Immobilization of Mercury Species under the Influence of Typical Organic Compounds in Waste Gases by the Circulating Fluidized Bed

Abstract

Hearth furnace coke (HOK), a special type of lignite (brown-coal)coke produced in a manufacturing process called `hearth furnace process', and portlandite (Ca(OH)2) particles were placed ina circulating fluidized bed reactor. Defined model waste gases containing HCl/SO2/Hg0/Hg2+ and organic compounds were injected into the reactor to investigate the adsorption of different mercury species. Elemental mercuryreacted immediately with HCl to form HgCl2, but for Hg2+ further investigations had to be made, because todaygas cleaning plants still have problems in observing national limits for the mercury output. The temperature, the mercury content of the gas, and its content of acid compounds as majorinfluences in cleaning exhaust gases were varied without relevantpositive effects on the adsorption rate which decreased from nearly 100% in the first five minutes to unsatisfactory20% some minutes later. The mercury load on the HOK particles onlyshowed a value of 60 μg Hg g-1 HOK. Then organic compounds (guide pollutants such as 1-chlorobutane, monochlorobenzene, toluene, and naphthalene, which are alwayspresent in incineration plant exhaust gases) were added to thegas stream and the results improved significantly. The mercuryload on the HOK particles varied depending on the chemical nature of the organic compound and amounted to 300 μg Hg g-1 HOK maximum. The measured values of mercury in the clean gas stream fell below 10 μg m-3. The characterization of the dynamic behavior of mercury in hot, acid waste gases and the analytical identification of mercurysticking to HOK under the influence of organic compounds leadto new methods for improving the effectiveness and performanceof gas cleaning plants.