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The Servopro Chroma from Servomex enables cryogenic ASU operators to measure the hydrocarbons present in ambient air.

The instrument combines the latest plasma emission detector technology with improved operational and communications capabilities, according to the company.

Constant hydrocarbon measurement is important in ASU production as hydrocarbons that build up in the cryogenic portion of the process pose an explosion risk when mixed with enriched air or pure oxygen.

Depending on the results of an ambient air test to determine the types and level of hydrocarbons present, plant operators must decide whether to measure for total hydrocarbons measurement (THC), methane and non-methane hydrocarbons (CH4 and NMHC) or to measure for individual hydrocarbons including methane, acetylene, propane, propylene, ethane and ethylene.

THC measurement, where the variety of hydrocarbons in ambient air is limited, can be monitored using flame ionisation detector (FID) technology such as that provided by Servomex’s Servopro FID.

However, when the ambient air at a plant contains a variety of hydrocarbons that have different lower explosive limits (LEL), many operators choose to separate the total measurement into two measurements: for methane and non-methane hydrocarbons.

These measurements usually require setting separate trip points at which a plant can be shut down to avoid an explosion, with CH4 usually measured over a 0-100ppm range and the lower-LEL NMHC measured over a 0-5ppm range.

However, if a plant trip point set for a FID analyser is based solely on a CH4 measurement range, the potential exists for non-methane hydrocarbons to accumulate above their LEL and the possibility of dangerous operating conditions.

Conversely, if a trip point is based on a lower NMHC ppm level, then the FID analyser may initiate an unnecessary and costly plant shutdown too early and too often as the safe CH4 level activates the lower NMHC trip point.

By housing two separate plasma emission detectors, each with separate valve and column channels to individually and simultaneously measure CH4 and NMHC, the Servopro Chroma is ideal for the coincident measurement of methane and non-methane hydrocarbons.

As the Chroma’s plasma technology requires only an argon or helium carrier gas to function and does not require the constant flowing fuel gas required by FID detection techniques, installation costs – including the installation of shutoff valves and LEL gas detectors – and the overall cost of ownership for the Chroma are reduced when compared with using FID technologies for this application.

The Chroma integrates software that improves on the instrument’s predecessor, the KA k4000, to offer full access to all functions, measurements and system status via an intuitive user interface.

There is also a range of communication options, with individual 4-20mA outputs available for each measurement and improved Ethernet and internet connectivity enabling the unit to be remotely monitored via a network or an internet browser.

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