PENETRATION THEORY ANALYSIS FOR NONISOTHERMAL GAS ABSORPTION ACCOMPANIED BY A SECOND-ORDER CHEMICAL REACTION

The penetration theory equations for nonisothermal gas absorption with second-order reaction were solved numerically using the Saul'yev method. Results for the enhancement factor and interfacial temperature rise were obtained for Hatta numbers between 1 and 10, It was found that the enhancement factor and interfacial temperature rise depend on four parameters; (i) the effective activation energy, ε_eff = (ε_R + ε_DA)/2 - ε_S, where ε_R, ε_DA, and ε_S are the activation energies for the reaction, diffusion, and solubility of the solute gas, respectively; (ii) the effective heat of generation, β_eff = (β_R + β_s)√Le, where β_R and β_s are the dimensionless heat of solution and reaction, respectively, and Le is the Lewis number; (iii) the product √rq where r is the ratio of the diffusivity of the liquid reactant to that of the solute gas and q is the ratio of the concentration of the liquid reactant in the bulk solution to that of the solute gas at the interface at the bulk temperature of the solution; and (iv) the activation energy for diffusion of the liquid reactant, ε_DB. This effectively reduces the number of parameters required to give a complete picture of the absorption from nine to four. The reduction is important since it reduces the number of van Krevelen-Hoftijzer plots and interfacial temperature-Hatta number plots required for the design of gas-liquid reactors.     

GAS ABSORPTION INTO A LIQUID FLOWING OVER A SPHERE WITH A SECOND-ORDER IRREVERSIBLE CHEMICAL REACTION

The objective of the work presented here is to theoretically investigate the absorption of a gas into a liquid flowing in laminar flow over a sphere with a second-order irreversible chemical reaction occurring between the absorbed gas and a nonvolatile solute present in the liquid. Commonly used simplifications in the diffusion-reaction equations and for the liquid velocity profile and the liquid film thickness on the sphere are investigated, and it is found that, under the experimental conditions usually encountered, these simplifications are justified. Numerical results for the absorption rate are presented graphically in two figures which may be used to estimate the second-order kinetic rate coefficient for the reaction between the absorbed gas and the nonvolatile liquid-phase solute. A criteria is developed for the conditions under which a second-order reaction may be considered to be pseudo-first-order,     

COUNTERCURRENT GAS ABSORPTION WITH CHEMICAL REACTION IN A LAMINAR FALLING FILM

An analytical solution for absorption of a gas with an accompanying first order reaction in a laminar falling film is developed. The gas flow is countercurrent to that of the liquid film. Change in the gas phase concentration because of the reaction, as it happens in practical situations, has been taken into account. Some computed results are presented to show the effects of the system parameters—namely, the reaction rate parameter, the Biot number, and the absorption factor— on the mass transfer enhancement factor and on the fractional removal of the feed gas over a given non-dimensional film length.     

PERTURBATION ANALYSIS OF GAS ABSORPTION WITH CHEMICAL REACTION: A NONVOLATILE LIQUID REACTANT

Enhancement factors for gas absorption in a liquid containing a nonvolatile reactant are calculated using a regular perturbation technique. The perturbation solutions are found to be quite accurate in the slow reaction regime but lead to erroneous results for moderate and large reaction rates. To extend these solutions to the intermediate and fast reaction regimes, we have used the method of Padé approximants and Shanks transformations. The results obtained by these acceleration techniques are shown to be in excellent agreement with the direct numerical solutions for the enhancement factors in the intermediate and fast reaction regimes.     

ENHANCEMENT FACTOR OF GAS ABSORPTION ACCOMPANIED BY REVERSIBLE CYCLIC CHEMICAL REACTIONS

Theoretical effect of mass transfer by reversible cyclic chemical reactions is studied in this paper. On the basis of the film theory, an analytical equation has been derived to express the enhancement factor of gas absorption with first-order reversible cyclic chemical reactions. The finite difference method has been used to study the enhancement of gas absorption with second-order reversible cyclic reactions. The results indicate that the gas absorption rate is enhanced by the forward reaction rate, while is suppressed by the backward reaction. Although the diffusivity has some effects on enhancement factor, the influence is not as much as that of reaction rate. The theoretical equations are used to predict the enhancement factors for absorptions of carbon dioxide in acidic solution and l-butene in liquid phosphoric acid.     

ENHANCEMENT FACTOR OF GAS ABSORPTION ACCOMPANIED BY REVERSIBLE CYCLIC CHEMICAL REACTIONS

Theoretical effect of mass transfer by reversible cyclic chemical reactions is studied in this paper. On the basis of the film theory, an analytical equation has been derived to express the enhancement factor of gas absorption with first-order reversible cyclic chemical reactions. The finite difference method has been used to study the enhancement of gas absorption with second-order reversible cyclic reactions. The results indicate that the gas absorption rate is enhanced by the forward reaction rate, while is suppressed by the backward reaction. Although the diffusivity has some effects on enhancement factor, the influence is not as much as that of reaction rate. The theoretical equations are used to predict the enhancement factors for absorptions of carbon dioxide in acidic solution and l-butene in liquid phosphoric acid.     

