Asymmetric combustion characteristics and NO x emissions of a down-fired 300 MW e utility boiler at different boiler loads

Abstract

To investigate the aerodynamic field, cold airflow experiments were conducted under different boiler loads in a cold small-scale model of a down-fired pulverized-coal 300 MW e utility boiler. At 300 MW e and 250 MW e loads, a deflected flow field appeared in the lower furnace. In contrast, at a 150 MW e load, a U-shaped flow field appeared in regions near the left- and right-side walls in the lower furnace. Concurrently, the regions near the two wing walls adjacent to the front arch had received deflected upward airflow emanating from the region near the rear wall. Moreover, a symmetric W-shaped flow field appeared in the central regions below the front and rear arches. Industrial-sized experiments on the full-scale furnace were also performed at different loads with measurements taken of gas temperatures in the burner region and near the right-side wall, as well as heat fluxes and gas components in the near-wall region. Asymmetric combustion appeared at 300 MW e and 250 MW e loads, with large differences arising in gas temperatures, gas components, and heat fluxes between zones near the front and rear walls. At 150 MW e load, gas temperatures, gas components and heat fluxes are, in general, symmetrically distributed throughout the furnace. By decreasing the load, differences in gas temperatures, gas components, and heat fluxes near the front and rear walls decrease, as did NO x emissions. Meanwhile, the carbon content in fly ash essentially decreased, yielding an increase in boiler efficiency assisted by a drop in exhaust gas temperature.