Research on hot-air drying and control model for dry basis moisture content of seed cotton

Abstract: The initial moisture content (dry basis) of seed cotton picked by machine is very high, occasionally exceeding 18%. However, research has shown that the moisture content between 6.5% and 8.5% is optimal for processing seed cotton. To obtain a higher drying efficiency and better drying quality of seed cotton before cleaning and ginning, it is necessary to control drying conditions within a narrow range. However, many cotton gins currently set and control the temperature of seed-cotton drying equipment based on personal judgments, which is inaccurate and risky. Based on a large number of experiments on hot air drying characteristics, this paper developed a hot-air drying model of seed cotton and solved the above problem. We used quadratic regression in a 3×3 factorial experimental design to model the effects on the final moisture content of three factors (hot air temperature, seed cotton feed rates and initial moisture content) and three levels of each factor. Results show that all three factors significantly influence the drying rate of seed cotton. In addition, the first 15 s of the drying process exhibits a faster drying rate, after which the drying rate rapidly decreases. Curve fitting with a monomial diffusion model, Page's drying model, and a quadratic polynomial model, we found that the monomial diffusion model fit the data more closely (R2=0.9549) than the other models. Analyzing the drying process more closely, we determined that our hot-air drying model of seed cotton could provide a theoretical basis for adjusting the control parameters in real time on the drying equipment. Of the three control parameters tested, the final moisture content of seed cotton is most sensitive to (a) the initial moisture content, (b) cotton feed rate, and (c) hot-air temperature, in decreasing order of sensitivity. The hot-air drying model developed in this paper has been applied in real-time control of seed cotton drying in actual production, confirming its utility in process effectiveness and consistency, energy efficiency, and net economic benefit to the ginner.