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Heterogeneous condensation of water vapor on particles at high concentration
Powder Technology 305 (2017) 71–77
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Heterogeneous condensation of water vapor on particles at high concentration Junchao Xu, Yan Yu, Jun Zhang ⁎, Qiang Meng, Hui Zhong Key Laboratory of Energy Thermal Conversion and Control of Ministry of Education, Southeast University, Nanjing, 210096, Jiangsu Province, China
a r t i c l e
i n f o
Article history: Received 9 May 2016 Received in revised form 23 September 2016 Accepted 27 September 2016 Available online 28 September 2016 Keywords: Heterogeneous condensation Fine particles Water vapor Supersaturation
a b s t r a c t Although heterogeneous condensation on fine particles is one of the most promising precondition technologies for particles abatement which has been proved by many works, little direct data were reported on the process of particles enlargement by vapor condensation. A direct measurement of enlarged particle size distribution in a lab scale growth tube by water vapor condensation is presented. Four parameters that affect the performance of the particle enlargement at high particle number by heterogeneous condensation were identified: supersaturation, particle size, residence time and particle wettability. The results show that particle enlargement exponentially increases with the increase of supersaturation. The particle size has a negative impact on particle growth ratio. The residence time is in favor of the particle enlargement which depends on the supersaturation level. Additionally, the residence time extension would weaken the vapor depletion on particle enlargement caused by particle number increase. Particle wettability may lead to different processes of particle enlargement. This work deeply revealed the process of vapor condensation on particles at high concentration by direct measurement. © 2016 Elsevier B.V. All rights reserved.
1. Introduction Interest in the study of the heterogeneous condensation of supersaturated vapor has increased in the last few years. This explosion of attention has been driven by the recognition of the central role that heterogeneous condensation plays in the atmospheric and environmental process of concern worldwide. In particular, the most promising particles abatement pretreatment by vapor condensation is strongly influenced by the heterogeneous condensation [1]. The traditional particle abatement devices are far less efficient in collecting submicron particles, especially for those in the range 0.1-1 μm [2], the removal efficiency decreases to 25% [3]. Improving the dimension of the particles is the main way to facilitate fine particles abatement. A couple of new technologies were proposed in the recent past for the enlargement of submicron particulates: wet electrostatic scrubbing [4] and heterogeneous condensation [5,6]. Among them, heterogeneous condensation of water vapor as a preconditioning technique for fine particles removal has been proved to be one of the most promising techniques to improve the performances of traditional devices [7].
⁎ Corresponding author at: School of Energy and Environment, Southeast University, Sipailou 2, Xuanwu district, Nanjing, Jiangsu Province, China. E-mail addresses: [email protected] (J. Xu), [email protected] (Y. Yu), [email protected] (J. Zhang), [email protected] (Q. Meng), [email protected] (H. Zhong).
http://dx.doi.org/10.1016/j.powtec.2016.09.078 0032-5910/© 2016 Elsevier B.V. All rights reserved.
Many works have been done on the heterogeneous condensation on submicron aerosols. The theory of nucleation on small insoluble particles was proposed by Fletcher [8]. He found the process of heterogeneous condensation is determined by the particle size and surface characteristics [9,10]. Porstendorfer et al. [11] investigated the heterogeneous condensation of vapor on Ag and NaCl particles and observed the significant dependence of the heterogeneous condensation on particle size and surface properties. Chen et al. [12] investigated the heterogeneous condensation on SiO2, Al2O3, TiO2 and carbon black particles and led to a significant understanding of the nucleation process and a conclusion that critical supersaturation primarily depended on particle size and contact angle. Lammel et al. [13] studied the vapor condensation on carbon black particles and concluded that the soluble fraction of carbonaceous material could influence the nucleation ability of the carbon black particles. The nucleation process of individual glass particles was researched with an electrostatic levitation and the critical diameters were determined [14,15]. It could be found that these studies mentioned above were concentrated on the heterogeneous condensation at the low particle concentration (b 103 cm− 3). Actually, the particle concentration in the flue gas discharged from the coal-fired boiler is much higher [16]. At the high particle concentration, above 104 cm−3, the possibility of heterogeneous condensation on the particles might be decreased due to vapor depletion [17]. Numerical result showed that the absolute value of nucleation rate decreased with the increase of particle concentration [18], and the experimental results also showed that the vapor depletion
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impacted supersaturation and droplet size N 10% if the particles concentration was N 5 × 103 cm−3 [19]. Hence there are some differences in the enlargement performance between the high particle concentration and the low particle concentration. Some research has been done with the particles at the high concentration. Measuring removal efficiency was the most usual way to estimate the enlargement performance of vapor condensation on submicron particles [20–22]. Heterogeneous condensation of residual particles, quartz particles, and paraffin oil droplets were experimentally investigated by employing removal efficiencies as a function [23]. Fan et al. [24] also experimentally studied the heterogeneous condensation on coal combustion particles through measuring the particles removal efficiency. Nevertheless, the process of the heterogeneous condensation on submicron particles at high concentration is hard to understand through measuring the removal efficiency. The aim of this work is to investigate the process of heterogeneous condensation on submicron particles at the high particle concentration (the order of magnitude is 106 cm−3). A lab scale equipment based on the growth tube was employed to examine the effects of supersaturation, particles size, gas residence time and particle wettability on heterogeneous condensation process. In particular, the process was not explored by the usual way, but was rather done by a direct measuring way. So the effect parameters of enlargement process could be better revealed by comparing the particle size distribution (PSD) at the inlet and the outlet of the growth tube. 2. Experimental section 2.1. Particles To estimate the size effect on the heterogeneous condensation of particles, the fine SiO2 particles and coarse ones were adopted. 94.8% of the fine SiO2 particles are concentrated in the range from 0.05 to 0.2 μm, while 93.0% of the coarse ones are concentrated in the range from 1 to 3 μm, and corresponding mean sizes are 0.133 and 2.100 μm, respectively. At the same time the fine particles of SiO2 were employed to study the effect of supersaturation and residence time. Specially, for understanding the effect of contact angle, the fine particles of CaSO4, SiO2, and Fe2O3 were used due to their different surface wettability with water. The percentages of the CaSO4 and Fe2O3 ranging from 0.05 to 0.2 μm are 90.4% and 95.6%, respectively. 2.2. Measurement of contact angle A contact angle goniometer (Model JC2000D2, China) with high resolution camera (Model Guppy pro, Germany) was applied to measure the contact angles of SiO2, CaSO4, and Fe2O3. The particles cylindrical thin slices were prepared by placing a powder sample in a compression die and applying a force of 5000 N by means of a hydraulic press. This force was maintained for 30 min. Then the thin slice was put on the measurement table and 1.5 μL water was dripped on its surface, this process would be captured by the high resolution camera and finally the picture of the water contacting moment could be analyzed by computer to obtain particle's contact angle. 2.3. Experimental setup As illustrated in Fig. 1, the experimental apparatus includes three parts as follows, aerosol generation part, the particles growth part and the measurement part. The aerosol generation part consists of an aerosol generator (Model SAG-410, Germany) and an air compressor which supplies pure air as carrier gas. The particles growth part consists of a growth tube, a cooling unit and a hot water thermostat. The growth tube was made of glass with an internal diameter of 1.5 cm and a length of 40 cm, the same one as
Fig. 1. Experimental apparatus.
