| The power generation technology by co-firing of biomass and coal is used more and more widely throughout the world.There is a great significance for the development and utilization of bimass energy to ease enegry shortage and reduce carbon emissions.Over the past few years,however,severe corrosion problems have been encountered by considerable KCI in the deposition when firing biomass in straw-fired boilers,which brings a great security risk,and restricted the development of biomass power generation technology.The additives can effectively reduce the corrosion on the boiler heating surface during biomass combustion.Therefore,it is significant for the safe and economic operation of the power plant to realize the efficient and clean utilization of biomass.In this paper,the effects of additives,including kaoline,fly ash,silica fume,dolomite,limestone and bauxite on the corrosion for pipes on the boliler heating surface was studied.Meanwhile,the Equilib module of Factsage software was used to simulate the thermodynamic equilibrium process for wheat straw combustion.The migiration and transformation of potassium and chlorine were studied.The effects of different additives to the corrosion on the heated surface of the biomass boiler were studied by using the horizontal tube funace.The results showed that the corrosion rate of metal samples was obviously reduced by adding kaoline,fly ash,silica fume,dolomite,limestone and bauxite as additives.When kaoline,fly ash,silica fume and bauxite were used as an additive,there was a significant inhibitory effect on the corrosion.When using dolomite and limestone as an additive,there was a poor inhibitory effect on the corrosion,but the corrosion rate was also reduced.Corrosion resistance of four kinds of tubing materials:T91>15CrMoG>12CrMoVG>20G.The corrosion resistance of T91 is much better than that of the other three kinds of tubing materials.15CrMoG is slightly better than 12CrMoVG.The corrosion resistance of 20G is the worst.The combustion process of wheat straw was simulated by using the Equilib module of Factsage software,and the main distribution forms of potassium and chlorine at different temperature range of 400～1600℃ were discussed.The results showed that the elements of potassium and chlorine are mainly precipitated in the form of KCl,HCl and KOH during combustion.In addition of kaoline,the content of potassium aluminosilicate increases about 20 times,and potassium aluminosilicate is present predominantly in the stable form of KAlSiO4.The contents of KCl and KOH in the gaseous product are reduced,and the alkali chloride in the flue gas is reduced correspondingly.The corrosive action on the heating surface has weakened.When the silica fume is used as the additive,the contents of potassium silicate and aluminosilicate in the solid product have been increased by about 12 times and is mainly in the form of K2Si4O9(s).The contents of KCl and KOH are reduced.But HCl has increased.There is a significant effect to reduce the alkali content in the flue gas with silica fume,but it can cause the increase of HCl in the flue gas.There is no obvious effect by adding dolomite and limestone alone to reduce the contents of potassium and chlorine in flue gas.After adding bauxite as an additive,the potassium is fixed in aluminosilicate.43.9%of the potassium is fixed at KAlSiO4 at 1200～1300℃.It makes the content of potassium in the gaseous state decreased obviously.When using fly ash as an additive,potassium can be fixed in the more stable silicate and aluminosilicate.KAlSiO4 and KAlSi2O6 are main forms above 1200℃.44.6%of the potassium element is fixed in the solid product.The content of potassium in the flue gas is obviously reduced,which has weakened the corrosion on heating surface. |
