Energy Fuels 2010, 24, 5002–5007 Published on Web 08/23/2010
: DOI:10.1021/ef100541c
Reaction of FeS with Simulated Slag and Atmosphere S. Ranjan,*,†,‡ S. Sridhar,§,† and R. J. Fruehan† †
Department of Material Science and Engineering, and ‡Department of Chemical Engineering, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, Pennsylvania 15213, and §National Energy Technology Laboratory (NETL), United States Department of Energy, 626 Cochrans Mill Road, Pittsburgh, Pennsylvania 15236 Received April 29, 2010. Revised Manuscript Received July 28, 2010
Dependent upon the size and density of coal particles used in gasifiers, the resulting ash may contain significant quantities of FeS. It is desirable to have these ash particles react and dissolve in the slag. The rate and rate-controlling reaction of FeS droplets with simplified reactor gas and slags were determined using a confocal scanning laser microscope (CSLM) and a thermogravimetric analyzer (TGA). The shrinking FeS droplets were found to remain at the slag/gas interface for a period and conformed to a lens shape, and size change was attributed to both the reaction and submersion into the slag. Whereas the exact rate could not be determined using the CSLM, the rate increased with increasing CO2, decreasing FeO in the slag, and was slow in argon. The change in the rate with experimental values is consistent with the hypothesis that the rate is controlled by mass transfer of the product gases, COS and SO2, away from the particles. TGA results indicated that the measured rate was consistent with the rate computed from the relevant mass-transfer equations and the experimentally determined mass-transfer coefficient. The results indicate that FeS should react, thereby forming FeO, which dissolves in the gasifier slag in a coal gasifier.
of pyrite are temperature-dependent, and the products of decomposition vary considerably under different gaseous, inert, oxidative and non-oxidative, and environmental conditions.5,6 In the present study, the dissolution of troilite FeS obtained directly from pyrite decomposition into a simplified gasifier slag and gas (CO-CO2) was investigated. The rate of dissolution of FeS into the slag was measured using a confocal laser scanning microscope (CSLM) and a thermogravimetric analyzer (TGA).
Introduction As discussed previously in detail, coal gasifiers, such as the integrated gasification combined cycle gasifier, can produce power from low-cost fuels, including coal.1 Much of the coal is gasified into a CO-CO2-H2-H2O gas mixture, with impurities in the coal-forming ash. The phases in the ash particles vary with the size and density of the coal particles.1 The ash can be captured in the gasifier slag system or enter the fly ash stream, which is entrained in the syngas. The fly ash can foul the syngas coater and the plant heat rate. In general, it is desirable to have the ash particles enter the slag. It was found that certain size and density fractions contain large amounts of iron, primarily as pyrite (FeS2). The FeS2 dissociates to non-stoichiometric Fe sulfide and then reacts with the gasifier gas and other ash particles to form the slag and, in some cases, solid or liquid pure phases of iron (Fe), iron oxide (FeO), and iron sulfide (FeS). The reaction of iron and iron oxide with the gasifier slag was previously studied.2 It was found that, in a simplified syngas composition containing CO and CO2, Fe formed FeO, which dissolved in the slag. Furthermore, the results indicated that the rate was controlled by gas-phase mass transfer of CO2 to the surface, which oxidizes the iron. As reported earlier, FeS, both pyrrhotite and troilite forms, is the dominant sulfide species in the ash during the coal gasification system.3,4 Thermal decompositions and reactions
Fundamental Considerations The FeS can react with the gas phase producing FeO and a volatile gaseous species, such as COS and SO2.7-9 The most thermodynamically favorable reaction is the one resulting in the formation of COS (reaction 1), followed by reaction 2, which produces SO2. ð1Þ
FeS þ 3CO2 f ðFeOÞ þ SO2 þ 3CO
ð2Þ
(4) Brooker, D. D.; Oh, M. S. Iron sulfide deposition during coal gasification. Fuel Process. Technol. 1995, 44, 181–190. (5) Yan, J.; Xu, L.; Yang, J. A study on the thermal decomposition of coal-derived pyrite. J. Anal. Appl. Pyrolysis 2008, 82, 229–234. (6) Bhargava, S. K.; Garg, A.; Subasinghe, N. D. In situ hightemperature phase transformation studies on pyrite. Fuel 2009, 88, 988–993. (7) Shannon, G. N.; Matsuura, H.; Rozelle, P.; Fruehan, R. J.; Pisupati, S.; Sridhar, S. Effect of size and density on the thermodynamic predictions of coal particle phase formation during coal gasification. Fuel Process. Technol. 2009, 90, 1114–1121. (8) Nagamori, M.; Yazawa, A. Thermodynamic observations of the molten FeS-FeO systems and its vicinity at 1473 K. Metall. Mater. Trans. B 2001, 32, 831–837. (9) Miura, K.; Mae, K.; Shimada, M.; Minami, H. Analysis of formation rates of sulfur-containing gases during the pyrolysis of various coals. Energy Fuels 2001, 15, 629–636.
