Study on the influence of secondary air on the distributions of flue gas composition at the lower part of a 600 MW supercritical CFB boiler

Abstract

In this paper, field tests were presented from the first 600 MW supercritical CFB boiler to investigate the effect of secondary air (SA) on flue gas composition. The furnace temperature, flue gas composition including oxygen, CO, CO2, SO2 and NOx along and near the horizontal line through the SA nozzles were measured at various loads. The outer upper SA (OUSA) had different effects on furnace temperature at high and low loads. Based on the oxygen concentration distributions, the SA trajectories were predicted and the distributions of flue gas composition were analyzed. The results showed that the oxygen concentration was uniform near the rear wall but all exhibited a “decrease-increase-decrease” profile along the horizontal line. In addition, the distributions of oxygen concentration and oxygen consumption at the cross section of OUSA were calculated, which indicated that the horizontal range of inner upper SA (IUSA) and OUSA could not cover the furnace width. Moreover, the oxygen consumption near the side wall was nearly twice that of the middle part along furnace width. The oxygen consumptions along the jet direction varied with the SA layout, and about 30% of the OUSA participated in the combustion below the OUSA nozzles.