Open AccessASH EMISSIVITY CHARACTERIZATION AND PREDICTION
Author(s) -
Christopher J. Zygarlicke,
Donald P. McCollor,
Charlene R. Crocker
Publication year - 1999
Language(s) - English
Resource type - Reports
DOI - 10.2172/778529
Subject(s) - emissivity , combustion , mineralogy , pulverized coal fired boiler , coal , particle size , fly ash , materials science , potassium , chemistry , metallurgy , composite material , optics , physics , organic chemistry
The increased use of western subbituminous coals has generated concerns regarding highly reflective ash disrupting heat transfer in the radiant zone of pulverized-fuel boilers. Ash emissivity and reflectivity is primarily a function of ash particle size, with reflective deposits expected to consist of very small refractory ash materials such as CaO, MgO, or sulfate materials such as Na{sub 2}SO{sub 4}. For biomass fuels and biomass-coal blends, similar reflectivity issues may arise as a result of the presence of abundant organically associated calcium and potassium, which can transform during combustion to fine calcium, and potassium oxides and sulfates, which may act as reflective ash. The relationship of reflectivity to ash chemistry is a second-order effect, with the ash particle size distribution and melting point being determined by the size and chemistry of the minerals present in the starting fuel. Measurement of the emission properties of ash and deposits have been performed by several research groups (1-6) using both laboratory methods and measurements in pilot- and full-scale combustion systems. A review of the properties and thermal properties of ash stresses the important effect of ash deposits on heat transfer in the radiant boiler zone (1)