Desulfurization characteristics of slaked lime and regulation optimization of circulating fluidized bed flue gas desulfurization process—A combined experimental and numerical simulation study

doi:10.1016/j.cjche.2024.05.017

Abstract

Abstract: Circulating fluidized bed flue gas desulfurization (CFB-FGD) process has been widely applied in recent years. However, high cost caused by the use of high-quality slaked lime and difficult operation due to the complex flow field are two issues which have received great attention. Accordingly, a laboratory-scale fluidized bed reactor was constructed to investigate the effects of physical properties and external conditions on desulfurization performance of slaked lime, and the conclusions were tried out in an industrial-scale CFB-FGD tower. After that, a numerical model of the tower was established based on computational particle fluid dynamics (CPFD) and two-film theory. After comparison and validation with actual operation data, the effects of operating parameters on gas-solid distribution and desulfurization characteristics were investigated. The results of experiments and industrial trials showed that the use of slaked lime with a calcium hydroxide content of approximately 80% and particle size greater than 40 μm could significantly reduce the cost of desulfurizer. Simulation results showed that the flow field in the desulfurization tower was skewed under the influence of circulating ash. We obtained optimal operating conditions of 7.5 kg·s^-1 for the atomized water flow, 70 kg·s^-1 for circulating ash flow, and 0.56 kg·s^-1 for slaked lime flow, with desulfurization efficiency reaching 98.19% and the exit flue gas meeting the ultraclean emission and safety requirements. All parameters selected in the simulation were based on engineering examples and had certain application reference significance.

Key words: Circulating fluidized bed flue gas desulfurization (CFB-FGD), Desulfurization characteristics, Computational particle fluid dynamics (CPFD) numerical simulation, Operational optimization, Gas-solid flow

摘要： Circulating fluidized bed flue gas desulfurization (CFB-FGD) process has been widely applied in recent years. However, high cost caused by the use of high-quality slaked lime and difficult operation due to the complex flow field are two issues which have received great attention. Accordingly, a laboratory-scale fluidized bed reactor was constructed to investigate the effects of physical properties and external conditions on desulfurization performance of slaked lime, and the conclusions were tried out in an industrial-scale CFB-FGD tower. After that, a numerical model of the tower was established based on computational particle fluid dynamics (CPFD) and two-film theory. After comparison and validation with actual operation data, the effects of operating parameters on gas-solid distribution and desulfurization characteristics were investigated. The results of experiments and industrial trials showed that the use of slaked lime with a calcium hydroxide content of approximately 80% and particle size greater than 40 μm could significantly reduce the cost of desulfurizer. Simulation results showed that the flow field in the desulfurization tower was skewed under the influence of circulating ash. We obtained optimal operating conditions of 7.5 kg·s^-1 for the atomized water flow, 70 kg·s^-1 for circulating ash flow, and 0.56 kg·s^-1 for slaked lime flow, with desulfurization efficiency reaching 98.19% and the exit flue gas meeting the ultraclean emission and safety requirements. All parameters selected in the simulation were based on engineering examples and had certain application reference significance.

关键词: Circulating fluidized bed flue gas desulfurization (CFB-FGD), Desulfurization characteristics, Computational particle fluid dynamics (CPFD) numerical simulation, Operational optimization, Gas-solid flow

Jing Chen, Wenqi Zhong, Guanwen Zhou, Jinming Li, Shasha Ding. Desulfurization characteristics of slaked lime and regulation optimization of circulating fluidized bed flue gas desulfurization process—A combined experimental and numerical simulation study[J]. Chinese Journal of Chemical Engineering, 2024, 73(9): 163-175.

