Mathematical simulation of furnace processes during fired pulverized coal

Abstract

The article presents the study of combustion and heat transfer processes in large-scale objects are extremely difficult both analytically and experimentally. The combustion of non-design coals in boiler units is often accompanied by a decrease in the completeness of fuel burnup, undesirable redistribution of heat flows and other negative factors due to different thermal characteristics of the fuel. The possibility of effective burnout of polyfractional non-design solid fuel in the combustion chamber of a boiler unit with solid ash removal is considered on the basis of a numerical study of jointly occurring aerothermochemical processes. The problem of numerical modeling of the staged burnout of coal particles is solved, starting from the evaporation of the moisture contained in them to the burning out of their coke residue when moving in the carrier phase. Numerical studies of physical and chemical processes in the combustion chamber were carried out for three loads (50%, 70%, 100%) based on the developed FIRE 3D calculation complex. The Euler-Lagrange model for a dusty flow is applied, the closure of the averaged Navier-Stokes equations is performed by the k-ε turbulence model, the second order of accuracy is used in numerical calculations. The main results of three-dimensional modeling are presented in the form of velocity and temperature fields, the distribution of O2 and CO concentrations along the height of the furnace volume. The results of mathematical modeling showed good agreement with the available analytical values. Based on the data obtained, it can be stated that it is possible to organize the combustion of non-design fuel in the boiler unit under consideration. It has been established that when operating at loads below the nominal, a redistribution of burner jets is observed, which negatively affects the reliability and efficiency of the boiler. To increase the efficiency of the boiler unit at reduced loads, a wider study of options for redistributing the proportions of the fuel-air mixture and secondary air is necessary.