The moving grate systems of waste-to-energy (WTE) mass-burn combustion chambers are designed for providing efficient flow and mixing of the municipal solid waste (MSW) over the length of the grade. This study presents results from a numerical analysis of the effect of number of reciprocating bars and reciprocation speed on the degree of mixing and residence time of MSW particles on the grate. 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 = 6–22cm diameter), reciprocation speed of moving bars (Rr = 0–90recip./h), and number of moving bars (Nb = 0 to 16 bars). This combination of mathematical modeling and experimental work has shown that: (1) different particle sizes result in different residence times, according to the Brazil Nut Effect (BNE) (2) The number of moving bars (from 0 to 16 bars) of a reverse-acting grate has the net effect of increasing the mean residence time of small and medium sized particles, while decreasing that of large particles. (3) The bar height, h, was found to be one of the major geometric parameters influencing mixing diffusion coefficient, D, and residence time.

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