reported by Tammaro's work [25]. The hot water inlet to the growth tube was designed as tangential to assure a perfect adhesion of water with the tube walls. In the experiment, the liquid temperature was kept at the desired value, Th, by means of a thermostatic bath. The cooling unit cooled the aerosol gas into dew point, and then the cooled and saturated gas was sent into the growth tube and then encountered the hot water supplied by the thermostatic bath. The water vapor was transferred from the tube wall into the cooled gas which generated a supersaturation environment for the mass diffusivity is bigger than the heat diffusivity of water vapor. And the supersaturations were controlled by hot water temperature control. The measurement part consists of a laser droplet measuring instrument (Model OMEC-DP-02, China), an optical measurement window, and a hot wind fan. The laser instrument allows the measurement of PSD in the range between 0.05 μm and 1500 μm. In particular, the instrument was customized to extend its measuring range from 1– 1500 μm to 0.05–1500 μm, and the software was customized to match the customized instrument, too. The optical measurement window, which was made of optical glass, is closed to the outlet of growth tube avoiding the evaporation of droplets containing particles. The hot wind fan provides a hot airflow around the optical window to avoid droplet evaporating and condensing on the window. This method have two advantages: 1. The PSD can be detected at the outlet of the growth tube once the particles finish growth; 2. the hot wind introduction prevents the droplet evaporating and condensing on the optical window so that the light detection of the droplets containing particle can be reached. Additionally, an electrical low pressure impactor (ELPI, Dekati, Finland) was used for particle concentration. 3. Result and discussion 3.1. Supersaturation effect The process of particle enlargement by the heterogeneous condensation can be divided generally into two steps [26]. First, the particles have to be activated, which is called nucleation or activation. Secondly, the nuclei grow to droplets by condensation of vapor. In the heterogeneous condensation, the supersaturation not only affects the nucleation process [27], but also does the particles growth [28]. The supersaturation profiles throughout the growth tube are described by employing a heat and mass transfer modeling [29]. It can be seen in Fig. 2. that the supersaturation in the growth tube increases with the water temperature increase and the location of maximum supersaturation moves towards inlet of the growth tube with the water temperature increasing (when the water temperature is 303 K, 313 K, and 323 K, the maximum supersaturation is 1.032, 1.143 and 1.324, and the corresponding location is 33.44 cm, 28.00 cm and 24.24 cm away from inlet of the growth tube, respectively).
J. Xu et al. / Powder Technology 305 (2017) 71–77
Fig. 2. The profile of supersaturation in the axis of growth tube.
Fig. 3 gives the results of particles enlargement under different supersaturation which was controlled by different temperatures of hot water. It could be seen that, when the maximum supersaturation is 1.032, the particles could be barely activated and grown. With the supersaturation increase, the PSD of the particles and the peaks of small particles (less 1 μm) move toward the big size range. It is worth to
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note that the peaks of PSD in the big size range maintain the same size location with the increase of supersaturation. These indicate that the increase of supersaturation has a strong impact on small particles growth. Fig. 3 also shows that all the particles could be activated in the supersaturation above 1.143 even though the particles number increase from 1.7 × 10 cm−3 to 3.4 × 10 cm−3. It can be seen in Fig. 3(a) and (b), the percentage of particles b1 μm increases substantially with the increase of the particles number at the supersaturation of 1.324, which indicates that the increase of the particles number has an adverse influence on particle enlargement obviously when the residence time is 0.94 s. Vapor depletion effect on supersaturation in a continuous-flow CCN (cloud condensation nuclei) chamber was calculated [19], and the results showed that increasing the particles concentration above 1000 cm−3 began to impact the supersaturation profile, but the location of the maximum supersaturation in the instrument was not affected. However, considering the supersaturation profile initially increases and then decreases, the fine particles at concentration of 1.7 × 106 cm−3 would be activated earlier than the fine particles at concentration of 3.4 × 106 cm−3 in the growth tube because of the former supersaturation is bigger than the latter, which led to a less effective growth time (time from particles activation to the outlet of the growth tube) for particles at higher concentration. In addition, the vapors supply from tube wall should not depend on particles number, so it can be taken as a constant at the same residence time, thus fewer vapors have been allocated to each particle at higher concentration which lowers the particle enlargement performance.
A
B
C
D
Fig. 3. Supersaturation effect on heterogeneous condensation of particles. a. (N = 1.7 × 106 cm−3, t = 0.94 s) b. (N = 3.4 × 106 cm−3, t = 0.94 s) c. (N = 1.7 × 106 cm−3, t = 2.12 s) d. (N = 3.4 × 106 cm−3, t = 2.12 s).
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By comparing Fig. 3(c) and (d), it can be found that the increase of the particles number has a little effect on the particle enlargement when the residence time is 2.12 s. It could be concluded that the effect of the particles number on the heterogeneous condensation could be weakened by increasing the residence time. With the increase of residence time the vapor being transferred from tube wall to gas flow increases, thus more water vapor supply weakens the effect of vapor depletion caused by particles number. The arithmetic average diameter was calculated and plotted in Fig. 4. It could be seen that that the average diameter rapidly increases with increasing the profile of supersaturation.
3.2. Size effect It can be seen in Fig. 5, the particles b 1 μm are almost all enlarged for the coarse SiO2 particles, while most of the grown fine SiO2 particles are concentrated in the range 0.09–1 μm. In addition, there are some fine SiO2 particles that catch up in size with coarse ones during the growth stage in the range 1–4 μm, which is consistent with the result reported by Seinfeld [2]. The grown peaks of the fine SiO2 particles move toward the big size more remarkably than those of the coarse SiO2 particles. This phenomenon can also be seen from the data shown in Table 1, the growth ratio is 6.0 and 1.4 for the fine SiO2 and the coarse SiO2, respectively. Eq. (1) gives the particle growth rate [30]:
drp ¼ dt
" ρr p
S−Sa
Rg T Sa L2 M v þ βm Mv DP ∞ f1 þ ðS þ Sa ÞgP ∞ =ð2P Þ βt Rg KT 2
#
ð1Þ
where rp is particle diameter; S is the supersaturation; Sa is saturation ratio at the droplet surface; ρ is density of particles; D is vapor mass diffusivity; Rg is gas constant; L is latent heat of vaporization; K is heat conductivity; Mv is the molecular weight of vapor; P∞ is saturation vapor pressure; P is total gas pressure; and βm, βt is the transitional correction factor for mass transfer and heat transfer. It can be found from the equation, the growth of particles is inversely proportional to their diameters, and so fine particles grow faster than coarse ones. This is because the surface area of the fine particle is less than the coarse one, leading to a more obvious growth of it with the same vapor mass condensation. Consequently, the growth performance of the coarse particles is worse than that of fine particles by the heterogeneous condensation, which is contrary to the size effect on the particle nucleation process according to classic nucleation theory [31].
Fig. 5. Size effect on heterogeneous condensation of the fine SiO2 and the coarse SiO2 (S = 1.143, t = 1.2 s, N = 1.7 × 106 cm−3).
