The grate systems of waste-to-energy (WTE) mass-burn combustion chambers, which historically stem from coal combustion technology, have an important role in controlling the mixing of heterogeneous MSW during the combustion process. They are designed for providing efficient flow and mixing of Municipal Solid Waste (MSW) in the combustion chamber. This study presents results from a numerical analysis for grate design and chamber operation, i.e., number of reciprocating bars and reciprocation speed that influence the degree of mixing and residence time of MSW particles. A particle-based bed model of MSW and a physical model of reverse-acting grate were used in order to quantify the mixing diffusion coefficient of MSW particles. We analyzed the particle mixing with different parameters: particle size (d = 6–22 cm diameter), reciprocation speed of moving bars (Rr = 0–90 recip./h), and number of moving bars (Nb = 1–16 bars). According to the size segregation in the particle mixing process in the MSW bed, the undersized waste particles in the MSW bed on the reverse-acting grate have a higher diffusion coefficient than those of oversized and mean size particles. Also the number of moving bars, Nb, as well as reciprocation speed, Rr, were quantitatively related to a diffusion coefficient equation for MSW particle mixing.

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