This article describes the evolution of the moisture content distribution in a population of wet particles during a semibatch drying process. The population balance model that is defined for this process includes falling particle drying rate, that is, the drying rate of a particle depends on its moisture content. This model is solved analytically using the method of moments and method of characteristics. Simulation experiments give realistic and meaningful results. Drying experiments still have to be performed to test the validity of the assumptions made in this model. (C) 2012 American Institute of Chemical Engineers AIChE J, 2012