The drill pipe crystallisers (DT and DTB) ensure the homogeneous mixture of the crystals in the crystallizer with an internal axial pump.

The energy provided by the pump is lesser than that deployed by a forced circulation, which significantly reduces attrition and breaking of crystals.

Crystal size may be greater than 2 mm and the residence time greater than 10 hours.

A surrounding decantation zone is often added to remove the fines and thereby increase the average size of the crystals.