Influence of Operating Conditions on SO3 Formation during Air and

Article pubs.acs.org/IECR

Influence of Operating Conditions on SO3 Formation during Air and Oxy-Fuel Combustion Daniel Fleig,* Klas Andersson, and Filip Johnsson Department of Energy and Environment, Division of Energy Technology, Chalmers University of Technology, SE-412 96 Göteborg, Sweden S Supporting Information *

ABSTRACT: Because SO3 participates in both high- and low-temperature corrosion processes, there is a general concern about the SO3 formation under oxy-fuel fired conditions. This work has the aim to evaluate the influence of combustion parameters on the formation of SO3. Experiments were conducted in oxy-fuel and air-fired experiments with propane as fuel and injection of SO2 in the oxidizer. The SO3 concentration was measured with a controlled condensation method at the furnace outlet as well as in the flame. The experiments show that the gas-phase is an important contributor to SO3 formation and that the SO3 formation is strong during burnout of the fuel. In oxy-fuel combustion with wet flue-gas recycle (FGR), more SO3 was formed than during dry FGR at similar temperature conditions, which indicates that H2O enhances SO3 formation. The experiments also show that the SO3 formation rises with an increase in furnace temperature. Because temperature and residence time in the furnace increases with reduced FGR ratio, the FGR ratio directly influences the SO3 formation in oxy-fuel combustion. This was obvious during the experiments, and the SO3 concentration rose with a reduced FGR ratio. oxy-fuel combustion compared to that of air-firing.8−14 Most of these SO3 measurements were done by extracting a sample of the exhaust gas. An exception is the work by Eddings et al.14 who measured SO3 concentrations by extracting flue-gas also at temperatures between 500 and 1000 °C. However, so far there are no published results of in-flame measurements and parametric studies to examine and compare the SO3 formation under air-fuel and oxy-fuel conditions. In fact, experience from in-flame SO3 measurements under air-fired conditions is limited as well.15−20 In our previous gas-phase modeling work,2 the formation of SO3 under oxy-fuel conditions was investigated by assuming plug-flow and postflame conditions. The main conclusion from that work was that an increase in SO2 concentration increases the SO3 outlet concentration, but the formation ratio SO3/SOx decreases, i.e., SO2 seems to inhibit its own oxidation. The SO3 formation increases with O2 and H2O concentration, and a CO2 atmosphere enhances the SO3 formation only slightly compared to a N2 atmosphere. All previous SO3 measurements under oxy-fuel conditions8−14 were performed using coal as fuel. However, during coal combustion, heterogeneous reactions influences the amount of SO3 formed. The heterogeneous reactions can either favor the formation of SO3, such as catalytic reactions by iron oxide (Fe2O3),21−24 or reduce the stack gas concentration of SO3 through reactions with basic oxides such as calcium oxide (CaO) in coal ash.21 Because heterogeneous reactions are strongly dependent on the fuel, it is difficult to draw general conclusions from the published SO3 measurements performed under oxy-fuel operation.8−14 Thus, to examine the SO3

1. INTRODUCTION During combustion of sulfur-containing fuels, mainly sulfur dioxide (SO2) and a minor fraction of sulfur trioxide (SO3) are formed. The gas-phase SO3 formation at high temperature is based on the direct oxidation of SO2, mainly by the reaction SO2 + O ( +M) ⇌ SO3 ( +M)

(1)

At lower temperatures, SO3 formation via HOSO2 occurs SO2 + OH ( +M) ⇌ HOSO2 ( +M)

(2)

HOSO2 + O2 ⇌ SO3 + HO2

(3)

Reactions 1−3 were identified as important SO3 formation reactions by Hindiyarti et al.1 This is confirmed by our previous modeling work.2 SO3 can also be reduced during combustion, and Hindiyarti et al.1 conclude that SO3 + H ⇌ SO2 + OH

(4)

is the major consumption reaction for SO3, whereas the reaction SO3 + O ⇌ SO2 + O2

