OCR Text |
Show significantly at lower firing rates, and the flue temperature decreased. At the maximum turndown ratio, the front wall temperature was about 700°F higher, and the flue temperature was about 200°F lower than at a nominal fuel input of 3 X 106 Btu/h. Additional tests were conducted to determine the effect of fuel moisture content on flame stability. No flame stability problems were found with up to 10% moisture in the fuel at a fuel input of 3.1 X 106 Btu/h, with up to 13% moisture at a fuel input of 1.2 X 106 Btu/h and with up to 22% moisture at an input of 0.7 X 10 Btu/h. It must be noted that these are the maximum amounts of moisture that we could add and are not the maximum amounts of moisture in the fuel at which the flame would be stable. The maximum amount of moisture that could be tested was limited by the capacity of our steam generator. Effect of Reduced CHA Concentration in Fuel on Flame Stability The flame was stable down to a methane concentration of 2.4% which represents a heating value of 55 Btu/SCF. It must be noted that as the methane concentration was decreased the firing rate also decreased and the residence time increased. The front wall temperature increased when CH^ was reduced, and the flue temperature dropped. At CH^ concentrations below 2.4%, the front wall temperature also started dropping. The flame started moving away from the front wall, and, finally, at a fuel CH^ concentration of 0.9% (41 Btu/SCF), front wall temperature of 550°F, and flue temperature of 1330°F, the flame lifted off. TESTS WITH MINIMUM HEATING VALUE GAS Following the combustor performance tests with the average heating value gas, stability tests were conducted to determine if the cyclonic combustor was capable of burning the minimum heating value gas. Anticipating stability problems, the combustor was set up at a lower fuel heat input (2.4 X 10 Btu/h) and at a higher fuel preheat temperature (420°F). The flame was stable with no moisture in the fuel; however, the flame became unstable after the required amount of moisture was added as dry steam. It was decided to increase the fuel preheat and reduce the firing rate. 5.7.20. INSTITUTE OF GAS TECHNOLOGY |