X-STREAM Flameproof Enclosure Gas AnalyzerSpecial Considerations for Analyzing Flammable Gases At Pressures Above Atmospheric Within an X-STREAM Flameproof Enclosure Gas Analyzer

X-STREAM Flameproof Enclosure Gas AnalyzerTechnical Note

X-STREAM Enhanced - Flameproof Gas Analyzer

Keypoints - Application Assumptions ■ The gas to be measured is flammable

■ Environmental and/or safety regulations prohibit releasing the gas into the atmosphere, therefore it is fed to a flare

■ The flare requires a gas pressure supply above atmospheric range, typically 5 to 7 psig

■ An X-STREAM flameproof process gas analyzer is selected

■ The analyzer is installed in a Zone 1 or Division 2 hazardous environment (area classification is dependent on local codes)

Basic Fundamentals for Explosion protection ■ Flameproof enclosures are designed to withstand an internal explosion

• All gaps are designed to extinguish flames and cool down gases in case of an internal explosion

• Integral flame arrestors prevent flame propagation into the sample gas inlet and outlet lines

■ ATEX standards and certifications cover both atmospheric and above atmospheric sample gas line pressures, except for in North America where only atmospheric conditions are covered

Analytical SolutionsOption 1. Reduce and then increase sample line pressureBefore supplying the sample gas to the X-STREAM gas analyzer, its pressure is reduced to atmospheric by means of a suitable external pressure reduction device. After flowing through the analyzer, the gas pressure must be increased to overcome the potential back pressure created by an operating flare.

Advantage

All pressures inside the flameproof enclosure are atmospheric.

Disadvantage

Due to the installation area classification of Zone 1or Division 2, all equipment has to meet explosion protection requirements. This also applies to the pressure reduction device and pump, which increases costs.

Option 2. Keep higher sample gas pressureThe sample gas pressure is not changed and the gas is supplied to the gas analyzer.

Advantage

No pump or pressure regulating device is required. This is the preferred solution by most customers.

Disadvantage

This may violate local safety regulations. In the event of an internal explosion, the analyzer may not contain the explosion.

Page 2

Technical Note

1. Risk AnalysisInitial ConfigurationAn internal risk analysis shows there is a potential source of ignition inside the sample gas path if either of these two conditions apply:

■ There is flammable sample gas at high pressures in the sample gas path

■ Increasing pressure inside the enclosure caused by leakage released in the sample gas cannot exit the X-STREAM flameproof enclosure due to high tightness (NEMA 4X / IP66).

No Internal Release of Flammable Sample Gas Internal Release of Flammable Sample Gas

What is the best method of providing customers with a competitive solution, without Compromising safety?

Use the Flow Chart Below to determine the potential Risk Involved

Page 3

Technical Note

First ModificationTests carried out by a third party indicate three internal flame arrestors (1 sample inlet, 1 sample vent, 1 enclosure breather) keep the internal pressure within 1.4 psig of atmospheric in case of a gas line leakage and prevents flame propogation to the outside of the X-STREAM analyzer.

Second ModificationIncludes the First Modification previously stated with an additional external flame arrestor, certified for high gas line pressure and installed on the sample inlet and outlet lines to protect the plant.

Technical Note

2. Proposed Technical SolutionBased on the risk analysis performed by Rosemount Analytical, the following recommended solution has been developed:

■ Purchase an X-STREAM flameproof gas analyzer with one breather (a variation of the standard integral flame arrestor used at both the gas inlet and outlet). It is recommended that this configuration be used with a flow rate of 1 L/min. The breather has been certified for use in the X-STREAM gas analyzer and is factory installed. The breather is internally open to the analyzer enclosure and externally open to the atmosphere and must be vented to a safe, or non-hazardous rated area. To minimize pressure drops, the vent line diameter should be as large as possible, with a minimum internal diameter equal to the sample inlet and outlet piping dimensions, typically ¼ of an inch. NOTE: The breather includes a sintered metal filter to protect against the ingress of external pollutants.

■ The installation of an external flame arrester is required at the sample gas inlet and one at the sample gas outlet. These flame arrestors are designed and approved for use with up to 3 bar / 28.8 psig pressures and protect the sample gas feed and vent lines in case of an explosion inside the gas analyzer. If flammable calibration gases are supplied by separate gas lines at higher than atmospheric pressure, these gas lines must also be protected by external flame arrestors.

SummaryRosemount Analytical has identified a potential flame propogation risk when flammable gases are analyzed at pressures above atmospheric. This potential risk is not, and cannot be, addressed or covered by North American standards. Rosemount Analytical recommends following the technical solution outlined above.NOTE: This recommendation only applies to X-STREAM flameproof installations that have flammable gases entering or leaving the X-STREAM gas analyzer at pressures higher than atmospheric.

3. Special Note for Users in North AmericaThe external flame arrestors offered by Rosemount Analytical are approved to European ATEX standards covering gas line pressures up to 3 bar / 28.8 psig.

CSA (and other North American agencies) do not have unique explosion protection standards covering pressures higher than atmospheric. For this reason, the X-STREAM is still covered by its CSA certification, without specific mention of the higher pressure use.Rosemount Analytical has communicated this to the CSA group, and CSA has responded with the following:

■ North American standards do not address the potential risks mentioned in this Technical Note. As such, the CSA certifications do not specifically mention the use of an analyzer with “greater than atmospheric pressure” sample inlets and outlets. Therefore, the X-STREAM analyzer CSA certification remains valid, regardless of the inlet or outlet pressure(s).

■ The recommended external flame arrestors do provide additional safety, even if not required or certified by a North American agency. The separate ATEX certification and test procedure provide proof of functionality and increased safety.

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