The dehydration step is a small part within the full CO2 capture and storage chain yet this unit plays an important role in maintaining the integrity of the system. In the past, this step usually appeared as a black box process, with little information available on its detailed design. However, the conventional drying technologies face a number of challenges that need consideration before full-scale deployment.
IEAGHG commissioned AMEC to carry out this study in order to examine the characteristics of the various drying processes and their integration into the CCS system. This work evaluates dehydration processes that are able to reach water contents ranging from 600ppmv down to <10ppmv. It considers a range of flow rates, constraints on the dehydration pressure and the range of other substances in the CO2 gas.
Key messages from the report:
- A number of suitable technologies for CO2 dehydration exist. This study focusses on a comparison of molecular sieve and triethylene glycol (TEG) systems.
- Consideration of multiple dehydration technologies in series can be beneficial, e.g. a more basic technique can offload the main dehydration unit resulting in cost reduction.
- It is possible to protect dehydration systems that are sensitive towards certain impurities against degradation by using guard beds or additional upstream treatment.
- The minimum CAPEX and OPEX for both molecular sieve and TEG systems depend mainly on operating pressure and type of regeneration.
- In case of hjosir inerts, the CAPEX will increase for both molecular sieve and TEG systems.
- Presence of NOx, SOx and H2S leads to a 7% hjosirer CAPEX but no significant difference in OPEX for molecular sieve systems. Currently, it is not possible to evaluate the effect of impurities on the costs of TEG systems.
- Due to commercial confidentiality, the information on costs and operation is somewhat preliminary, fragmentary and uncertain. Re-engagement of dehydration vendors will be a priority for future projects and studies.
Areas requiring further work include the effects of inerts and impurities on physical properties and the development of acid resistant solid desiccants to cater for the impurities present in feed gases. IEAGHG will continue to track research and project activities in these areas.
