Kaidi Wan

Online-CPD-Coupled Large-Eddy Simulation of Pulverized-Coal Pyrolysis in a Hot Turbulent Nitrogen Jet

ABSTRACT The pyrolysis characteristics of pulverized-coal particles in a hot turbulent nitrogen jet were investigated using large-eddy simulation (LES). In the present study an advanced pyrolysis model, the chemical percolation devolatilization (CPD) model, has been incorporated into LES in real time. The simulation results of the developed online-CPD-coupled LES were used to calibrate the kinetic parameters of the conventional single first-order reaction model (SFOM). Through the comparison between the CPD-coupled LES and the LES using the SFOM model, the CPD-coupled LES approach is found to be able to give a better prediction on particle pyrolysis in the high-temperature turbulent flow. Finally, the effects of important parameters, including the particle diameter, coal type, coal-feeding rate, carrier-phase velocity, and pyrolysis temperature, on the pulverized-coal pyrolysis process were investigated through parametric studies using the online-CPD-coupled LES method.

Modelling alkali metal emissions in large-eddy simulation of a preheated pulverised-coal turbulent jet flame using tabulated chemistry

The numerical modelling of alkali metal reacting dynamics in turbulent pulverised-coal combustion is discussed using tabulated sodium chemistry in large eddy simulation (LES). A lookup table is constructed from a detailed sodium chemistry mechanism including five sodium species, i.e. Na, NaO, NaO2, NaOH and Na2O2H2, and 24 elementary reactions. This sodium chemistry table contains four coordinates, i.e. the equivalence ratio, the mass fraction of the sodium element, the gas-phase temperature, and a progress variable. The table is first validated against the detailed sodium chemistry mechanism by zero-dimensional simulations. Then, LES of a turbulent pulverised-coal jet flame is performed and major coal-flame parameters compared against experiments. The chemical percolation devolatilisation (CPD) model and the partially stirred reactor (PaSR) model are employed to predict coal pyrolysis and gas-phase combustion, respectively. The response of the five sodium species in the pulverised-coal jet flame is subsequently examined. Finally, a systematic global sensitivity analysis of the sodium lookup table is performed and the accuracy of the proposed tabulated sodium chemistry approach has been calibrated.