Methods and systems for producing steel or similar molten-iron-containing materials in melting or smelting furnaces utilizing pre-reduced iron ore, known also as direct reduced iron (DRI) or sponge iron, wherein the emission of CO.sub.2 and other greenhouse gases is significantly low. Such methods and systems are based on producing DRI in a direct reduction furnace with a reducing gas comprising hydrogen; melting at least a portion of the DRI in a melting furnace in order to generate hot gases; producing steam and/or hot water using the heat contained in the hot gases. From the steam and/or hot water hydrogen is produced by electrolysis, at least a portion of which is fed to the direct reduction furnace as a component of the reducing gas to produce the DRI.

A system for reducing ore includes a hydrogen supply unit configured to supply hydrogen, a furnace configured to reduce the ore using the supplied hydrogen, and a hydrogen recovery unit configured to recover hydrogen from an exhaust gas that is exhausted from the furnace.

A plant complex for producing steel, having a blast furnace for producing pig iron; a converter steel works for producing crude steel; a gas pipeline system for gases that occur in the production of pig iron and/or the production of crude steel; a chemical plant and/or a biotechnology plant which are/is connected to the gas pipeline system, wherein the plant complex additionally includes a biogas plant which is connected to the gas pipeline system.

A system for reducing ore includes a hydrogen supply unit configured to supply hydrogen, a furnace configured to reduce the ore using the supplied hydrogen, and a hydrogen recovery unit configured to recover hydrogen from an exhaust gas that is exhausted from the furnace.

A system for reducing ore includes a hydrogen supply unit configured to supply hydrogen, a furnace configured to reduce the ore using the supplied hydrogen, and a hydrogen recovery unit configured to recover hydrogen from an exhaust gas that is exhausted from the furnace.

A method for producing direct reduction iron includes reducing an iron oxide raw material by a reducing gas containing hydrogen gas to generate direct reduction iron; removing water from an exhaust gas in the reducing and thus hydrogen gas is separated from the exhaust gas; carbonizing and cooling the direct reduction iron using a cooling gas containing carbon as an element, and separating hydrogen gas and methane gas from an exhaust gas in the carbonizing and cooling, wherein the cooling gas is methane gas, wherein the reducing gas further contains the hydrogen gas separated in the removing and the hydrogen gas separated in the separating, and wherein the cooling gas further contains the methane gas separated in the separating.