*To whom correspondence should be addressed. E-mail: sranjan@ andrew.cmu.edu. (1) Kwong, K.; Petty, A.; Bennett, J.; Krabbe, R.; Thomas, H. Wear mechanism of chromia refractory in slagging gasifiers. Int. J. Appl. Ceram. Technol. 2007, 4, 503–513. (2) Shannon, G. N.; Fruehan, R. J.; Sridhar, S. Removal of metallic iron on oxide slags. Metall. Mater. Trans. B 2009, 40, 727–737. (3) Lambert, J. M., Jr.; Simkovich, G.; Walker, P. L., Jr. Production of pyrrhotites by pyrite reductions. Fuel 1980, 59, 687–690. r 2010 American Chemical Society
FeS þ CO2 f ðFeOÞ þ COS
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: DOI:10.1021/ef100541c
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that the thin layer of slag is saturated with FeS at unit activity in equilibrium with the particle. In this case, the reaction can occur on the slag surface. Another possibility is that there is no slag layer and the particle reacts with the gas producing pure FeO at unit activity. In this case, the pressures of COS and SO2 are over a magnitude lower. However, in this case, the rate would be independent of the FeO content in the slag (this is contrary to the results presented in the next section). FeS can also dissolve directly into the slag primarily as CaS, as given by reaction 3. Small amounts of FeS and MgS could dissolve into the slag. Equilibrium calculations indicate that the equilibrium concentration of the dissolved sulfide is very low; for example, 0.01 mol fraction for CaS and less for FeS and MgS. The calculations indicate that, for the current experiments, only about 10% of FeS will dissolve directly by reaction 3 without a reactive CO-CO2 gas. Mass-Transfer Considerations. The rates of reactions 1 and 2 can be controlled by the transfer of CO2 to the surface or, more likely, COS and SO2 away. Initially, when there is no FeO in the slag, the equilibrium pressure of COS is high. Consequently, the flux of JCOS given by eq 6 will be high. The pressure of COS in the bulk gas will be low and close to 0
Figure 1. Schematic diagram showing possible reactions for the reaction and dissolution of FeS in slag.
In both cases, FeO forms and dissolves into the slag. The parentheses indicates that the species is dissolved in the slag. In addition, FeS can react directly with the slag, primarily forming CaS dissolved in slag. FeS þ ðCaOÞ f ðCaSÞ þ FeO
ð3Þ
Sulfur could also form smaller amounts of FeS and MgS dissolved in the slag. Therefore, we must consider both a gas-FeS-slag and a FeS-slag reaction occurring simultaneously as indicated in Figure 1. In theory, reaction 3 can occur at the particle-slag interface, whereas the gas-FeS-slag reactions 1 and 2 are three-phase reactions, and three phases can only have contact along the circumference of the particle-slag interface. However, FeO formed at the gas-particle interface may move rapidly to the slag, so that the entire particle-gas interface contributes to the reaction. On the other hand, if FeO would remain on the surface as a layer, this would contribute to an increased wetting between the particle and slag, promoting a submersion of the particle into the slag. It should be noted here that movement of FeO into the slag has been determined by experimental observation to an extent of ∼20% of FeO present in terms of slag saturation and is discussed in a later section. Summary of Thermodynamics. The equilibrium constants for reactions 1 and 2 from which the equilibrium pressures of COS and SO2 can be computed with available database FactSage10,11 at 1400 °C are given. K1 ¼
K2 ¼
aFeO pCOS ¼ 2:8 10- 3 aFeS pCO2
3 aFeO pCO pSO2 3 aFeS pCO 2
¼ 3:4 10- 3
JCOS ¼
mCOS g ðpe - pBCOS Þ RT COS
ð6Þ
is the gas-phase mass-transfer coefficient (D/δ) where mCOS g for COS, with D being diffusivity and δ being boundary layer thickness, and peCOS and pBCOS are the equilibrium and bulk pressures of COS, respectively. Similar expressions can be written for SO2 and S2 and combined to determine the total flux. Therefore, if there is no FeO in the slag initially and the pressure and flux of COS is high, the rate will be controlled by mass transfer of CO2 given by eq 7 or mass transfer of FeO in the slag phase away from the surface given by eq 8 JCO2 ¼
2 mCO g ðpBCO2 - peCO2 Þ RT
ð7Þ
B e and pCO are the bulk and equilibrium pressures where pCO 2 2 of CO2, respectively.
