Zhijiang Jin

The Influence of Impeller Combination on the Gas-Liquid Dispersion Performance of a Coaxial Mixer in Viscous Fluids

Abstract As a kind of mixer with wide adaptability, coaxial mixer has a wide-application in the process industry. With the help of experiment and numerical simulation, the gas-liquid dispersion performance of four impeller combinations in viscous system was studied in terms of the global gas holdup, local gas holdup, local bubble size and liquid phase flow field. Wall-scraping anchor is the common outer impeller of the four impeller combinations, and the four inner impellers are Rushton turbine, six-straight-blade turbine (SBT), 45° six-pitched-blade turbine pumping downwards (PBTD) and 45° six-pitched-blade turbine pumping upwards (PBTU). The experimental results indicate that the global gas holdup of the Rushton impeller combination is the highest among the four impeller combinations and that of PBTU is the lowest. The local gas holdup of Rushton and PBTU combinations are all high, but the gas distribution with the Rushton combinations is more uniform. Besides, the local bubble size of the four impeller combinations has the same tendency with the local gas holdup. Under the same conditions, the flow field and distribution of gas holdup of the four impeller combinations in stirred tank were simulated numerically. Compared with the experimental results, the simulation results show a good agreement on the value and distribution of local gas holdup. Among the four coaxial mixers, the Rushton impeller combination is more suitable for gas-liquid dispersion.

Research on Protective Measures to High-Temperature Corrosion of a Novel Energy-Saving Phosphorus Reaction Tower

To recycle and utilize the reaction heat in the production of furnace grade phosphoric acid and to improve the security and economy of the whole production system, a novel phosphorus reaction tower with circulating water wall was developed on the basis of the analysis of present manufacturing process and equipment, and the mechanism of high-temperature corrosion was also analyzed according to experimental tests and operating conditions. Meanwhile, the measures of the whole life cycle anti-corrosion taken to new phosphorus reaction tower were proposed, considering multiple factors including design, manufacture, and operation. The research suggested that the fins close to phosphorus burner, heat exchange tubes toward phosphorus burner and the welds between fin and tube were dangerous zones to be corroded and should be given special protection. In addition, it has been proved that 390-440xa0°C surface temperature of water wall, local water cooling jacket around the oblique burner, plasma-sprayed ZrO2 ceramic coating on heating surface, ultralow carbon austenitic stainless steel rich in Cr and Ni elements are beneficial to avoid the corrosion of high-temperature phosphoric acid and its polymer.