Particle Transport and Deposition in a Hot-Gas Cleanup Pilot Plant

ABSTRACT

Development of hot-gas filtration systems for advanced clean coal technologies has attracted considerable attention in recent years. The Integrated Gasification and Cleanup Facility (IGCF), which is an experimental pilot plant for testing performance of ceramic candle filters for hot-gas cleaning, has been operational at the Federal Energy Technology Center (FETC) in Morgantown, West Virginia, for several years. The present work describes a computer simulation study of gas flow and particle transport and deposition in the IGCF filter vessel with four filters. The stress transport model of FLUENT? code is used for evaluating the gas mean velocity and the root mean-square fluctuation velocity fields in the IGCF filter vessel. The instantaneous fluctuation velocity vector field is simulated by a filtered Gaussian white-noise model. Ensembles of particle trajectories are evaluated using the recently developed PARTICLE code. The model equations of the code include the effects of lift and Brownian motion in addition to gravity. The particle deposition patterns on the ceramic filters are evaluated, and the effect of particle size is studied. The results show that, for a clean filter (just after the backpulse), the initial deposition rate of particles on the candle filters is highly nonuniform. Furthermore, particles of different sizes have somewhat different deposition patterns, which could lead to nonuniform cake compositions and thicknesses along the candle filters. The effects of variations in the filter permeability on the vessel gas flow patterns and the pressure drop, as well as on particle transport patterns, are also studied.     

Charged Particle Trajectory Statistics and Deposition in a Turbulent Channel Flow

The statistical properties of charged particles and their wall deposition in a turbulent channel flow in the presence of an electrostatic field is studied in this paper. For a dilute concentration, the influence of small particles on the fluid motion is neglected. The instantaneous velocity field is generated by a direct numerical simulation of the Navier-Stokes equation via a pseudospectral method. The case in which each particle carries a single unit of charge and the case in which the particles have a saturation charge distribution are analyzed. Ensembles of 8192 particle trajectories are used for evaluating various statistics. Effects of size and electric field intensity on particle trajectory statistics and wall deposition rate are studied. RMS particle velocities and particle concentrations at different distances from the wall are evaluated and discussed. The results for deposition rates are compared with those obtained from empirical equations.     

Efficient Degradation of a Biorecalcitrant Pollutant from Wastewater Using a Fluidized Catalyst-Bed Reactor

This study investigated the treatment of an azo dye, as a biorecalcitrant model, from industrial wastewater by using Cu/Mg/Al-chitosan in a fluidized catalyst-bed reactor. A number of variables were used to study the impact they had on the oxidation process involving azo dye. The maximum degradation of the azo dye was achieved at 7 g Cu/Mg/Al-chitosan. The chloride and sulfate ions had a synergistic effect on azo dye removal. The oxidation of the azo dye under the selected conditions was of pseudo-first-order. Textile wastewater could effectively be treated using a low concentration of about 7 g of Cu/Mg/Al-chitosan in a short hydraulic retention time of 10 min. The use of Cu/Mg/Al-chitosan demonstrated a promising method to eliminate the azo dye from the wastewater.     

Direct Numerical Simulation of Curly Fibers in Turbulent Channel Flow

Wall deposition of rigid-link fibrous aerosols in a turbulent channel flow is studied. The instantaneous turbulent velocity vector field is generated by the direct numerical simulation of the Navier-Stokes equation with the aid of a pseudospectral code. It is assumed that the fiber is composed of five rigidly attached ellipsoidal links. The dynamic behavior of these elongated and irregular shaped particles is markedly different from the spherical ones. The hydrodynamic forces and torques acting on the fiber are evaluated and the equations governing the translational and rotational motions of the fiber are analyzed. Euler's four parameters are used, and motions of fibrous particles in the turbulent channel flow field are studied. Ensembles of 8000 fiber trajectories are generated and are used for evaluating various statistics. Root mean-square fiber velocities and fiber concentrations at different distances from the wall are evaluated and discussed. Empirical models for the deposition rate of curly fibers are also developed. The model predictions are compared with the simulation data and good agreement is observed.     

