The steelmaking industry is a traditional end-user of gases, including oxygen, argon and nitrogen. Oxygen, especially, has played an integral role in the way the steelmaking industry has transformed over the past 40 years.
Basic oxygen steelmaking (BOS) now accounts for 60% of the world’s total output, making it the dominant force in steel production on a global level. However, newer innovations in the creation of steel furnaces have begun to emerge, threatening the role BOS has played for many years. One such innovation in this area is the advent of the electric arc furnace. Even with the newer furnaces, it remains true that oxygen steelmaking is the primary method of turning pig iron into low-carbon steel.
Since the replacement of open-hearth methods, BOS processes have received a number of incremental improvements that have continued to advance productivity and efficiency. The steel industry has also found ways to increase the lifespan of furnaces. Such cost-cutting methods have made use of nitrogen in ensuring corrosion of furnaces is no longer the problem it once was. On average, newer furnaces are expected to last for 20 years, if not longer.
Innovations surrounding carbon emissions have also been at the top of the list for steel companies. There is constant pressure ensuring that international emissions standards are closely adhered to. Many of the large steel companies have recognised that one of the main drivers of new technologies, is the need to find environmentally sound ways to continue to produce ferrous metals.
As long as steel demand is growing, which it is doing on a global scale through emerging market economies, the driving force for the sustainable delivery of oxygen and other gases will continue to grow.
Ulrich Hanke, Global Marketing and Business Development Manager for Metals and Glass at Linde, explained that the need to find environmentally viable ways of providing oxygen and other gases is essential to meeting production targets as well as emissions regulations.
He said, “The utilisation of increased oxygen in production over air-fuel solutions will enable major advantages in terms of reducing fuel consumption and increased capacity and throughput, with the added benefit of lowering direct and indirect greenhouse gases to help meet increasingly stringent emissions targets.”
Oxygen has always had a large role to play in the production of steel, whether it involves oxygen-cutting of large steel sections, or the actual process of steelmaking itself.
In oxygen steelmaking, molten carbon-saturated pig iron, plus a combination of other elements, is charged into a convertor where it is blown with pure oxygen. This converter is known as a Basic Oxygen Furnace (BOF), and will typically blow 250 tons of molten metal with 99% pure oxygen at a rate of 600 cubic meters per minute.
The oxygen, which is blasted at the molten metal at velocities faster than Mach 1 through a vertically orientated water-cooler lance (in some cases), reacts with the iron, dissolved silicon and manganese to make a liquid slag containing FeO. The point of this is for the oxygen to lower the carbon content of the alloy, changing it into low-carbon steel and at the same time producing monoxide and carbon dioxide.
Innovations to improve the rate of reaction between oxygen and pig iron have been at the forefront of research and development projects. Linde Gases has been a leader in this area, pioneering new oxygen enriching technologies that have been indispensable in creating more efficient, productive solutions to steelmaking. Linde’s oxyfuel technology has led innovation in oxygen enrichment systems for steel reheat furnaces and annealing lines. The application of this technology even has the potential to overhaul the petrochemicals industry.
Hanke explains that oxyfuel technology helps in the delivery of oxygen, helping to increase the thermal efficiency of the furnace, “The use of oxyfuel combustion substantially increases the thermal efficiency of a furnace by employing greater levels of oxygen, and not only air, to combust a fuel, a much faster and more even heating process occurs.”
“This allows for greater capacity in terms of production yield - of up to 50% per tonne per hour - and because total heating time is reduced, energy costs can also be cut by up to 50%.”
Technology using oxygen enrichment process can lower gas use considerably. In some cases 80% less gas is used, mainly due to the fact that when purer oxygen content is used alongside more efficient delivery methods, the overall volume of gas needed is lower. An additional benefit of oxygen enrichment technology is that it can significantly lower direct and indirect greenhouse gas emissions.
Lowering CO2 emissions is a major concern for the EU, and the steelmaking industry has already begun to take action to align itself with environmental policies being issued by EU regulators.
Currently the European Commission is supporting projects through the European Steel Technology Platform (ESTEP).ULCOS (Ultra-Low CO2 Steelmaking) is the most ambitious project, aiming to reduce CO2 emissions in the steel industry by 50% by 2050. ULCOS acts as a consortium for 48 European companies, spanning across 15 European countries. The idea is to invest in research and development initiatives that can drastically reduce CO2 emissions by bringing together all of the major EU steelmakers, universities and engineering partners.
In March 2009, the EU stated that it would provide €800m for the research and development of new blast furnace technologies, incorporating top gas recycling and carbon capture with underground storage (CCS). The idea is to have the new blast furnace technology ready for wider industrial application after 2020. Alongside EU emission standards and cross-country projects, there has been an interest in providing environmentally friendly technologies through the private sector.
The above mentioned oxyfuel technologies currently being pioneered by Linde have considerable effects on reducing CO2 emissions by up to 50%, while at the same time guaranteeing that NOx emissions are below 70 mg/MJ.The use of industrial grade oxygen can avoid the nitrogen ballast, making combustion and heat transfer far more efficient.
There has also been significant progress in the development of oxy-coal injection systems, which promise to raise coal injection rates to allow for complete combustion. Studies suggest that this is now being considered a major breakthrough in decreasing the coke rates of furnaces through coal injection, and will prove to be a giant step forward for the steelmaking industry in finding more efficient, environmentally-safe ways of increasing production, while meeting EU emission standards.
The use of oxy-coal injection systems will enable European countries to meet global demand without necessarily exporting the manufacture of steel to developing nations where less stringent rules will allow for inefficient coke production and continued use in furnaces. Developers of oxy-coal are leading new methods of carbon capture, lowering emissions across the board. In some cases, developers have managed to create oxycoal solutions that manage to capture up to 98% of carbon dioxide emissions.
This carbon dioxide can then be pumped deep underground and absorbed by geological formations, making the whole process far more ecological.
As long as steel remains the industrial backbone of post-modern society, improvements in how gases are delivered for the purposes of pig iron decarbonisation and alloying materials will need to be a major consideration. Steel demand is expected to rise as emerging economic powers see a steep increase in demand.
International CO2 emission regulations will also put a hamper on the amount of steel that nations can produce, unless innovations in the steelmaking industry provide means of lowering carbon emissions or eliminating them altogether.
While the steelmaking industry is often considered a matured industry, there have been a number of technological developments that have contributed to higher production yields. Most importantly, the development of oxygen enrichment technologies and oxy-coal injection procedures have had a dramatic effect on lowering greenhouse gas emissions and generating renewed interest in making the steel industry a greener business.
The ongoing development of new technologies can, with the support of the EU and European Steel Technology Platform, find ways to constantly improve upon the oxygen steelmaking process. However, this must be fairly balanced with the complexities of a modern marketplace, where the cost and limited tolerance for failed technology concepts makes research and development risks very high indeed.