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Carbon capture and storage

Carbon capture and storage (or CCS for short) refers to the capture, transport and storage of carbon dioxide (CO2) from emissions, to prevent it from entering the atmosphere. In order to be useful to climate change mitigation, storage CO2 will need to be stored for many 100s of years until well past the end of the fossil fuel era.

Carbon capture

Carbon capture is best applied to large stationary sources, such as power stations and industrial plants, where carbon dioxide (CO2) can be separated from the flue gases at some stage of the process. Therefore, applying CO2 capture to the UK's energy industries has the greatest potential to reduce current emissions. There is a range of capture technologies at different stages of development. The most developed carbon capture technology has been used in the petroleum and gas industry for almost a century and has already been applied to a few small power plants abroad, which produce CO2 for Enhanced Oil Recovery (EOR) or industrial uses. In principle, and subject to scale-up issues, this technology could be retrofitted to the UK's existing power stations, as well as included in new builds. All capture technologies consume energy and reduce the efficiency of the power station.

Transport

Carbon generally needs it to be compressed, cooled and dried for transport, requiring greater energy input and reducing plant efficiency. Bulk transport may be by tanker or pipeline. Tankers may have a role in smaller projects, but for larger volumes pipelines are the only practical option. Carbon dioxide transport by pipeline is an established commercial technology. Over 3000km of pipelines are currently used to transport several million tonnes of CO2 per year for Enhanced Oil Recovery in the US and Canada.

Storage

There are several potential options for storing captured CO2. Currently the most viable and environmentally acceptable is geological storage. Carbon capture and storage in geological formations involves capturing CO2 and then injecting it into rock layers. There are three main storage options:

• Depleted or near-depleted oil and gas fields
• Deep saline aquifers (porous rock layers containing salty water deep underground)
• Unmineable coal seams

Under most storage conditions in permeable rock CO2 is buoyant and moves to the top of the rock layer. If the rock above offers an effective seal it is trapped and stored. Other processes can also result in efficient long-term storage in geological structures. For example, permeable rocks commonly have their pore spaces filled with water in which injected CO2 may dissolve and/or CO2 may react chemically with water or minerals in the rock and be immobilised.

The key issue is the ability of geological structures to retain CO2 over 100s to 1,000s of years without it leaking out, which is essential for the inclusion of carbon capture and storage in emissions trading and in any environmental impacts. Technology for CO2 storage in coal seams is at an early stage, but there is greater understanding of storage in oil and gas fields and saline aquifers. The oil and gas fields and aquifers in the UK sector of the North Sea are estimated to have large storage potential.

Current implementation

As a form of Enhanced Oil Recovery (EOR), CO2 is already being pumped into near-depleted oilfields in the US and elsewhere to extend their lifetimes. In Norway, Statoil has been re-injecting CO2 co-produced with natural gas into a deep aquifer overlying its offshore Sleipner field, solely for storage. Since 1996, 1 million tonnes of CO2 per year has been stored here.

SEPA's role

SEPA is the environmental regulator in Scotland for the primary environmental legislation which will cover carbon capture and storage. These include the EU Emissions Trading Scheme (EU ETS), the Pollution Prevention and Control (PPC) Directive and the Large Combustion Plant Directive (LCPD). Through these pieces of regulation, SEPA regulates some of the largest stationary sources of carbon dioxide in Scotland. In addition to direct influence through regulation, SEPA will also be involved through statutory duties within the land use planning system and Local Air Quality Management system (LAQM), and through day to day communication and influencing with EU, UK and Scottish Government, industry and the general public.