determined by difference, will be reported in a subsequent paper.” Yield values reported below are in all cases averages from several experiments.
system
The reactor used in this study was designed for flash heating of raw coal in flowing hydrogen at pressures up to 101.3 MPa. Reactions in the vapour phase play an important role in the product formation and the reactor system allows for the independent selection of vapour residence time. The reactor (Figure 1) is a 30.48 cm section of 0.63 cm (0.25 in) stainless steel tubing. A 10 to 20 mg sample of powdered coal ( - 325 mesh) is placed at a selected point in the tube and hydrogen at pressure continuously flows through the tube to downstream analytical equipment. A high current is passed through the tube wall to provide heating rates typically of 650°C per second. After reaching the preset temperature, a lower current is used to maintain the temperature for the duration of the run, usually 10 s. Quenching of vapour occurs at the right hand electric lead which, because of its large mass, remains at its initial temperature. The distance from the coal sample to this lead and the hydrogen flowrate are adjusted to provide the desired vapour residence time. Flash hydrogenation of the coal is followed by in situ combustion of residual char with oxygen. Carbon dioxide obtained in this step measures carbon in the residual char, and is added to the carbon contained in the species determined during hydrogenation to construct a carbon balance. Further details of the reactor system and its operation have been reported previously.3 Two modifications have been made. First, the procedure for depositing a 10 mg sample of ground coal as a thin ring on the inside wall of the reactor tube has been found to be unnecessary. Samples in the form of a layer of ground coal held in place
Coal samples
Eight coals were selected for this study from the coal bank of the Pennsylvania State University.* The coals (Tables 2 and 2) range from hvA bituminous coal having 85.15 wt % dmmf carbon to lignite with 71.86 wt % dmmf carbon and represent tive provinces. In addition, Figures 2 and 6 include data for two samples of Illinois No. 6 coal, one of Pittsburgh No. 8 and one of Texas lignite. Data for the first sample of Illinois No. 6(A) are taken from our previous paper.4 The composition of the second sample of Illinois No. 6(B) (taken on the same date from the same mine) and of the other two coals are listed in Table 3. To compare these four coals with others in the group, an estimate of dmmfcarbon is required. This has been made using the Parr formula” to estimate mineral matter content. To correct the carbon content for CO, evolved from mineral matter, it is assumed that 10 % of the mineral matter is carbonate. RESULTS For this study all coal samples hydrogenation in 101.3 MPa 10s. A residence time of 0.6s volatile products. Measurements
Thermocouple
vopour product residence zone 1
Figure
1
Table 1
Flash hydrogenation
Identification
were subjected to flash of pure hydrogen for was provided for the were conducted in the
I * The authors are grateful to Professor Peter Given for selecting these coals and to others at Penn State for making samples available.
I
reactor
and analysis of selected coals (wt% drnmf)a
Sample no.
Rank
Province
Aga
State
Moist
M.M. direct
c dmmf
0 dmmf
Dry
DAF
PSOC PSOC PSOC PSOC P6OC P6OC P$OC PSOC
HVA HVA HVA HVA HVC S.8it.A S.Bit.8 Lignite
Eastern Eastern Interior Rocky M. Interior Rocky M. Pacific North Gr.Plains
Carb. Carb. Carb. Crat. Carb. Cret. Tart. Tart.
PA AL IL UT IN WY WA ND
2.21 1.27 3.11 4.08 11.32 19.17
21.18 17.72 25.08 11.55 18.31 3.34
84.49 85.15 83.71 81.47 81.58 75.44
5.56 4.85 7.12 10.13 9.51 17.04
4.36 2.34 5.23 0.76 3.78 0.64
5.28 2.77 6.70 0.84 4.50 0.66
19.73
16.47
73.96
18.98
0.50
0.60
34.12
10.99
71.85
21.22 ----
0.65
326 270 284 314 280 248 240 8, 246
a Properties
of the coals from the Pennsylvania
State University
collection
S
__
0.72 .-
used in the present study
FUEL,
1983, Vol 62, January
57
Flash hydrogenation Table 2
Petrographic
Chen et al.
of coal: W.-Y. compositions
of selected coals (wt% dmmfja
PSOC Coal No.
Vitrinite
PseudoVitrinite
Fusinite
SemiFusinite
Massive Micrinite
Granular Micrinite
Exinite
Resinite
326 270 284 314 280 248 240 82 246
69.4 68.1 78.9 73.3 92.1 68.2 67.2 53.3
7.6 3.2 8.2 8.8 0.0 8.1 12.7 25.3
3.2 8.6 3.8 4.5 1.2 0.7 3.0 7.8
7.3 4.6 1.6 4.7 1.1 11.8 4.0 3.8
2.0 0.6 0.3 2.1 0.0 0.0 2.5 0.7
6.0 9.0 4.4 0.7 2.7 9.5 4.1 4.9
4.4 5.0 2.7 5.2 2.1 1.2 3.5 3.6
0.1 0.9 0.1 0.6 0.7 0.4 2.7 0.4
a Petrographic composition of the coals from the Pennsylvania been adjusted to a dry, mineral fre,e basis
Table 3
Properties
of coals used in flash hydrogenation
State University
collection
used in this study.
studies (other than those listed in Tab/e Ultimate
I)
Note that compositions
have
.
analysis
Coal
Carbon %mf
Hydrogen %mf
Oxygen %mf
Nitrogen %mf
Sulphur %mf
Ash %mf
Carbon (dmmf) --
Illinois No.6 A Illinois No.6 B Pittsburgh No.8 Texas lignite
68.2 66.3 69.6 58.7
5.1 4.98 4.91 4.63
9.3 11.49 5.8 15.07
1.1 1.16 1.21 1.13
4.2 3.3 5.72 1.63
12.1 12.77 12.76 18.84
80.4 78.25 83.4 74.2
c
2
.z 9
Y =-0.23C
?
+ 78
p = 0.19
s 5 ‘Z
I
a = 5.9
ao-
&z f70-
.
i-60-
.=*
_.*
l
.
