Optimization of Hot-Air and Microwave Combined Drying Technical Parameters for Extruded Cotton Stalks Based on Response Surface Methodology

Drying is an important process of cotton-stalk reconstituted material. The aim of this study was to find the best drying process of extruded cotton stalks by using three drying methods and applying single-factor experiments combined with response surface methodology (RSM). For experimental design, the central composite design approach was used. The hot-air temperature, moisture content at the conversion point, and microwave power were selected as influencing factors; the drying rate and energy consumption per unit precipitation were selected as experimental indexes. The regression equation between each experimental factor and the performance index was established, and the optimization calculation was carried out. The experimental results showed that the optimum drying parameters were as follows: hot-air temperature 95 °C, moisture content at the conversion point 57%, and microwave power 700 W. With these experimental conditions, it was verified that the drying rate was 4.14 kg (100 kg min) −1 and the energy consumption per unit precipitation was 70.89 MJ kg −1 , which were 106.7% and 10.4% lower than that of hot-air drying and microwave drying, respectively. The research results will provide a theoretical and technical basis for the large-scale drying process of cotton stalks and the design of drying equipment.