Numerical optimization of a waste-to-energy plant's operating parameters using CFD

Abstract

The combustion process for using municipal solid waste as a fuel within a waste to energy plant calls for a detailed understanding of the following phenomena. Firstly, this process depends on many input parameters such as proximate and ultimate analyses, the season of the year, primary and secondary inlet air velocities and, secondly, on output parameters such as the temperatures or mass fraction of the combustible products. The variability and mutual dependence of these parameters can be difficult to manage in practice. Another problem is how these parameters can be tuned to achieving optimal combustible conditions with minimal pollutant emissions, during the plant-design phase. In order to meet these goals, a waste-to-energy plant with bed combustion was investigated by using computational fluid-dynamics approach. The adequate variable input boundary conditions based on the real measurement are used and the whole computational work is updated using real plant geometry and the appropriate turbulence, combustion, or heat transfer models. The operating parameters were optimized on output parameters through a trade-off study. The different operating conditions were varied and the combustible products were predicted and visualized. Finally, the response charts and matrix among the input and output parameters during the optimization process are presented, which monitored the dependence among these parameters. emissions, during the WTEP project phase. In order to meet these goals, WTEP with bedcombustion was numerically investigated by using the computational fluid dynamics (CFD) approach [1][2][3][4][5][6][7][8][9][10][11][12][13], by the non-stationary calculation of the ANSYS CFX 12.0 code in a WORKBENCH 2 environment. By using this complex numerical tool, the input and output parameters were followed and their mutual interaction visualized. Mathematical models for boundary-condition predictions were developed, such as FLIC [6,[8][9][10][11]] and the TAMARA [3] test project to find out combustible products distribution within the gaseous phase above the fuel bed and along the moving grate. The combustion of MSW during the gaseous combustion phase has many phases such as moisture evaporation, waste devolatilisation, combustion of volatiles, mixing and fixed carbon combustion during heterogeneous chemical reactions [10]. So the input boundary conditions have to be harmonized using these phenomena. Some optimization methods are described in literature [5,14,15], but these work do not discuss the interaction among the parameters, as used here. Models description

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