Leveraging blast furnace operations to reduce emissions

Using a blast furnace is the primary method used to extract iron from iron ore, a process during which raw materials - iron ore, coke, and limestone - are added at the top of the furnace, where the temperature is coolest, while very hot air is blown in from the bottom. Molten iron, the primary ingredient in steelmaking, is the ultimate product, tapped off at the furnace’s base. This process accounts for over 90% of global iron ore-based steel production and is a major contributor to global CO₂ emissions. 

A recently published study from the engineering and public policy (EPP) and materials science and engineering (MSE) departments at Carnegie Mellon University analyzes variations in operations across the global blast furnace fleet and its impact on CO₂ emissions, finding that emissions could have been reduced by as much as 9.6% globally and 15.5% nationally from 2011 to 2021 if each furnace had operated at either its own historical minimum emissions intensity or the observed national minimum. 

The research team, composed of EPP postdoctoral researcher Elina Hoffmann and professors Valerie Karplus and Chris Pistorius, compiled and analyzed plant-level data for a sample of global blast furnaces and furnace-level data for the United States. Using fuel and reductant consumption data, they calculated the equivalent coke rate for each plant or furnace. In their review, they examined the mix of input materials using reductant emissions factors and determined plant or furnace-level CO₂ emissions intensity. The work was part of the activities of the Industrial Decarbonization Analysis, Benchmarking and Action Partnership, funded by the U.S. National Science Foundation.

“Our goal was to quantify how much variation exists in blast furnace operations and what that variation implies for CO₂ emissions reduction opportunities,” Hoffmann said. “By looking at historically observed performance, we can estimate how much emissions could have been reduced using operating practices that have already been demonstrated at commercial scale.”

Our results suggest meaningful opportunities for blast furnaces to improve today, while net-zero-compatible technologies are developed and deployed

Elina Hoffmann, Postdoctoral Researcher, Carnegie Mellon University

While efforts to reduce emissions across the iron and steel industry have expanded in recent years, they have often focused on emerging technologies that require significant capital investment, additional research and testing, and long deployment timelines. In contrast, this study focuses on opportunities to reduce CO₂ emissions using existing operations observed in historical data.The analysis reveals substantial variation in emissions intensity both across blast furnaces and within individual furnaces over time, variation that is often obscured when furnaces are treated as operationally uniform or represented using static “best available technology” assumptions. In practice, such static representations may discourage operators from fuel switching or other process adjustments that reduce emissions but do not affect regulatory benchmarks.   Recognizing such operational heterogeneity is therefore crucial to identifying near-term emissions reductions opportunities using current steelmaking technologies. 

Ultimately, the researchers emphasize that recognizing the substantial heterogeneity in blast furnace operations carries implications for policy design. Given this variation, future research could explore how different policy instruments—such as performance-based standards, benchmarking schemes, or carbon pricing—might encourage plants to operate closer to their lower-bound CO₂ emissions intensity.

“We hope this work informs industry or policy action that leverages process-level variation to lower CO₂ emissions from the operation within current technologies,” said Hoffmann. “Our results suggest meaningful opportunities for blast furnaces to improve today, while net-zero-compatible technologies are developed and deployed.”