50E
I
E
Figure 2 Reaction
. I
I
75 a0 Coal carbon content
70
Conversion conditions:
to total volatiles 8Oo”C, 101.3
I a5
I 90
(wt%,dmmf)
as a function
I 70
of coal rank.
MPa Hz, 10 s could contact
time
I 75 Carbon
I a0 (wt%,dmmf
I a5 1
Figure 4 Maximum yields of ethane as a function of rank and the temperature at which the maximum appears. Reaction conditions: 101.3 MPa Hz, 10 s solid contact time, 0.6 s gas residence time
151 70
I
I a5
I a0
75 Carbon
(wt%,dmmf
)
Figure 3 Conversion to methane as a function of coal rank. Reaction conditions: 800°C. 101.3 MPa H,, 10 s solid contact time, 0.6 s gas residence time
58
FUEL, 1983, Vol 62, January
I 90
temperature range 750 to 850°C where maximum yields of ethane and BTX are found at the hydrogen pressure employed. A heating rate of 650°C s- ’ was uniformly used. In the presentation of results below, a reaction temperature of 800°C is used as the point of comparison for the different coals. The yields obtained from the different coals at these fixed conditions are displayed against carbon content (rank) in Figures 2 to 6. Total carbon conversion to volatiles (Figure 2) correlates poorly with rank. Although linear regression shows a small decrease in total volatiles yield with increasing rank, no statistical significance can be attached to this result. The conversion of coal to methane presents a clear negative correlation with carbon content (Figure 3). Low rank coals give the highest yields of methane, but the conversion decreases rapidly with increasing rank.
Flash hydrogenat;on
Carbon
(wt % , d mmf )
Figure 5 The conversion of oxygen to carbon oxides as a function of coal rank. The yields of CO, have been corrected for the carbon oxides evolved from the minq;al matter, assuming . Reaction conditions: that 10% of the mineral matter is carbonate 101.3 MPa Hz, 10 s solid contact time, 9.6 s gas residence time
50-
45l
40-
25-
15 0
0
10 BTX 5 I
OL 70
I,,
1
1
75 Carbon
1
80 (wt %,dmmf
I
I
of coal: W. - Y. Chen et al.
Oxygen appearing as CO, (total carbon oxides, CO, +CO) is very nearly a uniform 70% of the coal oxygen content, as shown in Figure 5. In the low rank coals 25 7; of the oxygen appears as CO,, but this rapidly drops to zero for HVA coals. As a result of the relation between oxygen and carbon in coals of different ranks, there is a uniform decrease in carbon conversion to CO, from about 13 % in lignite to a few per cent for HVA coals. The most important contributor to the variability in total volatile yields observed in Figure 2 is the total liquid yield. Both total liquid yields and yields of single ring aromatics (BTX) are plotted as a function of rank in Figure 6. The yield of BTX is a maximum for coals of intermediate ranks (subbituminous A). However, the total liquid yield (which includes BTX and heavier liquids) generally increases with increasing rank and is markedly high for some coals (30 to 43%). Correlation
Although the conversions to individual species during flash hydrogenation show interesting trends with respect to coal rank, this single variable is inadequate to correlate and predict product distribution. For empirical purposes, correlations in two variables have been constructed using the technique of stepwise regression.” The dependent variables of interest are total conversion to volatiles and the yields of methane, ethane, CO,, and BTX and total liquids. In all cases the dependent variables were obtained from experiments performed at 800°C 10 s contact time, 0.6 s vapour residence time. Yields are expressed as a percentage of the initial carbon present in the coal. The field of independent variables tested consisted of the following: petrographic composition (dmmf), elemental composition (dmmf) and the mineral matter, volatile matter and the reactive maceral content (the sum of vitrinite, pseudo-vitrinite, exinite and resinite), 16 variables in all. A stepwise linear regression was carried out for each dependent variable as a function of independent variables. In all cases, two variables were found to yield correlations whose standard deviation was of the order of magnitude of the accuracy of the experimental data. The resulting relations, from all possible variable pairs, were compared according to their correlation coefftcient (p) and standard deviation (a) and the best fit chosen. These correlations are listed in Table 4. Total conversion to volatiles are best correlated with
I
85
)
Figure 6 Conversion to total liquids and BTX as a function of coal rank. Reaction conditions: 8Oo’C. 101.3 MPa H,, 10 s solid contact time, 0.6 s gas residence time
For all coals, the yields of ethane as a function of temperature were found, to behave as reported by Dobner et ~1.~in the case of Illinois No. 6 coal. Ethane yields vs. temperature curves are bell-shaped, presenting a maximum whose position and size depend upon the coal. For tie coals under study in this paper, peak ethane yields dange from 6.4 to 9% carbon, while the temperature of bcation of the maximum varies from 760 to 795°C. In Figure 4 a trend of decreasing peak yields and increasing peak temperatures with increasing rank is evidend, althoug modest.
Table 4
Summary
of correlations
of yields with coal propertiesa
Total volatiles = 54.54 + 3.93 (exinite) - 0.49 (mineral matter) p = 0.94 o = 2.40/o Methane = 17.97 - 0.5 (sulphur) + 0.33 (pseudo-vitrinite) p = 0.97 D = 0.87% Total liquids = 2.55 (carbon) - 4.2 (sulphur) D = 2.92% p = 0.96 Carbon oxides = 26.63 + 0.35 (oxygen) - 4.3 (hydrogen) c = 0.62% p = 0.99 BTX = 16.65 - 0.08 (vitrinite) - 0.58 (fusinite) D = 0.87% p = 0.88 Ethane = 1.44 + 0.086 fvitrinite) - 0.35 (sulphur) CJ= 0.19% p = 0.98 Heavy liquids = 5.29 + 5.64 fexinite) - 0.71 (pseudo-vitrinite) c = 2.4% p = 0.97 a Fixed reaction conditions: 800°C. 100 atm H,, 10 s solid contract time, 0.6 s gas residence time
FUEL,
1983,
Vol 62, January
59
Flash hydrogenation
of coal: W. - Y. Chen
et al.
