Hydrogen heating steel to achieve no carbon dioxide emissions

Swedish special steel manufacturer Ovako Group and industrial gas supplier Linde Gas recently conducted a comprehensive test at the former’s Hofors steel plant, using hydrogen before rolling Heating steel has made historic progress, revealing how to eliminate carbon dioxide emissions from the rolling process.

Environmental goals promote steel companies to reduce carbon emissions

At present, the Swedish steel industry is formulating ambitious environmental goals, and has proposed and promoted many promising greenhouse gas emission reduction programs. The focus of most projects is to replace coal and coke with hydrogen in the iron ore reduction process, and iron ore reduction is the main source of carbon dioxide emissions in the long-term steel production. Steel producers using scrap steel as raw materials need to focus on other processes of carbon dioxide emissions, the most important of which is the power source used in electric arc furnace (EAF) smelting.

For all industries, in order to form a complete life cycle process, the focus should be placed on the upstream links of the supply chain, which has formed a consensus. In order to make large-scale beneficial environmental improvements, it is very important that all participants in the value chain understand and support this view. Environmental factors should become an important criterion for purchasing decisions.

Hydrogen-oxygen-enriched combustion heating steel new program

In the downstream process of steel smelting, the important areas of carbon dioxide emission reduction are the heating process before hot rolling or forging, and the final heat treatment of steel products. Ovako is a steel manufacturer that completely uses scrap steel as raw materials. The electric arc furnace is powered by fossil-free electricity, and the final heat treatment is developing in the direction of completely using fossil-free electricity. The main remaining challenge for Ovako is how to reduce the carbon dioxide generated by the heating process before rolling.

While Ovako produces high-quality special steel products, it has a very low carbon dioxide footprint throughout its life cycle. This is due to years of unremitting efforts. Ovako has achieved a carbon footprint that is 80% lower than the global average, but is still striving to get better. Ovako purchases 100% fossil-free electricity from Nordic Power. The average carbon dioxide emissions of the electricity industry in Sweden is 12g/kWh, and the carbon dioxide emissions of the electricity used by Ovako are even lower than the domestic average.

In recent years, Ovako has made a lot of investment in the replacement of fossil fuels with renewable energy power. When all furnace temperatures are below 1000 ℃, heat treatment furnaces have been converted to electric heating. In hot rolling mills, hot charging methods are used as much as possible, which greatly saves fuel usage and reduces carbon dioxide emissions at the same time. Ovako also changed the fuel from petroleum to liquefied petroleum gas (LPG), thereby significantly reducing carbon dioxide (containing sulfur dioxide and particulate matter) emissions, and confirmed the possibility of switching to other carbon dioxide-free fuels, such as green hydrogen produced by electrolyzed water .

In Hofors Steel Plant, Ovako cooperated with Linde to convert almost all 57 high-temperature furnaces (furnace temperature is about 1200℃) to adopt oxy-fuel combustion technology, which avoids the nitrogen ballast in the air, thereby greatly reducing The heat taken away by the flue gas is reduced, and the radiation heat transfer is improved. The use of oxy-fuel combustion can reduce energy consumption and achieve a 20%-50% reduction in CO2 emissions, depending on the process.

Up to now, Ovako and Linde have cooperated for about 30 years. Through the development, implementation and upgrade of oxy-fuel combustion technology, other uses of industrial gases have been expanded to adapt to different practical applications and their impact on economy, product quality and emissions. Requirements. In order to improve temperature uniformity and reduce nitrogen emissions, Ovako switched from the original conventional oxyfuel combustion to Linde's REBOX® series of flameless oxyfuel combustion solutions. Ovako and Linde decided to explore the feasibility of using hydrogen-oxygen combustion technology to heat steel before hot rolling and forging. In addition to using hydrogen as fuel, flameless oxyfuel combustion technology is also used, applying the innovative concept of "REBOX Hyox". During hydrogen-oxygen-enriched combustion, steam instead of flue gas is produced.

In order to be able to heat different steel grades in a 100% water vapor atmosphere, a series of questions must be answered. These questions involve the impact on the quality of the steel, the capacity/uniformity during the heating process, nitrogen emissions, safety issues, and changes in the combustion system .

In order to evaluate oxidation, descaling, decarburization, hydrogen embrittlement, heating capacity, temperature uniformity, and nitride formation, pilot tests were carried out at the Linde Combustion Laboratory located outside Stockholm. These tests covered trials of different steel grades. In this way, the hydrogen-oxygen-enriched combustion technology was used and compared with the LPG-oxygen-enriched combustion results adopted by Ovako. All test results are exciting, and there are no adverse effects on raw materials, combustion or emissions.

After the successful pilot test, Ovako and Linde decided to conduct a large-scale hydrogen-oxygen-enriched combustion heating test in a pit-type heating furnace at Hofors Steel Works. Ovako upgraded the existing combustion system to use hydrogen and LPG as fuel. The conversion between fuels can be completed in one second under absolutely safe conditions, and all norms and regulations are followed.

The demonstration test was carried out in March 2020, when 24 bearing steel ingots from the Hofors Steel Plant were loaded into four pits. One of the pits uses "REBOX Hyox" hydrogen-oxygen-rich fuel combustion, while the other three pits use conventional fuel (LPG-oxygen fuel) for combustion.

All relevant data (flow rate, temperature, oxygen level in the flue gas, etc.) show that the capacity, temperature uniformity and controllability of the combustion system are at least the same as the operation of conventional fuel combustion technology. After the billet is heated and soaked, it is successfully rolled into a bar on the rolling mill, and the rolling force, size, scale and temperature are all maintained at the same level. A comprehensive inspection and analysis of the final billet showed that heating with hydrogen as fuel does not affect the quality of high-quality products. This is the first time in history that hydrogen and oxygen have been successfully used to heat steel before rolling. In addition, the use of hydrogen in combustion systems can have a very positive impact on the environment, because the only emissions produced are water vapor.

Bring a demonstration effect for the application of hydrogen in other industries

Ovako said that this is the first time that hydrogen has been used to heat steel in an existing production environment. From this demonstration test, it can be seen that hydrogen can be used simply and flexibly without affecting the quality of the steel, and it means that the carbon footprint is greatly reduced. .

An expert from the Ovako Energy and Heating Furnace Technology Group said: “It is very exciting that we now have evidence that it is possible to use hydrogen for heating without affecting the quality of steel. If we can make this investment , Will undoubtedly have a huge positive impact on the environment. We estimate that this investment will reduce about 20,000 tons of carbon dioxide per year, and this is just the beginning. In addition to the Hofors Steel Plant, it can also be fully promoted in other rolling mills. "

This demonstration test proves that hydrogen heating is feasible in large-scale production. Using green hydrogen and oxygen produced by electrolysis of water, and using a flexible oxygen-enriched combustion system, carbon dioxide emissions related to steel heating may be eliminated. Ovako is now actively seeking industry partners to obtain the necessary financial support to complete the financing. If full operation can be achieved in a relatively short period of time, this will provide a powerful demonstration for the wider use of hydrogen in many industries. Through the development of the above hydrogen heating steel project, it can be expected that innovative steel products and innovative steelmaking processes will build a better future in the near future.

(Source: World Metal Herald)