Ind. Eng. Chem. Res. 1997, 36, 2849-2854
2849
RESEARCH NOTES Thermochemical Decomposition of Phosphogypsum with Oil Shale in a Fluidized-Bed Reactor: A Kinetic Study Y. Suyadal, A. O 2 ztu 1 rk, H. Ogˇ uz,* and R. Berber Chemical Engineering Department, Ankara University, Tandogˇ an, 06100 Ankara, Turkey
This study involves thermochemical decomposition of phosphogypsum (PG) in the presence of oil shale (OS) as the source of carbon in a bench-scale fluidized-bed reactor, with air flowing as the gaseous feed. Experiments were carried out thermochemically under isothermal conditions in a batchwise manner at different added weight fractions of OS varying from 0.1 to 0.3 (w/w). The temperature range considered was in the range of 1123-1273 K. The gas phase obtained from thermochemical decomposition of the sample was monitored by gas analyzers (MSI 5600, Germany; MIR 9000, France), and all process data were recorded on-line at regular intervals by a data acquisition system specifically developed for this purpose. Concentration-time data were evaluated for each run to obtain conversion-time curves. The overall reaction was found to be reaction rate controlled in compliance with the Avrami equation which represented the observed data reasonably well. The rate constant was found to have an activation energy of 184 kJ/mol for the 0.30 weight fraction of OS in the feedstock. The activation energy which was determined using the Avrami equation dropped from 631 kJ/mol at 0.1 weight fraction to 184 kJ/mol at 0.3 weight fraction. Increased operating temperature at a preset feed ratio of OS to PG increased the SO2 concentration and decreased the CO concentration. This indicated the possibility that the complete oxidation of the carbon source would be taking place at higher temperatures as the reducing atmosphere diminished. Introduction Thermochemical decomposition of CaSO4 is of technical interest and has been receiving academic as well as industrial attention mainly for two reasons: The first is that the reductive decomposition of calcium sulfate (phosphogypsum (PG) or natural gypsum) gives rise to two desirable products: sulfur, which can be converted to sulfuric acid, and CaO as a cement throughput (Hull et al., 1957; Kuehle and Knoesel, 1988; Wheelock et al., 1988). The importance of production of CaO through this process is in the fact that the process causes no CO2 emission to the atmosphere compared to the conventional calcination of carbonates in the cement industry. The second factor is that this process allows the regeneration of undesirable sulfate waste products (desulfogypsum) from flue-gas desulfurization (FGD) processes (Montagna et al., 1975; Hansen et al., 1993; Kamphuis et al., 1993). As the limestone is extensively used to reduce the SO2 emission from power plants, the growing amount of desulfogypsum is becoming an environmentally important problem. Calcium sulfate can be reduced to calcium oxide at high temperatures using a reducing agent. Most of the investigations of the reductive decomposition of calcium sulfate reported in the literature have been carried out either in bench-scale reactors or thermoanalyzers utilizing CO, H2, and CH4 as reducing agents. A selection of published studies for reductive decomposition is given in Table 1. This table indicates that the available information in the area is somewhat controversial and is far from being sufficient for drawing conclusive * To whom correspondence should be addressed. S0888-5885(96)00184-4 CCC: $14.00
results. Therefore, a commercially viable process should make use of the energy content of the oil shale so that the process could be attractive. This requires an oxidative atmosphere in the fluidized bed. On the other hand, the decomposition reaction takes place in a reductive environment. It seems to be very crucial to keep this balance such that both requirements are met. In this respect this study disclosed valuable results for obtaining reductive conditions in the bed. Further study is, however, needed to gain insight into the energy economics of the process. One other difficulty that is foreseen is the fluoro and P2O5 content of the PG. These impurities may deteriorate the quality of the cement when the solid product of