3.3. Residence time effect Fig. 6 gives the result of residence time effect on fine SiO2 particle enlargement. It clearly shows that the high residence time is favorable to particle growth. The peaks of PSD in Fig. 6 (a) and (b) basically coincide with each other at low supersaturation and the PSD moves to big size particles. It can be explained as follows, the residence time extension lead to more vapor transfer onto the particles which makes the PSD movement, however, due to the low supersaturation, small particles cannot be enlarged sufficiently. Comparing Fig. 6 (c) and (d), it could be found that the increase of the residence time leads to the shape change of the PSD in small particles range and the percentage of small particles decreases obviously at high supersaturation. Obviously, more vapor could be supplied with residence time extension and more small particles could be activated at high supersaturation region of the growth tube. Thus much more small particles could be enlarged further at high supersaturation, while these vapor supplied by residence time extension could not be condensed on the small particles for they could not be activated at low supersaturation. Consequently, these reasons result in the shape change of the PSD in the small particles range. Additionally, it can also be noted that the increase of particles number weaken the improvement of particles enlargement by residence time extension through comparing between Fig. 6 (a) and (b) and between (c) and (d). This phenomenon might be caused by vapor competition among particles. Fig. 7 gives the results of arithmetic average diameter of the fine SiO2 particles. Comparing the average diameter of grown particles, it can be found that the residence time has a little impact on final average diameter of particles at low supersaturation, while has a moderate impact on final average diameter of particles at high supersaturation.
3.4. Wettability effect The contact angles of the particles studied are listed in Table 2. It can be seen that three kinds of particle's wettability are quite different.
Table 1 Arithmetic diameter of the fine SiO2 and the coarse SiO2.a
Fig. 4. The relation between arithmetic average diameter and the maximum supersaturation (N = 1.7 × 106 cm−3, t = 0.94 s).
Particles
Fine SiO2
Grown fine SiO2
Coarse SiO2
Grown coarse SiO2
Mean diameter Growth ratio
0.133 μm 6.0
0.795 μm
2.100 μm 1.4
2.900 μm
a
S = 1.143, t = 1.2 s, N = 1.7 × 106 cm−3.
J. Xu et al. / Powder Technology 305 (2017) 71–77
A
B
C
D
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Fig. 6. Residence time effect on heterogeneous condensation of the fine SiO2. a. S = 1.143, N = 1.7 × 106 cm−3 b. S = 1.143, N = 3.4 × 106 cm−3 c. S = 1.324, N = 1.7 × 106 cm−3 d. S = 1.324, N = 3.4 × 106 cm−3.
Wettability effect on heterogeneous nucleation of water vapor on submicron particles had been investigated with SiC, SiO2, and naphthalene particles [32]. The results showed that the nucleation ability of SiC, SiO2, and naphthalene aerosols is qualitatively consistent with the theoretical prediction based on their wettability. In addition, Heidenreich et al. [23] also have investigated the heterogeneous condensation of quartz, residual and paraffin oil particles, the collection efficiencies
vary according to the particles properties. Fig. 8 shows the particle enlargement performance of CaSO4, SiO2, and Fe2O3 by water vapor condensation. It can be seen that all the three particles have been activated under this supersaturation condition. The performance of particle enlargement decreases with the contact angle increase which has a negative influence on particle wettability. The percentages of initial particles less 1 μm are 92.11%, 96.19%, and 97.14% for CaSO4, SiO2, and Fe2O3, and each corresponds to a percentage of 36.16%, 73.15%, and 87.50% when the particles have been enlarged. Moreover, there is still some fine particles of Fe2O3 in the range b 0.1 μm after heterogeneous condensation has taken place. In the supersaturation effect section, it was proposed that the process of particles enlargement by heterogeneous condensation can be divided generally into two steps. It was assumed that heterogeneous condensation on particles will be activated once the condition reaches the critical saturation, and will continue the same way as the growth of a homogenous liquid droplet [33]. Indeed, this approximation becomes reasonable when the embryos enlarge enough to surround the particle or nucleation rate is very large, so that it fails to describe the process when the particle wettability or the nucleation rate is small. Therefore, a transition stage [34]should be taken into account for small wettability particles such as Fe2O3. As Table 2 Contact angle of different particles.
Fig. 7. Arithmetic average diameter of the fine SiO2 with different residence times.
Particles
CaSO4
SiO2
Fe2O3
Contact angle
17.0°
35°
55°
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J. Xu et al. / Powder Technology 305 (2017) 71–77
A
Fig. 9. Three stages of the whole process of heterogeneous condensation on an insoluble spherical particle. [34].
B
that all the small particles can be activated but the particles could not be enlarged enough as particles of CaSO4. We suppose that the process of part of the small size Fe2O3 particles only contains the stages of nucleation and transition for the low wettability of Fe2O3 particles. However, no further comments on quantitative of small particles can be made which need a visible measurement technology on heterogeneous condensation. Besides, due to the supersaturation in the growth tube increase with the increase of distance from inlet, the low wettability particles would be activated later than the high wettability particles which lead to the effective length (the distance from the location of particles being activated to the outlet of the growth tube) decrease for the former particles. The arithmetic average diameter of different particles is shown in Table 3. It can be seen that the growth ratio is 6.6, 6.0, and 2.8 for particles of CaSO4, SiO2, and Fe2O3 even though the particles of CaSO4 have a negative size effect on growth ratio which can be concluded from the Size effect section. Clearly it can be found that the wettability has a strong impact on particle enlargement performance. 4. Conclusion
C
Fig. 8. Wettability effect on heterogeneous condensation of the fine particles (S = 1.132, t = 1.2 s, N = 1.7 × 106 cm−3) a. CaSO4 b. SiO2 c. Fe2O3.
