Study On Gas Holdup,Heat Transfer In A Stirred Tank Equipped With Helical Coils And Its Application

Some compounds in many strong exothermic reaction processes may decompose if the temperature is not well controlled,resulting in the production of gases.Consequently,it will worsen product quality and process safety.As the jacket of the tank cannot meet the requirement of the heat exchange for the above processes,usually a helical coil is adopted to extend the area of heat transfer to enhance the heat transfer.However,the helical coils also bring the complexity for gas-liquid reactor design.Therefore,it is very important to study the convective heat transfer coefficient of the gas-liquid two-phase flow in the stirred tank equipped with helical coils.In this work,water and air were used as the liquid and gas phase,respectively.The gas holdup and convective heat transfer in stirred tank equipped with helical coils were studied.Finally,a reactor for the strongly exothermic reaction was designed.The main contents are as follows:1.The effects of impeller type(propeller(PRO),four-pitched blade turbine(PBT),hydrofoil impeller(CBY)),impeller diameter(D/2 and D/3),superficial gas velocity(0.00393?0.0197 m·s-1)and impeller speed(150?300 rpm)on gas holdup equipped helical coils have been investigated in detail.Some correlations about gas holdup have been proposed.The results show that the D/2 propeller(PRO_L)is superior to the others in terms of gas holdup.When the gas flow rate is small,the large diameter mixing impeller should be used,and the small diameter mixing impeller should be used in the high gas flow rate.2.External coil convective heat transfer coefficients of liquid single-phase and gas-liquid two-phase were investigated.Under the action of axial impeller,the influences of impeller type,impeller diameter,rotating speed and superficial gas velocity on heat transfer have been studied in detail.A series of comparative analysis of the external coil heat transfer coefficients for aerated and non-aerated systems were provided.The external coil heat transfer coefficients of the helical coil were correlated with the number of ventilation(Na = QG/(Nd3))based on 216 groups of experimental data,which provides a good reference for the design and operation of some special exothermic reactors.3.Taking gas holdup and coefficient of heat transfer comprehensively into consideration,the PRO_L is a good choice for stirring and heat transfer.Thus,a 7000 L stirred tank reactor with the PRO_L was designed,and used in a synthetic process of energetic compounds.The 7000 L reactor operated well.