Experimental study and kinetic analysis of the impact of ammonia co-firing ratio on products formation characteristics in ammonia/coal co-firing process

Abstract

Ammonia is a carbon-free, hydrogen-rich fuel, which is considered as an alternative energy source with high utilization potential. Ammonia/coal co-firing in air-staged coal-fired boilers has attracted the attention of a number of academics in order to meet the aim of low carbon and NOx emissions. In this paper, ammonia/coal co-firing experiments were conducted under air-staged condition in a one-dimensional combustion-temperature controlled down-fired furnace with multi-path air inlets at 1100℃. The influence of ammonia co-firing ratio on NO and CO2 emissions, as well as CO and H2S release characteristics, was studied using Shenhua bituminous coal in air-staged and non-staged combustion conditions. Chemical reaction kinetic calculations were conducted to provide a qualitative analysis of the experimental results. Ammonia plays a complex role in the ammonia/coal co-firing process. An effective CO2 reduction was achieved with ammonia co-firing, and it was found that air-staged combustion is also effective for NO emission control in the ammonia/coal co-firing process. Considering the economy issue and NO emission control, 20–30 % ammonia co-firing ratio is recommended. However, ammonia/coal co-firing can greatly promote the coal gasification reaction, which leads to a higher concentration of CO in the reduction zone in air-staged combustion, compared with coal combustion. Meanwhile, ammonia co-firing has a significant inhibitory effect on the release of H2S from coal and will promote the subsequent decomposition process. This study explains the NO release pattern in ammonia/coal co-firing processes based on experimental results and chemical kinetics calculations, which provides a promising technical advancement direction for the coal-fired power plants to achieve a signification reduction of both CO2 and NO emissions.