Design of Gas-Inducing Reactors

Abstract

A gas-inducing impeller enables efficient recycling of gas from the headspace into the liquid. Historically, these impellers were used for the first time in froth flotation machines. The various designs of gas-inducing impellers (including those used in froth flotation) could be classified into three categories, depending on the flow pattern coming into and leaving the impeller zone. These are denoted as type 11, type 12, and type 22 systems. The critical impeller speed for the onset of gas induction (N CG) is governed by a balance between the velocity head generated by the impeller and the hydrostatic head above the impeller. A number of correlations (for types 11 and 22) are based on this balance (Bernoulli's equation). The rate of gas induction (Q G) for the type 11 system can be accurately determined by equating the pressure difference (between the impeller zone and the headspace) generated by the impeller and the pressure drop required for the flow of gas. For type 22 systems, the correlations for Q G are mainly empirical in nature. Correlations for the power consumption, fractional gas holdup, mass-transfer coefficient, and so forth are also available in the literature, although these studies on are not comprehensive. A process design algorithm has been presented for the design of gas-inducing impellers. The algorithm consists of the determination of the rate-controlling step, selection of geometry and the operating conditions, and an economic analysis to choose the optimum design. Guidelines have been given about the desired geometry of gas-inducing impellers for achieving different design objectives such as heat transfer, mass transfer, mixing, solid suspension, froth flotation, and so forth. It has been shown that the use of a gas-inducing impeller in a conventional stirred vessel can lead to a substantial increase in the productivity. It has been shown that the optimum geometry may not correspond to the maintenance of equal power consumption per unit volume, or equal tip speed on scale-up. Suggestions have been made for future work in this area.

Ozonation of Phenolic Wastewater in a Gas-Induced Reactor with a Fixed Granular Activated Carbon Bed

“…For the test runs shown in Figure a, the inlet and outlet ozone concentrations were measured to be 141.6 and 12.3 mg/L, respectively, for 99% phenol removal. This is equivalent to a 91.3% ozone utilization efficiency and is in line with those of Hsu and Huang, , who reported an ozone utilization efficiency between 90% and 97% depending on the operating conditions. Gould and Weber 25 found that the ozone dose required for complete phenol removal was between 4 and 6 mol of ozone/mol of phenol present in the original wastewater.…”

Ozonation of Phenolic Wastewater in a Gas-Induced Reactor with a Fixed Granular Activated Carbon Bed

“…For the test runs shown in Figure a, the inlet and outlet ozone concentrations were measured to be 141.6 and 12.3 mg/L, respectively, for 99% phenol removal. This is equivalent to a 91.3% ozone utilization efficiency and is in line with those of Hsu and Huang, , who reported an ozone utilization efficiency between 90% and 97% depending on the operating conditions. Gould and Weber 25 found that the ozone dose required for complete phenol removal was between 4 and 6 mol of ozone/mol of phenol present in the original wastewater.…”

Hydrodynamic and Mass Transfer Parameters in Agitated Reactors Part I: Critical Mixing Speed, Induced Gas Flow Rate, and Wavy Surface in SARs and GIRs

“…This finding is in agreement with available literature on GIRs (Martin, 1972;Aldrich and van Deventer, 1995;Forrester et al, 1998;Patwardhan and Joshi, 1999). Increasing liquid height decreases the pumping capacity of the impeller, and therefore Q GI decreases, as reported in the literature (Sawant et al, 1980;Sawant et al, 1981;Heim et al, 1995;Patwardhan and Joshi, 1999). Increasing liquid height decreases the pumping capacity of the impeller, and therefore Q GI decreases, as reported in the literature (Sawant et al, 1980;Sawant et al, 1981;Heim et al, 1995;Patwardhan and Joshi, 1999).…”

“…As can be seen in this figure, at mixing speeds greater than N CRI , Q GI values appear to increase due to the increase of the pumping capacity of the impeller (Martin, 1972). This finding is in agreement with available literature on GIRs (Martin, 1972;Aldrich and van Deventer, 1995;Forrester et al, 1998;Patwardhan and Joshi, 1999). Q GI values were also found to strongly decrease with increasing liquid height at mixing speeds < 16 Hz.…”

“…Figure 2 also shows that N CRI slightly decreases with increasing temperature, which can be related to the decrease of liquid viscosity as previously reported by several investigators (Sawant and Joshi, 1979;Aldrich and van Deventer, 1995;Fillion, 2001). Thus, at mixing speeds below N CRI , the pumping capacity of the impeller is mainly dependent on the liquid and not the gas properties as discussed by Patwardhan and Joshi (1999). At low mixing speeds, the hollow shaft is full or partially full of liquid, and as the mixing speed increases, the liquid level inside the hollow shaft decreases until the first gas bubbles exits through the orifice, indicating N CRI .…”

Critical Review of Gas–Liquid Mixing Using Gas-Inducing Impellers: Modeling, CFD Simulation, and ANN Applications

“…Their findings revealed that as the applied average bubble size increased from 3.5 to 4.5 mm, the distribution of predicted gas holdup exhibited minimal changes. It is crucial to highlight that this study examined a limited range of bubble sizes, which deviates from findings in previous studies on GIRs. ,,, Therefore, additional investigation is required to enhance our comprehension of the influence of bubble size.…”

Ozonation of Phenolic Wastewater in a Gas-Induced Reactor with a Fixed Granular Activated Carbon Bed

