Experimental and mechanism research on volatilization characteristics of HCl in desulfurization wastewater evaporation process using high temperature flue gas

Abstract

Due to the promulgation of “water pollution control action plan” in China, zero liquid discharge of desulfurization wastewater has become a new trend for water pollution control in power plants. The HCl volatilization in desulfurization wastewater evaporation process is the key problem that may influence the application of evaporation technology, so experiment was carried out in self-made experimental system. The effects of temperature, pH, Cl− concentration, total dissolved solids and main metal ions on HCl volatilization were explored. Results have shown that HCl volatilization increases respectively from 5.42% to 20.43% and 2.22% to 9.18% with the increasing temperature from 180°C to 380°C in two kinds of actual desulfurization wastewater evaporation process. When pH<7, Cl− concentration is the main influencing factor on HCl volatilization; the higher Cl− concentration is, the higher HCl volatilization will be observed. While pH>7, pH becomes the dominant factor, increasing pH will inhibit HCl volatilization; Mechanism of HCl volatilization was studied simultaneously by XRD and TGA. Gaseous HCl mainly comes from the combination of free H+ and Cl−, hydrolysis of Ca2+ and Mg2+ in liquid phase and hydrolysis of hydrate in high temperature solid phase; Ways to inhibit HCl volatilization in process were put forward according to the experimental results. The use of Ca(OH)2 to adjust the pH of desulfurization wastewater to 9.0–10.0 can inhibit HCl volatilization economically and efficiently. This study provides the key data for the application of flue gas evaporation technology under high temperature. The research results have important theoretical and practical values for the engineering practice of this technology.