(5)

is too slow to consume a significant fraction of the formed SO3. The presence of SO3 is undesired during boiler operation Because SO3 is involved in high- and low-temperature corrosion. An exception is the injection of SO3 upstream of the electrostatic precipitator (ESP) to improve the dust precipitation for certain coal ashes because the injection of SO3 reduces the electrical resistivity of fly ash.3 In oxy-fuel combustion, the combustion atmosphere is different from that during air-firing, and the SO2 concentration is several times higher than during air firing,4−11 because of the absence of air-borne nitrogen (N2). Previous experimental work also shows an increase in the measured SO3 concentration in © 2012 American Chemical Society

Received: Revised: Accepted: Published: 9483

January 8, 2012 June 18, 2012 June 25, 2012 June 25, 2012 dx.doi.org/10.1021/ie301303c | Ind. Eng. Chem. Res. 2012, 51, 9483−9491

Industrial & Engineering Chemistry Research

Article

Figure 1. Chalmers oxy-fuel test unit. Letters (M) denote measurement positions: in-flame measurements in M2−M5, SO3 outlet concentration in M8, flue-gas composition in M13, and feed-gas composition in M15.

formation under different oxy-fuel conditions it is, in a first approach, reasonable to investigate the gas-phase isolated from the heterogeneous reactions by using gaseous fuels. In this experimental work, the SO3 formation under oxy-fuel and airfired conditions was investigated by using propane as fuel, and SO2 was injected in the feed gas in a 100 kW oxy-fuel test facility; the experimental results are relevant for industrial applications. Measurements were carried out downstream of the furnace as well as within the flame, applying a controlled condensation method to measure the SO3 concentration in the flue gas. The in-flame SO3 measurements are compared with modeled SO3 concentrations obtained from a simple plug-flow reactor model.

2. EXPERIMENTS Chalmers Oxy-Fuel Test Unit. Figure 1 outlines Chalmers oxy-fuel test unit with its cylindrical furnace and top-fired burner. The flue-gas measurement positions indicated as M1 to M15. Table 1 lists the distance from

the the are the Figure 2. Schematic of the gas burner.

Table 1. Furnace Measurement Levels measurement position

distance from burner inlet [m]

M2 M3 M4 M5

0.215 0.384 0.553 0.800

into the burner via a primary and secondary register respectively. The primary swirl register has an angle of 45°, and the secondary swirl register has an angle of 15°. During our SO3 measurement campaign,26 it was obvious that SO3 formation increases with an increasing temperature level in the furnace. It was therefore of interest to quantify the temperature level in the furnace. This was done by calculating an average wall temperature from 14 continuously logged thermocouples placed 2 cm from the inner surface of the furnace wall. Test Cases. Tests were performed during air and oxy-fuel combustion. The flue-gas composition was measured downstream of the flue-gas condenser (M13), and the feed-gas composition of the oxy-fuel cases was measured downstream of

burner inlet to each furnace measurement level used during inflame measurements (M2 to M5). For detailed information about the Chalmers test unit, see Andersson et al.25 The burner was fed with propane as fuel, and SO2 with a minimum purity of 99.8% was injected in the oxidizer downstream of the O2 injection. A schematic of the burner used is shown in Figure 2 with the fuel injected in the center of the furnace top via an annular burner nozzle. The feed gas (oxidizer) is transported 9484

dx.doi.org/10.1021/ie301303c | Ind. Eng. Chem. Res. 2012, 51, 9483−9491


Article

Table 2. Experimental Conditions of the Main Test Cases in This Work outlet flue-gas composition (M13) (on wet basis) test case

O2 in feed gas [vol %, dry]

OF30 ref case OF25 ref case Air ref case OF25 (low SO2) OF30 (low SO2) OF30 75 kW case OF46w OF40

