Low Concentrations Of So <sub> 2 </ Sub> Flue Gas Treatment And No <sub> 2 </ Sub> And Co <sub> 2 </ Sub> Process

SO2 emission in China tops the forefront of the world. The resulting air pollution and acid rain problems are very serious and the economic loss is very huge, which has become one of the main factors to restrict the economic and social sustainable development. Therefore, it is imperative to control SO2 pollution.Wet FGD is of high desulphurization efficiency, adapts to wide range, and its technology is very mature. For these advantages, wet FGD is widely used. Among wet FGD, limestone-gypsum washing is the most widely used, but there are many disadvantages, such as easy rolling skin and blocking devices, serious corroding and abrading equipments, high cost of operation and maintenance, and less comprehensive utilization of by-products and so on. Sodium sulfide solution absorption-reduction of sulfur FGD, whose operation is simple, solid waste is less, waste water discharge is none, desulfurization efficiency is high and product is easy to store and transport, will be a promising desulfurization technology of SO2 gas in future.In order to apply sodium sulfide solution absorption-reduction of sulfur method to SO2 gas in low concentration, sodium sulfide solution absorbing SO2 gas and the impacts of NO2 and CO2 in flue gas on the absorption process were studied in this paper by thermodynamic analysis and conditional experiments, and draw the following conclusions:(1) The thermodynamic analysis of SO2-Na2S-H2O system shows that the liquid mainly includes S2O32-, HSO3-, H2SO3, and a small amount of HS-. When the absorption solution's pH value is from 3 to 8, the liquid is essentially only S2O32-; when the absorption solution's pH value is less than 3, the liquid phase includes only S2O32-and HSO3-.(2) Na2S solution is of a good absorption of SO2 gas in low concentration, and the total absorption rate reaches 100%.The liquid content is mainly affected by gaseous flow rate and final pH value. So changing gaseous flow rate and final pH of absorption solution may control suitable concentration ratio between HSO3-and S2O32-.(3) NO2 in the flue gas does not affect the absorption efficiency of SO2 gas,but it consumes absorbent(Na2S) and affects the type and concentration of ions in absorption solution. NO2 inhibites the generation of HSO3- during SO2 absorption process, while promoting the formation of S2O32-and SO42-, which decreases the concentration ratio between HSO3-and S2O32-.(4) CO2 in the flue gas does not affect the absorption efficiency of SO2 gas either.However,it will reduce the absorption solution's pH rapidly, and speed up the consumption of S2- in the solution. CO2 will reduce the formation of HSO3- during SO2 absorption process, and increase the generation of S2O32-.