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

Abstract

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.

Keywords:

• large-eddy simulation
• tabulated chemistry
• pulverised-coal combustion
• sodium
• alkali metal

Acknowledgements

This work was performed by the first author KDW when he was a Research Assistant at Brunel University London. Special thanks are due to Prof. Peter Glarborg of Technical University of Denmark, who provided us the detailed chemical mechanism of alkali metal species. This work used the ARCHER UK National Supercomputing Service (http://www.archer.ac.uk).

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by Royal Society, Engineering and Physical Sciences Research Council (EPSRC) of the UK, National Natural Science Foundation of China [grant number 51390491], [grant number 51422605], and China Scholarship Council.