Effects of diverging angle and fuel molecular weight on NOx emissions in converging and diverging ducts

The present paper developed and validated a numerical procedure for the calculation of turbulent combustive flows in converging and diverging ducts. Through simulation of the heat transfer processes, the amounts of production and spread of NOx pollutants were measured. Also, this paper reported the results of a numerical investigation of the effects of the fuel Molecular Weight on NOx emissions in converging and diverging ducts. The fuels which were examined were methane, naphtha, and kerosene. The differential equations in the Von-Misses coordinate system were transformed to a cross-stream coordinate system in order to concentrate more grid lines near wall boundaries. A marching integration solution procedure employing the TDMA (Tri diagonal Matrix Algorithm) was used to solve the discretized equations. In this system, by using a general variable, mass, momentum, energy, and chemical species conservation equations were written in a general form. The nature of the governing differential equation was parabolic. The flow behavior in the vicinity of the walls was determined utilizing the wall function method. The turbulence model was the Prandtl Mixing Length model. Modeling of the combustion process, was done with Arrhenius and Eddy Dissipation method. Thermal mechanism was used for modeling the formation of the nitrogen oxides. Finite difference method and Genmix numerical code were used for numerical solution of equations. Our results indicated the important influence of the limiting diverging angle of diffuser on the coefficient of pressure recovery. Also, the converging and diverging effects of duct on its output behavior were indicated. Moreover, due to its intense dependence on the maximum temperature in the domain, the NOx pollutant amount attained also maximum level. Heavier fuel molecules, increased temperature and resulted in the increase of NOx mass fraction

Numerical simulation of the effect of sulfide concentrate particle size on pollutant emission from flash smelting furnace

© 2021, Islamic Azad University (IAU). In this research, numerical simulation of three-phase flow (airflow, sulfide concentrate particles, and liquid fuel droplets) within a copper flash smelting furnace was conducted to investigate the effect of combustion of the sulfur present in the sulfide concentrates on temperature distribution and species production. The effect of sulfide concentrate size, amount of sulfur present in concentrates and air enriched with oxygen on sulfur combustion were numerically analyzed. The simulation was conducted using the Eulerian method for the continuous phase and the Lagrangian approach for discrete phases. The probability density function and the renormalization group K-epsilon model were used for combustion modeling and simulation of turbulence effects on the rate of chemical reactions. The discrete ordinate method was used to calculate the effect of radiative heat transfer. Results showed that when the amount of sulfur present in the concentrate particles increases, a higher level of sulfur release leads to an increase in the concentration of SO2, SO3, and SO. Also, by decreasing the concentrate particle size and increasing the rate of heat transfer to the particles, the amount of sulfur released increases. Since sulfur combustion occurs by high radiation, an increase in the sulfur released makes the temperature distribution more uniform within the furnace. Besides, by increasing the sulfur released, the concentration of CO2 decreases because gasoil competes with sulfur for oxygen consumption. Finally, it has been revealed that the amount of all species such as SO2, SO3, SO, CO2, and NOx, and the temperature increase using air enriched with oxygen

The Numerical Study of the Gas-Solid Flow in a Conventional Cyclone Separator

This paper presents a numerical study of the gas–powder flow in a typical Lapple cyclone with division of gas and particle flow in a vortex finder. The Navier-Stokes equations along with the RNG k-ε turbulent model are solved numerically. The separation efficiency and the trajectory of particles are simulated and the effects of the particle size on the separation efficiency and the particle residence time are investigated. The effect of the particle density on the particle size in the range which results 100% cyclone separation efficiency and particle residence time is investigated. Large particles generally have a higher concentration in the wall region and small particles have a higher concentration in the inner vortex region. The particles enter from different sides give different separation efficiency and trajectory. A particle with a size exceeding a critical diameter or a critical density would stagnate on the wall of the cyclone’s cone. This phenomenon is regarded as a main reason for the deposition on the inner conical surface in such cyclones used in the cement industry

Numerical study of inlet air swirl intensity effect of a Methane-Air Diffusion Flame on its combustion characteristics

In this paper, the effect of inlet air swirl number of a Methane-Air Diffusion Flame on dynamic flow behavior, temperature, and radiation heat flux distribution was investigated using ANSYS-Fluent CFD code. Based on the swirling effect on dynamic flow behavior, a specific equation in terms of axial and tangential velocity components was used to reach the swirl number. The modeling of the chemical reaction was carried out by applying the Eddy Dissipation Model (EDM). Furthermore, radiation heat flux and turbulent flow characteristics were performed by using P-1 and standard k-ϵ models. The results showed that the elevating swirl number of the inlet air from 0.0 to 0.6 develops the furnace internal recirculation zone which leads to producing the combustion products in the internal recirculation zone. Consequently, fuel and air are mixed more efficiently, which results in the enhancement of combustion efficiency by removing the high-temperature zones as the leading cause of producing nitrogen oxides (NOx). Moreover, as the swirl number increases, the radial flow distribution improves, and the flame heat exchange area enhances regardless of the maximum flame temperature reduction, which will increase the flux radiation efficiency by 36.5% and reduces the pollutant NOx by 58.6%