30 25 21 25 30 30 46 40

type of FGR

oxidizer volume flow m3(STP)/h

dry dry − dry dry dry wet dry

50.1 63.0 77.7 63.0 50.1 62.6 56.5 35.6

the O2 mixing point (M15) (Figure 1). The main experimental test conditions and flue-gas concentrations of O2, SO2, H2O, and CO2 are given in Table 2. Three reference cases are given: an air-fired case and two oxy-fuel cases with dry flue-gas recycle (FGR). The O2 concentration in the feed gas of the oxy-fuel cases was 30% and 25% on dry basis, hereafter referred to as OF30 and OF25, respectively. The SO2 concentration of the OF30 reference case was set to 3000 ppm on dry basis, which equals a SO2 concentration of 2438 ppm on wet basis. The OF25 reference case was adapted to the same SO 2 concentration on wet basis. The oxygen-fuel equivalence ratio, λ, for the OF30 reference case was set to 1.25. The O2 outlet concentration was kept the same in all cases, which results in different λ for the different cases. The oxidizer volume flow decreases with increasing O2 concentration in the feed gas, e.g., reduced FGR ratio. The fuel input by the propane was 60 kW on the basis of the LHV, except for one OF30 case with a fuel load of 75 kW. The O2 concentration in the feed gas of the oxy-fuel case with wet FGR was 46% on dry basis (27 vol % on wet basis), hereafter referred to as OF46w. The OF46w case has a similar adiabatic flame temperature as the OF30 case. The oxidizer volume flow in the OF46w case was increased by 13% compared to that of the OF30 case, but the oxidizer mass flow was reduced. There were also some additional experiments with varied SO2 concentrations and λ, although these are not included in Table 2 but are reported in the Results and Discussion section. Measurements. SO3 measurements were performed after the furnace in measurement position M8 in all cases. In case of double or triple measurement data sets in the Results and Discussion section, these measurements were carried out on different days to check the repeatability of the measurements. In-flame SO3 data were sampled along the center line from measurement level M2 to M5 for the three reference cases and the OF25 case with the low SO2 concentration. In addition to SO3 measurements, flame temperature measurements were performed, and the concentrations of SO2, O2, and CO were measured to characterize the gas composition of the flames. The O2, CO, CO2, and SO2 concentrations were measured with conventional gas analyzers. SO2 was analyzed with nondispersive infrared (NDIR) analyzers (NGA 2000 from Fisher Rosemount). A standard water-cooled suction pyrometer with a type-B thermocouple was used to measure the flame temperature. The thermocouple was shielded with a ceramic tube (see Andersson et al.25 for details on the used water-cooled suction pyrometer). The applied controlled condensation method for SO3 measurement is based on the British Standard BS 1756: Part 4. A schematic of the used glass cooler is shown in Figure 3.

λ

XO2 [%]

XSO2 [ppm]

XH2O [%]

XCO2 [%]

1.25 1.31 1.38 1.31 1.25 1.25 1.28 1.18

5.39 5.39 5.39 5.39 5.39 5.39 5.39 5.39

2438 2438 885 885 813 1625 870 and 1379 2438

18.7 15.6 12.0 15.6 18.7 18.7 54.0 24.7

∼71 ∼74 8.6 ∼74 ∼71 ∼71 37.9 64.6

Figure 3. Schematic of the glass cooler applied in the controlled condensation method.

The principle is that the SO3 concentration is determined by condensation and extraction of the sulfuric acid (H2SO4) content in a flue-gas sample. This is possible because SO3 starts to form gaseous H2SO4 below 500 °C.27−29 An oil-heated probe was used to secure a flue-gas sampling temperature (around 200 °C) sufficiently above the acid dew-point temperature. The oil-heated probe was equipped with a quartz-glass tube in the center to avoid surface reactions. Because only gas-fired experiments were performed, no particle filter was used. A flue-gas flow of around 1 L/min was extracted during 30 min after recommendations by Gustavsson et al.30 The cooler was flushed with a 5% isopropanol solution after each sampling sequence. The amount of sulfate ions in the isopropanol solution was analyzed using ion chromatography (ICS-90 Ion Chromatography System from DIONEX). The SO3 concentrations obtained from the controlled condensation method were in good agreement with data obtained from other 9485



Article

measurement techniques tested during our SO3 measurement campaign.26 Plug-Flow Reactor Model. The SO3 formation along the center line of the furnace was modeled with a simple plug-flow reactor model. The gas-phase chemistry model is based on the chemical kinetic schemes presented by Giménez−López et al31 and Glarborg and co-workers.32 The same mechanism was applied in our previous modeling work.2 The modeling was done with the Chemkin-Pro software.33 The measured temperature profile and O2 concentration along the center line were used as input data. The fuel (C3H8) and recycled flue gas without O2 were injected at the inlet of the plug-flow reactor, and oxygen was injected gradually to match the measured O2 concentration at the centerline in the experiments. Thus, in this approach, we aim to capture the mixing conditions of the center line of the experimental furnace; the approach was validated and successfully applied in previous modeling work of the same experimental unit.34

Figure 5. Measured SO3 outlet concentration in the air reference case and in the OF25 and OF30 cases with low SO2 concentration.

