(729a) >90% Purity Syngas Generation for Direct Reduction of Iron Ore By Integration of Biomass-Based Chemical Looping with Carbon Dioxide Capture

Decarbonizing the iron and steel-making industry is critical in achieving the net zero carbon emission goal by 2050. The iron-making sector is responsible for 7% of global greenhouse gas emissions, making it a significant contributor to global warming. As such, these industries must strive to achieve a net zero carbon emission goal. The state-of-the-art technology for producing iron is the MIDREX process, which utilizes syngas (primarily contains carbon monoxide (CO) and hydrogen (H₂)) produced from natural gas reforming for direct reduction of iron (DRI). As part of this process, the off-gas from the shaft furnace is burned to generate heat for the reformer, leading to carbon dioxide (CO₂) emissions. The MIDREX process utilizes acid gas remover to capture CO₂, which is highly energy intensive. Therefore, processes that can facilitate efficient CO₂ capture while also utilizing renewable and carbon-neutral fuels such as biomass for syngas generation would lead to fossil-free iron and steel making.

The Ohio State University’s (OSU) moving bed Chemical looping technology leverages biomass to produce syngas. This technology can be coupled with DRI as it offers several advantages. It eliminates the need for costly investments in a tar reformer and air separation unit. Additionally, the moving bed design and catalytic properties of oxygen carrier particles ensure full conversion of biomass char. The integration of OSU’s moving bed chemical looping technology and the DRI process will be helpful in making the DRI process carbon-negative. The integration of these technologies involves redirecting off-gases from the shaft furnace into a chemical looping system with the aim of achieving carbon negativity.

The proposed process scheme couples off gases from the DRI plant into the chemical looping system to generate a capture-ready CO₂ stream and also generate high-purity syngas from carbon-neutral biomass, which can be used as a reducing gas in the DRI process. The proposed scheme consists of three reactors. The off-gas stream from the DRI plant is fed into moving bed reactor 1, where the off-gas reacts with iron-based oxygen carrier (OC) particles, generating sequestration-ready carbon dioxide in moving bed reactor 1. These oxygen carrier particles are partially reduced in reactor 1 and then moved to moving bed reactor 2. These particles get further reduced, donating their lattice oxygen for the gasification of lignocellulosic biomass to generate high-purity syngas in moving bed reactor 2. The reduced oxygen carrier particles leaving reactor 2 get regenerated using air in fluidized bed reactor 3, called a combustor. These regenerated oxygen carrier particles are sent back to reactor 1 via the riser, completing the loop.

This process scheme was simulated in Aspen Plus, and the preliminary experimental studies were conducted in a 2.5 kW thermal bench scale setup. The process simulations have shown that the off-gas from the DRI plant in reactor 1 generate sequestration-ready CO₂ while reducing oxygen carrier particles. The dry purity of carbon dioxide from reducer 1 is approximately greater than 95%. In reactor 2, these oxygen carriers react with biomass at high temperatures, producing high-purity syngas. In the proposed method, the syngas has a purity greater than 90%. Moreover, the quality of syngas required for the DRI process is measured by a parameter called reducing potential. For effective DRI, the reducing potential should be greater than 9. Presently, the process produces syngas with a reducing potential of 10, surpassing the required threshold. The experimental results are coherent with the process simulations.