The alkali metals released from combustion process of high alkali fuels such as Zhundong coal and biomass are probable to cause fouling and slagging on heating surfaces of furnace and affect the operation safety. Therefore

quantitative measurement of alkali metals in combustion process is of great significance to combustion optimization. The widely used in-situ measurement techniques of alkali metals include two types: active and passive. The former includes laser-induced fluorescence

laser-induced breakdown spectroscopy and absorption spectroscopy

while the latter includes flame emission spectroscopy and image processing. The basic principles of various measurement techniques and their application in industrial furnace combustion are introduced in detail. Considerable progress has been made in in-situ measurement of alkali metals. The active measurement has almost no interference to the flame

and the spectral states of atoms and molecules in the combustion process can be observed with high temporal and spatial resolution

which has been widely used in laboratory combustion detection research with high measurement accuracy. While the passive alkali metal in-situ measurement technology has been proved to have potential application in real industrial conditions due to its advantages of simple equipment and strong adaptability to harsh environment. Finally

the main equipment

applications

components and detection limits of all kinds of technologies involved in the review are summarized

and the shortcomings and future development trends of the current detection technology of alkali metals are pointed out.