Combustion and NOx formation characteristics from a 330 MWe retrofitted anthracite-fired utility boiler with swirl burner under deeply-staged-combustion

Abstract

In order to achieve peak carbon dioxide emissions and carbon neutrality goals, a higher requirement is put forward for coal type adaptability medium, load stable combustion performance, and pollutant emission for wall-fired boiler with swirl burners. In this work, through industry experiments, the combustion characteristics of a retrofitted wall-firing mode 330 MWe power unit feed with anthracite were investigated. The combustion system was retrofitted employing the centrally fuel-rich (CFR) swirl burner and deeply-staged combustion technology. The experiment data were measured, including flue gas temperature and composition, furnace temperature, and the main operational parameter under high-load (300 MWe), medium-load (230 MWe), and low-load (150 MWe) conditions. The stable combustion of anthracite is achieved at various loads. With the excessive air coefficients of the main combustion region increase, the corresponding second air damper opening increase under high-load condition or over-fire-air damper opening decrease, both the flue gas temperature and heating rate of pulverized coal increase advance the ignition and promote the stable combustion and burn-out of anthracite coal. In the initial combustion stage, the O2 given into the chamber increase, both O2 consumption rate and CO concentration decrease, but NOx concentration increases. While in the later stage, both the O2 and CO concentration tend to become flat. Meanwhile, the O2 concentration is lower than 2.1%, the CO concentration maintains a relatively high level, and NOx production is inhibited effectively and becomes flat gradually. With the excess air coefficient increase, the temperature in the main combustion region increases, and the difference in furnace temperature between the burn-out region and the main combustion region diminishes. The unburned carbon content in fly ash and exhaust gas temperature decreases, while NOx emission increases. There is little difference for the flue gas temperature distribution in the side-wall region, and the measured O2 concentration is always higher than 3.5% with the different mass flux of secondary air and over-air-fire. With decreasing load, the NOx emission decreases from the highest 1392.66 to the lowest 958.38 mg/m3 (O2 6%), and the boiler efficiency improves. Compared with high-load and medium-load, the slagging tendency of the water wall is lower under low-load condition.