Numerical Analysis of Coal Combustion in Circulating Fluidized Bed
combustion of coal is used in circulating fluidized bed combustion system. This work is concerned about gas–solid two-phase mixtures flowing upwards through the fast beds. The type of information resulting from various ways of analyzing the pressure variations and the effect of superficial velocity on pressure in fluidized beds are discussed. This paper presents the standard k–є and two-phase turbulence model used to describe the gas–solids flow in a CFB.The analysis of temperature and density in coal combustion is done by discrete phase model (DPM) and non pre mixed combustion in species model through the PDF file creation in DPM model. The flow temperature and density in the system were modeled by solving the continuity and momentum equations of the gas flow by using the CFD analysis. The fluidizing velocity has been taken as 4 m/s and the effects of operating parameters on mole fraction, mean density and mean temperature are discussed in this paper. It is observed that the mean density of minimum and maximum mean mixture fraction along the scaled variance is significant.
Numerical Investigation on Hydrodynamic Combustion and NOx Emission Behavior in 8 MW Circulating Fluidized Bed
Multi-phase flow is one of the types of flow which is frequently observed in natural phenomena and engineering applications. Circulating fluidized beds constitute an important application of multi-phase flow. The combustion and emission behaviours in circulating fluidized beds are determined by hydrodynamic of bearing. The most appropriate combustion can be provided with the hydrodynamic structure of bearing, taking into account fuel and operating parameters. Therefore, the hydrodynamic structure of circulating fluidized beds should be displayed with mathematical/physical modelling and simulation approach for its analysis and synthesis. Mathematical analysis in today’s conditions is very difficult or impossible because of excessive turbulence, unstable and two-phase flow characteristics of the bed. Therefore, the most effective way to do this is the use the physical modelling and simulation approach. In this study, 8 MW circulating fluidized bed hydrodynamic analysis are made by ANSYSFLUENT R14 commercial CFD code and then combustion and emissions analysis are made with hydrodynamic analysis results. These analysis results show that combustion chamber exit mean NOx emission was 38.5 ppm and combustion chamber exit mean temperature was 1123 K.
Large-eddy simulation of equilibrium plasma-assisted combustion in supersonic flow
Abstract A large-eddy simulation (LES) model with a new localized dynamic subgrid closure for the magnetohydrodynamics (MHD) equations is used to investigate plasma-assisted combustion in supersonic flow. A 16-species and 74-reactions kinetics model is used to simulate hydrogen-air combustion and high-temperature air dissociation. The numerical model is validated with experimental data for non-reacting and reacting supersonic flow over a rearward-facing step. The creation of a plasma source near the step corner is shown to have a strong localized effect with the high temperature region resulting in an increase of the radical species concentration in the mixing region. This has the potential for enhancing combustion. In addition, downstream fuel–air mixing is improved, primarily by the creation of a strong baroclinic torque effect in the near field of the plasma source. Furthermore, by adding an uniform external magnetic field, the Lorentz force effect helps to further enhance mixing by lifting the shear layer and increasing fuel penetration by approximately 20%.