A flue gas conditioning system uses the waste heat of the flue gas to heat a conditioning agent such as water to add sufficient heat energy to the water to generate steam that can be used to atomize the water into a very fine mist with droplets less than 50 microns injected into the flue gas. The fine mist evaporates quickly conditioning the flue gas to enhance particulate removal by a precipitator or filter. Also, humidification of the flue gas causes trace heavy metals--arsenic, mercury, selium, copper, zinc, etc.--to condense on fly ash particles. Such metals are targeted for removal by the EPA under the blanket description "air toxics."

http://www.freepatentsonline.com/5370720.html