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A New Gas Chromatographic Method for Continuous Monitoring of Non-methane Hydrocarbons as an Analogy of Volatile Organic Compounds in Flue Gas

Category: Air Pollution and Health Effects

Article In Press
DOI: 10.4209/aaqr.2018.05.0193
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Chieh-Heng Wang1, Hsi-Che Hua2, Wei-Chuan Lin2, Hsin-Cheng Hsieh2, Jia-Lin Wang 2

  • 1 Center for Environmental Studies, National Central University, Taoyuan 32001, Taiwan
  • 2 Department of Chemistry, National Central University, Taoyuan 32001, Taiwan

Highlights

On-line monitoring of total non-methane hydrocarbons in flue gas is proposed.
Back-flush allows self-cleaning of the separation column to avoid saturation.
Saturation is unavoidable with the old filtration method.
Methane can be fully separated from ethane and non-methane hydrocarbons.


Abstract

A new on-line method of monitoring the total non-hydrocarbons (TNMHC) from the flue or waste gas of stationary sources, which significantly improves upon the current method commonly used in both Taiwan and China, is described. The major problem with the current method is that higher-boiling-point compounds in the waste gas saturate porous materials within the molecular-sieve column used to immobilize TNMHC and elute methane, which sabotages the fixability of TNMHC and leads to false methane and TNMHC readings during continuous monitoring. Our new method effectively circumvents this issue by incorporating a dual-column and back-flush design, rendering it a true gas chromatography (GC) method. Applying this GC method, light hydrocarbons, such as methane, ethane, and propane, can be fully separated by the dual column set. After methane enters the analytical column, a reverse carrier flow immediately back-flushes the pre-column while keeping the analytical column flowing forward by a second flow of the carrier gas for eluting methane. The field application, particularly upon repeated analyses of flue gas laden with complex and elevated levels of volatile organic compounds (VOCs), has shown that self-cleaning by back-flush is necessary when operating at a constant oven temperature.

Keywords

Volatile organic compounds (VOCs) Flue gas Continuous emission monitoring system (CEMS)


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