Modeling of Pulverized Coal Combustion in Cement Rotary Kiln
In this paper, based on analysis of the chemical and physical processes of clinker formation, a heat flux function was introduced to take account of the thermal effect of clinker formation. Combining the models of gas-solid flow, heat and mass transfer, and pulverized coal combustion, a set of mathematical models for a full-scale cement rotary kiln were established. In terms of commercial CFD code (FLUENT), the distributions of gas velocity, gas temperature, and gas components in a cement rotary kiln were obtained by numerical simulation of a 3000 t/d rotary kiln with a four-channel burner. The predicted results indicated that the improved model accounts for the thermal enthalpy of the clinker formation process and can give more insight (such as fluid flow, temperature, etc,) from within the cement rotary kiln, which is a benefit to better understanding of combustion behavior and an improvement of burner and rotary kiln technology.
Numerical Simulation of Coal and Natural Gas Co-Combustion in a Rotary Kiln with Different Excess Air Coefficient
In this paper, numerical simulation of co-combustion of coal and natural gas was carried out aiming at a rotary kiln in wulongquan limestone mine of WISCO. Combining the models of turbulent gas flow, gas-solid flow, heat and mass transfer and combustion of pulverized coal and natural gas, the temperature field, the species concentration field and the concentration of nitrogen oxides were displayed. The optimization approach was proposed by changing the excess air coefficient. The predicted results indicated that the excess air coefficient had great influence on flame temperature, flame length and the generation of NOX, while the generation of NOX was mainly connected with the temperature and oxygen concentration. All in all, the influence of the excess air coefficients on the combustion in the rotary kiln will provide important theoretical references to the optimized combustion of the co-combustion of coal and natural gas in the kiln.
The effect of gas flow patterns on radiative transfer in cylindrical furnaces
Abstract The prediction of performance of industrial furnaces is conventionally estimated by making gross assumptions as to the effect of temperature variations in the gas. The zone method of allowing for the effect, on radiative transfer, of the temperature variation in furnace enclosures has been applied to the problem of interaction between radiation and other modes of heat transfer. The effect of different flow patterns on the gas temperature-field and wall-flux distribution in a cylindrical furnace has been examined by use of the following flow models : plug flow ; parabolic velocity profiles ; ducted-jet flow (axial feed) with recirculation rates of 0, 1, and 11 times the flue-gas flow rate. A sixteenfold range of diameters and firing densities was studied. The reduced efficiencies were correlated, for a fixed surface temperature and for each of the flow models, in terms of a reduced firing rate. The wide range of heat flux distribution patterns found in the study emphasizes the need to include allowance for gas temperature variation in any furnace analysis in which the heat flux pattern is important.