Study On Characteristics Of Corrosion Related To Ash Deposition On Heating Surface Of Biomass Boiler Superheater

The utilization of biomass resources is of great significance to the increasingly tense environmental pollution and energy problems,and has attracted wide attention.However,the characteristics of high chlorine and high alkali metals make it easy to cause deposition and corrosion of heating surfaces during utilization.The higher the steam temperature of the boiler is,the greater the pressure,the higher the efficiency of the unit.Compared with the coal-fired unit,the characteristics of the biomass are more likely to cause the corrosion of the biomass boiler,which is the difficult problem for the utilization efficiency of the biomass boiler.Therefore,it is of theoretical significance and practical application value to discuss the corrosion and protection of the boiler.In this paper,the horizontal tube furnace system is used to study the law of biomass corrosion and to explore the corrosion law when using fly ash as additive.When the temperature is low,the rate of corrosion reaction is relatively slow.As the temperature rises,the corrosion rate increases exponentially and the metal surface appears cracking and peeling.This is due to the rapid increase of the reaction rate,which leads to the oxidation of a large number of metal elements in a short period of time and the accumulation of internal stress.The corrosion resistance of the four metal materials is from weak to strong:12CrlMoV<15CrMo<T91<TP347H.The alloy elements of four metals are analyzed and compared.It is believed that the high Cr metal has strong corrosion resistance because of forming a dense layer of oxide film.The trace Mo can improve the corrosion resistance of the metal,and the Ni has a strong anti-corrosion ability.Appropriate trace elements in the alloy can effectively improve the microstructure of the metal and obtain strong corrosion resistance.The corrosiveness of biomass fuels is:wheat straw>cotton rod,and the difference of corrosiveness is caused by different elements content of different biomass ash.The wheat straw ash contains more potassium and chlorine and other key elements of corrosion,so it has strong corrosiveness.The thermal analysis model of high temperature corrosion was established by thermal analysis.According to the fitting degree and fitting error of G(a)-t curve,the corrosion reaction type of T91 was D2 type at 480 ? to 680 ?,and the corrosion mechanism function was G(a)=[-ln(1-?)]-1,the former factor k0=0.079497s-1 and the corrosion reaction live.Chemical energy E=8100.40715J · mol-1,heat surface corrosion kinetics equation d a/dt=0.079497exp(-974.32728/T)[-In(1-?)]-1.The feasibility of pulverized fuel ash as additive is discussed by using pulverized fuel ash as additive.By analyzing the element of pulverized fuel ash and combining the result of corrosion test,it is found that the effect of the additive is affected by the joint action of silicon,aluminum,potassium,sodium and calcium in the ash.When there are more alkali metals in the biomass,a higher silicon and aluminum element is used.Fly ash is a good choice.The additive of pulverized fuel ash can be used to make a general judgment on the corrosivity of ash with the final(Si+Al)/(Na+K)molar ratio of ash.The larger the mole ratio,the smaller the corrosivity of the ash.The ratio of silicon and aluminum also affects the effect of corrosion.The influence of the molar ratio of silicon and aluminum to the corrosion effect is analyzed.It is believed that the ratio of silicon and aluminum to 1 can effectively reduce the corrosion and the content of aluminum can be slightly higher.The purpose is to prevent the production of low melting point of potassium silicate from the safety and increase the ash accumulation and decay in the furnace.Erosion.In terms of economic considerations,in order to minimize the amount of additives,it is suggested that the molar ratio of(Si+Al)/(Na+K)is 2,the ratio of silicon to aluminum to 1 is the best,and the pulverized fuel ash with low calcium and magnesium content is chosen as far as possible.For the general fly ash,the content of silicon is generally greater than that of aluminum element,and some alum can be added to the fly ash.Soil to increase the content of aluminum.