| OCR Text |
Show During the tests, a thermal load consisting of sixteen pieces of steel, was positioned as shown in Fig. 1. This prevented the temperature of the furnace from rising too rapidly to obtain consistent results and allowed measurements to be taken over a range of furnace temperatures and hence air preheat temperatures. The upper limit of this range was determined by the maximum operating temperature of the furnace refractories, which was nominally 1573K. The air preheat temperature obtainable was generally within 473 - 573K of the furnace chamber temperature, depending on the percentage of combustion products that were extracted through the regenerators. When operating at a typical thermal input (firing rate) of about 480 kW, the furnace temperature rose to I573K in approximately 6 hours from a cold start. The burners investigated are available commercially (Hotwork development Ltd., UK.). Schematic diagrams of both the unstaged and air-staged type burner designs used are shown in Figs. 2(a) and (b), respectively. Both burners were operated within the range of 0.438 - 0.441MW with approximately 10% excess air preheated to temperatures in the range of 1160 - I274K. In addition a flared quart is utilised, when operating the air-staged burner, to maximise the entrainment of furnace gases into the flame, with the object of suppressing the flame temperature at the burner exit. Oxy/Fue/ Combustion The combustion test chamber is 5.3m long with an internal diameter of 1.5m. The walls are constructed of three layers of castable refractory, the outer layer being a low conductivity insulate. In normal operation the refractory obtains a temperature of 1473 - I673K at the inner face with the burner firing rates in the range of 1.0 - 1.4MW. A water-cooled load along the entire length of the chamber extracted heat from the furnace. the furnace is equipped with 10 observation ports along one side and 11 sampling ports along the other. Furnace pressure is controlled by a damper in the flue ductwork. The oxylNatural gas fired burner investigated, Fig. 3, comprises of six trumpet shaped oxygen ports. The natural gas is conveyed between the oxygen carrier tube and the inner tube of the water jacket. During normal firing the oxygen acts as a high velocity fluid which entrains the natural·gas into the flame. This burner type is widely used in industry for ladle preheating and in reverbatory furnaces. Results Air/Fuel combustion The results are presented in graphical form for the individual burners. Figure 4 shows typical measured and predicted profiles for the unstaged and air-staged burner, at a distance of 8 |