shown in Fig. 9, the first stage is heterogeneous nucleation, which is the beginning of the condensation process. The second stage is the transition from nucleation to growth. In this stage, the former embryos continue to grow and new critical embryos are formed simultaneously. The last stage is the growth of the droplet. When the total surface area of the particle is covered by embryos, it can be assumed that a thin liquid film is formed uniformly on the particle surface. In this stage, the condensation can be considered as the growth of a homogenous liquid droplet which contains the solid particle and the liquid film. Considering
The process of heterogeneous condensation on particles at high particle concentration was investigated. It is found that supersaturation not only affects the particle nucleation process but also does the growth process. In addition, the average diameter exponentially increases with the increase of supersaturation. Size effect on particle enlargement and the nucleation ability of particle is opposite, and the growth ratio of fine particles is larger than the coarse particles. Residence time is in favor of particle enlargement which depends on supersaturation level, and it has a little impact on particle enlargement at low supersaturation, while it has a moderate impact on average diameter at high supersaturation. Specially, residence time weakens the vapor depletion effect on particle enlargement. The wettability of particle may lead to different processes of heterogeneous condensation and it has a strong impact on particle enlargement performance. This work demonstrated that the heterogeneous condensation of water vapor is one of the most promising pretreatments for industrial emission particles abatement once again. In addition, with reference to the industrial application of growth tube devices, the experimental results can be easily applied to large scale industrial process. Acknowledgments This work was supported by the National Natural Science Foundation of China [Grant No. 51576043], the Scientific Research Foundation Table 3 Arithmetic average diameter and growth ratio of different particles. Particles
CaSO4
SiO2
Fe2O3
Initial Grown Growth ratio
0.258 μm 1.695 μm 6.6
0.133 μm 0.795 μm 6.0
0.143 μm 0.398 μm 2.8
J. Xu et al. / Powder Technology 305 (2017) 71–77
of Graduate School of Southeast University [Grant No. YBJJ1607], the Research Innovation Program for College Graduates of Jiangsu Province [Grant No. KYLX16_0202] and the Major State Basic Research Development Program of China [973 Program Grant No. 2013CB228504]. References [1] B. Jingjing, Y. Linjun, Y. Jinpei, et al., Experimental study of fine particles removal in the desulfurated scrubbed flue gas, Fuel 108 (2013) 73–79. [2] J.H. Seinfeld, S.N. Pandis, Atmospheric Chemistry and Physics, John Wiley, Hoboken, NJ, New York, 1998. [3] M. De Joannon, G. Cozzolino, A. Cavaliere, et al., Heterogeneous nucleation activation in a condensational scrubber for particulate abatement, Fuel Process. Technol. 107 (2013) 113–118. [4] A. Jaworek, W. Balachandran, A. Krupa, J. Kulon, M. Lackowski, Wet electroscrubbers for state of the art gas cleaning, Environ. Sci Technol. 40 (2006) 6197–6207. [5] S. Heidenreich, F. Ebert, Condensational droplet growth as a preconditioning technique for the separation of submicron particles from gases, Chem. Eng. Process. Process Intensif. 34 (1995) 235–244. [6] S.V. Hering, M.R. Stolzenburg, A method for particle size amplification by water condensation in a laminar, thermally diffusive flow, Aerosol Sci. Technol. 39 (2005) 428–436. [7] J. Bao, L. Yang, S. Song, et al., Separation of fine particles from gases in wet flue gas desulfurization system using a cascade of double towers, Energy Fuel 26 (2012) 2090–2097. [8] N.H. Fletcher, Size effect in heterogeneous nucleation, J. Chem. Phys. 29 (3) (1958) 572–576. [9] G. Hänel, The properties of atmospheric aerosol particles as functions of the relative humidity at thermodynamic equilibrium with the surrounding moist air, Adv. Geophys. 19 (1976) 73–188. [10] P. Winkler, The growth of atmospheric aerosol particles with relative humidity, Phys. Scr. 37 (1988) 223–230. [11] J. Porstendorfer, H.G. Scheibel, F.G. Pohl, O. Preining, G. Reischl, P.E. Wagner, Heterogeneous nucleation of water vapor on monodispersed Ag and NaCl particles with diameters between 6 and 18 nm, Aerosol Sci. Technol. 4 (1985) 65–79. [12] C.C. Chen, L.C. Hung, H.K. Hsu, Heterogeneous nucleation of water-vapor on particles of SiO2, Al2O3, TiO2, and carbon black, J. Colloid Interface Sci. 157 (1993) 465–477. [13] G. Lammel, T. Novakov, Water nucleation properties of carbon black and diesel soot particles, Atmos. Environ. 29 (1995) 813–823. [14] O.V. Sharoichenko, A New Apparatus for Study of Heterogeneous Nucleation on Single Micron-sized Insoluble Particles, State University of New York, New York, 2000. [15] O.V. Hogrefe, R.G. Keesee, Heterogeneous vapor-to-liquid nucleation of water on individual glass particles, Aerosol Sci. Technol. 36 (2002) 239–247. [16] H. Wu, L. Yang, J. Yan, G. Hong, B. Yang, Improving the removal of fine particles by heterogeneous condensation during WFGD processes, Fuel Process. Technol. 145 (2016) 116–122.
77
[17] S.P. Fisenko, W. Wang, M. Shimada, K. Okuyama, Vapor condensation on nanoparticles in the mixer of a particle size magnifier, Int. J. Heat Mass Transf. 50 (2007) 2333–2338. [18] Z. Kožíšek, P. Demo, Influence of vapor depletion on nucleation rate, J. Chem. Phys. 126 (2007) 184510. [19] T.L. Lathem, A. Nenes, Water vapor depletion in the DMT continuous-flow CCN chamber: effects on supersaturation and droplet growth, Aerosp. Sci. Technol. 45 (2011) 604–615. [20] T. Yoshida, Y. Kousaka, K. Okuyama, F. Nomura, Application of particle enlargement by condensation to industrial dust collection, J. Chem. Eng. Jpn 11 (1978) 469–475. [21] L. Yang, J. Bao, J. Yan, J. Liu, S. Song, F. Fan, Removal of fine particles in wet flue gas desulfurization system by heterogeneous condensation, Chem. Eng. J. 156 (2010) 25–32. [22] J. Yan, J. Bao, L. Yang, F. Fan, X. Shen, The formation and removal characteristics of aerosols in ammonia-based wet flue gas desulfurization, J. Aerosol Sci. 42 (2011) 604–614. [23] S. Heidenreich, U. Vogt, H. Büttner, F. Ebert, A novel process to separate submicron particles from gases — a cascade of packed columns, Chem. Eng. Sci. 55 (2000) 2895–2905. [24] F.X. Fan, L.J. Yang, J.P. Yan, J.J. Bao, X.L. Shen, Experimental investigation on removal of coal-fired fine particles by a condensation scrubber, Chem. Eng. Process. 48 (2009) 1353–1360. [25] M. Tammaro, Heterogeneous Condensation for Submicronic Particles Abatement, Università degli Studi di Napoli Federico II, 2010. [26] F. Fan, L. Yang, J. Yan, Z. Yuan, Numerical analysis of water vapor nucleation on PM2.5 from municipal solid waste incineration, Chem. Eng. J. 146 (2009) 259–265. [27] J.C. Barrett, T.J. Baldwin, Aerosol nucleation and growth during laminar tube flow: maximum saturations and nucleation rates, J. Aerosol Sci. 31 (2000) 633–650. [28] X. Luo, Y. Fan, F. Qin, H. Gui, J. Liu, A kinetic model for heterogeneous condensation of vapor on an insoluble spherical particle, J. Chem. Phys. 140 (2014) 024708. [29] S.V. Hering, M.R. Stolzenburg, A method for particle size amplification by water condensation in a laminar, thermally diffusive flow, Aerosol Sci. Technol. 39 (5) (2005) 428–436. [30] M. Kulmala, Condensational growth and evaporation in the transition regime, Aerosol Sci. Technol. 19 (1993) 381–388. [31] V.I. Kalikmanov, Nucleation Theory, Springer Netherlands, 2013. [32] C. Chin, G. Ming-S, T. Yi, H. Chong, Heterogeneous nucleation of water vapor on submicrometer particles of SiC, SiO2, and naphthalene, J. Colloid Interface Sci. 198 (1998) 354. [33] M. Tammaro, F. Di Natale, A. Salluzzo, A. Lancia, Heterogeneous condensation of submicron particles in a growth tube, Chem. Eng. Sci. 74 (2012) 124–134. [34] Y. Fan, F. Qin, X. Luo, L. Lin, H. Gui, J. Liu, Heterogeneous condensation on insoluble spherical particles: modeling and parametric study, Chem. Eng. Sci. 102 (2013) 387–396.
