Formaldehyde removal from air during membrane air humidification evaporative cooling: Effects of contactor design and operating conditions

Date
2009
Authors
Rangappa, Ajay Simha
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Abstract

Formaldehyde is a colorless gas at room temperature and pungent in nature. Over 2 million workers in US and many more people are exposed to this pollutant environmentally daily that causes burning sensations in the eyes and throat, it causes difficult breathing and is a suspected human carcinogen. Sources of formaldehyde in buildings include pressed wood products, urea-formaldehyde foam insulation and combustion sources. Average formaldehyde concentrations in buildings are typically below 0.1 parts per million (ppm) although it is not uncommon for levels to exceed 0.3 ppm if substantial quantities of new pressed wood products are present. The world health organization recommends exposure should not exceed 0.05 ppm. The generally recommended procedure to reduce concentrations is to increase fresh air ventilation rates, which increases operating costs due to the necessity of conditioning the fresh air for human comfort.

Formaldehyde is highly soluble in water and can be removed from air by contacting the air with an aqueous phase; allowing the formaldehyde to partition into the water. Hollow fiber membranes are ideal candidates for use in air treatment applications because of their large surface areas for contaminant transfer. In the past, gas permeable membranes have been used as gas/liquid contactors for a variety of mass transfer applications including evaporative cooling of air. This research explores the use of hollow fiber gas permeable membranes with water on the lumen side to strip formaldehyde from air.

Counter current parallel flow membrane contactors were studied to estimate likely formaldehyde removal rates from air occurring during membrane air humidification evaporative cooling applications. Numerical modeling and experimental measurements of formaldehyde removal were made to assess the impact of operating conditions and contactor configurations on expected formaldehyde removal rates. Removal efficiencies were predominately controlled by shell side mass transfer coefficients. However, removals decrease when water velocity within the fiber lumens is low and water supplied to the modules approach module evaporative losses. While removal rates were found to be adequate to control formaldehyde emissions in residential housing, large volumes of water usage would be necessary.

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Keywords
Air, Formaldehyde, Removal
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Department
Civil and Environmental Engineering