ð4Þ
JFeO ¼ ð5Þ
mS FS ½ð% FeOÞS - ð% FeOÞB 100ðMWÞ
ð8Þ
where FS is the density of the slag, mS is the mass-transfer coefficient in the slag, (% FeO)S and (% FeO)B are the equilibrium and bulk FeO contents, respectively, and MW is the molecular weight of FeO. Initially, for the base slag (A) used, there was no FeO. Therefore, initially, the equilibrium of COS and SO2 will be high. For the very initial reaction, the rate may be controlled by the flux of CO2. However, as the FeO content increases, the equilibrium COS and SO2 pressures decrease. For an initial FeS particle of 6 mg and 50 mg of slag, there will be approximately 10 wt % FeO in the final slag if all FeS reacts to FeO. The value of mg for the experimental conditions involving the same CO/CO2 (1.8) gaseous mixture was previously measured for the confocal experiments and is about 2030 cm/s at 1400 °C.2 The mass-transfer coefficients in slag phases at 1400 °C are typically about 0.002-0.008 cm/s. As the FeO content of the slag increases, both the flux of COS
Under reducing conditions that exist in a gasifier, COS predominates. If the CO2/CO ratio exceeds 1, SO2 becomes the most abundant gaseous species. Possible Reaction Mechanism. The thermodynamics given above assumes FeO that forms is in equilibrium with the bulk slag. This implies that the reaction is occurring along the line of contact between the gas-slag-particle or the top of the particle is wetted with a very thin layer of slag in equilibrium with the bulk slag (Figure 1). However, this would mean that the gas is not in contact with the particle. It could be possible (10) Bale, C. W.; Chartrand, P.; Degterov, S. A.; Eriksson, G.; Hack, K.; Ben Mahfoud, R.; Melanc-on, J.; Pelton, A. D.; Petersen, S. FactSage thermochemical software and databases. CALPHAD: Comput. Coupling Phase Diagrams Thermochem. 2002, 26, 189–228. (11) Waldner, P.; Pelton, A. D. Thermodynamics modeling of Fe-S system. J. Phase Equilib. Diffus. 2005, 26, 23–38.
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which the reaction stopped and the sample was quenched to determine whether the formed droplet of FeS sinks or remains afloat on the surface of the slag and the shape of the reacting FeS droplet at 1400 °C. As discussed later, it is difficult to obtain accurate kinetic data with the CSLM experiments. Therefore, additional experiments were conducted in a TGA. The TGA consisted of a Mettler Toledo (AT-261) electronic balance and a Lindberg Blue vertical tube furnace. FeS (0.18-1.0 g) was placed in platinum foil in an alumina crucible (12 mm diameter). After the furnace was purged for 2 h with argon, the sample was lowered into the hot zone and CO (64%)-CO2 (36%) gas was introduced at 900 mL/min. In addition, a separate experiment was conducted using 4 g of slag A and 0.8 g of FeS in an alumina crucible at 1400 °C, with the specific purpose of analyzing the slag for sulfur to determine the amount of sulfur that entered the slag by reaction 3. The slag was analyzed by the West Penn Testing Group of Pittsburgh, PA, using a Leco analyzer. Because the TGA experiments may be influenced by gasphase mass transfer, the mass-transfer coefficient for the experimental conditions was measured. This technique was used previously, and details are given elsewhere.12 The rate of vaporization of pure magnesium (800 mg) was determined in an alumina crucible (12 mm diameter) in flowing ultra-high-purity argon at 900 mL/min at 800 °C. The mass-transfer coefficient of Mg in Ar at 800 °C (1073 K) (m1073 Mg-Ar) was computed from the rate of vaporization, JMg, using eq 10
Table 1. Chemical Compositions (in wt %) of the Slags Used in the Present Work slag
SiO2
Al2O3
CaO
MgO
FeO
A B C D
42.0 37.8 33.6 47.0
21.0 18.9 16.8 25.0
36.0 32.4 28.8 5.0
1.0 0.9 0.8 1.0
10.0 20.0 22.0
and CaS and, consequently, the rate of dissolution of FeO will decrease. On the basis of these considerations, if the rate is controlled by gas-phase mass transfer, it implies that (1) the rate should increase with CO2, (2) the rate should decrease if FeO is initially in the slag, (3) if there is no reacting CO-CO2, the rate should be slow and limited, and (4) the rate should decrease with time because the surface area is decreasing and the equilibrium pressures of COS and SO2 are decreasing because of FeO increasing in the slag. Experimental Section Materials. Iron sulfide (FeS) used in the experiments was prepared from high-purity pyrite (FeS2) obtained from the American Museum of Natural History (AMNH), Central City, CO (AMNH 32740). A resistance furnace at 1260 °C was flushed with high-purity argon for 2 h prior and during the reaction of FeS2, which was contained in an alumina crucible. Thermodynamic calculations indicate that FeS2 will dissociate according to reaction 9. 1 ð9Þ FeS2 ¼ FeS þ S2 2
