Carbon Capture and Storage
Carbon Capture and Storage (CCS) is a technological process designed to reduce greenhouse gas emissions by capturing carbon dioxide (CO₂) from industrial and energy-related sources, transporting it, and storing it in secure underground geological formations. CCS is considered one of the key mitigation strategies for addressing climate change, particularly in industries that are difficult to decarbonise, such as cement, steel, and power generation.
Basics and Processes
The CCS process typically involves three main stages:
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Capture: CO₂ is separated from other gases produced in industrial or energy-related processes. Capture methods include:
- Post-combustion capture: CO₂ is removed from flue gases after fossil fuel combustion using solvents, membranes, or solid sorbents.
- Pre-combustion capture: Fuel is converted into a mixture of hydrogen and CO₂ before combustion, and the CO₂ is then separated.
- Oxy-fuel combustion: Fossil fuels are burned in oxygen instead of air, producing a flue gas with high CO₂ concentration, making separation easier.
- Transport: Captured CO₂ is usually compressed into a supercritical state and transported through pipelines, although ships and road tankers can also be used.
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Storage: The CO₂ is injected deep underground into geological formations where it can be securely stored. Suitable storage sites include:
- Depleted oil and gas reservoirs
- Deep saline aquifers
- Unmineable coal seams (where CO₂ may also enhance methane recovery)
Types of Storage
- Geological storage: The most common form, involving injection into deep porous rock formations capped by impermeable rock layers.
- Mineral carbonation: A process where CO₂ reacts chemically with natural minerals to form stable carbonates.
- Ocean storage (experimental): Injection into deep ocean waters, though this raises ecological concerns and is not widely pursued.
Applications of CCS
CCS is applied in various sectors, including:
- Power generation: Especially in coal and gas-fired power plants, where it reduces emissions significantly.
- Industrial processes: Used in cement, steel, chemical, and fertiliser production.
- Enhanced oil recovery (EOR): Injected CO₂ increases pressure in oil reservoirs, helping extract additional oil while storing CO₂.
Advantages of CCS
- Climate mitigation: Can prevent up to 90% of CO₂ emissions from large point sources from entering the atmosphere.
- Flexibility: Applicable to existing fossil-fuel infrastructure and hard-to-abate industrial processes.
- Energy transition support: Allows continued use of fossil fuels while renewable energy capacity expands.
- Job preservation: Supports industries and regions dependent on fossil fuels by providing a pathway to lower emissions.
Challenges and Criticism
Despite its potential, CCS faces significant challenges:
- High cost: Capture and compression require substantial energy, increasing operating costs.
- Energy penalty: Power plants with CCS consume more fuel to produce the same net electricity output.
- Storage risks: Concerns about CO₂ leakage, though evidence suggests well-managed storage is safe.
- Limited deployment: Despite decades of research, global CCS deployment remains modest compared to total emissions.
- Perception issues: Critics argue CCS may prolong reliance on fossil fuels instead of accelerating renewable energy adoption.
Evidence and Key Projects
Several large-scale CCS projects are in operation worldwide:
- Sleipner Project (Norway): Operating since 1996, stores CO₂ in a saline aquifer beneath the North Sea.
- Quest Project (Canada): Captures CO₂ from hydrogen production at an oil sands facility.
- Petra Nova Project (USA): Applied CCS to a coal-fired power plant, though operations were later suspended due to economic challenges.
- Gorgon Project (Australia): One of the largest CCS projects, linked to liquefied natural gas production.
These projects demonstrate the technical feasibility of CCS, though scaling up remains a major challenge.
Historical Development and Science
The concept of CO₂ storage dates back to proposals in the 1970s, initially linked to enhanced oil recovery. From the 1990s onwards, attention shifted to its climate mitigation potential. Advances in geophysics, reservoir modelling, and monitoring technologies have significantly improved confidence in long-term storage security.
Modern and Future Perspectives
CCS is increasingly integrated with emerging technologies:
- Carbon Capture, Utilisation, and Storage (CCUS): Where CO₂ is not only stored but also used for producing fuels, chemicals, and building materials.
- Direct Air Capture (DAC): Removing CO₂ directly from the atmosphere, combined with storage, represents a form of negative emissions technology.
- Bioenergy with CCS (BECCS): Using biomass for energy and capturing the resulting CO₂, potentially achieving net negative emissions.
Global climate strategies, such as those set out by the Intergovernmental Panel on Climate Change (IPCC), highlight CCS as necessary for meeting the Paris Agreement goals, especially in pathways limiting warming to 1.5–2 °C.
Significance
Carbon Capture and Storage is regarded as a critical transitional technology. While not a stand-alone solution to climate change, it offers a way to decarbonise sectors that are otherwise difficult to address, complementing renewable energy, efficiency improvements, and behavioural changes. Its long-term role will depend on advances in technology, reductions in cost, public acceptance, and political commitment to large-scale deployment.
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