Experimental Study Of Mercury Oxidation And The Effect On NO And SO₂ During Coal Combustion

The emission of pollutants during coal combustion process has become a hot issue of global interest, especially the emission of mercury, NO and SO₂ have caused great harm to human's health. And the relative researches about the emission and control of the mercury during coal combustion is recently an active topic. In order to reduce the emisson of the pollutants, it is necessary to find a method that can remove mercury, NO and SO₂ at the same time.The bromine compounds additives were chosen to promote mercury oxidation and decrease the emission of NO and SO₂. The experiments were carried on laboratory horizontal tube furnace, Liuzhi, Liupanshui and Gaoping coal were chosen to investigate mercury species transformations and NO, SO₂ reduction in coal flue gas when co-combusting bromine compounds with three kinds of coal. We considered four factors such as, combustion temperature, different bromine compound, the mass of bromine compound and the type of the coal to study mercury species transformations and NO, SO₂ emissions during the combustion process. So we can get the results that how bromine compounds effect mercury species transformations and NO, SO₂ emissions.The experimental results show that bromine compounds additives can partly enhance mercury oxidation during coal combustion. Different type of coal has different oxidantion effect. Overall, the oxidation of calcium brominate is better than brominate sodium. The combustion temperture is an important factor that can affect mercury volatile and species. Under low temperature the oxidation effect is better at larger addition proportion, because HgX2 decompose under high temperture. But at higher additive ratio, it will cause some degree of corrosion.Adding three kinds of bromine compounds are conducive to the reduction of nitric oxide (NO), and both NO generative process and the total amount of NO have changed. NO reduction was influenced by the combustion temperture. The same kind of coal under different temperture, NO emission characteristics were different. Cofiring coal with bromine compounds at the same temperture all resulted a better denitrification effect compared to firing the coal alone, and the effect is better when cofiring at lower temperture.Considering adding bromine compounds to restrain the emission of SO₂, ammonium brominate is the best, and then calcium brominate, sodium brominate comes last. Inhibition effect is better at high temperature, larger adding ratio also helped to reduce SO₂ emissions.In addition,We also studied a method based on mercury adsorption tube in flue gas. To make the sorbent trap achieving maximum adsorption capacity, the temperature of the flue gas should be 120℃and SO₂ concentration should below 1000 ppm.