Analysis and flamelet modelling for laminar pulverised coal combustion considering the wall effect

Abstract

In this work, the wall effect on the characteristics of pulverised coal combustion is examined. To this end, laminar pulverised coal flames stabilised near a planar non-slip wall with isothermal and adiabatic boundary conditions are simulated with detailed chemistry. The phenomenon of side-wall quenching is observed in the non-adiabatic case due to significant wall heat losses. The temperature difference between the adiabatic flame and non-adiabatic flame at the planar non-slip wall can be as high as 1200 K. It is found that the distributions of different species show various sensitivities to the wall effect. Particularly, the species involved in the volatile matter and char off-gases are significantly influenced by the wall heat losses. In addition, the conventional flamelet model for pulverised coal combustion is extended to consider the heat transfers between the flame and wall. The performance of the extended flamelet model on prediction of the thermo-chemical quantities in both adiabatic and non-adiabatic flames is evaluated through a priori tests. The results show that the thermo-chemical quantities in both adiabatic and non-adiabatic flames can be overall reproduced by the extended flamelet model at both upstream and downstream locations. Interestingly, it is found that the gaseous temperature and CH mass fraction in the non-adiabatic flame can be better predicted by the extended flamelet model than those in the adiabatic flame at the downstream location.