SO3 Reduction in the Flue Gas by Adding a Chemical Agent - Energy

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SO3 reduction in the flue gas by adding chemical agent Hu Bin, Yi Yang, Zhang Shuping, Cai Liang, Szczepan Roszak, and Linjun Yang Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b01704 • Publication Date (Web): 26 Sep 2017 Downloaded from http://pubs.acs.org on September 27, 2017

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SO3 reduction in the flue gas by adding chemical agent Hu Bina, Yi Yangb*, Zhang Shupinga, Liang Caia, Szczepan Roszakb, Yang Linjuna* a

Key Laboratory of Energy Thermal Conversion and Control, Ministry of Education, School of Energy and Environment, Southeast University, Nanjing 210096, China b

Advanced Materials Engineering and Modelling Group, Faculty of Chemistry, Wroclaw University of Science and Technology, Wroclaw 50-370, Poland

*Corresponding author a*. Tel.: +86 25 83795053; Email: [email protected]（Yang Linjun） *Corresponding author b*.Tel.: +48 713204310; Email: [email protected] (Yi Yang) ABSTRACT: Chemical agglomeration is presented as a promising process to reduce the submicron particles and SO3 in coal-fired power plant, which uses chemical agent to induce particles and SO3 agglomerate and improves the removal efficiency of electrostatic precipitation (ESP). In this study, an experimental plant containing a chemical agglomeration chamber connected to an ESP unit has been built to investigate the particles and SO3 removal effect. The results showed that chemical agglomeration technology increased the average size of particles and the fine particle and SO3 concentration reduced at the ESP outlet, the improvement of collection efficiency was over 5%-20%. The removal mechanism was investigated by Density Functional Theory (DFT) calculations at molecular level, the reasonable calculation model with pectin as agglomeration agent was established, the interactions between SO3, H2SO4, SiO2 and pectin were explored. In the results, adsorption ability of pectin for H2SO4 is better than SiO2 and relative energy of complex between H2SO4 and TOS is lower than H2O. Meanwhile, we also studied chemical structures, atomic changes and molecular orbitals to explore their basic properties. Combining computational and experimental results together, the fine particle and SO3 mechanism with pectin adsorption can be determined. KEY WORDS: Particle aggregation; SO3; ESP; DFT calculations

1. Introduction Haze has become an extremely serious environmental problem in China in recent years causing 600 million people suffered. Many factors contribute to the haze formation, among which an important one is nitrogen oxides, sulfur oxides and fine particles emission from Coal-fired

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power1, 2. Nitrogen oxides and sulfur oxides not only cause acid rain and other hazards, but also an important precursor of PM2.53, 4. In addition, they generated secondary particles in the atmosphere which become the main source of PM2.5. The development of control technologies of PM2.5 including combustion modification, electrically enhanced fabric filtration and novel agglomeration approach (acoustic, magnetic, dipolar-electrostatic and thermophoresis) is proposed to alleviate the harm of PM2.5. Therefore, research on fine particle emission properties and control technologies has drawn growing attention5. Among the above mentioned methods, chemical agglomeration technology is considered as one of the potential technology for the treatment of the gaseous pollutants in the Coal-fired power plants. The chemical agglomeration technology is cheaper than other techniques, and it can control the emissions of submicron particles and other gaseous pollutants without changing the operation parameters of Electrostatic precipitation (ESP)6, 7. Judging from previous experience, chemical agglomeration technology investment costs were 850,000 dollars, and operating costs were 200,000 dollars per year for 340MV unit. ESP is the main equipment to removal of fine particles, a well-designed modern ESP removal particles efficiency can reach 99.5% or even higher. However, more than 20% of the fine particles (0.1-1 µm) can escape from the ESP 8-10, but ESP collection efficiency is still not ideal and hard to meet the latest Chinese environmental standard, i.e. Emission Standard of Air Pollutants for Boiler (GB13271-2014) requires the emission concentration of particle matter to 30-50 mg/m3

