Radiative heat transfer in pulverized-coal-fired boilers: Development of the absorptive/reflective character of initial ash deposits
- Brigham Young Univ., Provo, UT (United States)
- Sandia National Labs., Livermore, CA (United States)
- Newcastle Univ., NSW (Australia). Dept. of Chemical Engineering
Emission Fourier transform infrared (FTIR) spectroscopy data provide in situ, time-resolved, spectral emissivity measurements for ash deposits generated from two US Powder River Basin coals under realistic combustion conditions. The first three hours of deposit growth on a tube in cross flow in Sandia`s Multifuel Combustor detail the development of surface emissivity with time. Measured emissivities vary significantly with wavelength, reflecting the influence of the physical, chemical, and optical properties of the deposit. At long wavelengths (>7{mu}m), emission bands exhibit characteristics of sulfates and silicates. The spectral emissivity measured in this region approaches a steady value, indicating that the deposit becomes opaque. In contrast, deposits are not opaque at shorter wavelengths where the measured emissivity is influenced by the properties of the underlying metal surface. Theoretical predictions of the emissivity of a particulate layer were performed and results are compared to the measured values. The theory adequately predicts the general features of spectral variation of the emissivity. The predicted trends in emissivity with particle size and deposit composition are also consistent with experimental observations. Total (Planck-weighted) emissivities are calculated from the measured spectral values for the deposits at flame temperatures. They increase with time from the clean tube value (0.2 to 0.3) to values typical of deposits formed from western US coals (0.45 to 0.55). The total absorptivities are also calculated based on wall temperatures and found to be somewhat lower than the corresponding emissivities (0.30 to 0.37). In all cases, the ash deposits exhibit more reflective behavior than deposits generated from most eastern US coals with emissivities of the order of 0.7 to 0.9.
- Research Organization:
- Sandia National Labs., Albuquerque, NM (United States)
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- AC04-76DP00789
- OSTI ID:
- 10121344
- Report Number(s):
- SAND-94-8481; CONF-940711-9; ON: DE94006394
- Resource Relation:
- Conference: 25. international symposium on combustion,Irvine, CA (United States),31 Jul - 5 Aug 1994; Other Information: PBD: [1994]
- Country of Publication:
- United States
- Language:
- English
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