Coal-fired power plants can supply reliable, low-cost electricity but have high greenhouse gas emissions.
Renewable energy sources such as wind and solar have very low emissions, but lack stability of supply due to the variability of the wind and sun, and the additional equipment required to stabilise their output dramatically increases their cost.
Natural gas can provide stable electricity supply, but the natural gas price continues to rise, and while its greenhouse gas emissions are generally lower than coal, they are still significant.
The challenge is to reduce emissions to acceptable levels at the lowest possible cost while maintaining reliable electricity supply. Meeting this challenge is likely to include a mix of all energy sources, with coal combined with carbon capture and storage (CCS) playing a vital role.
A long-term plan is required including adopting emerging technologies to assist the integration of coal with CCS to support reliable, affordable and low-emission energy in the future.
By adopting a long-term plan including fitting existing power stations with partial capture, progressively increasing the proportion of emissions captured and stored over time, and replacing coal-fired power stations at the end of their economic life with high-efficiency, low-emissions (HELE) plant fitted with CCS, the costs can be minimised in the near term and phased in over the long term.
Yet closing coal-fired power stations with many years of operating life remaining and replacing them with HELE plant is very costly.
In the short term, CCS can be fitted to existing plant, enabling deep reductions in emissions for the remaining life of the plant and avoiding the unnecessary cost of replacing a power station prematurely.
However, CCS can also be fitted to capture any amount of CO2 emissions considered necessary at a lower cost than full capture.
For example, if the emissions from a new coal-fired power station were reduced by 40 to 50 per cent, this reduction would be equivalent to the emissions from a new gas-fired power station, and be cost competitive at projected gas prices. Similar cost advantages are possible for CCS fitted to existing power stations.
New capture processes
Current carbon capture processes using post-combustion capture (PCC) need to remove impurities such as oxides of sulphur and nitrogen (SOx and NOx) before removing the carbon dioxide. The removal of these gases makes up a significant proportion of the total capture cost.
If the process could be modified to eliminate the need for such removal, the costs of the process would be greatly reduced. Carbon capture processes that are tolerant to SOx and NOx are not currently available commercially for large scale application such as power generation from coal. These processes are being developed in Canada and could become available by 2030 or earlier with a well-funded scale-up and demonstration development program. Such a development program could also extend the applicability of such SOx and NOx tolerant PCC processes to large scale industrial applications such as iron and steel and cement.
The emerging technologies discussed above aim to improve CCS in its current state.
There are also several technologies in development which may significantly change the way electricity is generated from coal and gas and capture carbon more efficiently, and at lower cost.
One example of such a technology is the Allam cycle turbine being developed by Net Power in the USA
Allam cycle turbine
Current CCS technologies capture emissions from coal or gas-fired power plants after the electricity is generated, a process that is relatively inefficient and costly.
The Allam cycle offers a more efficient and cost-effective way to capture CO2 during the power generation process rather than after the power has been produced. This means the CO2 that leaves the turbine is ready for geological storage with very little requirement for further processing. The fuel used can be natural gas or gasified coal.