Hydrodynamics of carbon dioxide fluid-particle mixtures are predicted using a low density ratio-based kinetic theory of granular flow in high pressure carbon dioxide fluid fluidized beds. A coexistence of particle waves and particle aggregates exists along bed height. The threshold to identify the occurrence of particle aggregates is suggested based on standard deviation of solid volume fractions in aggregative fluidization. The existence time fractions and frequencies of particle aggregates are predicted along axial direction. The effect of carbon dioxide fluid temperature and pressure on volume fraction and velocity distributions are analyzed at different inlet carbon dioxide velocities and particle densities in high pressure carbon dioxide fluidized beds. Simulated results indicate that the carbon dioxide-particles fluidization transits from particulate to aggregative states with the increase of inlet carbon dioxide velocities. The computed fluid volume fractions and heterogeneity indexes are close to the measurements in a high pressure carbon dioxide fluidized bed.(c) 2022 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.

氧化铝是重要的工业原料,氧化铝工业关系国民命脉。氧化铝焙烧炉是氧化铝制备工艺流程中进行氧化铝焙烧的主要设备,其中流化床氧化铝焙烧炉相较其它炉型具有热效率高、自动化程度高、占地小等优点,已经成为发展的主流趋势。就流化床氧化铝焙烧炉本身而言,目前其采用的燃料多为重油,重油燃烧热效率低、污染大,已经不符合工业发展要求。随着气体燃料的开发普及以及运输成本的降低,其燃料选择也由液体燃料转而向更加清洁高效的高燃值气体燃料方向发展。流化床氧化铝焙烧炉内同时进行着复杂的多相流动,传热和化学反应过程,这些过程相互耦合,通过常规技术手段难以复原炉内流场,分析焙烧过程,给焙烧炉的设计改进增加了难度。因此针对流化床氧化铝焙烧炉,通过数值模拟手段对采用柴油燃料和天然气燃料时炉内焙烧情况进行了探究。以内蒙古地区某厂循环流化床氧化铝焙烧炉为研究对象,建立了几何模型,基于欧拉-欧拉双流体模型模拟炉内多相流动,考虑气固相间换热,辐射换热,建立了炉内热解反应和燃烧反应模型。模拟过程中,将焙烧原料结晶氯化铝和产物氧化铝分别简化为单一粒径,将柴油和天然气的燃烧简化为单一气体组分的燃烧,得到了不同燃料条件下炉内的颗粒浓度分布、颗粒速度分布、气体组分分布、温度分布以及化学反应速率分布等数据,分析了每一种分布的特点以及产生的原因。焙烧过程中,燃料燃烧释放的热量分为两部分给入炉膛。一部分在流化床布风板下方的床下燃烧器内燃烧,加热流化风室内的流化风,由高温流化风将这部分热量送入炉膛,另一部分燃料由布置在炉膛侧墙的床上燃烧器直接给入炉膛,在炉内进行燃烧反应,释放热量。针对采用柴油燃料的焙烧过程,探究了流化床焙烧炉床上床下燃烧器的燃料分配以及循环倍率对床内温度分布、结晶氯化铝热解速率分布等的影响。模拟了采用天然气作为燃料的焙烧过程,得到了炉内颗粒浓度分布、颗粒速度分布、气体组分分布、温度分布以及化学反应速率分布的特点并分析了产生原因。设定了两种燃烧器布置方案,一种由炉膛一面侧墙单侧给入,另一种由炉膛两面侧墙两侧给入,探究了两种方案对焙烧过程的影响,对模拟结果进行了比较分析。

循环流化床锅炉（Circulating Fluidized Bed,CFB）包含多种不同直径和密度的颗粒,不同物性颗粒具有不同的流化和化学反应特性,进而影响循环流化床反应器的性能,优化设计与运行控制,因而亟待需要进行不同物性颗粒的流动动力特性和化学反应过程的研究与分析。本文采用四种不同的颗粒,它们分别是:床料颗粒,粗煤颗粒,细煤颗粒和回料颗粒,其中给煤颗粒（粗/细）和回料颗粒分别通过进料口和回料口输送。采用多组分颗粒动力学理论,用仿真软件模拟了多组分颗粒情况下循环流化床的流动特性,得到了复杂气固流动的主要特征:各组分颗粒的瞬时云图分布,各组分颗粒的浓度和速度时均分布,各组分颗粒的颗粒拟温度分布等。此外,还探究了镜面反射系数和表观速度对各组分颗粒流动特性的影响。在探究富氧燃烧过程中,首先对中试规模的循环流化床燃烧室进行了模型验证,通过比较炉膛内温度场分布和炉膛出口处气体成分的体积浓度,发现数值仿真结果与实验结果比较吻合,验证了模型的有效性与正确性。接着在已验证化学反应理论的基础上,建立二维的双组份颗粒循环流化床锅炉内煤燃烧的数学模型,探究了空气燃烧模式和富氧燃烧模式下原煤的燃烧特性。煤燃烧过程中的化学反应主要考虑水分蒸发,挥发分热解,热解气态产物氧化,焦炭氧化和气化以及污染物的形成。利用该模型详细分析了流体动力学,温度场分布,化学反应速率分布,气体组分分布,以及炉膛出口处主要气体组分的体积浓度和污染物的排放。通过空气燃烧模式下和富氧燃烧模式下原煤燃烧特性的比较,说明富氧燃烧在CO2捕获和污染物排放方面具有独特优势。此外,还探究了富氧燃烧模式下,不同O2浓度对循环流化床整体性能的影响,成功预测了煤在高氧气浓度下的燃烧过程。

