Research On Heat Transfer And Flame Emission Characteristics Of Premixed Flame Jet Heating Aluminum Rods

Flame jet heating technology is to directly jet high temperature flame to the surface of the object to be heated,forming a high-efficiency heating technology based on convection heat transfer.It has the advantages of fast heating rate and high thermal efficiency.It is widely used in metal bar heating,glass processing and other industrial fields.In the face of increasingly strict emission standards and the development goals of energy conservation and emission reduction,it is necessary to further improve the heating efficiency of flame jets and reduce pollutant emissions,and it is necessary to study the heat transfer and emission laws,which will help design high-efficiency,low-emission bar heating furnace provide experimental data reference and heating method basis.In this thesis,aiming at the goal of high efficiency and low emission of flame jet heating technology,the flame jet heating technology is combined with full premixed combustion and rich-lean combustion technology to design a single-row multi-fire-hole strip that can meet the requirements of low nitrogen emission and flame stable combustion.The full premixed burner is used as the research object to build an experimental bench for premixed flame jet heating aluminum rods,and conduct experimental research and analysis on the premixed flame vertical upward jet aluminum rods,mainly on the heat transfer and flame emission of flame jet heating aluminum rods.Conduct experimental research on the characteristics of different burner operating conditions and structure parameters on the heating rate of a single aluminum rod and CO and NO_Xemissions,the relationship between adjacent flames on local pollutants,and multi-rod heating experimental research.Experimental studies show that:（1）For different burner operating conditions,when the air coefficientαis between 1.00and 1.30,with the increase ofα:the heating rate of the aluminum rod decreases from11.03℃/min to 6.90℃/min,with a decrease of 37%;CO emissions gradually increase;NO_Xemissions gradually decrease.When the flame load Q is between 5.4kw and 6.9kw,with the increase of Q:the heating rate of the aluminum rod increases from 8.98℃/min to 10.67℃/min;the CO and NO_Xemissions increase gradually.When the premixed air temperature T_airis between-5℃and 25℃,with the increase of T_air:the heating rate of the aluminum rod and the emissions of CO and NO_Xare basically unchanged.When the premixed air humidity d_airis between 30%and 90%,with the increase of d_air:the heating rate of the aluminum rod decreases linearly from 10.00℃/min to 5.49℃/min;the CO emission gradually increases;the NO_Xemission gradually decreases.（2）For different structural parameters,when the distance H between the fire hole and the aluminum rod is between 35mm-90mm,with the increase of H:the heating rate of the aluminum rod increases first and then decreases,and there is an optimal H=50mm to make the heating rate of the aluminum rod.The highest temperature is 10.62℃/min,and the heating rate is the lowest when H=90mm,which is 7.10℃/min;the CO emission gradually decreases;the NO_Xemission decreases first and then increases,and the lowest temperature is 26.65mg/m~3when H=55mm.When the fire hole spacing S is 18mm,36mm,and 54mm,with the increase of S,the heating rate of the aluminum rod continues to increase,and the increase of the heating rate from S=18mm to 36mm is larger than that from 36mm to 54mm;CO emissions gradually increase;NO_Xemissions gradually decrease.（3）Whenαand Q are large or H and S are small,the adjacent flame jets will expand along the surface of the aluminum rod,intersect with each other and deflect downward.The emission has increased sharply,the local CO emission has increased by 215%,and the NO_Xemission has increased by 52%.It is determined that the optimal flame shape of the flame jet heating the aluminum rod is:the flame extends the largest distance in the axial direction of the aluminum rod and has no intersecting direction down deflection.In addition,when the temperature of the aluminum rod T_alis between 100℃and 500℃,with the increase of T_al,the CO emission gradually decreases.Less affected by Q.Therefore,the heating of the aluminum rod is divided into a low temperature section(T_al<250℃)and a high temperature section(T_al=250℃-500℃),and an efficient and low-emission heating method is proposed.After adding the endothermic rod,when the heating furnace runs continuously,it can not only reduce the exhaust gas temperature,but also avoid the generation of CO during the low temperature section of heating the aluminum rod;In the furnace opening stage,the temperature of the heated aluminum rod is low,and the variable load heating method is adopted,the low-temperature section adopts low-load heating to avoid the generation of CO,and the high-temperature section adopts high-load heating.This method avoids high CO emissions during the opening stage and has little effect on the heating rate of aluminum rods.Finally,the experiment verifies the feasibility of this heating method,and provides a reference for the heating method of the aluminum rod heating furnace.