NO(X) absorption in water is quite difficult by comparison with other exhausted gas, such as SO(2), CO(2), and NH(3) because of low solubility of NO(X) in water. We have been developed a NO(X) absorption equipment with a glass fiber filter having high porosity and surface area. When feed NO(X) gas concentration was high, high NO(X) 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 NO(X) 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 NO(X) removal efficiency, and HNO(3) 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 NO(X) in the gas (up to 120 ppm). This result indicated the importance of aqueous phase oxidation of HNO(2), which produces NO in the gas phase.
A model for a dehumidifying device using a solid polymer electrolyte membrane (Nafion 117, Dupont) is proposed. The dehumidifier in the model is represented by a physical model composed of a two-layer membrane and electrodes on the membrane surfaces. Measurement of the membrane weight shows that the ratio of the water content of the membrane to humidity in the surrounding air is a function of temperature under equilibrium conditions. The results for the water ratio are used for determining the parameters required for the modeling. The electrical resistance of the dehumidifier was measured and is given as a function of temperature and the membrane water content. Simulation of the characteristics of the dehumidifying device is presented and the results are found to agree with the measured characteristics of the device. We also report an attempt to determine the parameters describing the dehumidifying processes.Keywords Dehumidifier Á Physical model Á Solid polymer electrolytic membrane Á Water transfer List of symbols Variables D Diffusion coefficient of water in the dehumidifying element e Electron charge = 1.602 9 10 -19 (C) I Current of the dehumidifying element (A) I st Current at steady state condition (A) J Current density of the dehumidifying element k g Coefficients relevant to the diffusion velocity of water from the air to the membrane k s Coefficient relevant to the diffusion velocity of water from the membrane to the air. This is defined by k s = k so exp(-W s /RT) L Thickness of the dehumidifying element (= 0.017 cm) M o Molecular weight of water m g,pWater mass in the space facing the anode (g) N A Avogadro number = 6.02 9 10 23 (mol -1 ) R Gas constant = 8.31 (Pa m 3 k -1 mol -1 ) RH t x Relative humidity at time t x R m Electrical resistance of the membrane of the device (X) p g,p , p g,n Water vapor pressure in the air facing the anode and the cathode, respectively R s Electrical resistance of the dehumidifying element (X) S Area of the dehumidifying element of the device t Time (s) T g Temperature of the gas space surrounding the dehumidifying element (K) U s Applied voltage to the dehumidifying element (V) V g,p , V g,n Volumes of the spaces facing the anode and the cathode, respectively
A two-layer model for a solid polymer electrolytic (SPE) dehumidifier is applied to a system in which the chamber to be dehumidified has some leakage area. By introducing this area, the attainable humidity in the chamber, which is the steady-state humidity to be attained after a long-time dehumidification, can be defined. Experimental results of dehumidification by an SPE dehumidifier are compared to the calculations based on the two-layer model for the SPE dehumidifier, which was presented in our previous paper. Equations for the two-layer model are simplified by making use of assumptions for the current characteristics and a constant environmental condition, and it is reduced to equations including a differential equation on the time variation of the humidity in the chamber. The differential equation to describe the attainable humidity in the chamber and time constant for the dehumidification is obtained. The current flowing in the dehumidifier under steady state conditions is also given as a function of the humidities in the spaces facing the anode and the cathode. A diagram to estimate the attainable humidity and the time required for dehumidification from the dehumidifying area and leakage area is also given.Keywords Dehumidifier Á Physical model Á Steady-state current characteristics Á Solid polymer electrolytic membrane List of symbols DDiffusion coefficient of water in the dehumidifying element (cm 2 s -1 ) eElectron charge = 1.602 9 10 -19 (C) I Current of the dehumidifying element (A) j g Coefficient relevant to the diffusion velocity of water from the air to the SPE membrane (cm s -1 ) j s Coefficient relevant to the diffusion velocity of water from the membrane to the air (cm s -1 ) L Thickness of the dehumidifying element (= 0.017 cm) N A Avogadro's number = 6.02 9 10 23 (mol -1 ) RHRelative humidity (%) R s Electrical resistance of the dehumidifying element (X) S Area of the dehumidifying element (cm 2 ) S' Equivalent leakage area with the rate constant kg of water transfer (cm 2 ) t time (s) T g Temperature of the gas space surrounding the dehumidifying element (K) U s Voltage applied to the dehumidifying element (=3 V) V g,p , V g,n Volumes of the spaces facing the anode and the cathode (cm 3 ), respectively aThe average number of water molecules carried by a proton moving to the cathode q g , q sWater density in the air surrounding the dehumidifying element and water content of the element (g cm -3 ), respectively
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