Method and system for controlling mercury emissions from coal-fired thermal processes

A method, comprising:

• providing a mercury-containing gas stream comprising vapor-phase mercury, a vapor-phase iodine, and particulates;
• passing the mercury-containing gas stream through a selective catalytic reduction zone;
• and
• thereafter removing particulates from the mercury-containing gas stream to form a treated stream, at least a portion of the vapor-phase mercury being removed from the mercury-containing gas stream with removal of the particulates, wherein at least one of the following is true:
• (i) the mercury-containing gas stream comprises about 3.5 ppmw or less vapor-phase iodine;
• (ii) in the mercury-containing gas stream, a molar ratio of vapor-phase iodine to vapor-phase mercury is no more than about 600;
• (iii) at an air preheater outlet, a concentration of vapor-phase iodine ranges from about 0.1 to about 10 ppmw;
• (iv) a concentration of the iodine is about 30 ppmw or less relative to a weight of a mercury-containing feed material producing the vapor-phase mercury.