Overview

CCS is an integrated process involving three distinct stages: capture, transportation and long-term storage

Capture

Large amounts of CO₂ are released when fossil fuels are burned to provide electricity, heat or transport. In the first stage of CCS, CO₂ is isolated and captured.
CO₂ capture can take place either before or after the fossil fuels are combusted, using one of several capture techniques.

In some industrial processes such as natural gas production, CO₂ is removed from the natural gas stream during processing to meet specific natural gas quality standards, and in plants that produce ammonia or hydrogen.

In other industrial activities, such as steel mills and cement plants, processes to capture CO₂ are being developed. Adaptations of post-combustion, pre-combustion and oxy-fuel combustion approaches have been proposed for these types of industrial facilities.

In some activities, notably cement kilns and iron reduction, the CO₂ emitted may come from chemical reactions involving the raw materials. In each case, the capture methods must be tailored to the specifics of the production process.

Compression and transportation

Once separated, the CO₂ is compressed, and transported to a suitable storage site.

CO₂ is already being transported today by road tanker and pipeline – primarily for use in industrial applications or in depleting oil and gas fields, where it is used to increase the production of oil.

The scale of transportation required for CCS is far more significant, calling for new economic and regulatory infrastructures.

Storage

The final stage of CCS sees the CO₂ injected into, and contained within, suitable subterranean geological structures, often at depths of one kilometre or more. At this depth,CO₂ is in a liquid (supercritical) phase and the possibility of CO₂ escaping the reservoir is negligible, providing the storage site has been well characterised.

Appropriate storage sites include depleted oil or gas fields or deep porous saline aquifers, which have impermeable rock (also known as a ‘seal’) above them. The seal prevents the CO₂ from returning to the surface and the CO₂ slowly permeates through the porous rock. These sites have securely contained fluids and gases for millions of years, and with careful selection, they offer confidence in the integrity of storage.

Once injected, a range of sensing technologies is applied to CCS sites to ensure ongoing monitoring of CO₂ levels in the storage site. These monitoring, reporting and verification processes provide an additional safeguard to storage activities.

Figure 2 - A range of CCS scenarios

Figure 2 - Download original copy [PDF, 4.4MB]