Production of second generation (2G) ethanol through fermentation of CO-rich exhaust gases generated in ironmaking / steelmaking

Blast furnace carbon-rich emissions are converted into fuel-grade ethanol using a technology developed by Lanzatech. Ethanol production started in 2023 at the ArcelorMittal’s Steelanol plant in Ghent. This technology relies on a specialised biocatalyst that consumes gaseous feedstocks in specially designed fermentation bioreactors. The main feedstocks for LanzaTech’s plants are industrial emissions rich in CO, e.g. emissions from steel mills and ferroalloy facilities.

INNOVATIVE TECHNIQUE DESCRIPTION:

The key steps involved in this innovative technique are as follows:

• Transport, treatment and storage of BF gas: The BF off gas is transported using a large pipeline, diverted from the previous use for power generation. The plant operates with 100% BF gases (typically containing between 20-28% of CO), however a certain proportion of Basic Oxygen Furnace (BOF) off gases (containing about 64% CO) have also been successfully tried. The plant is currently treating about 1/7th of the excess BF process gas flow from two blast furnaces in operation at ArcelorMittal Ghent. Additional bioreactors could be built to increase this share, particularly as electricity grids decarbonise and there is less need to use BF gases for power generation.
The BF off gas requires minimal treatment prior to being transferred to the adsorption unit. This cleaning step consists in passing the gas through a dry dedusting system to remove particulate matter. In this phase, the gas is also cooled down.

• Compressor: The BF gases, which are at low pressure, are compressed once in the process to increase their pressure, and this facilitates the subsequent treatment steps.

• Pressure Swing Adsorption (PSA) unit: The compressed gases are fed into a PSA unit composed of 8 vessels of 70 m3 capacity, which separates the gas into two streams: a CO-rich stream and a CO2-rich stream. Typically, two vessels are in production mode (i.e. ad-sorption) while six other vessels are in regeneration mode (i.e. desorption). The CO2-rich stream is currently sent back to the power plant for post-combustion, while the CO-rich stream is directed to the bioreactor. In the future, the CO2 rich stream could undergo CO2 liquefaction and storage (CCS) or the stream could be used to produce more ethanol when H2 could be made available at affordable price.

• Bioreactor: The CO-rich stream is injected into the bioreactor, which operates at mild conditions (temperature and pressure) for the conversion of CO into ethanol. Each reactor contains water, ethanol, biocatalyst and other metabolites. The bacteria (Clostridium autoethanogenum) are natural, non-genetically modified supplied exclusively by LanzaTech. Overall, the design of the bioreactor enables a high CO utilisation of over 90%.

• Distillation column: The ethanol produced in the bioreactor is separated from the bacteria and other impurities through a distillation column. The final ethanol has a concentration of 98.7%, making it suitable for use as a sustainable fuel or chemical feedstock for production of e.g. synthetic fibres for the textiles market of for household cleaners or fragrances.

• Water treatment: Wastewater is generated as part of the process, but it is treated using an anaerobic treatment plant. After treatment, the treated water is reused entirely, minimising the need for clean water use.

DEGREE OF MATURITY:

The construction of the demonstration plant started in 2019. It was fully commissioned in September 2023. The plant production capacity is about 64,000 tons of ethanol (i.e. 80 million litres of ethanol). The ethanol is suitable for conversion via the Alcohol-to-Jet process into sustainable aviation fuels (SAF). The technology readiness level achieved is 9.

APPLICABILITY / TRANSFERABILITY TO OTHER SECTORS:
The LanzaTech fermentation process is applicable to multiple feedstocks and has been implemented in several commercial plants around the world for ethanol production. To date, six commercial facilities (four in China treating steel mill and ferroalloy off gases, one in India (treating refinery off gases) and one in Belgium (Steelanol) — use this technology, captur-ing carbon in industrial off gas and producing ethanol.

CROSS MEDIA EFFECTS:
No significant cross-media effects are reported.

BARRIERS TO IMPLEMENTATION:
There are regulatory barriers which constitute an obstacle for successful implementation of this technology. In particular, the ethanol produced is not currently recognised under EU legislation as either an 'advanced biofuel' or a 'recycled fuel'. Without classification, the ethanol cannot be used by fuel suppliers to meet decarbonisation targets and has limited commercial value.
For financial viability of this project, it is important that ethanol is recognised as a recycled fuel. To obtain such classification, the CO₂ footprint of the Steelanol plant should be at least 70% lower than an external fossil reference. This calculation must include the electricity no longer produced (Steelanol uses part of the BF gas to produce ethanol, which is no longer available to the power plant for electricity production). Because Steelanol is connected to the Belgian electricity grid with relatively high CO₂ footprint, this target is not met. Furthermore, the recent changes in RED II concerning the measurement of carbon isotopes and the allocation of bio-components to steel or ethanol significantly disadvantage the Steelanol. The CO₂ savings achieved with the Steelanol plant can only be deducted from the total emissions of the installation if the CO₂ is stored for a very long period (over 100 years), on the other hand the use in fuels does not count because the CO₂ is eventually released during combustion. Additionally, there is no integrated, regulated market focused on replacing fossil carbon in chemicals and products, leaving a significant gap in environmental circularity as 92% of carbon in EU-manufactured chemicals derives from virgin fossil feedstock. Difficulties in obtaining a classification of the ethanol produced as biofuel or recycled fuel and the fact that CO₂ savings from the Steelanol plant cannot be deducted present significant obstacles to the long-term profitability of the project.

Basic information about the technique

Production data

Associated main production process(es) and product(s): Production of 2G ethanol

Production data: 64,000 tons of ethanol per year

Participant Companies