References

[1] X.K. Li, J.R. Han, Y. Liu, Z.H. Dou, T.A. Zhang, Summary of research progress on industrial flue gas desulfurization technology, Sep. Purif. Technol. 281 (2022) 119849.
[2] T.F. Zhang, Q. Tang, C. Pu, L. Zhang, Numerical simulation of gas-droplets mixing and spray evaporation in rotary spray desulfurization tower, Adv. Powder Technol. 33 (2) (2022) 103420.
[3] G. Cheng, C.X. Zhang, Desulfurization and denitrification technologies of coal fired flue gas, Pol. J. Environ. Stud. 27 (2) (2018) 481-489.
[4] T. Nakazato, Y.Y. Liu, K. Kato, Removal of SO₂ in semi-dry flue gas desulfurization process with a powder-particle spouted bed, Can. J. Chem. Eng. 82 (2008) 110-115.
[5] Q.M. Guo, I. Noriaki, K. Kato, Process development of effective semi-dry flue gas desulfurization by powder-particle spouted bed, Kagaku Kogaku Ronbunshu 22 (6) (1996) 1400-1407.
[6] X. Ma, T. Kaneko, G. Xu, K. Kato, Influence of gas components on removal of SO₂ from flue gas in the semidry FGD process with a powder-particle spouted bed, Fuel 80 (5) (2001) 673-680.
[7] X.X. Ma, T. Kaneko, T. Tashimo, T. Yoshida, K. Kato, Use of limestone for SO₂ removal from flue gas in the semidry FGD process with a powder-particle spouted bed, Chem. Eng. Sci. 55 (20) (2000) 4643-4652.
[8] X. Wang, Y.J. Li, W. Zhang, J.L. Zhao, Z.Y. Wang, Simultaneous SO₂ and NO removal by pellets made of carbide slag and coal char in a bubbling fluidized-bed reactor, Process. Saf. Environ. Prot. 134 (2020) 83-94.
[9] Y. Zhao, P.Y. Xu, X.J. Sun, L.D. Wang, Experimental and mechanism studies on simultaneous desulfurization and denitrification from flue gas using a flue gas circulating fluidized bed, Sci. China Ser. B Chem. 50 (1) (2007) 135-144.
[10] Z.H. Meng, C.Y. Wang, X.R. Wang, Y. Chen, H.Q. Li, Simultaneous removal of SO₂ and NOx from coal-fired flue gas using steel slag slurry, Energy Fuels 32 (2) (2018) 2028-2036.
[11] J.E. Jeong, I.A. Cho, C.Y. Lee, Desulfurization characteristics of limestone slurry with added organic acid, Fuel 336 (2023) 126859.
[12] D. Xie, C.F. You, Q.X. Liu, Experimental study on in situ preparation of supported sorbent for moderate temperature CFB-FGD, Energy Fuels 32 (3) (2018) 3690-3696.
[13] M.I. Ortiz, A. Garea, A. Irabien, F. Cortabitarte, Flue gas desulfurization at low temperatures. Characterization of the structural changes in the solid sorbent, Powder Technol. 75 (2) (1993) 167-172.
[14] Y.P. Fan, C. Li, H.W. Fan, M. Yu, C.X. Lu, Core-annulus radial solids concentration distribution in riser, Chem. Eng. Sci. 192 (2018) 318-334.
[15] M. Nikku, A. Daikeler, A. Stroh, K. Myohanen, Comparison of solid phase closure models in Eulerian-Eulerian simulations of a circulating fluidized bed riser, Chem. Eng. Sci. 195 (2019) 39-50.
[16] P. Ostermeier, S. DeYoung, A. Vandersickel, S. Gleis, H. Spliethoff, Comprehensive investigation and comparison of TFM, DenseDPM and CFD-DEM for dense fluidized beds, Chem. Eng. Sci. 196 (2019) 291-309.
[17] L. Lerotholi, R.C. Everson, L. Koech, H.W.J.P. Neomagus, H.L. Rutto, D. Branken, B.B. Hattingh, P. Sukdeo, Semi-dry flue gas desulphurization in spray towers: A critical review of applicable models for computational fluid dynamics analysis, Clean Technol. Environ. Policy 24 (7) (2022) 2011-2060.
[18] C.Y. Chu, S.J. Hwang, Flue gas desulfurization in an internally circulating fluidized bed reactor, Powder Technol. 154 (1) (2005) 14-23.
[19] Q. Tang, Q. Wang, P.F. Cui, W.W. Cao, S.F. Hou, Numerical simulation of flue gas desulfurization characteristics in CFB with bypass ducts, Process. Saf. Environ. Prot. 91 (5) (2013) 386-390.
[20] X.W. Hao, C.Y. Ma, Y. Dong, J.G. Yang, Composite fluidization in a circulating fluidized bed for flue gas desulfurization, Powder Technol. 215 (2012) 46-53.
[21] G.P. Wu, Y. He, L. Luo, W. Chen, Dynamic characterizations of gas-solid flow in a novel multistage fluidized bed via nonlinear analyses, Chem. Eng. J. 359 (2019) 1013-1023.
[22] G.P. Wu, W. Chen, Y. He, Investigation on gas-solid flow behavior in a multistage fluidized bed by using numerical simulation, Powder Technol. 364 (2020) 251-263.
