A selective catalytic reduction system, comprising: a duct; a catalyst positioned within said duct; and means for injecting compressed air into said duct at a position upstream of said catalyst, wherein the means for injecting compressed air further comprise: means for generating compressed air; and an air injection header joined with said means for generating compressed air and joined with said duct via one or more holes in said duct, said air injection header including a sub-header joined with a plurality of injection lances, each of said plurality of injection lances having an end nozzle, wherein said air injection header is adapted to inject compressed air from means for generating compressed air to said duct, characterized in that said sub-header further comprises a box-like manifold including a top, a bottom and sides that form an interior cavity, wherein the top includes a top surface including an outside lip resting on the duct to ensure an airtight fit between the sub-header and the duct, the sub-header having the plurality of injection lances for directing a plurality of compressed air injections to said duct, the system further comprising a means for moving said manifold laterally to facilitate the movement of dust in said duct. a duct; a catalyst positioned within said duct; and means for injecting compressed air into said duct at a position upstream of said catalyst, wherein the means for injecting compressed air further comprise: means for generating compressed air; and an air injection header joined with said means for generating compressed air and joined with said duct via one or more holes in said duct, said air injection header including a sub-header joined with a plurality of injection lances, each of said plurality of injection lances having an end nozzle, wherein said air injection header is adapted to inject compressed air from means for generating compressed air to said duct, characterized in that said sub-header further comprises a box-like manifold including a top, a bottom and sides that form an interior cavity, wherein the top includes a top surface including an outside lip resting on the duct to ensure an airtight fit between the sub-header and the duct, the sub-header having the plurality of injection lances for directing a plurality of compressed air injections to said duct, the system further comprising a means for moving said manifold laterally to facilitate the movement of dust in said duct. means for generating compressed air; and an air injection header joined with said means for generating compressed air and joined with said duct via one or more holes in said duct, said air injection header including a sub-header joined with a plurality of injection lances, each of said plurality of injection lances having an end nozzle, wherein said air injection header is adapted to inject compressed air from means for generating compressed air to said duct, characterized in that said sub-header further comprises a box-like manifold including a top, a bottom and sides that form an interior cavity, wherein the top includes a top surface including an outside lip resting on the duct to ensure an airtight fit between the sub-header and the duct, the sub-header having the plurality of injection lances for directing a plurality of compressed air injections to said duct, the system further comprising a means for moving said manifold laterally to facilitate the movement of dust in said duct.