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1、High Efficiency Absorption of High NOx Concentration in Water orPEG Using Capillary Pneumatic Nebulizer Packed with an ExpandedGraphite FilterDengxin LiCorresponding author: Tel: +86 21 67792541, Fax: +86 21 67792522E-mail address: (Dengxin Li), Penghui Shi, Jianbo Wang, Jiebing Li, Ruijing SuColle
2、ge of Environment Science and Engineering, Donghua University, Shanghai 201620, PR ChinaABSTRACT: Nitrogen oxide (NOx) absorption in water is more difficult compared with other exhausted gases such as SO 2, CO2, and NH3 because NOx has low water solubility and nitrous acid is easily decomposed. We d
3、eveloped a NOx absorption equipment with a capillary pneumatic nebulizer equipped with an expanded graphite demister. The key parameters of the pneumatic atomizing absorption system were optimized. The selected parameters related to the high absorbent amount of NOx are as follows: diameter of the sp
4、ray liquid pipe of 0.5 mm to 1.1 mm, inlet gas pipe of 0.5 mm to 1.1 mm diameter ratio of the gas-liquid pipe of 0.8 to 1.3, 0.740 m of the spray height, MSP (minimum spray pressure) of 3 to 4, and R (gas -liquid mass flow ratio) of 300. With the optimal parameters, NOx removal efficiency and absorb
5、ent amount are highly relative to the absorbent, absorbent temperature, and absorbent time. A high feed NOx gas concentration results in high NOx removal efficiency because the surface area per water, nitric acid or polyethylene glycol (PEG) droplet volume was higher than that of the common gas -liq
6、uid surface. For the verification test, a high NOx gas concentration (200,000 ppm) was treated with a series of absorption experiments and a NOx removal efficiency of 99.1% was attained. Furthermore, using PEG instead of water as an absorbent resulted in a larger absorbent amount at the same absorbe
7、nt time and complete NOx removal in the gas.INTRODUCTIONExhaust gases from automobiles and boilers contain low nitrogen oxide (NOx) concentrations. In manufacturing nitric acid and metal finishing and in dissolution processes, the wasted gases contain large amounts and high concentrations of NOx. Bo
8、th the amount and concentration of NOx in waste gases must be restricted to low levels because NOx gas is toxic for human beings and can cause acid rain. 1-3 The major NOx components generated by fuel combustion are NO and NO2, although equilibrium small amounts of N2O4 and N2O3 exist. The low solub
9、ility of NO that accounts for more than 90% of all NOx and NO2 in water compared with other waste gases, such as CO2, SO2 and NH3 is a problem because low solubility results in the high mass transfer resistance of water. 4-6 Therefore, a gas absorption system using alkaline solution or oxidants6-8 i
10、s usually adopted to decrease NOx concentration in waste gases. These approaches are divided into absorption-oxidation process9-14 and oxidation-absorption process.15-20 In the absorption-oxidation process, liquid oxidants with strong oxidability are used as absorbents, such as HNO 3, sodium chlorit
11、e, 10-12 hydrogen peroxide,13 and potassium permanganate.14 Although strong oxidizing agents can improve NOx removal efficiency, certain drawbacks exist such as the expensive cost of oxidizing agents 14 and disposal problems of the absorption solution.21 In the oxidation-absorption process, gas phas
12、e oxidants, such as hydrogen peroxide14,15 and ozone8,17-21, are first injected into the flue gas to oxidize NO to NO 2, which is highly soluble in water. NO2 and SO2 can then be removed simultaneously via wet removal process. Ozone is an efficient gas phase oxidant with advantages of selectivity, h
13、igh oxidation efficiency, fast oxidation speed, and non-polluting decomposition products, among others.8,17-21 With respect to the liquid phase absorption of the oxidized flue gas, NOx removal efficiency can reach more than 80% regardless of the alkali liquor8,18,19 or reducing Na2S20,21 used.A new
14、absorption equipment combined with alkaline solutions or oxidants was developed to achieve a high NOx removal efficiency. Masahiro Yasuda2 studied NOx absorption in water, and a new glass fiber unit with high porosity and low-pressure drop was developed. High NOx absorption efficiencies with ozone-s
15、aturated water as absorbent water can be attained at a high inlet NOx concentration.The liquid atomizing method22-29 increases the contact area formed between the absorption solution droplet and the waste gas and enhances the absorption efficiency. Thus, the gas resistance and the absorbent equipmen
16、t volume are greatly lowered. An efficient defogger was set-up in the systems, which solves the problem of water removal from the absorbent solution by the gas. In addition, the liquid absorption solution can be recycled or reutilized. Therefore, this kind of absorbent device without wastewater absorption from basic production is widely used.30-36The major purpose of the present work is to investigate a pneumatic atomizing absorption device, which is a