GAS ABSORPTION WITH CHEMICAL REACTION INVOLVING A VOLATILE LIQUID REACTANT: PENETRATION THEORY SOLUTION

A penetration theory analysis is presented for the problem of gas absorption, with chemical reaction involving a volatile liquid reactant. Model equations are derived and solution techniques are presented. It is shown that as long as the diffusivities of two reactants are equal, the enhancement factors predicted by film and penetration theories only mildly differ. Except for slow and instantaneous reaction regimes, the liquid reactant volatility can be markedly detrimental to enhancement of absorption rate by chemical reaction.     

ADIABATIC GAS ABSORPTION AND STRIPPING WITH CHEMICAL REACTION IN PACKED TOWERS

In the design of adiabatic gas absorption, the temperature distribution within the column is an important consideration. Temperature influences the degrees of heat and mass transfer through the thermodynamic phase equilibrium relationships and reaction rates. The capacity of an absorber is limited through the formation of a temperature plateau. Gas absorption in a chemically reactive solvent in an adiabatic packed column is modelled rationally for the first time taking into account the major heat effects. An iterative computational method for computing packed bed height is presented. The design procedure is illustrated by sample calculations for carbon dioxide (CO₂) absorption in monoethanolamine (MEA).     

GAS ABSORPTION WITH INSTANTANEOUS CHEMICAL REACTION IN A FALLING FILM FOR PARALLEL AND COUNTERCURRENT FLOWS

A theoretical analysis is presented for the absorption of a gas accompanied by instantaneous chemical reaction with a dissolved reagent in a falling liquid film of liquid. The reaction occurs on a moving front inside the liquid film separating the zones containing either of the reactants. The governing equations are solved by using a coordinate transformation to immobilize the reaction front. The effects of the different system parameters on the reaction front profile, absorption rate and enhancement factor are presented for both cocurrent and countercurrent flow of the gas. In the former case the reaction front profile shows a maximum, but in the later case it is monotonic in the axial distance along the film. The enhancement factor plots exhibit maxima in both the cases.     

THE DIFFUSIONAL LIMITATION ON THE TEMPERATURE RISE IN THE ABSORPTION OF CHEMICALLY REACTIVE GASES

The interfacial temperature is important in gas absorption because it sets the solubility. If the gas undergoes an exothermic reaction this temperature ordinarily exceeds the bulk liquid temperature. For a bimolecular reaction the pseudo-first-order approximation leads to a serviceable model; yet it must overestimate the temperature rise under fast reaction conditions. We correct this estimate by accounting for the depletion of the liquid-phase reactant near the surface. To do this we use an enhancement factor based on the van Krevelen-Hoftijzer approximation. This implies a simple formula for the temperature rise not unlike that based on the pseudo-first-order approximation. We investigate this formula and show that it exhibits either one or three solutions. We deduce criteria for predicting, a priori, both what the multiplicity is and whether or not the maximum temperature rise corresponding to instantaneous reaction obtains.     

低温等离子体烟气脱硫的反应机制

关于用脉冲电晕或电子束照射（产生低温等离子体）脱除烟气二氧化硫的主要反应机制，有过两种推测，即气相反应和异相反应.本文所列结果表明，在有适当的水蒸气压条件下，在反应器内部的表面会生成液膜，液相中自由基SO_3~-亚硫酸根离子氧化为硫酸根离子的链过程中起主要作用．解动力方程发现，液相吸收的羟基产生85％以上的脱硫率，超过了气相脱硫率的十多倍，说明主要机制是活化液相反应．计算结果与实验相符，预言的面积因子效应也得到实验证实．     

A MATHEMATICAL MODEL AND SIMULATION FOR NON ISOTHERMAL GAS ABSORPTION WITH CHEMICAL REACTION

In this paper, the principles of mass and heat transfer for a non-isothermal gas absorption with chemical reaction have been described. The examples of carbon monoxide complexing with aluminum cuprous tetrachloride solution and carbon dioxide absorbed by monoethanolamine aqueous solution in packed column have been simulated and computed with a mathematical model which considered of both mass and heat transfer, gas and liquid resistance. The fundamental differential equations of the process are treated with forth order Runge-Kutta method. Through simulating and computing, the temperature profiles and concentration profiles of both gas and liquid phase along the packed height have been visualized. The results are reasonably accurate and conform with pilot plant experimental data.     

