Study On The Regularity Of Composite Additive To Inhibit Corrosion On Metal Heating Surface In Biomass-fired Boiler

Environmental pollution and shortage of fossil energy are the two problems facing the countries in the world.In the current situation,the development of renewable energy is not only an international trend,but also the direction of China's energy structure reform.As a renewable energy source,biomass energy has become a hot spot.However,corrosion on metal heating surface in biomass-fired boiler has seriously restricted the promotion of biomass power generation.Adding additives to biomass fuel can effectively alleviate this problem.The pulverized coal ash containing Al2O3?SiO2?CaO?Fe2O3 can inhibit the corrosion.The compound additive made of CaO based on pulverized coal ash can effectively inhibit corrosion.In this paper,the law of corrosion inhibition of composite additives was studied by combining experimental research and simulation analysis,and the influence of the proportion of elements in the additives and the proportion of additives on the corrosion was explored,so as to provide a basis for the selection of appropriate additives for biomass-fired boiler.The horizontal tube furnace was used to study the influence of the proportion of CaO in compound additives,the proportion of compound additives,the type of biomass and the type of heating surface pipe on the corrosion inhibition of additives.The results show that when the proportion of CaO in the compound additive is 3%-6%,the additive has a better corrosion inhibition effect,and the optimal proportion of CaO is 4%.For wheat straw,when the proportion of compound additives is between 4%and 7%,the additive has a significant effect on corrosion inhibition,and the optimal proportion is 6%.For corn straw,when the proportion of compound additives is between 5%and 9%,the additive has a significant effect on corrosion inhibition,and the optimal proportion is 8%.The corrosion performance of corn straw was higher than that of wheat straw because the alkali metal content of corn straw was higher than that of wheat straw.The corrosion resistance of several metal pipes is ranked as TP347H>T91>15CrMoG>20G,which is related to the content of elements Mo,Cr and Ni in the metal pipes.The higher the content of elements Mo,Cr and Ni,the better the corrosion resistance of the metal pipes is.A1 reacts with KCl and K2SO4 to produce aluminosilicate with high melting point and improve the melting characteristics of ash,thereby inhibiting corrosion.Si can reduce the content of KCl in ash by reacting with alkali chloride and alkali sulfate,thereby inhibiting corrosion.Ca reacts with S and Si to form complex compounds,resulting in a reduction of the Si element content in the additive that cooperates with Al,which intensifies the corrosion.When the ratio of the three elements changes,the additive's ability to inhibit corrosion also changes.For wheat straw,when the ratio of the three elements in the fuel after adding composite additives is Si/Al/Ca=4.37:1:1.50,the composite additive had the best effect.For corn stalks,the optimal ratio is Si/Al/Ca=2.61:1:1:1.4Use the thermodynamic software FactSage to simulate the combustion process of biomass fuel under different conditions,analyze the distribution patterns and conversion rules of K and Cl components in the ash under different elements when the temperature changes,and explore the role of Al,Si,Ca.The results showed that during the combustion of wheat straw,the products in the gas phase were mainly KCl(g),and KCl(g)would form accumulation on the heating surface,which would cause corrosion.After the addition of Al,the amount of KCl(g)in the gas phase decreases,the potassium silicate compound in the solid phase disappears and the amount of potassium aluminosilicate increases,which is beneficial to increase the melting point of ash and reduce corrosion.After the addition of Si,the amount of KCl(g)in the gas phase decreases a little,and the amount of K2Si4O9(l)in the liquid phase increases,which aggravated the corrosion.After the addition of Ca,the amount of HCl(g)in the gas phase decreases,the amount of high-melting point compounds in the solid phase increases,and the amount of KCl(g)in the gas phase also increases,which is not conducive to the improvement of corrosion.When Si and Al are added at the same time,the corrosion inhibition effect is more significant when the content of Al is not lower than Si,and the optimal ratio of Si and Al is 11:1.When Si,A1 and Ca were added at the same time and the content of Ca was controlled within a certain range,the additive could effectively transform KCl.When Si:Al:Ca=1:1:1,the composite additive had the best corrosion inhibition effect.