Amminex City-SCR upgrade delivers gaseous ammonia for improved SCR conversion of NOx; avoiding high off-cycle emissions
16 May 2014
Amminex has introduced City-SCR—an aftertreatment upgrade system that replaces original equipment urea dosing systems, and instead provides gaseous ammonia for existing SCR systems in heavy-duty vehicles. The Amminex Ammonia Storage and Delivery System, in combination with the SCR-catalyst, delivers significant reductions in emissions under all real-life driving conditions.
Studies have found that despite meeting more stringent regulatory standards for exhaust emissions during type approval, many vehicles equipped with selective catalytic reduction (SCR) systems have significantly elevated emissions of NOxduring in-use driving—particularly when operating in urban traffic.
The technical reason for these high “off-cycle” NOx emissions is poor NOx conversion efficiency of installed SCR systems when exhaust temperature is low. Urea-driven SCR system use exhaust heat to convert the urea solution to ammonia, which then reduces the NOx.
SCR effectiveness is also temperature-dependent: Below some threshold for exhaust temperature, the injected urea cannot be converted to ammonia. At low exhaust temperatures, catalyst activity also falls off sharply. The exact temperature threshold at which SCR conversion effectiveness diminishes varies with system design; for most European trucks and buses equipped with SCR, catalyst activity falls off sharply below approximately 280°C, and urea cannot be injected below approximately 200°C because it will not convert to ammonia.—Lowell and Kamakaté
With its direct supply of gaseous ammonia, City-SCR reduces the magnitude of the problem of low-temperature SCR performance. Tests of the City-SCR technology in buses in Copenhagen have shown an improvement on the order of 300 kg NOxper year.
|The green diamonds show the improved performance with the City-SCR technology. Source: Amminex. Click to enlarge.|
The ammonia gas is stored in solid AdAmmine material, packaged in cartridges, and is released upon heating using electric energy and/or the engine coolant. A block of AdAmmine holds ~450g ammonia per liter solid for use in the NOx conversion.
Only the additive needs to be changed with the upgrade—the original exhaust system and catalyst stay on the vehicle. Through a quick connector the used cartridges can easily be replaced and refilled—just like a propane bottle.
Dana Lowell and Fanta Kamakaté (2012) Urban off-cycle NOx emissions from Euro IV/V trucks and buses, ICCT White Paper Nº 18
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