Sorption-Enhanced Water-Gas Shift (SEWGS) for production of hydrogen from steelmaking process gases combined with CO2 capture (STEPWISE)

The STEPWISE technology combines an energy efficient CO2 capture technology with a highly efficient H2 production step through a Sorption-Enhanced Water-Gas Shift (SEWGS) process. It converts a CO/CO2 rich gas into a H2-rich gas by maximising the water-gas-shift conversion of CO into H2 and CO2 while simultaneously capturing CO2 using a solid adsorbent material that interacts with the CO2 in a pressure swing adsorption process. This technology is developed by TNO (The Netherlands).

TECHNICAL DESCRIPTION
The STEPWISE technology is based on the Sorption- Enhanced Water-Gas Shift (SEWGS) technology operating as a PSA (Pressure Swing Adsorption) unit with an upstream high temperature catalytic Water-Gas Shift (WGS) unit in case of high CO-content feeds. The technology captures CO2 at elevated temperatures (350-450°C) and medium pressures (5-25 bar) using a solid adsorption material that reversibly interacts with CO2 and steam while simultaneously converting CO in the feed to H2 and further CO2 that is also captured. The CO2-loaded sorbent is regenerated at the same temperature but reduced pressure and using steam as a purge gas. The regenerated sorbent is then ready for the next adsorption cycle. Accordingly, the SEWGS technology is a multi-column system operating in pressure swing mode, producing a CO2 product and a H2-rich product, using steam for the WGS reaction and the separation. The use of steam to drive the CO2 / H2 separation in the SEWGS process allows high recoveries of both these products in a single unit. A typical SEWGS cycle consists of a multi-column system where always at least 1 column produces a H2-rich product at high pressure and at least 1 column the CO2 product at low pressure.
The solid sorbent material is a magnesium/aluminium mixed metal-oxide, promoted with a potassium salt to enhance the capacity and kinetics of the CO2 interaction. This class of materials is known for its excellent stability under the demanding hydrothermal conditions of the SEWGS cycle, where e.g. the rinse represents 400°C superheated steam of 5-25 bar. Moreover, Mg, Al and K raw materials for sorbent production are abundantly available and cost-effective.
For high CO content feeds, an upstream catalytic WGS section is required for the bulk CO conversion. Because the SEWGS process converts the last fraction of CO, the steam requirement for the total WGS conversion can be optimised as deep CO conversion in the upstream WGS section is not required. This allows the minimisation of the steam requirement for WGS as energy penalty.
An additional benefit important for the processing of process gases from the iron and steel sector is the robustness of the sorbent material in presence of contaminants such as COS, H2S and NOx. Moreover, the upstream WGS section allows the use of high-temperature WGS catalysts, which are also more robust than their low-temperature counterparts with these impurities.

DEGREE OF MATURITY
The STEPWISE technology has been demonstrated at TRL6 at the pilot facilities of SWERIM in Sweden, using BFG in the STEPWISE and FReSMe projects and BOFG in the INITIATE project, both sourced from the adjacent SSAB steel plant.
These piloting campaigns illustrates the potential of the technology. The 4 campaigns realised in the STEPWISE and FReSMe projects represent in total about 4,000 h operation. In each campaign of about 1,000 h operation, typically 3,000-5,000 sorbent CO2 loading and unloading cycles were performed. Additionally, on-going lab-scale endurance testing campaigns showed stable operation of the sorbent produced by Kisuma for 55,000 loading and unloading cycles currently, further supporting the technology’s robustness. The current ongoing INITIATE project will demonstrate the technology at TRL7 on completion of the project in 2026 to decarbonise BOFG using a multi column set-up as well as the production of NH3 from the N2/H2 SEWGS product. The next steps in the technology implementation roadmap are the development of a TRL8 First-of-a-Kind plant, aiming at building a STEPWISE unit size of 50-100 kt CO2/year capture capacity.

CROSS-MEDIA EFFECTS
For the implementation of STEPWISE technology, the following cross-media effects have to be considered:
 Disposal of end-of-life sorbents: The sorbent is composed of a magnesium/aluminium mixed metal-oxide, promoted with a potassium salt. As such, the sorbent constitutes a benign material, using elements that are abundantly present in nature. End-of-life adsorbent, however, can have accumulated trace elements that are present in the feed. Upon the large-scale implementation of the STEPWISE technology, the disposal of end-of life sorbents could result in large quantities intended for landfill. Sorbent recycling options, therefore, are being developed in conjunction to the identification of critical sorbent failure mechanisms to prolong sorbent life.
 Land-use: As for most carbon capture technologies, the amount of CO2 that can be separated is large, meaning that carbon capture installations are large and require significant land usage. This can be a limiting factor especially for brownfield applications that have limited available space.
 Water consumption: The STEPWISE technology uses steam as driving medium for the WGS conversion and the CO2 / H2 separation. Ideally, the steam is integrated with the power island of the plant in case this involves a steam cycle. Initial conservative estimates indicate that a steel plant water consumption would be increased by <10% for an implementation of the STEPWISE technology applying conventional water recuperation systems. However, this would need to be quantified in more detail on a case per case basis.


BARRIERS TO IMPLEMENTATION
When the H2 product is used for methanol synthesis, the methanol produced would classify as Recycled Carbon Fuels only if indeed the methanol is used as a fuel, as opposed to chemical feedstock for synthesising other products. In the field of product classification regarding chem-icals, the situation is not entirely clear at present and still under development which could cre-ate legislative hurdles for the implementation of the STEPWISE technology.
For the STEPWISE technology, the success of the implementation hinges on several critical factors, including CO2 transport and storage costs, availability of natural gas/green electricity, market dynamics, and regulatory frameworks. Regulatory frameworks relate to certainty on CO2 pricing mechanisms such as the ETS and CBAM directives, of which avoided costs present a benefit in the business case. Moreover, regulatory aspects related to CO2 transport and stor-age need to be clarified towards e.g. CO2 quality specifications and liability aspects related to long term sequestration (monitoring, certification). These factors will significantly influence the viability of scaling up the technology, as is the general case for CO2 capture technology imple-mentation.

Basic information about the technique

Participant Companies