Experimental Study On Sorbents Derived From Sewage Sludge For Mercury Removal From Flue Gas

Mercury from coal-fired utility boilers is identified as the largest atmospheric mercuryemission source in China. Activated carbon injection is an efficient and feasible technologyfor mercury emission control. Because of the high cost of activated carbon, it’s very signif-icant to develop a low-cost and high-efficient sorbent for mercury control.In the thesis, urban sewage sludge was used to produce carbon-based sorbent with theactivation of zinc chloride solution. The mechanism of sorption of elemental mercury ontothe carbon-based sorbent had been investigated. Fixed-bed adsorption experiments werecarried out to investigate the influence of temperature, inlet mercury concentration, flue gascomponents and sorbent’s properties on the mercury removal efficiency. Furthermore, tem-perature programmed decomposition desorption technique was applied to identify the mer-cury species adsorbed on the sorbent to investigate the mechanism of adsorption.According to the results obtained in the fixed-bed experiments, temperature was one ofthe most important factors for mercury removal ability. The sorbent showed high mercuryremoval efficiency at80℃and140℃, but a relatively low mercury removal efficiency at170℃was obtained. Mercury removal ability of the sorbent by Cl-contained functionalgroups which facilitated the chemisorptions of Hg0on the sorbent through the reactionswith Cl-contained functional groups. Concentrations of activating agent solution(zinc chlo-ride) showed bigger impact on the mercury removal efficiency than pyrolysis temperature.Mercury removal efficiency of the sorbent decreased with the increase of the inlet mercuryconcentration. Mercury removal efficiency of the sorbent increased with the addition ofoxygen. Moreover, relatively high concentration of sulfur dioxide obviously depressed themercury removal ability of the sorbent, while with the addition of oxygen the depressionweakened. Nitric oxide showed litter impact on the mercury removal efficiency.The results of temperature programmed decomposition desorption experiment showedthat the Cl-contained functional groups resulted in high mercury removal efficiency of thesorbent by forming chemical bonds with elemental mercury at140℃. The mercury speciesadsorbed on the sorbent was similar to mercury chloride (HgClx) species. According to the way of Boehm sorbent had been treated by different processing methods to remove specificsurface functional groups, Cl-contained surface functional groups played an important role inthe mercury removal processing.