Energy-carbon comprehensive efficiency evaluation of hydrogen metallurgy system considering low-temperature waste heat recovery

TL;DR

The paper tackles the challenge of achieving low-carbon, energy-efficient ironmaking by proposing a zero-carbon hydrogen metallurgy system that integrates low- and high-temperature waste heat recovery and uses green hydrogen as both reducing gas and heat carrier. It develops detailed energy and exergy models for system components, and defines energy efficiency ($EE$), exergy efficiency ($EX$), and energy-carbon efficiency ($CE$) to evaluate performance on a full life-cycle energy basis using electricity as the common currency. Through case studies and comparisons with traditional DRI processes using $H_2/CO=6/4$ and $8/2$, the zero-carbon design shows higher exergy and energy-carbon efficiency, with thermal energy recovered from low-temperature waste heat converted to electricity by an ORC unit demonstrating substantial energy potential (e.g., $W_{ORC+expander}^{in}=1.74\times10^{9}$ J vs $W_{top\ gas}^{heat}=1.11\times10^{9}$ J at 1000$^{\circ}$C). The work also highlights the critical role of renewable electricity and carbon pricing, presenting a penalty-based CE metric to penalize carbon-intensive inputs and advocating green electricity to maximize the practical impact of zero-carbon metallurgy on steel production.

Abstract

To address the lack of energy-carbon efficiency evaluation and the underutilization of low-temperature waste heat in traditional direct reduction iron (DRI) production, this paper proposes a novel zero-carbon hydrogen metallurgy system that integrates the recovery and utilization of low-temperature and high-temperature waste heat, internal energy, and cold energy during hydrogen production, storage, reaction and circulation. Firstly, the detailed mathematical models are developed to describe energy and exergy characteristics of the operational components in the proposed zero-carbon hydrogen metallurgy system. Additionally, energy efficiency, exergy efficiency, and energy-carbon efficiency indices are introduced from a full life-cycle perspective of energy flow, avoiding the overlaps in energy inputs and outputs. Subsequently, the efficiency metrics of the proposed zero-carbon hydrogen metallurgy system are then compared with those of traditional DRI production systems with H$_2$/CO ratios of 6:4 and 8:2. The comparative results demonstrate the superiority and advancement of the proposed zero-carbon hydrogen metallurgy system. Finally, sensitivity analysis reveals that the overall electricity energy generated by incorporating the ORC and expander equipments exceeds the heat energy recovered from the furnace top gas, highlighting the energy potential of waste energy utilization.

Figures (18)

• Figure 1: The zero-carbon hydrogen metallurgy production system
• Figure 2: The variations of reducing gas temperature and pellet temperature along the length of the reduction zone
• Figure 3: The furnace top gas temperatures and DRI temperatures of different reducing gas temperatures
• Figure 4: The schematic diagrams of the ORC system
• Figure 5: The efficiencies of the zero-carbon hydrogen metallurgy system