Absorption of Sulfur Dioxide with Sodium Hydroxide Solution in Spray

Article pubs.acs.org/IECR

Absorption of Sulfur Dioxide with Sodium Hydroxide Solution in Spray Columns Zhanke Wang, Yu Peng, Xiaocong Ren, Shaoyong Gui, and Guangxu Zhang*

Downloaded by SUNY UPSTATE MEDICAL UNIV on August 28, 2015 | http://pubs.acs.org Publication Date (Web): August 27, 2015 | doi: 10.1021/acs.iecr.5b02146

School of Chemistry, Chemical Engineering and Life Science, Wuhan University of Technology, Wuhan 430070, Hubei, China ABSTRACT: The absorption of sulfur dioxide into highly concentrated sodium hydroxide in a spray column from simulated flue gas was investigated. The influences of different operating conditions on the SO2 removal efficiency, such as sodium hydroxide concentration, liquid-to-gas ratio, gas velocity and SO2 concentration, were examined. The overall volume transfer coefficients (kGa), under moderate conditions, were obtained by introducing the instantaneous and irreversible chemical reaction into the two-film theory to establish a model that allowed the calculation of theoretical values of the overall volume-transfer coefficient. It was found that the absorption process was controlled by diffusion through gas film when a highly concentrated caustic soda solution was adopted. The overall volume-transfer coefficient was essentially independent of concentration of SO2 in gas phase and positively related to the gas and liquid flow rates. The formula of kGa was fitted for the process and found to be in good agreement with experimental results.

1. INTRODUCTION Air pollution caused by sulfur oxides (SOX) in exhausted gas from marine diesel engine has been a global issue and a hot research topic. The emission limits for SOX has been dictated in International Maritime Organization (IMO) Regulation 14. However, naturally occurring low-sulfur fuel is insufficient and refining to remove sulfur content is expensive. It is an alternative method of mitigating SOX emissions by the lessexpensive high-sulfur-content oil in combination with an exhaust gas scrubber.1,2 Attributed to the low-cost advantage of the raw material source, desulfurization with limestone gypsum system has been a common flue gas desulfurization (FGD) technique mainly used in coal power stations. However, the practical marine application of this treatment is limited by the large cubage, easy blockage, and the produced large amount of solid waste. Wet ammonia FGD is prevalent for its byproduct of ammonium sulfate fertilizer recently,3 but it is swept aside for the ammonia escape and the constraint of the discharge of wastewater containing the ammonia nitrogen. As an important industrial absorption process to reduce air pollution, removing sulfur dioxide from gas mixtures by contacting it with an aqueous alkali hydroxide solution has been considered to minimize scaling, plugging, and erosion problems in the absorbent circuit.4,5 Several studies were reported previously about the chemical absorption mechanism for the SO2−OH− ion system.6−12 The transfer mechanism,6,7 theoretical calculation approaches,8,9 and some experiment researches about various types of reactors on a laboratory scale10−12 have been investigated. However, only few studies involving the overall volume-transfer coefficient of absorption SO2 with sodium hydroxide solution in a spray column were reported. Zidar6 discussed desulfurization in the NaOH−SO2−H2O system on a laboratory scale using a falling film reactor to scale down criteria for the spray columns, which reported the enhancement factor and the overall mass-transfer coefficients and presented the gas−liquid equilibrium operation graphically in the low concentration of caustic soda solution. However, in a practical application of © XXXX American Chemical Society

ships, the concentrated sodium hydroxide solution would be adopted to increase the absorption rate.13 The main purpose of this study is the overall volume-transfer coefficient of the purification of effluent gases containing sulfur dioxide with high concentration sodium hydroxide solution in a spray tower. Furthermore, the significant rate of SO2 reduction affected by the different operation conditions in the system was also investigated.

