Lowered emissions from coal-fired generation
Researchers at LeHigh University's Energy Research Centre and Great River Energy (GRE) have decreased emissions from the burning of lignite and coal with a high moisture content through partial drying.Use of these fuels has increased as they are inexpensive and low in sulphur. However, both types of fuel are high in moisture resulting in lower boiler efficiency.
GRE's Coal Creek power station has two units, which generate over 1,100MW. The units fire lignite with 40% moisture and 12% ash.
GRE is using energy from hot circulating water leaving the condenser to provide the heat for drying, improving performance and reducing stack emissions.
Theoretical analysis shows heat rate will be reduced by about 5%, due to a lower stack loss and reduced fan and mill power requirements. The CO2 and SO2 mass emissions will also be reduced by 5%.
A test burn was conducted at Coal Creek Unit Two to determine the effect on unit operations.
Approximately 12,000t of lignite were dried for this test by an outdoor stockpile coal-drying system. On average, coal moisture was reduced by 6.1%, from 37.5 to 31.4%. Analysis of boiler efficiency and net unit heat rate showed that with coal drying, the improvement in boiler efficiency was approximately 2.6%, and the improvement in net unit heat rate was 2.7-2.8%. The test data also showed the fuel flow rate was reduced by 10.8% and the flue gas flow rate was reduced by 4%.
The combination of lower coal flow rate and better grindability combined to reduce mill power consumption by approximately 17%. Fan power was reduced by 3.8% due to lower air and flue gas flow rates. The average reduction in total auxiliary power was approximately 3.8%.
GRE is designing a fluidised bed lignite drying system for the site. An investigation is being carried out at LeHigh into the effects of fluidising velocity and bed design parameters on rate of in-bed heat transfer and rate of drying of lignite.
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