6, 11

. We focused on chemical agglomeration

because it uses chemical agglomeration agents sprayed into the flue before the ESP unit to accelerate the agglomeration between submicron particles, and its effects have been studied and proved. For example, Zhang et al. have built a dedicated experimental plant and found the phenomenon of agglomeration7. Yang et al. designed an ESP with an evaporation chamber and measured the ESP outlet dust concentration below 30 mg/m3 6. To the best of our knowledge, the research only pay attention to the fine particle, the removal of SO3 by chemical agglomeration has not been studied both theoretically and experimentally. Coal-fired power install selective catalytic reduction (SCR) or selective noncatalytic reduction (SNCR) to reduce NOx emissions. Meanwhile, some studies have confirmed that SCR or SNCR may promote the oxidation of SO2 to SO312, 13. Although SO3 concentration is smaller than SO2 when the temperature below the acid dew point, sulfuric acid (H2SO4) is formed by SO3


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in the flue gas4. It affects equipment corrosion and the safe operation of equipment. SO3 also forms the sulfuric acid aerosols, which leads to acid rain and forms blue visible plumes. Conversely, SO3 improves electrostatic precipitator (ESP) efficiency by adsorbing and condensing on fly ash surface14-15. There are many technologies to control SO3, such as spray alkaline substances in the boiler, gas duct and installation wet electrostatic precipitator etc. Chemical agglomeration technology provides a new method for removal of SO3 when chemical agglomeration droplets spray into the flue and vast heterogeneous condensation nuclei for SO3 form sulfate droplets. Meanwhile, particles agglomeration is helpful to sulfuric acid droplets condensing adsorption on the particles surface. In order to explore the removal performance and mechanism of PM2.5 and SO3 with chemical agglomeration, an experimental device was designed for PM2.5 and SO3 removal effects with chemical agglomeration, and some factors such as temperature and concentration were investigated. Additionally, to know the mechanism of interactions between submicron particles, SO3 and the agglomeration agent, we used DFT calculations to investigate the interactions between. We also chosen pectin used as agglomeration solution and silica crystals representing the submicron particles. In flue gas chemical structures, relative energies, atomic charges, and molecular orbitals were discussed. Finally, the results of both theoretical and experimental investigations were thoroughly discussed, compared and summarized.

2. Material and methods 2.1 Simulation All computational studies were performed with the Gaussian09 program package16. And we performed density functional theory (DFT) calculations17-19. The hybrid B3LYP functional was applied for all studies20-22, with standard lanl2dz atomic basis set adopted for all atoms23. Vibrational frequencies and thermodynamic properties of complexes were calculated applying the ideal gas, rigid rotor, and harmonic oscillator approximation24, and carried out in order to confirm the stationary states, including TS structures. IRC calculations have been performed in all cases in order to verify that localized TS structures connect with the corresponding minimum stationary points associated with the reactant and products. Interaction energies were corrected for basis set


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superposition error (BSSE)25. The special care was taken to prevent artifact interactions (e.q. involving border-OH groups) due to imposed structural restrictions in the model definition. In order to evaluate the values of energy of the different optimized geometries, we used Eq. 1 to calculate the adsorption energy. The counterpoise method corrects this energy as given in Eq. 2. Eads = Efin - Eint (1) Eads,CP = Eads - EBSSE (2) Where the Eads corresponds to the adsorbed energy, Efin is reactant energy and Eint is product energy. Which Eads, CP is counterpoise corrected adsorption energy of related complexes and EBSSE is basis set superposition errors energy.

2.2 Experimental setup and Measuring methods Laboratory experiment device as shown in Fig.1, the device is mainly made up of a flue gas generation system, a chemical agglomeration system, an ESP system, a WFGD system. The Flue gas with volume flux 350 m3/h is generated by the boiler, which burns anthracite. SO3 is generated by catalytic oxidation of SO2, and then it is added to the flue gas in the buffer vessel. In the evaporation system, a metering pump and an air compressor provide 0.3 MPa fluid for two fluid atomization nozzles with a mean droplet size of approximately 20 µm. A barb-plate ESP operating voltage is -40 kV. A WFGD system has three spray layers and uses limestone as the SO2 absorbent. This operation is conducted under different conditions in the experiment and the specific parameters are shown in Table1. An electrical low-pressure impactor (ELPI) was used to measure distributions of particle in real-time. The operating principle was based on well-known ELPI technology. It measured particles in 13 size fractions in the range from 0.03 to 10 µm. In this work, all of the sampling lines were as short as possible to avoid large particle losses. According to national standard, a schematic diagram of the sulfuric acid mist sampling procedure is illustrated in Fig.2. The full automatic flue gas sampling device and spiral condenser were used for collecting sulfate droplets during the measurement, meanwhile, the sampling lines were set to 180 ℃ to avoid the sulfuric acid condensation and spiral condenser was set to 65 ℃, which was adjusted by thermostatic waterbath. The condensate was analyzed with an ion chromatograph analyzer (ICS-2100, American) to determine the SO42- concentrations. Combined


