Control And Optimization Of The Heat Exchanger Wall Temperature Of The Biomass Fuel Hot Air Furnace

In the nowadays,with the development of society and economy,human need more and more energy and the environmental problems brought by the traditional fossil energy is increasingly prominent.In China,there is a contradictory relation between the growing demand for energy and the deterioration of environment.But the using of biomass energy provides a reliable way to ease the strained relations.Especially in recent years,national emission standards for coal-fired boilers become more and more strict.For the hot blast stoves which are widely used in the production and life,many factories have used hot blast stoves which burn biomass briquette instead of coal after reforming.But after reforming,the conditions of inadequate fuel combustion and shortened life of heat exchanger happen in a lot of hot blast stoves.In response to this situation,hot blast stove which burns biomass briquette is studied deeply in this paper,the research content includes:In view of the problems that the coal biomass stove exists in practical using,hot blast heater which is suitable for the burning of biomass briquette is designed,according to the combustion characteristic of it.The paper will focus on the problem that the heat exchanger pipe is badly damaged in the running process of hot air furnace.Using the knowledge of thermodynamics and heat transfer,the author deduces the formula of tube wall temperature of the heat exchanger.Through analysis,it is concluded that fume temperature and convective heattransfer coefficient will have a great effect on tube wall temperature of the heat exchanger.To reduce the flue gas temperature,the following two ways are putforward with.One is to mix the cold air from the outside world with the hightemperature flue gas at the entrance of heating surface,the other is to recycle the low-temperature flue gas off the hot blast stove and mix it with the hightemperature flue gas at the entrance of heating surface.Both of the two ways can make flue gas temperature at the heating entrance reduced.Through qualitative and quantitative analysis,the influence of two ways on thermal efficiency of hot blast stove is different.Pre-treatment software GAMBIT is used to create the three-dimensional physical model and mesh for the heat exchanger of hot air furnace.The numerical simulation software,FLUENT,is applied to simulate the operation of the hot air furnace heat exchanger.Then the flow field and temperature field of heat exchanger can be obtained.Through analyzing distribution status of heat exchanger tube wall under different flue gas temperature and air velocity,the author will find the optimization for prolonging the service life of heat exchanger,according to the fact that the extreme heat-deformation temperatures of the metallic material that the heat exchange tube is limit of 450 degree centigrade.