Urea pyrolysis chamber and process for reducing lean-burn engine NOx emissions by selective catalytic reduction

Claim 1

A method for reducing the emissions of NO x from a lean-burn engine having associated therewith an exhaust system having an exhaust passage leading to an SCR reactor effective for selective catalytic NO x 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 NO x reduction and maintain 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; spraying an aqueous solution of urea from the injector into a pyrolysis chamber having openings therein to permit discharge of gases generated by pyrolysis of the urea and vaporization of water; maintaining the solution within the pyrolysis chamber for a time sufficient to evaporate water from the solution and pyrolyze the urea; introducing gaseous products discharged from the pyrolysis chamber into exhaust gases from the lean-burn engine; and contacting the exhaust gases containing the gaseous products discharged from the pyrolysis chamber with an SCR reactor at an exhaust gas temperature effective for selective catalytic reduction.

Claim 2

A method for reducing the emissions of NO x from a lean-burn engine having associated therewith an exhaust system having an exhaust passage leading to an SCR reactor effective for selective catalytic NO x 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 NO x reduction and maintain 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; spraying an aqueous solution of urea from the injector into a pyrolysis chamber having openings therein to permit discharge of gases generated by pyrolysis of the urea and vaporization of water; maintaining the solution within the pyrolysis chamber for a time sufficient to evaporate water from the solution and pyrolyze the urea; introducing gaseous products discharged from the pyrolysis chamber into exhaust gases from the lean-burn engine; and contacting the exhaust gases containing the gaseous products discharged from the pyrolysis chamber with an SCR reactor at an exhaust gas temperature effective for selective catalytic reduction.

Claim 12

A method for reducing the emissions of NO x from a lean-burn engine having associated therewith an exhaust system having an exhaust passage for carrying exhaust gases containing NO x to a reactor effective for selective catalytic NO x 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 NO x reduction and maintain 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; spraying the urea solution into a pyrolysis chamber to fully pyrolyze the urea prior to introducing it into the exhaust gases at an exhaust gas temperature sufficient for SCR; and passing the exhaust gas through an SCR reactor.

Claim 13

A method for reducing the emissions of NO x from a lean-burn engine having associated therewith an exhaust system having an exhaust passage for carrying exhaust gases containing NO x to a reactor effective for selective catalytic NO x 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 NO x reduction and maintain 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; spraying the urea solution into a pyrolysis chamber to fully pyrolyze the urea prior to introducing it into the exhaust gases at an exhaust gas temperature sufficient for SCR; and passing the exhaust gas through an SCR reactor.