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with the sampling volume of the flue gas, the SO3 concentration in flue gas can be determined. The efficiency of removal of sulfuric acid droplets is described as follows: η =

Cinlet − Coutlet × 100% Cinlet

Where Cinlet and C outlet , respectively, are the concentrations of sulfuric acid mist at the inlet and outlet of device.

2.3 Chemical agent Many materials have adsorbing and flocculating effects, also limitations in industrial application. Chemical agent has the functions as following: (1) good adsorption and flocculation performance; (2) good solubility and polarity in water; (3) excellent abrasion-resistance and chemical stability; (4) good compatibility with other chemicals (acid, alkali, surfactants, preservatives, etc.); (5) harmless influences for human and environment; (6) cheap and available effect. According to the above, we choose pectin as the chemical agent. Pectin is a kind of polysaccharide and sustainable development of resources, which has abundant resources, low price and natural biodegradability. It can form a polymer chain in solution, the gaseous pollutants were adsorbed by active group in a polymer chain. Some scholars have made experimental research on its flocculation characteristic. MYKOLA found that pectin can adsorb strongly various heavy metal ions (Pb(II), Co(II), Cu(II) and Ni(II))26. Yoloi has discovered that Al (III) and Fe (III) enable to strengthen pectin removal of suspended solids (SS) in water27. More importantly, the large quantity of discharging pomace causes seriously pollution. Extracting and using of pectin in pomace is an effective way to protect the environment and preserve the resources, which will be benefit both the society and the economy significantly.

3. Results and discussion 3.1 Analysis the ability of removing fine particles by adding chemical agent To evaluate the agglomeration effects of the particle size distribution, the evaporation


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temperature was set at 150 ℃, agglomeration solution flow was 15 L/h and SO3 concentration was 70 mg/m3. The particle number distributions are shown in Fig.3, the surface tension and relative contact angle on fine particles are presented in Table 2. The initial particle size distribution, measured without any external field, is a bimodal distribution with a peak diameter at 0.1 µm and 1 µm. It could be seen that the particle diameter increases substantially when adding water and pectin, it can be indicated that the droplets can attach to the surface of the ash particles due to the respective adhesive forces28, 29. Relative contact angle measurement results are presented in table2. The water surface tension is 74.30 mN/m, for the used pectin solution it is 31.26 mN/m. The pectin solution surface tension is the lower, leading more easily to form a liquid film on the surface of particles and enhancing the liquid bridge forces between the particles. On the other hand, surface tension also influences the atomization properties in the nozzle leading to formation of smaller particles when the surface tension is low. Small droplets with larger specific surface area can enhance significantly the contact between the particles11, 30. From the view of energy analysis, pectin solution reduces the relative energy between the particles, hence the particles are more likely to reunite together. The relative energy will discuss in detail in the following. The ESP outlet particle concentration are shown in Fig.4, the ESP temperature is set at 130 ℃ and discharging voltage is -40 kV, respectively. It can be seen from Fig.4 the ESP outlet particle number concentration and mass concentration are 8.4×106 /cm3 and 100 mg/m3, the number concentration and mass concentration reduce to 5.6×106 /cm3 and 68 mg/m3 after injection water droplet. Finally, the particle concentration reduces to 3.2×106 /cm3 and 38 mg/m3 after injection pectin solution. The ESP outlet is mainly small particle and pectin solution can promote fine particles grew up, therefore, ESP outlet particles number concentration significantly reduces. In order to exploring the effect on removal efficiency of different diameter, the ESP grade collection efficiencies was discussed. And particle number concentration ratio in a certain channel, it can be written as:

ηNi =

Ni0 − Nit × 100% Ni0

Where η Ni is the resolved efficiency, N i0 is the initial state particle number concentration, and N it is the removal of particle number concentration at the outlet of the ESP. The results are


