Optimal integration of solid sorbent CO₂ capture / H₂ production technology in the iron and steel industry

Dr Sergey Martynov, Department of Chemical Engineering, University College London gives an overview the research he undertook in collaboration with researchers from University College London and the University of Manchester. The project was funded by the UKCCSRC through the Scientific Collaboration Award.

The carbon footprint of the iron and steel industry is about 1.83 Mt of CO₂ per tonne of steel produced. Given that around 78 % of the CO₂ emissions from the integrated iron and steelworks are produced by combustion of CO and CO₂ containing off-gases, there is a huge interest in developing schemes that combine the CO₂ capture with conversion of off-gases into valuable chemical products.

To address this challenge, the group of researchers from UCL (Dr Richard Porter, Professor Haroun Mahgerefteh and Dr Sergey Martynov) and University of Manchester (Dr Vincenzo Spallina and Dr Syed Zaheer Abbas) have collaborated together to investigate the potential of integrating Calcium Assisted Steel-mill Off-gas Hydrogen (CASOH) CO₂ capture technology, which separates CO₂ from the Blast Furnace Gas (BFG) emitted in steelworks while simultaneously generating a hydrogen-rich syngas, with the Fischer-Tropsch process to synthesise liquid fuels.

We have aimed at the preliminary design of the technology processing approximately 5Mt of BFG per year, i.e. at a scale of a large integrated steel plant. The following figure shows the block flow diagram constructed for the CASOH technology integrated with the Fischer-Tropsch synthesis. The corresponding process model was built in Aspen Plus v.10.

Figure 1. Process block flow diagram for integration of the CASOH CO₂ capture from BFG stream with the FT synthesis. Dashed lines indicate the recycle streams.

Based on the process simulations, the performance of the CASOH CO₂ capture technology combined with the Fischer-Tropsch synthesis has been assessed in terms of:

1. The CO₂ emissions reductions: the technology captures more than 92% of CO₂ from otherwise combusted Blast Furnace Gas (BFG), with the Fischer-Tropsch synthesis adding ca. 15£/tCO₂ avoided on the top of ca. 40 £/tCO₂ avoided corresponding to the CASOH step;
2. The conversion rate of the blast furnace gas (BFG) into synthetic fuels, such as kerosene, diesel or petrol: the technology produces ca. 15 kg of synthetic fuel per tonne of BFG feed stream;
3. Additional benefit of generating high-temperature heat in CASOH reaction: this heat could be integrated with other processes in the steel plant, or otherwise utilised for the local district heating or electricity generation.

Analysis of the economic potential of the CASOH technology coupled with the Fischer-Tropsch synthesis showed that adapting efficient schemes of integration of the CASOH high-temperature heat is critical for driving down the technology costs. In particular, we have estimated that increasing the heat integration efficiency by 10% helps reducing the cost of CO₂ avoided by ca. 5£/tCO₂.