3-Dimensional simulation of air mixing in the MSW incinerators

Combustion control strategies to minimize the pollutants emission from municipal solid waste (MSW) incinerators are formulated based on the improved mixing of air with the products of incomplete combustion and the subsequent increase in oxidative destruction. Secondary air injection into the combustion chamber plays the key role in this mixing process. However, design variables of the air jet into the combustion gas stream are not clearly identified, and the performance of mixing and reaction is not fully understood. Three-dimensional flow simulation was performed to study the mixing performance of a full-scale incinerator combustion chamber according to the secondary air nozzle configuration. A detailed flow was analyzed and the degree of mixing was quantitatively evaluated by introducing a statistical parameter based on the chemical species distribution. The gas residence time distribution was analyzed using the particle trajectory. The overall flow field was strongly influenced by the nozzle configuration. It was demonstrated that the degree of mixing could be improved by selecting larger inter-jet spacing and stronger jet velocity. The staggered arrangement of two opposite nozzle arrays was found to be more effective in terms of mixing and gas residence time distribution.