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Ende pulverized coal gasifier (EPCG), as a typical representative of circulating fluidized bed gasifier, has been widely used in gasification field. The return conduit of EPCG is generally not equipped with a feedback control device (FCD), which tends to result in a low solid circulation rate (Gs) and high unburned combustibles in fly ash. To address these issues, a new technique using the ejector as the FCD was designed to provide a stable pressure barrier and improve solid circulation. Preliminary thermal experiments demonstrated the feasibility of improving the EPCG with injector system. Currently, the specific mechanisms that contribute to further optimize this technology have not been systematically studied. Considering the large impact of ejector operation on solid circulation rate and stability as well as syngas production, this work adopts a gas/particle 1:15 cold EPCG bench to investigate the gas/particle flow and pressure variation characteristics before and after ejector operation and under different working medium pressures (Pp). When the ejector operates at the design pressure Ps = 0.187 MPa, the outlet pressure of the return conduit is slightly larger than the furnace bottom pressure, thus preventing the reverse gas flow at the furnace bottom. The particle velocity and concentration distribution in the furnace are basically consistent with that without the ejector, showing a similar central spout region and near‐wall annulus flow region. As Pp increases from 0.04 to 0.24 MPa, the average particle velocity in the return conduit increases from 0.95 to 2.4 m/s, the particle concentration decreases from 0.088 to 0.051, and the solid circulation rate increases from 0.37 to 0.53 kg/h. The ejector outlet pressure gradually increases, the inlet pressure decreases, and the pressure barrier provided by the ejector rises from 1052 to 3640 Pa. When Pp is 0.12 MPa, the ratio of GN2/Gair is 0.91%, which can achieve the purpose of continuous and stable pressurization with a small amount of nitrogen. [ABSTRACT FROM AUTHOR]

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Gas–solid fluidized beds are commonly used in applications where high heat and mass transfer is required, which are influenced by the quality of mixing in the bed. This largely depends on the design of gas distributor and operating conditions. Hence, in the current work, the influence of distributor design on hydrodynamics in a 3D bubbling fluidized bed column is investigated using CFD. Here, Euler-Euler model is used to predict the flow field. The predicted bed pressure drop is analyzed for various superficial gas velocities, and it has been validated with the experimental data. The solid circulation rate is calculated to quantify the flow field, and it is improved by incorporating various gas distributors such as flat, convex and concave perforated plates. The magnitude of solid circulation rate is found to be the highest for convex plate, showing that it is more advantageous than the conventional flat plate configuration. Further, the effect of operating temperature and the influence of baffle on gas–solid flow are analyzed. The rate of solid circulation is found to decrease with increase in temperature and in the presence of baffle. [ABSTRACT FROM AUTHOR]

Effects of attrition of bed material on the solid circulation rate in a recirculating fluidized bed (RCFB) were studied in detail. Effects of different operating and design parameters such as operation time, superficial velocity, bed inventory, particle size, and spacing between jet top and draft tube bottom on the solid circulation rate in terms of attrition were studied. A mathematical model was developed on the basis of experimental results to identify the effects of attrition of bed particles on the solid circulation rate incorporating the effects of the various operating and design parameters. To develop the model, dimensional analysis and nonlinear regression were used. The model equation was a nonlinear equation, which implies a relationship between the solid circulation rate and other operating and design parameters. The model equation can estimate the solid circulation rate over a range of operation time and other parameters. Decrease in solid circulation rate can be predicted with increasing operation time, using the model equation. [ABSTRACT FROM AUTHOR]

Effect of bed geometry on the hydrodynamics of slot-rectangular spouted beds was studied by means of CFD-DEM simulations. Axial and lateral velocity distributions of particles as well as axial gas velocity distribution were used for validation of the simulation with experimental data. Static bed height and U 0 / U ms were constant in all simulations. Minimum spouting velocity as well as velocity, voidage and axial flux distributions of particles were determined and compared for six bed cone angles (20°–70°). An improved correlation for minimum spouting velocity was proposed which includes the effect of bed cone angle for the first time. Novel curved bed geometry, inspired from improvement of particle motion, was also proposed. Solids circulation rates for beds with different cone angles were evaluated by tracing sample particles in the bed. Axial distribution of lateral solids flux, which shows the insertion location of particles from annulus to spout, was determined for different cone angles. Combination of solids circulation rate (speed of circulation) and lateral flux (quality of circulation) was used to discuss about the effect of geometry on the circulation of particles. The best circulation behavior was observed in the curved bed. [ABSTRACT FROM AUTHOR]

