T H E HEAT OF REACTION OF HYDROGEN AND COAL A. L. LEE, H . L. FELDKIRCHNER, F. C. SCHORA, AND J. J . HENRY1 Institute of Gas Technology, Chicago, Ill.
The heat of reaction of hydrogen with coal and chars was studied at 1300' to 1500' F. and 1000 p.s.i.a. The coal studied was a high-volatile-content bituminous coal from the Ireland mine with a size range of - 2 0 to $325 mesh. The chars studied, which consisted of the pretreated coal, low-temperature residue, and high-temperature residue, were the residues from the IGT hydrogasification process. The heat of reaction of the coal pretreatment, which i s a controlled partial oxidation of the coal, was also studied at 700' and 800" F.
HIS investigation was conducted to obtain the necessary Tinformation for designing an efficient coal hydrogasification plant which was discussed by Feldkirchner and Huebler (1965), Huebler and Schora (1966), Kavlick and Lee (1966), Linden (1966), Pyrcioch et al. (1966), Pyrcioch and Linden (1960), Tajbl et al. (1966), and von Fredersdorff and Vandaveer (1965). A thorough literature search reveals that there is no reported data on the heat of reaction of hydrogen and coal. Therefore, two calorimeters were designed, constructed, and operated-one to measure the heat of reaction and the other to measure heat capacity by the drop method. The heat-of-reaction calorimeter can be operated at temperatures up to 1500' F. and pressures up to 1500 p.s.i.a.; the drop calorimeter operates at atmospheric pressure and temperatures up to 1500' F. This paper reports the results of the heat of reaction of coal pretreatment and of the heat of reaction of hydrogen with coals and coal chars at and after various degrees of gasification.
conditions at which the desired temperature and pressure are stabilized. Therefore, the method of introducing the sample to the reaction conditions is critical. The coal must not react before the conditions are set, and the pressure must not be disturbed when the coal is introduced.
Apparatus and Procedure
The heat-of-reaction calorimeter (Dynatech Corp.) is shown in Figure 1. The sample is placed in the upper portion of the neck, which is cold. The calorimeter body is filled with hydrogen and heated. The temperature of the calorimeter body is measured by four Chromel-Alumel thermocouples and two platinum resistance thermometers. The sample is lowered into the body after the temperature has remained steady for two hours. The change in temperature due to a reaction is then measured as a function of time. The drop calorimeter (Dynatech Corp.) is shown in Figure 2. The sample is placed in the top furnace until it reaches the desired temperature. I t is then dropped into the copper receiver, and the heat capacity of the sample is determined from the temperature rise and heat capacity of the copper receiver. The coal studied was a high-volatile-content bituminous coal from the Ireland mine (Pittsburgh No. 8 seam) with a size range of -20 to +325 mesh. Experimental Results
Because coals decompose when heated, the major problem encountered in determining the heat of coal reactions at high temperature and high pressure is prereaction. Meaningful results can be obtained only if the coal and hydrogen react at Present address, Dynatech Corp., Cambridge, Mass. 244
l&EC PROCESS D E S I G N A N D DEVELOPMEtjT
Figure 1
.
Heat-of-reaction calorimeter
T h e present method is to keep the sample a t room temperature inside the calorimeter drop tube so that the reaction will not take place prematurely. Convection shields are installed t o prevent a large heat loss from convection and t o ensure that the sample is in a cold zone while the calorimeter is being stabilized at the reaction conditions. Establishing a heat balance around the calorimeter was necessary t o calculate the heat of reaction from experimental data. T h e heat balance is best expressed by:
convection shield, the chain, and the empty sample basket were determined in the calorimeter. T h e change of heat input with time was measured as shown in Equation 2 :
K(e)
=
s,”
calorimeter
(mCP4T ) s b i e ~ d- (mCp4T)chain
s,” -
-
[(hi,
( m c p AT ) b a s k e t ) lde
(2)
where K(0) = calorimeter calibration constant dependent only on time. Combining Equations 1 and 2,
-4BR = where hi, = heat input from the neck heater. Each term in Equation 1 must be either established by calibration or accurately measured. The heat capacity of the calorimeter body metal was determined in the drop calorimeter. These data are shown in Figure 3. T h e effective mC, of the reaction calorimeter was calibrated by a constant-heat-input technique in a hydrogen atmosphere a t 1000 p.s.i.a. and at temperatures from 840’ and 1460’ F. T h e results are presented in Figure 4. After the calorimeter constants were determined, the effective ( m C p 4 T ) ’ s of the
de =
(mC,4T)e,pty
(mCpAT)calorimeter
f (mCpAT)co8i - K ( 0 )
(3)
Equation 3 was used to calculate the heat-of-reaction data reported in this paper. T h e reproducibility of the calorimeter constant, K(B), was found to have a deviation no larger than =kl.5% for all temperatures, and the magnitude of this constant is about 5 t o 30% of the over-all measured quantity, depending on the temperature a t which the measurement was taken and the duration of the experiment. Design of a hydrogasification plant requires data on the heats of reaction of raw coal in the coal pretreatment process,
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Figure 3.
