(83d) Mercury Control by Fixed Bed Adsorption

Many combustion and gasification processes use mercury-containing fuels and the mercury must be removed from the flue gas or produced gas. The concentrations are normally very low and the species can vary. Dry scrubbing processes can be used for both mercury and other contaminants and are preferred when the flue gas volumes are very high such as in a coal fired power plant. When the gas volumes are relatively low, such as in gasification processes and combustion of toxic wastes, fixed bed adsorption is more appropriate.

Physical adsorption of mercury on activated carbon is a reversible process. When the carbon is impregnated with sulfur or a sulfide salt, irreversible chemisorption is operative. The result is that the adsorbent has a very high capacity for removing mercury. The type of activated carbon and the appropriate impregnant has a significant impact on the performance. Process conditions such as temperature, residence times, type of fluid, and mercury concentration impact the performance and life of the adsorbent. Laboratory, bench scale and pilot plant data will be presented.

Mercury containing wastes are destroyed in a variety of combustion processes. Several will be discussed along with the performance of fixed bed adsorbers to remove the mercury. Syngas is produced for power generation and other chemical synthesis processes. The mercury can be removed from the relatively low volume gas stream making the fixed bed process for mercury removal preferable.