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Powder Technology journal homepage: www.elsevier.com/locate/powtec
Heterogeneous condensation of water vapor on particles at high concentration Junchao Xu, Yan Yu, Jun Zhang ⁎, Qiang Meng, Hui Zhong Key Laboratory of Energy Thermal Conversion and Control of Ministry of Education, Southeast University, Nanjing, 210096, Jiangsu Province, China
a r t i c l e
i n f o
Article history: Received 9 May 2016 Received in revised form 23 September 2016 Accepted 27 September 2016 Available online 28 September 2016 Keywords: Heterogeneous condensation Fine particles Water vapor Supersaturation
a b s t r a c t Although heterogeneous condensation on fine particles is one of the most promising precondition technologies for particles abatement which has been proved by many works, little direct data were reported on the process of particles enlargement by vapor condensation. A direct measurement of enlarged particle size distribution in a lab scale growth tube by water vapor condensation is presented. Four parameters that affect the performance of the particle enlargement at high particle number by heterogeneous condensation were identified: supersaturation, particle size, residence time and particle wettability. The results show that particle enlargement exponentially increases with the increase of supersaturation. The particle size has a negative impact on particle growth ratio. The residence time is in favor of the particle enlargement which depends on the supersaturation level. Additionally, the residence time extension would weaken the vapor depletion on particle enlargement caused by particle number increase. Particle wettability may lead to different processes of particle enlargement. This work deeply revealed the process of vapor condensation on particles at high concentration by direct measurement. © 2016 Elsevier B.V. All rights reserved.
1. Introduction Interest in the study of the heterogeneous condensation of supersaturated vapor has increased in the last few years. This explosion of attention has been driven by the recognition of the central role that heterogeneous condensation plays in the atmospheric and environmental process of concern worldwide. In particular, the most promising particles abatement pretreatment by vapor condensation is strongly influenced by the heterogeneous condensation [1]. The traditional particle abatement devices are far less efficient in collecting submicron particles, especially for those in the range 0.1-1 μm [2], the removal efficiency decreases to 25% [3]. Improving the dimension of the particles is the main way to facilitate fine particles abatement. A couple of new technologies were proposed in the recent past for the enlargement of submicron particulates: wet electrostatic scrubbing [4] and heterogeneous condensation [5,6]. Among them, heterogeneous condensation of water vapor as a preconditioning technique for fine particles removal has been proved to be one of the most promising techniques to improve the performances of traditional devices [7].
⁎ Corresponding author at: School of Energy and Environment, Southeast University, Sipailou 2, Xuanwu district, Nanjing, Jiangsu Province, China. E-mail addresses: [email protected] (J. Xu), [email protected] (Y. Yu), [email protected] (J. Zhang), [email protected] (Q. Meng), [email protected] (H. Zhong).
http://dx.doi.org/10.1016/j.powtec.2016.09.078 0032-5910/© 2016 Elsevier B.V. All rights reserved.
Many works have been done on the heterogeneous condensation on submicron aerosols. The theory of nucleation on small insoluble particles was proposed by Fletcher [8]. He found the process of heterogeneous condensation is determined by the particle size and surface characteristics [9,10]. Porstendorfer et al. [11] investigated the heterogeneous condensation of vapor on Ag and NaCl particles and observed the significant dependence of the heterogeneous condensation on particle size and surface properties. Chen et al. [12] investigated the heterogeneous condensation on SiO2, Al2O3, TiO2 and carbon black particles and led to a significant understanding of the nucleation process and a conclusion that critical supersaturation primarily depended on particle size and contact angle. Lammel et al. [13] studied the vapor condensation on carbon black particles and concluded that the soluble fraction of carbonaceous material could influence the nucleation ability of the carbon black particles. The nucleation process of individual glass particles was researched with an electrostatic levitation and the critical diameters were determined [14,15]. It could be found that these studies mentioned above were concentrated on the heterogeneous condensation at the low particle concentration (b 103 cm− 3). Actually, the particle concentration in the flue gas discharged from the coal-fired boiler is much higher [16]. At the high particle concentration, above 104 cm−3, the possibility of heterogeneous condensation on the particles might be decreased due to vapor depletion [17]. Numerical result showed that the absolute value of nucleation rate decreased with the increase of particle concentration [18], and the experimental results also showed that the vapor depletion
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impacted supersaturation and droplet size N 10% if the particles concentration was N 5 × 103 cm−3 [19]. Hence there are some differences in the enlargement performance between the high particle concentration and the low particle concentration. Some research has been done with the particles at the high concentration. Measuring removal efficiency was the most usual way to estimate the enlargement performance of vapor condensation on submicron particles [20–22]. Heterogeneous condensation of residual particles, quartz particles, and paraffin oil droplets were experimentally investigated by employing removal efficiencies as a function [23]. Fan et al. [24] also experimentally studied the heterogeneous condensation on coal combustion particles through measuring the particles removal efficiency. Nevertheless, the process of the heterogeneous condensation on submicron particles at high concentration is hard to understand through measuring the removal efficiency. The aim of this work is to investigate the process of heterogeneous condensation on submicron particles at the high particle concentration (the order of magnitude is 106 cm−3). A lab scale equipment based on the growth tube was employed to examine the effects of supersaturation, particles size, gas residence time and particle wettability on heterogeneous condensation process. In particular, the process was not explored by the usual way, but was rather done by a direct measuring way. So the effect parameters of enlargement process could be better revealed by comparing the particle size distribution (PSD) at the inlet and the outlet of the growth tube. 2. Experimental section 2.1. Particles To estimate the size effect on the heterogeneous condensation of particles, the fine SiO2 particles and coarse ones were adopted. 94.8% of the fine SiO2 particles are concentrated in the range from 0.05 to 0.2 μm, while 93.0% of the coarse ones are concentrated in the range from 1 to 3 μm, and corresponding mean sizes are 0.133 and 2.100 μm, respectively. At the same time the fine particles of SiO2 were employed to study the effect of supersaturation and residence time. Specially, for understanding the effect of contact angle, the fine particles of CaSO4, SiO2, and Fe2O3 were used due to their different surface wettability with water. The percentages of the CaSO4 and Fe2O3 ranging from 0.05 to 0.2 μm are 90.4% and 95.6%, respectively. 2.2. Measurement of contact angle A contact angle goniometer (Model JC2000D2, China) with high resolution camera (Model Guppy pro, Germany) was applied to measure the contact angles of SiO2, CaSO4, and Fe2O3. The particles cylindrical thin slices were prepared by placing a powder sample in a compression die and applying a force of 5000 N by means of a hydraulic press. This force was maintained for 30 min. Then the thin slice was put on the measurement table and 1.5 μL water was dripped on its surface, this process would be captured by the high resolution camera and finally the picture of the water contacting moment could be analyzed by computer to obtain particle's contact angle. 2.3. Experimental setup As illustrated in Fig. 1, the experimental apparatus includes three parts as follows, aerosol generation part, the particles growth part and the measurement part. The aerosol generation part consists of an aerosol generator (Model SAG-410, Germany) and an air compressor which supplies pure air as carrier gas. The particles growth part consists of a growth tube, a cooling unit and a hot water thermostat. The growth tube was made of glass with an internal diameter of 1.5 cm and a length of 40 cm, the same one as
Fig. 1. Experimental apparatus.
