Photofragmentation spectroscopy is combined with tunable diode laser absorption spectroscopy to measure the line shape of the fragment species. This provides flexibility in choosing the UV pulse location within the line shape and accurate quantification of both target species and background fragment concentrations, even under optically thick conditions. The technique is demonstrated by detection of potassium hydroxide (KOH) and atomic potassium K(g) above solid KOH converted in a premixed methane-air flat flame. Time series of KOH(g) and K(g) concentrations are recorded as a function of solid KOH mass and flame stoichiometry. The total substance released during the conversion is in good agreement with the initial solid KOH mass. Under fuel-rich conditions, increased K(g) concentrations at the expense of KOH(g) are observed compared to thermodynamic equilibrium.

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Gaseous potassium (K) species released from biomass during thermochemical conversion pose challenges to reactors and human health. Photofragmentation tunable diode laser absorption spectroscopy (PF-TDLAS) was used for simultaneous, high-dynamic range measurements of atomic K, potassium hydroxide (KOH) and potassium chloride (KCl) in flat flames seeded with KCl salt. An expression for the PF-TDLAS signal is presented and experimentally verified. Axial K species concentration profiles recorded at fuel-air equivalence ratios of 0.8 and 1.3 are compared to 2D axisymmetric reacting flow simulations. An overall good agreement is found, but KOH is over-predicted in simulations of fuel-rich flames at the expense of atomic K. Quantification of K species close to softwood and wheat straw particles converted in the flames is demonstrated.

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In this study, a Eulerian−Lagrangian model is used to study biomass gasification and release of potassium species in a 140 kW atmospheric entrained flow gasifier (EFG). Experimental measurements of water concentration and temperature inside the reactor, together with the gas composition at the gasifier outlet, are used to validate the model. For the first time, a detailed K-release model is used to predict the concentrations of gas-phase K species inside the gasifier, and the results are compared with experimental measurements from an optical port in the EFG. The prediction errors for atomic potassium (K), potassium chloride (KCl), potassium hydroxide (KOH), and total potassium are 1.4%, 9.8%, 5.5%, and 5.7%, respectively, which are within the uncertainty limits of the measurements. The numerical model is used to identify and study the main phenomena that occur in different zones of the gasifier. Five zones are identified in which drying, pyrolysis, combustion, recirculation, and gasification are active. The model was then used to study the transformation and release of different K species from biomass particles. It was found that, for the forest residue fuel that was used in the present study, the organic part of K is released at the shortest residence time, followed by the release of inorganic K at higher residence times. The release of inorganic salts starts by evaporation of KCl and continues by dissociation of K 2 CO 3 and K 2 SO 4 , which forms gas-phase KOH. The major fraction of K is released around the combustion zone (around 0.7−1.3 m downstream of the inlet) due to the high H 2 O concentration and temperature. These conditions lead to rapid dissociation of K 2 CO 3 and K 2 SO 4 , which increases the total K concentration from 336 to 510 ppm in the combustion zone. The dissociation of the inorganic salts and KOH formation continues in the gasification zone at a lower rate; hence, the total K concentration slowly increases from 510 ppm at 1.3 m to 561 ppm at the outlet.