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|Title:||Experimental studies of single particle coal combustion: Ignition, sulfur retention, and the contributions of morphology|
|Author(s):||Bayless, David James|
|Doctoral Committee Chair(s):||Buckius, Richard O.; Peters, James E.|
|Department / Program:||Mechanical Science and Engineering|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Abstract:||Single particle pulverized coal combustion experiments were conducted in a drop tube furnace facility in order to investigate various aspects of coal combustion. Included in the study were the effects of natural gas cofiring on particle ignition and sulfur capture in ash, and the effects of morphology on burning rates at diffusion-limited conditions.
Measurements of particle ignition delay indicated that cofiring 1% methane by volume reduced the ignition delay of low-volatile coal particles to the value of the ignition delay of high-volatile particles of the same size in air alone. Ignition delays were accurately predicted using two separate models--one based on energy absorption and the other on devolatilization.
Cofiring coal with natural gas was shown to increase sulfur retention in ash. This increase, known as leveraging, was affected by particle residence time and furnace temperature, while original sulfur form and coal sorbent capacity had little effect. Experimental results indicated that the primary mechanism for sulfur leveraging was the gas phase conversion of SO$\sb2$ to SO$\sb3$. These results were supported by numerical modeling of particle combustion and sulfur evolution.
A technique was developed to more accurately quantify particle burning area by including the effects of voids (pores on the particle surface that are deeper than their surface radius). Scanning electron microscopy and digital processing of images of quenched particles were used to quantify surface void area, perimeter, and reacting void wall area for voids with diameters larger than 1 $\mu$m. Burning rates determined from in situ measurements of a wide range of reacting coal particles indicated that calculated burning rates more closely matched diffusion-limited burning rates when burning area was corrected for void surface area and reacting void wall area.
Results of quantifying void area distributions indicated that mean void area increased with coal volatility, heating rate, and heterogeneous combustion, but was not significantly affected by oxygen concentration. Numerical results indicated that burning rate calculations did not strongly depend on specific void distribution shape. However, results suggested that errors in burning rate caused by assuming a void distribution were minimized by using a pore distribution model modified for the effects of void combination and assuming a mean void area of 20%.
|Rights Information:||Copyright 1995 David James Bayless|
|Date Available in IDEALS:||2011-05-07|
|Identifier in Online Catalog:||AAI9543528|
This item appears in the following Collection(s)
Dissertations and Theses - Mechanical Science and Engineering
Graduate Dissertations and Theses at Illinois
Graduate Theses and Dissertations at Illinois