Absorption sulfur dioxide

Flue Ga.s Desulfuriza.tion. Citric acid can be used to buffer systems that can scmb sulfur dioxide from flue gas produced by large coal and gas-fired boilers generating steam for electrical power (134—143). The optimum pH for sulfur dioxide absorption is pH 4.5, which is where citrate has buffer capacity. Sulfur dioxide is the primary contributor to acid rain, which can cause environmental damage. 

Recovery as liquid sulfur dioxide (absorption of clean dry off-gas in water or chemical absorbtion by ammonium bisulfite or dimethyl aniline),... 

To model sulfur dioxide absorption by the blood through the walls of the upper airways, as demonstrated by Frank et one must include the transport rates of sulfur dioxide across a mucus-tissue interface, a tissue layer, and a tissue-blood interface (Figure 7-2). For the case of release of dissolved gas back into the exhaled air, which is depleted of gas in the lower lung, the mucus layer would still represent the greatest resistance to transfer. Consequently, the overall transfer coefficient, kg, would still be given by ki/H. 

An improved gas-uptake model should incorporate the features of the DuBois and Rogers model and the McJilton et al. model. As shown in Figure 7-2 the model for gas uptake in the airways should include separate layers for mucous-serous fluid epithelial tissue and blood. Development of such a model awaits reliable data and methods for predicting the coefficient of diffusion of pollutant gases in tissue and information on the rates of local perfusion of blood and lymph in the bronchial epithelium. Experimental data from humans and animals on the rate of sulfur dioxide absorption in blood could be used to make improved estimates of the tissue-diffusion coefficients in vivo. 

National Dust Collector, developed a process based on dry limestone injection in the boiler. By 1972, the Combustion Engineering process had been installed on five boilers, but these installations proved inadequate owing mainly to boiler plugging, low sulfur dioxide absorption, and reduced particulate collection efficiency in the electrostatic precipitator. 

J. Vanderschuren, Modeling of dilute sulfur dioxide absorption into calcium sulfite slurries, Chem. Eng. 

During the experiments, contrary to the pure reactive absorption, a stationary regime is pursued. The solid mass content of the suspension is much higher than is theoretically required for sulfur dioxide absorption. Thus, the process times will be reduced and the granulation effect with overlapped reactive absorption can be achieved within a few hours. In order to achieve a better granulating effect, carboxyl methyl cellulose (CMC) was added to the suspension as a binder. 

R. M. Counce, et ah, Mathematical model of sulfur dioxide absorption into a calcium hydroxide slurry in a spray dryer, Separation Sci. Technol.,... 

Strandberg, L.G. 1964. Sulfur dioxide absorption in the respiratory tract. Studies on die absorption in rabbits, its dependence on concentration and breathing phase. Arch. Environ. Health... 

It (1 ) deals with the derivation of relations giving the particle size distribution in the bed, overflow, and carryover streams and their respective weights. This theory will be extended to include the effects of particle growth or shrinkage (Z>1 or Z<1). For typical combustion of char containing sulfur followed by sulfur dioxide absorption by limestone, relations will be derived to determine the extent of sulfur retention. The reaction, carryover, and overflow rates will be evaluated with particular attention to their dependence on Z. 

A flow scheme of the unit, which features two parallel-passage reactors operated in the swing mode with automatic sequence control and sulfur dioxide absorption/stripping system to smoothen the fluctuating sulfur dioxide stream, is shown in Fig. 28. Figure 29 shows a photograph of the unit. 

Absorption measurements with 0.2N sodium hydroxide solution and operating conditions approximately the same as for the low sulfur limestone tests gave a mass-transfer coeflBcient of 1.18 Ib-mole/hr-ft -atm (5). This compares closely with the values measured with CaCOa at 100% stoichiometric feed. For sodium hydroxide/sulfur dioxide absorption, the liquid phase resistance can be considered negligible. This suggests that the limestone/S02 system at low sulfur coal conditions falls within a gas phase-resistant process. By selecting a tower height and a limestone feed, one could set the absorption eflSciency at a level suitable for the emission codes. 

