Emission and Formation Characteristics of Aerosols from

Dec 17, 2015 - The particle characteristics before and after desulfurization were measured in a power plant. The aerosol formation characteristics and...
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Emission and Formation Characteristics of Aerosols from AmmoniaBased Wet Flue Gas Desulfurization Danping Pan,† Ran Yu,† Jingjing Bao,‡ Hao Wu,† Rongting Huang,† and Linjun Yang*,† †

Key Laboratory of Energy Thermal Conversion and Control of Ministry of Education, Southeast University, Nanjing, Jiangsu 210096, People’s Republic of China ‡ School of Energy and Mechanical Engineering, Nanjing Normal University, Nanjing, Jiangsu 210042, People’s Republic of China ABSTRACT: The emission and formation characteristics of aerosols were studied during the ammonia-based wet flue gas desulfurization (WFGD) process. The particle characteristics before and after desulfurization were measured in a power plant. The aerosol formation characteristics and effects of operation parameters were investigated with an experimental system. The results indicated that the aerosol emission was related to the type of ammonia-based desulfurization technology and the particle morphology and elements changed significantly during desulfurization. Aerosols formed during desulfurization were from the heterogeneous reactions and the entrainment and evaporation of desulfurization liquid. The heterogeneous reactions made greater contribution to the aerosol formation with different components, and smaller aerosols were generated. With the decrease of gas flow velocity and the solid content of desulfurization liquid, the aerosol concentration from the entrainment and the evaporation of the desulfurization liquid decreased. The formation of aerosols through the heterogeneous reactions could be inhibited with the decrease of the pH value of the desulfurization liquid and the inlet flue gas temperature. the industrial ammonia-based WFGD process.15,16 Bao et al.17,18 and Yan et al.19,20 studied the aerosol emission during the ammonia-based WFGD and proposed that aerosols could be formed by two different mechanisms, which were the entrainment and evaporation of desulfurization liquid droplets and the heterogeneous reactions between SO2, H2O, and gaseous ammonia volatilizing from ammonia solution. However, the aerosol emission in industry has not yet been measured, and there is a lack of investigation on the formation characteristics and effects of operation parameters on aerosol emission. In this work, the particle characteristics before and after desulfurization were measured in a power plant. The aerosol formation characteristics and effects of operational parameters on the aerosols formed from different mechanisms were also investigated with an experimental system.

1. INTRODUCTION Coal is still one of the major fuels used in energy production, despite the awareness of the potential adverse environmental and health impacts and high contribution to the emissions of SO2, NOx, and particles. To control the SO2 emission, various flue gas desulfurization processes have been developed and applied worldwide. As a result of the advantages of high desulfurization efficiency, fast gas−liquid reaction speed, low investment, and useful byproducts, ammonia-based wet flue gas desulfurization (WFGD) has attracted increasing attention. Most of the ammonia-based WFGD studies focused on the influences of operation parameters on desulfurization efficiency and reclamation of desulfurization byproducts.1−3 However, the new finding of the emission of a large numbers of aerosols during desulfurization4−6 induced great concerns as related to the equipment corrosion and regional haze.7 Aerosol particles formed during desulfurization can easily escape from the demister and enter the atmosphere. After the release of particles into the atmosphere, the reactions between particles and chemical matter would generate the secondary pollutants. With great surface area, aerosol particles can also easily absorb toxic matter. Removal of these particles from the flue gas is difficult by desulfurization liquid scrubbing. Currently, the only effective solution is to install a wet electrostatic precipitator after the desulfurization scrubber,8,9 which results in higher investment cost and operating expense. Therefore, it is necessary and urgent to solve the aerosol emission problem during ammoniabased WFGD. At present, aerosol formation in industrial gas−liquid contact devices has been described and explained in various publications.10−14 However, they mainly discussed HCl− aerosol, and the scrubbing process addressed was between acid flue gas and water. The investigations on particle formation from NH3−SO2 reactions showed a significant difference from © 2015 American Chemical Society