J¼
m1073 Mg- Ar RT
poMg
ð10Þ
where poMg is the vapor presence of magnesium at 1073 °C. The mass-transfer coefficient of Mg in Ar at 800 °C (33.3 cm/s) was extrapolated to the transfer of COS and SO2 in CO-CO2 at 1400 °C using the dependence of the diffusivity upon the critical parameters. The mass-transfer coefficient at 1400 °C for the sulfur species m“S” was estimated to be 26 ( 30% cm/s (see the Supporting Information).
The stoichiometric conversion to the troilite phase of FeS was confirmed by weight loss measurements and X-ray diffraction. The slags were made from reagent-grade CaO, SiO2, MgO, FeO, and Al2O3. The chemical compositions are listed in Table 1. Experimental Equipment and Technique. Two experimental techniques were employed. Experiments were conducted in a CSLM. This equipment and experimental technique were described previously by Shannon et al.2 The slags weighing about 50 mg were melted in an alumina crucible. The gaseous atmosphere was a flowing CO-CO2 gas mixture or Ar at ∼400 mL/min. A FeS particle (5-10 mg) was added to the surface of the slag, and the reaction was observed. A video was recorded in situ using the microscope. Experiments were conducted at 1400, 1500, and 1600 °C under CO/CO2 (1.8), CO/CO2 (1.0), CO/CO2 (0.33), and argon atmosphere, respectively. In these experiments, the observed liquid FeS particle remained whole or unbroken as a single particle. The diameter of the single FeS particle was tracked and measured from the beginning (∼850 μm, maximum) to the end (∼10 μm, minimum) in each experiment as a function of time. Before carrying out each experiment, FeS particles placed inside the concave meniscus of the premelt slag were stabilized under an ultra-high purity argon atmosphere for ∼10 min. A steady flow of CO-CO2 was maintained prior to the initial heating at a rate of 70 °C/min. Gaseous bubbles during experiments were observed in most of the cases. FeS melts at 1194 °C and, therefore, is liquid during the reaction. The vapor pressure of FeS is very low at 1400 °C. Therefore, the gas phase does not appear most likely. The equilibrium partial pressure of gaseous FeS as determined by FactSage is 3.14 10-7 atm. Hence, it can be ignored for all practical purposes. Furthermore, the density of FeS is greater than that of the slag, 4.84 versus about 2.70 g/cm3. Because the wettability of both molten oxide slags and molten FeS are poor, lensing of liquid FeS over slags A-D was observed. It is believed that minimum interfacial energy allowed a liquid droplet to remain on the surface before the work of adhesion overcame it and the particle began to sink. Several experiments were conducted in
Results and Discussion Dissolution of FeS Slag in the CSLM Experiments. Particle Shape. One of the first issues that should be resolved is the shape of the liquid FeS drop in the slag. Surface tension considerations suggest that it may form a lens shape, which would result in a larger drop diameter than that for a spherical shape. A picture of the quenched slag with a partially reacted FeS is shown in Figure 2, which supports a lens shape. On the basis of the density for liquid FeS, the diameter of a 10 mg drop assuming a spherical shape is about 160 μm. If the particle was a lens shape, the diameter would be even larger. The observed diameter of the exposed drop was 80-100 μm. One possible explanation is that the drop is partially submerged into the slag, exposing a smaller diameter. This uncertainty in the shape and exposed area makes a detailed analysis of the rates difficult. Visual Observation. One of the experimental advantages of the CSLM is that the reaction can be observed. It was observed that gas bubbles formed near the surface of the FeS particle, as shown in Figure 2. In most experiments, the particle remained intact as a single particle (Figure 3). Rate of Dissolution in CSLM. The particle diameter is shown as a function of time for CO/CO2 = 1.8 and slag A in Figure 4 for 1400, 1500, and 1600 °C. The rate of decrease (12) Corbari, R.; Fruehan, R. J. Reduction of iron oxide fines to wustite with CO/CO2 gas of low reduction potential. Metall. Mater. Trans. B 2010, 41, 318–329.
