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A Design Concept to Reduce Fuel NOx in Catalytic Combustion of Gasified Biomass
KTH, Superseded Departments, Chemical Engineering and Technology.
KTH, Superseded Departments, Chemical Engineering and Technology.
2003 (English)In: AIChE Journal, ISSN 0001-1541, E-ISSN 1547-5905, Vol. 49, no 8, 2149-2157 p.Article in journal (Refereed) Published
Abstract [en]

A reactor concept was studied to reduce the fuel NOx at conditions relevant to catalytic combustion of gasified biomass containing ammonia. A hybrid reactor is modeled with passive and active channels, where only part of the fuel is combusted catalytically in the active channels. The completion of the reactions is carried out in the subsequent homogeneous zone. The air-fuel ratio is found to be the most important parameter for the NOx emission level. When the primary zone is operated fuel-lean, no favorable conditions are established for selective noncatalytic reduction reactions in the homogeneous zone, and the fuel nitrogen is largely oxidized to NO. However, if the air supply to the monolith is staged rich-lean, a 95% reduction in NO is possible. The NO reduction is facilitated by the remaining fuel components, CO and H-2.

Place, publisher, year, edition, pages
2003. Vol. 49, no 8, 2149-2157 p.
Keyword [en]
MODELS; OXIDATION; MONOLITH; BIOGAS; FLOW; NH3
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:kth:diva-12276DOI: 10.1002/aic.690490822ISI: 000184795500021OAI: oai:DiVA.org:kth-12276DiVA: diva2:307381
Note
QC 20100505Available from: 2010-04-01 Created: 2010-04-01 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Wall Related Lean Premixed Combustion Modeled with Complex Chemistry
Open this publication in new window or tab >>Wall Related Lean Premixed Combustion Modeled with Complex Chemistry
2002 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Increased knowledge into the physics and chemistrycontrolling emissions from flame-surface interactions shouldhelp in the design of combustion engines featuring improvedfuel economy and reduced emissions.

The overall aim of this work has been to obtain afundamental understanding of wall-related, premixed combustionusing numerical modeling with detailed chemical kinetics. Thiswork has utilized CHEMKIN®, one of the leading softwarepackages for modeling combustion kinetics.

The simple fuels hydrogen and methane as well as the morecomplex fuels propane and gasified biomass have been used inthe model. The main emphasis has been on lean combustion, andthe principal flow field studied is a laminar boundary layerflow in two-dimensional channels. The assumption has been madethat the wall effects may at least in principle be the same forlaminar and turbulent flames.

Different flame geometries have been investigated, includingfor example autoignition flames (Papers I and II) and premixedflame fronts propagating toward a wall (Papers III and IV).Analysis of the results has shown that the wall effects arisingdue to the surface chemistry are strongly affected by changesin flame geometry. When a wall material promoting catalyticcombustion (Pt) is used, the homogeneous reactions in theboundary layer are inhibited (Papers I, II and IV). This isexplained by a process whereby water produced by catalyticcombustion increases the rate of the third-body recombinationreaction: H+O2+M ⇔ HO2+M. In addition, the water produced at higherpressures increases the rate of the 2CH3(+M) ⇔ C2H6(+M) reaction, giving rise to increased unburnedhydrocarbon emissions (Paper IV).

The thermal coupling between the flame and the wall (theheat transfer and development of the boundary layers) issignificant in lean combustion. This leads to a sloweroxidation rate of the fuel than of the intermediatehydrocarbons (Paper III).

Finally in Paper V, a well-known problem in the combustionof gasified biomass has been addressed, being the formation offuel-NOx due to the presence of NH3 in the biogas. A hybridcatalytic gas-turbine combustor has been designed, which cansignificantly reduce fuel-NOx formation.

Keywords:wall effects, premixed flames, flamequenching, numerical modeling, CHEMKIN, boundarylayerapproximation, gasified biomass, fuel-NOx, hybrid catalytic combustor.

Place, publisher, year, edition, pages
Stockholm: Kemiteknik, 2002. 73 p.
Series
Trita-KET, ISSN 1104-3466 ; 164
Keyword
Wall effects, premixed flames, flame quenching, numerical modeling, chemkin, boundary layer approximation, gasified biomass, fuel-NOx, hybrid catalytic combustor.
National Category
Natural Sciences
Identifiers
urn:nbn:se:kth:diva-3455 (URN)91-7283-391-2 (ISBN)
Public defence
2002-12-17, 00:00 (English)
Note
QC 20100504Available from: 2002-12-11 Created: 2002-12-11 Last updated: 2010-05-04Bibliographically approved

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