The Study On The Thermal Characteristics Of Self-preheating Radiation Tube Under Oxygen-enriched Condition

The self-recuperative radiant tube is an important indirect heating device.It is mainly composed of two parts:self-recuperative burner and radiant tube.Since the flue gas in the radiant tube is not in contact with the heated material during the heating process directly,defects such as oxidation and decarburization generated during the heating process can be effectively avoided.Therefore it is widely used in metal heat treatment and billet heating.At present,there are two main problems with self-preheating radiant tubes.There are low heat exchange efficiency and the surface temperature of the radiant tube is not uniform,resulting in poor heating quality of the product,and the radiant tube has large thermal stress and low life.Aiming at the above two problems,this paper proposes an oxy-fuel combustion type self-preheating directional radiation tube.On the one hand,the use of oxygen-enriched combustion technology increases the proportion of O2 in the combustion-supporting gas,which can accelerate the combustion speed and strengthen heat exchange,improving productivity and thermal efficiency;meanwhile,the proportion of N2 in the combustion-supporting gas is reduced or even does not contain N2,thereby reducing it avoids the NOx produced by the reaction in the radiant tube.On the other hand,the directional radiation heat transfer technology is adopted,and the uneven structure is adopted in the low-temperature section of the tube wall of the radiant tube,which increases the effective radiation area of the low-temperature section,thereby increasing the surface radiant heat flow there,which in turn makes the surface temperature of radiant tube tends to be uniform.A mathematical model of thermal process of self-recuperative radiant tube is established in this paper,and region discretization using a structured grid.The numerical simulation method is used to study the influence of oxygen concentration on the thermal process.The results show that as the oxygen concentration increases,the maximum temperature of the flue gas increases,the flame length becomes shorter,and NOx increases first and then decreases.Considering the material of the radiation tube and the actual application,the reasonable range of oxygen concentration is 0.21～0.6.At the same time,the oxygen concentration,the surface structure of the radiant tube and the pressure of the gas outlet on the uniformity of the surface temperature of the radiant tube were investigated.The results show that when the oxygen concentration is 0.5,the temperature uniformity of the radiant tube is the best.When the directional surface is used in the low temperature region of the radiant tube,it can effectively improve the uniformity of the radiant tube temperature.As the outlet pressure increases,the maximum temperature of the flue gas decreases,so natural exhaust smoke should be used whenever possible.Finally,in order to verify the correctness of this simulation,an experimental study is carried out in this paper.Taking into account practical factors such as experimental costs and site conditions,three typical experiments are carried out in this paper,they are oxygen-enriched combustion experiment,smooth tube experiment and corrugated tube experiment.The experimental results show that the mathematical model established in this paper is correct and the calculation results are more accurate and reliable.