Circumstances Affecting the fresh Performance 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 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.
Low 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.
Features off Gasoline Stage and you will Drinking water Phase: The brand new actual services of one’s gas phase haven’t any affect the performance of your own column, however, the ones from new liquids stage, elizabeth.grams., body stress, viscosity, are serious. A rise in the fresh new viscosity from liquid phase otherwise a fall regarding the epidermis pressure advances the productive interfacial urban area thus escalates the bulk transfer rates. The existence of electrolyte on water stage effects the fresh performance greatly. An electrolytic services gives reduced bubble proportions and consequently increased productive interfacial urban area and higher price off mass 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.
Introduction from Packing or Manufactured Ripple Column: Incorporating packing reduces the axial combination out of water. And this, a stuffed ripple line can be used in which liquids backmixing are undesirable. Gas-h2o responses where big fuel shrinking takes place in this https://datingranking.net/de/lokale-singles/ new reactor have quite reduced shallow gasoline velocities, which after that lead to a bad rate of mass transfer in the the top a portion of the reactor. In these instances, position packings regarding the higher area is effective. The new loading increases the active interfacial town and gas holdup to a level. In addition brings a higher level away from bulk import. not, a packed bubble column is not put when the good strong dust can be found from the system because the catalyst otherwise as the reactant. Packing is also maybe not prominent to have extremely exothermic otherwise endothermic responses, given that manufactured towers keeps worst heat transfer coefficients. Reactions like packaged towers render poor temperature import coefficient. Desk 21-5 shows the huge benefits and you can cons between a bubble column and you can a prompted container reactor, and Dining table 21-six listing industrial samples of bubble line reactor.