(Basic knowledge) What is the critical fluidization velocity of a circulating fluidized bed boiler?

In a bed composed of particles with uniform particle size, when the gas flow rate through the fixed-bed is very low, as the wind speed increases, the bed pressure drop increases in proportion. When the wind speed reaches a certain value, the bed pressure drop reaches its maximum value, which is slightly greater than the static pressure of the bed. If the wind speed is increased further, the fixed bed suddenly loses its stability, and the bed pressure drop drops to the level of the bed’s static pressure. If the bed is composed of widely separated particles, its characteristic is that before the larger particles start to move, the smaller particles in the bed are already partially fluidized. The transition of the bed from a fixed-bed state to a fluidized-bed state is not distinct; instead, stratified fluidization tends to occur. The minimum velocity required for a granular bed to transition from a stationary state to a fluidized state is known as the critical fluidization velocity.

The minimum velocity required for a granular bed to transition from a stationary state to a fluidized state is known as the critical fluidization velocity.

The fluidization velocity refers to the wind speed required for the medium, in a fluidized state, to move upward against its own gravity. In a circulating fluidized bed boiler, the air volume at which the bed resistance stops increasing is known as the minimum fluidization air volume, and the corresponding wind speed is the minimum fluidization velocity. Critical fluidization velocity: The airflow velocity at which the drag force exerted by the fluid on the particles is equal to the weight of the particles.

Critical fluidization velocity: the airflow velocity at which the drag force exerted by the fluid on the particles is equal to the weight of the particles