2. EXPERIMENTAL SECTION 2.1. Experimental Setup. As shown in Figure 1a, two different technologies of ammonia WFGD systems with countercurrent absorbers were used in the same power plant, and the flue gas from coal combustion flowed into different towers to remove SO2. The WFGD systems were installed after the selective catalytic reduction (SCR) and electrostatic precipitator (ESP). Table 1 presents the parameters of two desulfurization technologies. In comparison to technology 1, which was a simple spray scrubber for desulfurization, technology 2 used a multi-function desulfurization tower consisting of an oxidization section, an enriching section, and an absorption section. The flue gas was in contact with the desulfurization liquid in the enriching section for the dust removal and cooling, followed by the desulfurization process in the absorption section. In contrast to the Received: July 23, 2015 Revised: November 30, 2015 Published: December 17, 2015 666

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hydroxide was added to the crystallization tank to ensure a constant pH value. The crystallization tank was placed in an electric-heated thermostatic water bath to keep the temperature of desulfurization liquid at 50 °C. To investigate the aerosol formation from different mechanisms during desulfurization, two experiment strategies were designed. When the addition of SO2 to the flue gas before the spray scrubber was stopped, the heterogeneous reactions among SO2, NH3, and H2O could be ignored; thus, the aerosols were formed from the entrainment and evaporation of the desulfurization liquid. For the other formation mechanism, a bypath at the inlet of the scrubber led the simulation flue gas to the middle of the spray scrubber over the nozzles. The flue gas with a SO2 concentration of 2857 mg/m3 went through the bypath to avoid the entrainment and evaporation of the desulfurization liquid. Therefore, the aerosols were formed from the heterogeneous reactions among SO2, NH3, and H2O. In the experiments, ammonium hydroxide was used as a SO2 absorbent to simulate the ammonia-based processes in the spray scrubber. To be closer to the actual conditions, the desulfurization liquid was circulated with a recycle ratio of nearly 100%. 2.2. Measurement Technique. The particle concentration and size distribution were measured in real time using an electrical lowpressure impactor (ELPI, Dekati, Ltd., Finland). There are 13 stages (12 channels), and the measurement range of the size is from 0.023 to 9.314 μm in aerodynamic diameter. The sample gas stream was withdrawn from the main gas stream and routed through a cyclone to a dilutor before it went into the ELPI. The cyclone separated the particles with the aerodynamic diameters larger than 9.314 μm, and the dilutor diluted the gas with the particle-free dry air (150 °C and dilution ratio of 8.18:1). In this way, the condensation of water vapor on the wall of sampling pipelines and on the impact plate of the ELPI could be avoided to prevent any of its possible influences on the particle size distribution and number concentration. Aerosol mass spectrometry (AMS, Aerodyne, Billerica, MA) was used to measure the chemical components and size distribution of the particle components with the sizes ranging from 0.04 to 1.0 μm. The particles were collected onto the aluminum film of the impact plate of the PM2.5/10 impactor or in the filter cartridge with the WJ-60B automatic smoke sampler for morphology and component analysis, which were carried out using Zeiss Ultra Plus scanning electron microscopy (SEM) equipped with an energy-dispersive spectroscopy (EDS) detector system and a D8 Advance X-ray diffraction (XRD).

Figure 1. Schematic diagram of WFGD systems: (1) air blower, (2) SO2, (3) static mixer, (4) heater, (5) gas analyzer, (6) pump, (7) ammonium hydroxide tank, (8) electric-hearted thermostatic water bath, (9) crystallization tank, and (10) spray scrubber.

