J.R. Fan

Study on coal combustion characteristics in a W-shaped boiler furnace

A numerical simulation approach is given to investigate the characteristics of coal particle flow, heat transfer and combustion processes in a W-shaped furnace. In order to obtain, in detail, behaviors of coal combustion, many different coal particle sizes of two different load cases are used to predict the characteristics of combustion. The conclusions of the characteristics of coal particle trajectories, devolatilization, ignition time, ignition distance and burnout are drawn out in detail. These conclusions can be used to optimize the design and operation of the W-shaped furnace.

Simulation of ash deposit in a pulverized coal-fired boiler

A model has been developed to simulate deposit growth under slagging conditions. The model was coupled with a comprehensive combustion code to predict the flow field, the temperature field and the deposit growth behavior. The predictions indicate that the numerical model can be used to optimize the design and operation of pulverized coal-fired boilers.

Numerical and experimental investigation on the reduction of NOx emission in a 600 MW utility furnace by using OFA

The paper describes a three-dimensional computer simulation, developed to predict the formation of nitric oxide in a tangentially fired boiler furnace burning pulverized fuel. The model was applied to a 600 MW utility boiler under different operating conditions. As fuel nitrogen is released in proportion to burnout of pulverized coal particles, the particles are treated in a Lagrangian framework in order to track burning pulverized coal particles through the gas continuum. The prediction yields encouraging results compared to experimental data.

Numerical investigation on two-phase flow in rich/lean pulverized coal nozzles

Abstract The investigation of particle-laden turbulent flow in a newly developed rich/lean pulverized coal nozzle interior is presented in this paper. A stochastic particle dispersion model and a model of particle–wall collision are employed for numerical simulation. Various cases of different particle diameters, positions of the baffle-board and the diaphragm are numerically investigated. The flow characteristics in the nozzle interior, such as flow equilibrium between the two sides of the diaphragm, particle distribution, rich/lean concentration ratio and characteristics of resistance are discussed. This paper analyzes the mechanism of the separating process of pulverized coal. The results not only show a good agreement with the experimental data, but also are of practical value.

A numerical model for dense particle-laden jets

A new approach has been developed for the study of dense gas-solid flows. The approach uses Eulerian and Lagrangian coordinates and takes account of inter-particle interactions. A numerical algorithm is presented and a dense, circular, particle-laden jet has been simulated numerically using the new model. Comparison of the calculations with published experimental data shows satisfactory agreement.

DNS of Particle Dispersion and Material Erosion in Gas-Solid Two-Phase Circular Cylinder Wakes

Particle dispersion and the resulting material erosion in a three-dimensional wake of circular cylinder were investigated by using direct numerical simulation (DNS). The domain decomposition method with patched grid and the high-order finite difference schemes were used to solve the flow. A new Lagrangian tracking solver was developed to trace the trajectories of particles in the non-uniform and unstructured grid. It is observed that particles at the smaller Stokes numbers can follow the vortex motion and have a relatively uniform distribution in the flow field. They usually collide with the downstream surface of the cylinder. The particles at the larger Stokes numbers tend to maintain their own motion and the particle-cylinder collision occurs in the upstream surface of the cylinder. But particles at the intermediate Stokes number of 1 are observed to assemble in the outer boundaries of the vortex structures and the thin band regions which connect two adjacent eddies. Due to the particular response characteristics, neither can these particles collide with the upstream surface, nor can they collide with the downstream surface of the cylinder. The increase of particle diameter leads to an exponential increase of the collision frequency and the material erosion. The local collision frequency is higher for each kind of particles when the inclination angle approximates zero. But the maximum local erosion happens when the inclination angle is between 30 degree and 60 degree. The larger the particle diameter is, the larger the inclination angle where the maximum erosion happens is. In addition, it is confirmed that the highest erosion ratio occurs when the collision angle between particles and cylinder is around 25 degree for the plastic material.Copyright

DIRECT NUMERICAL SIMULATION OF VORTEX STRUCTURES AND PARTICLE DISPERSION IN TURBULENT FREE SHEAR FLOWS

In order to provide references for the study of jets from combustor and associated industrial applications, direct numerical simulation was employed to study a three-dimensional temporally evolving plane mixing layer laden with particles in the upper region initially. The coherent structures in the mixing layer between two parallel streams were simulated using a pseudo-spectral method. Particles with different Stokes numbers were traced using the Lagrangian approach based on one-way coupling between the continuous and the dispersed phases. Both the large-scale vortex structures and the particle dispersion patterns with different Stokes numbers were investigated. The results clearly showed that particle dispersion is closely related to the large-scale organized structures and the three-dimensionality. Particles with Stokes number of the order of unity were found to have the largest concentration on the outer edges of the large-scale vortex structures, and the variation of particle concentration along the spanwise direction increased with the development of the three-dimensionality, which was mainly due to the presence of the streamwise large-scale structures. When the counter-rotating “rib” large-scale vortices paired, part of the particles were thrown out from the high concentration area in the upper region to the lower region of the mixing layer and finally developed into a “mushroom” pattern of the particle distribution along the spanwise direction.

NUMERICAL ANALYSIS OF A PROTECTION TECHNIQUE FOR TUBE EROSION IN UTILITY BOILERS

Abstract Erosion of heat-exchanger tubes by coal particles and coal-ash impingement has caused serious problems to utility boilers. In this paper, we present results of numerical investigations of finned-tube erosion protection techniques. These indicate that fins fixed on the tubes provide a simple and efficient erosion protection method for particle-laden systems, which have erosion problems.