the suggested process is used as the clinker. This side of the process, although it deserves careful attention, has not been investigated yet. Particularly, the decomposition of PG in the presence of oil shale requires deeper consideration, because in this case, some impurities of PG may disappear by thermochemical decomposition whereas new ones may be formed by some side reactions between the components of the oil shale and PG. Furthermore, some additional impurities that may originate from oil shale are also expected to remain in the ash. This point should be taken into account if the solids remaining from the thermochemical decomposition of PG with oil shale are to be considered as cement additives. In fact, there is very little information in the open literature about an attempt to use oil shale itself to produce cement (Feige, 1992). Current knowledge of the dissociation of calcium sulfate under the reducing medium of coal or coke suggests the following reactions (Oh and © 1997 American Chemical Society
2850 Ind. Eng. Chem. Res., Vol. 36, No. 7, 1997 Table 1. Selected Studies on the Reductive Decomposition of Gypsum or Anhydrite reference
gas/solid-system
Wheelock and Boylan (1960) %2-6 CO-gypsum Swift and Wheelock (1975)
Montagna et al. (1975)
Gruncharov et al. (1985a) Gruncharov et al. (1985b)
Diaz-Bossio et al. (1985)
Wheelock et al. (1988)
Kuehle and Knoesel (1988)
Kamphuis et al. (1993)
Hansen et al. (1993)
reactor
model used
remarks
packed bed
1st-order reaction with respect to CO, optimum temp. 1200-1230 °C natural gas/gypsum two-zone bench-scale lower reducing zone by partial combustion and anhydride fluidized-bed of natural gas, upper oxidizing zone reactor by the addition of secondary air in temp 1043-1221 °C; conversion to calcium sulfide avoided Rav ) kYCH4YO20.68h-1.33 Rav average rate of SO2 generation from CO, H2, CH4/sulfated bench-scale dolomite-limestone fluidized-bed sulfated dolomite, Y concentrations reactor of CH4 and O2 in feed gas, h fluidizedbed height, k rate constant (temperature dependency nonArrhenius type for 1010-1095 °C); establishing two reaction zone is (lower oxidizing, upper reducing) is a very effective way to minimize CaS H2-CO2-H2O-Ar/PG thermoanalyzer Polany-Wigner representative for 950-1000 °C, R is a equation: R ) kt fraction of decomposition, t ) time and k ) rate constant thermoanalyzer Avrami equation: CO-CO2-Ar/PG representative for temperature range (-ln(1 - R)1/3)) ) kt 1000-1075 °C, R is a fraction of decomposition, t ) time and k ) rate constant thermoanalyzer grain model of 1st-order with respect to H2 or CO, 1-6% CO, H2/ reagent-grade Szekely et al. (1976) overall reaction rate controlled by CaSO4 chemical reaction rate, with activation energies being 242 and 288 kJ/mol for CO, and H2, respectively, fairly well representation of exp. conversiontime data with spherical grain model natural gas/PG & bench- and pilotin one version coal in the feed to serve waste gypsum/coal plant-scale as a solid reductant whereas in fluidized-bed another version powdered coal or reactor natural gas as the source of gaseous reductants CO and H2, similar results with both versions, two-zone operation (lower part: reducing) for 1098-1149 °C air/dried & calcined circulating experiences of LURGI to make use out raw mix (PG, clay, fluidized-bed of PG to produce two products, sand)/reduction reactor conc. SO2 and cement clinker, 99% agent (anthracite) decomposition degree at 1060 °C, two-zone operation (lower reducing) thermoanalyzer Ri ) dχ/dt, Ri fractional study of apparent solid-solid reaction 5%H2-N2/CaSO4 production rate, χ between CaS and CaSO4 in an atmosphere of N2 or N2-SO2 gas mixt., fractional production degree T: 950-1100 °C, initial mole fract. CaSO4: 0.1-0.9, instant. formation of eutectic liquid phase and redox reaction of sulfate and sulfur anions as ratedetermining step for SO2 production synthetic flue gas fixed-bed laboratory study of the effect of periodically changing CO/FGD-gypsum quartz reactor oxidizing and reducing conditions, dependency of transformation of CaSO4 to CaS by CaO, reaction mechanisms based on past experimental findings
model parameter were determined from extensive conversion-time data describing sigmoidal behavior.
