Analytical Investigation of Urea Deposits in SCR System

Weeks, Colin L.; Ibeling, Dan R.; Han, Sonia; Ludwig, Lindsey; Ayyappan, Ponnaiyan

doi:10.4271/2015-01-1037

Cited by 39 publications

(23 citation statements)

References 13 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…From the IR spectra, the chemical composition of the solid deposit elements can be revealed, which were formed at different operating temperature. The IR spectra of the primary components are presented in Figure 12 [21], used as the standard for the identification of the chemical species available in the urea deposit samples generated at different operating temperatures. The UV-visible spectra of the deposit components showed a single strong peak in the UV region, mostly for a very low wavelength.…”

Section: Characterization Of Urea Depositsmentioning

confidence: 99%

“…HNCO + H 2 O → NH 3 + CO 2 (2) The SCR solid deposit chemical composition is temperature dependent [20], and several deposit components can be produced at various decomposition temperatures [17,21]. In the first step of the urea decomposition process, the generated isocyanic acid can make a chemical reaction with the undecomposed urea, which produces biuret, triuret, and other heterocyclic compounds like ammelide, cyanuric acid, melamine, and ammeline; these contribute to the solid deposit formation depending on the decomposition temperature [17,22,23].…”

Section: Introductionmentioning

confidence: 99%

“…Moreover, deposit accumulated on the SCR catalyst can lower the catalyst activity, which seriously affects the NO x conversion rate. In order to prevent the solid deposit formation or to remove the accumulated deposits efficiently, it is important to investigate the chemical composition [20,21] and thermal decomposition behavior of the urea solid deposits [24]. Figure 1 shows the overall process (spray to solid deposit formation) in the SCR system.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

A Study on Urea-Water Solution Spray-Wall Impingement Process and Solid Deposit Formation in Urea-SCR de-NOx System

Shahariar

2018

Energies

View full text Add to dashboard Cite

Selective catalytic reduction (SCR) has been exhibited as a promising method of NOx abatement from diesel engine emissions. Long-term durability is one of the key requirements for the automotive SCR system. A high NOx conversion, droplet distribution and mixing, and fluid film and solid deposit formation are the major challenges to the successful implementation of the SCR system. The current study is therefore three-fold. Firstly, high-speed images disclose detailed information of the spray impingement on the heated impingement surface. The spray impingement investigation took place in a specially-designed optically-accessible visualization chamber where the Z-type shadowgraph technique was used to capture the high-speed images. Wall temperature has a great influence on the film formation and wall wetting. A higher wall temperature can significantly increase the droplet evaporation, and consequently, wall wetting decreases. The numerical analysis was performed based on the Eulerian-Lagrangian approach using STAR CCM+ CFD code. Secondly, the resultant phenomena due to spray-wall impingement such as fluid film generation and transport, solid deposit formation, and thermal decomposition were recorded using a high-speed camera operating at a low frame rate. Infrared thermal imaging was used to observe the spray cooling effect after impingement. Spray impingement caused local cooling, which led to wall film formation, which introduced urea crystallization. Finally, solid deposits were analyzed and characterized using Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). FTIR analysis revealed that urea decomposition products vary based on the temperature, and undecomposed urea, biuret, cyanuric acid, ammeline, and melamine can be formed at different temperatures. TGA analysis showed that accumulated deposits were hard to remove. Moreover, complete thermal decomposition of deposits is not possible at the regular exhaust temperature, as it requires a comparatively long time span.

show abstract

Section: Characterization Of Urea Depositsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

A Study on Urea-Water Solution Spray-Wall Impingement Process and Solid Deposit Formation in Urea-SCR de-NOx System

Shahariar

2018

Energies

View full text Add to dashboard Cite

show abstract

“…Because of the low diesel exhaust gas temperature and high exhaust flow velocity, it is usually difficult for the injected DEF to completely decompose to NH 3 before entering the SCR catalyst (Munnannur et al, 2012;Weeks et al, 2015). The unevaporated DEF can cause liquid-wall interaction on the exhaust wall, the exhaust mixer, and even the inlet face of SCR catalyst.…”

Section: Introductionmentioning

confidence: 99%

“…This phenomenon causes the SCR catalyst to have a high risk of being soaked by DEF, causing urea deposits and catalyst deactivation issues. Previous studies have shown that the unevaporated and undecomposed DEF has a great tendency to generate high molecular solid byproducts, such as biuret, cyanuric acid, ammelide, and ammeline (Smith et al, 2014;Weeks et al, 2015). Most of them need a higher temperature to decompose again, leaving urea deposits in the diesel exhaust system.…”

