Mathematical modeling of aerodynamics and physicochemical processes in the freeboard region of a circulating fluidized bed furnace. 2. Interaction of particles (pseudoturbulence)

Formulas are obtained for determining the energy generation and dissipation rates of random (turbulent and pseudoturbulent) motion of particles due their collisions and the effect of the aerodynamic drag force. The averaged force of interparticle interaction, pseudoturbulent transfer coefficients for the gas of particles, and other quantities are calculated which are necessary to complete the set of equations describing the aerodynamics of the pneumatic transport zone of a circulating fluidized bed reactor [1].Institute for Power Supply Problems, Kiev, Ukraine. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 66, No. 2, pp. 159–167, February, 1994.     

Heat transfer in a circulating fluidized bed

On the basis of similarity theory a relationship is established for calculating the conductive-convective component of the coefficient of heat transfer in a circulating bed. Recommendations on the calculation of the total coefficient of heat transfer in a high-temperature bed are given. The gas gap between the heat-transfer surface and the first row of particles is evaluated. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 71, No. 3, pp. 447–453, May–June, 1998.     

Mathematical modeling of the aerodynamics and physicochemical processes in the freeboard zone of a circulating fluidized bed furnace. 3. Boundary conditions. Some numerical results

Boundary conditions are formulated for differential equations describing two-dimensional motion of gas and polydisperse coke and ash particles in a high-concentration flow [1, 2]. Specific features of the aerodynamics of the pneumatic transport zone in the freeboard zone was investigated numerically in a circulating fluidized bed reactor. The model constructed is verified by experimental data [3].Institute of Problems of Energy Conservation, Academy of Sciences of Ukraine, Kiev, Ukraine. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 66, No. 6, pp. 681–688, June, 1994.     

Mathematical modeling of aerodynamics and physicochemical processes in the freeboard zone of a circulating fluidized bed furnace. 1. Statement of the problem. Basic aerodynamic equations

The authors have obtained a set of equations describing two-dimensional motion of gas and polydisperse char and ash particles in a high-concentration two-phase ascending flow. Interphase interaction, turbulent and pseudoturbulent particle transfer, and effects of the channel walls and mass forces are taken into consideration.Institute of Problems of Energy Conservation, Academy of Sciences of Ukraine, Kiev, Ukraine. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 65, No. 5, pp. 521–526, November, 1993.     

Hydrodynamics of a circulating fluidized bed

Within the framework of similarity theory and using the Fr_t and J_s criteria, which are the generalized characteristics of a circulating fluidized bed, we obtain dimensionless dependences that describe the available experimental data on the wall mass fluxes of particles and the tangential stress on riser walls. The influence of the scale factor and other parameters of the system on the Fr_t and J_s quantities is revealed. A procedure to calculate mass fluxes of particles in the bed core is developed.     

Aerodynamics of a circulating fluidized bed

The authors present results of an experimental determination of the aerodynamic drag, density, velocity and dwell time of disperse material in a circulating bed.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 57, No. 5, November, 1989.     

Mathematical modeling of the aerodynamics and physicochemical processes in the free board zone of a circulating fluidized bed furnace. IV. Heat and mass transfer and combustion

A mathematical model describing the motion of a highly concentrated coke-ash mixture in the pneumatic transport region within the free board zone of a circulating fluidized bed reactor was developed earlier in [1–3]. In the present work it is extended to the case of a nonisothermal flow with heterogeneous combustion of carbon. Equations of mass, momentum, and energy conservation are obtained for the gas components and the coke fractions. Distinctive features of the heat transfer, combustion, and particle motion are investigated numerically.Institute of Problems of Energy Conservation, Academy of Sciences of Ukraine, Kiev, Ukraine. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 67, Nos. 1–2, pp. 32–38, July–August, 1994.     

Mixing of particles in apparatuses with a circulating fluidized bed

A phenomenological model of mixing of particles in a circulating fluidized bed has been formulated; a distinctive feature of the model is allowance for convective particle fluxes in the radial direction that ensure a substantial decrease observed in practice in the concentration of the particles over the risers height. As a result of a comparison of experimental and calculated mixing curves it has been established that the value of the coefficient of radial dispersion of the particles lies in the interval 0.0006–0.006 m²/sec.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 77, No. 6, pp. 148–158, November–December, 2004.     

Mixing of a fine-grained material and internal heat transfer in the furnace of a boiler with a fluidized bed

Results are presented from measurements and calculations of the temperature fields in the furnace of a boiler with a fluidized bed.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 44, No. 2, pp. 219–227, February, 1983.     

