Affairs Affecting the fresh new Show of the Bubble 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 how to hookup in Topeka 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.
Superficial Energy Velocity
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.
Qualities of Energy Phase and you may H2o Stage: The brand new physical properties of your fuel stage don’t have any affect the fresh new efficiency of column, but those of the fresh new drinking water phase, age.g., epidermis stress, viscosity, is powerful. A rise in this new viscosity off h2o phase or a decrease on the skin tension escalates the productive interfacial urban area thus increases the bulk transfer speed. The presence of electrolyte on the liquids stage consequences the brand new show significantly. A keen electrolytic services gets quicker ripple dimensions and consequently a higher energetic interfacial town and better price out of bulk transfer.
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.
Inclusion out-of Packing otherwise Packaged Bubble Line: Including packing reduces the axial fusion of liquid. Hence, a loaded bubble column is utilized where h2o backmixing is actually undesirable. Gas-drinking water responses where nice energy shrinkage takes place in the new reactor have very reasonable superficial fuel velocities, and therefore then lead to a poor price regarding mass transfer for the top of the a portion of the reactor. In such cases, establishing packings regarding the higher area is effective. The newest loading increases the productive interfacial urban area and you will gas holdup so you’re able to a level. Additionally, it provides a higher rate out of size transfer. not, a loaded bubble line isn’t used in the event that fine solid dirt exists in the program because the catalyst or while the reactant. Loading is even maybe not prominent to own extremely exothermic otherwise endothermic responses, given that packed systems has bad temperature import coefficients. Reactions eg packaged towers offer poor heat transfer coefficient. Desk 21-5 reveals the pros and you can cons anywhere between a ripple line and you will a stimulated container reactor, and Table 21-6 listings commercial samples of bubble line reactor.