Every year about 25 billion tonnes of carbon dioxide (CO2) is emitted into the atmosphere. This amount is more than the emission target set by some agencies. Two seemingly different approaches could reduce CO2 emissions. One approach advises implementation of carbon-neutral technologies as a measure to reduce CO2 buildup in the atmosphere. The other approach is deployment of CO2 capture and storage (CCS) system.

In the fossil fuel-dominated energy infrastructure, it is estimated that about 40 per cent of the human-made CO2 could be captured and stored to achieve the goal of global greenhouse gas emission stabilisation. It has been estimated that without CCS in the technology mix, the cost of climate stabilisation would increase by 70 per cent.

Some of the large generators of CO2 are power plants, industrial plants (such as iron, steel, cement, chemicals), oil refining and natural gas processing facilities. Efficient CO2 capture technologies are already available in several industrial scale manufacturing processes and these can be used in the CCS system. The transportation of CO2 through pipelines and CO2 injection underground are well-known approaches of transportation and storage. Among the available CO2 capture technologies, the pre-combustion option is considered the most efficient and the cheapest.

The compression of CO2 is needed to reduce the volume of gas for transportation to an appropriate storage location. It is, however, an energy intensive proposition. Among the alternatives of storing CO2, geological storage is considered a promising approach. It involves direct injection of CO2 into underground geologic formations, including depleted oil and gas reservoirs, and deep saline aquifers. The substantial experience gained with CO2 injection to enhance oil recovery can also be used for CO2 storage.

One of the safety concerns of CCS technology is gas leak. CO2 is non-toxic at low concentrations, but at high concentrations it can cause asphyxiation, primarily by displacing oxygen. Large and sudden leak (due to pipeline rupture) could be disastrous. CO2 being denser than air, when released, tends to accumulate in shallow depressions. This increases the risk in confined spaces close to the ground. CO2 leakage from an underground reservoir into the atmosphere could have local effects, such as ground and water displacement, groundwater contamination, and biological interactions. Effective containment of the gas is possible by monitoring and measuring CO2 concentrations in and around a storage location.

Economics will largely determine whether CCS can compete with carbon-mitigating energy alternatives. According to an International Energy Agency (IEA) report, CCS alone is insufficient to drive large-scale development and deployment of CCS to meet the required levels of CO2 mitigation. Beneficial uses for CO2 (like enhanced oil recovery) have been shown to financially offset CCS implementation costs in some cases. As of now, CO2 capture technology is energy-intensive and requires a substantial share of the electricity generated. The cost estimates are dominated by the cost of capture (including compression). JC Stephens and B van der Zwann write, “If transport distances are less than a few hundred miles, the cost of capture constitutes about 80 per cent of the total costs.”

Despite the extensive commercial experience with technological components in other applications, minimal experience in integrating capture, transport, and storage into one system so far means that current cost projections are quite uncertain, believe Stephens and van der Zwann.

The promise of launching between 19 and 43 large-scale CCS integrated demonstration projects with the support of governments by 2020 will surely pave the way to overcome the final hurdles. Another critical factor to CCS deployment is public outreach.

(The writer is a biotechnologist and ED, Birla Institute of Scientific Research, Jaipur)