Paper
Optimising the Coinjection of Natural Gas and Pulverized Coal for Indian Blast Furnaces Toward Productivity Gains and Lower-Carbon Emissions
Viswanathan N. Nurni, Ananthu Hari, Tirtha Biswas, and Srinivasan Rajagopalan
April 2022 | Industrial Sustainability
Suggested citation: Nurni, Viswanathan N., Ananthu Hari, Tirtha Biswas and Srinivasan Rajagopalan. 2022. Optimising the Coinjection of Natural Gas and Pulverized Coal for Indian Blast Furnaces toward Productivity Gains and Lower‐Carbon Emissions. Steel Research International 93, Nr. 9 (29. May). doi:10.1002/srin.202200091, https://doi.org/10.1002/srin.202200091.
Overview
India's stated goals to more than double steelmaking production capacity by 2030 merit consideration of new technical pathways for productivity gains and emission reduction. Already the second-largest steel producer globally, India primarily relies on coal-based technologies for ironmaking, with heavy reliance on imported metallurgical-grade coal.
This paper develops an integrated thermodynamic modelling approach by iteratively coupling the raceway adiabatic flame temperature (RAFT) and Rist models to explore the ability to consider various hydrocarbon injectants through the tuyeres of a blast furnace. RAFT is a theoretical concept which is considered as an empiric parameter for stable blast furnace operation. The Rist diagram predicts changes in blast furnaces when operating conditions are altered due to a change in fuel or raw material. Based on the thermodynamic criteria set in the modelling framework, optimal coinjection rates for natural gas (as a low-carbon feed) are identified along with pulverised coal injection as a function of various operating parameters, including top gas temperature, RAFT temperature, and ore processing (pelletisation). The potential for productivity gains and CO2 emission reduction in the blast furnace process is discussed.
While the study bears specificity to Indian operating conditions related to raw material composition and blast furnace process parameters, the learnings may apply to other global studies, with potential extension to deeper decarbonisation pathways, such as increased use of hydrogen.
Key Highlights
- Based on the thermodynamic modelling, optimal coinjection rates for natural gas as a low-carbon feed are identified along with pulverised coal injection as a function of various operating parameters, including top gas temperature, RAFT temperature, and ore processing (pelletisation) while also discussing productivity gains and CO2 emission reduction.
- It is estimated that 60 normal cubic meter (Nm3) of natural gas (NG) can be injected into the blast furnace per tonne of hot metal (THM) to meet the RAFT of 1950oC and top gas temperature of 100oC in the base case.
- An increase in alumina to silica ratio in the iron ore from 0.4 to 0.7, the NG input rate can be increased by 12 Nm3 per THM. Corresponding decrease in carbon emission is 0.5 per cent. There is a slight decrease of 2.5 per cent in production rate, owing to lesser amount of oxygen enrichment required.
- The natural gas injection can be maximised with a higher share of pellets replacing sinter use. It is seen that, for a pulverized coal injection (PCI) rate of 100 kg/THM, the NG injection increases from 60 NM3/THM to 130 NM3/THM for an increase in pellet share from 20 per cent to 80 per cent.
Recommendations
- Use natural gas as an important lever to mitigate emissions from blast furnaces until no-carbon fuels like green hydrogen are commercially available.
- Maximise the natural gas uptake in blast furnaces by increasing the pellet consumption in the process.
"Considering that the Indian steel plants have invested heavily in coal-based blast furnaces, industries must explore all options for mitigating emissions from the production process, including injecting alternative fuels like natural gas to the maximum extent possible."
