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.
Highlights
Biomass plays an increasingly important role as a renewable energy source for production of heat, power, transportation fuels and other chemicals via thermochemical conversion processes, such as combustion and gasification [1,2]
An efficient way to improve the understanding of fuel conversion is to perform well-controlled studies of volatile release from biomass particles combusted in laboratory reactors [11,12,13,14,15,16,17,18]
A robust wavelength-multiplexed Tunable diode laser absorption spectroscopy (TDLAS) spectrometer was employed for simultaneous time-resolved detection of atomic potassium, H2 O and gas temperature close to softwood, Miscanthus, wheat straw and Salix particles combusted in a laboratory reactor
Summary
Biomass plays an increasingly important role as a renewable energy source for production of heat, power, transportation fuels and other chemicals via thermochemical conversion processes, such as combustion and gasification [1,2]. Biomass, in particular the low-grade types, contains large amounts of potassium (K) and other ash-forming elements that may form hazardous compounds in solid, liquid or gaseous phase. This causes severe operational problems, such as fouling, agglomeration and corrosion, in industrial boilers [3,4], which today prevents the large-scale use of these fuels. An efficient way to improve the understanding of fuel conversion is to perform well-controlled studies of volatile release from biomass particles combusted in laboratory reactors [11,12,13,14,15,16,17,18]
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