Study On Gaseous Mercury Adsorption By Powder Activated Carbon On Bag Filter

Control of mercury emissions from combustion flue gas has been paid more attention at home and abroad. In mercury capture by activated carbon injection upstream bag filters used widely in MSW at present, the utilization rate and mercury efficiency of activated carbon were very low because the amount of activated carbon was only 5% in the mixture attaching on the surfaces of the bags. The purpose of the current study is to improve Hg0 removal efficiency of activated carbon injection upstream a bag filter and the utilization ratio of powder activated carbon (PAC). Mercury removal experiments were conducted in a small-scale bag filter with different proportions of powder activated carbon (PAC) and fly ash, and and to investigate the influence factors on mercury removal by PAC in bag filter.For comparison, many mercury removal experiments were conducted in a small-scale bag filter with mixture of different proportions of PAC and fly ash. The results indicated that the average mercury removal efficiency (AMRE) was 99.1% within 85 minutes for the first adsorption, and the adsorption time was 1335 minutes with removal efficiency above 75% with pure PAC as sorbent, while the AMRE within 85 minutes for the first adsorption was 19.3% and the removal efficiency fell to nil after 165 minutes with fly ash as the sorbent. The AMRE within 85 minutes for the first adsorption were 99.1% ,95%, 85.3%, 79.7% and 59.6%, and the mercury adsorption capacity with removal efficiency above 75% were 196.1 172.5, 133.8, 123.6 and 21.7μg Hg/g AC with the sorbents of fly ash proportion of 0%, 20%, 50%, 80% and 95% respectively. The PAC had a saturation capacity of 1667μg Hg/g AC at 80℃. These results indicated that the mercury removal technology by pure PAC on bag filter had the obvious superiority in mercury removal efficiency and the utilization ratio of PAC compared to the traditional process by PAC together with fly ash.Experiments on the influence factors on mercury removal by pure PAC in bag filter were performed. The results indicated that the average mercury removal efficiency (AMRE) decreased from 99.6% to 43.2% within 65min as the adsorption temperature increased from 80℃to 170℃, and increased from 75.5% to 84.6% as the volume fraction of flue gas H2O(g) increased from 0% to 8% at 100℃, but the Hg0 removal efficiency reduced instead when H2O(g) content further increased to 12%. Higher PAC mass loading and lower filtration flow velocity could also improve the AMRE of the PAC. The AMRE decreased as the inlet Hgo concentration increased at 150℃.For flue gas of 1500000m3/h in a 300 MW (thermal power) coal-fired power plant boiler, the estimated annual consumption of PAC is about 492 tons with the mercury removal by pure PAC on bag filter, which is only about 1/9 of that by PAC together with fly ash on bag filter, thus it will save $15.792 million RMB in consumption of PAC every year.