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🏛️國立陽明交通大學機構典藏

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Now showing 1 - 6 of 6
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    Item type:Item,
    A refined model for ozone mass transfer in a bubble column
    (1998-01-01)
    Huang, WH
    ;
    Chang, CY
    ;
    Chiu, CY
    ;
    Lee, SJ
    ;
    Yu, YH
    The mathematical model proposed by Marinas et ai. (1993) for a bubble column gas-liquid contactor is refined to described the mass transfer of ozone absorption and decomposition in the aqueous solution with the decomposition rate expression of general reaction orders (not necessarily integers). Three system equations are employed to describe the ozone concentrations in the bulk liquid (C-ALb), the hold-up gas (C-AGb), and the superficial gas rise velocity (u(G)), respectively. The variation of u(G) and the effect of ozone decomposition on the mass transfer, which is reflected by the enhancement factor (E-r) defined as the ratio of chemical to pure physical mass fluxes according to the film model of gas liquid absorption, are considered in the refined model. This analysis thus extends the applicability of the model of Marinas et al. (1993) and is of special importance for the ozone mass transfer in the cases of basic solutions and of low mass transfer coefficients, in which the effect of decomposition on absorption is significant. An example of such case is the cyanide wastewater treatment in the strong basic condition.
  • Thumbnail Image
    Item type:Item,
    Modeling ozone mass transfer with combined effects of ozone decomposition and reaction with pollutants in a bubble column
    (2001-09-01)
    Huang, WH
    ;
    Chang, CY
    ;
    Chiu, CY
    ;
    Chen, YH
    ;
    Yu, YH
    This paper analyzes the countercurrent single-stage bubble column reactor (BCR) for gas-liquid ozonation systems. The effects of system variables on ozonation performance are examined. The aspects of ozonation performance considered include the efficiency of ozone utilization, the efficiency of pollutant removal, and the emission concentration of ozone gas. This analysis takes into account the effects of ozone decomposition and the ozonation of pollutants on the ozone mass transfer (i. e., enhancement factror, E-r), the variation of pressure (P) and of gas velocity (U-G) along the column, and dispersion effects (Pe(G), Pe(L)). The obtained detailed single-stage BCR model may be used in further development of multi-stage BCR model in the future. The results of this study can provide useful information for rational design of a BCR ozonation contactor, and are important with respect to the treatment of pollutants via ozonation. For the simplified case without ozonation of pollutants, this analysis reduces to that of Huang et al. (1998).
  • Thumbnail Image
    Item type:Item,
    A dynamic model of ozone disinfection in a bubble column with oxygen mass transfer
    (2002-05-01)
    Chen, YH
    ;
    Chang, CY
    ;
    Yu, YH
    ;
    Chiang, PC
    ;
    Chiu, CY
    The dynamic process of disinfection with ozone in a bubble column is studied for model establishment. Bubble columns have been widely used for ozone disinfection in plants and laboratories. Ozone is produced by passing oxygen-enriched gas through an ozone generator, and introduced into the bottom of a column equipped with a gas-diffuser. There certainly exists a temporary and unsteady period before the ozone disinfection system reaches steady state. Available ozone disinfection models employed to describe dissolved ozone and surviving microorganism profiles have commonly been developed for steady state. Moreover, oxygen mass transfer has usually been neglected in previous ozone disinfection models. However, this information is desirable for the proper operation of ozone disinfection in a bubble column. Thus, the objective of this study was to model and investigate the dynamic ozone disinfection process in a bubble column with oxygen mass transfer. A dynamic axial dispersion model is proposed and was employed to predict the variation of the ozone, microorganism and oxygen concentrations along the column. The results of prediction were obtained based on the conditions of Marinas et al. (1993). E. coli was chosen as the model microorganism. The dynamic model of ozone inactivation is useful for proper prediction of the variables of an ozone disinfection system in a bubble column.
