Optimization of steam drying conditions for seedling-growing tray made of paddy-straw

Abstract: The seedling-growing tray was produced by mixing such materials as straw powder, biological glue, and fertilizer soil with nutrient media, and shaping it by pressing and drying. The drying process is one of the important parts of the production. Which drying method and process to be used is a key factor to ensure the drying quality of the seedling tray. The seedling tray drying quality includes such aspects as warpage, crack, wet strength, and corrosion. The warpage and cracks not only affect the tray modeling rate and agronomic requirements of mechanized cultivation, but also increase the cost of the production. The corrosion of the seedling tray determines the seedling quality and its shelf life. The wet strength determines the shape of the seedling tray as it is steeped in water and the mechanized planting agronomic requirements. The seedling tray drying methods include natural environmental ventilation drying, hot air drying, and steam drying. On an experimental basis, the three kinds of drying methods effects on the quality of seedling tray drying and the advantages of steam drying were considered in this paper. Then the steam drying method was determined to be the major way of drying the seedling tray. The wet strength is also an important indicator of steam drying quality, which is one of the key factors meeting the demands of seedling-growing tray molding and mechanized cultivating to ensure that the wet strength of a seedling-growing tray could fulfill the demands above. In this paper, a seedling-growing tray made of paddy-straw was taken as the research object, and the steam drying technology was used, with the wet strength after steam drying taken as experimental indicators. Through single-factor tests, we analyzed some elements which could affect the wet strength of a seedling-growing tray, such as natural environment pretreatment time, drying time, drying temperature, and drying time in a dryer after stopping steam supplying of a tray, and ascertained the influencing factors and the range of these factors. Based on single-factor tests, we utilized a quadratic orthogonal rotation combination test to establish a seedling-growing tray steam drying mathematics modeling, and analyzed the relationship between each factor and evaluation indicators based on a two-factor analysis method, and prioritized factors in mathematics modeling. Experiments showed the optimum process conditions of a seedling-growing tray made of paddy-straw drying we obtained: seedling tray pretreatment time was 10h, drying time was 21h, drying temperature was at 130℃. In this condition, the predicted wet strength of a seedling-growing tray was 0.4MPa. And the actual wet strength was 0.395MPa in validation tests. By comparing the theoretical predictions and the actual results, the relative error was 1.25%.The research result could provide certain theory directions for the industrial production of a seedling-growing tray made of paddy-straw.