| CPC C03B 5/237 (2013.01) [C25B 1/042 (2021.01); F27D 17/10 (2025.01); F27D 17/13 (2025.01)] | 18 Claims |

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1. A method for operating a fired furnace, comprising:
heating a fired furnace using a fuel gas stream and forming a combustion product stream,
forming a steam stream using heat from at least a part of the combustion product stream,
subjecting at least a part of the steam stream to a high temperature electrolysis to form a hydrogen-containing substance stream and an oxygen-containing substance stream, and
using at least a part of the hydrogen-containing substance stream as the fuel gas stream,
wherein formation of the steam stream comprises a plurality of heat exchange steps to which the combustion product stream or a part thereof is subjected, wherein water used to form the steam stream and/or steam used to form the steam stream is heated in the heat exchange steps, and
wherein the plurality of heat exchange steps comprises a first heat exchange step in which
(a) the combustion product stream or a portion thereof is cooled from a temperature level of 1400 to 1600° C. to a temperature level of 900 to 1100° C., and in which saturated steam used to form the steam stream is superheated from a temperature level of 100 to 120° C. to a temperature level of 700 to 900° C., or
(b) the combustion product stream or a portion thereof is cooled from a temperature level of 1400 to 1600° C. to a temperature level of 600 to 700° C., and in which water used to form the steam stream is evaporated to form saturated steam.
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