Adsorption of dioxins and furans from flue gases in an entrained flow or fixed/moving bed reactor

Abstract

Under certain operating conditions, polychlorinated dioxins and furans occur in the flue gases of thermal processing plants. Current EU Directives limit the concentration of these emissions to less than 0.1 ng toxicity equivalents (TEQ) per standard cubic metre of dry gas at 11 vol% O 2 . These Directives have been included in the emission regulations of most of the EU countries. Dioxins and furans are not particular to incinerators; they can also originate from metallurgical and other thermal processes when these are operated under unfavourable conditions. Adsorption methods employing non-flammable carbonaceous adsorbents (activated carbon, lignite) are particularly well suited for removing PCDD/Fs. For adsorption, which requires the sorbent to be brought in contact with the gas to be cleaned, various processes are currently available, ie classical adsorption in moving/fixed bed filters or the technique of adsorption in an entrained dust cloud with a downstream fabric filter or electrostatic precipitator to remove the spent sorbent from the waste gas (entrained process). The paper will firstly assess both adsorption concepts; it will then use results obtained from operational tests in incineration plants for municipal and industrial waste to describe the efficiency of the dioxinsorption in an entrained bed (pneumatic transport of pulverized adsorbent) and a fixed/moving bed (granular adsorbent). Variations in the dosing rate and the use of different adsorbents, as well as the operating temperature, identify the selection criteria for determining the process-engineering optimum for flue gas cleaning. The paper will demonstrate that the PCDD/F emissions can be reduced to below 0.1 ng TEQ Nm À3 and will identify the operating conditions required to achieve this standard.

Minimum feeding rate of activated carbon to control dioxin emissions from a large-scale municipal solid waste incinerator

“…Therefore, dioxin removal efficiency by AC injection is significantly dependent upon the dioxin molecular transport phenomena in the flue gas [21]. Because gaseous and solid phase dioxins in the flue gas are not removed with the same mechanism, the dioxin removal mechanism can be described in two key steps [11,22,23]. The first is the adsorption between gaseous phase dioxins and AC particles in the flue gas.…”

“…Meanwhile, Chang and Lin [10] stated that dioxin removal efficiency would decrease due to the dioxin memory effect, which increased the dioxin concentration in flue gas under AC injection and caused a lowering of removal efficiency. Everaert et al [11] assessed the dioxin adsorption concepts. They used the results obtained from operational tests in incineration plants for municipal and industrial waste, to describe the efficiency of dioxin-sorption in an entrained bed (pneumatic transport of pulverized adsorbent) and a fixed/moving bed (granular adsorbent).…”

The Possibilities of Reduction of Polychlorinated Dibenzo-P-Dioxins and Polychlorinated Dibenzofurans Emission

“…Active carbon should be replaced at the regular time intervals. The variations of those devices are the adsorbers with a moving bed of active carbon, which operate in the flowing manner [59][60][61]. The carbon used is the most frequently directed to combustion taking place in waste incineration plant.…”

Formation and Elimination of Pollutant during Sludge Decomposition in the Presence of Cement Raw Material and Other Catalysts

“…Additionally, during the contact of flue gas-CRM in the cyclones, the elimination of the pollutants could also be possible by the action of CRM through adsorption or catalytic oxidation. There are many papers about the study of the adsorption of organic pollutants in different substances like fly ash, coke or active carbon [11,12] where PCDD/Fs are adsorbed up to 90%, but unfortunately, there are not enough scientific references to analyze this fact over other materials.…”