Cold-flow simulation of municipal waste incinerators

Abstract

Configurations of combustion chamber and air distribution are major parameters that influence theperformance of incinerators. Cold-flow simulations have been performed experimentally and numerically for selected designs of grate-type municipal waste incinerators. Counterflow and parallel-flow arrangements are considered for the combustion chamber configuration. Two-dimensional water table models of 1/20 scale were made for cold-flow tests, and numerical models have been developed. Flow visualizations using water table flow models and computational results using the numerical model are in good agreement. Velocity vector fields and concentrations of tracer gases are evaluated, and the effects of combustion chamber geometry, amount of overfire air, and jet direction have been investigated. Mixing characteristics in the combustion chamber are examined by adopting a newly defined mixing parameter, which has value of zero when gases are mixed completely and whose departure from zero indicates the degree of nonmixing. In representing the degree of mixing over the entire chamber, probability density function of this mixing parameter is more adequate. It is useful in comparative assessments of incinerator chambers and flow designs. Interpretation of flow field predictions in terms of residence time of combustion gases and velocity uniformity is also presented. It is suggested that understanding of local flow characteristics should be preceded in assessing the incinerator performance. © 1994 Combustion Institute.