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shown in Fig.5, which can be seen that Pectin can effectively increase the particle collection efficiency. For the particle diameter between 0.1-1 µm the removal efficiency is low because the electric charging mechanism of fine particles is divided into two kinds31, 32. One mechanism is by ions moving under the action of electric field force which charges the dust particles through impact and adhesion. The other mechanism is by the thermal motion of chaotically spreading ions colliding with the dust particles and charging the effectively the dust particles. It is usually assumed that the particles with size greater than 1 µm are rather charged by the electric field. While the particles of size less than 0.1 µm, are more likely charged according to the diffusion mechanism. The effectiveness of charging the particles of the diameter 0.1-1 µm is rather small, hence the most of particles escaping from ESP is are 0.1-1 µm particles. Generally, the chemical agglomeration can improve the collection efficiency by 5%-25% for all diameter ranges, respectively. The efficiency of particles removal for the sizes between 0.1-1 µm increase substantially. Water droplets are acting mainly through liquid bridge force to agglomerate the particles, while the pectin solutions droplets are exhibiting the influence of the respective macromolecules promoting the particles coalescence. It is therefore evident that chemical agglomeration can cover the shortage of low removal efficiency for particles of diameter between 0.1-0.1 µm.

3.2 Analysis the ability of removing SO3 by adding chemical agent The removal efficiency of SO3 at different SO3 concentrations is shown in Fig.6, the pectin solution flow was 15 L/h, the evaporation chamber temperature was 130℃, the ESP voltage was -40 kV, and adjust the SO3 generator maintain the evaporation chamber entrance SO3 concentration from 40 to 100 mg/m3. It can been seen from Fig.6 that the sulfuric acid mist removal efficiency increases from 43% to 68% in the evaporation chamber, further, the removal efficiency increases from 65% to 88.2% in the evaporation chamber and ESP. To compare data of these two groups ESP has synergy removal effect for SO3 because of the higher SO3 concentration which forms larger sulfuric acid droplets4. Meanwhile, the number concentration of sulfuric acid droplets was not changed considerably because the larger sulfuric acid droplets were easily


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condensed and adsorbed on the fly ash and chemical agglomeration with higher removal efficiency33, 34. The electric outlet SO3 removal efficiency is higher than the evaporation chamber which is caused by the chemical agglomeration evaporation time affecting the nucleation and condensation of SO3. SO3 combines with water molecules to form sulfuric acid droplets in the evaporation chamber, which are partly adsorbed onto the fly ash particles and another adsorbed by the chemical agglomeration. Chemical agglomeration droplets are completely evaporated before entering the electric, this part of the SO3 are fixed on the fly ash particles and removed by ESP. Fig.7 provides the removal efficiency of SO3 at different temperature, the chemical agent flow was 15 L/h, the SO3 concentration was 70 mg/m3, the evaporation chamber temperature was ranged from 90 to 150 ℃. It can be seen from Fig.7 that the flue gas temperature is important for removal efficiency of SO3, and SO3 removal efficiency rises with decreasing temperature. It seems that when the temperature is lower than acid dew point SO3 condenses to form H2SO4 acid fog and the dust particles enlarge specific surface area. H2SO4 acid fog is condensed and adsorbed on the particle surface, which is removed together with the dust by ESP. Relatively, when the temperature is higher than acid dew point, the residual carbons play a major role to adsorb gas SO3 because of the few amount of residual carbon in fly ash, and SO3 removal efficiency was low. In our case the flue gas volume is directly proportional to the temperature. When the temperature of the flue gas decreases, the volume of the flue gas decreases as well. Accordingly, the superficial gas velocity decreases with the gas residence time increasing in the evaporation chamber and ESP. Hence, the sulfuric acid droplets and fly ash contact time were increased with the more H2SO4 acid fog condensed and adsorbed on the particle surface. The SO3 removal efficiency increased from 15.6 to 60.6 mg/m-3 and the evaporation chamber temperature changed from 150 to 90 ℃ without adding water and pectin. The SO3 removal efficiency is higher with adding the water and pectin solution droplet in evaporation chamber. The water and pectin solution droplets evaporation are resulting in enhancement of the moisture content, SO3 combines water molecules to form larger droplet by homogeneous nucleation and the enlarged droplets are more easily condensation on the fly ash by inertial collision35, 36. As a consequence, resulting in an improvement in removal efficiency.


