Numerical Study Of Heat Transfer And Flow Characteristics Within The Furnace

As main heating equipment in petrochemical industry, furnace consumes a lot ofenergy. The energy-saving of furnace is the focus of energy conservation. The study ofheat transfer process of the furnace to improve energy efficiency has become the focusof technological innovation. The object of research in this subject is an atmosphericfurnace of3.5million tons/year. With the basic principles of computational fluiddynamics, the mathematical model of tube furnace was established. According to themathematical model, the steady-state heat transfer process in the furnace wassimulated. Compared with the site operation data, the feasibility of the mole wasvalidated.In this article, a three-dimension numerical simulation process in a restrictedspace for steady-state was conducted by Fluent6.3.κ-εequation model, PDFnon-premixed combustion model, discrete coordinate radiation model (DO model)wasused in this paper. Influences of furnace structure and combustion parameters havebeen systematic investigated. The results indicate that the physical model andcalculation method can simulate the process of high temperature air combustion well,and the calculated results are convinced. The calculated results can be used asfundamental data for developing the high temperature air combustion technology.Through the analysis of results, we conclude that:(1) In this paper, we simulated flame combustion process of furnace with differentdiameter of nozzle. The results show that velocity of fuel increased with the decreaseof the diameter, and then mixing and combustion rate between fuel and air wasincreased. It made combustion completed in the shorter region and the length of flamedecreased. But in fact, the length of furnace tube is10~20m, then if the length of flameis1~2m, it will make the area of high temperature too small. So heat transmission offurnace tube was nonuniform. In conclusion, the appropriate diameter of nozzle is9.5mm. (2) In the combustion process, with the angle of oxidant increased, reflux ofsmoke was enhanced. It made the combustion reaction area expansion and then thetemperature gradient was reduced. In addition, with the angle of oxidant increased, thegeneration of NOX was reduced. However, the angle of oxidant is not too large, or itwill make the air distribution anomalous. And the length of flame will shorten, so heattransfer efficiency will reduce. In conclusion, the appropriate angle of oxidant is10°~20°.(3) In the combustion process, with the preheating temperature of oxidantincreased, the average temperature in the furnace was increscent. And the temperaturedistribution is more uniform. But with the average temperature of oxidant increased,the generation of NOX was increased. It will contaminate the environment. Inconclusion, the appropriate preheating temperature of oxidant is500K.(4) In the combustion process, with the flux of oxidant increased, the mixing ratebetween fuel and air was increased. Then the velocity of combustion was increased. Atthe same time, the temperature distribution is more uniform. The generation of NOXwas reduced with the flux of oxidant increased. However, if the flux of oxidant isoversize, it will lead to cold air enter into the furnace. The cold air will absorbenthalpies of reactions. It will make the average temperature reduced. In conclusion,the appropriate flux of oxidant is300m3/h.