Abstract

The degree of intensification is estimated for heterogeneous reduction and dissolution reactions by solving the problem of describing the hydrodynamics, mass transfer, and shielding of a reaction surface upon the formation and action of gas-phase products in the form of bubbles. Some theoretical postulates on the formation of gas bubbles in the course of a heterogeneous solid–liquid–gas reaction are considered. Based on the analogy with boiling and bubbling heat hydraulics, theoretical dependences are derived for the bubble growth rate in the presence of a liquid reagent microsublayer. The analytical dependences derived in this work are in qualitative agreement with the empirical relationships of other authors. Due to the complexity of the problems, no special emphasis is laid on quantitative interpretation, but quantitative coincidence may be attained via the introduction of small corrections. The dynamics of a heterogeneous solid–liquid–gas reaction with mass transfer between a liquid reagent and a solid reducer is studied with consideration for the specific features of the hydrodynamics of gas–liquid media. Some relationships for estimating the reagent concentration and the surface-area fraction shielded by liberated bubbles are derived. Estimates show that the effect of shielding is negligible. This seems to be the reason shielding is not taken into account in the technical calculations of reactions with the liberation of bubbles. Reaction stability is investigated to reveal that gas–liquid structures providing the alternation of shielded and unshielded reaction surface areas are formed under equilibrium, thus creating the gas content gradient, which provokes the motion of liquid-reagent layers with intense stirring. An analysis of criterial equations for mass transfer on a reaction surface gives the dependence, which qualitatively and, partially, quantitatively characterizes mass-transfer processes and coincides with the experimental dependence. The results of this work may be used to form the regimes offering the optimal operation of technological reactors.

中文翻译：

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气泡释放引起的多相还原反应的强化机理

摘要

通过解决描述气泡形式的气相产物的形成和作用时描述反应的流体动力学，传质和屏蔽问题，可以估算异质还原和溶解反应的增强程度。考虑了一些在固-液-气非均相反应过程中形成气泡的理论假设。基于沸腾和沸腾热力学的类比，在存在液体试剂微亚层的情况下，得出了气泡生长速率的理论依赖性。在这项工作中得出的分析依赖性与其他作者的经验关系在质量上是一致的。由于问题的复杂性，没有特别强调定量解释，但是可以通过引入较小的更正来实现定量一致。考虑了气-液介质的流体动力学的特定特征，研究了在液体试剂和固体还原剂之间进行传质的固-液-气多相反应动力学。得出了一些估计试剂浓度和释放的气泡所遮盖的表面积的关系。估计表明屏蔽的影响可以忽略不计。这似乎是在气泡释放反应的技术计算中未考虑屏蔽的原因。对反应稳定性进行了研究，发现在平衡状态下会形成气-液结构，提供受保护和不受保护的反应表面积交替，从而产生气体含量梯度，在剧烈搅拌下引起液体试剂层的运动。对反应表面上的传质的标准方程式的分析给出了相关性，该相关性在质量上和部分上定量地表征了传质过程，并与实验相关性相吻合。这项工作的结果可以用来形成提供技术反应堆最佳运行的机制。