The flame temperature and the average furnace wall temperature are significantly lower in the OF25 case than in the air-fired and OF30 cases (Figures 4 and 5). The lower temperature level in the furnace during OF25 firing is one of the main reasons for the lower SO3 formation during the OF25 case compared to the other cases. Crumley and Fletcher35 obtained an increase in SO3 formation for an increase in the furnace wall temperature and flame temperature and concluded that this was most probably due to an increase in concentration of O-radicals. The increased SO3 formation during the air-fired case compared to the oxy-fuel cases can be explained by the significant higher temperature in measurement level M5 (Figure 4) combined with a relatively high O2 concentration, as discussed below during in-flame measurement results. Influence of SO 2 Concentration and λ on SO 3 Formation. Figure 6 shows the measured SO3 concentration

3. RESULTS AND DISCUSSION Flame Temperature Profiles. Figure 4 gives the measured temperature profiles along the center line of the furnace for the

Figure 4. Measured temperature profiles along the center line for the air, OF30 and OF25 reference cases.

air, OF30, and OF25 reference cases. The temperature profiles of the air and the OF30 cases are similar, except in measurement level M5 where the temperature in the OF30 case is lower than in the air-fired case, which is mainly due to a reduced volumetric flow of the feed gas. The OF25 conditions result in a flame temperature level, which is approximately 100 °C lower at the center line from M2 to M4 compared to the airfired case but has roughly the same temperature in M5 as the OF30 case. Formation of SO3: Air versus Oxy-Fuel Combustion. Figure 5 shows the measured SO3 concentration at the furnace outlet for the air reference case and for the OF25 and OF30 cases with low SO2 concentrations. The measured SO3 concentration during the OF25 case was less than half of the concentration determined during the air-fired case. The OF30 case yielded a slightly lower SO3 outlet concentration than the air-fired case. The different SO3 concentrations of the cases, despite the same SO2 concentration, indicate that there cannot be a significant influence during the controlled condensation measurements caused by absorption of SO2.

Figure 6. SO3 concentration at the furnace outlet for different SO2 concentrations in the flue gas of the OF30 case.

on wet basis for the OF30 case at different SO2 concentrations. The SO3 concentration increases as expected for an increasing SO2 concentration. Figure 7 shows the influence of λ on the SO3 outlet concentration for the OF30 case and for the air-fired case. As shown, the SO3 outlet concentration increases with increasing λ. This is in line with the present knowledge through experimental studies.36−38 The concentration of O and OH 9486



Article

Figure 8 for two different SO2 concentrations. The measured SO3 concentration was on average almost 50% higher for the OF46w case than for the OF30 case. An increase in SO3 formation due to higher H2O concentrations was also obtained during our previous modeling work.2 Reasons for the higher SO3 formation for oxy-fuel with wet FGR are the higher third body efficiencies for H2O than for CO2 and N2 (reaction 1 and 2), and an increased formation of OH-radicals, considerable by reaction2 H 2O + O ⇌ OH + OH

(6)

To conclude, an increase in H2O concentration enhances the formation of SO3. However, for an industrial oxy-fuel plane, the SO2 concentration will be lower for wet FGR conditions compared to dry recycling. This is because of the fact that SO2 is not enriched to the same extent in wet compared to dry FGR; in the latter case, the water is continuously removed in the recycle stream. This will, to some extent, counteract the effect of an enhanced SO3 formation in the presence of a large fraction of water in the flue gas. Influence of FGR Ratio. The measured SO3 concentrations for the OF25, OF30, and OF40 cases are shown in Figure 9.

