Urea Decomposition for Urea-SCR Applications
Doktorsavhandling, 2010

Volatile emissions produced by the combustion of fossil fuels may be converted on a catalyst to less harmful products. During lean combustion an excess of oxygen in the exhaust gases together with a catalyst effectively oxidizes carbon monoxide and hydrocarbons into carbon dioxide and water. This leaves a deficit of reductants to reduce nitrogen oxides. In order to manage the conversion of nitrogen oxides into nitrogen a commonly used technology is selective catalytic reduction (SCR). In the SCR system an extra reductant such as ammonia or hydrocarbons are added to complete the conversion of nitrogen oxides. During the last few years SCR-systems for mobile applications using urea as an onboard source of ammonia have been developed and commercialized. Commonly, a solution of urea and water (commercially known as AdBlue) is injected trough an atomizer upstream of the catalyst. However, several problems still exist with the urea-SCR system. During conversion of the urea into ammonia and isocyanic acid stable high molecular compounds that can accumulate within the exhaust gas system may form. The abundance of these by-products depend on the conditions under which the urea is injected. In order to optimize spraying conditions new models and more fundamental knowledge of the urea decomposition processes are needed. In this thesis flow reactor experiments using Differential Scanning Calorimetery (DSC), Fourier Transformed Infrared spectroscopy (FT-IR) and Mass Spectrometry (MS) have been undertaken to study the pyrolysis of urea. Results show that the conditions under which urea is pyrolyzed governs which by-products are formed. Computational Fluid Dynamics (CFD) has been used to simulate the injection and decomposition of AdBlue for a urea-SCR application. New models for the decomposition and evaporation of urea have been developed and exhibit remarkable agreement with data found in the literature. The results from the CFD simulations were found to be sensitive to which sub models that were used.

NOx

Selective Catalytic Reduction

Urea

Thermolysis

Modeling

Computational Fluid Dynamics

Sal 10:an, Kemivägen 10, Chalmers tekniska högskola
Opponent: Dr. Oliver Kröcher, General Energy Research Department, Bioenergy and Catalysis Division, Exhaust Gas Aftertreatment Group, Paul Scherrer Institut, Switzerland

Författare

Andreas Lundström

Chalmers, Kemi- och bioteknik, Kemisk reaktionsteknik

Kompetenscentrum katalys (KCK)

Choice of urea-spray models in CFD simulations of urea-SCR systems

Chemical Engineering Journal,; Vol. 150(2009)p. 69-82

Artikel i vetenskaplig tidskrift

Urea thermolysis studied under flow reactor conditions using DSC and FT-IR

Chemical Engineering Journal,; Vol. 150(2009)p. 544-550

Artikel i vetenskaplig tidskrift

Drivkrafter

Hållbar utveckling

Fundament

Grundläggande vetenskaper

Ämneskategorier

Annan kemiteknik

Annan kemi

Strömningsmekanik och akustik

Kemi

ISBN

978-91-7385-482-5

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 3163

Sal 10:an, Kemivägen 10, Chalmers tekniska högskola

Opponent: Dr. Oliver Kröcher, General Energy Research Department, Bioenergy and Catalysis Division, Exhaust Gas Aftertreatment Group, Paul Scherrer Institut, Switzerland

Mer information

Skapat

2017-10-08