Physical based LNT regeneration strategy
View Patent ↗A lean NO X trap is a diesel exhaust aftertreatment system is selectively denitrated in a manner that addresses unreliability of NOX sensor data. According to one concept, data from a NO X is ignored or given decreased weight in a period immediately following a denitration. According to another concept, denitration is made contingent on both a first and a second criteria being met. The first criteria relates to the amount of NO X stored in the LNT or remaining NO X storage capacity of the LNT. The second criteria relates to the current performance of the exhaust treatment system, or a portion thereof, as determined from one or more measurements of NO X concentration in the exhaust. This reduces premature denitrations and associated unnecessary fuel expenditures resulting from inaccurate NO X concentration data and transient events.
1. A method of operating a power generation system, comprising:
operating a diesel engine to produce a lean exhaust comprising NO X ;
passing the lean exhaust through an exhaust aftertreatment system comprising a lean NO X trap;
operating the exhaust aftertreatment system in lean phases during which the lean NO X trap adsorbs a portion of the NO X from the exhaust; and
selectively denitrating the lean NO X trap in rich phases based on both a first and a second criteria being met;
wherein the first criteria is a threshold amount of NO X stored in the NO X trap, a threshold saturation of the NO X trap, or remaining a threshold NO X storage capacity remaining in the NO X trap;
the second criteria is one or more measurements of NO X concentration in the exhaust showing that the lean NO X trap, or the lean NO X trap in combination with one or more other devices, has reached a threshold level for NO X removal efficiency or effectiveness at limiting NO X emissions;
during the lean phase if only one criteria is met, the other criteria is recursively examined and the lean phase continued at least until the other criteria is also met; and
the rich phases comprise providing an overall rich exhaust-reductant mixture to the lean NO X trap, whereby the lean NO X trap releases and reduces stored NO X .
2. The method of claim 1 , wherein the second criteria relates to current performance of the lean NO X trap normalized for one or more of exhaust flow rate and a temperature of the lean NO X trap.
3. The method of claim 1 , wherein the second criteria relates to whether a concentration of NO X in the exhaust downstream from the lean NOx trap exceeds a critical value.
4. The method of claim 1 , wherein the second criteria relates to the combined performance of the lean NO X trap and an ammonia-SCR catalyst configured downstream from the lean NO X trap.
5. The method of claim 4 , wherein the combined performance is determined using a NO X sensor positioned downstream from the ammonia-SCR catalyst.
6. The method of claim 1 , wherein the amount of NO X stored in the NO X trap or remaining NO X storage capacity of the lean NO X trap is estimated by integrating an estimate for the flow rate of NO X into the lean NO X trap multiplied by an estimate for the efficiency with which the lean NO X trap adsorbs NO X from the exhaust.
7. The method of claim 1 , denitrating the lean NO X trap comprises reducing a NO X loading of the lean NO X trap to a target loading level that depends on the amount of NO X stored in the NO X trap or remaining NO X storage capacity of the NO X trap at the time regeneration was begun.