Figure 7. SO3 concentration at the furnace outlet for different λ. The test cases applied are the OF30 case with a SO2 concentration of 2438 ppm and the air case with a SO2 concentration of 885 ppm.

radicals increases with higher λ, which promotes the SO3 formation through reactions 1−3. With respect to industrial oxy-fuel applications, it should be mentioned here that when λ is decreased, the SO2 concentration increases, assuming that the burnout of sulfur from the fuel is not affected, which counteracts the benefit of a reduced SO3 formation at low λ. Influence of Fuel Load. In Figure 8 the SO3 concentrations at the furnace outlet are shown for the OF30 case with

Figure 9. Influence of FGR ratio on SO3 outlet concentration. The measured SO3 outlet concentrations in the OF25, OF30, and OF40 cases.

The SO3 formation was significantly enhanced in the OF30 cases compared to that of the OF25 cases. The measured SO3 concentration was highest for the OF40 case. In general, the increase in SO3 outlet concentration with increasing OF number, e.g., reduced FGR ratio, can be explained by an increase in both residence time and average temperature in the furnace due to an increase of flame temperatures because of reduced gas volume. A main conclusion from our previous modeling work2 is that a residence time in the temperature range between 1450 and 600 °C is governing the SO3 formation given that oxygen is available. The increased O2 concentration in the feed gas might also contribute to increased SO 3 formation. However, the O2 concentration after combustion was the same in all cases (Table 2). In-Flame Measurements of SO2, O2, and CO. Figure 10 shows the measured SO2, O2, and CO concentration for the three reference cases and the OF25 case with the low SO2 concentration along the center line of the furnace. The gas concentrations are shown on dry basis because the H2O concentration was not measured. The flame measurements

Figure 8. Influence of fuel load and wet FGR on SO3 outlet concentration.

75 kW, and these data are compared to the OF30 reference case. The thermal load has a significant impact on the SO3 outlet concentration. The measured SO3 concentration was on average 40% higher in the OF30 case with 75 kW fuel load compared to the reference conditions at 60 kW. As mentioned in the discussion on air-fired conditions, it is likely that the SO3 formation is increased when the average temperature in the furnace is raised, which is the case when comparing the SO3 formation for the 75 kW and the 60 kW case. The average furnace wall temperature was around 50K higher in the 75 kW case as in the 60 kW case, and the flue gas temperature at the furnace outlet was around 200 K higher. Influence of Wet Flue-Gas Recycle. The SO3 outlet concentrations measured for the OF46w case are also shown in 9487



Article

Figure 10. SO2, CO, and O2 concentration along the center line for (a) air-fired reference case, (b) OF25 case with a low SO2 concentration, (c) OF25 reference case, and (d) OF30 reference case.

tends to be lowest in position M2, especially in the air and OF30 cases. SO3 Formation in the Flame. The SO3 concentration measured along the center line is shown in Figure 11 for the three reference cases and the OF25 case with the low SO2 concentration. The SO3 concentration measured in M2 is low in all cases and lowest for the OF30 reference case. The strongest SO3 formation occurs between positions M2 and M4 for the OF25 cases and for the air and OF30 reference cases between positions M3 and M5. This is within the burnout region in which the O2 concentration increases (Figure 10), and therefore, also in principle the concentration of O-radicals increases, although the temperature decrease reduces this effect. In our previous modeling work,2 we found that in the burnout region, where the conversion of CO occurs, the SO3 formation is strong. During conversion of CO, reaction 7 is reversed, and H-radicals are formed. This favors the formation of O-radicals, according to

show a good repeatability, which becomes obvious when the CO and O2 concentrations for the two OF25 cases are compared (Figure 10b,c), considering that the data were sampled at different occasions. All test cases present a high concentration of CO in position M2 when the O2 concentration is depleted. At measurement level M5, the fuel oxidation is completed because the CO concentration is insignificant. The burnout is faster in the OF25 case than in the other test flames, and the fraction of CO in the OF25 flame is already low at measurement position M3. The OF30 case exhibits the slowest burnout, and a large CO concentration is present in the center of measurement level M2 (23 vol %). The OF30 case presents a significantly higher CO concentration than the air-fired case despite similar flame temperatures. This is due to the fact that the high CO2 concentration causes increased CO formation, mainly due to the reaction39 CO2 + H ⇌ CO + OH

(7)

