EFFECT OF FLUIDIZED-BED PROCESS VARIABLES ON CONTROLLED-RELEASE OF NITROGEN AND COATING

Abstract Pristine urea is lost due to ammonia volatilization and leaching causing toxic emissions and eutrophication. Controlled-release urea is employed as an abatement strategy. Most of the synthetic polymers used to produce controlled-release urea are non-biodegradable and expensive. To offset this problem, modified-starch biopolymer is used as coating material to produce controlled-release urea in fluidized bed. The effect of different process variables is studied on release characteristics and coating uniformity of coated urea. The product has better release characteristics. The statistical analysis reveals that fluidizing gas temperature and coating time are the most influential variables. The nutrient release time increases with increase in coating time and decreases with increase in fluidizing gas temperature beyond a certain limit. Coating uniformity, significant thickness and film integrity are required for promising release characteristics. Urea release followed non-Fickian diffusion and Case-II transport. This study can help produce green fertilizer at bigger scale.

摘要：纯净尿素会因氨挥发与淋溶作用发生损失，进而引发有毒气体排放与水体富营养化问题。控释尿素被用作此类问题的减排策略。当前多数用于制备控释尿素的合成聚合物不可生物降解且成本高昂。为解决这一问题，本研究采用改性淀粉生物聚合物作为包膜材料，在流化床（fluidized bed）中制备控释尿素，并探究了不同工艺变量对包膜尿素的养分释放特性与包膜均匀度的影响。研究结果显示，所得产品具备更优异的养分释放特性。统计分析表明，流化气体温度与包膜时间是影响效果最显著的工艺变量：养分释放时长随包膜时间延长而增加，而当流化气体温度超过特定阈值后，释放时长会随温度升高而缩短。优异的养分释放特性需要具备良好的包膜均匀度、合适的包膜厚度与完整的膜结构。尿素的养分释放遵循非菲克扩散（non-Fickian diffusion）与Case-II型输运（Case-II transport）机制。本研究可为规模化生产绿色肥料提供有力的技术支撑。