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3.3 Function mechanism In earlier sections, fine particles and SO3 removal behavior in evaporation chamber and ESP were briefly discussed. In order to research fine particles, pectin solution and SO3 interaction mechanism, the DFT analysis was carried out. In our experimental system, SO3 was generated by catalytic oxidation of SO2 and its concentration was adjusted from 30 to 90 mg/m3 at the evaporation chamber inlet according to the actual conditions in the coal-fired power plant. For this reason, it is significant to explore the chemical mechanisms of SO3 in our system. We performed our calculations at the B3LYP/lanl2dz level and got pathway of SO3 shown in Fig.8. In our results SO3 interacted with H2O, and droplets of sulfuric acid were formed with the activation energy value of 8.6 kcal/mol. In the transition state of this step, hydrogen atom of H2O has a tendency to lose and be close to oxygen atom of SO3 in transition state, the distance between them is 1.254 Å and the distance between this hydrogen atom and oxygen atom of H2O is 1.238 Å. After H2SO4 are formed by SO3 and H2O, we would like to study its further reaction. The H2SO4, SiO2 (Tetrasilyl orthosilicate (TOS)) and pectin interaction were discussed. The relative energy between H2SO4 and TOS/pectin is 14.5 kcal/mol and 28 kcal/mol, respectively. It seems to indicate that the stability of complex H2SO4, pectin which we chose two units is stronger than TOS. Both reactions between TOS and pectin with H2SO4 are hydrogen bonding interactions, but the difference is that there are two hydrogen bonds in pectin system and TOS system only has one. Fig.8 shows hydrogen bond lengths of H2SO4 with TOS (2.474 Å) and with pectin (2.480 Å and 2.571 Å) as well systems. In order to verify H2SO4 has increasing effect for particles from fly ash, we add other TOS in our primary TOS system. There are two hydrogen bonds formed by 2 hydrogen atoms from H2SO4 and 2 oxygen atoms in each of the TOSs in the new TOS system, and the relative energy is 11.6 kcal/mol. In the actual process, it has been proved that water droplets without chemical agent capture particles, so we are interested in the interaction energy of the system consisting of TOS particles interacting with water (H2O). In results are shown in Fig.9, it seems that H2SO4 and H2O have same effect for increasing particles. In our approach, water and H2SO4 molecule with TOS structures are integrated by hydrogen bonds: each of the hydrogen bond (O-H…O) are formed by oxygen atom of SiO2 and hydroxy group of H2SO4/H2O, H2O system with values at 2.840 Å and


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H2SO4 system with values at 2.571 Å and 2.523 Å. Depending on the values of relative energy, H2SO4 system is more stable than H2O system which values are -11.6 kcal/mol and -8 kcal/mol, respectively. The results provide an evidence that effect of increasing particles agglomeration in H2SO4 system is better than H2O system. We focused on interaction between TOS and H2SO4 with pectin as well. We simulated 2 units pectin with TOS and H2SO4 to compare their hydrogen bonding interaction. The results are shown in Fig.10, one hydrogen bond is formed in TOS system: units of pectin contributes to hydroxyl group interacting with oxygen atom of TOS structure to form hydrogen bond (O…H-O), with value at 2.561 Å. And there are two hydrogen bonds formed in H2SO4 system, H2SO4 contributes one oxygen atom and one hydroxyl group interacting with pectin units, and hydrogen bonds with values at 2.571 Å and 2.480 Å. Finally, we got result of relative energy of TOS with pectin: with value at -7.4 kal/mol, which is higher than H2SO4 with value at -28 kcal/mol. In our results, we found that the active site was the oxygen atom of TOS and the hydroxyl group of the pectin fragment, but both hydroxyl group and oxygen atom of pectin has possibility to become active sites in H2SO4 system. Depending on the results above, we could image that after absorption fragments containing pollutant are eliminated by ESP and discharged to the air. NAP is an important tool for studying intra/inter-molecular bonding interactions. In addition, it is a suitable basis for examination of charge transfer at molecular systems. Some orbitals are electron donor and some are acceptor, so the energy differentiation among such bonding and anti-bonding orbitals makes the molecules susceptible for interaction37. In our results as shown in Fig.11, electronic structures were changed by charge transfer. The results of NBO charge transfer, HOMO energies, LUMO energies and HOMO/LUMO gaps are given in Table3. In TOS system we saw a higher charge transfer in the case of H2SO4 (0.112 eV) rather than H2O (0.06 eV) and H2SO4 (0.099) has higher charge transfer than TOS (0.046) in pectin system. These values are consistent with relative energies above which we have obtained.

