Carbon capture and storage – a commercial conundrum (Part 1)

Scientists have advised governments to focus on carbon removal to achieve COP21 Paris agreements. Although the UK pledged for net zero carbon emissions by 2050-2100, climate advisors have warned this is simply not enough. Realistically, carbon emissions from agriculture and aviation will not reduce to net zero. It is becoming increasingly unlikely that we will fall below the 400ppm carbon dioxide threshold. 

Thus, radical CDR technologies are required to reduce atmospheric carbon concentration.
Although I have discussed afforestation as a potential solution, I will now explore CDR in an industrial manner.

Carbon capture & storage (CCS) is a CDR technology to reduce atmospheric emissions. CCS technologies are comprised of 3 components:

• ‘Capture' CO₂ by separating carbon emissions from other gases produced in industrial processes – typically via pre-combustion capture, post-combustion capture and oxyfuel combustion. Seperation can be achieved via membranes, adsorption and cryogenic distillation (Leung et al, 2014)
• Carbon is transported safely for storage, via pipelines or ships
• It is deposited and stored long-term where it is confined from atmospheric contact, generally below the Earth’s surface (CCSA, 2011).

This video effectively sums up the reasoning behind the establishment of CCS technologies. The UK's CCS storage capacity has been estimated at 70 billion tonnes. Approximately 2-5 billion tonnes of carbon need to be stored to meet the UK's decarbonisation target - which could potentially be met (DECC, 2012). 

Carbon can be stored in:

     1)  Deep geological formations (e.g. depleted oil and gas reservoirs, saline aquifers and unmineable coal beds)

     2)   Deep ocean

     3)   Mineral carbonates (IPCC, 2005). 

Figure 1: Carbon capture and storage process

Although oceans are considered the Earth’s largest carbon sink, there are concerns that injecting CO₂ can enhance acidification and prove detrimental to marine life (Pires et al, 2011). Mineralisation of carbon into solid inorganic carbonates, using chemical reactions, can provide safe, long-term storage (Allen and Brent, 2010), however its application is limited by its costliness (Sanna et al, 2014).

Geological storage is considered the most viable due to its potential, low-risk, safe storage and relative cost. One site can hold several million tonnes of CO_2, with saline aquifers storing 400-10,000 Gigatonnes. This can effectively reduce global atmospheric carbon concentrations if undertaken on a large scale (Leung et al, 2014).

Requirements for geological storage

(i)           Suitable porosity and volume (reflecting storage capacity)

(ii)         Suitable permeability (eases injection of carbon)

(iii)       A layer of hard rock to seal the carbon and prevent atmospheric contact

(iv)       A safe environment to maintain the structural integrity of the storage site (Global CCS Institute)

Risks and feasibility

Like all other geoengineering options I have explored, CCS does come with its risks. One of the most important issues is potential leakage into the atmosphere, groundwater sources and ocean which would be catastrophic to marine and terrestrial ecosystems (Widdicombe et al, 2013). 

In earthquake-prone regions, CCS would prove particularly hazardous (Zoback and Gorelick, 2012). Contamination of groundwater aquifers in developing countries can compromise rural livelihoods. Lastly, high concentrations of CO₂ can cause immediate human and animal asphyxiation – a well-known example being the 1986 Lake Nyos Disaster. The lethal outgassing of CO₂ killed over 1,700 people in a 15-mile radius (BBC, 2011). Thus, if the integrity of CCS storage sites is undermined, the consequences can be fatal.