Ultraviolet Absorption Cross Sections of KOH and KCl for Nonintrusive Species-Specific Quantitative Detection in Hot Flue Gases

Abstract

An understanding of potassium chemistry in energy conversion processes supports the development of complex biomass utilization with high efficiency and low pollutant emissions. Potassium exists mainly as potassium hydroxide (KOH), potassium chloride (KCl), and atomic potassium (K) in combustion and related thermochemical processes. We report, for the first time, the measurement of the ultraviolet (UV) absorption cross sections of KOH and KCl at temperatures between 1300 K and 1800 K, using a newly developed method. Using the spectrally resolved UV absorption cross sections, the concentrations of KOH and KCl were measured simultaneously. In addition, we measured the concentrations of atomic K using tunable diode laser absorption spectroscopy, both at 404.4 and 769.9 nm. The 404.4 nm line was utilized to expand the measurement dynamic range to higher concentrations. A constant amount of KCl was seeded into premixed CH4/air flames with equivalence ratios varied from 0.67 to 1.32, and the concentrations of KOH, KCl, and atomic K in the hot flue gas were measured nonintrusively. The results indicate that these techniques can provide comprehensive data for quantitative understanding of the potassium chemistry in biomass combustion/gasification.

TDLAS-based photofragmentation spectroscopy for detection of K and KOH in flames under optically thick conditions

“…The measured plateau concentrations as a function of equivalence ratio are similar to the results presented in Ref. [7] and in good agreement with equilibrium calculations for fuel-lean flames. However, significant deviations from equilibrium are evident close to stoichiometry and in fuel-rich flames.…”

“…Existing spectroscopic techniques to selectively detect KOH(g) in situ include direct UV absorption [5][6][7], laser induced fluorescence [8], and collinear photofragmentation (PF) atomic absorption spectroscopy (CPFAAS) [9,10]. The latter method was developed by Sorvajärvi et al and bears similarities to other implementations of photofragmentation absorption spectroscopy [11,12].…”

“…The K(g) concentrations were obtained by fitting the K(g) absorption profiles to the models presented in Refs. [7,18] with K(g) concentration and collisional width as open parameters. The KOH(g) concentrations were determined by fitting the K(g) decay curves following the UV pulse to the model in Ref.…”

“…The detection limit in the fuel-rich case could be improved by employing a high-power probe laser or a UV laser with higher pulse energy. Employing the weaker K(g) absorption lines around 404 nm [7] would shift the dynamic range towards higher concentrations and impair the detection limits, but facilitate the investigation of fuel-rich flames.…”

Ultraviolet Absorption Cross-Sections of Ammonia at Elevated Temperatures for Nonintrusive Quantitative Detection in Combustion Environments

“…However, to manage spatially resolved quantitative measurements, UV absorption spectroscopy must be combined with other techniques, such as laser-induced fluorescence or LIPF. Moreover, it should be noted that many species, such as SO 2 , 33 KOH, and KCl, 34 also have strong absorption in the UV region. This might introduce interference to NH 3 measurements.…”