4. Conclusions In this study, the experimental and theoretical methods were used to investigate the chemical agglomeration technology for removal particles and SO3. An experimental device containing a chemical agglomeration chamber connected to an ESP unit has been built to investigate the


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effectiveness of chemical agglomeration on particle and SO3 removal efficiency. The results proved that particles diameter distribution increased from 0.1 to 1 µm, meanwhile, the SO3 and particles concentration obviously decreased at ESP outlet by using chemical agglomeration technology. The important is that 0.1-1 µm particles removal efficiency increased by 20% for ESP. In order to understand the mechanism of chemical agglomeration technology deeply, chemical structures, relative energies, atomic charges and atomic orbitals were calculated by using DFT at molecular level. We also explored the pathway of SO3 in experiment system, which relative energy of H2SO4 with TOS and pectin were -11.6 kcal/mol and -28 kcal/mol, respectively. From calculated data in agreement with the experimental conclusions seems to indicate that the effect of increasing particles agglomeration in H2SO4 system is better than H2O system. A higher charge transfers in the case of H2SO4 (0.112 eV) rather than H2O (0.06 eV) and H2SO4 (0.099) has higher charge transfer than TOS (0.046) in pectin system, which are consistent with relative energies above. For these reasons our study not only offered a new technology and method to removal particles and SO3, but also explored the internal mechanisms at the molecular level.

Acknowledgments This work was supported by the national key research and development plan of China (NO.2016YFB0600602).

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8. Laitinen, A.; Hautanen, J.; Keskinen, J.; Kauppinen, E.; Jokiniemi, J.; Lehtinen, K., Bipolar charged aerosol agglomeration with alternating electric field in laminar gas flow. J. Electrostat. 1996, 38, (4), 303-315. 9. Xu, F.; Luo, Z.; Bo, W.; Zhao, L.; Gao, X.; Fang, M.; Cen, K., Experimental investigation on charging characteristics and penetration efficiency of PM2.5 emitted from coal combustion enhanced by positive corona pulsed ESP. J. Electrostat. 2009, 67, (5), 799-806. 10. Zhu, J.; Zhang, X.; Chen, W.; Shi, Y.; Yan, K., Electrostatic precipitation of fine particles with a bipolar pre-charger. J. Electrostat. 2010, 68, (2), 174-178. 11. Hu, B.; Yi, Y.; Yang, C.; Zhang, L.; Yang, L., Improving the electrostatic precipitation removal efficiency by desulfurized wastewater evaporation. Rsc Adv. 2016, 6, (114), 113703-113711. 12. Shi, Y.; Zhang, X.; Li, F.; Ma, L., Engineering acid dew temperature: the limitation for flue gas heat recovery. Chinese Sci. Bull. 2014, 59, (33), 4418-4425. 13. Hu, B.; Zhang, L.; Yi, Y.; Luo, F.; Liang, C.; Yang, L., PM2.5 and SO3 collaborative removal in electrostatic precipitator. Powder Technol. 2017, 318, 484-490. 14. Li, Z.; Sun, F.; Ma, L.; Wei, W.; Li, F., Low-pressure economizer increases fly ash collection efficiency in ESP. Appl. Therm. Eng. 2016, 93, 509-517. 15. Spörl, R.; Walker, J.; Belo, L.; Shah, K.; Stanger, R.; Maier, J.; Wall, T.; Scheffknecht, G., SO3 emissions and removal by ash in coal-fired oxy-fuel combustion. Energ. Fuel 2014, 28, (1), 123-135. 16. Frisch, M. J.; Trucks G. W.; Schlegel, H. B.; Scuseria G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A.; Peralta, J. E., Ogliaro, F., Bearpark, M., Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega; Millam, N. J.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.; Adamo, C., Jaramillo, J.; Gomperts, R. E.; Stratmann, O.; Yazyev, A. J.; Austin, R.; Cammi, C.; Pomelli, J. W.; Ochterski, R.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, O.; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J. and Fox, D. J. Gaussian 09, Revision D.01 2009. 17. Foresman, J. B.; Frisch, Æ., Exploring chemistry with electronic structure methods. Gaussian Inc 1996. 18. Labanowski, J. K.; Andzelm, J. W., Density functional methods in chemistry. Springer-Verlag, 1991, 309-309. 19. Chong, D. P., Recent advances in density functional methods, 1995, 1-2. 20. Lee, C. T.; Yang, W. T.; Parr, R. G., Development of the colle-salvetti correlation-energy formula into a functional of the electron-density. Phys. Rev. B 1988, 37, (2), 785-789. 21. Becke, A. D., Density-functional thermochemistry. The role of exact exchange. J. Chem. Phys. 1993, 98, (7), 5648-5652. 22. Miehlich, B.; Savin, A.; Stoll, H.; Preuss, H., Results obtained with the correlation energy density functionals of becke and Lee, Yang and Parr. Chem. Phys. Lett. 1989, 157, (3), 200-206. 23. Hay, P. J.; Wadt, W. R., Abinitio effective core potentials for molecular calculations potentials for k to au including the outermost core orbitals. J. Chem. Phys. 1985, 82, (1), 299-310. 24. Davidson, N., Statistical mechanics (McGraw Hill series in advanced chemistry). New York,