reported by Tammaro's work [25]. The hot water inlet to the growth tube was designed as tangential to assure a perfect adhesion of water with the tube walls. In the experiment, the liquid temperature was kept at the desired value, Th, by means of a thermostatic bath. The cooling unit cooled the aerosol gas into dew point, and then the cooled and saturated gas was sent into the growth tube and then encountered the hot water supplied by the thermostatic bath. The water vapor was transferred from the tube wall into the cooled gas which generated a supersaturation environment for the mass diffusivity is bigger than the heat diffusivity of water vapor. And the supersaturations were controlled by hot water temperature control. The measurement part consists of a laser droplet measuring instrument (Model OMEC-DP-02, China), an optical measurement window, and a hot wind fan. The laser instrument allows the measurement of PSD in the range between 0.05 μm and 1500 μm. In particular, the instrument was customized to extend its measuring range from 1– 1500 μm to 0.05–1500 μm, and the software was customized to match the customized instrument, too. The optical measurement window, which was made of optical glass, is closed to the outlet of growth tube avoiding the evaporation of droplets containing particles. The hot wind fan provides a hot airflow around the optical window to avoid droplet evaporating and condensing on the window. This method have two advantages: 1. The PSD can be detected at the outlet of the growth tube once the particles finish growth; 2. the hot wind introduction prevents the droplet evaporating and condensing on the optical window so that the light detection of the droplets containing particle can be reached. Additionally, an electrical low pressure impactor (ELPI, Dekati, Finland) was used for particle concentration. 3. Result and discussion 3.1. Supersaturation effect The process of particle enlargement by the heterogeneous condensation can be divided generally into two steps [26]. First, the particles have to be activated, which is called nucleation or activation. Secondly, the nuclei grow to droplets by condensation of vapor. In the heterogeneous condensation, the supersaturation not only affects the nucleation process [27], but also does the particles growth [28]. The supersaturation profiles throughout the growth tube are described by employing a heat and mass transfer modeling [29]. It can be seen in Fig. 2. that the supersaturation in the growth tube increases with the water temperature increase and the location of maximum supersaturation moves towards inlet of the growth tube with the water temperature increasing (when the water temperature is 303 K, 313 K, and 323 K, the maximum supersaturation is 1.032, 1.143 and 1.324, and the corresponding location is 33.44 cm, 28.00 cm and 24.24 cm away from inlet of the growth tube, respectively).
J. Xu et al. / Powder Technology 305 (2017) 71–77
Fig. 2. The profile of supersaturation in the axis of growth tube.
Fig. 3 gives the results of particles enlargement under different supersaturation which was controlled by different temperatures of hot water. It could be seen that, when the maximum supersaturation is 1.032, the particles could be barely activated and grown. With the supersaturation increase, the PSD of the particles and the peaks of small particles (less 1 μm) move toward the big size range. It is worth to
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note that the peaks of PSD in the big size range maintain the same size location with the increase of supersaturation. These indicate that the increase of supersaturation has a strong impact on small particles growth. Fig. 3 also shows that all the particles could be activated in the supersaturation above 1.143 even though the particles number increase from 1.7 × 10 cm−3 to 3.4 × 10 cm−3. It can be seen in Fig. 3(a) and (b), the percentage of particles b1 μm increases substantially with the increase of the particles number at the supersaturation of 1.324, which indicates that the increase of the particles number has an adverse influence on particle enlargement obviously when the residence time is 0.94 s. Vapor depletion effect on supersaturation in a continuous-flow CCN (cloud condensation nuclei) chamber was calculated [19], and the results showed that increasing the particles concentration above 1000 cm−3 began to impact the supersaturation profile, but the location of the maximum supersaturation in the instrument was not affected. However, considering the supersaturation profile initially increases and then decreases, the fine particles at concentration of 1.7 × 106 cm−3 would be activated earlier than the fine particles at concentration of 3.4 × 106 cm−3 in the growth tube because of the former supersaturation is bigger than the latter, which led to a less effective growth time (time from particles activation to the outlet of the growth tube) for particles at higher concentration. In addition, the vapors supply from tube wall should not depend on particles number, so it can be taken as a constant at the same residence time, thus fewer vapors have been allocated to each particle at higher concentration which lowers the particle enlargement performance.
A
B
C
D
Fig. 3. Supersaturation effect on heterogeneous condensation of particles. a. (N = 1.7 × 106 cm−3, t = 0.94 s) b. (N = 3.4 × 106 cm−3, t = 0.94 s) c. (N = 1.7 × 106 cm−3, t = 2.12 s) d. (N = 3.4 × 106 cm−3, t = 2.12 s).
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By comparing Fig. 3(c) and (d), it can be found that the increase of the particles number has a little effect on the particle enlargement when the residence time is 2.12 s. It could be concluded that the effect of the particles number on the heterogeneous condensation could be weakened by increasing the residence time. With the increase of residence time the vapor being transferred from tube wall to gas flow increases, thus more water vapor supply weakens the effect of vapor depletion caused by particles number. The arithmetic average diameter was calculated and plotted in Fig. 4. It could be seen that that the average diameter rapidly increases with increasing the profile of supersaturation.
3.2. Size effect It can be seen in Fig. 5, the particles b 1 μm are almost all enlarged for the coarse SiO2 particles, while most of the grown fine SiO2 particles are concentrated in the range 0.09–1 μm. In addition, there are some fine SiO2 particles that catch up in size with coarse ones during the growth stage in the range 1–4 μm, which is consistent with the result reported by Seinfeld [2]. The grown peaks of the fine SiO2 particles move toward the big size more remarkably than those of the coarse SiO2 particles. This phenomenon can also be seen from the data shown in Table 1, the growth ratio is 6.0 and 1.4 for the fine SiO2 and the coarse SiO2, respectively. Eq. (1) gives the particle growth rate [30]:
drp ¼ dt
" ρr p
S−Sa
Rg T Sa L2 M v þ βm Mv DP ∞ f1 þ ðS þ Sa ÞgP ∞ =ð2P Þ βt Rg KT 2
#
ð1Þ
where rp is particle diameter; S is the supersaturation; Sa is saturation ratio at the droplet surface; ρ is density of particles; D is vapor mass diffusivity; Rg is gas constant; L is latent heat of vaporization; K is heat conductivity; Mv is the molecular weight of vapor; P∞ is saturation vapor pressure; P is total gas pressure; and βm, βt is the transitional correction factor for mass transfer and heat transfer. It can be found from the equation, the growth of particles is inversely proportional to their diameters, and so fine particles grow faster than coarse ones. This is because the surface area of the fine particle is less than the coarse one, leading to a more obvious growth of it with the same vapor mass condensation. Consequently, the growth performance of the coarse particles is worse than that of fine particles by the heterogeneous condensation, which is contrary to the size effect on the particle nucleation process according to classic nucleation theory [31].
Fig. 5. Size effect on heterogeneous condensation of the fine SiO2 and the coarse SiO2 (S = 1.143, t = 1.2 s, N = 1.7 × 106 cm−3).
