STEEL & IRON

In 2020 steel was responsible for 7% of carbon emissions and about 9% when emissions from the electricity used are considered. The purpose of this page is to highlight the role of processed Iron ore in the ongoing global efforts to reduce the carbon emissions of steel.

Steel is an alloy of Iron and Carbon, and the key factors to achieving low embodied carbon steel are the type of furnace used, the makeup of the electric grid used, the content of scrap steel, and the method used to process the Iron ore.

Structural steel is manufactured in three basic ways: OHF - Open Hearth Furnace, BOF - Basic Oxygen Furnace, EAF - Electric Arc Furnace. The simplified diagram below separates steel production into Primary and Secondary, with Secondary defined as using 100% recycled steel in the EAF process. EAF steel production represents about 75% of the production in the U.S. and about 30% globally.

There are currently two primary types of Iron being used in Electric Arc Furnace mills in the U.S., Pig Iron and Direct Reduced Iron (DRI). The U.S. produces about 22 million metric tons (Mt) of pig iron per year and about 5.2 Mt of Direct Reduced Iron. The amount of steel produced in the U.S. in 2023 was 81.4 (Mt).

The amount and type of Iron used in a typical EAF production facility varies. Pig Iron is processed in a blast furnace and DRI is processed in several ways with natural gas and coal being the fuels commonly used.

ADVANCES IN IRON MAKING

Direct Reduced Iron (DRI): DRI requires significantly less fuel than smelting Iron ore into Pig Iron in a blast furnace, although Pig Iron is still dominant in the U.S. as mills slowly switch to DRI. If Hydrogen is used as the fuel for DRI, the process approaches zero carbon emissions. There is a plant under construction in Sweden (STEGRA) that is targeting the production of 5 Mt per year by 2030 using renewable energy based hydrogen - the carbon emissions of the steel will be reduced by about 95% compared to conventional methods. To put the 5 Mt of the STEGRA plant in perspective, global steel production in 2024 was 1,886 Mt (x 377).

Electrowinning: The ELECTRA iron product (Boulder, CO) is a new Iron process for steel making. ELECTRA is scheduled to start producing high purity iron in Boulder in 2026, with plans for a 500 metric ton capacity per year. Their product can be used as a direct substitute for recycled steel, and if renewable energy is used in the process, it is proported to result in zero carbon emissions.

To understand what the production of 500 metric tons means regarding steel production, NUCOR steel, the largest steel producer in the U.S., produces about 25,000,000 metric tons per year (50,000x). NUCOR has in-fact comitted to purchase iron from the demonstration facility to add to its EAF steel process. NUCOR EAF plants in the U.S. use an average of about 23% Iron content, so the initial 500 metric tons per year can be used in conjunction with scrap steel to produce about 2,200 metric tons of steel per year using the average figures (roughly equivalent to 484,000 square feet of steel floor framing).

An approximation of the GWP of EAF steel with different types of Iron.

It is difficult to find any steel EPDs with data on the amount and type of Iron used. For the purpose of developing these values, the GWP of the steel product is based on several simplifying assumptions:

1. Steel is produced in an Electric Arc Furnace.

2. The percent Iron used was based on the average for Nucor in the U.S., or 23%.

3. The efficacy of the Iron in steel making is a function of the type of iron used. This fact has been ignored and the three steels all have 77% of scrap metal and 23% Iron.

4. Other raw materials that may be required for these mixes were not considered.

Values chosen for the GWP of the unfabricated steel and three iron types:

GWP of steel made from 100% scrap is based on a Nucor Highrec steel EPD at 585 kgCO2e/kg.

GWP of Pig Iron is based on a MetalOne EPD (Brazil) at 799 kgCO2e/kg.

GWP of Direct Reduced Iron is based on a TrueGreen EPD (UAE) at 213 kgCO2e/kg.

GWP of Electra Iron is based on data from the supplier (no EPD or LCA found) at 0 kgCO2e/kg, based on the use of renewable energy.

Resulting approximate GWP for the three steels using the different Iron types:

Steel using Pig Iron: 634 kgCO2e/kg

Steel using Direct Reduced Iron: 499 kgCO2e/kg

Steel using Electra Iron: 450 kgCO2e/kg

Steel produced by STEGRA in Sweden: approximately 50 kgCO2e/kg

Compare with 2025 Buy Clean Colorado Limits:

Using 230 kgCO2e for fabrication of hot-rolled sections (Nucor EPD), fabricated steel made with Pig Iron would have an approximate GWP of 864 kgCO2e/kg; the BCCO limit is 1220 kgCO2e/kg. It must be noted here that comparing the approximate GWP for fabricated hot-rolled steel derived above with the BCCO limit is fraught with problems, and this comparison is only provided for reference.

CONCLUSIONS

  1. The steel industry is working on reducing its carbon emissions.

  2. Innovators are finding other ways to process Iron.

  3. The current electricity grid used for steel production contributes about 2% of global carbon emissions.

  4. In order to use green Hydrogen to produce DRI at scale, renewable electricity resources must increase dramatically.

RECOMMENDATION

Short of a phenomonally rapid increase in renewable energy coupled with a retooling of global steel production, designers need to find ways to reduce the amount of steel to bridge the years before steel becomes a low-carbon material. These reductions must come from all directions including efficiency of design, reusing steel instead of treating it as scrap, and using alternate structural materials with a lower carbon footprint.