Ensuring Quality Of Aqueous Urea For SCR Systems
BY STAN SMITH AND JIM KLIPPEL A s of Jan. 1, 2010, selective catalytic reduction (SCR) will become the method by which the majority of heavy-duty truck manufacturers will meet the EPA NOx reduction standards that take effect on that date. Europe is already using SCR technology to reduce NOx emis- sions in over-the-road diesel vehicles, and the technology dates back to the 1950s, when it was developed to con- trol emissions from coal burning plants, boilers for marine and utility applications and larger stationary diesel equipment. SCR uses ammonia to convert NOx
26 DIESEL PROGRESS NORTH AMERICAN EDI TION February 2010
compounds in exhaust gases into ni- trogen and water. In the case of aftertreatment technology on diesel vehicles, the source of the ammonia is an aqueous urea solution. The aqueous urea solution is known in Europe as AdBlue and is commonly referred to in the U.S. as diesel ex- haust fluid (DEF). DEF, in the form of a fine mist, is injected into the hot exhaust gas flow before passing through the front portion of the SCR unit, where it forms ammo- nia. As the hot exhaust gas/ammonia mixture continues to pass through the SCR unit, the NOx compounds react with the ammonia to form nitrogen gas and water. The last phase of the SCR catalyst is designed to render any remaining unreacted ammonia in the exhaust stream and convert it to additional nitro- gen gas and water. Stan Smith is quality assurance manager and Jim Klippel is business manager, Western U.S. Region for ALS Staveley Services, a North American-based provider of independent oil, coolant, fuel and metalworking testing services.
The International Organization for Standardization (ISO) is working on two standards — one for the packaging, trans- portation and storage of the urea solutions used in selec- tive catalytic reduction (SCR) systems and the other for the refilling interface. Maintaining the integrity and purity of the urea-water solution is vital to proper function and longevity of SCR systems, which are being used by the majority of U.S. heavy-duty truck manu- facturers as of 2010.
Purity of both the urea and water for blending the aqueous solution is very important to achieve proper perform- ance. Dedicated transportation and storage systems are required to ensure the purity of aqueous urea solution used in SCR for vehicles. The International Organization for Stan- dardization (ISO) has established two standards specifying quality require- ments and test methods for the urea solution. ISO is also working on two additional standards, one for the pack- aging, transportation and storage of the urea solution and the other for the refill- ing interface. The first standard, ISO 22241-1, addresses the quality characteristics or purity, the chemical characteristics and the precision of the test methods used for analyzing the urea solutions. The second standard, ISO 22241-2, includes the procedures for sampling