exinite and mineral matter content as independent variables. The correlation coefficient is close to one, and the standard deviation is close to that of the experimental data. The mineral matter content appears in the correlation with a negative coefficient indicating that increased mineral matter will decrease the yield of total volatiles in flash hydrogenation. Although for the short residence times and high temperatures used in flash hydrogenation experiments, the catalytic effect of the mineral matter should be minimal (in contrast with the results obtained in coal liquefaction, at low temperatures and longer residence times), the presence of a negative effect is unexpected. The strong correlation of total volatile yield with exinite content indicates that this is the most important variable in the correlation. Further, the magnitude of the coefficient may have chemical significance. If exinite simply reacts to give volatiles, then its coefficient should not be much greater than unity. However, the coefficient is nearly four, so that it must be assumed that the exinite decomposes in such a way that it enhances the conversion of other macerals to volatiles. A possible explanation may be found in the fact that exinite is the most aliphatic of all coal macerals. Under heating, most of the aliphatic material will decompose to alkyl free-radicals which are very effective reaction initiators. This can result in the detachment of fragments from less reactive structures in other coal macerals. An alternative, suggested by Solomon,13 is based on hydrogen transfer. Exinite, rich in hydrogen, may provide the internal hydrogen required for the stabilization of large free-radical fragments. The stabilized fragment is less likely to enter into repolymerization reactions leading to the formation of coke or char. The best correlation for methane yields is with pseudovitrinite and sulphur. Sulphur has a negative coefficient in contrast to the results from coal liquefactionL4 where a positive effect of sulphur content is observed. Ethane yields correlate with vitrinite and sulphur content, with sulphur having a negative coefficient. BTX yields correlate best with vitrinite and fusinite content. The coefficients for both macerals are negative. The observed positive correlation of carbon dioxide yield with oxygen is to be expected, since in flash hydrogenation the only source of oxygen is what is contained in the coal. Hydrogen content appears to decrease these yields. The yield of liquids heavier than BTX correlates with exinite and pseudo-vitrinite. Again, exinite appears with a coefficient larger than one, indicating that it promotes the production of liquids. All correlation coefficients are about 0.9 or better, and the standard deviations are all quite low. The largest deviations (2.91% for total liquids and 2.4% for total volatiles) are about the same as the standard deviation obtained from the experimental scattering of the data for these two yields. This results from the correlation of yield values which are themselves averages of several experimental measurements and, hence, expected to have smaller standard deviations. DISCUSSION The scatter observed in Figures 2 to 6 clearly shows that rank alone is inadequate to correlate the experimental
60
FUEL, 1983, Vol62,
January
yields. This result is, perhaps, obvious considering the complex chemical and physical structure of coal which cannot be described with a single variable. Indeed, liquefaction studies have also shown that coals of the same rank can show a completely different behaviour under similar reaction conditions.’ 3 However, some general trends can be noted. According to the now classic study of the chemical nature of coal by Hirsch” the average number of aromatic rings per cluster increases with increasing rank. This increase in cluster aromaticity can explain a decrease in reactivity of coal with increasing rank consistent with the trend in Figure 2. The decrease in hydrogen content with increasing rank allows fewer aliphatic groups. This results in a decrease in light paraffin production with increasing rank, as seen in Figures 3 and 4. In Figure 5, the CO, produced corresponds to 25% of the oxygen in the coal at low rank, and that is approximately the fraction of oxygen in carboxylic acid groups in low rank coals. At higher rank, carboxylic acid groups in coals decrease and disappear.16 In Figure 5, the yields of CO, tend to zero at higher ranks. Both observations suggest that CO, is produced from the carboxylic acid groups present in the coal. The shape of the curve corresponding to total carbon oxides produced by flash hydrogenation in Figure 5 is readily understood in terms of the distribution of oxygen functional groups in coals of different rank (see for example, Figure 4a in Tingey et al.’ 6). If it is assumed that most of the oxygen in hydroxyl groups reacts to form water while oxygen in other groups forms either CO or CO,, and using the values in the literature,’ ‘j total carbon oxides production as a function of rank is predicted as in Figure 5. Hence, the assumption that hydroxyl oxygens are primarily converted to water is supported. Note that the total liquid yields increase with increasing rank, suggesting an increased evolution of heavier species with increasing aromaticity of the coal. One may speculate that molecules of the coal’s ‘heavier fractions’ would have a higher aromaticity and higher average molecular weight with increasing rank and would accordingly show less reactivity towards thermal hydrocracking. Since the thermal hydrocracking of these molecules is believed to be the rate determining step in the formation of BTX,” this would explain the decay of BTX yields in the higher rank coals. The high total liquid yields from flash hydrogenation, however, indicate a large potential for the production of synthetic liquid fuels, given an adequate treatment for the liquids produced. Regarding the correlation of flash hydrogenation yields with coal properties, it may be asked if a linear relation can be understood on theoretical grounds. Consider that the reactions involved occur in two consecutive stages. In the first stage coal decomposes thermally, yielding both light gas and heavy fragments of the coal structure. The second stage occurs in the gas phase where hydrogenation and further hydrocracking of the fragments produces light species. Flash hydrogenation may, accordingly, be treated by combining a coal pyrolysis model (modified for the effects of hydrogen) with suitable kinetics for vapour phase hydrocracking. In the pyrolysis models of both Gavalas’ ’ and Solemon’ * the reactions of ‘structural elements’ present in the starting material are described by a set of differential equations having universal kinetic constants. The proper-
Flash hydrogenation
ties of different coals are reflected only in the different amounts of these structural elements originally present, i.e. in the initial conditions for the integration of the governing differential equations. It is reasonable to postulate a linear relation between coal properties and the concentration of various structural elements in coal. With respect to the vapour phase reactions of stage two, it has been demonstrated that simultaneous thermal decomposition and hydrogenation of hydrocarbons are well described, in the case of constant hydrogen pressure, by a first order reaction scheme.‘9~20 It is a consequence of the general theory of first order kinetic networks,’ 6*’’ that the yield of each product species is a linear combination of the initial conditions, the conditions of reaction being fixed. It is thus possible, in a general way, to understand the empirical correlating equations presented above in terms of more fundamental kinetic models.
