SpectraSensors Offers Accurate Acetylene Measurement

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Fast, repeatable and dependable, the tunable diode laser constantly measures contaminants during ethylene production, assuring high-quality product while eliminating costly waste.

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SpectraSensors, Inc., of Houston, TX provides a superb technology for accurately measuring acetylene content in ethylene. That technology is a sophisticated application of the tunable diode laser (TDL), which was first developed by NASA to measure gas species even in extremely low concentrations.

The purity of ethylene feedstock is critical to the quality of a wide range of petrochemical products, particularly polyethylene plastics. Yet, periodically there are problems when contaminant concentrations exceed stringent purity specifications, rendering valuable ethylene feedstock unacceptable for use in producing such materials.

One of the most problematic of those impurities is acetylene (C2H2), which can be difficult to measure accurately using conventional analyzers, and can also drift off spec due to slow analyzer response.

Because it is one of the more problematic contaminants that can spoil the ethylene production, it is removed from the ethylene during the purifying proves via the Acetylene Converter Unit. This series of reactors converts the acetylene in the hydrogen to form ethylene. When performing accurately, the converter reduces the amount down to low PPM or even PPB levels as required.

TDL versus GC
There are several advantages of the TDL-based analyzer over the gas chromatograph (GC), which has been the primary tool for measuring impurities in ethylene until now.

To begin with, the TDL analyzer is extremely accurate, and remains so for the life of the analyzer. It is quite capable of measuring the concentrations of impurities at sub parts per million levels. The TDL analyzer, developed by NASA-spinoff SpectraSensors, Inc. (Houston, TX), has become the state-of-the-art tool for accurately and continuously measuring very low levels of moisture, H2S and other impurities in hydrocarbon streams for several years.

The accuracy of the TDL analyzer is especially applicable to measuring impurities in ethylene today, not only because ethylene is such a valuable commodity, but also because excessive levels of such impurities will corrupt downstream uses of the ethylene.

In addition to dependable and repeatable accuracy, the speed of measurements is vital to maintaining consistent purity in ethylene production. TDL analyzer offers the advantage of very high-speed readings.

When using the GC technology, the readings are relatively slow, commonly taking from 3 - 6 minutes to provide measurements. Conversely, the TDL analyzer provides almost continuous readings, with intervals taking only from 1-4 seconds.

Beyond measurement
In addition to high-speed accuracy, the TDL laser offers ethylene producers other significant benefits over the traditional GC technology.

GCs are traditionally very complex mechanically, and require a lot of labor-based maintenance, Kania says. They also require a lot of consumables in order to maintain proper operation. However, the TDL analyzer requires very little maintenance and no consumables.

Another advantage of the TDL analyzer is the ability of ethylene producers to standardize on equipment. There is an assortment of contaminants they need to monitor, and the TDL analyzer is an ideal solution for a large number of these contaminants.

The SpectraSensors analyzer, for instance, measures H2O, NH3, H2S and CO2 as well as acetylene. It is possible for users to standardize on SpectraSensors analyzers, operating them from the same control center. Headquartered in Houston, Texas SpectraSensors is a leading manufacturer of optically based gas analyzers and moisture analyzers for analytical process markets. SpectraSensors uses Tunable Diode Laser (TDL) Absorption Spectroscopy in an array of products.

For information contact Sam Miller at SpectraSensors, Inc., 4333 W Sam Houston Pkwy, Ste. 100, Houston, TX 77043; Phone (800) 619-2861, (713) 466-3172; Fax: (713) 856-6623; Email smiller (at) spectrasensors.com; or visit the web site: http://www.spectrasensors.com

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HEATHER METCALFE

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