Time-Resolved Temperature Measurements of Individual Coal Particles During Devolatilization

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Abstract
The wide difference in reported coal devolatilization rates during rapid heating can be attributed to inadequate determinations of particle time-temperature profiles. The sensitivity of predicted particle temperature in a rapid heating environment is studied as a function of heat capacity, treatment of local gas temperature, and diameter. An in situ method for measuring simultaneously the size, temperature, and velocity of individual coal particles during pyrolysis is presented. Thermal emission from moving particles is collected using a reflecting microscope assembly and passes through a specially designed aperture, yielding a double pulse signal. The aperture is designed such that the ratio of peak heights yields particle diameter. The emitted light from the particle is split and filtered at wavelengths of 1.36 and 2.2 μm, and particle temperature is determined by applying two-color pyrometry. Particle velocity is obtained from the same emission signals using transit timing. Particle temperature measurements as a function of size are compared with predicted temperatures, showing that the particle temperature history in this system is well understood. Future determinations of devolatilization kinetic parameters from this system will not be subject to uncertainties about the particle temperature history.

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