Fine particle entrainment in fountain confined conical spouted beds I. Estiati a, ⁎, M. Tellabide a , J.F. Saldarriaga b , H. Altzibar a , M. Olazar a a Department of Chemical Engineering, University of the Basque Country, P.O. Box 644, E48080 Bilbao, Spain b Department of Civil and Environmental Engineering, Universidad de los Andes, Cr. 1 Este 19A-40, Bogotá, Colombia abstract article info Article history: Received 16 May 2018 Received in revised form 25 September 2018 Accepted 5 December 2018 Available online 07 December 2018 Many applications of the conical spouted beds involve operations using coarse and fine particle mixtures, which require high gas velocities due to the coarse particles, thereby leading to fine particle entrainment. In order to avoid entrainment, a new device has been proposed to confine the fountain. Thus, a study has been conducted on the influence the geometry and configuration of both confiner and draft tube have on particle entrainment, operating pressure drop, operating air flow rate and maximum cycle time. The results show that the fountain confiner greatly stabilises the operation and significantly reduces (above 50%) particle entrainment, but its influ- ence on the other parameters is of rather low significance. Furthermore, the distance between the lower end of the device and the bed surface has a great impact on the performance of the spouted bed regime. Entrainment monitoring throughout time showed that its rate depends on the configuration, but remains constant with time. © 2018 Elsevier B.V. All rights reserved. Keywords: Particle entrainment Conical spouted bed Fountain confiner Open-sided draft tube Nonporous draft tube 1. Introduction Conical spouted beds have been successfully used in different appli- cations, such as, combustion [1,2], gasification [3] and pyrolysis [4,5]. Most of these applications require the use of inert materials and/or catalysts for the treatment of waste matter. Therefore, they involve operations using coarse (waste particles) and fine (inert and/or catalyst particles) particle mixtures with very wide particle size distributions, which require rather high gas velocities due to the coarse particles. Therefore, fine particles are entrained from the bed and, in the best case, they should be returned into the bed. Spouted beds may also be used for the treatment of fine or very fine particles using draft tubes to stabilise the bed [6–8]. However, very high fountains are formed when these fine particle beds are treated, with the consequence being particle entrainment from the bed. As a result, this loss of material (catalyst) in- volves high cost, damage on the environment and reduction of the flow rate in the feed, thus minimizing the gas-solid contact [9]. In order to avoid these problems, a modification of the conventional spouted bed re- gime has been proposed by our research group [10]. This modification consists in a new internal device called fountain confiner, which has been developed specifically to avoid fine particle entrainment and stabi- lise the spouted bed regime. The new device has a positive impact on the whole bed hydrodynamics, but especially on the fountain of the conical spouted beds. Furthermore, the insertion of the confiner improves fluid- ization and the efficiency of the conical spouted bed, allowing operation in a wide range of particle sizes, covering A, B and D Geldart particles and particles with highly irregular texture. To our knowledge, no similar device has been reported in the litera- ture to avoid fine particle entrainment and confine the fountain. Thus, cups above the fountain are the more similar devices used to stabilise the bed. Another alternative to improve the spouted performance in chemical reactions has been reported by Hattori and Takeda [11,12], who described a new type of contactor called “side-outlet spouted bed with inner draft tube”. In this configuration, the outlet for both the gas and the solid is located at an intermediate position in the annulus (half-way between the inlet and the bed surface), thereby the residence time of the gas being higher [13] and the gas-solid contact more efficient for solid treatment [11,12]. Other advantages of this system are high gas conversions in first order catalytic reactions and capability for operating with fine particles [12]. Furthermore, different configurations of the side-outlet spouted bed with inner draft tube had been developed in order to overcome the lim- itations and drawbacks of this system [12–14], as are those related to the operation with fragile materials, given that these materials cause blockage of the outlet screen and significant increase in pressure drop. Another serious limitation of all these variants lies in the formation of dead zones with irregular materials. The modifications of the conical spouted bed (regarding the geome- try of the contactor and the gas inlet) allowed improving the capacity of the bed to operate with fine particles, reducing the operating pressure drop, improving the cyclic movement of the particles and attaining sta- ble operation in a wide range of gas velocities [15–17]. In spite of these improvements, the operation with materials like agroforestry wastes and fine particles involves problems related to unstable spouting and particle entrainment. These limitations have been partially overcome with the insertion of draft tubes of different configurations [6–8,18], but the operation with biomass also involves the formation of big Powder Technology 344 (2019) 278–285 ⁎ Corresponding author. E-mail address: idoia.estiati@ehu.es (I. Estiati). https://doi.org/10.1016/j.powtec.2018.12.035 0032-5910/© 2018 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Powder Technology journal homepage: www.elsevier.com/locate/powtec