Papers by Keyword: Urea

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Authors: Nejat Rahmanian, Marjan Homayoonfard
Abstract: In this paper, a model for urea prilling tower with co-current flow of cooling air and urea prills (particles) is presented. The process is modelled by simultaneous solution of the differential equations for hydrodynamics, heat and mass transfer between the air and prills. The process variables such as temperature, absolute and relative humidity of air along the height of the tower were obtained from this model. Temperature and moisture distribution of urea prills and their radial and vertical velocities were also calculated. The results of the present model were compared with the counter-current operation model available in the literature. The simulation results show that heat transfer performance for co-current operation is significantly less than that of the counter-current scenario. This is more pronounced for small prills, i.e. 1.0 mm than that of the large prills. The advantage of the model is that it can be used to investigate influence of operating parameters on efficiency of the co-current process. This also helps us to set the process control strategies for design and quality control purposes of the process.
Authors: M. Zha, C. Paorici, C. Razzetti, M. Ardoino, L. Zanotti, G. Zuccalli
Authors: Jiang Jun Hu, Jing Liu, Ying Zheng, Chao Ping Cen, Fu Xing Gan
Abstract: The removal of NOx in simulated flue gas was studied using urea/ potassium permanganate solution with different concentrations as absorbent. Experiments were carried out in a packed absorption reactor filled with steel pall rings at about 70°C. The effect of amount of urea, amount of potassium permanganate, effective height of absorption solution and addition of SO2 on denitrification efficiency was examined. The results show that a high removal efficiency of NOx can be attained using urea/ potassium permanganate solution process, In the solution of 5% urea and 600mg/L potassium permanganate, the removal efficency of NOx could be achieved 91.5%. Increasing the amount of potassium permanganate and the effective height of absorption solution could improve denitrification efficiency remarkably. Whereas, no obvious improvement in NOx removal efficiency was observed when increasing the amount of urea without potassium permanganate. The adding of SO2 resulted in a decline of denitrification efficiency.
Authors: Jian Li, Xun Zhang Yu, Kai Zhang
Abstract: In this article, konjac flour, super absorptive resin and pellet urea were added into flexible polyurethane foamed plastic with polyether polyol and isocyanate as the raw materials by a new water-foamed technology to manufacture a kind of absorptive and biodegraded polyurethane foamed fertilizer. Polyurethane foam was used as a carrier material and konjac flour was used as a biodegradable agent. The results showed that the slow-release velocity of urea could be controlled by regulating the densities of polyurethane foams, the content of konjac flour and super absorptive resin. The carrier material could be degraded konjac flour by naturally.
Authors: Jin Feng Wang, Xiao Qing Wang, Wei Zhao
Abstract: Glutin-urea system was used in alumina gelcasting. And alumina suspension with 53vol% solid loading was prepared. Urea was decomposed by using urease therefore it was possible that hydrogen bond could be rebuilt. Alumina green bodies with 8.26MPa bending-strength were prepared when the dose of urease was 20 iu per milimole urea.
Authors: Sujith Vijayan, Rajaram Narasimman, Kuttan Prabhakaran
Abstract: Alumina powder dispersions in molten urea medium were prepared using ammonium poly (acrylate) dispersant. The dispersant concentration for achieving very good dispersion of the powder was optimized through rheological measurements. The optimum dispersant concentration for alumina powder dispersion in molten urea (1.25 wt.% of alumina) is higher than that required in aqueous medium (0.35 wt%). The dispersions with alumina loading as high as 55 vol.% having low viscosity could be achieved in molten urea medium at 135 °C. The viscosity and yield stress of the alumina powder dispersions in molten urea is low enough for casting.
Authors: Chun Yan Ding, Lan Wang, Jun Xiong Lin, Duan Ni
Abstract: In order to resolve the problem of water pollution owing to using a large number of urea in silk printing with reactive dyes, TEG (Triethylene glycol/3, 6-dioxaoctane-1/8-diol) was used to replace the urea. The effects of TEG on the performance of monochromic and combination printed fabrics were studied through testing K/S values (color depth) and Delta E (color differences) of printed fabrics. Meanwhile, the effect of TEG and urea on the solubility of reactive dye and the moisture absorbency of silk fabric were compared by testing the solubility of reactive dyes and the diameter of silk fiber respectively. The results indicated that the best replacement ratio of TEG to urea was 75%.
Authors: Azlinda Ab Azlinda, Zuraida Khusaimi, Saifollah Abdullah, Mohamad Rusop
Abstract: Zinc oxide (ZnO) nanostructures prepared by immersion method were successfully grown on gold-seeded silicon substrate using Zinc nitrate hexahydrate (Zn (NO3)2.6H2O) as a precursor, separately stabilized with non-toxic urea (CH4N2O) and hexamethylene tetraamine (HMTA). The effect of changing the stabilizer of ZnO solution on the crystal structure, morphology and photoluminescence properties of the resultant ZnO is investigated. X-ray diffraction of the synthesized ZnO shows hexagonal zincite structure. The morphology of the ZnO was characterized using Field Emission Scanning Electron Microscope (FESEM). The growth of ZnO using urea as stabilizer shows clusters of ZnO nanoflower with serrated broad petals were interestingly formed. ZnO in HMTA showed growth of nanorods. The structures has high surface area, is a potential metal oxide nanostructures to be develop for optoelectronic devices and chemical sensors. The formation of ZnO nanostructures is found to be significantly affected by the stabilizer.
Authors: Diego Pereira Tarragó, Célia de Fraga Malfatti, Vânia Caldas de Sousa
Abstract: For the combustion synthesis of strontium doped lanthanum manganite (LSM), different fuels can be used influencing the phase formation and also the powder morphology. Both are important features that can improve the material performance when used in a solid oxide fuel cell cathode. Urea and sucrose are fuels used to synthesize distinct LSM powders, thus the purpose of this work was to mix these fuels in order to obtain nanocrystalline LSM powders with a differentiated morphology, more convenient for the desired application. After calcination at 750°C for 3 hours the powder generated a pure phase LSM X-ray diffraction pattern and the micrographs taken in the transmission and scanning electron microscopes revealed a very peculiar morphology with specific surface area (BET) of 13 m²/g. Calcination led to a single phase and more crystalline material but showed no influence in the powder morphology.
Authors: Normanda Lino de Freitas, Elias Fagury-Neto, Hélio Lucena Lira, Lucianna Gama, Ruth Herta Goldsmith Aliaga Kiminami, Ana Cristina Figueiredo de Melo Costa
Abstract: Among ceramic materials, the alumina has high importance because of its characteristics of resistance and refractory. The possibility to improve the final characteristics of this material, open possibilities for new applications. The aim of this work is to synthesize (α-Al2O3) alumina powders by combustion reaction and to evaluate the effect of the urea content in the final characteristics of the α-Al2O3 powders. Three compositions were studied : a) stoichiometric, b) with 10% of urea reduction and c) with 20% of urea reduction. The initial solution composition was based on the total valence of the reagents by using chemical concepts of the propellant. This powders were characterized by X-ray diffraction (XRD), granulometric determination by laser diffraction, nitrogen adsorption by BET, scanning electron microscopy (SEM), infrared spectroscopy (IR) and helium picnometer. The results showed that the urea reduction change the temperature of the reaction from 525 to 463oC , the characteristics of the powders, and principally the reduction of the particles size.
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