OCR Text |
Show traced to the presence of flow restrictions or disturbances in the fuel train. Pipe fittings such as "tees" and "crosses" were then replaced with "Y-fittings," standard pipe elbows were replaced with long-radius elbows, and the piping was streamlined whenever possible. All manual control valves were replaced with ball valves having port diameters equal to the inside diameter of the connecting pipe. These changes .have eliminated problems related to settling out of the coal particles. Combustion Related Equipment With minimal modifications, burner nozzles designed for oil-firing can be retrofitted for coal slurries. In all COM tests in the 700-hp boiler, an inside-mix, steam-atomized, oil-designed burner nozzle was used (Figure 3). Satisfactory atomization and combustion were obtained by adjusting atomizing, steam flows and pressures, and by controlling COM viscosities and firing temperatures. In recent CWM tests, the same burner nozzle was used with only slight changes, which included doubling the nozzle hole cross-section area, reducing the burner spray angle, and utilizing air atomization. In the 100-hp boiler, an inside-mix, air-atomized, oil-designed burner nozzle (Figure 4) has been used without physical modifications for CWM and CMM tests. Because of the abrasive nature of coal slurries, wear in the burner nozzles becomes one of the important problems. By properly selecting materials for burner nozzle construction, the wear problem can be greatly reduced. Table 1 gives data on burner nozzle wear obtained during coal slurry tests at PETC. The combustion air system and air register (single-air-zone or dual-air-zone) in the 700-hp boiler required no modifications when converting the fuel from No. 6 oil to COM. When converting to CWM, preheating of combustion air, air register modifications, and start-up fuel introduction were necessary. 14-8 |