Wheelock, 1990): 1000 °C
CaSO4 + 2C 98 CaS + 2CO2 1200 °C
CaS + 3CaSO4 98 4CaO + 4SO2 2CaSO4 + C f 2CaO + 2SO2 + CO2 However, a close look at Table 1 reveals that little fundamental kinetic data are available on the thermochemical decomposition of gypsum, and the reaction mechanism seems not to be yet fully understood (Kim, 1988). It is, therefore, clear that there is incentive for further studies in this area which would pave the way to the solution of some of the current environmental problems. In the present study, SO2 and CO evolution from thermochemical decomposition of phosphogypsum in the presence of oil shale was investigated experimentally in a laboratory-scale fluidized-bed reactor. Both the oil shale fraction in the sample and the bed temperature were varied. Activation energy, frequency factor, and
Experimental Section Apparatus. The experimental setup consists of mainly a stainless steel fluidized-bed reactor (FBR) surrounded by an electrically heated tubular ceramic furnace and auxiliary equipment for fluidizing air preparation, gas analysis, and on-line data logging system. The experimental setup is shown schematically in Figure 1. The fluidized-bed reactor illustrated in Figure 2 is a stainless steel tube of 46 mm inside diameter and 500 mm length. It is fitted with a stainless steel sieve (325 mesh) gas distributor. The reactor is heated by a Kanthal-A1 heating wire, and the bed temperature is measured by a NiCr/Ni thermocouple and controlled by a feedback PID loop using the heating power supplied to the furnace as a manipulated variable. A preheater is connected to the FBR for heating the incoming fluidizing air before it is introduced to the reactor. In the course of the experiments gas samples of decomposition product were taken from the top of the cyclone, cooled through a heat exchanger,
Ind. Eng. Chem. Res., Vol. 36, No. 7, 1997 2851
and CO versus time in the effluent stream from the reactor for the sample with 0.30 (w/w) OS. As is also reflected in this figure, the results indicate that decomposition of PG can be substantially achieved at temperatures considerably lower than the thermodynamic thermochemical decomposition temperature of 1473 K due to the reducing atmosphere created by the presence of OS. Increased operating temperature at a preset feed weight fraction of OS showed an increase in the SO2 concentration and a decrease in the CO concentration. This can be explained by the diminution of the reducing atmosphere at higher temperatures because of the possible complete oxidation of the carbon source. SO2 evolution (P), as g of SO2/kg of sample, is calculated from experimental SO2 concentration-time curves by the following equation:
MSO2 t)t
P)Q
W
CSO ∆t ∑ t)0 2
Figure 1. Schematic diagram of the experimental setup.
