Control of fines suspension density in the fines loop of a continuous KCI crystallizer using transmittance measurement and an FBRM® probe

The control of crystal size distribution (CSD) is investigated in a 1.5 L laboratory cooling KCI crystallizer using fines dissolution rate as the manipulated variable. The controlled variable was either the fines suspension density in the fines withdrawal loop, measured by an innovative double-sensor turbidity meter manufactured in-house, or the chord length distribution (CLD) measured by the Focused Beam Reflectance Measurement (FBRM(R)) probe (model: Par-Tec(R) 100, Lasentec(R), Redmond, WA). It was shown that effective control of mean crystal size and fines suspension density in the presence of setpoint and disturbance changes is feasible with both control schemes. The double sensor turbidity sensor proved to be very rugged even in the presence of insoluble clay background particles. The FBRM(R) probe was more sensitive and capable of detecting particle breakage and flocculation.