5 6
8
9
10 11
12
ACKNOWLEDGEMENTS John Bodnaruk provided valuable assistance in the design and construction of the experimental equipment. Application of the mass spectrometer, digital computer and the required software was developed by Eli Gilbert. This work was supported by the United States Department of Energy under contract EX-76-S-01-2340. REFERENCES 1 2 3 4
Squires, A. M., Graff, R. A. and Dobner, S. Science 1975,189,793795 Anthony, D. B. and Howard, .I. B. AIChE J. 1976, 22, 625 Graff, R. A., Dobner, S. and Squires, A. Fuel 1976, 55, 109 Dobner, S., Graff, R. A. and Squires, A. Fuel 1976, 55, 113
13 14 15 16 17 I8
19 20 21 22
of coal: W.-Y. Chen et al.
Steinberg, M. and Fallon, P. ‘Flash Hydropyrolysis of Coal’, Reuort to the US Denartment ofEnerev, BNL 51 IO?, No, 9,1979 Frikdman, J., ‘Deveiopment of a Single-Stage, Entrained-Flow Short Residence Time Hydrogasifier’, Report to the US Department of Energy, FE 2518-24, 1979. An account of the work performed by Cities Services given on pp. 28-82 and in Appendix B Friedman, J., ‘Development of a Single Stage, Entrained-Flow Short Residence Time Hydrogasifier’, Report to the US Department of Energy, FE 2518 24, 1979 Duncan, D. A., Beeson, J. L. and Oberle, R. D. ‘Research and Development of Rapid Hydrogenation for Coal Conversion to Synthetic Motor Fuels (Riser Cracking of Coal)‘, Report to the US Department of Energy, FE 2307 50, 1979 Gray, J. A., Appendix A, pp. 101-157 in J. Freidman, ‘Hydrogasifier Development for the Hydrane Process’, Report to the US Department of Energy, FE 2518 17, 1978 Shen, S. J., Chen, W. Y., Suzuki, Y., LaCava, A. I. and Graff, R. A. in preparation Given, P. H. and Yarzab, R. F. ‘Problems and Solutions in the Use of Coal Analyses’, Technical Report No. 1, Pennsylvania State University, FE 0390-I. to the US ERDA. Contract No. E (49-18) 390, 1975 Himmelblau, D. M. ‘Process Analysis by Statistical Methods’, Wiley, New York, 1970 Solomon, P. R., private communication, 1979 Abdel-Baset, M. B., Yarzab, R. F. and Given P. Fuel 1978,57,89 Hirsch, P. B. J. Inst. Fuel 1958, p. A29 Tingey, G. L. and Morrey, J. R. ‘Coal Structure and Reactivity’, Battelle, Richland, Washington, 1975 Cheong, P. H. ‘A Modelling Study of Coal Pyrolysis’, PhD Thesis, California Institute of Technology, 1976 Solomon, P. R. and CoIket, M. 8. ProceedingsoftheSeventeenth Symposium (International) on Combustion, The Combustion Instiiute, p. 131, Pittsburgh, PA, 1979 LaCava. A. I. and Trimm. D. L. Chem. Eng. J. 1978, 15, 63 LaCava; A. I. ‘Pyrolysis’ and Thermal Hydrogasification of Hydrocarbons’, PhD Thesis, University of London, 1976 Wei, J. and Prater, Ch. D. ‘Advances in Catalysis’, 1962,13,303, Academic Press Inc., New York Ravera, C. A., LaCava, A. I. and Cassano, A. E. Rev. Fat. Ing. Quirn., Univ. Nat. litoral 1971-1972, 1973, &dl, 195-211
FUEL,
1983,
Vol62,
January
61
Chen,
Albert0
I. LaCava and Robert
A. Graff
The Clean Fuels Institute, The City College, of The City University York, NY 10031, USA (Received 6 February 1981; revised 9 August 1982)
of New
York, New
The susceptibility of a group of US coals to the production of light gaseous and liquid hydrocarbons during flash hydrogenation is examined. Eight coals ranging from lignite to high-volatile A bituminous and representing five provinces, have been flash heated in 101.3 MPa of flowing hydrogen using a bench scale reactor. A 0.6 s gas phase residence time was provided to hydrocrack the vapour products. Temperatures ranged from 750 to 85o”C, where maximum yields of ethane and BTX (benzene+toluene +xylene) are found. The carbon conversion decreased with increasing rank at fixed reaction conditions. Methane yields are highest for lignite. Peak ethane yields range from 6.4 to SE&carbon conversion. BTX yields have a shallow maximum at intermediate ranks, decreasing towards high and low rank coals. Total liquid yields range from 14 to 43%. Although a definite variation of yield with rank is evident, the trends, especially total liquid yields, are attended by considerable scatter. Rank is not the only, and indeed may not be the most significant variable in determining the yield of individual species in flash hydrogenation. To establish the significant variables a stepwise regression procedure was applied to the experimental data using information from the elemental, proximate and petrographic compositions of the coals as independent variables. Two variables are adequate in all cases to correlate species yield and coal properties. Exinite appears to be capable of increasing the amount of liquid obtained from other macerals. (Keywords:
coal; flash hydrogenation;
US)
Flash hydrogenation of coal has potential as a process for the production of synthetic fuels, namely, substitute natural gas, light aromatic liquids (to be used as a fuel or as petrochemical feedstock) and low sulphur char. The process is based on the thermal reactions of coal and the volatiles generated by rapid heating under hydrogen at high pressure. Rapid heating of coal enhances the yield of light species.’ Early work on rapid-heating coal devolatilization in inert or hydrogen atmospheres and the effect of operating conditions on the total coal weight loss has been reviewed.2 The effect of the operating variables, including gas phase residence time for the upgrading of volatiles, on the total coal weight loss and the yield of individual products (methane, ethane, carbon oxides and single ring aromatics) has been reported for the flash hydrogenation of Illinois No. 6 coal in small scale, captive sample equipment. 3*4 Dilute phase entrained bed reactors have been built and operated by Brookhaven National Laboratories,’ Cities Service,6 Rockwell International’ and the Institute of Gas Technology.* However, because of plugging problems, studies in these reactors have been largely restricted to lignites and subbituminous coals. Only three bituminous coals have been tested by Rockwell,’ at temperatures above 700°C. Cities Service’ has operated with low-temperature air preoxidized bituminous coal, Brookhaven’ and the Institute of Gas Technology’ with CaO pretreated bituminous coals, as well as with mixtures of bituminous coals with sand and with char. 0016~2361/83/01005~06$3.00 01983 Butterworth & Co. (Publishers) Ltd
56
FUEL,
1983,
Vol 62, January
Gray,’ in a study comparing the available hydropyrolysis data, concluded that the variability in reported yields was largely the result of differences in equipment used by various investigators. Mass transfer limitations were cited as a likely cause. This conclusion, however, was without foundation since little or no data were available on different coals run under identical conditions in the same equipment. The study reported in this Paper attempts to remedy this situation. Indeed, the extreme variability of coals, even those close in rank (as discussed below), suggests that the use of different coals is the most important reason for the inconsistent yields reported by different investigators. In view of the limited number of coals which have been studied under flash hydrogenation, in particular those using the same equipment, yield data for a sampling of US coals under identical conditions in a single apparatus were obtained. Eight coals, broadly representative of the US spectrum, were selected for study. The results described below show the range in performance to be expected from US coals under flash hydrogenation. Empirical correlations are presented and some inferences are drawn regarding the basic reasons for the observed variations. Practical considerations limited the number of different coals which could be tested in this study. A far larger group would be required to provide an adequate statistical sample of US coals. This must be noted, therefore, when viewing the results presented here.
