Trace Sulfur Testing
The increasing interest in monitoring of sulfur in hydrocarbon gas and LPG streams has led Brimstone STS to develop new sampling and analytical techniques that provide immediate, accurate, and reliable analyses. Now, complete speciation of the sulfur compounds at trace level concentrations to as low as 0.1 ppm is possible in difficult gas and LPG streams.
The extreme reactivity of the various sulfur compounds with sampling equipment materials and with each other create fundamental difficulties in both the sampling and analytical areas of this type of test work.
Reactions of the sulfur components with commonly used sample lines cause serious deterioration of the sample. Similar degradation reactions occur when the sample is collected into and stored in ill-suited sample containers. Exposure of the sample gas to any metal will result in loss of sample integrity. For this reason and others, standard metal sample bombs cannot be used for trace sulfur sampling. Because of such problems, it is impractical to collect and ship these samples to remote labs. Such an approach often results in the reporting of sulfur concentrations much lower than were actually present in the process stream. For operating, design, and environmental concerns, these “false negative” results can be misleading and very expensive. It is therefore necessary to conduct this sort of test work onsite.
LPG and LNG streams pose special problems. Because of the inherent pressure involved, glass cannot be used to contain the sample in liquid form. However, as described earlier, collection and storage in metal cylinders results in sample contamination. Even surface-treated metal containers suffer from this problem because of the inability to completely treat or surface coat all metal parts.
Vaporizing the liquid sample as it is collected solves the above problems. This is accomplished using a specially designed sampling apparatus that allows controlled vaporization of the liquid stream during the sampling process. In vapor form, these low-pressure samples can safely be stored in glass for up to several hours without undergoing degradation. Coupled with the use of the Teflon-lined sample probes, the liquid/gas samples can be handled safely in a manner that eliminates dropout of low-level sulfur compounds in the sampling system.
Brimstone gas chromatographic procedures are based on ASTM and EPA protocol standards. The analytical system provides concentrations for important hydrocarbon, inorganic, and sulfur compounds from 100 percent to below 0.010% (100 ppmv), and is accurate to within ±2% relative.
Specialized analytical systems used for trace sulfur species allows analysis of trace sulfur compounds even in the presence of relatively high concentrations of H2S. The trace sulfur analytical system is sensitive to sulfur compounds to below 0.1 ppmv, and typical accuracy for trace sulfur analysis is ±6% relative.
Calibration for trace sulfur test work is done using permeation tube calibrators. This portable, NIST/NBS-traceable system is highly accurate and reliable. It allows on-site generation of a wide variety of trace level sulfur standards over a wide range of concentrations.
Since all analytical work is done onsite, preliminary analytical data is available during the tests. This allows on-the-fly evaluation of the data and corrections to the test plan or plant operation which, left uncorrected, might adversely affect the quality of the project results. Minimal plant support is required because of our self-contained approach.