Region-dependent oxygen transfer rate in the rectangular airlift reactor

Abstract

Gas hold-up and the oxygen transfer in the zones of the internal loop airlift reactor with rectangular cross-section was studied. It was found, that the downcomer to the riser gas hold-up ratio depends on the gas ow rate, the physicochemical properties of the system and on the reactor height. The ratio of the downcomer mass transfer coef®cient to the global mass transfer coef®cient was less than 6%. The ratio of the downcomer to the global mass transfer coef®cient slightly increased with increase of the gas¯ow rate and decreased with increase of the liquid viscosity. The proposed correlation for the global overall mass transfer coef®cient predicts the experimental data well within 16.6% deviation. It was con®rmed that the reactor height is the important parameter for a design and a scale-up of the airlift reactors. List of symbolsa m length A m 2 cross-section area A ± proportionality constant in Eq. (9) b ± exponent in Eq. (9) b m width c ± exponent in Eq. (9) c kg á m A3 oxygen concentration in the liquid c à kg á m A3 equilibrium liquid phase dissolved-oxygen concentration d ± exponent in Eq. (9) d R m equivalent riser diameter (= 4´¯ow area/wetted perimeter) D m 2 á s A1 diffusivity in liquid phase DTAR ± cylindrical draft-tube airlift reactor ELAR ± cylindrical external loop airlift reactor Fr u 2 GR g Á d R Froude number g m á s A2 gravitational acceleration h R m reactor height Dh m difference between the liquid level in the upper and the lower piezometric tube Dh m m distance between the manometer tube location k L a s À1 liquid-phase volumetric mass transfer coef®cient Mo g 4 L Á g q L Á r 3 Morton number RILAR ± rectangular inner loop airlift reactor Sc g L q L Á D Schmidt number Sh k L a Á d 2 R D Sherwood number t s time, residence time t C s circulation time u GR m á s A1 super®cial gas velocity based on the riser cross-section u C m á s A1 mean liquid circulation velocityGreek letters e ± gas hold-up g mPa á s liquid dynamic viscosity q kg á m A3 density r mN á m A1 surface tension s s time-constant f ± correction factor in Eqs (3, 4)

A novel split-cylinder airlift reactor for fed-batch cultures

“…7). These results agree with those reported by Kawalec-Pietrenko and Holowacs [8] who found that the mass-transfer coef®cient decreased with increasing reactor height.…”

“…The gas hold-up values obtained in this work were similar to those reported by Tung et al [16] and Wu and Wu [17], who used airlift reactors with net tubes, and higher than those estimated for other reactor types, such as in concentric tube airlift reactors [2,9,10,14] and in a rectangular airlift reactor [8], for similar super®cial gas velocities. Figure 7 shows the variation of the overall volumetric oxygen transfer coef®cient in the reactor, as a function of the super®cial air velocity for three liquid heights (120, 240, and 420 mm).…”

A novel split-cylinder airlift reactor for fed-batch cultures

“…7). These results agree with those reported by Kawalec-Pietrenko and Holowacs [8] who found that the mass-transfer coef®cient decreased with increasing reactor height.…”

“…The gas hold-up values obtained in this work were similar to those reported by Tung et al [16] and Wu and Wu [17], who used airlift reactors with net tubes, and higher than those estimated for other reactor types, such as in concentric tube airlift reactors [2,9,10,14] and in a rectangular airlift reactor [8], for similar super®cial gas velocities. Figure 7 shows the variation of the overall volumetric oxygen transfer coef®cient in the reactor, as a function of the super®cial air velocity for three liquid heights (120, 240, and 420 mm).…”

Generation of small bubbles and small bubble-liquid mass transfer in airlift reactors containing highly viscous liquids

“…The mass transfer coef®cient is obtained to be 5.4 10 A4 s A1 . A similar value of 6.10 A4 s A1 is obtained [7] during the aeration in the airlift reactor for the much higher gas¯ow rate of 5.10 A3 m.s A1 and similar liquid viscosity of 49.1 mPas. It should be noted that the riser mass transfer coef®cient value is highest during the aeration in the airlift reactor [7].…”

“…A similar value of 6.10 A4 s A1 is obtained [7] during the aeration in the airlift reactor for the much higher gas¯ow rate of 5.10 A3 m.s A1 and similar liquid viscosity of 49.1 mPas. It should be noted that the riser mass transfer coef®cient value is highest during the aeration in the airlift reactor [7]. Because the mass transfer coef®cient is approximately proportional to the gas¯ow rate it could be concluded that the small bubble mass transfer coef®cient is approximately one order of magnitude higher than the overall mass transfer coef®cient during aeration.…”

Region-dependent mass transfer behavior in a forced circulation airlift loop reactor