“…For the test runs shown in Figure a, the inlet and outlet ozone concentrations were measured to be 141.6 and 12.3 mg/L, respectively, for 99% phenol removal. This is equivalent to a 91.3% ozone utilization efficiency and is in line with those of Hsu and Huang, , who reported an ozone utilization efficiency between 90% and 97% depending on the operating conditions. Gould and Weber 25 found that the ozone dose required for complete phenol removal was between 4 and 6 mol of ozone/mol of phenol present in the original wastewater.…”

Hydrodynamic and Mass Transfer Parameters in Agitated Reactors Part I: Critical Mixing Speed, Induced Gas Flow Rate, and Wavy Surface in SARs and GIRs

“…This finding is in agreement with available literature on GIRs (Martin, 1972;Aldrich and van Deventer, 1995;Forrester et al, 1998;Patwardhan and Joshi, 1999). Increasing liquid height decreases the pumping capacity of the impeller, and therefore Q GI decreases, as reported in the literature (Sawant et al, 1980;Sawant et al, 1981;Heim et al, 1995;Patwardhan and Joshi, 1999). Increasing liquid height decreases the pumping capacity of the impeller, and therefore Q GI decreases, as reported in the literature (Sawant et al, 1980;Sawant et al, 1981;Heim et al, 1995;Patwardhan and Joshi, 1999).…”

“…As can be seen in this figure, at mixing speeds greater than N CRI , Q GI values appear to increase due to the increase of the pumping capacity of the impeller (Martin, 1972). This finding is in agreement with available literature on GIRs (Martin, 1972;Aldrich and van Deventer, 1995;Forrester et al, 1998;Patwardhan and Joshi, 1999). Q GI values were also found to strongly decrease with increasing liquid height at mixing speeds < 16 Hz.…”

“…Figure 2 also shows that N CRI slightly decreases with increasing temperature, which can be related to the decrease of liquid viscosity as previously reported by several investigators (Sawant and Joshi, 1979;Aldrich and van Deventer, 1995;Fillion, 2001). Thus, at mixing speeds below N CRI , the pumping capacity of the impeller is mainly dependent on the liquid and not the gas properties as discussed by Patwardhan and Joshi (1999). At low mixing speeds, the hollow shaft is full or partially full of liquid, and as the mixing speed increases, the liquid level inside the hollow shaft decreases until the first gas bubbles exits through the orifice, indicating N CRI .…”

Critical Review of Gas–Liquid Mixing Using Gas-Inducing Impellers: Modeling, CFD Simulation, and ANN Applications

“…Their findings revealed that as the applied average bubble size increased from 3.5 to 4.5 mm, the distribution of predicted gas holdup exhibited minimal changes. It is crucial to highlight that this study examined a limited range of bubble sizes, which deviates from findings in previous studies on GIRs. ,,, Therefore, additional investigation is required to enhance our comprehension of the influence of bubble size.…”

Ozonation of Phenolic Wastewater in a Gas-Induced Reactor with a Fixed Granular Activated Carbon Bed

“…For the test runs shown in Figure a, the inlet and outlet ozone concentrations were measured to be 141.6 and 12.3 mg/L, respectively, for 99% phenol removal. This is equivalent to a 91.3% ozone utilization efficiency and is in line with those of Hsu and Huang, , who reported an ozone utilization efficiency between 90% and 97% depending on the operating conditions. Gould and Weber 25 found that the ozone dose required for complete phenol removal was between 4 and 6 mol of ozone/mol of phenol present in the original wastewater.…”

Hydrodynamic and Mass Transfer Parameters in Agitated Reactors Part I: Critical Mixing Speed, Induced Gas Flow Rate, and Wavy Surface in SARs and GIRs

“…This finding is in agreement with available literature on GIRs (Martin, 1972;Aldrich and van Deventer, 1995;Forrester et al, 1998;Patwardhan and Joshi, 1999). Increasing liquid height decreases the pumping capacity of the impeller, and therefore Q GI decreases, as reported in the literature (Sawant et al, 1980;Sawant et al, 1981;Heim et al, 1995;Patwardhan and Joshi, 1999). Increasing liquid height decreases the pumping capacity of the impeller, and therefore Q GI decreases, as reported in the literature (Sawant et al, 1980;Sawant et al, 1981;Heim et al, 1995;Patwardhan and Joshi, 1999).…”

“…As can be seen in this figure, at mixing speeds greater than N CRI , Q GI values appear to increase due to the increase of the pumping capacity of the impeller (Martin, 1972). This finding is in agreement with available literature on GIRs (Martin, 1972;Aldrich and van Deventer, 1995;Forrester et al, 1998;Patwardhan and Joshi, 1999). Q GI values were also found to strongly decrease with increasing liquid height at mixing speeds < 16 Hz.…”

“…Figure 2 also shows that N CRI slightly decreases with increasing temperature, which can be related to the decrease of liquid viscosity as previously reported by several investigators (Sawant and Joshi, 1979;Aldrich and van Deventer, 1995;Fillion, 2001). Thus, at mixing speeds below N CRI , the pumping capacity of the impeller is mainly dependent on the liquid and not the gas properties as discussed by Patwardhan and Joshi (1999). At low mixing speeds, the hollow shaft is full or partially full of liquid, and as the mixing speed increases, the liquid level inside the hollow shaft decreases until the first gas bubbles exits through the orifice, indicating N CRI .…”

Critical Review of Gas–Liquid Mixing Using Gas-Inducing Impellers: Modeling, CFD Simulation, and ANN Applications

“…Their findings revealed that as the applied average bubble size increased from 3.5 to 4.5 mm, the distribution of predicted gas holdup exhibited minimal changes. It is crucial to highlight that this study examined a limited range of bubble sizes, which deviates from findings in previous studies on GIRs. ,,, Therefore, additional investigation is required to enhance our comprehension of the influence of bubble size.…”