Experimental Investigation of Gaseous Sodium Release in Slag-Tapping Coal-Fired Furnaces by Spontaneous Emission Spectroscopy

Abstract

High-alkali coal is rich in alkali metals, which can cause serious effects such as slagging and corrosion on the heating surface during combustion and utilization. A portable spectral system was utilized to simultaneously measure gaseous Na concentration and temperature in a 20 kW slag-tapping combustor and a slagging boiler furnace of a 300 MW power generation unit by flame spontaneous emission spectroscopy (FES) for simultaneous measuring. The result shows that both ZD-FK and ZD-HSQ (Fukang coal and Hongshaquan coal, Xinjiang Zhundong high-alkali coal) combustion flame temperatures are around 1400 °C at the outlet of the cyclone burner while the latter is slightly higher. The sodium concentration in the gas phase increases with the rising of the initial combustion temperature and unit load for one kind of coal, and the level of sodium concentration has a strong correlation with the Na content for different coal. Most of the sodium in the high temperature zone of the furnace exists in the form of gas phase, and more sodium migrates to fly ash. Combined with the analysis of fly ash and liquid slag samples, a closed-loop analysis of the Na migration path could be established.

Investigation of Slagging Condition in a Zhundong Coal-Fired Boiler via In Situ Optical Measurement of Gaseous Sodium

“…[ 9 , 10 ]. Without the need for an additional light source to produce the spectrum, the emission spectrum can be directly measured, which makes this method inexpensive, portable, and useful for the simultaneous determination of the gaseous alkali metal concentrations and the temperature in flames; it has been applied in ZD coal [ 11 , 12 , 13 , 14 ], biomass [ 15 , 16 , 17 , 18 , 19 ], and municipal solid waste (MSW) [ 20 , 21 ] combustion, from lab-scale burners to pilot-scale furnaces (20 kW) and industrial facilities (350 MW). In addition, the advantage of SES also promoted its application in temperature measurement in coal gasification [ 22 ].…”

“…In addition, the advantage of SES also promoted its application in temperature measurement in coal gasification [ 22 ]. These studies show that in the temperature range of 1400 °C–1500 °C, for the Na gas concentration and temperature in the 20 kW slagging combustion chamber and 300 MW furnace of a slagging boiler, silicon and aluminum oxides have a high trapping effect on alkali metals [ 13 ]. The gas-phase Na and K released in the waste incinerator are closely related to the temperature [ 20 ].…”