籽棉热风烘干控制干基含水率模型的研究

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

为了使机采籽棉在清棉、轧花等加工前把水分控制到合适的范围以提高加工质量,需要对籽棉进行一定的烘干处理,并对烘干过程进行实时控制。该文设计了籽棉热风烘干的三因素三水平正交回归旋转试验,研究了喂花量、籽棉初始干基含水率和热风温度这3个因素对籽棉烘干后干基含水率的影响。试验结果表明喂花量、籽棉初始干基含水率和热风温度对籽棉干燥速率都有较明显的影响,烘干过程的前15s干燥速率变化较快,之后趋于平缓。分别使用单项式扩散模型、Page模型和二次多项式模型进行拟合,发现单项式扩散模型拟合效果最好,决定系数R2均值为0.9549。该模型应用于实际生产中籽棉烘干的实时控制。效果表明使用该模型后烘干效率更高,籽棉烘干后干基含水率一致性更好。

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.