A NEW SCALING STRATEGY OF BUBBLING FLUIDIZED BED REACTORS BASED ON POPULATION-BALANCE MODEL

This work proposes a new strategy for the scaling of bubbling fluidized bed reactors. This strategy is based on the bubble size distribution, bubble coalescence phenomenon, and the chemical reactivity, allowing to deduct the dimensionless number Chejne-Macias-Maya that must remain constant at different scales to guarantee the fluidization regime. The proposed strategy is validated from computational simulations carried out at different operating conditions. Additionally, limits for the validity of this scaling strategy were determined, which agrees with those reported in the literature.

Granular Stack Density’s Influence on Homogeneous Fluidization Regime: Numerical Study Based on EDEM-CFD Coupling

FLUENT and EDEM were applied to simulate liquid–solid coupling in a 3D homogenous fluidization. The dynamics of destabilization of the granular material immersed by homogeneous fluidization were observed. The effect of initial packing density of granular stack and fluidization rate on the fluidization’s transient regime, the configuration of particles in the fluidized bed and the variation of bed height were analyzed and discussed. According to the results, there was an original observation of a strong impact of the initial density of an initially static granular stack on the transient fluidization regime. Depending on the material initial volume fraction, there was a difference in grain dynamics. For an initially loose stack, a homogeneous turbulent fluidization was observed, whereas for an initially dense stack, there was a mass takeoff of the stack. The propagation of wave porosity instability, from the bottom to the top of the stack with fast kinetics that decompacted the medium, followed this mass takeoff.

OPERATIONAL INFLUENCE OF THE MONO-CHAMBER AERATION MODE IN THE LOOP SEAL OF A CIRCULATING FLUIDIZED BED

Fluidization numbers varying from 0.84 to 1.68 were used in the loop seal valve of a bench-scale circulating fluidized bed (CFB) system to analyze the influence of the mono-chamber aeration mode on both the solids circulation rate and the static pressure drop inside the solids recycle device. Runs were carried out using 4 kg of overall solids inventory and particles of 183 µm in Sauter mean diameter, which were kept under fast fluidization regime at superficial gas velocity of 4 m/s. Results showed that the choice of the chamber to be aerated can noticeably affect the gas-solid hydrodynamics. In this sense, the analysis of variance applied on the experimental data indicated that the aeration into the recycle chamber of the loop seal offers lower levels of solids circulation rate but also allows to control it within a wider range of fluidization numbers and with less pressure drop or energy demand.

Systematic Study of Pressure Fluctuation in the Riser of a Dual Inter-Connected Circulating Fluidized Bed: Using Single and Binary Particle Species

This study systematically investigates the pressure fluctuation in the riser of a dual interconnected circulating fluidized bed (CFB) representing a 10 kWth cold-flow model (CFM) of a chemical-looping combustion (CLC) system. Specifically, a single-species system (SSS) and a binary-mixtures system (BMS) of particles with different sizes and densities were utilized. The pressure fluctuation was analyzed using the fast Fourier transform (FFT) method. The effect of introducing a second particle, changing the inventory, composition (i.e., 5, 10 to 20 wt.%), particle size ratio, and fluidization velocity were investigated. For typical SSS experiments, the results were similar to those scarcely reported in the literature, where the pressure fluctuation intensity was influenced by varying the initial operating conditions. The pressure fluctuations of BMS were investigated in detail and compared with those obtained from SSS experiments. BMS exhibited different behaviour; it had intense pressure fluctuation in the air reactor and in the riser when compared to SSS experiments. The standard deviation (SD) of the pressure fluctuation was found to be influenced by the fluidization regime and initial operating conditions, while the power spectrum density (PSD) values were more sensitive to the presence of the particles with the higher terminal velocity in the binary mixture.

Design of a Fast Internal Circulating Fluidized-Bed Gasifier with a conical bed angle

The main purpose of a fast internal circulating fluidized bed gasifier is the steam reforming of solid organic matter, like biomass, to a nearly nitrogen-free syngas. The calorific value of this syngas is approximately three times higher than the gas from common air-driven gasifiers. This article deals with a study of the particle dynamics in a 1 MWt fast internal circulating fluidized bed plant and focuses on the design of the gasification reactor?s geometry. Superheated steam is used for the fluidization and gasification in the reactor. The gasification of solid fuels causes an increase in the volume flow of the fluidizing gas and at the same time also a change in the fluidization regime. Approaching a turbulent fluidization regime or even fast fluidization is not desirable. However, with the proper design of reactor, i. e., an appropriately conical bed angle, suitable gasification conditions in the form of a fluidizing regime can be achieved across the entire height of the bed. For the purposes of the experimental research, a semi-industrial unit was set-up. The process was designed and experimentally tested on a lab-scale, cold-flow model and scaled-up to a semi-industrial process. The guidelines for designing the geometry of the gasification reactor were set.

Discussions on Particle Flux Measurement in Gas-Solids Risers

In gas-solids risers of fast fluidization regime, the gross particle flux determined by integrating the product of the measured average particle concentration and velocity is always found several times or even larger than that measured by direct experimental methods. Based on analysis of the measurement mechanisms and a simple model for two-phase flow structure in gas-solids risers, this big unidirectional deviation is first explained in depth in this study. It is concluded that the unique two-phase flow structure (i.e. the low-velocity dense phase and high-velocity dilute phase in a gas-solids riser) and the bad coupling quality of the measured transient particle concentration and velocity during data processing lead to this big unidirectional deviation. Finally, this explanation is extended to wider multiphase flow systems and advices are proposed in measuring phase fluxes.