and fed continuously to the gas analyzers MSI 5600 (based on electrochemical sensors) and MIR 9000 (based on IR with an interference filter) for on-line simultaneous measurements of SO2, O2, and CO. In the case of the use of an MSI 5600 analysis system, the exit gas was passed through a dilution system to meet the limits imposed by the sensors. The necessary corrections were then made to obtain the real values for concentration. Materials. A mixture of OS and PG with different weight fractions was used as the reactant in the experiments. PG was provided by TU ¨ GSAS¸ Samsun fertilizer plant, while OS samples were from Beypazari deposits. The chemical analyses of PG and elemental analyses of OS and their characterization tests are given in Tables 2-4. PG and OS particles were first pelletized with a saturated solution of CaSO4 and then dried at ambient temperature. The OS to total sample weight fractions employed in the experiments were 0.1, 0.2, and 0.3. Since Diaz-Bossio et al. (1985) in their study of reductive decomposition of calcium sulfate noted no significant difference between runs made with pellets of different diameters, the pellet size was not considered as a parameter in the runs. Procedure. The fluidized-bed reactor system was operated batchwise with a single charge of pelletized particles. Reactor operating parameters are given in Table 5. In each run, 5 g of solid sample was loaded into the reactor and reacted for a period of 150 s. Experiments were carried out at temperatures of 1123, 1173, 1223, and 1273 K and oil shale weight fractions of 0.1, 0.2, and 0.3 (g of OS/g of sample). In the course of the experiments, the flow rate of air was set to the corresponding value so that a constant ratio of Uo/Umf ) 6 was maintained, and when steady-state temperature was reached, the sample to be decomposed was introduced into the reactor. For each batch run, gas samples were continuously taken from the reactor outlet streams and analyzed by the gas analysis equipment. Results Experimental concentration-time curves for SO2 and CO evolution were obtained at each set of experimental conditions within the ranges listed in Table 5. These results enabled evaluation of the SO2 liberated from the decomposition of the sample used. An examplary set of data are given in Figure 3 as concentrations of SO2
where Q is the volumetric flow rate of gas, MSO2 is the molecular weight of SO2, and W is the weight of the sample used. By using P values, conversion-time curves were determined as given in detail in the appendix. The results showing the change in conversion with time are illustrated in Figure 4. Application of the Reaction Models To Evaluate Kinetics. In order to evaluate the kinetics of decomposition, several models were considered. Most of the models previously suggested in the literature as given in Table 1 were tested to find the best fit to the conversion-time curves obtained from experimental SO2 evolution. It was consequently found that the experimental data could best be represented by the Avrami equation as proposed by Gruncharov et al. (1985b) for the thermochemical decomposition of PG in TGA. Thus, the apparent sigmoidal shape of the experimental conversion-time curves fit to the following “nucleation model” of Avrami (Doraiswamy and Sharma, 1984):
X ) 1 - exp[-(kt)m] where k is the reaction rate constant, t is time, and m is the model parameter accounting for the reaction mechanism, number of nuclei present, composition of the parent and product phases, and geometry of the nuclei. To test the validation of this kinetic model, the values of ln[-ln(1 - X)] vs ln(t) were evaluated to obtain k and m. Arrhenius plots of the kinetic rate constants for decomposition of PG with OS are shown in Figure 5. The parameters of the Arrhenius equation k0 and E and Avrami model parameter m were evaluated by using the Marquardt method to minimize a leastsquares objective function between observed and predicted values (Kuester and Mize, 1973). The application of the Avrami model to the experimental data obtained in this work implies that the assumption of negligible solid loss with the gas phase as fly ash holds. Table 6 shows the optimized frequency factors and activation energies using the initial estimates of Arrhenius plots and Avrami model parameter m. To test whether the interparticle diffusion had any significant effect on the rate of decomposition, the jD factor was calculated with the equation of Chu et al. (Smith, 1981). The results indicated that the interpar-
2852 Ind. Eng. Chem. Res., Vol. 36, No. 7, 1997 Table 2. Complete Chemical Analyses of PG weight %
CaO
MgO
Al2O3
Fe2O3
SO3
SiO2
TiO2
Na2O
K2O
P2O5
heating loss
32.68
0.07
0.36
0.07
42.28
1.17
0.09
0.04
0.02
0.49
21.82
Figure 2. Details of the fludized-bed reactor. Table 3. Elemental Analyses of OS dry (wt %)
dry, ash-free (wt %)
C
H
O+N
S
ash
C
H
N+O
S
13
1
15
1
70
42
3
51
4
Table 4. Characterization Tests of OS and PG material and characterization test 1. oil shale + phosphogypsum (sieve analysis with brass sieve ASTM E11.87) 2. phosphogypsum (simultaneous thermal analysis with STA 429)
results
Figure 3. Concentration-time curves of SO2 and CO.
