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Jun 2, 2021

The quest to decarbonize stainless steel production

Stainless steel is a corrosion resistant alloy, which is widely used in variety of applications. As economic prosperity increases around the world, so does the consumption of the material. Stainless steel is durable and 100% recyclable, making it sustainable choice for different types of appliances and structures. The industry is actively working towards carbon-neutrality, mainly through energy-efficient processes and the use of clean energy.

Ferrochrome is one of the most important raw materials in the production of stainless steel, providing its corrosion resistance. It is estimated that 90% of it is consumed in the production of stainless steel. Producing ferrochrome from chromite ores usually requires the concentrating and agglomeration of chromite fine ore and then smelting it in a carbothermic reduction process. The smelting process to produce the alloy is conventionally done in a submerged arc furnace (SAF), which is a very energy-intensive process. Smelting consumes large amounts of carbon, which can be in the form of anthracite or metallurgical coke. Because of its high energy and carbon consumption, ferrochromium production – like other ferroalloy smelting processes – produce large amounts of greenhouse gas emissions.

“In recent years, the ferrochrome industry has done a lot of work to improve their energy efficiency and reduce CO2 emissions. In practice, this means minimizing the amount of carbon, capturing and reusing it, and minimizing energy consumption. A preheating unit and CO gas capture, allowing the reuse of gas as an energy source, are the two most important process elements in improving energy efficiency. The most obvious way to further reduce the CO2 emissions is to use clean energy,” says Joseph Hamuyuni, Metallurgist, Smelting at Metso Outotec.

Tornio Ferrochrome works

Solving the challenge with energy efficient technology

Metso Outotec’s ferrochrome production technology has been designed to minimize the energy consumption and carbon footprint in the production of stainless steel. The technology is also one of the more than 100 Planet Positive products at Metso Outotec.

“The key factors that impact the energy consumption in the process are: the quality of raw materials (especially the chromite quality), their pre-treatment before smelting - such as pelletizing - and the utilization of the carbon monoxide rich off-gas for preheating and cogeneration. The FeCr smelting process is very energy intensive requiring a lot of electrical energy,” explains Lauri Närhi, Director, Sales at Metso Outotec.

“Metso Outotec’s proprietary ferrochrome process technology consists of steel belt sintering (SBS), a preheating kiln, a closed submerged arc furnace (SAF) and an off-gas handling system. The intelligent design of the process results in high efficiency and a small carbon footprint.”
Lauri Närhi, Director, Sales at Metso Outotec

Steel belt sintering process is based on recycling the energy inside the process so that it requires very little additional fuel. Excess CO-gas from smelting operation can be used as fuel in SBS process. As a result, it has the smallest carbon footprint when compared to other technologies for producing sintered pellet. Similarly, the preheating kiln uses CO-rich off-gas as fuel.

The company’s industry-leading submerged arc furnace maximizes energy efficiency with a closed set-up and preheater pairing. As a result, the specific energy consumption of the furnace is decreased by an estimated 70 kWh per metric ton of alloy for a 100 °C increase in preheating temperature.

“Each year, we calculate our handprint, i.e. the positive environmental effect our customers get by using our sustainable technologies. In 2020, ferrochrome smelting accounted for 43% of Metso Outotec’s CO2 handprint. By using our technology, our customers avoided more than 3.5 million tons of CO2 emissions in 2020. Here’s an example to illustrate this: if the average CO2 footprint of a Finnish citizen is approximately 11 tons of CO2, the handprint we helped our customers avoid covers the CO2 emissions of about 320,000 inhabitants in Finland,” says Mari Lindgren, Director RTD smelting.

Tornio Ferrochrome works

Calculating the total energy consumption of ferrochrome

The global annual production of stainless steel is approximately 51 million tonnes. Based on the 2019 production of high-carbon ferrochrome (13,719 ktonnes) and the lowest emission factor of 2.3 tCO2/ton of alloy, the global CO2 emissions are estimated to be at least 31.55 Mt CO2 equivalent. With the same production value for 2019 and with an average electricity consumption of 3.5 MWh/ton of alloy, the total energy consumption of ferrochrome is 48 TWh.

https://www.worldstainless.org/statistics/stainless-steel-meltshop-production/stainless-steel-meltshop-production-2020/

Calculating our handprint

In 2020, Metso Outotec’s ferrochrome technologies produced 5,727 ktonnes, which is about 42% of global HC ferrochrome production. This resulted in a CO2 handprint of 3.53 ktonnes, which was 68% of MO’s smelting handprint, or 43% of the handprint of all MO products. So, the ferrochrome handprint is the largest contributor to MO’s handprint [MO GRI supplement 2020].

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