Experience Gained from Applying Low Emission Burners in a Coal Fired CHPP Power Generating Boiler for Reducing Nitrogen Oxide Emissions

Abstract

For the Omsk combined heat and power plant no. 5 (Omsk CHPP-5), which is located in the central part of a large city, there is an acute need to reduce the atmospheric emissions of pollutants. Grade KSN (coking low-caking low-metamorphized) high-ash Ekibastuz coal is the design fuel for this power plant. For reducing the solid fuel fly ash and nitrogen oxide NO_x emissions, it was proposed to make a shift for combustion of other coals having a higher heating value and lower ash content. To see whether or not off-design coals can be used, experimental combustion of such coals as grade DR (as-received, jet) Vinogradov coal, grade DR Shubarkol coal, and grade DR Maikubensk coal was carried out; the furnace process mathematical simulation was performed out in the ANSYS Fluent software, and the thermal balance was compiled in the Boiler Designer software. As a result of the studies performed, a conclusion has been drawn that for securing efficient use of off-design fuel, it is necessary to modernize the existing combustion system with installing new low emission vortex burners. Based on the data of a computational study carried out in the ANSYS Fluent software, the design of a new burner was developed. The simulation results have shown that by using the new burners it will be possible to achieve a significantly lower amount of nitrogen oxide emissions produced. After the design documentation had been developed, the new burners were manufactured and installed in BKZ-420-140 boiler No. 7 at the Omsk CHPP-5. The tests of the boiler equipped with the new burners carried out with combustion of design grade KSN Ekibastuz coal have confirmed the effectiveness of the adopted technical solutions: the concentration of nitrogen oxides in the boiler flue gases is a factor 1.7 lower in comparison with the values that were before the boiler refurbishment. A lower level of carbon-in-ash losses and the corresponding increase in the boiler efficiency have been recorded. Preliminary experiments on combusting off-design grade DR Vinogradov coal confirm the possibility of using it on a regular basis jointly with grade KSN Ekibastuz coal provided that the project has been implemented in a full scope.