Discharge valve and associated device

The invention provides a highly practical on-site regeneration method for a denitrification catalyst for exhaust gas purification systems that use denitrification catalysts meant for low temperature ranges in which the temperature of the exhaust gas from a diesel engine of a ship or the like is 200 to 400 DEG C and add reducing agents such as alcohol, said on-site regeneration method being such that denitrification catalyst performance is restored by suitable heat treatment that is achieved by the reducing agent, air, and a dedicated reducing agent oxidization catalytic layer and does not necessitate usage of conventional special heating devices or fuels, thereby allowing for on-site regeneration of the denitrification catalyst. A reducing agent oxidization catalytic layer (2) is installed in an exhaust gas purification system provided with a denitrification catalytic layer (1), a reducing agent and air are supplied to the reducing agent oxidization catalytic layer (2) when regenerating the catalyst in the denitrification catalytic layer (1) so that a high temperature oxidation reaction gas is produced by the reaction heat generated by the oxidation reaction of the reducing agent and air in the reducing agent oxidization catalytic layer (2), and the high-temperature oxidation reaction gas is introduced into the denitrification catalytic layer (1) to heat the denitrification catalyst and restore the denitrification performance of the catalyst.