Study On The Function Regularity Of Pulverized Coal Ash Additive To Inhibit Metal Corrosion On Superheater In Biomass-fired Boiler

The development of renewable energy has become an effective way to relieve the energy pressure in the world when the fossil energy are increasingly exhausted and the energy pressure is doubled.Biomass energy is an important part of renewable energy,and biomass energy has the characteristics of preparing chemicals instead of fossil energy.Therefore,the development of biomass energy will be an important part of the development of renewable energy in the future.Biomass contains a large number of alkali metal elements and Cl elements.In the combustion process of biomass-fired boiler,it is easily to generate KCl and NaCl,resulting in ash deposition and corrosion on the metal surface.Pulverized coal ash is rich in Al2O3 and CaO,the use of pulverized coal ash as an additive can effectively inhibit the high temperature corrosion of biomass-fired boiler.In this paper maize straw and wheat straw were mixed with two kinds of pulverized coal ash in different adding proportion.The corrosion inhibition of pulverized coal ash on 15CrMoG,12CrlMoVG,T91,SUS316 and TP347H during biomass combustion were studied experimentally.The corrosion inhibition mechanism of biomass with pulverized coal ash combustion on metal heating surface was analyzed,and the gray correlation analysis of various elements which can inhibit corrosion is also carried out.A regression prediction model of pulverized coal ash corrosion inhibition was established,and the relationship between the loss of corrosion and various elements was determined.Firstly,the effect of pulverized coal ash content,the type of pulverized coal ash,the type of biomass,the type of metal and temperature on corrosion was studied experimentally on a horizontal tubular furnace.The results showed that the corrosion weight gain curves under various conditions conform to the parabolic regularity.It was found that the corrosiveness of corn straw ash to metal pipes was stronger than that of wheat straw ash,and the causticity was related to alkali metal and Cl in the ash sample;the corrosion resistance of the five kinds of metal pipes is related to the contents of Cr,Ni and Mo.Al2O3 and SiO2 in pulverized coal ash can react with KCl to reduce the KC1 content in deposition ash and reduce the corrosion significantly.The ability of corrosion inhibition of pulverized coal ash is mainly related to Si and Al elements in pulverized coal ash.By studying the effect of different pulverized coal ash addition proportion on corrosion,it was found that with the increase of pulverized coal ash addition proportion,the inhibition effect of metal corrosion increased before and then became weak,it’s not that the bigger the proportion of additions,the better.Temperature is an important factor that affects the corrosion inhibition of pulverized coal ash additives.With the rise of temperature,the number of activated molecules involved in the reaction increases,which leads to the aggravation of corrosion.Secondly,by comparing the microstructure of the outer metal corrosion layer with three different adding proportion,the corrosion inhibition regularity of different adding ratios were explored.The corrosion of oxide film on metal surface is obvious without pulverized coal ash,the oxide film is fractured and exfoliated,and loosely bonded with the metal matrix.When the pulverized coal ash adding proportion is 4%and 6%,the ash content of the outer corrosion layer is obviously reduced,and the holes are also greatly reduced,and the surface is relatively dense.The middle layer and inner layer are of close vane structure,and the surface holes are reduced.When the addition ratio is 6%,the corrosion inhibition ability is better than 4%.By comparing the microscopic morphology of the corrosion layer with the addition of no.1 pulverized coal ash metal block and that with the addition of no.2 pulverized coal ash metal block,the corrosion inhibition rule of the types of pulverized coal ash was explored.When no.2 pulverized coal ash was added in the same proportion,the outer microstructure of the metal corrosion layer was narrow and dense,the middle layer and the inner layer were like leaves,and the number of holes in the metal corrosion layer was much more than that in the case of no.1 pulverized coal ash addition in the same area range,and the holes in each metal corrosion layer were less than that in the case of no.1 pulverized coal ash addition,it shows that no.2 pulverized coal ash is better than no.1 pulverized coal ash in inhibiting corrosion.The results of microstructure analysis were consistent with the weight gain curve of the corrosion experiment,indicating that the higher Al2O3 content in the deposition ash sample,the corrosion inhibition ability is better.Thirdly,the grey correlation theory is adopted to analyse the correlation of various elements to inhibit corrosion,the major effect of elements to inhibit corrosion are determined,the regression prediction model of the loss of corrosion weight is established,and the prediction correlation formula is polynomial y=-228.3966+928.9764x1-154.4052x2-367.9273x3-26.32969x4-354.5426x12+31.24339x22+156.9674x32+15.38631x42 y is the loss of dimensionless corrosion weight,andx1,x2,x3,andx4are the contents of Si,Al,Ca and Fe in pulverized coal ash,respectively.This model is a simple and convenient method for predicting the loss of corrosion of metal heating surface corrosion in the combustion process of biomass adding pulverized coal ash,which has certain guiding significance for the prediction of corrosion inhibition of biomass-fired boilers,and is also convenient for screening pulverized coal ash additives with best corrosion inhibition performance.