nox emissions

ammonia air

unburned carbon

Fuel

NH 3 co-firing in a commercial 1000 MW e pulverized coal-fired boiler has been considered for reducing CO 2 emissions. However, the abundance of fuel-N in NH 3 co-firing may cause an increase in NO emissions. The effects of the NH 3 co-firing ratio on NO emissions in a commercial boiler are studied through a zero-dimensional numerical calculation with detailed chemistry. A simplified boiler system is composed of a burner zone, an over-fire zone, and two downstream zones. A network of perfectly stirred reactors is used to determine NO emissions in flue gas. The NH 3 co-firing ratio is varied from 0 to 80%. NH 3 is injected into the flame zone, which is part of the burner zone. As a result of calculation, amount of CO 2 emission decreases as an increase in the NH 3 co-firing ratio. Since the location where NH 3 reacts shifts to the downstream side with an increase in the co-firing ratio, the peak of NO also tends to transfer to the downstream side. Nevertheless, NH 3 is almost completely dissociated in the burner zone and unburned NH 3 emissions are approximately zero independent of the co-firing ratio. Within the range of 20–60%, NO emissions increase monotonically with the co-firing ratio. However, at 80% co-firing, the NO emission decreases from the value attained at 60% co-firing. With a co-firing ratio higher than 40%, reactions of rich NH 3 chemistry, which are characteristic in rich and low-temperature NH 3 flame become effective. Due to these reactions, fuel(NH 3 )–NO production tends to decrease in the location where NH 3 reacts.

Numerical calculation with detailed chemistry on ammonia co-firing in a coal-fired boiler: Effect of ammonia co-firing ratio on NO emissions