416382 Flow Patterns in High-Density Circulating Fluidized Beds

Wednesday, November 11, 2015: 3:45 PM
254B (Salt Palace Convention Center)
Timo Hensler and Karl-Ernst Wirth, Institute of Particle Technology, University of Erlangen-Nuremberg, Erlangen, Germany


T. Hensler1,x, K.-E. Wirth1,*

1 Institute of Particle Technology, University of Erlangen-Nuremberg, D-91058 Erlangen, Germany

x Presenting author: Timo Hensler, Cauerstr. 4, D-91058 Erlangen, Germany, e‑mail: timo.hensler@fau.de, phone: +49/9131/85-28291, fax: +49/9131/85-29402

* Corresponding author: Prof. Dr.‑Ing. habil. KarlErnst Wirth, Cauerstr. 4, D-91058 Erlangen, Germany, e‑mail: karl-ernst.wirth@fau.de, phone: +49/9131/85-29403, fax: +49/9131/85-29402

KEYWORDS:                         Circulating fluidized bed, high-density riser, multi-phase flow, fluid‑solid interaction, solids distribution, X-ray computer tomography, residence time behavior, tracer gas, capacitance probe, state diagram


SCIENTIFIC FIELD:               Particle Technology Forum


The presented work deals with the investigation of flow patterns in a high-density gas‑solid circulating fluidized bed riser in pilot plant scale. Circulating fluidized beds provide excellent conditions for gas-solid reactions due to intense contacting of the reactants. In order to intensify the interaction of the reacting phases, investigations have focused on the maximization of the solids holdup in the reaction zone within the past two decades [ISSANGYA 1999]. Recent results show that solid concentrations up to 30 vol.% [WANG 2014, HENSLER 2014] can be achieved in the riser section of high-density circulating fluidized beds. Even though high-density risers offer good prospects for exceedingly efficient operation of future processes, their implementation and stable handling of the desired flow condition remains challenging. In order to gain detailed insight into the flow behavior of the gas and the solid phase within high-density risers, fluid-dynamic investigations are performed in a pilot plant scale cold‑flow circulating fluidized bed riser with an inner diameter of 190 mm and a height of 11.3 m. Within the scope of the measurements the solids holdup within the riser is varied in the range from 3 to 35 vol.% and superficial gas velocities range from 3.3 to 11.5 m s-1. Experimental investigations focus on the characterization of flow patterns in the riser section with regard to both the solid and the fluid phase. For determination of the distribution of the solids over the cross section of the riser, the plant is equipped with a 160 kV X‑ray computer tomography system. This allows for non-invasive scanning of the riser cross section, by which the time averaged distribution of particles is derived with high spatial resolution. Moreover the motion of particle clusters is investigated using capacitance probes. In this way radial velocity profiles of particle clusters are derived under various flow conditions. The behavior of the fluid phase is investigated by the injection of a tracer gas. By tracking the distribution of the tracer gas in axial and radial direction of the riser, the residence time behavior of the gas as well as the coefficient of axial dispersion is determined. Based on the experimental findings the investigated flow conditions are categorized according to the dense suspension upflow model proposed by Grace et al. [GRACE 1999] and Wirth's steady state diagram of vertical multi-phase flow [WIRTH 1991]. Subsequently both models are compared to identify analogies. The gained insight into the flow structures of high-density risers provides valuable information for the design of multiphase reactors for fast catalytic reactions. Moreover, the results allow for drawing conclusions on the interaction of the fluid and the solids phase in vertical upflow and thus provide a strong basis for the optimization of multi-phase simulations.

GRACE J. R., ISSANGYA A. S., BAI D., BI H., (1999), Situating the High-Density Circulating Fluidized Bed, AIChE Journal, 45, 2108-2116

HENSLER T., ZHANG Y., MLECZKO L., ASSMANN J., BELLINGHAUSEN R., SCHWIEGER W., WIRTH K.-E., (2014), High-Density Risers as Reactor System for Benzene Synthesis by Non-oxidative Dehydroaromatization of Methane, Proceedings of the 11th International Conference on Fluidized Bed Technology, Chemical Industry Press, 155-160

ISSANGYA A. S., BAI D., BI H. T., LIM K. S., ZHU J., GRACE J. R., (1999), Suspension Densities in a High-density Circulating Fluidized Bed Riser, Chem. Eng. Sci., 54, 5451-5460

WANG C., ZHU J., Li C., BARGHI S., (2014), Detailed Measurements of Particle Velocity and Solids Flux in a High Density Circulating Fluidized Bed Riser, Chem. Eng. Sci., 114, 9-20

WIRTH K.-E., (1991), Fluid Mechanics of Circulating Fluidized Beds, Chem. Eng. Technol., 14, 29-38

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