O2 + H ⇌ O + OH

However, the OF25 flame produces a significantly lower CO concentration along the center line compared to the OF30 case because of the lower flame temperatures. The fraction of SO2 in the center line remains relatively constant compared to the CO and O2 concentration, but it

(8)

An increase in O-radicals increases the formation of OHradicals by reaction 6. An increase in O- and OH-radicals favors the formation of SO3 (reactions 1−3). To conclude, the strong SO3 formation in the burnout region is not only caused by an 9488



Article

Figure 11. SO3 concentration along the center line for (a) air-fired reference case, (b) OF25 case with a low SO2 concentration, (c) OF25 reference case, and (d) OF30 reference case.

the oxy-fuel cases no additional SO3 is formed. This is because the temperature is still sufficiently high in M5 during air-firing (Figure 4). This leads to increased SO3 formation in the airfired case compared to that of the oxy-fuel combustion for similar SO2 concentrations (Figure 5).

increase in oxygen concentration but also by the conversion of CO itself. Further downstream, between positions M4 and M5, the formation of SO3 increases for the air and the OF30 reference cases but not for the two OF25 cases. Both OF25 cases peaks in position M4 instead, which was confirmed when repeating the measurements. In-flame/postflame SO3 peaks have been reported by several authors.15−19 By comparing the OF25 and OF30 reference cases, it is shown that the SO 3 concentration in position M3 is almost three times higher for OF25 than the OF30 reference case. The reason is that in position M3 more oxygen is available in the OF25 case than in the OF30 case. The SO3 concentration then reaches similar values for the OF25 and OF30 reference cases in position M4. Figure 11 shows also the results from the plug-flow reactor modeling. The SO3 formation obtained with the model is slower than in the experiments. The agreement in measurement level M5 between the measured SO3 concentrations and the modeled SO3 concentrations is good if one considers the simple mixing conditions applied in the model. The modeling shows that the SO3 formation in the air reference case is still increasing downstream of measurement level M5, whereas in

4. CONCLUSIONS The formation of SO3 under different oxy-fuel and air-fired conditions is analyzed on the basis of experiments in the Chalmers oxy-fuel test unit. SO3 measurements were done after the furnace as well as in the flame, applying a controlled condensation method for SO3 measurements. A main conclusion is that SO3 is formed in the burnout region where oxygen is in excess and the temperature is high. The in-flame SO3 measurements indicate by the relatively high SO3/SOx ratios that the gas-phase is a major contributor to SO3 formation during the combustion process. The SO3 formation was increased during air-firing compared to oxy-fuel combustion for similar SO2 concentrations. As anticipated, the experiments show that increase in SO2 concentration increases the SO3 outlet concentration. The 9489



Article

SO3 concentration also increases with an increase in λ. In our experiments, an oxy-fuel case with wet FGR conditions results in a higher SO3 concentration than an oxy-fuel case with dry recycle. Thus, an increased H2O concentration promotes the SO3 formation. However, for an industrial oxy-fuel power plant with wet FGR, the SO2 concentration will be lower compared to dry recycling, which might balance the effect of H2O on the formation of SO3. In general, our experiments show that the SO3 formation is enhanced for a reduced FGR ratio or an increased O2 concentration in the feed gas by two important factors: increased furnace temperature level and a prolonged furnace residence time due to a reduced flue-gas flow. From a SO3 formation point of view, it can therefore be recommended to operate oxy-fuel power plants at moderate O2 concentrations in the feed gas.

