The Study Of Co,Mn Series Sorbents For The Removal Of Element Mercury From Simulated Flue Gas

Mercury is one of the most toxic pollutants and can easily be released into the atmosphere and severely threat human health and environment. Power plants are the largest mercury discharging resources. In China, coal is the major one-off energy and Hg pollution from combustion in air is severe environmental issue.Many technologies have been applied to control the mercury emission of coal-fired power plants, such as air pollution control devices (APCDs), sorbent injection (SI), electro-catalytic oxidation (ECO), photochemistry oxidation, oxidant injection, and catalytic oxidation, etc. Among them, SI is the most promising technology. However, there exist several problems with activated carbon and other sorbents such as low adsorption capacity, instability, low adsorption velocity, high operation costs and second pollution, which strictly confine SI application. In this paper, Co, Mn serial sorbents are selected as research object. High adsorption capacity and velocity materials for mercury are screened out, and the regeneration tests are processed to lower the operation costs and second pollution problem.Firstly, the preparation methods and qualification of Co, Mn serial sorbents, metal doping and non-metal doping effects on sorbent's mercury removal ability are studied. How the preparation factors affect sorbents'chemical and physical property is investigated by BET,XRD,XPS,TEM,TGA and TPR. At the same time, the relationship between construction of sorbents and their mercury removal ability are analyzed.(一) Al2O3 carrier sorbentMnO2 and Co3O4 show some activity to remove the Hg from the simulated gas, but they lost activity when SO2 exist. The doping of Co3O4 by Cu can generate Cu-Co-AL which has similar Hgo removal ability to Co3O4 but better SO2 anti-poisoning ability. NH4Cl/NH4Br doping is beneficial to Co-AL and Cu-Co-AL's Hgo removal ability, especially the dopant NH4Cl/NH4Br doped Cu-Co-AL whose Hg removal ability can increase 45%. The XPS and XRD results manifest that O atom of Co3O4 and CuCo2O4 surface has been replace by N atom, BET and SEM results manifest that NH4Cl/NH4Br doped Co-AL and Cu-Co-AL have higher specific surface area. Therefore, the Hgo removal ability improvement of NH4Cl/NH4Br doped sorbent can attribute to above phenomenon. Except that, the XPS results of spent NH4Cl/NH4Br doped Co3O4 or CuCoO4 manifest that anion Cl-/Br- participate the Hgo oxidation reaction. Cu-Co-Cl-AL and Cu-Co-Br-AL's longevity reach 158 h and 208 h, respectively, which are far longer than Cu-Co-AL's 26 h.(二) AC carrier sorbentAmong the three different chlorine-impregnated AC, CoCl2/AC shows the highest Hgo removal ability and MgCl2/AC show the lowest Hgo removal ability. The loading of metal oxides on AC can increase AC's Hg removal ability. When oxides loaded on Al2O3, Mn-AL shows the highest Hgo removal ability. However, when oxides loaded on AC, Co-AC shows the highest Hgo removal ability. Cu-Co-Cl-AC and Cu-Co-Br-AC show higher Hgo removal ability than Cu-Co-AC. When adsorption temperature increases from 80℃to 150℃, Cu-Co-Cl-AC and Cu-Co-Br-AC's Hgo removal ability increase from 91% and 92.1% to 92.5% and 100%, respectively. Cu-Co-Cl-AC and Cu-Co-Br-AC's breakthrough time increase from Cu-Co-AC's 24 h to 90 h and 105 h, respectively.(三) the experiments under actual flue gasThe experiment results show that when the loading value is 20 wt%, the mercury removal ability of CoCl2/AC activated at 300℃reach 99% at 150℃,and has perfect anti-SO2 ability. The mercury adsorption capacity of CoCl2/AC is 171mgHg/gAC,and 826 times as AC. CoCl2/AC was applied to the actual flue gas Hg adsorption. The combustion test was carried out on small-scale equipment in lab. The result showed that improved AC adsorbed 97% of the gaseous element Hg, compared with 3% of element Hg adsorbed by solution, which indicated that improved AC was feasible in the actual gas treatment. Secondly, spent sorbents can be regenerated by heating. Both Co-AL and Cu-Co-AL can be regenerated. The regeneration ratio of Co-AL is above 90%,and Cu-Co-AL's activity can be improved during the process of regeneration. The regenerated element mercury can be collected by cold trap or react with other chemicals. The collected mercury can be sold to decrease the operation costs, and eliminate the second pollutions.DFT study show that N-doping can decrease the chemical adsorption activation energy (Ea) on Co3O4(110) and CuCo2O4(110) surface. There exist correlation between Ea and OVFE. Through investigating the OVFE variation of non-metal doped Co3O4(110), we find that the non-metal, which can increase the lattice oxygen activity of Co3O4(110) surface, include as follows: Si > N > Se > S > P > I > Te = C > B,and the non-metal, which can decrease the lattice oxygen activity of Co3O4(110), include as follows: Cl > F > Br。In conclusion, catalytic oxidation technique can not only remove element mercury pollutants effectively but also eradicate the potential second pollution. The technique might be practically applied in the field of flue gas mercury control.