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Figure 2. Scanning electron microscopy (SEM) image of the FeS particle quenched into slag A at (1) 30 s, (2) 1 min, and (3) 2 min using CSLM. The corresponding energy-dispersive spectrometry (EDS) element maps of samples 1 and 2 are shown for Fe and S.
Figure 3. State of liquid FeS droplet on top of slag A at 1500 °C temperatures (on-screen temperature ∼ 1504 °C).
The rates for varying CO/CO2 ratios and argon at 1400 °C are shown in Figure 6. The rate increase with CO2 pressure and in argon is very slow. The effect of varying the initial FeO content of the slag is shown in Figure 7. As expected for gasphase mass transfer, the rate decreases with more FeO in the slag. The rates in argon and for initially 22 wt % FeO are both slow and very similar. The observed decrease in the diameter may be simply due to the particle sinking into the slag
does not change significantly with the temperature, suggesting that mass transfer may be a major factor in controlling the rate. It should be noted that the visual particle diameter may decrease simply because of the particle sinking into the slag. The rate for different original particle sizes at 1500 °C is shown in Figure 5 for slag A and CO/CO2 = 1.8. Within the experimental error, the rate of decrease does not seem to vary significantly. 5005
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Figure 4. Experimental results in CSLM as the decrease in observed particle diameter with CO/CO2 = 1.8 at (a) 1400, (b) 1500, and (c) 1600 °C in slag A.
Figure 7. Experimental results in the CSLM, understanding the effect of FeO initially in slags B and D on the rate of dissolution of FeS at 1400 °C with CO/CO2 = 1.8.
Figure 5. Experimental results in CSLM as the decrease in observed particle diameter with CO/CO2 = 1.8 at 1500 °C, with (a) ∼5 mg, (b) ∼7 mg, and (c) ∼8 mg of FeS particles placed on the concave meniscus of slag A (∼50 mg).
Figure 8. Effect of the initial particle size on the rate of weight loss of FeS in CO/CO2 (ratio = 1.8) gas at 1400 °C.
being controlled by gas-phase mass transfer of the product gas (COS and SO2) away from the surface or CO2 to the surface at very low FeO contents. In particular, the rate increased with CO2 pressure, decreased with the FeO content of the slag, and was very slow in argon when no CO2 was present. A more precise rate can be obtained in the TGA experiments. Reaction of FeS in CO-CO2 in the TGA Experiments. The rate of weight loss for 0.21, 0.5, and 1.0 g of FeS at 1400 °C is shown in Figure 8, which was carried out under a CO/CO2 (1.8) gas mixture with a flow rate of 900 mL/min. For complete reaction, the weight loss should be 0.037, 0.091, and 0.182 g, respectively. According to the proposed ratecontrolling step, gas-phase mass transfer of COS and SO2 away from FeS, the rate should remain relatively constant until/if the contact area between FeS and the gas phase begins to decrease. The theoretical rate was computed using eq 6 and is shown by solid lines. The total pressure of sulfur is given by eq 11. The area is 1.10 cm2, and m“S” is 26 cm/s.
