Experimental Study On Combined Removal Of SO₂ And Hg By Activated Coke

The activated coke adsorption with high desulfurization efficiency is an advanced dry removal technology. The desulfurization process does not consume water and generate waste. The process costing less investment is simple, and does not produce secondary pollution. The activated coke technology has good development prospect in our country. Currently, the activated coke desulfurization technology in foreign countries has been more mature, but the study on combine removal of SO2 and heavy metals is few. What's more, different cokes, different performance. The process parameters can affect the efficiency of removal of active coke, which few studies have been reported. This paper, on the basis of experiments with different process parameters, tested the removal efficiency of SO2 and mercury of activated coke, and modified activated coke to improve the efficiency of the original activated coke.Several kinds of modified activated coke were prepared by HNO3, NaOH and NaBr solution with a certain concentration. The specific surface area, pore volume, average pore diameter of the cokes were tested using BET analyzer, Scanning electron microscopy and Infrared Spectroscopy. A series of studies on the characteristic of the removal of SO2 and mercury in simulated flue gas were conducted with a laboratory-scale fixed-bed reactor. The results indicated that impregnation could increase the specific surface area of activated coke and improve their pore structure and promote the formation of surface oxygen functional groups.Firstly, a series of studies on the characteristic of the combined removal of SO2 and mercury in simulated flue gas were conducted with a laboratory-scale fixed-bed reactor and the interactive effect of operation parameters, such as temperature, the concentration of SO2, NO and O2 on the removal capacities of SO2 and Hg0 using activated coke was investigated. The experiment results indicated that the adsorption performance of SO2 and Hg0 with activated coke was influenced by temperature obviously and the lower temperature was in favor of the removal process with activated coke in the range of 130 to 190℃. With the increasing of the concentration of SO2, the adsorptive capacity had a tendency of increasing. Compared with the baseline condition, the average adsorptive capacity of Hg0 decreased about 33% under the conditions of Baseline (BL)+1500ml/m3 SO2. There was competitive adsoption between SO2 and Hg0 on the surface of activated coke and the appearance of SO2 suppressed the Hg0 removal. The NO will react with O2 and generate NO2, O atom with oxidizability which result in about 24% increasing of average adsorptive capacity of Hg0 with 400 ml/m3 NO additive in baseline condition. In the BL+SO2+NO gas condition, the adsorptive capacity of Hg0 decreased 3.8% compared with baseline condition. The competition between SO2 and NO caused a little decrease in Hg0 capture capacity of the sorbent.Secondly, the ability of removal of SO2 and mercury in simulated flue gas of modified activated coke was tested with the fixed bed reactor. Among the three kinds of activated coke with Fe2O3 of different decomposition temperature, the SO2 and Hg removal ability of 300℃-Fe/AC is the best. Compared with the original coke, the average adsorptive capacity of SO2 increased about 27% and the average adsorptive capacity of mercury increased 16.2%.The experiment results indicated that HNO3 and NaOH impregnation could increase the specific surface area of activated coke and improve their pore structure. Compared with the original activated coke, the average adsorptive capacity of SO2 and mercury of the HNO3 modified activated coke increased by 43%,32%. The NaOH modified coke increased by 79% and 18%, respectively. Changes of surface functional groups after the modification are another important factor affecting adsorption performance.The specific surface area of the activated coke increased after impregnation with a certain concentration of NaBr solution. And the impregnation also enhanced the chemical interaction between atom Br and atom Hg on the surface of activated coke:Compared those several kinds of activated coke, impregnation with acid and base are most favorable increasing the activity of the desulfurization effect. Loaded halogen compounds NaBr could help to increase the activity of mercury removal.