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Mixing It Up For SCR

Online wire mesh mixer targets urea SCR applications; designed for higher gas flow uniformity; shorter mixing distance

ACS Industries has introduced a new online wire mesh mixer for use with urea SCR aftertreatment systems. The construction of the wiremesh allows for a more uniform flow pattern, which is designed to be more beneficial in reducing NO
x .

BYDAWN M. GESKE

Online wire mesh mixer - 50188 A

s the on-highway vehicle in-dustry begins looking ahead to the 2010 exhaust emis-sions standards, many engine and exhaust system manufacturers are looking at urea-injected selective cat- alytic reduction (SCR) as a viable option to meet Tier 4 NO along with Lean NO
x traps and retro-fit systems. Using it in an SCR sys- tem, said Sivanandi Rajadurai, ACS vice president of engineering, ex- haust products, provides a more uni- form distribution of urea. “The flow uniformity is maintained because of the wire mesh. “If you look at regular flow, it isgoing in a longitudinal way, but with the wire mesh you have longitudinal and radial. The gas can go any- where. It has a larger spread and a torturous path because the gas mol- ecules go around and around in a zigzag pattern.”In a conventional urea SCR system,urea solution is injected through the exhaust pipe and into the catalyst. “A gas molecule going into a substrate channel can only go straight and is not able to redistribute,” said Rajadurai. “The molecules are in the center only. They cannot go anywhere else.”The construction of the mire mesh allows the gas molecules to gothroughout the body of the sub- strate, said Rajadurai. “When they get in here (the wire mesh mixer) they can go any way because the wire mesh is like a sponge. It pro- vides a lot of contact time, lots of distribution and the efficiency of the flow is better.”The optimized flow-through of themixer also allows the thermal load to remain uniform throughout the body of the mixer, as no heat degradation occurs as exhaust passes through the mixer. This, ACS said, prevents urea crystallization and allows instal- lation at the cone of the catalyst. Because the exhaust temperature is not reduced, a shorter mixing dis- tance is achievable with the wire mesh mixer.“Knitted wire mesh mixer has effi-cient mixing properties with low back- pressure,” said Rajadurai. “Its flexible construction gives it optimal flow dis-
x regulations.With the European market readily adopting this technology, and Mack and Volvo announcing SCR as its strat- egy going forward in North America, a number of manufacturers are develop- ing SCR-compatible products. Among these is ACS IndustriesInc., Lincoln, R.I., which is capitaliz- ing on its wire mesh portfolio by offer- ing a noncatalyzed online knitted wire mesh mixer specifically aimed at SCR systems.While the wire mesh mixer is target-ed toward dosing applications such as SCR aftertreatment systems that use urea to reduce NO
x , it can alsobe applied in fuel reformers used
DIESEL PROGRESS NORTH AMERICAN EDITION June 2007