Potassium Release from Biomass Particles during Combustion—Real-Time In Situ TDLAS Detection and Numerical Simulation

Abstract

Potassium (K) is one of the main and most hazardous trace species released to the gas-phase during thermochemical conversion of biomass. Accurate experimental data and models of K release are needed to better understand the chemistry involved. Tunable diode laser absorption spectroscopy (TDLAS) is used for simultaneous real-time in situ measurements of gas-phase atomic K, water (H2O) and gas temperature in the vicinity (boundary layer) of biomass particles during combustion in a laboratory single-particle reactor. Atomic K is detected in a wide dynamic range, including optically thick conditions, using direct absorption spectroscopy at the wavelength of 770 nm, while H2O and temperature are determined by calibration-free scanned wavelength modulation spectroscopy at 1398 nm. The high accuracy and repeatability of the setup allows to distinguish measurements with varying initial particle mass, laser beam height above the particle and fuel type. Four types of biomass with different ash composition are investigated: softwood, Salix, Miscanthus and wheat straw. For Salix and wheat straw, the K release behaviour is, for the first time, compared to a detailed numerical particle model taking into account the interaction between K/S/Cl composition in the particle ash. A good agreement is achieved between the measured and calculated time-resolved atomic K concentrations for the devolatilization phase of the biomass particles.

Numerical Study and Experimental Verification of Biomass Conversion and Potassium Release in a 140 kW Entrained Flow Gasifier

“…This is in agreement with other experiments on a small batch of biomass particles where the maximum K-release was observed during the combustion stage. 21 , 32 The evaporation and dissociation of K 2 CO 3 and K 2 SO 4 continue during the gasification stage, but the release of K from K 2 CO 3 has a higher rate. The gasifier has a high water vapor concentration, so the dissociation rate of the salts will be orders of magnitude higher than their evaporation rate, 19 which leads to a high amount of KOH formation.…”

“…The release of alkali metals and inorganic elements from biomass is commonly studied in lab-scale apparatus on a small batch of biomass particles under pyrolysis, combustion, or gasification conditions. , In most experiments, the K content in the solid, as the most abundant alkali metal in biomass, was measured before and after the experiments to calculate the K-release at different operating conditions. , It was found that, other than temperature and water vapor concentration, CO 2 concentration surrounding the particle is important as it prohibits the K-release . On the other hand, the type of biomass and the composition of the ash-forming elements are also important, since, for instance, Cl and S facilitate while silicon (Si) and aluminum (Al) hinder the K-release .…”

Application and algorithm research of TDLAS

“…Zhechao Qu et al used TDLAS for simultaneous in-suit detection of K atoms, water in gas phase and temperature near bio-particles in the process of burning of the laboratorial single-particle reactor. For the first time, the K release behavior of willow and wheat straw was compared with the numerical model considering K/S/Cl interaction in ash, proving fine linearity between the simulated and measured K concentration in the devolatilization stage [30]. Yong Bao et al developed a relative entropy tomographic reconstruction (RETRO) algorithm to solve errors of TDLAS in in-situ combustion, retrieved the reconstructed double-line absorbance distribution, and verify feasibility of this algorithm through performing numerical simulations and proof-of-concept tests [31].…”

Quantitative Tomographic Laser Absorption Imaging of Atomic Potassium during Combustion of Potassium Chloride Salt and Biomass

“…Atomic K imaging has previously been performed using spontaneous emission and laser-induced fluorescence. , Imaging of KOH/KCl and K 2 SO 4 aerosols has been achieved by photofragmentation fluorescence spectroscopy and Mie scattering, respectively. One drawback of the techniques mentioned above is the need for calibration procedures to obtain species concentrations, which is important for, e.g., the validation of numerical particle models …”

“…One drawback of the techniques mentioned above is the need for calibration procedures to obtain species concentrations, which is important for, e.g., the validation of numerical particle models. 21 …”