AFBC (Atmospheric fluidised bed combustion) process consists of forming a bed of inert materials like
finely sized ash or ash mixed with sand, limestone (for sulphur removal), and solid fuel particles in a
combustor and fluidising it by forcing combustion air up through the bed mixture. The gas flows thorugh
bed without disturbing particles significantly but gas velocity is high enough to support the total weight
of bed (fluidisation). At slightly higher velocity excess gas passes through the bed as bubbles (fluidised
bed) and gives the bed the appearance of a boiling liquid.