3.3. Residence time effect Fig. 6 gives the result of residence time effect on fine SiO2 particle enlargement. It clearly shows that the high residence time is favorable to particle growth. The peaks of PSD in Fig. 6 (a) and (b) basically coincide with each other at low supersaturation and the PSD moves to big size particles. It can be explained as follows, the residence time extension lead to more vapor transfer onto the particles which makes the PSD movement, however, due to the low supersaturation, small particles cannot be enlarged sufficiently. Comparing Fig. 6 (c) and (d), it could be found that the increase of the residence time leads to the shape change of the PSD in small particles range and the percentage of small particles decreases obviously at high supersaturation. Obviously, more vapor could be supplied with residence time extension and more small particles could be activated at high supersaturation region of the growth tube. Thus much more small particles could be enlarged further at high supersaturation, while these vapor supplied by residence time extension could not be condensed on the small particles for they could not be activated at low supersaturation. Consequently, these reasons result in the shape change of the PSD in the small particles range. Additionally, it can also be noted that the increase of particles number weaken the improvement of particles enlargement by residence time extension through comparing between Fig. 6 (a) and (b) and between (c) and (d). This phenomenon might be caused by vapor competition among particles. Fig. 7 gives the results of arithmetic average diameter of the fine SiO2 particles. Comparing the average diameter of grown particles, it can be found that the residence time has a little impact on final average diameter of particles at low supersaturation, while has a moderate impact on final average diameter of particles at high supersaturation.
3.4. Wettability effect The contact angles of the particles studied are listed in Table 2. It can be seen that three kinds of particle's wettability are quite different.
Table 1 Arithmetic diameter of the fine SiO2 and the coarse SiO2.a
Fig. 4. The relation between arithmetic average diameter and the maximum supersaturation (N = 1.7 × 106 cm−3, t = 0.94 s).
Particles
Fine SiO2
Grown fine SiO2
Coarse SiO2
Grown coarse SiO2
Mean diameter Growth ratio
0.133 μm 6.0
0.795 μm
2.100 μm 1.4
2.900 μm
a
S = 1.143, t = 1.2 s, N = 1.7 × 106 cm−3.
J. Xu et al. / Powder Technology 305 (2017) 71–77
A
B
C
D
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Fig. 6. Residence time effect on heterogeneous condensation of the fine SiO2. a. S = 1.143, N = 1.7 × 106 cm−3 b. S = 1.143, N = 3.4 × 106 cm−3 c. S = 1.324, N = 1.7 × 106 cm−3 d. S = 1.324, N = 3.4 × 106 cm−3.
Wettability effect on heterogeneous nucleation of water vapor on submicron particles had been investigated with SiC, SiO2, and naphthalene particles [32]. The results showed that the nucleation ability of SiC, SiO2, and naphthalene aerosols is qualitatively consistent with the theoretical prediction based on their wettability. In addition, Heidenreich et al. [23] also have investigated the heterogeneous condensation of quartz, residual and paraffin oil particles, the collection efficiencies
vary according to the particles properties. Fig. 8 shows the particle enlargement performance of CaSO4, SiO2, and Fe2O3 by water vapor condensation. It can be seen that all the three particles have been activated under this supersaturation condition. The performance of particle enlargement decreases with the contact angle increase which has a negative influence on particle wettability. The percentages of initial particles less 1 μm are 92.11%, 96.19%, and 97.14% for CaSO4, SiO2, and Fe2O3, and each corresponds to a percentage of 36.16%, 73.15%, and 87.50% when the particles have been enlarged. Moreover, there is still some fine particles of Fe2O3 in the range b 0.1 μm after heterogeneous condensation has taken place. In the supersaturation effect section, it was proposed that the process of particles enlargement by heterogeneous condensation can be divided generally into two steps. It was assumed that heterogeneous condensation on particles will be activated once the condition reaches the critical saturation, and will continue the same way as the growth of a homogenous liquid droplet [33]. Indeed, this approximation becomes reasonable when the embryos enlarge enough to surround the particle or nucleation rate is very large, so that it fails to describe the process when the particle wettability or the nucleation rate is small. Therefore, a transition stage [34]should be taken into account for small wettability particles such as Fe2O3. As Table 2 Contact angle of different particles.
Fig. 7. Arithmetic average diameter of the fine SiO2 with different residence times.
Particles
CaSO4
SiO2
Fe2O3
Contact angle
17.0°
35°
55°
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A
Fig. 9. Three stages of the whole process of heterogeneous condensation on an insoluble spherical particle. [34].
B
that all the small particles can be activated but the particles could not be enlarged enough as particles of CaSO4. We suppose that the process of part of the small size Fe2O3 particles only contains the stages of nucleation and transition for the low wettability of Fe2O3 particles. However, no further comments on quantitative of small particles can be made which need a visible measurement technology on heterogeneous condensation. Besides, due to the supersaturation in the growth tube increase with the increase of distance from inlet, the low wettability particles would be activated later than the high wettability particles which lead to the effective length (the distance from the location of particles being activated to the outlet of the growth tube) decrease for the former particles. The arithmetic average diameter of different particles is shown in Table 3. It can be seen that the growth ratio is 6.6, 6.0, and 2.8 for particles of CaSO4, SiO2, and Fe2O3 even though the particles of CaSO4 have a negative size effect on growth ratio which can be concluded from the Size effect section. Clearly it can be found that the wettability has a strong impact on particle enlargement performance. 4. Conclusion
C
Fig. 8. Wettability effect on heterogeneous condensation of the fine particles (S = 1.132, t = 1.2 s, N = 1.7 × 106 cm−3) a. CaSO4 b. SiO2 c. Fe2O3.
