What is Carbon Capture and Storage?

What is CCS?

CCS is a 3 step process which involves capturing the CO2 from power plants and other industrial and energy-related sources, transporting it to storage points then storing it safely in depleted oil and gas fields, deep saline aquifers as well as possible sites onshore.

CCS process

1. Capture

CO2 capture is the process of removing CO2 (carbon dioxide) produced by hydrocarbon combustion (coal, oil and gas) before it enters the atmosphere. The process will be most cost effective when it is used on large point sources of CO2 such as power stations and industrial plants. These currently make up more than half of all man-made CO2 emissions.

There are currently three main methods of capturing CO2:

  • Post-combustion capture - removing the dilute CO2 from flue gases after hydrocarbon combustion
  • Pre-combustion capture - removal of CO2, prior to combustion, to produce hydrogen
  • Oxy-fuel combustion capture - burning fossil fuels in pure oxygen as opposed to air resulting in a more complete combustion

2. Transport

CO2 capture is likely to be most economic at large point sources of CO2 such as power stations and large industrial plants. In most cases these will not be close to a suitable underground reservoir for storing the CO2 and therefore the CO2 will have to be transported.

Transport is currently the least complicated element in the CO2 capture and storage chain as the technology is already in existence and costs can be realistically estimated.

The main complication with CO2 transport is that CO2 behaves differently under varying pressures and temperatures and therefore transport of CO2 must be carefully controlled to prevent solidification and blockages occurring.

There are currently two methods used to transport large volumes of CO2 by industry:

  • Pipeline Transport
  • Ship Transport

3. Storage

CO2 storage is simply the process of taking captured CO2 and then placing in a location where it will not be in contact with the atmosphere for thousands of years. Storage of the CO2 in underground sites beneath a layer of impermeable rock (cap rock) which acts as a seal to prevent the CO2 from leaking out is the most obvious option at present.

There are three main types of proposed underground storage sites:

  • Depleted Oil and Gas Reservoirs
  • Deep Saline Aquifers
  • Deep Unminable Coal Seams

You can read more about CCS at The Scottish Centre for Carbon Storage http://www.geos.ed.ac.uk/sccs