Study On Corrosion Regularity During CO-Combustion Of Straw And Coal

As a kind of clean and renewable energy, more and more attention has been paid to biomass. At present, a feasible way in bioenergy utilization is to co-fire biomass and coal in large power plants directly. Co-combustion can take advantage of the present infrastructure and huge investments in coal-fired power plants with low initial investment and low risk. However, because the high levels of alkali metal and chloride in biomass, Co-combustion of biomass and coal can lead to serious fouling, slagging and corrosion on boiler heating surface. Therefore, study on the release characteristics of alkali and chlorine and mechanism of chlorine corrosion in co-combustion is significant to prevent the corrosion of heating surface and promote efficient use of biomass. In this paper, release characteristics of K and Cl and corrosion characteristics of chlorine during the co-combustion of biomass (wheat-straw, cornstalk) and coal (lean coal) were investigated.First of all, common methods of detecting chloride were studied by experiment in order to determine the best method. Silver nitrate titration, Volhard method and Mercuric thiocyanate spectrophotometric method are widely used to detect the released chlorine. It is found that Mercuric thiocyanate spectrophotometric method is better becouse its high-precision and low minimum detectable limit, c ompared to Silver nitrate titration and Volhard method. Experiment showed that the maximum error by Mercuric thiocyanate spectrophotometric method was less than 3.5%.Secondly, a study on static chlorine corrosion of T91 was carried out in tube-type furnace. The result shows that corrosion dynamic curves accord with parabola rule: y=kpt1/2+c The rate of chlorine corrosion at the initial stage is high but decreases with the reaction progressing. The influence of ash, temperature and HC1 on corrosion was studied by experiment. The ash inhibits the corrosion rate at the initial stage, but increases the sustainability of corrosion which ultimately aggravate corrosion. The corrosion rate increases exponentially with the increase of temperature, which complies with Arrhenius Law. The corrosion reaction is first-order reaction and its rate increases linearly with the increase of HCl concentration in gas phase. After microscopic analysis to the corrosion product, it shows that the metal T91 presents good corrosion resistance at 500℃. The corrosion belongs point corrosion, while the corrosion is relatively serious at 600℃, which presents as uniform attack with a obvious corrosion oxide film. EDS analysis to the oxide film shows that, the chlorine is gathered in the oxide film, resulting in active oxidation corrosion. Furthermore with the temperature and the HCl concentration increase, the content of Cl in oxide film increases, and the corrosion becomes more serious.Finally, the thermal analysis kinetics of chlorine corrosion reaction was studied at constant temperature. Draw the conclusion that the corrosion reaction accords with one-dimensional pervasion mode, and corrosion rate obeys the calculating formulas: which represents the process of Cl corrosion reaction quantitatively.