Circulating fluidized beds disadvantages

Circulating fluidized-bed reactors have been operated successfully at Sasol for many years. The major disadvantages for them are the need to operate at high temperature to obtain sufficient productivity with the lower surface area catalysts that are needed to obtain attrition resistance, the low alpha operation where only vapor-phase products are produced as is required to eliminate catalyst agglomeration, the energy required for catalyst... 

The low index of the Reynolds number indicates that values of kj change little with increases in u of as much as 200%. This reflects the unusual hydrodynamic characteristics of fluidization where particle motion within the bed is quite random and increasing u causes an increase in the circulation of particulates. Relative velocities between solid and liquid, which in fact determine hydrodynamics, do not increase linearly with u. Although Eq. (2.37) appears to correlate Nassifs results, it suffers from a basic disadvantage u occurs on both sides of Eq. (2.37) be careful that values of u do not swamp the influence of other variables. Nevertheless one can use Eq. (2.37) to get an order-of-magnitude value for /c. ... 

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