What type of fuel residence time does continuous circulation of solids in CFB provide?

Continuous circulation of solids in a circulating fluidized bed (CFB) system results in a long fuel residence time. This is because the design of a CFB allows for the solids to be circulated through the system repeatedly, providing ample opportunity for the combustion or gasification processes to take place.

In a CFB, the solids are maintained in a fluidized state by the upward flow of gas, which keeps them suspended. As the solids circulate, they experience a longer residence time compared to other combustion systems where fuel particles may be moved through the system more rapidly. This extended residence time allows for improved heat transfer and more thorough reactions, whether it is combustion or gasification of the fuel.

The long residence time also contributes to better efficiency and reduced emissions, as it allows for more complete combustion of the fuel and adequate gas-solid interactions, ensuring that unreacted materials are minimized. Thus, the characteristic of continuous circulation of solids effectively supports a longer fuel residence time in a CFB setup.