Extended CFD/DEM model for the simulation of circulating fluidized bed

The Euler–Lagrange approach combined with a deterministic collision model, so-called discrete element method, is investigated. In this work, the physical values of fluid and particle phases are determined in separated grids. The proposed procedure allows the variation of the fluid grid resolution independent of the particle size and consequently improves the calculation accuracy. A validation study has been performed to assess the results obtained from an in-house CFD/DEM code and a quasi-2D spouted–fluidized bed of Plexiglas®. The results suggest that the extended CFD/DEM model can predict accurately the particles motion and the pressure gradients in the bed. In view of the high computing cost, special emphasis is put on an effective program design such as the application of the multi-grid method and the parallel calculation. Hence, the influence of increasing the processor numbers (up to 36) on the calculation efficiency of the extended CFD/DEM model will be analysed. Finally, the improved CFD/DEM model is applied to simulate relevant engineering equipments but in small scale with relative large particles and thus less number of particles. In this context, the hydrodynamic behaviour of gas–solid flow in a 3D circulating fluidized bed with a particle separator (cyclone) will be estimated.     

Investigation of heat transfer between a surface and a fluidized bed in drying processes

Results are presented of an experimental investigation of heat transfer between a surface and a moist fluidized bed. The test data have been reduced by means of criterial relations.     

Experimental study of heat transfer from the walls of a channel to a circulating fluidized bed

Results are presented from an experimental study of external heat transfer in a circulating fluidized bed.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 59, No. 6, pp. 975–979, December, 1990.     

Heat transfer in a retarded fluidized bed

An oscillation model of a fluidized bed is used to examine the effect of the degree of retardation of the bed on external heat transfer.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 50, No. 3, pp. 445–451, March, 1986.     

Effect of pressure on mass transfer in heterogeneous chemical processes in a fluidized bed

A heterogeneous process in a fluidized-bed reactor with continuous feed and removal of material was investigated at pressures ranging from 0 to 196.1·10⁴ N/m². A general relationship connecting the rate of mass transfer between the gas flow and the particles in the bed in the Re range 15–274 with the pressure from 0 to 196.1·10⁴ N/m² is found.     

Heat transfer in a three-phase fluidized bed

The authors present results of a theoretical and experimental investigation of heat transfer between a fluid of a fluidized bed and the solid surface under conditions where air is bubbling through the bed.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 55, No. 5, pp. 784–788, November, 1988.     

Interfhase pass transfer in a fluidized bed with a packing

Measurements are made of interphase mass-transfer coefficients in a fluidized bed with small- and medium-volume packings. Our experimental data and material from other studies are generalized on the basis of a proposed model.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 48, No. 6, pp. 937–943, June, 1985.     

Application of the theory of Markov chains to theoretical study of processes in a circulating fluidized bed

Abstract

The objective of the study is to develop a simple yet informative model to investigate the features of the process of particulate flows formation in a circulating gas-solid fluidized bed. The proposed model is based on the theory of Markov chains. The riser is presented as a chain of perfectly mixed cells. The conversion of particles of a source material into particles of an end product occurs in these cells due to this or that chemical or thermo-physical process. The transportation of material over the chain is controlled by a matrix of transition probabilities. The return flow that comes from a separator is routed to the downer, which is described as a plug flow apparatus that has a time delay between the inflow and outflow issuing from it. The outflow is routed back into the riser. The numerical experiments were carried out for the batch fluidization. It is found that the batch circulating fluidization only has advantages over the dense bed under a small time delay in the downer and a relatively high gas flow velocity in the riser. The results of laboratory tests performed at the circulating fluidized bed demonstrated a good qualitative correlation with the theoretical data.     

Verification of optimal models for 2D-full loop simulation of circulating fluidized bed

To verify the optimal models for a two-dimensional (2D) full loop simulation of a circulating fluidized bed (CFB), different turbulent models and drag models are studied according to relevant pressure profile, voidage distribution and particle collision energy. With regard to a laminar model and turbulent models including Standard k-ε, RNG k-ε and Realizable k-ε, the experimental data reveals that the RNG k-ε model is the best at predicting pressure, voidage, axial solid velocity and granular temperature. Besides, through the comparison of four drag models, it is found that the Gidaspow model can achieve a higher accuracy of prediction. Therefore, it can be concluded that the combination of the RNG and Gidaspaw models is suitable for the 2D full loop simulation of a CFB, and therefore potential models for the prediction of flow characteristics.