“…However, the separator region's contribution was ignored, probably because of small volume of the region, which was inconsistent with previous findings [11]. Kawalec-Pietrenko and Holowacz [14] divided the IALR into two regions, the annulus and the enlarged riser which included the riser and gas-liquid separator regions. The downcomerto-global volumetric mass transfer coefficient ratio was less than 6% and slightly increased with increasing gas flow rate and decreasing liquid viscosity.…”

A novel split-cylinder airlift reactor for fed-batch cultures

“…7). These results agree with those reported by Kawalec-Pietrenko and Holowacs [8] who found that the mass-transfer coef®cient decreased with increasing reactor height.…”

“…The gas hold-up values obtained in this work were similar to those reported by Tung et al [16] and Wu and Wu [17], who used airlift reactors with net tubes, and higher than those estimated for other reactor types, such as in concentric tube airlift reactors [2,9,10,14] and in a rectangular airlift reactor [8], for similar super®cial gas velocities. Figure 7 shows the variation of the overall volumetric oxygen transfer coef®cient in the reactor, as a function of the super®cial air velocity for three liquid heights (120, 240, and 420 mm).…”

Generation of small bubbles and small bubble-liquid mass transfer in airlift reactors containing highly viscous liquids

“…The mass transfer coef®cient is obtained to be 5.4 10 A4 s A1 . A similar value of 6.10 A4 s A1 is obtained [7] during the aeration in the airlift reactor for the much higher gas¯ow rate of 5.10 A3 m.s A1 and similar liquid viscosity of 49.1 mPas. It should be noted that the riser mass transfer coef®cient value is highest during the aeration in the airlift reactor [7].…”

“…A similar value of 6.10 A4 s A1 is obtained [7] during the aeration in the airlift reactor for the much higher gas¯ow rate of 5.10 A3 m.s A1 and similar liquid viscosity of 49.1 mPas. It should be noted that the riser mass transfer coef®cient value is highest during the aeration in the airlift reactor [7]. Because the mass transfer coef®cient is approximately proportional to the gas¯ow rate it could be concluded that the small bubble mass transfer coef®cient is approximately one order of magnitude higher than the overall mass transfer coef®cient during aeration.…”

Region-dependent mass transfer behavior in a forced circulation airlift loop reactor

“…However, the separator region's contribution was ignored, probably because of small volume of the region, which was inconsistent with previous findings [11]. Kawalec-Pietrenko and Holowacz [14] divided the IALR into two regions, the annulus and the enlarged riser which included the riser and gas-liquid separator regions. The downcomerto-global volumetric mass transfer coefficient ratio was less than 6% and slightly increased with increasing gas flow rate and decreasing liquid viscosity.…”

A novel split-cylinder airlift reactor for fed-batch cultures

“…7). These results agree with those reported by Kawalec-Pietrenko and Holowacs [8] who found that the mass-transfer coef®cient decreased with increasing reactor height.…”

“…The gas hold-up values obtained in this work were similar to those reported by Tung et al [16] and Wu and Wu [17], who used airlift reactors with net tubes, and higher than those estimated for other reactor types, such as in concentric tube airlift reactors [2,9,10,14] and in a rectangular airlift reactor [8], for similar super®cial gas velocities. Figure 7 shows the variation of the overall volumetric oxygen transfer coef®cient in the reactor, as a function of the super®cial air velocity for three liquid heights (120, 240, and 420 mm).…”

Generation of small bubbles and small bubble-liquid mass transfer in airlift reactors containing highly viscous liquids

“…The mass transfer coef®cient is obtained to be 5.4 10 A4 s A1 . A similar value of 6.10 A4 s A1 is obtained [7] during the aeration in the airlift reactor for the much higher gas¯ow rate of 5.10 A3 m.s A1 and similar liquid viscosity of 49.1 mPas. It should be noted that the riser mass transfer coef®cient value is highest during the aeration in the airlift reactor [7].…”

“…A similar value of 6.10 A4 s A1 is obtained [7] during the aeration in the airlift reactor for the much higher gas¯ow rate of 5.10 A3 m.s A1 and similar liquid viscosity of 49.1 mPas. It should be noted that the riser mass transfer coef®cient value is highest during the aeration in the airlift reactor [7]. Because the mass transfer coef®cient is approximately proportional to the gas¯ow rate it could be concluded that the small bubble mass transfer coef®cient is approximately one order of magnitude higher than the overall mass transfer coef®cient during aeration.…”

Region-dependent mass transfer behavior in a forced circulation airlift loop reactor

“…However, the separator region's contribution was ignored, probably because of small volume of the region, which was inconsistent with previous findings [11]. Kawalec-Pietrenko and Holowacz [14] divided the IALR into two regions, the annulus and the enlarged riser which included the riser and gas-liquid separator regions. The downcomerto-global volumetric mass transfer coefficient ratio was less than 6% and slightly increased with increasing gas flow rate and decreasing liquid viscosity.…”