Denitrification catalyst regeneration method

1. A denitrification catalyst regeneration method, comprising:

denitrifying exhaust gas produced by the combustion of ultraheavy oil with the sulfur content of 1% or higher by a denitrification catalyst;

then applying heat-treatment to the used denitrification catalyst to transform substantially all vanadium oxysulfate deposited on the denitrification catalyst into vanadium pentoxide;

then cleaning said denitrification catalyst with an aqueous solution of oxalic acid; and

then finish washing said denitrification catalyst with water to regenerate said denitrification catalyst.

2. The denitrification catalyst regeneration method according to claim 1 , further comprising:

performing said heat-treatment;

then roughly washing said denitrification catalyst with water; and

then cleaning said denitrification catalyst with an aqueous solution of oxalic acid.

3. The denitrification catalyst regeneration method according to claim 1 , wherein an oxalic acid concentration of said aqueous solution of oxalic acid is 4 to 25% by weight.

4. The denitrification catalyst regeneration method according to claim 2 , wherein an oxalic acid concentration of said aqueous solution of oxalic acid is 0.5 to 25% by weight.

5. The denitrification catalyst regeneration method according to claim 1 , wherein a temperature of said heat-treatment is 450 to 600° C.