consuming dedusting device is therefore inevitable. [2] Urea rotary steel-band chilling granulation can partly alleviate the serious dust problem at the expense of the spherical appearance and moisture resistance of the particles, although a small amount of dust emission will still occur during production while unloading the products. [3] Our previous studies proposed a new dust-free large urea granulation (DLUG) process based on the super-repellency effect of the urea melt on a superhydrophobic surface. [4] A single urea melt droplet (UMD) forms a spherical shape spontaneously owing to its surface tension and easily achieves rolling-spheronization granulation after solidification. During this process, no dust is theoretically generated if no collisions occur. However, this hypothesis cannot be realized because the collisions between UMDs and urea solid particles are unavoidable if continuous production is required. Therefore, preventing UMDs from breaking into tiny particles or coalescing into oversized granules, thereby eliminating possible dust generation during a collision, is necessary for the practicality of the DLUG process. In addition, some unexpected occurrences have been observed during a lengthy operation, including surface adhesion of the urea, destroying the superhydrophobicity and resulting in a tailing of the urea granules and a decreased sphericity. Further improving UMD strengthen and decreasing the destructive effect of urea melt on superhydrophobic surface are necessary aspects for enhancing applicability of DLUG process.To overcome the above problems, liquid marble can be applied during the DLUG process. Liquid marble is obtained by covering the liquid droplet surface with non-wetting nanoscale or microscale particles as a type of "armor," [5] providing attractive properties similar to those of solid elastic granules. A high contact angle (CA) on both hydrophilic and hydrophobic surfaces is realized, [6,7] which is helpful for maintaining perfect sphericity under static conditions and exhibiting a low rolling friction under dynamic conditions. [8] Most notably, liquid marbles can endure an elastic deformation of ≈30%. Within Urea melt droplets (UMDs) spontaneously spheronize and form large urea granules after condensation on superhydrophobic surfaces without dust generation. However, they break and coalesce when colliding with each other; moreover, they adhere to the surface and form tails when rolling. These problems limit the practicality of the process using UMDs for large urea granulation directly. Urea melt marbles (UMMs) are introduced to overcome these drawbacks by enwrapping UMDs with superhydrophobic polytetrafluoroethylene (PTFE) powder, thus enhancing the elasticity and maintaining the sphericity. A premixing-melting process is developed to obtain UMMs and lower the PTFE powder consumption to half of that required in the traditional liquid marble preparation. The best determined elasticity modulus of UMMs reaches 44.9 ± 3.6 Pa, and the sphericity is 0.9992. No adhering or tailing...

Traditional sulfur granulation process is often accompanied by high dust and mechanical friction, which are dangerous and harmful to the environment. In this work, the application of the superhydrophobic surface to sulfur granulation is expected to solve the above problem. Two superhydrophobic metal sheets were prepared, and the rolling angles of the two samples are both less than 10°. The contact angles of liquid sulfur are 152.7 ± 0.5 and 151.3 ± 0.1°, respectively. The adhesion rates of both samples are less than 0.5 wt %. The solidifying process of a sulfur drop on the superhydrophobic surface was recorded and simulated, conforming that the substrate temperature has a great influence on the solidifying process. Based on the above findings, static granulation and rolling to granulation were proposed. The product obtained by the two methods has uniform particle size distribution and excellent compressive strength, showing a good industrial application prospect. This study provides a referral strategy for an economical and environmentally friendly sulfur granulation process.

Steel strip granulation is a promising technology for preparing large urea granules; however, easy blocking of the feeding nozzle by urea melt limits its industrial applications. In this study, a dust-free and anticlogging urea granulation process for the mass production of large urea granules is proposed by introducing a urea melt marble (UMM) formed by covering urea melt with super-urea-phobic poly­(tetrafluoroethylene) (PTFE) particles to improve steel strip granulation. Large urea granules are obtained by directly cutting a large-sized cake-shaped mother-UMM into segments. These segments shrink into spherical baby-UMMs and solidify after condensation to form rigid particles. The results confirm that the PTFE powder distribution density for constructing a stable mother-UMM by the segmentation process is crucial. The PTFE powder distribution density for obtaining usable baby-UMMs and subsequent qualified large urea granules should be within 0.0009–0.0011 g/cm2. Super-urea-phobic honeycomb-shaped cutters are used for the batch preparation of qualified urea products with adequate quality distribution. This study provides a promising strategy for improving the production of urea granules.