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1962. 25. Boys, S. F.; Bernardi, F., Calculation of small molecular interactions by differences of separate total energies-some procedures with reduced errors. Mol. Phys. 1970, 19, (4), 553-556. 26. Kartel, M. T.; Kupchik, L. A.; Veisov, B. K., Evaluation of pectin binding of heavy metal ions in aqueous solutions. Chemosphere, 1999, 38, (11), 299-310. 27. Yokoi, H.; Obita, T.; Hirose, J.; Hayashi, S.; Takasaki, Y., Flocculation properties of pectin in various suspensions. Bioresource Technol., 2002, 84, (3), 287-290. 28. Balakin, B. V.; Shamsutdinova, G.; Kosinski, P., Agglomeration of solid particles by liquid bridge flocculants: Pragmatic modelling. Chem. Eng. Sci. 2015, 122, 173-181. 29. Balakin, B. V.; Kutsenko, K. V.; Layrukhin, A. A.; Kosinski, P., The collision efficiency of liquid bridge agglomeration. Chem. Eng. Sci. 2015, 137, 590-600. 30. Chang, Y. I.; Wang, Y. F., Adhesion of an elastic particle to a plane surface: Effects of the inertial force and the van der Waals force. Colloid Surface A 1996, 111, (1-2), 21-28. 31. Barranco, R.; Gong, M.; Thompson, A.; Cloke, M.; Hanson, S.; Gibb, W.; Lester, E., The impact of fly ash resistivity and carbon content on electrostatic precipitator performance. Fuel 2007, 86, (16), 2521-2527. 32. Qi, L.; Zhang, Y., Effects of water vapor on flue gas conditioning in the electric fields with corona discharge. J. Hazard. Mater. 2013, 256, 10-15. 33. Cao, Y.; Zhou, H.; Jiang, W.; Chen, C.; Pan, W., Studies of the fate of sulfur trioxide in coal-fired utility boilers based on modified selected condensation methods. Environ. Sci. Technol. 2010, 44, (9), 3429-3434. 34. Spoerl, R.; Walker, J.; Belo, L.; Shah, K.; Stanger, R.; Maier, J.; Wall, T.; Scheffknecht, G., SO3 emissions and removal by ash in coal-fired oxy-fuel combustion. Energ. Fuel 2014, 28, (8), 5296-5306. 35. Anderlohr, C.; Brachert, L.; Mertens, J.; Schaber, K., Collection and generation of sulfuric acid aerosols in a wet electrostatic precipitator. Aerosol Sci. Tech. 2015, 49, (3), 144-151. 36. Noda, N.; Makino, H., Influence of operating temperature on performance of electrostatic precipitator for pulverized coal combustion boiler. Adv. Powder Technol. 2010, 21, (4SI), 495-499. 37. James, C.; Raj, A. A.; Reghunathan, R.; Jayakumar, V. S.; Joe, I. H., Structural conformation and vibrational spectroscopic studies of 2,6-bis(p-N,N-dimethyl benzylidene) cyclohexanone using density functional theory. J. Raman. Spectrosc. 2006, 37, (12), 1381-1392.


