Strategies to control CO2 emissions from the Steel sector

A state-of-the-art Steel Mill is a much optimized system in terms of consumption of fuels and reducing agents. The Blast Furnace itself operates 5% away from thermodynamics and the whole mill has a potential of energy savings of roughly 10% only. This is due to several decades of cost management, as high energy prices have driven the industry to optimize its processes as close as possible to physical limits. The Industry rightfully claims energy savings and, correspondingly, CO2 cuts which range between 50 and 60% over the last 40 years, depending on the local conditions: this is the highest level of energy conservation achieved by any industrial sector.

Cutting CO2 emissions further, to the level that post-Kyoto policies require, raises therefore specific challenges: it is indeed necessary to uncouple energy savings and CO2 reduction in the Steel sector – an original feature compared to other sectors.

First, a more or less obvious fact that ought to be stated, anyway, is that the usage of steel scrap should be kept at the high level that it has reached today. It is estimated that the collecting rate of obsolete scrap is around 85% today, which forms the basis of a strong recycling economy, complete with scrap dealerships and a specific steel production route based on the EAF. In simple words, value is created by the recycling of virtually all available scrap. In the long term, this situation will continue.

It should also be pointed out that the indirect emissions related to electricity production will evolve with time. For example, ULCOS has shown that, under a strong carbon constraint, the carbon intensity of the European electricity grid will drop form 370 gCO2/kWh in 2006, to 144 g in 2050, a specific drop of 55%, which will be translated at the same level in indirect emissions [58].

The major source of CO2 emissions from steel mills still remains the ore-based route, which will retain an important role in the long term, at least until a recycling society can replace the 20th and 21st century economy of production growth that is mainly driven by population growth – probably some time in the next century or at the very end of the present one [59].

Solutions to curtail emissions from the ore-based route have to be exhibited and it is clear from the previous sections that there is no simple process, available from the shelf, that can accomplish this. Deep paradigm shifts in the way steel is produced have to be imagined and the corresponding breakthrough technologies designed and developed, by strong R&D programs.

The largest such program called ULCOS, for Ultra Low CO2 Steelmaking, has been running in the EU since 2004 to progress in this direction [55 ,60, 61,59].

The analysis that ULCOS has proposed in terms of Breakthrough Technologies is shown in Figure 24, which explains how reducing agents and fuels have to be selected from three possibilities, carbon, hydrogen and electrons, mostly in the form of electricity13. The mock ternary diagram of the figure is meant for didactic clarity: all existing energy sources can be represented on the triangle sides (e.g. coal is close to carbon on the carbon-hydrogen line, natural gas is closer to hydrogen, hydrogen from water electrolysis is on the hydrogen-electricity line, etc.).

The present steel production technology is based on coal, i.e. mostly on carbon, on natural gas, a mix of carbon and hydrogen and on electric arc furnaces. They are shown in red boxes in the figure.

To identify CO2-lean process routes, 3 major solution paths stand out and three only: either a shift away from coal, called decarbonizing, whereby carbon would be replaced by hydrogen or electricity, in processes such as hydrogen reduction or electrolysis of iron ore, or the introduction of CCS technology, or the use of sustainable biomass. They are shown in yellow boxes in the diagram.

ULCOS has investigated about 80 different variants of these concept routes in the initial phase of its research program, using modeling and laboratory approaches to evaluate their potential, in terms of CO2 emissions, energy consumption, operating cost of making steel and sustainability [25].

Figure 24 – pathways to breakthrough technologies for cutting CO2 emissions from the ore-based steel production routes

Among all of these, 6 families of process routes have been selected within the ULCOS program for further investigation and eventual scale up to a size where commercial implementation can take over:

  • a blast furnace variant, where the top gas of the Blast Furnace goes through CO2 capture, but the remaining reducing gas is reinjected at the base of the reactor, which is moreover operated with pure oxygen rather than hot blast (air). This has been called the Top Gas Recycling Blast Furnace (TGR-BF) or ULCOS-BF. The CO2-rich stream is sent to storage (cf. Figure 25).
  • a smelting reduction process based on the combination of a hot cyclone and of a bath smelter called HIsarna and incorporating some of the technology of the HIsmelt process [62]. The process also uses pure oxygen and generates off-gas which is almost ready for storage (cf. Figure 26).
  • a direct reduction process, called ULCORED, which produces DRI in a shaft furnace, either from natural gas or from coal gasification. Off-gas from the shaft is recycled into the process after CO2 has been captured, which leaves the DR plant in a concentrated stream and goes to storage cf. Figure 27).
  • two electrolysis variants, ULCOWIN and ULCOLYSIS, which respectively operate slightly above 100°C in a water alkaline solution populated by small grains of ore (electrowinning process), or at steelmaking temperature with a molten salt electrolyte made of a slag (pyroelectrolysis).
  • two more options are available: one consists in using hydrogen for direct reduction, when and if it is available without any carbon footprint; the other is based on the use of sustainable biomass, the first embodiment of which is charcoal produced from eucalyptus sustainable plantations grown in tropical countries.

Figure 25 – schematics of the TGR-BF process; the furnace is in the center and is shown in a separate window, where the CO2 separation unit and gas reheater are shown feeding two rows of tuyeres; ; the cones show iron ore (brown) and coal (black); CO2 is sent to underground storage through a pipeline (from www.ulcos.org).