Solids circulation establishment in a cold model and industrial scale reactor has been investigated via visual observation, bed density, pressure drop, particle loss and acoustic emission (AE) techniques. The gas-solid flow pattern in the cold model and industrial unit share similar features based on the visual observation and bed density detection respectively. The circulating fluidized bed (CFB) with sweeping bend return initially exhibits stable fluidization in the riser and downer. As time elapses, the resistance fluctuation in the riser and downer is induced by the imbalance between the inlet and the outlet solids flow in the downer, leading to the unstable gas-solids flow pattern in riser and downer. The alternation between fluidized bed and moving bed is observed in the downer during the unstable stage, and further induces high-pressure drop fluctuations, heavy particle loss. Besides, the detection of pressure drop, particle loss rate and corresponding AE energy could be used to determine the time range of unstable stage. [ABSTRACT FROM AUTHOR]

Proper solid circulation is of crucial importance for the stable operation of circulating fluidized beds. There should be a pressure barrier between the riser and the downcomer to avoid reverse gas flow through the downcomer and to maintain a stable solid circulation. In conventional systems, loop seals, L, J, V, valves are mostly used as solid circulation valves. In this study, ejector (eductor) type solid circulation was investigated in an experimental CFB setup (94 mm in diameter, 7950 mm in height). The solid flux at the downcomer (34 mm in diameter) and the motive gas flowrate of the ejector were investigated under different cold flow conditions. There are two different operation modes of the ejector type solid circulation depending on the solid flux through the downcomer. For low solid fluxes, there is no solid accumulation at the downcomer. As the solid flux increases, a solid column formation is observed above the ejector system. The desired pressure difference obtained with the ejector is higher for the latter mode of operation and requires less motive gas flow compared to the former for proper operation. The experimental results show that the ejector is capable to provide the required pressure barrier for the CFB loop in both cases. In addition to the experimental study, ejector system was analyzed with CFD model in order to investigate the effect of basic geometric and operational parameters on the pressure difference generated by the ejector. Furthermore a novel semi-empirical method was proposed as a tool for predicting the ejector performance comparable with CFD results. [ABSTRACT FROM AUTHOR]

A three-dimensional computational fluid dynamic (CFD) model has been developed for simulating full-loop solid circulation in a dual circulating fluidized bed (DCFB) chemical loop combustion (CLC) reactor model. The standard k-ε turbulence model and kinetic theory of granular theory based Eulerian multiphase model were used to describe the gas and solid motions, respectively. The simulations focused on the investigation of solid circulation in a CLC reactor model which consists of an air reactor (AR, height of 1.36 m, diameter of 0.05 m) and a fuel reactor (FR, height of 0.97 m, diameter of 0.054 m). Key gas–solid flow behaviors related to gas–solid circulation behaviors, e.g. the transient flow regime, solid velocity, solid distribution and circulation characteristics, were numerically investigated. It was found that a core–annulus flow structure appeared in FR. The influences of FR and LLS fluidization flow rate on global and internal circulation rate were studied separately. With FR fluidization flow rate increasing, the time-averaged axial solid volume fraction in the top region of FR first increased and then decreased. The influences of FR and LLS fluidization rate on circulation dynamic characteristics, including circulation fluctuation strength and circulation stability, were also numerically investigated in this work. [ABSTRACT FROM AUTHOR]

Highlights: [•] Coal of three kinds was burned in a twin-fluidized bed for Calcium Looping Process. [•] Residence time of solids in regenerator could be controlled by staging gas feed. [•] CO and CO2 were formed in the absorber from char particles in circulating solids. [•] NOx formation in regenerator was related with CO and CO2 emissions from absorber. [•] Oxygen enrichment to the bottom of regenerator was favorable for NOx reduction. [ABSTRACT FROM AUTHOR]

Abstract: Biomass drying is performed mainly in rotary dryers, which occupy a large footprint. To explore the efficient drying of biomass, a fluidized bed dryer was proposed. Good circulation of biomass particles could be established in the fluidized bed without the use of inert particle or mechanical aids. The initial moisture content of the input sawdust affected its fluidization performance. For the drying of sawdust of high-moisture content, the fluidization behavior could be divided into three stages: partial fluidization, full fluidization with increasing drying rate, and full fluidization with decreasing drying rate. A high drying rate could be achieved because of the fast mass and heat transfer rate in the fluidized bed. The fluidized bed dryer has a drying performance similar to the binary mixture fluidized bed dryer but more compact, and requires no separation of dried biomass particles from the inert bed particles. [Copyright &y& Elsevier]

