| OCR Text |
Show to the burner nozzle and a gas pilot is usually used to ignite the main fuel stream. Steam or compressed air may be used to atomize the fuel. The sequence of burner operation from start up through shut down is governed by the programmed control devices. Automatic safety devices shut the boiler down in case of flame failure. A typical firetube boiler is shown in Figure 1. Analysis Preliminary calculations were made to determine if the standard 50-50 COM with coal particle sizes such that 80% pass 200 mesh would be completely burned in the boiler furnace tube. Residence times were determined by the equation: T = -2- Q V = Volume of the Furnace Ft. 3 Q = Volumetric Flow Rate Ft. /Sec. The actual residence time could not be accurately established because of limited data on the swirl characteristics of the burner. However, the calculation showed that particle sizes of 74um and larger would not be completely burned prior to reaching the end of the furnace tube. Further, since the temperature of the combustion gases are expected to vary from a maximum of about 3000°F in the combustion chamber to about 2100°F at the end of the furnace tube, ash deposits may occur depending on the characteristics of the ash in the coal. Since the heat transfer in the furnace tube is primarily by radiation, a study was made to qualitatively determine the impact of burning COM instead of fuel oil. Further, since more excess air is required to burn COM than straight oil, and since the combustion forced air fan is of fixed capacity, the boiler output is reduced when burning coal. 15-4 |
