(216d) Fluidized Packed Beds (FPB) – an Alternative for Process Gas Treatment in “Dirty” Systems?

Columns with fixed internals, such as random or structured packings, are well known and widely used in fluid separation processing. However, there are applications where the immobilized packings fail or cause serious operational problems due to their susceptibility to clogging during the treatment of solid loaded media.

Fluidized packed beds are discussed as an alternative for gas-liquid operations in systems with a high solid content. Continuous movement of the packings allows self-cleaning of the packing and thus promises stable operation even in systems with very high solid content. Unless the possible advantage in "dirty" systems, fluidized packed beds are far less common compared to fixed packed beds, this is partly due to the lack of reliable design data for this type of apparatus.

In order to design a fluidized bed packed column, experimental investigations of the fluid dynamics and mass transfer behavior have to be performed in order to generate design principles. In this work, the results of extensive experimental investigation of fluidized beds are carried out in a specially designed test plant with a diameter of ds = 0.6 m. The hydraulics of fluidized beds made of polypropylene have been investigated using the air/water system under ambient conditions in the gas load range up to the flooding point and at specific liquid loads between 0 and 80 m3/(m2h). Particular attention was paid to the determination of the fluidization point, characterizing the lower limit of the operating range of the fluidized bed. The start of fluidization of the packing is crucial to characterize the operating range of the fluidized bed. Based on the SBD model [1], a model equation has been developed on the basis of the experiments, allowing a prediction of the fluidization point and pressure drop of the wetted bed. The separation efficiency and the effective mass transfer area of the fluidized bed were determined based on experiments with different standard test systems, including the system CO2/air-NaOH under ambient conditions. The results were discussed in detail in the context of literature data and compared with conventional Pall rings.

Additionally, specific challenges in design and scale-up of fluidized beds are addressed.

The design data developed in this work has been used for the design of an industrial plant for H2S absorption from flue gas, experiences in design, fabrication and operation of the industrial plant are presented as well.

From the presented work it can be concluded, that fluidized packed beds may be a good alternative for gas-liquid operations like scrubbing and stripping in systems with a high solid content.