Mean heat capacity of calorimeter
From 70” F. to temperatures indicated
I
800
1
900
1000
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1300
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Figure 2. Drop calorimeter
Figure 4.
Calibration of heat-of-reaction calorimeter VOL. 7
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245
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Figure 5.
Time temperature data for heat of reaction of hydrogen and coal
2200
Table 1.
Analysis of Coal and Coal Chars Raw Pretreated Low- Temp. High-Temp. Coal Coal Residue Residue
n e2000 0
K w
Proximate Analysis, Wt.
%
0 0
Moisture Volatiles Fixed Carbon Ash Total Ultimate Analysis, Wt.
%
Carbon Hydrogen Nitrogen Oxygen Sulfur Ash Total
1800 d
'
1.3 34.6 52.0 _12.1 _ 100.0
0.5 23.3 63.5 12.7 ~ _ 100.0
0.6 4.6 77.6 -1 7 . 2_ 100.0
0.6 3.3 71.6 24.5 _ 100.0
f 1600 m L
'5 1400 1200
70.1 76.9 71.2 3.70 2.05 5.14 1.37 1.01 1.23 6.03 8.30 0.65 4.19 3.80 2.09 12.73 17.30 _12.21 _ _ _ _ _ 100.00 100.00 100.00
72.6 1.08 0.54 0.00 1.24 24.62 100.00
40
42
44
46
48
52
50
54
% COAL REACTED
Figure 6. raw coal
Heat of reaction of hydrogen and
5c 3400 3200
the pretreated coal in the low-temperature gasifier, the residue from the low-temperature gasifier in the high-temperature gasifier, and the residue from the high-temperature gasifier (Kavlick and Lee, 1966; Pyrcioch et al., 1966). Table I presents the coal and coal char analyses before the reaction with hydrogen takes place. Table I1 presents the heat of reaction of hydrogen and coal a t 1300' F. and 1000 p.s.i.a., Table I11 presents the results a t 1500' F. and 1000 p.s.i.a., and Table IV presents the heat of reaction of coal pretreatment -a controlled partial oxidation of the coal. These tables also present analyses of coal after reaction. Data from a typical experimental run are shown in Figure 5 , and the heats of reaction of hydrogen and coal and coal chars a t various percentages reacted are presented in Figures 6, 7 , and 8. The heat of reaction of the pretreatment of coal is presented in Figure 9. Little devolatilization was noticed at 700' F., but the coal devolatilized rapidly a t 800' F., as shown by the presence of tars. Thus, because a good portion of the coal weight loss a t 800' F. was due to devolatilization and not to the oxidation reaction, the heat of reaction of the pretreatment of coal was also calculated for 800' F., based on the data obtained a t 700'
246
l & E C PROCESS D E S I G N A N D DEVELOPMENT
0" 3000 -1
28W
. 0
.p 2600
2 2400 9 2200
? 2000 17
19 21 23 % COAL REPCTED
25
Figure 7. Heat of reaction of hydrogen and low-temperature residue at 1000 p.5.i.a. and 1500" F.
F. and the heat capacity information of both reactants and products that was obtained from sample analysis. The results are presented as the dotted line in Figure 9, and the percentage of pretreatment is defined as the weight loss divided by the initial total weight of the coal. Although these experiments were carried out in a static-bed reactor, the IGT pilot plant pretreatment of coal is carried out in a fluidized-bed reactor. At 800" F., the rate of the devolatilization reaction apparently competes with that of the oxida-
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VOL. 7
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Table IV.
~
Heat of Reaction of Pretreatment of Ireland Mine Coal and Analyses of Coal after Reaction TL-35 TL-38 TL-40 TL-41 TL-42 TL-43 TL-44 TL-45 TL-46 TL-47
TL-48
Proximate Analysis, Wt.
