Evaluation of Australian PCI coals in the co-injection of coal and hydrogen into blast furnaces using a 3D computer model

This project aimed to determine whether the co-injection of coal and H₂ can enhance the combustion performance of Australian PCI coals in ironmaking blast furnaces (BFs) using Computational Fluid Dynamics (CFD) modelling. It was of particular interest to assess the impacts of coal/H₂ co-injection on the coal's combustion behaviour in the raceway using different lance types and configurations, e.g., a single co-axial lance and an eccentric double lance, for a suite of typical Australian PCI coal types, co-injected at feasible rates with H₂. It is hoped that the insights from this project will help to enhance Australian PCI coal marketing during the transition to a net-zero CO₂ future ironmaking.

Significance and gap

As an alternative reducing agent for iron ore, hydrogen is a promising fuel, with excellent combustibility and zero CO₂ emissions, to possibly replace coal in ironmaking for a sustainable and competitive steel industry in the future. Many hydrogen-based metallurgical technologies have been proposed in several large initiatives, and several projects have entered the stage of construction or testing. Among these technologies, hydrogen may replace coal fully or partly via tuyere or shaft injection.

From previous hypothetical analysis, hydrogen may exhibit extremely fast combustion but may cool the raceway significantly and therefore may have a poor ability to replace coke because additional heat is required to compensate for the cooling effect. On the other hand, coals have high replacement ratios (RR), but much poorer combustibility and produce CO₂ emissions. The co-injection of coal and H₂ through the BF's tuyeres is regarded as a possible method to enhance the performance of both coal and H₂. Determination needs to be made whether the co-injection of Australian PCI coal and H₂ can enhance the performance of both Australian PCI coal and H₂, and especially that of Australian PCI coal, and thereby can help to enhance PCI coal markets during the transition to net-zero CO₂ ironmaking.

Previous experimental studies of H₂ mainly focus on iron ore reduction under simplified BF conditions. Because of the high temperatures and pressures, in-situ measurements cannot easily access the in-furnace phenomena related to the injection operation. Lab or pilot scale experiments are expensive and cannot observe the in-furnace phenomena under industry-scale conditions. Mathematical modelling is a cost-effective method to study this process by means of describing the in-furnace phenomena under various industry-scale conditions; however, the existing models are for co-injection of hydrogen-rich gas (COG and natural gas (NG)) and coal rather than co-injection of coal/H₂. The main concerns related to the co-injection of coal and H₂ include the impacts of H₂ on the raceway flame temperature and the corresponding increase in oxygen required to maintain the RAFT; the upper limits of H₂ injection rates for feasible BF operation, the unburnt coal char problem and CO₂ emission reduction issues. The project handles this challenge by means of a 3D CFD model. The project aims to enhance the research and marketing capability of Australia PCI coal producers and/or distributors, provides a new role for PCI where co-injection with green hydrogen can support the transition to lower CO₂ emissions by enhancing the performance of hydrogen as an injectant, and finally help Australian PCI coal industry, and ultimately promote Australian PCI coals' global markets for a green and sustainable ironmaking future.

The methodology in this project includes two stages:

• A Heat and Mass Balance (HMB) Model has been applied for the overview investigation of co-injection of different ACARP PCI coals and H₂ using base-case operating data for a BSL BF, and generation of the feasible BF operating conditions for CFD studies;
• An industrial-scale 3D CFD model with two lance configurations, a single co-axial lance and an eccentric double lance, has been developed for the local combustion studies of coal and H₂.

3D steady-state industrial-scale CFD models with two lance configurations were developed for the co-injection of coal and H₂. The CFD models were developed for studying the in-furnace phenomena associated with co-injection operation in the lower part of the BF under full-scale BF conditions for the range of Australian PCI coals. The first step was to create the computational domain with a finite number of discrete cells, which consists of the blowpipe, lance, tuyere, raceway and the surrounding coke bed. There are two lance configurations, namely, a single co-axial lance and an eccentric double lance. Then, the physical properties (e.g. density and viscosity) and chemical reactions of the gas-particle-coke bed can be assigned to the model. The steady-state Reynolds averaged Navier-Stokes equations closed by the standard κ-ε turbulence model equations were used to describe the gas phase flow. The boundary conditions were applied based on the operating conditions provided by the HMB results. After completing the steps outlined above, the discretised equations were solved, and hence multi-phase reacting flow was simulated and visualised.

Key findings and conclusions

The project evaluated a suite of five Australian PCI coals in the co-injection of coal and H₂ operations using 3D CFD-based PCI models, including how and how much Australian PCI coals may be impacted under different co-combustion conditions.

The outcomes of this project include:

• Detailed in-furnace phenomena under different co-injection conditions with two lance configurations under industrial-scale BF conditions;
• A database of the simulated impacts of H2 on the combustion performance of a range of ACARP PCI coals under different co-injection scenarios;
• Suitable H2 injection designs under different co-injection conditions;
• A standalone simulator for the co-injection of ACARP PCI coals and H2.