2. THEORETICAL BACKGROUNDS 2.1. Physical and Chemical Properties of the System. When sulfur dioxide is absorbed into aqueous alkaline solution, the diffusion of sulfur dioxide molecules from current gas phase core to the gas/liquid interface and the dissolution in the washing agent should be considered initially, according to the equality of the chemical potentials in the phases, which could be described by eq 1. It is often thought that the dissolution process obeys Henry’s Law in low concentrations of the sulfur dioxide predominant in effluent gases in practice. Some dissolved acid gas molecules would be dissociated according to eq 2, and others react with hydroxide ion directly, according to eq 3, whereby hydrogen sulfite reacts, in turn, with the additional hydroxide ion to sulfite, as shown in eq 4. The hydrogen sulfite could also react with the dissolved sulfur dioxide molecules, according to eq 5. The above processes would have something with the dissociation of the water (according to eq 6), the caustic soda (according to eq 7), and the products of the processes (according to eqs 8−10). Dissolution: SO2 (g ) ↔ SO2 (l)

(1)

Received: June 15, 2015 Revised: August 17, 2015 Accepted: August 24, 2015

A

DOI: 10.1021/acs.iecr.5b02146 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Industrial & Engineering Chemistry Research Dissociation: SO2 + H 2O ↔ HSO−3 + H+

(2)

Reaction: SO2 + OH− ↔ HSO−3

(3)

Consecutive Reaction: HSO−3 + OH− ↔ SO32 − + H 2O

(4)

Reaction: SO2 + SO32 − + H 2O ↔ 2HSO−3

(5)

Dissociation:


H 2O ↔ H+ + OH−

(6) Figure 1. Concentration distribution of instantaneous and irreversible reaction.

Dissociation: NaOH ↔ Na + + OH−

(7)

⎛δ ⎞ ⎛ DS,L ⎞ NS = ⎜ ⎟cS,i = ⎜ L ⎟kLcS,i ⎝ δ1 ⎠ ⎝ δ1 ⎠

Dissociation: Na 2SO3 ↔ 2Na + + SO32 −

(8)

The diffusing rate of NaOH is expressed as ⎛ δ ⎞⎛ D N,L ⎞ ⎛ D N,L ⎞ NN = ⎜ ⎟c N,L ⎟c N,L = ⎜ L ⎟⎜ ⎝ δ 2 ⎠⎝ δ L ⎠ ⎝ δ2 ⎠

Dissociation: NaHSO3 ↔ Na + + HSO−3

(9)

(10)

In the case of the scrubbing process in the spray tower, which acts as a multiple-staged feeding reactor, the fresh sodium hydroxide solution is fed at different stages, which leads to the sufficient fresh reactants and lower concentration of SO2− 3 in the column. In addition, the fresh sodium hydroxide solution is the strong alkaline with high ionization equilibrium constant,7 because of eq 7, which will provide the surplus of the hydroxide ion. The result of the circumstance is that eq 5 could be ignored and eq 4 follows close behind eq 3. Therefore, the overall reaction in the scrubber is described as shwn in eq 11. Besides, eq 3 is very fast with a rate constant exceeding 109 (mol−1 s−1 L), and the eq 4 has a very much higher rate constant because of the proton transfer reaction.9 As a result, the reaction 11 could be regarded as an instantaneous and irreversible reaction under the condition of high concentration of reactants.6,14 SO2 + 2OH− → SO32 − + H 2O

(13)

Regarding eq 11, 2NS = NN is obtained for the relationship of stoichiometry. Therefore, eq 12 can be converted to the form of eq 15, with the removal of the factors δ1 and δ2, using the following relationship between δL, δ1, and δ2:

Dissociation:

HSO−3 ↔ H+ + SO32 −

(12)

δ L = δ1 + δ2

(14)

⎛ D N,L c N,L ⎞ ⎟⎟kLcS, i NS = 1 + ⎜⎜ ⎝ (2DS,L cS, i) ⎠

(15)

D N,L c N,L δL =1+ δ1 2DS,L cS,i

(16)

According to eqs 15 and 16, the increase in cN,L will promote the absorption of sulfur dioxide for the decrease of δ1, and the limiting case of cS,i = 0 would occur when the absorbent concentration is high enough. In this case, the absorption process conducts with the maximum rate expressed by eq 17, and the appropriate critical concentration is calculated by eqs 18−20:

(11)

