The present invention relates generally to the field of emission control equipment for boilers, heaters, kilns, or other flue gas-, or combustion gas-, generating devices (e.g., those located at power plants, processing plants, etc.) and, in particular to a new and useful method and apparatus for: (i) reducing halogen levels necessary to affect gas-phase mercury control; (ii) reducing or preventing the poisoning and/or contamination of an SCR catalyst; and/or (iii) controlling various emissions. In still another embodiment, the present invention relates to a method and apparatus for: (A) simultaneously reducing halogen levels necessary to affect gas-phase mercury control while achieving a reduction in the emission of mercury; and/or (B) reducing the amount of selenium contained in and/or emitted by one or more pieces of emission control equipment for boilers, heaters, kilns, or other flue gas-, or combustion gas-, generating devices (e.g., those located at power plants, processing plants, etc.).