Making steel without coal

Can the world produce steel without using coal?

 

The short answer to this question is no, not at scale, at the present time.

The issue

Steel is an alloy of iron with carbon (0.002% - 2.1% by weight), and with other metals as needed. Typical additives are: nickel, chromium, manganese, molybdenum, titanium, vanadium, or tungsten, depending on the physical properties sought, e.g., anti-rust, light, tough, heat resistant, elastic, or cheap. As a material, steel combines high tensile strength with low cost. It is one of the building blocks of civilisation. Uses are divided mainly between building and construction (52%), mechanical equipment (16%), automotive (12%), and metal products (10%).

For an idea of scale, the world produces around 1.9 billion tonnes of steel every year, slightly more than half of this in China. Other major producers are: India, Japan, India, the US, Russia, and Korea. This is an energy-intensive business, in which technology advances have reduced the energy requirement by 60% over the last 50 years.

Today, around 0.77 tonnes of coal are used and 1.85 tonnes of CO2 emitted from the raw materials to produce every tonne of steel (separate from any coal or gas used to generate the electricity also required). The World Steel Association estimates that the global iron and steel industry accounts for 7-9% of world fossil fuel-related CO2 emissions. This is a significant figure, and will need to improve as the world transitions to a low-carbon future. This will be challenging.

Making steel using traditional methods

First, iron is smelted from its mineral ore. This is usually an iron oxide such as haematite or magnetite. A furnace temperature exceeding 1600C will release the iron, in the form of "pig iron", so called for the shape of the ingots. This is a brittle material containing as much as 4.5% carbon. Historically the first fuels used to heat the smelters were wood and, later, charcoal (which is made from wood).

The earliest steels appeared in Anatolia (from 1800 BCE), East Africa (from 1400 BCE), South India (from 600 BCE), and in China (from 400 BCE). The Roman military used steel weapons. The production of steel from pig iron requires a reduction in carbon content, to produce a useful metal.

The change to using coal in steel-making dates from the 11th Century in the Yellow River region of China, where trees were sparse. Specifically, the coal was converted into "coke" by heating it in oxygen-starved conditions to drive off embodied water and volatile organic chemicals. This produces a hard, grey, porous material composed mainly of carbon. This has a much higher energy value than coal, and is better geared to producing high temperatures for smelting.

Coke came into use in Great Britain in the 1700s, partly because of its superior crushing strength to that of coal. Blast furnaces for making iron and steel could be built taller and bigger, to improve economies of scale. The growing demand for steel as the Industrial Revolution progressed far exceeded the ability of forests to provide the fuel and source of carbon.

Now, nearly all new steel globally is produced using iron oxide and coking coal. Coking coal is usually bituminous-rank coal with special qualities that are needed in the blast furnace.

While an increasing amount of steel is being recycled, there is currently no technology to make steel at scale without using coal.

New Zealand exports of coking coal provide jobs, much needed export revenue and do not contribute to New Zealand's carbon emissions account. New Zealand coking coal has certain special qualities and is in high demand internationally. If we don't supply our coking coal, customers will purchase elsewhere, often from producers with lower environmental standards, and typically with a higher carbon footprint.

Bathurst Resources has calculated that its exports of coking coal from the Stockton mine lead to 260,000 tonnes of CO2 emissions avoided every year that would otherwise occur from using inferior coals. This statistic is being independently peer reviewed.

Making steel in New Zealand

New Zealand Steel mines a titano-magnetite ironsand in coastal Waikato for use at its Glenbrook plant. Taharoa Ironsands exports the same ironsand from a more southern site to be used as a minor contribution in conventional steel plants. Glenbrook uses a direct reduction process to make iron from the ironsand before this is turned into steel. No other operation in the world makes steel in the same way. Major improvements have been made in energy efficiency through co-generation (using waste heat) where NZ Steel produces up to 70% of its own electricity requirements.

Making steel without coal

This is a holy grail for emissions chasers and there has been considerable international research on ways of reducing or eliminating CO2 emissions from steel making.

Recycling steel

Around 650 million tonnes of steel are recycled every year from scrap, or 37% of total global steel production, according to the World Steel Association. This is a very high percentage of recycling for any material. When claims are made that steel can be made in electric-arc furnaces (instead of emissions-intensive blast furnaces for producing iron, the first stage in steel making), this is what is being talked about. This level of recycling is an increase on 31% in 2016.

To highlight the importance of recycling in steel production, from an emissions perspective, the WSA says that the average blast furnace needs 800kg of coal to produce the iron needed to make a tonne of steel while the average electric arc furnace (using mainly recycled steel) needs just 16kg of coal.

Download the fact sheet here.

Of course, to reduce the CO2 emissions in steel production via  recycling, the electricity input would have to be renewable.

In general, recycling is done as economics, or regulations or conscience dictates. As to claims that 80% of steel could be recycled, this will depend on the sector. NZ Steel has estimated that for buildings, the level of steel recycling could reach as high as 85%.

Making steel with hydrogen

In 2016, SSAB, LKAB and Vattenfall joined forces to create HYBRIT – an initiative aimed at producing steel using hydrogen as a reductant. Instead of CO2 emissions from coal, this process would produce emissions of water. Construction of a pilot plant to demonstrate the technology started in 2018 in Luleå, Sweden. HYBRIT is partly funded by the Swedish government. Its goal is to produce a commercially viable, fossil fuel-free steel by 2035. If the programme is successful, the HYBRIT technology would deliver 10% CO2 emissions reduction in Sweden, and 7% in Finland, alone.

The foregoing explanation is taken mainly from the HYBRIT website. It shows that hydrogen technology for steelmaking has a long way to go before being proven as a solution, or not. 

Use bio-carbon in steel making

Bio-carbon is made from wood, or wood waste. Importantly, this source of carbon for steel-making can only qualify as renewable if wood is being created more quickly (by growing trees) than it is being chopped down and burned.

To the extent that charcoal could be used in steel-making (or cement-making) around the world to replace coal, it is questionable whether this use of wood would be considered environmentally sustainable, especially if this huge shift in land use displaced food production.

In New Zealand, NZ Steel sought to trial 9000 tonnes of bio-carbon in 2015, to be supplied by Carbonscape, as a method of making low-emissions steel. However, the company could only produce a few kilograms of the material at a time. The broader context is that NZ Steel uses around 800,000 tonnes of New Zealand or imported coal each year to make iron and then steel at its Glenbrook mill in South Auckland. At this stage biochar or biocarbon is a non-viable technology, in New Zealand.

Smelt iron using electrolysis

An intriguing way of separating iron from its ore at MIT was reported in Scientific American (May 2013). There was a flurry of media interest at the time but a promised commercial-scale demonstration did not materialise. The latest news on this topic appeared in 2018 from Boston Metal, a spinoff company of MIT, the technology still at the trial stage.

The method is to use a receiving environment of molten metal oxides, in which the iron ore would dissolve, and then pass an electric current through it, to precipitate the iron out onto positively- charged electrodes. Initially, very expensive platinum or iridium were used as an electrode, because these metals can withstand 1600C. Boston Metals’ contribution has been to create a much cheaper chromium alloy to do the job.

So while research continues in New Zealand and around the globe, there is currently no viable alternative to using coal in large-scale production of steel.