Experimental Study On The Removal Of SO₂,NO And Hg⁰ From Coal-fired Flue Gas By Plasma Oxidation-activated Carbon Adsorption Technology

Conventionally,the removal of sulfur dioxide,nitric oxide and elemental mercury are realized by the desulfurization,denitrification and activated carbon injection methods,respectively.The deficiencies of this strategy are larger occupying area,higher cost of construction and operation and poor stability of systems.On the basis of summing up all kinds of pollution control techniques,we proposed a novel method,combing plasma with activated carbon adsorption,to removal SO₂,NO and Hg0 from flue gas.Using this method,SO₂,NO and Hg0 were oxidized to SO3,NO₂ and Hg2+,then these oxidation products were removed by activated carbon.The corn stalk was used as raw material in this research.A variety of sorbents were prepared through pyrolysis carbonization and modification under different conditions by plasma.The plasma treatment could significantly change the content and species of functional groups on bio-char surface,however,it caused less damage to physical structure.Increasing O₂ and H2O concentrations in discharge gas and treatment time would introduction more oxygen function groups onto carbon surface,which resulted in an enhancement of Hg0 adsorption capacity.The activated carbons were modified by benzoic acid to introduce some particular groups on carbon surface.The Hg0 adsorption mechanisms was studied by combining characterization and Hg0 adsorption experiments.The results showed that the adsorption of Hg0 included both physisorption and chemisorption,and chemisorption was dominant.OCFGs,especially carboxylic groups,played crucial roles in adsorption process.HCl and NO could react with carbon surface which introduced additional active sites for Hg0 adsorption,thus Hg0 adsorption was promoted.The Hg adsorption was inhibited due to the blocking of pores and competitive adsorption by SO₂.A flue gas discharge method was used to remove SO₂,NO and HgO.The results indicated that NO was reduced to N2 under hypoxic and anaerobic conditions.The oxidative species produced by ionizing gases?O₂,H2O and CO₂?promoted the oxidation of NO.For SO₂,increasing O₂ concentrations and applied voltage would not have significant effects on its oxidation efficiencies.In DBD discharge,not only ·O and O3 but also ·Cl and Cl2 can enhance HgO oxidation.Increasing applied voltage,O₂ and HCl concentrations would produce more active species,which promoted Hg0 oxidation.However,the presence of NO or H2O resulted in a significant decrease of Hg0 oxidation efficiency due to the competition for reactive species.The pollutant conversion and activation of carbon surface by active species greatly increased the removal efficiency.However,the removal efficiency of NOx by combined processes was only 29%due to the poor oxidation efficiency by plasma and regeneration of NO during Activated carbon adsorption.The synergistic removal efficiency of SO₂,NO and Hg0 was 100%,29%and 100%respectively.Due to the poor discharge conditions during and low NO oxidation efficiency during flue gas discharge,the removal of SO₂,NO and HgO was carried out using active species injection method.During active species injection process,increasing active species injection flowrate favored the Hg0 oxidation rate.The consumed power converted into heat energy played an essential role in the re-dissociation of reactive species,and thus further increasing applied voltage would resulted in the decrease of Hg0 oxidation efficiency.The inhibitory effects of NO and SO₂ on Hg0 oxidation were observed,which was attributed to their preferential consumption of reactive species.The flue gas temperature has little impact on Hg0 oxidation within the test temperature range.The active species injection oxidation-AC adsorption always maintained high removal efficiencies for S02 and Hg0.NOx removal efficiency increased with the active species injection flowrate.The corn straw bio-char showed the best performance for the simultaneous removal of NO,SO₂ and Hg0.The simultaneous removal efficiency of NO,SO₂ and Hg0 was nearly 100%under the optimal process parameters.In addition,due to the reactivation of active species,the bio-char after heating regeneration achieved above 90%denitration efficiency in cyclic adsorption experiments.