OCR Text |
Show Note that Figures 3 and 5 show the oxidation rate of Indiana pulverized coal and West Virginia micronized coal decreasing shortly after a positive ignition. Without further ignition, oxidation might not be sustained; this phenomenon is called false ignition and is typical of certain coals. The burning profile technique and application of the results are described in more detail by Wagoner and Duzy [6]. Volatile-Release Profiles Comparison of volatile-release profiles of micronized and parent Indiana, Ohio, and West Virginia coals are shown in Figures 6, 7 and 8 respectively. The small peak for each sample centered at about 212°F represents a loss of residual moisture. The remaining peak temperatures and intensities provide a relative evaluation of ignition characteristics of test fuels. Figures 6, 7, and 8 show that the peak intensities of volatile release are relatively lower for the micronized Indiana and West Virginia coals and are moderate for Ohio micronized coal. This is compared to the higher intensities observed for the respective parent coals. Moreover, the volatile-release temperature peaks have skewed toward higher temperatures for all three micronized coals. The ignition behavior predicted from the volatile-release test of the micronized coals is not consistent with that in the burning profile and LAF tests. The results of the volatile-release profile tests of micronized coals may be a consequence of the test procedure, where a sample is heated and spread in a thin uniform layer across the bottom of a crucible. The fineness of the micronized coal gives increased surface area and consequently increased sites for fusion (caking) of the particles into a solid sheet while the coal particles are in a plastic state. Because of this, the micronized coals transform into a plastic sheet at a lower temperature; therefore, the rate of release of volatiles is decreased. 9-17 |