新型表面吸气式搅拌器气液传质特性研究

发布时间：2018-08-17 17:24

【摘要】：本文以一种新型表面吸气式长短桨搅拌器LSB为研究对象,采用亚硫酸钠稳态法测量了搅拌釜内液相体积传质系数kLa,考察了实验操作参数(搅拌器浸没深度S、液位高度H和釜底间隙C)和搅拌器结构参数(长桨位置和长桨宽度WLB)对表面吸气临界转速Nc、釜内气泡分散状态、单位体积功率消耗P/V(或功率准数NP)和体积传质系数kLa的影响。研究表明,当长桨在外环且部分浸没时,搅拌器具有良好的吸气性能,表面吸气临界转速Nc维持在很低的1.5～2.0 rps之间,且Nc随着液位高度H/T和釜底间隙C/T的变化基本保持不变；功率准数NP随着搅拌转速N的增大而减小,单位体积功率消耗P/V对转速N的幂指数β都小于3 (P/V=αNβ),且随着H/T降低,β偏离3的程度越大；体积传质系数kLa在某一临界转速后,随着搅拌转速N的增大呈直线上升趋势,而且相较于安装位置固定的传统涡轮搅拌桨,随着液位高度H/T的增大,kLa值只出现小幅下降,特别适合于反应釜中反应液体积不断增大的气液两相反应过程。当长桨在内环或者长桨全部浸没时,搅拌器的吸气效率明显降低,相同转速下,釜内气含率明显低于长桨在外环且部分浸没时。长桨全部浸没时,随着浸没深度S的增大,表面吸气临界转速Nc快速增大；长桨在内环上时,表面吸气临界转速Nc比外环时大50%左右,在部分浸没时甚至出现了气泛现象。本文中还比较了LSB搅拌器长桨浸没前后和内外环上的气液体积传质系数kLa。发现长桨在外环和部分浸没时,体积传质系数kLa明显更高,同时发现在釜底间隙C/T=0.25时,具有最大的kLa值；并且给出了长桨在外环、部分浸没、釜底间隙C/T=0.25时体积传质系数的拟合方程。具体方程为：kLa=0.0346(P/V)1.596(H/T)-0.512 (C/T=0.25, WLB/T=0.05, P/V=0.5～6kW/m3)本文最后比较了不同长桨宽度(WLB/T=0.05,0.06,0.07)下的传质规律,发现WLB/T=0.06时,体积传质系数kLa对单位体积功率消耗P/V的幂指数β最大,且三组桨型幂指数β都远大于传统的涡轮式搅拌桨(β小于1)。
[Abstract]:In this paper, a new type of surface inspiratory long and short paddle agitator (LSB) is studied. The volumetric mass transfer coefficient of liquid phase in agitator was measured by sodium sulfite steady-state method. The experimental operating parameters (agitator immersion depth S, liquid level height H and bottom gap C) and agitator structure parameters (long propeller position and long propeller) were investigated. Width WLB) on the surface of the suction critical speed Nc, bubble dispersion state in the kettle, The effects of P / V (or power criterion NP) and kLa on the unit volume power consumption. The results show that the stirrer has good inspiratory performance when the outer ring of the propeller is partially immersed, and the critical suction speed of the impeller is maintained at a very low 1.5 ~ 2. 0 rps. With the increase of the stirring speed N, the NC remained unchanged with the liquid level H / T and the cauldron gap C / T, and the power number NP decreased with the increase of the stirring speed. The power exponent 尾 of unit volume power consumption P / V to rotational speed N is less than 3 (P / V = 伪 N 尾), and with the decrease of H / T, the degree of 尾 deviation from 3 increases, and the volume mass transfer coefficient (kLa) increases linearly with the increase of stirring speed N after a certain critical speed. Compared with the traditional turbine agitator with fixed installation position, the KLA value decreases slightly with the increase of the liquid level H / T, which is especially suitable for the gas-liquid two-phase reaction process in which the volume of the reaction fluid increases continuously. When the long propeller is immersed in the inner ring or the long propeller, the suction efficiency of the agitator is obviously decreased. At the same speed, the gas holdup in the kettle is obviously lower than that in the outer ring of the long propeller and partially immersed. When the long propeller is fully immersed, the critical suction speed NC increases rapidly with the increase of the immersion depth S, and when the long propeller is on the inner ring, the suction critical speed of the long propeller is about 50% larger than that of the outer ring, and even the phenomenon of gas flooding occurs during partial immersion. In this paper, the gas-liquid volume mass transfer coefficient kLa. before and after the LSB agitator long propeller is immersed and on the inner and outer ring is also compared. It is found that the volume mass transfer coefficient (kLa) is significantly higher in the outer ring and partial immersion of the long propeller, and the maximum kLa value is found at the bottom gap C/T=0.25, and the outer ring and partial immersion of the long propeller are given. Fitting equation of volumetric mass transfer coefficient for C/T=0.25 of bottom gap. The specific equation is 0. 0346 (P / V) 1.596 (H / T) -0.512 (C / T 0. 25, WLB / T 0. 05, P/V=0.5~6kW/m3). At the end of this paper, we compare the law of mass transfer under different long propeller widths (WLB / T 0. 05 0. 06). It is found that when WLB/T=0.06, the volume mass transfer coefficient kLa has the largest power exponent 尾 for unit volume power consumption. The power exponent 尾 of three groups of propellers is much larger than that of traditional turbine impellers (尾 < 1).
【学位授予单位】：东南大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ051.72

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