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Show Performance Requirements: As this large diameter reformer tube can collapse radially, the circumferential wall temperature distribution is required to be uniform so that no significant thermal stress occurs. Also, the combustion gas must be evenly distributed in order to achieve even heat supply to the reformer tube. Performance of radiative heat transfer from the flame is less important for a reformer design having a combustion tube that prevents the reformer tube from directly contacting flame. In such design, combustion gas is passed through an annular channel formed between the reformer tube and the combustion tube, and heat transfer to the wall takes place by convection. For a design without the combustion tube, as flame radiation becomes directly relevant to the heat transfer to the reformer tube, an optimum heat flux pattern is being pursued. 2. Pressurized Combustion Tests Combustion tests for various types of reformer burner, using a small experimental furnace, were carried out to compare burner performance and to identify experimentally the effect of pressure on flames. 2.1 Experimental Apparatus Experimental Furnace: A vertical furnace having a burner at its top wall was used to test burners under pressurized condition. ( See Figure 1 ) The furnace is water-cooled and has 4 separate cooling sections, of which the inner metal surface is lined with ceramic thermal insulation. Combustion gas is forcibly cooled in a cooling chamber at the bottom of the combustion chamber, and then exhausted through a pressure regulation valve. The system pressure can be varied from atmospheric to 0.76MPa. Utilities: Methane and SFG ( Simulated Fuel Gas ) were used as fuel. SFG is a mixture of hydrogen and carbon dioxide ( H2 = 50%/C02 = 50%, HHV = 5.4 MJ/Nm3 ) simulating spent fuel from the fuel cell anode. Methane and carbon dioxide were supplied from pressurized cylinders having a steam heated type evaporator, and hydrogen, by pressurized gas cylinders. Combustion air is delivered from a compressor and heated up to 673K by an electric preheater. Though the air can be diluted by nitrogen to simulate spent air, fresh air was mainly used in the experiments. Measurement: Thermocouples are planted along the metal wall surface. Temperature and gas composition in flames can be measured by pressure-tight probes having an automatic traversing device. Heat extraction rate measurement can be performed at each cooling section. 3 |