Draft Tube Baffle Crystallizer

The Draft Tube Baffle Crystallizer is an elaborated Mixed Suspension Mixed Product Removal (MSMPR) design, which has proven to be well suited for vacuum cooling and for processes exhibiting a moderate evaporation rate. The concept is such that if no (or little) heat make-up is required, it results in a rather compact arrangement; therefore the initial investment is minimized.

As a rule, these units operate with a rather low supersaturation, which is sometimes a limitation to crystal growth, so that very large crystals can be produced only by providing extensive and costly dissolving of fines.

The Draft Tube Baffle unit (Figure 1) includes a baffled area (settling zone), peripherical to the active volume, from where excess of mother liquor and/or fines are removed for further processing. The necessary agitation of the suspension mixed with the incoming feed solution is provided by a bottom entry agitation at moderate energy consumption.

Figure 1 Draft Tube Baffle Crystallizer

Draft Tube Baffle crystallizers are often equipped with an elutriation leg below the body to classify the crystals.

When destruction of fines not needed or wanted, baffles are omitted and the internal circulation rate is set to have the minimum nucleating influence on the suspension (Draft Tube design, draft-tube crystallizer).

When large evaporation rates are required, an external heating loop must be provided, making the arrangement less competitive from an initial cost standpoint.

The Draft Tube Baffle Crystallizer, which can be considered when crystallization can be achieved with natural suspension, has proven to be well suited to many applications such as:

• boric acid
• Na₂SO₄. 10H₂0 (Glauber salt)
• melamine
• citric acid
• NaCIO₃

For more products see in section Product Experience.