Table 1. Parameters of Two Technologies parameter

technology 1

technology 2

tower type inlet gas temperature (°C) outlet gas temperature (°C) inlet concentration of SO2 (mg/m3) gas flow rate (Nm3/h) gas/liquid ratio (L/Nm3) solid content of desulfurization liquid (%) pH value of desulfurization liquid

spray scrubber 135−142 50−70 1700−2100 51−58 × 104 12 8−15

packed tower 135−142 50−60 1700−2100 51−58 × 104 8 3−5

5.2−6.0

5.0−6.0

3. RESULTS AND DISCUSSION 3.1. Aerosol Emissions from Ammonia-Based WFGD in the Power Plant. 3.1.1. Particle Concentrations before and after Desulfurization. As shown in Figure 2, fine particle concentrations before and after desulfurization in a power plant were measured with different technologies. The number and mass concentrations before desulfurization were 0.8−1.2 × 106 cm−3 and 50−100 mg cm−3, respectively. It was inevitable to form large numbers of aerosols during the desulfurization process. The flue gas purification before desulfurization reduced the fine particle concentrations at the inlet of the desulfurization tower but had little impact on the aerosol emission after the desulfurization. The number and mass concentrations of technology 1 after desulfurization increased to 1.0−1.2 × 108 cm−3 and 600−900 mg cm−3, respectively, almost 100 times the inlet number concentrations. There were fewer aerosols formed during the desulfurization in technology 2 because the aerosol number and mass concentrations were approximately 1.8 × 107 cm−3 and 350 mg cm−3, respectively. In comparison to technology 1, technology 2 used a multi-function desulfurization tower with a lower gas/liquid ratio and a lower solid content in the desulfurization liquid. The stuffing in the multifunction desulfurization tower served as a multi-stage filter to prevent the particles escaping from the tower with the flue gas.

flow direction of the flue gas, the desulfurization liquid entered the oxidation section from the absorption section through pipes and was then sprayed into the enriching section. The experimental system, outlined in Figure 1b, was made up of a simulation flue gas system, a spray scrubber, and a desulfurization liquid preparation and feeding system, which was similar to the desulfurization system of technology 1. The rated flue gas consisting of air and SO2 was generated from a static mixer. The flue gas was heated before entering the spray scrubber, in which the flue gas and desulfurization liquid maintained a countercurrent. The three-level scrubber with a demister at the top was made up of the polycarbonate pipes and plates with excellent heat resistance. During the desulfurization process, the desulfurization liquid went back to the crystallization tank for oxidation and recycling. Meanwhile, ammonium 667

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Figure 4b. For the two technologies, most of these aerosols resided at a particle size below 0.2 μm. Among such size range, the particle impaction and separation forces were negligible and most of them escaped from the WFGD and persisted as fine particles leaving the tower. In comparison to the results in Figure 3, the peak positions in Figure 4 obviously shifted to the smaller end, indicating that aerosols formed during the desulfurization with technology 2 were smaller than that formed with technology 1. The removal and formation mechanisms in the different desulfurization towers would exert different influences on the particles around the desulfurization liquid, which corresponded to the size distributions obtained with the two technologies. The scrubbing liquid contacting with the high-temperature flue gas could be concentrated to allow for the formation and growth of particles in scrubbing liquid. Considering the process of technology 2 with a lower solid content in the desulfurization liquid, smaller particles were generated as a consequence of the lower supersaturation degree in the desulfurization liquid. As opposed to the spray scrubber, the particle removal efficiency in a packed tower was higher and the removal efficiency declined when the particle size decreased, which also caused a higher proportion of small particles after the desulfurization. 3.1.3. Morphology and Element. Figure 5 shows micrographs and elements of particles at the inlet and outlet of the spray scrubber in the power plant with technology 1. The particles were collected in the filter cartridge, and the vimineous matter shown in Figure 5 was the image of glass fibers from the filter cartridge. Before desulfurization, as indicated in Figure 5a, particles were uniform in size with a spherical appearance. These micrometer particles easily gathered together to become bigger particles. The main particle elements were Si, Ca, and Al, together with the lesser proportions of Na, S, K, and Mg. After the desulfurization, the particle elements changed and the morphology became pronouncedly distinct from those before the desulfurization. Most particles showed smooth surfaces with prismatic crystal-like appearances. The main elements were S and O, while the element contents of Al, Ca, and Si were extremely low. Before the desulfurization, the fine particles were primarily fly ashes from coal combustion. Sub-micrometer particles were formed via vaporization and recondensation of a smaller portion of mineral matter and might form spherical structures. However, in the ammonia-based desulfurization process, the crystalline particles, such as (NH 4 ) 2 SO 3 , NH4HSO3, and (NH4)2SO4, may be generated from the