2.2. Absorption Model. A comparison was made between the predicted effects of chemical reaction on the absorption process for some of the rigorous models (including penetration theory, film theory, eddy diffusion theory, and surface theory) and approximate methods by Glasscok and Rochelle.15 They concluded that the steady-state model (for example, film theory) was the most effective for illustrating experimental data and conducting the numerical simulation of acid gas-treating process. On the basis of the film theory, the instantaneous irreversible reaction occurs only on the specific plane in liquid film and the plane is called the reaction surface.16 As shown in Figure 1, in order to supply the plane with reactants, the sulfur dioxide molecules diffuse from the gas/liquid interface and the sodium hydroxide molecules diffuse from the liquid bulk. The diffusing rate of SO2 is expressed as

NS = k GpS,G

(17)

⎛ D N,L ⎞ NN = ⎜ ⎟(c N,L,C − 0) = 2NS = 2k GpS,G ⎝ δL ⎠

(18)

kL =

DS,L δL

⎛ 2k ⎞⎛ DS,L ⎞ ⎟⎟p c N,L,C = ⎜ G ⎟⎜⎜ ⎝ kL ⎠⎝ D N,L ⎠ S,G

(19)

(20)

When cN,L ≫ cN,L,C, as shown in Figure 2, the absorption process is controlled by gas film mass transfer, and the rate can be calculated by eq 17 under the consideration of cS,i = 0.16 B


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Industrial & Engineering Chemistry Research

3. EXPERIMENTAL METHODS AND DATA INTERPRETATION 3.1. Experimental Work. A schematic diagram of the experimental setup for the desulfurization is shown in Figure 3. The experimental system consists of a mixing tank, an air heater, a scrubber column, a spraying system, a demister, and an instrumentation section. An air-mixing chamber simulates different air velocities in the range of 3.0−5.0 m/s and SO2 concentrations of exhaust gas from diesel engine. The system is equipped with a SO2 gas tank, a mixing section, and an air compressor. SO2 concentrations can be controlled by the flow of SO2 in the system with the rotameter. The SO2-laden air flows to the vertical spray column and contacts counter-current with the absorption solvent, which is pumped into the tower through the atomizing nozzles and rotameter. The scrubber is a cylindrical stainless steel column with a diameter of 0.125 m and a height of 1.8 m. There are three nozzles with the interval distance of 0.4 m inside the column. Figure 4 shows information about the scrubber. In the experiment, the concentration of SO2 ranged from 0 to 800 ppm. Experiments were performed by keeping the liquid flow rate constant and varying the gas flow rate (100−200 m3 h−1), and by keeping the gas flow rate constant and varying the liquid flow rate (750−2000 L h−1). The liquid recirculation duration was controlled to be less than half an hour and the change of liquid concentration could be ignored, resulting from the presence of little SO2 and a large sum of NaOH in each run. The pressure drop (Δp) between points A and B shown in Figure 3 was measured to evaluate the flow resistance of the equipment. 3.2. Data Interpretation. The mass-transfer coefficient (kG) is an important parameter, but it is difficult to measure,


Figure 2. Concentration distribution of instantaneous and irreversible reaction (in the case of cN,L ≫ cN,L,C).

When cN,L < cN,L,C, the absorption is governed by both gas film and liquid film. The absorption rate of sulfur dioxide is obtained with the help of gas film transfer rate expressed by eq 21 and the equilibrium condition of gas/liquid interface described by eq 22.

NS = k G(pS,G − pS,i )

(21)

cS,i = HpS,i

(22)

NS =

pS,G + D N,L /(2HDS,L )c N,L 1/(HkL) + 1/k G

(23)

Figure 3. Schematic diagram of the experimental setup. C


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Industrial & Engineering Chemistry Research k Ga =

ΔMS VR pS,G,lm Δt

(30)


4. RESULTS AND DISCUSSION Experiments on the SO2 scrubbing have been conducted by altering various process operating parameters, including sodium hydroxide concentration, liquid-to-gas ratio (L/G), gas velocity, and SO2 concentration. The scrubber SO2 removal efficiencies for field tests are calculated using eq 31: cSO2,out − cSO2,in η (%) = × 100 cSO2,out (31) where cSO2,in and cSO2,out are the concentrations of SO2 at the inlet and outlet of the column, respectively. 4.1. Influence of Sodium Hydroxide Concentration on the Sulfur-Removal Efficiency. Based on the preceding description, the critical concentration of the sodium hydroxide solution is the key point to determine the controllability of the SO2 absorption process via gas-phase mass transfer. Figure 5 Figure 4. Brief schematic view of the spray column.

