Factors Affecting this new Abilities of one’s Ripple Column 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.
Shallow Gas Speed
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.
Attributes regarding Gasoline Stage and you will Liquid Stage: The real characteristics of the gasoline stage don’t have any effect on the latest efficiency of your own column, but that from the brand new drinking water phase, age.grams., skin pressure, viscosity, are going to be deep. A boost in the newest viscosity off drinking water phase otherwise a drop throughout the skin tension increases the effective interfacial city and hence increases the bulk transfer rate. The existence of electrolyte on h2o stage effects this new show significantly. A keen electrolytic provider offers faster ripple proportions and consequently a higher effective interfacial city and higher rates from size 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.
Addition of Packing otherwise Manufactured Ripple Column: Adding loading decreases the axial mixing of liquid. And that, a stuffed ripple line can be used in which h2o backmixing are undesirable. Gas-h2o reactions where nice gasoline shrinkage takes place in the brand new reactor have very reasonable superficial energy velocities, hence then cause a terrible speed off mass transfer when you look at the the top an element of the reactor. In such cases, establishing packings regarding the higher part works well. Brand new packing escalates the energetic interfacial city and you can gasoline holdup to help you a degree local hookup app Sioux Falls. In addition, it provides a high rate away from size transfer. But not, a packed bubble line isn’t put if good solid dust can be found regarding the program as the catalyst or because reactant. Packing is additionally not preferred getting extremely exothermic otherwise endothermic responses, since the packed towers have bad temperatures transfer coefficients. Reactions such as for instance packaged systems render bad temperatures import coefficient. Table 21-5 reveals the huge benefits and you can drawbacks ranging from a bubble column and an impressed container reactor, and Desk 21-six listing commercial samples of ripple line reactor.