In-situ measurement method of crystal concentration in a seeded batch crystallizer

In solid-liquid mixing, the distribution of solid particles in a vessel is one of the most important knowledge for the design or the operation of the process. The most popular method to measure the local solid concentration is the direct sampling method of the suspension by the withdrawal tubes, in which the sample must be truly representative and this is extremely difficult to achieve. In this work, an in-situ measurement method of solid concentration at different heights in a vessel was proposed by using infrared light emitting diodes and phototransistors. This was applied to get the information about the crystal concentration in a seeded batch crystallization of aluminum potassium sulfate in a crystallizer agitated by a 6-bladed flat paddle or a 6-bladed pitched paddle. It was found that the method proposed in this work could follow the crystallization rate accurately, which indicates that the pitched paddle produces a narrow crystal size distribution compared to the flat paddle.