Health and Environmental Impacts of Amine-based CO2 Capture Plant – A literature review

Introduction

In-situ oil sands extraction (SAGD) is widely used in Western Canada to produce the large reserves of hydrocarbon resources in the region. These plants are energy intensive with large volumes of natural gas required for steam generation. The associated emission of greenhouse gases (GHG) from combustion processes is attracting increased attention from all stakeholders in the context of efforts toward mitigation of global warming. Various approaches have been proposed to limit the emissions of CO₂, and among those approaches, amine-based CO₂ absorption systems have received significant attention for combustion-based plants for the following reasons [1]:

(1) These systems are effective for dilute CO₂ streams (typically flue gas has 10%-12% CO₂ by volume).

(2) Amine-based systems are a proven technology which has been widely used in gas sweetening.

(3) Amine-based CO₂ capture systems can operate at normal temperatures and pressures.

(4) A major effort worldwide has been made to improve and investigate this process.

An amine-based CO₂ capture plant in Mongstad, Norway is shown in Figure 1 [8]:

Figure 1. CO₂ Capture Plant in Technology Centre Mongstad (Norway) [8].

Assuming that the technology can be successfully deployed, there have been concerns related to the large-scale use of amines and to the potential environmental and health effects of monoethanolamine (MEA). This review focuses on these impacts and in potential effects on surface water.

Health and Environmental Impacts of Amine-based CO₂ Capture Plant

Process Ecology conducted an extensive literature review on the subject of amine emissions (including emissions of amine degradation products) under PTAC sponsorship [2].

Figure 2 shows the possible emission sources of amine and its degradation products from the typical configuration of the CO₂ capture process.

Figure 2: Possible emission sources of amine and amine degradation products from CO₂ capture [3].

For the amine-based CO₂ capture process, most of the amine losses would be released to air directly, unless there is some control technology on the absorber overhead. Without control, entrainment and vapourization losses would be released to atmosphere from the top of the absorber. The amine degradation products (largely due to the impurities in the flue gas) would also be released directly to air. A water wash section can help in reducing the amine and amine degradation products emissions to the air. It has been reported that amine losses may be reduced significantly with a water wash step [5]. Moreover, a variety of degradation products including nitrosamine can be formed in the CO₂ capture process (mainly in the absorber) and they would also be released.

After amines are released to air, they degrade into other chemical compounds. The atmospheric reactions are complex and compounds including nitrosamines can be formed. A 2% conversion rate from MEA released to atmosphere to nitrosamine has been used in the literature to conduct a worst case study [6]. The amines and amine degradation products' fate can deposit them in surface waters in the long term, which may pose a risk to drinking water sources.

Process Ecology also conducted an environmental fugacity study through a third party company to investigate the concentration of MEA which may be released to various media, including water, using emission data from literature. With a conservative 2% conversion rate from MEA to nitrosamine, it was shown that the amine-based CO₂ capture process has the potential to put surface drinking water sources at risk in Alberta that near CO₂ capture facilities. Of course, some advanced emission control technologies may be able to reduce or eliminate the risk. Nitrosamine and nitramine degradation products are found to pose the highest risk to human health and environment for a CO₂ capture facility.

Although a significant amount of literature is available, there is still a lack of real plant data and online measurements on the issue of amine emissions for companies and policy-makers to make sound decisions. With CO₂ capture attracting increasing attention in order to reduce GHG emissions from SAGD and other industrial plants, including power plants, it is important to fully understand and control the risk of amine emissions from this process. One report [3] recommended no commercial amine based CO₂ capture plants should be built before the knowledge gaps are filled (not expected by 2020). Another study [7] pointed out that since most CO₂ emission facilities are concentrated in the proximity of major industrial regions, it is important to realize the potential overlapping of amine emissions (including nitrosamines and nitramines emissions) in the same area.

Further studies need to be performed to: 1) Further fill knowledge gaps, especially on amine emission rates from real plants – by direct measurement and additional modelling; 2) Further develop control technologies to reduce amine emissions directly to air; 3) Further investigate the fate of amines when released to air; 4) Establish regulations on amine and amine degradation product emissions for the CO₂ capture process once sufficient data is available.

Conclusions

Amine-based solvent absorption is considered to be a suitable technology for the CO₂ capture process using currently best available technology. Health and environmental impacts need to be fully understood to make sound decisions. Process Ecology conducted an extensive literature review on this subject under PTAC sponsorship, and results show that the amine-based CO₂ capture process has the potential to put at risk surface drinking water sources in Alberta that are near CO₂ capture facilities.

References

Anand B. Rao and and Edward S. Rubin A Technical, Economic, and Environmental Assessment of Amine-Based CO₂ Capture Technology for Power Plant Greenhouse Gas Control Environmental Science & Technology 2002 36 (20), 4467-4475.
PTAC website http://auprf.ptac.org/air/literature-review-use-environmental-impact-of-amines-2/
Shao, Renjie, and Aage Stangeland. "Amines Used in CO2 Capture." Oslo, Norway: The Bellona Foundation (2009).
Bhurisa Thitakamol, Amornvadee Veawab, Adisorn Aroonwilas, Environmental impacts of absorption-based CO₂ capture unit for post-combustion treatment of flue gas from coal-fired power plant, International Journal of Greenhouse Gas Control, Volume 1, Issue 3, July 2007, Pages 318-342.
Kentish, S.,Hooper, B.,Stevens, G.,Perera, J.,Qiao, G.(2008).An overview of technologies for carbon capture.AIE National Conference.
Karl, Matthias, et al. "Worst case scenario study to assess the environmental impact of amine emissions from a CO₂ capture plant." International Journal of Greenhouse Gas Control 5.3 (2011): 439-447.
Karl, Matthias, et al. "Uncertainties in assessing the environmental impact of amine emissions from a CO₂ capture plant." Atmospheric Chemistry and Physics 14.16 (2014): 8533-8557.
Technology Centre Mongstad (TCM) Press Center Website:http://www.tcmda.com/en/Press-center/

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