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Lab Study of Urea Deposit Formation and Chemical Transformation Process of Diesel Aftertreatment System
ISSN: 0148-7191, e-ISSN: 2688-3627
Published March 28, 2017 by SAE International in United States
This content contains downloadable datasetsAnnotation ability available
Diesel exhaust fluid, DEF, (32.5 wt.% urea aqueous solution) is widely used as the NH3 source for selective catalytic reduction (SCR) of NOx in diesel aftertreatment systems. The transformation of sprayed liquid phase DEF droplets to gas phase NH3 is a complex physical and chemical process. Briefly, it experiences water vaporization, urea thermolysis/decomposition and hydrolysis. Depending on the DEF doser, decomposition reaction tube (DRT) design and operating conditions, incomplete decomposition of injected urea could lead to solid urea deposit formation in the diesel aftertreatment system. The formed deposits could lead to engine back pressure increase and DeNOx performance deterioration etc. The formed urea deposits could be further transformed to chemically more stable substances upon exposure to hot exhaust gas, therefore it is critical to understand this transformation process. In this work, lab experiments were designed to simulate urea deposit formation process by treatment of pure urea at 100-250 °C for various durations up to 100 h. The effect of water vapor was also investigated. The lab formed urea deposits were subsequently characterized by thermogravimetric analysis (TGA) and then compared to the TGA curves of pure reference chemicals of urea, biuret, cyanuric acid (CYA) and ammelide. The TGA results indicate that 1) below urea melting temperature (130 °C), the formed urea deposits are still primarily urea; 2) in the temperature range 130-190 °C, urea transforms to a combination of urea, biuret and CYA; 3) above biuret melting temperature (190 °C), CYA is primarily formed with some features of ammelide. Above 200 °C exposure, urea experiences fast chemical transformation via urea decomposition, biuret formation followed by subsequent biuret decomposition, and turns into CYA in a short time. A model was also built and validated to estimate the main chemical composition of urea deposit.
CitationZhang, H., Xi, Y., Su, C., and Liu, Z., "Lab Study of Urea Deposit Formation and Chemical Transformation Process of Diesel Aftertreatment System," SAE Technical Paper 2017-01-0915, 2017, https://doi.org/10.4271/2017-01-0915.
Data Sets - Support Documents
|[Unnamed Dataset 1]|
|[Unnamed Dataset 2]|
- Koebel M., Elsener M., Kleemann M., “Urea-SCR: a promising technique to reduce NOx emissions from automotive diesel engines,” Catal. Today, 59, 335-345, 2000, doi:10.1016/S0920-5861(00)00299-6.
- Schaber, P. M., Colson, J., Higgins, S., Thielen, D., et al., “Thermal decomposition (pyrolysis) of urea in an open reaction vessel,” Thermochim. Acta, 424, 131-142, 2004, doi:10.1016/j.tca.2004.05.018.
- Brack, W., Heine, B., Birkhold, F., Kruse, M., et al., “Kinetic modeling of urea decomposition based on systematic thermogravimetric analyses of urea and its most important by-products,” Chemical Engineering Science, 106, 1-8, 2014, doi:10.1016/j.ces.2013.11.013.
- Zheng, G., Fila, A., Kotrba, A., and Floyd, R., "Investigation of Urea Deposits in Urea SCR Systems for Medium and Heavy Duty Trucks," SAE Technical Paper 2010-01-1941, 2010, doi:10.4271/2010-01-1941.
- Strots, V., Santhanam, S., Adelman, B., Griffin, G. et al., "Deposit Formation in Urea-SCR Systems," SAE Int. J. Fuels Lubr. 2(2):283-289, 2010, doi:10.4271/2009-01-2780.
- Dong, H., Shuai, S., and Wang, J., "Effect of Urea Thermal Decomposition on Diesel NOx-SCR Aftertreatment Systems," SAE Technical Paper 2008-01-1544, 2008, doi:10.4271/2008-01-1544.
- Munnannur, A. and Liu, Z., "Development and Validation of a Predictive Model for DEF Injection and Urea Decomposition in Mobile SCR DeNOx Systems," SAE Technical Paper 2010-01-0889, 2010, doi:10.4271/2010-01-0889.
- Way, P., Viswanathan, K., Preethi, P., Gilb, A. et al., "SCR Performance Optimization Through Advancements in Aftertreatment Packaging," SAE Technical Paper 2009-01-0633, 2009, doi:10.4271/2009-01-0633.
- Zheng, G., Palmer, G., Salanta, G., and Kotrba, A., "Mixer Development for Urea SCR Applications," SAE Technical Paper 2009-01-2879, 2009, doi:10.4271/2009-01-2879.
- Eakle, S., Kroll, S., Yau, A., Gomez, J. et al., "Investigation of Urea Derived Deposits Composition in SCR Systems and Their Potential Effect on Overall PM Emissions," SAE Technical Paper 2016-01-0989, 2016, doi:10.4271/2016-01-0989.
- Eakle, S., Kroll, S., and Henry, C., "Investigation of Urea Derived Deposits Composition in SCR Systems," SAE Technical Paper 2016-01-2327, 2016, doi:10.4271/2016-01-2327.
- Munnannur, A., Chiruta, M., and Liu, Z., "Thermal and Fluid Dynamic Considerations in Aftertreatment System Design for SCR Solid Deposit Mitigation," SAE Technical Paper 2012-01-1287, 2012, doi:10.4271/2012-01-1287.
- Yim S.D., Kim S.J., Baik J.H., Nam I.-S., “Decomposition of urea into NH3 for the SCR process,” Ind. Eng. Chem. Res., 43, 4856-4863, 2004, doi: 10.1021/ie034052j.
- Koebel M., Elsener M., “Determination of urea and its thermal decomposition products by high-performance liquid chromatography,” J. Chromatogr. A, 689, 164-169, 1995.
- Stradella L., Argentero M., “A study of the thermal decomposition of urea, of related compounds and thiourea using DSC and TG-EGA,” Thermochim. Acta, 219, 315-323, 1993, doi:10.1016/0040-6031(93)80508-8.
- Tang, T., Zhang, J., Shuai, S., and Cao, D., "Urea Decomposition at Low Temperature in SCR Systems for Diesel Engines," SAE Technical Paper 2014-01-2808, 2014, doi:10.4271/2014-01-2808.
- Weeks, C., Ibeling, D., Han, S., Ludwig, L. et al., "Analytical Investigation of Urea Deposits in SCR System," SAE Int. J. Engines 8(3):1219-1239, 2015, doi:10.4271/2015-01-1037.
- Fang H.L., DaCosta H.F.M., “Urea thermolysis and NOx reduction with and without SCR catalysts,” Applied Catalysis B: Environmental, 46, 17-34, 2003.
- Eichelbaum M., Farrauto R.J., Castaldi M.J., “The impact of urea on the performance of metal exchanged zeolites for the selective catalytic reduction of NOx: Part I. Pyrolysis and hydrolysis of urea over zeolite catalysts,” Appl. Catal. B 97, 90-97, 2010.
- Ebrahimian V., Nicole A., Habchi C., “Detailed Modeling of the Evaporation and Thermal Decomposition of Urea-Water Solution in SCR Systems”, AIChE J. 58(7), 1998-2009.
- Seifer G.B., “Cyanuric Acid and Cyanurates”, Russian Journal of Coordination Chemistry, 28(5), 301-324, 2002.
- Santa Cruz Biotechnology. https://www.scbt.com/scbt/home
- ChemIDplus. https://chem.nlm.nih.gov/chemidplus/