%
Moisture Volatile Matter Fixed Carbon Ash Ultimate Analysis, wt. % Carbon
HP
0.5 25.7 61.1 12.7
0.0 20.9 66.0 13.1
0.8 17.6 67.0 14.6
0.3 17.5 67.9 14.3
0.2 18.9 67.8 13.1
0.2 25.8 60.7 13.3
0.2 23.5 63.0 13.3
0.5 18.3 68.0 13.2
0.4 21.3 64.2 14.1
0.5 21.2 64.8 13.5
14.6 19.7 54.9 10.8
71.2 3.97
71.1 3.16 1.03 7.82 3.83 13.06 701 170 18.1
72.2 3.29
69.9 3.08 0.96 7.03 4.70 14.33 800 120 17.8
71.1 3.42 1.33 7.13 3.93 13.09 801 47 3.47
69.9 3.86 1.31 7.39 4.22 13.32 708 80 9.2
70.1 3.96 0.87 7.53 4.19 13.35 707 110 12.3
74.5 3.01 1.33 3.49 4.37 13.30 796 120 17.8
71.5 3.32 1.37 5.31 4.35 14.15 797 60 5.15
73.2 3.62 1.41 3.94 4.25 13.58 794 120 17.3
83.9 2.23 1.20
... ...
Nz
0 2
S Ash
i2:73 702 170 11.7
Temperature, F. Pressure, p.s.i.a. yo pretreatment -AHR, B.t.u./lb. coal reacted 5255 -ARE, B.t.u./lb. char produced 696
... ...
i4:n 799 160 18.3
...
5.01 12.71 796 80 14.6
6195
4747
3756
1243
4814
4795
4306
1127
4580
3240
1372
1064
817
225
486
674
931
179
956
555
g4000
c
y 3800 (r
3600
8 g 3400 3
z
'
IP3200 3000
% COAL REACTED
Figure 8. Heat of reaction of hydrogen and high-temperature residue at 1000 p.s.i.a. and 1500'
F. 300
tion reaction. In the static reactor, the poor gas-solid contact favors devolatilization, while the intimate gas-solid contact in the fluidized reactor favors oxidation. Therefore, for a fluidized pretreater, the calculated values of the heat of reaction a t 800' F. more nearly approach the actual values. Discussion
Until now, the heat of the coal hydrogasification reaction has only been determined by calculation. These calculations have become more precise as more data became available, but no measurements were made t o check the validity of the calculated data. Initially (in the absence of accurate pilot plant yield data), the heat of reaction was estimated by assuming that coal and carbon were equivalent and that the hydrogasification reaction could be approximated by using values from JANAF Thermochemical Tables (1965) and/orRossini et al. (1953): C
+ 2Hz+
CH4
(4)
This approach, of course, is very crude and could not be expected to give a reliable answer, but it could be useful for comparing the thermal efficiencies of various gasification processes. T h e next approach, using pilot plant data (Pyrcioch and Linden, 1960), was t o calculate the heat of reaction from the heats of combustion of the reactants and products. T h e heats of combustion of various coals.could be obtained by a 248
l & E C PROCESS D E S I G N A N D D E V E L O P M E N T
J A
200
i
[
100
A
&-
t 0
2
--
/
4
6
I
8
IO
12
P R E TR E ATM E N T,
14
16
18
20
%
Figure 9. Heat of reaction of coal pretreatment
Parr bomb calorimeter or calculated by the modified Dulong formula. But if one attempts to calculate the heat of reaction of hydrogen and coal from heats of combustion, there are two drawbacks. First, because the calculation involves taking the differences of large numbers of the same order of magnitude, chemical analyses of all reactants and products must be very accurate and pilot material balances must be quite close to 100% or else the balance must be forced. If this is not the case, large errors can be made in this calculation. This makes the calculated heat of reaction dependent on the quality of the analytical data and on the method used to force the balance. The second drawback is that because the calculated heat of reaction is determined for 25' C., no information is obtained on the reaction heat a t actual reaction temperatures. Furthermore, because only over-all values are obtained by using calculated heats of reaction, they d o not show whether the coal conversion level affects the heat of reaction. Previous studies of coal hydrogasification kinetics and mechanism
3900 I I 3700
>-
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0 PILOT PLANT DATA
2100 I PRETREATED COAL
V LOW-TEMP RESIDUE 0 HIGH-TEMP RESIDUE
1900
1700
I500
SAT-OF.FORYATION
I
1
1
0
IO
20
I
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I
30 40 50 CARBON G A S I F I E D , X
6C
70
Bo
0
10
20 30 40 50 % CARBON GASIFIED
60
70
Figure 10. Comparison of data for heat of reaction of hydrogen and coal
Figure 11. Heat of reaction of hydrogen and Ireland mine coal
