Study On Corrosion Characteristics Of Sulfur-chlorine During Biomass And Coal Co-firing

In order to mitigate the energy crisis and environmental pollution, clean and renewable energy sources must be developed. Biomass energy has the advantages of renewable, low pollution and huge reserves, the techonology of biomass and coal co-firing is clean and also decreases the excessive use of fossil fuels. However co-firing will cause serious high temperature corrosion problems, which mainly related to alkali metal (K, Na), S, Cl and other elements in gase, liquid and solid phases. By the change of operating conditions, sulfur-chlorine corrosion was studied by the change of atmospheres, temperatures and metal pipes. Furthermore, corrosion mechanism was analyzed. By the change of fuel type and blending ratio, the deposition corrosion was studied, the interaction between deposition melting characteristics and corrosion were also explored. By thermodynamic equilibrium calculation the release and deposition characteristics of corrosion composition were investigated, and heating surface corrosion was simulation analyzed.Corrosion during co-firing of biomass and coal were studied in tube furnace through static corrosion weigh gain method, mechanism of corrosion was analyzed through XRD, EDS and other methods. The results showed that corrosion of metal samples were serious when HCl exists in flue gas, it was restrained significantly by SO2through forming protective film and prevent HCl from diffusing to metal base. Deposition can exacerbate HCl/SO2synergistic corrosion, corrosion increased along with the increase of SO2concentration, which mainly caused by sulfation reaction and active oxidation corrosion. Corrosion rate increased quickly above600℃. The corrosion of metal samples with deposition increased at different temperatures, but the effect of deposition on corrosion decreased with the increase of temperature, which due to the low stability of complex alkali metal sulphates. The corrosion resistances of metal pipes were:T91>12CrlMoVG>20G, due to the addition of Cr, Mo, Ni and other alloy elements, a compact protective film was found above T91sample through SEM, T91can be taken as the optimal heating surface material because of its excellent corrosion resistance property.Deposition corrosion was further investigated, corrosion increased with the increase of biomass blending ratio of to coal, and mainly due to the high content of Cl and alkali elements in biomass fuel. When coal was blended, deposition corrosion can be inhibited immediately by the generation of alkali sulfates, inert alkali aluminosilicate was also generated by the effect of Si and Al in coal. The degree of corrosion during biomass and coal co-firng was:straw>corn>cottin, corrosion of meagre coal was more serious than bituminous coal during co-firing of biomass and coal. The chemical form of sulfur and chlorine components has great effect on deposition corrosion:when chlorine content is high, deposition can significantly exacerbate corrosion through KCl regardless of the atmosphere, SO2can inhibit deposition corrosion when Cl content decreases, and in this case corrosion is mainly caused by low temperature eutectic such alkali sulfates.The corrosion of heating surface was simulation analyzed through thermodynamic equilibrium calculation. Temperature of heating surface had little effect on the deposition of KC1, NaCl, K2CO3, they were mainly affected by flue gas temperature. Alkali metal compounds especially KCl increased rapidly along with gas temperature and finally induced severe deposition corrosion. The increase of Cl content can aggravate HCl corrosion, while KCl, NaCl, K2SO4deposition amount increased rapidly and resulted in serious deposition corrosion. KCl can be completely converted to K2SO4when S content was high enough, and deposition corrosion decreased, however HCl/SO2corrosion began to appear and intensified. Amount of alkali metal compounds increased along with the increase of K and Na content, K2SO4and Na2SO4were gradually replaced by KCl and NaCl, and tended to cause serious corrosion problem, and K compounds were the main cause of corrosion. Ca can decrease K2SO4amount in deposition, HCl amount near heating surface can also be decreased with the increase of Ca content, but KCl deposition amount increased and could leading to serious corrosion.