Gas combustion treatment device, combustion treatment method, and gas purification system including gas combustion treatment device

A gas combustion treatment device configured to subject an ammonia-containing gas, a hydrogen cyanide-containing gas, and a hydrogen sulfide-containing gas to combustion treatment comprising:

• a first combustion unit configured to introduce therein fuel, the ammonia-containing gas, the hydrogen cyanide-containing gas, and air to burn and reduce the fuel and the gases at an air ratio lower than 1, the air ratio being a value obtained by dividing an amount of air supplied for burning the fuel by a theoretical amount of air;
• a second combustion unit provided downstream of the first combustion unit and configured to burn and reduce, in a reducing atmosphere, nitrogen oxide in a first combustion gas sent from the first combustion unit;
• and
• a third combustion unit provided downstream of the second combustion unit and configured to introduce therein the hydrogen sulfide-containing gas with air in addition to a second combustion gas sent from the second combustion unit and burn the gases.