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Show temperature or composition displayed as contours. Flue gas velocities (vectors) are represented by arrows pointing in the direction of flow, the length of which are proportional to the magnitude of velocity. When viewed perpendicularly to the cross section, the velocity arrows are the two-dimensional projections of the velocity onto the cross-sectional plane. The velocity might be very fast or very slow and have the same projection; in this case color imaging would reveal the difference between high and low velocities. Figures 1 through 4 show results for a tangentially-fired coal furnace. The flue gas flow is indicated at several different horizontal planes in Figure 1. A major benefit of the model is the ability to choose any plane for examining flow conditions. The levels represent from low to high a coal firing level, the secondary air inlet, an intermediate level, the flow around the bullnose, and flow through the superheater tubes, respectively. The flow is highly turbulent and swirling, and as a consequence of the swirl a high temperature zone exists in the middle of the furnace. Figures 2 and 3 show the temperature contours in a vertical and horizontal cross section revealing this hot zone. Figure 3 is at the level of secondary air injection, showing considerably lower temperatures near the air inlet ducts. For this unit it was determined that injection should be up near the superheater tubes using relatively coarse droplets (several hundred micron average size). Several interesting patterns were found for tangentially-fired units. It was observed that the bullnose tends to force the swirl off-center towards the front and one of the side walls, depending on the direction of the swirl. The swirl can influence droplets differently depending on nozzle locations, as seen in Figure 4. Not visible in these figures is the vertical component of the droplet trajectories. The drops rise approximately three meters above the injection level before they are predicted to evaporate. The field results demonstrated very good NOx reduction, indicating effective chemical distribution and injection into a favorable temperature zone. The chemical distributions for components with different volatilities are demonstrated in Figures 5 and 6. In each figure are shown three nozzles with the same mass flow rates of liquid but different average droplet sizes. The smaller droplets (on the left side of the figures) evaporate relatively quickly, resulting in nearly identical distributions of more volatile (Figure 5) and less volatile (Figure 6) chemicals. The larger drops (rightmost) have much longer lifetimes, and the less volatile components are released at the end of the trajectories. Because of the discrete number of droplet trajectories, the chemical distribution shows several regions of high concentrations. Actual sprays would tend to give a smoother distribution than the predicted one. For small droplets or droplets moving along with the flue gas, the resulting chemical distribution is only slightly affected by volatility. For larger droplets moving tangentially through the flue gas, however, the less volatile species are dispersed over a much more broad region than the more volatile species. This is one of the advantages of using an aqueous solution of chemicals for the NOxOUT Process; the water can be used to control the distribution of the chemicals within the furnace by adjusting solution concentration, droplet sizes, and droplet velocities. -7- |