Abstract: The gas–solid flow in a 3-D bubbling fluidized bed is numerically simulated with the coupling of computational fluid dynamics (CFD) and discrete element method (DEM). The gas phase is described by the Navier–Stokes equations while the solid phase is tracked individually. The distribution properties of the local and global dispersion coefficients of solid phase are initially investigated. The granular temperature of solid phase is studied to capture its turbulent behavior. Then, solid circulating pattern is explored. Besides, the influences of superficial velocity, the particle diameter and the scale-up of the bed width on these aspects are discussed. The results show that the vigorous lateral dispersion of solid phase appears in the central region near the inlet, while intensively vertical ones exists in the region of bubble eruption. Furthermore, the vertical dispersion intensity of solid phase is larger than the lateral ones in nearly an order of magnitude. Vigorously turbulent behavior of the solid phase is observed to be in the upper central region of the bed. The larger the superficial velocity or the smaller the particle diameter, the enhanced dispersion and more chaotic motion of solid phase appear. The scale-up of the bed width not only enlarges the lateral dispersion intensity but also leads to more chaotic and turbulent motion of solid phase. Besides, three patterns of solid circulation can be observed, namely the gross circulation, the local circulation and the local exchange. The numbers and intensities of both gross and local circulations increase with enlarging the superficial velocity. [Copyright &y& Elsevier]

Highlights: [•] Coal was burned at Calcium Looping process regenerator temperature. [•] A dual-fluidized bed system and a circulating fluidized bed combustor were used. [•] NOx emissions from two types of reactors were compared for three kinds of coal. [•] For dual-fluidized bed, a part of char was consumed in the carbonator. [•] An empirical relationship between NOx conversion and char combustion was obtained. [ABSTRACT FROM AUTHOR]

Highlights: [•] A baffle-type ICFB is investigated comprehensively using the LES–DEM method. [•] The circulation mechanisms, especially the role of solid rotation is emphasized. [•] Influences of gas–solid properties on the circulation are quantified and normalized. [•] Particularity and consistency with other previous investigations are discussed. [•] The minimum fluidization velocity is critical to the control of bed performance. [Copyright &y& Elsevier]

Particle image velocimetry was used to investigate the evolution of multiple inlet gas jets located at the distributor base of a two-dimensional fluidized bed setup. Results were used to estimate the solid circulation rate of the fluidized bed as well as particle-entrainment into the individual jets. The effects of fluidization velocity, orifice diameter, orifice pitch, particle diameter, and particle density were studied. It was determined from this study that the solid circulation rate linearly increased with an increase in the fluidization velocity until the multiple jet system transitioned from isolated to an interacting system. In the interacting system of jets, the solid circulation increased with fluidization velocity but at a much lower rate. For multiple jet systems, this phenomenon may indicate the presence of an optimum operating condition with high circulation rate and low air input in the bed. © 2011 American Institute of Chemical Engineers AIChE J, 58: 3003-3015, 2012 [ABSTRACT FROM AUTHOR]

Abstract: The hydrodynamics of a circulating fluidized bed gasification system with dual fluidized bed concept has been studied through a cold model investigation. The article focuses on the axial voidage, the pressure drops across various components and the solid circulation under different operating conditions. The control of solids circulation between the dual fluidized beds has been done through an L-valve system. A mathematical model of hydrodynamic behavior of the system has been presented. It is observed from the investigated operating parameters that the aeration flow, the secondary air flow and particle diameter have the strongest influence on system pressure drop and solid circulation. [ABSTRACT FROM AUTHOR]

Abstract: Flow behaviors of particles in a two-dimensional spouted bed with a porous draft plates are studied using a fluid dynamic computation with kinetic–frictional stresses models. Gas flow through the porous draft tube is simulated by Brinkman–Darcy–Forchheimer formulation. The distributions of concentration and velocities of particles are predicted. Simulated results predict the solid circulation rate and gas flux rate measured in the spouted bed with a porous draft tube (Ishikura et al., 2003). The solid circulation rate in the spouted bed with a porous draft tube is larger than that with a non-porous draft tube. The predicted bed pressure drop with the porous draft tube is high in comparison to the spouted bed with non-porous draft tube. The effect of the porosity of the porous draft tube on distributions of gas flux rate through the annulus and solid circulation rate are discussed. [Copyright &y& Elsevier]

Abstract: Flow behavior of particles in a two-dimensional spouted bed with a draft tube is studied using a continuous kinetic-friction stresses model. The kinetic stress of particles is predicted from kinetic theory of granular flow, while the friction stress is computed from a model proposed by . A stitching function is used to smooth from the rapid shearing viscous regime to the slow shearing plastic regime. The distributions of concentration and velocities of particles are predicted in the spouted bed with a draft tube. Simulated results compare with the vertical velocity of particles () measured and in the spout bed with draft plates and solid circulation rate () measured in the spouted bed with a draft tube. The impact of the friction stress of particles on the spout, annulus, fountain and entrancement regions is analyzed in gas–solid spouted bed with a draft tube. Numerical results show that the gas flow rate through the annulus increases with the increase of the entrainment zone. The solids circulation rate decreases with the decrease of inlet gas velocity and the height of the entrainment zone. The effect of spouting gas velocity on distributions of concentration, velocity and particle circulation is discussed. [Copyright &y& Elsevier]

