Sorption-Enhanced Water-Gas Shift Technology Platform for Cost Effective CO2 Reduction in the Iron & Steel Industry

1. Introduction

The interest in CO₂ capture, storage, and utilisation has grown significantly in recent years because CO₂ emissions are the major cause of global warming. A large share of global CO₂ emissions is related to industrial facilities. To avoid major climate change in the long term, it is imperative that each industrial sector looks to improving energy efficiency and decreasing CO₂ output. As an example, the iron and steel industry is responsible for an annual output of ~2.5-3.0 GtCO₂/yr, representing 6% of total CO₂ emissions, and 16% of total industrial CO₂ emissions. The STEPWISE project, executed within the European H2020 LCE program, aims at decreasing CO₂ emissions related to the steel-making process from about 2 t_CO2/t_steel to below 0.5 t_CO2/t_steel by means of CO₂ removal from the Blast Furnace Gas (BFG) (i.e., an average dry composition of 19% CO, 25% CO₂, 3% H₂, 20 ppm H₂S+COS and 53% N₂) [1-3]. The STEPWISE project has at its heart the Sorption-Enhanced Water-Gas Shift (SEWGS) technology − a solid sorption technology for CO₂ capture from fuel gases in combination with water-gas shift and acid gas removal [4]. SEWGS has advantage over conventional approaches adopted for pre-combustion CO₂ capture requiring at least two water-gas shift reactors with interstage cooling to effect a high conversion of CO to CO₂ (Figure 1). Downstream the water-gas shift (WGS) section, further cooling is then necessary to enable the capture of CO₂ by absorption with a solvent. Using the SEWGS process, both the 2^nd WGS reactor section and the H₂/CO₂ separation unit are replaced. A combination of bulk conversion of CO in the WGS unit followed by CO₂/H₂ separation in the SEWGS unit enables generation of a high purity CO₂-rich stream intended for storage or further utilisation (such as for production of chemicals) and a H₂-rich stream intended for electricity production. In the STEPWISE project, the SEWGS technology is brought to TRL6 by means of design, construction, operation and modelling a pilot installation in the Iron and Steel industry using actual Blast Furnace Gas. This pilot plant is designed for a 800 Nm³/h BFG feed (i.e., the capability of processing up to 14 tonnes CO₂ per day) and is located at the facilities of Swerea Mefos in Luleå, northern Sweden next to the SSAB (Sweden) blast furnace from which the pilot receives its BFG feed gas [1-3].

 

 
  Figure 1. (a) Conventional layout of a shift section and H₂/CO₂ separation for high-pressure CO₂ capture; and (b) layout for improved CO conversion and CO₂ capture section using the SEWGS technology.

 

2. Experimental

The project covers the design, construction, operation and modelling of a 14 t_CO2/day capture unit, consisting of a BFG compression section, an advanced pre-shift section and a single column SEWGS unit. Pilot construction and commissioning was completed Q4, 2017. The 1^st pilot plant campaign at Swerea Mefos, Luleå Sweden, using the KATALCO^TM 71-6 WGS catalyst for the pre-shift section and the potassium-promoted magnesium-aluminium-based sorbent HT1.5 for the SEWGS unit has been completed. The environmental evaluation of the SEWGS process through Life Cycle Assessment (LCA) and the techno-economic assessment were performed within the STEPWISE project and compared with competitive technologies (reference case consists of post-combustion CO₂ capture via amine scrubbing).

3. Results and discussion

For the WGS section, a commercial iron-based WGS catalyst KATALCO 71-6 was evaluated. The suitability of this catalyst was established during lab-scale testing under BFG conditions, which are considerably different from typical ammonia- or hydrogen-plant conditions. The catalyst showed good resistance towards the low sulphur feed content associated with BFG. Pilot plant testing confirms the catalyst stability of the pre-shift section at lowered steam operation, i.e. H₂O/CO = 2.0 - 1.5. A gradual increase in CH₄ production that indicates destructive excessive overreduction of the catalyst was not observed, confirming the catalyst robustness demonstrated earlier during lab-scale testing campaigns. Modelling of the catalyst bed activity in time indicated that the catalyst stability appeared to be good. No significant decrease of the catalyst activity in time was observed throughout the 1^st long campaign (i.e., 1000 h operation). Following the campaign, the KATALCO 71-6 catalyst was discharged and samples were taken from different sections of the WGS reactor for characterization. The catalyst appeared to be in very good condition. Post-test characterization indicates that no over-reduction or sulphidation of iron occurred, that the structure of the active catalyst is preserved and that there was no sign for carbon accumulation. The findings agree well with the results of the post-characterization study following lab-scale catalytic testing.

 

With respect to the SEWGS unit, major achievements are the demonstration of sorbent production at tonnage scale, robust operation of the pre-shift section at lowered steam conditions, and SEWGS performance at >90% H₂S removal efficiency and >90% CO₂ capture rate at <1 mol steam/mol CO₂ and >90% product purity, illustrating that the SEWGS technology provides simultaneous decarbonization and desulphurization.

The preliminary techno-economic evaluation illustrates that the SPECCA coefficient - the energy requirement for capture - is below 2 which is around 30% lower than the amine-based case. The LCA indicates that all impact parameters are lower for the STEPWISE cases compared to post combustion amine scrubbing reference case.  

4. Conclusions

  In the STEPWISE project, the SEWGS technology for CO₂ capture is brought to TRL6 by means of design, construction, operation and modelling a pilot installation in the Iron and Steel industry using Blast Furnace Gas. This advanced CO₂ removal technology makes use of regenerative solid adsorbents. For the WGS section, a commercial iron-based catalyst was evaluated. The suitability of the commercial catalyst under the atypical conditions for BFG operation was established, illustrating the catalyst robustness at the low sulphur conditions associated with BFG. The LCA and techno-economic assessment indicates that the SEWGS technology has potential to reduce carbon footprint in the Iron and Steel industry.  

Acknowledgments

This work is part of the STEPWISE project that has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 640769.

KATALCO^TM is a trademark of Johnson Matthey PLC.

References

[1]    http://www.stepwise.eu/project/

[2]    https://www.youtube.com/watch?v=7_xbe-EMyRc

[3]    H. A. J. (Eric) van Dijk et al., Johnson Matthey Technol. Rev., 62, 4 (2018) 395–402.

[4]     M. Gazzani et al., Int. J. of Greenhouse Gas Control 41 (2015) 249-267.