Transport and Deposition of Angular Fibers in Turbulent Channel Flows

Transport and deposition of angular fibrous particles in turbulent channel flows were studied. The instantaneous fluid velocity field was generated by the direct numerical simulation (DNS) of the Navier-Stokes equation via a pseudo-spectral method. An angular fibers was assumed to consist of two elongated ellipsoids attached at their tips. For a dilute suspension of fibers, a one-way coupling assumption was used in that the flow carries the fibers, but the coupling effect of the fiber on the flow was neglected. The particle equations of motion used included the hydrodynamic forces and torques, the shear-induced lift and the gravitational forces. The hydrodynamic interactions of the high aspect ratio linkage were assumed to be negligibly small. Euler's four parameters (quaternions) were used for describing the time evolution of fiber orientations. Ensembles of fiber trajectories and orientations in turbulent channel flows were generated and statistically analyzed. The results were compared with those for spherical particles and straight fibers and their differences were discussed. Effects of fiber size, aspect ratio, fiber angle, turbulence near wall eddies, and various forces were studied. The DNS predictions were compared with experimental data for straight fibers and a proposed empirical equation model.     

Inter-particle heat transfer in a riser of gas-solid turbulent flows

Effects of the particle-particle heat transfer in a gas-solid turbulent flow in a riser were evaluated. An Eulerian/Lagrangian four-way interaction formulation including the particle collisions in conjunction with the k − τ and the k_θ − τ_θ model equations were used in the numerical simulation. Inter-particles and particle-wall interactions were accounted for with an inelastic collision model, where the restitution coefficient was evaluated for each collision. The special case when the flow initially contains two groups of hot and cold particles was treated in details. Particular attention was given to the nature of heat transfer to particles due to inter-particle interactions. The results showed that the effect of particle-particle heat transfer was more significant for smaller sizes, lower flow Reynolds numbers, and for higher loading ratios. Solid thermal properties, however, did not have a noticeable effect on the inter-particle heat transfer. The simulation results indicates that although the heat transferred to each group of hot and cold particles was significant, the mean values of gas and particle temperatures and suspension heat transfer was insensitive to the inter-particle heat transfer.     

Prediction of restrained shrinkage based on restraint factors in patching repair mortar

Shrinkage of repair material, especially in patching repairs, is the major factor inducing cracking in concrete repairs. Induced cracks in repair materials are due to restrained shrinkage. Although in usual practice, the free shrinkage of the repair mortar is measured, in reality, cracking is not due to free shrinkage. It is well known that cracking is due to restrained shrinkage. It is very hard to measure the restrained shrinkage; therefore, to overcome this problem a restraint factor (R) is used to modify the free shrinkage and come up with the restrained shrinkage. The restraint factor is influenced by the surface and boundary condition.In this study, the restraint factor for patching repair with different boundary conditions (with eaves and without eaves) and surface condition (rough and smooth) of the substrate concrete is investigated.The results show that the restraint factor R lies between 0.1 and 0.94; with an increase of restraint, the restraint factor is increased. In situations with a high level of restraint (eaves at the perimeter and a rough surface of substrate), the average R is 0.83. while with a low level of restraint (without eaves at the perimeter and a smooth surface of the substrate), the average R is 0.22.     

PARTICLE REMOVAL MECHANISMS IN CRYOGENIC SURFACE CLEANING

Particle removal mechanisms in cryogenic surface cleaning are examined. The effect of impacting solid carbon dioxide particles and the hydrodynamic forces and torques are included in the model. Sliding detachment models and rolling detachment models in conjunction with the theory of critical moment are used. The critical conditions for removal of particles of different sizes are evaluated. For various carbon dioxide pellet diameters, incoming flow angles, nozzle, and cleaning surface separation distances, the critical shear velocities for particle detachment are evaluated.     

Indirect Synthesis of Bis(2‐PhInd)ZrCl2 Metallocene Catalyst,Kinetic Study and Modeling of Ethylene Polymerization

Bis(2‐phenylindenyl)zirconium dichloride (bis(2‐PhInd)ZrCl₂) catalyst was synthesized via the preparation of bis(2‐phenylindenyl)zirconium dimethyl (bis(2‐PhInd)ZrMe₂) followed by chlorination to obtain the catalyst. Performance of the catalyst for ethylene polymerization and its kinetic behavior were investigated. Activity of the catalyst increased as the [Al]:[Zr] molar ratio increased to 2333:1, followed by reduction at higher ratios. The maximum activity of the catalyst was obtained at a polymerization temperature of 60 °C. The rate‐time profile of the reaction was of a decay type under all conditions. A general kinetic scheme was modified by considering a reversible reaction of latent site formation, and used to predict dynamic polymerization rate and viscosity average molecular weight of the resulting polymer. Kinetic constants were estimated by the Nelder‐Mead numerical optimization algorithm. It was shown that any deviation from the general kinetic behavior can be captured by the addition of the reversible reaction of latent site formation. Simulation results were in satisfactory agreement with experimental data.