Clean coal technology (CCT) has become the industry watchword for innovations intended to reduce carbon dioxide (CO2) emissions in coal-fired power generation.
CO2 can be stored in geological formations such as oil and gas fields, unmined coal seams and deep saline formations, and there is potential as well for deep sea CO2 storage.
CCT's current vogue (download podcast) comes from the growing belief that CO2 from coal burning is a principal contributor to global warming. Heightened public awareness of this issue has led to pressure on coal burning industries to reduce emissions.
A proliferation of high-profile government and academic studies concerning the impact of global warming has given the issue a sense of urgency in recent years, and some governments have set emissions targets and offered incentives to utilities to reduce CO2 output.
National governments and companies are likewise driven by the enormous business potential of developing and marketing viable CCT. While CCT are available now, most have not been proven at a commercial scale.
The most common CCT process involves carbon capture and storage (CCS).
Captured technologies include flue gas scrubbing or the 'oxyfuel' method.
The former involves treating the flue gases from coal burning with chemical scrubbers to remove sulfur dioxide, and then reheating the resulting solvent to release high purity CO2 for sequestration.
In the oxyfuel method, coal is burned in an oxygen, rather than air, reducing gas volumes in the system. The resulting exhaust is more than 80% CO2 and easier to isolate and capture.
CO2 can be stored in geological formations such as oil and gas fields, unmined coal seams and deep saline formations, and there is potential as well for deep sea CO2 storage.
Other routes to cleaner coal burning are co-firing biomass such as crops or forestry waste with coal, or employing the Integrated Gasification Combined Cycle (IGCC).
This process pre-treats the coal chemically and transforms it into synthetic gas before burning it to make electricity. IGCC plants can have high levels of efficiency; current coal-fired 'efficiency' plants run at rates of around 37-43%.
Clean coal is seen by politicians as an emissions solution pleasing to both those demanding action against CO2 emissions and those concerned about the continued viability of the coal industry.
As such, dissatisfaction with CCT comes from both sides. Environmental activists claim that coal extraction and burning can never be sufficiently 'clean,' while the industry points to the high costs of implementing CCT.
A 2003 UN study estimated that costs for CCS from a coal-fired power plant could range from $30-71/mt of CO2 captured, with boosts in electricity costs from 43-91%.
The wide range results from site-specific factors such as distances, depth and geological characteristics of storage locations. A 2005 UK Parliamentary Study estimated that building a 500MW IGCC plant would cost $686 million without CCS and $930 million with it.
The cost of retrofitting CCS applications on existing plants is even higher than implementing them on new builds.
Those favoring CCT are hoping that a carbon trading scheme would provide sufficient incentives to explore these options.
However, most carbon currently trades at figures far below the Euro 60/mt figure that utilities require to make investment economically feasible.
At present, there are no coal-fired power stations in commercial production which capture all CO2, and estimates are that it will be fifteen to twenty years before any commercial-scale clean coal power stations are commercially viable.
Created: July 23, 2007
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