(227e) Capture of Mercury from Wet Combustion Streams Using a New Powder

Low temperature thermal desorption (LTTD) treatment of contaminated soils is a process by which the soils are excavated and fed to a kiln. The soils are exposed to heat to volatilize the contaminants away from the soil into the gas stream. Low-temperature volatilization treatment is a new and promising method for soil cleanup and is more economical than incineration because of its lower thermal input and especially the reduction of gas volume flow that must be treated prior to discharge. The soil is usually heated in a rotary kiln, thermal screw, conveyor furnace, or stationary heating furnace. The most commonly used heating device is the rotary kiln. Rotary kilns are large, baffled, reclining, and refractory-lined cylinder. The cylinder is rotated slowly and the soils are heated by direct contact with the kiln wall. The kiln walls are heated by either radiant heating from external or internal flames, by hot gas convection, or by electrical contact heating. The angular velocity of the kiln and the inclination will determine the residence time of the contented soils.

Once the contaminants volatilize and move to the air stream, they can be treated either by catalytic destruction, thermal oxidizers, or condensation. Thermal oxidizers are the most commonly used. By applying very high temperatures and excess Air, the contaminants are oxidized to CO2, Cl2, NOx, and SOx. However, metals such as Mercury will not be destroyed and will move with the exhaust gasses.

The high temperature gas stream is usually cooled either by water quenching or by heat exchangers. The most common method is water quenching. After quenching, the saturated gas stream is treated to reduce metals, HCl, SOx, and NOx emissions. Acid scrubbers, carbon beds, condensation units, and adsorption powder addition are common. This paper describes all experiments performed to develop a powder that efficiently can remove metals (mercury in particular) and acids (HCl in particular) from high temperature, high moisture gas streams. The powder is injected in the gas stream, and then captured using a bag house. The capture efficiency for mercury is 99% and above. The powder was tested in the field and same results were obtained. The powder composition is patented.