Comparison of Thermoelectric and Permeation Dryers for Sulfur Dioxide Removal During Sample Conditioning of Wet Gas Streams

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Presented at the Air & Waste Management Association's 90th Annual Meeting & Exhibition
June 8-13, 1997, Toronto, Ontario, Canada

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Thomas A. Dunder

Entropy, Inc., Research Division, P.O. Box 12291, Research Triangle Park, NC 27709-2291

David A. Leighty

Perma Pure, Inc., 8 Executive Drive, Toms River, NJ 08754

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Abstract

Flue gas conditioning for moisture removal is commonly performed for criteria pollutant measurements, in particular for extractive CEM systems at combustion sources. An implicit assumption is that conditioning systems specifically remove moisture without affecting pollutant and diluent concentrations. Gas conditioning is usually performed by passing the flue gas through a cold trap (Peltier or thermoelectric dryer) to remove moisture by condensation, which is subsequently extracted by a peristaltic pump. Many air pollutants are water-soluble and potentially susceptible to removal in a condensation dryer from gas interaction with liquid water. An alternative technology for gas conditioning is the permeation dryer, where the flue gas passes through a selectively permeable membrane for moisture removal. In this case water is transferred through the membrane while other pollutants are excluded, and the gas does not contact condensed liquid. Laboratory experiments were performed to measure the relative removal of a water-soluble pollutant (sulfur dioxide, SO2) by the two conditioning techniques. A wet gas generating system was used to create hot, wet gas streams of known composition (15% and 30% moisture, balance nitrogen) and flow rate. Pre-heated SO2 was dynamically spiked into the wet stream using mass flow meters to achieve concentrations of 20, 50, and 100 ppm. The spiked gas was directed through a heated sample line to either a thermoelectric or a permeation conditioning system. Two gas analyzers (Western Research UV gas monitor, KVB/Analect FTIR spectrometer) were used to measure the SO2 concentration after conditioning. Both analytic methods demonstrated that SO2 is removed to a significantly greater extent by the thermoelectric dryer. These results have important implications for SO2 monitoring and emissions trading.

Figures 3 and 4 exerpted from the paper and shown below, demonsrate the superior performance of the permeation drier for SO2 measurements