• ISSN 1008-505X
  • CN 11-3996/S
田虹雨, 董晶晶, 解臣硕, 崔静, 段建杭, 张天骄, 代佳颖, 王硕, 张丽莉, 魏占波, 武良, 郭武松, 刘之广, 张民. 利用离散元仿真及微结构分析法研究高铝瓷球对尿素表面改性和养分控释的效果[J]. 植物营养与肥料学报, 2023, 29(5): 900-911. DOI: 10.11674/zwyf.2022495
引用本文: 田虹雨, 董晶晶, 解臣硕, 崔静, 段建杭, 张天骄, 代佳颖, 王硕, 张丽莉, 魏占波, 武良, 郭武松, 刘之广, 张民. 利用离散元仿真及微结构分析法研究高铝瓷球对尿素表面改性和养分控释的效果[J]. 植物营养与肥料学报, 2023, 29(5): 900-911. DOI: 10.11674/zwyf.2022495
TIAN Hong-yu, DONG Jing-jing, XIE Chen-shuo, CUI Jing, DUAN Jian-hang, ZHANG Tian-jiao, DAI Jia-ying, WANG Shuo, ZHANG Li-li, WEI Zhan-bo, WU Liang, GUO Wu-song, LIU Zhi-guang, ZHANG Min. Using discrete element simulation and microstructure observation to study the urea surface modification and nutrients release performance of coated urea[J]. Journal of Plant Nutrition and Fertilizers, 2023, 29(5): 900-911. DOI: 10.11674/zwyf.2022495
Citation: TIAN Hong-yu, DONG Jing-jing, XIE Chen-shuo, CUI Jing, DUAN Jian-hang, ZHANG Tian-jiao, DAI Jia-ying, WANG Shuo, ZHANG Li-li, WEI Zhan-bo, WU Liang, GUO Wu-song, LIU Zhi-guang, ZHANG Min. Using discrete element simulation and microstructure observation to study the urea surface modification and nutrients release performance of coated urea[J]. Journal of Plant Nutrition and Fertilizers, 2023, 29(5): 900-911. DOI: 10.11674/zwyf.2022495

利用离散元仿真及微结构分析法研究高铝瓷球对尿素表面改性和养分控释的效果

Using discrete element simulation and microstructure observation to study the urea surface modification and nutrients release performance of coated urea

  • 摘要:
    目的 尿素表面改性是提高包膜质量和养分控释能力的关键措施之一。我们研究了不同磨料对肥料核芯表面的改性效果,以及改性提高肥料养分控释的效果。
    方法 供试肥芯为大颗粒尿素(直径3~5 mm,N 46%),供试磨料包括白刚玉、棕刚玉、高铝瓷球、高铝瓷柱和氧化锆球。经测量不同磨料研磨后尿素的休止角,证明采用堆密度1.336 g/cm3、直径6 mm的球形高铝瓷在10 min内对尿素表面改性效率最高,故用作后期的试验磨料。将1.5 kg的高铝瓷球与1 kg大颗粒尿素加入转鼓中,采用离散元仿真软件 (EDEM) 模拟磨料摩擦与尿素颗粒自摩擦的粒子运动、碰撞、受力和分布特征;使用扫描电子显微镜分析磨料、表面改性尿素和包膜尿素的表面和切面结构特性,采用原子力显微镜测试包膜尿素膜表面结构微观特征与粗糙度;采用静水溶出率法测定纳米SiO2改性蓖麻油基聚氨酯包膜的表面改性尿素的养分释放特征。
    结果 EDEM仿真结果表明,转鼓底部颗粒运动快(1.125 m/s),边缘运动慢(0.00309 m/s),转动过程中,小颗粒物聚集在转鼓底部产生偏析。尿素自摩擦力约0.035 N,加入密度大于尿素的球形高铝瓷磨料后,混合体系的摩擦力变大(约0.042 N),尿素颗粒间的碰撞次数较自摩擦体系高出13.0%,因此改性效率得以提高。表面改性显著降低了颗粒表面粗糙度,在1 μm2检测范围内,粗糙度(Ra)平均降低了79.2%。由扫描电镜图可以看出,普通尿素表面粗糙,膜材料填充在凹陷部位,包膜耗费的膜材料较多,且膜与尿素贴合不紧密,在运输或长期储存过程中易发生膜破损,失去养分控释能力;改性后的尿素表面光滑,减少了无功能的膜材浪费,且膜厚均匀,膜层与核芯结合紧密,膜切面结构均匀,不易破损。养分释放结果表明,以5%包膜率的纳米SiO2改性蓖麻油基聚氨酯对尿素包膜,表面改性尿素相较普通尿素可使养分释放期延长6倍,由表面改性前的24天提升至169天。
    结论 依据EDEM离散元软件模拟,球形高铝瓷作为磨料与尿素混合后,提高了尿素颗粒的摩擦效率,大大降低了尿素表面的粗糙度。表面改性后的尿素作为控释肥核芯,不仅节省了膜材料的用量,且膜层与肥芯结合紧密均匀,延长了等膜量下的养分释放期。

