SO2 absorption

Pulverized lime or limestone injected into flue gas (often through burner). SO2 absorbed on soHd particles. High excess alkah required for fairly low SO2 absorption. Finer grindings lime preheat, flue gas humidification benefit removal. Particulate collected in baghouse. 

The influence of Zn-deposition on Cu(lll) surfaces on methanol synthesis by hydrogenation of CO2 shows that Zn creates sites stabilizing the formate intermediate and thus promotes the hydrogenation process [2.44]. Further publications deal with methane oxidation by various layered rock-salt-type oxides [2.45], poisoning of vana-dia in VOx/Ti02 by K2O, leading to lower reduction capability of the vanadia, because of the formation of [2.46], and interaction of SO2 with Cu, CU2O, and CuO to show the temperature-dependence of SO2 absorption or sulfide formation [2.47]. 

This study has demonstrated that absorbent prepared from oil palm ash does have a high reactivity towards SO2 absorption. The reactivity of the absorbent was found to increase with higher reaction temperature up to 300°C and lower feed concentration of SO2. 

Buffers in the pH range of 3.5 to 5.5 provide for reversible SO2 absorption as bisulfite (HSOj) by the acid/base reaction ... 

In a perfectly-buffered solution the SO2 vapor pressure will be directly proportional to the total concentration of SO2 and bisulfite, giving a linear equilibrium relationship. In simple alkali sulfite solution without added buffer, the equilibrium relationship is highly nonlinear, because H-1" accumulates as SO2 is absorbed. Under these conditions is it not possible to carry out reversible SO2 absorption/stripping in a simple system, resulting in greater steam requirements than expected with a linear equilibrium relationship. Weak acid buffers such as sodium citrate have been proposed to "straighten" the equilibrium relationship and thereby reduce ultimate steam requirements (Jl, 2, 7). Citrate buffer is attractive because it is effective over a wide range, from pH 2.5 to pH 5.5 in concentrated solutions. 

Table IV gives minimum steam requirement (infinite stages) at several different solution capacities. The factor attribu-able to equilibrium nonlinearity increases as more SO2 is absorbed, because the buffer capacity is consumed to a greater extent. Any capacity for SO2 absorption can be achieved by varying Na concentration (pH) in the solution. At low pH ([Na] = 1.5 M) the solution capacity for SO2 absorption is small, but the nonlinearity factor is also small (1.05). Solution capacity can be increased by operating at higher pH ([Na] = 2.5 M), but nonlinearity is more severe (1.32).

Optimized steam requirement is relatively insensitive to solution pH. Solution capacity for SO2 absorption can reasonably vary from 0.1 to 0.4 g-moles S02/liter. The SO2 gas sensing electrode is an effective tool for vapor/liquid equilibrium at room temperature. 

SO2 absorption and particulate removal begins at the quench section and continues as the flue gas rises up through the main spray tower where the gas is again contacted with high-density water curtains produced by additional spray nozzles. The spray tower itself is an open tower with multiple levels of the BELCO spray... 

The scrubbing liquid is controlled to a neutral pH with reagent addition to drive SO2 absorption. Caustic soda (NaOH) is typically used as the alkaline reagent. However, other alkalis, such as soda ash, magnesium hydroxide, and lime have also been utilized with excellent results in terms of performance and reliability. For FCCU applications, however, where a 5-7 year continuous operation is required, the use of lime as a reagent is not recommended. Multiple levels of spray nozzles provide sufficient stages of gas/liquid contact to remove both particulate and SO2. An illustration of the spray tower and the spray nozzles is provided in Figure 16.6. 

Chromium(II) double sulfates can be crystallized by the addition of ethanol to concentrated aqueous solutions containing equimolar quantities of the components. The hexahydrates A2S04>CrS04-6H20 (A = NH4, Rb or Cs) are high-spin and have reflectance spectra compatible with the presence of tetragonally distorted [Cr(H20)6]2+ ions (Table 24). 4 The potassium and sodium salts crystallize as pale blue dihydrates with similar properties, and from the splittings of the SO2- absorption bands in their IR spectra it seems that coordinated sulfate anions are present. 

The high capital investment cost of the Asahi process is due to the necessity for large absorbers, evaporators, crystallizers, dryers, rotary kiln crackers and screw decanter separators. The major operating and maintenance costs are electricity, fuel oil, steam and chemicals such as soda ash, EDTA and limestone. The requirement for consumption of large amounts of utilities is associated with the operation principle and design of the Asahi process. According to the economic evaluation, equipment required for N0X and SO2 absorption (such as packed-bed absorbers) accounts for 20% of total direct capital investment for treatment of dithionate ion (such as evaporator, crystallizer, dryer, and cracker) it accounts for about 40% and for treatment of nitrogen-sulfur compounds (such as screw decanter and cracker) it accounts for only 2%. 

