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

1. 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.

2. The gas combustion treatment device according to claim 1 , wherein the hydrogen sulfide-containing gas is introduced with air into the second combustion unit to be burned and reduced.

3. The gas combustion treatment device according to claim 1 , wherein the air ratio in the second combustion unit is higher than the air ratio in the first combustion unit.

4. The gas combustion treatment device according to claim 1 , wherein a plurality of fuel introduction units configured to introduce the fuel into the first combustion unit is provided.

5. A gas combustion treatment method for subjecting an ammonia-containing gas, a hydrogen cyanide-containing gas, and a hydrogen sulfide-containing gas to combustion treatment comprising:

a first combustion step of introducing fuel, the ammonia-containing gas, the hydrogen cyanide-containing gas, and air for burning and reducing 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 step, performed downstream of the first combustion step, for burning and reducing, in a reducing atmosphere, nitrogen oxide in a first combustion gas sent from the first combustion step; and

a third combustion step, performed downstream of the second combustion step, for introducing the hydrogen sulfide-containing gas with air in addition to a second combustion gas sent from the second combustion step, and for burning the gases.

6. The gas combustion treatment method according to claim 5 , wherein at the second combustion step, the hydrogen sulfide-containing gas is introduced with air to be burned and reduced.

7. The gas combustion treatment method according to claim 5 , wherein the air ratio at the second combustion step is higher than the air ratio at the first combustion step.

8. A gas purification system comprising:

a gasification power plant including a gasification furnace configured to produce a product gas from fuel and an oxidizing agent;

a carbonyl sulfide (COS) conversion unit configured to convert COS in the product gas produced in the gasification furnace into hydrogen sulfide;

a water-washing unit provided downstream of the COS conversion unit and configured to wash the product gas;

a hydrogen sulfide removal column provided downstream of the water-washing unit and configured to remove hydrogen sulfide in the product gas;

an ammonia removal unit configured to remove ammonia in waste water sent from the water-washing unit;

a waste-water treatment unit configured to treat the waste water from which ammonia has been removed; and

the gas combustion treatment device according to claim 1 configured to subject a gas containing hydrogen sulfide from the hydrogen sulfide removal column, a gas containing ammonia from the ammonia removal unit, and a gas containing hydrogen cyanide from the waste-water treatment unit to combustion treatment.