Simultaneous Desulfurization And Denitrification By Using Urea Solution

With the fast development of economy in China, the discharges of coal-fired flue gas have greatly increased. And the pollution of SO2 and NOx becomes increasingly serious, which causes lots of environmental problems such as acid rain etc. For a long time, flue gas cleaning technologies have been focused on the removal of dust and sulfur oxides. As hazard of NOx has been gradually realized, the reduction of NOx becomes an urgent task. The developments of the technologies for simultaneous desulfurization and denitrification, which have the advantages of being simple with less equipment, more convenient management and operation, smaller areas, lower capital and operating costs, etc, attract more interest in air pollution control field.Firstly, the dissertation introduced the current research status and trend of technologies for simultaneous desulfurization and denitrification in the world. And then different kinds of technologies had been compared and estimated. It has been found that urea technology has the following advantages: its final products are N2 and CO2 that can be let directly, and another product (NH4)2SO4 can be made into fertilizer, hence the nitrogen and sulfur resources can be recycled. Therefore, this method is worth of more research.Secondly, according to thermodynamic theory, the limitation of the absorption reaction was analyzed and calculated. The results showed that rising temperature went against the reaction. While according to chemical kinetics, the reaction rate constant increased with an increase in temperature. Therefore, the optimal absorption temperature could be determined by experimental investigation.Thirdly, the author paid more attention to the removal of NOx by using urea solution and the effects of operating parameters on NOx removal efficiency had been studied. Since the flue gas desulfurizarion technologies are well-developed and SO2 can be removed more easily compared to NOx. It was concluded that the optimal parameters were: 5% urea solution and basic condition. Moreover, the effects of different additives and concentrations on NOx removal had been also investigated. The results showed that potassium permanganate was the best one, then came sodiumchlorite and chloride of lime. Based on the above results, a pilot scale experiment was set up. The SO2 and NOx removal efficiencies could reach 98% and 30% respectively by using the blend slurry of urea and CaO. It was also found a higher NOx removal efficiency could be obtained by using chloride of lime. Furthermore, the economy analysis had been made for a boiler of 35t/h. And the cost of desulfurization and denitrification was 1240 RMB/t(SO2+NOx).The simultaneous desulfurization and denitrification process by using urea solution has a lot of advantages. If the reaction mechanism can be known clearly and appropriate additives and cheap urea source can be found, the urea technology will have a promising future.