Study On The Effect Of Modified Pulverized Coal Ash Additives On Characteristics Of Ash Deposition And Corrosion During Biomass Combustion

Biomass as a source of energy has the characteristics of wide sources and diverse uses,and is an ideal substitute for fossil energy.At present,biomass direct combustion technology has gradually matured and taken shape in the field of renewable energy utilization.However,the content of alkali metals,alkaline earth metal elements such as potassium,sodium and calcium and chlorine in biomass fuel is usually high.The content of potassium is very high,which will cause a series of problems of biomass boiler at high-temperature superheater surface during combustion,such as slagging in the furnace and equipment corrosion.These problems will seriously affect the safety and economy of biomass boiler operation.In view of these problems,this paper studies the mechanism of ash slagging and corrosion of biomass boiler heating surface from the perspective of biomass deposit ash characteristics.Basis on this,it is proposed to use silicon aluminum additives as anti-slagging corrosion additives for biomass fuels,and in-depth research and discussion on the effect of silicon aluminum additive and additive ratio;further proposed the use of modulated fly ash as an additive program,and through experiments to explore the effect of fly ash modulation of silicon aluminum additive.Two types of biomass fuels,wheat straw and cotton straw,were used to analyze the morphological characteristics and phase composition characteristics of biomass ash.The experiment found that as the temperature increased,the ash formation rate gradually decreased,and the phenomenon of surface shrinkage and slagging became more serious.The content of potassium,silicon and chlorine in wheat straw ash is very high.As the combustion temperature increases,the KC1 in the ash will be gradually released in gaseous,which will cause chlorine corrosion of the heat exchange surface in the boiler;the potassium concentration in the ash is as high as 225.55 mg/g,which results in a very low melting point of the ash.CaO and MgO crystal phases appear at high temperatures above 800℃ and are the main components of the slag melt.Using SiO2 and Al2O3 to prepare silicon-aluminum additives to simulate the main action components of fly ash additives,the influences and principles of silicon-aluminum-based additives to suppress slagging and corrosion problems were discussed through experimental research.After using the silicon aluminum additive,more potassium was fixed in the wheat straw ash and cotton straw ash.The amount of potassium fixed in the wheat straw ash was increased from 57.29mg to more than 150mg,which effectively reduced the KCl in the gas phase;the potassium concentration of the cotton straw ash Then reduced from 225.55mg/g to below 100mg/g,which reducing slagging.The two kinds of biomass have the best potassium fixation capacity when the additive silicon-aluminum ratio is 3:2;the best additive usage of wheat straw is 15%,and the best additive usage of cotton straw is 10%.After using silicon aluminum additive,the KC1 in both biomass ash is reduced,more potassium is fixed in the ash,and the slag-forming alkaline earth metal oxides CaO,MgO,etc.in the cotton straw ash are also significantly reduced.The additive converts potassium,calcium,and other metal elements in the ash into aluminosilicates with stable properties,high melting point,and less gaseous potassium compounds released,which can effectively reduce slagging and corrosion.On the basis of the research on silicon aluminum additives,the preparation method and the optimal addition ratio of the modified fly ash additive are proposed,and the effect of the adjusted fly ash additive is verified through experiments.By adding Al2O3 powder with a mass fraction of 4.8%to the fly ash selected in the experiment,a modulated fly ash additive with a silicon to aluminum ratio of 3:2 can be obtained.According to the test,the best addition ratio of wheat straw using modified fly ash additives is 17%,and the best addition ratio of cotton straw is 15%.The two potassium fixation amounts are 154.03mg and 82.82mg respectively,which are similar with silicon aluminum additive.From the morphological characteristics,under the action of the two additives,the texture of the ash is more loose and delicate,and there are almost no sticking blocks.The problem of slagging has been effectively improved.The size of the two biomass ash particles is significantly reduced.Reunion is also greatly reduced.The ash-like particles using silicon aluminum additives are fine and loose,and the ash-like particles using the modulated fly ash additives are mostly spherical.After using the prepared fly ash additive,the potassium concentration and KCl content in the wheat straw ash decreased significantly.Under the action of the additive,KCl was converted into aluminosilicates with high melting point and stable properties,such as KAlSi3O8,which are similar with the ash with silicon aluminum additive;the main components in the cotton straw ash are completely changed to aluminosilicates,and the CaO,MgO,KCl and other components that cause slagging and corrosion problems are almost non-existent in the ash,and the reaction is more thorough.So the effect of coal ash additives is better.