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Show the target wall which is also necessary to simultaneously yield the lowest C O and lowest NOx. In practice, the same size burner has been installed in many different furnace shapes. Figure 3 shows two examples of furnaces shaped differently from the precise fit in Figure 2. Both have lower volumetric heat loading than the best fit in Figure 2, but neither will have as low a yield of C O and N O x simultaneously. Designing flame shapes using individual Figure 2. P R E C I S E F L A M E FIT. streamline analytical methods, permits precise flame fits in all three furnace shapes, and simultaneously reduced emissions. Figure 3. INACCURATE FLAME FITS. FLAME SHAPE METRICS Visual determination of the flame fit in a furnace is a valuable metric, one that has been the most important determinant of a good flame fit or a bad flame fit. Observed clearance between flame tails and the target wall, between the side walls, floor and roof provide confirmation that nothing untoward is likely to occur due to flame impingement. All experienced burner commissioning engineers have visually determined the size of the flames in the furnaces they are characterizing. With the advent of flames shaped during the burner design phase, prior to installation, it has become apparent that visual determination of the flame dimensions is not sufficiently precise. More accurate measures are now being used. They are based on emissions measurements and superheater temperatures. Subsequent to the evolution of the scientific analytical methods of flame shaping at Peabody Engineering Corp., an extensive matrix of validation tests were conducted in the Advanced Combustion Research and Development Centre, Hamworthy Combustion Engineering, Ltd., Poole, Dorset, England, a sister division of Peabody Engineering. The facility has a dozen separate fired furnaces which are supported by state of the art instrumentation and measurement tools. Testing was carried out full scale, for more than one-hundred hours on high nitrogen heavy oil, low nitrogen light oil and natural gas. The baseline gross heat input rating selected was one-hundred million Btu's per hour. These expensive tests, which received no financial support from outside of the company, have proven to be of considerable value. The flame shaping analytical methods have been validated for liquid and gaseous fuels. In addition, they have proven that precisely fitting flames into furnaces, produces the lowest combination of emissions. The full scale test facility employed has twenty-three, large viewing ports. These are used to measure the length of the flame by eye, viewing sequentially through each axial port which are spaced one meter apart along the walkway which extends the length of the furnace. There are also multiple viewing ports for looking along the side walls, looking directly into the burner from the rear, looking up into the burner from below and down from above. There are also view ports providing direct viewing parallel to the furnace front wall directly across the burner throat, and from forty-five degrees through the side wall directly into the throat. This facility enables extensive spatial characterization of flame position and size. The human eye can see the entire flame. The flame behavior can be observed over the entire load range, and compared in test after test as configurations are changed. The human eye can quickly assess flame shapes. However, there is a more accurate means of determining which flame fit is precise. That is by measuring emissions. The preferred method for assessing the effect of flame fit accuracy when changing from one array of jet trajectories to another is to evaluate the change in C O and NOx, using the uncorrected mole fraction of C O and N O x actually measured. |