The aim of this study was to investigate the effectiveness of the application of design tools such as Composite Central Design (CCD) and Response Surface Methodology (RSM) in modelling and optimization of spruce drying. The models were developed based on drying simulation in a pilot-scale kiln. Optimization assumed three criteria, namely, minimization of drying time, energy consumption and drying stress. In addition, the influence of air parameters (temperature, relative humidity and velocity) on time, energy consumption and drying stress was analyzed. Optimal process parameters were obtained (3 m/s velocity, 72 ᵒC temperature, 44% relative humidity) using the desirability function approach. The temperature was the most important factor that affected all responses. The second important one was the relative humidity of air and the last important one was the air velocity. The interaction between temperature (T) and relative humidity (RH) on responses was stronger than the other interactions (T vs. V, RH vs. V).

Keywords: convective drying, spruce, drying simulation, composite central design, response surface methodology.