Factors Impacting the Results of Bubble 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 Gasoline Acceleration
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.
Characteristics out of Gas Stage and you will Liquid Stage: The brand new physical functions of the fuel stage have no affect the latest performance of your column, however, those of the latest liquids phase, age.g., body pressure, viscosity, shall be serious. An increase in the viscosity from drinking water stage otherwise a fall in the skin pressure escalates the active interfacial urban area so because of this advances the mass import price. The current presence of electrolyte from the h2o phase consequences the performance considerably. A keen electrolytic solution gives shorter bubble proportions and therefore a higher effective interfacial area and better rates from 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 out of Packing or Manufactured Ripple Line: Including packing reduces the axial fusion out of water. And that, a stuffed ripple column is utilized in which h2o backmixing was unwanted. Gas-liquids responses in which large gas shrinking happens in the fresh new reactor have quite lowest superficial gas velocities, and this subsequently result in a negative rates from mass import into the the top area of the reactor. In these instances, placing packings from the upper region is beneficial. New packing advances the effective interfacial urban area and you can gas holdup in order to a degree. In addition, it will bring a higher rate out-of mass import. Yet not, a loaded ripple line is not put if the okay solid dirt can be found about system just like the catalyst or given that reactant. Packing is additionally not popular having extremely siti web incontri asessuali exothermic otherwise endothermic reactions, due to the fact manufactured systems has bad heat transfer coefficients. Responses for example packed systems provide worst temperatures transfer coefficient. Desk 21-5 shows the pros and you will disadvantages anywhere between a bubble line and you will a determined tank reactor, and you can Table 21-six listings industrial examples of ripple column reactor.