| Fossil energy and environment are the two pressing issues all over world. People focus on renewable and environmentally friendly energy. Biomass energy, a kind of renewable clean energy, has the characteristics of widely distributed, enormous reserves, zero-carbon emission and low sulfur and nitrogen emission. At the present stage, biomass combustion for electricity generation is one of the ways in which biomass large-scale use and co-combustion of biomass and coal can even solve the problems of high initial investment of biomass power plant, unstable raw material supply, limited capacity scale and low economic efficiency. However because of the high content of alkali metal and chlorine element in biomass and sulfur element in coal, the alkali chloride, alkali metal sulfates and HC1 generated during co-combustion can cause serious problems such as slag, deposition and corrosion on metal of boilers heating-surface. This paper studied on corrosion characteristics of synthesis deposition to heating-surface metal under different condition, thermal analysis kinetics of corrosion reaction at constant temperature and the influence regular of additives caused to corrosion to heating-surface metal of boilers during co-combustion of biomass and coal.The experiment on characteristics of corrosion to heating-surface metal was carried out in tube furnace by simulating reaction condition and synthesis deposition on 20G. The method of corrosion mass gain also was taken. The results showed that all of characteristics curves of corrosion to heating-surface metal follow the parabola regularity and ash deposition on metal had great influence on corrosion rate which increased 40% than no deposition on metal. The content of Cl in corrosion products is higher after deposition corrosion. Different components of synthetic ash had different degree on corrosion to heating-surface metal. The corrosion resistance of deposition increased greatly after mixed with sodium chloride and potassium chloride, but had no relationship with the ratio of mixture. The mix of alkali metal sulfates decreased corrosion rate, far below the corrosion rate of sodium sulfate or potassium sulfate.The corrosion rate of synthesis deposition on metal reached the max because of the synergistic effect of sodium chloride and sodium sulfate. When the ratio of potassium chloride and potassium sulfate was one, the corrosion rate was lowest and the change of corrosion rate had no obvious regularity with the change of kali salt ratio. The corrosion rate had linear relationship with HC1 concentration. The corrosion rate had exponential relationship with temperature and had a rapid rise with temperature increasing from 550℃ to 600℃.The thermal analysis kinetics of corrosion to heating-surface metal coated with synthesis deposition was studied at constant temperature. Draw the conclusion that the corrosion reaction accorded with two-dimensional pervasion mode, and the kinetic equation was which represented the process of corrosion reaction quantitatively.The characteristics curves of synthesis deposition corrosion with additives to heating-surface metal follow the parabola regularity and the rank of corrosion resistance of synthesis deposition D17 with additives from strong to weak were: Al2O3>D17> SiO2> CaO> kaolin. The rank of corrosion resistance of synthesis deposition D6 with additives from strong to weak were:SiO2>D6>CaO> Al2O3> kaolin. The reaction of aluminium silicate and alkali metal formed aluminosilicate which slowed down the corrosion effectively because of high melting point. In conclusion, different additives had different influence on corrosion resistance of synthesis deposition and compared with other additives, Al2O3 and kaolin had better effect on reducing corrosion rate and slowing down corrosion resistance. Added kaolin to alkali chloride, corrosion rate had 16.1% reduction and added Al2O3 to alkali metal sulfate, sodium salt and kali salt, corrosion rate had 45.3%,13.1% and 34.3% reduction respectively. |
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