Method for operating an emission control system having nitrogen oxide storage

A method for operating an emission control system having a nitrogen oxide storage for cleaning a nitrogen oxide-containing, sulfur-contaminated exhaust gas of a combustion device, comprising the steps of:

• performing desulfating phases time to time to release sulfur intercalated in the nitrogen oxide storage, the desulfating phases including a main desulfating mode for substantially completely the nitrogen oxide storage and a partial desulfating mode for partially desulfating the nitrogen oxide storage, the partial desulfating phase having a predefined lower nitrogen oxide storage minimum temperature and a predefined shorter desulfating target duration than the main desulfating phase;
• monitoring a nitrogen oxide storage capability of the nitrogen oxide storage and a quantity of sulfur brought into the nitrogen oxide storage since a last main desulfating phase;
• determining a necessity for a main desulfating phase when one of the nitrogen oxide storage capability has decreased by a predefinable amount and the quantity of sulfur brought into the nitrogen oxide storage exceeds a predefinable main desulfating threshold value;
• monitoring a quantity of sulfur brought into the nitrogen oxide storage since a last partial desulfating phase;
• and
• determining a necessity for a partial desulfating phase when the quantity of sulfur brought into the nitrogen oxide storage exceeds a predefinable partial desulfating threshold value, the predefinable partial desulfating threshold value being lower than the predefinable main desulfating threshold value.

A method for operating an emission control system having a nitrogen oxide storage for cleaning a nitrogen oxide-containing, sulfur-contaminated exhaust gas of a combustion device, comprising the steps of:

• performing desulfating phases time to time to release sulfur intercalated in the nitrogen oxide storage, the desulfating phases including a main desulfating mode for substantially completely desulfating the nitrogen oxide storage and a partial desulfating mode for partially desulfating the nitrogen oxide storage, the partial desulfating phase having a predefined lower nitrogen oxide storage minimum temperature and a predefined shorter desulfating target duration than the main desulfating phase;
• monitoring a nitrogen oxide storage capability of the nitrogen oxide storage and a quantity of sulfur brought into the nitrogen oxide storage since a last main desulfating phase;
• determining a necessity for a main desulfating phase when one of the nitrogen oxide storage capability has decreased by a predefinable amount and the quantity of sulfur brought into the nitrogen oxide storage exceeds a predefinable main desulfating threshold value;
• and
• making a transition from the partial desulfating phase to the main desulfating phase, without a determined necessity for the transition, when the nitrogen oxide storage temperature has reached the main desulfating minimum temperature during the partial desulfating phase and in accordance with an operational state of the combustion device and when the sulfur quantity brought into the nitrogen oxide storage since the last main desulfating phase exceeds a predefinable threshold value, which is smaller than the main desulfating threshold value.