mean particle diameter range: 64 e dp (µm) e 77
observed peaks: 170 °C, endo, CaSO4‚1/2H2O 210 °C, endo, CaSO4 1200 °C, endo, crystal collapse 3. phosphogypsum (scanning mean particle diameter with electron microscopy with secondary electron Polaron E5100-Leitz Amr1000) photograph: 20-30 µm homogen particle distribution was observed 4. oil shale + phosphogypsum observed peaks: (X-ray diffraction with Philips anhydride: CaSO4 PW 1730 Cu KR) bassanide: CaSO4.1/2H2O quartz: SiO2
Table 5. Ranges of Experimental Conditions Used parameters
range
reactor operating temperature reactor operating pressure OS fraction in the feedstock mean particle diameter of the feedstock space velocity Uo/Umf
1123 e T (K) e 1273 101.3 kPa 0.1 e g of OS/g of sample e 0.3 64 e dp (µm) e 77
Figure 4. Conversion-time curves evaluated for decomposition of PG with OS.
7880 e S (h-1) e 13074 6
ticle diffusion was unimportant to be considered as a rate-determining step. Using optimized values of the kinetic parameters in the temperature range worked, parity plots according to the Avrami model are given in Figures 6-8, for oil shale weight fractions 0.1, 0.2, and 0.3, respectively. Conclusions The chemical analysis of the effluent gas from the reactor shows that, by making use of the oil shale, reductive conditions can be obtained for thermochemical decomposition of phosphogypsum. Results also indicate that an increased proportion of OS in the samples used leads to increased CO evolution, providing evidence to support this argument. The activation energies shown
Figure 5. Arrhenius plots of kinetic rate constants obtained.
in Table 6, on the other hand, demonstrate that the more oil shale in the mixture, the lower is the activation energy for the decomposition. From this perspective, therefore, in the range of experimental conditions employed in the present work, the most favorable proportion of the OS in the feedstock appears to be that with a weight fraction of 0.3. The activation energy for 0.30 weight fraction of oil shale in the sample is 184
Ind. Eng. Chem. Res., Vol. 36, No. 7, 1997 2853
Figure 6. Parity plot according to the Avrami model for 10% oil shale.
Figure 7. Parity plot according to the Avrami model for 20% oil shale.
Table 6. Estimated Kinetic Parameters g of OS/g of sample
k0, s-1
E, kJ/mol
m
r2
0.10 0.20 0.30
1.663 × 2.055 × 1015 6.620 × 104
631 455 184
0.354 0.425 0.702
0.941 0.932 0.935
1022
complished by utilizing oil shale which can provide not only the reductive atmosphere as observed by the presence of CO in the reactor but also part of the necessary heat for decomposition under carefully controlled conditions. One needs to bear in mind that increasing the operating temperature at a preset feed ratio of OS to PG increases the SO2 concentration and decreases the CO concentration. This gives evidence to the possibility that complete oxidation of the carbon source at higher temperatures may be occurring as the reducing atmosphere diminishes. The thermochemical decomposition suggested in this work, therefore, holds promise for converting PG wastes into utilizable products provided that the remaining technological problems are resolved. However, since the suggested process is novel, the number of questions remaining to be answered is higher than that of the resolved problems. A lot more work needs to be done to gain a valuable insight into the mechanism of thermochemical decomposition under such chemically complex conditions and into the practical problems. Research work continues in our group to run the reactor under differential conditions and to conduct the reductive decomposition in the same fluidized bed but in continuous operation. We hope that the results of further investigations will provide some useful information toward the understanding of the complexity that the process involves. The findings of these studies will be reported in a subsequent paper. Acknowledgment Financial support provided by the Scientific and Technical Research Council of Turkey (TU ¨ BITAK) under Grant No. MISAG/KTC¸ AG-116 and Cement Producers Association of Turkey for this work is gratefully acknowledged. Nomenclature
Figure 8. Parity plot according to the Avrami model for 30% oil shale.
