You may recall Shane from earlier gas chromatograph-related posts. In this video he highlights how the Danalyzer 370XA Gas Chromatograph (GC) is designed to provide a simpler analysis of C6+ natural gas in Fiscal and Custody Transfer applications as well as improve the measurement performance of C6+ BTU/CV analysis. C6 refers:
…to hexanes. The addition of “+” is a term of art used in analytical chemistry that refers to a grouping of compounds (or fraction). For example, C6+ represents C6, as well as C7, C8 and higher molecular weight hydrocarbons. C9+ refers to C9 plus C10, C11 and so forth.
Shane describes how the use of expensive calibration gas is reduced by more than half over conventional GCs through the sequencing of purge and sample cycles. First, the sample loop is purged with the sample to ensure a representative analysis before it is injected. The sample loop is a short length of tubing inside the analytical oven that is filled with the sample to be analyzed.
He described the full sequence from equalizing the sample to atmospheric pressure to ensure that the same amount of sample is always injected to the injection into the chromatographic columns were the sample is separated into individual components. The individual components are measured across a detector to give the sample’s composition.While the analysis in occurring, the next sample stream comes in to purge the lines and prepare for being sampled. A C+ analysis typically takes 4 minutes. A typical calibration run for a C6+ custody transfer application consists of multiple runs of calibration gas to reduce the effective measurement uncertainty on the calculation of the component response factors.
During a purging cycle, the expensive calibration gas is being purged. The Cal-Gas Saver works by not purging during the entire analysis, but only for the last 30 seconds to save a considerable amount of calibration gas. This savings operation is performed on subsequent purging cycle after the first cycle is fully purged. Typically 3 calibration gas purging cycles are performed before a sample gas purging cycle begins. This processes saves more the half the calibration gas typically consumed.
This means the calibration bottle will last twice and long and need to be replaced half as often. Also, a smaller sized calibration bottle can be used reducing footprint and simplifying transport.