OCR Text |
Show 3 theory, radical species increase as the flame temperature rises. If radical species influence reducing ability, high flame temperature is an effective method to improve it. In this report, we examined two effective methods by which the flame temperature is raised, air preheating and oxygen enrichment.4,5) The air preheating heats the flame directly and is excellent for conservation of energy by the waste heat collection from the combustion exhaust gas. The oxygen enrichment increases the oxygen content by adding oxygen to combustion air and raises the flame temperature with decreases of Nitrogen that does not contribute to the combustion. In addition, other component concentrations increase relatively because of the decrease in nitrogen, and reducing ability performance improvement can be expected. 3.Experiments on Reducing Flame Burner 3.1. Structure of Burner The burner tested in these experiments is an SNM type burner shown in Figure 3. The S N M burner was developed mainly to form reducing flame with nozzle-mixed type. The structure of this burner will be described below. The fuel from the burner center axis blows and cools the wall of nozzle tip, and is preheated. The reversed fuel is ejected from 6 holes perpendicularly to the circumference. The air from the circumference is swirled by the swirl impeller, and is mixed with the fuel ejected from these holes. The mixed fuel and air jet leaves the burner from a ring slit nozzle. 3.2 Improvement of reducibility by air preheating To examine the effect on the reduction performance of air preheating, the reducing and direct-fired flame heating in a small furnace was tested. The test apparatus consisted of the direct fired heating furnace and the non-oxidation cooling compartment as shown in Figure 4. In a 0.6m wide x 0.5m high x 0.6m long castable refractory furnace, coke oven gas was burnt as a fuel at a combustion rate of 70kW, a 30-400°C pre-heated air temperature range, and a 0.82-0.9 air ratio range. This furnace had two 3 0 m m wide x 300mm long slits on the top and bottom of this furnace to insert the steel sheet from above and remove from below. A S N M burner was installed in this furnace, and the distance of 300mm was maintained between the burner and the steel sheet. In a 0.2m wide x 0.8m high x 0.4m long steel compartment, nitrogen gas was blown in as a non-oxidizing atmosphere at blowing rate of 50Nm3/hr. Steel sheet of low carbon is 150mm wide x 600mm long x 1.2mm thick. The test was carried out as follows |