To achieve the climate goal of carbon neutrality, the steel industry needs to undergo a low-carbon revolution. Hydrogen-based direct reduction is an effective way for the high-carbon-emitting steel industry to achieve a low-carbon and green transformation upgrade. By establishing mathematical models to estimate the gas utilisation ratio and energy requirement based on thermodynamic equilibrium and energy balance laws, this paper discusses the effects of key factors such as H2/CO ratio in the input gas, water–gas shift reaction and CH4 content on the gas utilisation ratio and energy requirement. The paper aims to provide theoretical guidance for formulating future strategies in hydrogen-based direct reduction processes and analyzing methods to improve the gas utilization ratio in the Midrex and Energiron processes. The results showed that both the inlet H2/CO ratio and the inlet gas temperature have a significant influence on gas utilisation ratio and energy requirement. When considering the water–gas shift reaction, as the H2/CO ratio increases, it is better to increase the top gas temperature when there is sufficient heat. Overall, based on the conclusions, a new set of process parameters was proposed, aiming to provide useful support for the development of hydrogen metallurgy in the steel industry.
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