Author: Kirsten Foy, BA BAI PhD CEng MIEI, principal engineer, Parsons Brinckerhoff
The devastating effects of extreme weather conditions are increasingly noticeable with every season. Most experts in the scientific community now accept that climate change is the key factor here.
The prevailing wisdom is that the worst of the damage can be avoided if the global temperature does not rise by more than 2°C, which would be achievable if the level of carbon dioxide (CO2) in the atmosphere does not increase beyond 450ppm . But this requires a massive global reduction in CO2 emissions, including a fall in European Union-country emissions to 20% below 1990 levels by 2020.
We could carry on regardless and allow climate change to continue unabated, or we could take drastic measures and shut down 20% of industry, transport and power production, severely impacting the economy and our way of life. So, how to maintain the economic recovery and a high standard of living without emitting vast amounts of CO2?
CCUS stands for carbon capture, utilisation and storage. CO2 from combustion of a fuel or industrial process is captured, compressed or cooled to liquid, then transported and used in other products or stored away from the atmosphere. Other methods seek to reduce the amount of CO2 produced.
With CCUS, CO2 continues to be produced before being captured and reused or stored. Coal and natural gas can still be used as energy sources and we can continue to produce CO2 in industrial processes, but without contributing to climate change.
CCUS VERSUS RENEWABLES
Many believe that renewables are the answer to global warming, so why not forget fossil fuels altogether? Firstly, even if all power were to be generated by renewables, it would still be worthwhile applying CCUS to the production of steel, cement, chemicals, fertiliser, paper and other products.
Secondly, most renewables are an intermittent source of power, requiring combustion plants as backup. Thirdly, many forms of renewable energy are currently more expensive than coal and gas plants with CCUS. Finally, there is a limit to how much renewable energy we can produce and how quickly we can access it, so fossil fuels will remain a dominant form of energy.
There are many ways of capturing CO2. Something as simple as pumping cleaned flue gas from a power plant through a greenhouse will trap some of the carbon in vegetative matter. This concept can be applied on an industrial scale to convert the CO2 in flue gas to biofuel using algal growth. However, once the vegetables are digested or the biofuel is combusted, the CO2 will be released again to atmosphere.
Extending forests or increasing ocean algae are also forms of carbon storage. Although this carbon will be released when the plant dies and decomposes, provided the overall mass of plant life is continually replenished, the carbon remains stored. These forms of CCUS collect and store CO2 from the atmosphere after it has been emitted. For large-point sources of CO2, such as power plants, steel foundries or cement works, it is more efficient to capture at the source, where the CO2 concentration is highest.
[caption id="attachment_11730" align="alignright" width="1022"] Levelised cost of electricity: current generation technologies (copyright: Parsons Brinckerhoff)[/caption]
There are many carbon-capture technologies in development. The three closest to commercialisation, which can be applied to large-point sources of CO2, are: post-combustion capture; reforming of fuel with pre-combustion capture; and oxy-combustion technology. Although the term ‘combustion’ is used, most forms of capture can also be applied to CO2 emissions from sources other than combustion of a fuel; e.g., CO2 released from a chemical reaction in an industrial process such as cement production.