Кемерово, Кемеровская область, Россия
В работе исследована возможность интенсификации ультрафильтрационного концентрирования растворов пищевых веществ путем отделения примембранной части потока, включающей обогащенный полезным компонентом концентрационный пограничный (диффузионный) слой. Предложена математическая модель продольного развития поляризации на мембране с учетом ее селективности (коэффициента задержания). На основе модели получена теоретическая оценка эффективности отделения примембранного слоя. Предложены конструкции мембранных модулей с отделением примембранного слоя. Эксперименты показали, что предложенный способ позволяет в проточном модуле добиться обогащения концентрата примерно на 9-10 %, что существенно выше, чем при использовании традиционного процесса концентрирования. Расчетные значения коэффициента концентрирования хорошо согласуются с экспериментальными значениями.
ультрафильтрация, концентрирование, интенсификация, концентрационная поляризация, коэффициент задержания, коэффициент концентрирования.
INTRODUCTION
The development of simple and economical methods for the separation, purification, and concentrating of liquid media is one of the most important problem in the food industry and, especially, in the dairy industry. Membrane technologies, which have a number of advantages in comparison with traditional separation methods, are especially noteworthy [1, 2]. This explains a profound interest in membrane processes, to which a considerable number of theoretical and experimental studies have been devoted.
However, membrane methods have some disadvantages reducing the efficiency of the process. The most essential of them is the formation of the diffusion boundary layer with an increased concentration of rejected substances on the membrane surface (i.e. concentration polarization), which promotes the formation of a gel layer hindering the removal of a solvent.
The weakening of concentration polarization is a traditional way of increasing the efficiency of membrane equipment [3]. It is attained via the turbulization of a flow with mechanical turbulizers [4‒7] or gas sparging [9‒13] or via the physical effect on a flow with mechanical vibrations [14‒16], ultrasound [17‒20], or an imposed electrical field [21]. All these methods lead to additional expenditures, complicate the structure of an apparatus, degrade the quality of a processed product, and increase its cost.
In this work, we consider the possibility of the intensification of ultrafiltration concentrating by the separation of the near-membrane part of a solution flow as a resulting product. It comprises the diffusion boundary layer, the concentration in which is appreciably higher than in the major part of a flow (flow middle). This enables the obtaining of a highly concentrated product at lower energy consumption, since a solution flows in the laminar regime.
The objective of our work is to perform the theoretical and experimental analysis of the efficiency of the separation of the near-membrane layer, to estimate the effect of geometrical and regime parameters, and to describe the technical implementation of the proposed idea.
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