Research On Alkali Reaction With Refractories

In face of increasingly severe environmental problems, as a kind of environmental friendly renewable energy, production of biomass increase year by year. Alkali metal problems of Biomass burning easily cause combustion furnace slagging, deposition, reunion, and high temperature corrosion problems.Basing on thermodynamics, according to Gibbs’s principle of free energy and the theory of multiple phase equilibrium, combining thermodynamic database FactSage7.0.With the increase of temperature, this paper studied on the influence factors of excessive air coefficient, Cl content and S content on the migration of alkali elements. During the combustion process, alkali metals are mainly existed in the form of NaCl and NaOH, KC1 and KOH, Na2SO4 and K2SO4, etc. The increase of temperature can promote the precipitation of alkali metal chloride, which is more obvious at 700 ℃; promoting the precipitation of alkali metal hydroxide, more than 800℃; the effect of the alkali metal sulfate was first promoted and then inhibited, which was more obvious at 800℃. The increase of excess air coefficient can inhibit the generation of gaseous alkali metal chloride, the equilibrium moves to generate alkali metal sulfate direction. Increasing the Cl of the raw material can make the reaction to the promotion of alkali metal chloride and inhibition of the direction of alkali metal hydroxide. The increase of S in raw materials can promote the formation of alkali metal sulfate, and the generation of alkali metal chloride is inhibited in a certain temperature range, but it has little effect on the hydroxide.Crcombining ability with alkali metal is larger than S. Much Na than K stay in silicate, adding Si of showed inhibitory effect on alkali vapors, but limited.Because of the corrosion of Alkali metal chloride, this paper also simulated the corrosion effect of NaCl on 5 oxides of the common refractory material. The results by thermodynamic calculation and XRD shows:(1) NaCl Does not react with MgO obviously; (2) When contained CaO, no material generated obviously; (3) Plus SiO2, within the scope of the test temperature, there is always Mg2SiO4 generated; (4) With the addition of Al2O3, above 1000℃ MgAl2O4 can be detected obviously;(5)With Cr2O3,at 800-1000℃ generated Na2CrC>4 significantly; (6) Samples containing Fe2O3 also detected the existence of magnesia spinel; (7) NaCl almost do not participate in the reaction, the phase transition occurs only. By changing the content of H2O and oxidizing or reducing atmosphere, no obvious effect on the result of the reaction.