00/02259 Evaporation of moisture from Kansk-Achinsk coals during heat treatment
- Publisher
- Elsevier Science
- Year
- 2000
- Weight
- 220 KB
- Volume
- 41
- Category
- Article
- ISSN
- 0140-6701
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✦ Synopsis
01 Solid fuels (sources. winrung, properties) 00102257
Electric polarization characteristics of Baijiao coal and methane-adsorbing coal Xu, L. er al. Ronlioo Humue Xuehao. 1999, 27, (I). [74][75][76][77][78][79] This study focuses on the polarization characteristics of Baijiao anthracite in an electric field. Because of the effect of displacement polarization and space polarization the electric current in d.c. electric field, which flogs coal and methane-adsorbing coal, attenuates with time: I=I, + ae
, and gradually reaches a stable value. In an a.c. electric field, the electric current through coal and methane-adsorbing coal is a constant owing to the polarization effect. 00102258 Evaluation of thermophysical and thermochemical heat requirements for coals at combustion level heat fluxes Sampath, R. er al. S,rmf (Inr.) Comhusr.. [Proc.], 1998. 2, (27), 2915-2923. Measurements were taken for heating and cooling transients for well characterized individual coal particles in the 100.pm size range at heat input rates representative of pulverized coal combustion applications (104-10. K/s). Particle temperatures rose steadily until volatile evolution commenced.
The rate of temperature rise then dropped quickly followed by a pronounced temperature plateau over which heavy volatile evolution proceeded.
These observations suggest a substantial thermophysical and thermochemical heat requirement associated with volatile evolution, A heat-transfer analysis was developed to assess the magnitude of these heat requirements.
The analysis included a first-order rate expression with rate constants selected to match observed devolatilization time-scales to account for volatile evolution (mass loss). Devolatilization heat requirements were treated using a lumped approach that considered the enthalpy of the volattles leaving the particle. Excellent agreement was obtained between model projections and measurements over a range of heat input conditions. This work suggests that the coal structure is initially constrained and, at high heating rates, a finite time is required for the structure to relax and respond to thermal input. This induction period may be responsible for pushing volatile evolution to higher temperatures and extending the devolatilization time-scale. The volatile enthalpy term in the analysis was of the same magnitude as the heat input required to brmg the coal to the temperature range where devolatilization occurred. This heat requirement cannot be ignored if accurate temperature projections are desired. The simplification applied in the present study yields reasonable energy balances and are applicable to coal combustion and should be considered in the development of engineering models.