Reducing NO.sub.x emissions from an engine by temperature-controlled urea injection for selective catalytic reduction
First Claim
1. A method for reducing the emissions of NOx from a lean-burn engine having associated therewith an exhaust system having an exhaust passage for carrying exhaust gases containing NOx to a reactor effective for selective catalytic NOx reduction, comprising:
- feeding an aqueous urea solution from a storage vessel through a line to an injector;
returning urea solution from the injector to the storage vessel, the rates of feed and return being sufficient to supply urea as needed to the exhaust gases for NOx reduction and maintain the temperature of the urea solution sufficiently low that it is not permitted sufficient time to hydrolyze the urea to such an extent that solids precipitate prior to injection of the urea solution into the exhaust gases;
injecting urea solution into the exhaust gases at an exhaust gas temperature sufficient for SCR; and
passing the exhaust gas through an SCR reactor.
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Accused Products
Abstract
A safe, reliable SCR system for reducing NOx emissions from a lean-burn internal combustion engine utilizes urea in aqueous solution. Overheating and hydrolysis of the solution are prevented by maintaining the temperature of the urea solution sufficiently low that it is not permitted sufficient time at elevated temperature to hydrolyze the urea to such an extent that solids precipitate. In a preferred embodiment, an injector system similar to those used for fuel injection provides a constant feed to injectors and a return line. The feed and injection can be controlled to provide sufficient urea for NOx reduction and sufficient cooling capacity for the feed and injection system to avoid hydrolysis and deposits of hydrolysis products.
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Citations
10 Claims
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1. A method for reducing the emissions of NOx from a lean-burn engine having associated therewith an exhaust system having an exhaust passage for carrying exhaust gases containing NOx to a reactor effective for selective catalytic NOx reduction, comprising:
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feeding an aqueous urea solution from a storage vessel through a line to an injector; returning urea solution from the injector to the storage vessel, the rates of feed and return being sufficient to supply urea as needed to the exhaust gases for NOx reduction and maintain the temperature of the urea solution sufficiently low that it is not permitted sufficient time to hydrolyze the urea to such an extent that solids precipitate prior to injection of the urea solution into the exhaust gases; injecting urea solution into the exhaust gases at an exhaust gas temperature sufficient for SCR; and passing the exhaust gas through an SCR reactor. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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Specification