Study on chlorine volatilization in low temperature flue gas concentration of desulphurization wastewater

With the increasingly strict national policies and industry standards， coal⁃fired power plants are required to have a zero discharge of desulfurization wastewater. Concentrating and reducing the amount of desulfuriza⁃ tion wastewater reduces the cost and workload of subsequent zero⁃discharge treatment，which is the research direction of zero⁃discharge of desulfurization wastewater. Using the low⁃temperature waste heat carried by the flue gas after the dust collector in the power plant，combined with the bypass concentration tower，the realization of the concen⁃ tration and reduction of desulfurization wastewater has become a new idea of zero discharge of desulfurization wastewater. However，due to the high chlorine content and strong acid environment of desulfurization wastewater，the volatilization and migration of chlorine during the evaporation and concentration process will affect the chlorine balance of the subsequent absorption tower and cause concern. This paper introduces the basic theory and research status of hydrogen chloride volatilization in the process of low⁃temperature flue gas concentration desulfurization wastewater， and conducts some single⁃factor influence experiments and orthogonal experiments on the volatilization and migration of chlorine in the process of evaporation and concentration of high⁃chlorinated brine with high chlorine content through a self⁃made simulation test bench. The study demonstrates that the migration of chlorine in the evaporation and concen⁃ tration process of high brine has two modes:vapor⁃phase chlorine volatilization and liquid⁃phase chlorine carryover，a⁃ mong which liquid⁃phase chlorine carryover is the main method，accounting for more than 70% of the total vola⁃ tile chlorine. The temperature of flue gas changes the gas⁃liquid mass transfer coefficient，which is the main factor af⁃ fecting the volatilization of hydrogen chloride gas. The change of the flow rate of the flue gas by the amount of air in⁃ take is the main factor affecting the chlorine carried by the droplets. In addition，the pH and salt concentration also af⁃ fect the volatilization and migration of chlorine. The volatilization model of hydrogen chloride in high brine environment was established according to the multi⁃component hydrogen chloride system，and the chlorine balance model of the by⁃ pass concentration tower was established based on the principle of material balance，and the volatilization of hydro⁃ gen chloride gas during the evaporation and concentration process was predicted. Combined with the experimental re⁃ sults and prediction models，some suggestions are put forward for the regulation of chlorine volatilization and migra⁃ tion during the evaporative concentration of desulfurization wastewater，which provides a theoretical support and data reference for low⁃temperature flue gas concentration desulfurization wastewater technology. Future research can carry out some field experiments on the actual engineering application of low⁃temperature flue gas concentration desulfuriza⁃ tion wastewater technology，and also conduct some researches on the impact of chlorine volatilization migration in the bypass concentration tower on the chlorine⁃water balance of absorption tower.