Multi-pollutant control for the portland cement industry

Meeting the compliance limits of the U.S. Environmental Protection Agency´s final rule revision to the National Emission Standards for Hazardous Air Pollutants from the Portland Cement Manufacturing Industry (Portland Cement MACT) regulation will be a challenge for cement kilns equipped with only dry particulate control devices (that is, electrostatic precipitator or fabric filter baghouse control devices). In addition to increases in operation and maintenance costs, installing additional control devices will require capital investment. Conventional control technologies, such as selective non-catalytic reduction (for nitrogen oxides control), wet flue gas desulfurization (for acid gases-sulfur dioxide /hydrogen chloride-control), and powder activated carbon with fiber filter baghouse collection (for mercury control), can be capital intensive. Limits on additional hazardous air pollutants (HAPs) such as dioxins/furans and surrogate HAPs, particulate matter, and total hydrocarbons further complicate air pollution control strategies for cement kilns. For units equipped with dry pollution control devices only, Shaw Environmental, Inc. and FMC Corporation offer a three-step approach toward meeting compliance with the proposed regulation: Step 1 - Back-End Scrubbing Mechanism: Injecting Trona (a sodium-based chemical additive) at the inlet of a dry particulate control device has been demonstrated to effectively remove 30% to 70% of SO₂ as well as 90% of HCI when Trona is collected by an electrostatic precipitator. Full-scale field trials have demonstrated 90% control of SO₂ and 95% control of HCI when Trona is collected in a baghouse. Step 2 - Shaw´s Enhanced Mercury Oxidization (EMO™) System Technology: From Shaw´s field studies, low concentrations of EMO oxidants in flue gas can promote up to 95% oxidation of elemental mercury that can then be captured by Trona in the electrostatic precipitator or baghouse. Back-end scrubbing with Trona - - has also been shown to effectively remove oxidized mercury from flue gas. Step 3 - FMC´s Multi-Pollutant Control (MPC) System Technology: Like EMO, the MPC process uses a patented oxidation process to convert NO to NO₂. NO, being both insoluble and difficult to collect, becomes more soluble and reactive and can be readily collected once converted to NO₂.