No abstract

No abstract

and useful discussions with J. F. Davidson are acknowledged. Nomenclature D = column diameter, m G = superficial gas mass velocity, kg/m2 sec g = gravitional acceleration, m/sec2 1 = length of tube section, m L = liquid volumetric flow rate, m3/sec A p / l = gas pressure gradient, N/m3 t = film thickness, m u = liquid velocity, m/sec UC, = superficial gas velocity, m/sec a = liquid fraction Ti = interfacial shear stress, N/m2 Literature CitedThe reaction of gaseous SO2 and NH3 in humid air at 23°C to form solid reaction products was studied experimentally in a flow-type reactor. With excess water vapor and oxygen, pure ammonium sulfate was formed in an initial concentration range of 4 to 60 mmol m-3. At equimolar ratios of NH3 and Son, ammonium sulfamate (3%) was also obtained. At water vapor concentrations approaching those of NH3 and SO2, the principal products were NH3.S02 and (NH3)2-S02 adducts with minor amounts of "$303, (NH4)2S207, NH4N3, and N3H7S04. At lower concentrations of 0 2 the reaction product was primarily (NH3)2-S02 with secondary products of N3H7S04 and NH3S03. The reaction rate was dependent on the amount of water vapor present but independent of the oxygen concentration. Rate constants were in the range 1-6 X l o 5 I. mol-' sec-'.

= thermal expansion coefficients (Equations 16 and 26), deg.? =(~'dp3'~, deg. -l cm.3I2 = dimensionless factor accounting for overlap of free volume = Lennard-Jones parameter for depth of potential well, ergs = bed void fraction, its average value, and value a t incipient fluidization, diniensionless = measured viscosity and its zero-shear limit, g./cm. sec. = bed thermal parameter and its average value (analogous to kT for molecular systems), ergs/part icle = viscosity of fluidizing medium or true liquid, g./cni. sec. = p / p f , kineiuatic viscosity, sq. em. per sec. = density of fluid and particle, g. per cc. = Lennard-Jones parameter for molecular di-= jump frequency for molecules, set.-' = nngular deflection measuring torque on vis-= visconieter spindle rotation rate, r.p.m. ameter, cni.cometer, deg.On the basis of a four-step reaction a mechanism is proposed for the catalytic oxidation of SO2 by aqueous aerosols of MnS04. Data were generated to permit the evaluation of the rate constants. A computer sohtion of the reaction rates indicates that the proposed model adequately explains the kinetics of the gasaerosol as well as the bulk phase situations. In principle the mechanism is applicable to reactions in which other metal-salt catalysts are involved.

~~Sulfur dioxide (500-3000 ppm) in a flowing humid air mixture was exposed t o a corona discharge in a wire-tocylinder reactor. Sulfuric acid mist was precipitated on the inside wall-electrode, and ozone and the remaining SO2 were monitored at the exit port. Residence times, humidities, oxygen, and SO, concentrations were varied to study the kinetics of the conversion of SO, to acid mist. The reaction was zero order with respect t o SO, in the range tested, and the ratedetermining step appeared to be the formation of atomic oxygen by the electrical discharge. Optimum reaction rates occurred at 70% r.h. and above 15% oxygen concentration. Studies of the precipitated droplets indicated a mean size of 6.36 before deposition.ulfur dioxide mixed with oxygen or air has been oxidized S in the presence of an electrical corona discharge by a number of investigators. Miklos et al. (1966) reported efficiencies on the order of 35 % for direct oxidation of SO, to SOs in a n airstream. Palumbo and Fraas (1971) concluded that a damped or pulsed high-frequency current was more effective than direct current for SOz conversion. In their tests the reactor was placed in a n oven at 130°C, and a conversion efficiency of 96% was obtained with a power expenditure of 9 W over a period of 30 min. In the absence of water vapor, only 67% of the SOs was converted. Reaction products were identified as elemental sulfur and sulfuric acid. The reaction mechanism was not studied. Moyes and Smith (1965) presented comparative results for the thermal-and electrical discharge-activation of mixtures of SO? and Os. They showed that the activation by electrical discharge was more efficient, but had doubts about its industrial application for exothermic reactions for which a suitable catalyst was available.Several questions as to the various reaction mechanisms in such a gas mixture exposed to a corona must be dealt with before launching into pilot scale studies. However, in the case of SO2, such information is useful especially in certain electrical precipitator operations. The generation of sulfuric acid mist in limited quantities, in power plant stack gases, may have the beneficial side effect of combining with and reducing the resistivity of some types of fly ash, thereby increasing the precipitator's efficiency. Overproduction of the mist, however, would initiate corrosion problems and decrease the overall performance of the precipitator in the long term. Reese and Greco (1968) have shown in tests with TVA precipitators that the presence of H2S04 mist seriously lowered the collection efficiency of electrostatic precipitators. Therefore, it is desirable to have a quantitative estimate of the extent to which various operating conditions in a corona discharge contribute to the conversion of SO, t o sulfuric acid mist. This paper treats several of the parameters influencing the SO? oxidation in a corona to include relative humidity, electrical potential, gas concentrations and flow rates; and reaction mechanisms are proposed, based on results of thes...