  • Thumbnail Image
    Item type:Item,
    Combined absorption and self-decomposition of ozone in aqueous solutions with interfacial resistance
    (1996-05-01)
    Chang, CY
    ;
    Chiu, CY
    ;
    Lee, SJ
    ;
    Huang, WH
    ;
    Yu, YH
    A theoretical analysis is performed employing the film model for the isothermal absorption and self-decomposition of ozone in aqueous solutions with interfacial resistance, which is inversely proportional to the interfacial mass transfer coefficient k(g). A closed-form solution has been obtained. The effects of system parameters on the ozone mass transfer rate are examined. These parameters include the interfacial resistance (1/k(g)),the acidic and basic self-decomposition reaction rate parameters (M(m)(0.5), M(n)(0.5); M(m) = [2D(A)k(m)C(Ai)(m-1)/((m+1)]/k(L)(0))(2), M(n) = (2D(A)k(n)C(Ai)(n-1)/(n+1))/k(L)(0))(2), the reaction orders (m,n), the pH value of solution, and the liquid-phase mass transfer coefficient (k(L)(0)). The results indicate that the reduction effect of the interfacial resistance on the absorption rate is most significant for the situation with the larger values of M(m) and M(n) as well as with higher pH values. Also, for any particular finite value of k(L)(0)/k(g), the reduction effect encountered is greater for a gas liquid contactor with a lower k(L)(0). The reduction effect should be avoided in order to maintain a higher mass transfer rate of ozone in aqueous solution. This analysis is of importance for the efficient use of ozone in water/wastewater treatment processes in the presence of interfacial resistance substances such as surface active agents. For some known special cases (for example, cases with no interfacial resistance), the present solution reduces to the previous works of other investigators.
  • Thumbnail Image
    Item type:Item,
    A refined model for ozone mass transfer in a bubble column
    (1998-01-01)
    Huang, WH
    ;
    Chang, CY
    ;
    Chiu, CY
    ;
    Lee, SJ
    ;
    Yu, YH
    The mathematical model proposed by Marinas et ai. (1993) for a bubble column gas-liquid contactor is refined to described the mass transfer of ozone absorption and decomposition in the aqueous solution with the decomposition rate expression of general reaction orders (not necessarily integers). Three system equations are employed to describe the ozone concentrations in the bulk liquid (C-ALb), the hold-up gas (C-AGb), and the superficial gas rise velocity (u(G)), respectively. The variation of u(G) and the effect of ozone decomposition on the mass transfer, which is reflected by the enhancement factor (E-r) defined as the ratio of chemical to pure physical mass fluxes according to the film model of gas liquid absorption, are considered in the refined model. This analysis thus extends the applicability of the model of Marinas et al. (1993) and is of special importance for the ozone mass transfer in the cases of basic solutions and of low mass transfer coefficients, in which the effect of decomposition on absorption is significant. An example of such case is the cyanide wastewater treatment in the strong basic condition.
  • Thumbnail Image
    Item type:Item,
    Catalytic decomposition of ozone in the presence of water vapor
    (1998)
    Tsai, WT
    ;
    Chang, CY
    ;
    Jung, FH
    ;
    Chiu, CY
    ;
    Huang, WH
    The catalytic decomposition of ozone in the presence of water vapor at the relative humidity (RH) of about 90 % was investigated by using a tubular fixed-bed reactor. The performance tests and reaction kinetic studies were conducted for catalyst, i.e., Pt/gamma-Al2O3 (symbolized as Dash-220). The experiments were carried out at various constant reaction temperatures (298 similar to 323 K) and space velocities (24,000 similar to 44,000 hr(-1)). About 75 % decomposition efficiencies of ozone with inlet concentration of about 0.17 mol/m(3) was achieved at catalyst contact time of 015 sec (space velocity of 24,000 hr(-1)), reaction temperature of 323 K and RH of about 90 % for the Dash-220 catalyst. However, about 97 % decomposition efficiencies of ozone without the presence of water vapor at the same reaction conditions. The results indicated that the Dash-220 catalyst with the presence of water vapor gave lower performance of ozone decomposition than without the presence of water vapor can be achieved at the same reaction conditions. For the reaction kinetics, it was found that the pseudo-first-order chemical reaction rate equation was appropriate for the catalytic decomposition of ozone in the presence of water vapor investigated in this study. The apparent activation energies for the decomposition reaction of ozone using the Dash-220 catalyst in the presence of water vapor at RH of 90 % is 19.32 kJ mol(-1). The corresponding pre-exponential factor is 0.0041 mol/(s g-catalyst (mol/m(3))).