Comparison of biomass and coal char reactivities Page: 1 of 6
This article is part of the collection entitled: Office of Scientific & Technical Information Technical Reports and was provided to Digital Library by the UNT Libraries Government Documents Department.
The following text was automatically extracted from the image on this page using optical character recognition software:
COMPARISON OF BIOMASS AND COAL CHAR REACTIVITIES
Sidney P. Huey, Kevin A. Davis, and Robert H. Hurt2
Combustion Research Facility
Sandia National Laboratories
Livermore, CA 94551-0969
'Currently at Reaction Engineering International
77 West 200 South, Suite 210
Salt Lake City, UT 84121
2Currently at Brown University
Division of Engineering, Box D
Providence, RI 02912
Keywords: combustion, biomass, char reactivity
Char combustion is typically the rate limiting step during the combustion of solid fuels. The magnitude
and variation of char reactivity during combustion are, therefore, of primary concern when comparing
solid fuels such as coal and biomass. In an effort to evaluate biomass' potential as a sustainable and
renewable energy source, the reactivities of both biomass and coal chars were compared using Sandia's-
Captive Particle Imaging (CPI) apparatus. This paper summarizes the experimental approach used to
determine biomass and coal reactivities and presents results from CPI experiments.
The reactivity of six types of char particles, two high-rank coal chars, two low-rank coal chars, and two
biomass chars, were investigated using the CPI apparatus. Results indicate that both of the high-rank
coal chars have relatively low reactivities when compared with the higher reactivities measured for the
low-rank coal and the biomass chars. In addition, extinction behavior of the chars support related
investigations that suggest carbonaceous structural ordering is an important consideration in
understanding particle reactivity as a function of extent of burnout. High-rank coal chars were found to
have highly ordered carbon structures, where as, both low-rank coal and biomass chars were found to
have highly disordered carbon structures.
Incomplete combustion of solid fuels in utility boilers remains an important concern for power
generation facilities [Hottel and Stewart, 1940]. The result of incomplete combustion is a high level of
unburned carbon in a boiler's flyash. This, in turn, causes a number of deleterious effects, including, a
significant decrease in combustion efficiency, an adverse effect on heat transfer and electrostatic
precipitator operation, and a greater difficulty marketing the flyash for recycling (i.e., for carbon
contents greater than 3 to 6 percent). Determining the relative level of unburned carbon from burning
coal and biomass fuels in boilers motivates this investigation.
In practice, the level of unburned carbon in the flyash is related to the fuel's rank. Coal rank is a
measure of volatile matter contained in the coal and is generally considered an indicator of its geologic
age. Past investigations have shown that coal rank is related to its reactivity [Hurt, 1993; Hurt and
Davis, 1994; Davis et a., 1995], and that reactivity is related to its elemental and structural composition
[Davis et al., 1995]. Our earlier work, using high resolution transmission electron microscopy to image
the carbonaceous structure of biomass chars at different stages of the combustion process, indicates
little ordering for low-rank coal and biomass chars and suggests that biomass chars should have
relatively low reactivities [Wornat'et aL, 1995] and produce low levels of unburned carbon.
Bituminous and high-rank coals produce high levels of unburned carbon, whereas, low-rank coals
produce lower levels of unburned carbon. Biomass, with a very high volatile matter content, high
oxygen content, and a correspondingly low heating value, is thermochemically similar in many respects
to a low-rank coal. Given the thermochemical similarity of low-rank coals and biomass chars, we
DISTIlIBUTION OF THIS DOCUMENT IS UNUIMtIED ..Dr
Here’s what’s next.
This article can be searched. Note: Results may vary based on the legibility of text within the document.
Tools / Downloads
Get a copy of this page or view the extracted text.
Citing and Sharing
Basic information for referencing this web page. We also provide extended guidance on usage rights, references, copying or embedding.
Reference the current page of this Article.
Huey, S.P.; Davis, K.A. & Hurt, R.H. Comparison of biomass and coal char reactivities, article, August 1, 1995; Livermore, California. (https://digital.library.unt.edu/ark:/67531/metadc627637/m1/1/: accessed March 25, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.