A first attempt is presented at investigating the problems of the automatic control of a diammonium phosphate granulation plant. This system is chosen for its simplicity, requiring one solid and one liquid feed stream to the granulator. A dynamic model is developed for the granulator in the form of a set of nonlinear differential equations in the zeroth, first and second moments of the granulator discharge stream particle size distribution. The equations are linearized and it is shown that the responses to similar disturbances of both the nonlinear and linear systems agree closely. Using the linear form, the model is extended to include the entire plant and a feedforward controller is designed by which disturbances in feed rate are used for manipulating the product recycle ratio to maintain constant the average particle size of granulator product.