A further gas-liquid interaction process to a useful product is the sodium carbonate-potassium carbonate eutectic melt process. This operates at a temperature of about 425°C, well above the melting point of the eutectic [43]. Sulfur dioxide absorption takes place with loss of carbon dioxide (Eq. 3.32). 

B. Skrbic, J. Cvejanov, and R. Paunovic, A... Cas-Liquid Equilibrium-Model for Sulfur-Dioxide Absorption in Aqueous Sodium-Citrate Solution. Chem. Eng. Sci. 46 (12), 3314-3317 (1991). 

As a direct result of this pilot effort, a wetted film packing was found which exhibits excellent sulfur dioxide absorption with an exceptionally low pressure drop. This packing has outstanding mass transfer characteristics and high specific surface area. The packing developed by Munters Corp. is a key element in the limestone-based sulfur dioxide removal system. 

Research-Cottrell is also supplying a gas cleaning system using an electrostatic precipitator for dry particulate collection followed by a multi-stage gas liquid contactor for sulfur dioxide removal. The first stage is a cyclonic quencher for gas saturation and moderate sulfur dioxide absorption followed by a spray and packed-tower section where the major sulfur dioxide absorption takes place. Again the reagent is applied countercurrent to the gas flow. 

Thus, if the total number of equivalents of basic species in a given volume of liquid is equal to the number of moles of sulfur dioxide in the volume of gas contacted by the liquid, the stoichiometry is satisfied and there should be as complete sulfur dioxide absorption as mass transfer allows, provided the sulfur dioxide partial pressure of the resulting solution is sufficiently low. 

Sulfur Dioxide Absorption and Conversion to Sulfur by the Citrate Process... 

The first phase determined that the citrate system best met all of the critical requirements for an ideal sulfur dioxide absorption medium, including the system s capability for efficient removal of sulfur dioxide over a broad concentration range, e.g., the high levels in smelter waste gas, the sulfur dioxide-lean stack gas emitted by power plants, and the intermediate range represented by Claus plants. The results of the second phase of the program, dealing with the process chemistry, forms the basis for much of this paper. 

The practical effects of pH on sulfur dioxide absorption are shown in Figure 2. From this laboratory work it can be seen that in the range studied, an increase of 0.17 pH unit reduces the sulfur dioxide concentration in the vent gas by about one-half. In the citrate process s operating range, above pH 4.0, the vent gas contained less than 60 ppm sulfur dioxide, indicating better than 97% absorption for a 2000-ppm inlet gas. 

Thus, the combination of citrate buffering capacity and thiosulfate concentration provides capacity for short-term overloads of either sulfur dioxide or hydrogen sulfide. There is no need for precise instantaneous adjustment of the hydrogen sulfide flow rate to match exactly the instantaneous sulfur dioxide absorption rate. This is in contrast with the gas phase reaction where precise stoichiometry must be maintained at all times. 

The process consida s the injection of lime into wall and tangentially fired boilers for the sulfur dioxide absorption. 

Plants eqnipped with continuous sulfur dioxide absorption towers can produce sodium sulfite solution that can be used for this process step. A sodium sulfite supply system (see Figure 11.10) is provided to store the sodium sulfite solution. An optional sulfite dissolver tank may be provided for dissolving dry sodium sulfite with water in case additional sodium sulfite may be required. Sodium sulfite solution is injected into the methanol/water condensate solution before injecting into the condensate surge tank inlet (see Figure 11.11) so that it thoroughly mixes into the solution. This ensures that the solution in the tank is free of peroxides and safe for tanporary storage of the condensate solntion. 

Quinn (1926) has stated that sulfur dioxide absorption is more rapid by fruits that are fully mature, which seems reasonable if reducing sugars... 

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