In this talk, experimental and theoretical investigations on the stability of coal-air flames in high-speed jets stabilized recirculating flow will be presented. The operational limits of high-ash coal air flames in MILD-like mode are to be discussed. The effects of the distribution of airflow between the primary and high-speed jets, particle size distribution,
and feed rate of coal are the main results of the study. Experiments re carried out with two different particle size distributions, a wide range of primary jet velocities, the mass flow rate of high-speed jets, and coal feed rates. Operating conditions for a self-sustained fuel-rich primary reaction zone without preheated air jets and no ash-fusion have been
identified. While variations in the primary jet velocity, particle size distribution, and feed rate have a strong influence on the flame stability, weak dependence is observed by changes in the high-speed jet flow rate. A non-dimensional ignition index (τ), ratio of the particle flow time to particle ignition time, captures the effects of all the operating parameters onto a stability map. Theoretical inferences on increase in stability of the flame by preheating coal and using bi-modal particle size distribution will be discussed. The different regimes of reactor operations with LPG and coal are summarized in the figures
below.