METALLURGICAL COAL
A Low Carb(on) Diet
June 2019
According to the Commonwealth Scientific and Industrial Research Organization (CSIRO), metal smelting—in particular iron and steel—is responsible for approximately 10% of the world’s greenhouse gas emissions, making it one of the world’s largest carbon emitting industry. Because steel is such a strategic material involved in different major industries, it remains particularly challenging to include it in the energy transition.

The World Coal Association estimates that over 71% of the steel produced globally uses metallurgical coal, making the steel industry heavily reliant on the high-quality commodity. Steel production requires two main raw materials: the first is coke, which uses low-sulphur/phosphorous coking coal and is obtained when coking coal is heated in the absence of air to around 1000-1100 ºC.

The coking process takes place over 12 to 36 hours in coke ovens, and result in a hard-porous material, absent of any impurities to leave almost pure carbon: this is coke. The second raw material used in the manufacturing of steel is iron ore. The iron-making process involves heating air to about 1200 ºC and blowing hot air in into a furnace through nozzles. The hot air results in the coke burning, which produces carbon monoxide which reacts with the iron ore. Finally, the molten iron and impurities are drained off from the bottom of the furnace.

Primary steel-making consists of two main methods:

  • Basic Oxygen Furnace (BOS): This method is the most-commonly-used for steel-making. In the BOS, iron is combined a number of steel scrap (less than 30%) and small amount of flux. 99% pure oxygen is blown into the furnace through a lance, resulting in temperature rising to 1700 ºC which generates liquid steel.

     

  • Electric Arc Furnaces (EAF): this method involves the reuse of existing steel; the furnace is charged with steel scrap and operates on the basis of an electrical charge between two electrodes providing the heat for the process. Unlike BOS, EAF do not use coal as a raw material in their process, but many are reliant on the electricity generated by coal-fired power plant; the World Coal Association estimated that around 150kg of coal are used to produce 1 tonne of steel in EAF.

 

 

In both cases, coal is needed in steel-making, whether it be to produce coke or to provide electricity to furnaces.

The CSIRO states that replacing a portion of the coal and coke used in steel-making could significantly reduce carbon dioxide emissions, without altering the quality of the final product or modifying the process significantly. In fact, Brazil already substitutes coal for charcoal due to poor regional resources available. Charcoal is a lightweight black carbon residue produced by pyrolysis of organic materials (typically plants or wood). However, availability of those organic materials might be limited in certain countries to create enough charcoal to keep up with steel manufacturing.

CSIRO is working to improve the pyrolysis process to produce larger volumes of charcoal from available organic materials. The CSIRO teamed up with industry partners to develop an innovative self-sustaining pyrolysis process to produce charcoal. The technology uses large reactors where material is hearted by pyrolysis reaction alone, which means no coal is needed to create additional heat. Replacing 50% of coal for charcoal in the steel industry alone would result in a 2% reduction of industrial carbon dioxide emissions in Australia.

Other companies are following the CSIRO initiative to create a low-carbon steel. Salzgitter Group—one of Europe’s largest producers of steel—has announced its project to slash its carbon dioxide emissions by 95%, using renewable hydrogen instead of coal to power its furnaces. Hydrogen is seen as a potentially low-carbon replacement for many fossil fuels (including thermal coal and natural gas) and can be used in industrial processes that require high temperatures, such as BOS and EAF. While using renewable hydrogen in steelmaking processes is technically possible, it is not financeable viable yet as it would be too expensive, and therefore not competitive in the current steel market. However, the company stated that the project could be realized with substantial public support for the initial investment— € 1.3bn (US$1.46bn).

Low-carbon steel projects keep gaining momentum, with Swedish power company Vattenfall planning to replace coking coal with fossil-free electricity, including hydrogen; ThyssenKrupp also said recently that it was looking to use hydrogen. Indian giant steel-maker Tata Steel has recently announced its plans to develop the largest green hydrogen cluster in the Netherlands, in a bid to produce carbon neutral steel.