Flash hydrogenation
EXPERIMENTAL Reactor
of coal: W.-Y.
Chen
et al.
between two quartz wool plugs, as shown in Figure 1, give identical results. In addition, the sample size can be increased to 20 mg without affecting the observed yields. In a second modification of the system the gas chromatograph has been replaced by a mass spectrometer for on-line analysis of products up to xylene. For those species determined by direct analysis the standard deviation has been calculated from the experimental data: methane 1.6 %, ethane 0.8 %, BTX 1.2 %, total carbon oxides 2.6x, char 4.1%. In the work reported here, heavy liquids are determined by difference with a standard deviation of 5.4%. Direct measurement of liquids by trapping has been carried out for Illinois No. 6 and Pittsburgh No. 8 coals. These measurements, which confirm the accuracy of liquids determined by difference, will be reported in a subsequent paper.” Yield values reported below are in all cases averages from several experiments.
system
The reactor used in this study was designed for flash heating of raw coal in flowing hydrogen at pressures up to 101.3 MPa. Reactions in the vapour phase play an important role in the product formation and the reactor system allows for the independent selection of vapour residence time. The reactor (Figure 1) is a 30.48 cm section of 0.63 cm (0.25 in) stainless steel tubing. A 10 to 20 mg sample of powdered coal ( - 325 mesh) is placed at a selected point in the tube and hydrogen at pressure continuously flows through the tube to downstream analytical equipment. A high current is passed through the tube wall to provide heating rates typically of 650°C per second. After reaching the preset temperature, a lower current is used to maintain the temperature for the duration of the run, usually 10 s. Quenching of vapour occurs at the right hand electric lead which, because of its large mass, remains at its initial temperature. The distance from the coal sample to this lead and the hydrogen flowrate are adjusted to provide the desired vapour residence time. Flash hydrogenation of the coal is followed by in situ combustion of residual char with oxygen. Carbon dioxide obtained in this step measures carbon in the residual char, and is added to the carbon contained in the species determined during hydrogenation to construct a carbon balance. Further details of the reactor system and its operation have been reported previously.3 Two modifications have been made. First, the procedure for depositing a 10 mg sample of ground coal as a thin ring on the inside wall of the reactor tube has been found to be unnecessary. Samples in the form of a layer of ground coal held in place
Coal samples
Eight coals were selected for this study from the coal bank of the Pennsylvania State University.* The coals (Tables 2 and 2) range from hvA bituminous coal having 85.15 wt % dmmf carbon to lignite with 71.86 wt % dmmf carbon and represent tive provinces. In addition, Figures 2 and 6 include data for two samples of Illinois No. 6 coal, one of Pittsburgh No. 8 and one of Texas lignite. Data for the first sample of Illinois No. 6(A) are taken from our previous paper.4 The composition of the second sample of Illinois No. 6(B) (taken on the same date from the same mine) and of the other two coals are listed in Table 3. To compare these four coals with others in the group, an estimate of dmmfcarbon is required. This has been made using the Parr formula” to estimate mineral matter content. To correct the carbon content for CO, evolved from mineral matter, it is assumed that 10 % of the mineral matter is carbonate. RESULTS For this study all coal samples hydrogenation in 101.3 MPa 10s. A residence time of 0.6s volatile products. Measurements
Thermocouple
vopour product residence zone 1
Figure
1
Table 1
Flash hydrogenation
Identification
were subjected to flash of pure hydrogen for was provided for the were conducted in the
I * The authors are grateful to Professor Peter Given for selecting these coals and to others at Penn State for making samples available.
I
reactor
and analysis of selected coals (wt% drnmf)a
Sample no.
Rank
Province
Aga
State
Moist
M.M. direct
c dmmf
0 dmmf
Dry
DAF
PSOC PSOC PSOC PSOC P6OC P6OC P$OC PSOC
HVA HVA HVA HVA HVC S.8it.A S.Bit.8 Lignite
Eastern Eastern Interior Rocky M. Interior Rocky M. Pacific North Gr.Plains
Carb. Carb. Carb. Crat. Carb. Cret. Tart. Tart.
