Process and apparatus for reducing acid plume

A process for reducing acid plume from stacks discharging combustion gases produced by burning a coal having high sulfur and high iron contents, comprising:

• a. in a combustion zone, burning coal having from 1.0 to 8.0% sulfur and from 6.5 to 30.0% iron, producing combustion gases containing sulfur dioxide and sulfur trioxide;
• b. introducing a slurry of magnesium hydroxide into the combustion gases in or directly downstream of the combustion zone;
• c. responsive one or more control signals during an increase in burning coal from a low load to a higher load, introducing a slurry of magnesium hydroxide into the combustion gases in an intermediate-temperature zone;
• and
• d. following reaching steady state operation at the higher load, stopping introduction of the magnesium hydroxide into the intermediate-temperature zone.