Gypsum saturation

Dissolved Concentrations of Calcium and SO2 Species. The equilibrium dissolved concentrations of total calcium and SO2 (sulfite plus bisulfite) species are important because comparison of these equilibrium concentrations with actual measured values determines the degree of gypsum saturation, and hence the potential for gypsum scale formation in the scrubber. As a first approximation, the fraction gypsum saturation of a scrubber liquor, having specified pH and specified concentrations of magnesium and chloride, is proportional to the measured calcium concentration, and inversely proportional to the measured S02 concentration. 

For a liquor of known pH and magnesium and chloride concentrations, the degree of gypsum saturation can be determined by measurement of either the total dissolved calcium or the total dissolved SO2 (sulfite plus bisulfite). The chemical model has been used to obtain correlations for gypsum saturation, presented below. The correlations, Equations 7 and 9, are valid for a typical scrubbing temperature of 50 °C, and for the same ranges of pH, magnesium, and chloride as for Equations 1-4. 

Gypsum Saturation From Measurements of Dissolved Calcium. Equation 7 below can be used with Equation 4 to calculate gypsum saturation from measurements of total dissolved calcium. 

For a typical limestone scrubber inlet liquor pH range of 5.2-6.0, and for liquors having a chloride-to-magnesium ratio of 0.2 mole/mole or less, the following simplified equation can be used to determine gypsum saturation from calcium measurements ... 

Equation 8 has a standard error of estimate of 0.07 fraction gypsum saturation over the saturation range of 0.5-2.0. The equation is useful for monitoring the actual gypsum saturation... 

Gypsum Saturation from Measurements of Dissolved SOg. Use of measurements of dissolved calcium to determine gypsum saturation is relatively easy from a computational standpoint use of measurements of dissolved SO2 is more difficult. However, wet chemical analyses for calcium are frequently subject to interference by high concentrations of magnesium. For installations where a quick and reliable analysis for calcium is not available, the use of dissolved SO2 is preferred, and the following correlation applies ... 

The degree of gypsum saturation of a 1imestone/magnesia scrubbing liquor can be calculated from either dissolved calcium or dissolved S02 (sulfite plus bisulfite) analyses. 

Any more detailed interpretation demands that both activity coefficients and the existence of complex species be taken into account (B90,G58). Gartner el til. (G58) showed that, for most cements, the solution is saturated in CH within 12 min and that the saturation factor (defined as the activity product divided by its value at saturation) reaches a maximum of between 2 and 3 within 2h. For gypsum, saturation is reached within 6 min, but the saturation factor never exceeded 1.3 in the cases studied. With cements high in K,0, the solution can become saturated in syngenite. Gartner el id. found that the and Na concentrations increased rapidly during the first 12 min and only slowly, or not at all, during the subsequent period up to 3 h. 

Compute the total or stoichiometric and effective ionic strengths, and corresponding total- and free-ion activity coefficients of Ca and SO in pure water saturated with gypsum at 25"C. It is given that the solubility product of gypsum, and that at gypsum saturation... 

Spray tower inlet liquor gypsum saturation, % 95 105 110... 

Limestone utilization averaged 92.6 percent. Sulfite oxidation was excellent at 99.8 percent and the filter cake solids content was high, averaging 86 percent. Gypsum saturation in the scrubber inlet liquor was only 93 percent. 

Onstream hours Fly ash loading Adipic acid concentration, ppm (controlled) Scrubber gas velocity, ft/sec Liquid-to-gas ratio, gal/Mcf Slurry solids concentration, wt % (controlled) Scrubber inlet pH (controlled) Oxidation tank level, ft Oxidation tank residence time, min Effluent hold tank residence time, min Average percent SO2 removal Average inlet SO2 concentration, ppm SO2 make-per-pass, m-moles/liter Percent oxidation of sulfite to sulfate Air stoichiometry, atoms oxygen/mole SO2 absorbed Oxidation tank pH Percent limestone utilization Scrubber inlet liquor gypsum saturation, % Filter cake solids content, wt % 1,688 High 1,300 1,700 5.4- 9.4 85 150 15 5.0- 5.1 18 2.8 8.3 93.4 2,660 4.0- 8.9 99.8 1.4- 2.4 4.9 92.6 93 86... 

Dispersant [Hoechst AG] Modifi polymers reduces vise, and gelling properties of water-based and gypsum saturated drilling fluids. 

First, an experiment for benzoic acid-water system was carried out to examine characteristics of liquid-phase mass transfer. Then experiments of limestone dissolution were carried out in sulfuric acid, sulfurous acid and sulfuric acid with gypsum saturation. 

Flg.4 Dissolution rate with and without gypsum saturation in H2S04(333 [K,] 7.5 [s ]). 

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