Activities Impacting the brand new Performance of your own Ripple Line Reactor
Superficial gas velocity : Increase in superficial velocity increases gas holdup, the effective interfacial area and the overall mass transfer rate. Further, an increase in superficial gas velocity decreases the size of bubbles, thus increasing the interfacial area of contact between the gas and liquid. The effect of superficial gas velocity is negligible on the mass transfer coefficient (KL), but significant on mass transfer area (a). For chemical reaction controlled gas-liquid reaction (slow or very slow gas-liquid reaction) a certain minimum KLa must be achieved to overcome the effect on mass transfer. It is recommended to keep the superficial gas velocity less than or equal to 10 m/s.
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Backmixing: Studies have shown that gas flow in bubble column operates in the plug flow manner without any backmixing while a considerable amount of backmixing in the liquid phase is observed. Backmixing in the liquid phase decreases the concentration of liquid reactant and thus the rate of chemical reaction. Consequently, it decreases the overall rate of reaction. Use of packings, trays or baffles reduces liquid backmixing and thus reduces dilution of reactants by products. Hence, this technique provides higher concentrations of reactant and a higher rate of chemical reactions, (?rA) = (?1/Vl) (?dNA/dt), but decreases the liquid holdup (Vl). The combined effect on the rate of consumption of limiting reactants in reaction (?dNA/dt) must be checked before using any internal in the bubble column. In the case of highly exothermic gas-liquid reactions, backmixing in the liquid phase is desirable to control the nature of the reaction or its temperature. In such cases, placing packings to improve the overall rate makes temperature control very difficult because it increases the heat duty required and decreases the heat transfer coefficient.
Functions from Energy Stage and you may Drinking water Phase: The new real attributes of fuel stage haven’t any influence on the newest overall performance of your column, but those of the liquid stage, e.grams., epidermis pressure, viscosity, are going to be powerful. A rise in new viscosity of liquids phase or a fall throughout the surface stress advances the productive interfacial area thus boosts the size transfer rates. The existence of electrolyte regarding the water stage effects the new results significantly. An enthusiastic electrolytic solution offers shorter ripple size and therefore increased energetic interfacial city and higher speed of bulk import.
Pulsation: The performance of bubble columns can be improved by pulsation. For very low superficial velocity of gas (0.8 to 2.4 cm/s), the value of KLa can be increased by as much as a factor of 3 by pulsation.
Introduction out-of Packing otherwise Packed Bubble Column: Adding packing decreases the axial mix away from water. Hence, a jam-packed bubble column is used in which liquid backmixing was undesirable. Gas-h2o responses in which big energy shrinkage happens in the fresh new reactor have quite reasonable low fuel velocities, which next result in a poor rate from mass transfer within the the upper area of the reactor. In these instances, placing packings in the higher area is very effective. This new loading advances the energetic interfacial town and you may energy holdup so you’re able to an extent. In addition it provides a higher level regarding mass import. However, a packed bubble line isn’t used in the event that okay good dust exist on the system once the catalyst otherwise due to the fact reactant. Packing is also not common getting extremely exothermic otherwise endothermic reactions, because packed towers possess worst heat import coefficients. Reactions such packaged towers bring bad heat transfer coefficient. Dining table 21-5 reveals the advantages and you can downsides ranging from a bubble line and you will a determined tank reactor, and you may Desk 21-six listings industrial types of ripple column reactor.
