Operations Of On-line Chromatographs

Author: Paul E. KizerDownload File

On-line Chromatography has at least two definitions today. The most common is that the Chromatograph, commonly known as a “GC,” is “on-line” when it extracts a sample from a continuously flowing line, injects this sample and analyzes it for composition, and then perhaps calculates BTU, SG, Relative Density, and/or Wobbe index or other parameters. This data is used on site or at a remote location to calculate volumes for custody transfer of the natural gas. This is the definition that will be used in this paper. The other definition of “on-line” is that the Chromatograph data is fed or downloaded to a flow computer(s) or RTU(s) on the flowing stream that was analyzed at the measurement site. This definition is illustrated in picture, Fig. 1 and the diagram in Fig. 2, seen below. Most gas composition analysis data, however, can be applied to more flow measurement sites than just the one where the gas is extracted from the flowing stream. This is because the gas stream will not change in composition unless there is another source of gas or there is drastic change in temperature or pressure. Some companies use what they call “Zoning” to assign a particular composition or BTU to a set of flow computers. With either definition, the gas analysis information must be applied to the gas volume somewhere to produce the energy amount that the meter station is flowing