because of the difficulty involved in determining the interface area. However, the volume-transfer coefficient (kGa) is easier to obtain, by interpreting the global data from the measurements at the inlet and outlet of the device. Based on the description given in Section 2, because of the instantaneous and irreversible reaction, the absorption of SO2 with concentrated NaOH solution is governed by the diffusion of SO2 through gas film, if the concentration of the solution is considerably higher than the critical concentration. The equilibrium concentration of SO2 at the gas/liquid interface is equal to 0 and the absorption flux can be calculated using eq 17. As a result, the absorption rate per unit volume is given as

NS′ = k GapS,G

Figure 5. Influence of sodium hydroxide concentration on the sulfurremoval efficiency (L/G = 5.55 L m−3, cSO2,in = 300 ppm, Tab = 30 °C).

(24)

and, overall, the effective volume of column is given as MS = VR k GapS,G

shows that the absorption efficiency of SO2 increases with the aqueous alkali concentration. At the beginning, the rate of desulfurization increases rapidly and then slowly when the concentration of absorbent is >0.4 mol/L. This phenomenon indicated that, when the cNaOH is low, the process is governed by both gas film and liquid film mass transfer, and the sulfurremoval efficiency increases as cNaOH because of the decrease in δ1. Under the high concentration of sodium hydroxide solution (for example, >0.9 mol/L), however, the distance between the interface and the reaction surface is infinitesimal, and the trend of increasing sulfur-removal efficiency slows for the control process of gas film mass transfer. Therefore, the critical concentration can be supposed to be between 0.05 mol/L and 0.41 mol/L, which can be affirmed by eq 20, where kG and kL can be calculated using the correlation obtained by Zidar.6 Furthermore, Schultes17 also reported that the rapid mass transfer rate was so dominant that resistance lay exclusively in the gas phase at a large mole fraction of sodium hydroxide solution. 4.2. Influence of Liquid-to-Gas Flow Rate Ratio on Sulfur-Removal Efficiency. The liquid-to-gas ratio (L/G) refers to the ratio between the spraying volume flow rate and the gas flow rate. It is a significant parameter to report the scrubbing performance, because a high ratio leads to high

(25)

The total amount of SO2 absorbed within the residence time of gas−liquid countercurrent in the effective volume of the scrubber can be obtained as ΔMS = VR k Ga

∫0

Δt

pS,G dt

(26)

where Δt is calculated by

Δt =

∫0

VR VG

(27)

Δt

pS,G dt = pS,G,lm Δt

(28)

where pS,G,lm is the logarithmic mean partial pressure of SO2, which is defined by the expression pS,G,in − pS,G,out pS,G,lm = ln(pS,G,in /pS,G,out ) (29) As a consequence, the volumetric overall mass-transfer coefficient is obtained as D


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Industrial & Engineering Chemistry Research sulfur-removal efficiency but high energy consumption and operation costs. To ensure the desulfurization efficiency, the value of L/G usually ranges from 8 L m−3 to 25 L m−3. Considering the high absorption ability of the strong base solution, the influence of a lower L/G value (varying from 5 L m−3 to 10 L m−3) on the efficiency of SO2 removal and the total pressure drop were studied under the fixed values of absorbing temperature and concentrations of SO2 and alkaline liquor. The results are shown in Figure 6. To keep the same


Figure 7. Influence of SO2 concentration on sulfur-removal efficiency and absorption rate (L/G = 5.55 L m−3, cNaOH = 0.4 mol L−1, Tab = 30 °C).

results of the effect of inlet gas velocity on the removal efficiency are displayed in Figure 8. To keep the same

Figure 6. Influence of liquid-to-gas ratio (L/G) on (■) sulfur-removal efficiency and (▼) total pressure drop (VG = 200 m3 h−1, cSO2,in = 575 ppm, cNaOH = 1 mol L−1, Tab = 25 °C).