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Table1 the experimental operation parameters Parameter

Range

Flue gas flow rate (m3/h)

350

The voltage (kV)

-40

Space between collection electrodes (mm)

300

Operation temperature (℃)

90-150

Gas velocity (m/s)

0.86

Specific collection area (SCA)

84.3

Agglomeration solution flow (L/h)

15

SO3 concentration (mg/m3)

40-100


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Energy & Fuels

Table2 Surface tension and relative contact angle on fine particles (25 ℃). Type

Water

Pectin

Surface tension (mN/m)

74.30

38.54

Relative contact angle (°)

85.23

70.49


Energy & Fuels

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Table3 Calculated charge transfer by NBO charge analysis (QNBO) and the HOMO energies (EHOMO), LUMO energies (ELUMO), HOMO/LUMO energy gap (Eg) QNBO (e)

EHOMO (eV)

ELUMO (eV)

Eg (eV)

H2 O

-

-8.152

1.658

9.81

H2SO4

-

-8.124

-2.986

5.138

TOS

-

-7.964

-0.313

7.651

Pectin units

-

-7.238

-1.646

5.592

TOS-H2O

-0.06

-7.204

-0.448

6.756

TOS-H2SO4

-0.112

-7.620

-4.582

3.038

Pectin-TOS

-0.046

-6.896

-1.478

5.418

Pectin-H2SO4

-0.099

-7.012

-5.272

1.74


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Energy & Fuels

11

Exhaust

Exhaust 7

4 2

3 6 10

9

13

8

5 12

1

Fig.1 Schematic diagram of pilot-scale system 1- coal-fired boiler；2- stirrer；3- buffer vessel；4- heat tube；5- SO3 generator；6- SO2 gas；7- evaporation chamber； 8- water channel；9- metering pump；10- air compressor；11- ESP；12- metering pump; 13- desulphurization tower


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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Thermostatic waterbath

Flue Sampling gun Filter cartridge

Spiral condenser

Dust parallel sampler

Fig.2 SO3 sampling device


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1.2x105

Origin flue Water Pectin

1.0x105 8.0x104

dN/dlogDp/1.cm-3

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

6.0x104 4.0x104

2.0x104

0.0 0.01

0.1

1

DP/µm

Fig.3 Diameter distribution of particles


10

Energy & Fuels

1.0x107

250

ESP outlet

8.0x106 150

Water

Pectin 6.0x106

100 4.0x106 50

0 0

100

200

300

400

500

Number concentration/1·cm-3

Mass concentration Number concentration

200

Mass concentration/mg/Nm3

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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2.0x106 600

Time/s

Fig.4 The mass and number concentration at ESP outlet


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100


95 90

Removal efficiency /%

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Energy & Fuels

85 80 75 70 65 60 0.01

0.1

1

10

Dp/µm

Fig.5 Grade removal efficiency of fine particles by the ESP


Energy & Fuels

100

Evaporation chamber Evaporation chamber+ESP 80

SO3 removel efficiency /%

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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60

40

20

0

40

70

100

SO3concentration/mg/m3

Fig.6 SO3 removal efficiency in the evaporation chamber and ESP


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100


80

SO3 removal efficiency /%

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

60

40

20

0 90

100

110

120

130

140

150

Temperature/ffi

Fig.7 SO3 removal efficiency under different temperature


Energy & Fuels

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Fig.8 Reaction progress for H2SO4 in pilot-scale system.


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Energy & Fuels

Fig. 9 Relative energy of TOS with H2O/H2SO4.


Energy & Fuels

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Fig.10 Relative energy of pectin with TOS/H2SO4.


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Energy & Fuels

Fig.11 HOMO and LUMO for H2O, H2SO4, TOS, pectin units and their complexes.


Energy & Fuels

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Highlights:

Collaborative removal of SO3 and particles by Chemical agglomeration technology.

SO3 conversion mechanism was explored in the flue gas.

Using DFT calculations to explore the SO3, H2SO4, SiO2 and pectin interactions.

Pectin is used as chemical agent.


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SO3 Reduction in the Flue Gas by Adding a Chemical Agent - Energy

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