SYSTEM AND METHOD OF DEFULFURIZING LEAN NOx TRAP

A method of desulfurizing a lean NOx trap (LNT) which absorbs or releases/reduces nitrogen oxide contained in exhaust gas according to air/fuel ratio, wherein the LNT is provided in an apparatus of purifying the exhaust gas, and the apparatus of purifying exhaust gas further comprises a particulate filter trapping particulate matter contained in the exhaust gas, the method comprises:

• regenerating the particulate filter;
• determining whether a soot regeneration amount of the particulate filter is greater than or equal to a predetermined regeneration amount;
• performing desulfurization of the LNT when the soot regeneration amount of the particulate filter is greater than or equal to the predetermined regeneration amount;
• determining whether a desulfurization stop condition of the LNT is satisfied;
• stopping the desulfurization of the LNT when the desulfurization stop condition of the LNT is satisfied;
• determining whether desulfurization stop numbers from previous completion of the desulfurization up to the present are greater than or equal to a predetermined value;
• determining whether a sulfur poisoning amount is less than a predetermined sulfur poisoning amount when the desulfurization stop numbers are greater than or equal to the predetermined value;
• and
• preparing to regenerate the particulate filter again when the sulfur poisoning amount is less than the predetermined sulfur poisoning amount.