Experimental and Modeling Studies on Sulfur Trioxide of Flue Gas in a


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Experimental and modeling studies on sulfur trioxide of flue gas in a coal-fired boiler Baixiang Xiang, Man Zhang, Yuxin Wu, Hairui Yang, Hai Zhang, and Junfu Lv Energy Fuels, Just Accepted Manuscript • Publication Date (Web): 16 May 2017 Downloaded from http://pubs.acs.org on May 17, 2017

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Experimental and modeling studies on sulfur trioxide of flue

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gas in a coal-fired boiler

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Baixiang Xiang, Man Zhang, Yuxin Wu, Hairui Yang, Hai Zhang, Junfu Lu*

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Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Department of Thermal

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Engineering, Tsinghua University, Beijing, 100084, China

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ABSTRACT

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Various damages, including corrosion, fouling, and blue plumes, can be caused by sulfur

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trioxide (SO3) in the flue gas of a coal-fired boiler on boiler equipment and the atmospheric

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environment. The increasing demand for energy conservation and emission reduction requires

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accurate knowledge on predicting and controlling SO3 concentration. Accurate knowledge on the

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effect of the factors that influence SO3 in flue gas is necessary as well. Therefore, in this study,

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various SO3 concentrations under different flue gas conditions are measured with measuring

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devices built based on controlled condensation and S balance methods. To study further the effect

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of the factors that influence SO3 in flue gas, an improved SO2/O2/H2O/CO2/CO/NO kinetic

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mechanism is built based on previously developed mechanisms and validated with previous

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experimental data. SO3 concentrations under the established flue gas conditions and with

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increasing residence time are numerically calculated. SO3 concentration in flue gas is mainly

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dependent on SO2, O2, and H2O concentrations as well as temperature and residence time. SO3

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concentration undergoes three stages of sharp increase, slow increase, and gradual decrease as the

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residence time increases. In addition, SO3 concentration increases significantly as CO and NO

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emerge in the flue gas. However, SO3 is constant as CO2 emerges.

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Keywords: coal-fired boiler, chemical kinetic model, sulfur trioxide, flue gas

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1. INTRODUCTION

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Given the presence of sulfur in coal, flue gas typically contains SO2, some of which further

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reacts with O2, H2O, CO2, CO, and NO in flue gas to generate SO3. Fleig et al. [1] found that

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SO3/SOx in flue gas ranges only from 0.1% to 1% for air-fired pulverized-coal combustion.

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However, with the development of selective catalytic reduction (SCR) deNOx technology in

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recent years and the increase in the installed power capacity of SCR systems to 250 GW around

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the world in 2015 [2], SO2/SO3 conversion has significantly increased from 2% to 3% for air-fired

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pulverized-coal combustion [3]. SO3 in the flue gas of a coal-fired boiler causes various damages

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on boiler equipment and the atmospheric environment [4–10]. Xiang et al. [4–5] found that the

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acid dew point of flue gas depends mainly on the partial pressure of SO3 and water vapor in flue

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gas, and the risk of corrosion and fouling of heating surfaces in the second pass of boilers

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increases significantly as SO3 emerges in the flue gas even at a small mole fraction (e.g., 5 ppm).

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Moser et al. [6–7] found that SO3 reacts with NH3 to form NH4HSO4 at temperatures ranging from

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450 K to 489 K, and if SO3 is present at a molar concentration that exceeds that of NH3, fouling

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will occur. When fouling occupies the flow channel, the induced draft fan increases significantly.

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Moser et al. [6–7] also found that Hg removal efficiency decreases significantly because SO3 is

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easily absorbed by fly ash in flue gas. When fabric filters are used in plants burning high-sulfur

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coals, the filters’ metal components and cake properties are adversely affected by SO3.

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Additionally, Moser et al. [6–7] and Fleig et al. [8] found that visual discoloration of plume occurs

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in the power plant stack because of the optical light-scattering effect, which is produced by

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sulfuric acid particles in flue gas. Therefore, accurate knowledge on the effect of the factors that

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influence SO3 in flue gas is required to meet the increasing demands for energy conservation and

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emission reduction.

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Several SO3 measurement methods, including controlled condensation, S balance, salt

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solution absorption, isopropanol solution, pentol SO3 monitoring, and use of spiral tubes, have

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been presented in previous studies [11–22]. Lisle et al. [11] and Cheney et al. [12] proposed the

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controlled condensation method based on the principle that sulfuric acid can be measured by

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cooling down flue gas to a temperature between its water and acid dew points. The researchers

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discovered that this method is more reliable than other measuring methods. However, Fleig et al.

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[13], Zhang et al. [14], Xiao et al. [15], and Guo et al. [16] found that the measured results

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obtained from using the controlled condensation method are affected by experimental conditions

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and the skill of the operator. Mueller et al. [17] and Fleig et al. [18] found that SO3 mole fraction

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is approximately an order of magnitude larger than that of any other sulfur-containing species,

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with the exception of SO2. Thus, SO3 mole fraction can be reasonably inferred from the measured

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SO2 consumption. Compared with those obtained from the controlled condensation method, the

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measured results from the S balance method are independent of experimental conditions and

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operator skill. Cooper et al. [19] found that SO3 in flue gas can be measured with alkali solutions,

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including NaCl, NaOH, KCl, CaCl2, and K2CO3. However, Vainio et al. [20] found that SO3

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concentration measured with the salt solution absorption method are affected by the salt solution

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and other factors. Fleig et al. [13], Xiao et al. [15], and Guo et al. [16] found that the results

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obtained with the salt solution absorption method are less reliable than those obtained with the

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controlled condensation method under similar conditions. The same researchers also found that

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the results obtained with the isopropanol solution method are affected by experimental conditions

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and operator skill and are less reliable than those obtained with the controlled condensation

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method under similar conditions. Therefore, among the SO3 measurement methods reported in

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previous studies, the controlled condensation method is more reliable than the other methods that

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involve operator skill. Furthermore, the S balance method is independent of experimental

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conditions and operator skill.

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With the SO3 measurement methods mentioned above as a reference, many studies have been

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conducted on the effect of the factors that influence SO3 in flue gas [1, 8, 23–30]. Liu et al. [23]

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and Xie et al. [24] found that the conversion rate of SO2 to SO3 in a fluidized bed combustion

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(FBC) system firing municipal solid waste (MSW) and refused derived fuel (RDF) can be

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increased either at a high concentration of HCl with a high temperature or at a low HCl

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concentration with a low temperature and can reach up to around 6% at 1000 ppm HCl and 873 K.

