Possibility of Reducing Formations of NO_x and SO₂ Simultaneously during Coal Combustion

Comparing with other NO_x and SO₂ control technologies, in-bed reducing NO_x and SO₂ simultaneously during coal combustion may lower the investment and operation cost. However, there are several possible contradictions between the reduction of NO_x and the capture of SO₂ during combustion: 1) CO rich atmosphere is favorable for the reduction of NO_x, whereas O_2 rich favorable for the capture of SO₂; 2) higher preheating temperature of coal is favorable for reducing NO_x, but unfavorable for reducing SO₂; 3) sulphation of some minerals may deactivate their catalytic effect on the reduction of NO_x. The attempts to eliminate such contradictions by coating coal granules with thin layer of monometallic oxides and mixed oxides were proposed. Ni₂O₃ and Fe₂O₃ showed high activity on NO_x reduction and CaO and Cr₂O₃ showed good effect on sulfur capture. The mixed metallic oxides, e.g., Fe₂O₃NiO, etc., showed effective for both NO_x reduction and SO₂ retention. It is possible to in-bed reduce NO_x and SO₂ simultaneously if the adhering materials are properly chosen to be difunctional materials of both active catalysts for NO_x reduction reactions and better sorbents for SO₂ retention.