Patent ID: 7905086

Claim:
A desulfurization control method for an exhaust gas purification system including a NOx conversion catalyst device with a NOx conversion catalyst that purifies the NOx in the exhaust gas of an engine, comprising: carrying out desulfurization control, in order to recover a deterioration from sulfur poisoning of the NOx conversion catalyst by setting an amount of fuel for raising temperature required to raise the temperature of a first detection temperature indicating the temperature of the catalyst of the NOx conversion catalyst device, to a desulfurization target temperature by using a heat quantity calculated from a first heat quantity required to raise the temperature of the NOx conversion catalyst device and a second heat quantity required to raise the temperature of the exhaust gas; and calculating the amount of fuel for raising temperature by calculating: the first heat quantity by multiplying the difference between the desulfurization target temperature and the first detection temperature by the heat capacity of the NOx conversion catalyst device; the second heat quantity by multiplying the difference between the desulfurization target temperature and the detection temperature of the exhaust gas introduced into the NOx purification device by the heat capacity of the exhaust gas; a heat quantity for raising temperature by adding together the first heat quantity, the second heat quantity and a third heat quantity released from the exhaust gas purification system; and the amount of fuel for raising temperature by dividing the heat quantity for raising temperature by the low calorific value of the fuel.