Abstract:
Ammonia (NH
3) is a carbon-free and hydrogen-rich fuel. NH
3 co-firing in coal-fired boiler is an effective approach to reduce carbon emissions from the combustion source. However, it can lead to problems such as high NO
x emissions and poor coal burnout. To address the issues above, this paper investigated the Fuel-N conversion and NO
x emissions during co-firing 20%NH
3 in gasifier (G-20% NH
3) and in combustor (C-20%NH
3) using a self-built mild gasification-combustion experimental rig. The research found that the co-firing NH
3 in the gasifier can decrease the gasifier temperature. However, it has little effect on the coal gasification reactions in gasifier. Compared with a pure coal condition, the conversion ratio of coal-nitrogen was only reduced by 3.64%, and the conversion ratio of volatile matter and fixed carbon decreased by only 0.70% and 2.54%, respectively. Besides, the conversion of NH
3 in the gasifier can reach 69.55% during the condition of G-20%NH
3. The 68.88% of total fuel-N was conversed to N
2 in the gasifier, with NH
3-N converting to N
2 was 67.73% in G-20%NH
3. In addition, the NH
3 co-firing in the gasifier promoted the transformation of coal-N and NH
3-N to HCN, with the value of 0.36%. Moreover, the coal pyrolysis in the gasifier promoted the NH
3 pyrolysis. Compared with pure coal, the NH
3 co-firing in the gasifier increased the H
2 concentration at the outlet of the gasifier by 69.23% than that of pure coal. The NH
3 co-firing also decreased the temperature during the preliminary stage of combustion. Compared with pure coal, the NH
3 co-firing in the gasifier and combustor decreased the temperature peak by 46 ℃ and 62 ℃, respectively. Simultaneously, the NH
3 co-firing delayed the occurrence of temperature peaks. Additionally, the NH
3 co-firing delayed the gasified char combustion in the combustor. The average temperature in the burnout zone increased by 135.8 ℃ and 72.8 ℃ during G-20%NH
3 and C-20%NH
3, respectively, compared to PC. It was more conducive to the burnout of pulverized coal. The NH
3-cofiring in combustor had more significant promoting effects on the burnout of pulverized coal, in which the unburned carbon in fly ash decreased by 1.8% compared PC. However, the NH
3 co-firing in gasifier was more effective in reducing NO
x emissions. During the G-20%NH
3, NO emissions were decreased by 23.51% compared to C-20%NH
3. The study offers some innovative ideas and data reference for the development of low NO
x emission technology for NH
3 co-firing in coal-fired boiler.