The kinetics of NO and N2O reduction over coal chars in fluidised-bed combustion

Li, YH, Lu, GQ and Rudolph, V (1998) The kinetics of NO and N2O reduction over coal chars in fluidised-bed combustion. Chemical Engineering Science, 53 1: 1-26. doi:10.1016/S0009-2509(97)87569-0


Author Li, YH
Lu, GQ
Rudolph, V
Title The kinetics of NO and N2O reduction over coal chars in fluidised-bed combustion
Journal name Chemical Engineering Science   Check publisher's open access policy
ISSN 0009-2509
Publication date 1998-01-01
Year available 1998
Sub-type Critical review of research, literature review, critical commentary
DOI 10.1016/S0009-2509(97)87569-0
Open Access Status Not yet assessed
Volume 53
Issue 1
Start page 1
End page 26
Total pages 26
Place of publication OXFORD
Publisher Elsevier Sci Ltd
Language eng
Abstract This paper presents a comprehensive and critical review of the mechanisms and kinetics of NO and N2O reduction reaction with coal chars under fluidised-bed combustion conditions (FBC). The heterogeneous reactions of NO and N2O with char/carbon surface have been well recognised as the most important processes in reducing both NOx and N2O in situ FBC. Compared to NO-carbon reactions in FBC, the reactions of N2O with chars have been relatively less understood and studied. Beginning with the overall reaction schemes for both NO and N2O reduction, the paper extensively discusses the reaction mechanisms including the effects of active surface sites. Generally, NO- and N2O-carbon reactions follow a series of step reactions. However, questions remain concerning the role of adsorbed phases of NO and N2O, and the behaviour of different surface sites. Important kinetics factors such as the rate expressions, kinetics parameters as well as the effects of surface area and pore structure are discussed in detail. The main factors influencing the reduction of NO and N2O in FBC conditions are the chemical and physical properties of chars, and the operating parameters of FBC such as temperature, presence of CO, O-2 and pressure. It is shown that under similar conditions, N2O is more readily reduced on the char surface than NO. Temperature was found to be a very important parameter in both NO and N2O reduction. It is generally agreed that both NO- and N2O-carbon reactions follow first-order reaction kinetics with respect to the NO and N2O concentrations. The kinetic parameters for NO and N2O reduction largely depend on the pore structure of chars. The correlation between the char surface area and the reactivities of NO/N2O-char reactions is considered to be of great importance to the determination of the reaction kinetics. The rate of NO reduction by chars is strongly enhanced by the presence of CO and O-2, but these species may not have significant effects on the rate of N2O reduction. However, the presence of these gases in FBC presents difficulties in the study of kinetics since CO cannot be easily eliminated from the carbon surface. In N2O reduction reactions, ash in chars is found to have significant catalytic effects, which must be accounted for in the kinetic models and data evaluation. (C) 1997 Elsevier Science Ltd.
Keyword Engineering, Chemical
No And N2o Reduction
Reaction Mechanisms
Char/carbon Surface
Kinetics And Modelling
Fluidised-bed Combustion And Operating Conditions
Gas Solid Reactions
Heat-treated Coals
Random Pore Model
Nitric-oxide
Activated Carbons
Nitrous-oxide
Pyrolysis Conditions
Percolation Concepts
Intrinsic Rates
Fbc Conditions
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status Unknown

Document type: Journal Article
Sub-type: Critical review of research, literature review, critical commentary
Collection: Australian Institute for Bioengineering and Nanotechnology Publications
 
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Created: Mon, 13 Aug 2007, 20:18:53 EST