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Fleig et al. [8], Reidick et al. [25], Belo et al. [26], Spörl et al. [27] and Jørgensen et al. [28] found

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that the concentrations of HCl and Cl2 in flue gas are relatively lower for coal combustion

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compared with that for MSW and RDF combustion. SO3 concentration in a coal-fired boiler

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depends mainly on the concentrations of SO2, O2, H2O, CO2, CO, and NO, residence time, and

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temperature, except for boilers equipped with an SCR system using V2O5/WO3 as catalysts and in

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which the alkali content in flue gas is relatively high. Ahn et al. [29] investigated the effects of

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increased oxygen and carbon dioxide concentration on SO3 formation in two types of pilot-scale

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furnaces, namely, pulverized coal and circulating fluidized-bed fired systems. They found that SO3

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emissions under air-fired conditions are higher than those under oxy-fired conditions for

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pulverized coal testing. However, SO3 emissions are similar under air-fired and oxy-fired

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conditions for circulating fluidized bed testing. Fleig et al. [1] focused on gas-phase chemistry,

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examined the effect of different combustion parameters and atmospheres on the formation of SO3

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in oxy-fuel and air-fuel flames, and found that SO3 formation is influenced by direct and indirect

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effects of SO2, O2, NO, and CO contents in flue gas. Moreover, Fleig et al. [30] studied the effects

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of different combustion parameters on SO3 formation in a flow reactor under post-flame

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conditions and found that the formation of SO3 increases as reactive gases (e.g., NO, CO, and

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CH4) emerge. However, previous studies [1, 8, 23–30] have found that knowledge on the effect of

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factors that influence SO3 in flue gas, including SO2, O2, H2O, CO2, CO, and NO concentrations,

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residence time, and temperature, is still insufficient to meet the increasing demands for energy

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conservation and emission reduction.

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Aside from experimental studies on the effect of influencing factors on SO3 in flue gas, many

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kinetic modeling studies have also been conducted [17, 31–38]. Mueller et al. [17] developed and

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validated a detailed chemical kinetic mechanism by using reaction profile measurements of CO,

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CO2, O2, NO, NO2, and SO2 in a flow reactor. Spencer et al. [38] proposed a detailed chemical

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kinetic scheme that includes gas-phase reactions that participate in the formation and destruction

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of SO3 during combustion and post-combustion. The reaction set and corresponding rates were

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experimentally and theoretically derived and found to be consistent with the experimental data.

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However, Alzueta et al. [31], Giménez-López et al. [32], Rasmussen et al. [33], Yilmaz et al. [34],

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and Hindiyarti et al. [35] found that the results of SO3 concentrations numerically calculated with

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the two kinetic mechanisms do not agree with the experimental data reported in previous research.

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Subsequently, Giménez-López et al. [32] revised and updated the sulfur subset according to an

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experimental study on the presence of SO2 in CO oxidation under CO2 atmosphere. Alzueta et al.

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[31] experimentally studied the interaction of SO2 with the radical pool under combustion

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conditions and revised and updated the reaction set and corresponding rates. Moreover,

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Rasmussen et al. [33] updated the kinetic model for the interaction of SO2 with H radical via ab

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initio calculations for key reactions. They re-examined the mechanism of fuel/SO2 interactions

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with the experimental results from batch and flow reactors as well as laminar flames.

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In the current work, SO3 concentrations under different flue gas conditions were measured

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with a measuring device built based on controlled condensation and S balance methods. The effect

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of SO2, O2, H2O, NO, CO2, CO, temperature, and residence time on SO3 concentration in flue gas

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at temperatures ranging from 973 K to 1273 K was investigated. Furthermore, to study the effect

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of the factors that influence SO3 in flue gas, an improved SO2/O2/H2O/CO2/CO/NO kinetic

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mechanism was built according to previous research achievements. The mechanism was validated

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with experimental data and mechanisms reported in previous studies. In addition, SO3

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concentrations under different flue gas conditions and with increasing residence time were

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numerically calculated with a perfectly stirred reactor system using the CHEMKIN-PRO software.

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2. EXPERIMENTAL SECTION

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2.1 Controlled condensation method

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The controlled condensation method is one of the most reliable measuring methods [8, 11–

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16, 20–21]. Thus, by referring to the controlled condensation method, a SO3 concentration

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measuring device was built in this study. The device was used to simulate the formation of SO3 in

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flue gas by heating mixture gases, including SO2, O2, NO, CO2, CO, and H2O, and studying the

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effect of SO2, O2, H2O, NO, CO2, CO, temperature, and residence time on SO3 concentration in

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the flue gas (Figure 1). During the experiment, H2O flowed through the mixing chamber to mix

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with other gases. The flow was simulated by atomizing pure deionized water with a highly

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effective nebulizer (Q-HEN-170-A0.05) and N2. Subsequently, the mixed gases flowed through

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the perfectly stirred reactor arranged in a heated tubular furnace, as shown in Figure 2. The

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perfectly stirred reactor is made of quartz glass, which is why it demonstrates good

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high-temperature performance (e.g., from 1000 K to 1300 K). Furthermore, quadruple circular–

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spiral nozzles exist in the perfectly stirred reactor. The presence of these nozzles can increase the

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efficiency of the components during flue gas contact. The flows of SO2, O2, NO, CO2, CO, and N2

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were controlled with a six-way mass flow meter (D07), and H2O flow was controlled with a

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micro-syringe pump (LSP01-1A). To ensure that the atomized deionized water evaporated

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completely, the temperature of the mixed gases in the perfectly stirred reactor in the tubular

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furnace was increased to above 973 K during the experiment. The residence time of the mixed

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gases in the furnace was sufficiently long. The shortest residence time was determined by

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repeatedly measuring the mole fraction of H2O in the flue gas with a humidity instrument

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(RHS-500) under the same conditions. Then, the flue gas flowed through a heated tube connected

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in series to the perfectly stirred reactor and glass cooler, the temperature of which was increased to

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above the corresponding acid dew point by using an electric heating belt. The flue gas was cooled

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down to a temperature between its water and acid dew points by using an electro-thermostatic

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water cabinet (HH-2) as it passed through the glass cooler. As the flue gas cooled down,

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H2SO4/SO3 condensed on the inner surface. However, SO2 remained in the flue gas. To ensure that

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H2SO4/SO3 in the flue gas was collected completely, the glass cooler was made long enough for

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the experiment. Similar to the method of determining the shortest residence time, the shortest

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length of the glass cooler was determined by repeatedly measuring the collected S concentration

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through inductively coupled plasma-optical emission spectroscopy (iCAP 6300) under the same

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conditions. The SO3 concentration in flue gas was obtained after the collected S concentration was

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measured.

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During the experiment, while maintaining the flow rates of the flue gas, O2, and H2O at 1,

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0.05, and 0.05 L/min, respectively, different flue gas conditions were adjusted by keeping N2 as

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the balance component (Table 1). To comply with the actual flue gas in a coal-fired boiler, the

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mole fraction of SO2 ranged from 500 ppm to 2000 ppm, whereas the mole fractions of CO2, CO,

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and NO ranged from 0% to 15%, ppm to 1000 ppm, and 0 ppm to 500 ppm, respectively, during

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the experiment. In addition, to study the effect of temperature on SO3 concentration in the flue

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gas, the temperature of the flue gas in the perfectly stirred reactor was increased to 973, 1073,

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1173, and 1273 K, respectively, during the experiment.

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2.2 S balance method

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The S balance method is independent of experimental conditions and operator skill compared

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with other measuring methods reported in previous studies. Thus, a SO3 concentration measuring

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device was also built by referring to the S balance method to verify the measured SO3

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concentrations under different flue gas conditions based on the controlled condensation method.

