Release characteristics of different alkali metal salts in Zhundong coal under O2/CO2 combustion atmosphere based on FES technology

Abstract

The O2/CO2 combustion technology is a clean coal-fired power generation technology. However, a large amount of alkali metals released during the combustion of high-alkali coal is usually an important substance that causes ash deposition, slagging and corrosion on the heating surface of boiler, which seriously affect the safe and stable operation of equipment. It is of great significance to study the release characteristics of alkali metal salts with different occurrences in the Zhundong coal under the O2/CO2 combustion atmosphere for the clean and efficient utilization of coal. Based on flame emission spectroscopy (FES), the release characteristics of different alkali metal salts in the O2/N2 and O2/CO2 atmospheres during pulverized coal combustion were studied in a metal wire mesh reactor. The results show that the combustion of volatile compounds produces a bright flame under the O2/N2 atmosphere. The combustion intensity and flame temperature of the pulverized coal in the O2/CO2 atmosphere decrease compared with that in the O2/N2 atmosphere, the ignition time is delayed, the combustion time of volatiles and coke is prolonged, and the release of Na(g) is inhibited. For NaAc, Na2CO3 and Na2SO4, the O2/CO2 atmosphere delays the decreasing time of mass concentration, so that the Na(g) in the pulverized coal enters a stable release stage from the beginning, and the mass concentration variation rate of Na(g) does not fluctuate much. However, the mass concentration variation rate of NaCl will turn negative about 4 seconds after release, resulting in a consistent decrease in the mass concentration of Na(g). At the same time, the CO2 atmosphere also causes the conversion of NaAc, NaCl and other types of salts to form Na2CO3, which is more difficult to release, and further inhibits the release process of Na(g). The main reason that the mass release rate of Na2CO3 also decreases under the O2/CO2 atmosphere is that CO2 inhibits the decomposition process of Na2CO3 to Na2O. The Na2SO4 is more difficult to release itself, so the main reason for the reduction of its mass release rate is due to the reduction of fuel combustion temperature and intensity.

Keywords

• o2/co2 combustion
• alkali metals
• flame emission spectroscopy
• metal wire mesh reactor
• release characteristics