CFD analysis of municipal solid waste combustion using detailed chemical kinetic modelling
Nitrogen oxides (NO x ) emissions from the combustion of municipal solid waste (MSW) in waste-to-energy (WtE) facilities are receiving renewed attention to reduce their output further. While NO x emissions are currently 60% below allowed limits, further reductions will decrease the air pollution control (APC) system burden and reduce consumption of NH3. This work combines the incorporation of the GRI 3.0 mechanism as a detailed chemical kinetic model (DCKM) into a custom three-dimensional (3D) computational fluid dynamics (CFD) model fully to understand the NO x chemistry in the above-bed burnout zones. Specifically, thermal, prompt and fuel NO formation mechanisms were evaluated for the system and a parametric study was utilized to determine the effect of varying fuel nitrogen conversion intermediates between HCN, NH3 and NO directly. Simulation results indicate that the fuel nitrogen mechanism accounts for 92% of the total NO produced in the system with thermal and prompt mechanisms accounting for the remaining 8%. Results also show a 5% variation in final NO concentration between HCN and NH3 inlet conditions, demonstrating that the fuel nitrogen intermediate assumed is not significant. Furthermore, the conversion ratio of fuel nitrogen to NO was 0.33, revealing that the majority of fuel nitrogen forms N2.
Process simulation of a large mass burn Waste-To-Energy boiler by the combination of CFD software programs
Although corrosion is inevitable in any WTE boiler due to nature of the fuel, corrosion rates can be affected through the control of a number of process variables. To have a quantitative tool for evaluating these variables, a three-dimensional numerical model of the mass burn WTE boiler was developed by using FLUENT and FLIC. This model is distinct in that it extends into the boiler convection passes in order to research corrosion mechanism in the superheaters. The mathematic model was validated through the comparison of the simulation results with measured data collected during extensive testing at real operating conditions.
Combustor design and modification integrates computational fluid dynamics
Vertical Velocity Distribution. The baseline condition illustrates the flow pattern expressing the vertical velocity components over the range front-10 to 15 m/s. The baseline case with only a single elevation of overfire air produces a high velocity flow channel attached to the front wall with an associated recirculation down the rear wall of the main combustor section. The optimized case includes a revised overfire air configured to centralize the vertical flow region. The peak vertical velocities and size of the recirculation zones are reduced in the optimized case.