certain injectants within the confines of a tuyere. These limits can be raised if the injectants are first gasified into a syngas (CO+H₂) externally, prior to injection into the tuyeres. This external gasification can be performed by, for example, Linde’s Hot Oxygen Technology (HOT) – a fuel- flexible tool to gasify solid, liquid, or gaseous feedstocks, including natural gas, coke oven gas, wide varieties of biomass, waste plastics, and MSW (see Figure 2 ). A typical HOT system is an efficient, small-scale gasifier to generate reducing gas or syngas up to 35,000 Nm 3 /h per unit. Multiple units can be employed to meet the requirements of a blast furnace. This approach helps to minimise the CO₂ footprint of an existing blast furnace without significant modifications to the production process. Typically, DRI is produced with natural gas as the reducing gas in a shaft furnace. A HOT system can also be used to deliver reducing gas or syngas to a DRI plant, derived from a variety of sources, including coke oven gas, and replacing the need for natural gas. Linde has worked with MIDREX to develop the thermal reactor system (TRS) that will produce clean syngas from coke oven gas and other hydrocarbon sources for DRI production. TRS utilises Linde’s partial oxidation technology,
using HOT, which offers the potential to do partial oxidation of hydrocarbons without steam injection. When this technology is combined with an extended reaction chamber into which a preheated stream of coke oven gas is added, the product gas leaving the chamber is suitable for direct use as a reducing gas to produce DRI. Accordingly, there is an option to produce a low carbon footprint syngas to be used both in blast furnaces and direct reduction shafts, which is based on waste plastics, MSW, biomass, and so on. Thereby we can not only reduce the steel industry’s carbon footprint but also help solve a waste problem and support a circular economy, as well as create a carbon sink. DRI-EAF The DRI-EAF route is the most commercially ready path to full decarbonisation for integrated steel mills. Over 80 Mt/a of DRI is produced today in shaft furnaces with natural gas as the reductant. Considering Scope 1-3, an integrated mill can decrease its CO₂ footprint from 2.3 to below 1.6 t/t of finished product by switching to this processing route, potentially at the time of blast furnace relines to minimise incremental investments. Thereafter, CO₂ emissions can be dropped further down to almost zero by
Linde’s Hot O x ygen Technology External gasification of low - carbon feedstocks
iron ore, limestone, and coke
Plastics Municipal solid waste
Flexible feedstock
O
Biom a ss/pyoil Coke oven gas
Hot oxygen burner
POx
blast furnace
hot air
Syngas (CO + H )
molten iron
slag
E cient, small-scale gasi er to generate hot syngas Up to 35,000 Nm /h syngas per unit
DRI
Blast furnace
Alternate approach to decarbonisation of RDI Advantages over H : Cost/economics
Maximise injectant levels, coke replacement Achieve CO savings without cost penalty Maximise BF decarbonisation, asset utilisation
Source of carbon for DRI
Figure 2 Gasification to produce low-carbon fuels
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