Study of optimal pulverized coal concentration in a four-wall tangentially fired furnace

The effect of fuel lean/rich conditions (1:1, 1:2, 1:3, 1:4, 1:5 and 1:6) on the furnace core temperatures, carbon in fly ash and slag and NOx emissions was investigated in a 1 MW four-wall tangentially horizontal bias fired furnace for Yibin anthracite and Shenmu bituminous, respectively. Results shown that furnace core temperatures increased at first and then decreased along the height of the furnace when anthracite burned. The furnace core temperature at the height of primary air nozzles was the highest when the bituminous lean/rich varied from 1:1 to 1:3, and its trend was similar to the anthracite when the bituminous lean/rich was changed from 1:4 to 1:6. The ignition of anthracite required a heating stage, while bituminous could timely ignite due to high volatile. However, when the bituminous lean/rich was too low resulting in the relative lack of oxygen, it still needed a heating stage. With increased coal concentration, the furnace core temperatures in the primary air section went up firstly and then down, but the carbon in fly ash and slag showed adverse behavior. This was due to the high coal concentration corresponding to high volatile concentration leading to the timely ignition and burnout, causing higher furnace core temperature in the primary air section and decreased carbon in fly ash and slag. Corresponding to the highest furnace core temperature in the primary air section and the lowest carbon in fly ash and slag, the optimal pulverized coal concentration of anthracite and bituminous was 0.796–0.810 kg coal/kg air and 0.586–0.607 kg coal/kg air, respectively. In addition, with increased pulverized coal concentration, the NOx emissions reduced quickly with a slight decrease in the range of the optimal pulverized coal concentration.