Research On High Temperature Corrosion Behavior Of Biomass Boiler Super-heater Tubes SUS316

With the depletion of fossil energy, the pollution and destruction of environmental, the energy structure will be intensified efforts to optimize and adjust globally. The biomass energy is very rich in our country and become one of the best energy which can balance the energy and environmental problems. It owes to less wastage produced in process of exploiting,low carbon and sulphur implemented, production of gas, liquid, solid renewable energy products transformed directly, fossil energy replaced on a large scale. Recently, a series of laws have been enacted to promote the rapid development of biomass power generation industry directly in China. Unlike general thermal power generating units, because of the own spontaneous combustion of biomass, especially the existence of alkali metal and cholrine, will accelerate the fouling, slagging and corrosion of boiler tubes, even lead to burst. As a result to study alkali corroding biomass boiler tubes has a great significance to ensure units safe and economical operation.In this paper, SUS316 material was studied. And the material was taken from biomass power station boiler in Zhanjiang city, Guangdong province. The corrosion test system of high chlorine was designed to simulate the high temperature corrosion of the biomass boiler superheater area. The high temperature corrosion behavior of the SUS316 material in saturated KCl steam atmosphere was investigated. Seven time gradients, including 1 h, 4 h, 7h, 10 h, 15 h, 20 h and 30 h, were set up. And the material was treated in saturated KCl steam and air under the temperature of 600 o C, 700 o C and 800 o C, respectively. The surrosion was analyzed and calculated. Then the corrosion dynamics fitting curves were got. The high temperature electrochemical test bench was also designed to simulate the hot corrosion process of the biomass alkali metal molten salt. The SUS316 material molten salt medium hot corrosion was studied. The corrosion potential, polarization resistance and electrochemical impedance of metal materials are test under different temperature. And the scanning electron microscope?SEM? and X-ray diffraction?XRD? are used to investigate the surface morphology and crystal structure of the corrosion products. The effect and corrosion mechanism of metal material treated by alkaline material were investigated. The main experimental results summarized as follows:1. The high temperature corrosion of SUS316 material can be obviously promoted by KCl steam with trace amounts. The reaction with the oxide film on the surface of the specimen can generate Cl₂. And Cl₂ can penetrate to the substrate interface generated volatile Fe of chloride.The corrosion behavior was accelerated, which can be explained by the theory of “activated oxidation”.2. In the initial stage of the molten salt corrosion, it takes place oxidization and generates a layer of oxide film under high temperature condition, then equivalent to ordinary electrode reaction, taking place galvanic cell reaction on both sides of the oxide film, and the reaction rate is controlled by diffusion. Late period electrochemical reaction speed is mainly controlled by the migration rate of charged particles metal corrosion in the oxide film.