OCR Text |
Show 3.3 Experimental Conditions The experimental programme was executed in IFRF Furnace Number 1. The furnace, presented in Figure 9, is a 2.0 x 2.0 x 6.25 m refractory chamber with seven double cooling loops spaced equidistant along the furnace length for heat extraction. This configuration resulted in a volumetric firing density of 0.1 MW/m3, a mean heat extraction of 40%, and a flue gas temperature of about 1000 o C. The first 1.2 m of the furnace was left uncooled. Two coals were selected for the experiments, Scotts Branch high volatile bituminous coal and Heinrich Robert medium volatile bituminous coal. Fuel properties are listed in Table 1. Both coals were dried, crushed and pulverized to 75% < 75 ~m. The primary air stream was fed to the burner at a nominal temperature of 70 0 C. Main combustion air was supplied at a nominal level of preheat of 300 o C. For both burners, velocities could be varied under constant input conditions using insert pipes. The excess air level was maintained constant at 15%. During the experiments, the first step studies on the two burners. For Burner A, parameters were varied:. - coal injector position, was parametric the following - Primary to secondary air momentum ratios (MI), - swirl level (So), - coal injection mode. For Burner B, the following parameters were varied: - precombustor residence time (Tp), - precombustor stoichiometry (SR1), - primary to secondary air momentum ratios (MI), - swirl level (So). Precombustor residence time, Tp, was varied at con~tant SR1 by varying the precombustor diameter and length. 4 RESULTS AND DISCUSSION 4.1 Burner A - Aerodynamically Air Staged Burner Figure 10 shows the behaviour of the AASB for various input conditions firing Scotts Branch coal. The design objective of the AASB is to promote devolatilisation within the IRZ. The experimental results may be explained by considering the effect of burner input parameters on mean coal particle trajectories and global mixing. 7 |