Crystallization Process Analysis by Population Balance Modeling

In the area of industrial crystallization, population balances are used to model how the number and properties of the crystals in a crystallizer are generated and eventually appear as the solid product. A population balance is a mathematical description of conservation of number of particles, and accounts for how the number of particles having a particular set of properties (e.g., size, shape, density) may change during the process. The population balance has the same format as a mass balance or an energy balance. However, while mass and energy are conserved, particles having specific properties are not, and the population balance aims to account for how various mechanisms lead to changes. Traditionally, a population balance is a number balance, accounting for the number of particles of each particular size. Even though linear size is by far the most common particle characteristic on which the balance is based, other independent variables of the particle phase space can be of interest and modeled. By particle phase space is meant the multidimensional space of various particle properties. The population balance can also be formulated with more than one independent variable describing different particle properties. For example, if two linear dimensions of the particle are used in its characterization and are included in the modeling, we obtain a balance that also contains a description of shape changes, not only size changes.