To accurately characterize the flow resistance of gas passing through fuel beds with different materials and varying bed depths (i.e.

210

420

and 635 mm)

this paper establishes an experimental bench to describe the flow characteristics within porous media. Nonlinear fitting is performed on the experimental data to determine the viscous and inertial resistance coefficients. On this basis

a novel three-dimensional non-decoupled model is developed using the porous media model and discrete phase model (DPM)

for the simultaneous combustion of fuel bed and freeboard in a biomass-fired grate furnace. The non-uniformity of biomass shape and size are sufficiently considered. Subsequently

comprehensive combustion modeling is conducted

and the impact of the flow resistance on the prediction accuracy is quantitatively investigated. Results show that: 1) As the gas flow rate increases

the bed height rises

and the packing porosity decreases

the flow resistance generated by the fuel bed to the passing gas becomes increasingly significant. For instance

when gas flows through bed of the three heights at 0.7 m/s

the pressure drops are 1289

2614 and 3 658 Pa

respectively; 2) The flow resistance caused by the packed bed should be sufficiently considered when developing the model

as it affects the gas escape velocity and residence time

thereby significantly influencing the prediction accuracy. When this resistance is fully taken into account

the prediction error of the outlet O2 concentration decreases from 21.4% to 4.2%; 3) The non-decoupled model achieving bidirectional coupling of momentum exchange between the gas and solid phases

which can comprehensively predict the high-temperature flame of both the gas and solid phases

as well as the transport behavior of slag and fly ash particles inside the furnace. This study provides a reliable modeling approach for high-accuracy prediction of gas-solid coupled combustion processes in grate-firing furnaces.