Method for treating waste gases from plants for pig iron production

1. A method for treating waste gases from plants for pig iron production, comprising:

receiving waste gas of a pig iron production plant;

separating the waste gas into a first sub-stream of the waste gas and a second sub-stream of the waste gas;

adding water and/or water vapor to the first sub-stream of the waste gas;

following the addition of water and/or water vapor, subjecting the first sub-stream of the waste gas to at least partial conversion of CO into CO 2 ;

subsequently subjecting the first sub-stream of the waste gas to CO 2 capture in a first CO 2 capture system to produce a first product gas;

without subjecting the second sub-stream of the waste gas to conversion of CO into CO 2 , subjecting the second sub-stream to CO 2 capture in a second CO 2 capture system separately from the first sub-stream to produce a second product gas;

using the first and the second product gases for carburization and for regulating the carbon content in a reducing reactor of a direct reduction plant by mixing a first part of the second product gas with the first product gas to obtain a preset ratio of hydrogen to CO, and feeding the mixed first and second product gases to the reducing reactor of the direct reduction plant; and

feeding a second part of the second product gas to the reducing reactor independently of the first part of the second product gas.

2. The method as claimed in claim 1 , wherein a tail gas following the CO 2 capture in the second CO 2 capture system is used for combustion in the reducing gas furnace of the direct reduction plant.

3. The method as claimed in claim 2 , further comprising mixing together a tail gas following the CO 2 capture in the first CO 2 capture system and the tail gas following the CO 2 capture in the second CO 2 capture system.

4. The method as claimed in claim 1 , wherein the waste gas contains at least one of the following gases:

top gas from a blast furnace, or from a reduction shaft of a smelting-reduction plant;

waste gas from a melter gasifier of a smelting-reduction plant;

waste gas from at least one fluidized reactor;

waste gas from at least one packed bed reactor for pre-heating iron oxides or iron briquettes of a smelting-reduction plant;

waste gas from at least one packed bed reactor for reducing iron oxides or iron briquettes of a smelting-reduction plant;

waste gas from a CO 2 capture system associated with the plant for pig iron production; and

waste gas from at least one reducing reactor of a direct reduction plant.

5. The method as claimed in claim 4 , wherein the blast furnace is an oxygen blast furnace with top gas recycling.

6. The method as claimed in claim 1 , wherein the first sub-stream of the waste gas contains exclusively top gas from a reducing reactor of a direct reduction plant.

7. The method as claimed in claim 1 , further comprising using waste heat from the plant for pig iron production for producing at least part of a steam for the conversion of CO into CO 2 .

8. The method as claimed in claim 1 , further comprising using waste heat from the waste gas for producing at least part of a steam for the conversion of CO into CO 2 .

9. A method for treating waste gases from plants for pig iron production, comprising:

receiving waste gas of a pig iron production plant;

separating the waste gas into a first sub-stream of the waste gas and a second sub-stream of the waste gas;

adding water and/or water vapor to the first sub-stream of the waste gas;

following the addition of water and/or water vapor, subjecting the first sub-stream of the waste gas to at least partial conversion of CO into CO 2 ;

generating a product gas by subsequently subjecting at least one of the first sub-stream and the second sub-stream of the waste gas to CO 2 capture; and

feeding at least a part of the product gas to a reducing reactor of a direct reduction plant to regulate the carbon content in the reducing reactor.