Vattenfall - SEA report

Strategic Environmental Assessment of CO₂ Capture, Transport and Storage

The adapted Strategic Environmental Assessment (SEA) methodology is found to be a useful tool when structuring the environmental aspects and performing the assessment. The methodology is also transparent and suitable for communication with stakeholders that show a greater interest in the concept.

The world is dependant on fossil fuels for its energy supply. The use of fossil fuels leads to emissions of carbon dioxide (CO₂) that contributes to climate change. Establishing a sustainable energy system without climate effects will take time, and it is urgent to mitigate global warming.

The concept of capturing CO₂ from coal fired power plants and storing it underground in geologic reservoirs is a way of keeping CO₂ away from the atmosphere, thereby minimising the effects on climate. Underground storage of CO₂ can be used as a bridging technology to minimise impacts on the climate while we develop and commercialise a new sustainable energy system.

Before commencing a CO₂ capture and storage project, it is important to perform a screening of potential environmental impacts that may occur, both during normal operations where the concept works according to plan, and in case of a leakage. In the screening process, the critical aspects from an environmental viewpoint are identified as focus areas for further studies. Comprehensive knowledge will aid the concept design and allocation of resources, and minimise or obviate environmental impacts and risks. An important challenge lies in the technical development of the concept and in calculations and preventions of risks for leakages and sudden gas releases, as well as studies of ecosystem effects. The adapted Strategic Environmental Assessment (SEA) methodology is found to be a useful tool when structuring the environmental aspects and performing the assessment. The methodology is also transparent and suitable for communication with stakeholders that show a greater interest in the concept.

The by far dominating environmental effect resulting from the CO₂ capture processes, is the reduction of emissions to air. A significant decrease in all air emissions, especially CO₂, is expected for all power plants with CO₂ capture. It is still important to consider other environmental aspects relating to capture of CO₂, such as the decrease in energy efficiency of the power plant. The choice of capture technology is however expected to be mainly influenced by factors relating to economy and technology, rather than differences in environmental effects.

The main questions of concern with respect to CO₂ capture, transport and storage relate to leakage:

• Will the storage reservoir leak?
• If it leaks, how much will it leak?
• What are the consequences of a leakage?

The magnitude and type of potential environmental impacts and hazards are very dependant on site characteristics. Detailed assessments of environmental effects are difficult to perform, other than at a general level, before a site has been chosen. The information gained in the strategic environmental assessment will be used in the site selection process in order to decrease the risks of environmental impacts and avoid sensitive areas.

At an organism level, tolerance thresholds relating to increased CO₂ concentrations will vary between species and phyla and thresholds have not been quantified for most organisms. Due to the differences in sensitivities between different species, a continuum of impacts on ecosystems is more likely than the existence of a well-defined threshold beyond which CO₂ cannot be tolerated.

In case of a leakage, it is important to be aware of the potential environmental consequences. There are still areas where the knowledge is very limited and these areas require more research. Most important is to develop good estimates of the concentration and duration time in case of a potential leakage. Research can be conducted through modelling, studies of analogue activities and through pilot and demonstration projects. Many research projects and efforts are currently on-going. In order to plan future work it is necessary to rank knowledge gaps so that the right priorities can be made with respect to research resources and funds.

Main conclusions - CO₂ capture

• The main environmental impact resulting from CO₂ capture is a significant decrease in all air pollutants.
• For CO₂ capture, the negative environmental impact is mainly associated with the increased energy demand.
• Other effects relate to the increased consumption of resources, such as fuel, water and chemicals, and the increased generation of waste, such as solid waste, sludge and by-products.
• The choice of capture technology will mainly be influenced by factors relating to economy and technology, rather than differences in environmental effects.
• The high CO₂ recovery of oxyfuel combustion makes it a very promising technology. An added advantage is that no additional pollutant species are introduced in the capture process. The technology still has to be verified at a large scale.

Main conclusions - CO₂ transport and storage

• Through an informed site selection, a good knowledge base and technical solutions for monitoring and safety, the environmental risk and effects can be managed and minimised.
• There is good knowledge on how environmental impacts, resulting from the operation and maintenance of a CO₂ transport and storage system, can be minimised and controlled.
• With respect to the risk of a leakage, there are two main types of leakage scenarios:

Short-term high leakage rate scenario

− Relatively easy to detect and measure
− Emissions easier to control / remediate
− Potential effects relate mainly to impacts on organisms, such as humans and mammals

Long-term low leakage rate scenario

− Difficult to detect and measure
− Effects are difficult to predict and quantify
− Emissions difficult to control / remediate
− Potential effects relate mainly to the climate and the biodiversity of ecosystems

Main risks identified are:

− Groundwater pollution (leaked CO₂ can cause a decreased pH in groundwater and lead to dissolution of heavy metals present in the soil)
− Leaked CO₂ accumulating in depressions and sheltered areas, causing hazard to humans and animals
− Long-term seepage of CO₂ resulting in climate effects and effects on the biodiversity of ecosystems

• It is easier to monitor losses from the transport system compared to the storage system, which results in a smaller risk for undetected longer-term leakages.
• Leakages from the transport system can only occur during the operational phase (<100 years), which simplifies monitoring and decreases the risk of leakage.
• Pipeline routes may cause some environmental disturbance and interfere with other interests (land owners, nature protection areas, military interests etc.).
• The magnitude and type of potential environmental impacts and hazards are very dependant on site characteristics.
• Local environmental impacts resulting from a release of CO₂ depend on the resulting concentration and ambient conditions, rather than the amount of CO₂ released.

What is known today?

• Human health and safety effects due to elevated CO₂ concentrations are relatively well known.
• There is knowledge on effects of increased CO₂ concentrations on individual organism groups.
• Experiences from natural analogues (hydrocarbon reservoirs) show that the CO₂ should be able to be stored for very long time periods (thousands of years).
• Experiences from natural leakages can be used to study environmental effects.

Gaps in knowledge

• Knowledge on environmental impacts of co-captured components, other than CO₂, in the gas stream is limited.
• There is little knowledge on environmental impacts at an ecosystem level.
• The effects on subsurface microbial populations are not well studied.
• Impacts on the energy system caused by the increased energy demand that results from CO₂ capture require further investigation.

The success of a CO₂ capture, transport and storage project relies on us, to make the right choices, such as proper site selection methods and criteria, use of best available technology, thorough monitoring and plans for mitigation and remediation. If efforts are made to minimize risks of leakage, then the probability of a leakage that reaches the shallow subsurface and the atmosphere is considered to be low.

SEA report - Full document (PDF 1418 kb)

SEA report - Appendix 1 (XLS 42 kb)

SEA report - Appendix 2 (XLS 97 kb)