Can magnesium oxide and ammonia water be added to the furnace and coal for denitrification?

Adding ammonia water into the combustion furnace will burn at high temperature first, and there is no time to react with nitrogen oxides, which may produce more nitrogen oxides. In the absence of catalyst, ammonia can reduce nitrogen oxides at 800~ 1 100℃. But the temperature in the combustion zone in the furnace is much higher than this temperature. So, I don't think denitrification can be done like this. To denitrate, ammonia water can only be sprayed into the appropriate temperature area in the furnace, and it is not necessary to add it casually. Why add magnesium oxide? What is the consideration?