FUEL 110 |
| Greenhouse gas emissions from fossil fuel combustion are a major issue for climate change. Oxy-fuel firing is one of the most promising methods to produce a stream of concentrated CO2 ready for sequestration. Oxy-fuel fired CFBC offers unique advantages such as the used of external solid heat exchangers to remove heat from the system, therefore reduce the amount of flue gas need to be recycled to main combustor temperatures at a reasonable level. However, for some fuels, such as anthracites and petroleum cokes are typically combusted at above 900„aC. At CO2 concentrations of 80-85% (typical of oxy-fuel CFBC conditions) calcination of limestone sorbent will happen. Therefore, when the ash cools to below the calcination temperature carbonation of fly ash deposited on to some heat exchanger surfaces may happen in CFBC because of the high CO2 concentrations. This phenomenon has the potential to cause operational difficulties. In this study, two fly ashes generated in utility CFBC boilers were carbonated in a thermogravimetric analyzer (TGA) under conditions expected to be seen at the exit in an oxy-fuel CFBC. The temperature range was 500„a-800„aC and CO2 concentrations in the range of 15-100%. Both the rate and the extent of the carbonation reaction were determined. The results showed that both temperature and CO2 concentrations play important roles in determining the carbonation reaction both in terms of reaction rate and the extent of the reaction. Higher temperatures increased the overall extent of conversion and for any given temperature, increasing CO2 concentrations also resulted in higher overall conversions to carbonate. The carbonation was initially very fast, but then the rate gradually reduced as the reaction proceeded. The activation energy of carbonation of the two fly ashes were calculated. Keywords: oxy-fuel firing, CO2, fly ash, carbonation |
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Hybrid Nanotechnologies for an Enhanced CO2 Fixation
1:00 PM-2:45 PM, Monday, April 7, 2008 Morial Convention Center -- Rm. 239, Oral
Division of Fuel Chemistry |