About this video

• Video Title: Carbon capture and storage technologies for the sustainable use of fossil fuels
• Channel: Solar Future Now
• Speakers: None specified
• Duration: 14:36

Overview

This video explains carbon capture and storage (CCS) technologies as a method to mitigate the environmental impact of fossil fuel usage. It details the three main phases of CCS: capture, transport, and storage, and discusses various capture methods like post-combustion, pre-combustion, and oxy-fuel combustion, along with their advantages and disadvantages. The video also touches upon the transportation and geological storage of captured CO2, and the current state and future potential of CCS technology.

Key takeaways

• Fossil Fuel Reliance: Despite environmental concerns, fossil fuels still meet approximately 80% of global primary energy demands, and are projected to account for about 40% even by 2050.
• CCS as a Solution: Carbon Capture and Storage (CCS) technologies are presented as a way to significantly reduce CO2 emissions from fossil fuel use, particularly from power stations, heavy industry, and the petrochemical sector.
• Three Phases of CCS: The CCS process involves capturing CO2 at the emission source, transporting it to a storage site, and injecting it underground into geological formations.
• Capture Technologies:
  • Post-combustion: The most diffused method, retrofittable to existing plants. It involves separating CO2 from flue gas after combustion, often using chemical absorption. It can reduce CO2 by over 90% but is energy-intensive and increases electricity costs.
  • Pre-combustion: CO2 is removed from the fuel before combustion. This method is less common due to higher costs and limited applications, though it produces hydrogen as a byproduct.
  • Oxy-fuel combustion: Fuel is burned in nearly pure oxygen instead of air, resulting in a flue gas primarily of CO2 and water, simplifying capture. It inherently produces fewer nitrogen oxides but is expensive due to the energy-intensive process of separating oxygen from air.
• Transport and Storage: Captured CO2 can be transported via ships, pipelines, or a combination, and stored underground in geological formations like depleted oil and gas fields or saline aquifers. Storage mechanisms include structural, where CO2 is trapped by impermeable rock, and mineral storage, where CO2 chemically binds with the rock. Enhanced oil recovery (EOR) is also a method of storage.
• Challenges and Future: While CCS can significantly contribute to emissions reductions, major barriers include high costs, potential CO2 leakage, public opposition, and the need for widespread implementation of carbon markets and government support for identifying and developing storage sites. Public acceptance and improved communication are also crucial for successful deployment.

Post-combustion carbon capture involves capturing CO2 after the combustion of fuel. The process generally works as follows:

1. Combustion: Fuel is burned in a boiler, generating heat used for industrial processes or electricity generation. This combustion produces flue gas, mainly composed of water, CO2, and nitrogen.
2. Absorption: The flue gas flows into an absorber tower. A liquid solvent (typically amines or ammonia) is introduced from the top. As the gas rises, the solvent reacts with the CO2, forming a solvent-CO2 solution.
3. Separation: The solvent-CO2 solution sinks to the bottom of the column and is then pumped to another column where it is heated to about 120 degrees Celsius. This heating separates the CO2 from the solvent.
4. Recycling and Compression: The solvent is recollected at the bottom of the column to be reused. The separated CO2 leaves from the top of the column and can be compressed for transportation and storage.

This method is considered an "end of pipe" technology and can be retrofitted into existing plants.

Here are the primary differences and challenges between pre-combustion and oxy-fuel combustion capture technologies:

Pre-combustion Capture:

• Process: CO2 is removed from the fuel before combustion. This typically involves gasification to break down the fuel into its basic components (like carbon monoxide, carbon dioxide, water, and hydrogen), followed by a shift reaction to convert carbon monoxide to carbon dioxide and more hydrogen. The CO2 is then separated from the hydrogen-rich gas stream.
• Key Differences:
  • CO2 is captured at a higher pressure and concentration compared to post-combustion.
  • Produces hydrogen as a byproduct, which can be used for electricity generation (burned in a gas turbine) or in industrial processes.
• Challenges:
  • Higher Cost: Involves more complex processes and equipment, leading to increased costs.
  • Limited Applications: Primarily suited for electricity generation and certain chemical production processes.
  • Not Retrofittable: Requires new plant designs and cannot easily be added to existing facilities.
  • Lower Capture Rates (in some variants): Some variations, like those using a "water-gas shift reactor" with a "moving bed" approach, can have significantly lower capture rates (18-30%).

Oxy-fuel Combustion Capture:

• Process: Fuel is burned in nearly pure oxygen instead of air. This results in a flue gas composed primarily of CO2 and water vapor. The water vapor is then condensed, leaving a concentrated stream of CO2 ready for compression and transport.
• Key Differences:
  • Combustion occurs with oxygen, not air (which is mostly nitrogen).
  • Produces a flue gas that is almost entirely CO2 and water, making separation much simpler.
  • Inherently results in low emissions of nitrogen oxides (NOx).
• Challenges:
  • Expensive Oxygen Separation: The main challenge is the energy-intensive and costly process of separating oxygen from air.
  • High Deployment Costs: The overall cost associated with implementing this technology is very high, acting as a major barrier.
  • Can Capture up to 100%: Theoretically, it can capture nearly all CO2 emissions.
  • Not Retrofittable: Similar to pre-combustion, it requires specific plant designs.

Captured carbon dioxide is stored underground in carefully selected geological rock formations, typically several kilometers below the Earth's surface. The conditions of pressure and temperature at these depths ensure that the CO2 is in a liquid or "supercritical" phase.

There are different types of geological storage:

1. Structural Storage: The captured CO2 moves upwards through the rock formations until it reaches an impermeable layer of rock, known as the "cap rock." This cap rock prevents the CO2 from escaping further upwards, effectively trapping it.
2. Mineral Storage: Over time, the trapped carbon dioxide can chemically bind with the surrounding rock, a process called mineral carbonation. This is a more permanent form of storage.
3. Enhanced Oil Recovery (EOR): This is an alternative to dedicated geological storage, particularly used in the United States. In this method, CO2 is injected into oil fields. The CO2 increases the pressure within the oil reservoir and interacts with the crude oil, making it more mobile and easier to extract. This process allows for the recovery of oil that would not be accessible through traditional methods, and the CO2 remains stored underground within the oil field.

Suitable storage sites can include former gas and oil fields, or deep saline formations.