Although gas handling and processing are far more economical than converting coal into coke (not to mention the associated constraints, such as bulk handling, high sensitivity of coking plants to production fluctuations, environmental impact, etc.), replacing coke with natural gas only makes direct reduction attractive to steelmakers with cheap gas resources. This point is essential, as European steelmakers pointed out in 1998:This explains the development of certain reduction-melting processes which, because of the high temperatures involved, have a surplus of reducing gas. Reduction-melting processes such as the COREX, capable of feeding an ancillary Midrex direct reduction unit, or the Tecnored, are justified by their ability to produce CO-rich gas despite their higher investment cost. In addition, coke oven gas is an essential co-product in the energy strategy of a steel complex: the absence of a coke oven must therefore be compensated for by higher natural gas consumption for downstream tools, notably hot rolling and annealing furnaces.
The worldwide distribution of direct reduction plants is therefore directly correlated with the availability of natural gas and ore. In 2007, the breakdown was as follows:
* natural gas processes are concentrated in Latin America (where many have already been developed) and the Middle East;
* coal-fired processes are remarkably successful in India, maintaining the proportion of steel produced by direct reduction despite the strong development of the Chinese steel industry.
China, a country with gigantic needs and a deficit of scrap metal, and Europe, lacking competitive ore and fuels, have never invested massively in these processes, remaining faithful to the blast furnace route. The United States, meanwhile, has always had a few units, but since 2012, the exploitation of shale gas has given a new impetus to natural gas processes.
However, because direct reduction uses much more hydrogen as a reducing agent than blast furnaces (which is very clear for natural gas processes), it produces much less CO, a greenhouse gas. This advantage has motivated the development of ULCOS processes in developed countries, such as HISARNA, ULCORED, and others. The emergence of mature gas treatment technologies, such as pressure swing adsorption or amine gas treating, has also rekindled the interest of researchers. In addition to reducing CO emissions, pure hydrogen processes such as Hybrit are being actively studied with a view to decarbonizing the steel industry.