Quantitative Measurement of Atomic Potassium in Plumes over Burning Solid Fuels Using Infrared-Diode Laser Spectroscopy

Solid fuels, such as coal and biomass, comprise a large portion of the current annual world energy supply, roughly equal to the annual oil consumption. During solid fuel combustion, certain species, though they are fairly benign outside of the combustion system, can cause damage in and around the combustion chamber. Alkali release from coal and biomass is known to cause severe problems in solid fuel fired boilers, such as fouling and corrosion of the heat transfer surfaces. In this work, the amount of atomic potassium in the plume of burning single coal, wood, and straw pellets (∼170 mg/piece) was measured using tunable diode laser absorption spectroscopy (TDLAS) of the potassium D1 line at 769.9 nm. The sample pellets were burned in an environment with stable temperature and gas composition provided by a laminar flame burner. More atomic potassium existed in the plume of burning biomass pellets compared with coal pellets, and the two temporal concentration profiles were dissimilar. This was attributed to the difference in the respective combustible components, ash compositions, potassium concentrations, and potassium compound state found in the two fuels. A high proportion of fixed carbon in coal induces potassium release mostly during the char-burnout period. In contrast, biomass has its strongest release during the devolatilization stage since its potassium presents mostly in a water-soluble form. Measurements of atomic potassium concentration during wood pellet gasification were performed in an oxygen deprived hot flue gas environment. The concentration of atomic potassium was found to be halved relative to combustion. The distribution of atomic potassium in the plume at different height above the pellets was also measured and is discussed in brief