kJ/mol. This is comparable with the estimation of DiazBossio et al. (1985), who gave 242 kJ/mol for reductive decomposition of CaSO4 utilizing 1-6% CO as the reducing gas, indicating a reaction-controlled rate. On the other hand, a much smaller activation energy was estimated by Gruncharov et al. (1985b), who found 114 kJ/mol for reductive decomposition of PG utilizing 4% CO, 10% CO2, and 86% Ar as reducing gases. Although their estimated activation energy was still high to draw this conclusion, Gruncharov et al. (1985b) suggested a diffusion-controlled rate. Considering the mass-transfer factor, jD, and also the arguments brought up by DiazBossio et al. (1985), the magnitudes of the activation energies found in this study suggest that the rates were determined under conditions of chemical reaction control. One further conclusion that can be drawn from the results is that the overall conversion data under the experimental conditions investigated are best represented by the Avrami model compared to the other models tested. Based on the findings of this study, it is concluded that the reductive decomposition of PG can be ac-
C ) concentration, % dp ) mean particle diameter, µm E ) activation energy, kJ/mol h ) fluidized-bed height, m jD ) mass-transfer factor k ) rate constant, s-1 ko ) frequency factor, s-1 m ) Avrami model parameter m0 ) initial amount of samples, g mSO2 ) SO2 weight, g MSO2 ) molecular weight of SO2, g/mol nSO2 ) SO2 mole number, mol P ) SO2 evolution, g of SO2/kg of sample Q ) volumetric flow rate of gas, L/min Ri ) fractional production rate reaction i, s-1 Rav ) average rate of SO2 generation from sulfated dolomite S ) space velocity, h-1 t ) time, s T ) reactor operating temperature, K Umf ) minimum fluidization velocity, m/s Uo ) superficial velocity, m/s W ) weight of sample, g X ) fractional conversion YCH4, YO2 ) fractions of CH4 and O2 in the feed gas Greek Letters R ) fraction of decomposition
2854 Ind. Eng. Chem. Res., Vol. 36, No. 7, 1997
In the above equations, the units of Q, m0, T, C, and t are respectively L/min, g, K, %, and s.
χ ) fractional production degree
Appendix: Evaluation of the Conversion-Time Curves from P Values The evaluation is based on the following reaction stoichiometry:
CaSO4‚2H2O f CaO + SO2 + 0.5O2 + 2H2O The conversion factor from percent to molar concentration of SO2 as mol/L can be given according to the following relation:
1% )
(0.122 T )
The area under the concentration-time curves can be calculated as follows:
area )
∫0150C dt
0.122 T
where area has the unit of (mol/L)‚s. SO2 mole number, nSO2, can be written as follows:
[
nSO2 ) Q
∫0150C dt] ) 2.032 × Q 150 10-3 ∫0 C dt T
L 1 min 0.122 min 60 s T
][
SO2 mole number is related to its weight mSO2 by
[
mSO2 ) [64 g/mol] 2.032 × 10-3
∫0150C dt mol] ) Q 150 0.130 ∫0 C dt T
Q T
From the reaction stochiometry given above, the converted amount of CaSO4‚2H2O to CaO can be written as follows:
mCaSO4‚2H2O )
Q 0.130 ∫ [172 64 ][ T
150
0
]
C dt )
∫0150C dt
Q T
0.350
