Three-dimensional CFD simulation and experimental validation of particle segregation in CFB riser
INTERNATIONAL JOURNAL OF NUMERICAL METHODS FOR HEAT & FLUID FLOW
Authors: Dwivedi, Krishna Kant; Pramanick, Achintya Kumar; Karmakar, Malay Kumar; Chatterjee, Pradip Kumar
Abstract
Purpose The purpose of this paper is to perform the computational fluid dynamics (CFD) simulation with experimental validation to investigate the particle segregation effect in abrupt and smooth shapes circulating fluidized bed (CFB) risers. Design/methodology/approach The experimental investigations were carried out in lab-scale CFB systems and the CFD simulations were performed by using commercial software BARRACUDA. Special attention was paid to investigate the gas-particle flow behavior at the top of the riser with three different superficial velocities, namely, 4, 6 and 7.7 m/s. Here, a CFD-based noble simulation approach called multi-phase particle in cell (MP-PIC) was used to investigate the effect of traditional drag models (Wen-Yu, Ergun, Wen-Yu-Ergun and Richardson-Davidson-Harrison) on particle flow characteristics in CFB riser. Findings Findings from the experimentations revealed that the increase in gas velocity leads to decrease the mixing index inside the riser. Moreover, the solid holdup found more in abrupt riser than smooth riser at the constant gas velocity. Despite the more experimental investigations, the findings with CFD simulations revealed that the MP-PIC approach, which was combined with different drag models could be more effective for the practical (industrial) design of CFB riser. Well agreement was found between the simulation and experimental outputs. The simulation work was compared with experimental data, which shows the good agreement (<4%). Originality/value The experimental and simulation study performed in this research study constitutes an easy-to-use with different drag coefficient. The proposed MP-PIC model is more effective for large particles fluidized bed, which can be helpful for further research on industrial gas-particle fluidized bed reactors. This study is expected to give throughout the analysis of CFB hydrodynamics with further exploration of overall fluidization.
CFB combustion of low-grade lignites: Operating stability and emissions
JOURNAL OF THE ENERGY INSTITUTE
Authors: Engin, Berrin; Atakul, Husnu; Unlu, Alper; Olgun, Zeki
Abstract
This work presents the results of a comprehensive experimental investigation on the combustion of the low grade Turkish lignites in a 30 kW(th) circulating fluidized bed combustor. This is the first study of this kind has ever been undertaken on these coals. Eighteen lignite samples procured from various lignite sites of Turkey have been burned under similar combustion conditions in order to access to their combustion stability and to determine the emissions of the major pollutants such as CO, NOx and SO2 in the flue gas from combustor. The qualities of lignites were evaluated based on van Krevelen graph which was highly scattered and diverse in respect to the degree of ageing. A steady and stable combustion was observed in the temperature range of 725-950 degrees C with an average operating temperature of around 850 +/- 50 degrees C for all lignites. Under the operating condition applied in the study, CO, NOx and SO2 emissions varied mostly in the ranges of 120-600 mg/Nm(3), 90-420 mg/Nm(3) and 1100 mg/Nm(3) 18000 mg/Nm(3), respectively. From the experimental results it seems that the most challenging problem may be faced during the CFB combustion of most of these lignites will be SO2 emissions. (C) 2018 Energy Institute. Published by Elsevier Ltd. All rights reserved.