The effects of tube bank configuration on forces and heat transfer were investigated for both two-dimensional and three-dimensional gas fluidized beds. Effective dynamic forces and heat transfer coefficients were measured for several tube bank configurations, and it was found that the average forces are smaller than for a single tube. The heat transfer coefficient can be increased by providing sufficient space for particles to descend around both sides of the tube bank. The results provide useful guidelines for optimizing the configuration of tube banks to achieve high heat transfer coefficients while reducing tube erosion due to dynamic forces. [ABSTRACT FROM AUTHOR]

Abstract: CFD simulations are carried out for the prediction of flow patterns in a liquid–solid fluidised bed using Eulerian–Eulerian framework. The CFD model predictions are compared with the experimental findings reported by Limtrakul et al. [S. Limtrakul, J. Chen, P.A. Ramachandran, M.P. Dudukovic, Solids motion and holdup profiles in liquid fluidised beds, Chem. Eng. Sci. 60 (2005) 1909–1920] and the comparison shows good agreement. The CFD model has been further extended to compute solid mass balance in the core and annular regions for verifying conservation of mass and energy flows due to various dissipation mechanisms. Energy required for solid expansion in liquid fluidised bed is also compared with energy required for solid suspension in an equivalent stirred tank contactor at similar operating conditions. The influence of various interphase drag models proposed by Gidaspow [D. Gidaspow, Multiphase Flow and Fluidisation, 1st ed., Academic Press, San Diego, 1994], Di Felice et al. [R. Di Felice, The voidage functions for fluid–particle interaction system, Int. J. Multiphase Flow 20 (1994) 153–159] and Syamlal and O’Brien [M. Syamlal, T.J. O’Brien, Simulation of granular layer inversion in liquid fluidised beds, Int. J. Multiphase Flow 14 (1988) 473–481] on solid motion in liquid fluidised bed have been investigated. Even though these models predict the flow pattern of solid motion inside the fluidised bed with reasonable accuracy, the model proposed by Gidaspow showed the better quantitative agreement with experimental data. For ensuring accuracy of numerical simulation prediction, comparisons between 2D and 3D simulation, the effect of grid sensitivity, time step sensitivity and effect of inlet feed conditions have been carried out and a comprehensive CFD methodology is proposed to model the hydrodynamics of liquid–solid fluidised bed. [Copyright &y& Elsevier]

Abstract: The solid residue that originates from virgin olive oil production has a consistency that falls between a paste and a particulate solid, consists of two phases: the crushed olive kernel and the fruit pulp. The kernel particles can be used as high quality solid fuel, while oil can be extracted from the pulp residue. Two technological problems should be tackled to optimize the extraction process: drying the solid residue at low temperature and separating the two phases. The pomace was dried batchwise in a 0.17m diameter spouted bed and continuously in a 0.29m diameter draft tube spout-fluid bed with independent control of the air flow rate to the spout and to the annulus. Experimental drying tests were carried out. The drying kinetics were measured during each test in the 0.17m diameter bed. The solids circulation rate was measured in the larger unit, under a wide range of air flow rates to both the spout and the annulus. An operation regime map has been obtained from a characterization of the quality of the fluidization under a wide range of hydrodynamical conditions. The drying efficiency of both apparatuses was studied. [Copyright &y& Elsevier]

This paper focuses on the determination of the solids circulation of a CFB gasification system with a dual fluidized bed concept, and the distribution of the solid hold up under different fluidization conditions. A mathematical model of the riser was designed and implemented in a model of a dual fluidized bed system. This model contains routines for calculation of each section of the dual fluidized bed system. The behaviour of the system was analysed regarding changes in solid inventory and variations of geometry. A diagram is presented which allows an illustration of the influence of changes in the dual fluidized bed system configuration on the resulting stable operation points. Analysis concerning the effect of counter pressure on the combustion and gasification side confirms the role of the seal loop in stabilizing the operation of the gasification system. [Copyright &y& Elsevier]

A twin fluidized bed solid circulation system, in which two adjacent fluidized beds exchange solids, was developed for coal gasification to produce middle heating value gas. The effects of bed material, operation velocity, and bed structure on the solid circulating rate were tested at a small-scale test facility. Experimental results showed that the solid circulation rate of the system could be adjusted by changing gas velocities of two beds and could attain 30–40 times of the fuel feed rate, which would meet the demands of heat supply to an endothermic process of a gasifier. On the basis of experiments, reasonable operation and design parameters were put forward, which can be used to as a reference for the commercial gasifier design. A mathematical model was erected to calculate the solid circulation rate of the system, and it could predict well the solid flow rate through a horizontal orifice by comparison with experimental data. [Copyright &y& Elsevier]