Near real-time LOI testing assists Southern Co.`s low-NOx efforts
Low-NOx burners are becoming common equipment as utilities strive to comply with the Clean Air Act Amendments, but in coal-fired units, the modified combustion process that reduces NOx formation can also negatively affect the burn-out of the pulverized coal, resulting in increased carbon in the flyash and reduced unit efficiency.
OOptimizing low-NOx burners on a unit based strictly upon the NOx emissions is not too difficult,O said Steve Minor, Southern Co. engineer. OThe trick lies in adjusting the burners to optimize the reduced NOx emissions against the increased carbon in the flyash as measured by the flyash?s LOI (loss on ignition) value.O
LOI measurement requires a sample of flyash extracted from the gas stream. The sample is weighed, then burned under controlled conditions. The measured weight loss after burning is the LOI. This process takes four hours to complete, and is not conducive to optimal low-NOx burner efficiency.
Southern Co. Services Plant Performance Group in Birmingham, Ala., was looking for a more timely method and recently purchased the Hot Foil? LOI instrument, manufactured and distributed by Fossil Energy Research, under license to the Electric Power Research Institute. The Hot Foil LOI measures a sample?s LOI within 10 minutes of extraction from the gas stream.
Laboratory and field tests have shown agreement between the Hot Foil LOI and traditional laboratory determined LOI. The instrument requires 110 Vac, 2 A power and is 15 inches by 15 inches by 8 inches, allowing portable on-site use.
OHaving an accurate value for the LOI allows us to assess whether the previous adjustment was appropriate and where to go next,O Minor said. OPreviously, we could not make an on-site, near real-time evaluation of the effectiveness of our adjustments. Now we can alter our tuning and optimization efforts based on the feedback provided by the rapid determination of the LOI.
Southern Co. has used the instrument at several plants for a variety of programs, including determination of baseline conditions for a
low-NOx burner installation, optimization and guarantee testing of an installation, and to measure effect of fuel switching on unit