Literature Cited Diaz-Bossio, L. M.; Squier, S. E.; Pulsifer, A. H. Reductive Decomposition of Calcium Sulfate Utilizing Carbon Monoxide and Hydrogen. Chem. Eng. Sci. 1985, 40, 319. Doraiswamy, L. K.; Sharma, M. M. Gas-Solid and Solid-Solid Reactions. Heterogenous Reactions: Analysis, Examples and Reactor Design; John Wiley and Sons: New York, 1984; Vol. 1. Feige, F. Cost-effective Utilization of Oil Shale at Rohrbach Zement. Zem.-Kalk-Gips 1992, 45, 53. Gruncharov, I.; Pelovski, Y.; Dombalov, I.; Kirilov, P. Thermochemical Decomposition of Phosphogypsum Under H2-CO2H2O-Ar Atmosphere. Thermochim. Acta 1985a, 93, 617. Gruncharov, I.; Pelovski, Y.; Dombalov, I.; Kirilov, P. Isothermochemical Gravimetric Kinetic Study of the Decomposition of Phosphogypsum Under CO-CO2-Ar Atmosphere. Thermochim. Acta 1985b, 92, 173. Hansen, P. F. B.; Dam-Johansen, K.; Ostergaard, K. High Temperature Reaction Between Sulphur Dioxide and LimestonesV. The Effect of Periodically Changing Oxidizing and Reducing Conditions. Chem. Eng. Sci. 1993, 48, 1325. Hull, W. Q.; Schon, F.; Zirngibl, H. Sulfuric Acid from Anhydrite. Ind. Eng. Chem. 1957, 49, 1204. Kamphuis, B.; Potma, A. W.; Prins, W.; Van Swaaij, P. M. The Reductive Decomposition of Calcium SulphatesI. Kinetics of the Apparent Solid-Solid Reaction. Chem. Eng. Sci. 1993, 48, 105. Kim, Y. K. Thermochemical Evaluation of Calcium Sulfate Decomposition Reactions. Proceedings of the Second International Symposium on Phosphogypsum, Miami, FL, 1988; Florida Institute of Phosphate Research, Publication No. 01-037-055: Bartow, FL, 1988; Vol II, p 168. Kuehle, K. H.; Knoesel, K. R. Energy Saving Process for Thermal Decomposition of Phosphogypsum and other Calcium Sulphates for the Production of H2SO4 and Cement Clinker by Applying the Circulating Fluid Bed. Proceedings of the Second International Symposium on Phosphogypsum, Miami, FL, 1988; Florida Institute of Phosphate Research, Publication No. 01-037-055: Bartow, FL, 1988; Vol II, p 15. Kuester, J. L.; Mize, J. H. Optimization Techniques with Fortran; McGraw-Hill, New York, 1973. Montagna, J. C.; Lenc, J. F.; Vogel, G. J.; Thodos, G.; Jonke, A. A. Proceedings of the 4th International Conference on FluidizedBed Combustion, McLean, VA, Dec 9-11, 1975; p 393. Oh, J. S.; Wheelock, T. D. Reductive Decomposition of Calcium Sulfate with Carbon Monoxide: Reaction Mechanism. Ind. Eng. Chem. Res. 1990, 29, 544. Smith, J. M. Chemical Engineering Kinetics, 3rd ed.; McGrawHill: Auckland, 1981. Swift, W. M.; Wheelock, T. D. Decomposition of Calcium Sulfate in a Two-Zone Reactor. Ind. Eng. Chem. Process Des. Dev. 1975, 14, 3. Wheelock, T. D.; Boylan, D. R. Reductive Decomposition of Gypsum by Carbon Monoxide. Ind. Eng. Chem. 1960, 52, 3. Wheelock, T. D.; Fan, C. W.; Floy, K. R. Utilization of Phosphogypsum for the Production of Sulfuric Acid. Proceedings of the Second International Symposium on Phosphogypsum, Miami, FL, 1988; Florida Institute of Phosphate Research, Publication No. 01-037-055: Bartow, FL, 1988; Vol II, p 3.
By using this relation given above, fractional conversion (X) of CaSO4‚2H2O to CaO can be calculated by
X)
Received for review April 1, 1996 Revised manuscript received March 21, 1997 Accepted March 21, 1997X
∫0150C dt
0.350Q m0T
IE960184J Abstract published in Advance ACS Abstracts, May 1, 1997. X
where m0 is the initial amount of samples.
