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Show AFRC - 1996 Int. Symposium Baltimore precombustor -----gas/air mixture (flue gas + air) dilution air venturi mixer gas flame tube \ flame holder Figure 1: scheme of experimental set-up September 30 - October 2 1996 Page 3 of 14 flue At Gasunie Research, significant experience has been gained using this type of metal-fiber material used here as flame holder. Flames, generated downstream of this material (Acotech AC200P2) are very stable. This good stability is due to the turbulent flow structure downstream of the material. A discussion regarding the flame stabilisation mechanism of a similar surface material has been presented by Yakahagi and Hase (1994). In the present experiments the thermal input ranged from 20 - 60 kW, which implies that the thermal load at the metal-fiber burner plate is between 800 and 2400 kW/m2 • In all experiments cited in this paper, the combustion occurs sufficiently far downstream of the flame holder to prevent any significant heat transfer from the flame towards the flame holder. Thus, in the experiments, the flames are essentially adiabatic. As mentioned above, the experiments are focused on the properties (stability and emission) of mixtures of natural gas, air and flue-gas at various initial (unbumt) temperatures. The flue-gas originates from the precombustor which is equipped with a premixed natural gas/air burner. The thermal input of this burner could be adjusted between 5 and 15 kW. The dilution air, also used for cooling of the precombustor, is injected in the gas stream at the exit of the precombustor. Natural gas is injected just upstream of the throat of a venturi mixer. The diameter of the venturi throat is 50 mm and its downstream half angle is 5.5 0 • At the downstream side, the venturi diameter is 180 mm. The total length of the venturi is approximately 1400 mm. |