residue time, the experiments were carried out at a constant gas flow rate (VG), while the liquid flow rate (VL) was changed according to the requested L/G value. Figure 6 shows that the percentage removal of SO2 increases sharply as the value of L/G increases at the beginning and then slowly at L/G > 8 L m−3, whereas the growth trend of pressure drop is totally opposite. When the L/G increases at a fixed value of VG, VL rises in the scrubber and, thus, the contact area of gas−liquid also increases. Meanwhile, the pressure drop increases for the highly loaded demister. When the ratio exceeds 8 L m−3, the droplet surface area is large enough, and further increases in this ratio become meaningless, whereas the load of the mist eliminator surges as a result of more droplets in the gas flow. The result is consistent with the report by Bandyopadhyay and Biswas.4 4.3. Influence of SO2 Concentration on SulfurRemoval Efficiency. The concentration of sulfur dioxide in diesel exhaust varies with the sulfur content of fuels and the operation points of engine. It is meaningful to consider the effect of SO2 concentration in the feeding gas (cSO2,in) on the sulfur-removal efficiency. The results are shown in Figure 7. It shows that higher removal efficiency is achieved at lower initial SO2 concentration. However, this does not mean higher absorption rate. Actually, the absorption rate is proportional to the initial SO2 concentration due to the increasing mass transfer driving force: the partial pressure of SO2 in gas bulk. This observation is in good agreement with eq 20 and it suggests that some measures (e.g., increasing L/G) should be taken to achieve higher sulfur removal efficiency in the case of high initial SO2 concentration. 4.4. Influence of Inlet Gas Velocity on the SulfurRemoval Efficiency. The velocity of inlet gas will affect both the volume of the scrubber and the total pressure drop, with regard to the cost of the device and operation, respectively. The

Figure 8. Influence of inlet gas velocity on the sulfur-removal efficiency (L/G = 7 L m−3, cSO2,in = 550 ppm, cNaOH = 0.4 mol L−1, Tab = 25 °C).

absorption conditions, the trial was conducted at a fixed L/G value, which indicated that the liquid flow rate varied with the gas flow rate, according to the given L/G value. As shown in Figure 8, an initial increase in the SO2 removal rate is observed from the elevation of inlet gas velocity and then a sharp decrease occurs after the gas velocity exceeds 4.0 m s−1. There are two major factors regarding the inlet gas velocity that influence the absorption rate. On one hand, the resistance of gas film declines as the turbulence intensifies when the gas flow rate increases, as well as the droplet Stokes diameter, which is inversely proportional to the gas−liquid contact area.18 On the other hand, as the gas flow rate increases, the residence time of vapor−liquid contact and mass transfer decreases. At the low velocity, the former is the dominant factor, so the removal rate of SO2 increases as the inlet gas velocity increases; at the high velocity, the process is dependent on the latter factor. 4.5. Interpretation of the Mass-Transfer Coefficient. In order to predict the removal efficiency of SO2 in an alkaline scrubber, empirical and semiempirical correlations were developed. Lorent et al.19 have studied the sulfur dioxide absorption process in the sodium sulfite solutions in a cable contactor. They developed a semiempirical calculation and found that the overall mass-transfer coefficients increased with the liquid flow rate and gas velocity and slowly with the pH. E


Article

Industrial & Engineering Chemistry Research Since a high concentration of sodium hydroxide solution was introduced in this experiment, the influence of pH could be considered to be negligible. However, it is necessary to take the inlet concentration of sulfur dioxide, as well as the gas and liquid flow rates, into consideration. The influence of the inlet SO2 concentration on volumetric overall mass-transfer coefficient is described in Figure 9. It


Figure 11. Influence of liquid flow rate on the volumetric overall masstransfer coefficient.

increase completely, because of the limited liquid holdup of the scrubber, which could also be observed through Figure 11. Based on the results of the experiments and previous reported studies, kGa is a function of VG and VL at a fixed temperature: Figure 9. Influence of the inlet SO2 concentration on the volumetric overall mass-transfer coefficient.

k Ga = AVG aVL β

(32)

where A is a constant when the temperature is fixed. With the regression analysis method, those coefficients were obtained at an absorption temperature of 25 °C, as follows:

shows that kGa remains constant, independent of the initial gas phase concentration, which means that kGa is irrelevant to cSO2,in. This fact further shows that the scrubbing process under consideration is controlled by gas-phase mass transfer. In contrast, the volumetric overall mass-transfer coefficient has a relationship with the gas flow rate and the liquid flow rate. As shown in Figure 10, kGa maintains an upward tendency with

k Ga = 3.379 × 10−3VG 0.9118VL 0.3037

(33)

The comparison between predicted values and the experimental data is presented in Figure 12. It can be seen

Figure 12. Comparison of calculated and experimental volumetric overall mass-transfer coefficient.

