Managing Atmospheric Pollution » Carbon Capture and Storage

What you'll learn this session

Study time: 30 minutes

What carbon capture and storage (CCS) is and why it's important
The three main steps in the CCS process: capture, transport and storage
Different carbon capture technologies and their applications
Storage methods and suitable geological formations
Benefits and limitations of CCS as a climate solution
Real-world examples and case studies of CCS projects
The role of CCS in meeting climate targets

Introduction to Carbon Capture and Storage

Carbon capture and storage (CCS) is a technology that can capture up to 90% of carbon dioxide emissions produced from the use of fossil fuels in electricity generation and industrial processes, preventing the CO₂ from entering the atmosphere. As global efforts to tackle climate change intensify, CCS is increasingly seen as a crucial tool in our toolkit to reduce greenhouse gas emissions.

Key Definitions:

Carbon Capture and Storage (CCS): A set of technologies aimed at capturing, transporting and storing carbon dioxide emissions from power plants and industrial facilities.
Carbon Dioxide (CO₂): A greenhouse gas produced by burning fossil fuels that contributes to global warming.
Sequestration: The process of storing carbon dioxide so that it doesn't enter the atmosphere.

🌎 Why CCS Matters

Even as we transition to renewable energy, many industries like cement, steel and chemical production will continue to emit CO₂. CCS offers a way to reduce these emissions while we develop cleaner alternatives. The Intergovernmental Panel on Climate Change (IPCC) has identified CCS as a critical technology for meeting climate targets.

📈 CCS and Climate Goals

To limit global warming to 1.5°C above pre-industrial levels, we need to reach net-zero emissions by 2050. CCS can help bridge the gap between our current energy system and a future low-carbon one, especially for hard-to-decarbonise sectors.

The Carbon Capture and Storage Process

CCS involves three main steps: capturing the CO₂, transporting it and storing it safely underground. Let's look at each stage in detail:

1. Carbon Capture Technologies

There are three main approaches to capturing carbon dioxide:

💡 Post-combustion

CO₂ is separated from flue gases after fossil fuel combustion. This can be retrofitted to existing power plants and uses chemical solvents to absorb CO₂.

💡 Pre-combustion

Fuel is converted into a mixture of hydrogen and CO₂ before combustion. The CO₂ is removed and the hydrogen is used as a clean fuel.

💡 Oxyfuel combustion

Fuel is burned in pure oxygen rather than air, resulting in a flue gas that is mainly CO₂ and water vapour, making CO₂ easier to separate.

2. Carbon Transport

Once captured, CO₂ needs to be transported to storage sites. This is typically done via:

Pipelines: The most common method for large-scale transport over land
Ships: Used for transport across seas or oceans
Road tankers: For smaller amounts over shorter distances

Before transport, CO₂ is compressed into a liquid-like state (supercritical fluid) to make it easier and cheaper to move.

3. Carbon Storage

The final step involves injecting CO₂ deep underground into suitable geological formations, where it can be stored permanently.

🔍 Suitable Storage Sites

Good storage sites include:

Depleted oil and gas reservoirs
Deep saline formations (layers of porous rock filled with salt water)
Unmineable coal seams

These sites need to be at least 800 metres deep, where pressure keeps CO₂ in a dense form and must have an impermeable cap rock to prevent leakage.

🛡 Storage Security

Several natural trapping mechanisms help keep CO₂ underground:

Structural trapping: Cap rock prevents upward migration
Residual trapping: CO₂ gets stuck in tiny rock pores
Solubility trapping: CO₂ dissolves in underground water
Mineral trapping: CO₂ reacts with rocks to form stable minerals

Direct Air Capture (DAC)

A newer technology in the CCS family is Direct Air Capture, which pulls CO₂ directly from the atmosphere rather than from point sources like power plants.

Uses chemical reactions to capture CO₂ from ambient air
Can help reduce historical emissions already in the atmosphere
Currently more expensive than point-source capture but costs are falling
Can be located anywhere, not just near emission sources

Case Study Focus: Sleipner Project, Norway

The Sleipner project in the North Sea was the world's first commercial CCS project, operating since 1996. Operated by Equinor (formerly Statoil), it captures CO₂ from natural gas processing and stores it in a deep saline formation 1,000 metres beneath the seabed. The project:

Stores about 1 million tonnes of CO₂ annually
Has stored over 20 million tonnes of CO₂ to date with no detected leakage
Was motivated by Norway's carbon tax, making it economically viable
Demonstrates that long-term, safe storage of CO₂ is possible

Benefits and Limitations of CCS

✅ Benefits

Can reduce CO₂ emissions by up to 90% from power plants and industrial facilities
Allows continued use of existing infrastructure while reducing emissions
Helps decarbonise industries where alternatives are limited (cement, steel)
Creates jobs in construction, operation and monitoring of CCS facilities
Can be combined with bioenergy (BECCS) to achieve negative emissions

❌ Limitations

High costs compared to some other mitigation options
Energy penalty (10-40% more energy needed to run capture equipment)
Public concerns about safety and potential leakage
Limited deployment to date despite decades of development
Requires suitable geology for storage, which isn't available everywhere

CCS Around the World

CCS deployment is growing globally, though not as rapidly as many climate scientists recommend:

UK: Plans for industrial CCS clusters in Teesside and Humberside
USA: Tax credits (45Q) supporting multiple projects
Canada: Boundary Dam power plant was the first commercial CCS facility on a coal plant
Australia: Gorgon project captures CO₂ from natural gas processing
China: Rapidly expanding CCS research and pilot projects

Case Study Focus: Drax BECCS Project, UK

Drax power station in North Yorkshire is developing bioenergy with carbon capture and storage (BECCS). This involves:

Burning sustainable biomass (wood pellets) instead of coal
Capturing the CO₂ emissions from this process
Storing the CO₂ under the North Sea

Since the biomass absorbs CO₂ as it grows and this CO₂ is then captured when the biomass is burned, the overall process can remove CO₂ from the atmosphere – creating "negative emissions." Drax aims to become carbon negative by 2030, removing more CO₂ from the atmosphere than it produces.

The Future of CCS

For CCS to play its expected role in climate mitigation:

Costs need to continue falling through technological improvements and economies of scale
Supportive policies like carbon pricing or tax incentives are needed
Public acceptance must be secured through transparent communication
Infrastructure for CO₂ transport and storage needs expansion

The IPCC suggests that without CCS, the cost of limiting global warming to 2°C could be more than twice as high. While renewable energy and energy efficiency remain crucial, CCS offers a way to address emissions from sectors that are difficult to decarbonise through other means.

Summary

Carbon capture and storage represents an important technology in our fight against climate change. By capturing CO₂ emissions before they enter the atmosphere and storing them safely underground, CCS can help reduce the impact of fossil fuel use while we transition to cleaner energy sources. Though challenges remain in terms of cost and scale, successful projects around the world demonstrate that CCS is a viable option that can contribute significantly to meeting our climate goals.

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