■

(10) Stanger, R.; Wall, T. Sulfur impacts during pulverised coal combustion in oxy-fuel technology for carbon capture and storage. Prog. Energy Combust. Sci. 2011, 37, 69−88. (11) Abele, A. R.; Kindt, G. S.; Clark, W. D.; Payne, R.; Chen, S. L. An Experimental Program To Test the Feasibility of Obtaining Normal Performance from Combustors Using Oxygen and Recycled Gas Instead of Air; Report ANL/CNSV-TM-204; Argonne National Laboratory, 1987. (12) Couling, D. Impact of Oxyfuel Operation on Emissions and Ash Properties Based on E.ON’s 1MW CTF. IEAGHG Special Workshop on Oxyfuel Combustion, January 25−26, 2011, London. (13) Kenney, J. R.; Clark, M. M.; Levasseur, A. A.; Kang, S. G. SO3 Emissions from a Tangentially-Fired Pilot Scale Boiler Operating under Oxy-Combustion Conditions. IEAGHG Special Workshop on Oxyfuel Combustion, January 25−26, 2011, London. (14) Eddings, E. G.; Ahn, J.; Okerlund, R.; Fry, A. SO 3 Measurements under Oxy-Coal Conditions in Pilot-Scale PC and CFB Combustors. IEAGHG Special Workshop on Oxyfuel Combustion, January 25−26, 2011, London. (15) Dooley, A.; Whittingham, G. The oxidation of sulphur dioxide in gas flames. Trans. Faraday Soc. 1946, 42, 354−362. (16) Hedley, A. B. Factors affecting the formation of sulphur trioxide in flame gases. J. Inst. Fuel 1967, 142, 142−151. (17) Durie, R. A.; Matthews, C. J.; Smith, M. Y. The catalytic formation of sulfur trioxide in fuel-rich propane-air flames. Combust. Flame 1970, 15, 157−165. (18) Merryman, E. L.; Levy, A. Sulfur trioxide flame chemistry: H2S and COS flames. Symp. (Int.) Combust., [Proc.] 1971, 13, 427−436. (19) Bayless, D. J.; Khan, A. R. Effects of gas stream temperature on homogeneous SO2 to SO3 conversion via natural gas reburning: Factors affecting the formation of sulphur trioxide in flame gases. Int. Jt. Power Gener. Conf. 1998, 1, 147−152. (20) Barrett, R. E.; Hummell, J. D.; Reid, W. T. Formation of SO3 in a noncatalytic combustor. J. Eng. Power 1966, 88, 165−172. (21) Maier, P.; Dibbs, H. P. The catalytic conversion of SO2 to SO3 by fly ash and the capture of SO2 and SO3 by CaO and MgO. Thermochim. Acta 1974, 8, 155−165. (22) Rees, O. W.; Shimp, N. F.; Beeler, C. W.; Kuhn, J. K.; Helfinstine, R. J. Sulfur Retention in Bituminous Coal Ash; Circular 396; Illinois State Geological Survey, 1966, pp 1−10. (23) Wickert, K. Die katalytische SO2-oxydation in Abhängigkeit von der Verweilzeit der gase im reaktionsraum. BWK 1962, 14, 20−21. (24) Jørgensen, T. L.; Livbjerg, H.; Glarborg, P. Homogeneous and heterogeneously catalyzed oxidation of SO2. Chem. Eng. Sci. 2007, 62, 4496−4499. (25) Andersson, K.; Normann, F.; Johnsson, F.; Leckner, B. Nitrogen oxide emission during oxy-fuel combustion of lignite. Ind. Eng. Chem. Res. 2008, 47, 1835−1845. (26) Vainio, E.; Fleig, D.; Brink, A.; Andersson, K.; Johnsson, F.; Hupa M. SO3 Measurement Techniques: A Study in a 100 kW Test Unit Fired with a SO2-Doped Propane Flame. 17th IFRF International Member Conference, June 11−13, 2012, Maffliers, France. (27) Stuart, D. D. ; Continuous Measurements of Acid Dewpoint and Sulfur Trioxide in Stack Gases. 101st Air and Waste Management Association Annual Conference and Exhibition, June 24−26, 2008, Portland, Oregon. (28) Francis, W. E. The measurement of the dewpoint and H2SO4 vapour content of combustion products. Gas Res. Board, Commun. 1952, 64, 1−37. (29) Hardman, R.; Stacy, R. Estimating Sulfuric Acid Aerosol Emissions from Coal-Fired Power Plants. Conference on Formation, Distribution, Impact, and Fate of Sulfur Trioxide in Utility Flue Gas Streams, Pittsburgh 1998, pp 1−11. (30) Gustavsson, L.; Nyquist, G. Vä rmeforsks Mät handbok; Värmeforsk Service AB, 2005. (31) Giménez-López, J.; Martínez, M.; Millera, A.; Bilbao, R.; Alzueta, M. U. SO2 effects on CO oxidation in a CO2 atmosphere, characteristic of oxy-fuel conditions. Combust. Flame 2011, 158, 48− 56.

