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;
• and
• a gas-conducting system for gases that occur in at least one of the production of pig iron and crude steel;
• wherein:
• the plant complex additionally comprises:
• a biotechnological plant connected to the gas-conducting system;
• chemical or electrochemical energy storage for storing electricity, wherein the stored electricity covers at least part of the electricity demand of the plant complex;
• a power-generating plant operably connected to the gas-conducting system;
• and
• an electrolysis plant for the electrolysis of water, the electrolysis plant:
• being connected to the biotechnological plant by a hydrogen line;
• and
• being connected to at least one of the blast furnace and the converter steel mill for producing crude steel and treating crude steel by means of an oxygen return device;
• wherein:
• the biotechnological plant produces alcohol, acetone, or organic acids by a fermentation of a syngas;
• the syngas consists of a hydrogen gas produced by the electrolysis plant, a blast furnace gas from the blast furnace, a converter gas from the converter steel mill, and a coke oven gas;
• the biotechnological plant is arranged in parallel with the power-generating plant with respect to the syngas;
• and
• for the purpose of supplying electricity to the electrolysis plant, the energy storage is electrically connected thereto.