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The effects of SO2, O2, H2O, NO, CO2, CO, temperature, and residence time on SO3 concentration

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in the flue gas were investigated, as shown in Figure 3. Similar to the procedure in the measuring

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device built according to the controlled condensation method, the formation of SO3 in the flue gas

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was simulated by heating mixed gases, including SO2, O2, NO, CO2, CO, and H2O, in a tubular

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furnace. However, unlike the measuring experiment based on the controlled condensation method,

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the SO2 concentrations in the gas mixture, including SO2, O2, NO, CO2, CO, and N2, were

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measured with a Fourier transform infrared spectrometer (Nicolet Antaris IGS) before the gases

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flowed through the perfectly stirred reactor during the experiment. The flue gas flowed through a

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heated tube connected in series to the perfectly stirred reactor and Fourier transform infrared

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spectrometer. The temperature was increased to above the corresponding acid dew point by using

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an electric heating belt. Then, the SO3 concentration in the flue gas was obtained as the difference

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between the SO2 concentration in the inlet and outlet of the flue gas after measuring the SO2

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concentration in the outlet of the flue gas.

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Similar to the measuring experiment based on the controlled condensation method, while

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maintaining the flow rate of flue gas at 1 L/min, different flue gas conditions were adjusted by

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keeping N2 as the balance component (Table 2). Moreover, to comply with the flue gas conditions

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in the experiment based on the controlled condensation method, the mole fractions of SO2, O2, and

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H2O ranged from 500 ppm to 2000 ppm, 1.25% to 5%, and 1.25% to 5%, respectively, whereas

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the mole fractions of CO2, CO, and NO ranged from 0% to 15%, 0 ppm to 1000 ppm, and 0 ppm

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to 500 ppm, respectively, during the experiment. Similar to the measuring experiment based on the

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controlled condensation method, the temperature of the flue gas in perfectly stirred reactor was

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increased to 973, 1073, 1173, and 1273 K to study the effect of temperature on SO3 concentration

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in the flue gas.

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3. MODELING WORK

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In addition to the experimental study on the effect of factors influencing SO3 in flue gas, an

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improved kinetic mechanism was built based on previously developed SO2/O2/H2O/CO2/CO/NO

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mechanisms to further study the effect of factors influencing SO3 in flue gas [17, 38]. SO3

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concentration in flue gas is mainly dependent on SO2, O2, H2O, CO2, CO, and NO concentrations,

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residence time, and temperature, except for boilers equipped with an SCR system using

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V2O5/WO3 as catalysts and in which the alkali content in flue gas is relatively high [8, 25–28].

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Thus, the scope of the improved kinetic mechanism in the present study is limited to SO3

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produced in flue gas by homogenous gas-phase reactions and does not include heterogeneous

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absorption and catalytic reactions on the heat exchanger’s surfaces and ash particles. Compared

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with previously developed SO2/O2/H2O/CO2/CO/NO mechanisms in references [17, 38], several

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reactions and rate constants within the sulfur submechanism were modified to incorporate the

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combination of SO2 and/or SO3 with H, O, and OH radicals reported in previous references [31–

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38]. Yilmaz et al. [34] derived the rate constant for SO3 + N2 <=> SO2 + O +N2 of

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5.7 ×1017 exp(−4000 / T ) cm3/(mol·s) for the temperature range of 1273 K to 1348 K and

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recommended a rate constant for SO3 + O <=> SO2 + O2 of 7.8×10 exp(−3065/ T) cm3/(mol·s)

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for the temperature range of 1000 K to 1400 K based on measured data with a laminar flow

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reactor at atmospheric pressure. Hindiyarti et al. [35] investigated the reactions of SO3 with H, O,

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and OH radicals via ab initio calculations and recommended the rate constants for SO3 + H <=>

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HOSO2 <=> OH + SO2 and SO3 + OH <=> SO2 + HO2 of 8.4×10 T

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cm3/(mol·s) for the temperature range of 700 K to 2000 K and 4.8×10 T

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cm3/(mol·s) for the temperature range of 800 K to 2000 K. Moreover, through ab initio

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calculations for several key reactions, Rasmussen et al. [33] found that the interaction of SO2 with

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the radical pool in flue gas is more complex than what was previously assumed in past research,

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including HOSO and SO at high temperatures and HSO, SH, and S. In addition, although the

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C/H/O/N submechanism was mainly derived from the reaction mechanisms of Mueller et al. [17]

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and Spencer et al. [38], it incorporates several important modifications from reference [39].

11

9 1.22

4

2.46

exp(−13900/ RT)

exp(−114100/ RT)

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The improved SO2/O2/H2O/CO2/CO/NO mechanism in the present study was validated.

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Figure 4 provides a comparison of SO3 concentrations from flue gas numerical calculations based

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on the improved reaction mechanism in the present work, the reaction mechanisms of Mueller et

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al. [17] and Spencer et al. [38] with a perfectly stirred reactor system using the CHEMKIN-PRO

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software [40–41], and the measured results by Mueller et al. [17] under the flue gas conditions

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listed in Table 3. As shown in Figure 4, the improved reaction mechanism in the present work

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produces numerically calculated SO3 concentrations in flue gas that are in better agreement with

230

the experimental data compared with the reaction mechanisms reported in references [17, 38]. To

231

further study the effect of factors influencing SO3 in the flue gas, the SO3 concentrations under the

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flue gas conditions listed in Table 4 with increasing residence time were numerically calculated

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with a perfectly stirred reactor system using the CHEMKIN-PRO software based on the improved

234

mechanism in the present work [40–41]. Similar to the measuring experiments based on the

235

controlled condensation and S balance methods, the numerically calculated flue gas temperature

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ranged from 973 K to 1273 K.

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4. RESULTS AND DISCUSSION

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4.1 Experimental results

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The SO3 concentrations under the different flue gas conditions listed in Table 1 at

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temperatures ranging from 973 K to 1073 K and measured based on the controlled condensation

242

method are shown in Table 5; those obtained at temperatures ranging from 1173 K to 1273 K are

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listed in Table 6. The SO3 concentrations under the different flue gas conditions listed in Table 2 at

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temperatures ranging from 973 K to 1273 K measured based on the S balance method are listed in

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Tables 7 to 10. As shown in Tables 5 to 10, the measurements based on the S balance method are

246

generally better than those based on the controlled condensation method. Furthermore, the

247

measured results listed in Tables 5 and 6 show that the SO3 concentration in flue gas increased

248

linearly as SO2 concentration increased, and the mole fraction of SO2 ranged from 500 ppm to

249

2000 ppm at temperatures between 973 and 1273 K. Moreover, as CO emerged in the flue gas,

250

SO3 concentration increased significantly at the same temperature range. Similarly, SO3

251

concentration increased significantly at temperatures ranging from 973 K to 1273 K when NO

252

emerged in the flue gas. However, CO2 did not exert any effect on SO3 concentration in flue gas

253

compared with the two gases at the aforementioned temperature range.

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Similar to the measured results based on the controlled condensation method, the measured

255

results listed in Tables 7 to 10 also show that the SO3 concentration in flue gas linearly increased

256

as SO2 concentration increased based on the measured results with the S balance method. The

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mole fraction of SO2 ranged from 500 ppm to 2000 ppm at temperatures between 973 and 1273 K.

