Aspirated Sampling Systems

AMEC

David Pollard Groveley Detection

Gas & Smoke detection for:

• Inaccessible areas• Where ambient temperatures are too extreme

for field devices, particularly point infrared & electrochemical based detectors

• Duct monitoring where high air velocities increase response time of diffusion based gas detectors

• Reliable & stable high sensitivity detection• Reduced maintenance

Typical sampling system applications

• Monitoring Sealed Vessels their vents• Monitoring Gas Turbines And Compressors• Flammable gas, toxic & smoke ingress into

HVAC ducts• Safe Refuge Protection• Monitoring For Hydrogen Sulphide In Drilling

Areas• Riser Caisson Monitoring• Monitoring For Flammable Gases In Moonpool

And Turrett Areas Of F.P.S.O.’S

Different Types of Sampling System Available

• Negative Pressure– GDA (Instrument Air Driven Aspirator)– GDAP (Pump Driven Aspirator)– GD-SCDP Self Compensating Duct Probes– GD-AutoDrain

• Positive Pressure

- GD-Analyser

GD-A Aspirators

• Requires Instrument Air• Can be used with any vendors

smoke, toxic & flammable gas detectors

• Design reduces compression fittings, hence maintenance

• Modular design (up to 5 channels)

• Custom Built from standard parts

• IS low flow alarm monitors for line blockages

• Suitable for use in Zones 1 or 2• Sample line purge and

calibration fail safe spring return switches for each channel

Retrofit Applications

• Use when direct mounted detectors fail to perform

• Aspirator requires flow failure diagnosis for fail safe operation

• Utilises existing detector cabling to also perform flow failure diagnostics

Low Temperature Applications

• Cabinet supplied fully insulated and heated

• Low flow alarms and smoke detectors are not certified below -20˚C.

• Certified temperature probes can be supplied to ensure the control system will only power up these devices once the minimum operating temperature has been exceeded.

GD-AP Aspirators

GD-Analyser

Old Aspirators

A Pre-Groveley Aspirator

• Old systems had lots of compression fittings, which needed to be undone during maintenance. This often introduced minor leaks which reduced system performance.

• To change an eductor took up to two hours.

• Line purge and gas detector calibration/testing was a far more involved process.

GD-A Aspirators

Aspirator Operation Schematic

• The sample is pulled under an adjustable vacuum created by an air driven eductor.

• Flow rates are controlled by an integral needle valve with the velocity being indicated on a flow meter.

• The sample is passed across the sensor and then exhausted, along with instrument air, via the exhaust port.

• Sample line blockages can be cleared by pressing the line purge button, diverting instrument air down the sample line.

• Calibration of the gas sensor is carried out via an AVS coupling.

Aspirator Operation Schematic

Operation Schematic – 3 Channel GD-A

HVAC Temporary Refuge Application

• Ingress HVAC monitoring from hazardous areas for:– Smoke– Hydrogen Sulphide– Combustible Gas

• Multiple detectors can be pneumatically connected in series*

• Internally pre-wired to external junction boxes

* Detectors Connected In Series

• Cost reduction and design simplification.• Some detection technologies irreversibly alter

the chemical nature of the sample being monitored. e.g. catalytic, electrochemical and semiconductor sensors.

• Non-destructive measurement technologies should be used wherever possible (e.g. point IR, optical smoke).

• Only one destructive technology should be used per sample line with the device used at the end of the sample run.

Duct Sampling Applications

For ducts with a greater width of 350mm Groveley Self-Compensating Duct Probe ensures a representative sample is taken from the whole width of the duct, thus reducing the chances of gas passing through the duct undetected

Self Compensating Duct Probes

• Representative duct samplingEqual volumes are drawn

from each duct sampling point, before combining them prior to introduction to an aspirator

The SCDP draws a representative sample from the whole width of a duct, no matter what the duct flow rate or pressure

• Suitable for use in hazardous areas

Self Compensating Duct Probes

• The SCDP utilises the “reverse wing” principle, i.e. The contour of the SCDP creates an area of negative pressure on the opposite side to the direction of flow.

• Samples are drawn from this area hence protecting the sample holes from becoming blocked

• Large particles which may block sampling points of traditional probes, will either be too heavy to be drawn into the negative pressure area, or will impact on the face of the SCDP. In either case the SCDP sampling holes remain unaffected.

Groveley SCDP: Reduced maintenance

Low Temperature Applications – SCDP’s

• Heat trace tape is embedded into the leading edge of the SCDP and wired to an external junction box.

• Trace heating tape is self regulating and is designed to keep the SCDP above 10°C, or another predetermined temperature.

• Consider using heated SCDP’s when duct air temperature can drop below -10°C.

GD-AutoDrain

• For negative pressure systems (GD-A; GD-AP)

• Designed to remove limited amounts of water droplets from a GD-Aspirator sample line.

• Sample gas and water droplets enter the GD-AutoDrain assembly via a sample line catch pot assembly, here water and vapour separate.

• Water droplets drips into the seal leg catch pot, due to gravity.

• Water vapour not eliminated by the first stage separator should condense in the sample line filter.

• Normal auto-drains do not work with aspirators

Over 500 units world wide.

• BHP Liverpool Bay 12 x 3pt, 9 x 3pt, 4 x 3pt• BG Armada 18 x various• BP ETAP’s, Schiehallion, Bruce, Shah Deniz (Caspian Sea)• Conoco CMS Banff, MacCulloch• Enron Teesside 16 x 3pt• Enppi Burrulus• KOC Daelim project• ONGC South Bassein• Shell Cormorant Alpha, Curlew, North Cormorant, Sakhalin II• TCO Sour Gas Injection / Second Generation Project• Total North Alwyn, Balal, Darood• Texaco Tartan Field• Woodside Laminaria

Summary

• Instrument Air, Pump or sample driven sampling systems• Can be used with any vendors smoke, toxic & flammable gas

detectors• Design reduces compression fittings, hence maintenance• Modular design (up to 5 channels)• Custom Built from standard parts• Self Compensating Duct Probes for representative sampling• Each system is provided with a dedicated manual, including general

assembly and electrical hook up and wiring details• Suitable for use in hazardous areas