Mercury And NO Removal By Br Based Sorbents Addition During Coal Combustion

As the largest source of atmospheric mercury and nitrogen oxides (NOx) emission,mercury and NOxemitted from coal-fired power plants have been identified as a hazardousto both human health and environment. In order to enhance the economic, social and envi-ronment benefits, it is necessary to study the different kinds of pollutions causedby.coal-fired power plants, especially the joint removal of mercury and NOx.The form of mercury species in coal flue gas has a significant influence in removal ofmercury in coal combustion. The NaBr and CaBr2additives were chosen to promote mer-cury oxidation and NO reduction by screening various additives in the paper. Experimentalstudies were conducted by a lab-scale fixed bed and a fluidized bed reactor to investigatemercury transformations and NO reduction in coal flue gas when firing Shanxi bituminouscoal with the NaBr and CaBr2addition. The experiment considered the combustion temper-ature, different kinds of bromine compound, the mass and additional percent of brominecompound to study mercury species transformations and NO emissions during the combus-tion process.The experimental data showed that bromine compounds additives can enhance mer-cury oxidation during coal combustion and promote the transformation of mercury from gasphase to particle phase in coal flue gas, which is beneficial to reduce the emission of mer-cury in coal flue gas. The concentration of bromine is an important factor that can affect therelease rate and existence species of mercury in flue gas during coal combustion. The oxi-dation effect of mercury is better when use calcium brominate than sodium brominate, atthe same condition of temperature and additional percentage.Metal mineral has the ability to catalyze the reduction of NO, the experiment identi-fied that the addition of calcium brominate and sodium brominate can enhance the coal de-nitrification. The mechanism of NO formation during coal combustion has changed afteraddition of two bromine compounds, and the catalysis of reducing NO by sodium bromi-nate is better than calcium brominate, at the same condition of temperature and additionalpercent.More mercury is easily to become vapor phase and emit into coal flue gas when thereaction temperature increased, and the content of mercury oxidation was also increased. The higher temperature of the fluidized bed was, the more NO formed after coal combus-tion. The efficiency of NO reduction became higher after added sodium and calcium at lowtemperature.Besides, in order to study the mechanism of NO reduction by metal oxides, such assodium and calcium, experiment of the impact of the sodium and calcium additive to theNO reduction has been studied. Sodium and calcium additives have the ability to catalyzethe reaction of coal char with NO, which is related to the reaction temperature, metal addi-tion ratio. In the same condition of addition ratio, calcium got a higher catalytic activitythan sodium in low temperature but contrary to it in high temperature.