Section: Introductionmentioning

confidence: 99%

Impact of diesel emission fluid soaking on the performance of Cu-zeolite catalysts for diesel NH3-SCR systems

Yao

Wang

2016

J. Zhejiang Univ. Sci. A

View full text Add to dashboard Cite

Diesel emission fluid (DEF) soaking and urea deposits on selective catalytic reduction (SCR) catalysts are critical issues for real diesel engine NH 3 -SCR systems. To investigate the impact of DEF soaking and urea deposits on SCR catalyst performance, fresh Cu-zeolite catalyst samples were drilled from a full-size SCR catalyst. Those samples were impregnated with DEF solutions and subsequently hydrothermally treated to simulate DEF soaking and urea deposits on real SCR catalysts during diesel engine operations. Their SCR performance was then evaluated in a flow reactor with a four-step test protocol. Test results show that the DEF soaking leached some Cu from the SCR catalysts and slightly reduced their Cu loadings. The loss of Cu and associated metal sites on the catalysts weakened their catalytic oxidation abilities and caused lower NO/NH 3 oxidation and lower high-temperature N 2 O selectivity. Lower Cu loading also made the catalysts less active to the decomposition of surface ammonium nitrates and decreased low-temperature N 2 O selectivity. Cu loss during DEF impregnation released more acid sites on the surface of the catalysts and increased their acidities, and more NH 3 was able to be adsorbed and involved in SCR reactions at medium and high temperatures. Due to lower NH 3 oxidation and higher NH 3 storage, the DEF-impregnated SCR catalyst samples showed higher NO x conversion above 400 °C compared with the non-soaked one. The negative impact of urea deposits during DEF impregnation was not clearly observed, because the high-temperature hydrothermal treatment helped to remove the urea deposits.

show abstract

Effects of thermal treatments on characteristics and morphological variations in the deposits of urea-SCR systems

Natesan²,

Nayak

2021

Environ Sci Pollut Res

View full text Add to dashboard Cite

Selective catalytic reduction (SCR) systems are employed by automobile manufacturers for the abatement of environmental pollutants like oxides of nitrogen (NOx) emitted from exhaust gases of diesel engines. In SCR, the urea-water solution (UWS) is injected to exhaust gases in the form of a spray to generate the reducing agent NH3. Deposit formation at lower temperatures is a major concern with this technology. The deposits not only create backpressure but also leak NH3 to the environment as they deplete. It is very important to know the depletion characteristics of deposits formed at lower temperatures in order to assess the NH3 leakage to the environment when the engine exhaust gases attain higher temperatures. In the present work, deposits formed at a low-temperature range of 150–200°C for continuous run along with UWS injection were investigated. Additionally, they were aged at 300°C in the absence of UWS to check the variation in characteristics with the rise of temperature. By gravimetric analysis, it is inferred that the deposits formed at higher pre-age temperatures are less prone to depletion as the temperature increases. The elemental analysis using energy-dispersive X-ray spectroscopy (EDX) indicates slight variation in carbon, nitrogen and oxygen compositions for all the pre-age conditions. As an extended study, the byproducts at pre-age and post-age conditions were investigated through X-ray diffraction (XRD). The compounds like cyanuric acid (CYA) and biuret were not observed when pre-age samples were aged at 300°C. Instead, the compounds like ammelide, ammeline, triuret and melamine were observed. Scanning electron microscope (SEM) study revealed morphological changes in both pre-age and post-age samples. Further, the crystallinity variations were also observed for the changes in the heating cycles during deposit formation. The gravimetric analysis of deposits in pre-age and post-age conditions helps in predicting the amount of deposits for transient load cycles.

show abstract

Analytical Investigation of Urea Deposits in SCR System

Cited by 39 publications

References 13 publications

A Study on Urea-Water Solution Spray-Wall Impingement Process and Solid Deposit Formation in Urea-SCR de-NOx System

A Study on Urea-Water Solution Spray-Wall Impingement Process and Solid Deposit Formation in Urea-SCR de-NOx System

Impact of diesel emission fluid soaking on the performance of Cu-zeolite catalysts for diesel NH3-SCR systems

Effects of thermal treatments on characteristics and morphological variations in the deposits of urea-SCR systems

Contact Info

Product

Resources

About