Optimization of Fluidized-Bed Process Parameters for Coating Uniformity and Nutrient-Release Characteristics of Controlled-Release Urea Produced by Modified Lignocellulosic Coating Material

Abstract

Controlled-release fertilizers are employed in precision agriculture to optimize technology-enabled farming without environmental deterioration. In this study, almond-shell lignocellulosic waste particles are chemically processed to synthesize a coating suspension for the production of controlled-release urea (CRU) in a Wurster fluidized-bed reactor. The interactive effect of process parameters such as atomizing air pressure (Pair), fluidized-bed temperature (Tfb), spray rate (Rspray), and fluidizing-air flow rate (Qair) on the (i) coating-film uniformity of CRU particles and (ii) longevity of nutrient-release from CRU is reported. CCRD is used with RSM to design the experiments for the optimization of nutrient-release performance and coating-film uniformity in terms of a coefficient-of-variance (CoV) of film thickness. The regression models indicate a good prediction of coating-film uniformity and nutrient-release time, with R2 = 0.971 and R2 = 0.98, respectively. The optimum conditions for coating-film uniformity are determined to be Pair = 3.5 bar, Tfb = 80 °C, Rspray = 0.15 mL/s, and Qair = 72 m3/h, with a predicted CoV film thickness of 11.5%. Similarly, Pair = 3.2 bar, Tfb = 78 °C, Rspray = 0.125 mL/s, and Qair = 75 m3/h are the optimum conditions for nutrient-release performance, with a prediction nutrient-release time = 56 h. The experimental validation yields a CoV of film thickness = 12.6% and a nutrient-release time = 49.5 h, indicating good agreement between predicted and experimental values. In addition, Tfb appears to be the most significant parameter.