Impact Of Desulfurization Additives On Characteristics Of Mercury Re-emission In WFGD Slurry

Mercury may be presented in flue gas as elemental mercury?Hg⁰?, oxidized mercury(Hg²⁺) or particle-bound mercury?Hgp?. Most particle-bound mercury can be captured by precipitators. Hg²⁺ is water-soluble and can be efficiently removed in the wet flue gas desulfurization?WFGD? processes. However, the elemental mercury is difficult to capture due to its volatility and chemical stability. Hg²⁺ captured by wet flue gas desulfurization?WFGD? systems can be reduced or influenced under certain conditions and result in re-emissions of elemental mercury?Hg⁰?, leading to a damping of the total mercury removal efficiency by WFGD systems. At the same time, desulfurization additives which meant to improve the desulfurization efficiency in WFGD systems will also affect the re-emissions of mercury. Under the conditions that simultaneous desulfurization and denitrification started late in our country, reserving no space for mercury removal. It is of great significance to study impact of desulfurization additives on characteristics of mercury re-emission to improve removal of mercury.The experiment on the re-emissions of Hg⁰ from WFGD slurry were carried out in a lab-scale bubbling reactor through two methods in this paper. The trend of mercury re-emissions were studied under different conditions and different additives by continous pumping Hg²⁺into the desulfurization slurry. Kinetic analysis of mercury re-emissions was carried out by injecting 5mL Hg²⁺ into the slurry. Experimental results showed that,different additives effected mercury re-emissions in a certain extent, the existence of MgSO₄ and Na₂SO₄ would promote mercury re-emissions and the adipic acid would reduce mercury re-emissions. A sequence of experiments were carried out in order to evaluate the influence of temperature, pH, the content of O₂ and concentration of desulfurization additive on mercury re-emissions. Under experimental conditions, both the increase in temperature and pH can promote mercury re-emissions to a certain extent,as well as the higher concentration of MgSO₄ and Na₂SO₄. The concentration of Hg⁰ decrease as the adipic acid concentration increase. The amount of O₂ would inhibit the oxidation of elemental mercury since it can oxidate SO₃^2-into SO₄2-, and provide an oxidizing environment for Hg⁰, so under conditions of higher O₂ concentrations, Hg⁰re-emission rate decreases and the effect was obvious. According to the calculations, the fitting curves of ln?C/C0? and time t were linear and the correlation coefficients were above respectively. It was found that first order reaction model can be used for the fitness of re-emissions of Hg⁰ from WFGD slurry.