ABSORPTION OF CARBON DIOXIDE BY IMPINGING, THIN LIQUID SHEETS

Pure carbon dioxide was absorbed in a thin liquid sheet that was formed by the impingement of two individual sheets. The sheets were produced by an impingement-sheet mixing device that was previously shown to provide rapid micromixing of two liquids (a few milliseconds for low-viscosity liquids). Three different impingement-sheet mixing devices were tested at flow rates between 3 and 20 L/min and at device pressure drops up to 3·0 bar. Despite the short exposure times (4 to 40 milliseconds) of the mixed sheet, significant amounts of carbon dioxide were absorbed (48 to 92% of saturation)

Carbon dioxide absorption was explained by a mathematical model of the diffusion within the sheet. Since the collision of the individual sheets produces turbulence within the impingement zone of the mixed sheet, the data were correlated assuming an overall effective diffusivity that was from 5 to 167 times the molecular diffusivity. The overall diffusivity enhancement factor was correlated with the component velocity of the single sheets that was destroyed upon impingement and whose associated energy was responsible for the turbulence created in the mixed sheet.     

GAS ABSORPTION IN A HOLLOW FIBER DEVICE

The absorption of S0² and NH³ from air and air/CO ² streams was studied for the first time in a certain novel hollow fiber mass transfer device, for various inlet gas compositions, liquid compositions, gas flow rates, and liquid flow rates. The gas and liquid flows were countercurrent. Analyses of the amounts of S0²and NH³ absorbed demonstrate that the hollow fiber unit has a relatively small membrane resistance and is an effective gas scrubbing device. Additionally, it offers a large interfacial area per unit volume, and avoids flooding problems entirely     

GAS ABSORPTION IN A HOLLOW FIBER DEVICE

The absorption of S0² and NH³ from air and air/CO ² streams was studied for the first time in a certain novel hollow fiber mass transfer device, for various inlet gas compositions, liquid compositions, gas flow rates, and liquid flow rates. The gas and liquid flows were countercurrent. Analyses of the amounts of S0²and NH³ absorbed demonstrate that the hollow fiber unit has a relatively small membrane resistance and is an effective gas scrubbing device. Additionally, it offers a large interfacial area per unit volume, and avoids flooding problems entirely     

ADVANCED CHEMICAL OXIDATION OF 2,4,6 TRICHLOROPHENOL IN AQUEOUS PHASE BY FENTON'S REAGENT-PART I: EFFECTS OF THE AMOUNTS OF OXIDANT AND CATALYST ON THE TREATMENT REACTION

Fenton's Reagent is a strong oxidant for 2,4,6 Trichlorophenol (TCP) in aqueous phase. This reaction can be effectively utilized to treat an industrial wastewater containing TCP, and reduce the toxicity of the discharge. This paper reports the effects of the amounts of the oxidant (hydrogen peroxide) and the catalyst (ferrous ions), relative to TCP, on the rates and extents of reaction. The progress of each reaction has been monitored in terms of TCP removal, chloride ions release from the organic structure, change in pH, and the reductions in COD and TOC. This information is important in order to maximize the level of treatment with minimum application of chemicals. A set of optimum molar ratios of oxidant to substrate, and catalyst to oxidant were determined.     

SIMULTANEOUS ABSORPTION OF AN ACID GAS (H2S) AND A BASIC GAS (NH3) IN A SCRUBBING DEVICE

H₂S and NH₃ are major contaminants in many synfuel process gas streams. The H₂S is frequently removed by dissociation and reaction in scrubbers using alkaline scrubbing liquids. Some of the NH₃ is removed by simple dissolution in the same unit; the remaining NH₃ can be removed in a second scrubber using a mildly acidic liquid. The first scrubbing stage in such a system is novel in that an acidic gas (H₂S) and a basic gas (NH₃) are absorbed simultaneously. In this paper, the interesting behavior of this simultaneous acid gas-basic gas scrubbing process is described and discussed. The percentage H₂S and NH₃, absorption as a function of the injected liquid pH, the liquid-to-gas ratio, and the NH₃ content of the gas stream have been determined.     

发生器、吸收器传质效率对高温吸收式热泵性能的影响

研究分析了水／二甘醇高温吸收式热泵的发生器、吸收器传质过程及效率对系统性能的影响。当发生器、吸收器传质效率提高,系统性能系数COP、Yong效率η及Yong指标I均增大,而溶液循环比FR减小,通过回归分析,获得了评价热泵性能的关联式。     

HEAT EFFECTS FOR PHYSICAL AND CHEMICAL ABSORPTION IN TURBULENT LIQUID FILMS

An eddy diffusivity model was used to describe simultaneous heat and mass transfer for chemical absorption in turbulent liquid films. For absorption accompanied by a first-order reaction an approximate expression for the mass transfer coefficient is derived and shown to be in excellent agreement with exact numerical calculations. An equation is developed for the temperature rise at the free surface due to both the heat of reaction and the heat of solution. Relationships are also developed for the concentration of the liquid phase product at the free surface and the depletion of the liquid phase reactant at the free surface.

The temperature rise at the free surface for gas absorption accompanied by an instantaneous reaction due to both the heat of solution and the heat of reaction was determined. An equation is also derived for the concentration of liquid phase product at the free surface for the case of an instantaneous reaction.