[23] J.L. Du, K. Yue, F. Wu, X.X. Ma, Z.Q. Hui, Numerical investigation on the water vaporization during semi dry flue gas desulfurization in a three-dimensional spouted bed, Powder Technol. 383 (2021) 471-483.
[24] M.M. Hong, G.L. Xu, P. Lu, F.H. Chen, G.W. Sheng, Q. Zhang, Numerical simulation on gas-droplet flow characteristics and spray evaporation process in CFB-FGD tower, Adv. Powder Technol. 34 (5) (2023) 104008.
[25] S. Wang, F. Wu, B.B. Di, Y. Yan, Y.C. Tang, Intensification effect of a multi-jet structure on a multiphase flow and desulfurization process in a fluidized bed, ACS Omega 8 (6) (2023) 5861-5876.
[26] L.T. Fan, F.L. Wang, H.R. Li, D.K. He, Modeling of a circulating fluidized bed for flue gas desulfurization process, 2010 Chinese Control and Decision Conference. Xuzhou, IEEE, 2010, pp. 2444-2448.
[27] P. Liu, X. Wu, Z.Y. Wang, Y.X. Bo, H.R. Bao, Numerical simulation study on gas-solid flow characteristics and SO₂ removal characteristics in circulating fluidized bed desulfurization tower, Chem. Eng. Process. Process. Intensif. 176 (2022) 108974.
[28] X. Wang, Y.J. Li, T.Y. Zhu, P.F. Jing, J.S. Wang, Simulation of the heterogeneous semi-dry flue gas desulfurization in a pilot CFB riser using the two-fluid model, Chem. Eng. J. 264 (2015) 479-486.
[29] Y. Yan, X.F. Peng, B.X. Wang, Investigation on the transport process of flue gas desulfurization in a circulating fluidized bed, Int. Commun. Heat Mass Transf. 30 (1) (2003) 71-82.
[30] L. Cai, Z.Y. Xu, X.R. Wang, H.C. Bai, L.C. Han, Y.F. Zhou, Numerical simulation and optimization of semi-dry flue gas desulfurization in a CFB based on the two-film theory using response surface methodology, Powder Technol. 401 (2022) 117268.
[31] X.L. Huang, X.L. Jin, L.X. Dong, R.Y. Li, K.X. Yang, Y.H. Li, L. Deng, D.F. Che, CPFD numerical study on tri-combustion characteristics of coal, biomass and oil sludge in a circulating fluidized bed boiler, J. Energy Inst. 113 (2024) 101550.
[32] B.H. Lee, Y.H. Bae, K.M. Kim, Y. Jiang, Y.H. Ahn, C.H. Jeon, Application of the CPFD method to analyze the effects of bed material density on gas-particle hydrodynamics and wall erosion in a CFB boiler, Fuel 342 (2023) 127878.
[33] J. Chang, X.R. Ma, X. Wang, X.H. Li, CPFD modeling of hydrodynamics, combustion and NOx emissions in an industrial CFB boiler, Particuology 81 (2023) 174-188.
[34] J.R. Grace, Contacting modes and behaviour classification of gas-solid and other two-phase suspensions, Can. J. Chem. Eng. 64 (3) (1986) 353-363.
[35] M. Tao, B.S. Jin, W.Q. Zhong, Y.P. Yang, R. Xiao, Modeling and experimental study on multi-level humidifying of the underfeed circulating spouted bed for flue gas desulfurization, Powder Technol. 198 (1) (2010) 93-100.
[36] F. Ruhland, R. Kind, S. Weiss, The kinetics of the absorption of sulfur dioxide in calcium hydroxide suspensions, Chem. Eng. Sci. 46 (4) (1991) 939-947.
[37] J. Klingspor, A.M. Stromberg, H.T. Karlsson, I. Bjerle, Similarities between lime and limestone in wet-dry scrubbing, Chem. Eng. Process. Process. Intensif. 18 (5) (1984) 239-247.
[38] J.Y. Qu, N.N. Qi, Z. Li, K. Zhang, P.C. Wang, L.F. Li, Mass transfer process intensification for SO₂ absorption in a commercial-scale wet flue gas desulfurization scrubber, Chem. Eng. Process. Process. Intensif. 166 (2021) 108478.
[39] E.N. Fuller, P.D. Schettler, J.C. Giddings, New method for prediction of binary gas-phase diffusion coefficients, Ind. Eng. Chem. 58 (5) (1966) 18-27.
[40] C.T. Hsu, S.M. Shih, Semiempirical equation for liquid-phase mass-transfer coefficient for drops, AIChE. J. 39 (6) (1993) 1090-1092.
[41] G.H. Newton, J. Kramlich, R. Payne, Modeling the SO₂-slurry droplet reaction, AIChE. J. 36 (12) (1990) 1865-1872.
[42] H.P. Liu, J.W. Li, Q. Wang, Simulation of gas-solid flow characteristics in a circulating fluidized bed based on a computational particle fluid dynamics model, Powder Technol. 321 (2017) 132-142.
[43] Y.G. Zhou, J. Peng, X. Zhu, M.C. Zhang, Hydrodynamics of gas-solid flow in the circulating fluidized bed reactor for dry flue gas desulfurization, Powder Technol. 205 (1-3) (2011) 208-216.