Skip to content
Licensed Unlicensed Requires Authentication Published by De Gruyter August 13, 2019

The Hydrodynamics Studies on Loop Seal in CFBC Boiler Using CFD Analysis

M. Vivekanandan, N. Anantharaman and M. Premalatha


In a circulating fluidized bed (CFB), the loop seal is an important component which recirculates the solids captured by the cyclone to the bottom of the riser and avoids the direct flow of gas from high-pressure riser to the low-pressure cyclone. Most of the CFBC systems employ a Non-Mechanical valve, and its function has been investigated by many researchers. In this work, the flow of solid particle within the loop seal has been studied elaborately, and various design and operating parameters of the loop seal were analyzed in detail using Computational Fluid Dynamics (CFD). The CFD study has handled a loop-seal of dimension 110 mm × 430 mm × 400 mm high. This analysis has been done with a 200 µm sand particle and it is checked for its flow ability through various sizes and by altering the L/H ratio for three solid mass fluxes and for three L/H ratios of loop seal. The rate of solid mass flux depends on the length of the horizontal passage connecting the recycle cycle compartment of the loop seal with the supply chamber and hence the solid flow rate and the pressure difference per unit length are directly proportional to the length of the chamber or passage. Hence, L/H ratio is taken as a driving variable for the optimum performance of loop seal. The CFD analysis results reveal that the aeration of the solid to be used within the loop-seal should be higher than the Minimum Fluidization velocity. Also, keeping the length of the horizontal passage constant and varying the height of the passage will reduce the pressure drop. The pressure drop across the horizontal passage decreases up to a certain L/H ratio after which it increases. By comparing the three L/H ratios, L/H ratio of 2.62 is having a lesser pressure drop for the three mass fluxes. L/H ratio of 2.62 is having a good fluidization phenomenon and also the flow from the recycle chamber is more in comparison to the other L/H ratios. Experimental data from the literature is in good agreement with the CFD results.


[1] Basu P. Combustion and gasification in fluidized beds, 2006 edn. United States: Taylor & Francis Group, CRC Press, 2006.10.1201/9781420005158Search in Google Scholar

[2] Geldart D, Jones P. The behaviour of L-valves with granular powders. Powder Technol. 1991;67:163–74.10.1016/0032-5910(91)80153-ASearch in Google Scholar

[3] Daous MA, Al-Zahrani AA. Modeling solids and gas flow through an L-valve. Powder Technol. 1998;99:86–9.10.1016/S0032-5910(98)00062-XSearch in Google Scholar

[4] Knowlton TM, Hirsan I. L-valves characterised for solids flow. Hydrocarbon Process. 1978;57:149–56.Search in Google Scholar

[5] Leung LS, Chong YO, Lottes J. Operation of V-valves for gas-solid flow. Powder Technol. 1987;49:271–6.10.1016/0032-5910(87)80136-5Search in Google Scholar

[6] Knowlton TM, Hirsan I. The effect of aeration tap location on the performance of a J-valve. In: Proceedings of Second Engineering Foundation Conference on Fluidization. Cambridge, England, 1978:128–33.Search in Google Scholar

[7] Cheng L, Basu P. Effect of pressure on loop-seal operation for a pressurised circulating fluidized bed. Powder Technol. 1999;103:203–11.10.1016/S0032-5910(99)00018-2Search in Google Scholar

[8] Basu P, Cheng L. An analysis of loop seal operations in a circulating fluidized bed. Trans I Chem E. 2000;78:991–9.10.1205/026387600528102Search in Google Scholar

[9] Yang WC. Modification and re-interpretation of Geldart’s classification of powders. Powder Technol. 2007;171:69–74.10.1016/j.powtec.2006.08.024Search in Google Scholar

[10] Knowlton T. Nonmechanical solids feed and recycle devices for circulating fluidized beds. In: Basu P, Large J, editors. Circulating fluidized bed technology II. Oxford, UK: Pergamon Press, 1988:31–41.10.1016/B978-0-08-036225-0.50008-3Search in Google Scholar

[11] Wang X, Rhodes M, Gibbs B. Solids flux distribution in a CFB riser operating at elevated temperatures. In: Large F, Lagu´erie C, editors. Fluidization VIII. New York, NY, USA: Engineering Foundation, 1996:236–44.Search in Google Scholar

[12] Davidson JF. Circulating fluidised bed hydrodynamics. Powder Technol. 2000;113:249–60.10.1016/S0032-5910(00)00308-9Search in Google Scholar

[13] Tong H, Li H, Lu X, Zheng Q. Hydrodynamic modelling of the L-valve. Powder Technol. 2003;129:8–14.10.1016/S0032-5910(02)00273-5Search in Google Scholar

[14] Gungor A, Eskin N. Effects of operational parameters on emission performance and combustion efficiency in smallscale CFBCs. J Chin Inst Chem Eng. 2008;39:541–56.10.1016/j.jcice.2008.05.007Search in Google Scholar

[15] Armstrong LM, Luo KH, Gu S. Two-dimensional and three-dimensional computational studies of hydrodynamics in the transition from bubbling to circulating fluidised bed. Chem Eng J. 2010;160:239–48.10.1016/j.cej.2010.02.032Search in Google Scholar

[16] Wang X, Wu X, Lei F, Lei J, Xiao Y. 3D full-loop simulation and experimental verification of gas–solid flow hydrodynamics in a dense circulating fluidized bed. Particuology. 2014;16:218–26.10.1016/j.partic.2013.11.010Search in Google Scholar

[17] Zhang N, Bona L, Wang W, Li J. Virtual experimentation through 3D full-loop simulation of a circulating fluidized bed. Particuology. 2008;6:529–39.10.1016/j.partic.2008.07.013Search in Google Scholar

[18] Basu P, Butler J. Studies on the operation of loop-seal in circulating fluidized bed boilers. Appl Energy. 2009;86:1723–31.10.1016/j.apenergy.2008.11.024Search in Google Scholar

[19] Bareschino P, Solimene R, Chirone R, Salatino P. Gas and solid flow patterns in the loop-seal of a circulating fluidized bed. Powder Technol. 2014;S0032-5910:00491–4.10.1016/j.powtec.2014.05.036Search in Google Scholar

[20] Changjin L, Zou Z. A hydrodynamic model of loop seal with a fluidized standpipe for a circulating fluidized bed. Particuology. 2018;36:50–8.10.1016/j.partic.2017.02.005Search in Google Scholar

[21] Kunii D, Levenspiel O. Fluidization engineering, 2nd ed. Boston: Butterworth-Heinemann, 1991.Search in Google Scholar

Received: 2019-02-22
Revised: 2019-06-04
Accepted: 2019-07-06
Published Online: 2019-08-13

© 2019 Walter de Gruyter GmbH, Berlin/Boston