Situations Affecting the fresh new Abilities of your own 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.
Superficial Gas 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.
Qualities of Gasoline Phase and you can Liquid Phase: Brand new physical qualities of your energy phase have no influence on new abilities of your column, however, that from this new water phase, age.grams., body pressure, viscosity, might be deep. A rise in the new viscosity out-of h2o stage or a decline about skin pressure boosts the effective interfacial city thus advances the mass import rates. The presence of electrolyte about drinking water stage consequences the newest results greatly. An enthusiastic electrolytic solution offers quicker bubble proportions and therefore a top energetic interfacial city and better speed 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.
Introduction out-of Loading otherwise Manufactured Ripple Column: Adding loading reduces the axial combination of drinking water. Hence, a stuffed ripple line can be used where drinking water backmixing try undesirable. Gas-drinking water responses in which big gas shrinkage takes place in the latest reactor have very reasonable low gas velocities, and therefore after that end in a poor speed off size transfer in the the upper part of the reactor. In such cases https://datingranking.net/local-hookup/squamish, position packings throughout the top region is effective. The newest packing advances the active interfacial town and you will gasoline holdup to a degree. In addition, it will bring a higher rate out of mass import. not, a packed bubble column isn’t utilized in the event that great good particles are present from the program because stimulant otherwise given that reactant. Packing is also maybe not prominent having highly exothermic or endothermic reactions, as manufactured towers have worst temperature import coefficients. Responses such as for example packed towers provide bad temperature transfer coefficient. Table 21-5 suggests the advantages and you will drawbacks anywhere between a bubble line and you may an empowered tank reactor, and Desk 21-6 listings commercial samples of ripple line reactor.