Basic principles of liquefaction

A. Formation of fluidized bed

1. Fluidization concept and formation of fluidized bed conditions
(1) Fluidization: Solid particles suspended in a fluid in motion is called fluidization of solids, referred to as fluidization or fluidization.
(2) Fluidized bed and formation conditions.
Fluidized bed:People call the container and the solid particles presenting fluidized state together as fluidized bed.
Formation conditions:
①There should be a container:
②There should be a sufficient number of solid particles in the container:
③There should be a fluidizing medium.

B.Some basic phenomena of fluidized bed

According to the different fluidization media can be divided into two fluidization for: bulk fluidization and poly-fluidization
(1) bulk fluidization: fluidized bed with liquid as the fluidizing medium.
Features: is the bed with fluid velocity increases and balance expansion, the solid particles in the bed spread out each other movement, fluidization is very uniform, so also called uniform fluidization.
(2) Poly-fluidization: fluidized le with gas as sizing external con.
Features: The solid particles in the bed are not alone, but many particles are agglomerated together in groups. The gas is in the form of bubbles through the bed, so it is also called inhomogeneous fluidized bed.
The fluidized bed for petroleum catalytic cracking is the agglomerated fluidized bed.

C.Pressure drop in fluidized bed

The reason for the change in the pressure drop in the bed
①Fixed bed: The space between the particles in the fixed bed forms many small curved channels, and the fluid flows through these small channels due to the ponding resistance and pressure drop, the ponding resistance is proportional to the square of the flow rate, so the larger the flow rate, the larger the bed pressure drop generated.
② fluidized bed: the whole bed is suspended and the solid particles are free to move, the forces acting on the bed reach equilibrium, namely: bed pressure drop X bed cross-sectional area = solid weight in the bed - solid buoyancy.
③Dilute phase transport
When the fluid velocity reaches a certain level, the catalyst particles are carried out and the total weight of the bed is
Therefore, the pressure drop of the bed becomes small until all the solids are taken out, and the pressure difference between the two ends of the empty bed is the pressure drop of the fluid through the empty bed.