Power Plant Exhaust Gases Could Be Recycled as a Raw Reaction Material

A research group at Nagoya University has developed a new technology that can drastically conserve the energy used to capture carbon dioxide (CO₂), one of the greenhouse gases, from facilities such as thermal power plants. Conventionally, a significant amount of energy (3 to 4 GJ/ton-CO₂) or high temperatures exceeding 100°C has been required to capture CO₂ from gases exhausted from a concentrated source, and there are expectations of the development of CO₂ capture technology that consumes less energy.

The research group led by Assistant Professor Hiroshi Machida has developed an unprecedented CO₂ capture technology, namely H₂ stripping regeneration technology, in which hydrogen (H₂) gas is supplied to the regeneration tower (desorber). It is indicated in this research that, with the implementation of this new technology, combustion exhaust gas can be replaced by CO₂/H₂ gas at lower temperatures (85°C) than those used in conventional technology. The further reduction of energy can be achieved when it is combined with technologies such as those involved in the promotion of exhaust heat utilization and recovery of reaction heat.

This new technology can exhibit the world's highest energy-saving performance (i.e., separation and collection of energy required is less than 1 GJ/ton-CO₂ when a desorber temperature is 60°C) when it is combined with the phase-separation solvent that this research group has also developed.

This technology is expected to be applicable to value-added material production such as the syntheses of methane, methanol, gasoline, etc., from CO₂ in the combustion exhaust gas and H2 from renewable energy, and is expected to contribute to carbon recycling.

H₂ stripping regeneration technology

In the conventional process to synthesize fuel or chemicals from CO ₂ and renewable H ₂ , pure CO ₂ is collected and is then mixed with H ₂ before being supplied to the reduction reactor. In the H ₂ stripping regeneration technology, H ₂ gas is supplied at the bottom of the desorber. As a result, CO ₂ partial pressure in the desorber is lowered, which promotes regeneration and lowers the regeneration temperature. The mixture of CO ₂ and H ₂ gases collected from the head of the desorber is supplied directly to the synthesis reactor.

Regeneration tower

In the amine absorption method, CO ₂ absorption and regeneration towers (i.e., absorber and desorber) are used to separate and collect CO ₂ in the exhaust gas mixture from facilities like power plants. Gases such as N ₂ and O ₂ , in addition to CO ₂ , are included in the combustion exhaust gas from these facilities and pure CO ₂ gas is collected with this amine absorption method. Only the CO ₂ gas is absorbed in the absorber by amine solution, and it is then heated in the desorber to regenerate pure CO ₂ gas. In other words, only CO ₂ gas can be extracted from the mixture of gases.

Reference

Machida et al. (2020). Energy-Saving CO ₂ Capture by H ₂ Gas Stripping for Integrating CO ₂ Separation and Conversion Processes. ACS Sustainable Chemistry & Engineering . DOI: https://doi.org/10.1021/acssuschemeng.0c02459

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