Combined system for producing steel and method for operating the combined system

A plant complex for steel production comprising

• a blast furnace for producing pig iron;
• a converter steel mill for producing crude steel;
• a chemical plant or a biotechnological plant;
• a hydrogen-producing plant;
• a power-generating plant;
• a gas-conducting system for gases that occur in the production of pig iron and/or the production of crude steel;
• and
• a closed-loop control system;
• wherein:
• the chemical plant or biotechnological plant is connected to the gas-conducting system and the hydrogen-producing plant;
• the hydrogen-producing plant is connected to the gas-conducting system via a hydrogen-carrying line and has an electrolysis plant for the electrolysis of water;
• the power-generating plant is designed as a gas-turbine and steam-turbine power-generating plant and is operated with a gas comprising blast furnace top gas occurring in the production of pig iron in the blast furnace and converter gas that occurs in the converter steel mill;
• the chemical plant or biotechnological plant is arranged in parallel with the power-generating plant with respect to the gas supply;
• the gas-conducting system comprises a connectable gas diverter operably connected to the closed-loop control system for selectively altering a ratio of the streams of gas that are fed to the power-generating plant and the chemical plant or biotechnological plant, wherein:
• at a first electricity price, a portion of the streams of gas is diverted from the power-generating plant to the chemical plant or biotechnological plant;
• at a second electricity price, a portion of the streams of gas is diverted from the chemical plant or biotechnological plant to the power-generating plant;
• and
• the second electricity price is greater than the first electricity price;
• and
• the hydrogen-carrying line is connected to a mixing device and is arranged upstream of the chemical or biotechnological plant relative to the direction of flow, and wherein at least one of the blast furnace top gas and the converter gas is enriched with hydrogen prior to entering the mixing device.