Carbon capture of blast furnace flue gas emissions by absorption using an amine demixing solvent (3D DMX)

This innovative technique enables carbon capture from blast furnace flue gases via a CO2 absorption process that employs a demixing solvent (designated as DMX), which is composed of a blend of two different amines. It was developed by IFP Energies Nouvelles and tested in a large-scale demonstration plant at ArcelorMittal in Dunkirk, in collaboration with Axens and TotalEnergies. This development was financially supported under the EU Horizon 2020 project 3D DMX, over the period 2019 - 2024.

TECHNICAL DESCRIPTION:
This innovative technique consists in an amine-based absorption process for capture of CO2 in blast furnace (BF) gas. Compared to other amine-based carbon capture processes, the DMX process enables liquid-liquid separation between a CO2-rich phase and a CO2-lean phase using a decanter. Indeed, the two amine compounds are demixing under certain conditions of temperature and CO2 partial pressure. Only the CO2-rich phase is further processed in the regeneration section (stripper) for production of a pure CO2 stream while the CO2-lean phase is sent back to the absorption section, resulting in significant reduction in the overall heat demand (reduced energy consumption).
The DMX technology comprises the following steps:

• BF conditioning and compression: The BF flue gases are taken from an existing process line and sent to a conditioning unit to remove particulate matter and to a compression unit, in order to compress the gas to the required level for the DMX absorber inlet and to test different operating pressures (different application cases studied).

• Absorption: The compressed feed gas enters the first absorber at the bottom, where it flows counter-currently to the solvent flow. After the absorber, the CO2-rich solvent is preheated using an heat exchanger, creating favourable conditions for demixing of the solvent in the decanter. On the other hand, the CO2-lean gas leaving is further treated in a second absorber before entering a water wash section. After the water wash section, the treated gas is sent back to the BF gas network. Typically, the absorption section operates at a temperature range between 22°C to 25°C.

• Decanter: After heating, the rich-CO2 solvent is fed into the decanter where it is allowed to settle and separate into two phases. The heavy phase, which is rich in CO2, is sent to the stripper for regeneration, where the CO2 is released and the solvent is regenerated. The light phase, which is lean in CO2, is recycled back to the absorber, where it can be reused to capture more CO2.

• Regeneration: The regeneration section consists of a stripper which is a vessel designed to heat the CO2-rich solvent and release the absorbed CO2. The stripper is typically operated under slight vacuum. The CO2-rich solvent is fed into the stripper where it is heated to a temperature of about 130°C and up to 150°C depending on the application case. Heat is generated using a reboiler that consumes steam. As the solvent is heated, the CO2 is released and rises to the top of the stripper. The lean solvent, now depleted of CO2, is cooled down to about 20°C to 40°C and recycled back to the absorber.

The industrial demonstration plant capacity is 0.5 ton CO2 captured / hour. Overall, a CO2 capture rate > 90% was reached during long term testing of the demonstration plant.


PROCESS OPERABILITY:
The DMX carbon capture pilot plant showed excellent performance and reliability during its operation. The key results and achievements are summarised below:
• Long-term operation: The plant has operated for approximately 5000 hours in capture mode, with more than 100 parametric tests carried out to optimise its performance. The unit has shown the ability to run at night and weekends without supervision, demonstrating its reliability and automation capabilities.
• Solvent degradation: The solvent has exhibited minimal degradation (<0.5% after 5000 hours), well below the initial target solvent degradation of 5%. However, it is important to note that the BF gas that was used during the testing contained low concentrations of NOx and SOx, compounds that could potentially degrade the amine solvents over time. Further degradability tests using a more contaminated feed gas are necessary to study the long-term stability of the solvent (depending on the future application case selected and the flue gas composition).
• Temperature resistance: The solvent has demonstrated excellent resistance to high temperatures, withstanding temperatures up to 158°C without significant degradation. Normally, the plant operates at around 130°C, actually the possibility of heating up the solvent to higher temperatures is a bonus, since it enables the compression of CO2 at higher pressures.

DEGREE OF MATURITY:
Key elements of the DMX process have reached TRL 7, in particular the absorber and the regeneration section.

PURITY OF CO2 CAPTURED:
the DMX process can lead to a CO2 purity over 99%. For storage, however, the CO2 has to meet fluid specifications of the storage facility, in particular regarding the acceptable level of impurities in the gas. Two key CO2 storage projects in Europe, envisaged to be used by ArcelorMittal Dunkirk, are Northern Lights in Norway and Porthos in the Netherlands.
For BF gases, the most important impurities to consider are water, CO and the sulphur content (e.g. H2S). For these, additional polishing techniques of the CO2 gas may need to be employed to reach the required fluid specifications. For instance, the CO content in the CO2 captured via the DMX process is currently too high to meet the very tight Northern Lights specifications, and additional treatment techniques (e.g. cryogenic separation, catalytic oxidation) are needed to meet these specifications.

CROSS-MEDIA EFFECTS
• Increased energy consumption: A high amount of energy (steam) is required to operate the DMX process, even if this technology has been shown to be one of the least heat consuming technologies.
• Generation of waste or residues: Solvent waste and solvent degradation products are generated during the process operation. These hazardous wastes are commonly destroyed by incineration in specific wastes treatment plant
• Use of hazardous substances: The DMX solvent is a hazardous substance which is corrosive and toxic for the environment. Operating procedures and systems are designed to prevent operator’s exposure to the solvent and environmental pollution.

Basic information about the technique

Cross media effects

• High consumption of energy/raw materials
• Increase of waste generation
• Use of hazardous substances

Participant Companies