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As CO and NO emerged in the flue gas, SO3 concentration increased significantly at temperatures

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ranging from 973 K to 1273 K. Moreover, similar to the measured results based on the controlled

260

condensation method, CO2 exerted little effect on SO3 concentration in the flue gas at said

261

temperature range. According to the measured results with the S balance method, SO3

262

concentration in flue gas increased nonlinearly as O2 concentration increased. The mole fraction of

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O2 ranged from 1.25% to 5% at temperatures between 973 and 1273 K. The increasing slope of

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SO3 concentration decreased with increased O2 concentration at high temperatures. For the effect

265

of H2O concentration in flue gas, SO3 concentration increased significantly as H2O emerged in the

266

flue gas at the set temperature range. However, a decreasing trend was observed as H2O

267

concentration increased. The mole fraction of H2O in flue gas ranged from 1.25% to 5% at the

268

aforementioned temperature range.

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4.2 Modeling results

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The SO3 concentrations in flue gas under the different flue gas conditions listed in Table 4 at

271

temperatures ranging from 973 K to 1273 K and with increasing residence time are shown in

272

Figures 5 to 10. These concentrations were numerically calculated based on the improved reaction

273

mechanism in the present work, the reaction mechanisms of Mueller et al. [17], and the

274

mechanism of Spencer et al. [38] with a perfectly stirred reactor system using the

275

CHEMKIN-PRO software [40–41]. Although the discrepancies between the numerically

276

calculated SO3 concentrations in flue gas and the experimental results are relatively large, the

277

improved reaction mechanism in the present work produces numerical calculations that are

278

relatively in better agreement with the experimental data compared with the reaction mechanisms

279

reported in references [17, 38]. Furthermore, as shown in Figure 5, similar to the measured results

280

based on controlled condensation and S balance methods, SO3 concentration in flue gas linearly

281

increased as SO2 concentration increased. The mole fraction of SO2 ranged from 500 ppm to 2000

282

ppm at temperatures between 973 and 1273 K. SO3 concentration increased significantly as CO

283

and NO emerged in the flue gas, whereas CO2 exerted little effect on SO3 concentration in the flue

284

gas at the aforementioned temperature range (Figures 8 to 10). As shown in Figure 6, SO3

285

concentration in flue gas increased nonlinearly as O2 concentration increased. The mole fraction of

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286

O2 ranged from 1.25% to 21% at temperatures between 973 and 1273 K. SO3 concentration in flue

287

gas decreased as H2O concentration increased, and the mole fraction of H2O ranged from 1.25% to

288

5% at temperatures between 973 and 1273 K (Figure 7). Moreover, SO3 concentration in the flue

289

gas underwent three stages of sharp increase, slow increase, and gradual decrease as the residence

290

time increased. The residence time reached 8.2075 s at temperatures ranging from 973 K to 1273

291

K.

292

The logarithmic sensitivity coefficients of the 11 most important reactions influencing SO3

293

concentration were calculated. With the mole fraction of O2 ranging from 1.25% to 5% at 1073 K,

294

the values were numerically calculated based on the improved reaction mechanism in the present

295

work as well as the reaction mechanisms of Spencer et al. [38] and Mueller et al. [17] with a

296

perfectly stirred reactor system using the CHEMKIN-PRO software [40–41]; the calculated values

297

are shown in Figures 11 to 13, respectively. The logarithmic sensitivity coefficient (Fsen,R) can be

298

calculated as

Fsen,R =

299

∂ ln m , ∂ ln k

(1)

300

where m is SO3 concentration in flue gas and k is the pre-exponential factor of the Arrhenius

301

formula. When the logarithmic sensitivity coefficient is greater than zero, the reaction results in an

302

increase in SO3 concentration; otherwise, SO3 concentration decreases. As shown in Figures 11 to

303

13, SO2, O2, H2O, CO, and NO exerted a significant effect on SO3 concentration in flue gas

304

compared with CO2. The effect of the influencing factors, namely, SO2, O2, H2O, CO, and NO, on

305

SO3 concentration can be attributed to the fact that the concentrations of H, O, and OH radicals

306

changed.

307

Moreover, the reaction rates of the 11 most important reactions influencing SO3 concentration

308

were calculated with the mole fraction of O2 ranging from 1.25% to 5% at a temperature of 1073

309

K. The rates were numerically calculated based on the improved reaction mechanism in the

310

present work, the reaction mechanism of Spencer et al. [38], and the reaction mechanism of

311

Mueller et al. [17] with a perfectly stirred reactor system using the CHEMKIN-PRO software [40–

312

41]; the calculated rates are shown in Figures 14 to 16, respectively. The reaction rates of the 11

313

most important reactions influencing SO3 concentration underwent three different stages, which

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314

explains why SO3 concentration in the flue gas underwent three stages of sharp increase, slow

315

increase, and gradual decrease as the residence time increased.

316 317

5. SUMMARY AND CONCLUSIONS

318

In this study, SO3 concentrations under different flue gas conditions were measured with a

319

measuring device built based on the controlled condensation method and another device built

320

based on the S balance method. The effects of SO2, O2, H2O, NO, CO2, CO, temperature, and

321

residence time on SO3 concentration in flue gas were investigated at temperatures ranging from

322

973 K to 1273 K. To further study the effect of the influencing factors on SO3 in flue gas, an

323

improved SO2/O2/H2O/CO2/CO/NO kinetic mechanism was built based on previous research

324

achievements. The mechanism was validated with experimental data and kinetic mechanisms

325

reported in previous studies. Moreover, the SO3 concentrations under the flue gas conditions

326

mentioned above with increasing residence time were numerically calculated based on the

327

improved kinetic mechanism presented in this work. The results measured with the controlled

328

condensation and S balance methods as well as the numerically calculated results in the present

329

work showed that SO3 concentration in the flue gas experienced three stages of sharp increase,

330

slow increase, and gradual decrease as the residence time increased. The residence time reached

331

8.2075 s at temperatures ranging from 973 K to 1273 K. SO3 concentration in the flue gas

332

increased linearly as SO2 concentration increased. The mole fraction of SO2 ranged from 500 ppm

333

to 2000 ppm. However, it increased nonlinearly as O2 concentration increased, with the mole

334

fraction of O2 in flue gas ranging from 1.25% to 21% at temperatures between 973 and 1273 K.

335

For the effect of H2O concentration in flue gas, SO3 concentration increased significantly as H2O

336

emerged; however, it decreased as H2O concentration increased, with the mole fraction ranging

337

from 1.25% to 5% and at temperatures between 973 and 1273 K. In addition, SO3 concentration in

338

the flue gas increased significantly as CO and NO emerged in the flue gas. CO2 exerted little

339

effect at temperatures ranging from 973 K to 1273 K.

