Sulfur coating of urea in shallow spouted beds

Abstract

Sulfur coated urea (SCU) is an effective and economical slow-release nitrogen fertilizer, and its production in a spouted bed was investigated. SCU was produced by batch and continuous operations. Higher quality products were typically produced by the batch process, but at significantly lower production rates than the continuous process. In order to understand such operations, mathematical models describing the coating process were developed and verified through experiments. The production of SCU was studied in shallow spouted beds fitted with a pneumatic molten sulfur spray nozzle located at the cone inlet. Bed hydrodynamics, coating mechanism, particle coating distribution and product quality were examined under the following conditions: Bed diameter of cylindrical section-0.24 and 0.45 m; bed height-0.11 to 0.63 m; included cone angle-60'; particle diameter-2.1 to 2.8 mm; particle density 930 to 1490 kg/m3; main spouting air 37 L(actual)/s; atomizing air S 0.87 L(actual)/s; urea feed rate-7.6 to 20 g/s; sulfur injection rate-2.1 to 6.1 g/s; orifice diameter-21 to 35 mm; bed temperature-18 to 70 °C; sulfur content < 60 %. The temperatures of atomizing air and molten sulfur were fixed for all runs at approximately 160 and 150 °C, respectively. The coating process was successfully modeled using mass and momentum balance equations, inertial sulfur droplet deposition as the dominant coating mechanism, and Monte Carlo simulations. The hydrodynamic model was based on the one-dimensional mass and momentum balances suggested by Lefroy and Davidson (1969) for gas and particle motion in the spout, the axial pressure correlation given by Morgan and Littman (1980), and the vector form of the Ergun (1952) equation for gas motion in the annulus. The effect of atomizing air entering through the spray nozzle was successfully incorporated into the model by considering the total momentum flux into the bed. Conical beds were found to behave similar to

Physico-chemical properties of carbohydrate polymer coatings for slow release urea industry

“…It verifies that 1.5 ml of solution will give better results for slow release urea. Similar kind of outcomes were predicted in the studies conducted by Choi and Meisen [14,15] on the sulfur coated urea samples. Shi et al [16] also coated the urea granules with plastic-starch compounds and showed that the nitrogen discharge duration of such coatings was greater when compared with coatings of other chemical materials.…”

Controlled‐release fertilizer based on poly(butylene succinate)/urea/clay and its effect on lettuce growth

“…Thus, the rational use of water resources and fertilizers is a crucial premise for agribusiness . However, the use of fertilizers also can generate severe environmental degradation, such as the eutrophication of water environments . Thus, new ways to spread up these fertilizers, promoting their more rational use, are more and more pursued.…”

Utilization of waste lignin to prepare controlled-slow release urea

“…Many materials have been reported to be used as coatings, such as sulfur, polyethylene, polysulfone, polyvinyl chloride, polystyrene, polyacrylic acid latex, chitosan, starch, polyvinyl alcohol, mixture of gypsum, limestone, cement, sulfur, and zeolite (Blouin et al 1971;Salman 1989;Al-Zahrani 2000;Hanafi et al 2000;Jarosiewicz and Tomaszewska 2003;Liang and Liu 2006;Lan et al 2011;Mohd Ibrahim et al 2014;Eghbali Babadi et al 2015). The sulfur layer is friable and many works have reported the improvement of the coating quality using costly sealants and conditioners (Cole and Simmons 1992;Choi and Meisen 1997;Liu et al 2008). Some of polymeric materials are non-biodegradable, toxic to the plants, and change the soil's pH, which is undesirable (Azeem et al 2014).…”