The feed solution is preheated in a heat exchanger (1) using the
steam condensate before being fed into the collecting tank (3). This
tank also receives the overflow from the crystallizer unit (5) and the
mother liquors from separation units (8, 9). There, a supplementary
steam is given via a preheater (2) to ensure the fine dissolution of the
mother liquor prior to entering the crystallizer.
The crystallizer is of special Messo design to suit the product
characteristics in temperature sensitivity. It consists of the main
crystallizer body with draft tube and internal circulation pump,
which is directly connected to the heat exchanger. A baffle for a
defined clear liquid over flow is part of the crystallizer design. The
heat exchanger is flanged under the crystallizer to minimize the
retention time of the suspension within the crystallizer.
The feed solution from (3) is then fed into the crystallizer unit (5)
which is heated via a heat exchanger and transferred to the liquid
level within the crystallizer via the internal draft tube. The internal
circulation rate is designed in order to ensure that the metastable
range of the product will not be exceeded during the operation. At
liquid level, the evaporation of the solvent takes place, reaching the
designed supersaturation level. In consequence, crystals are formed.
The crystals slurries are withdrawn and fed into a thickener (8). The
underflow of the thickener is fed into a centrifuge in order to
separate crystals from the mother liquor. Product purities are
enhanced by washing on the centrifuge.
The overflow of the thickener and the filtrate from the centrifuge is
collected in an agitated vessel (3) in which also the solution from the
evaporator is fed as mentioned above.
The vapors evolved in the crystallizer are condensed by cooling
water in a surface condenser (9), where the vacuum condition is
controlled (10)