Figure 2. Fine particle concentrations before and after desulfurization in the power plant: (1) inlet number concentration of fine particles, (2) inlet mass concentration of fine particles, (3) inlet number concentration of fine particles from technology 1, (4) inlet mass concentration of fine particles from technology 1, (5) inlet number concentration of fine particles from technology 2, and (6) inlet mass concentration of fine particles from technology 2.

The gas/liquid ratio and solid content of the desulfurization liquid were related to the amount of particles formed during the desulfurization. Less desulfurization liquid was sprayed into the tower with a lower gas/liquid ratio, resulting in fewer fineparticle-contained droplets entrained from the tower. The solid content of desulfurization liquid means the mass percentage of solids in the desulfurization liquid. The fine particle concentration could also be reduced from the desulfurization liquid with a lower solid content because the fine particle concentration in the droplet was lower. Therefore, the differences between technology 1 and technology 2 led to different particle emissions, and the concentration of the fine particles generated with technology 1 was much higher than that with technology 2. 3.1.2. Particle Size Distribution. Figures 3 and 4 show the aerosol size distributions after the desulfurization in the power plant with technology 1 and technology 2, respectively. For either technology, there was an apparent unimodal number concentration distribution in the measurement range of the ELPI and the majority of the aerosols were in the submicrometer range. The peak values of the number concentration in Figure 3a or 4a occurred at the size of 0.07−0.1 or 0.03 μm or less, respectively. The size distributions of mass concentrations show distinct micrometer peaks. The peaks occurred at the sizes of 0.4 and 10 μm in Figure 3b and 3 μm in

Figure 3. Aerosol size distribution after desulfurization of technology 1. 668

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Figure 4. Aerosol size distribution after desulfurization of technology 2.

Figure 5. SEM micrographs and elements of particles of technology 1.

desulfurization with the experimental system. The particles were collected by the PM2.5/10 impactor. Most of the aerosols were (NH4)2SO4, which corresponded to the changes of particle micrographs and elements after desulfurization. Because the chemical reactions, such as oxidation, during specimen preservation were inevitable, the online measurement is essential to obtain direct results. As shown in Figure 3a, the majority of the aerosols after desulfurization were in the submicrometer range. Therefore, AMS for particles with the sizes between 0.04 and 1.0 μm was used to obtain the size distributions of the aerosol components in real time (Figure 7b). The results showed that the main aerosol components

chemical reactions in the gas phase followed by the desublimation of the products. The solid aerosols could also be generated via the entrainment and evaporation of the desulfurization liquid droplets. Hence, the desulfurization devices that employed the ammonia-based method could synergistically remove the particles from the flue gas, and the particles formed during desulfurization contributed to the particle components after the desulfurization and simultaneously changed the morphology. 3.2. Aerosol Formation Mechanisms during Desulfurization. 3.2.1. Aerosol Components. As shown in Figure 6, the XRD was used to analyze the aerosol components after the 669

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Figure 6. XRD spectrum and size distributions of particle components after desulfurization.

of the initial concentration. In summary, aerosols formed during desulfurization were from both heterogeneous reactions and the evaporation of the desulfurization liquid droplets. 3.2.3. Aerosol Characteristics Generated through Two Mechanisms. Considering the effects of scrubbing on the aerosols generated from the heterogeneous reactions, the gas samples were withdrawn with a sampling pipe at the inlet of the demister and injected into another spray scrubber, before the treatment with the water scrubbing and the demister. The aerosol concentrations and size distributions at the outlet of the two spray scrubbers were measured by the ELPI, which indicated that no obvious change happened. Thus, the experimental investigation on different aerosol formation mechanisms could be carried out, as mentioned in section 2.1. The number and mass concentrations of the aerosols formed by these two different mechanisms were obtained, as shown in Figure 8. The concentrations of the aerosols from the

