Experimental And Simulative Investigation Of The Low NOx Combustion On Coal-fired Boiler

The nitrogen oxides(NOx) generated by the combustion in the power station is a very harmful atmospheric pollutants, so it is very important to investigate the method and principle to control nitric oxide. This PhD thesis is to research the low NOx burners transformation on a420t/h boiler of Zhejiang energy group.The ignition, combustion, burn out experiments of Zhunhu, Dahun and Zhehun coal were performed on the thermal gravimetric analyzer and drop tube furnace. The results showed that the coal reactivity enhanced with the increase of heating rate, and the combustion process became more intense. The combustion characteristic of the three coals can also be improved with the heating rate. The FTIR results of Zhehun coal showed that the gas release under different heating rates are basically same, but the enhancement of the heating rate can delay the combustion process and promote the pollutant generating. The NO emissions of the three coal increased with the increase of the excess air ratio, the most obvious impact of the excess air ratio was a=0.85～1.15for Zhunhun and Dahun coal and α=0.8～1.2for Zhehun coal. The NO production volume increases with the increase of the combustion temperature, either in an oxidizing atmosphere or in a reducing atmosphere. Zhunhun and Dahun coal performed a good reducing characteristic in a reducing atmosphere. The air coefficient should be0.85or less in the once burning or reburning areas if the air staging or fuel staging combustion technology was used.Applying the density functional theory and cluster modeling to study the NO adsorption characteristics under the different structures, such as pure carbon and nitrogen-containing coke surface. And get the adsorption product and adsorption heat release/absorption heat. The calculated results showed that the adsorption heat release in the Zigzag structure carbon surface is more than Armchair carbon surface. To the armchair carbon surface, the NO trends to adsorb in the empty site by side-on type to form hexatomic ring other than to adsorb in the outside shoulder site by side-on type to form four-membered ring. Compared to adsorb on the coke nitrogen surface, NO is more likely to adsorb on the pure carbon surface. When the NO was adsorbed on the nitrogen-containing coke surface, N-N type release more heat than N-O type.The rehabilitation program is focused on the SOFA air staged combustion technology, together with the CCOFA air staged combustion in the main burner region, low oxygen combustion technology, deflecting secondary air technology to control the NOx formation in the combustion process.Cold experimental results showed that the wind uniformity of all secondary air layers and SOFA were very good. By adjusting the layers of the throttle opening degree, the boiler burners could work under design.The thermal experiments show that after transformation of low NOx burners, boiler operation is stable, the main steam pressure, flow, temperature, and other parameters can meet the operational requirements of the boiler. The Boiler NOx emissions between223mg/Nm3-383mg/Nm3.