ARTICLE pubs.acs.org/est
High-Efficiency NOX Absorption in Water Using Equipment Packed with a Glass Fiber Filter Masahiro Yasuda,*,† Nobuhiro Tsugita,† Katsuaki Ito,‡ Shiro Yamauchi,‡ Wilhelm R. Glomm,§ Izumi Tsuji,|| and Hideaki Asano|| †
Department of Chemical Engineering, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka 5998531, Japan Tada Electric Co. Ltd., 488 Shimokasaka, Oku-cho, Setouchi, Okayama 7014247, Japan § Department of Chemical Engineering, Norwegian University of Science and Technology, Sem Sælands vei 4, Trondheim N-7491, Norway Pollution Prevention Apparatus Laboratory Co., Ltd., Reosu otoshi, 12-13, Otoshi-cho, Neyagawa, Osaka 5720048, Japan
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ABSTRACT: NOX absorption in water is quite difficult by comparison with other exhausted gas, such as SO2, CO2, and NH3 because of low solubility of NOX in water. We have been developed a NOX absorption equipment with a glass fiber filter having high porosity and surface area. When feed NOX gas concentration was high, high NOX removal efficiency was obtained. This was because the surface area per glass fiber filter volume was about 40 to 600 times higher than for common packing materials. For verification test and industrial application, a high concentration of NOX gas (206 000 ppm) produced by a metal dissolution process was treated with a series of two absorption experiments. We can attain 97.6% of NOX removal efficiency, and HNO3 concentration in water was concentrated up to 56.3 wt %. Furthermore, ozone addition to gas and usage of ozone saturated water as an absorbent resulted in complete removal of NOX in the gas (up to 120 ppm). This result indicated the importance of aqueous phase oxidation of HNO2, which produces NO in the gas phase.
’ INTRODUCTION Exhaust gases derived from automobiles and boilers contain low concentrations of nitrogen oxide (NOX). Especially, automobile exhaust gases comprise 50% of the total emissions of NOX.1 In the manufacture of nitric acid and metal finishing and dissolution processes, the wasted gases contain large amounts and high concentrations of NOX.2 Since NOX gas is toxic for human beings and may cause acid rain, both the amount and concentration of NOX in waste gas are restricted to low levels.3 The major components of NOX generated by fuel combustion are NO and NO2, and equilibrium small amounts of N2O4 and N2O3 exist.4,5 The low solubility of NO and NO2 in water compared to other waste gases, such as CO2, SO2, and NH3, is a problem,6-8 and the low solubility results in high mass transfer resistance of water. Therefore, to decrease the concentration of NOX in waste gases, a catalytic reduction 9,10 or gas absorption system using alkaline solution or oxidants 6-8 is usually adopted. Gas absorption systems have been studied thoroughly, and there exists an abundance of reports on NOX absorption equilibria (see, e.g., ref 7 and references therein) and the effect of oxidant on the enhancement of NOX absorption.2,11-13 We have studied NOX absorption in water, and a new glass fiber unit whose porosity is high while its pressure drop is low has been developed.14 High absorption efficiencies of NOX with r 2011 American Chemical Society
water can be attained at a high inlet NOX concentration (>10 000 ppm). This may be because the glass fiber unit has a large area of gas-liquid interface. However, absorption efficiency with water at a low NOX concentration (
