Effect of pH on Absorption Efficiency

From the equation above, it is clear that a higher pH value indicates a higher concentration of limestone in the slurry, which is beneficial for the absorption of SOâ‚‚. To achieve a high SOâ‚‚ absorption rate, maintaining an appropriate pH level is essential. The pH in the absorption tower is typically maintained by continuously adding limestone slurry. However, it's important to note that a higher pH is not always better. While a high pH promotes the absorption of sulfur dioxide, a lower pH encourages the precipitation of the reaction products. These two factors are essentially opposing each other.

Within a certain range, increasing the pH of the slurry leads to improved desulfurization efficiency. This is because a higher pH means more CaCO₃ is available in the slurry, which directly enhances the desulfurization process. However, once the pH exceeds 5.8, the desulfurization efficiency begins to decline. This happens because as the H⁺ concentration decreases, the precipitation of calcium sulfate becomes increasingly difficult, which negatively impacts the overall efficiency.

At a pH of 5.9, the CaCO₃ content in the slurry reaches about 2.98%, while the CaSO₄·2H₂O content remains below 90%. This suggests that the reaction between SO₂ and the desulfurization agent is not complete at this point, leading to unnecessary consumption of limestone and a decrease in the quality of the gypsum produced. When the pH drops again, the CaSO₄·2H₂O content increases, while the CaCO₃ content decreases. Therefore, the pH must be carefully controlled to avoid both excessively high and low values.

Under normal operating conditions, keeping the pH of the absorption tower between 5.4 and 5.5 helps maintain a Ca/S ratio of approximately 1.02, which ensures efficient desulfurization and good product quality. This balance is crucial for both performance and cost-effectiveness in the flue gas desulfurization process.

It is evident that pH control plays a critical role in wet flue gas desulfurization. The pH level directly affects the desulfurization efficiency and the purity of the final product. Choosing the right pH electrode is therefore a key factor in ensuring accurate and reliable measurements, which in turn supports optimal system performance.