Methods and apparatus for generating a vapor to be injected into a flue gas stream are described. Apparatus comprises a fluid vaporization and injection assembly further comprising: a stripper for producing first ammonia vapor and a first aqueous ammonia solution from a second aqueous ammonia solution; a reflux tank for producing a second ammonia vapor and the second aqueous ammonia solution from the first ammonia vapor and the first aqueous ammonia solution; and a first outlet for outputting the second ammonia vapor for introduction into the flue gas.