340

In this study, the scope of the factors that influence SO3 in flue gas is limited only to SO3

341

produced in flue gas by homogenous gas-phase reactions and does not include heterogeneous

342

absorption and catalytic reactions on the heat exchanger’s surfaces and ash particles. However,

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343

several researchers have argued that these exert a significant effect on SO3 concentration in flue

344

gas. Therefore, future research should focus on the effect of heterogeneous absorption and

345

catalytic reactions on the heat exchanger’s surfaces and ash particles in flue gas, including alkali

346

metals, V2O5, WO3, and Fe2O3.

347 348

AUTHOR INFORMATION

349

Corresponding author

350

*E-mail address: [email protected] (J. Lu). Tel.: +86-01-62792647

351

Notes

352

The authors declare no competing financial interest.

353 354 355 356

ACKNOWLEDGEMENTS The financial support provided by the National Program on Key Basic Research Project (973 Program) of China (No. 2014CB744305) is gratefully acknowledged.

357 358

REFERENCES

359

(1) Fleig, D.; Andersson, K.; Normann, F.; Johnsson, F. SO3 Formation under Oxyfuel

360 361 362

Combustion Conditions. Ind. Eng. Chem. Res. 2011, 50 (14), 8505-8514. (2) Li, B. Temperature dependence of selective catalytic reduction of NOx and mechanisms of its resistance to SO2 induced catalyst deactivation. Zhejiang University, 2016.

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(3) Schwämmle, T.; Bertsche, F.; Hartung, A.; et al. Influence of geometrical parameters of

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honeycomb commercial SCR-DeNOx-catalysts on DeNOx-activity, mercury oxidation and

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SO2/SO3-conversion. Chem. Eng. J. 2013, 222, 274-281.

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(4) Xiang, B. X.; Zhang, M.; Yang, H. R.; Lu, J. F. Prediction of Acid Dew Point in Flue Gas of Boilers Burning Fossil Fuels. Energy Fuels 2016, 30(4): 3365-3373. (5) Xiang, B. X.; Tang, B.; Wu, Y. X.; Yang, H. R.; et al. Predicting Acid Dew Point with A Semi-empirical Model. Appl. Therm. Eng. 2016, 106(5), 992-1001. (6) Moser, R. E. SO3's impacts on plant O&M: Part I. Power 2006, 150(8): 40-40.

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(7) Moser, R. E. Benefits of effective SO3 removal in coal-fired power plants: beyond opacity

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control. Power Plant and Air Pollutant Control MEGA Symposium, August 28-31, 2006,

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(8) Fleig, D. Experimental and modeling studies of sulfur-based reactions in oxy-fuel combustion. Chalmers University of Technology, 2012. (9) Chen, P. Study on the Influence Factor of Collection Efficiency of the Electrostatic Precipitator. Northeastern University, 2009 (in Chinese).

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(10) Qi, L. Q.; Yuan, Y. T.; Shi, Y. W. Influence of SO3 on Electrostatic Precipitation of Fine

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Particles in Flue Gas. Journal of Chinese Society of Power Engineering 2011, 31(7), 539-543

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(in Chinese).

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(11) Lisle, E. S.; Sensenbaugh, J. D. The determination of sulfur trioxide and acid dew point in flue gases. Combustion 1965, 36(1), 12-16. (12) Cheney, J. L.; Homolya, J. B. Sampling parameters for sulfate measurement and characterization. Environ. Sci. Technol. 1979, 13(5), 584-588. (13) Fleig, D.; Vainio, E.; Andersson, K.; et al. Evaluation of SO3 measurement techniques in air and oxy-fuel combustion. Energy Fuels 2012, 26(9), 5537-5549. (14) Zhang, Y. Research and application of SO3 measurement in flue gas. Zhejiang University, 2013 (in Chinese).

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(15) Xiao, Y. T.; Jia, M.; Xu, L.; et al. The Analytic Method of Sulfur Trioxide and Sulfuric Acid

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Mist in Flue Gas. Environmental Science and Technology 2012, 25(5), 43-48 (in Chinese).

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(16) Guo, Y.; Li, Y.; Wang, Y. W.; et al. Comparison of SO3 Testing and Sampling Methods in

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Flue Gas for SCR Denitration System. Electric Power Construction 2013, 34(6), 69-72 (in

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Chinese).

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(17) Mueller, M. A.; Yetter, R. A.; Dryer, F. L. Kinetic modeling of the CO/H2O/O2/NO/SO2

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system: Implications for high-pressure fall-off in the SO2+ O (+ M) = SO3 (+ M)

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reaction. Int. J. Chem. Kinet. 2000, 32(6), 317-339.

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(18) Fleig, D.; Andersson, K.; Johnsson, F.; et al. Conversion of sulfur during pulverized oxy-coal combustion. Energy Fuels 2011, 25(2), 647-655.

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(19) Cooper, D.; Andersson, C. Bestämning av SO3 i Rökgaser med NaCl-metoden-en Jämförelse

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av Olika Metoder, Värmeforsk Report 616; Institutet för Vattenoch Luftvaårdsforskning

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(IVL):

Göteborg

1997.

Available

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http://www.varmeforsk.se/rapporter?action=show&id=1808 (in Swedish).

online:

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(20) Vainio, E.; Fleig, D.; Brink, A.; Andersson, K.; Johnsson, F.; et al. Experimental evaluation

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and field application of a salt method for SO3 measurement in flue gases. Energy Fuels

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2013, 27(5), 2767-2775.

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(21) Jaworowski, R. J.; Mack, S. S. Evaluation of Methods for Measurement of S03/H2S04 in Flue Gas. Journal of the Air Pollution Control Association 1979, 29(1), 43-46.

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(22) Wieder, R. K.; Lang, G. E.; Granus, V. A. An evaluation of wet chemical methods for

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quantifying sulfur fractions in freshwater wetland peat. Limnol. Oceanogr. 1985, 30(5),

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1109-1115.

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(23) Liu, K.; Pan, W. P.; Riley, J. T. A study of chlorine behavior in a simulated fluidized bed combustion system. Fuel 2000, 79(9), 1115-1124. (24) Xie, W.; Liu, K.; Pan, W. P.; et al. Interaction between emissions of SO2 and HCl in fluidized bed combustors. Fuel 1999, 78(12), 1425-1436. (25) Reidick, H.; Reifenhauser, R. Catalytic SO3 formation as function of boiler fouling. Combustion 1980, 51(8), 17-21.

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(26) Belo, L. P.; Elliott, L. K.; Stanger, R. J.; et al. High-Temperature Conversion of SO2 to SO3:

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Homogeneous Experiments and Catalytic Effect of Fly Ash from Air and Oxy-fuel firing.

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Energy Fuels 2014, 28 (11), 7243-7251.

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(27) Spörl, R.; Walker, J.; Belo, L.; et al. SO3 Emissions and Removal by Ash in Coal-Fired Oxy-Fuel Combustion. Energy Fuels 2014, 28 (8), 5296-5306. (28) Jørgensen, T. L.; Livbjerg, H.; Glarborg, P. Homogeneous and heterogeneously catalyzed oxidation of SO2. Chem. Eng. Sci. 2007, 62(16), 4496-4499. (29) Ahn, J.; Okerlund, R.; Fry, A.; et al. Sulfur trioxide formation during oxy-coal combustion. Int. J. Greenh. Gas Control 2011, 5, S127-S135.

