OCR Text |
Show welded to minimize leakage of air into it or combustion gases out of it. With this combination of good insulation, low leakage and adjustable cooling loads, it was possible to vary the furnace temperature by about 400° F at each of the firing rates that were used. In addition, the furnace's low leakage permitted the air/fuel ratio to be controlled and measured. Natural gas and air flows were measured by variable area flow meters. The oxygen and combustibles in the flue gas were measured by means of oxygen and combustibles analyzers. The firebox temperature was measured with a Type K thermocouple. Measurements of NO were made with a chemiluminescence analyzer or with an electrochemical sensor. ~ - Types of Burners Tested Four burners manufactured by the Selas Corporation of America were tested: 1. The K-976 burner (Figure 1) uses a high-velocity jet of gaseous fuel to entrain primary combustion air and furnace draft to induce the flow of secondary combustion air. The primary air and fuel are completely mixed by this entrainment process before being burned. The secondary air does not mix with the fuel until combustion has begun. The version tested had a burner block with a cup-shaped cavity. It was tested witnand without secondary air. 2. The K926 burner (Figures 2) is similar to the K976 but has only primary air. This version has a burner block with a cup-shaped cavity. 3. The K926 burner (Figure 3) with a flat block. 4. A new ultra-low NOx (ULNx) burner (Figure 4) using staged combustion. About half of the fuel is premixed in the first stage with about half of the combustion air. In the second stage, the remaining fuel is mixed with the combustion products from the first stage and then with secondary air. The burner block has a flat surface and projects beyond the hot-face of the furnace wall. Burner Emission Performance NOx emission data for the burners are shown in Figures 5 and 6. On the figures, the P and S after K976 refer to primary and secondary air, respectively. K926-CUP refers to the burner with a cup-block. K926 FF is the burner with a flat block. Figure 5 shows NOx emission versus flue temperature with excess oxygen in the combustion products held constant at 2.1% which corresponds to 10% excess air. Figure 6 shows the effect of excess oxygen at a constant firebox temperature of 2282°F. -3- |