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Choosing the correct type of mixer for your liquid phase chemical reaction process
Agitators and static mixers are both commonly used in chemical reaction processes. They have quite
different characteristics and the correct choice is vital to an efficient, successful, optimised and low energy
consuming process.
Agitated systems can benefit from the use of expert design software and CFD simulation as well as the use of
high efficiency impellers to minimise energy consumption and reduce batch mixing times to achieve specific
targeted objectives.
Images below show multistage agitated cascade reaction vessels and a 3D CFD image modelling flow patterns
in a gas liquid reactor.
Static mixer reaction systems can be employed in many traditionally batch processes. Static mixer
reactors offer benefits in both capital cost, plant size and reaction selectivity. Image below
shows a typical skid mounted continuous static mixer reactor system.
First consider the chemistry and the process objectives and decide on the best available technology
|
Process Objective |
Mixer type |
|
|---|---|---|
|
Best technology |
Second best technology |
|
|
Mixing for instantaneous reactions |
Static mixer |
Agitator |
|
Reaction, reaction times |
Static mixer |
Agitator |
|
Reaction, reaction times |
Agitator |
Static mixer |
|
Competing, consecutive |
Static mixer |
Agitator |
|
Non competing reactions. |
Either technology can be used successfully, sometime both together for even better results. |
|
|
Liquid solid reactions |
Agitator |
Static mixer |
Choose the correct type of static mixer dependent on the flow regime:
|
Flow regime |
Mixer type |
Image |
|---|---|---|
|
Laminar |
KMX (structured) or |
|
|
Transitional |
KM (helical) |
|
|
Turbulent |
HEV Vortex inducing) or |
|
Selection of the correct type of static mixer can reduce energy consumption by 3-4 times for the same quality
of mixing (CoV or Coefficient of Variation).
Selection of the correct type of static mixer can reduce energy consumption by 3-4 times for the same quality
of mixing (CoV or Coefficient of Variation).
Choose the correct type of agitator impeller dependent on the flow regime:
|
Flow regime |
Impeller type |
Image |
|---|---|---|
|
Laminar |
Helix, anchor |
|
|
Transitional |
HE-3, MW4, 4P |
|
|
Turbulent |
HE-3, SC-3, MW4 |
|
Selecting the correct type of impeller for the duty and optimising the impeller diameter and speed can
potentially reduce energy consumption by up to 10 times for the same blend time.
Summary:
- Select the correct technology for the process objectives.
-
Allow your supplier to select the correct type of static mixer for the process. Don’t assume that all
static mixers are the same. -
Allow your supplier to select the correct type of agitator impeller, speed and diameter to minimise
blend time and energy consumption. Don’t impose agitator specifications without expert advice.
