| As a dangerous and harmful pollutant in coal-fired flue gas,mercury has became a research hotspot by the international community.The most commonly used technology for mercury removal in coal-fired power plants is the activated carbon injection?ACI?.However,the cost of activated carbon is relatively high.The complex component of gas and coverage of adsorbed mercury on the surface active sites of the adsorbent will cause decrease of the carbon activity.Besides,improper treatment of the deactivated adsorbent will cause second pollution.Therefore,developing low cost,high efficiency and regenerable adsorbent is significance for the widespread application of mercury removal technology and meeting the most stringent environmental requirements.The mercury adsorption,desorption and mechanisms of sulfur loaded activated carbon and its regenration characteristics were studied in this paper.Firstly,a kind of commercial sulfur-loaded activated carbon was selected and sieved to get particles in the range of 5896?m diameters as the raw adsorbent sample?SAC?in this experiment.The samples that experienced a fixed bed mercury adsorption experiment for 2 h and whose mercury breakthrough rate was beyond 50%were designated as used sulfur-loaded activated carbon?USAC?.The physicochemical properties of the original and used samples were characterized by the specific surface area and porosity?Brunner-Emmet-Teller,BET?and X-ray photoelectron spectroscopy?XPS?analysis.The results showed that the sulfur-loaded activated carbon have stronger strength and sulfur element is more evenly distributed on the carbon-based surface.Once the activated carbon is deactivated,the specific surface area decreases,the micropore volume and micropore volume ratio decrease,and the microscopic morphology and pore structure have a slight destructive effect.The results showed that the specific surface areas and the content of oxygen functional groups as well as non-oxidized sulfur on surface decreased after mercury adsorption.It is deduced that the deactivation of the sulfur-loaded activated carbon is due to the decrease of oxygen and sulfur content,and the decrease of sulfur content is related to the form conversion of sulfur.In addition,there are a large number of oxygen functional groups and non-oxidized sulfur on the surface of the adsorbent,which reacts with mercury and adsorbs mercury in the form of HgO and HgS.The content of oxygen functional groups and non-oxidized sulfur decreased significantly after adsorption,indicating that the chemisorption site was occupied during the adsorption process,which led to the deactivation of the adsorbent.Secondly,mercury adsorption experiment research was done using a fixed bed system,and the effects of reaction temperature,mercury concentration and flue gas composition on the mercury removal characteristics of activated carbon were investigated.And the desorption experiments was conducted on a TPD furnace after the sample was tested in the fixed-bed reactor.The experimental results showed that the suitable mercury removal temperature is70?,and the mercury removal efficiency decreases with the increase of mercury concentration.The worst mercury removal temperature is 26?.The initial mercury removal efficiency decreases with the increase of Hg0concentration in flue gas,and the greater the concentration,the more obvious the inhibition.The experimental data were fitted by internal diffusion model,Quasi-First-Order and second-order kinetics model and Elovich kinetics model respectively,which indicated that chemical adsorption was the key step of the whole adsorption reaction process.The presence of O2 is beneficial to the removal of Hg0,while the presence of SO2 can inhibit the removal of Hg0.However,when they both exist,the inhibition of SO2 can be weakened by O2.The activated carbon mainly relies on the formation of HgO and HgS to achieve mercury removal.The removal process of mercury can be described as follows:sulfur atoms are loaded on the surface of porous structure of activated carbon,forming C-S bond.Gaseous mercury atoms react with electron-deficient sulfur ions on the surface of activated carbon to form HgS molecules in the pore of activated carbon,thus removing Hg from the gas phase.Finally,three regenerative adsorbents were obtained by direct desorption thermal regeneration method,SO2 activation thermal regeneration method and sulfur-loaded thermal regeneration method respectively,and the cyclic mercury removal experiments were carried out.The results indicated that the sulfur-loaded thermal regeneration is the best way to obtain high regenration efficiency.The optimal paremeters are the mass ratio of carbon to sulphur is1:1,the regeneration temperature is 600?and the regeneration time is 1 h.After five regeneration cycles,the average two-hour mercury removal efficiency of the adsorbent are86.89%,97.26%,96.35%,97.46%and 95.69%,respectively,demonstrating that the regenerated adsorbent has good mercury removal effect. |
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