Gypsum scaling

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. 

Therefore, it would be advantageous to operate a low pH, adipic acid-enhanced limestone or lime system with within-scrubber-loop forced oxidation which, in addition to improved SO2 removal, requires low adipic acid makeup, minimizes gypsum scaling potential, and produces a sludge with good disposal properties. Based on Figure 9, 90 percent SO2 removal can be achieved at 5.0 inlet pH and only 1,100 ppm adipic acid, or at 4.6 inlet pH with 1,400 ppm adipic acid. 

Screening Tests for EveJuating the Effectiveness of Gypsum Scale Removers... 

Gypsum Scale formation Control in Pipe Flow Systems A Systematic Study on the Effects of Process Parameters and Additives... 

Keywords additives, crystallisation, gypsum scale, hydrometallurgical processes. 

Conflicting results on tlie effect of flow rate or fluid velocity on scale deposition have been reported by Andritsos and Karabelas [21]. They showed that the flow rate either increased or decreased the mass of scale deposited over a certain period of time. Clearly, this is due to the nature of the solid-fluid interface layer and the shear sti ess induced to the scale by the flow. These two incompatible forces are further complicated by other parameters such as the presence of additives, which may exert a significant effect on the nature of the interface layer as well as on the characteristics of the scale deposited [26]. Fluid velocity also affects the orientation of the growing scale or crystals [2, 27, 28]. The tendency is that the scale to orient to the direction of the fluid flow [2]. A rather recent study on gypsum and calcium carbonate scaling of membrane desalination by He and co-workers [29] shows that a faster flow rate increases more deposition of gypsum scale. 

The systematic gypsum scale fonnation and control study was carried out in four stages of experiments, namely seeded batch crystallization, seeded continuous crystallization, single pipe flow, and multiple pipe flow, respectively. For all the experiments, the supersaturated gypsum scale forming solutions were prepared by dissolving in distilled water at room... 

Gypsum Scale Formation Control in Pipe Flow Systems A Systematic Study. 

Figure 16. SEM images of gypsum scale g. h. 10 M NDPA i. j. 10 MNPDA k. 1. 10" M HEDP (taken from ref 1).

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