Solution Crystallization Plants
Solution Crystallization Plants
In the field of mass crystallization, GEA 's expertise encompasses all basic types of crystallizers for the crystallization from solutions, such as the forced circulation or draft-tube (MSMPR) crystallizer, the turbulence (DTB) crystallizer, and the fluidized bed (OSLO) crystallizer. GEA is thus in an unique position to address the special needs of each of its clients, depending on the required product crystal quality and size. GEA routinely supplies upstream and downstream components, such as the preconcentration (in multiple effect, mechanical vapor recompression, flash, and other evaporator configurations), the debrining (thickening, filtration or centrifugation), drying, solids handling and packaging. GEA also supplies piping and instrumentation and process control systems for its plants, installations in prefabricated and modularized sections as required by the client.
Every specific crystallization processes is influenced by several other factors. Some of the most important are mentioned below.
The surface-cooling process produces supersaturation directly on the heat exchanger surface. The supersaturation in the heat exchanger is the highest in the entire crystallizer. Incrustations on the heat transfer surface and eventual plugging of the tubes are the normal consequences. This can be an acceptable situation for discontinuous operation, because with each next batch the incrustations may be dissolved again. For continuous processes, however, the surface cooling is only an option if the low operating temperature required in the crystallizer makes vacuum cooling crystallization impractical. If a continuous crystallizer must employ surface-cooling, especially large heat exchanger surface area is supplied, in an effort to increase the operating cycle.
Vacuum-cooled crystallization is the preferred cooling crystallization method for continuous operation. Because cooling is generated by adiabatic expansion of the solvent, and the condensing of the vaporized solvent is done in a separate heat exchanger, scaling of cooling surfaces is not experienced. Vacuum cooling becomes uneconomical (or impractical) only if operation at very low temperatures is required.
The evaporative crystallization is generally a vacuum process, much like vacuum-cooled crystallization. The difference is that this process is independent of the concentration and temperature of the feed solution. External heat can be added to the system and the concentration of mother liquor can be adjusted by evaporation. Like vacuum-cooled crystallization, there are no special encrustation problems in evaporative crystallization. Operating difficulties may arise in the case of concentration of inversely soluble substances, like some sulfates and carbonates. In such cases the same encrustation model exists as in surface-cooled crystallization. High suspension velocities in the heater tubes and high suspension density (to increase the desupersaturation rate) and can improve the operating cycle. Multiple-effect evaporative crystallization plants are supplied in cases where low energy consumption is especially important.