Figure 7. Effect of the SO2 concentration on the aerosol number concentration after desulfurization.

were sulfate, ammonium, and water, all with similar size distribution peaks at 0.2 μm. According to the calculated sulfate/ammonium mass ratios of (NH4)2SO4, (NH4)2SO3, NH4HSO4, and NH4HSO3, which are 2.67, 2.22, 4.50, and 5.39, respectively, AMS confirmed that the components of the fine particles were (NH4) 2SO4/(NH4) 2SO 3 and NH4HSO4/ NH4HSO3 because the sulfate/ammonium mass ratio was 2.73 (sulfate, 59.7%; ammonium, 21.9%). 3.2.2. Effect of the SO2 Concentration on Aerosol Emission. As mentioned above, the aerosols could be formed by two different mechanisms during the ammonia-based WFGD process, including the entrainment and evaporation of the desulfurization liquid droplets and the heterogeneous reactions among SO2, H2O, and NH3. To further clarify the two aerosol formation mechanisms during the desulfurization, the effects of the SO2 concentration on the aerosol number concentration after the desulfurization were shown in Figure 7. The experiments were conducted at the constant desulfurization liquid pH value of 5.5. The aerosol concentration sharply decreased with the SO 2 concentration. When the SO 2 concentration changed from 2857 to 0 mg cm−3, the corresponding aerosol number concentration decreased by 70%. To keep the pH value of the desulfurization liquid constant, the ammonia amount added to the desulfurization liquid decreased with the reduction of the SO2 concentration. Therefore, the reactions among SO2, NH3, and H2O became weakened, and less aerosols were generated. When the SO2 concentration turned to 0 mg cm−3, there were still a large number of aerosols emitted from the desulfurization, which was attributed to the entrainment and evaporation of the desulfurization liquid droplets and accounted for almost 30%

Figure 8. Concentrations of aerosols by two formation mechanisms.

heterogeneous reactions were higher than that from the entrainment and evaporation of the desulfurization liquid, which matched the results shown in Figure 7. In contrast, the number and mass concentrations of the aerosols generated from the entrainment and evaporation of the desulfurization liquid were 75 and 50% lower, respectively. Therefore, the heterogeneous reactions probably made greater contribution to the aerosol formation, which corresponded to the comparisons of the aerosol emission from the ammonia-based WFGD and limestone−gypsum flue gas desulfurization (FGD). Because the desulfurization reactions during the limestone−gypsum FGD 670

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Figure 9. Aerosol size distributions of number concentrations by two different mechanisms.

Figure 10. Size distributions of aerosol components by two formation mechanisms.

gaseous ammonia volatilizing from the desulfurization liquid could be adsorbed by the particles, the aerosol components were similar to those of the desulfurization liquid, which were mainly (NH4)2SO4 and (NH4)2SO3. If the aerosols were generated form the heterogeneous reactions, the contents of sulfate and ammonium were 48.8 and 12.6%, respectively, with the sulfate/ammonium mass ratio of 3.01. Such a ratio was higher than that of (NH4)2SO4/(NH4)2SO3 and lower than that of NH4HSO4/NH4HSO3. The heterogeneous reactions among NH3 volatilizing from the desulfurization liquid and SO2 and H2O from the flue gas were as follows:

