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Wafer technology has chromatograph

InTech, Apr 2004 by Gokeler, Ulrich

Silicon, modular GC has traditional flexibility, additional analytical capabilities, and a shorter cycle time.

It is common practice to use online process gas chromatographs (GCs) to automatically measure natural gas both qualitatively and quantitatively.

Typical applications involve the determination of the heating value contents and other relevant parameters for quality control and custody transfer purposes.

Further applications involve measurements to control the various steps in the purification and fractionated separation of hydrocarbons in natural gas. Because of the huge natural gas quantify processed and the valuation of the product correlating directly to its energy content, the demand for analytical precision and instrumental reliability are very high.

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These performance requirements grow larger by the practice of installing such analytical systems directly at the sampling points, typically without extensive infrastructure. The installation is often remote and operates entirely automatically-from sample preparation, analysis, operation, and calibration to data transmission. Another important consideration is the frequent limitations of the local operating and maintenance personal due to lack of expertise and maintenance experience.

There's a new type of small and compact process gas Chromatograph that platforms on silicon wafer technology with modular design and that has the flexibility of traditional process gas for a wide range of applications. One can specifically apply this type of GC to the measurement of heating values. Because of its design and analytical capabilities, it provides very short analytical cycle times. It also eliminates the influence of sample pressure or ambient pressure variations on the measurement accuracy.

Due to the requirements for long-time stability, rcproducibility, and independency of environmental changes, the design permits one to routinely monitor analytical results, precision, and hardware performance. Consequently this allows one to recognize performance deviations and intervene proactively before failure. Both are important criteria for analytical online reliability and measurement precision. Furthermore, due to the modular design, providing reproducible and self-contained analytical modules, maintenance reduces to a quick exchange of modules.

Standardized in design

The online process GC uses the latest miniaturization techniques, such as silica wafer technology and microelectromechanical systems (MEMS), and has been designed specifically to be suitable for the environment, requiring no extensive infrastructure. The applied manufacturing technique posilively affects the electronics and analytics with regard to size and capability, as well as design, mechanical reproducibility, and cost. Consequently, the analyzer consists of the housing and three modules: analytical, pneumatic, and electronic. Each module is standard in design, connections, and interfacing and can swap out individually. The analytical module is so precise that one can swap a specific separation setup with another module and still generate identical separation and retention times.

All three modules integrate into a small cast alloy housing, making them suitable for installation in a hazardous environment without purge requirements. The design also permits installation into field locations without the need for extensive analyzer shelters. To have the widest possible separation flexibility, narrow bore capillary columns are the basis of the actual separation system. Using valveless, maintenance-free column switching configurations is typically superior to valve switching. Combining these requirements and facts, and applying silicon wafer technology, the necessary injection, valveless column switching, and detection devices reach unsurpassed miniaturization, inertness, and flexibility in online process gas chromatographs.

A diaphragm valve injects a certain sample volume into the carrier gas stream, thereby equilibrating the sample precisely to the carrier gas pressure. By means of a valveless injection technique, only a slice from the initially injected sample volume goes into the first separation column. The unused portion vents. The sample volume size actually injected can be varied by the width of the slice, which is time controlled. Therefore the initial sample pressure and sample pressure stability have no influence on the measurement precision. Furthermore, ambient or sample vent backpressure changes no longer influence the injection volume. Another significant advantage of this injection system is if the primary diaphragm valve is leaking, it does not affect the actual injection size and quality, and consequently does not affect the analytical results as long as the sample pressure does not exceed the carrier gas pressure.

In general the separation system consists of at least two columns coupled in series by the valveless switching system capable of performing back-flush operations. The carrier gas flows and column switching operations respond to electronic pressure regulators that permit not only very simple but also remote pressure setup and monitoring.

Wafer technology has chromatograph

InTech, Apr 2004 by Gokeler, Ulrich

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