What is the dense phase zone, transition zone and dilute phase zone of a circulating fluidized bed boiler?

　　The dense phase zone refers to the lower part of the circulating fluidized bed combustion chamber, where the gas-solid two-phase flow contains the zone with a high concentration of solid particles.

　　The dilute phase zone refers to the upper part of the circulating fluidized bed combustion chamber (usually above the secondary air nozzle), and the gas-solid two-phase flow contains the zone where the concentration of solid particles is low.

　　The transition zone is the section between the dense phase zone and the dilute phase zone. The transition zone of the circulating fluidized bed boiler is the area that is relatively easy to have abrasion.