Figure 10. Influence of gas flow rate on the volumetric overall masstransfer coefficient.

that the predicted values fit well with the experimental values (well within a deviation of ±10%) when the absorption temperature is ∼25 °C and the absorbent concentration is >0.9 mol L−1. In addition, an interesting phenomenon should be given attention: experimental values that are obtained under the conditions of higher temperature or lower absorbent concentration diverge greatly from the calculative values. Obviously, a lower concentration of the absorption liquid does not conform to the model assumption. With regard to the absorption temperature, the dissolution process of SO2 is accompanied by an evolution of heat; therefore, sulfur dioxide solubility decreases as the temperature increases. Actually, the dissolved sulfur dioxide molecules in liquid begin to desorb at

the increasing gas flow rate, which may be induced by the increase in kG. The high gas flow rate implies intensified turbulence, which may contribute to the decreased resistance in the gas film and the increase in kG. Although the value of kGa increases with the liquid flow rate, a slow tendency should be given attention when the liquid flow rate surpasses 1600 L h−1, which can be observed in Figure 11. This phenomenon may be attributed to the fact that the increased spray rate is likely to lead to an increase in the spraying density and a decrease in the droplet Stokes diameter, both of which give rise to an increase in the specific interface area, according the equation given by Wu et al.20 Furthermore, the specific interface area could not F


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δ2 = distance between the reaction surface and liquid bulk, m δL = thickness of liquid film, m η = sulfur-removal efficiency


20 °C and the amount of desorption is proportional to the temperature.21 In conclusion, eq 33 is applicable to the low adsorption temperature and high concentration of absorption solution.

Subscripts

5. CONCLUSIONS The theoretical analysis presented and the experimental results described reveal that the absorption of SO2 into a highly concentrated sodium hydroxide solution in a spray tower is controlled by gas side film mass-transfer resistance, and the reaction is instantaneous and irreversible. The increase in the vapor−liquid contact area and the decrease of the gas film resistance are beneficial to increasing the sulfur-removal efficiency. The volumetric overall mass-transfer coefficient increases with the liquid and gas flow rate. The inlet sulfur dioxide concentration has no influence on kGa. A semiempirical equation is in good agreement with the experimental data under certain conditions. In addition, diesel engine exhaust contains many different species that would have potential effects on the desulfurization, so further study will focus on the impacts of other acid species in exhaust gas, as well as particulates, upon the removal of sulfur dioxide.

■

■

C = critical value i = interface G = gas or gas film L = liquid or liquid film lm = logarithmic mean N = sodium hydroxide R = reactor S = sulfur dioxide

