Eaton Hybrid LNT/SCR System for 2010 NOx Emissions Requirements
22 August 2006
Eaton Corporation is developing an aftertreatment system that combines a fuel reformer catalyst with doser, Selective Catalytic Reduction system (SCR) and Lean NOx Trap (LNT) technology to create an exhaust aftertreatment system capable of meeting 2010 EPA diesel emissions requirements without the need for a urea storage and injection system.
The fuel reformer generates a mixture of reformate gases (H2 and CO) to improve LNT regeneration efficiency. During lean exhaust conditions, the LNT stores NOx. During rich exhaust conditions (LNT regeneration), the LNT converts stored NOx to nitrogen and produces ammonia.
This ammonia is stored by the downstream SCR catalyst and is used to convert remaining NOx that slips past the LNT. NOx reduction thus takes place in two stages: first by the LNT and second by the SCR catalyst, supported by ammonia from the LNT system.
The SCR NOx reduction compensates for the loss in LNT performance over time due to fuel sulfur poisoning. Less frequent desulfation is required compared to an LNT-only system, according to Haoran Hu, who presented the system at DEER 2006.
Because the system does not require a urea storage and injection subsystem, it is also more space-efficient, according to Hu.
Essentially, Eaton has taken two NOx-reducing technologies, packaged them in a system that allows them to work together, and taken advantage of a naturally occurring chemical reaction to eliminate a major cost and logistics hurdle that exists for urea-based systems.—Vishal Singh, Eaton marketing and business development manager for new technologies
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