To deduce and analyze the hydrodynamics of molten salt fluid and particles, computational simulations were performed using a low density ratio kinetic theory of granular flow with two-fluid model in a flu-idized bed. Two types of transition fluidization of molten salt fluid-particle mixtures were found in the fluidized bed. One represented the coexistence of wave-like flow at the bottom regime and large scale turbulent regime with chunk-like flow at the bed upper. The other characterized the coexistence of par-ticulate fluidization near the bottom regime and particle aggregations at the upper part along bed height. The molten salt fluid-particle mixtures transited from particulate fluidization to transition state with increasing molten salt fluid temperatures, inlet fluid velocities and particle diameters and densities. The computed expansion heights and fluid volume fractions agreed with measured data in a water -particles fluidized bed.(c) 2022 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.

The molten salt fluid-particles transition state is modelled using KTGF-based TFM and CFD-DEM in fluidized beds. The solid phase constitutive equations are modelled using a low density ratio KTGF model. The normal and tangential forces of discrete particles are simulated using CFD-DEM. Two-equation model is used to characterize molten salt fluid turbulence. Wavy-like flow near the bottom and aggregates/fluid voids flow at the upper part coexist along bed height. The molten salt fluid pressure drops and dominant frequencies of wavy-like flow using TFM agree with simulated results using CFD-DEM. The simulated transition state from TFM and CFD-DEM co-incides with predictions using four different criteria in literature. The effect of molten salt temperature on normal and tangential Reynolds stresses is discussed. The predicted expansion height and water volume fractions using TFM and CFD-DEM agree with experimental data in an ambient water fluidized bed.

Hydrodynamics of sub- and super-critical ethanol fluid and particles were simulated using a low density ratio kinetic theory of granular flow in fluidized beds. The coexistence of a wave-like flow near the bottom and chunk-like flow at the upper part was observed in subcritical ethanol fluidized beds. During the fluidization of supercritical ethanol fluid-particle mixtures, aggregate-like structures of particles were found with increasing ethanol fluid temperatures and decreasing ethanol fluid pressures in supercritical ethanol fluidized beds. The simulated fluidization states identified reasonably with predictions using three different dimensionless numbers and stability function according to kinematic wave and dynamic wave velocities. The predicted bed expansion heights agreed with experimental data in supercritical carbon dioxide fluidized beds. (c) 2022 Elsevier Ltd. All rights reserved.

Fluidization of fluid-particles suspension is simulated using two-fluid model (TFM) and discrete element method (DEM) according to the open source code MFIX-DEM and MFIX-TFM with a low density ratio-based kinetic theory of granular flow (KTGF) in sub-and super-critical water fluidized beds (FB). Both approaches illustrate that a transition fluidization state with wavy-like flow near the bottom and churn-like flow at the upper parts is behaved in subcritical water FB, unlike aggregative fluidization in supercritical water FB. The fluidization is evaluated using three different dimensionless numbers and stability function. Quantitatively, the difference in solid volume fractions, fluid Reynolds stresses and dominant frequencies of volume fraction fluctuations exist between MFIX-DEM and low density ratio KTGF-based TFM in sub-and super-critical water FBs. The simulated fluid volume fractions and expansion heights using a low density ratio KTGF-based TFM agree well with the experimental data in an ambient water FB.

Hydrodynamics of fluid and particles were simulated using a low density ratio-based kinetic theory of granular flow (KTGF) in supercritical methanol (ScM) fluidized beds (FB). Results indicated that the fluidization state of the methanol fluid and particle mixtures change progressively from particulate to aggregative fluidization. A transition exists with wavy-like flows near the bottom and churn-like flows at the upper part along bed height, unlike the homogeneous fluidization in atmospheric methanol fluid FB and turbulent fluidization regime with particle strands in ScM FB. The threshold to identify the occurrence of strands was proposed in terms of mean value and standard deviation of solid volume fractions. The frequencies of particle strands increased with increasing methanol fluid temperatures and pressures. The computed fluid volume fractions agreed with experimental data in a supercritical carbon dioxide fluid fluidized bed.

The knowledge of pulsation active method is essential for reliable regulation of particle clusters in pulsating fluidized bed risers. This study presents a comparison of the computed occurrence of particle clusters using a computational criterion in an inlet gas pulsation-assisted riser. The occurrence of clusters is identified according to the minimum rate of energy dissipations using dynamic cluster structure dependent drag model. The influences of inlet gas velocity, frequency and amplitude on cluster characteristics are analyzed along lateral and axial directions. The cluster diameters and existence time fractions as well as the gas volume fractions of the dense phase vary with changing inlet gas velocity frequencies and amplitudes when compared to a constant inlet gas velocity. The particle cluster number is reduced from a large fraction at a constant inlet gas velocity to a low fraction in an inlet gas pulsation assisted fluidized bed risers.CO 2021 Elsevier Ltd. All rights reserved.