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Show All of the foregoing work conducted by AGA Research was reviewed and a set of scaling bench numbers was developed for mixer and flameholder design. Scaling parameters were verified on a boiler with 1.5 million BtuIhr input rate in Phase IT of the project. The 1.5 million BtuIhr boiler's heat exchanger (combustion chamber) has the same diameter as the 0.5 million BtuIhr boiler's, only is longer. It has 3 times the input rate, but the equipment footprint is the same as the 0.5 million Btu/hr boiler. 4.1 Mixer Scalability Experimental investigations have been conducted at AGAR to develop the empirical design data for the mixer. It has proven to be very difficult to predict the performance of actual design. Experience and trial-and error method still playa major role in development work. This is mainly due to lack of accurate theoretical models for the mixing process. Furthermore, there is still no practical and repeatable method to determine the degree of the mixedness. The mixer of the combustion system for 0.5 million BtuIhr input rate boiler has been extrapolated to the 1.5 million BtuIhr boiler's using AGAR's design experience data. Tests show that these two combustion systems have comparable emission results even with the difference in input rates. 4.2 Flameholder and Combustion Chamber Scalability A flameholder configuration with both swider and bluff-body has been systematically studied in the gas turbine industry. Much useful information is available, but this information is mainly focused on high pressure applications, which normally have a pressure loss of several PSI through the flameholder. It is generally accepted that the higher pressure drop across the flameholder, the more stable the flame, however the ultra-lean premixed combustion system for the commercial market is a low pressure application. The maximum allowable pressure drop across the flameholder is only a few inches of water column. At the same time, the combustion chamber geometry differs depending on the application. Experiments were conducted at AGAR to investigate the scaling parameters for the flameholder design. The flame stability was tested by turndown test and combustion performance at different amounts of excess air and with both coverging and diverging nozzle angles. The emissions were measured by emission analyzers. The shape of the flame was documented with a digital imaging system. This system consists of an RGB camera and RGB video tape recorder, computer frame grabber, and an image processing computer with software. The videos were taken through a quartz tube at the exit of the burner. By digitizing the video picture, the image processing system can be used to quantify flame shape, size and color. It is found that the swirling number and the heat release rate within the refractory tunnel are the most important factors for scaling of flameholder and combustion chamber. The flame shape is controlled by the swider angles and the burner nozzle configurations. 10 |