REFERENCES

(1) Ü lpre, H.; Eames, I. Environmental policy constraints for acidic exhaust gas scrubber discharges from ships. Mar. Pollut. Bull. 2014, 88, 292. (2) Bartholomew, K.; Panagiotopoulos, A. Options for lower sulphur marine fuels. Pet. Technol. Q. 2011, 16, 123. (3) Srivastava, R. K.; Jozewicz, W.; Singer, C. SO2 scrubbing technologies: A review. Environ. Prog. 2001, 20, 219. (4) Bandyopadhyay, A.; Biswas, M. Critical flow atomizer in SO2 spray scrubbing. Chem. Eng. J. 2008, 139, 29. (5) Huang, B.; Yang, G. H. Research progress of ship exhaust gas cleaning desulfurization denitration and PM removal equipment. Chem. Ind. Eng. Prog. 2013, 32, 2826 (URL: http://www.hgjz.com.cn/ EN/Y2013/V32/I12/2826). (6) Zidar, M. Gas-liquid equilibrium-operational diagram: Graphical presentation of absorption of SO2 in the NaOH−SO2−H2O system taking place within a laboratory absorber. Ind. Eng. Chem. Res. 2000, 39, 3042. (7) Pasiuk-Bronikowska, W.; Rudziński, K. J. Absorption of SO2 into aqueous systems. Chem. Eng. Sci. 1991, 46, 2281. (8) Bandyopadhyay, A.; Biswas, M. N. Modeling of SO2 scrubbing in spray towers. Sci. Total Environ. 2007, 383, 25. (9) Hikita, H.; Asai, S.; Tsuji, T. Aborption of sulfur dioxide into aqueous sodium hydroxide and sodium sulfite solutions. AIChE J. 1977, 23, 538. (10) Duan, Z. Y.; Hu, J. B.; Zong, R. K. Mass Transfer Model for SO2 absorption by NaOH solution in venturi scrubber. J. Tianjin Univ. 2006, 39, 1180. (11) Liu, C.-F.; Shih, S.-M. Effects of flue gas components on the reaction of Ca(OH)2 with SO2. Ind. Eng. Chem. Res. 2006, 45, 8765. (12) Rahmani, F.; Mowla, D.; Karimi, G.; Golkhar, A.; Rahmatmand, B. SO2 removal from simulated flue gas using various aqueous solutions: Absorption equilibria and operational data in a packed column. Sep. Purif. Technol. 2015, in press (10.1016/j.seppur.2014.10.028). (13) Henriksson, T. SOx scrubbing of marine exhaust gas. Wärtsilä Technol. J. 2007, 2, 55. (14) Chang, C. S.; Rochelle, G. T. SO2 absorption into NaOH and Na2SO3 aqueous solutions. Ind. Eng. Chem. Fundam. 1985, 24, 7. (15) Glasscock, D. A.; Rochelle, G. T. Numerical simulation of theories for gas absorption with chemical reaction. AIChE J. 1989, 35, 1271. (16) Zhu, B. C. Chemical Reaction Engineering; Wiley: Beijing, 2006. (17) Schultes, M. Absorption of sulphur dioxide with sodium hydroxide solution in packed columns. Chem. Eng. Technol. 1998, 21, 201. (18) Zhu, J.; Wu, Z. Y.; Ye, S. C.; Liu, Z. H.; Yang, Y. F.; Bai, J. Drop size distribution and specific surface area in spray tower. CIESC J. 2014, 65, 4709. (19) Lorent, P.; Gerard, P.; Vanderschuren, J. Sulphur dioxide absorption in the sodium sulphite solutions in a cable contactor. Gas Sep. Purif. 1992, 6, 125. (20) Wu, Y.; Li, Q.; Li, F. Desulfurization in the gas-continuous impinging stream gas−liquid reactor. Chem. Eng. Sci. 2007, 62, 1814.

AUTHOR INFORMATION

Corresponding Author

*Tel./Fax: +8627 87859019. E-mail address: zhanggx2002@ 163.com. Author Contributions

Concepts for research program were conceived by all authors. Experiments were devised by G.X.Z., together with Z.K.W., who carried them out and performed data analysis. All authors have given their approval to the final version of the manuscript. Notes

The authors declare no competing financial interest.

■ ■

ACKNOWLEDGMENTS The authors are grateful to Yunfeng Yang, Rui Shi, Guomeng Zhang, and Jun Deng for discussions and assistance. ABBREVIATIONS IMO = International Maritime Organization FGD = flue gas desulfurization L/G = liquid-to-gas ratio eq = equation eqs = equations

■

NOTATION a = specific interface area, m2 m−3 c = concentration, mol L−1 or ppm D = diffusion coefficient, m2 s−1 H = Henry constant, kPa k = film mass transfer coefficient, mol m−2 kPa−1 s−1 or m s−1 M = absorption rate of whole the column, mol s−1 or mol N = mass flux, mol m−2 s−1 N′ = absorption rate per unit volume, mol m−3 s−1 p = pressure, kPa t = time, h V = volume or volumetric flow rate, m3 or m3 h−1 or L h−1 α = constant β = constant Δ = increment δ1 = distance between the interface and reaction surface, m G


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(21) Liu, S. Y.; Nengzi, L. C.; Qiu, W.; Xu, Y. Y.; Liu, J. Y. Process and kinetics of SO2 absorption by carbide slag in spray tower. CIESC J. 2012, 63, 1543.

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Absorption of Sulfur Dioxide with Sodium Hydroxide Solution in Spray

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