LNT regeneration strategy to reduce NOx spike
View Patent ↗Systems and methods are disclosed for ameliorating NOx slip from a lean NOx trap by reducing the amount of hydrocarbons reaching the lean NOx trap during the early stages of, or in a period immediately preceding, a rich regeneration. In one embodiment, a hydrocarbon absorber is configured downstream from a fuel reformer, but upstream from the lean NOx trap, in order to reduce the quantity of hydrocarbons that reach the lean NOx trap during lean reformer warm-up and rich regeneration phases. In another embodiment, the fueling rate to a fuel reformer configured in an exhaust line upstream from the lean NOx trap is limited to reduce NOx slip.
1. A method of operating a power generation system, comprising:
operating a diesel engine to produce exhaust comprising NO x ;
passing at least a portion of the exhaust from the engine to a lean NO x trap through a fuel reformer;
adsorbing NO x from the exhaust under lean conditions using the lean NO x trap;
preparing to regenerate the lean NO x trap by heating the fuel reformer by at least 100° C. to a temperature of at least about 500° C. by injecting fuel at rates that leave the exhaust entering the fuel reformer lean, while at times limiting the fuel injection rates to limit the amount of NO x that slips from the lean NO x trap; and
wherein limiting the fuel injection rates to limit the amount of NO x that slips from the lean NO x trap comprises either:
(a) setting the fuel injection rate to an upper limit determined by a relationship between fuel injection rate and hydrocarbon slip from the fuel reformer or NO x slip from the lean NO x trap; or
(b) adjusting the fuel injection rate based on measurements of hydrocarbon slip from the fuel reformer or NO x slip from the lean NO x trap.
2. The method of claim 1 , wherein so limiting the fuel injection rate limits the reformer heating rate to about 50° C. per second or less.
3. The method of claim 1 , wherein so limiting the fuel injection rate limits the reformer heating rate to about 20° C. per second or less.
4. The method of claim 1 , wherein so limiting the fuel injection rates comprises setting the fuel injection rate to an upper limit determined by a relationship between fuel injection rate and hydrocarbon slip from the fuel reformer or NO x slip from the lean NO x trap.
5. The method of claim 1 ,wherein so limiting the fuel injection rates comprises adjusting the fuel injection rate based on measurements of hydrocarbon slip from the fuel reformer or NO x slip from the lean NO x trap.
6. The method of claim 1 , wherein the fuel injection rate limits increase based on increasing lean NO x trap temperature.
7. The method of claim 1 , further comprising, while heating the fuel reformer, adsorbing hydrocarbons slipping from the fuel reformer using a hydrocarbon absorber positioned upstream from the lean NO x trap.
8. The method of claim 1 , further comprising passing the exhaust from the lean NO x trap to a ammonia-selective catalytic reduction catalyst.
9. A method of operating a power generation system, comprising:
operating a diesel engine to produce exhaust comprising NO x ;
passing at least a portion of the exhaust from the engine to a lean NO x trap through a fuel reformer;
using the lean NO x trap, adsorbing NOx from the exhaust under lean conditions; and
injecting fuel at rates that leave the exhaust entering the fuel reformer rich, whereby the fuel reformer produces syn gas that regenerates the lean NO x trap, wherein the fuel injection rates are at times limited to limit the amount of NO x that slips from the lean NO x trap;
wherein limiting the fuel injection rates to limit the amount of NO x that slips from the lean NO x trap comprises either:
(a) setting the fuel injection rate to an upper limit determined by a relationship between fuel injection rate and hydrocarbon slip from the fuel reformer or NO x slip from the lean NO x trap; or
(b) adjusting the fuel injection rate based on measurements of hydrocarbon slip from the fuel reformer or NO x slip from the lean NO x trap.
10. The method of claim 9 , further comprising preparing to regenerate the lean NOx trap by heating the fuel reformer by at least 100° C. to a temperature of at least about 500° C. by injecting fuel at rates that leave the exhaust entering the fuel reformer lean.
11. The method of claim 9 , wherein so limiting the fuel injection rates comprises setting the fuel injection rate to an upper limit determined by a relationship between fuel injection rate and hydrocarbon slip from the fuel reformer or NO x slip from the lean NO x trap.
12. The method of claim 9 , wherein so limiting the fuel injection rates comprises adjusting the fuel injection rate based on measurements of hydrocarbon slip from the fuel reformer or NO x slip from the lean NO x trap.
13. The method of claim 9 , wherein the fuel injection rate limits increase based on increasing lean NO x trap temperature.
14. The method of claim 9 , further comprising, while regenerating the lean NOx trap, adsorbing hydrocarbons slipping from the fuel reformer using a hydrocarbon absorber positioned upstream from the lean NO x trap.
15. The method of claim 9 , further comprising passing the exhaust from the lean NOx trap to a ammonia-selective catalytic reduction catalyst.