     

    Abstract:
    Objectives Surface modification is a key step towards realization of nutrient-release control of coated urea production. We tested several abrasives, and studied the basis for modification in improving the coating property.
    Methods In this study, large granular urea (3–5 mm, N 46%) was used as the fertilizer core, while the tested abrasives included brown-fused alumina, white-fused alumina, zirconia beads, alumina porcelain beads, and aluminum porcelain column. By measuring the repose angle of polished urea after polishing with the abrasives, alumina porcelain beads with a bulk density of 1.336 g/cm3 and a diameter of 6 mm were chosen as the abrasive in the later research stage. 1 kg urea and 1.5 kg alumina porcelain beads were loaded into a drum granulator, discrete element software (EDEM) was used to simulate the motion, collision, force and distribution of particles in system of abrasive friction and urea particle self-friction. The surface and sectional structure and the roughness of modified urea were scanned using electron microscopy. The microstructure of the coating was observed using atomic force microscopy (AFM). The nutrient release characteristics of polished and ordinary urea, coated with 3%, 5% and 7% of nano-SiO2 modified castor oil-based polyurethane, were determined by static water dissolution method.
    Results According to the simulation of EDEM, the urea particles near the bottom moved fast (1.125 m/s), and those at the edge moved slowly (0.00309 m/s), causing the segregation of small pAccording to the simulation of EDEM, the urea particles near the bottom moved fast (1.125 m/s), and those at the edge moved slowly (0.00309 m/s), causing the segregation of small particles at the bottom of the drum during the mixing process. The self-friction force of pure urea was about 0.035N, while the total friction force when mixed with the abrasive increased to about 0.042 N. This enlarged force increased the collision number of urea-abrasive mix system by 13.0% than that of the self-friction system, thus creating more efficient modification. The modification significantly reduced the surface average roughness (Ra) by 79.2% within 1 μm2 of detection area. From the electric micro-morphology images we could see, common urea surface was rough, film material filled into the low parts causing extra consume of film materials and obstructing the close bonding of coating layer with the urea chip, thereby the coating film was fragile during transportation or long-time storage and lost controlling capacity of nutrient release. While the modified urea surface was smooth, preventing the waste of film materials. The film layer was even in thickness and uniform in intersecting surface, and closely bonded with the core. The nutrient release period of urea coated with 5% nano-SiO2 modified castor oil-based polyurethane increased by 6 times, from 24 days before polishing to 169 days after polishing.
    Conclusions According to the simulation of EDEM discrete element software, the mixture of alumina porcelain beads and urea greatly increased the modification efficiency, reduced the surface roughness of urea significantly. The surface microstructure of the modified urea core of controlled release fertilizer was significantly improved, the amount of coating material was reduced, and the nutrient release period was prolonged under the same coating rate.

     

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