PA AL IL UT IN WY WA ND
2.21 1.27 3.11 4.08 11.32 19.17
21.18 17.72 25.08 11.55 18.31 3.34
84.49 85.15 83.71 81.47 81.58 75.44
5.56 4.85 7.12 10.13 9.51 17.04
4.36 2.34 5.23 0.76 3.78 0.64
5.28 2.77 6.70 0.84 4.50 0.66
19.73
16.47
73.96
18.98
0.50
0.60
34.12
10.99
71.85
21.22 ----
0.65
326 270 284 314 280 248 240 8, 246
a Properties
of the coals from the Pennsylvania
State University
collection
S
__
0.72 .-
used in the present study
FUEL,
1983, Vol 62, January
57
Flash hydrogenation Table 2
Petrographic
Chen et al.
of coal: W.-Y. compositions
of selected coals (wt% dmmfja
PSOC Coal No.
Vitrinite
PseudoVitrinite
Fusinite
SemiFusinite
Massive Micrinite
Granular Micrinite
Exinite
Resinite
326 270 284 314 280 248 240 82 246
69.4 68.1 78.9 73.3 92.1 68.2 67.2 53.3
7.6 3.2 8.2 8.8 0.0 8.1 12.7 25.3
3.2 8.6 3.8 4.5 1.2 0.7 3.0 7.8
7.3 4.6 1.6 4.7 1.1 11.8 4.0 3.8
2.0 0.6 0.3 2.1 0.0 0.0 2.5 0.7
6.0 9.0 4.4 0.7 2.7 9.5 4.1 4.9
4.4 5.0 2.7 5.2 2.1 1.2 3.5 3.6
0.1 0.9 0.1 0.6 0.7 0.4 2.7 0.4
a Petrographic composition of the coals from the Pennsylvania been adjusted to a dry, mineral fre,e basis
Table 3
Properties
of coals used in flash hydrogenation
State University
collection
used in this study.
studies (other than those listed in Tab/e Ultimate
I)
Note that compositions
have
.
analysis
Coal
Carbon %mf
Hydrogen %mf
Oxygen %mf
Nitrogen %mf
Sulphur %mf
Ash %mf
Carbon (dmmf) --
Illinois No.6 A Illinois No.6 B Pittsburgh No.8 Texas lignite
68.2 66.3 69.6 58.7
5.1 4.98 4.91 4.63
9.3 11.49 5.8 15.07
1.1 1.16 1.21 1.13
4.2 3.3 5.72 1.63
12.1 12.77 12.76 18.84
80.4 78.25 83.4 74.2
c
2
.z 9
Y =-0.23C
?
+ 78
p = 0.19
s 5 ‘Z
I
a = 5.9
ao-
&z f70-
.
i-60-
.=*
_.*
l
.
50E
I
E
Figure 2 Reaction
. I
I
75 a0 Coal carbon content
70
Conversion conditions:
to total volatiles 8Oo”C, 101.3
I a5
I 90
(wt%,dmmf)
as a function
I 70
of coal rank.
MPa Hz, 10 s could contact
time
I 75 Carbon
I a0 (wt%,dmmf
I a5 1
Figure 4 Maximum yields of ethane as a function of rank and the temperature at which the maximum appears. Reaction conditions: 101.3 MPa Hz, 10 s solid contact time, 0.6 s gas residence time
151 70
I
I a5
I a0
75 Carbon
(wt%,dmmf
)
Figure 3 Conversion to methane as a function of coal rank. Reaction conditions: 800°C. 101.3 MPa H,, 10 s solid contact time, 0.6 s gas residence time
58
FUEL, 1983, Vol 62, January
I 90
temperature range 750 to 850°C where maximum yields of ethane and BTX are found at the hydrogen pressure employed. A heating rate of 650°C s- ’ was uniformly used. In the presentation of results below, a reaction temperature of 800°C is used as the point of comparison for the different coals. The yields obtained from the different coals at these fixed conditions are displayed against carbon content (rank) in Figures 2 to 6. Total carbon conversion to volatiles (Figure 2) correlates poorly with rank. Although linear regression shows a small decrease in total volatiles yield with increasing rank, no statistical significance can be attached to this result. The conversion of coal to methane presents a clear negative correlation with carbon content (Figure 3). Low rank coals give the highest yields of methane, but the conversion decreases rapidly with increasing rank.
Flash hydrogenat;on
Carbon
(wt % , d mmf )
Figure 5 The conversion of oxygen to carbon oxides as a function of coal rank. The yields of CO, have been corrected for the carbon oxides evolved from the minq;al matter, assuming . Reaction conditions: that 10% of the mineral matter is carbonate 101.3 MPa Hz, 10 s solid contact time, 9.6 s gas residence time
50-
45l
40-
25-
15 0
0
10 BTX 5 I
OL 70
I,,
1
1
75 Carbon
1
80 (wt %,dmmf
I
I
of coal: W. - Y. Chen et al.
Oxygen appearing as CO, (total carbon oxides, CO, +CO) is very nearly a uniform 70% of the coal oxygen content, as shown in Figure 5. In the low rank coals 25 7; of the oxygen appears as CO,, but this rapidly drops to zero for HVA coals. As a result of the relation between oxygen and carbon in coals of different ranks, there is a uniform decrease in carbon conversion to CO, from about 13 % in lignite to a few per cent for HVA coals. The most important contributor to the variability in total volatile yields observed in Figure 2 is the total liquid yield. Both total liquid yields and yields of single ring aromatics (BTX) are plotted as a function of rank in Figure 6. The yield of BTX is a maximum for coals of intermediate ranks (subbituminous A). However, the total liquid yield (which includes BTX and heavier liquids) generally increases with increasing rank and is markedly high for some coals (30 to 43%). Correlation
Although the conversions to individual species during flash hydrogenation show interesting trends with respect to coal rank, this single variable is inadequate to correlate and predict product distribution. For empirical purposes, correlations in two variables have been constructed using the technique of stepwise regression.” The dependent variables of interest are total conversion to volatiles and the yields of methane, ethane, CO,, and BTX and total liquids. In all cases the dependent variables were obtained from experiments performed at 800°C 10 s contact time, 0.6 s vapour residence time. Yields are expressed as a percentage of the initial carbon present in the coal. The field of independent variables tested consisted of the following: petrographic composition (dmmf), elemental composition (dmmf) and the mineral matter, volatile matter and the reactive maceral content (the sum of vitrinite, pseudo-vitrinite, exinite and resinite), 16 variables in all. A stepwise linear regression was carried out for each dependent variable as a function of independent variables. In all cases, two variables were found to yield correlations whose standard deviation was of the order of magnitude of the accuracy of the experimental data. The resulting relations, from all possible variable pairs, were compared according to their correlation coefftcient (p) and standard deviation (a) and the best fit chosen. These correlations are listed in Table 4. Total conversion to volatiles are best correlated with
I
85
)
Figure 6 Conversion to total liquids and BTX as a function of coal rank. Reaction conditions: 8Oo’C. 101.3 MPa H,, 10 s solid contact time, 0.6 s gas residence time
For all coals, the yields of ethane as a function of temperature were found, to behave as reported by Dobner et ~1.~in the case of Illinois No. 6 coal. Ethane yields vs. temperature curves are bell-shaped, presenting a maximum whose position and size depend upon the coal. For tie coals under study in this paper, peak ethane yields dange from 6.4 to 9% carbon, while the temperature of bcation of the maximum varies from 760 to 795°C. In Figure 4 a trend of decreasing peak yields and increasing peak temperatures with increasing rank is evidend, althoug modest.
