ClosedCarbonLoop (CCL)

The X-Energy sub-project ClosedCarbonLoop (CCL) explored the optimisation of the CO₂ cycle when using atmospheric carbon dioxide for power-to-gas (PtG) technologies. For this purpose, an existing plant at the CC4E Energy Campus Technology Centre consisting of electrolysis, biological methanisation and reconversion into electricity (using combined heat and power generation) was supplemented by a CO₂ adsorption plant, a so-called Direct Air Capture (DAC) plant, from the project partner Climeworks.

The plant uses a process to capture carbon dioxide from the ambient air, which is then used in a downstream methanisation process to produce methane (CH₄). PtG and power-to-liquid (PtL) concepts will be necessary in the future to temporarily store large surpluses from renewable energies over a longer period of time. Moreover, the DAC technology is flexible in terms of operation over time, which is essential for stabilising the electricity grid.

The DAC system on the roof of the CC4E Technology Centre at HAW Hamburg has been in regular operation since June 2021. During this time, extensive characterisation of the mass flows and detailed mass balancing as part of the power-to-gas process have been carried out. The concept of the DAC pilot plant was supplemented by the installation of an elaborate dehumidification system to minimise the formation of corrosive carbonic acid in order to ensure accurate flow measurements and the installation of additional sensors to monitor the test cycles. The system was controlled automatically using MQTT signals.

Results

Three computer models were developed, one for predicting future generation data with acceptable accuracy, one for precise forecasts of future electricity consumption and an additional optimisation model. This optimisation prevents a positive residual load so that the DAC system is operated in a way that is beneficial to the system. The optimised mode of operation has shown that the plant can be operated in a way that serves the system by more than 80 %.

To analyse the performance of the CO₂ adsorber, the influence of weather conditions and the CO₂ concentration in the air on the CO₂ yield of the DAC system was examined. For this purpose, the data from the continuous recording of the sensors for temperature, CO₂ concentration and humidity were analysed.

The investigations into the potential analysis of DAC technology for CO2 adsorption showed that, assuming the speed of technological DAC development, the prime costs of CO2 capture by a DAC through the combined use of fossil-free electricity, industrial waste heat and high CO2 certificate prices could generate the first annual profits for a fictitious cement company from 2033 at a cost point of approx. 320 €/t CO2 at national level, or 2036 at a cost point of approx. 380 €/t CO2. The implementation of flexibly operated DAC plants in the Hamburg district heating system for the year 2045 showed that DAC plants can be a building block in achieving the NET-Zero target.

A more detailed presentation of the results can be found in the final report of the project. 

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Further background information on the X-Energy sub-project ClosedCarbonLoop (CCL) can be found on the CC4E YouTube channel: How the direct air capture system at the Bergedorf Technology Center works. (only German)