Quadratic performance index variations with respect to the dynamic parameters of a PI control with feedforward action in a plant pilot spray dryer were obtained by simulation. Dynamics of plant pilot spray dryer was assumed as first order, using outlet product humidity as response variable and air temperature, moisture and flow, and product moisture and flow as input variables. Initial time constants and gains were obtained experimentally in a plant pilot spray drying with a drying chamber of 1.3 m(3). Control action was simulated by taking air flow as action variable. Thus, air temperature may be altered, and therefore a complementary air temperature control was implemented. The results show that PI control tuning by Routh criteria is robust with respect to variation in time constants and gains. The main performance indexes remain in the same magnitude order when the dynamic characteristics were changed to 80%.