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(30) Fleig, D.; Alzueta, M. U.; Normann, F.; et al. Measurement and modeling of sulfur trioxide

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formation in a flow reactor under post-flame conditions. Combust. Flame 2013, 160(6),

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1142-1151.

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(31) Alzueta, M. U.; Bilbao, R.; Glarborg, P. Inhibition and sensitization of fuel oxidation by SO2. Combust. Flame 2001, 127(4), 2234-2251.

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(32) Giménez-López, J.; Martínez, M.; Millera, A.; et al. SO2 effects on CO oxidation in a CO2

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atmosphere, characteristic of oxy-fuel conditions. Combust. Flame 2011, 158(1), 48-56.

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(33) Rasmussen, C. L.; Glarborg, P.; Marshall, P. Mechanisms of radical removal by SO2. Proc.

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Combust. Inst. 2007, 31(1), 339-347. (34) Yilmaz, A.; Hindiyarti, L.; Jensen, A. D.; et al. Thermal dissociation of SO3 at 1000-1400 K. The Journal of Physical Chemistry A 2006, 110(21), 6654-6659.

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(35) Hindiyarti, L.; Glarborg, P.; Marshall, P. Reactions of SO3 with the O/H radical pool under

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combustion conditions. The Journal of Physical Chemistry A 2007, 111(19), 3984-3991.

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(36) Sendt, K.; Jazbec, M.; Haynes, B. S. Chemical kinetic modeling of the H/S system: H2S

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thermolysis and H2 sulfidation. Proc. Combust. Inst. 2002, 29(2), 2439-2446. (37) Allen, M. T.; Yetter, R. A.; Dryer, F. L. High pressure studies of moist carbon monoxide/nitrous oxide kinetics. Combust. Flame 1997, 109(3), 449-470.

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(38) Spencer, H.; Romero, C.; Levy, E.; Yao, Z.; Bilirgen, H.; Caram, H. Modeling of SO3

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Formation Process in coal-fired boilers. Electic Power Research Institute, Palo Alto, CA:

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1012689, 2007.

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(39) Smith, G.P.; Golden, D. M.; Frenklach, M.; Moriarty, N. W.; Eiteneer, B.; Goldenberg, M.;

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Bowman, C.T.; Hanson, R. K.; Song, S.; Lissianski, V. V.; Qin, Z. available at:

448

http://www.me.berkeley.edu/gri_mech/.

449 450 451

(40) Kee, R. J.; Rupley, F. M.; Miller, J. A. The Chemkin Thermodynamic Data Base, Sandia Report SAND87-8215B, Livermore, CA, 1987. (41) Chemkin-Pro. Release 15101, Reaction Design, San Diego.

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452

LIST OF TABLES

453

1. Table 1. Experimental flue gas conditions for the controlled condensation method

454

2. Table 2. Experimental flue gas conditions for the S balance method

455

3. Table 3. Experimental flue gas conditions in reference [17]

456

4. Table 4. Numerically calculated flue gas conditions

457

5. Table 5. Experimental results at 973 K to 1073 K for the controlled condensation method

458

6. Table 6. Experimental results at 1173 K to 1273 K for the controlled condensation method

459

7. Table 7. Experimental results at 973 K for the S balance method

460

8. Table 8. Experimental results at 1073 K for the S balance method

461

9. Table 9. Experimental results at 1173 K for the S balance method

462

10. Table 10. Experimental results at 1273 K for the S balance method

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Page 18 of 44

Table 1. Experimental flue gas conditions for the controlled condensation method

463

SO2

O2

CO2

CO

NO

H2 O

N2

ppm

%

%

ppm

ppm

%

%

1

500

5

15

1000

500

5

74.80

2

1000

5

15

1000

500

5

74.75

3

1500

5

15

1000

500

5

74.70

4

2000

5

15

1000

500

5

74.65

5

2000

5

0

0

0

5

89.80

6

2000

5

0

1000

500

5

89.65

7

2000

5

15

0

500

5

74.75

8

2000

5

15

1000

0

5

74.70

9

2000

5

0

0

500

5

89.75

10

2000

5

15

0

0

5

74.80

11

2000

5

0

1000

0

5

89.70

No.

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Energy & Fuels

Table 2. Experimental flue gas conditions for the S balance method

464 No.

SO2

O2

CO2

CO

NO

H2O

N2

ppm

%

%

ppm

ppm

%

%

1

0

5

15

1000

500

5

74.85

2

500

5

15

1000

500

5

74.80

3

1000

5

15

1000

500

5

74.75

4

1500

5

15

1000

500

5

74.70

5

2000

5

15

1000

500

5

74.65

6

2000

0

15

1000

500

5

79.65

7

2000

1.25

15

1000

500

5

78.40

8

2000

2.5

15

1000

500

5

77.15

9

2000

3.75

15

1000

500

5

75.90

10

2000

5

15

1000

500

0

79.65

11

2000

5

15

1000

500

1.25

78.40

12

2000

5

15

1000

500

2.5

77.15

13

2000

5

15

1000

500

3.75

75.90

14

2000

5

0

0

0

5

89.80

15

2000

5

0

1000

500

5

89.65

16

2000

5

15

0

500

5

74.75

17

2000

5

15

1000

0

5

74.70

18

2000

5

0

0

500

5

89.75

19

2000

5

15

0

0

5

74.80

20

2000

5

0

1000

0

5

89.70

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Page 20 of 44

Table 3. Experimental flue gas conditions in reference [17]

465 Pressure

Temperature

CO

O2

H2O

NO

SO2

N2

atm

K

%

%

%

ppm

ppm

%

1.2

950

0.51

0.75

0.49

97

496

98.1907

3.0

954

0.52

0.76

0.48

99

504

98.1797

6.5

952

0.52

0.75

0.48

97

484

98.1919

10

951

0.51

0.75

0.48

103

478

98.2019

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Energy & Fuels

Table 4. Numerically calculated flue gas conditions

466

SO2

O2

CO2

CO

NO

H2 O

N2

ppm

%

%

ppm

ppm

%

%

0

5

15

1000

500

5

74.85

2

500

5

15

1000

500

5

74.80

3

1000

5

15

1000

500

5

74.75

4

1500

5

15

1000

500

5

74.70

5

2000

5

15

1000

500

5

74.65

6

2000

0

15

1000

500

5

79.65

7

2000

1.25

15

1000

500

5

78.40

8

2000

2.5

15

1000

500

5

77.15

9

2000

3.75

15

1000

500

5

75.90

10

2000

8

15

1000

500

5

71.65

11

2000

11

15

1000

500

5

68.65

12

2000

14

15

1000

500

5

65.65

13

2000

17

15

1000

500

5

62.65

14

2000

21

15

1000

500

5

58.65

15

2000

5

15

1000

500

0

79.65

16

2000

5

15

1000

500

1.25

78.40

17

2000

5

15

1000

500

2.5

77.15

18

2000

5

15

1000

500

3.75

75.90

19

2000

5

0

0

0

5

89.80

20

2000

5

0

1000

500

5

89.65

21

2000

5

3

1000

500

5

86.65

22

2000

5

6

1000

500

5

83.65

23

2000

5

9

1000

500

5

80.65

24

2000

5

12

1000

500

5

77.65

25

2000

5

15

0

500

5

74.75

26

2000

5

15

200

500

5

74.73

No. 1

27

2000

5

15

400

500

5

74.71

28

2000

5

15

600

500

5

74.69

29

2000

5

15

800

500

5

74.67

30

2000

5

15

1000

0

5

74.70

31

2000

5

15

1000

100

5

74.69

32

2000

5

15

1000

200

5

74.68

33

2000

5

15

1000

300

5

74.67

34

2000

5

15

1000

400

5

74.66

35

2000

5

0

0

500

5

89.75

36

2000

5

15

0

0

5

74.80

37

2000

5

0

1000

0

5

89.70

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467

Page 22 of 44

Table 5. Experimental results at 973 K to 1073 K for the controlled condensation method Time