Table 4
Summary
of correlations
of yields with coal propertiesa
Total volatiles = 54.54 + 3.93 (exinite) - 0.49 (mineral matter) p = 0.94 o = 2.40/o Methane = 17.97 - 0.5 (sulphur) + 0.33 (pseudo-vitrinite) p = 0.97 D = 0.87% Total liquids = 2.55 (carbon) - 4.2 (sulphur) D = 2.92% p = 0.96 Carbon oxides = 26.63 + 0.35 (oxygen) - 4.3 (hydrogen) c = 0.62% p = 0.99 BTX = 16.65 - 0.08 (vitrinite) - 0.58 (fusinite) D = 0.87% p = 0.88 Ethane = 1.44 + 0.086 fvitrinite) - 0.35 (sulphur) CJ= 0.19% p = 0.98 Heavy liquids = 5.29 + 5.64 fexinite) - 0.71 (pseudo-vitrinite) c = 2.4% p = 0.97 a Fixed reaction conditions: 800°C. 100 atm H,, 10 s solid contract time, 0.6 s gas residence time
FUEL,
1983,
Vol 62, January
59
Flash hydrogenation
of coal: W. - Y. Chen
et al.
exinite and mineral matter content as independent variables. The correlation coefficient is close to one, and the standard deviation is close to that of the experimental data. The mineral matter content appears in the correlation with a negative coefficient indicating that increased mineral matter will decrease the yield of total volatiles in flash hydrogenation. Although for the short residence times and high temperatures used in flash hydrogenation experiments, the catalytic effect of the mineral matter should be minimal (in contrast with the results obtained in coal liquefaction, at low temperatures and longer residence times), the presence of a negative effect is unexpected. The strong correlation of total volatile yield with exinite content indicates that this is the most important variable in the correlation. Further, the magnitude of the coefficient may have chemical significance. If exinite simply reacts to give volatiles, then its coefficient should not be much greater than unity. However, the coefficient is nearly four, so that it must be assumed that the exinite decomposes in such a way that it enhances the conversion of other macerals to volatiles. A possible explanation may be found in the fact that exinite is the most aliphatic of all coal macerals. Under heating, most of the aliphatic material will decompose to alkyl free-radicals which are very effective reaction initiators. This can result in the detachment of fragments from less reactive structures in other coal macerals. An alternative, suggested by Solomon,13 is based on hydrogen transfer. Exinite, rich in hydrogen, may provide the internal hydrogen required for the stabilization of large free-radical fragments. The stabilized fragment is less likely to enter into repolymerization reactions leading to the formation of coke or char. The best correlation for methane yields is with pseudovitrinite and sulphur. Sulphur has a negative coefficient in contrast to the results from coal liquefactionL4 where a positive effect of sulphur content is observed. Ethane yields correlate with vitrinite and sulphur content, with sulphur having a negative coefficient. BTX yields correlate best with vitrinite and fusinite content. The coefficients for both macerals are negative. The observed positive correlation of carbon dioxide yield with oxygen is to be expected, since in flash hydrogenation the only source of oxygen is what is contained in the coal. Hydrogen content appears to decrease these yields. The yield of liquids heavier than BTX correlates with exinite and pseudo-vitrinite. Again, exinite appears with a coefficient larger than one, indicating that it promotes the production of liquids. All correlation coefficients are about 0.9 or better, and the standard deviations are all quite low. The largest deviations (2.91% for total liquids and 2.4% for total volatiles) are about the same as the standard deviation obtained from the experimental scattering of the data for these two yields. This results from the correlation of yield values which are themselves averages of several experimental measurements and, hence, expected to have smaller standard deviations. DISCUSSION The scatter observed in Figures 2 to 6 clearly shows that rank alone is inadequate to correlate the experimental
60
FUEL, 1983, Vol62,
January
yields. This result is, perhaps, obvious considering the complex chemical and physical structure of coal which cannot be described with a single variable. Indeed, liquefaction studies have also shown that coals of the same rank can show a completely different behaviour under similar reaction conditions.’ 3 However, some general trends can be noted. According to the now classic study of the chemical nature of coal by Hirsch” the average number of aromatic rings per cluster increases with increasing rank. This increase in cluster aromaticity can explain a decrease in reactivity of coal with increasing rank consistent with the trend in Figure 2. The decrease in hydrogen content with increasing rank allows fewer aliphatic groups. This results in a decrease in light paraffin production with increasing rank, as seen in Figures 3 and 4. In Figure 5, the CO, produced corresponds to 25% of the oxygen in the coal at low rank, and that is approximately the fraction of oxygen in carboxylic acid groups in low rank coals. At higher rank, carboxylic acid groups in coals decrease and disappear.16 In Figure 5, the yields of CO, tend to zero at higher ranks. Both observations suggest that CO, is produced from the carboxylic acid groups present in the coal. The shape of the curve corresponding to total carbon oxides produced by flash hydrogenation in Figure 5 is readily understood in terms of the distribution of oxygen functional groups in coals of different rank (see for example, Figure 4a in Tingey et al.’ 6). If it is assumed that most of the oxygen in hydroxyl groups reacts to form water while oxygen in other groups forms either CO or CO,, and using