Experimental study on co-firing characteristics of ammonia with pulverized coal in a staged combustion drop tube furnace

Utilizing ammonia as a co-firing fuel to replace amounts of fossil fuel seems a feasible solution to reduce carbon emissions in existing pulverized coal-fired power plants. However, there are some problems needed to be considered when treating ammonia as a fuel, such as low flame stability, low combustion efficiency, and high NO x emission. In this study, the co-firing characteristics of ammonia with pulverized coal are studied in a drop tube furnace with staged combustion strategy. Results showed that staged combustion would play a key role in reducing NO x emissions by reducing the production of char-NO x and fuel(NH 3 )-NO x simultaneously. Furthermore, the effects of different ammonia co-firing methods on the flue gas properties and unburned carbon contents were compared to achieve both efficient combustion and low NO x emission. It was found that when ammonia was injected into 300 mm downstream under the condition of 20% co-firing, lower NO x emission and unburnt carbon content than those of pure coal combustion can be achieved. This is probably caused by a combined effect of a high local equivalence ratio of NH 3 /air and the prominent denitration effect of NH 3 in the vicinity of the NH 3 downstream injection location. In addition, NO x emissions can be kept at approximately the same level as coal combustion when the co-firing ratio is below 30%. And the influence of reaction temperature on NO x emissions is closely associated with the denitration efficiency of the NH 3 . Almost no ammonia slip has been detected for any injection methods and co-firing ratio in the studied conditions. Thus, it can be confirmed that ammonia can be used as an alternative fuel to realize CO 2 reduction without extensive retrofitting works. And the NO x emission can be reduced by producing a locally NH 3 flame zone with a high equivalence ratio as well as ensuring adequate residence time. & COPY; 2022 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Automated summary

Using ammonia as a co-firing fuel in coal-fired power plants is a feasible solution to reduce carbon emissions, but it presents challenges such as low flame stability, low combustion efficiency, and high NOx emissions. This study investigates the co-firing characteristics of ammonia and pulverized coal, showing that staged combustion effectively reduces NOx emissions by minimizing char-NOx and NH3-NOx production. The injection of ammonia downstream achieves lower NOx emissions and unburned carbon content compared to pure coal combustion. The presence of a high local equivalence ratio of NH3/air and the denitration effect contribute to this reduction.