| OCR Text |
Show measurement locations. The signal strength histograms are given in normalized intensity units and represent the measured peak intensities for particles traversing the measurement volume. The particle size histograms shown on the same graphs are the size distributions which have been deconvoluted from the signal intensity histograms. The deconvolution was performed by solving the N x N matrix equation (where N=7 for our data) for the size distribution. Calculations of the particle trajectory probability distribution were used to obtain the N x N matrix. One major distinction between the size histograms and the signal intensity histograms is that the size histogram accounts for particles in the low end of the size range which passed through the edge of the measurement volume and were not counted because the scattered signal intensity was too low. For this reason, the size histogram contains a higher total number of counts than the signal histogram. The most notable feature of the measurement results is the size difference between particles measured in the acid spray area (location 1 on Figure 1) and those measured in the other locations. This was expected since the sulfuric acid evaporates rapidly in a 1300 K gas stream, with a 1 mm diameter droplet vaporizing in approximately 2.5 seconds. The primary question however was whether any sulfuric acid droplets entered the main section of the boiler. This question could not be answered by the size measurements alone, since the measurement cannot distinguish between ash particles and sulfuric acid droplets, but it can be answered by a combination of the measurement results and a knowledge of droplet vaporization times. The vaporization time of sulfuric acid droplets scales with the square of the droplet diameter. Thus, a 10 ym droplet vaporizes in 0.25 ms. Since the largest observed particle at locations 2 and 3 was less than 10 ym in diameter, it would have vaporized in less time than it took to traverse the measurement volume if it were a sulfuric acid droplet. In addition, the particle size distributions for locations 2 and 3 are very similar while the mean gas flow time between the two locations is roughly 10 seconds. For these reasons, the measurement results strongly support the conclusion that no sulfuric acid droplets enter the main section of the burner. The size histogram for location 4, though, is at first rather puzzling in that larger particles were observed at this location than at 24-15 |