Figure 6. Experimental results in the CSLM, understanding the effect of CO2 and argon on the rate of dissolution of FeS at 1400 °C in slag A.
pCOS þ pSO2 þ 2pS2 ¼ 6:6 10- 3 atm
for these two cases and not a chemical reaction with the gas or slag. Without knowledge of the particle shape and the exposed area to the gas phase, it is difficult to assess the rate. For example, if the particle was spherical, the rate of weight loss could be computed from the change in the particle diameter. However, the particle may be lens shape and significantly submerged.2 Whereas the precise rate could not be determined, the experimental results were consistent with the rate
ð11Þ
The equilibrium pressures were computed using FactSage. The rates of weight loss in the TGA contained in Pt for different initial particle sizes along with the theoretical rate are shown in Figure 8. In theory, the conversion of FeS to FeO should cause about an 18% weight loss. The rate is approximately constant because the area for the reaction is the cross-sectional area of the crucible and will not change until almost all of the FeS has reacted. The decrease in the 5006
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Figure 10. Understanding the effect on the rate of the weight loss of (1) 0.18 g of FeS in 1.0 g of slag A and (2) 0.21 g of FeS without slag, in CO/CO2 = 1.8 at 1400 °C.
Figure 9. Understanding the effect of CO2 on the rate of weight loss of FeS (0.5 g) at 1400 °C with CO/CO2 = (A) 1.8 and (B) 1.0.
rate is depicted by the dashed portion of the curve in Figure 8. Dash lines represent the theoretical weight loss upon completion of the reaction, as given by the eq 1, for 0.21, 0.5, and 1.0 g of FeS. With respect to eqs 1 and 2, the corresponding amount of FeO formed at any given time upon completion of the reaction would be 0.173, 0.409, and 0.818 g, respectively. Consequently, the calculated weight loss for 0.21 g of FeS will be 0.21 minus 0.173, which is equal to 0.037 g. It is to be noted that the formed FeO remains in the crucible, and the lost amount belongs to gaseous sulfur species. Similarly, the calculated weights of sulfur species coming out from 0.5 and 1.0 g of FeS are 0.091 and 0.182 g, respectively. The experimental results gave the weight loss values of 0.040, 0.126, and 0.158 g upon termination of experiments for samples 0.21, 0.5, and 1.0 g of FeS in 1, 5, and 5 h, respectively. These experimental results do not precisely agree with the calculated rates; they are within 27%. However, considering uncertainties in the mass-transfer coefficient ((30%), the reacting area (1.10 cm2), and the computed sulfur species pressure ((10%), the results are consistent with the proposed mechanism. Experiments were further conducted in different gaseous environments and were compared (Figure 9). The pattern of rates of weight loss of FeS was found to increase with the CO2 concentration, as expected for mass-transfer control. To better understand the reactivity of FeS, the weight loss measurement was carried out using 0.18 g of FeS in 1.0 g of slag A at 1400 °C and the conditions were maintained very similar to 0.21 g of FeS without slag. As shown in Figure 10, the rate of weight loss of FeS in slag A is in close agreement with the theoretical weight loss of 0.032 g. Furthermore, the
rate is about the same as for reacting FeS in the absence of a slag. This clearly suggests that the reaction proceeds via eq 1, leading to the formation of FeO, followed by its dissolution in slag A, as observed in CSLM experiments. Summary and Conclusions Dependent upon the size and density of coal particles used in a gasifier, the particles may contain significant amounts of iron as FeS2. FeS2 converted to FeS reacts with the atmosphere and enters the slag as FeO. The rate of the reaction of FeS with a CO/CO2 atmosphere and a slag was investigated using a CSLM and a TGA. Whereas the exact rate could not be determined from the CSLM, observations of the results were consistent with gas-phase mass transfer of COS and SO2 controlling the rate. TGA experiments indicated that the measured rate agreed reasonably well with that calculated for mass-transfer control. The results indicate that, if FeS contacts the slag in a gasifier, it will react rapidly to FeO, which is dissolved in the slag. The actual rate will depend upon flow and mass-transfer conditions in the reactor. Acknowledgment. This work was carried out through the RDS site support contract for Multiphase Flow Collaboratory Contract 41817.606.07.02 funded by the Gasification Technology Program at the National Energy Technology Laboratory (NETL). Supporting Information Available: Calculations of the masstransfer coefficient for the sulfur species and equilibrium pressures (from FactSage) of sulfur species. This material is available free of charge via the Internet at http://pubs.acs.org.
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