Background

Amine based post combustion CO₂ capture technology is widely seen as a promising option for reducing atmospheric emissions of CO₂. Great efforts have been made to develop and demonstrate this technology. However less attention has been given to the likely emissions of amines and their degradation products, some of which are well known to be harmful to human health and the environment. The components of concern do not currently figure in the emission slate of power plants. Standards and legislation are thus not fully developed for their control, particularly considering the scale on which CCS plants may be deployed. A full understanding of the nature of the likely emissions and the limits which need to be imposed is necessary so that appropriate improvements in the capture process can be made to protect human health and the environment from adverse impacts. This study was executed to identify the chemical species likely to be emitted, estimate the levels of emission expected from the present generation of capture plant designs, assess what emission limits might be applied and research the process modifications needed to meet these limits.

Conclusions

The main conclusions of the report can be summarised as follows:-

• Detectable levels of lighter components will probably be emitted to atmosphere from amine based capture plants employing single water wash technology.

• Emissions to air of heavier degradation products will be at well below detectable levels.

• Application of an additional acid wash is an effective way of eliminating emissions of the lighter components.

• The preferred choice of demister seems to be the Swirl Mist Eliminator (SME).

• Emissions standards are not yet set for many of the substances which are likely to be emitted.

• Stringent emissions standards and regulatory requirements to adopt best available techniques can be expected particularly so if even the presence of trace amounts of known carcinogens are confirmed.

• More research into emissions and their measurement is required.

• Regulatory authorities have much work to do to create an appropriate emission standards which can be applied to MEA based CO₂ capture processes.

• Some alternative solvents have lower emissions but may still need to apply similar additional clean up steps

Recommendations

Further work on chemical emissions from solvents should be promoted and in particular pilot and demonstration projects should be encouraged to monitor actual measurements of these emissions during normal operation and make detailed measurements during test runs. They should also be encouraged to measure and report on the build-up of the full range of degradation products with time. Requests for this type of information should be included in surveys of demonstration projects under the Phase 2 of the “What We have Learned” data collection and analysis initiative.

Work is also needed to assess the fate of any emissions in the atmosphere and the programme could consider carrying out a study of available results once a substantial body of scientific information on this is available.

The inclusion of an acid wash in the post combustion capture process appears to offer a simple but robust catch all solution to this emerging issue. Further work needs to be done to establish how this should be implemented including whether a final water wash is needed. Development of this could be the domain of process licensors but this could be controversial given the additional cost and complexity implications. The programme should in the first instance promote adoption of a completely “clean” solution but could also consider commissioning an engineering contractor to further study and cost out suitable designs.