Research On Mercury Re-emission And Its Inhibition In WFGD In The Process Of Mercury Oxidation Enhanced By The CaBr₂-blended Coal Combustion Technology

The removal effect of WFGD on mercury pollutants in coal-fired power station depends largely on the proportion of oxidized mercury in the flue gas.The mercury re-emission in WFGD slurry also can weaken the mercury removal performance of WFGD.The bromide-blended coal combustion technology is a simple and effective technology for enhancing mercury removal.The application of the technology can increase the content of oxidized mercury in flue gas,but the accumulation of bromine in WFGD slurry might affect the mercury re-emission behavior.In order to improve the mercury removal performance of WFGD,the effect of bromide ion on mercury re-emission in WFGD was simulated experimentally in this paper.Then the effect of the mercury re-emission inhibition technology was explored on the actual coal-fired power plant.In this paper,the effects of bromide ion on mercury re-emission were investigated through a bench-scale experimental system,and the inhibiting effect of bromide ion on mercury re-emission was confirmed,the mercury re-emission was reduced by 89.5%under10m M Br^-.Then the control variable method was employed to analyze the influence of factors such as slurry temperature,slurry p H value and S（IV）concentration on mercury re-emission.It was found that in the presence of bromide ion,lower temperature,higher p H value and higher S（IV）concentration all had an inhibitory effect on mercury re-emission.A mechanism was proposed by using UV-visible spectra analysis and quantum chemistry calculation.The Hg Br₂ and Br_nHg SO₃^n-complexes were formed,which inhibits the mercury re-emission.In order to predict the Hg²⁺absorption and Hg⁰ re-emission in actual WFGD,mathematical models were established.The model was universal to WFGD,and the predicted values could be obtained by inputting WFGD operating parameters and the kinetic parameters of mercury re-emission reaction.Through the model study,it was found that the Hg²⁺absorption of WFGD was mainly affected by the cumulative concentration of Hg²⁺in the slurry.The higher the cumulative concentration of Hg²⁺was,the lower the Hg²⁺absorption rate of WFGD.The model study also showed that bromide introduced by the bromide-blended coal combustion technology could still inhibit the mercury re-emission under the actual condition of large smoke volume and slurry re-circulation volume.Finally,the application of the bromide-blended coal combustion technology in a 600MW power plant was carried out in this paper.The removal effect of WFGD on different forms of mercury was studied by changing Ca Br₂ concentration.It was found that the proportion of oxidized mercury in flue gas increased from the 73.83%to 97.61%,and the removal rate of total mercury increased from 90.88%to 96.86%.The total mercury removal performance of WFGD was enhanced.The re-emission of mercury was also found in the field experimental data.In order to inhibit the mercury re-emission,chelating agent DTCR was added to the slurry directly under the application of the bromide-blended coal combustion technology.The inhibition effect of different concentrations of DTCR on mercury re-emission was studied.With the increase of DTCR concentration,the Hg escape rate of WFGD decreased from 15.68%to 7.16%,which indicated that DTCR had a significant inhibition effect on Hg re-emission in actual slurry.