SNCR stands for "Selective Non-Catalytic Reduction," which is a mature NOx control technology. Its working principle involves spraying ammonia water or urea, which contain amino groups, into the boiler furnace or cement kiln decomposition furnace at temperatures ranging from 850 to 1100℃. In this narrow temperature range, these amino-based reductants selectively react with NOx in the flue gas, producing harmless and non-polluting N2 and H2O. Under conditions where the operating cost of the reductant is appropriate and ammonia slip does not exceed 10 ppm, a denitrification efficiency of over 80% can generally be achieved.

SCR stands for "Selective Catalytic Reduction," a mature commercial technology for NOx control. Its principle involves using liquid ammonia as a reductant, which selectively reacts with NOx in flue gas at temperatures between 280 to 420℃ under the action of a catalyst. The reaction produces harmless and non-polluting N2 and H2O, effectively removing NOx from the flue gas. The catalyst used can be either honeycomb or plate type, and NOx and NH3 in the flue gas react almost at a 1:1 molar ratio, achieving a denitrification efficiency of 80 to 90%.