Numerical Calculation and Optimisation of a large Municipal Solid Waste Incinerator Plant
Publications of 1999 - Abstract
Numerical calculation and optimisation of a large municipal solid waste incinerator plant
Dipl.-Ing. Klasen, T.; Prof. Dr.-Ing. K. Görner
Institute of Environmental Process Engineering and Plant Design, University of Duisburg-Essen
Incineration of municipal waste is one of the most complex unit processes presently in use. An optimisation in the emissions, specially of NOx, is possible by a separate addition of the combustion air via primary and secondary air. The mixing of the secondary air in the furnace is the most important feature to reach uniform oxygen, temperature and velocity distributions.
The description of the physical and chemical operations, which are proceeding on the grate and in the furnace (e.g. the heterogeneous combustion of the solid waste, the drying of the waste or the turbulent combustion of the gas species) are very complicated because of the large range of the waste composition.
At the Institute of Environmental Process Engineering and Plant Design (Lehrstuhl für Umweltverfahrenstechnik und Anlagentechnik, LUAT) simple mathematical submodels were developed for the heterogeneous combustion of the solid waste. The thermal input is defined as the integral of the function “generation of heat“ over the grate. The heat release profile along the grade is a function of the axial distance of the waste input and the partition of volatile matter in relation to the sensitive heat at the waste surface. Volatiles emitted from the waste surface are CO and CxHy. The gas products CO2, CO, H2O and CxHy releasing from the packed bed are calculated in the same way as the heat generation. The concentrations of the oxygen are described by an opposite profile over the grate.
Three-dimensional gaseous phase simulations with FLUENT® were made in a complete furnace and burnout chamber respectively the radiational part of a large MSW incinerator for several cases. Temperature, species and velocity distributions could be improved by a so called „Prism“ . That´s an additional secondary injection port between the furnace and the first path.
For special conditions measured data were available at different control sections (grid measurements) and could compared to the simulation results. The difference between the simulated and experimental data was very low for the reference case.