Carbon conversion of solid fuels in the freeboard of a laboratory-scale fluidized bed combustor--application, of in situ laser spectroscopy

摘要

The carbon conversion of different solid fuels (i.e. beech wood, fir wood, bituminous coal) was investigated in the freeboard of a laboratory-scale fluidized bed combustor by in situ tunable diode laser absorption spectroscopy. A room temperature continuous wave InGaAsSb/AlGaAsSb quantum well ridge diode laser emitting at 2.3-2.35 (mu)m was wavelength tuned at 300 Hz to determine simultaneously CH_4 and CO during devolatilization and char combustion in situ 10 mm above the fuel particles. The lower detection limit was 0.2 vol percent (5000 ppm m) for both species. In addition, CO, CO_2 and O_2 were determined ex situ by conventional methods. The experimental results obtained for the bituminous coal were compared to a detailed chemical kinetic model. The in situ measurements proved to be advantageous compared to conventional ex situ concentration measurements, The calculations confirm the determination of the primary products of solid fuel combustion during devolatilization and char combustion. A rather simple model for the devolatilization products was proven to describe well the release rates of CH_4 and CO for the bituminous coal.