Mineral interactions and their impacts on the reduction of PM 10 emissions during co-combustion of coal with sewage sludge

Abstract

In this study, mixtures of dried Municipal Sewage Sludge (MSS) and pulverized coal were combusted. The MSS contains high amounts of Ca, Fe, P, S, and Zn in the minerals, while, the pulverized coal contains abundant amounts of Si and Al in the minerals. The mineral transformation behaviors and their effects on the solid emitted pollutants, mainly referring to the fine suspended particles of PM 10 (aerodynamic diameter smaller than 10 μm) were investigated. Experimental work was conducted at 1473 K in a lab-scale drop tube furnace (DTF). The experimental results show that both of PM 1 (particles with the aerodynamic diameter smaller than 1 μm) and PM 1–10 (particles with the aerodynamic diameter ranging from 1 μm to 10 μm) generated by the co-combustion of MSS with coal are reduced comparing with their corresponding linear combination results. The reason appears to be that, during combustion, the transformations of P, S, Al, and Si from submicron particles to supermicron particles result in decreasing of PM 1 emissions, and the transformations of Al and Si from PM 10 to coarse particles larger than 10 μm in diameter lead to the reduction of PM 1–10 emissions. The fine Al–Si (<10 μm in diameter) particles, mainly provided by the coal minerals are captured by larger melted Ca–Fe–Al–Si or Ca–Fe–P–Al–Si particles, provided by the sludge minerals, to form Ca–Fe–Al–Si or Ca–Fe–P–Al–Si coarse particles (>10 μm in diameter). Meanwhile, the larger melted Ca–Fe–Al–Si or Ca–Fe–P–Al–Si particles have or possess large viscous surface. And then the high amounts of volatile elements like P, S, and toxic elements, such as Zn, can be captured by these large particles, and therefore the emissions of PM 1 are partially reduced.