In the nearer term, the TGR-BF seems the most promising solution, as existing Blast Furnaces can be retrofitted to the new technology and thus extensive capital expenditures that would be necessary to switch over to the Breakthrough Technologies is maintained under some control. Moreover, the very principle of the process delivers energy savings because the capture of CO2 and the recycling of the purified gas displaces high temperature chemical equilibria (Boudouard reaction) and uses coke and coal with a higher efficiency inside the BF than is possible with conventional operation. This balances the extra costs incurred by the capture and storage, to some extent. The concept has in addition been tested on a large scale laboratory blast furnace in Luleå, with positive outcome [63].

Figure 26 – schematics of the HIsarna process; the reactor, in the center, is also shown in a more detailed window, where the cyclone sits on top of the bath smelter and char from a screw reactor feeds carbon into the furnace; the cones show iron ore (brown) and coal (black); CO2 is sent to underground storage through a pipeline (from www.ulcos.org).

Where natural gas is available, ULCORED is an attractive option. A 1 t/h pilot is planned to be erected in Luleå in the next few years by LKAB, an ULCOS partner, to fully validate the concept.

Somewhat later and probably for greenfield steel mills, the HIsarna process will also be an option. An 8t/h pilot is to be erected and tested in the course of the ULCOS program.

The electrolysis processes have been developed from scratch within the ULCOS program and therefore are still at operating at laboratory scale. Although they hold the promise of zero emissions, if they have access to green electricity, time is required to scale them up to a commercial size (10 to 20 years).

Hydrogen steelmaking will depend heavily on the availability of “green hydrogen”, while the use of charcoal, far way from growing countries, would require the set up of complex logistics, including heavy infrastructure across several continents.

The discussions have been centered until now on the major sources of CO2, which allows cutting emissions for the whole steel mill by more than 50%. It is possible to cut emissions further, by treating the other stacks of the steel mill: the cost of abatement would of course be higher. With this rationale, though, zero emissions could be achieved.

Figure 27 – schematics of the ULCORED process: the reactor is in the center; to the left is the pelletizing plant for iron ore; the grey box is the CO2 separation unit and the gas flows through a pipeline to the underground storage site (from www.ulcos.org)

There are also other programs addressing this challenge: along with ULCOS, they are part of the CO2 Breakthrough Program of worldsteel – the international Iron & Steel Association, a Forum for the various initiatives to exchange about their progress [64].

Japan has a large national program led by the Japanese Iron and Steel federation (JISF) called COURSE 50, which focuses on the development of a new amine scrubbing technologies for blast furnace gas and the use of hydrogen separated from coke oven gas, a by-product of the steel industry [65]. The ready-to-use technology concepts should be available by 2030.

POSCO, in Korea, runs its own program, with various dimensions including the adaptation of CCS to the FINEX and to the COREX process and the development of an ammonia-based scrubbing process [66].

The American Iron and Steel Institute (AISI), in North America, runs a program where high-temperature electrolysis is examined at MIT, hydrogen reduction of iron ore in the laboratory, preparatory to transposing to a flash furnace reactor, at Utah University, mineral sequestration at Columbia University and CO2 collection from EAF fumes using lime at Missouri Rolla University [67].

A Canadian program, run by the Canadian Steel Producers Association (CSPA), has a strong focus on the use of biomass in iron and steelmaking as a substitute for fossil fuels, as biomass per capita is quite important in this large country [68].

Arcelor Brazil has been reporting its development of a biomass steel production route based on sustainable plantations of eucalyptus trees, production of charcoal and small charcoal blast furnaces [69], which is already used in Brazil but at a small scale (300,000 tpy BF) and is most probably a local solution.

There are also participating programs from Bao Steel in China, China Steel in Taiwan and SAIL in India [57].

The rationale of all of these programs is similar to ULCOS’. They are less advanced in terms of making Breakthrough Technologies available and their progress is not widely reported yet. These are the main reasons why this chapter is heavily based on ULCOS’ approach, which is very typical of what is done elsewhere.

The long development lead time of Breakthrough Technologies shows that there is no simple recipe for cutting the present CO2 emissions of the Steel Industry by 50% or more (the objective of the ULCOS program): new technologies have to be developed, which means a high level of risk, incompressible development time, large budgets for R&D and then large capital expenditures to convert steel mills to the Breakthrough processes. Moreover, the economic viability of these solutions, which definitely are not no-regret, will depend on the price of CO2 and on the implementation of a level playing field for climate policies all around the world that avoid “carbon-havens” and therefore carbon leakage, especially out of Europe.

With all these caveats, the Steel Industry can cut its emissions significantly and continue to provide a material that the world needs to ensure a good life to its citizen and cut CO2 emissions in other sectors.

There is project of MASDAR and Emirates Steel in Abu Dhabi to capture CO2 in a DRI Steel Mill as an end-of-pipe feature and to use it for EOR in the local oil and gas fields. There is little information available about the details of the project, but it is equivalent in size to what the European call a demonstrator.

Both the ULCOS-BF and the UAE projects should go on stream around 2015, with full CCS implemented.

13 Bacteria would also sit on the electron apex, if microbiological metallurgy was considered