the values in the literature,’ ‘j total carbon oxides production as a function of rank is predicted as in Figure 5. Hence, the assumption that hydroxyl oxygens are primarily converted to water is supported. Note that the total liquid yields increase with increasing rank, suggesting an increased evolution of heavier species with increasing aromaticity of the coal. One may speculate that molecules of the coal’s ‘heavier fractions’ would have a higher aromaticity and higher average molecular weight with increasing rank and would accordingly show less reactivity towards thermal hydrocracking. Since the thermal hydrocracking of these molecules is believed to be the rate determining step in the formation of BTX,” this would explain the decay of BTX yields in the higher rank coals. The high total liquid yields from flash hydrogenation, however, indicate a large potential for the production of synthetic liquid fuels, given an adequate treatment for the liquids produced. Regarding the correlation of flash hydrogenation yields with coal properties, it may be asked if a linear relation can be understood on theoretical grounds. Consider that the reactions involved occur in two consecutive stages. In the first stage coal decomposes thermally, yielding both light gas and heavy fragments of the coal structure. The second stage occurs in the gas phase where hydrogenation and further hydrocracking of the fragments produces light species. Flash hydrogenation may, accordingly, be treated by combining a coal pyrolysis model (modified for the effects of hydrogen) with suitable kinetics for vapour phase hydrocracking. In the pyrolysis models of both Gavalas’ ’ and Solemon’ * the reactions of ‘structural elements’ present in the starting material are described by a set of differential equations having universal kinetic constants. The proper-
Flash hydrogenation
ties of different coals are reflected only in the different amounts of these structural elements originally present, i.e. in the initial conditions for the integration of the governing differential equations. It is reasonable to postulate a linear relation between coal properties and the concentration of various structural elements in coal. With respect to the vapour phase reactions of stage two, it has been demonstrated that simultaneous thermal decomposition and hydrogenation of hydrocarbons are well described, in the case of constant hydrogen pressure, by a first order reaction scheme.‘9~20 It is a consequence of the general theory of first order kinetic networks,’ 6*’’ that the yield of each product species is a linear combination of the initial conditions, the conditions of reaction being fixed. It is thus possible, in a general way, to understand the empirical correlating equations presented above in terms of more fundamental kinetic models.
5 6
8
9
10 11
12
ACKNOWLEDGEMENTS John Bodnaruk provided valuable assistance in the design and construction of the experimental equipment. Application of the mass spectrometer, digital computer and the required software was developed by Eli Gilbert. This work was supported by the United States Department of Energy under contract EX-76-S-01-2340. REFERENCES 1 2 3 4
Squires, A. M., Graff, R. A. and Dobner, S. Science 1975,189,793795 Anthony, D. B. and Howard, .I. B. AIChE J. 1976, 22, 625 Graff, R. A., Dobner, S. and Squires, A. Fuel 1976, 55, 109 Dobner, S., Graff, R. A. and Squires, A. Fuel 1976, 55, 113
13 14 15 16 17 I8
19 20 21 22
of coal: W.-Y. Chen et al.
Steinberg, M. and Fallon, P. ‘Flash Hydropyrolysis of Coal’, Reuort to the US Denartment ofEnerev, BNL 51 IO?, No, 9,1979 Frikdman, J., ‘Deveiopment of a Single-Stage, Entrained-Flow Short Residence Time Hydrogasifier’, Report to the US Department of Energy, FE 2518-24, 1979. An account of the work performed by Cities Services given on pp. 28-82 and in Appendix B Friedman, J., ‘Development of a Single Stage, Entrained-Flow Short Residence Time Hydrogasifier’, Report to the US Department of Energy, FE 2518 24, 1979 Duncan, D. A., Beeson, J. L. and Oberle, R. D. ‘Research and Development of Rapid Hydrogenation for Coal Conversion to Synthetic Motor Fuels (Riser Cracking of Coal)‘, Report to the US Department of Energy, FE 2307 50, 1979 Gray, J. A., Appendix A, pp. 101-157 in J. Freidman, ‘Hydrogasifier Development for the Hydrane Process’, Report to the US Department of Energy, FE 2518 17, 1978 Shen, S. J., Chen, W. Y., Suzuki, Y., LaCava, A. I. and Graff, R. A. in preparation Given, P. H. and Yarzab, R. F. ‘Problems and Solutions in the Use of Coal Analyses’, Technical Report No. 1, Pennsylvania State University, FE 0390-I. to the US ERDA. Contract No. E (49-18) 390, 1975 Himmelblau, D. M. ‘Process Analysis by Statistical Methods’, Wiley, New York, 1970 Solomon, P. R., private communication, 1979 Abdel-Baset, M. B., Yarzab, R. F. and Given P. Fuel 1978,57,89 Hirsch, P. B. J. Inst. Fuel 1958, p. A29 Tingey, G. L. and Morrey, J. R. ‘Coal Structure and Reactivity’, Battelle, Richland, Washington, 1975 Cheong, P. H. ‘A Modelling Study of Coal Pyrolysis’, PhD Thesis, California Institute of Technology, 1976 Solomon, P. R. and CoIket, M. 8. ProceedingsoftheSeventeenth Symposium (International) on Combustion, The Combustion Instiiute, p. 131, Pittsburgh, PA, 1979 LaCava. A. I. and Trimm. D. L. Chem. Eng. J. 1978, 15, 63 LaCava; A. I. ‘Pyrolysis’ and Thermal Hydrogasification of Hydrocarbons’, PhD Thesis, University of London, 1976 Wei, J. and Prater, Ch. D. ‘Advances in Catalysis’, 1962,13,303, Academic Press Inc., New York Ravera, C. A., LaCava, A. I. and Cassano, A. E. Rev. Fat. Ing. Quirn., Univ. Nat. litoral 1971-1972, 1973, &dl, 195-211
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1983,
Vol62,
January
61