SO2 absorption into aqueous NaHC03/Na2C03 solutions 9.2... 

SO2 Absorption into Aqueous NaHC03/Na C03 Solutions 9.5.4.1 Chemical System... 

Fig. 9.23. Comparison of simulated absorption/desorption rates with experimental data of Hikita and Konishi [100] for SO2 absorption into aqueous Na2CC>3 solutions (adapted from Ref. [70]). (a) SO2 absorption rate (b) CO2 desorption rate.

The film phenomena influence the process variables along the column. The partial pressures of SO2 and CO2 are shown in Fig. 9.24. It can be seen that CO2 is absorbed in the fresh alkaline solution at the column top. Then, as the pH decreases from the top to the bottom due to SO2 absorption, the CO2 concentration increases, and the direction of the CO2 flux at the interface changes (see Fig. 9.25). CO2 desorption also occurs when the concentration in the reaction plane is higher than that at the interface, even if in the bulk it may be lower [70], The co-existence of absorption and desorption phenomena shown in Figures 9.24 and 9.25 is similar to the phenomena discussed elsewhere [104]. Further sensitivity studies regarding the effect of the buffer concentration and SO2 gas concentration can also be found [70]. 

R. Kleerebezem, et ah, Rate-based modelling of SO2 absorption into aqueous NaHC03/Na2CC>3 solutions accompanied by the desorption of CO2, Chem. Eng. Sci., 2003, 58, 3589-3600. 

Chang and Rochelle [12-15] investigated some aspects of SO2 absorption in an agitated cell filled with aqueous solution or suspension, and compared their measurements with those of other authors with simulated absorbed mass flows, based on enhancement factors from the film and surface renewal theory. The results showed that mass transfer, when corrected by an enhancement factor from the surface renewal theory, agreed clearly with the measurements. 

Experimental investigations and theoretical computations of SO2 absorption in a spray drier [47] showed that, with an excess of calcium hydroxide absorption is limited only by the gas-phase mass transfer. In addition, the flow in a spray drier could be described by the model of an ideal stirred vessel. Newton et al. [70] considered the subprocesses of mass transfer of SO2 from the gaseous phase to the drop surface, the absorption, the dissociation of SO2, the diffusion of the produced species and the dissolution of calcium hydroxide particles in the drop. 

SO2 absorption into NaOH and Na2SC>3 aqueous solutions, Ind. Eng. Chem. Fundam., 1985, 24 (1), 7-11. 

C. S. Chang, G. T. Rochelle, Effect of organic acid additives on SO2 absorption into CaO/CaCC>3 slurries, AIChEJ. 1982, 28 (2), 261-266. 

FIGURE 5.2 (a) High resolution SO2 absorption spectrum from 190 to 220 nm at 213 K [21]. Approximate spectrum for (blue) is also shown as a red-shifted version of the... 

It should be noted that the highest possible absorption rates will occur under conditions in which the liquid-phase resistance is negligible and the equilibrium back pressure of the gas over the solvent is zero. Such situations would exist, for instance, for NH3 absorption into an acid solution, for SO2 absorption into an alkali solution, for vaporization of water into air, and for H2S absorption from a dilute-gas stream into a strong alkali solution, provided there is a large excess of reagent in solution to consume all the dissolved gas. This is known as the gas-phase mass-transfer limited condition, when both the liquid-phase resistance and the back pressure of the gas equal zero. Even when the reaction is sufficiently reversible to allow a small back pres-... 

Lane A. L. and Domingue D. L. (1997) lUE s view of Callisto detection of an SO2 absorption correlated to possible toms neutral wind alterations. Geophys. Res. Lett. 24, 1143-1146. 

This insensitivity to limestone feed is illustrated in Figure 3. At 1000 ppm, the SO2 absorption is more than doubled as the limestone feed is increased from 100 to 140%, while at 1600 ppm the same limestone increase improved the absorption by approximately 50%. 

NO2—SO2 Absorption by Hydroxides and Carbonates. Several metal hyroxide slurries were screened for NO2-SO2 scrubbing potential. In addition a limestone (CaCOa) slurry was investigated. Magnesia, lime, and limestone scrubbing systems are under consideration for SO2 scrubbing, so our results on the combined scrubbing are pertinent. A summary of the data is contained in Table VI. 

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