(Feldkirchner and Linden, 1963) showed that the initial reaction involved (in addition to the direct attack of hydrogen on the solid coal matter) formation of intermediates by devolatilization, which was followed by vapor-phase hydrogenation and hydrogenolysis. T h e initial pyrolysis reactions are endothermic. I t is expected, then, that the reaction a t low coal conversions would be less exothermic than that a t high conversiqns. T h e lack of this knowledge would seriously hamper the efficient design of coal hydrogasification reactors. Of course, if the heat of reaction could be determined a t one temperature, the heat of reaction a t various temperatures could be calculated from heat capacity data. Some heat capacity data for coals and cokes are available in the literature, but none are available for the particular coals used here. Moreover, the measurement methods used thus far are not very accurate. I n most cases the gaseous decomposition products \?ere allowed to escape from the calorimeters during coal heat-up, and, consequently, the heat capacity data are rather doubtful. A comparison of the heats of reaction of hydrogen and coal obtained from the heat of formation data for C 2H2 + CHI and from the pilot plant data with those obtained from the calorimetry studies is shown in Figure 10. Note that the pilot plant data were based on a 77’ F. reference temperature, M hile the present experimental data were obtained a t operating conditions. Moreover, the experimental data were obtained from coals at four different stages of reaction: raw coal, pretreated coal, low-temperature gasification residue, and high-temperature gasification residue. Ash balances were used to put these results on a common basis. T h e ash balance calculations gave the per cent of carbon gasified in each coal or char. R a w coal was assumed t o have 070 carbon gasified. Thus, Figure 10 shows the average value of the heat of reaction and the general trend of the heat of reaction. Using the technique for the preparation of Figure 10, the effect of temperature on the heat of reaction of hydrogen and coal is shown in Figure 11. T h e horizontal lines associated with each point in Figures 10 and 11 indicate the carbon content (in per cent) of the coal before and after the reaction took place. Accurate heat-of-reaction data are given in Tables 11, 111, and IV. Although the pilot plant data are considerably scattered, the average value is not too different from that obtained by the other methods. The calorimetry data also show some scattering, which is due to the heterogeneous nature of the coal and the characteristics of the calorimeter and the
sensing instruments. Examination of the temperature measurement, the pressure measurement, the temperature distribution in the calorimeter, the total mass balance, and the calibration results obtained from the constant-heat-input method and the experimental runs on hydrogen and n-decane reactions indicate that the data reported in Tables 11, 111, and IV should not have a deviation greater than 10%.
+
Acknowledgment
Valuable advice and discussions were provided by B. S. Lee, S. A. M‘eil, and C. W. Solbrig of the Institute of Gas Technology. J. R. DeSando assisted in the experimental work. Nomenclature
C,
hi,
= =
AgR=
K(e) = m AT
e
=
= =
heat capacity, B.t.u/lb.-’ F. heat input, B.t.u. heat of reaction, B.t.u. calorimeter calibration constant, B.t.u. mass, pounds temperature change, ’ F. time, minutes
Literature Cited
Feldkirchner, H. L., Huebler, J., IND. ENG. CHEM. PROCESS DESIGN DEVELOP. 4, 134 (1965). Feldkirchner, H. L., Linden, H. R., IND. ENG. CHEM.PROCESS DESIGN DEVELOP. 2,153-62 (1963). Huebler, J., Schora, F. C., Chem. Eng. Progr. 62, 87 (1966). “JANAF Thermochemical Tables,” Clearinghouse for Federal Scientific and Technical Information, Springfield, Va., 1965. Diu. Fuel Chem. Preprints Kavlick, V. J., Lee, B. S., Am. Chem. SOC. 10(4), 131 (1966). Linden, H. R., Coal Age 71,64 (1966). Pyrcioch, E. J., Lee, B. S., Schora, F. C., Am. Chem. SOC.Diu. Fuel Chem. Preprints 10(4), 206 (1966). Pyrcioch, E. J., Linden, H. R., Znd. Ene. Chem. 52. 590 (1960). Rossini, F. D.,.Pitzer, K.S.,Arnett, R. L., Braun, R. M., Pimentel, G. C., “Selected Values of Physical and Thermodynamic Properties Hydrocarbons and Related Compounds,” Carnegie Press. Pittsburph. Pa.. 1953. Tajbl, D. G., FeTdkirchher, H. L., Lee, A. L., Am. Chem. SOC. Diu. Fuel Chem. Preprznts 10(4), 235 (1966). von Fredersdorff, C. G., Vandaveer, F. E., “Gas Engineers Handbook,” Segeler, C. G., Ed., Section 3, Chap. 9, 3;pp. 100-123, Industrial Press, New York, 1965. RECEIVED for review July 26, 1967 ACCEPTEDJanuary 17, 1968 This work was jointly sponsored by the American Gas Association, Research and Development, and the U. S. Department of the Interior, Office of Coal Research. Their support is gratefully acknowledged. VOL. 7
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