Kinetics and Mechanisms of NO(x) - Char Reduction. Page: 34 of 70
This report is part of the collection entitled: Office of Scientific & Technical Information Technical Reports and was provided to UNT Digital Library by the UNT Libraries Government Documents Department.
Extracted Text
The following text was automatically extracted from the image on this page using optical character recognition software:
more and more available even in zone II. Therefore, reaction may be in the pore diffusion
limited regime only until a certain level of burn-off. The conditions under which restricted
diffusion controls gasification, causing a limited participation of porous surface area, are
not well established, except in the most idealized theoretical cases.
3.4 Improvement of transport models
In a char, the morphology and porosity play a fundamental role in transport and
reaction in the system. Recent theoretical studies have developed a number of
models19,20,24 for these systems. The modeling of the evolution of the porosity or
reactivity with bum-off is a complex task. The porosity development with burn-off
involves several processes that take place simultaneously and many of the important steps
are included in these transport models. However, the current study has experimentally
recognized processes that are excluded from these models and these will be discussed in
this section.
3.4.1 Opening of closed porosity
The total porosity of the carbon is not always accessible to reactant at low levels of
burn-off because it is partially or totally blocked by the carbon deposited during pyrolysis
or because some of the carbon crystallites form a closed structures. These new surfaces
become available after a partial gasification (after about 1-2% bum-off in Wyodak char). It
was recognized that opening of closed pores can be the main process of pore development
during the first few percent of burn-off.
We know that the presently studied chars are non-graphitizable carbons, which
means that there is no long range order of the graphitic units. Still, local ordering to an
extent that depends on the heat treatment temperature, is expected. Considerable evidence
for small structural units of about 40 A size within char have been proposed58. In non-
graphitizable carbons the porous structure is formed by strong cross-linking of structural34
Upcoming Pages
Here’s what’s next.
Search Inside
This report 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 Report.
Suurerg, E.M.; Lilly, W.D. & Aarna, I. Kinetics and Mechanisms of NO(x) - Char Reduction., report, December 31, 1997; Providence, Rhode Island. (https://digital.library.unt.edu/ark:/67531/metadc690356/m1/34/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.