Studies On Simultaneous Desulfurization And Denitrification In A Flue Gas CFB Based On The Multi-composite Active Absorbent

The current status of the researches about flue gas simultanteous desulfurization and denitrification and the absorbents were reviewed by consulting a large number of literatures in this dissertation. Two multicomposite active absorbents, named SHC and SHF respectively, were prepared from sodium hypochlorite and different additives. Meanwhile, a new semi-dry process of simultaneous desulfurization and denitrification were proposed by spraying the multicomposite acitive absorbents into a flue gas circulating fluidized bed (CFB) using the humidifying activation, and a series of experimental studies of semi-dry flue gas desulfurization and denitrification simultaneously were carried out in a fixed bed, fluidized bed, CFB, and in the industrial pilot plant respectively, by amplifing the condition step by step. Through the analysis of removal products and the investigations of thermodynamic processes, the mechanism of simultaneous desulfurization and denitrification in a CFB by the multicomposite active absorbents were disclosured.By screening of additives on activity, NaCIO and additives A and A'were determined as the basic raw materials for prepared the two multicomposite active absorbents SHC and SHF. Scanning electron microscopy (SEM), X-ray spectroscopy (EDS), ion chromatography (IC) and X-ray diffraction (XRD) characterization results indicate that multicomposite active absorbents have large surface areas and high activities. The removal experiments show that SHC and SHF can rapidly oxidize NO, which is difficult to dissolve in the water, and then achieve high simultaneous removal efficiencies of SO2and NOx.Through the orthogonal experiment in fixed bed, the main impact factors of multicomposite active absorbents on simultaneous desulfurization and denitrification were determined.Then, the dynamic experiments of simultaneous desulfurization and denitrification by the multicomposite active absorbents were performed in a small-scale fluidized bed, and various effect of absorbent concentration, pH, Ca/(S+N), inlet temperature and et al. on the removal efficiencies were also studied.According to the experimental results of small-scale fluidized bed, and further amplification of experimental conditions, the experiments of simultaneous desulfurization and denitrification in the flue gas circulating fluidized bed were carried out, and various factors such as the absorbent concentration, molar ratio, pH of humidified water, Ca/(S+N), reaction temperature, gas humidity, oxygen content of flue gas and so on the efficiencies of simultaneous desulfurization and denitrification were investigated, therefore, the optimum conditions were confirmed. At the optimum condition, the efficiencies of desulfurization and denitrification by SFIC can achieve96.5%and73.5%, respecitively; meanwhile, the efficiencies of desulfurization and denitrification by SHF can reach96.1%and67.2%, respecitively. In addition, the high precise data of removal efficienies showed that the proposed semidry flue gas simultaneous desulfurization and denitrificaiton process runs stable, and has broad application prospects.The reaction products were analyzed by using a variety of modern testing techniques and chemical analysis. The results showed that, the removal products of SO2and NO by SHC are mainly calcium sulfate and calcium nitrate, respecitively, followed by calcium sulfate and calcium nitrite; while for SHF, its desulfurization and denitrification products are calcium sulfate and calcium nitrate, respecitively, which means the oxidizability of SHF is higher than that of SHC. Though the above results of products, it can be inferred that NO can be rapidly oxidized to NO2by multicomposite active absorbents, and then absorbed by Ca(OH)2with SO2, thus the simultaneous removal were achieved. These conclusions can also be confirmed by the thermodynamic analysis.A pilot-scale test were implemented in a flue gas circulating fluidized bed combined with200MW boiler unit of a power plant in Hebei by the multicomposite active absorbent. By examining various effect of the absorbent concentration, pH of humidified water, molar ratios of absorbent, Ca/(S+N), near-adiabatic saturation temperature, circulation rate and et al. on the removal efficiencies, the optimal operating conditions were determined, on which a higher removal efficiencies of SO2and NO were reached. The results of the pilot-scale tests showed that the new flue gas treatment technology with independent intellectual property rights developed in the dissertation has the merits of simple operation, low cost, low energy dissipation and simultaneous removal of multi-pollutants from flue gas, which can generate significant economic, environmental and social benefits and has a broad application.Based on FLUENT computing platforms, the flue gas flow field and temperature field in the CFB were simulatied under a variety of operating conditions on both SO2and NO removal process, which can provide a basis for the industrial application.