Performance of agitated gas-liquid contactors
Performance of agitated gas-liquid contactors
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DOI：
10.1021/ie50414a005
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发表时间：
1944-01-01
影响因子：
--
通讯作者：
Miller, SA
中科院分区：
文献类型：
--
作者：
Cooper, CM;Fernstrom, GA;Miller, SA
对于传统的塔板或填料塔不太适合的吸收应用，如涉及两个以上相的气液反应，搅拌气液接触器是有用的。除了几个在搅拌瓶中进行的特定反应的实验室研究外，还没有关于机械气体分散器的研究报道，也没有为这类重要设备的设计提供合理的依据。本文描述了一种评估变量的实验室方法。为工厂气液反应器的设计提供了依据。气体在液体中的溶解速度是下列因素的函数：气液界面面积、温度、接触时间、驱动力大小和搅拌强度。如果同时发生吸收(物理)和反应(化学)，则可能涉及诸如溶质或催化剂浓度、pH和光照强度等附加因素。在一个给定的体系中，这些反应因素、温度和驱动力通常是固定的或容易控制的，以提供最佳条件，接触面积、接触时间和搅拌成为气液接触装置设计中最重要的变量。严格地说，气体分散器只关心接触面积和时间的变量，因为它们的功能是将气体分成气泡并将这些气泡分散到液体中。然而，在这样做的过程中，它们总是在液体中产生一定程度的湍流，其程度可能不同，从从喷雾器流入非搅拌反应器的气流所产生的湍流，到在隔板容器中运行的高速叶轮所产生的湍流。液体湍流本身并不是不可取的，因为大多数吸收是部分或完全由液膜阻力控制的，因此液体的搅拌提高了传质速度。此外，液体体内的涡流可以通过直接增加分散气泡上的液体剪切力和延长气泡的平均停留时间来改善接触器的性能。因此，评价分散剂性能的最直接方法是对产生的气泡进行计数和测量，这显然不是一个实用的方案。一种间接但更实用的方法是测量某些完全由气膜阻力控制的体系的气体溶解速率。这种测量不区分接触面积和停留时间，但在很大程度上消除了搅拌强度的变化。不幸的是，阻力主要在气膜中的体系不容易进行简单、可靠的测量；必须在液膜阻力相当大的体系上进行最容易、最可靠的批量实验室测定吸收率。这种系统提供了第三种评估分散剂的方法，虽然从发展基础知识的角度来看不太可取，但当应用于在通常具有高液膜阻力的系统中运行的商业设计时，应该是令人满意的。
FOR absorption applications to which conventional plate or packed columns are not well suited, such as gas-liquid reac-tions involving more than two phases, agitated gas-liquid contactors are useful. Outside of a few laboratory studies of specific reactions carried on in agitated flasks, no investigations of mechanical gas dispersers have been reported, and no rational basis for the design of this important type of equipment exists. This paper describes a laboratory method of evaluating the variables. pertinent to such equipment and proposes a basis for the design of plant gas-liquid reactors. The rate of solution of a gas in a liquid is a function of the following factors: area of gas-liquid interface, temperature, time of contact, magnitude of driving force, and intensity of agitation. If simultaneous absorption (physical) and reaction (chemical) are occurring, such additional factors as solute or catalyst con-centration, pH, and light intensity may be involved. In a given system, these reaction factors and the itemsof temperature and driving force are usually either fixed or easily controllable to give the optimum conditions; area of contact, time of contact, and agitation thus become the variables most important to the design of gas-liquid contacting equipment. Strictly speaking, gas dispersers are concerned only with the variables of area and time of contact, since it is their function to divide the gas into bubbles and to disperse these bubblesthrough the liquid phase. In so doing, however, they always produce within the liquid phase a degree ofturbulence which may vary from that produced by the gas stream emanating from a sparger into an unagitated reactor, to that developed by a high-speed impeller operating in a baffled vessel. Liquid turbulence is in itself not undesirable, since most absorptions are controlled par-tially or entirely by the liquid-film resistance, and agitation of the liquid phase therefore enhances the rate of mass transfer. Also, eddy currents in the body of the liquid may improve con-tactor performance by directly increasing the liquid shear on the dispersed bubbles and by lengthening the average retention time of the bubbles. The most direct method, then, of evaluating disperser performance is by count and measure-ment of the bubbles pro-duced, obviously not a practical scheme. An indirect but more practi-cal procedure is to measure the rate of gas solution for some system in which the gas-film resistance entirely controls. Such meas-urement does not differentiate between area of contact and re-tention time, but it does largely eliminate the variable of agitation intensity. Unfortunately systemswhose resistance is pri-marily in the gas film are not susceptible to simple, dependable measurement; the easiest, most reliable, batch laboratory de-terminations of absorption rate must be made on systems in which the liquid-film resistance is considerable. Such a system pro-vides a third means of disperser evaluation which, although less desirable from the standpoint of developing fundamental knowl-edge, should be satisfactory when applied to commercial designs operating in systems with the usual high liquid-film resistance.