Temperature

Volume

S

SO3

s



mL

µg/mL

ppm

1

89

60

115





2

95

60

115

0.0248

1.2609

3

89

60

120

0.0323

1.8291

4

86

60

140

0.0485

3.3160

5

90

60

140

0.0340

2.2213

6

90

60

130

0.0380

2.3053

7

88

60

125

0.0330

1.9688

Test case

973 K

1073 K

8

92

60

150

0.0275

1.9038

19

90

60

130

0.0305

1.8503

10

89

60

150

0.0328

2.3218

11

94

60

175

0.0322

2.5178

1

150

60

120

0.0586

1.9690

2

120

60

135

0.0457

2.1593

3

83

60

120

0.041

2.4896

4

93

60

155

0.0597

4.1790

5

88

60

120

0.0476

2.7262

6

90

60

110

0.0373

1.9147

7

84

60

125

0.0764

4.7750

8

87

60

140

0.0629

4.2512

19

96

60

145

0.0519

3.2924

10

89

60

155

0.0413

3.0209

11

87

60

140

0.0583

3.9403

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Energy & Fuels

468

Table 6. Experimental results at 1173 K to 1273 K for the controlled condensation method Time

Temperature

Volume

S

SO3

s



mL

µg/mL

ppm

1

89

60

165

0.0570

4.4383

2

90

60

130

0.0886

5.3751

3

89

60

135

0.1702

10.8431

4

84

60

125

0.2654

16.5875

5

89

60

110

0.1105

5.7361

6

89

60

120

0.0748

4.2359

7

86

60

150

0.1607

11.7722

8

103

60

105

0.4578

19.6010

19

85

60

125

0.0657

4.0579

10

84

60

145

0.0809

5.8653

11

92

60

140

0.0584

3.7325

1

158

60

170

0.1499

6.7740

2

114

60

145

0.2170

11.5924

3

86

60

170





4

80

60

185





5

88

60

170

0.0887

7.1968

6

91

60

130

0.1213

7.2780

7

105

60

145

0.3296

19.1168

8

91

60

170

0.0568

4.4566

19

94

60

210

0.1083

10.1618

10

144

60

175

0.4284

21.8663

11

91

60

225

0.1229

12.7627

Test case

1173 K

1273 K

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Page 24 of 44

Table 7. Experimental results at 973 K for the S balance method

469

SO2 in feed gas

SO2 in flue gas

SO3 in flue gas

Mean value

ppm

ppm

ppm

ppm

566.80

563.16

3.64

563.28

559.98

3.30

1062.39

1052.10

10.29

1060.19

1054.85

5.34

1541.87

1526.58

15.29

1537.24

1517.84

19.40

1779.63

1757.44

22.19

1778.09

1761.07

17.02

1779.63

1774.24

5.39

1778.09

1773.93

4.16

1779.63

1765.69

13.94

1778.09

1766.20

11.89

1779.63

1759.60

20.03

1778.09

1764.84

13.25

1871.51

1866.35

5.16

1869.97

1865.44

4.53

1871.51

1841.40

30.11

1869.97

1844.45

25.52

1871.51

1845.03

26.48

1869.97

1845.06

24.91

1871.51

1850.00

21.51

1869.97

1849.72

20.25

1779.63

1764.11

15.52

1778.09

1762.28

15.81

1972.74

1950.05

22.69

1971.20

1946.23

24.97

1880.86

1872.08

8.78

1879.32

1875.38

3.94

1871.51

1858.72

12.79

1869.97

1859.72

10.25

1880.86

1875.41

5.45

1879.32

1871.28

8.04

1779.63

1774.54

5.09

1778.09

1773.50

4.59

1871.51

1864.02

7.49

1869.97

1864.45

5.52

Test case

2

3

4

5

7

8

9

10

11 973 K 12

13

14

15

16

17

18

19

20

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3.47

7.82

17.35

19.61

4.78

12.92

16.64

4.85

27.82

26.70

20.88

15.67

23.83

6.41

11.52

6.75

4.84

6.51

Page 25 of 44

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Energy & Fuels

Table 8. Experimental results at 1073 K for the S balance method

470

SO2 in feed gas

SO2 in flue gas

SO3 in flue gas

Mean value

ppm

ppm

ppm

ppm

451.34

446.38

4.96

445.17

440.57

4.60

1002.78

989.26

13.52

1004.98

993.77

11.21

1372.85

1360.39

12.46

1377.74

1369.09

8.65

1875.72

1852.31

23.41

1876.74

1855.78

20.96

1875.72

1870.11

5.61

1876.74

1872.50

4.24

2030.78

2021.59

9.19

2031.80

2021.67

10.13

2113.19

2099.53

13.66

2114.21

2101.93

12.28

2030.78

2027.87

2.91

2031.80

2025.84

5.96

2113.19

2084.96

28.23

2114.21

2088.00

26.21

2113.19

2086.16

27.03

2114.21

2086.94

27.27

2008.91

1984.21

24.70

2004.27

1981.36

22.91

1779.95

1774.76

5.19

1775.31

1767.95

7.36

1958.13

1933.23

24.90

1959.15

1936.48

22.67

1936.26

1908.65

27.61

1931.62

1906.40

25.22

1935.01

1928.08

6.93

1930.37

1925.47

4.90

1779.95

1775.79

4.16

1775.31

1777.40

0

1779.95

1778.17

1.78

1775.31

1769.42

5.89

1935.01

1927.80

7.21

1930.37

1925.42

4.95

Test case

2

3

4

5

7

8

9

10

11 1073 K 12

13

14

15

16

17

18

19

20

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4.78

12.37

10.56

22.19

4.93

9.66

12.97

4.44

27.22

27.15

23.81

6.28

23.79

26.42

5.92

2.08

3.84

6.08

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Page 26 of 44

Table 9. Experimental results at 1173 K for the S balance method

471

SO2 in feed gas

SO2 in flue gas

SO3 in flue gas

Mean value

ppm

ppm

ppm

ppm

670.66

661.33

9.33

666.13

659.02

7.11

1201.47

1187.07

14.40

1200.04

1190.33

9.71

1561.58

1545.38

16.20

1558.85

1537.11

21.74

2004.53

1971.40

33.13

1998.64

1967.92

30.72

2004.53

1992.02

12.51

1998.64

1988.33

10.31

2004.53

1985.22

19.31

1998.64

1982.80

15.84

2004.53

1978.63

25.90

1998.64

1975.09

23.55

2004.53

1994.40

10.13

1998.64

1984.00

14.64

2004.53

1952.59

51.94

1998.64

1943.67

54.97

2004.53

1961.33

43.20

1998.64

1958.10

40.54

2004.53

1963.11

41.42

1998.64

1958.43

40.21

1888.20

1871.79

16.41

1882.31

1868.00

14.31

1888.20

1851.97

36.23

1882.31

1852.11

30.20

1888.20

1865.92

22.28

1882.31

1862.60

19.71

1888.20

1877.31

10.89

1882.31

1874.53

7.78

1888.20

1876.09

12.11

1882.31

1875.13

7.18

1888.20

1879.60

8.60

1882.31

1872.91

9.40

1888.20

1878.09

10.11

1882.31

1875.30

7.01

Test case

2

3

4

5

7

8

9

10

11 1173 K 12

13

14

15

16

17

18

19

20

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8.22

12.06

18.97

31.93

11.41

17.58

24.73

12.39

53.46

41.87

40.82

15.36

33.22

21.00

9.34

9.66

9.00

8.56

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Energy & Fuels

Table 10. Experimental results at 1273 K for the S balance method

472

SO2 in feed gas

SO2 in flue gas

SO3 in flue gas

