Capture of heavy metals by sorbents in incineration flue gas

The emission of heavy metals can be controlled by injecting solid sorbents into the flue during incineration processes. Feed waste elemental compositions and types of sorbents influence the controlling efficiency of the sorbents for heavy metal compounds. The objective of this work is to experimentally study the controlling efficiency of different sorbents for heavy metals in the flue of an incineration system, and study the effects of feed waste composition on the controlling efficiency of sorbents. The investigated heavy metals are Pb, Cd, Cu and Cr. The operating parameters evaluated included: (1) different sorbents (kaolinite, limestone, aluminum oxide, and water); (2) the feed waste contained organic chloride (PVC); (3) the feed waste contained inorganic chloride (NaCl); (4) the feed waste contained sulfate (Na2SO4); (5) comparing the controlling efficiency of sorbents used in the combustion chamber and injected in the flue of an incineration system. Experimental results indicated that the control efficiency of the four sorbents for heavy metals under various feed waste composition follows the sequence of limestone>water>kaolinite>aluminum oxide. The best sorbent for the four heavy metals is limestone, especially as the feed waste contained organic chloride PVC, because limestone slurry provides a lot of calcium and alkali to react with the metal chlorides and acid gas. The presence of inorganic chloride NaCl and sulfate Na2SO4 in the feed waste is helpful to increase the capture efficiency of the sorbents for heavy metals. By comparison, the capture efficiency of the sorbent injected in the flue is lower than that added in the combustion chamber.