Mixer-settlers are classed as stage-wise or equilibrium contactors because they manifest a step concentration profile as the aqueous and solvent phases pass from stage to stage. They consist of two compartments (Fig. 3.12): [2]
|
Contactor
|
Differential (D) or stage-wise (S)
|
Reliability
|
Flexibility
|
Ease of critically safe design
|
Size relative to capacity
|
Comments
|
|
Spray column
|
D
|
Excellent
|
Poor
|
Good
|
Farge
|
|
|
Packed column
|
D
|
Good
|
Poor
|
Good
|
Farge
|
|
|
Rotating disc
|
D
|
Poor
|
Fair
|
Good
|
Medium
|
|
|
column
|
|
Disk & Donut
|
D
|
Excellent
|
Poor
|
Good
|
Medium
|
In use at Fa Hague,
|
|
column Rotary annular
|
D
|
Fair
|
Fair
|
Good
|
Medium
|
France
Proposal only
|
|
contactor
|
|
Pulsed packed
|
D
|
Good
|
Fair
|
Good
|
Medium
|
Packing tends to
|
|
column
Pulsed perforated
|
D
|
Excellent
|
Good
|
Good
|
Medium
|
orientate with pulses
In use at Sellafield, UK
|
|
plate column
|
|
Reciprocating
|
D
|
Poor
|
Good
|
Good
|
Medium
|
|
|
plate column
|
|
Raining bucket
|
D
|
Fair
|
Poor
|
Poor
|
Farge
|
Each phase dispersed
|
|
contactor
Mixer-settler
|
S
|
Excellent
|
Fair
|
Poor
|
Farge
|
alternately In use at Fa Hague,
|
|
Pump-mix
|
S
|
Good
|
Good
|
Poor
|
Medium
|
France and Sellafield UK
|
|
mixer-settler
|
|
Centrifugal
|
S
|
Good
|
Good
|
Good
|
Small
|
In use at Savannah
|
|
contactor Static mixer
|
S
|
Excellent
|
Poor
|
Good
|
Small
|
River USA Proposal only
|
|
|
 |
|
|
|
Table 3.2 Chemical engineering attributes of mixer-settlers (typical for a used nuclear fuel recycling plant throughput of 5 MTHM/year)
|
Attribute
|
Value or description
|
|
Dimensions
|
12 m by 3 m by 2 m
|
|
Total liquid volume
|
60 m3
|
|
Total liquid residence time
|
18 hours
|
|
Criticality safety
|
Not safe by geometry. This restricts mixer-settler application to processing solutions dilute in fissile material.
|
|
Design
|
Well-established using well-proven algorithms. One mixer-settler equivalent to one theoretical stage.
Internal design details include aqueous and solvent weirs, mixed phase port, speed and design of impeller, aqueous off-take weir control system.
|
|
Operability
|
Contactor can be simply restarted without pre-flushing after minor shutdowns. Long residence time provides operators with a long time to respond to process malfunctions.
|
|
