Method for gasifying a material using a circulating fluidized bed

Claim 1

In a method for gasifying a combustible material in a first circulating fluidized bed comprising introducing the material to be gasifying in the form of particles in a fluidization chamber provided at its base with means for effecting a fluidization by an ascending flow of a first fluidization gas at a speed which is so regulated as to operate as a circulating bed, discharging the gases and entrained particles through a discharge circuit connected to an upper part of the fluidization chamber and passing through a particle recovering means, returning the recovering particles to the first fluidized bed through a recycling circuit and subjecting the recovered particles in the return path to a processing which is carried out in a second fluidized bed in a device outside the fluidization chamber and comprising a filtration compartment traversed by a second fluidization gas and a processing compartment adjacent to said filtration compartment and separated by a first partition wall therefrom; the improvement comprising causing the second fluidization gas to traverse the filtration compartment at a speed which is so regulated as to put into suspension only fine particles having sizes smaller than a given limit, recovering the largest particles and directly recycling them in the first fluidized bed and flowing the fine particles over the first partition wall into the processing compartment and subjecting the fine particles to a processing with a comburent gas in the processing compartment so as to agglomerate ashes by formation in the processing compartment of a high temperature zone, withdrawing the agglomerated ashes at the base of the processing compartment and returning unburnt fine particles to the first fluidized bed through a second recycling circuit by flowing the unburnt fine particles over a second partition wall to an adjacent storage compartment and returning the unburnt fine particles to the first fluidized bed from the bottom of said storage compartment.