Capture

This stage of the process involves separating the CO2 from the smoke and fumes (mainly water vapor and nitrogen) given off during combustion. This is by far the most costly part of the process (about two-thirds of overall cost).

But this stage is necessary, for two main reasons:

• the smoke and fumes from combustion usually contain between 3% and 15% CO2. Separating the CO2 reduces the quantity of gas to be compressed and stored, and therefore reduces costs;
  
• geological storage sites must meet certain criteria, and only a limited number are suitable for CO2, so reducing gas volume by separating the CO2 optimises the available storage capacity.

Storage

Most of the suitable storage sites are :

• end-of-life oil and gas fields,
• deep saline aquifers
• coal beds that are too deep to be mined.