shown in Fig. 9, the first stage is heterogeneous nucleation, which is the beginning of the condensation process. The second stage is the transition from nucleation to growth. In this stage, the former embryos continue to grow and new critical embryos are formed simultaneously. The last stage is the growth of the droplet. When the total surface area of the particle is covered by embryos, it can be assumed that a thin liquid film is formed uniformly on the particle surface. In this stage, the condensation can be considered as the growth of a homogenous liquid droplet which contains the solid particle and the liquid film. Considering
The process of heterogeneous condensation on particles at high particle concentration was investigated. It is found that supersaturation not only affects the particle nucleation process but also does the growth process. In addition, the average diameter exponentially increases with the increase of supersaturation. Size effect on particle enlargement and the nucleation ability of particle is opposite, and the growth ratio of fine particles is larger than the coarse particles. Residence time is in favor of particle enlargement which depends on supersaturation level, and it has a little impact on particle enlargement at low supersaturation, while it has a moderate impact on average diameter at high supersaturation. Specially, residence time weakens the vapor depletion effect on particle enlargement. The wettability of particle may lead to different processes of heterogeneous condensation and it has a strong impact on particle enlargement performance. This work demonstrated that the heterogeneous condensation of water vapor is one of the most promising pretreatments for industrial emission particles abatement once again. In addition, with reference to the industrial application of growth tube devices, the experimental results can be easily applied to large scale industrial process. Acknowledgments This work was supported by the National Natural Science Foundation of China [Grant No. 51576043], the Scientific Research Foundation Table 3 Arithmetic average diameter and growth ratio of different particles. Particles
CaSO4
SiO2
Fe2O3
Initial Grown Growth ratio
0.258 μm 1.695 μm 6.6
0.133 μm 0.795 μm 6.0
0.143 μm 0.398 μm 2.8
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of Graduate School of Southeast University [Grant No. YBJJ1607], the Research Innovation Program for College Graduates of Jiangsu Province [Grant No. KYLX16_0202] and the Major State Basic Research Development Program of China [973 Program Grant No. 2013CB228504]. References [1] B. Jingjing, Y. Linjun, Y. Jinpei, et al., Experimental study of fine particles removal in the desulfurated scrubbed flue gas, Fuel 108 (2013) 73–79. [2] J.H. Seinfeld, S.N. Pandis, Atmospheric Chemistry and Physics, John Wiley, Hoboken, NJ, New York, 1998. [3] M. De Joannon, G. Cozzolino, A. Cavaliere, et al., Heterogeneous nucleation activation in a condensational scrubber for particulate abatement, Fuel Process. Technol. 107 (2013) 113–118. [4] A. Jaworek, W. Balachandran, A. Krupa, J. Kulon, M. Lackowski, Wet electroscrubbers for state of the art gas cleaning, Environ. Sci Technol. 40 (2006) 6197–6207. [5] S. Heidenreich, F. Ebert, Condensational droplet growth as a preconditioning technique for the separation of submicron particles from gases, Chem. Eng. Process. Process Intensif. 34 (1995) 235–244. [6] S.V. Hering, M.R. Stolzenburg, A method for particle size amplification by water condensation in a laminar, thermally diffusive flow, Aerosol Sci. Technol. 39 (2005) 428–436. [7] J. Bao, L. Yang, S. Song, et al., Separation of fine particles from gases in wet flue gas desulfurization system using a cascade of double towers, Energy Fuel 26 (2012) 2090–2097. [8] N.H. Fletcher, Size effect in heterogeneous nucleation, J. Chem. Phys. 29 (3) (1958) 572–576. [9] G. Hänel, The properties of atmospheric aerosol particles as functions of the relative humidity at thermodynamic equilibrium with the surrounding moist air, Adv. Geophys. 19 (1976) 73–188. [10] P. Winkler, The growth of atmospheric aerosol particles with relative humidity, Phys. Scr. 37 (1988) 223–230. [11] J. Porstendorfer, H.G. Scheibel, F.G. Pohl, O. Preining, G. Reischl, P.E. Wagner, Heterogeneous nucleation of water vapor on monodispersed Ag and NaCl particles with diameters between 6 and 18 nm, Aerosol Sci. Technol. 4 (1985) 65–79. [12] C.C. Chen, L.C. Hung, H.K. Hsu, Heterogeneous nucleation of water-vapor on particles of SiO2, Al2O3, TiO2, and carbon black, J. Colloid Interface Sci. 157 (1993) 465–477. [13] G. Lammel, T. Novakov, Water nucleation properties of carbon black and diesel soot particles, Atmos. Environ. 29 (1995) 813–823. [14] O.V. Sharoichenko, A New Apparatus for Study of Heterogeneous Nucleation on Single Micron-sized Insoluble Particles, State University of New York, New York, 2000. [15] O.V. Hogrefe, R.G. Keesee, Heterogeneous vapor-to-liquid nucleation of water on individual glass particles, Aerosol Sci. Technol. 36 (2002) 239–247. [16] H. Wu, L. Yang, J. Yan, G. Hong, B. Yang, Improving the removal of fine particles by heterogeneous condensation during WFGD processes, Fuel Process. Technol. 145 (2016) 116–122.
77
[17] S.P. Fisenko, W. Wang, M. Shimada, K. Okuyama, Vapor condensation on nanoparticles in the mixer of a particle size magnifier, Int. J. Heat Mass Transf. 50 (2007) 2333–2338. [18] Z. Kožíšek, P. Demo, Influence of vapor depletion on nucleation rate, J. Chem. Phys. 126 (2007) 184510. [19] T.L. Lathem, A. Nenes, Water vapor depletion in the DMT continuous-flow CCN chamber: effects on supersaturation and droplet growth, Aerosp. Sci. Technol. 45 (2011) 604–615. [20] T. Yoshida, Y. Kousaka, K. Okuyama, F. Nomura, Application of particle enlargement by condensation to industrial dust collection, J. Chem. Eng. Jpn 11 (1978) 469–475. [21] L. Yang, J. Bao, J. Yan, J. Liu, S. Song, F. Fan, Removal of fine particles in wet flue gas desulfurization system by heterogeneous condensation, Chem. Eng. J. 156 (2010) 25–32. [22] J. Yan, J. Bao, L. Yang, F. Fan, X. Shen, The formation and removal characteristics of aerosols in ammonia-based wet flue gas desulfurization, J. Aerosol Sci. 42 (2011) 604–614. [23] S. Heidenreich, U. Vogt, H. Büttner, F. Ebert, A novel process to separate submicron particles from gases — a cascade of packed columns, Chem. Eng. Sci. 55 (2000) 2895–2905. [24] F.X. Fan, L.J. Yang, J.P. Yan, J.J. Bao, X.L. Shen, Experimental investigation on removal of coal-fired fine particles by a condensation scrubber, Chem. Eng. Process. 48 (2009) 1353–1360. [25] M. Tammaro, Heterogeneous Condensation for Submicronic Particles Abatement, Università degli Studi di Napoli Federico II, 2010. [26] F. Fan, L. Yang, J. Yan, Z. Yuan, Numerical analysis of water vapor nucleation on PM2.5 from municipal solid waste incineration, Chem. Eng. J. 146 (2009) 259–265. [27] J.C. Barrett, T.J. Baldwin, Aerosol nucleation and growth during laminar tube flow: maximum saturations and nucleation rates, J. Aerosol Sci. 31 (2000) 633–650. [28] X. Luo, Y. Fan, F. Qin, H. Gui, J. Liu, A kinetic model for heterogeneous condensation of vapor on an insoluble spherical particle, J. Chem. Phys. 140 (2014) 024708. [29] S.V. Hering, M.R. Stolzenburg, A method for particle size amplification by water condensation in a laminar, thermally diffusive flow, Aerosol Sci. Technol. 39 (5) (2005) 428–436. [30] M. Kulmala, Condensational growth and evaporation in the transition regime, Aerosol Sci. Technol. 19 (1993) 381–388. [31] V.I. Kalikmanov, Nucleation Theory, Springer Netherlands, 2013. [32] C. Chin, G. Ming-S, T. Yi, H. Chong, Heterogeneous nucleation of water vapor on submicrometer particles of SiC, SiO2, and naphthalene, J. Colloid Interface Sci. 198 (1998) 354. [33] M. Tammaro, F. Di Natale, A. Salluzzo, A. Lancia, Heterogeneous condensation of submicron particles in a growth tube, Chem. Eng. Sci. 74 (2012) 124–134. [34] Y. Fan, F. Qin, X. Luo, L. Lin, H. Gui, J. Liu, Heterogeneous condensation on insoluble spherical particles: modeling and parametric study, Chem. Eng. Sci. 102 (2013) 387–396.