Mean value

ppm

ppm

ppm

ppm

465.75

454.90

10.85

460.48

450.82

9.66

1094.54

1079.01

15.53

1090.69

1072.28

18.41

1644.31

1617.18

27.13

1645.23

1620.67

24.56

2189.19

2152.11

37.08

2186.12

2143.16

42.96

2189.19

2174.34

14.85

2186.12

2170.06

16.06

2189.19

2178.88

10.31

2186.12

2177.14

8.98

2189.19

2150.11

39.08

2186.12

2144.33

41.79

2189.19

2179.15

10.04

2186.12

2171.05

15.07

2189.19

2131.47

57.72

2186.12

2121.51

64.61

2189.19

2139.40

49.79

2186.12

2133.77

52.35

2189.19

2145.43

43.76

2186.12

2140.75

45.37

1992.83

1967.81

25.02

1989.76

1974.88

14.88

2189.19

2146.96

42.23

2186.12

2143.70

42.42

2107.94

2050.52

57.42

2115.58

2061.28

54.30

2071.64

2059.83

11.81

2079.28

2071.01

8.27

2107.94

2094.97

12.97

2115.58

2099.13

16.45

1991.61

1954.46

37.15

1999.25

1953.50

45.75

2071.64

2058.94

12.70

2079.28

2071.05

8.23

Test case

2

3

4

5

7

8

9

10

11 1273 K 12

13

14

15

16

17

18

19

20

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10.26

16.97

25.85

40.02

15.46

9.65

40.44

12.56

61.17

51.07

44.57

19.95

42.33

55.86

10.04

14.71

41.45

10.47

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473

LIST OF FIGURES

474

1. Figure 1. SO3 concentration measurement apparatus based on the controlled concentration

475

method

476

2. Figure 2. Perfectly stirred reactor

477

3. Figure 3. SO3 concentration measurement apparatus based on the S balance method

478

4. Figure 4. Comparison of the values predicted using the reaction mechanisms and previous

479

experimental data [17]

480

5. Figure 5. Effect of SO2 and residence time on SO3 in flue gas at 973 K to 1273 K

481

6. Figure 6. Effect of O2 and residence time on SO3 in flue gas at 973 K to 1273 K

482

7. Figure 7. Effect of H2O and residence time on SO3 in flue gas at 973 K to 1273 K

483

8. Figure 8. Effect of CO2 and residence time on SO3 in flue gas at 973 K to 1273 K

484

9. Figure 9. Effect of CO and residence time on SO3 in flue gas at 973 K to 1273 K

485

10. Figure 10. Effect of NO and residence time on SO3 in flue gas at 973 K to 1273 K

486

11. Figure 11. Sensitivity coefficients of the 11 most sensitive reactions in the present model at

487

1073 K

488

12. Figure 12. Sensitivity coefficients of the 11 most sensitive reactions in the EPRI model at

489

1073 K

490

13. Figure 13. Sensitivity coefficients of the 11 most sensitive reactions in the Mueller model at

491

1073 K

492

14. Figure 14. Reaction rates of the 11 most sensitive reactions in the present model with the

493

residence time increasing at 1073 K

494

15. Figure 15. Reaction rates of the 11 most sensitive reactions in the EPRI model with the

495

residence time increasing at 1073 K

496

16. Figure 16. Reaction rates of the 11 most sensitive reactions in the Mueller model with the

497

residence time increasing at 1073 K

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498

Figure 1. SO3 concentration measurement apparatus based on the controlled concentration method (1) standard gas, (2) syringe pump, (3) nebulizer, (4) mixing chamber, (5) temperature instrument, (6) glass cooler, (7) electro-thermostatic water cabinet, (8) ammeter, (9) perfectly stirred reactor, (10) tubular furnace, (11) voltmeter

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499

Figure 2. Perfectly stirred reactor (1) reaction chamber, (2) thermocouple, (3) spiral nozzle

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500

Figure 3. SO3 concentration measurement apparatus based on the S balance method (1) standard gas, (2) syringe pump, (3) nebulizer, (4) mixing chamber, (5) temperature instrument, (6) ammeter, (7) perfectly stirred reactor, (8) tubular furnace, (9) voltmeter, (10) computer, (11) Fourier transform infrared spectrometer

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501 502

Figure 4. Comparison of the values predicted using the reaction mechanisms and previous experimental data [17]

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503

Figure 5. Effect of SO2 and residence time on SO3 in flue gas at 973 K to 1273 K

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504

Figure 6. Effect of O2 and residence time on SO3 in flue gas at 973 K to 1273 K

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505

Figure 7. Effect of H2O and residence time on SO3 in flue gas at 973 K to 1273 K

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506

Figure 8. Effect of CO2 and residence time on SO3 in flue gas at 973 K to 1273 K

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507

Figure 9. Effect of CO and residence time on SO3 in flue gas at 973 K to 1273 K

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508

Figure 10. Effect of NO and residence time on SO3 in flue gas at 973 K to 1273 K

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509 510

Figure 11. Sensitivity coefficients of the 11 most sensitive reactions in the present model at 1073 K

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511

Figure 12. Sensitivity coefficients of the 11 most sensitive reactions in the EPRI model at 1073 K

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512 513

Figure 13. Sensitivity coefficients of the 11 most sensitive reactions in the Mueller model at 1073 K

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514 515

Figure 14. Reaction rates of the 11 most sensitive reactions in the present model with the residence time increasing at 1073 K

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516 517

Figure 15. Reaction rates of the 11 most sensitive reactions in the EPRI model with the residence time increasing at 1073 K

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518 519

Figure 16. Reaction rates of the 11 most sensitive reactions in the Mueller model with the residence time increasing at 1073 K

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