occurred in the gas−liquid−solid phase, the aerosols were mainly formed from the entrainment and evaporation of the desulfurization slurry, which resulted in a distinct decrease of fine particle emission. Figure 9 illustrates the aerosol size distributions of number concentrations from the heterogeneous reactions and the entrainment and evaporation of the desulfurization liquid. In contrast, the peak value of the aerosol size distribution at 0.03 μm during the heterogeneous reactions increased, while those at other particle sizes decreased. Hence, the aerosols from the heterogeneous reactions were with a smaller size, which could be as a result of the consequence of the instantaneous reactions among SO2, H2O, and NH3. The size distributions of the aerosol components that resulted from two formation mechanisms were also investigated using AMS, with the results shown in Figure 10. The unimodal distributions were observed with the remarkable similarity at the size of around 0.2 μm, while the aerosol component peak values of the heterogeneous reactions shifted to the left slightly. Table 2 lists the aerosol components formed by two formation mechanisms. For the aerosols generated from the entrainment and evaporation of the desulfurization liquid, the contents of sulfate and ammonium were 51.5 and 22.6%, respectively. Thus, the sulfate/ammonium mass ratio was 2.28, which was between those of (NH4)2SO4 and (NH4)2SO3. Because the

percentage (%)

entrainment and evaporation heterogeneous reaction

water

NH4+

SO42−

23.3 31.8

22.6 16.2

51.5 48.8

(1)

NH3(g) + SO2 (g) + H 2O(g) = NH4HSO3(s)

(2)

Because there was O2 in the air, further reactions could happen as follows: 2(NH4)2 SO3(s) + O2 (g) = 2(NH4)2 SO4 (s)

(3)

2NH4HSO3(s) + O2 (g) = 2NH4HSO4 (s)

(4)

On the basis of the reactions listed above, it could be concluded that NH4HSO4 and NH4HSO3 exist in the aerosols. 3.3. Effects of Operational Parameters on Aerosol Formation Mechanisms. Because the flow velocity and solid content of the desulfurization liquid, pH value, and inlet flue gas temperature are related to the aerosol formation from the entrainments and evaporations of the desulfurization liquid and the heterogeneous reactions, the effects of the operation parameters on the aerosol emission from the two formation mechanisms were investigated, as mentioned in section 2.1.

Table 2. Aerosol Components by Two Formation Mechanisms aerosol composition

2NH3(g) + SO2 (g) + H 2O(g) = (NH4)2 SO3(s)

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3.3.2. Aerosols Generated from Heterogeneous Reactions. The pH value of the desulfurization liquid is usually maintained between 5.0 and 7.0 in the industry. The aerosol concentrations after the desulfurization at three pH values were assessed, as shown in Figure 13. The aerosol number concentration

3.3.1. Aerosols Generated from the Entrainment and Evaporation of Desulfurization Liquid. The experiments were conducted at an inlet flue gas temperature of 120 °C and a pH value of 5.5 for the desulfurization liquid. Gas flow velocity in the scrubber was an important parameter for the relative movement of flue gas and desulfurization liquid. Hence, it exerted great impact on the aerosol formation from the entrainment and evaporation of the desulfurization liquid. Figure 11 shows the aerosol number concentrations at different

Figure 13. Effect of the pH value of desulfurization liquid on the number concentration of aerosols from heterogeneous reactions.

significantly increased by 140% when the pH value increased from 5.0 to 7.0. When the ammonia concentration in the desulfurization liquid became higher, more intense NH3 volatilization was induced for more aerosol particle generation from the heterogeneous reactions. Figure 14 shows the aerosol

Figure 11. Effect of the gas flow velocity on the number concentration of aerosols from the entrainment and evaporation of desulfurization liquid.

gas flow velocities. When the gas flow velocity increased from 1.5 to 3.5 m s−1, the aerosol number concentration was boosted by 150%. When a higher gas flow velocity was applied, more solid particles and droplets were entrained and evaporated during the desulfurization, resulting in more generation of aerosols. Thus, the number concentration was directly proportional to the gas velocity. The profile of aerosol number concentration varying with the solid content of the desulfurization liquid was shown in Figure 12. When the

Figure 14. Effect of the inlet flue gas temperature on the number concentration of aerosols from heterogeneous reactions.

number concentrations varying with the inlet flue gas temperatures from 120 to 80 °C. The aerosol number concentration decreased with the decline of the inlet flue gas temperature. When the inlet flue gas temperature decreased, less ammonia volatilized from the desulfurization liquid, which slowed the reaction rate and generated fewer aerosols. Figure 12. Effect of the solid content of desulfurization liquid on the number concentration of aerosols from the entrainment and evaporation of desulfurization liquid.

