Emissions of benzene, toluene, ethyl benzene, and the xylene isomers (BTEX) and volatile organic compounds (VOC) from the reboiler still vent of glycol dehydration units have become a major concern for the natural gas industry as a result of increasing regulatory pressure. The Clean Air Act Amendments (CAAA) of 1990 have provided an impetus for air toxics regulations, and several states are regulating or considering regulation of these units.
A key issue in developing approaches for handling these emissions has been accurate measurement of the emissions. The primary method used to date has been rich/lean glycol sampling at atmospheric pressure, which is favored for its simplicity. However, there are several potential errors associated with this approach, including the flashing and loss of BTEX and VOC during sampling. Direct (stack) measurement of these emissions has not been widely used because of the stream temperature and water content.
To address these difficulties, the Gas Research Institute (GRI) is sponsoring a program to develop and refine sampling and analytical methods. Input to the program is provided by an Industry Working Group that contains representatives from several industry organizations. After an initial field experiment was performed to screen potential methods, surviving methods were refined in the laboratory using a synthetic still vent overhead stream. The refined methods are being evaluated in two additional field experiments, and the final, recommended methods will be validated in a series of experiments in mid-1993.