Experimental Study On High Temperature Corrosion Of Heat Exchangers In Waste To Energy Plant

With the rapid development of economy,people's living standards and the level of urbanization,China's municipal solid waste(MSW)output is steadily on the increase.Waste to Energy technology,as a green new method,is gradually replacing the traditional landfill technology due to its rapid reduction capacity,short storage period and energy conversion system.However,MSW's component is totally complexand large amounts of corrosive particles carried in the flue gas will condense on the superheaters resulting in the problems of slagging and corrosion and further inhibiting the improvement of power efficiency in Waste to Energy plants.Based on the high chlorine content in MSW and the high alkali metal content in the ash deposit,this paper focuses on the deposition and corrosion on heat exchangers induced by chlorine and alkali metals.A small waste incineration corrosion device is designed for this paper.With the help of this device,three experimental studies were conducted.Firstly,in order to explore whether the oxide layer will accelerate the process of corrosion,this paper compares the corrosion degree of stainless steel under two conditions.One is oxidize the stainless steel in advance and then spread the NaCl on the them.The other is only let the stainless steel be covered with NaCl.At the same time,the corrosion performance of Fe-Cr-Ni alloy in different corrosive situations were studied,including SO2 containing atmosphere,different alkali metal chlorides medias and different Fe-Cr-Ni alloys.Besides,with the purpose of exploring the the fouling and corrosion degree of actual MSW incineration power plant in Chengdu Xiangfu WTE plant,ash deposits and corrosive tubes of pre-protector and 3rd superheater were analyzed in morphology and mineralogy,by means of scanning electron microscope equipped with energy dispersive spectrometer(SEM/EDS),X-ray diffraction analysis instrument and X-ray fluorescence spectrometer.The results of experiments in laboratory and WtE plant showed that:(1)the oxide layer can accelerate the corrosion induced by alkali metal chlorides due to the reaction the generation of Na2Fe2O4,which destroyed the the protective role of oxide layer.(2)the addition of SO2 can effectively inhibit the corrosion of alkali metal chloride on the stainless steel 304.(3)the corrosion resistance of KCl is slightly higher than that of NaCl,and the CaCl2 does not have the corrosive capability.(4)the corrosion resistance of Inconel 625 alloy was the strongest,followed by the stainless steel 304,and the last was 12 CrMoV.Moreover,the results in actual WtE plant showed that:(1)the ash deposit in pre-protector was more KCl with less CaSO4,and the ash deposit in 3rd superheater was more CaSO4 with less KCl.(2)the chlorine of ash deposit in 3rd superheater distributed in the outer layer while the alkali metals in the interface,which confirmed the corrosion mechanism induced by alkali metal chlorides well.(3)3rd superheater suffered severer corrosion than pre-protector.Therefore,the primary anti-corrosive methods were put up with,including adding sulfur rich agent in furnace,co-combustion with rich silicate materials and using Ni-Cr composite coatings or anticorrosive board equipped with ventilating brick and so on.