4. CONCLUSION The particle characteristics before and after the ammonia-based WFGD process were measured in a power plant. The aerosol formation and effects of the operation parameters on the aerosol emission were investigated with an experimental system in this study at the same time. The conclusions can be drawn from the results as follows: (1) The aerosol concentrations and size distributions after the desulfurization were related to the type of ammonia-based desulfurization technology. The particle morphology and elements changed significantly during the

solid content of the desulfurization liquid increased, the aerosol number concentration became higher accordingly. The increase of the solid content of the desulfurization liquid from 3 to 10% caused an increase in the aerosol number concentration from 1.3 × 107 to 1.8 × 107 cm−3, which could be due to the increasing number of solid particles in the desulfurization liquid. 672

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(14) Wix, A.; Brachert, L.; Sinanis, S.; Schaber, K. J. Aerosol Sci. 2010, 41 (12), 1066−1079. (15) Bai, H.; Biswas, P.; Keener, T. C. Ind. Eng. Chem. Res. 1992, 31 (1), 88−94. (16) Bai, H.; Biswas, P.; Keener, T. C. Ind. Eng. Chem. Res. 1994, 33, 1231−1236. (17) Bao, J. J.; Yin, H. B.; Yang, L. J.; Yan, J. P. J. Chem. Eng. Chin. Univ. 2010, 24 (2), 325−330. (18) Bao, J. J.; Yang, L. J.; Yan, J. P.; Liu, J. H.; Song, S. J. J. Chem. Ind. Eng. 2009, 60 (5), 1260−1267. (19) Yan, J. P.; Yang, L. J.; Bao, J. J. J. Southeast Univ. 2011, 41 (2), 387−392. (20) Yan, J. P.; Yang, L. J.; Bao, J. J.; Jiang, Z. H.; Huang, Y. G.; Shen, X. L. Proc. CSEE 2009, 05, 21−26.

desulfurization. (2) The main components of the formed aerosols were (NH 4 ) 2SO 4/(NH 4 ) 2SO 3 and NH 4HSO4 / NH4HSO3. The aerosols could be formed from either the entrainment and evaporation of the desulfurization liquid droplets or the heterogeneous reactions among SO2, H2O, and NH3 during the ammonia-based WFGD process. (3) The investigations on the two aerosol formation mechanisms revealed that the heterogeneous reactions among SO2, H2O, and NH3 provided greater contribution to the aerosol formation with smaller aerosols generated. The compositions of the aerosols from the entrainment and evaporation of the desulfurization liquid were similar to the desulfurization liquid, while NH4HSO4 and NH4HSO3 were found in the aerosols from the heterogeneous reactions. (4) With the decline of the gas flow velocity and solid content of the desulfurization liquid, aerosols from the entrainment and evaporation of the desulfurization liquid decreased. While the aerosol number concentration after desulfurization from the heterogeneous reactions was reduced with the decrease of the pH value in the desulfurization liquid and the inlet flue gas temperature.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors thank the National Natural Science Foundation of China (21276049), the National High Technology Research and Development Program of China (863 Program, 2013AA065004), the National Basic Research Program of China (973 Program, 2013CB228505), the National Natural Science Foundation of China (Grant 51208092), the Natural Science Foundation of Jiangsu Province, China (Grant BK2012124), the National Natural Science Foundation of China (51506099), the Natural Science Foundation of Jiangsu Province (BK20130906), and the Natural Science Foundation for Colleges of Jiangsu Province (13KJB610011) for their financial support.

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REFERENCES

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