ASSOCIATED CONTENT

* Supporting Information S

This material is available free of charge via the Internet at http://pubs.acs.org.

■

AUTHOR INFORMATION

Corresponding Author

*Tel.: +46-(0)31-772-1453. E-mail: daniel.fl[email protected]. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS

■

REFERENCES

The financial support by Vattenfall AB is gratefully acknowledged. We also express our gratitude to Mr. Torgny Viberg from Force Technology Sweden AB for his assistance with the SO3 measurements.

(1) Hindiyarti, L.; Glarborg, P.; Marshall, P. Reactions of SO3 with the O/H radical pool under combustion conditions. J. Phys. Chem. 2007, 111, 3984−3991. (2) Fleig, D.; Andersson, K.; Normann, F.; Johnsson, F. SO3 Formation under oxyfuel combustion conditions. Ind. Eng. Chem. Res. 2011, 50, 8505−8514. (3) Klipstein, D. H. Improved percipitator performance by gas conditioning. Combustion 1975, 47, 43−47. (4) Woycenko, D.; Ikeda, I.; van de Kamp, W. L. Combustion of Pulverised Coal in a Mixture of Oxygen and Recycled Flue Gas; Technical Report IFRF, Doc F98/Y/1; International Flame Research Foundation, 1994, . (5) Croiset, E.; Thambimuthu, K. V. NOx and SO2 emissions from O2/CO2 recycle coal combustion. Fuel 2001, 80, 2117−2121. (6) Kiga, T.; Takano, S.; Kimura, N.; Omata, K.; Okawa, M.; Mori, T.; Kato, M. Characteristics of pulverized-coal combustion in the system of oxygen/recycled flue gas combustion. Energy Convers. Manage. 1997, 38, 129−134. (7) Fleig, D.; Andersson, K.; Johnsson, F.; Leckner, B. Conversion of sulfur during pulverized oxy-coal combustion. Energy Fuels 2011, 25, 647−655. (8) Mönckert, P.; Dhungel, B.; Kull, R.; Maier, J. Impact of Combustion Conditions on Emission Formation (SO2, NOx) and Fly Ash, 3th Workshop IEAGHG International Oxy-Combustion Network, Yokohama 2008. (9) Tan, Y.; Croiset, E.; Douglas, M. A.; Thambimuthu, K. V. Combustion characteristics of coal in a mixture of oxygen and recycled flue gas. Fuel 2006, 85, 507−512. 9490



Article

(32) Glarborg, P.; Alzueta, M. U.; Dam-Johansen, K.; Miller, J. A. Kinetic modeling of hydrocarbon/nitric oxide interactions in a flow reactor. Combust. Flame 1998, 115, 1−27. (33) Chemkin-Pro, Release 15101; Reaction Design, San Diego. (34) Kuehnemuth, D.; Normann, F.; Andersson, K.; Johnsson, F.; Leckner, B. Reburning of nitric oxide in oxy-fuel firing: The Influence of combustion conditions. Energy Fuels 2011, 25, 624−631. (35) Crumley, P. H.; Fletcher, A. W. The formation of sulphur trioxide in flue gases. J. Inst. Fuel 1956, 29, 322−327. (36) Wendt, J. O. L.; Sternling, C. V.; Matovich, M. A. Reduction of sulfur trioxide and nitrogen oxides by secondary fuel injection. Symp. (Int.) Combust., [Proc.] 1973, 14, 897−904. (37) Fernando, R. SO3 Issues for Coal-Fired Plant; PF 03-03; IEA Clean Coal Centre, 2003; pp 1−53. (38) Reidick, H.; Reifenhäuser, R. Katalytische SO3: Bildung in Abhängigkeit von der Kesselverschmutzung. VGB Kraftwerkstechnik 1978, 58, 915−921. (39) Glarborg, P.; Bentzen, L. L. B. Chemical effects of a high CO2 concentration in oxy-fuel combustion of methane. Energy Fuels 2008, 22, 291−296.

9491


Influence of Operating Conditions on SO3 Formation during Air and

Recommend Documents