What is clean coal?

4 Nov 2009, 12:05 pm   -   Source: SBS and other sources

Clean coal technologies seek to reduce emissions from coal-fired power generation. How does carbon capture and storage work and by when will it be commercially viable?

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Clean coal technologies seek to reduce emissions from coal-fired power generation. But how do these work exactly?

Carbon Capture and Storage (CSS) -- probably the most promising clean coal technology --  involves capture, transportation and long term storage of carbon dioxide and other greenhouse gases in deep geological formations underground.

How does carbon capture and storage work?

Instead of allowing carbon dioxide and other greenhouse gases to be released into the atmosphere, they are captured at the emission site where they are separated from other substances.

The separated stream is then compressed into a concentrated volume and transported from the source location (emission site) to the injection location. Geological storage comprises:

*the injection of the compressed stream into geological formations in the deep sub-surface

*its migration away from the immediate vicinity of the injection point

*its subsequent trapping in geological formations

Carbon capture in Australia 

The Australian government is in the process of developing legislation to enable CCS in Commonwealth offshore waters. Several states are also developing legislation to enable CCS in their jurisdictions. 

MORE on Carbon Capture and Storage in Australia

When will carbon capture be available on a commercial scale?

There is no agreement yet on when CCS will be available on a commercial scale. Industry leaders emphasise that the technology should be available by 2020. Meanwhile, others question its feasibility in that time frame.

The UN's intergovernmental panel on Climate Change suggests that industrialised countries need to reduce greenhouse emissions by between 25 and 40 per cent by 2020. No commercial scale coal-fired power plant currently exists that captures the majority of its emissions. 

Criticism to carbon capture technology

* There are concerns that 'no CO2 storage project that is currently operating has the necessary modelling, monitoring, and verification capability to resolve outstanding technical issues.

*The volume of greenhouse pollution that would need to be buried is vast and unprecedented. The larges CCS experimentation project in existence (Sleiper in Norway) currently buries 1 million tonnes per annum (Mtpa) of carbon dioxide. Current global emissions from fuel combustion are 27 billion tonnes per annum (Gtpa). Burying just 3.6 (Gtpa) per year (or 13% of present emissions would require an injection of 50 million barrels of CO2 per day).

*It has been claimed there is no suitable geology for carbon storage within 500 km of the Hunter Valley and Sydney Basin regions of NSW, or of Port Augusta in South Australia. These regions account for 39%of Australia's greenhouse pollution from electricity generation.

Other types of clean technology

Some technologies clean coal before it burns. Coal washing removes unwanted minerals by mixing crushed coal with a liquid and allowing the impurities to settle.

Other systems control the coal burn to minimise emissions of sulphur dioxide, nitrogen oxides and particulates. Wet scrubbers remove sulphur dioxide, a major cause of acid rain, by spraying flue gas with limestone and water.

Low nitrogen oxide burners reduce the creation of nitrogen oxides, a cause of ground-level ozone, by restricting oxygen and manipulating the combustion process.

Gasification avoids burning coal all together. With integrated gasification combined cycle (IGCC) systems, steam and hot pressurised air or oxygen combine with coal in a reaction that forces carbon molecules apart. The resulting product is then cleaned and burned in a gas turbine to make electricity.


 

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